U.S. Department of the Interior

Bureau of Ocean Energy Management

Gulf of Mexico OCS Region

OCS EIS/EA

BOEM 2016-049

Gulf of Mexico OCS 

Proposed Geological and Geophysical Activities

Western, Central, and Eastern Planning Areas

Draft Programmatic Environmental Impact Statement

Volume III: Appendices E-L 

U.S. Department of the Interior

Bureau of Ocean Energy Management

Gulf of Mexico OCS Region

OCS EIS/EA

BOEM 2016-049

Gulf of Mexico OCS 

Proposed Geological and Geophysical Activities

Western, Central, and Eastern Planning Areas

Draft Programmatic Environmental Impact Statement

Volume III: Appendices E-L 

Author

Bureau of Ocean Energy Management

Gulf of Mexico OCS Region

Prepared under

Contract No. GS-10F-0443M

and

Task Order No. M1PD00025

by

CSA Ocean Sciences Inc.

8502 SW Kansas Avenue

Stuart, Florida 34997

Published by 

New Orleans

September 2016 

Gulf of Mexico G&G Activities Programmatic EIS iii

TABLE OF CONTENTS

Volume I

Page

EXECUTIVE SUMMARY ..................................................................................................................... vii

LIST OF FIGURES.............................................................................................................................lxvii

LIST OF TABLES................................................................................................................................lxix

ABBREVIATIONS AND ACRONYMS ..............................................................................................lxxiiI

CONVERSION CHART ....................................................................................................................lxxix

1 INTRODUCTION ............................................................................................................................ 1-3

1.1 Proposed Action and Purpose and Need............................................................................. 1-3

1.1.1 Proposed Action....................................................................................................... 1-3 

1.1.2 Purpose and Need................................................................................................... 1-4 

1.1.3 Area of Interest......................................................................................................... 1-5 

1.2 Background .......................................................................................................................... 1-6

1.2.1 History of G&G Environmental Review in the GOM................................................ 1-7 

1.2.2 Petition for Authorization to Take Marine Mammals Incidental to Conducting 

Oil and Gas Exploration Activities in the Gulf of Mexico ......................................... 1-8 

1.2.3 Litigation Settlement ................................................................................................ 1-9 

1.2.4 Environmental Baseline and the Deepwater Horizon Explosion, Oil Spill, and 

Response ............................................................................................................... 1-14

1.2.5 Exposure Versus Take of Listed Species.............................................................. 1-15

1.2.6 NMFS’ Acoustic Guidelines ................................................................................... 1-17

1.2.7 Risk Assessment Framework ................................................................................ 1-20

1.3 Regulatory Framework ....................................................................................................... 1-22

1.3.1 Federal Laws, Regulations, and Agreements........................................................ 1-22

1.3.2 State Laws, Regulations, and Agreements ........................................................... 1-23

1.4 Programmatic Approach to the NEPA Process ................................................................. 1-23

1.5 Objectives and Scope ........................................................................................................ 1-25

2 ALTERNATIVES INCLUDING THE PROPOSED ACTION ........................................................... 2-3

2.1 Overview............................................................................................................................... 2-3

2.2 Additional Information Applicable to the Alternatives........................................................... 2-3

2.3 Alternative A – Pre-Settlement (June 2013) Alternative ...................................................... 2-7

2.3.1 Description ............................................................................................................... 2-7 

2.3.2 Mitigation Measures................................................................................................. 2-7 

2.3.3 Rationale.................................................................................................................. 2-8 

2.4 Alternative B – Settlement Agreement Alternative............................................................... 2-8

2.4.1 Description ............................................................................................................... 2-8 

2.4.2 Mitigation Measures................................................................................................. 2-9 

2.4.3 Rationale................................................................................................................ 2-10

2.5 Alternative C – Alternative A Plus Additional Mitigation Measures.................................... 2-11

2.5.1 Description ............................................................................................................. 2-11

2.5.2 Mitigation Measures............................................................................................... 2-11

2.5.3 Rationale................................................................................................................ 2-12
iv Table of Contents

2.6 Alternative D – Alternative C Plus Marine Mammal Shutdowns........................................ 2-12

2.6.1 Description ............................................................................................................. 2-12

2.6.2 Mitigation Measures............................................................................................... 2-13

2.6.3 Rationale................................................................................................................ 2-14

2.7 Alternative E – Alternative C At Reduced Activity Levels .................................................. 2-14

2.7.1 Description ............................................................................................................. 2-14

2.7.2 Mitigation Measures............................................................................................... 2-14

2.7.3 Rationale................................................................................................................ 2-16

2.8 Alternative F – Alternative C Plus Area Closures .............................................................. 2-16

2.8.1 Description ............................................................................................................. 2-16

2.8.2 Mitigation Measures............................................................................................... 2-16

2.8.3 Rationale................................................................................................................ 2-17

2.9 Alternative G – No New Activity Alternative....................................................................... 2-19

2.9.1 Description ............................................................................................................. 2-19

2.9.2 Mitigation Measures............................................................................................... 2-20

2.9.3 Rationale................................................................................................................ 2-21

2.10 Issues ................................................................................................................................. 2-21

2.10.1 Issues to be Analyzed............................................................................................ 2-21

2.10.2 Issues Considered but Not Analyzed .................................................................... 2-23

2.11 Alternatives Considered but Not Carried Forward ............................................................. 2-24

2.11.1 Shutdown for All Marine Mammals Within the Level A Harassment Exclusion 

Zone ..............................................................................................................................

............................................................................................................................... 2-24

2.11.2 Require Alternative Technology Use..................................................................... 2-24

2.11.3 Requirement to Obtain an LOA or IHA Prior to Receiving BOEM’s G&G 

Approval ................................................................................................................. 2-26

2.12 Mitigation Measures Considered But Not Carried Forward ............................................... 2-27

2.12.1 Active Acoustic Monitoring..................................................................................... 2-27

2.12.2 Aerial Surveys........................................................................................................ 2-28

2.13 Comparison of Impacts by Alternative ............................................................................... 2-29

2.14 Mitigation, Monitoring, and Effectiveness .......................................................................... 2-36

2.14.1 Time and Area Restrictions and Closures............................................................. 2-37

2.14.2 Minimum Separation Distances............................................................................. 2-38

2.14.3 Non-Duplicative Surveys and Lowest Practicable Source .................................... 2-39

2.14.4 Exclusion Zone....................................................................................................... 2-40

2.14.5 Exclusion Zone Monitoring .................................................................................... 2-41

2.14.6 Ramp-Up................................................................................................................ 2-45

2.14.7 Shutdowns of Sources for Protected Species ....................................................... 2-46

2.14.8 Reduction in G&G Activity Levels.......................................................................... 2-47

3 G&G ACTIVITIES AND PROPOSED ACTION SCENARIO.......................................................... 3-3

3.1 Introduction........................................................................................................................... 3-3

3.2 Proposed Action Scenario by Program Area ....................................................................... 3-3

3.2.1 Oil and Gas Program G&G Surveys........................................................................ 3-4 

3.2.1.1 Proposed Action Scenario......................................................................... 3-4

3.2.1.2 Projected Activity Levels ........................................................................... 3-5

3.2.2 Renewable Energy Program G&G Surveys ............................................................ 3-6 

3.2.2.1 Proposed Action Scenario......................................................................... 3-7

3.2.2.2 Projected Activity Levels ........................................................................... 3-9

3.2.3 Marine Minerals Program G&G Surveys ................................................................. 3-9 

3.2.3.1 Proposed Action Scenario....................................................................... 3-11

3.2.3.2 Projected Activity Levels ......................................................................... 3-14
Gulf of Mexico G&G Activities Programmatic EIS v 

3.3 Impact-Producing Factors from the Proposed Action........................................................ 3-16

3.3.1 Impact-Producing Factors for Routine Activities ................................................... 3-17

3.3.1.1 Active Acoustic Sound Sources .............................................................. 3-17

3.3.1.1.1 Airguns.................................................................................. 3-17

3.3.1.1.2 Non-Airgun (Electromechanical) HRG Sources................... 3-18

3.3.1.2 Vessel and Equipment Noise.................................................................. 3-19

3.3.1.2.1 Vessel Noise......................................................................... 3-19

3.3.1.2.2 Equipment Noise Including Drilling Noise ............................ 3-20

3.3.1.3 Vessel Traffic........................................................................................... 3-21

3.3.1.3.1 Surveys for Oil and Gas Exploration .................................... 3-22

3.3.1.3.2 Renewable Energy Surveys ................................................. 3-23

3.3.1.3.3 Marine Minerals Surveys...................................................... 3-24

3.3.1.4 Aircraft Traffic and Noise......................................................................... 3-25

3.3.1.5 Stand-Off Distance.................................................................................. 3-26

3.3.1.6 Vessel Discharges................................................................................... 3-27

3.3.1.7 Trash and Debris..................................................................................... 3-27

3.3.1.8 Seafloor Disturbance............................................................................... 3-29

3.3.1.8.1 Seafloor or Bottom Sampling Activities ................................ 3-30

3.3.1.8.2 Placement of Anchors, Nodes, Cables, and Sensors.......... 3-30

3.3.1.8.3 COST Wells and Shallow Test Drilling................................. 3-31

3.3.1.8.4 Bottom-Founded Monitoring Buoys ...................................... 3-31

3.3.1.9 Drilling Discharges .................................................................................. 3-32

3.3.1.10 Entanglement .......................................................................................... 3-33

3.3.2 Impact-Producing Factors for Accidental Fuel Spills............................................. 3-33

3.4 Cumulative Activities Scenario........................................................................................... 3-34

3.4.1 OCS Program......................................................................................................... 3-36

3.4.1.1 OCS Oil and Gas Exploration and Development.................................... 3-37

3.4.1.2 Decommissioning.................................................................................... 3-38

3.4.1.3 Renewable Energy Development............................................................ 3-39

3.4.1.4 Marine Minerals Use ............................................................................... 3-39

3.4.2 Oil and Gas Activities in State Waters................................................................... 3-40

3.4.3 Other Major Factors Affecting Offshore Environments ......................................... 3-41

3.4.3.1 Deepwater Ports...................................................................................... 3-41

3.4.3.2 Commercial and Recreational Fishing.................................................... 3-41

3.4.3.3 Shipping and Marine Transportation....................................................... 3-43

3.4.3.4 Dredged Material Disposal...................................................................... 3-44

3.4.3.5 Existing, Planned, and New Cable Infrastructure ................................... 3-44

3.4.3.6 Military Activities...................................................................................... 3-45

3.4.3.7 Scientific Research.................................................................................. 3-46

3.4.3.8 Maintenance Dredging of Federal Channels .......................................... 3-47

3.4.3.9 Coastal Restoration Programs................................................................ 3-47

3.4.3.10 Mississippi River Hydromodification and Subsidence ............................ 3-47

3.4.3.11 Ancillary Considerations.......................................................................... 3-48

4 DESCRIPTION OF THE AFFECTED RESOURCES AND IMPACT ANALYSIS .......................... 4-3

4.1 Introduction........................................................................................................................... 4-3

4.1.1 Preliminary Screening of Activities and Affected Resources .................................. 4-4 

4.1.1.1 Activity Screening...................................................................................... 4-5

4.1.1.2 Resource Screening.................................................................................. 4-5

4.1.2 Impact Levels and Impact Significance Criteria ...................................................... 4-8 

4.1.3 Impact-Producing Factors........................................................................................ 4-9 
vi Table of Contents

4.1.4 Other Considerations............................................................................................. 4-10

4.1.4.1 Analysis and Incomplete or Unavailable Information.............................. 4-10

4.1.4.2 Cumulative Scenario Summary............................................................... 4-11

4.1.4.3 NMFS’ Acoustic Guidelines..................................................................... 4-12

4.1.4.4 Risk Assessment Framework.................................................................. 4-15

4.1.4.5 Space-Use Conflicts................................................................................ 4-17

4.1.5 Effects of the Deepwater Horizon Oil Spill............................................................. 4-18

4.2 Marine Mammals................................................................................................................ 4-21

4.2.1 Description of the Affected Environment ............................................................... 4-21

4.2.2 Impacts – Alternative A (Pre-Settlement [June 2013] Alternative)........................ 4-25

4.2.2.1 Impacts of Routine Activities ................................................................... 4-27

4.2.2.1.1 Characteristics of Active Acoustic Sound Sources .............. 4-27

4.2.2.1.2 Analysis of Active Acoustic Sound Sources......................... 4-50

4.2.2.1.3 HRG Survey Activities .......................................................... 4-60

4.2.2.1.4 Vessel and Equipment Noise ............................................... 4-66

4.2.2.1.5 Drilling-Related Noise........................................................... 4-69

4.2.2.1.6 Vessel Traffic........................................................................ 4-70

4.2.2.1.7 Aircraft Traffic and Noise...................................................... 4-71

4.2.2.1.8 Trash and Debris .................................................................. 4-73

4.2.2.1.9 Entanglement........................................................................ 4-74

4.2.2.1.10 Routine Activities Impact Conclusions ................................. 4-75

4.2.2.2 Impacts of Accidental Events .................................................................. 4-76

4.2.2.3 Cumulative Impacts................................................................................. 4-77

4.2.2.3.1 Noise..................................................................................... 4-77

4.2.2.3.2 Vessel and Aircraft Traffic .................................................... 4-83

4.2.2.3.3 Trash and Debris .................................................................. 4-84

4.2.2.3.4 Entanglement........................................................................ 4-85

4.2.2.3.5 Cumulative Impact Conclusions ........................................... 4-85

4.2.2.3.6 Accidental Fuel Spills ........................................................... 4-87

4.2.3 Impacts – Alternative B (Settlement Agreement Alternative)................................ 4-88

4.2.3.1 Impacts of Routine Activities ................................................................... 4-88

4.2.3.1.1 Coastal Waters Seasonal Restrictions (January 1 to 

April 30)................................................................................. 4-88

4.2.3.1.2 Expanded PSO Program...................................................... 4-91

4.2.3.1.3 Minimum Separation Distances............................................ 4-92

4.2.3.1.4 Seismic Restrictions in the Areas of Concern within the 

EPA....................................................................................... 4-94

4.2.3.1.5 Use of PAM Required........................................................... 4-95

4.2.3.1.6 Routine Activities Impact Conclusions ................................. 4-97

4.2.3.2 Impacts of Accidental Events .................................................................. 4-98

4.2.3.3 Cumulative Impacts................................................................................. 4-98

4.2.4 Impacts – Alternative C (Proposed Action – Alternative A Plus Additional 

Mitigation Measures).............................................................................................. 4-99

4.2.4.1 Impacts of Routine Activities .................................................................4-100

4.2.4.1.1 Coastal Waters Seasonal Restrictions (February 1 to 

May 31)...............................................................................4-100

4.2.4.1.2 Expanded PSO Program....................................................4-100

4.2.4.1.3 Use of PAM Required.........................................................4-101

4.2.4.1.4 Non-Airgun HRG Survey Protocol......................................4-102

4.2.4.1.5 Routine Activities Impact Conclusions ...............................4-103

4.2.4.2 Impacts of Accidental Events ................................................................4-104

4.2.4.3 Cumulative Impacts...............................................................................4-105
Gulf of Mexico G&G Activities Programmatic EIS vii

4.2.5 Impacts – Alternative D (Alternative C Plus Marine Mammal Shutdowns).........4-105

4.2.5.1 Impacts of Routine Activities .................................................................4-106

4.2.5.1.1 Expanded PSO Program with Additional Shutdowns ........4-106

4.2.5.1.2 Routine Activities Impact Conclusions ...............................4-106

4.2.5.2 Impacts of Accidental Events ................................................................4-108

4.2.5.3 Cumulative Impacts...............................................................................4-108

4.2.6 Impacts – Alternative E (Alternative C at Reduced Activity Levels)....................4-109

4.2.6.1 Impacts of Routine Activities .................................................................4-109

4.2.6.1.1 Reduced Level of Activity ...................................................4-109

4.2.6.1.2 Routine Activities Impact Conclusions ...............................4-110

4.2.6.2 Impacts of Accidental Events ................................................................4-111

4.2.6.3 Cumulative Impacts...............................................................................4-111

4.2.7 Impacts – Alternative F (Alternative C Plus Area Closures)................................4-112

4.2.7.1 Impacts of Routine Activities .................................................................4-112

4.2.7.1.1 Closure Areas.....................................................................4-112

4.2.7.1.2 Routine Activities Impact Conclusions ...............................4-117

4.2.7.2 Impacts of Accidental Events ................................................................4-119

4.2.7.3 Cumulative Impacts...............................................................................4-119

4.2.8 Impacts – Alternative G (No New Activity Alternative) ........................................4-120

4.2.8.1 Impacts of Routine Activities .................................................................4-120

4.2.8.1.1 Active Acoustic Sources.....................................................4-120

4.2.8.1.2 Vessel and Equipment Noise .............................................4-121

4.2.8.1.3 Vessel Traffic......................................................................4-121

4.2.8.1.4 Aircraft Traffic and Noise....................................................4-121

4.2.8.1.5 Trash and Debris ................................................................4-121

4.2.8.1.6 Routine Activities Impact Conclusions ...............................4-121

4.2.8.2 Impacts of Accidental Events ................................................................4-123

4.2.8.3 Cumulative Impacts...............................................................................4-123

4.3 Sea Turtles .......................................................................................................................4-123

4.3.1 Description of the Affected Environment .............................................................4-123

4.3.2 Impacts – Alternative A (Pre-Settlement [June 2013] Alternative)......................4-126

4.3.2.1 Impacts of Routine Activities .................................................................4-127

4.3.2.1.1 Characteristics of Active Acoustic Sound Sources ............4-127

4.3.2.1.2 Analysis of Active Acoustic Sound Sources.......................4-135

4.3.2.1.3 Vessel and Equipment Noise .............................................4-139

4.3.2.1.4 Vessel Traffic......................................................................4-141

4.3.2.1.5 Aircraft Traffic and Noise....................................................4-142

4.3.2.1.6 Trash and Debris ................................................................4-143

4.3.2.1.7 Entanglement/Entrapment..................................................4-145

4.3.2.1.8 Routine Activities Impact Conclusions ...............................4-145

4.3.2.2 Impacts of an Accidental Fuel Spill .......................................................4-146

4.3.2.3 Cumulative Impacts...............................................................................4-148

4.3.2.3.1 Noise...................................................................................4-148

4.3.2.3.2 Vessel and Aircraft Traffic ..................................................4-151

4.3.2.3.3 Trash and Debris ................................................................4-152

4.3.2.3.4 Entanglement and Entrapment...........................................4-152

4.3.2.3.5 Cumulative Impact Conclusions .........................................4-153

4.3.2.3.6 Accidental Fuel Spills .........................................................4-154

4.3.3 Impacts – Alternative B (Settlement Agreement Alternative)..............................4-155

4.3.3.1 Impacts of Routine Activities .................................................................4-155

4.3.3.1.1 Coastal Waters Seasonal Restrictions (January 1 to 

April 30)...............................................................................4-155

4.3.3.1.2 Expanded PSO Program....................................................4-157
viii Table of Contents

4.3.3.1.3 Minimum Separation Distances..........................................4-158

4.3.3.1.4 Seismic Restrictions in the Areas of Concern within the 

EPA.....................................................................................4-159

4.3.3.1.5 Routine Activities Impact Conclusions ...............................4-160

4.3.3.2 Impacts of an Accidental Fuel Spill .......................................................4-160

4.3.3.3 Cumulative Impacts...............................................................................4-161

4.3.4 Impacts – Alternative C (Proposed Action – Alternative A Plus Additional 

Mitigation Measures)............................................................................................4-162

4.3.4.1 Impacts of Routine Activities .................................................................4-162

4.3.4.1.1 Coastal Waters Seasonal Restrictions (February 1 to 

May 31)...............................................................................4-162

4.3.4.1.2 Expanded PSO Program....................................................4-162

4.3.4.1.3 Non-Airgun HRG Survey Protocol......................................4-163

4.3.4.1.4 Routine Activities Impact Conclusions ...............................4-164

4.3.4.2 Impacts of an Accidental Fuel Spill .......................................................4-165

4.3.4.3 Cumulative Impacts...............................................................................4-165

4.3.5 Impacts – Alternative D (Alternative C Plus Marine Mammal Shutdowns).........4-166

4.3.5.1 Impacts of Routine Activities .................................................................4-166

4.3.5.2 Impacts of an Accidental Fuel Spill .......................................................4-166

4.3.5.3 Cumulative Impacts...............................................................................4-166

4.3.6 Impacts – Alternative E (Alternative C at Reduced Activity Levels)....................4-167

4.3.6.1 Impacts of Routine Activities .................................................................4-167

4.3.6.1.1 Reduced Level of Activity ...................................................4-167

4.3.6.2 Impacts of an Accidental Fuel Spill .......................................................4-167

4.3.6.3 Cumulative Impacts...............................................................................4-168

4.3.7 Impacts – Alternative F (Alternative C Plus Area Closures)................................4-168

4.3.7.1 Impacts of Routine Activities .................................................................4-168

4.3.7.1.1 Closure Areas.....................................................................4-168

4.3.7.2 Impacts of an Accidental Fuel Spill .......................................................4-169

4.3.7.3 Cumulative Impacts...............................................................................4-169

4.3.8 Impacts – Alternative G (No New Activity Alternative) ........................................4-169

4.3.8.1 Impacts of Routine Activities .................................................................4-169

4.3.8.1.1 Active Acoustic Sound Sources .........................................4-169

4.3.8.1.2 Vessel and Equipment Noise .............................................4-170

4.3.8.1.3 Vessel Traffic......................................................................4-170

4.3.8.1.4 Aircraft Traffic and Noise....................................................4-170

4.3.8.1.5 Trash and Debris ................................................................4-170

4.3.8.1.6 Routine Activities Impact Conclusions ...............................4-170

4.3.8.2 Impacts of Accidental Events ................................................................4-171

4.3.8.3 Cumulative Impacts...............................................................................4-171

4.4 Fish Resources and Essential Fish Habitat .....................................................................4-171

4.4.1 Description of the Affected Environment .............................................................4-171

4.4.2 Impacts – Alternative A (Pre-Settlement [June 2013] Alternative)......................4-174

4.4.2.1 Impacts of Routine Activities .................................................................4-175

4.4.2.1.1 Background: Potential Effects of Noise on Fishes............4-175

4.4.2.1.2 Analysis of Active Acoustic Sound Sources.......................4-178

4.4.2.1.3 Vessel and Equipment Noise .............................................4-181

4.4.2.1.4 Trash and Debris ................................................................4-182

4.4.2.1.5 Seafloor Disturbance..........................................................4-183

4.4.2.1.6 Drilling Discharges..............................................................4-184

4.4.2.1.7 Entanglement......................................................................4-184

4.4.2.1.8 Routine Activities Impact Conclusions ...............................4-184

4.4.2.2 Impacts of an Accidental Fuel Spill .......................................................4-185
Gulf of Mexico G&G Activities Programmatic EIS ix

4.4.2.3 Cumulative Impacts...............................................................................4-186

4.4.2.3.1 Noise...................................................................................4-186

4.4.2.3.2 Trash and Debris ................................................................4-188

4.4.2.3.3 Seafloor Disturbances ........................................................4-189

4.4.2.3.4 Drilling Discharges..............................................................4-189

4.4.2.3.5 Entanglement......................................................................4-190

4.4.2.3.6 Cumulative Impact Conclusions .........................................4-191

4.4.2.3.7 Accidental Fuel Spills .........................................................4-191

4.4.3 Impacts – Alternative B (Settlement Agreement Alternative)..............................4-192

4.4.3.1 Impacts of Routine Activities .................................................................4-193

4.4.3.1.1 Coastal Waters Seasonal Restrictions (January 1 to 

April 30)...............................................................................4-193

4.4.3.1.2 Minimum Separation Distances..........................................4-193

4.4.3.1.3 Seismic Restrictions in the Areas of Concern within the 

EPA.....................................................................................4-194

4.4.3.1.4 Routine Activities Impact Conclusions ...............................4-194

4.4.3.2 Impacts of an Accidental Fuel Spill .......................................................4-195

4.4.3.3 Cumulative Impacts...............................................................................4-195

4.4.4 Impacts – Alternative C (Proposed Action – Alternative A Plus Additional 

Mitigation Measures)............................................................................................4-196

4.4.4.1 Impacts of Routine Activities .................................................................4-196

4.4.4.1.1 Coastal Waters Seasonal Restrictions (February 1 to 

May 31)...............................................................................4-196

4.4.4.1.2 Routine Activities Impact Conclusions ...............................4-197

4.4.4.2 Impacts of an Accidental Fuel Spill .......................................................4-197

4.4.4.3 Cumulative Impacts...............................................................................4-197

4.4.5 Impacts – Alternative D (Alternative C Plus Marine Mammal Shutdowns).........4-198

4.4.5.1 Impacts of Routine Activities .................................................................4-198

4.4.5.2 Impacts of an Accidental Fuel Spill .......................................................4-198

4.4.5.3 Cumulative Impacts...............................................................................4-198

4.4.6 Impacts – Alternative E (Alternative C at Reduced Activity Levels)....................4-199

4.4.6.1 Impacts of Routine Activities .................................................................4-199

4.4.6.1.1 Reduced Level of Activity ...................................................4-199

4.4.6.2 Impacts of an Accidental Fuel Spill .......................................................4-200

4.4.6.3 Cumulative Impacts...............................................................................4-200

4.4.7 Impacts – Alternative F (Alternative C Plus Area Closures) ................................4-200

4.4.7.1 Impacts of Routine Activities .................................................................4-200

4.4.7.1.1 Closure Areas.....................................................................4-200

4.4.7.2 Impacts of an Accidental Fuel Spill .......................................................4-201

4.4.7.3 Cumulative Impacts...............................................................................4-201

4.4.8 Impacts – Alternative G (No New Activity Alternative) ........................................4-202

4.4.8.1 Impacts of Routine Activities .................................................................4-202

4.4.8.2 Impacts of Accidental Fuel Spills ..........................................................4-202

4.4.8.3 Cumulative Impacts...............................................................................4-203

4.5 Benthic Communities .......................................................................................................4-203

4.5.1 Description of the Affected Environment .............................................................4-203

4.5.1.1 Soft Bottom Communities......................................................................4-204

4.5.1.2 Hard Bottom Communities ....................................................................4-204

4.5.1.2.1 Deepwater Coral Communities ..........................................4-205

4.5.1.2.2 Live Bottoms (Pinnacle Trend)...........................................4-205

4.5.1.2.3 Live Bottoms (Low Relief)...................................................4-206

4.5.1.2.4 Topographic Features ........................................................4-206

4.5.1.2.5 Artificial Reefs.....................................................................4-206
x Table of Contents

4.5.1.3 Chemosynthetic Communities ..............................................................4-207

4.5.1.4 Listed, Candidate, and Species of Concern..........................................4-208

4.5.2 Impacts – Alternative A (Pre-Settlement [June 2013] Alternative)......................4-208

4.5.2.1 Impacts of Routine Activities .................................................................4-209

4.5.2.1.1 Active Acoustic Sound Sources .........................................4-209

4.5.2.1.2 Trash and Debris ................................................................4-211

4.5.2.1.3 Seafloor Disturbance..........................................................4-212

4.5.2.1.4 Drilling Discharges..............................................................4-214

4.5.2.1.5 Routine Activities Impact Conclusions ...............................4-215

4.5.2.2 Impacts of an Accidental Fuel Spill .......................................................4-215

4.5.2.3 Cumulative Impacts...............................................................................4-216

4.5.2.3.1 Active Acoustic Sound Sources .........................................4-216

4.5.2.3.2 Trash and Debris ................................................................4-217

4.5.2.4 Seafloor Disturbances...........................................................................4-217

4.5.2.4.1 Drilling Discharges..............................................................4-218

4.5.2.4.2 Cumulative Impact Conclusions .........................................4-218

4.5.2.4.3 Accidental Fuel Spills .........................................................4-219

4.5.3 Impacts – Alternative B (Settlement Agreement Alternative)..............................4-219

4.5.3.1 Impacts of Routine Activities .................................................................4-219

4.5.3.1.1 Coastal Waters Seasonal Restrictions (January 1 to 

April 30)...............................................................................4-219

4.5.3.1.2 Seismic Restrictions in the Areas of Concern within the 

EPA.....................................................................................4-220

4.5.3.1.3 Routine Activities Impact Conclusions ...............................4-220

4.5.3.2 Impacts of an Accidental Fuel Spill .......................................................4-220

4.5.3.3 Cumulative Impacts...............................................................................4-220

4.5.4 Impacts – Alternative C (Proposed Action – Alternative A Plus Additional 

Mitigation Measures)............................................................................................4-221

4.5.4.1 Impacts of Routine Activities .................................................................4-221

4.5.4.1.1 Coastal Waters Seasonal Restrictions (February 1 to 

May 31)...............................................................................4-221

4.5.4.1.2 Routine Activities Impact Conclusions ...............................4-221

4.5.4.2 Impacts of an Accidental Fuel Spill .......................................................4-221

4.5.4.3 Cumulative Impacts...............................................................................4-221

4.5.5 Impacts – Alternative D (Alternative C Plus Marine Mammal Shutdowns).........4-222

4.5.5.1 Impacts of Routine Activities .................................................................4-222

4.5.5.2 Impacts of an Accidental Fuel Spill .......................................................4-222

4.5.5.3 Cumulative Impacts...............................................................................4-223

4.5.6 Impacts – Alternative E (Alternative C at Reduced Activity Levels)....................4-223

4.5.6.1 Impacts of Routine Activities .................................................................4-223

4.5.6.1.1 Reduced Level of Activity ...................................................4-223

4.5.6.1.2 Routine Activities Impact Conclusions ...............................4-223

4.5.6.2 Impacts of an Accidental Fuel Spill .......................................................4-223

4.5.6.3 Cumulative Impacts...............................................................................4-224

4.5.7 Impacts – Alternative F (Alternative C Plus Area Closures) ................................4-224

4.5.7.1 Impacts of Routine Activities .................................................................4-224

4.5.7.1.1 Closure Areas.....................................................................4-224

4.5.7.1.2 Routine Activities Impact Conclusions ...............................4-224

4.5.7.2 Impacts of an Accidental Fuel Spill .......................................................4-224

4.5.7.3 Cumulative Impacts...............................................................................4-225
Gulf of Mexico G&G Activities Programmatic EIS xi

4.5.8 Impacts – Alternative G (No New Activity Alternative) ........................................4-225

4.5.8.1 Impacts of Routine Activities .................................................................4-225

4.5.8.2 Impacts of Accidental Fuel Spill ............................................................4-225

4.5.8.3 Cumulative Impacts...............................................................................4-226

4.6 Marine and Coastal Birds.................................................................................................4-226

4.6.1 Description of the Affected Environment .............................................................4-226

4.6.1.1 Unlisted Species....................................................................................4-226

4.6.1.2 Listed Species .......................................................................................4-228

4.6.1.3 Baseline Populations and the Deepwater Horizon Explosion, Oil Spill, 

and Response .......................................................................................4-228

4.6.2 Impacts – Alternative A (Pre-Settlement [June 2013] Alternative)......................4-230

4.6.2.1 Impacts of Routine Activities .................................................................4-231

4.6.2.1.1 Active Acoustic Sound Sources .........................................4-231

4.6.2.1.2 Vessel and Equipment Noise and Vessel Traffic ...............4-234

4.6.2.1.3 Aircraft Traffic and Noise....................................................4-239

4.6.2.1.4 Trash and Debris ................................................................4-240

4.6.2.1.5 Routine Activities Impact Conclusions ...............................4-241

4.6.2.2 Impacts of an Accidental Fuel Spill .......................................................4-241

4.6.2.3 Cumulative Impacts...............................................................................4-242

4.6.2.3.1 Noise...................................................................................4-243

4.6.2.3.2 Vessel and Aircraft Traffic ..................................................4-245

4.6.2.3.3 Trash and Debris ................................................................4-247

4.6.2.3.4 Cumulative Impact Conclusions .........................................4-247

4.6.2.3.5 Accidental Fuel Spills .........................................................4-248

4.6.3 Impacts – Alternative B (Settlement Agreement Alternative)..............................4-248

4.6.3.1 Impacts of Routine Activities .................................................................4-248

4.6.3.1.1 Coastal Waters Seasonal Restrictions (January 1 to 

April 30)...............................................................................4-249

4.6.3.1.2 Minimum Separation Distances..........................................4-249

4.6.3.1.3 Seismic Restrictions in the Areas of Concern within the 

EPA.....................................................................................4-250

4.6.3.1.4 Routine Activities Impact Conclusions ...............................4-251

4.6.3.2 Impacts of an Accidental Fuel Spill .......................................................4-251

4.6.3.3 Cumulative Impacts...............................................................................4-252

4.6.4 Impacts – Alternative C (Proposed Action – Alternative A Plus Additional 

Mitigation Measures)............................................................................................4-252

4.6.4.1 Impacts of Routine Activities .................................................................4-252

4.6.4.1.1 Coastal Waters Seasonal Restrictions (February 1 to 

May 31)...............................................................................4-252

4.6.4.1.2 Routine Activities Impact Conclusions ...............................4-253

4.6.4.2 Impacts of an Accidental Fuel Spill .......................................................4-254

4.6.4.3 Cumulative Impacts...............................................................................4-254

4.6.5 Impacts – Alternative D (Alternative C Plus Marine Mammal Shutdowns).........4-255

4.6.5.1 Impacts of Routine Activities .................................................................4-255

4.6.5.2 Impacts of an Accidental Fuel Spill .......................................................4-255

4.6.5.3 Cumulative Impacts...............................................................................4-256

4.6.6 Impacts – Alternative E (Alternative C at Reduced Activity Levels)....................4-256

4.6.6.1 Impacts of Routine Activities .................................................................4-256

4.6.6.1.1 Reduced Level of Activity ...................................................4-256

4.6.6.1.2 Routine Activities Impact Conclusions ...............................4-258

4.6.6.2 Impacts of an Accidental Fuel Spill .......................................................4-258

4.6.6.3 Cumulative Impacts...............................................................................4-258
xii Table of Contents

4.6.7 Impacts – Alternative F (Alternative C Plus Area Closures)................................4-258

4.6.7.1 Impacts of Routine Activities .................................................................4-259

4.6.7.2 Impacts of an Accidental Fuel Spill .......................................................4-259

4.6.7.3 Cumulative Impacts...............................................................................4-259

4.6.8 Impacts – Alternative G (No New Activity Alternative) ........................................4-260

4.6.8.1 Impacts of Routine Activities .................................................................4-260

4.6.8.2 Impacts of Accidental Fuel Spill ............................................................4-260

4.6.8.3 Cumulative Impacts...............................................................................4-261

4.7 Marine Protected Areas....................................................................................................4-261

4.7.1 Description of the Affected Environment .............................................................4-261

4.7.1.1 Offshore Marine Protected Areas..........................................................4-262

4.7.1.2 Coastal Marine Protected Areas ...........................................................4-264

4.7.2 Impacts – Alternative A (Pre-Settlement [June 2013] Alternative)......................4-267

4.7.2.1 Impacts of Routine Activities .................................................................4-268

4.7.2.1.1 Active Acoustic Sound Sources .........................................4-268

4.7.2.1.2 Trash and Debris ................................................................4-273

4.7.2.1.3 Seafloor Disturbance..........................................................4-273

4.7.2.1.4 Drilling Discharges..............................................................4-274

4.7.2.1.5 Routine Activities Impact Conclusions ...............................4-275

4.7.2.2 Accidental Fuel Spills ............................................................................4-276

4.7.2.3 Cumulative Impacts...............................................................................4-277

4.7.2.3.1 Noise...................................................................................4-277

4.7.2.3.2 Trash and Debris ................................................................4-277

4.7.2.3.3 Seafloor Disturbances ........................................................4-278

4.7.2.3.4 Drilling Discharges..............................................................4-278

4.7.2.3.5 Cumulative Impact Conclusions .........................................4-279

4.7.2.3.6 Accidental Fuel Spills .........................................................4-279

4.7.3 Impacts – Alternative B (Settlement Agreement Alternative)..............................4-279

4.7.3.1 Impacts of Routine Activities .................................................................4-279

4.7.3.1.1 Coastal Waters Seasonal Restrictions (January 1 to 

April 30)...............................................................................4-280

4.7.3.1.2 Expanded PSO Program....................................................4-280

4.7.3.1.3 Minimum Separation Distances..........................................4-280

4.7.3.1.4 Seismic Restrictions in the Areas of Concern within the 

EPA.....................................................................................4-280

4.7.3.1.5 Use of PAM Required.........................................................4-280

4.7.3.1.6 Routine Activities Impact Conclusions ...............................4-280

4.7.3.2 Accidental Fuel Spills ............................................................................4-281

4.7.3.3 Cumulative Impacts...............................................................................4-281

4.7.4 Impacts – Alternative C (Proposed Action – Alternative A Plus Additional 

Mitigation Measures)............................................................................................4-282

4.7.4.1 Impacts of Routine Activities .................................................................4-282

4.7.4.1.1 Coastal Waters Seasonal Restrictions (February 1 to 

May 31)...............................................................................4-282

4.7.4.1.2 Expanded PSO Program....................................................4-282

4.7.4.1.3 Use of PAM Required.........................................................4-282

4.7.4.1.4 Non-Airgun HRG Survey Protocol......................................4-283

4.7.4.1.5 Routine Activities Impact Conclusions ...............................4-283

4.7.4.2 Accidental Fuel Spills ............................................................................4-283

4.7.4.3 Cumulative Impacts...............................................................................4-283
Gulf of Mexico G&G Activities Programmatic EIS xiii

4.7.5 Impacts – Alternative D (Alternative C Plus Marine Mammal Shutdowns).........4-284

4.7.5.1 Impacts of Routine Activities .................................................................4-284

4.7.5.2 Accidental Fuel Spills ............................................................................4-284

4.7.5.3 Cumulative Impacts...............................................................................4-285

4.7.6 Impacts – Alternative E (Alternative C at Reduced Activity Levels)....................4-285

4.7.6.1 Impacts of Routine Activities .................................................................4-285

4.7.6.2 Accidental Fuel Spills ............................................................................4-286

4.7.6.3 Cumulative Impacts...............................................................................4-286

4.7.7 Impacts – Alternative F (Alternative C Plus Area Closures)................................4-287

4.7.7.1 Impacts of Routine Activities .................................................................4-287

4.7.7.2 Accidental Fuel Spills ............................................................................4-287

4.7.7.3 Cumulative Impacts...............................................................................4-288

4.7.8 Impacts – Alternative G (No New Activity Alternative) ........................................4-288

4.7.8.1 Impacts of Routine Activities .................................................................4-288

4.7.8.2 Impacts of Accidental Fuel Spill ............................................................4-289

4.7.8.3 Cumulative Impacts...............................................................................4-289

4.8 Sargassum and Associated Communities .......................................................................4-289

4.8.1 Description of the Affected Environment .............................................................4-289

4.8.2 Impacts – Alternative A (Pre-Settlement [June 2013] Alternative)......................4-291

4.8.2.1 Impacts of Routine Activities .................................................................4-292

4.8.2.1.1 Vessel Traffic......................................................................4-292

4.8.2.1.2 Vessel Discharges..............................................................4-293

4.8.2.1.3 Trash and Debris ................................................................4-293

4.8.2.1.4 Routine Activities Impact Conclusions ...............................4-294

4.8.2.2 Impacts of an Accidental Fuel Spill .......................................................4-295

4.8.2.3 Cumulative Impacts...............................................................................4-296

4.8.2.3.1 Vessel Traffic......................................................................4-296

4.8.2.3.2 Vessel Discharges..............................................................4-297

4.8.2.3.3 Trash and Debris ................................................................4-297

4.8.2.3.4 Cumulative Impact Conclusions .........................................4-298

4.8.2.3.5 Accidental Fuel Spills .........................................................4-298

4.8.3 Impacts – Alternative B (Settlement Agreement Alternative)..............................4-298

4.8.3.1 Impacts of Routine Activities .................................................................4-299

4.8.3.1.1 Coastal Waters Seasonal Restrictions (January 1 to 

April 30)...............................................................................4-299

4.8.3.1.2 Seismic Restrictions in the Areas of Concern within the 

EPA.....................................................................................4-299

4.8.3.1.3 Routine Activities Impact Conclusions ...............................4-300

4.8.3.2 Impacts of an Accidental Fuel Spill .......................................................4-300

4.8.3.3 Cumulative Impacts...............................................................................4-300

4.8.4 Impacts – Alternative C (Proposed Action – Alternative A Plus Additional 

Mitigation Measures)............................................................................................4-301

4.8.4.1 Impacts of Routine Activities .................................................................4-301

4.8.4.1.1 Coastal Waters Seasonal Restrictions (February 1 to 

May 31)...............................................................................4-301

4.8.4.1.2 Routine Activities Impact Conclusions ...............................4-301

4.8.4.2 Impacts of an Accidental Fuel Spill .......................................................4-302

4.8.4.3 Cumulative Impacts...............................................................................4-302

4.8.5 Impacts – Alternative D (Alternative C Plus Marine Mammal Shutdowns).........4-302

4.8.5.1 Impacts of Routine Activities .................................................................4-303

4.8.5.2 Impacts of an Accidental Fuel Spill .......................................................4-303

4.8.5.3 Cumulative Impacts...............................................................................4-303
xiv Table of Contents

4.8.6 Impacts – Alternative E (Alternative C at Reduced Activity Levels)....................4-304

4.8.6.1 Impacts of Routine Activities .................................................................4-304

4.8.6.2 Impacts of an Accidental Fuel Spill .......................................................4-304

4.8.6.3 Cumulative Impacts...............................................................................4-304

4.8.7 Impacts – Alternative F (Alternative C Plus Area Closures)................................4-305

4.8.7.1 Impacts of Routine Activities .................................................................4-305

4.8.7.2 Impacts of an Accidental Fuel Spill .......................................................4-305

4.8.7.3 Cumulative Impacts...............................................................................4-305

4.8.8 Impacts – Alternative G (No New Activity Alternative) ........................................4-306

4.8.8.1 Impacts of Routine Activities .................................................................4-306

4.8.8.2 Impacts of Accidental Fuel Spill ............................................................4-306

4.8.8.3 Cumulative Impacts...............................................................................4-306

4.9 Commercial Fisheries.......................................................................................................4-306

4.9.1 Description of the Affected Environment .............................................................4-306

4.9.2 Impacts – Alternative A (Pre-Settlement [June 2013] Alternative)......................4-308

4.9.2.1 Impacts of Routine Activities .................................................................4-309

4.9.2.1.1 Routine Activities Impact Conclusions ...............................4-314

4.9.2.2 Impacts of an Accidental Fuel Spill .......................................................4-314

4.9.2.3 Cumulative Impacts...............................................................................4-315

4.9.2.3.1 Active Acoustic Sound Sources .........................................4-315

4.9.2.3.2 Vessel Traffic......................................................................4-316

4.9.2.3.3 Stand-Off Distance .............................................................4-317

4.9.2.3.4 Seafloor Disturbance..........................................................4-317

4.9.2.3.5 Entanglement......................................................................4-318

4.9.2.3.6 Cumulative Impact Conclusions .........................................4-319

4.9.2.4 Accidental Fuel Spills ............................................................................4-319

4.9.3 Impacts – Alternative B (Settlement Agreement Alternative)..............................4-320

4.9.3.1 Impacts of Routine Activities .................................................................4-320

4.9.3.1.1 Coastal Waters Seasonal Restrictions (January 1 to 

April 30)...............................................................................4-321

4.9.3.1.2 Minimum Separation Distances..........................................4-321

4.9.3.1.3 Seismic Restrictions in the Areas of Concern within the 

EPA.....................................................................................4-322

4.9.3.1.4 Routine Activities Impact Conclusions ...............................4-322

4.9.3.2 Impacts of an Accidental Fuel Spill .......................................................4-323

4.9.3.3 Cumulative Impacts...............................................................................4-323

4.9.4 Impacts – Alternative C (Proposed Action – Alternative A Plus Additional 

Mitigation Measures)............................................................................................4-323

4.9.4.1 Impacts of Routine Activities .................................................................4-323

4.9.4.1.1 Coastal Waters Seasonal Restrictions (February 1 to 

May 31)...............................................................................4-324

4.9.4.1.2 Routine Activities Impact Conclusions ...............................4-324

4.9.4.2 Impacts of an Accidental Fuel Spill .......................................................4-324

4.9.4.3 Cumulative Impacts...............................................................................4-325

4.9.5 Impacts – Alternative D (Alternative C Plus Marine Mammal Shutdowns).........4-325

4.9.5.1 Impacts of Routine Activities .................................................................4-325

4.9.5.2 Impacts of an Accidental Fuel Spill .......................................................4-325

4.9.5.3 Cumulative Impacts...............................................................................4-326

4.9.6 Impacts – Alternative E (Alternative C at Reduced Activity Levels)....................4-326

4.9.6.1 Impacts of Routine Activities .................................................................4-326

4.9.6.2 Impacts of an Accidental Fuel Spill .......................................................4-327

4.9.6.3 Cumulative Impacts...............................................................................4-328
Gulf of Mexico G&G Activities Programmatic EIS xv

4.9.7 Impacts – Alternative F (Alternative C Plus Area Closures)................................4-328

4.9.7.1 Impacts of Routine Activities .................................................................4-328

4.9.7.1.1 Closure Areas.....................................................................4-328

4.9.7.1.2 Routine Activities Impact Conclusions ...............................4-329

4.9.7.2 Impacts of an Accidental Fuel Spill .......................................................4-329

4.9.7.3 Cumulative Impacts...............................................................................4-329

4.9.8 Impacts – Alternative G (No New Activity Alternative) ........................................4-330

4.9.8.1 Impacts of Routine Activities .................................................................4-330

4.9.8.2 Impacts of Accidental Fuel Spills ..........................................................4-330

4.9.8.3 Cumulative Impacts...............................................................................4-330

4.10 Recreational Fisheries......................................................................................................4-331

4.10.1 Description of the Affected Environment .............................................................4-331

4.10.2 Impacts – Alternative A (Pre-Settlement [June 2013] Alternative)......................4-333

4.10.2.1 Impacts of Routine Activities .................................................................4-334

4.10.2.1.1 Routine Activities Impact Conclusions ...............................4-337

4.10.2.2 Impacts of an Accidental Fuel Spill .......................................................4-337

4.10.2.3 Cumulative Impacts...............................................................................4-337

4.10.2.3.1 Active Acoustic Sound Sources .........................................4-337

4.10.2.3.2 Vessel Traffic......................................................................4-338

4.10.2.3.3 Stand-off Distance ..............................................................4-339

4.10.2.3.4 Cumulative Impact Conclusions .........................................4-340

4.10.2.3.5 Accidental Fuel Spills .........................................................4-340

4.10.3 Impacts – Alternative B (Settlement Agreement Alternative)..............................4-342

4.10.3.1 Impacts of Routine Activities .................................................................4-342

4.10.3.1.1 Seasonal Restriction for Federal Coastal Waters 

(January 1 to April 30) ........................................................4-342

4.10.3.1.2 Minimum Separation Distances ..........................................4-342

4.10.3.1.3 Seismic Restrictions in the EPA.........................................4-343

4.10.3.1.4 Routine Activities Impact Conclusions ...............................4-344

4.10.3.2 Impacts of an Accidental Fuel Spill .......................................................4-344

4.10.3.3 Cumulative Impacts...............................................................................4-344

4.10.4 Impacts – Alternative C (Proposed Action – Alternative A Plus Additional 

Mitigation Measures)............................................................................................4-345

4.10.4.1 Impacts of Routine Activities .................................................................4-345

4.10.4.1.1 Seasonal Restriction for all Coastal Waters (February 1 to 

May 31)...............................................................................4-345

4.10.4.1.2 Routine Activities Impact Conclusions ...............................4-346

4.10.4.2 Impacts of an Accidental Fuel Spill .......................................................4-346

4.10.4.3 Cumulative Impacts...............................................................................4-346

4.10.5 Impacts – Alternative D (Alternative C Plus Marine Mammal Shutdowns).........4-346

4.10.5.1 Impacts of Routine Activities .................................................................4-347

4.10.5.2 Impacts of an Accidental Fuel Spill .......................................................4-347

4.10.5.3 Cumulative Impacts...............................................................................4-347

4.10.6 Impacts – Alternative E (Alternative C at Reduced Activity Levels)....................4-347

4.10.6.1 Impacts of Routine Activities .................................................................4-347

4.10.6.1.1 Reduction of G&G Activity Levels ......................................4-348

4.10.6.2 Impacts of an Accidental Fuel Spill .......................................................4-348

4.10.6.3 Cumulative Impacts...............................................................................4-348

4.10.7 Impacts – Alternative F (Alternative C Plus Area Closures)................................4-349

4.10.7.1 Impacts of Routine Activities .................................................................4-349

4.10.7.1.1 Area Closures.....................................................................4-349

4.10.7.1.2 Routine Activities Impact Conclusions ...............................4-349
xvi Table of Contents

4.10.7.2 Impacts of an Accidental Fuel Spill .......................................................4-349

4.10.7.3 Cumulative Impacts...............................................................................4-350

4.10.8 Impacts – Alternative G (No New Activity Alternative) ........................................4-350

4.10.8.1 Impacts of Routine Activities .................................................................4-350

4.10.8.2 Impacts of Accidental Fuel Spills ..........................................................4-350

4.10.8.3 Cumulative Impacts...............................................................................4-351

4.11 Archaeological Resources................................................................................................4-351

4.11.1 Description of the Affected Environment .............................................................4-351

4.11.2 Impacts – Alternative A (Pre-Settlement [June 2013] Alternative)......................4-352

4.11.2.1 Impacts of Routine Activities .................................................................4-354

4.11.2.1.1 Seafloor Disturbance and Entanglement ...........................4-354

4.11.2.1.2 Drilling Discharges..............................................................4-355

4.11.2.1.3 Routine Activities Impact Conclusions ...............................4-356

4.11.2.2 Impacts of an Accidental Fuel Spill .......................................................4-356

4.11.2.3 Cumulative Impacts...............................................................................4-357

4.11.2.3.1 Seafloor Disturbance and Entanglement ...........................4-357

4.11.2.3.2 Drilling Discharges..............................................................4-358

4.11.2.3.3 Accidental Fuel Spills .........................................................4-359

4.11.2.3.4 Cumulative Impact Conclusions .........................................4-359

4.11.3 Impacts – Alternative B (Settlement Agreement Alternative)..............................4-359

4.11.3.1 Impacts of Routine Activities .................................................................4-359

4.11.3.2 Impacts of an Accidental Fuel Spill .......................................................4-360

4.11.3.3 Cumulative Impacts...............................................................................4-360

4.11.4 Impacts – Alternative C (Proposed Action – Alternative A Plus Additional 

Mitigation Measures)............................................................................................4-361

4.11.4.1 Impacts of Routine Activities .................................................................4-361

4.11.4.2 Impacts of an Accidental Fuel Spill .......................................................4-361

4.11.4.3 Cumulative Impacts...............................................................................4-361

4.11.5 Impacts – Alternative D (Alternative C Plus Marine Mammal Shutdowns).........4-362

4.11.5.1 Impacts of Routine Activities .................................................................4-362

4.11.5.2 Impacts of an Accidental Fuel Spill .......................................................4-363

4.11.5.3 Cumulative Impacts...............................................................................4-363

4.11.6 Impacts – Alternative E (Alternative C at Reduced Activity Levels)....................4-363

4.11.6.1 Impacts of Routine Activities .................................................................4-363

4.11.6.2 Impacts of an Accidental Fuel Spill .......................................................4-364

4.11.6.3 Cumulative Impacts...............................................................................4-364

4.11.7 Impacts – Alternative F (Alternative C Plus Area Closures)................................4-365

4.11.7.1 Impacts of Routine Activities .................................................................4-365

4.11.7.2 Impacts of an Accidental Fuel Spill .......................................................4-365

4.11.7.3 Cumulative Impacts...............................................................................4-365

4.11.8 Impacts – Alternative G (No New Activity Alternative) ........................................4-366

4.11.8.1 Impacts of Routine Activities .................................................................4-366

4.11.8.2 Impacts of Accidental Fuel Spill ............................................................4-366

4.11.8.3 Cumulative Impacts...............................................................................4-367

4.12 Other Marine Uses ...........................................................................................................4-367

4.12.1 Description of the Affected Environment .............................................................4-367

4.12.1.1 Shipping and Marine Transportation.....................................................4-368

4.12.1.2 Military Warning Areas and Other Military Uses ...................................4-368

4.12.1.3 Sand and Gravel Mining........................................................................4-368

4.12.1.4 Renewable Energy Development – Wind Energy.................................4-369

4.12.1.5 Ocean Dredged Material Disposal Sites...............................................4-369

4.12.1.6 Oil and Gas Exploration, Development, and Production ......................4-369
Gulf of Mexico G&G Activities Programmatic EIS xvii

4.12.2 Impacts – Alternative A (Pre-Settlement [June 2013] Alternative)......................4-370

4.12.2.1 Impacts of Routine Activities .................................................................4-371

4.12.2.1.1 Vessel Traffic and Stand-Off Distance ...............................4-371

4.12.2.1.2 Shipping and Marine Transportation Vessel Traffic...........4-372

4.12.2.1.3 Military Warning Areas and Other Military Uses ................4-372

4.12.2.1.4 Sand and Gravel Mining.....................................................4-372

4.12.2.1.5 Renewable Energy Development.......................................4-373

4.12.2.1.6 Ocean Dredged Material Disposal Sites ............................4-373

4.12.2.1.7 Oil and Gas Exploration, Development, and Production....4-373

4.12.2.1.8 Pipeline and Cable Infrastructure.......................................4-373

4.12.2.1.9 Routine Activities Impact Conclusions ...............................4-374

4.12.2.2 Impacts of an Accidental Fuel Spill .......................................................4-374

4.12.2.3 Cumulative Impacts...............................................................................4-374

4.12.2.3.1 Vessel Traffic and Stand-Off Distances .............................4-375

4.12.2.3.2 Aircraft Traffic and Noise....................................................4-376

4.12.2.3.3 Seafloor Disturbances ........................................................4-376

4.12.2.3.4 Cumulative Impact Conclusions .........................................4-376

4.12.2.3.5 Accidental Fuel Spills .........................................................4-377

4.12.3 Impacts – Alternative B (Settlement Agreement Alternative)..............................4-377

4.12.3.1 Impacts of Routine Activities .................................................................4-377

4.12.3.1.1 Coastal Waters Seasonal Restrictions (January 1 to 

April 30)...............................................................................4-378

4.12.3.1.2 Minimum Separation Distances..........................................4-378

4.12.3.1.3 Routine Activities Impact Conclusions ...............................4-378

4.12.3.2 Impacts of an Accidental Fuel Spill .......................................................4-378

4.12.3.3 Cumulative Impacts...............................................................................4-379

4.12.4 Impacts – Alternative C (Proposed Action – Alternative A Plus Additional 

Mitigation Measures)............................................................................................4-379

4.12.4.1 Impacts of Routine Activities .................................................................4-379

4.12.4.1.1 Coastal Waters Seasonal Restrictions (February 1 to 

May 31)...............................................................................4-380

4.12.4.1.2 Routine Activities Impact Conclusions ...............................4-380

4.12.4.2 Impacts of an Accidental Fuel Spill .......................................................4-380

4.12.4.3 Cumulative Impacts...............................................................................4-380

4.12.5 Impacts – Alternative D (Alternative C Plus Marine Mammal Shutdowns).........4-381

4.12.5.1 Impacts of Routine Activities .................................................................4-381

4.12.5.2 Impacts of an Accidental Fuel Spill .......................................................4-381

4.12.5.3 Cumulative Impacts...............................................................................4-381

4.12.6 Impacts – Alternative E (Alternative C at Reduced Activity Levels)....................4-381

4.12.6.1 Impacts of Routine Activities .................................................................4-381

4.12.6.2 Impacts of an Accidental Fuel Spill .......................................................4-382

4.12.6.3 Cumulative Impacts...............................................................................4-382

4.12.7 Impacts – Alternative F (Alternative C Plus Area Closures)................................4-382

4.12.7.1 Impacts of Routine Activities .................................................................4-383

4.12.7.2 Impacts of an Accidental Fuel Spill .......................................................4-383

4.12.7.3 Cumulative Impacts...............................................................................4-383

4.12.8 Impacts – Alternative G (No New Activity Alternative) ........................................4-384

4.12.8.1 Impacts of Routine Activities .................................................................4-384

4.12.8.2 Impacts of Accidental Events ................................................................4-384

4.12.8.3 Cumulative Impacts...............................................................................4-384
xviii Table of Contents

4.13 Human Resources and Land Use....................................................................................4-384

4.13.1 Description of the Affected Environment .............................................................4-384

4.13.1.1 Land Use and Coastal Infrastructure ....................................................4-385

4.13.1.2 Environmental Justice ...........................................................................4-386

4.13.1.3 Demographics .......................................................................................4-387

4.13.1.4 Socioeconomics ....................................................................................4-388

4.13.2 Impacts – Alternative A (Pre-Settlement [June 2013] Alternative)......................4-389

4.13.3 Impacts – Alternative B (Settlement Agreement Alternative)..............................4-389

4.13.4 Impacts – Alternative C (Proposed Action – Alternative A Plus Additional 

Mitigation Measures)............................................................................................4-389

4.13.5 Impacts – Alternative D (Alternative C Plus Marine Mammal Shutdowns).........4-390

4.13.6 Impacts – Alternative E (Alternative C at Reduced Activity Levels)....................4-390

4.13.7 Impacts – Alternative F (Alternative C Plus Area Closures)................................4-392

4.13.8 Impacts – Alternative G (No New Activity Alternative) ........................................4-392

4.13.9 Economic Factors ................................................................................................4-394

4.13.9.1 Impacts – Alternative A (Pre-Settlement [June 2013] Alternative) .......4-396

4.13.9.2 Impacts – Alternative B (Settlement Agreement Alternative) ...............4-397

4.13.9.3 Impacts – Alternative C (Proposed Action – Alternative A Plus 

Additional Mitigation Measures)............................................................4-398

4.13.9.4 Impacts – Alternative D (Alternative C Plus Marine Mammal 

Shutdowns)............................................................................................4-398

4.13.9.5 Impacts – Alternative E (Alternative C at Reduced Activity Levels) .....4-399

4.13.9.6 Impacts – Alternative F (Alternative C Plus Area Closures).................4-401

4.13.9.7 Impacts – Alternative G (No New Activity Alternative)..........................4-403

4.14 NMFS’ Analysis of Chronic Effects in the Gulf of Mexico in Support of the MMPA 

Petition for Incidental Take Regulations ..........................................................................4-405

5 OTHER NEPA CONSIDERATIONS............................................................................................... 5-3

5.1 Unavoidable Adverse Impacts of the Proposed Action........................................................ 5-3

5.2 Irreversible and Irretrievable Commitment of Resources .................................................... 5-4

5.3 Relationship Between Short-Term Uses of the Environment and the Maintenance 

and Enhancement of Long-Term Productivity ..................................................................... 5-5

6 PUBLIC INVOLVEMENT AND AGENCY CONSULTATION AND COORDINATION ................... 6-3

6.1 Development of the Proposed Action................................................................................... 6-3

6.2 Notice of Intent ..................................................................................................................... 6-3

6.3 Scoping and Development of the Draft Programmatic EIS.................................................. 6-3

6.3.1 Scoping Meetings .................................................................................................... 6-4 

6.3.2 Comments Received During Scoping...................................................................... 6-4 

6.3.3 Cooperating Agencies.............................................................................................. 6-5 

6.3.3.1 Bureau of Safety and Environmental Enforcement................................... 6-6

6.3.3.2 National Oceanic and Atmospheric Administration................................... 6-7

6.4 Distribution of the Draft Programmatic EIS.......................................................................... 6-8

6.5 Public Meetings .................................................................................................................. 6-12

6.6 Regulatory Framework ....................................................................................................... 6-12

6.6.1 Federal Agencies and Regulations........................................................................ 6-12

6.6.2 State Agencies and Regulations............................................................................ 6-13

6.7 Consultation with the National Marine Fisheries Service .................................................. 6-13

7 LITERATURE CITED...................................................................................................................... 7-3
Gulf of Mexico G&G Activities Programmatic EIS xix

8 PREPARERS AND REVIEWERS .................................................................................................. 8-3

8.1 BOEM, BSEE, and NMFS Preparers................................................................................... 8-3

8.2 BOEM and NMFS Reviewers............................................................................................... 8-3

8.3 Contractor Preparers............................................................................................................ 8-4

 
xx Table of Contents

Volume II 

Page

LIST OF FIGURES.............................................................................................................................. xxi

LIST OF TABLES...............................................................................................................................xxiii 

FIGURES ................................................................................................................................. Figures-3 

TABLES......................................................................................................................................Tables-3 

APPENDIX A AGREEMENTS AND COOPERATING AGENCY LETTERS................................... A-1 

APPENDIX B PROTECTIVE MEASURES AND MITIGATION AND REGULATORY 

REQUIREMENTS..................................................................................................... B-1 

APPENDIX C SETTLEMENT AGREEMENT AND STIPULATION TO AMEND SETTLEMENT 

AGREEMENT ........................................................................................................... C-1 

APPENDIX D ACOUSTIC PROPAGATION AND EXPOSURE MODELING ................................. D-1 

Volume III

Page

LIST OF FIGURES.............................................................................................................................. xxi

LIST OF TABLES............................................................................................................................... xxiii

APPENDIX E EXPANDED AFFECTED ENVIRONMENT INFORMATION .................................... E-1 

APPENDIX F G&G SURVEY DESCRIPTIONS.............................................................................. F-1 

APPENDIX G SCREENING OUT TEAM REPORT......................................................................... G-1 

APPENDIX H MARINE MAMMAL HEARING AND SENSITIVITY TO ACOUSTIC IMPACTS....... H-1 

APPENDIX I SEA TURTLE HEARING AND SENSITIVITY TO ACOUSTIC IMPACTS ................. I-1 

APPENDIX J FISH HEARING AND THE SENSITIVITY OF FISH TO HEARING LOSS AND 

INJURY FROM EXPOSURE TO ANTHROPOGENIC SOUND................................ J-1 

APPENDIX K CUMULATIVE AND CHRONIC EFFECTS IN THE GULF OF MEXICO ................. K-1 

APPENDIX L PANEL REPORTS..................................................................................................... L-1 
Gulf of Mexico G&G Activities Programmatic EIS xxi

LIST OF FIGURES

Page

Figure ES-1. Area of Interest for the Proposed Action. .................................................................. ix

Figure 1.1-1. Area of Interest for the Proposed Action. ..................................................... Figures-3

Figure 2.2-1. Alternative B Seasonal Restrictions for Coastal Waters Between 

January 1 and April 30 and Areas of Concern as Defined in the 

Settlement Agreement. ................................................................................. Figures-4

Figure 2.3-1. Alternatives C through F Seasonal Restrictions for Coastal Waters 

Between February 1 and May 31 and Areas Requiring PAM for All 

Seismic Airgun Surveys................................................................................ Figures-5

Figure 2.6-1. Alternative F Closure Areas (the CPA Closure Area; the EPA Closure 

Area; the Dry Tortugas Closure Area; and the Flower Gardens Closure 

Area) and Seasonal Restrictions for Coastal Waters Between February 1 

and May 31 and Areas Requiring PAM for All Seismic Airgun Surveys. ..... Figures-6

Figure 3.4-1. Cumulative Activities Occurring in the AOI................................................... Figures-7

Figure 4.1-1. Locations of Selected Northern Gulf of Mexico Cetacean Stocks in 

Relation to the Cumulative Surface Oiling Footprint of the Deepwater 

Horizon Oil Spill............................................................................................. Figures-8

Figure 4.2-1. Distribution of Sperm Whale Sightings from Vessel Surveys....................... Figures-9

Figure 4.2-2. Manatee Sightings in the AOI..................................................................... Figures-10

Figure 4.2-3. Distribution of Bryde’s Whale Sightings from Vessel Surveys ................... Figures-11

Figure 4.2-4. Bays and Sounds of the Northern GOM..................................................... Figures-12

Figure 4.3-1. Sea Turtle Nesting Locations Reported for Individual Counties Adjacent 

to the AOI from 1992 to 2014 ..................................................................... Figures-13

Figure 4.3-2. Location of the Four Recovery Units for the Loggerhead Turtle 

in the U.S. ................................................................................................... Figures-14

Figure 4.3-3. Designated Critical Habitat for Hatchling Loggerhead Turtles, Including 

Sargassum Habitat. .................................................................................... Figures-15

Figure 4.3-4. Frequency Range of Hearing in Sea Turtles and Typical Frequency 

Output from Seismic Airguns ...................................................................... Figures-16

Figure 4.4-1. Smalltooth Sawfish and Gulf Sturgeon Critical Habitat in the AOI............. Figures-17

Figure 4.5-1. Distribution of Known Hard/Live Bottom and Chemosynthetic 

Communities Locations in the AOI for Which NTLs Apply......................... Figures-18

Figure 4.5-2. Topographic Features Located in the AOI.................................................. Figures-19

Figure 4.5-3. Location of Artificial Reefs (deliberately placed objects/structures 

of human origin) in the AOI......................................................................... Figures-20

Figure 4.6-1. Mississippi Flyway Migratory Routes.......................................................... Figures-21

Figure 4.6-2. Bird Conservation Regions ......................................................................... Figures-22

Figure 4.6-3. U.S. Important Bird Areas........................................................................... Figures-23

Figure 4.6-4. IBAs of Louisiana that Include Nearshore Waters Within the AOI............. Figures-24

Figure 4.7-1. National System Offshore Marine Protected Areas Within the AOI........... Figures-25

Figure 4.7-2. National System Coastal Marine Protected Areas Within the AOI............. Figures-26

Figure 4.9-1. Locations of Selected Seasonal and/or Area Closures to Commercial 

Fishing in the AOI. ...................................................................................... Figures-27

Figure 4.12-1. Aids to Navigation, Shipping Lanes, Precaution Areas, Fairways, and 

Traffic Separation Schemes in the AOI. ..................................................... Figures-28

Figure 4.12-2. Military Use and Ordnance Disposal Areas in the AOI............................... Figures-29

Figure 4.12-3. OCS Sand and Gravel Borrow Areas Within the AOI................................. Figures-30

Figure 4.12-4. Ocean Dredged Material Disposal Sites in the AOI ................................... Figures-31

Figure 4.12-5. Gulf of Mexico Energy Security Act (GOMESA) Areas. ............................. Figures-32
xxii List of Figures

Figure 4.12-6a. Oil and Gas Platforms and Pipelines in the Western Planning Area 

in the AOI .................................................................................................... Figures-33

Figure 4.12-6b. Oil and Gas Platforms and Pipelines in the Central Planning Area 

in the AOI. ................................................................................................... Figures-34

Figure 4.12-6c. Oil and Gas Platforms and Pipelines in the Eastern Planning Area 

in the AOI .................................................................................................... Figures-35

Figure 4.12-7. Existing Submarine Telecommunications Cables Located in the AOI....... Figures-36

 
Gulf of Mexico G&G Activities Programmatic EIS xxiii

LIST OF TABLES

Page

Table ES-1 Applicability of Mitigation Measures to G&G Surveys by Alternative.......................xiii

Table ES-2 Preliminary Screening of Potential Impacts (Leopold Matrix) ................................. xvii

Table 1.1-1. Federal Regulations Applicable to Pre-Lease and Post-Lease Activities 

by Mineral Resource of Interest......................................................................Tables-3

Table 1.4-1. Program Area, G&G Activity, Permitting Authority, and Typical NEPA 

ActionTables-5

Table 2-1. Applicability of Mitigation Measures to G&G Surveys by Alternative.............Tables-6

Table 2-2. Summary of Mitigation Measures Included in Alternatives A through F ........Tables-7

Table 2.5-1. Alternative E1: 10-Percent Reduction of Deep-Penetration Seismic, 

Multi-Client Activities’ (in line miles) Projected Levels of G&G Activities 

for Oil and Gas Exploration in the AOI .........................................................Tables-11

Table 2.5-2. Alternative E2: 25-Percent Reduction of Deep-Penetration Seismic, 

Multi-Client Activities’ (in line miles) Projected Levels of G&G Activities 

for Oil and Gas Exploration in the AOI .........................................................Tables-13

Table 2.7-1. Alternative G, the No New Activity Alternative: Projected Levels of G&G 

Activities in the AOI Over the 10-Year Period ..............................................Tables-15

Table 2.10-1. Impact Levels by Resource and Applicable IPF Across Alternatives A 

Through G, as Discussed in Chapter 2.10 ...................................................Tables-16

Table 3.1-1. Types of G&G Activities Included in this Programmatic EIS........................Tables-20

Table 3.2-1. Projected Levels of Acoustic Geophysical Activities for Oil and Gas 

Exploration in the AOI Over the 10-Year Time Period (numbers of 

surveys) and Survey Line Distance (miles)..................................................Tables-22

Table 3.2-2. Projected Levels of Non-Acoustic and Geological Activities for Oil and 

Gas Exploration in the AOI Over the 10-Year Time Period (numbers 

of surveys) and Survey Line Distance (miles) or Cores ...............................Tables-24

Table 3.2-3. Projected Levels of G&G Activities for Renewable Energy Site 

Characterization and Assessment in the AOI Over the 10-Year Time 

Period............................................................................................................Tables-25

Table 3.2-4. Projected Levels of Geological Surveys for OCS Marine Minerals 

Projects in the AOI Over the 10-Year Time Period ......................................Tables-26

Table 3.2-5. Projected Levels of Geophysical Surveys for Marine Minerals Projects 

in the AOI Over the 10-Year Time Period.....................................................Tables-27

Table 3.2-6. Characteristics of the Proposed G&G Activities Scenario in the AOI 

Over the 10-Year Time Period......................................................................Tables-29

Table 3.2-7. Vessel and Helicopter Traffic Associated with the Proposed Action............Tables-33

Table 3.2-8. Summary of All Projected Levels of G&G Activities in the AOI Over 

the 10-Year Time Period for the Oil and Gas, Renewable Energy, and 

Marine Minerals Program Areas...................................................................Tables-34

Table 3.3-1. Impact-Producing Factor Descriptions .........................................................Tables-35

Table 3.3-2. Characteristics of Active Acoustic Sound Sources Included in the 

Proposed Action............................................................................................Tables-36

Table 3.4-1. Cumulative Scenario Activities that Include Coincident Impact-Producing 

Factors with the Proposed Action G&G Activities ........................................Tables-37

Table 3.4-2. Summary of Oil and Gas Exploration and Development Activities in the

U.S. Gulf of Mexico Projected 10-Year Projections (based on 40-year 

projections)....................................................................................................Tables-38

Table 3.4-3. Structure Removal Permit Applications on the AOI, 2002 to 2013 ..............Tables-39

Table 3.4-4. Structures Removed from the AOI, 2002 to 2013 ........................................Tables-39
xxiv List of Tables

Table 3.4-5. Summary of Annual Oil and Gas Production from State Waters of 

Several Gulf States.......................................................................................Tables-39

Table 3.4-6. Summary of Deepwater Ports in the AOI .....................................................Tables-40

Table 3.4-7. Summary of Commercial Vessel Port Visits for Vessels >1,000 Gross 

Tons to AOI Ports in 2012 ............................................................................Tables-42

Table 3.4-8. Vessel Trips in the AOI in 2012 Recorded by Vessels Equipped with 

Automatic Identifications Systems................................................................Tables-43

Table 3.4-9. Cruise Ship Departures from Gulf Ports, by Year ........................................Tables-44

Table 4.1-1. Types of G&G Activities, by Survey Type, and Associated IPFs 

Associated with Each Survey Type as Described in Appendix F.................Tables-45

Table 4.1-2. Preliminary Screening of Potential Impacts (Leopold Matrix) ......................Tables-47

Table 4.1-3. Length and Area of Oiling of State and Federal Lands along the 

Northern Gulf Coast Caused by the Deepwater Horizon Oil Spill................Tables-48

Table 4.2-1. Marine Mammals Potentially Occurring in the AOI.......................................Tables-49

Table 4.2-2. Stocks of Bottlenose Dolphins within the AOI ..............................................Tables-53

Table 4.2-3. Functional Marine Mammal Hearing Groups, Associated Auditory 

Bandwidths, and Marine Mammal Species Present in the AOI....................Tables-54

Table 4.2-4. Dual Injury Criteria for Marine Mammals Exposed to Impulsive Noise 

Over a 24-Hour Period..................................................................................Tables-54

Table 4.2-5. Existing and Proposed Injury and Behavior Exposure Criteria for 

Cetaceans and Manatees Exposed to Pulsed Sounds ................................Tables-55

Table 4.2-6. Density Ratios for Each of the Modeling Zones and Seasonal 

Restrictions/Closure Areas ...........................................................................Tables-56

Table 4.3-1. Sea Turtles Occurring in the AOI..................................................................Tables-57

Table 4.4-1. Hard Bottom Species and Life Stages with Essential Fish Habitat 

Identified within the AOI................................................................................Tables-58

Table 4.4-2. Coastal Migratory Pelagic Species and Life Stages with Essential Fish 

Habitat Identified within the AOI ...................................................................Tables-65

Table 4.4-3. Highly Migratory Species and Life Stages with Essential Fish Habitat 

Identified within the AOI................................................................................Tables-66

Table 4.4-4. Shark Species and Life Stages with Essential Fish Habitat Identified 

within the AOI................................................................................................Tables-68

Table 4.5-1. Topographic Features (Banks) of the Gulf of Mexico...................................Tables-70

Table 4.6-1. Families of Seabirds, Waterfowl, and Shorebirds Occurring in the AOI ......Tables-71

Table 4.7-1. National System MPAs Within or Partially Within the AOI ...........................Tables-74

Table 4.9-1. 2012 Economic Impacts of the Gulf of Mexico Region Seafood Industry 

(thousands of dollars) ...................................................................................Tables-79

Table 4.9-2. Total Landings and Landings of Key Species/Species Groups 

(thousands of pounds)..................................................................................Tables-79

Table 4.9-3. Primary Commercial Fishing Methods, Target Species, Seasons, and 

General Areas Fished in the Gulf of Mexico.................................................Tables-80

Table 4.9-4. Summary of Seasonal and/or Area Closures to Commercial Fishing in 

Federal Waters in the Gulf of Mexico ...........................................................Tables-81

Table 4.10-1. Recreational Fishing Effort by Mode (thousands of angler-trips).................Tables-82

Table 4.10-2. 2012 Economic Impacts of Recreational Fishing Expenditures 

(thousands of dollars) ...................................................................................Tables-82

Table 4.10-3. Recreational Harvest (H) and Release (R) of Key Species and Species 

Groups (thousands of fish) ...........................................................................Tables-82

Table 4.10-4. Summary of Recreational Fishing Tournaments in the Gulf of Mexico........Tables-83

Table 4.12-1. Recent Marine Mineral Projects in Florida and Louisiana............................Tables-92

Table 4.13-1. Population Living in Gulf of Mexico Coastal Watershed Communities 

(1970 to 2010)...............................................................................................Tables-92

Table 4.13-2. 2012 Economic Impact of the Gulf of Mexico on Coastal Communities ......Tables-92
Gulf of Mexico G&G Activities Programmatic EIS xxv

Table 4.13-3. 2012 Minority Populations in Geographic Areas Associated with Ports 

Serving the G&G Industry in the AOI............................................................Tables-93

Table 4.13-4. 2012 Low-Income Populations in Geographic Areas Associated with 

Ports Serving the G&G Industry in the AOI ..................................................Tables-94

Table 4.13.9-1. Survey Incremental Cost and Percent Cost Change by Alternative ............Tables-95

Table 4.13.9-2. Total Annual Survey Incremental Cost by Alternative..................................Tables-96

Table 4.13.9-3. Percent Change in Operational Efficiency by Alternative.............................Tables-97

APPENDIX E 

EXPANDED AFFECTED ENVIRONMENT INFORMATION

Gulf of Mexico G&G Activities Programmatic EIS E-iii

TABLE OF CONTENTS

LIST OF FIGURES............................................................................................................................... vii

LIST OF TABLES................................................................................................................................. vii

ABBREVIATIONS AND ACRONYMS .................................................................................................. ix

1 INTRODUCTION ............................................................................................................................. 1

2 MARINE MAMMALS........................................................................................................................ 3

2.1 Cetaceans – Mysticetes ......................................................................................................... 3

2.1.1 Bryde’s Whale............................................................................................................ 3

2.2 Cetaceans – Odontocetes...................................................................................................... 6

2.2.1 Sperm Whale ............................................................................................................. 6

2.2.2 Pygmy and Dwarf Sperm Whales............................................................................13

2.2.3 Cuvier’s Beaked Whale ...........................................................................................15

2.2.4 Mesoplodon Beaked Whales...................................................................................18

2.2.5 Rough-Toothed Dolphin...........................................................................................21

2.2.6 Common Bottlenose Dolphin...................................................................................23

2.2.7 Pantropical Spotted Dolphin....................................................................................29

2.2.8 Clymene Dolphin......................................................................................................31

2.2.9 Striped Dolphin ........................................................................................................33

2.2.10 Atlantic Spotted Dolphin ..........................................................................................35

2.2.11 Spinner Dolphin .......................................................................................................37

2.2.12 Fraser’s Dolphin.......................................................................................................40

2.2.13 Risso’s Dolphin ........................................................................................................ 42

2.2.14 Melon-Headed Whale..............................................................................................44

2.2.15 Pygmy Killer Whale..................................................................................................46

2.2.16 False Killer Whale....................................................................................................48

2.2.17 Killer Whale..............................................................................................................50

2.2.18 Short-Finned Pilot Whale.........................................................................................53

2.3 Sirenians – West Indian Manatee ........................................................................................56

2.3.1 Population................................................................................................................56

2.3.2 Distribution and Abundance ....................................................................................56

2.3.3 Habitat......................................................................................................................57

2.3.4 Behavior...................................................................................................................57

2.3.5 Vocalizations and Hearing.......................................................................................57

2.3.6 Threats.....................................................................................................................58

2.3.7 Status.......................................................................................................................58

3 SEA TURTLES ..............................................................................................................................58

3.1 Loggerhead Sea Turtle.........................................................................................................62

3.1.1 Range and Spatial Distribution................................................................................62

3.1.2 Population Status.....................................................................................................63

3.1.3 Ecology and Life History..........................................................................................64

3.1.4 Threats.....................................................................................................................65

3.1.5 Current Status..........................................................................................................65
E-iv Expanded Affected Environment Information

3.2 Green Sea Turtle..................................................................................................................65

3.2.1 Range and Spatial Distribution................................................................................65

3.2.2 Population Status.....................................................................................................66

3.2.3 Ecology and Life History..........................................................................................66

3.2.4 Threats.....................................................................................................................67

3.2.5 Current Status..........................................................................................................67

3.3 Hawksbill Sea Turtle.............................................................................................................68

3.3.1 Range and Spatial Distribution................................................................................68

3.3.2 Population Status.....................................................................................................68

3.3.3 Ecology and Life History..........................................................................................69

3.3.4 Threats.....................................................................................................................70

3.3.5 Current Status..........................................................................................................70

3.4 Kemp’s Ridley Sea Turtle.....................................................................................................71

3.4.1 Range and Spatial Distribution................................................................................71

3.4.2 Population Status.....................................................................................................71

3.4.3 Ecology and Life History..........................................................................................72

3.4.4 Threats.....................................................................................................................73

3.4.5 Current Status..........................................................................................................73

3.5 Leatherback Sea Turtle........................................................................................................73

3.5.1 Range and Spatial Distribution................................................................................73

3.5.2 Population Status.....................................................................................................75

3.5.3 Ecology and Life History..........................................................................................75

3.5.4 Threats.....................................................................................................................76

3.5.5 Current Status..........................................................................................................76

3.6 Summary of Sea Turtle Hearing Capabilities.......................................................................77

4 FISH RESOURCES AND ESSENTIAL FISH HABITAT ...............................................................79

4.1 Listed Species ......................................................................................................................79

4.1.1 Smalltooth Sawfish ..................................................................................................80

4.1.2 Gulf Sturgeon...........................................................................................................81

4.2 Candidate Species and Species of Concern .......................................................................82

4.3 Non-Listed Species ..............................................................................................................82

4.3.1 Continental Shelf Fishes..........................................................................................82

4.3.2 Oceanic Fishes ........................................................................................................87

4.4 Essential Fish Habitat...........................................................................................................89

5 BENTHIC COMMUNITIES ............................................................................................................90

5.1 Soft Bottom Communities.....................................................................................................91

5.1.1 Megafauna...............................................................................................................93

5.1.2 Macrofauna..............................................................................................................93

5.1.3 Meiofauna ................................................................................................................93

5.1.4 Microbiota ................................................................................................................94

5.2 Hard Bottom Communities ...................................................................................................94

5.2.1 Deepwater Coral Communities................................................................................94

5.2.2 Live Bottoms (Pinnacle Trend) ................................................................................95

5.2.3 Live Bottoms (Low Relief)........................................................................................96

5.2.4 Topographic Features..............................................................................................99

5.2.5 Artificial Reefs........................................................................................................101

5.3 Chemosynthetic Communities ...........................................................................................103

5.4 Listed and Candidate Species............................................................................................104
Gulf of Mexico G&G Activities Programmatic EIS E-v 

6 MARINE AND COASTAL BIRDS ................................................................................................104

6.1 Listed Species ....................................................................................................................105

6.2 Non-Listed Species ............................................................................................................107

6.2.1 Seabirds.................................................................................................................107

6.2.2 Waterfowl ...............................................................................................................108

6.2.3 Shorebirds..............................................................................................................109

6.3 Migration.............................................................................................................................109

6.4 Bird Conservation Regions and Birds of Conservation Concern.......................................110

6.5 Important Bird Areas...........................................................................................................110

7 MARINE PROTECTED AREAS ..................................................................................................111

7.1 National Marine Sanctuaries ..............................................................................................112

7.1.1 Florida Keys National Marine Sanctuary...............................................................113

7.1.2 Flower Garden Banks National Marine Sanctuary ................................................113

7.2 Other Federal Fishery Management Areas........................................................................115

7.3 Coastal Marine Protected Areas ........................................................................................118

7.3.1 National Park System (National Seashores).........................................................118

7.3.2 National Wildlife Refuges.......................................................................................119

7.3.3 National Estuarine Research Reserves ................................................................122

7.3.4 State-Designated Marine Protected Areas............................................................123

8 SARGASSUM AND ASSOCIATED COMMUNITIES..................................................................124

8.1 Sargassum Distribution ......................................................................................................125

8.2 Fish Habitat ........................................................................................................................125

8.3 Sea Turtle Habitat...............................................................................................................125

8.4 Invertebrate Habitat............................................................................................................126

9 COMMERCIAL FISHERIES ........................................................................................................126

9.1 Commercial Landings.........................................................................................................127

9.2 Commercial Fishing Gears................................................................................................. 127

9.3 Time and Area Closures and Gear Restrictions ................................................................128

10 RECREATIONAL FISHERIES.....................................................................................................128

10.1 Recreational Fishing Effort................................................................................................. 129

10.2 Recreational Fishing Locations..........................................................................................130

10.3 Recreational Catch Characteristics....................................................................................130

10.4 Recreational Fishing Tournaments ....................................................................................130

11 ARCHAEOLOGICAL RESOURCES ...........................................................................................131

11.1 Historic Shipwrecks ............................................................................................................131

11.2 Prehistoric Resources ........................................................................................................133

12 OTHER MARINE USES ..............................................................................................................135

12.1 Shipping and Marine Transportation..................................................................................135

12.2 Military Warning Areas and Other Military Uses ................................................................136

12.3 Sand and Gravel Mining.....................................................................................................138

12.4 Renewable Energy Development.......................................................................................140

12.5 Ocean Dredged Material Disposal Sites ............................................................................140

12.6 Oil and Gas Exploration, Production, and Development ...................................................142

12.6.1 Gas Hydrates.........................................................................................................142

12.6.2 Offshore Deepwater Ports .....................................................................................142

12.6.3 Pipeline and Cable Infrastructure ..........................................................................143
E-vi Expanded Affected Environment Information

13 HUMAN RESOURCES AND LAND USE....................................................................................143

13.1 Land Use and Coastal Infrastructure .................................................................................144

13.2 Environmental Justice ........................................................................................................145

13.3 Demographics ....................................................................................................................146

13.4 Socioeconomics .................................................................................................................147

14 RECREATIONAL RESOURCES AND TOURISM ......................................................................148

15 AIR QUALITY...............................................................................................................................150

16 WATER QUALITY .......................................................................................................................155

16.1 Coastal Water Quality ........................................................................................................158

16.2 Marine Water Quality..........................................................................................................159

16.2.1 Continental Shelf West of the Mississippi River....................................................160

16.2.2 Continental Shelf East of the Mississippi River.....................................................161

16.2.3 Deep Water............................................................................................................162

17 GEOGRAPHY AND GEOLOGY..................................................................................................162

17.1 Regional Geologic Description...........................................................................................163

17.2 Geologic History and Sedimentary Basins.........................................................................166

17.3 Sediments...........................................................................................................................167

18 PHYSICAL OCEANOGRAPHY ...................................................................................................168

19 COASTAL BARRIER ISLAND BEACHES ..................................................................................172

20 SEAGRASS ................................................................................................................................. 178

20.1 Western Planning Area ......................................................................................................180

20.2 Central Planning Area ........................................................................................................180

20.3 Eastern Planning Area .......................................................................................................181

20.3.1 Big Bend – Overview .............................................................................................181

20.4 Offshore Halophila Beds ....................................................................................................183

21 WETLANDS................................................................................................................................. 183

22 REFERENCES CITED ................................................................................................................187
Gulf of Mexico G&G Activities Programmatic EIS E-vii

LIST OF FIGURES

Figure E-1. Geographic Boundary of the Gulf of Mexico G&G Programmatic EIS Area 

of Interest. .................................................................................................................... E-2

Figure E-2. Coastal Areas Designated as PSD Class I and Counties Designated as 

Nonattainment Areas Adjacent to the Area of Interest. ........................................... E-153

Figure E-3. Distribution of Bottom-Water Dissolved Oxygen July 27-August 1 (West of the 

Mississippi River Delta), 2014.................................................................................. E-161

Figure E-4. Bathymetry in the Gulf of Mexico............................................................................. E-165

Figure E-5. Physiographic Provinces in the Gulf of Mexico ....................................................... E-165

Figure E-6. Primary Geologic Provinces of the Gulf of Mexico as Indicated by the Dashed 

Lines......................................................................................................................... E-167

Figure E-7. Sediment Distribution Map Showing the Distribution of the Primary Classes 

of Sediment .............................................................................................................. E-168

Figure E-8. Tidal Regimes of the Gulf of Mexico........................................................................ E-169

Figure E-9. Strong Loop Current in the Eastern Gulf of Mexico. ................................................ E-171

Figure E-10. Texas Coastal Barrier Island Beaches. ................................................................... E-174

Figure E-11. Louisiana to Alabama Coastal Barrier Island Beaches. .......................................... E-175

Figure E-12. Florida Coastal Barrier Island Beaches. .................................................................. E-177

Figure E-13. Seagrass Locations Along the Gulf Coast Within the Area of Interest. ................... E-179

Figure E-14. Wetland Locations Along the Gulf Coast Within the Area of Interest. ..................... E-185

LIST OF TABLES

Table E-1. OCS Lease Blocks with Significant Sediment Resources...........................................139

Table E-2. Number of Public Beaches, Number of Visitors, and Number of Visitor Days in 

Coastal Areas of the Gulf of Mexico (From: USDOC, NOAA, 2008)..........................148

Table E-3. Selected Economic Statistics for the Tourism Industry for 2013 (From: U.S. 

Travel Association, 2015a-e). ......................................................................................149

Table E-4. USEPA’s National Ambient Air Quality Standards for the Six “Criteria” 

Pollutants (From: USEPA, 2015b)..............................................................................151

Table E-5. Total Platform and Non-Platform Emission Estimates for Criteria Pollutants .............154

Gulf of Mexico G&G Activities Programmatic EIS E-ix

ABBREVIATIONS AND ACRONYMS

μg microgram

μm micrometer

μPa micropascal

μs microsecond

μV microvolt

ABR auditory brainstem response

ac acre

AEP auditory evoked potential

AOI Area of Interest

ATOC Acoustic Thermometry of Ocean Climate

AWOIS Automated Wreck and Obstruction Information System

B.P. before present

BCR Bird Conservation Region

BOEM Bureau of Ocean Energy Management

BP British Petroleum

BSEE Bureau of Safety and Environmental Enforcement

CAA Clean Air Act

CEI Coastal Environments, Inc.

CI confidence interval

CITES Convention on International Trade in Endangered Species of Wild Fauna and Flora

CO2 carbon dioxide

CV coefficient of variation

dB decibel

DDE dichlorodiphenyldichloroethylene

DDT dichlorodiphenyltrichloroethane

DOSS dioctyl sodium sulfoscuccinate

DPS distinct population segment

DTRU Dry Tortugas Recovery Unit (loggerhead turtles)

EEZ Exclusive Economic Zone

EFH Essential Fish Habitat

Eh oxidation reduction potential

EIS Environmental Impact Statement

ENC Electronic Navigational Charts (NOAA)

EO Executive Order

EPAct Energy Policy Act of 2005

ESA Endangered Species Act

EWTA Eglin Water Test Area

FDEP Florida Department of Environmental Protection

FDHR Florida Division of Historical Resources

FGB Flower Garden Bank

FGBNMS Flower Garden Banks National Marine Sanctuary

FKNMS Florida Keys National Marine Sanctuary

FM frequency modulation

FMC Fishery Management Council
E-x Expanded Affected Environment Information

FMP Fishery Management Plan

FR Federal Register

ft foot

FWC Florida Fish and Wildlife Conservation Committee

FWRI Fish and Wildlife Research Institute

FWS Fish and Wildlife Service (USDOI)

G&G geological and geophysical

GDP gross domestic product

GIS geographic information systems

GMFMC Gulf of Mexico Fishery Management Council

GMWD Global Maritime Wrecks Database

GOM Gulf of Mexico

GOMESA Gulf of Mexico Energy Security Act

ha hectare

HAPC Habitat Area of Particular Concern

HCB hexachlorobenzene

HCH hexachlorocyclohexane

Hz hertz

IBA Important Bird Area

IUCN International Union for Conservation of Nature

kHz kilohertz

km kilometer

kn knot

L liter

LNG liquid natural gas

LOOP Louisiana Offshore Oil Port

m meter

mg milligram

mm millimeter

MMPA Marine Mammal Protection Act

MMS Minerals Management Service

MPA Marine Protected Area

mph miles per hour

ms millisecond

MSA Metropolitan Statistical Area

MSFCMA Magnuson-Stevens Fisheries Conservation and Management Act

MWA Military Warning Area

NAAQS National Ambient Air Quality Standards

NABCI North American Bird Conservation Initiative

NavAids NOAA Aids to Navigation

NAVFAC Naval Facilities Engineering Command

NEPA National Environmental Policy Act

NERR National Estuarine Research Reserve

NGMCS Northern Gulf of Mexico Continental Slope (study)

NGMRU Northern Gulf of Mexico Recovery Unit (loggerhead turtles)

NMFS National Marine Fisheries Service
Gulf of Mexico G&G Activities Programmatic EIS E-xi

nmi nautical mile

NO2 nitrogen dioxide

NOx nitrogen oxides

NOAA National Oceanic and Atmospheric Administration

NOS National Ocean Service

NPDES National Pollutant Discharge Elimination System

NPS National Park Service

NTL Notice to Lessees and Operators

NWA National Wilderness Area

NWR National Wildlife Refuge

O3 ozone

OCS Outer Continental Shelf

OCSLA Outer Continental Shelf Lands Act

ODMDS ocean dredged material disposal site

OSAT Operational Science Advisory Team

OSP optimum sustainable population

P.L. Public Law

PAH polycyclic aromatic hydrocarbon

PBDE polybrominated diphenyl ether

PBR potential biological removal

PCB polychlorinated biphenyl

PDARP Programmatic Damage Assessment and Restoration Plan

PFRU Peninsular Florida Recovery Unit (loggerhead turtles)

pH potential of hydrogen

PM particulate matter

ppb parts per billion

ppm parts per million

PSD Prevention of Significant Deterioration

RESTORE 

Act

Resource and Ecosystem Sustainability, Tourist Opportunities, and Revived 

Economies of the Gulf Coast States Act

RL receiving level

SAFMC South Atlantic Fishery Management Council

SAR Stock Assessment Report

SE standard error

SEMARNAT Secretariat of Environment & Natural Resources

SL source level

SO2 sulfur dioxide

TAMU Texas A&M University

TED turtle excluder device

TEWG Turtle Expert Working Group

TNASS Trans-North Atlantic Sighting Survey

TPH total petroleum hydrocarbons

TPY tons per year

UME unusual mortality event

U.S. United States

U.S.C. United States Code

USACE U.S. Army Corps of Engineers
E-xii Expanded Affected Environment Information

USCG U.S. Coast Guard

USDOC U.S. Department of Commerce

USDOI U.S. Department of the Interior

USEPA U.S. Environmental Protection Agency

VK Viosca Knoll

VOC volatile organic compound

YONAH Years of the North American Humpback 
Gulf of Mexico G&G Activities Programmatic EIS E-1 

1 INTRODUCTION

The affected environment descriptions in Chapter 4 of this Programmatic Environmental 

Impact Statement (EIS) succinctly describe and summarize the existing environment of the Area of 

Interest (AOI) (Figure E-1) in sufficient yet concentrated detail necessary to support the impact 

analysis of the alternatives. The succinct descriptions avoid an encyclopedic Programmatic EIS and 

promote an analytic approach to the document. This appendix provides expanded, more 

comprehensive information, including additional details regarding the affected environment 

resources, and was indirectly considered during the preparation of this Programmatic EIS.

As described in Chapter 4.1.1 and shown in Table 4.1-2 of this Programmatic EIS, 

preliminary screening was conducted to identify the resources at risk of impact from the proposed 

and anticipated geological and geophysical (G&G) activities in the Gulf of Mexico (GOM). Screening 

allows for completion of a focused impact analysis by eliminating (from detailed analysis) resources 

with no potential for adverse or significant impact. This approach focuses the analysis on the 

resources at greatest risk for impact, which resulted in the identification of 12 resources carried 

forward for detailed analysis. The comprehensive affected environment information for those 

12 resources is provided in Sections 2 through 13. To further describe the environmental setting, 

affected environment descriptions for additional resources (those that did not receive a detailed 

impact analysis) are provided in Sections 14 through 21. 

In October 2015, the National Oceanic and Atmospheric Administration (NOAA) released a 

Draft Programmatic Damage Assessment and Restoration Plan and Draft Programmatic EIS 

(PDARP/PEIS) (USDOC, NOAA, 2015a). In February 2016, the Final PDARP/PEIS was released 

(Deepwater Horizon Natural Resource Damage Assessment Trusstees, 2016). The PDARP/PEIS 

considers programmatic alternatives to restore natural resources, ecological services, and 

recreational use services damaged or lost because of the 2010 Deepwater Horizon explosion, oil 

spill, and response (including the sinking of the drilling unit), oil spill, and response. The 

PDARP/PEIS includes an assessment of “injury” to natural resources resulting from the Deepwater 

Horizon explosion, oil spill, and response. Resources screened out of the impact analysis (Sections 

14 through 21) have summarized information therein.
E-2 Expanded Affected Environment Information

Figure E-1. Geographic Boundary of the Gulf of Mexico G&G Programmatic EIS Area or Interest. 
Gulf of Mexico G&G Activities Programmatic EIS E-3 

2 MARINE MAMMALS

Chapter 4.2.1 of this Programmatic EIS provides the succinct description of the affected 

environment for marine mammals in sufficient detail to support the impact analyses. Mammals 

potentially occurring in the AOI are listed and described in Table 4.2-1 of this Programmatic EIS. 

The following descriptions provide additional information on marine mammal life histories. 

Information from the Final PDARP/PEIS (Deepwater Horizon Natural Resource Damage 

Assessment Trusstees, 2016) is included below where appropriate. Information on each species is 

separated into the following subsections: population; distribution and abundance; habitat; behavior; 

vocalization and hearing; threats; and status.

2.1 CETACEANS – MYSTICETES

2.1.1 Bryde’s Whale

Bryde’s whales (Balaenoptera edeni) are large animals (considered medium-sized for 

balaenopterids) with a sleek body that is dark gray in color and white on the ventral side (USDOC, 

NMFS, 2015a). They can reach lengths ranging from 13 to 16.5 m (43 to 54 ft) and weigh up to 

approximately 40,000 kg (90,000 lb). Males are usually slightly smaller than females.

2.1.1.1 Population

The species complex includes one species, Balaenoptera edeni (Bryde’s whale), that occurs 

in the Pacific, Indian, and Atlantic Oceans between approximately 40° N. and 40° S. latitude, and 

two subspecies that occur within the Indian and Pacific Oceans: B. e. edeni (Eden’s whale) and 

B. e. brydei (offshore Bryde’s whale) (Committee on Taxonomy, 2013). For management purposes, 

Bryde’s whales inhabiting U.S. waters have been divided into three stocks: the Eastern Tropical 

Pacific stock; Hawaiian stock; and Northern GOM stock (USDOC, NMFS, 2015a). It is possible that 

Bryde’s whales found in the GOM may represent a resident stock (Schmidly, 1981; Leatherwood 

and Reeves, 1983); however, no information on stock differentiation is available. Rosel and Wilcox, 

(2014) characterized genetic diversity and phylogenetic relationships of GOM resident whales to 

other members of the Bryde’s whale complex. Their low abundance in the region was consistent 

with extremely low levels of genetic diversity found in both mitochondrial DNA and nuclear genomes, 

and places these whales at risk from decreased fitness and evolutionary potential, and demographic 

stochasticity (Rosel and Reeves, 2000). The high level of genetic divergence of GOM Bryde’s 

whales, when compared with the two recognized Bryde’s whale subspecies (B. e. edeni and

B. e. brydei) and other balaenopterids, suggests that they have been isolated for a relatively long 

period of time. The combination of low genetic diversity, low population size, restricted distribution, 

and multiple potential sources for human-induced mortality elevates the level of concern for this 

population (Rosel and Wilcox, 2014).

2.1.1.2 Distribution and Abundance

Bryde’s whales are distributed globally in tropical and subtropical waters of the world 

(Omura, 1959; Kato, 2002). In the western Atlantic Ocean, Bryde’s whales are reported to occur in 
E-4 Expanded Affected Environment Information

waters with average temperatures of 16.3°C (61.3°F) from the southeastern U.S. and the southern 

West Indies to Brazil, or roughly between 40° N. and 40° S. latitude (Leatherwood and Reeves, 

1983; Kato, 2002). Bryde’s whales occur in coastal and pelagic waters and often are sighted in shelf 

break waters or near topographic features such as the De Soto Canyon or Florida Escarpment in the 

GOM (Mullin et al., 1994; Davis et al., 2000). Figure 4.2-3 of this Programmatic EIS shows the 

distribution of Bryde’s whale sightings in the AOI. The Bryde’s whale is considered the most 

common mysticete in the GOM and appears to occur in the GOM year-round (Würsig et al., 2000), 

although only rarely.

The CetMap abundance estimate for GOM Bryde’s whales is 44 individuals (Roberts et al., 

2016). Similarly, from the National Marine Fisheries Service’s (NMFS) Stock Assessment Report’s 

(SAR) data, the best current abundance estimate available for northern GOM Bryde’s whales is 

33 individuals (CV = 1.07). This estimate was based on results from a summer 2009 oceanic survey 

covering waters from the 200-m (168-ft) isobath to the seaward extent of the U.S. Exclusive 

Economic Zone (EEZ) (Waring et al., 2014). Historically, the estimate from surveys within oceanic 

waters was 35 individuals (CV = 1.10) between 1991 and 1994 (Hansen et al., 1995), 40 individuals 

(CV = 0.61) between 1996 and 2001 (Mullin and Fulling, 2004), and 15 individuals (CV = 1.98) 

between 2003 and 2004 (Mullin, 2007).

2.1.1.3 Habitat

Shipboard and aerial surveys conducted by the NMFS in oceanic waters of the northern 

GOM at various times throughout all seasons only observed Bryde’s whales between the 100- and 

300-m (328- and 984-ft) isobaths (maximum depth, 302 m [991 ft]; in the eastern Gulf of Mexico from 

south of Pensacola (head of De Soto Canyon) to northwest of Tampa Bay, Florida (Maze-Foley and

Mullin, 2006; Waring et al., 2013; Rosel and Wilcox, 2014). Additionally, Rice et al. (2014) recorded 

sounds associated with Bryde’s whales from several autonomous recording units deployed south of 

Panama City, Florida, from June through October 2010. An area has been designated as a 

Biologically Important Area for GOM Bryde’s whales, based on extensive expert review and 

synthesis of published and unpublished information (LaBrecque et al., 2015). 

2.1.1.4 Behavior

Bryde’s whales typically are seen alone or in pairs (Tershy, 1992) but have been observed in 

groups of up to 10 individuals (Miyazaki and Wada, 1978). In the GOM, they occur alone or in 

groups of up to seven individuals (Mullin and Hoggard, 2000). Bryde’s whales have been recorded 

swimming at speeds of 10.8 kn (12.4 mph) (Cummings, 1985) with dives lasting as long as 

20 minutes; dive depths are not known. Bryde’s whales feed primarily on euphausiids, copepods, 

and schooling fish such as sardines, herring, pilchard, and mackerel (Best, 1960; Nemoto and 

Kawamura, 1977; Cummings, 1985; Tershy, 1992; Tershy et al., 1993).
Gulf of Mexico G&G Activities Programmatic EIS E-5 

2.1.1.5 Hearing and Vocalizations

Bryde’s whales are classified within the low-frequency, cetacean functional, marine mammal 

hearing group (7 Hz to 30 kHz) (Au et al., 2006; Lucifredi and Stein, 2007; Southall et al., 2007; 

Ketten and Mountain, 2009; Tubelli et al., 2012). There is no direct measurement of auditory 

threshold for Bryde’s whales (Ketten, 2000; Theweissen, 2002). They are known to produce a 

variety of low-frequency sounds in the 20- to 900-Hz band (Cummings, 1985; Edds et al., 1993; 

Oleson et al., 2003). A pulsed moan has been recorded in frequencies ranging from 100 to 900 Hz. 

Oleson et al. (2003) reported call types with a fundamental frequency below 60 Hz. These lower 

frequency call types have been recorded from Bryde’s whales in the Caribbean, eastern tropical 

Pacific, and off the coast of New Zealand. Calves produce discrete pulses at 700 to 900 Hz (Edds 

et al., 1993). The function of these sounds is unknown, but it is assumed to be used for 

communication. Source levels (SLs) range between 152 and 174 dB re 1 μPa at 1 m (Frankel, 

2002).

2.1.1.6 Threats

Annual human-caused mortality and serious injury is unknown for the Northern GOM stock of 

Bryde’s whales. There is no documented mortality or serious injury associated with commercial 

fishing. In 2009, there was one known Bryde’s whale mortality as a result of a ship strike. The 

species is currently hunted outside the U.S. (Japanese whalers) and artisanal whalers have hunted 

and taken Bryde’s whales off the coasts of Indonesia and the Philippines. The Final PDARP/PEIS 

(Deepwater Horizon Natural Resource Damage Assessment Trustees, 2016) quantified the impacts 

from the 2010 Deepwater Horizon oil spill on Bryde’s whales. Forty-eight percent of the population 

was impacted by Deepwater Horizon oil, resulting in an estimated 22 percent maximum decline in 

population size. Due to their already small population size, Bryde’s whales are highly susceptible to 

any threats that can reduce productivity and resiliency to perterbations.

2.1.1.7 Status

The Bryde’s whale is currently protected under the Convention on International Trade in 

Endangered Species of Wild Fauna and Flora (CITES) as well as the MMPA and is classified as 

data deficient by the International Union for Conservation of Nature (IUCN). In 2014, the Natural 

Resources Defense Council (NRDC) petitioned the Secretary of Commerce, through the NMFS, to 

list the Gulf of Mexico population of the Bryde’s whale as an endangered species and to designate 

critical habitat to ensure its recovery pursuant to Section 4(b) of the Endangered Species Act (ESA). 

In the petition, it is argued that the Bryde's whale in the Gulf of Mexico is significant because of its 

unique genetic characteristics, its behavior and morphology, and because it is the only resident 

baleen whale population in the Gulf of Mexico (NRDC, 2014). The genetic differentiation of the Gulf 

of Mexico Bryde's whale makes it evolutionarily significant (Rosel and Wilcox, 2014). Based on 

criteria specified in 50 CFR § 424.14(b)(2), the petition cites the following threats as contributing to 

the present or threatened destruction, modification, or curtailment of habitat or range of the Gulf of 

Mexico Bryde's whale: ship strikes; acoustic impacts; oil spills; other toxic chemicals; ocean 

acidification; entanglement in fishing gear; and trophic impacts due to overfishing. The current 
E-6 Expanded Affected Environment Information

status of Bryde’s whales in the northern GOM, relative to its optimum sustainable population (OSP), 

is unknown. There are insufficient data to determine the population trends for this stock. Total 

human-caused mortality and serious injury for this stock is not known; however, one human-caused 

mortality was documented in 2009. Population modeling from the Final PDARP/PEIS (Deepwater 

Horizon Natural Resource Damage Assessment Trustees, 2016) indicates that the ability of the 

GOM population to recover from the Deepwater Horizon injury is unknown. The northern GOM 

Bryde’s whale is a strategic stock because the average annual human-caused mortality and serious 

injury exceeds potential biological removal (PBR) (PBR = 0.16) (Waring et al., 2014).

2.2 CETACEANS – ODONTOCETES

2.2.1 Sperm Whale

The sperm whale (Physeter macrocephalus) is the largest odontocete, with adult lengths 

ranging from 12 to 18 m (40 to 60 ft). Sperm whales also are the most sexually dimorphic whale in 

terms of body length and weight, with adult males being up to approximately 50 percent larger than 

females (Whitehead, 2002; Jefferson et al., 2008). Sperm whales are mostly dark gray, though 

some individuals have white patches on the ventral side, with an extremely large head that takes up 

approximately one-third of its total body length. The most distinctive feature of the sperm whale is 

this massive head and specialized nasal complex, which functions as a pneumatic sound generator 

(Madsen et al., 2002).

2.2.1.1 Population

There is no clear understanding of the global population structure of sperm whales (Dufault 

et al., 1999). Recent ocean-wide genetic studies indicate low, but statistically significant, genetic 

diversity and no clear geographic structure, but strong differentiation between social groups (Lyrholm 

et al., 1996; Lyrholm and Gyllensten, 1998; Lyrholm et al., 1999). Sperm whale populations appear 

to be structured socially at the clan level rather than geographically (Whitehead, 2003; Whitehead 

et al., 2008).

The International Whaling Commission currently recognizes four sperm whale stocks: North 

Atlantic, North Pacific, northern Indian Ocean, and Southern Hemisphere (Reeves and Whitehead, 

1997; Dufault et al., 1999). Genetic studies indicate that movements of both sexes through 

expanses of ocean basins are common, and that males, but not females, often breed in different 

ocean basins than the ones in which they were born (Whitehead, 2003). Matrilinear groups in the 

eastern Pacific share nuclear DNA within broader clans, but North Atlantic matrilinear groups do not 

share this genetic heritage (Whitehead et al., 2012). Genetic studies of GOM sperm whales found 

significant genetic differentiation in matrilineally inherited mitochondrial DNA among whales 

examined from the northern GOM and animals examined from the western North Atlantic Ocean, 

North Sea, and Mediterranean Sea. However, similar comparisons of biparentally inherited nuclear 

DNA showed no significant difference between GOM whales and whales from the other areas of the 

North Atlantic. The overall results from these studies indicate that some mature male sperm whales 

move in and out of the GOM (Engelhaupt et al., 2009). Results from satellite tagging studies of 
Gulf of Mexico G&G Activities Programmatic EIS E-7 

individual GOM sperm whales found no evidence of seasonal migrations of groups outside of the 

GOM but documented Gulfwide movements, primarily along the northern continental slope and (in a 

few cases) into the southern GOM. Only one sperm whale (an adult male) tagged during this study 

left the GOM for the North Atlantic and returned after a period of approximately 2 months (Jochens 

et al., 2008).

Sperm whale vocalization patterns called “codas” have distinct patterns and are believed to 

be culturally transmitted. Coda patterns have been examined and, based on the degree of social 

affiliation of these patterns, can be used to place mixed groups of sperm whales worldwide in 

discrete “acoustic clans” (Watkins and Schevill, 1977; Whitehead and Weilgart, 1991; Rendell and 

Whitehead, 2001; Rendell and Whitehead, 2003). These vocal dialects indicate parent-offspring 

transmission that suggests differentiation in populations (Rendell et al., 2011). Coda patterns from 

mixed groups of sperm whales in the GOM were compared with those from other areas of the 

Atlantic and suggest that GOM sperm whales may constitute a distinct acoustic clan. However, the 

study also found variation in coda patterns between sperm whales in the north-central GOM and the 

northwest GOM. From these results, it was suggested that groups of sperm whales from other 

acoustic clans (e.g., from the North Atlantic) may occasionally enter the northern GOM (Gordon 

et al., 2008).

On average, the total length of GOM sperm whales is 1.5 to 2 m (5 to 7 ft) smaller than 

sperm whales measured in other areas (Waring et al., 2013). Older males, which (based on tagging 

data) may enter the GOM only for breeding, are larger than the younger males that have not yet 

migrated out of the GOM (78 FR 68032). Sperm whale group size in the GOM is smaller on average 

than in other oceans; however, group size is variable throughout the global range of sperm whales. 

For example, female/immature sperm whale group size in the GOM is one-quarter to one-third that 

found in the Pacific Ocean but similar to group sizes observed in the Caribbean (Richter et al., 2008; 

Jaquet and Gendron, 2009).

In summary, although movements between the North Atlantic and GOM have been 

documented, GOM sperm whales are genetically distinct from their Mediterranean and North Atlantic 

relatives (Engelhaupt, 2004; Waring et al., 2013). The acoustic dialect used by this group is also 

different from sperm whales in the North Atlantic (Waring et al., 2013). For these and other reasons 

(e.g., average size, photo identification studies), sperm whales in the GOM constitute a stock that is 

distinct from other Atlantic Ocean stocks, considered as the Northern GOM stock (Waring et al., 

2013).

2.2.1.2 Distribution and Abundance

Sperm whales are cosmopolitan in their distribution, ranging from tropical latitudes to pack 

ice edges in both hemispheres. Mature males in the Atlantic range between 70° N. and 70° S. 

latitude (Reeves and Whitehead, 1997; Perry et al., 1999), whereas mature females and immature 

individuals of both sexes are seldom found higher than 50° N. or 50° S. latitude (Reeves and 
E-8 Expanded Affected Environment Information

Whitehead, 1997). In winter, sperm whales migrate closer to equatorial waters, primarily to breed 

(Kasuya and Miyashita, 1988; Waring et al., 1993).

In the GOM, systematic aerial and ship surveys indicate that sperm whales are widely 

distributed during all seasons in continental slope and oceanic waters, particularly along and 

seaward of the 1,000-m (3,280-ft) isobaths and within areas of steep depth gradients (Figure 4.2 1

of this Programmatic EIS) (Mullin et al., 1991, 1994, and 2004; Hansen et al., 1996; Jefferson and 

Schiro, 1997; Davis et al., 1998; Mullin and Hoggard, 2000; Ortega Ortiz, 2002; Fulling et al., 2003; 

Mullin and Fulling, 2004; Maze Foley and Mullin, 2006; Mullin, 2007; Jefferson et al., 2008). The 

spatial distribution of sperm whales within the GOM is also strongly correlated with mesoscale 

physical features such as Loop Current eddies that locally increase primary production and the 

availability of prey (Biggs et al., 2005).

The CetMap abundance estimate for northern GOM sperm whales is 2,128 individuals 

(Roberts et al., 2016). From NMFS SAR data, the best abundance estimate available for northern 

GOM sperm whales, derived from a summer 2009 oceanic survey, is 763 individuals (CV = 0.38) 

(Waring et al., 2013). The minimum population estimate resulting from these data is 560 sperm 

whales. From 1991 through 1994 and from 1996 through 2001 (excluding 1998), annual surveys 

were conducted within oceanic waters during spring along a fixed plankton-sampling trackline. Due 

to the limited number of surveys in any given year, the survey effort-weighted estimated average 

abundance of sperm whales for all surveys was combined. From 1991 to 1994, the estimate was 

530 individuals (CV = 0.31) (Hansen et al., 1996), and for 1996 to 2001, the estimate was 

1,349 individuals (CV = 0.23) (Mullin and Fulling, 2004). During summer 2003 and spring 2004, 

surveys dedicated to estimating cetacean abundance were conducted along a grid of uniformly 

spaced transect lines from a random start. The abundance estimate for sperm whales, pooled from 

2003 to 2004, was 1,665 individuals (CV = 0.20) (Mullin, 2007).

Jochens et al. (2006) estimated the number of sperm whales off the Mississippi River Delta 

to be 398 individuals (CI = 253 to 607). Mullin et al. (2004) estimated the number of whales in the 

north-central and northwestern GOM at 87 individuals (95% CI = 52 to 146).

2.2.1.3 Habitat

Sperm whales have a strong preference for waters deeper than 1,000 m (3,280 ft) (Watkins, 

1977; Reeves and Whitehead, 1997) and are rarely found in waters <300 m (984 ft) deep (Clarke, 

1956; Rice, 1989). Sperm whales are frequently found in locations of high productivity resulting from 

upwelling or steep underwater topography, such as continental slopes, seamounts, or canyon 

features (Jaquet and Whitehead, 1996; Jaquet et al., 1996). Cold-core eddy features are also 

attractive to sperm whales in the GOM, likely because of the large numbers of squid that are drawn 

to the high concentrations of plankton associated with these features (Biggs et al., 2000; Davis et al., 

2000 and 2002; Wormuth et al., 2000).
Gulf of Mexico G&G Activities Programmatic EIS E-9 

2.2.1.4 Behavior

Reproduction and Social Behavior

Female sperm whales become sexually mature at an average of 9 years or 8.2 to 8.8 m 

(27 to 29 ft) (Kasuya, 1991). Males reach lengths of 10 to 12 m (33 to 39 ft) at sexual maturity and 

take 9 to 20 years to become sexually mature, but they require another 10 years to become large 

enough to successfully breed (Kasuya, 1991; Würsig et al., 2000). Mean age at physical maturity is 

45 years for males and 30 years for females (Waring et al., 2004). Adult females give birth after 

roughly 15 months of gestation and nurse their calves for 2 to 3 years (Waring et al., 2004). The 

calving interval is estimated to be every 4 to 6 years between the ages of 12 and 40 (Kasuya, 1991; 

Whitehead et al., 2008). It has been suggested that some mature males may not migrate to 

breeding grounds annually during winter, and instead may remain in higher latitude feeding grounds 

for >1 year at a time (Whitehead and Arnbom, 1987).

Sperm whale age distribution is unknown, but sperm whales are believed to live at least 

60 years (Rice, 1978). Stable, long-term associations among females form the core of sperm whale 

societies (Christal et al., 1998). Up to a dozen females usually live in such groups, accompanied by 

their female and young male offspring. Young individuals are subject to alloparental care by 

members of either sex and may be suckled by non-maternal individuals (Gero et al., 2009). Groups 

may be stable for long periods, such as for 80 days in the Gulf of California (Jaquet and Gendron, 

2009). Males start leaving these family groups at approximately 6 years of age, after which they live 

in “bachelor schools,” but this may occur more than a decade later (Pinela et al., 2009). The 

cohesion among males within a bachelor school declines with age. During their breeding prime and 

old age, male sperm whales are essentially solitary (Christal and Whitehead, 1997).

Diving

Sperm whales are probably the deepest and longest diving mammalian species, with dives 

to a depth of 3 km (1.9 mi) and durations in excess of 2 hours (Clarke, 1976; Watkins et al., 1985; 

Watkins et al., 1993). However, dives are generally shorter (25 to 45 minutes) and shallower (400 to 

1,000 m [1,312 to 3,280 ft]). Dives are separated by 8- to 11-minute rests at the surface (Gordon, 

1987; Papastavrou et al., 1989; Würsig et al., 2000; Jochens et al., 2006; Watwood et al., 2006). 

Sperm whales typically travel approximately 3 km (1.9 mi) horizontally and 0.5 km (0.3 mi) vertically 

during a foraging dive (Whitehead, 2003). Differences in night and day diving patterns are not 

known for this species, but, like most diving air-breathers for which there are data (rorquals, fur 

seals, and chinstrap penguins), sperm whales probably make relatively shallow dives at night when 

prey are closer to the surface.

Feeding

Sperm whales appear to feed regularly throughout the year (USDOC, NMFS, 2006). It is 

estimated they consume approximately 3 to 3.5 percent of their body weight daily (Lockyer, 1981). 

They seem to forage mainly on or near the seafloor, often ingesting stones, sand, sponges, and 

other non-food items (Rice, 1989). A large proportion of a sperm whale’s diet consists of low-fat, 
E-10 Expanded Affected Environment Information

ammoniacal, or luminescent squids (Clarke, 1980 and 1996; Martin and Clarke, 1986). While sperm 

whales feed primarily on large and medium-sized squids, the list of documented food items is fairly 

long and diverse. Prey items include other cephalopods, such as octopuses, and medium- and 

large-sized demersal fishes, such as rays, sharks, and many teleosts (Berzin, 1972; Clarke, 1977; 

Clarke, 1980; Rice, 1989; Angliss and Lodge, 2004). The diet of large males in some areas, 

especially in high northern latitudes, is dominated by fish (Rice, 1989).

2.2.1.5 Vocalization and Hearing

Sound production and reception by sperm whales are better understood than in most 

cetaceans. Sperm whales produce broadband clicks in the 100 Hz to 20 kHz range that can be 

extremely loud for a biological source (200 to 236 dB re 1 μPa at 1 m), although lower SL energy 

has been suggested at approximately 171 dB re 1 μPa at 1 m (Weilgart and Whitehead, 1993 and

1997; Goold and Jones, 1995; Møhl et al., 2003). Most of the energy in sperm whale clicks is 

concentrated at approximately 2 to 4 kHz and 10 to 16 kHz (Weilgart and Whitehead, 1993; Goold 

and Jones, 1995; USDOC, NMFS, 2006). The highly asymmetric head anatomy of sperm whales is 

likely an adaptation to produce the unique clicks recorded from these animals (Norris and Harvey, 

1972; Cranford, 1992). Long, repeated clicks are associated with feeding and echolocation 

(Weilgart and Whitehead, 1993 and 1997; Goold and Jones, 1995). However, clicks are also used 

in short patterns (codas) during social behavior and intragroup interactions (Weilgart and Whitehead,

1993). They may also aid in intraspecific communication. Another class of sound, “squeals,” are 

produced at frequencies of 100 Hz to 20 kHz (e.g., Weir et al., 2007).

The understanding of sperm whale hearing stems largely from the sounds they produce. 

The only direct measurement of hearing was from a young stranded individual from which auditory 

evoked potentials were recorded (Carder and Ridgway, 1990). From this whale, responses support 

a hearing range of 2.5 to 60 kHz. Sperm whales therefore are classified within the mid-frequency, 

cetacean functional, marine mammal hearing group (150 Hz to 160 kHz) (Southall et al., 2007). 

However, behavioral responses of adult, free-ranging individuals also provide insight into hearing 

range; sperm whales have been observed to frequently stop echolocating in the presence of 

underwater pulses made by echosounders and submarine sonar (Watkins and Schevill, 1975; 

Watkins et al., 1985). They also stop vocalizing for brief periods when codas are being produced by 

other individuals, perhaps because they can hear better when not vocalizing themselves (Goold and 

Jones, 1995). Because they spend large amounts of time at depth and use low-frequency sound, 

sperm whales are likely to be susceptible to low-frequency sound in the ocean (Croll et al., 1999).

2.2.1.6 Threats

Natural

Sperm whales are known to be occasionally preyed upon by killer whales (Jefferson et al., 

1991; Pitman et al., 2001) and large sharks (Best et al., 1984) as well as harassed by pilot whales 

(Arnbom et al., 1987; Rice, 1989; Whitehead, 1995; Palacios and Mate, 1996; Weller et al., 1996). 

Whitt et al. (2015) reported a prolonged interaction between killer whales and sperm whales in the 
Gulf of Mexico G&G Activities Programmatic EIS E-11

GOM during 2011. Strandings are relatively common events, with one to dozens of individuals 

beaching themselves and dying during any single event. Although several hypotheses have been 

proposed, such as navigation errors, illness, and anthropogenic stressors (Goold et al., 2002; 

Wright, 2005), direct widespread causes of strandings remain unclear. An additional natural threat 

to humback whales includes calcivirus and papillomavirus pathogens (Smith and Latham, 1978; 

Lambertsen et al., 1987).

Anthropogenic

Sperm whales historically faced severe depletion from commercial whaling operations. From 

1800 to 1900, the International Whaling Commission estimated that nearly 250,000 sperm whales 

were killed by whalers, with another 700,000 killed from 1910 to 1982. However, other estimates 

have included 436,000 individuals killed between 1800 and 1987 (Carretta et al., 2005). However, 

all of these estimates are likely underestimates due to illegal and inaccurate killings by Soviet 

whaling fleets between 1947 and 1973. Additionally, Soviet whalers disproportionately killed adult 

females in any reproductive condition (pregnant or lactating) as well as immature sperm whales of 

either gender. Following a moratorium on whaling by the International Whaling Commission, 

significant whaling pressures on sperm whales were eliminated.

There were eight sperm whale strandings in the northern GOM between 2006 and 2010 

(Waring et al., 2013). For one stranding, no evidence of human interaction was detected; for the 

remaining seven strandings, it could not be determined if there was evidence of human interactions. 

During June 2010, one dead sperm whale was found floating 124 km (77 mi) due south of the 

Deepwater Horizon spill site. It was not found in oiled waters; however, the location of its death is 

unknown. The cause of death is also unknown; the animal did not appear oily. The Final 

PDARP/PEIS (Deepwater Horizon Natural Resource Damage Assessment Trustees, 2016) 

summarized injuries to GOM sperm whales and stated that 16 percent of the population was 

exposed to Deepwater Horizon oil and 6 percent of the population was killed as a result. In addition, 

7 percent of females likely experienced reproductive failure, and 6 percent of the population has 

experienced adverse health effects. Stranding data probably underestimate the extent of human 

related mortality and serious injury because (1) not all marine mammals that die or are seriously 

injured in human interactions wash ashore; (2) not all that wash ashore are discovered, reported, or 

investigated; and (3) not all that wash ashore show signs of entanglement or other human 

interaction. Sperm whales (and other oceanic species) that die in waters greater than 20-m (66-ft) 

depth are extremely unlikely (<1%) to be found as beached carcasses in the GOM (Deepwater 

Horizon Marine Mammal Injury Quantification Team, 2015). Finally, the level of technical expertise 

among stranding network personnel varies widely as does the ability to recognize signs of fishery 

interactions. Two sperm whale deaths have been considered to be part of the ongoing GOM 

cetacean unusual mortality event (UME).

In U.S. waters, sperm whales are known to have been incidentally captured in drift gillnet 

operations (Barlow et al., 1997), resulting in serious injury and mortality. Interactions between 

longline fisheries and sperm whales have been reported, primarily in Alaskan fisheries (Rice, 1989; 
E-12 Expanded Affected Environment Information

Hill and Demaster, 1998), and observers have documented sperm whales feeding on fish caught in 

longline gear. The available evidence does not indicate sperm whales are being killed or seriously 

injured as a result of these interactions, although the nature and extent of interactions between 

sperm whales and longline gear is not yet clear. In the GOM, sperm whales are most likely to 

interact with pelagic longlines. No fishing-related mortality or serious injury of a sperm whale was 

reported in the GOM between 1998 and 2010. However, in 2008, there was one sperm whale 

released alive with no serious injury after an entanglement interaction with the pelagic longline 

fishery and one mortality due to entanglement in the sea anchor (parachute anchor and lines) of a 

longline fishing vessel (Garrison et al., 2009).

Contaminants have been identified in sperm whales but vary widely in concentration based 

on life history and geographic location, with northern hemisphere individuals generally carrying 

higher burdens (Evans et al., 2004). Contaminants include dieldrin, chlordane, DDT, DDE, PCBs, 

HCB, and HCHs as well as several heavy metals in a variety of body tissues (Aguilar, 1983; Law 

et al., 1996; Evans et al., 2004). However, unlike other marine mammals, females appear to 

bioaccumulate toxins at greater levels than males, which may be related to possible dietary 

differences between females who remain at relatively low latitudes compared wirh more migratory 

males (Aguilar, 1983; Wise et al., 2009). Ingestion of trash and debris can have fatal consequences 

even for large whales, with multiple instances of stranded sperm whales found having ingested 

plastic debris (e.g., Lambertsen, 1990; Viale et al., 1992; USDOC, NMFS, 2009a; de Stephanis 

et al., 2013).

There have not been any recent documented ship strikes involving sperm whales, although 

there are a few records of ship strikes in the 1990s. The lack of recent evidence should not lead to 

the assumption that no mortality or injury from collisions with vessels occurs as carcasses that do 

not drift ashore may go unreported, and those that do strand may show no obvious signs of having 

been struck by a ship (USDOC, NMFS, 2009a). Worldwide, sperm whales are known to have been 

struck 17 times out of a total record of 292 strikes of all large whales, 13 of which resulted in 

mortality (Laist et al., 2001; Jensen and Silber, 2004). One sperm whale mortality, possibly resulting 

from a vessel strike, has been documented for the GOM. The incident occurred in 1990 in the 

vicinity of Grand Isle, Louisiana. Deep cuts on the dorsal surface of the whale indicated the ship 

strike was probably pre-mortem (Jensen and Silber, 2004). Given the current number of reported 

cases of injury and mortality, it does not appear that ship strikes are a significant threat to sperm 

whales (Whitehead, 2003).

2.2.1.7 Status

Sperm whales were originally listed as endangered in 1970 (35 FR 18319), and this status 

remains under the ESA. The IUCN has classified the sperm whale as vulnerable. Sperm whales 

are designated as depleted because of the species’ listing under the ESA, and the Northern GOM 

stock is classified as strategic under the MMPA. The current PBR for GOM sperm whales is 

1.1 individuals (Waring et al., 2013). The NMFS has not designated critical habitat for sperm 

whales. Sperm whales were widely harvested from the northeastern Caribbean (Romero et al., 
Gulf of Mexico G&G Activities Programmatic EIS E-13

2001) and the GOM, where sperm whale fisheries operated during the late 1700s to the early 1900s 

(Townsend, 1935; USDOC, NMFS, 2006). Presumably from the effects of whaling pressure, sperm 

whale populations remain small. Because of their small population size, small changes in 

reproductive parameters, such as the loss of adult females, may significantly affect the growth of 

sperm whale populations (Chiquet et al., 2013). No population trends can be interpreted from data 

available for the GOM; however, recent information from the Final PDARP/PEIS (Deepwater Horizon 

Natural Resource Damage Assessment Trustees, 2016) suggests that sperm whales in the GOM 

have experienced a population decline (6%) as a result of injury from the spill. Changes in 

abundance will be difficult to interpret without a Gulfwide understanding of sperm whale abundance. 

Studies based on abundance and distribution surveys restricted to U.S. waters are unable to detect 

temporal shifts in distribution beyond U.S. waters that might account for any changes in abundance 

(Waring et al., 2013).

2.2.2 Pygmy and Dwarf Sperm Whales

Pygmy (Kogia breviceps) and dwarf (Kogia sima) sperm whales are in the family Kogiidae. 

Pygmy sperm whales reach lengths of approximately 3.5 m (11 ft) and weigh between 315 and

450 kg (700 and 1,000 lb). Dwarf sperm whales can reach lengths of approximately 2.7 m (9 ft) and 

weigh between 135 and 270 kg (300 and 600 lb). Females may be slightly smaller than males.

2.2.2.1 Population

For management purposes, pygmy and dwarf sperm whales inhabiting U.S. waters have 

been divided into four stocks: the California/Oregon/Washington stock; the Hawaiian stock; the 

Northern GOM stock; and the Western North Atlantic stock. Although GOM populations of the two 

Kogia species are provisionally being considered as separate stocks for management purposes, 

there is currently no information to differentiate these stocks from the Atlantic Ocean stock(s) 

(Waring et al., 2012).

2.2.2.2 Distribution and Abundance

Pygmy and dwarf sperm whales are distributed worldwide, primarily in temperate to tropical 

oceanic waters from 40° S. to 60° N. latitude. Both Kogia species are believed to occur year-round 

in the GOM (Würsig et al., 2000). Dwarf and pygmy sperm whales are difficult to differentiate at sea, 

and sightings usually are categorized as Kogia spp. (Waring et al., 2012). Sightings of this category 

were documented in all seasons during GulfCet aerial surveys of the northern GOM from 1992 to 

1998 (Hansen et al., 1996; Mullin and Hoggard, 2000). They have been known to strand along the 

coast of the GOM, especially in fall and winter, which may be associated with the calving season 

(Würsig et al., 2000). Dwarf sperm whales do not strand as frequently as pygmy sperm whales 

(Würsig et al., 2000). Breeding areas for both species include waters off Florida (Evans, 1987). 

There is little evidence of whether pygmy and dwarf sperm whales have a seasonal migration 

pattern (McAlpine, 2002).
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The CetMap abundance estimate for dwarf and pygmy sperm whale (combined) is 

2,234 individuals (Roberts et al., 2016). From NMFS SAR data, the best abundance estimate 

available for northern GOM dwarf and pygmy sperm whales is 186 individuals (CV = 1.04). This 

estimate is from a summer 2009 oceanic survey covering waters from the 200-m (656-ft) isobath to 

the seaward extent of the U.S. EEZ (Waring et al., 2012). Historically, for surveys conducted in 

oceanic waters from 1991 to 1994, the estimate was 547 individuals (CV = 0.28); for 1996 to 2001 

(excluding 1998), 742 individuals (CV = 0.29); and from 2003 to 2004, the estimate was 

453 individuals (CV = 0.35) (Waring et al., 2012).

2.2.2.3 Habitat

Dwarf sperm whales generally have been sighted in warmer waters than pygmy sperm 

whales (Caldwell and Caldwell, 1989). Pygmy sperm whales typically are sighted in water depths of 

100 to 2,000 m (328 to 6,562 ft) while dwarf sperm whales are thought to be more pelagic and 

deeper divers (Barros et al., 1998).

2.2.2.4 Behavior

Dwarf sperm whales are found at the surface in groups of up to 10 individuals while pygmy 

sperm whales are found in smaller groups of 1 to 6 individuals (Caldwell and Caldwell, 1989). These 

groups can vary based on age and sex, but little else is known about the social organization of these 

species. Kogia are rarely active or aerial at the surface, and it is very uncommon for them to 

approach boats. Usually they are seen slowly swimming (3 kn; 3.5 mph) or “logging” (floating 

motionless) at the surface, showing only a small portion of their body. Before diving, they will slowly 

roll or sink and disappear from view without displaying their flukes. This species is very difficult to 

visually spot at sea given their timid behavior, lack of a visible blow, and low profile in the water. 

They usually are only detected in ideal (i.e., calm) sea state and weather conditions (e.g., low wind 

speeds and little or no swells) (USDOC, NMFS, 2015a). Swim speeds vary and were found to reach 

up to 5.9 kn (6.8 mph) (Scott et al., 2001). In the GOM, the maximum dive time for dwarf sperm 

whales was recorded as 43 minutes (Breese and Tershy, 1993; Willis and Baird, 1998). Their diet 

consists of cephalopods (e.g., squids and octopuses), crustaceans (e.g., crabs and shrimp), and 

fish. Based on the structure of their lower jaw and analysis of stomach contents, these animals 

forage and feed in mostly mid-water and deepwater environments as well as near the seafloor. 

Pygmy sperm whales may feed in slightly deeper waters than dwarf sperm whales (USDOC, NMFS, 

2015a).

Dwarf sperm whales become sexually mature at 2.5 to 5 years of age, whereas pygmy 

sperm whales become sexually mature at 4 to 5 years of age. Gestation is estimated to be 9 to 

11 months, and newborn pygmy sperm whale calves are approximately 1.2 m (4 ft) in length and 

weigh 50 kg (110 lb); newborn dwarf sperm whale calves are approximately 1 m (3 ft) in length and 

weigh 40 to 50 kg (88 to 110 lb). Calves probably are weaned after 1 year. Females may give birth 

to calves in consecutive years. The estimated lifespan for these species is 22 to 23 years (USDOC, 

NMFS, 2015a).
Gulf of Mexico G&G Activities Programmatic EIS E-15

2.2.2.5 Vocalizations and Hearing

Sparse data are available on the hearing sensitivity for pygmy or dwarf sperm whales. An 

auditory brainstem response (ABR) study on a rehabilitating pygmy sperm whale indicated that this 

species has an underwater hearing range that is most sensitive between 90 and 150 kHz (Carder 

et al., 1995; Ridgway and Carder, 2001). Thomas et al. (1990) recorded a low-frequency sweep 

between 1,300 and 1,500 Hz from a captive pygmy sperm whale in Hawaii. Richardson et al. (1995) 

reported pygmy sperm whale click frequency ranging from 60 to 200 kHz, with the dominant 

frequency at 120 kHz. Recent recordings from captive and stranded pygmy sperm whales indicate 

that they produce sounds between 60 and 200 kHz with peak frequencies at 120 to 130 kHz, while 

echolocation pulses were documented with peak frequencies at 125 to 130 kHz (Marten, 2000; 

Ridgway and Carder, 2001). No geographical or seasonal differences in sounds have been 

documented. No information is available on sound production in dwarf sperm whales.

2.2.2.6 Threats

The commercial fishery that could interact with the Northern GOM stock is the large pelagic 

longline fishery. Total human-caused mortality and serious injury for this stock is not known. There 

is insufficient information available to determine whether the total fishery-related mortality and 

serious injury for this stock is insignificant and approaching zero mortality and serious injury rate. 

The Final PDARP/PEIS (Deepwater Horizon Natural Resource Damage Assessment Trustees, 

2016) summarized injuries to GOM pygmy and dwarf sperm whales from the Deepwater Horizon oil 

spill. Fifteen percent of the population was exposed to Deepwater Horizon oil and 5 percent of the 

population was killed as a result. In addition, 7 percent of the females likely experienced 

reproductive failure, and 6 percent of the population has experienced adverse health effects.

2.2.2.7 Status

Both Kogia species are protected under the MMPA and classified as least concern by the 

IUCN. The species are not listed as threatened or endangered under the ESA. The status of Kogia 

in the northern GOM, relative to OSP, is unknown. There are insufficient data to determine the 

population trends for the two species; however, recent information from the Final PDARP/PEIS 

(Deepwater Horizon Natural Resource Damage Assessment Trustees, 2016) suggests that they 

have experienced a population decline (5%) as a result of injury from the Deepwater Horizon oil spill. 

They are not considered strategic stocks because it is assumed that average annual human-related 

mortality and serious injury does not exceed combined PBR (PBR = 0.9). However, the continuing 

inability to distinguish between species of Kogia raises concerns about the possibility of mortalities of 

one stock or the other exceeding PBR (Waring et al., 2012).

2.2.3 Cuvier’s Beaked Whale

Cuvier’s beaked whales (Ziphius cavirostris) are members of the beaked whale family 

Ziphiidae. They can reach lengths of 4.5 to 7 m (15 to 23 ft) and weigh 1,845 to 3,090 kg (4,000 to 

6,800 lb). There is no significant sexual dimorphism in regards to body size for this species 

(USDOC, NMFS, 2015a).
E-16 Expanded Affected Environment Information

2.2.3.1 Population

For management purposes, Cuvier’s beaked whales inhabiting U.S. waters have been 

divided into five stocks: the Alaska stock; the California/Oregon/Washington stock; the Hawaiian 

stock; the Northern GOM stock; and the Western North Atlantic stock. The Northern GOM stock is 

provisionally being considered a separate stock for management purposes, although there is 

currently no information to differentiate this stock from the Western North Atlantic stock (Waring 

et al., 2012).

2.2.3.2 Distribution and Abundance

Cuvier’s beaked whales are found in deep offshore waters of all oceans from 60° N. to 60° S. 

latitude (Jefferson et al., 1993) but are more common in subtropical and temperate waters (Evans, 

1987). Cuvier’s beaked whales are reported in the GOM from strandings and live individuals sighted 

during surveys. Strandings records are primarily from the eastern GOM along the Florida coast. 

Sightings of live individuals were made primarily within the central and western GOM, in areas with 

water depths of approximately 2,000 m (6,562 ft) (Würsig et al., 2000). During GulfCet surveys, they 

were sighted only during spring (Davis and Fargion, 1996).

The CetMap abundance estimate for GOM beaked whales, including Cuvier’s, Gervais’, and 

Blainville’s (combined) is 2,910 individuals (Roberts et al., 2016). From NMFS SAR data, the best 

abundance estimate available for Cuvier’s beaked whales in the northern GOM is 74 individuals 

(CV = 1.04). This estimate is from a summer 2009 oceanic survey covering waters from the 200-m 

(656-ft) isobath to the seaward extent of the U.S. EEZ. This abundance estimate is negatively 

biased because only sightings of beaked whales that could be positively identified to species were 

used, and estimates for undifferentiated beaked whales (Mesoplodon spp. and unidentified 

Ziphiidae) made during the same time period may also include an unknown number of Cuvier’s 

beaked whales (Waring et al., 2012). Historically, for surveys conducted in oceanic waters from 

1991 to 1994, the estimate was 30 individuals (CV = 0.50); for 1996 to 2001 (excluding 1998), the 

estimate was 95 individuals (CV = 0.47); and from 2003 to 2004, the estimate was 65 individuals 

(CV = 0.67) (Waring et al., 2012).

2.2.3.3 Habitat

Cuvier’s beaked whales can be found in temperate, subtropical, and tropical waters. They 

prefer deepwater habitats (usually >1,000 m [3,280 ft]) of the continental slope and edge as well as 

steep underwater geologic features like banks, seamounts, and submarine canyons. Recent 

surveys suggest that Cuvier’s beaked whales, like other beaked whale species, may favor 

oceanographic features such as currents, current boundaries, and core ring features (USDOC, 

NMFS, 2015a).

2.2.3.4 Behavior

Mullin and Hoggard (2000) reported that Cuvier’s beaked whales have been sighted in 

groups of 1 to 4 individuals, but Mullin et al. (2004) and MacLeod and D’Amico (2006) later reported 
Gulf of Mexico G&G Activities Programmatic EIS E-17

that Cuvier’s beaked whales may occur in groups ranging from 1 to 15 individuals. Swimming 

speeds of Cuvier’s beaked whales have been recorded between 2.7 and 3.3 kn (3.1 and 3.8 mph) 

(Houston, 1991). Dive durations range between 20 and 87 minutes, with an average dive time of 

approximately 30 minutes (Heyning, 1989; Jefferson et al., 1993; Baird et al., 2004). Baird et al. 

(2004 and 2006) recorded Cuvier’s beaked whales diving as long as 87 minutes to depths up to 

1,990 m (6,529 ft). Cuvier’s beaked whales consume squids and deep-sea fishes (Clarke, 1996).

2.2.3.5 Vocalization and Hearing

The hearing sensitivity of Cuvier’s beaked whales has not been determined (Ketten, 2000; 

Thewissen, 2002). Cuvier’s beaked whales have been recorded producing high-frequency clicks 

between 13 and 17 kHz and lasting for 15 to 44 seconds (Frantzis et al., 2002). These sounds were 

recorded during diving activity and may be associated with echolocation. Whistle frequencies have 

been measured at 2 to 12 kHz and pulsed sounds range in frequency from 300 Hz to 135 kHz. 

However, it is possible that higher frequencies could not be recorded due to equipment limitations 

(MacLeod and D’Amico, 2006). No data are available regarding seasonal or geographical variation 

in the sound production of Cuvier’s beaked whales. Beaked whales are capable of producing SLs of 

200 to 220 dB re 1 μPa at 1 m (peak peak) (Johnson et al., 2004).

Zimmer et al. (2005) also studied Cuvier’s beaked whales and their echolocation clicks. The 

highest measured SL was 214 dB re 1 μPa at 1 m (peak-peak). It is possible that Cuvier’s beaked 

whales cannot produce higher SLs, but it is more likely that the full capabilities of the Cuvier’s 

beaked whales are underestimated by this study. Therefore, the maximum SL shown in this study 

may be the result of the whales reducing the volume when ensonifying each other (Zimmer et al., 

2005).

2.2.3.6 Threats

Threats to Cuvier’s beaked whales include entanglement in fishing gear, ship strikes, and 

anthropogenic noise (USDOC, NMFS, 2015a). The commercial fishery that could interact with the 

Northern GOM stock in the GOM is the large pelagic longline fishery. Stranding data probably 

underestimate the extent of human-related mortality and serious injury because (1) not all marine 

mammals that die or are seriously injured in human interactions wash ashore; (2) not all that wash 

ashore are discovered, reported, or investigated; and (3) not all that wash ashore show signs of 

entanglement or other fishery interaction (Waring et al., 2012). Total human-caused mortality and 

serious injury for this stock is not known; however, the Final PDARP/PEIS (Deepwater Horizon 

Natural Resource Damage Assessment Trustees, 2016) summarized injuries from the Deepwater 

Horizon oil spill to GOM beaked whales (Cuvier’s, Gervais’, and Blainesville’s) and stated that 

12 percent of the population was exposed to Deepwater Horizon oil and 4 percent of the population 

was killed as a result. In addition, 5 percent of females likely experienced reproductive failure and 

4 percent of the population has experienced adverse health effects There is insufficient information 

available to determine whether the total fishery-related mortality and serious injury for this stock is 

insignificant and approaching zero mortality and serious injury rate. Disturbance by anthropogenic 
E-18 Expanded Affected Environment Information

noise may prove to be an important habitat issue in some areas of this population’s range, notably in 

areas of oil and gas activities or where shipping or naval activities are high (USDOC, NMFS, 2015a).

2.2.3.7 Status

The Cuvier’s beaked whale is currently classified as data deficient by the IUCN and is 

protected under the MMPA. The species is not listed as threatened or endangered under the ESA. 

Abundance estimates of the global population size for this species are unknown. The status of 

Cuvier’s beaked whales and other beaked whales in the northern GOM, relative to OSP, is unknown. 

There are insufficient data to determine the population trends for this species; however, recent 

information from the Final PDARP/PEIS (Deepwater Horizon Natural Resource Damage 

Assessment Trustees, 2016) suggests that the beaked whale complex (Cuvier’s, Gervais’, and 

Blainesville’s) have experienced a population decline (4%) as a result of injury from the Deepwater 

Horizon oil spill. This is not a strategic stock because it is assumed that the average annual humanrelated mortality and serious injury does not exceed PBR (PBR = 0.4) (Waring et al., 2012).

2.2.4 Mesoplodon Beaked Whales

Two species of Mesoplodon beaked whales may occur in the GOM: Blainville’s beaked 

whale (M. densirostris) and Gervais’ beaked whale (M. europaeus). Many species of beaked whales 

(especially those in the genus Mesoplodon) are very difficult to distinguish from one another due to 

their cryptic and skittish behavior, low profile, and small inconspicuous blow at the water’s surface; 

therefore, much of the available characterization for beaked whales is to genus level only. 

Uncertainty regarding species identification of beaked whales often exists because of a lack of easily 

discernable or distinct physical characteristics (USDOC, NMFS, 2015a).

2.2.4.1 Population

For management purposes, Blainville’s beaked whales inhabiting U.S. waters have been 

divided into three stocks (i.e., Hawaiian stock, Northern GOM stock, and Western North Atlantic 

stock) and Gervais’ beaked whales have been divided into two stocks (i.e., Western North Atlantic 

stock and Northern GOM stock).

2.2.4.2 Distribution and Abundance

Mesoplodon whales are distributed in offshore pelagic waters between 72° N. and 60° S. 

latitude (Leatherwood and Reeves, 1983; Jefferson et al., 1993; Wade and Gerrodette, 1993; 

Carlström et al., 1997). Along the East Coast of the U.S., beaked whales may be associated with 

the Gulf Stream and warm core eddies (Waring et al., 1992). Globally, beaked whales typically 

inhabit the continental slope and deep oceanic waters (>200 m [656 ft]) (Cañadas et al., 2002; 

Pitman, 2002; MacLeod et al., 2004; Ferguson et al., 2006; MacLeod and Mitchell, 2006). In the 

GOM, beaked whales have been sighted during all seasons and in waters depths ranging from 

420 to 3,487 m (1,378 to 11,440 ft) (Ward et al., 2005; Waring et al., 2009).
Gulf of Mexico G&G Activities Programmatic EIS E-19

Blainville’s beaked whales appear to be widely but sparsely distributed in temperate and 

tropical waters of the world’s oceans (Leatherwood et al., 1976). Blainville’s beaked whales appear 

to be pelagic and mainly found in deep waters but also occur in some coastal areas (Davis et al., 

1998). They generally are sighted in water depths >200 m (656 ft) and have also been frequently 

sighted in water depths >1,000 m (3,280 ft) (Ritter and Brederlau, 1999; Gannier, 2000; MacLeod 

et al., 2004; Ferguson, 2005; MacLeod and Zuur, 2005). Blainville’s beaked whales have been 

reported as far north as Nova Scotia and as far south as Florida, the Bahamas, and the GOM 

(Leatherwood et al., 1976; Mead, 1989; Würsig et al., 2000; MacLeod et al., 2006). There have 

been two sightings and four documented strandings of Blainville’s beaked whales in the northern 

GOM (Hansen et al., 1995; Würsig et al., 2000).

Gervais’ beaked whales appear to be primarily oceanic and sparsely distributed in temperate 

and tropical waters. Strandings of this species have occurred along the U.S. East Coast from Cape 

Cod, Massachusetts, south to Florida as well as in the Caribbean Sea and GOM (Leatherwood 

et al., 1976; Mead, 1989; MacLeod et al., 2006), with 16 strandings occurring in the GOM (Würsig 

et al., 2000). The strandings may coincide with calving, which takes place in shallow water (Würsig 

et al., 2000).

Differentiated abundance estimates for Blainsville and Gervais’ beaked whales in the 

northern GOM are not available. The CetMap abundance estimate for GOM beaked whales, 

including Cuvier’s, Gervais’, and Blainville’s (combined) is 2,910 individuals (Roberts et al., 2016). 

From NMFS SAR data, the best available abundance estimate of Blainville’s and Gervais’ beaked 

whales is 149 individuals (CV = 0.91) (Waring et al., 2014). Historically, for surveys conducted in 

oceanic waters from 1996 to 2001 (excluding 1998), the estimate was 106 individuals (CV = 0.41); 

and from 2003 to 2004, the estimate was 57 individuals (CV = 0.1.4) (Waring et al., 2012).

2.2.4.3 Habitat

Blainville’s beaked whales occur in tropical to temperate waters worldwide, generally within 

deep offshore waters of the continental shelf. This species is often associated with steep 

underwater geologic structures such as banks, submarine canyons, seamounts, and continental 

slopes (USDOC, NMFS, 2015a). Gervais’ beaked whales prefer deep tropical, subtropical, and 

warm temperate waters of the Atlantic Ocean, but they are occasionally found in colder temperate 

seas (USDOC, NMFS, 2015a).

2.2.4.4 Behavior

Blainville’s beaked whales typically are found in groups of 1 to 11 individuals (Mullin and 

Fulling, 2004), whereas other Mesoplodon species are found alone or in groups of up to 

15 individuals (MacLeod and D’Amico, 2006). General swimming speeds for beaked whales 

average 2.7 kn (3.1 mph) (Kastelein and Gerrits, 1991). Dives of Blainville’s beaked whales average 

7.5 minutes during social interactions at the surface (Baird et al., 2004). Dives longer than 

45 minutes have been recorded for some Mesoplodon species (Jefferson et al., 1993).
E-20 Expanded Affected Environment Information

Gervais’ beaked whales usually are found individually or in small closely associated social 

groups (USDOC, NMFS, 2015a). Females may become sexually mature at 4.5 m (15 ft) and will 

give birth to a single newborn calf that is approximately 1.5 to 2 m (5 to 7 ft) long and weighs 

approximately 80 kg (176 lb). The estimated lifespan of this species is at least 27 years, but it may 

be up to 48 years (Reeves et al., 2002).

Mesoplodon whales are deep-diving species that consume small cephalopods and benthopelagic fish (Sullivan and Houck, 1979; Leatherwood et al., 1988; Mead, 1989; Jefferson et al., 1993; 

MacLeod et al., 2003). Blainville’s beaked whales diving to depths near 900 m (2,625 ft) for 

20 minutes or longer are most likely foraging (Leatherwood et al., 1988; Baird et al., 2004). Barlow 

(1999) and Baird et al. (2006) have recorded dive durations of >20 minutes for Mesoplodon species.

2.2.4.5 Vocalizations and Hearing

No direct measurements of the hearing sensitivity of Mesoplodon species have been made 

(Ketten, 2000; Thewissen, 2002). There are sparse data available on sound production of 

Mesoplodon species and no data regarding seasonal or geographical variation in sound production. 

A stranded Blainville’s beaked whale in Florida produced chirps and whistles from <1 to 6 kHz 

(Caldwell and Caldwell, 1971a). Johnson et al. (2004) found that Blainville’s beaked whales started 

clicking at an average depth of 400 m (1,312 ft), ranging from 200 to 570 m (656 to 1,870 ft), and 

stopped clicking when they started their ascent at an average depth of 720 m (2,362 ft), with a range 

of 500 to 790 m (1,640 to 2,592 ft). The intervals between regular clicks were approximately 

0.4 seconds. Trains of clicks often end in a rapid increase in the click rate, which is also called a 

buzz. The Cuvier’s beaked whale and the Blainville’s beaked whale have a somewhat flat spectrum 

that was accurately sampled by Johnson et al. (2004) between 30 and 48 kHz. There may be a 

slight decrease in the spectrum above 40 kHz, but the 96-kHz sampling rate was not sufficient to 

sample the full frequency range of clicks from either species (Johnson et al., 2004).

2.2.4.6 Threats

Mesoplodon species have been incidentally taken in the pelagic drift gillnet fishery off the 

U.S. Atlantic Coast. Blainville’s beaked whales have been incidentally taken by Japanese fishing 

boats (Jefferson et al., 2008). This species occasionally has been taken in hunts targeting small 

cetaceans. Gervais’ beaked whales have been incidentally taken as bycatch in fishing gear, such as 

pound nets, driftnets, and gillnets, off the U.S. Atlantic Coast. This species may be hunted in the 

Caribbean Sea for food (USDOC, NMFS, 2015a).

Beaked whales may be sensitive to underwater sounds and anthropogenic noise. Recently, 

strandings of Blainville’s beaked whales in the Bahamas, due to acoustic trauma, have been 

associated with active sonar during Naval military activities and exercises.
Gulf of Mexico G&G Activities Programmatic EIS E-21

2.2.4.7 Status

Mesoplodon species currently are classified as data deficient by the IUCN and are protected 

under the MMPA. The status of beaked whales in the northern GOM, relative to OSP, is unknown. 

The species are not listed as threatened or endangered under the ESA. There are insufficient data 

to determine the population trends for these species; however, recent information from the Final

PDARP/PEIS (Deepwater Horizon Natural Resource Damage Assessment Trustees, 2016) 

suggests that the beaked whale complex (i.e., Cuvier’s, Gervais’, and Blainesville’s) have 

experienced a population decline (4%) as a result of injury from the Deepwater Horizon oil spill. 

Total human-caused mortality and serious injury for the stocks are not known. The Final

PDARP/PEIS (Deepwater Horizon Natural Resource Damage Assessment Trustees, 2016) 

summarized injuries from the Deepwater Horizon spill to GOM beaked whales (i.e., Cuvier’s, 

Gervais’, and Blainesville’s) and stated that 12 percent of the population was exposed to Deepwater 

Horizon oil and 4 percent of the population was killed. In addition, 5 percent of females likely 

experienced reproductive failure and 4 percent of the population has experienced adverse health 

effects. There is insufficient information available to determine whether the total fishery-related 

mortality and serious injury for these stocks is insignificant and approaching zero mortality and 

serious injury rate. They are not strategic stocks because it is assumed that the average annual 

human-related mortality and serious injury does not exceed PBR (Waring et al., 2012).

2.2.5 Rough-Toothed Dolphin

The rough-toothed dolphin (Steno bredanensis) is a relatively robust dolphin that can grow to 

2.7 m (9 ft) in length (Jefferson et al., 2008). It is characterized by a long, conical head with no 

demarcation between the melon and beak.

2.2.5.1 Population

The GOM population of rough-toothed dolphin is provisionally being considered one stock for 

management purposes, although there currently is no information to differentiate this stock from the 

Atlantic Ocean stock(s) nor is there information on whether more than one stock may exist in the 

GOM. Additional morphological, genetic, and behavioral data are needed to provide further 

information on stock delineation (Waring et al., 2013).

2.2.5.2 Distribution and Abundance

The rough-toothed dolphin is distributed within deep tropical and subtropical waters between 

40° N. and 35° S. latitude. Records from the Atlantic are mostly from between the southeastern U.S. 

and southern Brazil (Jefferson, 2002a). In the GOM, rough-toothed dolphins occur in oceanic and, 

to a lesser extent, continental shelf waters (Fulling et al., 2003; Mullin and Fulling, 2004; Maze-Foley 

and Mullin, 2006). Rough toothed dolphins were recorded in all seasons during GulfCet aerial 

surveys of the northern GOM between 1992 and 1998 (Hansen et al., 1996; Mullin and Hoggard, 

2000).
E-22 Expanded Affected Environment Information

The CetMap abundance estimate for northern GOM rough-toothed dolphins is 

4,853 individuals (Roberts et al., 2016). From NMFS SAR data, the current population size for the 

rough-toothed dolphin in the northern GOM is estimated to be 624 individuals (CV = 0.99) (Waring 

et al., 2012). This estimate is from a summer 2009 oceanic survey covering waters from the 200-m 

(656-ft) isobath to the seaward extent of the U.S. EEZ. Historically, for surveys conducted in 

oceanic waters from 2000 to 2001, the estimate was 1,145 individuals (CV = 0.83); and from 2003 to 

2004, the estimate was 1,508 individuals (CV = 0.39 (Waring et al., 2012). 

2.2.5.3 Habitat

Rough-toothed dolphins prefer deeper areas of tropical and warmer temperate waters, which 

is where their prey are concentrated (USDOC, NMFS, 2015a; Würsig et al., 2000).

2.2.5.4 Behavior

Rough-toothed dolphins are not known to be fast swimmers, instead skimming the surface at 

a moderate speed, and they have a distinctive splash (Jefferson, 2002b). Swim speeds of this 

species vary from 3 to 8.6 kn (3.5 to 10 mph). Rough-toothed dolphins can dive to depths between 

30 and 70 m (98 and 230 ft) (Croll et al., 1999). The dive duration ranges from 0.5 to 3.5 minutes 

(Ritter, 2002). The maximum dive depth recorded was 70 m (230 ft); however, due to their 

morphology, it is believed that they are capable of diving much deeper. Dives up to 15 minutes have 

been recorded for groups of dolphins (Croll et al., 1999). Rough-toothed dolphins feed mainly on 

cephalopods and fish, including large fish like dolphinfish (Coryphaena hippurus) (Miyazaki and 

Perrin, 1994; Reeves et al., 1999; Pitman and Stinchcomb, 2002).

2.2.5.5 Vocalization and Hearing

There are no direct measurements of auditory threshold for the hearing sensitivity of roughtoothed dolphins (Ketten, 2000; Thewissen, 2002); however, Cook et al. (2005) performed auditory 

tests on 5 of 36 stranded rough-toothed dolphins in Florida. The amplitude modulation rate used in 

auditory evoked potential (AEP) measurements was 1.5 kHz to determine the evoked-potential 

hearing thresholds between 5 and 80 kHz. The results of these tests show that the rough-toothed 

dolphin can hear sounds in this frequency range and most likely can hear frequencies much higher 

than 80 kHz as well (Cook et al., 2005).

Rough-toothed dolphins produce vocalizations ranging from 0.1 to 200 kHz (Popper, 1980; 

Miyazaki and Perrin, 1994; Richardson et al., 1995; Yu et al., 2003). Clicks have peak energy at 

25 kHz, while whistles have a maximum energy between 2 and 14 kHz (Norris and Evans, 1967; 

Norris, 1969; Popper, 1980). There are no available data regarding seasonal or geographical 

variation in the vocalization production of this species.

2.2.5.6 Threats

The commercial fishery that could interact with this stock in the GOM is the Atlantic Ocean, 

Caribbean, GOM large pelagic longline fishery (Waring et al., 2012). However, there is no reported 
Gulf of Mexico G&G Activities Programmatic EIS E-23

bycatch from U.S. fisheries, but they are known to take bait in commercial and recreational fisheries 

in the Hawaiian Islands. Strandings are moderately common; two in the GOM region are thought to 

be related to fishery interactions. A mass stranding of 62 animals occurred off Marathon, Florida, in 

March 2005 (USDOC, NMFS, 2015a). Information from the Final PDARP/PEIS (Deepwater Horizon 

Natural Resource Damage Assessement Trustees, 2016) summarized injuries from the Deepwater 

Horizon oil spill to rough-toothed dolphins and stated that 41 percent of the population was exposed 

to Deepwater Horizon oil and 14 percent of the population was killed as a result. In addition, 15

percent of females likely experienced reproductive failure and 19 percent of the population has 

experienced adverse health effects.

2.2.5.7 Status

Rough-toothed dolphins are currently classified as data deficient under the IUCN and are 

protected under the MMPA. The status of rough-toothed dolphins in the northern GOM, relative to 

OSP, is unknown. The species is not listed as threatened or endangered under the ESA. There are 

insufficient data to determine the population trends for this species; however, recent information from 

the Final PDARP/PEIS (Deepwater Horizon Natural Resource Damage Assessment Trustees, 2016) 

suggests that rough-toothed dolphins in the GOM have experienced a population decline (14%) as a 

result of injury from the Deepwater Horizon oil spill. This is not a strategic stock because it is 

assumed that the average annual human-related mortality and serious injury does not exceed PBR 

(PBR = 3.1) (Waring et al., 2012).

2.2.6 Common Bottlenose Dolphin

Adult common bottlenose dolphins (Tursiops truncatus) are medium-sized dolphins that 

range in length from 1.9 to 3.8 m (6 to 12 ft), with much variation among populations (Würsig et al., 

2000; Jefferson et al., 2008). Male bottlenose dolphins may be somewhat larger than females in 

some populations (Jefferson et al., 2008). Two genetically distinct geographic varieties (ecotypes) of 

bottlenose dolphins are known to occur in the western North Atlantic and GOM: a “coastal” ecotype 

and an “offshore” ecotype (Hersh and Duffield, 1990; LeDuc and Curry, 1998). The coastal ecotype 

differs from the offshore ecotype mainly in features of the skull associated with feeding, and 

suggests that it may feed on larger and tougher prey than the offshore ecotype. Other 

morphological differences may reflect differences in diving behavior and sound production, and may 

indicate evolutionary adaptation to different physical environments (Perrin et al., 2011). The two 

bottlenose dolphin ecotypes are genetically distinct according to mitochondrial and nuclear markers 

(Hoelzel et al., 1998).

2.2.6.1 Population

Bottlenose dolphins inhabiting the northern GOM are currently divided into 37 management 

stocks (from Waring et al., 2013):

• Northern GOM Oceanic stock;

• Northern GOM Continental Shelf stock;
E-24 Expanded Affected Environment Information

• GOM Coastal stocks (comprising 3 individual stocks); and

• Northern GOM Bay, Sound, and Estuary Stocks (comprising 32 individual 

stocks). 

Details of each stock or stock group, including their distribution in the GOM, are described in 

the following subsections.

Northern GOM Oceanic Stock

The Northern GOM Oceanic stock encompasses the waters from the 200-m (656-ft) isobath 

to the seaward extent of the U.S. EEZ. This stock is considered separate from Atlantic Ocean 

stocks of bottlenose dolphins for management purposes. The Northern GOM Oceanic stock is 

thought to be composed entirely of individuals of the “offshore” ecotype.

Northern GOM Continental Shelf Stock

The Northern GOM Continental Shelf stock of bottlenose dolphins inhabits waters from 20 to 

200 m (66 to 656 ft) deep from the U.S.-Mexico border to the Florida Keys. This stock probably 

includes a mixture of both coastal and offshore ecotypes. It is believed that Bay, Sound, and 

Estuary stocks; Coastal stocks; and the Oceanic stock are separate from the Continental Shelf 

stock. However, the Continental Shelf stock may overlap with the other stocks in some areas and so 

may be genetically indistinguishable (Sellas et al., 2005).

GOM Coastal Stocks

Bottlenose dolphins inhabiting northern GOM coastal waters (defined as water depths <20 m 

[66 ft]) have been divided for management purposes into the following three separate stocks:

• Eastern Coastal stock – Florida coastal waters from 84° W. longitude to Key 

West;

• Northern Coastal stock – coastal waters from 84° W. longitude (Florida) to the 

Mississippi River Delta (Louisiana); and

• Western Coastal stock – Mississippi River Delta (Louisiana) to the Texas-Mexico 

border.

It is assumed that the dolphins occupying GOM coastal habitats with dissimilar climatic, 

coastal, and oceanographic characteristics may be restricted in their movements between these 

habitats, and so constitute separate stocks. Portions of the three coastal stocks may also occur with 

the Northern GOM Continental Shelf stock and Bay, Sound, and Estuary stocks. The seaward 

boundary for GOM Coastal stocks (the 20-m [66-ft] isobath) generally corresponds to historical 

survey strata (Scott, 1990; Blaylock and Hoggard, 1994; Fulling et al., 2003) and so represents a 

management boundary rather than an actual ecological boundary for these stocks. The GOM 

Coastal stocks may include coastal and offshore ecotypes of bottlenose dolphins.
Gulf of Mexico G&G Activities Programmatic EIS E-25

Northern GOM Bay, Sound, and Estuary Stocks

Distinct stocks of bottlenose dolphins are currently identified in 32 areas of contiguous, 

enclosed, or semi-enclosed bodies of water adjacent to the northern GOM, based on descriptions of 

relatively discrete dolphin “communities” in some of these areas. A “community” in this case has 

been defined by the NMFS as a group of resident dolphins that regularly share large portions of their 

ranges, exhibit similar distinct genetic profiles, and interact with each other to a much greater extent 

than with dolphins in adjacent waters (Waring et al., 2013). The geographic nature of these areas 

and long-term stability of residency patterns suggest that many of these communities exist as 

functioning units and under the MMPA are being maintained as separate management stocks. The 

Northern GOM Bay, Sound, and Estuary stocks are listed in Table 4.2 2 of this Programmatic EIS. 

The relative distributions of the 32 stocks, as referenced to NMFS’ Southeast Fisheries Science 

Center logistical aerial survey areas, are shown in Figure 4.2-4 of this Programmatic EIS.

2.2.6.2 Distribution and Abundance

The common bottlenose dolphin is distributed worldwide in tropical and temperate waters, 

mostly between 50° S. to 45° N. latitude (Croll et al., 1999). It is the most widespread and common 

cetacean species in coastal waters of the GOM. During GulfCet surveys, bottlenose dolphins were, 

in almost all cases, sighted in areas with water depths <1,000 m (3,280 ft) (Würsig et al., 2000). 

Common bottlenose dolphins in the northern GOM are divided into 37 separate stocks. Details of 

each stock, including their relative distributions in the northern GOM, are discussed below.

The CetMap abundance estimate for all northern GOM bottlenose dolphin stocks is 

138,602 individuals (Roberts et al., 2016). From NMFS SAR data, estimates of abundance for each 

separate stock are presented in Table 4.2 2 of this Programmatic EIS.

2.2.6.3 Habitat

Common bottlenose dolphins are found in temperate and tropical waters around the world. 

There are coastal populations that migrate into bays, estuaries, and river mouths as well as offshore 

populations that inhabit pelagic waters along the continental shelf (USDOC, NMFS, 2015a).

2.2.6.4 Behavior

In the GOM, common bottlenose dolphins show seasonal and diel patterns in their behavior, 

such as feeding, socializing, and traveling. During the summer months, they feed primarily during 

the morning and for a short time in the afternoon. Social behaviors increase as feeding decreases, 

with socializing peaking in the afternoon. In the fall, they feed throughout the day and spend less 

time socializing and traveling (Bräger, 1993). Bottlenose dolphins feed primarily on fish in the 

summer and on cephalopods and crustaceans in the winter (Bräger, 1993). The diet of the 

bottlenose dolphin is diverse, as they are opportunistic feeders, and ranges from various fishes (with 

a preference for sciaenids, scombrids, and mugilids), cephalopods, and shrimp (Wells and Scott, 

1999 and 2002).
E-26 Expanded Affected Environment Information

Different age classes and sexes may feed in different localities. Lactating females and 

calves have been reported foraging in the nearshore zone, while adolescents feed farther offshore. 

Male adults and females without young may feed still farther offshore (Wells and Scott, 2002). 

Bottlenose dolphins appear to be active during the day and at night. Their activities are influenced 

by the season, time of day, tidal state, and physiological factors such as reproductive seasonality 

(Wells and Scott, 2002). Bottlenose dolphins also have recurrent feeding behaviors in the northern 

GOM. They are known to feed on fishes dumped from the decks of shrimp boats; herd schools of 

fishes by encircling and charging; crowd small fishes onto shoals or banks and then drive the fish 

onto shore, sliding on the banks to retrieve them; and feed individually (Würsig et al., 2000).

Bottlenose dolphins can sustain swimming speeds between 2 and 11 kn (2.3 and 12.7 mph). 

Speeds commonly range from 4 to 6 kn (4.6 to 6.9 mph) and may reach speeds as high as 16 kn 

(18.4 mph) for 7.5 seconds (Croll et al., 1999). Dive times range from 38 seconds to 1.2 minutes, 

but they have been known to last as long as 10 minutes (Mate et al., 1995; Croll et al., 1999). The 

dive depth of a bottlenose dolphin in Tampa Bay was measured at 98 m (322 ft) (Mate et al., 1995). 

The deepest dive recorded for a bottlenose dolphin is 535 m (1,755 ft), reached by a trained 

individual (Ridgway, 1986).

2.2.6.5 Vocalizations and Hearing

Common bottlenose dolphins are known to use active echolocation and to listen for the 

sounds that their prey produce, which is called “passive listening” (Barros and Myrberg, 1987; 

Gannon et al., 2005). Bottlenose dolphins hear underwater sounds in the range of 150 Hz to 

135 kHz (Johnson, 1967; Ljungblad et al., 1982). Their best underwater hearing occurs at 15 kHz, 

where the threshold level range is 42 to 52 dB (Sauerland and Dehnhardt, 1998). Bottlenose 

dolphins also have good sound location abilities and are most sensitive when sounds arrive from the 

front (Richardson et al., 1995).

Bottlenose dolphins produce vocalizations as low as 0.05 kHz and as high as 150 kHz with 

dominant frequencies at 0.3 to 14.5 kHz, 25 to 30 kHz, and 95 to 130 kHz (Johnson, 1967; Popper, 

1980; McCowan and Reiss, 1995; Schultz et al., 1995; Croll et al., 1999; Oswald et al., 2003). The 

maximum SL is 228 dB re 1 μPa at 1 m (Croll et al., 1999). Bottlenose dolphins produce a variety of 

whistles, echolocation clicks, and burst-pulse sounds. Echolocation clicks with peak frequencies 

from 40 to 130 kHz are hypothesized to be used in navigation, foraging, and predator detection (Au, 

1993; Houser et al., 1999 and 2004; Jones and Sayigh, 2002). According to Au (1993), sonar clicks 

are broadband, ranging in frequency from a few kHz to >150 kHz, with a 3-dB bandwidth of 30 to 60 

kHz (Croll et al., 1999). The echolocation signals usually have a 50- to 100-μs duration with peak 

frequencies ranging from 30 to 100 kHz and fractional bandwidths between 10 and 90 percent of the 

peak frequency (Houser et al., 1999). Electrophysiological experiments with bottlenose dolphins 

suggest that their brain has a dual analysis system: one specializing in ultrasonic clicks and the 

other for lower frequency sounds like whistles (Ridgway, 2000).
Gulf of Mexico G&G Activities Programmatic EIS E-27

Burst-pulses, or squawks, are commonly produced during social interactions. These sounds 

are broadband vocalizations that consist of rapid sequences of clicks with inter-click intervals of 

<5 ms. Burst-pulse sounds typically are used during escalations of aggression. Each individual 

bottlenose dolphin has a fixed unique FM pattern, or contour whistle, called a signature whistle. 

These signal types have been well studied and are presumably used for recognition, but they may 

have other social contexts (Frankel, 2002; Sayigh, 2002). Up to 52 percent of whistles produced by 

mother calf pairs in the group can be classified as signature whistles (U.S. Department of the Navy, 

2007). Stereotypically, signature whistles have a narrow-band sound with the frequency between 

4 and 20 kHz, duration between 0.1 and 3.6 seconds, and an SL of 125 to 140 dB re 1 μPa at 1 m 

(Croll et al., 1999).

McCowan et al. (1999) discussed bottlenose dolphins and their structure and organization of 

communication mathematically. Zipf’s law is applied, which examines the first-order entropic relation 

and evaluates the signal composition of a repertoire by examining the frequency of use of signals in 

a relationship to their ranks. It measures the potential capacity for information transfer at the 

repertoire level by examining the optimal amount of diversity and redundancy necessary for 

communication transfer across a noisy channel. The results from this experiment suggest that Zipf’s 

statistic can be applied to animal vocal repertoires, in this case dolphin whistle repertoires, and their 

development. Zipf’s statistic may be an important comparative measure of repertoire complexity, 

both interspecies, and as an indicator for vocal acquisition or learning of vocal repertoire structure 

within a species. The results also suggest that dolphin whistles contain some higher-order internal 

structure, enough to begin to predict statistically what whistle types might immediately follow the 

same or another whistle type. A greater knowledge of the higher-order entropic structures could 

allow the reconstruction of dolphins’ whistle sequence structure, independent of additional data 

inputs such as actions and non-vocal signaling (McCowan et al., 1999).

In contrast to the signature whistle theory, McCowan and Reiss (2001) stated that 

predominant whistle types produced by isolated dolphins were the same whistle types that were 

predominant for all adult subjects and for infant subjects by the end of their first year in socially 

interactive and separation contexts. No evidence for individually distinctive signature whistle 

contours was found in the bottlenose dolphins studied. Ten of 12 individuals produced one shared 

whistle type as their most predominant whistle during contexts of isolation. The two other individuals 

produced two other predominant whistle types that could not be considered signature whistles 

because both whistle types were shared among many different individuals within and across 

independent captive social groups (McCowan and Reiss, 2001).

Jones and Sayigh (2002) reported geographic variations in behavior and in the rates of vocal 

production. Whistles and echolocation varied between Southport, North Carolina; the Wilmington 

North Carolina Intracoastal Waterway; the Wilmington, North Carolina coastline; and Sarasota, 

Florida. Dolphins at the Southport site whistled more than the dolphins at the Wilmington site, who 

whistled more than the dolphins at the Intracoastal Waterway site, who whistled more than the 

dolphins at the Sarasota site. Echolocation production was higher at the Intracoastal Waterway site 

than all of the other sites. Dolphins in all three North Carolina sites spent more time in large groups 
E-28 Expanded Affected Environment Information

than the dolphins at the Sarasota site. Echolocation occurred most often when dolphins were 

socializing (Jones and Sayigh, 2002).

2.2.6.6 Threats

Worldwide, threats to bottlenose dolphins include incidental injury and mortality from fishing 

gear such as gillnets, seines, and trawls and from longline commercial and recreational operations; 

exposure to pollutants and biotoxins; viral outbreaks; and direct harvest in Japan and Taiwan 

(USDOC, NMFS, 2015a). According to Waring et al. (2012), the commercial fisheries that could 

interact with bottlenose dolphins in the GOM are listed by management stock group:

• Northern GOM Bay, Sound, and Estuary stocks: shrimp trawl, blue crab trap/pot, 

stone crab trap/pot, menhaden purse seine, gillnet, and Atlantic Ocean 

commercial passenger fishing vessel (hook and line) fisheries; 

• Northern GOM Continental Shelf stock: Southeastern U.S. Atlantic, GOM shark 

bottom longline fishery; Southeastern U.S. Atlantic, GOM shrimp trawl fishery; 

Southeastern U.S. Atlantic, GOM, Caribbean snapper-grouper and other reef fish 

fishery; and the GOM butterfish trawl fishery; 

• Eastern, Northern, and Western Coastal stocks: shark bottom longline, shrimp 

trawl, blue crab trap/pot, stone crab trap/pot, spiny lobster trap/pot, and Atlantic 

Ocean commercial passenger fishing vessel (hook-and-line) fisheries; and

• Northern GOM Oceanic stock: Atlantic Ocean, Caribbean, GOM large pelagic 

longline fishery; and the GOM butterfish trawl fishery. 

The Final PDARP/PEIS (Deepwater Horizon Natural Resource Damage Assessment 

Trustees, 2016) identified 13 GOM stocks (i.e., 9 BSE stocks, 2 coastal stocks, 1 shelf stock, and 1 

oceanic stock) that were found in areas within the Deepwater Horizon oil-spill footprint.

2.2.6.7 Status

The bottlenose dolphin is classified as data deficient by the IUCN and is protected under the 

MMPA. The Northern GOM Oceanic, Northern GOM Continental Shelf, and the Eastern Coastal 

stocks are classified as non-strategic. The Western and Northern Coastal stocks of bottlenose 

dolphins currently are classified as strategic due to the ongoing UME that began on February 1, 

2010. The NMFS considers each of these stocks to be strategic because most of the stock sizes 

are currently unknown but likely small, so relatively few mortalities and serious injuries would exceed 

PBR. The stocks also are considered strategic because stock areas in Louisiana, Mississippi, 

Alabama, and the western Florida Panhandle have been impacted by the aforementioned UME 

(Waring et al., 2013). In addition to the UME, bottlenose dolphins in the GOM (13 of 37 stocks) were 

negatively impacted by the Deepwater Horizon oil spill. Impacts included increased mortality, 

increased reproductive failure, and adverse health effects. Information from the Final PDARP/PEIS 

(Deepwater Horizon Natural Resource Damage Assessment Trustees, 2016) summarizes injuries 
Gulf of Mexico G&G Activities Programmatic EIS E-29

(refer to Table 4.9-12) for marine mammal stocks affected by the spill. It builds from the measured 

injuries in Barataria Bay and Mississippi Sound bottlenose dolphins to other BSE stocks of 

bottlenose dolphins, and then to the coastal and oceanic stocks of bottlenose dolphins (and other 

cetacean species) within the Deepwater Horizon oil-spill footprint. Depending on the stock, up to 

59 percent of the population was killed, 46 percent of females likely experienced reproductive failure, 

and 37 percent of the population has experienced adverse health effects.

The current PBR estimates for the Northern GOM stocks of bottlenose dolphins are listed in 

Table 4.2-2 of this Programmatic EIS.

2.2.7 Pantropical Spotted Dolphin

The pantropical spotted dolphin (Stenella attenuata) varies significantly in size and coloration 

throughout its range. There is one species recognized in the GOM and Northern Atlantic Ocean. 

One subspecies (S. a. graffmani) is recognized and occurs only in coastal waters of the eastern 

tropical Pacific. Adults range in length from 1.6 to 2.4 m (5.2 to 7.9 ft). 

2.2.7.1 Population

The GOM population of pantropical spotted dolphins is provisionally being considered a 

separate stock for management purposes; however, there currently is no information to differentiate 

this stock from the Atlantic Ocean stock(s). Additional morphological, genetic, and behavioral data 

are needed to provide further information on stock delineation (Waring et al., 2013).

2.2.7.2 Distribution and Abundance

Pantropical spotted dolphins are primarily distributed within offshore (oceanic) tropical zones. 

It is the most common cetacean within deep GOM waters, with most sightings between the 100- and 

2,000-m (328- and 6,562-ft) depth contours (Würsig et al., 2000). During the GulfCet surveys, 

average group sizes of 46.2 and 55.1 individuals were estimated from ship and aircraft, respectively 

(Davis and Fargion, 1996). Seasonally, pantropical spotted dolphin densities peaked during spring 

and were lowest during fall.

The CetMap abundance estimate for northern GOM pantropical spotted dolphins is 

84,014 individuals (Roberts et al., 2016). From NMFS SAR data, the best abundance estimate 

available for northern GOM pantropical spotted dolphins is 50,880 individuals (Waring et al., 2013). 

This estimate is from a summer 2009 oceanic survey covering waters from the 200-m (656-ft) 

isobath to the seaward extent of the U.S. EEZ. Historically, for surveys conducted in oceanic waters 

from 1991 to 1994, the estimate was 31,320 individuals (CV = 0.20); from 1996 to 2001 (excluding 

1998), the estimate was 91,321 individuals (CV = 0.16); and from 2003 to 2004, the estimate was 

34,067 individuals (CV = 0.18) (Waring et al., 2012).
E-30 Expanded Affected Environment Information

2.2.7.3 Habitat

Pantropical spotted dolphins spend the majority of the daytime in shallower water between 

90 and 300 m (295 and 984 ft) deep. At night, they dive into deeper waters to search for prey 

(USDOC, NMFS, 2015a).

2.2.7.4 Behavior

Pantropical spotted dolphins commonly are observed in large groups of up to thousands of 

individuals. Groups may segregate according to sex and age. They are fast swimmers and often 

engage in acrobatics (Jefferson et al., 2008). Pantropical spotted dolphins feed primarily on small 

epipelagic and mesopelagic fishes, squids, and crustaceans that associate with deep scattering 

layers.

2.2.7.5 Vocalizations and Hearing

Pantropical spotted dolphins produce sounds that range from 0.1 to 160 kHz (Richardson 

et al., 1995). As a group, Stenella are classified within the mid-frequency cetacean functional 

marine mammal hearing group (150 Hz to 160 kHz) (Southall et al., 2007). There is no direct 

measurement of auditory threshold for the hearing sensitivity of the pantropical spotted dolphin.

The results of a study on pantropical spotted (and spinner) dolphins conducted by Lammers 

et al. (2003) revealed that the whistles and burst pulses of the two species span a broader frequency 

range than traditionally reported for delphinids. The fundamental frequency contours of whistles 

occur in the human hearing range, but the harmonics typically reach 50 kHz and beyond. 

Pantropical spotted dolphin whistles range in frequency from 3.1 to 21.4 kHz (Thomson and 

Richardson, 1995). Clicks typically are bimodal, meaning they have two frequency peaks, one at 

40 to 60 kHz and another at 120 to 140 kHz, with an estimated SL of up to 220 dB re 1 μPa at 1 m 

(peak-peak) (Schotten et al., 2004).

There are no available data regarding seasonal variation in the sound production of Stenella 

dolphins, although geographic variation is evident. SLs as high as 210 dB re 1 μPa at 1 m (peakpeak) have been measured for echolocation clicks (Au et al., 1998; Au and Herzing, 2003).

2.2.7.6 Threats

Stocks of pantropical spotted dolphins have been the targets of the tuna purse seine fishery 

within the eastern tropical Pacific that uses the dolphins’ locations to find tuna. Many dolphins used 

to be caught in the nets and drowned. Currently, fishing methods for tuna imported into the U.S. 

under the Dolphin Safe program do not allow such destructive fishing practices. The commercial 

fishery that could interact with this stock in the GOM is the Atlantic Ocean, Caribbean, GOM large 

pelagic longline fishery (Waring et al., 2012). Interactions with tourists are a growing issue for the 

Hawaiian stock (USDOC, NMFS, 2015a). Information from the Final PDARP/PEIS (Deepwater 

Horizon Natural Resource Damage Assessment Trustees, 2016) summarized injuries from the 

Deepwater Horizon spill to pantropical dolphins and stated that 20 percent of the population was 
Gulf of Mexico G&G Activities Programmatic EIS E-31

exposed to Deepwater Horizon oil and 7 percent of the population was killed as a result. In addition, 

9 percent of females likely experienced reproductive failure and 7 percent of the population has 

experienced adverse health effects.

2.2.7.7 Status

The GOM population of pantropical spotted dolphins is provisionally considered a separate 

stock (Northern GOM stock) for management purposes; however, there currently is no information to 

differentiate this stock from the Atlantic Ocean stock(s). The status of pantropical spotted dolphins 

in the northern GOM is unknown. The species is not listed as threatened or endangered under the 

ESA, and there are insufficient data to determine the population trends for this stoc; however, recent 

information from the Final PDARP/PEIS (Deepwater Horizon Natural Resource Damage 

Assessment Trustees, 2016) suggests that pantropical dolphins in the GOM have experienced a 

population decline (7%) as a result of injury from the Deepwater Horizon oil spill. It is not a strategic 

stock because it is assumed that the average annual human-related mortality and serious injury 

does not exceed PBR. The current PBR for the Northern GOM stock of pantropical spotted dolphins 

is 407 individuals (Waring et al., 2013).

2.2.8 Clymene Dolphin 

The Clymene dolphin (Stenella clymene) is the smallest member of the genus Stenella. 

Adult individuals are known to reach 2.0 m (6.5 ft) (males) and 1.9 m (6.2 ft) (females) in length.

2.2.8.1 Population

The GOM population is provisionally being considered a separate stock for management 

purposes; however, there currently is no information to differentiate this stock from the Atlantic stock. 

Additional morphological, genetic, and behavioral data are needed to provide further information on 

stock delineation (Waring et al., 2013).

2.2.8.2 Distribution and Abundance

The Clymene dolphin is restricted to tropical and warm temperate waters of the Atlantic 

Ocean, including the Caribbean Sea and GOM. It is a deepwater oceanic species and is considered 

relatively common in oceanic waters (Würsig et al., 2000; Jefferson, 2002b; Jefferson et al., 2008). 

Clymene dolphins were sighted offshore Louisiana in every season during the GulfCet surveys. 

Sightings made during these surveys occurred almost exclusively beyond the 100-m (328-ft) isobath.

The CetMap abundance estimate for northern GOM Clymene dolphins is 11,000 individuals 

(Roberts et al., 2016). From NMFS SAR data, the best abundance estimate available for northern 

GOM Clymene dolphins is 129 individuals (Waring et al., 2013). This estimate is from a summer 

2009 oceanic survey covering waters from the 200-m (656-ft) isobath to the seaward extent of the 

U.S. EEZ. Historically, for surveys conducted in oceanic waters from 1991 to 1994, the estimate 

was 5,571 individuals (CV = 0.37); from 1996 to 2001 (excluding 1998), the estimate was 
E-32 Expanded Affected Environment Information

17,355 individuals (CV = 0.65); and from 2003 to 2004, the estimate was 6,575 individuals 

(CV = 6.0) (Waring et al., 2012).

2.2.8.3 Habitat

Clymene dolphins prefer deep tropical, subtropical, and warm temperate waters in the 

Atlantic Ocean, including the GOM. This species generally occurs in oceanic waters in depths of 

250 to 5,000 m (820 to 16,400 ft).

2.2.8.4 Behavior

Clymene dolphins commonly are observed in groups of 60 to 80 individuals within the GOM. 

These groups often appear to be segregated by age group and sex, and they often occur with other 

cetacean species such as spinner dolphins. Very little is known about the ecology of Clymene 

dolphins. Based on few examinations of stomach contents, the species feeds mostly on 

mesopelagic fishes and squids, presumably at night (Jefferson et al., 2008).

2.2.8.5 Vocalizations and Hearing

Stenella species produce sounds that range from 0.1 to 160 kHz (Richardson et al., 1995). 

As a group, Stenella species are classified within the mid-frequency cetacean functional marine 

mammal hearing group (150 Hz to 160 kHz) (Southall et al., 2007). There is no direct measurement 

of auditory threshold for the hearing sensitivity of the Stenella dolphins, except for striped dolphins 

(Ketten, 2000; Thewissen, 2002). There are very little data on Clymene dolphin acoustics and 

hearing. Their whistles generally are higher in frequency, ranging from approximately 6.3 to 

19.2 kHz (Mullin et al., 1994). Striped dolphin (also a Stenella species) whistles range from 6 to 

>24 kHz, with dominant frequencies ranging from 8 to 12.5 kHz (Thomson and Richardson, 1995). 

There are no available data regarding seasonal variation in the sound production of Stenella 

dolphins, although geographic variation is evident. The SLs as high as 210 dB re 1 μPa at 1 m 

(peak-peak) have been measured for echolocation clicks (Au et al., 1998; Au and Herzing, 2003).

2.2.8.6 Threats

Throughout their range, threats to Clymene dolphins include incidental take (as bycatch) in 

fisheries such as gillnets in Venezuela and possibly tuna purse seine nets off the coast of West 

Africa, and harvesting by artisan whalers using harpoons in the Caribbean Sea. The commercial 

fishery that could interact with this stock in the GOM is the Atlantic Ocean, Caribbean, GOM large 

pelagic longline fishery (Waring et al., 2013). Information from the Final PDARP/PEIS (Deepwater 

Horizon Natural Resource Damage Assessment Trustees, 2016) summarized injuries from the 

Deepwater Horizon oil spill to Clymene dolphins and stated that 7 percent of the population was 

exposed to Deepwater Horizon oil and 2 percent of the population was killed as a result. In addition, 

3 percent of females likely experienced reproductive failure and 3 percent of the population has 

experienced adverse health effects.
Gulf of Mexico G&G Activities Programmatic EIS E-33

2.2.8.7 Status

The GOM population is considered a separate stock (Northern GOM stock) for management 

purposes; however, there currently is no information to differentiate this stock from the Atlantic 

Ocean stock(s). The status of Clymene dolphins in the northern GOM is unknown. The species is 

not listed as threatened or endangered under the ESA, and there are insufficient data to determine 

species population trends; however, recent information from the Final PDARP/PEIS (Deepwater 

Horizon Natural Resource Damage Assessment Trustees, 2016) suggests that clymene dolphins in 

the GOM have experienced a population decline (2%) as a result of injury from the Deepwater 

Horizon oil spill. It is not a strategic stock because average annual human-related mortality and 

serious injury does not exceed PBR. The current PBR for the Northern GOM stock of Clymene 

dolphins is 0.6 individuals (Waring et al., 2013).

2.2.9 Striped Dolphin 

Striped dolphins (Stenella coeruleoalba) are similar in general body shape to other small 

oceanic dolphins but are easily distinguished by their robust body and coloration (Archer, 2002). 

Average body length is 2.5 m (8.2 ft) for males and 2 m (6.6 ft) for females, but there is geographical 

variation in adults from different populations (Jefferson et al., 2008).

2.2.9.1 Population

The GOM population is provisionally being considered a separate stock for management 

purposes; however, there currently is no information to differentiate this stock from the Atlantic 

Ocean stock(s). Additional morphological, genetic, and behavioral data are needed to provide 

further information on stock delineation (Waring et al., 2013).

2.2.9.2 Distribution and Abundance

Striped dolphins are widely distributed, ranging from tropical to cool temperate waters within 

the Atlantic, Pacific, and Indian Oceans. They are restricted to oceanic regions and are commonly 

associated with convergence zones and regions of upwelling (Archer, 2002). Sightings of these 

animals in the northern GOM also occur in oceanic waters (Mullin and Fulling, 2004; Maze-Foley 

and Mullin, 2006). Striped dolphins were seen in all seasons during GulfCet aerial surveys of the 

northern GOM between 1992 and 1998 (Hansen et al., 1996; Mullin and Hoggard, 2000).

The CetMap abundance estimate for northern GOM striped dolphins is 4,914 individuals 

(Roberts et al., 2016). From NMFS SAR data, the best abundance estimate available for northern 

GOM striped dolphins is 1,849 individuals (Waring et al., 2013). This estimate is from a summer 

2009 oceanic survey covering waters from the 200-m (656-ft) isobath to the seaward extent of the 

U.S. EEZ. Historically, for surveys conducted in oceanic waters from 1991 to 1994, the estimate 

was 4,858 individuals (CV = 0.44); from 1996 to 2001 (excluding 1998), the estimate was 

6,505 individuals (CV = 0.43); and from 2003 to 2004, the estimate was 3,325 individuals 

(CV = 0.48) (Waring et al., 2012).
E-34 Expanded Affected Environment Information

2.2.9.3 Habitat

Striped dolphins prefer highly productive tropical to warm temperate (10°C to 26°C [52°F to 

84°F]) deep oceanic waters. These dolphins often are linked to upwelling areas and convergence 

zones (USDOC, NMFS, 2015a).

2.2.9.4 Behavior

Striped dolphins usually are observed in groups of 10 to 30 individuals but may be seen in 

aggregations of up to 500 individuals. As with other oceanic dolphins, these groups may be 

segregated by age and sex, with individuals moving between groups. Striped dolphins perform a 

variety of aerial behaviors (Archer, 2002). Striped dolphins feed on a variety of pelagic and 

benthopelagic fishes (e.g., lanternfish and cod) as well as squids at depths of 200 to 700 m (656 to 

2,297 ft) (Jefferson et al., 2008).

2.2.9.5 Vocalizations and Hearing

Stenella produce sounds that range in frequency from 0.1 to 160 kHz (Richardson et al., 

1995). Striped dolphin whistles range from 6 to >24 kHz, with dominant frequencies ranging from 

8 to 12.5 kHz (Thomson and Richardson, 1995). As a group, Stenella are classified within the midfrequency cetacean functional marine mammal hearing group (150 Hz to 160 kHz) (Southall et al., 

2007). Based on ABRs, striped dolphins hear sounds ≥120 dB in the range of <10 to >100 kHz 

(Popper, 1980). The behavioral audiogram developed by Kastelein et al. (2003) shows hearing 

capabilities from 0.5 to 160 kHz. The best underwater hearing of the species appears to be from 

29 to 123 kHz (Kastelein, et al., 2003). Striped dolphins have relatively less hearing sensitivity 

below 32 kHz and above 120 kHz. There are no available data regarding seasonal variation in the 

sound production of Stenella dolphins, although geographic variation is evident. SLs as high as 

210 dB re 1 μPa at 1 m (peak-peak) have been measured for echolocation clicks (Au et al., 1998; Au 

and Herzing, 2003).

2.2.9.6 Threats

Striped dolphins are taken as bycatch or interact with several fisheries such as in pelagic 

trawls, gillnets, driftnets, purse seine nets, and hand harpoons. They have been subjected to drive 

hunts in Japan and taken in the Caribbean and Sri Lanka. During the mid-20th century, it is 

estimated that as many as 21,000 striped dolphins were caught and killed each year. The 

commercial fishery that could interact with this stock in the GOM is the Atlantic Ocean, Caribbean, 

GOM large pelagic longline fishery (Waring et al., 2013). Information from the Final PDARP/PEIS 

(Deepwater Horizon Natural Resource Damage Assessment Trustees, 2016) summarized injuries 

from the Deepwater Horizon oil spill to striped dolphins and stated that 13 percent of the population 

was exposed to Deepwater Horizon oil and 5 percent of the population was killed as a result. In 

addition, 6 percent of females likely experienced reproductive failure and 5 percent of the population 

has experienced adverse health effects.
Gulf of Mexico G&G Activities Programmatic EIS E-35

2.2.9.7 Status

The GOM population is considered a separate stock (Northern GOM stock) for management 

purposes; however, there currently is no information to differentiate this stock from the Atlantic 

Ocean stock(s). The status of striped dolphins in the northern GOM is unknown. The species is not 

listed as threatened or endangered under the ESA, and there are insufficient data to determine the 

population trends for this species; however, recent information from the Final PDARP/PEIS 

(Deepwater Horizon Natural Resource Damage Assessment Trustees, 2016) suggests that striped 

dolphins in the GOM have experienced a population decline (5%) as a result of injury from the 

Deepwater Horizon oil spill. It is not a strategic stock because average annual human-related 

mortality and serious injury does not exceed PBR. The current PBR for the Northern GOM stock of 

striped dolphins is 10 individuals (Waring et al., 2013).

2.2.10 Atlantic Spotted Dolphin

The Atlantic spotted dolphin (Stenella frontalis) is highly variable geographically, leading to 

much taxonomic confusion and misidentification of individuals (Perrin et al., 1994a). There is 

significant variability in osteological characteristics and color patterns in this species (Jefferson et al., 

2008). Adults range from 1.7 to 2.3 m (5.6 to 7.5 ft) in length (Perrin, 2002a).

2.2.10.1 Population

The GOM population is being considered a separate stock for management purposes. 

Adams and Rosel (2005) presented strong genetic support for differentiation between GOM and 

western North Atlantic management stocks using mitochondrial and nuclear markers. However, this 

study did not test for further population subdivision within the GOM (Waring et al., 2013).

2.2.10.2 Distribution and Abundance

The Atlantic spotted dolphin is endemic and common in tropical and temperate waters of the 

Atlantic Ocean. In the western Atlantic, they generally occur on the OCS and upper continental 

slope, usually between the 20- to 200-m (66- to 656-ft) depth contours (Jefferson et al., 2008). This 

species may conduct seasonal nearshore-offshore movements in response to the availability of prey 

species (Würsig et al., 2000). During GulfCet surveys, Atlantic spotted dolphins were sighted near 

the 100-m (328-ft) isobath, throughout the length of the survey area and during all seasons (Davis 

and Fargion, 1996). The current population size for the Atlantic spotted dolphin in the northern GOM 

is unknown (survey data are >8 years old).

The CetMap abundance estimate for northern GOM Atlantic spotted dolphins is 

47,488 individuals (Roberts et al., 2016). From NMFS SAR data, the most recent best abundance 

estimate for the Atlantic spotted dolphin in the northern GOM is 37,611 individuals, which is a 

combined estimate of abundance for animals sighted in OCS (fall surveys, 2000-2001) and oceanic 

waters (spring and summer surveys, 2003-2004) (Waring et al., 2013). Historically, for surveys 

conducted in OCS waters from 2000 to 2001, the estimate was 37,611 individuals (CV = 0.28) and 
E-36 Expanded Affected Environment Information

for surveys conducted in oceanic waters from 2003 to 2004, the estimate was 0 (CV = n/a) (Waring 

et al., 2013).

2.2.10.3 Habitat

Atlantic spotted dolphins prefer the tropical to warm temperate waters along the continental 

shelf of the Atlantic Ocean, occurring in water depths of 20 to 250 m (66 to 820 ft), but occasionally 

can be found in deeper oceanic waters (USDOC, NMFS, 2015a).

2.2.10.4 Behavior

Atlantic spotted dolphins have been observed in small to moderate-sized groups of 

<50 individuals (Jefferson et al., 2008). These groups may be segregated by age and sex (Perrin, 

2002a). They may interact with bottlenose dolphins, sometimes aggressively (Jefferson et al., 

2008). Atlantic spotted dolphins feed on a variety of epipelagic and mesopelagic fishes and squids 

as well as benthic invertebrates. They forage at depths between 40 and 60 m (131 and 197 ft), but 

most time is spent at depths <10 m (33 ft) (Perrin, 2002a).

2.2.10.5 Vocalizations and Hearing

Stenella produce sounds that range from 0.1 to 160 kHz (Richardson et al., 1995). As a 

group, Stenella are classified within the mid-frequency cetacean functional marine mammal hearing 

group (150 Hz to 160 kHz) (Southall et al., 2007). There is no direct measurement of auditory 

threshold for the hearing sensitivity of the Stenella dolphins, except for striped dolphins (Ketten, 

2000; Thewissen, 2002). Atlantic spotted dolphins produce a variety of sounds, including whistles, 

whistle-squawks, buzzes, burst pulses, synch pulses, barks, screams, squawks, tail slaps, and 

echolocation clicks. Like other odontocetes, they produce broadband, short-duration echolocation 

signals. Most of these signals have a bimodal frequency distribution. They project relatively highamplitude signals with a maximum SL of approximately 223 dB re 1 μPa at 1 m (Au and Herzing, 

2003). Their broadband clicks have peak frequencies between 60 and 120 kHz. Atlantic spotted 

dolphins produce whistles with frequencies below 20 kHz, with multiple harmonics extending to 

approximately 100 kHz (Lammers et al., 2003). Burst pulses consist of frequencies above 20 kHz 

(Lammers et al., 2003). Many of the vocalizations from Atlantic spotted dolphins have been 

associated with foraging behavior (Herzing, 1996). Thomson and Richardson (1995) reported that 

squawks, barks, growls, and chirps typically range from 0.1 to 8 kHz. Echolocation clicks have two 

dominant frequency ranges, one at 40 to 50 kHz and the other at 110 to 130 kHz, depending on the 

SL (lower SLs typically correspond to lower frequencies, and vice versa) (Au and Herzing, 2003). 

There are no available data regarding seasonal variation in the sound production of Stenella 

dolphins, although geographic variation is evident. SLs as high as 210 dB re 1 μPa at 1 m (peak 

peak) have been measured for echolocation clicks (Au et al., 1998; Au and Herzing, 2003).

2.2.10.6 Threats

Throughout their range, Atlantic spotted dolphins have been incidentally taken as bycatch in 

fisheries using gillnets and purse seines. This species has been observed interacting with various 
Gulf of Mexico G&G Activities Programmatic EIS E-37

fishing vessels, often following vessels and feeding on discarded catch. The commercial fisheries 

that could interact with this stock in the GOM are the Atlantic Ocean, Caribbean, GOM large pelagic 

longline fishery and the Southeastern U.S. Atlantic/GOM shrimp trawl fishery (Waring et al., 2013). 

A few Atlantic spotted dolphins have been harpooned in the Caribbean, South America (e.g., Brazil), 

West Africa, and other offshore islands for food and bait. Information from the Final PDARP/PEIS 

(Deepwater Horizon Natural Resource Damage Assessment Trustees, 2016) summarized injuries 

from the Deepwater Horizon oil spill to “continental shelf” dolphins, which included both Atlantic 

spotted and shelf bottlenose dolphins. It stated that 13 percent of the population was exposed to 

Deepwater Horizon oil and 4 percent of the population was killed as a result. In addition, 6 percent

of females likely experienced reproductive failure and 5 percent of the population has experienced 

adverse health effects.

2.2.10.7 Status

The GOM population of Atlantic spotted dolphins is considered a separate stock (Northern 

GOM stock) for management purposes. Adams and Rosel (2005) presented strong genetic support 

for differentiation between GOM and Western North Atlantic management stocks using mitochondrial 

and nuclear markers but did not test for further population subdivision within the GOM. The status of 

Atlantic spotted dolphins in the northern GOM is unknown. The species is not listed as threatened 

or endangered under the ESA, and there are insufficient data to determine population trends for this 

species; however, recent information from the Final PDARP/PEIS (Deepwater Horizon Natural 

Resource Damage Assessment Trustees, 2016) suggests that continental shelf dolphins (this 

includes Atlantic spotted) in the GOM have experienced a population decline (4%) as a result of 

injury from the Deepwater Horizon oil spill. It is not a strategic stock because previous estimates of 

population size have been large compared to the number of cases of documented human-related 

mortality and serious injury. The current PBR for the Northern GOM stock of striped dolphins is 

10 individuals (Waring et al., 2013).

2.2.11 Spinner Dolphin

Like other dolphins of the genus Stenella, spinner dolphins (Stenella longirostris) are 

relatively small. Adults range in length between 1.4 and 2.0 m (4.6 and 6.6 ft) (females) and 1.6 and 

2.1 m (5.2 and 6.9 ft) (males) (Jefferson et al., 2008). They weigh approximately 59 to 77 kg (130 to 

170 lb) at adulthood. They have long, slender beaks, and there is a lot of color variation based on 

region (USDOC, NMFS, 2015a).

2.2.11.1 Population

There are four recognized subspecies of spinner dolphins: S. l. longirostris (Gray’s spinner 

dolphin); S. l. orientalis (eastern spinner dolphin); S. l. centroamericana (Central American spinner 

dolphin); and S. l. roseiventris (dwarf spinner dolphin) (Committee on Taxonomy, 2013). The Gray’s 

spinner dolphin is the typical form of spinner dolphin that is found in most areas of the world, 

including the GOM. The GOM population is provisionally being considered a separate stock for 

management purposes; however, there currently is no information to differentiate this stock from the 
E-38 Expanded Affected Environment Information

Atlantic Ocean stock(s). Additional morphological, genetic, and behavioral data are needed to 

provide further information on stock delineation (Waring et al., 2013).

2.2.11.2 Distribution and Abundance

Spinner dolphins are distributed worldwide in tropical to temperate oceanic waters. Much of 

their range is oceanic. Sightings of the Gray’s spinner dolphin in the northern GOM occur in oceanic 

waters, generally east of the Mississippi River (Mullin and Fulling, 2004; Maze-Foley and Mullin, 

2006). Spinner dolphins were recorded in all seasons during GulfCet aerial surveys of the northern 

GOM between 1992 and 1998 (Hansen et al., 1996; Mullin and Hoggard, 2000).

The CetMap abundance estimate for northern GOM spinner dolphins is 13,485 individuals 

(Roberts et al., 2016). From NMFS SAR data, the best abundance estimate available for northern 

GOM spinner dolphins is 11,441 individuals (Waring et al., 2013). This estimate is from a summer 

2009 oceanic survey covering waters from the 200-m (656-ft) isobath to the seaward extent of the 

U.S. EEZ. Historically, estimates within oceanic waters for 1991 to 1994 was 6,316 individuals 

(CV = 0.43); from 1996 to 2001 (excluding 1998), the estimate was 11,971 individuals (CV = 0.71); 

and from 2003 to 2004, the estimate was 1,989 individuals (CV = 0.48) (Waring et al., 2013).

2.2.11.3 Habitat

In most places, spinner dolphins are found in the deep ocean where they likely track prey. 

The Hawaii population has a more coastal distribution. There, the animals rest in bays and 

protected areas during the day and then fuse into larger groups at night to feed on fish and squid in 

deeper water (USDOC, NMFS, 2015a).

2.2.11.4 Behavior

Spinner dolphins are highly gregarious and form groups ranging in size from a few 

individuals to several thousand (Perrin, 2002b; Jefferson et al., 2008). They commonly school with 

other cetacean species (Perrin, 2002b). The social organization of these groups is fluid and may be 

composed of temporary (days or weeks) associations of family units (Perrin, 2002b). Adult males 

may form groups of approximately 12 individuals; the function of these groups is unknown (Perrin, 

2002b). Spinner dolphins are one of the most aerial of all dolphin species. Spinner dolphins feed on 

small midwater fishes, squids, and crustaceans, usually at night and at depths of 600 m (1,969 ft) or 

greater (Perrin, 2002b).

2.2.11.5 Vocalizations and Hearing

Stenella produce sounds that range from 0.1 to 160 kHz (Richardson et al., 1995). As a 

group, Stenella are classified within the mid-frequency cetacean functional marine mammal hearing 

group (150 Hz to 160 kHz) (Southall et al., 2007). There is no direct measurement of auditory 

threshold for the hearing sensitivity of the Stenella dolphins, except for striped dolphins (Ketten, 

2000; Thewissen, 2002). Spinner dolphins produce burst-pulse calls, echolocation clicks, whistles, 

and screams (Norris et al., 1994; Bazúa-Durán and Au, 2002). Pulses and whistles have a dominant 
Gulf of Mexico G&G Activities Programmatic EIS E-39 

frequency range of 5 to 60 kHz and 8 to 12 kHz, respectively (U.S. Department of the Navy, 2007). 

Their whistles range in frequency from 16.9 to 17.9 kHz, with a maximum frequency for the 

fundamental component of 24.9 kHz (Bazúa Durán and Au, 2002; Lammers et al., 2003). Ketten 

(1998) stated that clicks from spinner dolphins have a dominant frequency of 60 kHz, and Lammers 

et al. (2003) reported that burst-pulses are predominantly ultrasonic with little or no energy below 

20 kHz. Schotten et al. (2004) reported that spinner dolphin clicks have SLs ranging from 195 to 

222 dB re 1 μPa at 1 m. The results of a study on pantropical spotted dolphins and spinner dolphins 

conducted by Lammers et al. (2003) revealed that the whistles and burst-pulses of the two species 

span a broader frequency range than traditionally reported for delphinids. The fundamental 

frequency contours of whistles occur in the human hearing range, but the harmonics typically reach 

50 kHz and higher. Pantropical spotted dolphin whistles range in frequency from 3.1 to 21.4 kHz 

(Thomson and Richardson, 1995). Clicks typically are bimodal, with frequency peaks at 40 to 

60 kHz and at 120 to 140 kHz, with an estimated SL of up to 220 dB re 1 μPa at 1 m (peak peak) 

(Schotten et al., 2004). There are no available data regarding seasonal variation in the sound 

production of Stenella dolphins, although geographic variation is evident. SLs as high as 210 dB re 

1 μPa at 1 m (peak-peak) have been measured for echolocation clicks (Au et al., 1998; Au and 

Herzing, 2003).

2.2.11.6 Threats

The Eastern Tropical Pacific stock of spinner dolphins has been used by the purse seine 

fishery to locate tuna. Dolphins can become trapped in the nets and drown. Stress from being 

encircled in purse seines has been documented as a very serious threat to dolphins. Currently, 

fishing methods for tuna imported into the U.S. under the Dolphin-Safe program do not allow such 

fishing practices (USDOC, NMFS, 2015a). The commercial fishery that could interact with this stock 

in the GOM is the Atlantic Ocean, Caribbean, GOM large pelagic longline fishery (Waring et al., 

2013). Interactions with tourists are a growing threat to the Hawaiian stock; because the species is 

active at night, daytime interactions with tourists inhibit necessary rest and sleep time. Information 

from the Final PDARP/PEIS (Deepwater Horizon Natural Resource Damage Assessment Trustees, 

2016) summarized injuries from the Deepwater Horizon oil spill to spinner dolphins and stated that 

47 percent of the population was exposed to Deepwater Horizon oil and 16 percent of the population 

was killed as a result. In addition, 21 percent of females likely experienced reproductive failure and 

17 percent of the population has experienced adverse health effects.

2.2.11.7 Status

The GOM population of spinner dolphins is considered a separate stock (Northern GOM 

stock) for management purposes; however, there currently is no information to differentiate this 

stock from the Atlantic Ocean stock(s). The status of spinner dolphins in the northern GOM is 

unknown. The species is not listed as threatened or endangered under the ESA, and there are 

insufficient data to determine the population trends for this species; however, recent information from 

the Final PDARP/PEIS (Deepwater Horizon Natural Resource Damage Assessment Trustees, 2016) 

suggests that spinner dolphins in the GOM have experienced a population decline (16%) as a result 

of injury from the Deepwater Horizon oil spill. This is not a strategic stock because it is assumed 
E-40 Expanded Affected Environment Information

that the average annual human-related mortality and serious injury does not exceed PBR (current 

PBR for the northern GOM spinner dolphin is 62 individuals) (Waring et al., 2013).

2.2.12 Fraser’s Dolphin

The Fraser’s dolphin (Lagenodelphis hosei) is easily identified by its stocky body, short beak, 

and small triangular or slightly falcate dorsal fin (Dolar, 2002). They grow to lengths of 

approximately 2.7 m (9 ft) (Jefferson et al., 2008).

2.2.12.1 Population

The GOM population is provisionally being considered a separate stock for management 

purposes; however, there currently is no information to differentiate this stock from the Atlantic 

Ocean stock(s). Additional morphological, genetic, and behavioral data are needed to provide 

further information on stock delineation (Waring et al., 2013).

2.2.12.2 Distribution and Abundance

The Fraser’s dolphin is a pantropical species, distributed in oceanic waters between 30° N. 

and 30° S. latitude in the Atlantic, Pacific, and Indian Oceans (Dolar, 2002; Jefferson et al., 2008). 

Sightings in the northern GOM have been recorded during all seasons in water depths >200 m 

(656 ft) (Leatherwood et al., 1993; Hansen et al., 1996; Mullin and Hoggard, 2000; Maze Foley and 

Mullin, 2006).

The CetMap abundance estimate for northern GOM Fraser’s dolphins is 1,665 individuals 

(Roberts et al., 2016). From NMFS SAR data, the best abundance estimate available for northern 

GOM Fraser’s dolphins is unknown. Recent surveys (summer 2009) estimated zero abundance for 

Fraser’s dolphins in oceanic waters in 2009. Because sightings of Fraser’s dolphins have been 

uncommon to rare in the past, it is probable that Fraser’s dolphins were not encountered during this

survey (Waring et al., 2013). Historically, for surveys conducted in oceanic waters from 1991 to 

1994, the estimate was 127 individuals (CV = 0.9); from 1996 to 2001 (excluding 1998), the estimate 

was 726 individuals (CV = 0.70); and from 2003 to 2004, the estimate was 0 individuals (CV = n/a) 

(Waring et al., 2013).

2.2.12.3 Habitat

Fraser’s dolphins occur in warm temperate, subtropical, and tropical pelagic waters 

worldwide, usually deeper than 1,000 m (3,280 ft). They often are associated with areas of 

upwelling (USDOC, NMFS, 2015a).

2.2.12.4 Behavior

Fraser’s dolphins are observed in large groups of hundreds to thousands of individuals, often 

mixed with other cetacean species such as melon-headed whales, pilot whales, Risso’s dolphins, 

spotted dolphins, and spinner dolphins (Jefferson et al., 2008). Swimming speeds of Fraser’s 
Gulf of Mexico G&G Activities Programmatic EIS E-41

dolphins have been recorded between 2 and 4 kn (2.3 to 4.6 mph) with speeds up to 15 kn 

(17.3 mph) when escaping predators (Croll et al., 1999). According to Watkins et al. (1994), Fraser’s 

dolphins herd when they feed, swimming rapidly to an area, diving for 15 seconds or more, 

surfacing, and splashing in a coordinated effort to surround the school of fish. Dive durations are not 

known, but several foraging depths have been recorded (250 to 500 m [820 to 1,640 ft]) (Perrin 

et al., 1994b). Fraser’s dolphins feed on mesopelagic fish (particularly Myctophidae and Stomiidae), 

crustaceans (particularly Oplophoridae), and cephalopods (Croll et al., 1999; Dolar, 2002).

2.2.12.5 Vocalizations and Hearing

Fraser’s dolphins produce sounds that range from 6.6 to 23.5 kHz (Oswald, 2006). They are 

classified within the mid-frequency cetacean functional marine mammal hearing group (150 Hz to 

160 kHz) (Southall et al., 2007). There is no direct measurement of auditory threshold for the 

hearing sensitivity of Fraser’s dolphins (Ketten, 2000; Thewissen, 2002). Echolocation clicks are 

described as short broadband sounds without emphasis at frequencies below 40 kHz, while whistles 

are FM tones concentrated between 4.3 and 24 kHz. Whistles have been suggested as 

communicative signals during social activity (Watkins et al., 1994). There are no available data 

regarding seasonal or geographical variation in the sound production of Fraser’s dolphins.

2.2.12.6 Threats

Threats to Fraser’s dolphins throughout their range include incidental catch in fisheries 

operating in pelagic waters using driftnets, gillnets, and trap nets as well as harvest by fisheries for 

meat and oil (Jefferson et al., 2008). Specifically, Fraser’s dolphins have been incidentally captured 

in tuna purse seine fisheries in the eastern tropical Pacific and the Philippines (USDOC, NMFS, 

2015a). The commercial fishery that could interact with this stock in the GOM is the Atlantic Ocean, 

Caribbean, GOM large pelagic longline fishery (Waring et al., 2013). Fraser’s dolphins are 

harvested in Indonesia, Japan, the Lesser Antilles, the Philippines, and Sri Lanka (USDOC, NMFS, 

2015a). There was not enough information for Fraser’s dolphins in the GOM to assess potential 

impacts of the Deepwater Horizon oil spill (Deepwater Horizon Natural Resource Damage 

Assessment Trustees, 2016).

2.2.12.7 Status

Fraser’s dolphin is classified as data deficient by the IUCN and is protected under the 

MMPA. The species is not listed as threatened or endangered under the ESA, and there are 

insufficient data to determine the population trends for this species. There were not enough data to 

make a determination about the overlap between the Deepwater Horizon oil-spill footprint and the 

ranges of Fraser’s dolphins in the GOM; therefore, the potential injuries to this population are 

unknown. Total human-caused mortality and serious injury for this stock is not known, but none has 

been documented. The PBR for the northern GOM Fraser’s dolphin is undetermined. Despite an 

undetermined PBR, this is not a strategic stock because there is no documented human-related 

mortality and serious injury (Waring et al., 2013).
E-42 Expanded Affected Environment Information

2.2.13 Risso’s Dolphin

The Risso’s dolphin (Grampus griseus) is a medium-sized dolphin with a characteristic blunt 

head and light coloration. Adults are covered with white scratches, spots, and blotches that may, in 

conjunction with dorsal fin scars, be used to identify individuals. It is thought that this scarring may 

be from the beaks and suckers of squid (their primary prey) and the teeth of other Risso’s dolphins 

(Jefferson et al., 2008). Adults of both sexes reach body lengths of more than 3.8 m (12 ft).

2.2.13.1 Population

The GOM population is provisionally being considered a separate stock for management 

purposes; however, there currently is little information to differentiate this stock from the Atlantic 

Ocean stock(s). Additional morphological, genetic, and behavioral data are needed to provide 

further information on stock delineation.

2.2.13.2 Distribution and Abundance

Risso’s dolphins are distributed worldwide in tropical to warm temperate waters 

(Leatherwood and Reeves, 1983). They occur throughout oceanic waters of the northern GOM but 

are concentrated in areas of the continental slope (Baumgartner, 1997; Maze-Foley and Mullin, 

2006). Risso’s dolphins were documented in all seasons during GulfCet aerial surveys of the 

northern GOM between 1992 and 1998 (Hansen et al., 1996; Mullin and Hoggard, 2000). Average 

group size during GulfCet surveys was 7.5 individuals (Davis and Fargion, 1996).

The CetMap abundance estimate for northern GOM Risso’s dolphins is 3,137 individuals 

(Roberts et al., 2016). From NMFS SAR data, the best abundance estimate available for northern 

GOM Risso’s dolphins is 2,442 individuals (CV = 0.57) (Waring et al., 2014). Historically, for surveys 

conducted in oceanic waters from 1991 to 1994, the estimate was 2,749 individuals (CV = 0.27); 

from 1996 to 2001 (excluding 1998), the estimate was 2,169 individuals (CV = 0.32); and from 2003 

to 2004, the estimate was 1,589 individuals (CV = 0.27) (Waring et al., 2012).

2.2.13.3 Habitat

Risso’s dolphins are found in temperate, subtropical, and tropical waters with a temperature 

range of 10°C to 30°C (50°F to 86°F) and in depths >1,000 m (3,280 ft) seaward of the continental 

shelf. The species may be limited by water temperature, as individuals are more common in waters 

of 15°C to 20°C (59°F to 68°F). In the northern GOM, Risso’s dolphins may prefer habitats on the 

continental slope where the seafloor topography is steeper. In the waters off northern Europe, they 

are known to inhabit shallower coastal areas (USDOC, NMFS, 2015a).

2.2.13.4 Behavior

Risso’s dolphins often are observed in groups of 10 to 100 individuals, but larger 

aggregations have been reported (Jefferson et al., 2008). In the GOM, pod sizes typically range 

from 3 to 30 individuals (Würsig et al., 2000). They commonly associate with other cetacean 
Gulf of Mexico G&G Activities Programmatic EIS E-43

species, including other delphinids and large whales (Baird, 2002a). They are thought to feed 

primarily on squid but are known to eat fishes and crustaceans (Würsig et al., 2000). Behavioral 

research suggests that Risso’s dolphins primarily feed at night (Baird, 2002a). Swimming speeds for 

Risso’s dolphins have been recorded at 1 to 7 kn (1.2 to 8.1 mph) off Santa Catalina Island (Shane, 

1995). There currently are no known studies on diving behavior, but Risso’s dolphins have been 

known to dive for up to 30 minutes and as deep as 600 m (1,969 ft) (DiGiovanni et al., 2005). They 

have been noted to demonstrate aggressive behavior toward other cetacean species. No data on 

breeding grounds are available, and Risso’s dolphins have been known to calve year-round, peaking 

in winter (Baird, 2002a).

2.2.13.5 Vocalization and Hearing

The species is classified within the mid-frequency cetacean functional marine mammal 

hearing group (150 Hz to 160 kHz) (Southall et al., 2007). Audiograms for Risso’s dolphins indicate 

hearing thresholds ≤65 to 125 dB in frequencies ranging from 1.6 to 110 kHz (Nachtigall et al., 

1995). Philips et al. (2003) reported that Risso’s dolphins are capable of hearing frequencies up to 

80 kHz, with best underwater hearing occurring between 4 and 80 kHz at threshold levels from 64 to 

74 dB re 1 μPa. Other audiograms obtained on Risso’s dolphins confirm previous measurements 

and demonstrated a hearing threshold of 140 dB re 1 μPa for a 1-second, 75-Hz signal (Au et al., 

1997; Croll et al., 1999).

Au et al. (1997) studied the hearing sensitivities of false killer whales and Risso’s dolphins to 

the Acoustic Thermometry of Ocean Climate (ATOC) signal. The ATOC program transmitted 75 Hz, 

phase modulated, 195 dB re 1 μPa at 1 m SL signals from two locations in the North Pacific to study 

ocean temperatures. The hearing thresholds for Risso’s dolphins were 142 ± 2 dB re 1 μPa 

receiving level (RL) for a 75 Hz pure tone signal and 141 ± 1 dB re 1 μPa RL for the ATOC signal. 

The results of this study concluded that small cetaceans, such as false killer whales and Risso’s 

dolphins, swimming directly over the ATOC source would not be able to hear the transmitted sound 

unless the animals dove to a depth of approximately 400 m (1,312 ft). If these animals were at a 

horizontal range >0.5 km (0.3 nmi) from the source, the level of the ATOC signal would be below 

their hearing threshold at any depth.

Risso’s dolphins produce vocalizations as low as 0.1 kHz and as high as 65 kHz. Their 

dominant frequencies are between 2 and 5 kHz and at 65 kHz (Watkins, 1967; Au, 1993; Croll et al., 

1999; Philips et al., 2003). The maximum SL, with dominant frequencies at 2 to 5 kHz, is 

approximately 120 dB re 1 μPa at 1 m (peak-to-peak) (Au, 1993). In one experiment conducted by 

Philips et al. (2003), clicks were found to have a peak frequency of 65 kHz and durations ranging 

from 40 to 100 ms. In a second experiment, Philips et al. (2003) recorded clicks with peak 

frequencies up to 50 kHz with durations ranging from 35 to 75 ms. Estimated SLs of echolocation 

clicks can reach up to 216 dB re 1 μPa at 1 m (Philips et al., 2003). Bark vocalizations consisted of 

highly variable burst-pulses and have a frequency range of 2 to 20 kHz. Buzzes consisted of a short 

burst-pulse of sound approximately 2 seconds in duration with a frequency range of 2.1 to 22 kHz. 

Low-frequency, narrow-band grunt vocalizations ranged between 400 and 800 Hz. Chirp 
E-44 Expanded Affected Environment Information

vocalizations were slightly higher in frequency than the grunt vocalizations, ranging in frequency 

from 2 to 4 kHz. There are no available data regarding seasonal or geographical variation in the 

sound production of Risso’s dolphin.

2.2.13.6 Threats

Threats to Risso’s dolphins throughout their range include bycatch in fishing gear, including 

gillnets, longlines, and trawls, as well as tuna purse seine fishing (in the eastern tropical Pacific 

Ocean); harvest for meat and oil in Indonesia, Japan (drive fishery), the Caribbean (the Lesser 

Antilles), and the Solomon Islands; and small numbers of Risso’s dolphins have been captured from 

the wild for the purpose of public display in aquariums and oceanariums (USDOC, NMFS, 2015a). 

The commercial fishery that could interact with this stock in the GOM is the Atlantic Ocean, 

Caribbean, GOM large pelagic longline fishery (Waring et al., 2013). Information from the Final 

PDARP/PEIS (Deepwater Horizon Natural Resource Damage Assessment Trustees, 2016) 

summarized injuries from the Deepwater Horizon oil spill to Risso’s dolphins and stated that 8

percent of the population was exposed to Deepwater Horizon oil and 3 percent of the population was 

killed as a result. In addition, 3 percent of females likely experienced reproductive failure and 3

percent of the population has experienced adverse health effects.

2.2.13.7 Status

Risso’s dolphin is classified as data deficient by the IUCN and is protected under the MMPA. 

The status of Risso’s dolphins in the northern GOM is unknown; however, recent information from 

the Final PDARP/PEIS (Deepwater Horizon Natural Resource Damage Assessment Trustees, 2016) 

suggests that Risso’s dolphins in the GOM have experienced a population decline (3%) as a result 

of injury from the Deepwater Horizon oil spill. The species is not listed as threatened or endangered 

under the ESA, and there are insufficient data to determine the population trends for this species. 

The stock is classified as non-strategic under the MMPA. The current PBR for the Northern GOM 

stock of Risso’s dolphins is 16 individuals (Waring et al., 2014).

2.2.14 Melon-Headed Whale

The melon-headed whale (Peponocephala electra) is a small, slender whale that reaches a 

maximum length of approximately 2.8 m (9.2 ft) (Jefferson et al., 2008).

2.2.14.1 Population

The GOM population is provisionally being considered as one stock for management 

purposes; however, there currently is no information to differentiate this stock from the Atlantic 

Ocean stock(s). Additional morphological, genetic, and behavioral data are needed to provide 

further information on stock delineation (Waring et al., 2013).
Gulf of Mexico G&G Activities Programmatic EIS E-45

2.2.14.2 Distribution and Abundance

Melon-headed whales are distributed worldwide in tropical to subtropical waters (Jefferson 

et al., 2008). They generally are found in oceanic waters with nearshore sightings limited to areas 

where deep waters are found near the coast (Perryman, 2002). Sightings in the northern GOM 

generally have occurred in water depths >800 m (2,625 ft) and usually offshore Louisiana to west of 

Mobile Bay, Alabama (Mullin et al., 1994; Mullin and Fulling, 2004; Maze-Foley and Mullin, 2006). 

Melon-headed whales were sighted in all seasons during GulfCet surveys of the northern GOM 

between 1992 and 1998 (Davis and Fargion, 1996; Hansen et al., 1996; Mullin and Hoggard, 2000).

The CetMap abundance estimate for northern GOM melon-headed whales is 

6,733 individuals (Roberts et al., 2016). From NMFS SAR data, the best abundance estimate 

available for northern GOM melon-headed whales is 2,235 individuals (CV = 0.75) (Waring et al., 

2012). Historically, for surveys conducted in oceanic waters from 1991 to 1994, the estimate was 

3,965 individuals (CV = 0.39); from 1996 to 2001 (excluding 1998), the estimate was 

3,451 individuals (CV = 0.55), and from 2003 to 2004, the estimate was 2,283 individuals 

(CV = 0.76) (Waring et al., 2012).

2.2.14.3 Habitat

Melon-headed whales prefer deeper areas of warmer tropical waters where their prey are 

concentrated (USDOC, NMFS, 2015a).

2.2.14.4 Behavior

Melon-headed whales are highly social animals and usually are observed in groups of 100 to 

500 individuals. Average group sizes reported from the GOM during GulfCet surveys were 

140.7 individuals (ship surveys) and 311.7 individuals (aircraft surveys) (Davis and Fargion, 1996). 

Melon-headed whales often are observed swimming with other delphinid species such as Fraser’s 

dolphins, spinner dolphins, and spotted dolphins, occasionally forming “super pods” of thousands of 

individuals. Melon-headed whales are known to feed mainly on deepwater squid, but fish and 

shrimp have been found in melon-headed whale stomachs as well (Perryman, 2002). Little is known 

of this species’ life history or reproductive biology. No swimming speeds, dive depths, or dive times 

are available for the melon-headed whale.

2.2.14.5 Vocalization and Hearing

Melon-headed whales are classified within the mid-frequency cetacean functional marine 

mammal hearing group (150 Hz to 160 kHz) (Southall et al., 2007). There is no direct measurement 

of auditory threshold for the hearing sensitivity of melon-headed whales (Ketten, 2000; Thewissen, 

2002). They produce sounds between 8 and 40 kHz (Watkins et al., 1997). Individual click bursts 

have frequency emphases between 20 and 40 kHz (Watkins et al., 1997). Dominant frequencies of 

whistles are 8 to 12 kHz, with FM upsweeps and downsweeps (Watkins et al., 1997). There are no 

available data regarding seasonal or geographical variation in the sound production of this species. 
E-46 Expanded Affected Environment Information

Maximum SLs are estimated at 155 dB re 1 μPa at 1 m for whistles and 165 dB re 1 μPa at 1 m for 

click bursts (Watkins et al., 1997).

2.2.14.6 Threats

Throughout their range, threats to melon-headed whales include bycatch in some fisheries. 

There has been some take of this species in the past by small cetacean fisheries in the Caribbean 

(Caldwell et al., 1976). The commercial fishery that could interact with this stock in the GOM is the 

Atlantic Ocean, Caribbean, GOM large pelagic longline fishery (Waring et al., 2013). Information 

from the Final PDARP/PEIS (Deepwater Horizon Natural Resource Damage Assessment Trustees, 

2016) summarized injuries from the Deepwater Horizon oil spill to melon-headed whales and stated 

that 15 percent of the population was exposed to Deepwater Horizon oil and 5 percent of the 

population was killed as a result. In addition, 7 percent of females likely experienced reproductive 

failure and 6 percent of the population has experienced adverse health effects.

2.2.14.7 Status

Melon-headed whales are categorized as least concern by the IUCN and are protected 

under the MMPA. The species is not listed as threatened or endangered under the ESA. The status 

of melon-headed whales in the northern GOM is unknown; however, recent information from the 

Final PDARP/PEIS (Deepwater Horizon Natural Resource Damage Assessment Trustees, 2016) 

suggests that melon-headed whales in the GOM have experienced a population decline (5%) as a 

result of injury from the Deepwater Horizon oil spill. This is not a strategic stock because it is 

assumed that the average annual human-related mortality and serious injury does not exceed PBR. 

The current PBR for the Northern GOM stock of melon-headed whales is 13 individuals (Waring 

et al., 2014).

2.2.15 Pygmy Killer Whale

The pygmy killer whale (Feresa attenuata) is a relatively small odontocete of the family 

Delphinidae. Adult pygmy killer whales can reach body lengths of 2.6 m (8.5 ft) (Jefferson et al., 

2008).

2.2.15.1 Population

The GOM population of pygmy killer whales is provisionally being considered a separate

stock for management purposes; however, there currently is no information to differentiate this stock 

from the Atlantic Ocean stock(s). Additional morphological, genetic, and behavioral data are needed 

to provide further information on stock delineation (Waring et al., 2013).

2.2.15.2 Distribution and Abundance

The pygmy killer whale is distributed worldwide in tropical to subtropical oceanic waters. 

They are rarely seen in nearshore waters, except in areas where deep water is close to shore 

(Jefferson et al., 2008). Historic sightings of these animals in the northern GOM are within oceanic 
Gulf of Mexico G&G Activities Programmatic EIS E-47

waters (Mullin and Fulling, 2004; Maze-Foley and Mullin, 2006). Through the GulfCet program, 

BOEM (formerly the Minerals Management Service [MMS]) had data collaboratively collected by 

external partners, including the NMFS, on the distribution and abundance of marine mammals in the 

northern GOM. Sightings of pygmy killer whales (in low numbers) were documented in all seasons 

during GulfCet aerial surveys of the northern GOM between 1992 and 1998 (Hansen et al., 1996; 

Mullin and Hoggard, 2000). No data are available to confirm seasonal migration patterns for pygmy 

killer whales, and there are no available data on breeding and calving grounds.

The CetMap abundance estimate for northern GOM pygmy killer whales is 2,126 individuals 

(Roberts et al., 2016). From NMFS SAR data, the best abundance estimate available for northern 

GOM pygmy killer whales is 152 individuals (CV = 1.02), based on data collected from a summer 

2009 survey covering waters from the 200-m (656-ft) isobath to the seaward extent of the U.S. EEZ 

(Waring et al., 2013). Historically, for surveys conducted in oceanic waters from 1991 to 1994, the 

estimate was 518 individuals (CV = 0.81); from 1996 to 2001 (excluding 1998), the estimate was 

408 individuals (CV = 0.60); and from 2003 to 2004, the estimate was 323 individuals (CV = 6.0) 

(Waring et al., 2012).

2.2.15.3 Habitat

Pygmy killer whales prefer deeper areas of warm tropical and subtropical waters where their 

prey are concentrated (USDOC, NMFS, 2015a).

2.2.15.4 Behavior

Little is known about the biology of the pygmy killer whale. Groups generally contain 

approximately 12 to 50 individuals, although pods of several hundred individuals have been reported 

(Würsig et al., 2000). Existing information indicates that pygmy killer whales feed on fishes and 

squids (Ross and Leatherwood, 1994). They have shown aggressive behavior with other animals, 

based on attacks on animals while in captivity or individual dolphins incidentally caught in tuna nets 

in the eastern tropical Pacific (Jefferson et al., 2008).

2.2.15.5 Vocalizations and Hearing

The pygmy killer whale is classified within the mid-frequency cetacean functional marine 

mammal hearing group (150 Hz to 160 kHz) (Southall et al., 2007). Little is known of the auditory 

range and sound production of the species. Pryor et al. (1965) described pygmy killer whales 

producing low-frequency “growls.” Pygmy killer whales emit echolocation clicks with centroid 

frequencies between 70 and 85 kHz, with bimodal peak frequencies between 45 and 117 kHz and 

an estimated SL between 197 and 223 dB re 1 μPa at 1 m (Madsen et al., 2004).

2.2.15.6 Threats

Throughout their range, few pygmy killer whales are caught in drive and gillnet fisheries. 

There has been some take of this species in the past by small cetacean fisheries in the Caribbean 

(Caldwell and Caldwell, 1971b). The commercial fishery that could interact with this stock in the 
E-48 Expanded Affected Environment Information

GOM is the Atlantic Ocean, Caribbean, GOM large pelagic longline fishery (Waring et al., 2013). 

However, there is no reported bycatch from U.S. fisheries. Information from the Final PDARP/PEIS 

(Deepwater Horizon Natural Resource Damage Assessment Trustees, 2016) summarized injuries 

from the Deepwater Horizon oil spill to pygmy killer whales and stated that 15 percent of the 

population was exposed to Deepwater Horizon oil and 5 percent of the population was killed as a 

result. In addition, 7 percent of females likely experienced reproductive failure and 6 percent of the 

population has experienced adverse health effects.

2.2.15.7 Status

Pygmy killer whales are classified as data deficient by the IUCN and are protected under the 

MMPA. The species is not listed as threatened or endangered under the ESA, and there are 

insufficient data to determine the population trends for this species or total human-caused mortality 

and serious injury for this stock. The status of pygmy killer whales in the northern GOM is unknown; 

however, recent information from the Final PDARP/PEIS (Deepwater Horizon Natural Resource 

Damage Assessment Trustees, 2016) suggests that pygmy killer whales in the GOM have 

experienced a population decline (5%) as a result of injury from the Deepwater Horizon oil spill. The 

GOM stock is not classified under the MMPA as a strategic stock. The current PBR for the Northern 

GOM stock of pygmy killer whales is 0.8 individuals (Waring et al., 2014).

2.2.16 False Killer Whale

The false killer whale (Pseudorca crassidens) is a medium-sized odontocete of the family 

Delphinidae. Males can reach 6 m (20 ft) in length and females can reach 5 m (16 ft) (Jefferson 

et al., 2008).

2.2.16.1 Population

The GOM population is provisionally being considered a single stock for management 

purposes; however, there currently is no information to differentiate this stock from the Atlantic 

Ocean stock(s). Additional morphological, genetic, and behavioral data are needed to provide 

further information on stock delineation (Waring et al., 2013).

2.2.16.2 Distribution and Abundance

The false killer whale is distributed worldwide throughout warm temperate and tropical 

oceans, generally in relatively deep offshore waters from 60° S. to 60° N. latitude (USDOC, NMFS, 

2015a; Stacey et al., 1994; Odell and McClune, 1999; Baird, 2002b; Waring et al., 2013). They are 

reported to occur over the continental shelf and may move into very shallow waters on occasion 

(Jefferson et al., 2008). Historic sightings of this species in the northern GOM are from oceanic 

waters (Mullin and Fulling, 2004; Maze Foley and Mullin, 2006). False killer whales were observed 

only during spring and summer during GulfCet aerial surveys between 1992 and 1998 (Hansen 

et al., 1996; Mullin and Hoggard, 2000) and in the spring during vessel surveys (Mullin and Fulling, 

2004). Sightings during the GulfCet surveys were not concentrated in any particular portion of the 

study area (Davis and Fargion, 1996).
Gulf of Mexico G&G Activities Programmatic EIS E-49

The CetMap abundance estimate for northern GOM killer whales is 3,204 individuals 

(CV = 0.32) (Roberts et al., 2016). From NMFS SAR data, the current estimate of abundance and 

the minimum population estimate of false killer whales in the GOM are unknown (existing estimates 

are >8 years old); the best population estimate is unknown (Waring et al., 2013). Historically, for 

surveys conducted in oceanic waters from 1991 to 1994, the estimate was 381 individuals 

(CV = 0.62); from 1996 to 2001 (excluding 1998), the estimate was 1,038 individuals (CV = 0.71); 

and from 2003 to 2004, the estimate was 777 individuals (CV = 0.56) (Waring et al., 2012).

2.2.16.3 Habitat

False killer whales prefer tropical to temperate waters that are deeper than 3,300 ft (1,000 m) 

(USDOC, NMFS, 2015a).

2.2.16.4 Behavior

False killer whales are highly social and commonly observed in groups of 10 to 

60 individuals, although larger groups have been documented (Würsig et al., 2000; Baird, 2002b). 

During GulfCet surveys, observed group sizes ranged from 2 to 35 individuals and averaged 3.5 and 

27.5 individuals estimated from ship and aerial platforms, respectively (Davis and Fargion, 1996). 

Details of false killer whale social organizations are not available; however, because of their 

propensity to strand in groups, it is assumed that there are strong bonds between individuals within 

groups (Baird, 2002b). They primarily feed on fishes and cephalopods, although they are known to 

attack other cetaceans. False killer whales have an approximate swimming speed of 2 kn (2.3 mph), 

although a maximum swimming speed of 15.5 kn (17.8 mph) (Brown et al., 1966; Rohr et al., 2002). 

Dive depths of 500 m (1,640 ft) have been recorded for this species (Odell and McClune, 1999). 

There are no available data on specific breeding grounds. Calving season may be considered yearround with a peak in late winter (Baird, 2002b). The calving interval for one group was reported as 

almost 7 years, and calving may occur year-round (Baird, 2002b).

2.2.16.5 Vocalizations and Hearing

False killer whales are classified within the mid-frequency, cetacean functional marine 

mammal hearing group (150 Hz to 160 kHz) (Southall et al., 2007). They hear underwater sounds in 

the range of <1 to 115 kHz (Johnson, 1967; Awbrey et al., 1988; Au, 1993). Their best underwater 

hearing occurs at 17 kHz, where the threshold level ranges between 39 and 49 dB re 1 μPa 

(Sauerland and Dehnhardt, 1998). Behavioral audiograms, supported by ABR studies that had 

similar results, show that the range of best hearing sensitivity is between 16 and 24 kHz, with peak 

sensitivity at 20 kHz (Yuen et al., 2005). Au et al. (1997) studied the hearing sensitivities of false 

killer whales and Risso’s dolphins to the ATOC signal. The ATOC program transmitted 75 Hz, 

phase-modulated, 195 dB SL signals from two locations in the North Pacific to study ocean 

temperatures. The hearing thresholds for false killer whales were 141 ± 1 dB re 1 μPa RL for a 

75-Hz pure tone signal and 139 ± 1 dB re 1 μPa RL for the ATOC signal. The results of this study 

concluded that small cetaceans, such as false killer whales and Risso’s dolphins, swimming directly 

over the ATOC source, would not be able to hear the transmitted sound unless the animals dove to 
E-50 Expanded Affected Environment Information

a depth of approximately 400 m (1,312 ft). If these animals were at a horizontal range >0.5 km 

(0.3 mi) from the source, the level of the ATOC signal would be below their hearing threshold at any 

depth.

False killer whales produce a wide variety of sounds from 4 to 130 kHz, with dominant 

frequencies between 25 and 30 kHz and 95 and 130 kHz (Busnel and Dziedzic, 1968; Kamminga 

and van Velden, 1987; Thomas and Turl, 1990; Murray et al., 1998). Most signal types are whistles, 

burst-pulses, and click trains (Murray et al., 1998). Whistles generally range between 4 and 9.5 kHz 

(Thomson and Richardson, 1995). False killer whales echolocate using highly directional clicks 

ranging between 20 and 60 kHz and 100 and 130 kHz (Kamminga and van Velden, 1987; Thomas 

and Turl, 1990). The SL of clicks has been measured to range from 200 to 228 dB re 1 μPa at 1 m 

(Thomas and Turl, 1990; Ketten, 1998). There are no available data regarding seasonal or 

geographical variation in the sound production of false killer whales.

2.2.16.6 Threats

Throughout their range, threats to false killer whales include bycatch and other fishery 

interactions, such as the Hawaii longline fishery and bottomfish fishery off the northwestern 

Hawaiian Islands, and hunting in Indonesia, Japan, and the West Indies (USDOC, NMFS, 2015a). 

The commercial fishery that could interact with this stock in the GOM is the large pelagic longline 

fishery (Waring et al., 2013). Pelagic swordfish, tunas, and billfish are the targets of the longline 

fishery operating in the northern GOM (Waring et al., 2013). Information from the Final 

PDARP/PEIS (Deepwater Horizon Natural Resource Damage Assessment Trustees, 2016) 

summarized injuries from the Deepwater Horizon oil spill to false killer whales and stated that 

18 percent of the population was exposed to Deepwater Horizon oil and 6 percent of the population 

was killed as a result. In addition, 8 percent of females likely experienced reproductive failure and 

7 percent of the population has experienced adverse health effects.

2.2.16.7 Status

False killer whales are classified as least concern by the IUCN and are protected under the 

MMPA. The species is not listed as threatened or endangered under the ESA. The status of false 

killer whales in the northern GOM is unknown, and there are insufficient data to determine 

population trends for this species; however, recent information from the Final PDARP/PEIS 

(Deepwater Horizon Natural Resource Damage Assessment Trustees, 2016) suggests that false 

killer whales in the GOM have experienced a population decline (6%) as a result of injury from the 

Deepwater Horizon oil spill. The species is not a strategic stock. The current PBR for the Northern 

GOM stock of false killer whales is undetermined (Waring et al., 2013).

2.2.17 Killer Whale

The killer whale (Orcinus orca) is the largest member of the ocean dolphin family 

Delphinidae (Würsig et al., 2000). Adults reach body lengths of 9.8 m (32 ft) for males and 8.5 m 

(28 ft) for females (Jefferson et al., 2008). In addition to body length, adult male killer whales 
Gulf of Mexico G&G Activities Programmatic EIS E-51

possess disproportionally larger appendages (pectoral flippers, dorsal fin, and tail flukes) than 

females (Ford, 2002). They are easily recognizable by their large size and characteristic black-andwhite coloration.

2.2.17.1 Population

A single species is recognized; however, genetic, morphological, and ecological evidence 

suggest separate forms that may represent distinct species (Jefferson et al., 2008). Currently, two 

unnamed subspecies of O. orca are recognized: killer whale unnamed subspecies (resident killer 

whale) and killer whale unnamed subspecies (transient killer whale, Bigg’s killer whale) (Committee 

on Taxonomy, 2013). The GOM population is provisionally being considered a separate stock for 

management purposes; however, there currently is no information to differentiate this stock from the 

Atlantic Ocean stock(s). Additional morphological, genetic, and behavioral data are needed to 

provide further information on stock delineation (Waring et al., 2013).

2.2.17.2 Distribution and Abundance

The killer whale’s distribution is cosmopolitan. Within the North Atlantic, its range extends 

from the Arctic ice-edge to the Caribbean Sea and includes the GOM. Historic sightings of killer 

whales in the northern GOM from 1921 to 1995 occurred primarily in oceanic waters ranging from 

256 to 2,652 m (840 to 8,700 ft) deep (averaging 1,242 m [4,075 ft]), primarily in the north-central 

region (O’Sullivan and Mullin, 1997).

Killer whales are characterized as uncommon or rare in waters of the U.S. Atlantic EEZ 

(Katona et al., 1988). Most sightings of this species within the GOM have been on the continental 

shelf edge and slope. Very few sightings of killer whales in the GOM have been made within 

continental shelf waters other than those reported in 1921, 1985, and 1987 (Katona et al., 1988). 

During GulfCet surveys conducted between 1992 and 1998, killer whales were seen near the 

continental shelf edge and slope only in the summer (Hansen et al., 1996; Mullin and Hoggard, 

2000). During shipboard surveys, killer whales were reported in the GOM from May through 

September and in November (Whitt et al., 2015; O’Sullivan and Mullin, 1997; Mullin and Fulling, 

2004; Maze-Foley and Mullin, 2006).

The CetMap abundance estimate for northern GOM killer whales is 185 individuals (Roberts 

et al., 2016). From NMFS SAR data, the best abundance estimate available for northern GOM killer 

whales is 28 individuals (CV = 1.02) (Waring et al., 2012). Historically, for surveys conducted in 

oceanic waters from 1991 to 1994, the estimate was 277 individuals (CV = 0.42); from 1996 to 2001 

(excluding 1998), the estimate was 133 individuals (CV = 0.49); and from 2003 to 2004, the estimate 

was 49 individuals (CV = 0.77) (Waring et al., 2012).
E-52 Expanded Affected Environment Information

2.2.17.3 Habitat

Killer whales are most abundant in polar waters; however, they can be fairly abundant in 

temperate waters. Killer whales also occur, though at lower densities, in tropical, subtropical, and 

offshore waters (USDOC, NMFS, 2015a).

2.2.17.4 Behavior

Killer whales usually are observed in groups of 5 to 20 individuals. In the GOM, group sizes 

averaged 11.2 individuals (Davis and Fargion, 1996). Killer whale groups appear to be temporally 

stable (Ford, 2002) and usually contain adults of both sexes, but adult females and young will 

sometimes segregate to form their own groups. Groups are highly cooperative and function as a 

unit when hunting (Würsig et al., 2000). In the northeastern Pacific Ocean, killer whales exhibit 

dietary specialization within different sympatric populations. In this region, these populations 

maintain social isolation from each other and differ in genetic structure, morphology, behavior, 

distribution patterns, and ecology. One population (referred to as residents) feed primarily on fish, 

whereas a second population (termed transients) are primarily mammal hunters (Ford, 2002). 

Evidence suggests that similar degrees of specialization may exist in other areas within their range. 

Whitt et al. (2015) reported a prolonged interaction between killer whales and sperm whales in the 

GOM during 2011.

Killer whale swimming speeds usually range from 3 to 5 kn (3.5 to 5.8 mph), but they can 

achieve speeds up to 20 kn (23 mph) in short bursts (Lang, 1966; LeDuc, 2002). In southern British 

Columbia and northwestern Washington, killer whales spend 70 percent of their time in the upper 

20 m (66 ft) of the water column but can dive to 100 m (328 ft) or more, with a maximum recorded 

depth for a wild individual of 201 m (660 ft) (Baird et al., 1998). The deepest dive recorded by a 

killer whale is 265 m (870 ft), reached by a trained individual (Ridgway, 1986). Recorded dive 

durations range from 1 to 10 minutes (Norris and Prescott, 1961; Lenfant, 1969; Baird et al., 1998).

2.2.17.5 Vocalization and Hearing

Killer whales are classified within the mid-frequency, cetacean functional marine mammal 

hearing group (150 Hz to 160 kHz) (Southall et al., 2007). Killer whales hear underwater sounds 

from <500 Hz to 120 kHz (Bain et al., 1993; Szymanski et al., 1999). Their best underwater hearing 

occurs between 15 and 42 kHz, where the threshold level is 34 to 36 dB re 1 μPa (Hall and Johnson, 

1972; Szymanski et al., 1999). Killer whales produce sounds as low as 80 Hz and as high as 

85 kHz, with dominant frequencies at 1 to 20 kHz (Schevill and Watkins, 1966; Diercks et al., 1971

and 1973; Evans, 1973; Steiner et al., 1979; Awbrey et al., 1982; Ford and Fisher, 1983; Ford, 1989; 

Miller and Bain, 2000). An average of 12 different call types (range 7 to 17), mostly repetitive 

discrete calls, exist for each pod in coastal waters of the eastern North Pacific (Ford, 2002). Pulsed 

calls, whistles, and called dialects carry information hypothesized as geographic origin, individual 

identity, pod membership, and activity level. Vocalizations tend to be between 500 Hz and 10 kHz 

and may be used for group cohesion and identity (Ford, 2002; Frankel, 2002). Whistles and 

echolocation clicks are included in killer whale repertoires as well but are not a dominant signal type 
Gulf of Mexico G&G Activities Programmatic EIS E-53

of the vocal repertoire compared with pulsed calls (Miller and Bain, 2000). Erbe (2002) recorded 

received broadband sound pressure levels of orca burst-pulse calls ranging between 105 and 

124 dB re 1 μPa RL at an estimated distance of 100 m (328 ft). Clicks and whistles range from 

0.5 to 25 kHz, with a dominant frequency range of 1 to 6 kHz (Thomson and Richardson, 1995). Au 

et al. (2004) recorded echolocation clicks at SLs ranging from 195 to 224 dB re 1 μPa at 1 m (peakpeak), with dominant frequencies ranging from 20 to 60 kHz and durations of 80 to 120 μs. Average 

SLs for other sounds were 140 dB re 1 μPa at 1 m for whistles, 147 dB re 1 μPa at 1 m for variable 

calls, and 153 dB re 1 μPa at 1 m for stereotyped calls (Veirs, 2004). Killer whales modify their 

vocalizations depending on the social context or ecological function; for example, short-range 

(<10 km [6.2 mi]) vocalizations typically are associated with social and resting behaviors and longrange (10 to 16 km [6.2 to 9.9 mi]) vocalizations are associated with travel and foraging (Miller, 

2006).

2.2.17.6 Threats

Throughout their range, threats to killer whales include commercial hunting; live capture for 

aquarium display, particularly of the southern resident stock (some live capture still occurs in 

Russia); culling due to depredation of fisheries; contaminants (e.g., PCBs); depletion of prey due to 

overfishing and habitat degradation; ship strikes; oil spills; noise disturbance from industrial and 

military activities; interactions with fishing gear; and whale watching (USDOC, NMFS, 2015a). There

was not enough information for killer whales in the GOM to assess the potential impacts of the 

Deepwater Horizon oil spill (Deepwater Horizon Natural Resource Damage Assessment Trustees, 

2016).

2.2.17.7 Status

The killer whale is classified as lower risk (data deficient) by the IUCN and is protected under 

the MMPA. The species is not listed as threatened or endangered under the ESA, and the Northern 

GOM stock is not classified as a strategic stock under the MMPA. There were not enough data to 

make a determination about the overlap between the Deepwater Horizon oil-spill footprint and the 

ranges of killer whales in the GOM; therefore, potential injuries to this population are unknown. The 

current PBR for the Northern GOM stock of killer whales is 0.1 individuals (Waring et al., 2014).

2.2.18 Short-Finned Pilot Whale

The short-finned pilot whale (Globicephala macrorhynchus) is a medium-sized whale with a 

characteristic bulbous head and broad-based dorsal fin. Adult short-finned pilot whales attain a body 

length of 7.2 m (24 ft) for males and 5.5 m (18 ft) for females (Jefferson et al., 2008). In addition to 

greater length, male pilot whales exhibit larger dorsal fins and a more pronounced melon than 

females (Olson and Reilly, 2002).

2.2.18.1 Population

The GOM population is being considered a separate stock for management purposes; 

however, there currently is no information to differentiate this stock from the Atlantic Ocean stock(s). 
E-54 Expanded Affected Environment Information

Additional morphological, genetic, and behavioral data are needed to provide further information on 

stock delineation.

2.2.18.2 Distribution and Abundance

The short-finned pilot whale is distributed worldwide in tropical to subtropical waters, 

generally on the continental shelf break and in deep oceanic waters (Leatherwood and Reeves, 

1983; Jefferson et al., 2008). Historical sightings of these animals in the northern GOM have been 

primarily on the continental slope, west of 89° W. longitude (Mullin and Fulling, 2004; Maze-Foley 

and Mullin, 2006). During GulfCet aerial and ship surveys of the northern GOM between 1992 and 

1998, short-finned pilot whales were recorded in all seasons, with sightings primarily offshore 

Louisiana and almost evenly distributed throughout the seasons (Davis and Fargion, 1996; Hansen 

et al., 1996; Mullin and Hoggard, 2000). Although seasonal movements for this species are reported 

for the Caribbean Sea, there is no evidence of migration in the GOM (Würsig et al., 2000).

The CetMap abundance estimate for northern GOM short-finned pilot whales is 

1,981 individuals (Roberts et al., 2016). From NMFS SAR data, the best abundance estimate 

available for northern GOM short-finned pilot whales is 2,415 individuals (CV = 0.66) (Waring et al., 

2014). Historically, for surveys conducted in oceanic waters from 1991 to 1994, the estimate was 

353 individuals (CV = 0.89); from 1996 to 2001 (excluding 1998), the estimate was 2,388 individuals 

(CV = 0.48); and from 2003 to 2004, the estimate was 716 individuals (CV = 0.34) (Waring et al., 

2012).

2.2.18.3 Habitat

Short-finned pilot whales prefer warmer tropical and temperate waters and can be found at 

varying distances from shore but typically in deeper waters. Areas with a high density of squid are 

their primary foraging habitats (USDOC, NMFS, 2015a).

2.2.18.4 Behavior

Short-finned pilot whales generally are found in aggregations of 10 to 60 individuals, but 

larger groups of several hundred individuals are not infrequent (Davis and Fargion, 1996; Würsig 

et al., 2000). Studies suggest that these aggregations are relatively stable and maternally based, 

and strong social bonds may be a reason why pilot whales are one of the species most often 

associated with mass strandings. A variety of group behaviors have been documented (Olson and 

Reilly, 2002). Aggregations of short-finned pilot whales are commonly associated with other 

cetacean species such as other delphinids and large whales (Jefferson et al., 2008). There are 

accounts of aggressive behavior of pilot whales toward other cetacean species (Olson and Reilly, 

2002). Short-finned pilot whales have swimming speeds ranging between 4 to 5 kn (4.6 to 5.8 mph)

(Norris and Prescott, 1961). Short-finned pilot whales are considered deep divers (deepest 

recording at 610 m [2,000 ft]), feeding primarily on fish and squid (Ridgway, 1986; Croll et al., 1999). 

They may stay submerged for up to 40 minutes (Mate et al., 2005).
Gulf of Mexico G&G Activities Programmatic EIS E-55

2.2.18.5 Vocalization and Hearing

Short-finned pilot whales are classified within the mid-frequency, cetacean functional marine 

mammal hearing group (150 Hz to 160 kHz) (Southall et al., 2007). There is no direct measurement 

of auditory threshold for the hearing sensitivity of short-finned pilot whales (Ketten, 2000; Thewissen, 

2002). Pilot whales echolocate with a precision similar to bottlenose dolphins and also vocalize with 

other pod members (Olson and Reilly, 2002). Short-finned pilot whales produce vocalizations as low 

as 280 Hz and as high as 100 kHz, with dominant frequencies between 2 and 14 kHz and 30 and 

60 kHz (Caldwell and Caldwell, 1969; Fish and Turl, 1976; Scheer et al., 1998). Vocalizations 

produced by this species average 7.87 kHz, higher than that of a long-finned pilot whale (Olson and 

Reilly, 2002). Echolocation abilities have been demonstrated during click production (Evans, 1973). 

The SLs of clicks have been measured as high as 180 dB re 1 μPa at 1 m (Fish and Turl 1976; 

Richardson et al., 1995). There are few available data regarding seasonal or geographical variation 

in the vocalizations production of the short finned pilot whale, although there is evidence of groupspecific call repertoires (Olson and Reilly, 2002).

2.2.18.6 Threats

Throughout their range, threats to short-finned pilot whales include bycatch in fishing gear 

such as gillnets, longlines, and trawls, and drive fisheries that specifically target pilot whales in 

Japan and the Lesser Antilles (USDOC, NMFS, 2015a). The commercial fishery that could interact 

with this stock in the GOM is the Atlantic Ocean, Caribbean, GOM large pelagic longline fishery 

(Waring et al., 2013). Ship strikes may pose a threat in the Hawaii Islands as propeller scarred 

whales have been documented there. Information from the Final PDARP/PEIS (Deepwater Horizon 

Natural Resource Damage Assessment Trustees, 2016) summarized injuries from the Deepwater 

Horizon oil spill to short-finned pilot whales and stated that 6 percent of the population was exposed 

to Deepwater Horizon oil and 2 percent of the population was killed as a result. In addition, 

3 percent of females likely experienced reproductive failure and 2 percent of the population has 

experienced adverse health effects.

2.2.18.7 Status

The short-finned pilot whale is classified as a lower risk (data deficient) species by the IUCN 

and is protected under the MMPA. The species is not listed as threatened or endangered under the 

ESA. The status of the short-finned pilot whale in the northern GOM is unknown (Waring et al., 

2013). There are insufficient data to determine population trends; however, recent information from 

the Final PDARP/PEIS (Deepwater Horizon Natural Resource Damage Assessment Trustees, 2016) 

suggests that short-finned pilot whales in the GOM have experienced a population decline (2%) as a 

result of injury from the Deepwater Horizon oil spill. It is not classified as a strategic stock under the 

MMPA. The current PBR for the Northern GOM stock of short-finned pilot whales is 15 individuals 

(Waring et al., 2014).
E-56 Expanded Affected Environment Information

2.3 SIRENIANS – WEST INDIAN MANATEE

The West Indian manatee (Trichechus manatus), the only sirenian found in the AOI and 

listed under the ESA, is divided into two subspecies: T. m. manatus (Antillean manatee) and T. m. 

latirostris (Florida manatee) (Committee on Taxonomy, 2013). The West Indian manatees can reach 

lengths of 4 m (13 ft), with females slightly larger than males.

2.3.1 Population

Studies of the Florida manatee identified four regional management units (formerly referred 

to as subpopulations), including two units within the GOM: a Northwest unit that occupies the 

Florida Panhandle south to Hernando County; and a Southwest unit that occurs from Pasco County 

to Whitewater Bay in Monroe County (USDOI, FWS, 2001 and 2007). While the Florida manatee 

population has been separated into these management units, the FWS identifies the Florida 

manatee population as a single stock. Significant genetic differences between the manatees of 

Florida and Puerto Rico do exist and, as a result, these populations are identified as separate stocks 

(Vianna et al., 2006).

2.3.2 Distribution and Abundance

The West Indian manatee is distributed from Virginia, U.S. to Espiritu Santo, Brazil 

(Shoshani, 2005). The Florida manatee subspecies is found throughout the southeastern U.S., with 

individuals sighted as far north as Massachusetts and as far west as Texas (Rathbun et al., 1982; 

Schwartz, 1995; Fertl et al., 2005). Locations of manatee sightings within the AOI are shown in 

Figure 4.2-2 of this Programmatic EIS. The Antillean manatee subspecies is found in the southern 

GOM (eastern Mexico and Central America), northern and eastern South America, and in the 

Greater Antilles (Lefebvre et al., 1989); therefore, its range is outside of the AOI.

The best available count of GOM manatees is based on an annual synoptic survey of warmwater refuges along the Florida west coast (at sites from the Wakulla River to the Everglades). The 

Florida Fish and Wildlife Conservation Commission (FWC) coordinates an interagency team that 

conducts broad, synoptic surveys from one to three times each year (weather permitting). The 

synoptic surveys are conducted in winter and cover all of the known wintering habitats of manatees 

in Florida. Surveys conducted in February 2015 recorded 2,730 individuals on the west coast of 

Florida. Historic estimates of manatee abundance off west Florida as generated from these synoptic 

surveys over the last decade are provided below (State of Florida, Fish and Wildlife Conservation 

Commission, Fish and Wildlife Research Institute, 2015a):

• 2014 – 2,509 individuals;

• 2011 – 2,402 individuals;

• 2010 – 2,297 individuals;

• 2009 – 1,654 individuals;
Gulf of Mexico G&G Activities Programmatic EIS E-57

• 2007 – 1,403 individuals;

• 2006 – 1,474 individuals; and

• 2005 – 1,549 individuals.

2.3.3 Habitat

Manatees are a subtropical species with little tolerance for cold water. As a result, the 

Florida manatee is generally restricted to the inland and coastal waters of peninsular Florida during 

the winter when individuals shelter in or near warm-water springs, industrial effluents, and other 

warm-water sites (Hartman, 1979; Lefebvre et al., 2001; Stith et al., 2006). In warmer months, 

manatees leave these sites and can disperse great distances. Manatees tend to show strong fidelity 

to specific ranges. Most individual Florida manatees within the southeastern U.S. migrate 

seasonally between a summer range and a more southern winter range. The presence of warmwater sources, such as coastal power plant outfalls, has affected their normal migration patterns.

2.3.4 Behavior

Florida manatees typically are seen alone or in groups of up to six individuals. These groups 

are “loosely knit” and the species generally is not behaviorally gregarious (Würsig et al., 2000). 

Florida manatees prefer shallow seagrass beds, especially areas with access to deep channels. 

Preferred coastal and riverine habitats (e.g., near the mouths of coastal rivers) are used for resting, 

mating, and calving (USDOI, FWS, 2001 and 2007). Manatees are aquatic herbivores that feed 

exclusively on vegetation such as turtle grass (Thalassia testudinum), manatee grass (Syringodium 

filiforme), and water hyacinth (Eichhornia crassipes). They appear to prefer submerged vegetation, 

followed by floating and emergent vegetation (Würsig et al., 2000). Manatees typically dive for 2 to 

3 minutes or less at a time but can remain underwater for more than 20 minutes. Their dives 

typically are shallow, based on where aquatic vegetation is able to grow (Reynolds and Powell, 

2002). There is no defined breeding season; calves are born year-round (O’Shea et al., 1995).

2.3.5 Vocalizations and Hearing

Manatees produce sounds, particularly squeaks and squeals, mostly in the 3- to 5-kHz range 

(Reynolds and Powell, 2002), with a full range of 0.6 to 12 kHz and sound durations of 0.18 to 

0.9 seconds (Steel and Morris, 1982; Thomson and Richardson, 1995; Niezrecki et al., 2003; 

O’Shea and Poche, 2006). Frisch and Frisch (2003) recorded vocalizations below 0.1 kHz (U.S. 

Department of the Navy, 2007). Average SLs range from 90 to 138 dB re 1 μPa at 1 m (Nowacek 

et al., 2003; Phillips et al., 2004). Gerstein et al. (1999) studied the underwater audiogram of the 

Florida manatee. Research was conducted at the Lowry Park Zoo in Tampa, Florida, in an 

acoustically insulated test pool. The results showed that the two manatees tested exhibited a typical 

mammalian U-shaped audiogram, with frequency sensitivity increasing from 0.4 kHz to a maximum 

sensitivity between 6 and 20 kHz (9 dB from maximum sensitivity). Based on this study, Gerstein 

et al. (1999) estimated the maximum hearing range for the West Indian manatee to be from 0.4 to 
E-58 Expanded Affected Environment Information

46 kHz. Hearing sensitivity “dropped approximately 40 dB per octave above 26 kHz and 

approximately 20 dB per octave below 0.8 kHz” (Gerstein et al., 1999).

2.3.6 Threats

Sources of human-caused manatee mortality and injury include watercraft-related strikes 

(direct impact and propeller strikes), water control structures (entrapment in flood gates and 

navigation locks), recreational and commercial fishing gear (entanglement or ingestion), among 

others (Waring et al., 2013). From 2010 through 2014, 2,477 manatee carcasses were salvaged in 

Florida; 760 of those animals died of undetermined causes and 707 were natural mortalities and 

perinatal deaths (State of Florida, Fish and Wildlife Conservation Commission, Fish and Wildlife 

Research Institute, 2015b). Additional causes of deaths were as follows:

• vessel collisions – 343 individuals;

• cold stress – 428 individuals; and

• water control structures (including flood gates and navigation locks) – 

14 individuals.

Natural threats include exposure to cold water and red tides (algal blooms). Mortality 

associated with these natural threats includes cold stress syndrome and brevetoxicosis, respectively 

(Waring et al., 2013). While the distribution of West Indian manatees overlaps with the Deepwater 

Horizon oil footprint, none were sighted in oil and no injury assessment was completed for this 

marine mammal species (Deepwater Horizon Natural Resource Damage Assessment Trustees, 

2016).

2.3.7 Status

The Florida manatee currently is listed as endangered under the ESA and by the IUCN, and 

as a strategic stock under the MMPA. The species also is protected under the Florida Manatee 

Sanctuary Act. The majority of the Atlantic population of the Florida manatee is located in eastern 

Florida and southern Georgia (Waring et al., 2013) and is managed within four distinct regional 

management units: Atlantic Coast (northeast Florida to the Florida Keys); Upper St. Johns River 

(St. Johns River, south of Palakta); Northwest (Florida Panhandle to Hernando County); and 

Southwest (Pasco County to Monroe County) (USDOI, FWS, 2001 and 2007). The Northwest and 

Southwest units are the most relevant to the AOI. Critical habitat was designated for the Florida 

manatee on September 24, 1976 (41 FR 41914). The current, revised critical habitat designation 

includes inland waterways in four northeastern Florida coastal counties (Brevard, Duval, St. Johns, 

and Nassau Counties) that are not within the AOI.

3 SEA TURTLES

Chapter 4.3.1 of this Programmatic EIS provides the succinct description of the affected 

environment for sea turtles in sufficient detail to support the impact analyses. The following 
Gulf of Mexico G&G Activities Programmatic EIS E-59

descriptions provide additional information on sea turtle life histories. Of the seven extant species of 

sea turtle, the following five occur in the AOI (Table 4.3-1 of this Programmatic EIS):

• green turtle (Chelonia mydas); 

• hawksbill turtle (Eretmochelys imbricata); 

• Kemp’s ridley turtle (Lepidochelys kempii); 

• loggerhead turtle (Caretta caretta); and

• leatherback turtle (Dermochelys coriacea).

The leatherback turtle is under the family Dermochelyidae, whereas the other four species 

are classified as hard-shelled turtles in the family Cheloniidae.

All sea turtles are protected under the ESA. Because sea turtles use terrestrial and marine 

environments at different life stages, the FWS and NMFS share jurisdiction under the ESA. The 

FWS has jurisdiction over sea turtles when they come ashore to nest, and the NMFS has jurisdiction 

over sea turtles in the marine environment. The hawksbill, Kemp’s ridley, and leatherback turtles are 

listed as endangered throughout their ranges under the ESA. As a species, the green turtle is listed 

as threatened under the ESA, but the Florida and Mexico Pacific breeding populations are listed as 

endangered. Loggerhead turtles recently have been divided into nine distinct population segments 

(DPSs); the Northwest Atlantic Ocean, South Atlantic Ocean, Southeast Indo-Pacific Ocean, and 

Southwest Indian Ocean DPSs are listed as threatened under the ESA, while the Northeast Atlantic 

Ocean, Mediterranean Sea, North Indian Ocean, North Pacific Ocean, and South Pacific Ocean 

DPSs are listed as endangered. A DPS is a population that is discrete from other populations of a 

species and significant in relation to the entire species. The GOM is part of the Northwest Atlantic 

Ocean DPS; therefore, loggerhead turtles occurring in the AOI are considered threatened. The 

ESA-designated critical habitat for the loggerhead turtle occurs within or adjacent to the AOI. 

Nearshore reproductive critical habitat for the Northwest Atlantic Ocean loggerhead turtle DPS has 

been designated in the State waters of Mississippi, Alabama, and Florida (79 FR 39856). Farther 

offshore in the AOI, a large portion of the northern GOM has been designated as Sargassum critical 

habitat for the Northwest Atlantic Ocean loggerhead turtle DPS (Figure 4.3-3 of this Programmatic 

EIS) (79 FR 39856). In March 2015, the NMFS published a proposed rule to revise the listing for the 

green turtle to list 11 green turtle DPSs, with 3 population segments to be listed as endangered and 

8 as threatened (80 FR 15272). The North Atlantic DPS, which includes the individuals that occur in 

the GOM, is proposed to be listed as threatened. The NMFS is currently compiling comments on the 

proposed rule, with a final rule expected to be published in late 2016.

Loggerhead, Kemp’s ridley, and leatherback turtles commonly occur in the GOM; green and 

hawksbill turtles are rarer. During aerial surveys conducted in 1980 to 1981, Fritts et al. (1983a and

1983b) observed loggerhead, green, Kemp’s ridley, and leatherback turtles across the northern 

GOM. Only loggerhead, Kemp’s ridley, and leatherback turtles were observed during the aerial and 

ship surveys conducted during the GulfCet I (central and northwestern GOM) and II (northern GOM) 
E-60 Expanded Affected Environment Information

programs (Davis and Fargion, 1996; Mullin and Hoggard, 2000). The greatest abundance of sea 

turtles in the GOM has been observed in continental shelf waters east of Mobile Bay (Lohoefener et 

al., 1990; Mullin and Hoggard, 2000). McDaniel et al. (2000) conducted aerial surveys for sea turtles 

over a broad area of the eastern GOM nearshore zone. Although the aerial surveys were unable to 

differentiate between species and likely missed smaller individuals, they found a pattern of 

increasing sea turtle abundance in nearshore waters as they moved from the northern GOM offshore 

of Louisiana and Mississippi (0.05 to 0.10 turtle observations per transect kilometer) to the Florida 

coastal waters, with the highest abundance recorded in the waters offshore of the Florida Keys 

(0.35 to 1.0 observations per transect kilometer). Inwater Research Group (2014) conducted 

2,300 km (1,429 mi) of vessel-based transect surveys for sea turtles in the near coastal waters of 

eastern Louisiana. These surveys were able to differentiate between species and estimated overall 

sea turtle abundance at 0.27 observations per transect kilometer (obs/km). Observations were 

dominated by Kemp’s ridleys (0.12 obs/km) and loggerheads (0.11 obs/km), with considerably lower 

numbers of leatherbacks (0.04 obs/km) and green turtles (0.006 obs/km).

Swimming loggerhead, leatherback, Kemp’s ridley, and green turtles are commonly found 

within the AOI at certain periods (e.g., nesting season) and life stages. Each of the species has a 

juvenile stage thought to be distributed almost exclusively in offshore pelagic habitats. These 

juvenile stages, which include post-hatchlings leaving nesting beaches and small oceanic-stage 

juveniles, are most often found in close association with Sargassum drift algae habitats, which they 

use as developmental habitat before making a transition to shallow-water habitats at 1-3 years of 

age (Bolten and Witherington, 2003). Witherington et al. (2012) conducted vessel-based transect 

surveys from five Florida ports from Pensacola to Key West extending up to 120 km (62 mi) offshore 

to evaluate the abundance, species composition, and behavior of oceanic-stage juvenile sea turtles 

in the eastern GOM. They found that 89 percent of all turtle observations occurred within 1 m (3.3 ft) 

of floating Sargassum and that turtle density estimates in Sargassum habitats were nearly 100 times 

higher than in open-water areas where Sargassum was not present. Ninety captures of oceanicstage juvenile turtles revealed a species composition dominated by green turtles (49%) and Kemp’s 

ridleys (42%) and lower abundances of hawksbills (7%) and loggerheads (2%). In addition, large 

numbers of post-hatchling sea turtles were observed, but only during hatching season on the 

adjacent Florida nesting beaches (July-October). On a broader scale, Putman et al. (2013) 

generated predicted distributions for the distribution of oceanic-stage Kemp’s ridley turtles 

throughout the GOM basin using simulated particle dispersal with ocean circulation models. They 

found that the predicted highest abundance for Kemp’s ridley oceanic-stage juveniles was in the far 

western GOM, with 50 percent of the individuals expected to remain west of 90° W. longitude.

The northern GOM possesses a diverse array of juvenile developmental and adult foraging 

habitats (from shallow-water habitats such as seagrass beds and coral reefs to deeper water 

habitats such as artificial reef [including oil and gas] structures and canyons, as well as open ocean 

Sargassum habitat) (Carr et al., 1982). Sea turtles often use the dominant currents of the northern 

GOM, such as the Loop and Florida Currents, for transport to distant areas of the northern Atlantic 

Ocean or Caribbean Sea (Fritts et al. 1983a and 1983b; Turtle Expert Working Group [TEWG], 
Gulf of Mexico G&G Activities Programmatic EIS E-61

1998). Important marine habitats for sea turtles in and near the AOI include nesting beaches, 

estuaries and embayments, and nearshore hard substrate areas.

Nesting of all five species of sea turtles has been documented along the coasts of western 

Florida, Mississippi, Alabama, and southern Texas adjacent to the AOI (Table 4.3-1 and Figure 

4.3-1 of this Programmatic EIS). With the exception of Florida, sea turtle nesting in the Northern 

GOM is often not systematically documented. Texas beaches support significant nesting by Kemp’s 

ridley turtles, mostly on North and South Padre Islands. An average of 136 Kemp’s ridley nests per 

year were documented from Texas from 2010 through 2014 (Shaver, official communication, 2015). 

In Louisiana and Mississippi, no regular surveys are conducted so nesting reports are anecdotal. 

Louisiana supports low levels of nesting by loggerhead and possibly Kemp’s ridley turtles, mostly on 

Breton and Chandeleur Islands and in Grand Isle. One leatherback turtle was observed nesting on 

Chandeleur Island in 1989 (Lauritsen, official communication, 2015). Mississippi beaches support 

low levels (zero to 15 nests per year) from loggerheads and possibly Kemp’s ridley turtles, primarily 

on Petit Bois and Horn Islands (Lauritsen, official communication, 2015). Alabama has documented 

an average of 68 loggerhead and 1 Kemp’s ridley nest per year from 2002 to 2014 (Ingram, official

communication, 2015). While nesting of all five species has occurred historically along the beaches 

of the northern GOM, nesting occurs most dominantly along western Florida and south Texas/Padre 

Island beaches (Table 4.3-1 of this Programmatic EIS). Most sea turtle species move seasonally 

between nesting and foraging or developmental habitats (Mansfield et al., 2009; Hawkes et al., 

2011).

While nesting beaches adjacent to the AOI are subject to human impacts such as the 

presence of artificial lighting or man-made structures on beaches, natural events such as tropical 

cyclones (including hurricanes and tropical storms) also impact sea turtle nests. Studies suggest 

that tropical cyclones are a significant factor in observed sea turtle nesting declines (van Houtan and 

Bass, 2007). It is anticipated that the frequency of these storm events is likely to increase with 

changes in global climate (Webster et al., 2005; Pike and Stiner, 2007). Generally, storm-induced 

impacts to nesting beaches include beach flooding and the displacement of large volumes of sand 

(Pike and Stiner, 2007). Sea turtle eggs lose and gain water quickly depending on nest conditions, 

and nests exposed to seawater may be lost because of inhibited oxygen exchange or rapid 

freshwater loss to saline seawater (Packard, 1999). Displacement of sand during storm events may 

expose and destroy established nests or may alter beach morphology to where it is not suitable 

nesting habitat. Factors that may affect nesting success during storm seasons include the distance 

of the nest from shore, nest depth, and nesting season.

Most sea turtles exhibit differential distributions throughout their various life stages 

(hatchling, juvenile, adult) (Márquez-M, 1990; Hirth, 1997; Musick and Limpus, 1997). Hatchling sea 

turtles typically spend the first years of life in the oceanic environment, drifting in convergence zones 

and Sargassum rafts where they find refuge and food (USDOC, NMFS and USDOI, FWS, 2008; 

Hirth, 1997). Post-hatchling sea turtles spend nearly a decade growing in the pelagic “early juvenile 

nursery habitat” before migrating to distant feeding grounds, which are known as the “later juvenile 

developmental habitat” (Musick and Limpus, 1997). Shallow nearshore and inshore waters 
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represent the later juvenile developmental habitat most often used by hard-shelled sea turtles. For 

leatherback turtles, however, the later developmental habitat can be a coastal feeding area in 

temperate waters or an offshore feeding area in tropical waters depending on the season (Frazier, 

2001).

Sea turtles undergo complex seasonal movements that are influenced by changes in ocean 

currents, turbidity, salinity, and food availability (Musick and Limpus, 1997). Migratory behavior of 

adult sea turtles is much better understood than that of hatchlings and juveniles due to the 

development and use of satellite telemetry. Many female sea turtles have been tracked after 

nesting. Some species have been tracked to a neritic environment (defined as a shallow-water 

environment or the nearshore marine zone extending from the low-tide level to a depth of 

approximately 200 m [656 ft] or the shelf break) where they sometimes stay for 1 to 4 years. 

Juvenile and subadult sea turtles may actively move across the GOM to neritic developmental 

habitats and adult foraging habitats, respectively. Adult foraging habitats may be, in some 

populations, geographically distinct from juvenile developmental habitats (Musick and Limpus, 

1997).

3.1 LOGGERHEAD SEA TURTLE

Loggerhead sea turtles are the most commonly occurring sea turtle species in U.S. waters, 

including the AOI. The loggerhead sea turtle is a large hard-shelled sea turtle, with adults reaching 

a carapace length of approximately 1 m (3 ft) and a weight of 116 kg (256 lb) in the U.S. Atlantic and 

GOM region (USDOC, NMFS and USDOI, FWS, 2008).

3.1.1 Range and Spatial Distribution

The loggerhead sea turtle has a circumglobal distribution in tropical and temperate waters 

and occurs throughout the GOM (USDOC, NMFS and USDOI, FWS, 2008). Loggerhead sea turtles 

nest almost exclusively in warm temperate regions throughout the world, with a major nesting 

population located in peninsular Florida that produces >1,000 nests per year; a smaller nesting 

subpopulation exists in the Florida Panhandle region of the northern GOM and produces 

<1,000 nests annually (TEWG, 2009). In the remainder of the northern GOM, a much smaller 

amount of loggerhead nesting occurs in Alabama, Mississippi, and Texas, but principally in Alabama 

(Conant et al., 2009; TEWG, 2009).

Loggerhead sea turtles are highly migratory, making seasonal and annual long-distance 

migrations between foraging and nesting sites (Godley et al., 2003). Moncada et al. (2010) reported 

that it is common for loggerhead sea turtles to make extended transoceanic journeys and then return 

to specific nesting beaches. Female loggerhead sea turtles tagged after nesting on GOM beaches 

traveled in shallow nearshore waters as well as deep offshore waters to an area between the Dry 

Tortugas and Cape San Blas, Florida, where many resided for up to a year, while others migrated 

out of the GOM (TEWG, 2009) or into the western GOM (Hart et al., 2014). Satellite tracking of 

tagged post-nesting loggerhead sea turtles in the northern GOM has shown the year-round use of 
Gulf of Mexico G&G Activities Programmatic EIS E-63

northern GOM habitat and five foraging areas for female loggerheads that nest along the northern 

GOM coast (Hart et al., 2014).

3.1.2 Population Status

Overall, the population structure of the loggerhead sea turtle is complex and difficult to 

evaluate (Bolten and Witherington, 2003). According to the Loggerhead Biological Review Team, 

there are nine DPSs of loggerhead sea turtles (Conant et al., 2009). The Northwest Atlantic Ocean 

DPS occurs in an area bounded by 60° N. latitude and the equator, with 40° W. longitude as the 

eastern boundary, and includes the GOM (76 FR 58868). Collectively, the Northwest Atlantic Ocean 

DPS hosts the most significant nesting assemblage of loggerhead sea turtles in the western 

hemisphere and is one of the two largest loggerhead nesting assemblages in the world (Conant 

et al., 2009). Within the most recent recovery plan for the Northwest Atlantic DPS of the loggerhead 

sea turtle, the NMFS has identified five recovery units, four of which are located in U.S. waters 

(USDOC, NMFS and USDOI, FWS, 2009) (Figure 4.3-2 of this Programmatic EIS). A recovery unit 

is defined as a management sub-unit of the listed entity (in this case, species), geographically or 

otherwise identifiable, that is essential to the recovery of the entire listed entity or conserves genetic 

or demographic robustness, important life history stages, or other feature for long-term sustainability 

of the entire listed entity. Three loggerhead sea turtle recovery units are located within the AOI: the 

Dry Tortugas Recovery Unit (DTRU), extending throughout the islands west of Key West, Florida; 

the Northern Gulf of Mexico Recovery Unit (NGMRU), extending from Franklin County on the 

northwest Gulf Coast of Florida through Texas; and the Peninsular Florida Recovery Unit (PFRU), 

which extends from the Florida-Georgia border through Pinellas County on the west coast of Florida, 

excluding the islands off Key West, Florida (USDOC, NMFS and USDOI, FWS, 2009).

Estimating sea turtle populations is difficult, and the status of the population often is 

estimated based on the number of annual nests at different locations within a region, anthropogenic 

threats, and mortality estimates (Conant et al., 2009). Nest counts always underestimate the 

population of sea turtles because they only include reproductively active females and do not take 

into account males, juveniles, or non-reproductive females. The PFRU represents approximately 

87 percent of all nesting that occurs in the Northwest Atlantic Ocean DPS (Ehrhart et al., 2003). In 

recent years, the counts of loggerhead nests in Peninsular Florida were highly variable, with a 

decline of more than 40 percent between 1998 and 2007 (Witherington et al., 2009), which was 

followed by a more recent increase in the number of loggerhead nests (State of Florida, Fish and 

Wildlife Conservation Commiission, Fish and Wildlife Research Institute, 2015c). The most current 

loggerhead nesting trend for the Northwest Atlantic Ocean DPS, from 1989 to 2010, is very slightly 

negative, but the rate of decline is not statistically different from zero (76 FR 58868). Recent aerial 

surveys of northwest Atlantic waters from Cape Canaveral, Florida, to the Gulf of St. Lawrence 

provided an abundance estimate of 801,000 loggerhead sea turtles in U.S. Atlantic waters; this 

estimate did not include loggerhead sea turtles in the northern GOM (76 FR 58868). The number of 

loggerhead sea turtles nesting in the NGMRU is the third largest of the four U.S. recovery units 

(USDOC, NMFS and USDOI, FWS, 2009). The most recent recovery plan reported that the number 

of nests in the PFRU averaged 64,513 annually between 1989 and 2007, with nesting during this 
E-64 Expanded Affected Environment Information

period declining by 1.6 percent (USDOC, NMFS and USDOI, FWS, 2009). The DTRU averaged 

246 nests per year, though only 9 years were surveyed and no trend was detected with such as 

small dataset. The NGMRU averaged 906 nests per year from 1995 through 2007, with analysis of 

western Florida nesting showing a declining trend of 42 percent annually during this period (USDOC, 

NMFS and USDOI, FWS, 2009). In 2014, loggerhead nest counts for the PFRU were approximately 

47,000 nests, which was slightly higher than the highest nest count in 1998 (State of Florida, Fish 

and Wildlife Conservation Commission, Fish and Wildlife Research Institute, 2015c).

3.1.3 Ecology and Life History

Loggerhead sea turtles use three different types of marine habitats during their life (i.e., 

terrestrial [beaches], neritic [nearshore waters], and oceanic [open ocean]) and feed primarily on 

mollusks and crustaceans (USDOC, NMFS and USDOI, FWS, 2009). Loggerhead sea turtle nesting 

generally occurs from April to September for the Northwest Atlantic Ocean DPS, with peak nesting 

occurring in June and July (Weishampel et al., 2006); females nest every 2.5 to 3.7 years (USDOC, 

NMFS and USDOI, FWS, 2009). Age at sexual maturity is late in life at approximately 35 years of 

age; average clutch size is between 100 and 126 eggs, and incubation is between 42 and 75 days. 

The mean number of clutches per laying female is 3 to 5.5 per breeding season, with inter-nesting 

intervals ranging from 12 to 15 days (USDOC, NMFS and USDOI, FWS, 2009). The lifespan of the 

loggerhead sea turtle is 57 years or more.

Immediately after loggerhead sea turtle hatchlings emerge from the nest, they actively swim 

offshore into oceanic areas of local convergence zones and major gyre systems, often characterized 

by accumulations of floating Sargassum. The duration of this oceanic post-hatchling juvenile stage 

is variable but generally ranges from 7 to 12 years (Bolten and Witherington, 2003). Afterward, 

oceanic juveniles actively migrate to nearshore (neritic) developmental habitats. Within the western 

North Atlantic, including the AOI, some neritic juveniles make seasonal foraging migrations into 

temperate latitudes as far north as New York. Most juveniles are south of Cape Hatteras, North 

Carolina, by January (Musick and Limpus, 1997). Neritic juvenile loggerhead sea turtles are likely to 

occupy shallow-water developmental habitats in nearshore areas of the AOI.

Information about daily movement and dive behaviors of loggerheads in the open ocean is 

limited, but new technology has recently allowed researchers to study this type of behavior in the 

sea turtles’ natural environment (Sobin, 2008). Houghton et al. (2000) recorded observations of 

loggerhead sea turtles around the Greek island of Kefalonia and discovered that these individuals 

made frequent shorter duration dives than previously reported in the literature; on average, four 

loggerhead sea turtles made 96 dives over 29 days, with dive durations ranging from 1 to 5 minutes. 

Off Hawaii, the dive depth distributions of four sea turtles (2 loggerhead sea turtles and 2 olive ridley 

sea turtles [Lepidochelys olivacea]) were monitored to understand how mitigation measures could be 

implemented for longline fisheries (Polovina et al., 2003). Based on the research, Polovina et al. 

(2003) found that there were diurnal and species differences in dive profiles. Overall, the 

researchers found that the sea turtles spent more time at the surface and dove deeper during the 

day than at night. Most (70%) of the dives were no deeper than 5 m (16 ft), and the deepest dive 
Gulf of Mexico G&G Activities Programmatic EIS E-65

recorded for one of the loggerhead sea turtles was 178 m (584 ft); loggerhead sea turtles generally 

dive to depths less than 100 m (328 ft). Loggerhead diving behavior has been investigated off 

Japan by Hatase et al. (2007), who found that diving behavior is somewhat size dependent. In 

southwest Florida, Sobin (2008) reported that loggerhead sea turtles spent more time near the 

surface in the morning than in the evening, which was different than previous studies.

3.1.4 Threats

Threats to the loggerhead population are similar to those for other sea turtles and include 

numerous anthropogenic threats such as commercial fisheries, habitat loss (nesting beaches), 

climate change (e.g., sea-level rise, shifts in prey availability, and increasing temperature), pollution, 

boat strikes, and disease (Conant et al., 2009; Hawkes et al., 2009; Witt et al., 2010a).

3.1.5 Current Status

The loggerhead turtle was listed as a threatened species on July 28, 1978 (43 FR 32800). In 

2011, the NMFS and FWS listed nine DPSs of loggerhead sea turtles under the ESA (76 FR 58868). 

Loggerhead sea turtles found in the GOM are part of the Northwest Atlantic Ocean DPS, which is 

listed as threatened under the ESA. In July 2014, the NMFS designated ESA critical habitat for the 

Northwest Atlantic Ocean DPS, which includes nearshore reproductive habitat, winter areas, 

breeding areas, constricted migratory corridors, and Sargassum habitat (79 FR 39856). Nearshore 

reproductive and Sargassum critical habitat for the loggerhead sea turtle are located in the northern 

GOM, but only the Sargassum habitat is located in the AOI (Figure 4.3-3 of this Programmatic EIS).

3.2 GREEN SEA TURTLE

The green sea turtle is the largest cheloniid sea turtle. Adults can reach 1 m (3 ft) in 

carapace length and weigh 136 to 159 kg (300 and 350 lb) (USDOC, NMFS and USDOI, FWS, 

2015). During the recent 5-year status review, 11 DPSs were identified, including the North Atlantic 

DPS, which encompasses animals found in the GOM (USDOC, NMFS and USDOI, FWS, 2015).

3.2.1 Range and Spatial Distribution

The green sea turtle is a circumglobal species found in the Mediterranean Sea and the 

Pacific, Indian, and Atlantic Oceans (Seminoff et al., 2015). The green sea turtle can be found in 

tropical and subtropical waters between 30° N. and 30° S. latitude, and to a lesser extent in 

temperate waters (Seminoff et al., 2015). Satellite tagging data indicate that, like other sea turtles, 

green sea turtles display highly migratory behavior, making vast seasonal coastal and annual 

transoceanic migrations (Godley et al., 2003, 2008, and 2010). Green sea turtles are vulnerable to 

cold temperatures, so in many locations they are found only seasonally within the AOI (Foley et al., 

2007). Based on satellite tagging research by Hart and Fujisaki (2010), green sea turtles display 

daily and seasonal movement patterns that are associated with foraging strategies. Hart and 

Fujisaki (2010) indicated that locations with optimal habitats (e.g., sources of marine algae) are likely 

where small juvenile green sea turtles may be found. Based on this study, it is possible that juvenile 

green sea turtles may be found in various shallow-water inshore areas in the AOI where macroalgae 
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is reported. Green sea turtles nest infrequently along the Gulf Coast on Florida, Alabama, and 

Texas beaches, with the most important nesting sites located outside of the AOI along the Atlantic 

Coast of Florida (USDOC, NMFS and USDOI, FWS, 2007a and 2015).

3.2.2 Population Status

The green sea turtle population is considered severely depleted in comparison to its 

estimated historical levels (USDOC, NMFS and USDOI, FWS, 2007a). Currently, there is no reliable 

green sea turtle population estimate, but inferences have been attempted using age-based 

survivability models and nesting data (Bjorndal et al., 2003). Nesting data indicate that between 

200 and 1,100 females nest annually on continental U.S. beaches, mostly outside of the AOI.

3.2.3 Ecology and Life History

Hatchling green sea turtles swim offshore to areas of convergence zones characterized by 

driftlines and patches of Sargassum. Musick and Limpus (1997) experiments with post-hatchling 

green sea turtles in the laboratory suggest that they are more open-water animals than loggerhead 

or hawksbill sea turtles and may avoid floatlines of Sargassum. In addition, their strong countercoloration suggest that they spend more time swimming in open water. Data also suggest that 

recruitment of green sea turtles into neritic developmental habitats occurs at smaller body sizes 

(30 to 40 cm [12 to 16 in]) than for loggerhead sea turtles (Bjorndal and Bolten, 1988). Neritic 

developmental habitats in the western North Atlantic range from Long Island Sound to southern 

Florida, the GOM, and the tropics. Within the AOI, these habitats include shallow nearshore hard 

substrate, embayments, and other inshore habitats along the west coast of Florida, Alabama, and 

southern Texas.

In the GOM, green sea turtle nesting generally occurs from June to mid-September; females 

nest at 2- to 4-year intervals. The majority of North Atlantic DPS nesting occurs on the east coast of 

Florida where a mean of 5,055 nests were deposited each year from 2001 to 2005 and 10,377 nests 

each year from 2008 to 2012 (USDOC, NMFS and USDOI, FWS, 2015). Nesting occurs in all 

coastal counties of Florida except the Big Bend area of west-central Florida. Nesting totals for the 

west coast of Florida in 2014 included 73 green sea turtle nests and 54 non-nesting emergences 

(State of Florida, Fish and Wildlife Conservation Commission, Fish and Wildlife Research Institute, 

2015d). Nesting also has been documented in Padre Island National Seashore and South Padre 

Island, Texas (USDOI, NPS, 2015), and in Alabama prior to 2003, though not confirmed by hatchling 

identification (USDOI, FWS, 2008a). Similar to other sea turtles, age at sexual maturity is not 

reached until late in life at approximately 20 to 50 years of age; clutch size ranges from 75 to 

200 eggs, and incubation is between 20 and 50 days. Female green sea turtles usually deposit 

three to five clutches per breeding season, with inter-nesting intervals of 12 to 14 days every 2 to 

3 years (USDOC, NMFS and USDOI, FWS, 2007a and 2015).

Hazel et al. (2009) documented various daily diving behaviors of green sea turtles in 

nearshore foraging habitats in Australia. The researchers found that the majority of the sea turtles 

spent most of time (89 to 100%) at depths (<5 m [16 ft]) near the surface. They also found that dives 
Gulf of Mexico G&G Activities Programmatic EIS E-67

were shorter and shallower during the day than at night, suggesting that green sea turtles rest at 

night and forage during the day. Hazel et al. (2009) also indicated that this phenomenon was 

consistent with the requirement to surface more often during increased activity (daytime foraging). 

In addition, Hazel et al. (2009) found that green sea turtle dives became longer as water

temperatures decreased. Despite the ability for sea turtles to dive to deep depths, Hazel et al. 

(2009) postulated that green sea turtles chose not to dive to deeper depths at night given the 

distance (3 or 6 km [1.9 or 3.7 mi]) it was from shallow (foraging areas) to deeper waters. Off the 

Hawaiian Islands, Rice and Balazs (2008) documented the diving behavior of two adult green sea 

turtles in the open-ocean environment. Findings demonstrated that green sea turtles also displayed 

a shallow daytime and deeper nighttime dive pattern. In general, the two green sea turtles spent the 

day near the surface taking shallow and short duration dives and made dives to 35 to 55 m (115 or 

180 ft) at night, with mean dive duration ranging from 33 to 44 minutes. The maximum depths 

recorded were two dives deeper than 135 m (445 ft) by one female and one dive to 100 m (328 ft) by 

one male (Rice and Balazs, 2008).

3.2.4 Threats

Green sea turtles have various anthropogenic threats such as commercial fishery 

interactions, habitat loss, global climatic changes, and fibropapillomatosis (USDOC, NMFS and 

USDOI, FWS, 2007a). Fibropapillomatosis is a disease characterized by the presence of internal 

and external tumors (fibropapillomas) that may grow large enough to hamper swimming, vision, 

feeding, and potential escape from predators (Herbst, 1994). While reported in all sea turtle species, 

the frequency of infection is much higher in green sea turtles for unknown reasons. Despite the 

uncertainty of population-level impacts of fibropapillomatosis to green sea turtles, a high percentage 

of strandings have been attributed to the disease (USDOC, NMFS and USDOI, FWS, 2007a). Given 

these inadvertent impacts, there are numerous global research priorities that focus on understanding 

these threats and how to reduce their negative impacts to sea turtle populations (Hamann et al., 

2010).

3.2.5 Current Status

The green sea turtle was listed as a threatened species on July 28, 1978, with all populations 

listed as threatened except for the breeding populations of Florida and the Pacific Coast of Mexico, 

which are endangered (43 FR 32800). Currently, 11 DPSs of the green sea turtle are proposed for 

listing under the ESA, with the North Atlantic DPS proposed as threatened (80 FR 15272).

The green sea turtle is protected and managed by the NMFS and FWS. Under the 

leadership of these Federal agencies, various conservation and recovery strategies have been 

implemented since green sea turtles were listed under the protection of the ESA. Some of these 

management measures include international and domestic environmental policies, which include 

numerous laws, rules, and regulations. Conservation measures include establishing various 

conservation programs under the green sea turtle recovery plan and implementing a variety of 

restrictions on commercial fishery activities (e.g., requiring the use of circle hooks in pelagic longline 

fisheries and sea turtle excluder devices [TEDs] in trawls) to prevent serious injury and mortality to 
E-68 Expanded Affected Environment Information

sea turtles; the NMFS has also developed a strategy for sea turtle conservation and recovery for 

Atlantic and Gulf of Mexico fisheries (gear-based approach). Moreover, there are various other 

restrictions to protect sea turtles such as beach lighting restrictions during the sea turtle nesting 

season, which is generally from late spring to late summer, and offshore hopper dredging 

restrictions. 

In 1998, the NMFS and FWS jointly designated critical habitat for the green sea turtle as the 

waters of Culebra Island, Puerto Rico, and its outlying keys (63 FR 46693). Under the designation 

process, the NMFS identified critical habitat for green sea turtles as specific geographical areas that 

have the physical or biological features essential to the conservation of the green sea turtle that may 

require special management considerations.

3.3 HAWKSBILL SEA TURTLE

The hawksbill sea turtle is a medium-weight cheloniid sea turtle. Adults can reach a 

carapace length of 1.1 m (3.5 ft) and weight of 82 kg (180 lb) (USDOC, NMFS and USDOI, FWS, 

2013a).

3.3.1 Range and Spatial Distribution

The hawksbill sea turtle is distributed circumglobally in the Pacific, Indian, and Atlantic 

Oceans (USDOC, NMFS and USDOI, FWS, 2013a). The hawksbill sea turtle can be found in 

tropical and subtropical waters between 30° N. and 30° S. latitude (USDOC, NMFS and USDOI, 

FWS, 2013a). Hawksbill sea turtles display highly migratory behavior, with satellite tagging data 

demonstrating that these sea turtles undergo short and long migrations from nesting to foraging 

grounds (Blumenthal et al., 2009; USDOC, NMFS and USDOI, FWS, 2013a). In the western North 

Atlantic, hawksbill sea turtles are widely distributed throughout the Caribbean Sea and occur 

regularly in southern Florida, the GOM, the Greater and Lesser Antilles, and along the Central 

American mainland south to Brazil. However, hawksbill sea turtle nesting on GOM beaches is 

extremely rare; one nest was documented on Padre Island, Texas, in 1998 (Mays and Shaver, 

1998). Hawksbill sea turtles use a wide range of habitats during their lifetime but have a foraging 

habitat preference for coral reefs, which are found in only a few isolated locations of the AOI. 

Limited information on home ranges of hawksbill sea turtles suggests they are smaller than for other 

sea turtle species (Witt et al., 2010b). In addition to offshore and reef habitats, hawksbill sea turtles 

are known to use mangrove-fringed bays, estuaries, and Caribbean seagrass habitats (Carr, 1952; 

Bjorndal and Bolten, 1988 and 2010).

3.3.2 Population Status

The hawksbill sea turtle population is severely depleted and continues to be threatened 

(Bjorndal, 1999). Although there is no reliable hawksbill sea turtle population estimate, conclusions 

have been made from nesting data. There are no nesting estimates for hawksbill sea turtles within 

the AOI, but the number of nesting females per season in the Caribbean ranges from 5 to 18 in 

Bonaire, Netherlands Antilles, to 400 to 833 in Cuba (USDOC, NMFS and USDOI, FWS, 2013a). 
Gulf of Mexico G&G Activities Programmatic EIS E-69

The recent 5-year status review (USDOC, NMFS and USDOI, FWS, 2013a) reported that, of 

63 nesting sites for which historic trends could be assessed, all 63 (100%) showed a decline during 

the long-term period of 20 to 100 years. Among 41 nesting sites for which recent trend data (past 

20 years) are available, 10 (24.4%) are increasing, 3 (7.3%) are stable, and 28 (68.3%) are 

decreasing. Although greatly depleted from historic levels, nesting populations in the Atlantic Ocean 

in general are doing better than in the Indo-Pacific. Limpus and Miller (2008) reported that the 

hawksbill sea turtle nesting population in north Queensland, Australia, has declined 3 percent in 

recent time. However, in Barbados, West Indies, hawksbill sea turtle nesting data show that the 

population may be improving (Beggs et al., 2007). Beggs et al. (2007) reported increases from 

316 nests and 77 females in 1992 to 2,016 nests and 492 females in 2004. Based on these data, 

Beggs et al. (2007) indicated that the hawksbill sea turtle population in Barbados could be the 

second largest rookery in the wider Caribbean; the largest rookery is in Mexico. Despite showing 

some signs of recovery, the hawksbill sea turtle population has not reached a level that warrants 

delisting or reclassification (USDOC, NMFS and USDOI, FWS, 2013a).

3.3.3 Ecology and Life History

Hatchling hawksbill sea turtles emerge from the nest and actively swim offshore at night to 

areas of water-mass convergence. Hawksbill post-hatchlings in the laboratory appear to be 

attracted to patches of floating Sargassum, which they use as protective cover (Musick and Limpus, 

1997). Data suggest that juvenile (or post-hatchling) hawksbill sea turtles move into neritic 

developmental habitats at a smaller size than loggerhead and green sea turtles; neritic 

developmental habitats include shallow coral reefs and mangrove estuaries (Witzell, 1983).

Adult hawksbill sea turtles specialize on a diet of sponges and feed very selectively on 

specific species in the class Demospongiae (Bjorndal, 1997). They may also consume other food 

items such as algae and other benthic invertebrates (Márquez-M, 1990). In the Caribbean, hawksbill 

sea turtles often are seen feeding among coral reefs and hard bottom communities (Blumenthal 

et al., 2009). Hawksbill sea turtles primarily nest on Mexican (Yucatán Peninsula) and Caribbean 

(Puerto Rico [Culebra, Mona, and Vieques Islands] to Barbados) beaches; some nesting has been 

reported in South Florida and the Florida Keys, but this is rare (USDOC, NMFS and USDOI, FWS, 

1993). Depending on the location, nesting season occurs during various summer and fall months 

(USDOC, NMFS and USDOI, FWS, 1993). For example, hawksbill sea turtle nesting occurs from 

July to October on Buck Island (U.S. Virgin Islands) and from August to October on Mona Island 

(Puerto Rico), with females nesting at 2- or 3-year intervals. In Barbados, Beggs et al. (2007) 

reported that nesting occurred year-round from 1997 through 2004, with peak months of June to 

August. Beggs et al. (2007) also discovered that the nesting interval ranged from 2 to 6 years, with 

a mean of 2.5 years. Overall, the average nesting season for the hawksbill sea turtle (6 months) is 

longer than for other sea turtles (USDOC, NMFS and USDOI, FWS, 1993). Female hawksbill sea 

turtles usually deposit three to five clutches per breeding season (at approximately 14-day intervals) 

(Beggs et al., 2007; USDOC, NMFS and USDOI, FWS, 2013a). Age at sexual maturity is between 

20 and 40 years; average clutch size is approximately 135 eggs, and incubation is approximately 

60 days.
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There is some information about the diving behavior of hawksbill sea turtles. In Milman 

Island, Australia, Bell and Parmenter (2008) recorded the diving behavior of nine female hawksbill 

sea turtles that had previously laid eggs and two females that had not successfully laid eggs. 

Results from the study showed that the nine hawksbill sea turtles primarily spent their time near the 

surface but occasionally made deeper dives. The maximum depth recorded was 21.5 m (71 ft), and 

the researchers did not find any significant difference between day and night diving behavior. On 

average, the dive time and surface interval for the sea turtles were 31.2 and 1.6 minutes, 

respectively. On the reefs of Mona Island, Puerto Rico, van Dam and Diez (1997) reported the 

diving patterns of five juvenile hawksbill sea turtles. Results showed that mean dive behavior 

associated with foraging ranged from 8 to 10 m (26 to 33 ft), dive durations ranged from 19 to 

26 minutes, and surface intervals ranged from 37 to 64 seconds. Night dives ranged from 7 to 10 m 

(23 to 33 ft), dive durations ranged from 35 to 47 minutes, and surface intervals ranged from 36 to 

60 seconds (van Dam and Diez, 1997).

3.3.4 Threats

The recovery of the hawksbill sea turtle population is threatened by many ongoing 

anthropogenic threats, including commercial fishery interactions, habitat loss (e.g., coral reefs), 

global climatic changes (e.g., sea-level rise), and fibropapillomatosis (USDOC, NMFS and USDOI, 

FWS, 2013a). The continued overutilization of hawksbill sea turtles for commercial, recreational, 

scientific, or educational purposes is another major threat to the recovery of the species (USDOC, 

NMFS and USDOI, FWS, 2013a).

3.3.5 Current Status

The hawksbill sea turtle was listed as endangered on June 2, 1970 (35 FR 8491), and is 

considered critically endangered by the IUCN based on global population declines of more than 

80 percent during the last 3 generations (105 years) (Meylan and Donnelly, 1999). The conservation 

and recovery of the hawksbill sea turtle is administered through various regulatory mechanisms such 

as designating critical habitat and implementing conservation regulations. Critical habitat for the 

hawksbill sea turtle was designated in 1982 and additional critical habitat was designated in 1998 

(63 FR 46693). Critical habitat for the hawksbill sea turtle includes Mona, Culebrita, and Culebra 

Islands in Puerto Rico, as well as the waters surrounding the islands of Mona and Monito (3 to 5 km 

[1.9 to 3.1 mi]). Critical habitat also includes specific beaches on Culebra Island (Playa Resaca, 

Playa Brava, and Playa Larga). Other conservation measures governed by Federal agencies 

include implementing various recovery plan and commercial fishery measures to prevent further 

serious injury and mortality to sea turtles. The agencies also support several international 

agreements for the conservation of sea turtles, such as the South-East Asian Marine Turtle 

Memorandum of Understanding in the Indian Ocean. Campbell et al. (2009) indicated that 

co-management by local communities and government agencies is a strategy to improve fisheries 

management that has the potential to reduce adverse interactions between sea turtles and fisheries.
Gulf of Mexico G&G Activities Programmatic EIS E-71

3.4 KEMP’S RIDLEY SEA TURTLE

The Kemp’s ridley is one of the smallest species of sea turtles; adults reach approximately 

60 to 65 cm (24 to 26 in) in carapace length and weigh 39 to 49 kg (86 to 108 lb) (USDOC, NMFS; 

USDOI, FWS; and SEMARNAT, 2011).

3.4.1 Range and Spatial Distribution

The distribution of the Kemp’s ridley sea turtle is restricted to the North Atlantic Ocean, 

principally in the GOM, with moderate numbers recorded along the U.S. Atlantic Coast from Florida 

to New England and up to the Grand Banks and Nova Scotia (Bleakney, 1955; Márquez-M., 1994; 

Watson et al., 2004). The primary habitat for adult Kemp’s ridley sea turtles is nearshore waters of 

37 m (121 ft) depth or shallower, with GOM survey data showing that the majority of Kemp’s ridley 

sea turtles occur in continental shelf waters. Juvenile and adult Kemp’s ridley sea turtles typically 

are found in shallow waters, especially in seagrass areas (Márquez-M., 1990; Ernst et al., 1994).

Historical data show that adult females have been seasonally abundant in prey-rich waters 

such as the mouth of the Mississippi River and the Campeche Banks, migrating toward Rancho 

Nuevo during the nesting season (Carr, 1963; Pritchard, 1969; Pritchard and Márquez-M., 1973; 

Hildebrand, 1995; Shaver et al., 2013). Shaver et al. (2013) reported that most areas defined as 

high-use foraging areas for Kemp’s ridley sea turtles in the GOM were relatively close to shore 

(mean distance of 2.2 km [1.4 mi] from shore) in water depths less than 68 m (223 ft) and within a 

narrow temperature range (24.1°C to 27.6°C [75.4°F to 81.7°F]). The concentration of these areas, 

particularly along the coast of Louisiana, suggests that the areas represent critical foraging hotspots. 

Females have been tracked to foraging areas from the Yucatan Peninsula to southwest Florida 

(USDOC, NMFS and USDOI, FWS, 2007b). Key foraging areas within the AOI include Sabine Pass, 

Texas; Caillou Bay and Calcasieu Pass, Louisiana; Bug Gulley, Alabama; Cedar Keys, Florida; and 

Ten Thousand Islands, Florida (USDOC, NMFS and USDOI, FWS, 2007b). Kemp’s ridley sea 

turtles display some seasonal and coastal migratory behavior; satellite tagging data indicate that 

Kemp’s ridley sea turtles transit between nearshore and offshore waters from spring/summer to 

fall/winter, which coincides with seasonal water temperature changes (USDOC, NMFS; USDOI, 

FWS; and SEMARNAT, 2011).

Kemp’s ridley sea turtles primarily nest on beaches in Mexico (i.e., Tamaulipas [Rancho 

Nuevo, Tepehuajes, and Playa Dos] and Veracruz [Lechuguillas and Tecolutla]) and to a lesser 

extent in Texas (i.e., South Padre Island, North Padre Island, and Boca Chica Beach). Nesting by 

Kemp’s ridley sea turtles has also been documented in Alabama and Florida (USDOC, NMFS; 

USDOI, FWS; and SEMARNAT, 2011).

3.4.2 Population Status

The Kemp’s ridley sea turtle population is severely depleted, and it is considered the most 

endangered sea turtle species (USDOI, FWS, 1999). The nesting population of Kemp’s ridley sea 

turtles has increased exponentially, which is indicative of a corresponding increasing trend in the 
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overall population. From 1988 to 2003, the number of nests observed at Rancho Nuevo and nearby 

beaches increased 15 percent per year (Heppell et al., 2005), and by 2009, the total number of nests 

recorded at Rancho Nuevo and adjacent beaches exceeded 20,000, which represents 

approximately 8,000 females nesting during the nesting season (USDOC, NMFS; USDOI, FWS; and 

SEMARNAT, 2011). From 2002 to 2010, 911 Kemp’s ridley nests were documented along the 

Texas coast, principally along the southernmost part of the coast, which is more than 11 times the 

81 nests recorded over the previous 54 years (1948 to 2001) (Shaver and Caillouet, 1998; Shaver 

et al., 2005). These increases in nest counts were a likely indication that the population is on its way 

to recovery. However, scientists reported at the Second International Kemp’s Ridley Sea Turtle 

Symposium in Texas that the total number of nests had declined during 2011 to 2013, with 

12,000 nests reported in 2013, and a similar decline reported for 2014 (Caillouet, 2014; CavazosLliteras and Gerardo-Cardenas, 2014; Shaver et al., 2014; Virata, 2014).

3.4.3 Ecology and Life History

Hatchling Kemp’s ridley sea turtles leave the nest at night and actively swim offshore into the 

anticyclonic Mexican Current and into the northern GOM. Some oceanic post-hatchling and juvenile 

Kemp’s ridley sea turtles remain in the northern GOM until they migrate inshore to neritic 

developmental habitats, while others may be swept into the Loop Current and then into the Gulf 

Stream (Collard, 1990). Neritic developmental habitats include shallow coastal areas in the GOM 

and areas of the western North Atlantic as far north as Long Island Sound. Neritic juvenile Kemp’s 

ridley sea turtles undergo seasonal migrations within the AOI.

The Kemp’s ridley sea turtle is a carnivore throughout its life cycle (Márquez-M, 1990). Adult 

and subadult Kemp’s ridley sea turtles are benthic feeders that primarily feed on crabs. Other 

preferred food items include shrimps, mollusks, sea urchins, and fishes (opportunistically) (USDOC, 

NMFS; USDOI, FWS; and SEMARNAT, 2011). Kemp’s ridley sea turtles primarily nest on GOM 

beaches in Mexico from April through July during daylight hours (Márquez-M., 1990). The mean 

clutch number is 2.5 per breeding season (14 to 28 days), average clutch size is approximately 

100 eggs, and incubation is between 45 and 58 days; females nest at 2-year intervals (USDOC, 

NMFS; USDOI, FWS; and SEMARNAT, 2011). Age at sexual maturity for wild Kemp’s ridleys has 

been reported to be between 10 and 16 years.

Available information about Kemp’s ridley sea turtles in the open ocean is limited. Dive times 

have been documented to range from a few seconds to a maximum of 167 minutes, with routine 

dives lasting between 16.7 and 33.7 minutes (Mendonca and Pritchard, 1986; Renaud, 1995). Over 

a 12-hour period, Kemp’s ridleys may spend 89 to 96 percent of the time submerged (Byles, 1989; 

Gitschlag, 1996). In the GOM, Schmid et al. (2002) reported a surface interval of 1 to 88 seconds 

and a mean submergence duration of 8.4 minutes; overall, these researchers did not find any 

differences between day and night surface activities but did find a diel difference in some years 

(1994 vs. 1995). The data also showed that the mean submergence interval at the night was longer 

than during the day (Schmid et al., 2002).
Gulf of Mexico G&G Activities Programmatic EIS E-73

3.4.4 Threats

The Kemp’s ridley sea turtle is threatened by many activities such as commercial fishery 

interactions (entrapment in shrimp trawl nets), ongoing habitat loss, disease, climatic changes, 

pollution, and ecosystem alterations (USDOC, NMFS; USDOI, FWS; and SEMARNAT, 2011). 

Given that the majority of the population nests in one location in Mexico, human population growth 

and urban development are serious threats to Kemp’s ridley nesting beaches (USDOI, FWS, 1999). 

Mexico and the U.S. (NMFS) collaborate to conserve and restore the species under the Kemp’s 

Ridley Restoration and Enhancement Program (Head Start) in Rancho Nuevo, Tamaulipas, Mexico. 

This government program and the expansion of the Rancho Nuevo Natural Reserve to include the 

state of Veracruz protects more than 200 km (124 mi) of nesting sites (Márquez-M, 2001). In 

addition to international collaboration efforts, the NMFS continues to implement various conservation

regulations in commercial fisheries such as the use of TEDs to protect all sea turtles, including the 

Kemp’s ridley sea turtle (USDOC, NMFS, 2015b). Other threats to sea turtles include dredging 

operations, and hopper dredging activities occur throughout the AOI on a regular basis.

3.4.5 Current Status

The Kemp’s ridley was listed as endangered on December 2, 1970 (35 FR 18319). The 

conservation and recovery of the Kemp’s ridley sea turtle is conducted through various regulatory 

mechanisms such as habitat protection efforts, protecting nesting females, and maintaining or 

increasing hatchling production levels. Other conservation measures include restrictions on 

commercial fishery activities to prevent serious injury and mortality to sea turtles as well as several 

international agreements such as CITES. Critical habitat has not been designated for the Kemp’s 

ridley sea turtle, but the NMFS and FWS were petitioned on February 17, 2010, to designate Kemp’s 

ridley critical habitat under the ESA (USDOC, NMFS, 2011); no decision on critical habitat 

designation has been forthcoming. The agencies continue to evaluate data and consider whether 

the scientific information warrants designating the proposed areas (i.e., nesting beaches along the 

Texas coast and marine habitats in the Gulf of Mexico and Atlantic Ocean to water depths of 40 m 

[131 ft]) as critical habitat.

3.5 LEATHERBACK SEA TURTLE

The leatherback sea turtle is the largest species of sea turtle and the largest reptile; adults 

reach up to 1.8 m (6 ft) in carapace length and can weigh as much as 907 kg (2,000 lb) (Ernst et al., 

1994). They are easily distinguished from all other sea turtle species by their large spindle-shaped, 

leathery, and unscaled carapaces that possess a series of parallel dorsal ridges, or keels 

(Márquez-M, 1990).

3.5.1 Range and Spatial Distribution

The leatherback sea turtle is the most oceanic of all sea turtle species and is a cosmopolitan 

species, occurring in the Mediterranean Sea and Indian, Pacific, and Atlantic Oceans, including the 

GOM (USDOC, NMFS and USDOI, FWS, 2013b). The leatherback sea turtle is the most abundant 

sea turtle in oceanic waters of the northern GOM, especially over the continental slope (Mullin and 
E-74 Expanded Affected Environment Information

Hoggard, 2000), but nesting on GOM beaches is rare. Leatherback nesting in the western North 

Atlantic Ocean is restricted to subtropical to tropical latitudes from Brazil to the southeastern U.S. 

and throughout the West Indies, with significant nesting occurring in French Guiana, Suriname, and 

Costa Rica (Ernst et al., 1994). Within the Atlantic Ocean, excluding Africa, 470 nesting sites have 

been identified (Dow Piniak and Eckert, 2011). Along the northern GOM, nesting of leatherback sea 

turtles is only known from Florida beaches; in 2014, four leatherback nests were documented along 

the west coast of Florida (USDOC, NMFS and USDOI, FWS, 1992; State of Florida, Fish and 

Wildlife Conservation Commission, Fish and Wildlife Research Institue, 2015d). Once nesting 

season is over, most leatherback sea turtles leave the waters adjacent to their nesting beaches and 

travel to feeding grounds in more temperate waters.

Leatherback sea turtles appear to use continental shelf and slope waters in the GOM (Fritts 

et al., 1983a and 1983b; Collard, 1990; Davis and Fargion, 1996). GulfCet I and II surveys suggest 

that the region from Mississippi Canyon to De Soto Canyon, especially near the shelf edge, appears 

to be an important habitat area for leatherback sea turtles (Mullin and Hoggard, 2000). Temporal 

variability in leatherback sea turtle distribution and abundance suggests that specific areas may be 

important to this species. During the GulfCet I and II surveys, leatherback sea turtles were sighted 

in significant numbers during summer and winter surveys. High variability in the relative numbers of 

leatherback sea turtles sighted within specific areas of the GOM suggests that their distribution and 

densities are likely associated with opportunistic foraging opportunities (Mullin and Hoggard, 2000). 

Leatherback sea turtles use the deep offshore waters of the northern GOM, particularly in the De

Soto Canyon and Mississippi Canyon areas, for foraging, resting, and as migratory corridors (Davis 

et al., 2000).

Leatherback sea turtles are highly migratory (Shillinger et al., 2008) and migrate farther than 

any other reptile (USDOC, NMFS and USDOI, FWS, 2013b). Satellite tagging data demonstrate 

that leatherback sea turtles display wide-ranging coastal and transoceanic movements (Hays et al., 

2006; USDOC, NMFS and USDOI, FWS, 2013b) and have the largest distribution of any sea turtle. 

Leatherback sea turtles appear to adapt quickly to local environmental conditions as they do not 

display any restricted distributional or movement behaviors that characterize other sea turtle species 

(Hays et al., 2006; USDOC, NMFS and USDOI, FWS, 2013b). James et al. (2005a and 2005b) 

described only a few high-use areas for leatherback sea turtles in the Atlantic compared with the 

total area traveled through, suggesting low fidelity to any particular area. Eckert (2006) reported that 

leatherback sea turtles tagged in Trinidad were later located off Newfoundland (Flemish Cap), 

Canada, and then in Mauritanian waters. Hays et al. (2006) concluded that leatherback sea turtles 

do not display highly migratory behavior to forage at specific “hotspots” but instead continuously feed 

as they travel. Leatherback sea turtles did remain in specific areas for short durations to forage, and 

their diving patterns were correlated with prey distribution and abundance (Hays et al., 2006).

Genetic techniques have distinguished five populations of leatherback sea turtles in the 

western North Atlantic Ocean: Florida; Northern Caribbean; Western Caribbean; Southern 

Caribbean (includes northern Brazil); and Southern Brazil (USDOC, NMFS and USDOI, FWS, 
Gulf of Mexico G&G Activities Programmatic EIS E-75

2013b). Genetic studies support the natal homing hypothesis, which has been reported for other 

sea turtles (Godley et al., 2010).

The distribution and developmental habitats of juvenile leatherback sea turtles are poorly 

understood. In an analysis of available sightings (Eckert, 2002), researchers found that leatherback 

sea turtles smaller than approximately 1 m (3 ft) in carapace length were only sighted in waters 26°C 

(79°F) or warmer, while adults were found in waters as cold as 0°C to 15°C (32°F to 59°F) off 

Newfoundland.

3.5.2 Population Status

Similar to other sea turtles, the leatherback sea turtle population is depleted; however, the 

population is considered stable or slightly increasing (USDOC, NMFS and USDOI, FWS, 2013b). 

The most recent population estimate for adult leatherback sea turtles in the Atlantic Ocean is 

34,000 to 94,000 individuals (TEWG, 2007). The leatherback sea turtle is found in Florida’s coastal 

waters, and a small number (30 to 60 individuals per year) nest in the state. The index of 

leatherback nesting in Florida from 1989 to 2014 indicates that there were 27 to 641 nests at core 

index nesting beaches in 2014. In Florida, the number of leatherback sea turtle nests has been 

increasing by 10.2 percent (range 3.1 to 16.3%) annually since 1979 (USDOC, NMFS and USDOI, 

FWS, 2013b). In 2014, four leatherback nests were reported in western Florida (State of Florida, 

Fish and Wildlife Conservation Commission, Fish and Wildlife Research Institute, 2015d).

3.5.3 Ecology and Life History

Like other sea turtle species, hatchling leatherback sea turtles leave the nest and actively 

swim offshore. However, post-hatchling and oceanic juvenile leatherback sea turtles are more 

active than other sea turtle species (Wyneken and Salmon, 1992). Oceanic juveniles virtually 

disappear for 4 years (Musick and Limpus, 1997). Their requirements for gelatinous prey (i.e., 

jellyfish) suggest that they may search for areas of major upwelling. Juvenile (as well as adult) 

leatherback sea turtles recruit seasonally to temperate and boreal coastal habitats to feed on 

concentrations of jellyfish (Lutcavage and Lutz, 1986). In the western North Atlantic, juveniles 

appear in these habitats at a body length of 110 to 120 cm (43 to 47 in) (Musick and Limpus, 1997). 

It is likely that post-hatchling and oceanic juvenile leatherback sea turtles may be present within 

offshore and coastal waters of the AOI.

Leatherback sea turtles have a wide-ranging distribution and apparently are able to adapt 

and tolerate cold water temperatures, thus they are the most far-ranging and most northerly 

occurring sea turtle species. Coles (1999) indicated that sea turtle distribution may not be random 

but instead may be associated with specific water temperature ranges. Adult leatherback sea turtles 

have been reported to migrate from equatorial to temperate waters to forage, which is unique for sea 

turtles (USDOC, NMFS and USDOI, FWS, 2013b). Leatherback sea turtles primarily feed on pelagic 

gelatinous invertebrates such as scyphomedusae (jellyfish) and pelagic tunicates (USDOC, NMFS 

and USDOI, FWS, 1992; Bjorndal, 1997), and seasonal movements appear to be correlated with 

jellyfish seasonal abundance (State of South Carolina, Dept. of Natural Resources, 2005). Unlike 
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other sea turtles, leatherback sea turtles may begin nesting much earlier in the year. Leatherback 

sea turtles have been reported to nest as early as February or March, with peak nesting in July; 

females nest at 2- or 3-year intervals. In Atlantic Outer Continental Shelf (OCS) waters and within 

the AOI, the leatherback sea turtle is reported to nest mainly on Florida beaches. Age at sexual 

maturity has been reported to be much younger than for other sea turtles, at approximately 6 to 

10 years. The average clutch size is approximately 100 eggs, and incubation is between 60 and 65 

days; females deposit 5 to 7 clutches per breeding season, with inter-nesting intervals of 

approximately 8 to 12 days (USDOC, NMFS and USDOI, FWS, 2013b).

Leatherback sea turtles are the deepest diving sea turtles, diving as deep as 1,200 m 

(3,937 ft) (Eisenberg and Frazier 1983; Davenport, 1988). Average dive depths from tagged 

leatherback sea turtles off the continental shelf of St. Croix ranged from 35 to 122 m (115 to 400 ft), 

with estimated maximum depths of more than 1,000 m (3,280 ft) (Eckert et al., 1989); typical dive 

durations averaged 6.9 to 14.5 minutes per dive, with a maximum of 42 minutes (Eckert et al., 1986

and 1989). The St. Croix studies of leatherback sea turtle diving patterns suggested nocturnal 

foraging on the deep scattering layer was taking place (Eckert et al., 1989). Off South Africa, Sale et 

al. (2006) investigated leatherback sea turtle diving behavior during oceanic movements and found 

that leatherback sea turtles primarily dove to depths less than 200 m (656 ft), with maximum dive 

durations between 30 and 40 minutes. Leatherback sea turtles displayed differences in dive 

patterns by time of day, with the longest dive times for most individuals being recorded at night. 

Using tagging data from nine leatherback sea turtles, Hays et al. (2006) recorded seasonal north 

and south movements between the Caribbean and northeastern U.S. coast; leatherback sea turtle 

dive depths lessened and dive durations became progressively shorter as the sea turtles moved 

northward. Mean dive duration ranged from 3 to 30 minutes, and mean dive depth ranged from 

surface waters to almost 250 m (820 ft). The overall distance traveled ranged from 2.5 to 82.5 km 

(1.6 to 51.3 mi) per day; however, most leatherback sea turtles traveled between 32.5 and 42.5 km 

(20 and 26 mi) per day (Hays et al., 2006).

3.5.4 Threats

Leatherback sea turtles have various anthropogenic threats to their recovery, including 

incidental capture by commercial fisheries; habitat loss (nesting); climatic change (e.g., sea-level 

rise, and shifts in prey availability); pollution; overutilization for commercial, recreational, scientific, or 

education purposes (e.g., egg harvesting); and disease (USDOC, NMFS and USDOI, FWS, 2013b).

3.5.5 Current Status

The leatherback sea turtle was listed as endangered on June 2, 1970 (35 FR 8491). Critical 

habitat was designated for the leatherback sea turtle in the U.S. Virgin Islands in 1979 (44 FR 

17710). Critical habitat is defined as a strip of land 0.2-mi (0.3-km) wide at Sandy Point Beach, 

St. Croix, and the waters adjacent to the site (shore to 100-fathom curve [183-m; 600-ft]). In 2010, 

there were two petitions to designate additional critical habitat in Puerto Rico; both petitions were 

denied by the NMFS after the 12-month determination (77 FR 32909). There is no critical habitat 

designation for leatherback sea turtles in the GOM (44 FR 17710).
Gulf of Mexico G&G Activities Programmatic EIS E-77

The conservation and recovery of the leatherback sea turtle is governed through various 

regulatory mechanisms such as attempting to meet specific recovery plan objectives, habitat 

protection efforts, and protecting nesting females. Other conservation measures include imposing 

restrictions on commercial fishery activities to prevent serious injury and mortality to sea turtles (e.g., 

circle hook requirements in the pelagic longline fishery and the use of TEDS in trawls) and 

supporting several international agreements such as the Inter-American Convention for the 

Protection and Conservation of Sea Turtles. Moreover, the NMFS has developed and is attempting 

to implement a strategy for sea turtle conservation and recovery in relation to Atlantic and Gulf of 

Mexico fisheries, which focuses on specific commercial fishing gear related criteria.

3.6 SUMMARY OF SEA TURTLE HEARING CAPABILITIES

A brief overview of sea turtle hearing is presented in this section; more information can be 

found in Appendix I. Few studies have examined the role acoustic cues play in the ecology of sea 

turtles (Mrosovsky, 1972; Cook and Forrest, 2005; Samuel et al., 2005; Nunny et al., 2008). There 

is evidence that sea turtles may use sound to communicate, but the few vocalizations described for 

sea turtles are restricted to the grunts and gular pumps of nesting females (Mrosovsky, 1972; Cook 

and Forrest, 2005). These low-frequency sounds are relatively loud (peak frequency recorded from 

nesting females were between 300 and 500 Hz), thus leading to speculation that nesting females 

use sounds to communicate with conspecifics (Mrosovsky, 1972; Cook and Forrest, 2005). Very 

little is known about the extent to which sea turtles use their auditory environment (“soundscape”) for 

navigation, environmental assessment, or identification of predators and prey. The passive acoustic 

environment for sea turtles changes with life cycle stages. In the inshore environment where 

juvenile and adult sea turtles generally reside, the ambient environment is noisier than the open 

ocean environment of the hatchlings and is dominated by low-frequency sound (Hawkins and 

Myrberg, 1983). Moreover, in highly trafficked inshore areas, virtually constant low-frequency noises 

from shipping and recreational boating compound the potential for acoustic impact (Hildebrand, 

2009) and might prevent the animal from hearing signals from biologically important stimuli (Fay, 

2009).

Much of the research on the hearing capacity of sea turtles is limited to gross morphological 

dissections (Wever, 1978; Lenhardt et al., 1985). Based on the functional morphology of the ear, it 

appears that sea turtles receive sound through the standard vertebrate tympanic middle-ear path. 

The sea turtle ear appears to be a poor receptor for aerial sounds but is well adapted to detect 

underwater sound. The dense layer of fat under the tympanum acts as a low-impedance channel for 

underwater sound (similar to the pathway found in odontocetes [Ketten et al., 1999]). Furthermore, 

the retention of air in the middle ear of sea turtles suggests that they are able to detect sound 

pressures (Hetherington, 2008).

Electrophysiological studies on hearing have been conducted on juvenile green sea turtles 

(Ridgway et al., 1969; Bartol and Ketten, 2006; Dow Piniak et al., 2012a); juvenile Kemp’s ridley sea 

turtles (Bartol and Ketten, 2006); post-hatchling, juvenile, and adult loggerhead sea turtles (Bartol 

et al., 1999; Lavender et al., 2012 and 2014; Martin et al., 2012); and hatchling leatherback sea 
E-78 Expanded Affected Environment Information

turtles (Dow Piniak et al., 2012b). Electrophysiological responses, specifically AEPs, are the most 

widely accepted measurement for hearing in situations in which normal behavioral testing is 

impractical. The AEPs reflect the synchronous discharge of large populations of neurons within the 

auditory pathway and thus are useful for monitoring the functionality of the auditory system. Some 

AEP research has concentrated the responses occurring within the first 10 ms following presentation 

of click or brief tone burst stimuli. This response is the ABR, which consists of a series of five to 

seven patterned and identifiable waves. These techniques are non-invasive and often are 

performed on conscious subject animals (Bullock, 1981; Corwin et al., 1982; Bartol et al., 1999).

Ridgway et al. (1969) measured auditory cochlear potentials of green sea turtles using aerial 

and vibrational stimuli. Thresholds were not measured; instead, cochlear response curves of 

0.1-microvolt (μV) potential were plotted for frequencies ranging from 50 to 2,000 Hz. Green sea 

turtles detect a limited frequency range (200 to 700 Hz) with best sensitivity in the low tone region of 

approximately 400 Hz. Though this investigation examined two separate modes of sound reception 

(i.e., air and bone conduction), sensitivity curves were relatively similar, suggesting that the inner ear 

is the main structure for determining frequency sensitivity. To measure electrophysiological 

responses to sound stimuli, Bartol et al. (1999) collected ABRs from juvenile loggerhead sea turtles. 

Thresholds were recorded for tonal and click stimuli. Best sensitivity was found in the low-frequency 

range of 250 to 1,000 Hz. The decline in sensitivity was rapid above 1,000 Hz, and the most 

sensitive threshold tested was 250 Hz.

More recently, Bartol and Ketten (2006) collected underwater ABRs from hatchling and 

juvenile loggerhead sea turtles and juvenile green sea turtles using speakers suspended in air while 

the sea turtle’s tympanum remained submerged. All tested sea turtles responded to sounds in the 

low-frequency range, from at least 100 Hz (lowest frequency tested) to no more than 800 Hz. 

Hearing sensitivity of green sea turtles varied with size; smaller green sea turtles had a broader 

range of hearing (100 to 800 Hz; greatest sensitivity at 600 to 700 Hz at 95 dB re 1 μPa) than that 

detected in larger subadult subjects (100 to 500 Hz, greatest sensitivity 200 to 400 Hz at 93 to 97 dB 

re 1 μPa). Dow Piniak et al. (2012a) recorded both in air and in water AEP responses from juvenile 

green sea turtles. The AEP signal signature recorded from green sea turtles was similar to that seen 

in studies of fish evoked potentials, with a frequency-doubling response (i.e., where response waves 

oscillate at twice the stimulus frequency). Juvenile green sea turtles responded to stimuli between 

50 and 1,600 Hz in water and 50 and 800 Hz in air. Ranges of maximum sensitivity were between 

50 and 400 Hz in water and 300 and 400 Hz in air. Though these animals responded to an 

expanded range of frequencies compared with those previously studied, sensitivity decreased 

sharply for frequencies above 400 Hz in both media.

Lavender et al. (2011, 2012 and 2014) have recorded underwater AEPs from post-hatchling 

to juvenile loggerhead sea turtles. The experiments involved submerging a restrained, fully 

conscious loggerhead sea turtle just below the air-water interface and presenting sound using a J-9 

underwater speaker. Under these conditions, post-hatchling and juvenile loggerhead sea turtles 

were found to respond to frequencies between 50 and 1,100 Hz. Post-hatchling sea turtles 

responded with the greatest sensitivity at 200 Hz (116 dB re 1 μPa), and juveniles were most 
Gulf of Mexico G&G Activities Programmatic EIS E-79

sensitive at 50, 100, and 400 Hz (117 to 118 dB re 1 μPa). Martin et al. (2012) acquired AEPs from 

a submerged adult loggerhead using an underwater pool speaker and reported thresholds between 

100 and 1,131 Hz, with highest sensitivity occurring at 100 to 400 Hz (threshold levels approximately 

109 dB re 1 μPa).

Only one study has looked at the hearing of leatherback sea turtles (Dow Piniak et al., 

2012b). This study measured hearing of hatchlings (immediately post-emergence) in water and in 

air. These animals reacted to low-frequency sounds, responding to stimuli between 50 and 

1,600 Hz in air and 50 and 1,200 Hz in water (lowest sensitivity recorded was 93 dB re 1 μPa at 

300 Hz). Finally, Bartol and Ketten (2006) recorded hearing from Kemp’s ridley sea turtles using the 

same methods described for juvenile and subadult green sea turtles. The two juvenile sea turtles 

tested had a restricted hearing range (100 to 500 Hz) with their most sensitive hearing between 

100 and 200 Hz (110 dB re 1 μPa) (Bartol and Ketten, 2006).

4 FISH RESOURCES AND ESSENTIAL FISH HABITAT 

Chapter 4.4.1 of this Programmatic EIS provides the succinct description of the affected 

environment for fish resources and Essential Fish Habitat (EFH) in sufficient detail to support the 

impact analyses. The following descriptions provide additional information on fish resources and 

EFH.

The AOI encompasses demersal (zone directly above and influenced by the benthic zone 

[seafloor]) and pelagic (the open water environment) habitats from the shoreline to the open ocean 

that support a large diverse group of fish families and species. Fish species distributions vary 

relative to major environmental factors such as water depth, salinity, temperature, and habitat type. 

Many commercial fish species spend all or part of their life cycle in the AOI, resulting in the majority 

of the AOI designated as EFH. The EFH is the habitat necessary for managed fish to complete their 

life cycle, thus contributing to a fishery that can be harvested sustainably; specifically defined by 

16 U.S.C. § 1801(10) as “those waters and substrate necessary to fish for spawning, breeding, 

feeding or growth to maturity”. The following sections describe the listed species (Section 4.1), 

candidate species and species of concern (Section 4.2), non-listed species (Section 4.3), and a 

brief summary of EFH (Section 4.4). Appendix I reviews the physics of underwater sound, 

mechanics of fish hearing, sources of anthropogenic sound and sound metrics, mechanisms of injury 

to fish from exposure to anthropogenic sound, and criteria for the protection of fish from exposure to 

injurious levels of G&G survey sounds.

4.1 LISTED SPECIES

The proposed AOI includes critical habitat for two endangered fish species that are managed 

by the NMFS and FWS under the ESA: smalltooth sawfish and Gulf sturgeon. Another endangered 

species, the largetooth sawfish Pristis perotteti (formerly P. pristis), was historically documented in 

the AOI; however, the population has been extirpated from the GOM and no critical habitat is 

designated for the species.
E-80 Expanded Affected Environment Information

4.1.1 Smalltooth Sawfish 

4.1.1.1 Distribution and Abundance

The smalltooth sawfish (Pristis pectinata) of the family Pristidae is a member of the 

cartilaginous class of fishes Chondrichthyes. The historic range of smalltooth sawfish extended 

throughout the GOM and north to Long Island Sound in the Atlantic but has contracted considerably 

in U.S. coastal waters over the past 200 years. Currently, the core of the U.S. smalltooth sawfish 

population is surviving and reproducing in the waters of southwest Florida and Florida Bay, primarily 

within the jurisdictional boundaries of Everglades National Park where important habitat features are 

still present and less fragmented than in other parts of the species’ historic range (Simpfendorfer and 

Wiley, 2005; USDOC, NMFS, 2009b). This area includes most of the critical habitat shown in 

Figure 4.4-1 of this Programmatic EIS. The smalltooth sawfish normally inhabits shallow waters 

(<10 m [33 ft]), often near river mouths or in estuarine lagoons over sandy or muddy substrates, but 

it may also occur in deeper waters (<50 m [164 ft]) of the continental shelf. Young sawfish generally 

prefer shallow water where the substrate is muddy and the shore is lined with mangrove trees 

(USDOC, NMFS, 2009b).

4.1.1.2 Behavior

Smalltooth sawfish grow slowly and mature at approximately 10 years of age. Females bear 

live young, and litters reportedly range from 1 to 20 embryos (USDOC, NMFS, 2009b). Smalltooth 

sawfish feed on fishes and benthic invertebrates. The toothed rostrum, or saw, has been considered 

a trophic apparatus, used to herd and even impale shallow-water schooling fishes such as herring 

and mullet (Breder, 1952). More recent research suggests that the saw is used to rake the seafloor 

to uncover partially buried invertebrates. Small juvenile sawfishes may be susceptible to predation 

from bull sharks (Carcharhinus leucas) and lemon sharks (Negaprion brevirostris) that inhabit similar 

water depths as the smalltooth sawfish.

4.1.1.3 Status

In response to a petition from the Ocean Conservancy, the NMFS conducted a status review 

of the smalltooth sawfish in 2000 (USDOC, NMFS, 2000). The status review determined that 

smalltooth sawfish in U.S. waters comprise a DPS that is in danger of extinction throughout its 

range. On April 1, 2003, the NMFS published a final rule (68 FR 15674) listing the U.S. DPS as 

endangered under the ESA.

Over the past 200 years, smalltooth sawfish populations have declined considerably, 

primarily because of incidental capture by fishing gear as well as destruction of habitat. The ESA 

listing was based on the following considerations: threatened destruction, modification, or 

curtailment of habitat or range; overutilization for commercial, recreational, scientific, or educational 

purposes; inadequacy of existing regulatory mechanisms; and other natural and man-made factors 

affecting the continued existence of the species. Critical habitat for the smalltooth sawfish includes 

two units on the southwest coast of Florida, within and adjacent to the Eastern Planning Area 

(Figure 4.4-1 of this Programmatic EIS): the Charlotte Harbor Estuary Unit and the Ten Thousand 
Gulf of Mexico G&G Activities Programmatic EIS E-81

Islands/Everglades Unit (50 CFR § 226.218). Recent studies indicate that key habitat features 

(particularly for immature individuals) are shallow water, especially near mangroves, with estuarine 

conditions (Simpfendorfer and Wiley, 2005; Simpfendorfer 2006; USDOC, NMFS, 2009b).

4.1.2 Gulf Sturgeon

4.1.2.1 Distribution and Abundance

The Gulf sturgeon (Acipenser oxyrinchus desotoi) is a geographical subspecies of the 

Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus) and is a member of the family Acipenseridae 

within the ray finned fishes (Class Actinopterygii). Gulf sturgeon occur in most major tributaries of 

the northeastern GOM from Lake Pontchartrain and the Mississippi River east to Florida’s 

Suwannee River, and in the central and eastern GOM waters as far south as Charlotte Harbor, 

Florida (Wooley and Crateau, 1985). Gulf sturgeon are currently found in the Pearl, Pascagoula, 

Escambia, Yellow, Blackwater, Choctawhatchee, Apalachicola, Ochlockonee, and Suwannee Rivers 

(Reynolds, 1993). Critical habitat for Gulf sturgeon is shown in Figure 4.4-1 of this Programmatic 

EIS.

Five genetically based stocks have been identified by the FWS and NMFS: (1) Lake 

Pontchartrain and Pearl River; (2) Pascagoula River; (3) Escambia and Yellow Rivers; 

(4) Choctawhatchee River; and (5) Apalachicola, Ochlockonee, and Suwannee Rivers. 

Mitochondrial DNA analyses of individuals from subpopulations indicate that adults return to natal 

river areas for feeding and spawning (Stabile et al., 1996; Sulak and Clugston, 1999; USDOI, FWS 

and USDOC, NMFS, 2009c).

4.1.2.2 Behavior

Gulf sturgeon are anadromous, meaning adults spend most of their lives in estuarine and 

marine waters and migrate into freshwater rivers and streams to spawn during the spring and early 

summer. As a result of this reproduction cycle, critical habitat for this species includes nearshore 

bays and estuaries from Louisiana to Florida, including the following river systems: the 

Apalachicola, Choctawhatchee, Escambia, Suwannee, Pascagoula, Pearl, and Yellow Rivers 

(50 CFR § 226.214). Free-jumping adult fish produce sounds during summer months but the 

adaptive significance of these sounds is unknown (Sulak et al., 2002).

Gulf sturgeon stop feeding while migrating upstream to spawn. Individuals only feed while in 

the GOM during winter. Sturgeons are bottom suction feeders that have ventrally located, highly 

extrudable mouths and primarily feed on benthic invertebrates. The sturgeon head is dorsoventrally 

compressed (flattened) with eyes dorsal, so they detect benthic prey using sensitive barbels. The 

barbels are also useful for navigation at night and in high-order streams if visibility is low.

Lovell et al. (2005) and Meyer et al. (2012) studied the hearing of lake sturgeon. Lovell et al. 

(2005) found that lake sturgeon are responsive to sounds ranging in frequency from 100 to 500 Hz. 

The lowest hearing thresholds from both species were acquired at frequencies between 200 and 
E-82 Expanded Affected Environment Information

300 Hz, with higher thresholds at 100 and 500 Hz. Sulak et al. (2002) hypothesized that sturgeons 

jump as a means of communication and found that the sounds produced from jumping sturgeon 

were distinct from other sounds; however, other studies suggest that jumping may occur for a 

number of other reasons. Appendix I provides a synopsis of fish hearing and the sensitivity of fish 

to hearing loss and injury.

4.1.2.3 Status

The FWS and NMFS listed the Gulf sturgeon as a threatened species on September 30, 

1991. A recovery plan was developed to ensure the preservation and protection of Gulf sturgeon 

spawning habitat (USDOI, FWS and Gulf States Marine Fisheries Commission, 1995). Critical 

habitat was designated on March 19, 2003 (68 FR 13370) (Figure 4.4-2 of this Programmatic EIS).

4.2 CANDIDATE SPECIES AND SPECIES OF CONCERN

On September 2, 2014, the NMFS announced a 12-month finding and listing determination 

on a petition to list the Nassau grouper (Epinephelus striatus) as threatened or endangered under 

the ESA (79 FR 51929). The Nassau grouper is a moderately large grouper (Family Epinephelidae) 

known to occur within the AOI only at the Flower Garden Banks (FGBs) off Texas and off the Dry 

Tortugas and Key West, Florida (77 FR 61559). Nassau grouper generally are found near high-relief 

coral reefs and rocky bottoms from inshore to a maximum depth of approximately 100 m (328 ft). 

The Alabama shad (Alosa alabamae) is undergoing a status review to determine if the petition to list 

it as threatened or endangered is warranted (78 FR 57611).

The NMFS also has evaluated the dusky shark (Carcharhinus obscurus) (78 FR 29100) for 

ESA listing, but announced on May 17, 2013, that a status review of the GOM population of dusky 

shark is needed. The great hammerhead shark (Sphyrna mokarran) is also currently under status 

review by the NMFS (78 FR 24701). Species of concern in the AOI include dusky shark, sand tiger 

shark (Carcharhinus taurus), speckled hind (Epinephelus drummondhayi), and Warsaw grouper 

(Epinephelus nigritus).

4.3 NON-LISTED SPECIES

The GOM’s marine habitats range from coastal marshes to the deep-sea abyssal plain and 

support a varied and abundant fish fauna. Within the AOI, distinctive fish assemblages are 

described using the following broad habitat categories: soft bottom fishes, hard bottom fishes, and 

coastal pelagic fishes on the continental shelf; and epipelagic, midwater fishes, and demersal fishes 

in oceanic waters (>200-m [656-ft] water depths).

4.3.1 Continental Shelf Fishes

4.3.1.1 Soft Bottom Fishes

The demersal, or bottom-dwelling, fish fauna of the continental shelf separates broadly into 

soft bottom and hard bottom assemblages. Soft bottom fish fauna vary along (east to west) and 
Gulf of Mexico G&G Activities Programmatic EIS E-83

across the GOM shelf (Chittenden and McEachran, 1976; Darnell et al., 1983; Darnell and Kleypas, 

1987). Major environmental factors influencing the distribution and abundance of soft bottom fishes 

include sedimentary characteristics, water temperature, dissolved oxygen, salinity, and water depth 

(e.g., Switzer et al., 2006).

In the eastern GOM (primarily the expansive West Florida Shelf), relatively clear water and 

coarse carbonate sediments on the open shelf support seabasses, mojarras, porgies, grunts, and 

sand flounders. Numerically dominant species include sand perch (Diplectrum formosum), silver 

jenny (Eucinostomus gula), dusky flounder (Syacium papillosum), and pigfish (Orthopristis 

chrysoptera). The West Florida Shelf also has vast areas of soft bottom covered by seagrasses and 

macroalgae. The Big Bend area and Florida Bay to the south support most of the seagrass acreage. 

Complex seagrass habitats attract diverse assemblages of fishes composed of herrings, pipefishes, 

snappers, grunts, porgies, drums, gobies, smooth puffers, and filefishes. Individual species 

characteristic of shelf seagrass meadows are false pilchard (Harengula jaguana), lane snapper 

(Lutjanus synagris), gray snapper (Lutjanus griseus), red drum (Sciaenops ocellatus), pinfish 

(Lagodon rhomboides), spotted seatrout (Cynoscion nebulosus), and spot (Leiostomus xanthurus).

West of the Florida Panhandle to the central GOM, carbonate sediments of the open shelf 

give way to coarser sand and shell hash. In water depths ranging from 20 to 40 m (66 to 131 ft) 

from Alabama to west of the Mississippi River Delta, soft bottom fish assemblages are composed of 

searobins, seabasses, porgies, flatfishes, goatfishes, and snake eels. Common species include 

longspine porgy (Stenotomus caprinus), leopard searobin (Prionotus scitulus), horned searobin 

(Bellator miliaris), and red goatfish (Mullus aratus). This particular horizon extends semicontinuously 

to the West Texas Shelf (Chittenden and McEachran, 1976). In water depths from 20 m (66 ft) to 

the shoreline, sediments become fine and muddy due to the massive discharges of Mobile Bay, the 

Mississippi River, and the Atchafalaya River. This region, centered on the Mississippi River Delta 

and often called the “fertile crescent,” supports a dense assemblage of catfishes, drums, cutlassfish, 

croakers, and seatrouts. Numerically dominant species are Atlantic croaker (Micropogonias 

undulatus), star drum (Stellifer lanceolatus), Atlantic cutlassfish (Trichiurus lepturus), sand seatrout 

(Cynoscion arenarius), silver seatrout (Cynoscion nothus), Atlantic threadfin (Polydactylus 

octonemus), and hardhead catfish (Ariopsis felis) (Chittenden and McEachran, 1976; Darnell et al., 

1983). In some areas of the central and western GOM, sediments form mosaics of mud, sand, and 

shell hash. Fishes will segregate among sediment types (Wells et al., 2009). Larger deposits of 

sediment may form shoals that rise gradually above the surrounding seafloor. Fishes associating 

with shell hash include dwarf sand perch (Diplectrum bivittatum), least puffer (Sphoeroides parvus), 

and juvenile red snapper (Lutjanus campechanus). Muddy substrates attract silver jenny, silver 

seatrout, and largescale lizardfish (Saurida undosquamis) (Wells et al., 2009).

Few soft bottom fish species are of fishery importance; however, because of prevalence of

shrimping over soft bottom habitats in all regions of the GOM, incidentally caught fish that are not 

discarded at sea end up as unclassified landings (Gulf and Atlantic Fisheries Foundation, 2009). 

The species most common in the bycatch include Atlantic croaker, anchovy (Anchoa mitchilli), 

hardhead catfish, and Gulf menhaden (Brevoortia patronus). Examples of economically important 
E-84 Expanded Affected Environment Information

species caught incidentally by shrimp trawls include red snapper, flounder (Paralichthys 

lethostigma), and blue crabs (Callinectes sapidus). Bycatch reduction devices that allow non-target 

fishes to escape the trawl net are required by shrimpers working in the Gulf of Mexico EEZ (Gulf and 

Atlantic Fisheries Foundation, 2009).

4.3.1.2 Hard Bottom Fishes

Hard bottom habitats in the GOM are composed mostly of rock (or clay) derived from ancient 

shorelines, bioherms, or other sedimentary features hardened into rock over time. Where rock 

surfaces are exposed, algae, sponges, octocorals, stony corals, hydrozoans, and tunicates attach 

and grow, creating a complex habitat for fishes. Water temperature, clarity, salinity, light 

penetration, and depth influence biological dynamics of hard bottom communities.

Hard bottom habitat is most extensive in the eastern GOM where relatively low-relief (<1 m 

[3 ft]) rock characterizes much of the West Florida Shelf. Although much of the exposed hard 

bottom habitat is low relief, several high-relief areas occur in the region, including the Florida Middle 

Grounds, Steamboat Lumps, and Pulley Ridge (Sections 5.2 and 7.2). Shallow-water (10 to 50 m 

[33 to 164 ft]) hard bottom habitats support common reef fishes: snappers, seabasses, grunts, 

porgies, angelfishes, damselfishes, butterflyfishes, surgeonfishes, wrasses, triggerfishes, and 

filefishes. Seabasses and groupers are the most species rich families of reef fish in the area (Smith, 

1976; Bullock and Smith, 1991; Coleman et al., 2011).

In water depths exceeding 30 m (98 ft) where reduced light penetration excludes most plants 

and therefore herbivores, a distinctive deep-reef or “mesophotic” assemblage occurs (Koenig et al., 

2000; Weaver et al., 2002 and 2006a). Conspicuous mesophotic reefs are found on the Florida, 

Mississippi, and Alabama continental shelves. The Mississippi-Alabama Pinnacle Trend represents 

a series of mounds, ledges, and high-relief features in water depths ranging from 70 to 100 m 

(230 to 328 ft) (Continental Shelf Associates, Inc. and Texas A&M University [TAMU], 2001; Weaver 

et al., 2002). Fish assemblages on mesophotic reefs are composed of seabasses, snappers, 

wrasses, bigeyes, butterflyfishes, angelfishes, jacks, and other reef-dwelling species (Koenig et al., 

2000; Continental Shelf Associates, Inc. and TAMU, 2001; Weaver et al., 2002). Red snapper, 

snowy grouper (Hyporthodus niveatus), scamp (Mycteroperca phenax), gag (Mycteroperca 

microlepis), speckled hind, and goldface tilefish (Caulolatilus chrysops), which are found at 

mesophotic reefs in the GOM, are not only large predatory fish but are members of the Gulf of 

Mexico Fishery Management Council’s (GMFMC’s) reef fish management unit. Table 4.4-1 of this

Programmatic EIS provides information on hard bottom species with essential fish habitat identified 

within the AOI.

Other species prevalent on the mesophotic reefs do not have direct fishery importance but 

do contribute to the mesophotic food web. These generally are small species that feed on 

invertebrates (attached or motile) living on the reefs or on plankton transported from surrounding 

areas. Species that feed mainly near or on the reef structure include short bigeye (Pristigenys alta), 

wrasse bass (Liopropoma eukrines), tattler (Serranus phoebe), bank butterflyfish (Prognathodes 
Gulf of Mexico G&G Activities Programmatic EIS E-85

aya), red hogfish (Decodon puellaris), and greenband wrasse (Halichoeres bathyphilus). 

Planktivorous fishes are abundant and are represented by small-bodied species such as the 

roughtongue bass (Pronotogrammus martinicensis), red barbier (Hemanthia vivanus), and yellowtail 

reeffish (Chromis enchrysura). These species form an important prey base for the larger predatory 

species (Weaver et al., 2002).

Offshore of Louisiana and Texas, a series of topographic features (called “banks”) created by 

subsurface salt intrusions dot the outer shelf (refer to Section 5.2.4). The portion of the banks 

closest to the surface (shallowest water depth) varies among the banks and greatly influences fish 

faunal composition. Two of the best known banks are the East and West FGBs, a pair of features 

rising from almost 100 m (328 ft) to within 25 m (82 ft) of the surface (Gardner et al., 1998). 

Because of the relatively shallow depth, the fish fauna at the East and West FGBs is similar to that 

of a southern Florida or Caribbean coral reef. Damselfishes, wrasses, parrotfishes, groupers, 

snappers, and other reef species occupy the mostly living coral reef that caps the East and West 

FGBs (Rooker et al., 1997). The deeper (>50 m [164 ft]) sloping sides of the banks provide sponge 

and rubble habitat for a suite of mesophotic reef fishes including wrasse bass, tattler, roughtongue 

bass, bank seabass, bank butterflyfish, and marbled grouper (Epinephelus inermis) (Dennis and 

Bright, 1988; Weaver et al., 2006b).

Deep reef fishes occur on hard bottom features in water depths of 50 to 100 m (164 to 328 ft) 

off southwest Florida, the Mississippi-Alabama Pinnacle Trend, the Texas-Louisiana shelf edge, and 

the south Texas carbonate banks.

In water depths >320 m (1,050 ft), deep coral reefs composed of Lophelia pertusa and other 

invertebrates harbor a different fish assemblage that includes barrelfish (Hyperoglyphe perciformis), 

black seabass (Centropristis striata), alfonsino (Beryx decadactylus), scorpionfish (Scorpaena 

plumieri), and conger eel (Conger oceanica) (Sulak et al., 2007).

Hard bottom fishes in the GOM often associate with artificial habitat, including oil and gas 

structures, artificial reefs, shipwrecks, and other debris. The approximately 2,900 oil and gas 

structures in the northern GOM may be grouped into coastal, offshore, and, blue water categories 

with respect to environmental conditions and species composition (Gallaway and Lewbel, 1982). 

Coastal platforms are found in water depths <30 m (98 ft) and are characterized by variable water 

column conditions (e.g., temperature, salinity, and turbidity). Typical fish assemblages at coastal 

platforms include sheepshead (Archosargus probatocephalus), Atlantic spadefish (Chaetodipterus 

faber), gray snapper, and gray triggerfish (Balistes capriscus).

The offshore platform assemblage is found in water depths of 30 to 60 m (98 to 197 ft) with 

variable but more stable water column conditions. Red snapper, gray triggerfish, Atlantic spadefish, 

sergeant major (Abudefduf saxatilis), cocoa damselfish (Stegastes variabilis), blue tang (Acanthurus 

coeruleus), blue angelfish (Holacanthus bermudensis), orangespotted filefish (Cantherhines pullus), 

and many other species reside near offshore platforms. Reef fish assemblages associated with 

offshore platforms are not particularly species rich when compared with natural reefs and lack 
E-86 Expanded Affected Environment Information

conspicuous components, including most parrotfishes, grunts, porgies, goatfishes, gobies, and 

others, that depend on more than just the presence of hard substrate (Rooker et al., 1997).

The blue water platform assemblage occurs along the outer margin of the continental shelf 

and upper continental slope in water depths >60 m (197 ft). Unlike natural hard bottom, oil and gas 

platforms span the entire water column providing shallow-water habitat over the OCS and upper 

continental slope where ambient water depths exceed 300 m (984 ft). This vertical structure 

combined with blue water conditions creates an environment conducive to the settlement (and 

attraction) of shallow-water tropical reef fishes in the upper water column and mesophotic species in 

depths greater than 30 m (98 ft). Reef fishes tend to distribute vertically based on species-specific, 

water-depth preferences with a general range from near the surface to approximately 60 m (197 ft) 

(Stanley and Wilson, 1998). Most species remain relatively near or under the structures (Stanley 

and Wilson, 2000 and 2003). Blue water platforms support assemblages consisting of all the 

species mentioned previously as well as Spanish hogfish (Bodianus rufus), scamp, rock hind 

(Epinephelus adscensionis), creole fish (Paranthias furcifer), redlip blenny (Ophioblennius 

macclurei), tessellated blenny (Hypsoblennius invemar), cocoa damselfish, sergeant major, spotfin 

butterflyfish (Chaetodon ocellatus), rock beauty (Holacanthus tricolor), blue angelfish, bluehead 

wrasse (Thalassoma bifasciatum), spotfin hogfish (Bodianus pulchellus), scrawled filefish (Aluterus 

scriptus), and orangespotted filefish. Most of these species feed on algae and invertebrates growing 

on the platform legs and cross members.

4.3.1.3 Coastal Pelagic Fishes

The primary water column fish assemblage found in coastal and shelf waters of the GOM is 

termed coastal pelagic. Table 4.4-2 of this Programmatic EIS provides information on coastal 

migratory pelagic species with EFH identified within the AOI. Major coastal pelagic fishes occurring 

in the GOM are sharks, rays, ladyfish, anchovies, herrings, mackerels, jacks, mullets, bluefish, and 

cobia. In general, coastal pelagic species are distributed across the entire GOM with little east-west 

differences; however, some species form distinct subpopulations. For example, king mackerel 

(Scomberomorus cavalla) appears to have eastern and western subpopulations. The eastern 

subpopulation migrates from near the Mississippi River Delta then southeast around the Florida 

peninsula for the winter (Sutter et al., 1991). The western subpopulation travels to waters off the 

Yucatan Peninsula during winter. In summer, both populations migrate to the northern GOM, where 

they intermix to an unknown extent (Johnson et al., 1994). Spanish mackerel (Scomberomorus 

maculatus), cobia (Rachycentron canadum), bluefish (Pomatomus saltatrix), crevalle jack (Caranx 

hippos), blacktip shark (Carcharhinus limbatus), Atlantic sharpnose shark (Rhizoprionodon 

terraenovae), bonnethead (Sphyraena tiburo), and smooth dogfish (Mustelus canis) are migratory, 

but their routes or potential population structure have not been well studied. Spanish mackerel, 

bluefish, and crevalle jack generally migrate westward along the shelf in warm months and back 

towards Florida during cold months (Barry A. Vittor and Associates, 1985). Gulf menhaden, thread 

herring (Opisthonema oglinum), Atlantic Spanish mackerel, and ladyfish (Elops saurus) form large 

schools, but other species such as cobia and bull shark travel alone or in small groups. The 
Gulf of Mexico G&G Activities Programmatic EIS E-87

distribution of most species depends on water column structure in temperature, salinity, and 

dissolved oxygen, which vary spatially and seasonally.

While migrating, many coastal pelagic species will associate with offshore oil and gas 

platforms (Gallaway and Lewbel, 1982). Table 4.4-3 of this Programmatic EIS provides information 

on highly migratory species with EFH identified within the AOI. Coastal platforms in water depths 

<20 m (66 ft) attract Spanish mackerel, bluefish, blue runners (Caranx crysos), and lookdowns 

(Selene vomer). Offshore platforms (20 to 60 m [66 to 197 ft]) are visited by blue runner, king 

mackerel, greater amberjack, jack crevalle, cobia and little tunny (Euthynnus alletteratus). Some 

coastal pelagic fishes, mostly jacks, frequent blue water platforms in water depths exceeding 60 m 

(197 ft). These species swim within a zone ranging from 10 to 50 m (33 to 164 ft) horizontally from 

the structure and vertically down to approximately 100 m (328 ft) (Stanley and Wilson, 2000). Blue 

runner form large schools that feed on surface plankton near platforms (Brown et al., 2010; Keenan 

et al., 2003). The vertical structure of a platform can slow the surface water flow, creating eddies 

that retain plankton in a way that may facilitate water column feeding. In addition, platform lights 

attract plankton at night and provide enough illumination to allow blue runners (and presumably 

other visual water column feeders) to forage day and night.

Coastal pelagic fishes form dynamic trophic interactions among different sized members of 

the assemblage. The larger predatory species such as coastal sharks, king mackerel, cobia, and 

little tunny feed on smaller fishes, including Spanish mackerel, bluefish, herrings, scads, and mullets. 

These smaller species typically form schools, undergo migrations, grow rapidly, mature early, and 

exhibit high fecundity. Species in the lower group in the trophic web are the planktivorous Gulf 

menhaden, thread herring, Spanish sardine, round scad, and anchovies, which are fed upon by all of 

the previously mentioned species.

The species discussed thus far are inhabitants of the open shelf in water depths >10 m 

(33 ft). Another component of the coastal pelagic assemblage occurs regularly along sandy 

beaches from the shoreline to the swash zone (<5 m [16 ft]) (e.g., Ross, 1983). This habitat occurs 

along the seaward shore of barrier islands off all Gulf Coast States. Fish species commonly 

occurring in this shallow habitat include scaled sardine (Harengula clupeola), Florida pompano 

(Trachinotus carolinus), sand drum (Umbrina coroides), kingfishes (Menticirrhus spp.), mullets (Mugil

spp.), and various anchovies (Anchoa spp.). Nearshore fish assemblages show considerable 

seasonal structuring in the northern GOM. The lowest abundance of all species occurs in winter, 

with peak numbers found during summer and fall. Larger predatory species (particularly bluefish, 

Spanish mackerel, and blue runner) may be attracted to large concentrations of anchovies, herrings, 

and silversides, which congregate in nearshore areas.

4.3.2 Oceanic Fishes

4.3.2.1 Epipelagic Fishes

Epipelagic fishes inhabit the upper 200 m (656 ft) of the water column and include several 

sharks, billfishes, tunas, dolphins, flyingfishes, halfbeaks, opahs, oarfishes, jacks, remoras, 
E-88 Expanded Affected Environment Information

pomfrets, butterfishes, molas, and triggerfishes. Table 4.4-4 of this Programmatic EIS provides 

information on shark species with EFH identified within the AOI. Several of these species, such as 

dolphinfish (Coryphaena hippurus), sailfish (Istiophorus platypterus), white marlin (Kajikia albida), 

blue marlin (Makaira nigricans), and tunas (Thunnus spp.), are important to commercial and 

recreational fisheries (refer to Sections 9 and 10). Most epipelagic species migrate great distances 

within or outside the GOM. Whale sharks (Rhincodon typus) aggregate periodically in predictable 

locations offshore of Louisiana (Hoffmayer et al., 2007). Blue marlin migrate across the entire GOM 

in response to seasonal changes in sea surface temperature and productivity (Kraus et al., 2011). 

Bluefin tuna migrate from outside the GOM to spawn in the eastern GOM (Rooker et al., 2008). 

Yellowfin tuna (Thunnus albacares) migrate across the northern GOM in response to temperature 

and food availability. Many of the oceanic species associate with flotsam, which provides forage 

areas and nursery refuge.

Floating seaweed (Sargassum) (Section 8), jellyfishes, siphonophores, logs, and other 

debris attract juvenile and adult epipelagic fishes. Many species such as young jacks, filefishes, 

chubs, driftfishes, and dolphinfish associate with drifting objects, and larger predators forage around 

flotsam. Many fish species are closely associated with floating Sargassum at some point in their life 

cycle, but only two spend their entire lives there: the sargassumfish (Histro histrio) and the 

Sargassum pipefish (Syngnathus pelagicus). Most fish associated with Sargassum are temporary 

residents, such as juveniles of species that reside in shelf or coastal waters as adults (e.g., jacks, 

triggerfishes, and filefishes). However, several larger species of recreational or commercial 

importance, including dolphinfish (Coryphaena hippurus), yellowfin tuna (Thunnus albacares), 

blackfin tuna (Thunnus atlanticus), skipjack tuna (Katsuwonus pelamis), Atlantic bonito (Sarda 

sarda), little tunny (Euthynnus alletteratus), and wahoo (Acanthocybium solandri), feed on the small 

fishes and invertebrates attracted to Sargassum (Dooley, 1972; Bortone et al., 1977; Wells and 

Rooker, 2004a and 2004b).

As with coastal pelagic fishes, many of the epipelagic species associate with fixed or moored 

oil and gas platforms. Several other pelagic species such as shortfin mako (Isurus oxyrinchus), 

longfin mako (Isurus paucus), silky shark (Carcharhinus falciformis), oceanic whitetip shark 

(Carcharhinus longimanus), dolphinfish, blackfin tuna, yellowfin tuna, blue marlin, sailfish, and 

wahoo are known to occur around blue water platforms (Gallaway and Lewbel, 1982; Franks, 2000; 

Stanley and Wilson, 2000). Most of these species associate with offshore structures in a transient 

fashion, usually in response to the availability of prey.

4.3.2.2 Midwater Fishes

Below the epipelagic zone the water column may be layered into mesopelagic (200 to 

1,000 m [656 to 3,280 ft]) and bathypelagic (>1,000 m [3,280 ft]) zones. Taken together, these two 

zones and their inhabitants may be referred to as midwater. In the mesopelagic zone of the GOM, 

fish assemblages are numerically dominated by lanternfishes, bristlemouths, and hatchetfishes 

(Gartner et al., 1987; Hopkins et al., 1997; Bangma and Haedrich, 2008). Lanternfishes are small 

silvery fishes that can be extremely abundant, often responsible for the deep scattering layer in 
Gulf of Mexico G&G Activities Programmatic EIS E-89

sonar images of the deep sea. Lanternfishes and other mesopelagic fishes spend the daytime in 

depths of 200 to 1,000 m (656 to 3,280 ft) but migrate vertically at night into food-rich, near-surface 

waters. Mesopelagic fishes, while less commonly known, are important ecologically because they 

transfer significant amounts of energy between mesopelagic and epipelagic zones over each daily 

cycle. Lanternfishes are important prey for meso- and epipelagic predators (e.g., tunas), and 

particularly the mesopelagic dragonfishes (Hopkins et al., 1997).

Deeper dwelling bathypelagic fishes inhabit the water column at depths >1,000 m (3,280 ft). 

This group is composed of little known species such as snipe eels, slickheads, deep-sea anglers, 

bigscales, and whalefishes (McEachran and Fechhelm, 1998). Most species are capable of 

producing and emitting light (bioluminescence) to aid in communicating in an environment devoid of 

sunlight. Little scientific information is available on bathypelagic fishes of the GOM.

4.3.2.3 Demersal Fishes

Demersal fishes are those that are in direct contact with the substrate or hover above it from 

the shelf-slope transition down to the abyssal plain. The deep-sea demersal fish fauna in the GOM 

includes approximately 300 species. The most diverse group is the cod-like fishes (e.g., hakes and 

grenadiers), followed by eels, cusk-eels, sharks, and flatfishes, as summarized by Pequegnat 

(1983), Gallaway (1988), and Powell et al. (2003). In general, fish species diversity decreases with 

increasing water depth. The highest diversity and density of demersal fishes is found along the 

continental slope in the eastern GOM. Deep-sea demersal fishes consume a wide variety of 

organisms, including other fishes as well as epifaunal, infaunal, meiofaunal, and planktonic 

invertebrates.

4.4 ESSENTIAL FISH HABITAT

The Magnuson-Stevens Fisheries Conservation and Management Act (MSFCMA) 

(16 U.S.C. § 1801-1882) established regional Fishery Management Councils (FMCs) and mandated 

that Fishery Management Plans (FMPs) be developed to responsibly manage exploited fish and 

invertebrate species in U.S. Federal waters. When Congress reauthorized the MSFCMA in 1996 as 

the Sustainable Fisheries Act, several reforms and changes were made. One change was to charge 

the NMFS with designating and conserving EFH for species managed under existing FMPs. This is 

intended to minimize, to the extent practicable, any adverse effects on habitat caused by fishing or 

non-fishing activities, and to identify other actions to encourage the conservation and enhancement 

of such habitat.

The EFH is defined as “those waters and substrate necessary to fish for spawning, breeding, 

feeding or growth to maturity” (16 U.S.C. § 1801(10)). The EFH final rule summarizing EFH 

regulation (50 CFR part 600) outlines additional interpretation of the EFH definition. Waters, as 

defined previously, include “aquatic areas and their associated physical, chemical, and biological 

properties that are used by fish, and may include aquatic areas historically used by fish where 

appropriate.” Substrate includes “sediment, hard bottom, structures underlying the waters, and 

associated biological communities.” Necessary is defined as “the habitat required to support a 
E-90 Expanded Affected Environment Information

sustainable fishery and the managed species’ contribution to a healthy ecosystem.” “Fish” includes 

“finfish, mollusks, crustaceans, and all other forms of marine animal and plant life other than marine 

mammals and birds,” whereas “spawning, breeding, feeding or growth to maturity” covers the 

complete life cycle of those species of interest.

The AOI covers a broad geographic and bathymetric region that features a dynamic mix of 

fishery species. Fishery resources within the AOI are primarily managed by the GMFMC utilizing 

seven FMPs. The seven FMPs manage 182 fishery species grouped as follows: reef fish (31), 

coastal migratory pelagic fish (3), red drum (1), shrimp (4), spiny lobster (1), and corals (142). The 

EFH for managed fisheries is described in the respective FMPs.

Migratory pelagic fish species are jointly managed by the GMFMC and South Atlantic Fishery 

Management Council (SAFMC). In addition to these FMPs, 39 highly migratory fishery species 

(tunas [5], billfishes [5], sharks [28], and swordfish [1]) occurring in the GOM are managed by the 

Highly Migratory Species Management Unit within the Office of Sustainable Fisheries under the 

NMFS.

BOEM, the Bureau of Safety and Environmental Enforcement (BSEE), and NMFS are under 

a programmatic EFH consultation. Pursuant to section 305(b) of the MSFCMA, Federal agencies 

are required to consult with the NMFS on any action that may result in adverse effects on EFH. In 

March 2000, BOEM consulted with the NMFS’ Southeast Regional Office, resulting in the preparing 

of a NMFS regional finding for the GOM that allows BOEM to incorporate the EFH assessments into 

National Environmental Policy Act (NEPA) documents as an appendix.

The programmatic EFH consultation was initiated during the 2012-2017 WPA/CPA Multisale 

EIS review process, continued with the NMFS’ conservation recommendations, and formally 

concluded with BOEM’s response to the NMFS’ conservation recommendations. The EFH 

assessment, which can be found in Appendix D of the 2012-2017 WPA/CPA Multisale EIS (USDOI, 

BOEM, 2012a), describes the OCS proposed activities, analyzes the effects of the proposed 

activities on EFH, and identifies proposed mitigation measures. It also includes an evaluation of the 

G&G activities described in this Programmatic EIS.

The programmatic consultation continues with active coordination among the NMFS, BOEM, 

and BSEE. This coordination includes annual reports from BOEM to the NMFS, meetings with GOM 

staff, discussions of mitigation, and other relevant topics.

5 BENTHIC COMMUNITIES

Chapter 4.5.1 of this Programmatic EIS provides the succinct description of the affected 

environment for benthic communities in sufficient detail to support the impact analyses. The 

following descriptions provide additional, expanded information.
Gulf of Mexico G&G Activities Programmatic EIS E-91

The benthic environment of the AOI is complex, with bathymetry and biological, geological, 

and geophysical features varying widely (Rowe and Kennicutt, 2009). The AOI encompasses 

several habitats within water depths ranging from <200 m (656 ft) near State boundaries along the 

northern edge of the AOI to depths of nearly 3,500 m (11,483 ft) in the south-central GOM. It is 

important to note that the AOI extends beyond the planning areas to account for the acoustic energy 

that could propagate beyond BOEM jurisdictional boundaries; as such, the description of benthic 

communities in the AOI includes benthic communities within the Florida Keys, Dry Tortugas National 

Park, Tortugas Ecological Reserve, and other sensitive shallow-water habitats within State waters 

(3 or 9 nmi [5.6 or 16.7 km; 3.5 or 10.6 mi] from shore).

The benthic faunal assemblages of the GOM can be loosely grouped by depth. Biological 

diversity is relatively low on the continental shelf, where a small number of species are locally 

abundant in high densities (Rowe and Kennicutt, 2009). Benthic fauna at water depths >200 m 

(656 ft) are dominated by infaunal (living in bottom sediments) worms, crustaceans (e.g., crabs, 

lobsters, shrimps), and mollusks (e.g., clams, scallops, oysters). Deposit-feeding polychaetes 

(segmented marine worms) are the most abundant organisms on the continental shelf (USDOI, 

BOEM, 2012a, 2013a, and 2013b).

The deepwater GOM can be separated into the continental slope and abyssal plain. The 

continental slope is unique, being influenced by the hydrographic processes of both the shelf and the 

abyssal plain. The continental slope includes varying ranges of productivity and, consequently, 

several different faunal assemblages. Across the GOM, the slope consists of fine muddy sediments 

that support high-diversity, low-density benthic communities (Rowe and Kennicutt, 2009). Demersal 

fishes, gastropods (snails), polychaetes, asteroids (sea stars), and other echinoids (i.e., sand 

dollars, sea cucumbers) are common in this zone (USDOI, BOEM, 2013a).

The abyssal plain (>1,000 m [3,280 ft]) contains the majority of benthic habitat within the 

AOI. The number of invertebrate species is higher and the number of fish species lower in the 

abyssal plain compared with shelf or slope habitats. In waters deeper than 2,300 m (7,546 ft), fishes 

are rare and echinoderms (i.e., sea stars, sand dollars, and sea cucumbers) are the dominant 

megafauna.

Although the GOM is dominated by soft bottom communities (Section 5.1), hard bottom 

(Section 5.2) and chemosynthetic (Section 5.3) communities are scattered throughout. Section 5.4

provides a discussion of listed and candidate coral species.

5.1 SOFT BOTTOM COMMUNITIES

The seafloor of the GOM is composed primarily of muddy and sandy sediments. Sediments 

in the eastern GOM consist primarily of sand, while sand, silt, and clay are the dominant constituents 

of sediment in the central and western GOM (Jenkins, 2011). Grain size is the most important 

substrate characteristic affecting the distribution of benthic fauna (Vittor, 2000) and is often used to 
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categorize faunal assemblages. Vittor (2000) divided the northern GOM continental shelf into the 

following four assemblages:

• Assemblage I: Nearshore sandy bottom with <5 percent silt/clay. This 

assemblage is found across the GOM and is dominated by filter- and depositfeeding mollusks and crustaceans as well as carnivorous polychaetes and 

mollusks.

• Assemblage II: Silty, sandy bottoms in shallower areas (<100 m [328 ft]) that 

are spread across the continental shelf. These areas contain >5 percent silt and 

generally are found in areas with terrigenous (land-based) sediments such as 

Mobile Bay. Dominant fauna are detritivores, especially polychaetes. 

Suspension and filter feeders, including crustaceans and polychaetes, are 

present as well.

• Assemblage III: Patchy areas with coarse sand and shell hash. These areas 

are found in shallow and deep waters and are dominated by motile benthic 

megafauna, filter feeders, and epibenthic deposit and suspension feeders.

• Assemblage IV: Fine sandy/silty sediments in waters deeper than 100 m 

(328 ft). This assemblage is dominated by demersal and burrowing depositfeeding polychaetes and mollusks as well as carnivorous polychaetes.

The continental slope is a complex transitional zone with varying ranges of productivity and 

faunal assemblages. Faunal assemblages of the continental slope and abyssal zone are described 

in BOEM’s 2012-2017 WPA/CPA Multisale EIS as follows:

• Shelf-Slope Transition Zone (150 to 450 m [490 to 1,475 ft]): A highly 

productive zone dominated by demersal fishes, asteroids, gastropods, and 

polychaetes.

• Archibenthal Zone Horizon A (475 to 740 m [1,560 to 2,430 ft]): Sea 

cucumbers become more abundant in this zone and demersal fishes become 

less abundant. Gastropods and polychaetes are also numerous.

• Archibenthal Zone Horizon B (775 to 950 m [2,545 to 3,120 ft]): Demersal 

fishes, asteroids, and echinoids are found in large numbers. Gastropods and 

polychaetes are also common.

• Upper Abyssal Zone (1,000 to 2,000 m [3,280 to 6,560 ft]): This zone has fewer 

fishes than are found in shallower depths. The number and types of invertebrate 

species increase, especially sea cucumbers and galatheid crabs.

• Mesoabyssal Zone (2,300 to 3,000 m [7,545 to 9,840 ft]): Few fish species are 

found in this deepwater zone. Echinoderms dominate the fauna.
Gulf of Mexico G&G Activities Programmatic EIS E-93

• Lower Abyssal Zone (3,200 to 3,800 m [10,500 to 12,470 ft]): The large 

asteroid Dytaster insignis is the dominant megafaunal species.

Fauna of the GOM can be divided into megafauna, macrofauna, meiofauna, and microbiota. 

Each of these groups is described briefly in the following subsections.

5.1.1 Megafauna

Megafauna are classified as organisms large enough to be easily distinguished with the 

naked eye. In the GOM, most megafauna are crustaceans, echinoderms, or demersal fishes 

(USDOI, BOEM, 2012a). Megafaunal distributions in the GOM traditionally have been described by 

depth, as discussed previously. It should be noted that, among other sampling issues, the methods 

used to sample megafauna may be selective and otherwise uncalibrated, which will result in 

variation in the estimates of species composition and abundances reported in literature. For 

example, in the Northern Gulf of Mexico Continental Slope (NGMCS) study of the 1980s, bottomtrawl samples were dominated by decapod crustaceans, but seafloor photographs showed that sea 

cucumbers, bivalves, and sea pens were the most common seafloor megafauna (Gallaway et al., 

2003). Gallaway et al. (2003) found that the composition of megafauna changes continuously with 

depth, resulting in gradual changes in the occurrence and abundance of species between the 

discrete zones used to describe the distribution of megafauna. Upper slope fauna is found to a 

depth of approximately 1,200 m (3,937 ft) (mostly decapods and fishes), and a distinct deepwater 

faunal assemblage is found deeper than 2,500 m (8,202 ft) (mostly echinoderms). A transition zone 

between 1,200 and 2,500 m (3,937 and 8,202 ft) typically has low faunal abundances and low 

diversity (Gallaway et al., 2003).

5.1.2 Macrofauna

Macrofauna are described as organisms larger than 0.3 millimeters (mm) but smaller than 

megafauna (USDOI, BOEM, 2012a). The NGMCS study (Gallaway et al., 2003) obtained 

69,933 individual macrofauna from 1,548 taxa. Further processing of samples by taxonomic experts 

resulted in classification of individual animals to 1,107 species. Some of the animals collected could 

not be classified to species. Polychaetes were the most common organism found in the study and 

included 407 species. Other macrofauna obtained in samples (in order of abundance) were 

nematodes (roundworms), ostracods and harpacticoid copepods (small crustaceans), bivalves 

(clams, oysters), tanaids (small shrimp-like animals), bryozoans (moss animals), isopods 

(crustaceans with seven pairs of legs), amphipods (small crustaceans), and others (Gallaway et al., 

1988). Density of benthic macrofauna ranged from 518 to 5,369 individuals/m2

, though transects in 

the central GOM had a higher mean density of macrofauna (4,938 individuals/m2

) than transects in 

the eastern (4,869 individuals/m2

) or western GOM (3,389 individuals/m2) (Gallaway et al., 2003).

5.1.3 Meiofauna

Meiofauna are small (0.063 to 0.3 mm) organisms. The most numerically abundant 

meiofauna in the GOM are nematodes and harpacticoid copepods, and those present in the greatest 
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biomass are polychaetes and ostracods (Gallaway et al., 2003). Nematodes, harpacticoid 

copepods, polychaetes, ostracods, and kinorhynchs (segmented wormlike invertebrates) made up 

98 percent of the meiofauna identified in samples taken by Gallaway et al. (2003) in the NGMCS 

study. Meiofauna are considerably more abundant than macrofauna or megafauna, with an overall 

density of 707,000 individuals/m2 in the area of study (Gallaway et al., 1988). Like megafauna and 

macrofauna, meiofaunal abundance appears to decrease with increasing depth. There is evidence 

that meiofaunal abundance can be locally high at greater depths concurrent with the presence of 

deepwater chemosynthetic communities (Gallaway et al., 2003).

5.1.4 Microbiota

Microbiota are organisms smaller than 0.063 mm. This poorly understood group consists 

primarily of bacteria with a small contribution from other microbenthos. Little data are available on 

the density of microbiota in the deepwater GOM. Cruz-Kaegi (1998) estimated the density of 

bacteria sampled from the GOM continental slope by counting (with epifluorescence microscopy 

techniques) the number of dyed bacteria in subsamples. The biomass of bacteria in samples was 

estimated using image processing of dyed bacteria photographs to estimate the volume of bacteria, 

literature estimates of bacterial carbon content (Bratbak and Dundas, 1984), bacteria density 

estimates, and adjustment for subsample volume. Estimates of bacterial biomass were 2.37 grams 

of carbon per square meter (g C/m2

) for the GOM slope and 0.37 g C/m2 for the abyssal plain. CruzKaegi (1998) found that bacteria, meiofauna, and macrofauna contributed on average 67, 13, and 

20 percent, respectively, to total benthic biomass.

5.2 HARD BOTTOM COMMUNITIES

While less common than ubiquitous soft bottom environments in the GOM, hard bottom 

environments are scattered across the GOM (Figure 4.5-1 of this Programmatic EIS). This section 

focuses on deepwater benthic communities; for discussion of benthic chemosynthetic communities 

in the GOM, refer to Section 5.3. 

The GMFMC manages GOM corals through a coral management unit that encompasses 

142 species of stony and soft corals, including fire or stinging corals, stony corals, and black corals. 

The EFH for the coral management unit includes the total distribution of coral species and life stages 

throughout the GOM, including coral reefs in the North and South Tortugas Ecological Reserves, 

East and West FGBs, McGrail Bank, and the southern portion of Pulley Ridge. Additionally, EFH 

includes hard bottom areas on the scattered pinnacles and banks from Texas to Mississippi, the 

shelf edge at the Florida Middle Grounds, the southwest tip of the Florida Reef Tract, and hard 

bottom offshore of Florida from approximately Crystal River south to the Florida Keys (GMFMC, 

2005).

5.2.1 Deepwater Coral Communities

Corals that rely on photosynthetic zooxanthellae (algae in the genus Symbiodinium) cannot 

live below the euphotic zone (where sunlight penetrates). Although the deepwater benthic 
Gulf of Mexico G&G Activities Programmatic EIS E-95

environment of the GOM consists primarily of mud and silt, occasional carbonate hard bottom exists 

that supports ahermatypic (non-reef building) corals. Moore and Bullis (1960) first described a 

deepwater coral community in the GOM and retrieving >136 kg (300 lb) of Lophelia pertusa. 

Deepwater coral reefs are now known to exist throughout the GOM. To help determine where such 

reefs may exist, BOEM has examined seismic data to identify areas of high reflectivity that indicate 

hard bottom areas. As of 2012, the database included >28,000 areas of anomalous (higher than 

typical) reflectivity that indicate possible hard bottom where deepwater reefs could exist (Shedd 

et al., 2012). These estimates suggest that deepwater reefs in the GOM may not be as rare as once 

thought (Shedd et al., 2012). Hard bottom areas of the GOM are thought to have been created by 

the precipitation of calcium carbonate by chemosynthetic bacteria. Although only a small number of 

the overall hard bottom patches have been investigated, those that have been studied suggest that 

most of the hard bottom areas available in the GOM have been colonized by chemosynthetic coral 

reefs created by bacteria living off hydrocarbon seepages (Shedd et al., 2012). Colonies of 

L. pertusa, as found in the Moore and Bullis (1960) trawls, are most commonly found in the upper 

shelf, but colonies have been found as deep as 3,000 m (9,842 ft) (USDOI, BOEM, 2012a and 

2013a). These findings suggest that suitable hard bottom areas exist throughout the AOI that could 

harbor deepwater coral communities as well as non-reef forming deepwater corals.

As discussed in Chapter 4.5.1 of this Programmatic EIS, at least one deepwater gorgonian 

coral community in Mississippi Canyon Block 294 is known to have been affected by the Deepwater 

Horizon explosion, oil spill, and response. White et al. (2012) documented highly localized damage 

to a coral community where 86 percent of corals showed signs of impact. Tests of flocculent oilbased material collected from the community confirmed that the oil was from the Deepwater Horizon

explosion and oil spill. Other continental shelf coral communities are discussed further in Sections 

5.2.2 through 5.2.4. 

5.2.2 Live Bottoms (Pinnacle Trend)

Vertical, high-relief, hard bottom features with extensions up to 15 m (49 ft) above the 

surrounding seafloor in the Gulf of Mexico OCS were reported by Ludwick and Walton (1957). 

These “pinnacles” are known to exist in 74 OCS lease blocks in a 64 x 16 mi (103 x 26 km) area of 

the northeastern CPA, particularly in parts of the Main Pass, Viosca Knoll, and Destin Dome Areas 

(Figure 4.5-2 of this Programmatic EIS). In Notice to Lessees and Operators (NTL) 2009-G39, 

BOEM (formerly the MMS) describes the Pinnacle Trend as “small, isolated low to moderate relief 

carbonate reef features or outcrops of unknown origin or hard substrates exposed by erosion that 

provide surface area for the growth of sessile invertebrates and attract large numbers of fish.

The Pinnacle Trend comprises several loosely organized hard bottom habitats of high and 

low relief (USDOI, BOEM, 2012a). The low-relief areas may rise only 1 to 2 m (3 to 7 ft) from the 

seafloor; however, both low- and high-relief areas provide usable hard bottom habitat. Low-relief 

hard bottom areas are discussed in Section 5.2.3. The Pinnacle Trend contains a variety of 

geologic features that provide a suitable environment for hard bottom biota, including patch reefs, 

flat-top reefs, reef-like mounds, ridges, scarps, and depressions (USDOI, BOEM, 2012a).
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High-relief pinnacles can rise as much as 20 m (66 ft) from the surrounding seafloor and be 

500 m (1,640 ft) in diameter (Thompson et al., 1999), though most are <200 m (656 ft) wide at their 

base (Gittings et al., 1992). Ludwick and Walton (1957) hypothesized that the pinnacles might be 

coral reefs that were gradually drowned to unsuitable depths with sea-level rise, a theory supported 

by Brooks (1991). The pinnacles are located in depth ranges of 74 to 82 m (243 to 269 ft) and 

105 to 120 m (344 to 394 ft). The relatively steep sides and tops of the pinnacles provide prime hard 

bottom habitat for coralline algae, sponges, octocorals (sea fans and sea whips), crinoids (sea lilies), 

byrozoans, and demersal fishes. Ahermatypic corals may be present in deeper waters (Continental 

Shelf Associates, Inc., 1992). Hermatypic (reef-building) coral typically do not live at the depth 

associated with the Pinnacle Trend due to a lack of available light. However, a hermatypic reef was 

observed with up to 60 percent live coral cover in 60 to 75 m (197 to 246 ft) of water near Pulley 

Ridge, on the southwest Florida platform margin (Jarrett et al., 2005).

The biological diversity of the fauna on the pinnacles has been found to be directly related to 

the height of the pinnacle feature (Gittings et al., 1992; Thompson et al., 1999). Biological diversity 

also increases with greater distance from the Mississippi River Delta as water turbidity decreases 

(Gittings et al., 1992). Biological diversity is highest on the tops of high-relief pinnacles. Near the 

seafloor, a persistent nepheloid (turbidity) emanating from the Mississippi River outflow precludes 

the colonization of most sessile organisms. Only a few upright invertebrate species such as sea 

whips and sea fans can withstand the high turbidity. High turbidity-tolerant fauna include comatulid 

crinoids, the ahermatypic coral Rhizopsammia manuelensis, and black coral (Antipathes spp.; 

deepwater tree-like coral) (Gittings et al., 1992). Roughtongue bass is the dominant fish species in 

the higher turbidity region near the base of high-relief pinnacles (Weaver et al., 2002).

The walls of pinnacles provide habitat supporting higher biological diversity. Continental 

Shelf Associates, Inc. (1992) reported at least 34 species of epifauna on the walls of a high-relief 

pinnacle, including black corals R. manuelensis and Antipathes spp., wire coral (Cirrhipathes 

leukeni), and soft coral and sea whips (Ellisella sp.). The crests of pinnacles also show high 

diversity with species assemblages similar to those on the pinnacle walls, though the gorgonian 

coral Bebryce sp. was most common (Gittings et al., 1992). High-relief pinnacles also provide 

habitat for fishes. Roughtongue bass, red barbier, greenband wrasse, and yellowtail reeffish are the 

more frequent members of the fish assemblages found near pinnacle crests (Weaver et al., 2002).

5.2.3 Live Bottoms (Low Relief)

Low-relief hard bottom habitats are found in the CPA and WPA. Low-relief live bottom 

habitats are found in the extreme northeastern corner of the CPA but are much broadly distributed in 

the EPA. BOEM has instituted a Live Bottom (Low Relief) Stipulation to protect low-relief hard 

bottom habitats from impact by OCS energy exploration activities. NTL 2009-G39 defines low-relief 

habitat as “seagrass communities, areas that contain biological assemblages consisting of sessile 

invertebrates living upon and attached to naturally occurring hard or rocky formations with rough, 

broken, or smooth topography; and areas where a hard substrate and vertical relief may favor the 

accumulation of sea turtles, fishes, or other fauna.” In addition, BOEM conducts case-by-case 
Gulf of Mexico G&G Activities Programmatic EIS E-97

reviews of plans, pipeline applications, structure removal applications, and ancillary activity 

applications in order to prevent routine bottom-disturbing activities from occurring within adequate 

distances from live bottom (low relief) areas.

Live Bottoms of the Mississippi-Alabama Shelf

Hard bottom areas made of sedimentary rock are found in shallow waters (18 to 40 m [60 to 

130 ft]) along the inner and middle Mississippi-Alabama Shelf and at the head of the De Soto 

Canyon. These hard bottom areas include many different habitat types, including reef-like 

structures, rubble fields, flat rocks, limestone ledges, rocky outcrops, and clustered reefs 

(Schroeder, 2000). Organisms that inhabit these shallow-water features include ahermatypic corals, 

soft corals, sponges, bryozoans, crinoids, fishes (Thompson et al., 1999), and algal communities 

(Brooks, 1991; Gittings et al., 1992). Schroeder et. al. (1988) described four low-relief, live bottom 

areas west of De Soto Canyon: Southeast Bank; Southwest Rock; Big Rock/Trysler Grounds; and 

17 Fathom Hole. Common fauna in low-relief habitats included the colorful sea whip (Leptogorgia 

virgulata), regal sea fan (Lophogorgia hebes), hydroids (stalked predators related to jellyfish), and 

byrozoans (Schroeder et al., 1988). Various other small patches of hard bottom have been identified 

on the Mississippi-Alabama Shelf (Shipp and Hopkins, 1978; Benson et al., 1997). Fauna observed 

at these small sites were similar to those described by Brooks (1991), including sponges, non-reefbuilding hard corals such as the diffuse ivory bush coral (Oculina diffusa), soft corals/sea fans, black 

and wire corals, and tropical fishes.

Live Bottoms of the West Florida Shelf

Most of the low-relief hard bottom in the GOM is found on the West Florida Shelf. Live 

bottoms are widely scattered on the West Florida Shelf, and BOEM has designated all OCS lease 

blocks on the West Florida Shelf out to 100-m (328-ft) depth as Live Bottom (Low Relief) Stipulation 

Blocks. The West Florida Shelf is flat, stable karst limestone covered in places by carbonate sand. 

Ephemeral hard bottom exists in many areas due to seasonally shifting sands that periodically 

expose the underlying bedrock. Faunal cover usually is limited on these ephemeral hard bottom 

patches, but some species of sea whips and sea fans can grow quickly enough and survive despite 

occasional partial burial (USDOI, BOEM, 2012a and 2013a). These patches usually are dominated 

by various algae species, including green algae (Chlorophyta) species such as Halimeda spp., 

Anadyomene menziesii, and Caulerpa spp.; coralline algae Cryptonemiales and Pessyonnelia 

simulans; and various brown (Phaeophyceae) and red (Rhodophyta) algae (Woodward-Clyde and 

Continental Shelf Associates, Inc., 1983).

Other portions of the West Florida Shelf have higher relief areas that are permanently 

exposed hard bottom. The NMFS has designated the following areas on the West Florida Shelf as 

Habitat Areas of Particular Concern (HAPCs): Madison Swanson Marine Reserve; Florida Middle 

Grounds; and Pulley Ridge. Other areas of permanent hard bottom on the West Florida Shelf 

include Steamboat Lumps Marine Reserve and Sticky Ground Mounds. Each of these areas is 

briefly discussed in the following subsections.
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Madison Swanson Marine Reserve

A detailed discussion of the Madison-Swanson Marine Reserve can be found in Section 7.2. 

Briefly, the reserve is the 400 km2 (155 mi2

) of protected area approximately 80 km (50 mi) south of 

Apalachicola, Florida, that consists of small outcrops as well as a few higher relief pinnacles (up to 

9 m [30 ft] high) (USDOI, BOEM, 2013a) at depths between 60 and 140 m (197 and 459 ft). 

Sponges, sea fans, corals (including bush/tree corals [Oculina spp.]), echinoderms, and crabs reside 

within the reserve (USDOI, BOEM, 2013a).

Florida Middle Grounds

The Florida Middle Grounds are a complex series of carbonate hard bottom outcroppings 

located approximately 138 km (86 mi) south of Apalachee Bay, Florida. The outcroppings are 

spread over an area of approximately 1,193 km2 (460 mi2

), with relief up to 17 m (56 ft). The Florida 

Middle Grounds are the northernmost extent of hermatypic corals in the U.S. (Puglise and Kelty, 

2007), and the fauna most closely resemble that found at tropical reefs. The branching fire coral 

(Millepora alcicornis), pineapple coral (Dichocoenia stokesii), and ten-ray star coral (Madracis 

decactis) are common, as are octocorals, sea fans of the genus Muricea, and the giant barrel 

sponge (Xestospongia muta) (Naar et al., 2007). Other fauna include hydroids, anemones, 

mollusks, crustaceans, echinoderms, polychaetes, and fishes (Hopkins et al., 1977; Coleman et al., 

2004a). It should be noted that the Florida Middle Grounds are not considered a true coral reef 

because the lack of abundance of hermatypic corals does not allow for the successful accretion of a 

carbonate reef (USDOI, BOEM, 2013a).

Pulley Ridge

Pulley Ridge is a submerged shoal colonized by reef-building organisms after sea-level rise 

left it submerged (Jaap and Halley, 2008). Pulley Ridge is approximately 300 km (185 mi) long, 

trending north-south, with carbonate hard bottom ranging in depth from 60 to 90 m (197 and 295 ft) 

approximately 250 km (155 mi) west of Cape Sable, Florida. Vertical relief is approximately 10 m 

(33 ft) (Puglise and Kelty, 2007). The southernmost end of Pulley Ridge supports a unique coral 

reef system that harbors traditional reef-building corals containing zooxanthellae and is one of the 

deepest reefs on the North American continental shelf. The most common corals at the site are the 

lettuce corals Leptoseris cucullata and Agaricia sp. (Jaap and Halley, 2008). Red and green algae 

are prevalent in deeper portions of Pulley Ridge. Pulley Ridge is also a significant area for 

commercial fishing, with >90 fish species present in appreciable numbers (Jaap and Halley, 2008).

Steamboat Lumps Marine Reserve

A detailed discussion of the Steamboat Lumps Marine Reserve can be found in Section 7.2. 

Briefly, the Steamboat Lumps Marine Reserve is located 161 km (100 mi) south-southwest of Cape 

San Blas, Florida, and approximately 32 km (20 mi) southwest of the Florida Middle Grounds. 

Steamboat Lumps Marine Reserve encompasses approximately 357 km2 (138 mi2

) and consists of a 

relic reef (Hine and Locker, 2008) in water depths of 60 to 140 m (197 to 459 ft). Fauna in the 
Gulf of Mexico G&G Activities Programmatic EIS E-99

Steamboat Lumps Marine Reserve is typical of a deepwater reef and includes sponges, sea fans, 

black corals, bush/tree corals, echinoderms, and crustaceans (USDOI, BOEM, 2013a).

Sticky Ground Mounds

The Sticky Ground Mounds are a series of mounds located 185 km (115 mi) west of Tampa, 

Florida, in 120 to 130 m (394 to 427 ft) of water (USDOI, BOEM, 2013a). The mounds form a 

narrow 2-km (1.2-mi) wide band of patch reefs that may have originated from carbonate 

sedimentation caused by methane seeps, though this hypothesis has not been proven (Hine and 

Locker, 2008). The mounds range in size, but they are approximately 20 m (66 ft) in diameter with a 

vertical relief of 10 m (33 ft). Fauna on the mounds are similar to other deepwater reefs, with biota 

dominated by sponges, sea fans, black corals, corals, echinoderms, and crustaceans (USDOI, 

BOEM, 2012a and 2013a).

Florida Reef Tract

The portion of the Florida Reef Tract that is part of the AOI includes the Florida Keys, Dry 

Tortugas National Park, and Tortugas Ecological Reserve (North and South Areas). Detailed 

discussions of the protected areas within the Florida Reef Tract are discussed in Section 7.1. 

Unlike many of the other low-relief hard bottom habitats previously discussed, much of the Florida 

Reef Tract is shallow, mostly with water depths of <3 m (10 ft) (Chiappone and Sullivan, 1994). 

Octocorals Palmer’s eunicea (Eunicea palmeri), porous sea rods (Pseudoplexaura jiagellosa), and 

corky sea finger (Briareum asbestinum) are dominant, but red algae (Laurencia intricata) and green 

algae (Halimeda opuntia); sponges, including ethereal sponge (Dysidea etheria), scattered pore 

rope sponge (Aplysina fulva), and chicken liver sponge (Chondrilla nucula); and stony corals such as 

the lesser starlet coral (Siderastrea radians), clubtip finger coral (Porites porites), smooth stone coral 

(Solenastrea bournoni), knobby star coral (Solenastrea hyades), golfball coral (Favia fragum), and 

diffuse ivory bush coral are also common (Chiappone and Sullivan, 1994), along with the branching 

fire corals. In recent years, the diversity and abundance of corals has significantly declined within 

the Florida Reef Tract as a result of numerous factors such as disease, tropical storms, agricultural 

runoff, coastal development, and overfishing of keystone species (Donahue et al., 2008).

5.2.4 Topographic Features

In the GOM, the term “topographic features” specifically refers to the 37 submerged banks 

that are protected from oil and gas activities and described in NTL 2009-G39 as “isolated areas of 

moderate to high relief that provide habitat for hard bottom communities of high biomass and 

diversity and large numbers of plant and animal species, and support, as shelter or food, large 

numbers of commercially and recreationally important fisheries.” These banks are located in the 

WPA (21 banks) and CPA (16 banks) (Figure 4.5-2 of this Programmatic EIS). The topographic 

features are a result of a thick stratum of salt that is present beneath the GOM seafloor that formed 

during periods of lower sea level in geologic history (USDOI, BOEM, 2012a). When subjected to 

high pressures, salt can liquefy and protrude up through seafloor faults, causing rock layers to 

project above the seafloor. These formations are known as salt diapirs. This process forms hard 
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bottom habitat that can be colonized by reef organisms in areas that usually are dominated by soft 

bottom communities (USDOI, BOEM, 2012a). BOEM has mandated “No Activity Zones” around 

major topographic features in the GOM (USDOI, MMS, 2008) to protect these submerged banks 

from anchoring and other disturbances that may occur during oil and gas exploration and production 

activities.

Table 4.5-1 of this Programmatic EIS lists the topographic features in the GOM that are 

protected by BOEM as described in NTL 2009 G39. The MMS (USDOI, MMS, 2008) presented 

maps of all 37 protected areas and graphically displayed the protected zones around each bank. 

True coral reefs are found at the East and West FGBs in the WPA, McGrail Bank in the CPA, and 

Pulley Ridge in the EPA (USDOI, BOEM, 2012a and 2013a). The other topographic features listed 

in Table 4.5-1 of this Programmatic EIS have varying degrees of biological diversity and reef 

development, depending on depth, sedimentation rates, and habitat complexity. Although many of 

the banks are too deep to harbor true hermatypic coral reefs, they feature vast biological diversity 

including gorgonians, black corals, soft corals, sponges, echinoderms, crustaceans, polychaetes, 

and other invertebrates, as well as complex fish assemblages (USDOI, BOEM, 2012a and 2013a). 

Unlike the shallow, easily damaged Caribbean coral reefs, deep reefs (>70 m [230 ft]) of the GOM 

are influenced by only the strongest tropical storms, and even then usually only by increased 

turbidity near the seafloor (Rezak et al., 1990).

Detailed descriptions of the East and West FGBs, as well as other topographic features that 

are managed areas (i.e., Alderdice Bank, Bright Bank, Geyer Bank, McGrail Bank, Stetson Bank, 

and Sonnier Bank), are fully discussed in Sections 7.1 and 7.2. The topographic features of the 

GOM have been grouped based on location on the shelf (refer to Rezak et al., 1983). Following this 

grouping, banks of the three major shelf locations are summarized in the following subsections. A 

more complete discussion of these banks can be found in the Multisale EISs published by BOEM 

(USDOI, BOEM, 2012a and 2013a).

Shelf Edge Banks

The best examples of shelf edge banks are the East and West FGBs. These banks are at 

depths between 100 and 150 m (328 and 492 ft) and are within 12 km (7.5 mi) of each other. 

Vertical relief extends to approximately 116 m (380 ft) at the East FGB and approximately 130 m 

(425 ft) at the West FGB, making the water shallow (<20 m [66 ft]) at the crest of the banks (Rezak 

et al., 1983). The banks were formed by salt diapirs, as described previously. This allows for the 

development of a coral reef system that thrives in clear warm waters. Most of the reef-building 

corals are in water depths of <50 m (164 ft) primarily because deeper waters can fall below 19°C 

(66°F) in the winter months. Coral species of the reef-building zone include lobed star coral 

(Orbicella annularis), symmetrical brain coral (Diploria strigosa), great star coral (Montastraea 

cavernosa), stony/brain coral (Colpophyllia spp.), and mustard hill coral (Porites astreoides). The 

endangered elkhorn coral (Acropora palmata) was discovered at the West FGB in 2001 (Precht 

et al., 2006) and at the East FGB in 2005 (Precht et al., 2008). In deeper portions of the FGBs, the 
Gulf of Mexico G&G Activities Programmatic EIS E-101

biota is dominated by coralline algae, octocorals, sponges, echinoderms, leafy algae, and 

ahermatypic corals (Rezak et al., 1983).

Mid-Shelf Banks

Rezak et al. (1983) defined mid-shelf banks as those that are located in 80 m (262 ft) or less 

of water and have vertical relief of 15 to 50 m (49 to 164 ft). There are eight mid-shelf banks within 

the AOI (i.e., 29 Fathom Bank, 32 Fathom Bank, Claypile Lump Bank, Coffee Lump Bank, Stetson 

Bank, Fishnet Bank, Sackett Bank, and Sonnier Bank). Stetson Bank has a different species 

composition than other nearby banks, likely due to its geographic location near the northern limit for 

hermatypic corals (USDOI, BOEM, 2012a and 2013a). Reef-building corals at Stetson Bank include 

symmetrical brain coral, blushing star coral (Stephanocoenia intersepta), ten-ray star coral, yellow 

pencil coral (Madracis mirabilis), and fragile saucer coral (Agaricia fragilis) (DeBose et al., 2008). 

DeBose et al. (2008) identified >180 species of reef and schooling fishes as well as 644 species of 

invertebrates at Stetson Bank.

South Texas Banks

The South Texas Banks are unique because they were not formed by salt diapirs as is likely 

for banks with similar features elsewhere in the GOM. The South Texas Banks are most likely 

drowned reefs originating in the late Pleistocene to early Holocene Epochs, approximately 18,000 to 

10,580 years ago (Rezak et al., 1983). Typical species assemblages for the South Texas Banks 

include black corals (Cirrhipathes spp.), vase sponges (Ircinia campana), feather stars (comatulid 

crinoids), sea fans, deepwater alcyonarians (sea pens), small solitary corals, basket stars, American 

thorny oyster (Spondylus americanus), brachiopods (Argyrotheca barrettiana), arrow crabs 

(Stenorhynchus seticornis), hermit crabs, black urchin (Diadema antillarum), sea cucumber 

(Isostichopus spp.), and fireworms (Hermodice spp.). A diverse fish fauna is also present on these 

banks, including yellowtail reeffish, roughtongue bass, spotfin hogfish, reef butterflyfish (Chaetodon 

sedentarius), wrasse bass, tattler, gobies (Family Gobiidae), and blue angelfish (Rezak et al., 1983). 

A variety of migratory game and commercially fished species inhabit South Texas Banks, including 

red snapper, vermilion snapper (Rhomboplites aurorubens), greater amberjack (Seriola dumerili), 

great barracuda (Sphyraena barricuda), and cobia (Rezak et al., 1983).

5.2.5 Artificial Reefs

In addition to natural hard bottom habitats, artificial reefs provide suitable substrate for the 

proliferation of live bottom communities (SAFMC, 2009) and associated fish assemblages. Figure 

4.5-3 of this Programmatic EIS shows locations of artificial reefs in the AOI. Under the existing 

regulations, when oil and gas platforms reach the end of their useful life, they must be 

decommissioned and dismantled. The USDOI’s Rigs-to-Reefs policy, implemented by the BSEE 

and BOEM, is a process by which operators of decommissioned oil and gas platforms donate the 

material to coastal states for use as artificial reefs. The platforms are prepared for decommissioning 

and can be toppled in place, partially removed near the surface, or towed to existing reef sites with 

proper permits obtained by the State from the U.S. Army Corps of Engineers (USACE) and in 
E-102 Expanded Affected Environment Information

accordance with applicable guidelines to ensure navigational safety, infrastructure security, and 

environmental protection. Recreational diving and fishing, as well as commercial fisheries, benefit 

from artificial reefs, which provide an additional option for conserving, managing, and developing 

fishery resources and which can provide potential habitats for endangered or threatened species. 

As of 2013, there are >500 sites that have been approved by BSEE as artificial reef sites on the 

OCS (USDOI, BSEE, 2013).

Artificial reef habitats are an integral part of the coastal and shelf ecosystem in the GOM and 

support a diverse and special biological community (Steimle and Zetlin, 2000). Artificial reefs 

typically are composed of objects that provide hard surfaces such as metal, wood, and concrete that 

can support algae, barnacles, sponge, tubeworms, hydroids, anemones, oysters, and tunicates 

(Steimle and Figley, 1996; Steimle and Zetlin, 2000). The communities often are similar to those 

occurring on natural hard bottoms, though the size, composition, location, and age affect the 

structure and habitat value of these reefs (Steimle and Zetlin, 2000; Wilson et. al., 2003).

The presence of oil and gas platforms (active, decommissioned, and sunken) adds areas of 

hard bottom to the dominantly soft bottom AOI (Stanley and Wilson, 2000). Artificial reefs can help 

enhance the amount of available hard bottom and create habitat for hard and soft corals and 

associated fauna. Wilson et al. (2003) concluded that free-standing oil and gas platforms supported 

significantly higher fish biomass and densities than those found around dismantled rigs or natural 

reefs. Artificial reefs created by dismantled rigs were found to have similar fish biomass as the 

upper terrace of a natural reef at the West FGB. The fish species composition at the West FGB was 

found to be composed of more reef-dependent species, while the species at artificial reefs generally 

were more pelagic in nature. Fish densities tended to be 10 to 1,000 times greater around artificial 

reefs than was found in surrounding open water soft bottom habitats (Wilson et al., 2003). Boswell 

et al. (2010) found similarly high fish densities around the Freeport Sulphur Mine Artificial Reef in the 

northern GOM. Wilson et al. (2003) provided support for the hypothesis that dismantled oil and gas 

platforms can create effective hard bottom habitat for reef organisms.

A more recent study has identified reef-building corals (mostly ten-ray star coral, symmetrical 

brain coral, and great star coral) and non-reef-building corals (mostly diffuse ivory bush coral and 

hidden cup coral [Phyllangia americana]) on 48 oil and gas platforms near the FGBs (Sammarco 

et al., 2008). Corals were more commonly found on platforms at the shelf edge than inshore, and 

brooding coral species were more effective than broadcasters at colonizing the extremely patchy 

hard bottoms created by oil and gas platforms (Sammarco et al., 2008). It is important to note that 

the majority of corals on decommissioned platforms are invasive cup corals (Tubastrea sp.), which 

can number in the hundreds of thousands of colonies on a single structure (Sammarco, 2008). 

These invasives do not contribute to reef building, and it is not known if these species are 

opportunists taking advantage of an open ecological niche or if they are excluding other native 

species from using available habitat (Sammarco et al., 2010). Sammarco (2014) showed that some 

Tubastrea species were existing at greater depths than in its native range and appears to readily 

outcompete native sessile epibenthic organisms. Artificial reefs created by existing and future oil 
Gulf of Mexico G&G Activities Programmatic EIS E-103

and gas infrastructure may contribute alternative habitat for corals and associated reef fauna by 

creating a complex habitat in a mostly featureless, soft bottom seafloor.

5.3 CHEMOSYNTHETIC COMMUNITIES

Chemosynthetic organisms are unique in that they use a carbon source other than the 

photosynthesis-based food webs that support all other life on Earth. Chemosynthetic bacteria have 

the ability to oxidize the chemicals present in seafloor vents (often hydrogen sulfide, hydrogen gas, 

or ammonia) into organic molecules used to produce biomass (often sugars). Since they were first 

discovered at the base of the Florida Escarpment in 1983 (Paull et al., 1984), more than 

70 chemosynthetic communities have been found in the GOM (USDOI, BOEM, 2012a and 2013a) 

and it is likely that many more exist (Figure 4.5-1 of this Programmatic EIS). All known 

chemosynthetic communities in the GOM are found in deep water (>300 m [984 ft]), well beyond the 

boundary of the continental shelf (USDOI, BOEM, 2012a). There is a relationship between 

commercial hydrocarbon discoveries in the GOM and the presence of chemosynthetic communities 

(Sassen et al., 1993). Most of the oil present in the GOM is found in geologic layers originating from 

the Upper Jurassic to Upper Cretaceous Periods (Sassen et al., 1993), while most hydrocarbon 

seeps are in areas where there is little sediment cover over underlying strata (USDOI, BOEM, 2012a 

and 2013a). Seeps occur where hydrocarbons can vertically migrate through faults or other conduits 

to the surface, a process which occurs slowly on the geologic time scale. Many areas that fit these 

general descriptions have been seismically surveyed, and more than 28,000 seismic amplitude 

anomalies have been identified (Shedd et al., 2012), some of which have been proven to harbor 

chemosynthetic communities (USDOI, BOEM, 2013a).

Chemosynthetic communities have been classified into four general types based on the 

dominant seep organism (MacDonald et al., 1990): those dominated by vestimentiferan tube worms 

(Lamellibrachia cf. brahma and Escarpia sp.), mytilid mussels (Bathymodiolus spp.), vesicomyid 

clams (Vesicomya cordata), and infaunal lucinid or thyasirid clams (Lucinoma sp. or Thyasira sp.). 

Each of these dominant organisms creates unique seep communities based on differing faunal 

density, chemical usage, and associated heterotrophic (non-carbon fixing) fauna (USDOI, BOEM, 

2012a). Powell (1995) found that, after a disturbance event where a large percentage of the 

dominant fauna were killed, the same chemosynthetic species recolonized the site.

Growth rates of many organisms in these communities are extremely slow, averaging 

approximately 2.5 mm per year for tube worms of the genus Lamellibrachia (Fisher, 1995). 

However, mytilid mussels have been found to reach reproductive age relatively quickly, with growth 

rates slowing in adulthood (Fisher, 1995). These factors lead to long-lived individuals and 

communities; Powell (1995) estimated that some clam and mussel communities at chemosynthetic 

sites have been present in the same location for 500 to 4,000 years. Powell (1995) noted that many 

sites stayed biologically and geologically, with most communities showing no evidence of changes in 

the dominant faunal organisms over time. Other heterotrophic organisms that are often found at 

chemosynthetic sites include a variety of mollusks, crustaceans, and echinoderms (Carney, 1994), 

as well as autotrophic (carbon-fixing) and non-chemosynthetic bacterial mats (MacDonald, 2002).
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5.4 LISTED AND CANDIDATE SPECIES

Two coral species were listed under the ESA as threatened in 2006: elkhorn coral (Acropora 

palmata) and staghorn coral (A. cervicornis). Following a petition in 2009 from the Center for 

Biological Diversity (2009) to list 83 species of reef-building corals under the ESA, the NMFS issued 

a Final Rule (79 FR 67356), listing five additional Caribbean corals as threatened under the ESA: 

pillar coral (Dendrogyra cylindrus); lobed star coral (Orbicella annularis); mountainous star coral 

(Orbicella faveolata); star coral (Orbicella franksi); and rough cactus coral (Mycetophyllia ferox). 

This brings the total number of listed coral species in the wider Caribbean to seven. All of the 

threatened Caribbean species of coral are found within the AOI (Puglise and Kelty, 2007). Most are 

limited to the patch reefs surrounding the Florida Keys, off the southwest coast of Florida, on the 

East and West FGBs (USDOC, NOAA, 2013a and 2013b), and on the 18 Fathom and Bright Bank 

reefs in the northwest GOM (Rezak et al., 1983 and 1990). Elkhorn coral was documented at the 

West and East FGBs in 2003 and 2005, respectively (Zimmer et al., 2006).

6 MARINE AND COASTAL BIRDS

Chapter 4.6.1 of this Programmatic EIS provides the succinct description of the affected 

environment for marine and coastal birds in sufficient detail to support the impact analyses. The 

following descriptions provide additional, expanded information.

The GOM supports a diverse avifauna assemblage and includes a variety of coastal habitats 

that are important to the ecology of coastal and marine bird species, including the following: 

• Sandwich Terns – the Breton National Wildlife Refuge off the Louisiana coast 

supports one of the world’s largest colonies of Sandwich Terns. The northern 

Gulf Coast harbors about 75 percent of the population of Sandwich Terns in the 

southeastern United States.

• Brown Pelican – nearly half the southeastern population of Brown Pelicans lives 

in the northern Gulf Coast, generally nesting on protected islands. The Brown 

Pelican is Louisiana’s State bird and has made a comeback in this region since 

Hurricanes Katrina and Rita in 2005. It was recently removed from the 

Endangered Species List.

• Wilson’s Plover – the northern Gulf Coast is home to about 25 percent of the 

southeast’s Wilson’s Plover population.

• Black Skimmer – 35 percent of the southeastern Black Skimmer population is 

found along the Gulf Coast.

• Forster’s Tern – 41 percent of the southeastern population is found along the 

Gulf Coast.

• Gull-Billed Terns – 16 percent of the southeastern population is found along the 

Gulf Coast.
Gulf of Mexico G&G Activities Programmatic EIS E-105

• Laughing Gulls – 25 percent of the southeastern population is found along the 

Gulf Coast.

• Least Terns – 42 percent of the southeastern population is found along the Gulf 

Coast.

• Royal Terns – 36 percent of the southeastern population is found along the Gulf 

Coast.

• Snowy Plover – 22 percent of the southeastern population are found along the 

Gulf Coast.

This discussion focuses on three distinct taxonomic and ecological groups: seabirds, 

waterfowl, and shorebirds. Seabirds are defined here as species that live in the marine environment 

and feed at sea (Schreiber and Burger, 2002). Seabirds may be categorized by the marine zones in 

which they tend to forage. Pelagic birds forage in the open ocean away from the coastal zone, and 

shorebirds forage in coastal waters; other seabirds use coastal and open ocean zones (Michel, 

2013). Seabirds within the AOI include members from five taxonomic orders: Charadriiformes 

(gulls, terns); Gaviiformes (loons); Pelecaniformes (pelicans, frigatebirds, gannets, boobies, 

tropicbirds, cormorants); Podicipediformes (grebes); and Procellariiformes (petrels, storm-petrels, 

shearwaters).

Certain waterfowl taxa commonly termed sea ducks (Order Anseriformes) feed and rest 

within coastal (nearshore and inshore) waters outside of their breeding seasons. They typically form 

large flocks and are often observed in large rafts on the sea surface. Members of the order 

Gaviiformes (loons) may also be present in coastal waters.

Shorebirds utilize coastal environments for nesting, feeding, and resting. They are included 

within the order Charadriiformes (with gulls and terns). The shorebird group consists of four families 

and includes sandpipers, plovers, oystercatchers, and stilts.

6.1 LISTED SPECIES

Under the ESA, there are three threatened species of marine and coastal birds present 

within the AOI that were analyzed within this Programmatic EIS: Piping Plover (50 FR 50726); 

Roseate Tern (52 FR 42064); and Red Knot (79 FR 73705). Although there are additional 

threatened and endangered species that occur in the coastal areas of the AOI, they are not 

considered marine or coastal birds based on their reliance on more terrestrial habitats or they are 

not documented in the AOI.

Piping Plover (Charadrius melodus) 

The Piping Plover is a small, migratory shorebird that inhabits coastal sandy beaches and 

mudflats. They use open, sandy beaches close to the primary dune of barrier islands or along 

shores of rivers for breeding, preferring sparsely vegetated open sand, gravel, or cobble for nesting 
E-106 Expanded Affected Environment Information

sites. They forage along the wrack zone, or line, where dead or dying seaweed, marsh grass, and 

other debris are left on the upper beach by the high tide (USDOI, FWS, 2011). Piping Plovers are 

very sensitive to human activities, and disturbances from anthropogenic activities can cause the 

parents to abandon their nests (USDOI, FWS, 2009).

The population of Piping Plovers that breeds in the Great Lakes States is listed as 

endangered, as amended (66 FR 36038). The Great Lakes Piping Plover wintering population is 

distributed along the Atlantic and GOM coastlines (Stucker and Cuthbert, 2006). The population of 

Piping Plovers that breeds in the Great Plains is listed as threatened (50 FR 50726). All Piping 

Plovers are considered threatened species under the ESA when on their wintering grounds (66 FR 

36038). Individuals from the Great Plains population have been reported in coastal counties in all 

Gulf Coast States except Mississippi; however, individuals from the endangered population (those 

that breed in Great Lakes States) have been reported in the coastal counties of Mississippi (USDOI, 

FWS, 2011).

The FWS first designated critical habitat for wintering Piping Plovers in 142 critical habitat 

conservation areas, including the coasts of Florida, Alabama, Mississippi, Louisiana, and Texas 

within the AOI on July 10, 2001 (66 FR 36038). Critical habitat conservation areas were 

subsequently revised in Texas in 2009 (74 FR 23476). Critical wintering habitat has been 

designated in each of the Gulf Coast States for all three breeding populations (i.e., Atlantic Coast, 

Great Lakes, and Northern Great Plains) (66 FR 36038). Specifically, there are 30 parcels of land 

designated as critical habitat in the panhandle and west coast of Florida within the AOI; 3 areas in 

Alabama; 15 in Mississippi; 7 in Louisiana; and 18 in Texas (66 FR 36038). Thirty-three percent of 

these designated critical habitat areas are known to be used by Great Lakes breeding population of 

Piping Plovers (Stucker and Cuthbert, 2006).

Roseate Tern (Sterna dougallii) 

The Roseate Tern is medium-sized and is primarily pelagic along seacoasts, bays, and 

estuaries, going to land only to nest and roost (Sibley, 2000). They often forage up to 30 km (19 mi) 

offshore and roost in flocks near tidal inlets in late July to mid-September. They nest on islands on 

sandy beaches, open bare ground, and grassy areas, typically near areas with cover or shelter.

Roseate Terns forage mainly by plunge-diving and contact-dipping (in which the bird’s bill 

briefly contacts the water) or surface dipping over shallow sandbars, reefs, or schools of predatory 

fish. They are adapted for fast flight and relatively deep diving and often submerge completely when 

diving for fish (USDOI, FWS, 2010).

Only one subspecies of Roseate Tern (S. d. dougallii) is located in the AOI. A population 

breeds on islands around the Caribbean Sea from the Florida Keys to the Lesser Antilles; this 

population, which is listed as threatened, is known to occur within the AOI in scattered colonies 

along the Florida Keys (USDOI, FWS, 2010). No critical habitat has been designated for the 

Roseate Tern.
Gulf of Mexico G&G Activities Programmatic EIS E-107

Red Knot (Calidris canutus rufa) 

The Red Knot (Calidris canutus rufa) is a medium-sized shorebird that migrates in large 

flocks long distances between breeding grounds in the mid- and high-arctic areas and wintering 

grounds primarily in southern South America along the coast of Patagonia, but with smaller 

populations wintering in northeast Brazil and in the southern U.S. along the Gulf Coast of Florida, 

Texas, and between Georgia and South Carolina. The largest concentrations of the birds that 

overwinter in the U.S. are found along the southwestern coast of Florida (Harrington, 2001; Morrison 

et al., 2001a; USDOI, FWS, 2013a; Normandeau Associates, Inc., 2011). They migrate northward 

through the contiguous U.S. in April to June and southward in July to October.

Within the AOI, Red Knots forage along sandy beaches, tidal mudflats, salt marshes, and 

peat banks. They also use mangrove and brackish lagoons in Florida and beaches, oyster reefs, 

and exposed bay bottoms in Texas (USDOI, FWS, 2013a). The Red Knot was added to the list of 

threatened species under the ESA (79 FR 73705) on January 12, 2015.

6.2 NON-LISTED SPECIES

Within the AOI, there are numerous marine and coastal bird species present, including 

resident and migratory species. Resident species are present throughout the year; migratory 

species may be present only during breeding or wintering seasons or they may only migrate through 

the AOI. The trans-Gulf migrant birds include various species of shorebirds, wading birds, and 

terrestrial birds.

Marine and coastal birds present within the AOI include seabirds, waterfowl, and shorebirds 

within 17 taxonomic families (Table 4.6-1 of this Programmatic EIS). Bird species within a family 

share common physical and behavioral characteristics. Because of these commonalities, birds will 

be presented by family rather than individual species in this document as the potential for exposure 

to G&G activities will be similar for species within a family.

6.2.1 Seabirds

Four taxonomic orders of seabirds (broadly defined as birds that spend a large portion of 

their lives on or over water), including 11 families, are found in offshore and coastal waters of the 

AOI during their annual life cycle. Many species are present throughout the entire AOI and can be 

grouped into four categories according to their spatial and temporal residence: summer migrant 

pelagics, summer residents, wintering marine species, or permanent residents. Other species are 

present in only portions of the AOI (Peterson, 1980; Clapp et al., 1982a, 1982b, and 1983).

Seabirds generally feed on localized concentrations of prey in single- or mixed-species 

aggregations. Modes of prey acquisition include picking from the sea surface, shallow diving below 

the sea surface, and diving to depths of several meters (Shealer, 2002). Species that dive below the 

sea surface may be exposed to underwater noise produced during G&G surveys. Seabird species 

from the Procellariidae (petrels, prions, and shearwaters), Pelecanoididae (diving petrels), Sulidae 
E-108 Expanded Affected Environment Information

(gannets and boobies), Phalacrocoracidae (cormorants and shags), and Laridae (gulls or seagulls) 

families occur within the AOI and regularly dive below the sea surface, and some species are known 

to deep dive for long durations.

Seabirds within the northern GOM were surveyed from ships during the GulfCet II program. 

Hess and Ribic (2000) reported that terns (Sterna spp.), Storm-Petrels (Family Hydrobatidae), 

shearwaters (Puffinus spp.), and jaegers (Stercorarius spp.) were the most frequently sighted 

seabirds in the deepwater area. During these surveys, seabirds in four ecological categories were 

observed in the deepwater areas of the GOM: (1) summer migrants (shearwaters, storm-petrels, 

and boobies [Sula spp.]); (2) summer residents that breed in the GOM (Sooty Tern [Sterna fuscata], 

Least Tern [Sternula antillarum], Sandwich Tern [Sterna sandvicensis], and Magnificent Frigatebird 

[Fregata magnificens]); (3) winter residents (gannets, gulls, and jaegers); and (4) permanent resident 

species (Laughing Gulls [Larus atricilla], Royal Terns [Sterna maxima], and Bridled Terns [Sterna 

anaethetus]) (Hess and Ribic, 2000). The GulfCet II study did not estimate bird population densities; 

however, Powers (1987) indicated that seabird densities over the open ocean are typically 

<10 birds/km2

. 

The distribution and relative densities of seabird species within the deepwater areas of the 

GOM vary temporally (i.e., seasonally) and spatially. In the GulfCet II studies, seabird species 

diversity and densities were found to vary with the hydrographic environment, particularly the 

presence and location of mesoscale features such as Loop Current eddies that may enhance 

nutrient levels and productivity of surface waters where seabirds forage (Hess and Ribic, 2000).

In general, seabirds tend to occur at low densities over much of the ocean and are patchily 

distributed in relatively higher densities at Sargassum lines, upwellings, convergence zones, thermal 

fronts, salinity gradients, and areas of high planktonic productivity (Ribic et al., 1997; Hess and Ribic, 

2000).

6.2.2 Waterfowl

Waterfowl that may occur within coastal and inshore waters of the AOI include species within 

the subfamilies Aythyinae (diving ducks) and Merginae (sea ducks) (Sibley, 2000). Diving ducks 

include the Canvasback (Aythya valisineria), Ring-Necked Duck (Aythya collaris), Lesser Scaup 

(Aythya affinis), Greater Scaup (A. marila), Bufflehead (Bucephala albeola), and Common 

Goldeneye (Bucephala clangula). Diving ducks are gregarious and mainly found in freshwater or 

estuarine environments, although species such as the Greater Scaup move to marine environments 

during the winter. Diving ducks feed on aquatic vegetation, mollusks, and crustaceans. Of the sea 

ducks in the AOI, the Hooded Merganser (Lophodytes cucullatus) is the most commonly occurring 

species.

Depending on species, all waterfowl feed on fishes, mollusks, and small invertebrates 

(Sibley, 2000). Similar to diving seabirds, sea ducks and some diving ducks may be vulnerable to 

underwater noise produced during G&G activities because they dive beneath the water surface in 
Gulf of Mexico G&G Activities Programmatic EIS E-109

coastal waters for feeding. However, most diving ducks and sea ducks are located in bays and 

estuaries, which are outside of the AOI.

6.2.3 Shorebirds

The term shorebird applies to a large group of birds commonly called sandpipers and plovers 

but also includes oystercatchers, avocets, and stilts. Shorebirds found along the coastline of the 

AOI include species within four families: Charadriidae (plovers), Haematopodidae (oystercatchers), 

Recurvirostridae (avocets and stilts), and Scolopacidae (sandpipers). Fifty-three species of 

shorebirds regularly occur in the U.S. (Brown et al., 2001) with 43 species occurring during 

migrational or wintering periods in the AOI. Six shorebird species breed in the GOM: American 

Oystercatcher (Haematopus palliates), Snowy Plover (Charadrius alexandrines), Wilson’s Plover 

(Charadrius wilsonia), Willet (Catoptrophorus semipalmatus), Killdeer (Charadrius vociferous), and 

Black-necked Stilt (Himantopus mexicanus) (Helmers, 1992). Recent trend analyses of shorebird 

abundance in various parts of the U.S. indicate that many species are declining, including species 

that are present along the shores adjacent to the AOI (Morrison et al., 2001b and 2006). This 

decline in shorebird abundance is believed to be from multiple factors, including the environmental 

degradation of the shoreline habitats, industrial and recreational development of multiple habitats 

(i.e., breeding and wintering), climate change affecting Arctic breeding sites, and alterations to 

coastal areas from sea-level rise. In addition, global climate change may alter prevailing wind 

patterns, which may affect ocean upwelling and productivity, subsequently affecting shorebird 

abundance and distribution (Morrison et al., 2001b). The Lower Mississippi/Western Gulf Coast 

Region is rich with a variety of shorebird habitats and the Gulf Coast has some of the most important 

shorebird habitat in North America, particularly the Laguna Madre ecosystem along the south Texas 

coast (Brown et al., 2001; Withers, 2002). Resident shorebirds primarily rely on the shorelines 

adjacent to the AOI for life functions; however, some shorebird species cross the AOI during their 

annual migration.

6.3 MIGRATION

A migratory bird is any species of bird that migrates and lives or reproduces within or across 

international borders at some point during its annual life cycle. Migratory birds and their nests are 

protected under the Migratory Bird Treaty Act (16 U.S.C. §§ 703-712). Migratory movements of 

most marine and coastal birds across North America are known only in general terms (Harrington 

and Morrison, 1979). Many North American birds seasonally migrate long distances between 

northern habitats in the high Arctic, New England, and Canada and southern habitats in Florida, 

Central America, and South America, traveling as far as 12,000 km (7,457 mi) from breeding to 

wintering grounds (Helmers, 1992). There are significant differences between species in migratory 

routes (Rappole, 1995). Many marine and coastal birds, as well as terrestrial birds, use the 

Mississippi Flyway, which runs through the peninsula of southern Ontario, Canada, across the U.S. 

to the mouth of the Mississippi River (Figure 4.6-1 of this Programmatic EIS). The longest bird 

migration route in the Western Hemisphere ranges from the Arctic Coast of Alaska to Patagonia 

(Brown et al., 2001; Morrison et al., 2001a; Nutty Birdwatcher, 2015). Many North American 

terrestrial birds migrating to the tropics follow the Mississippi Flyway and take a shortcut across the 
E-110 Expanded Affected Environment Information

GOM (Nutty Birdwatcher, 2015). During migration, stopover areas provide resting and feeding 

opportunities needed by migrating birds to sustain them during their migration (Brown et al., 2001; 

McWilliams and Karasov, 2005). Disturbance along the shoreline where migrating birds forage can 

deny them the rest and food needed to complete their migration in good health (Helmers, 1992).

6.4 BIRD CONSERVATION REGIONS AND BIRDS OF CONSERVATION CONCERN

The Fish and Wildlife Coordination Act was amended in 1988 to mandate the FWS to 

“identify species, subspecies, and populations of all migratory nongame birds that, without additional 

conservation actions, are likely to become candidates for listing” under the ESA. The FWS (USDOI, 

FWS, 2008b) prepared a document to identify birds of conservation concern to comply with this 

mandate. The goal of the document was to identify all migratory and non-migratory bird species with 

high conservation priorities in addition to species already designated as federally threatened or 

endangered. The development of the birds of conservation concern took into account variable 

geographic scales addressed by three bird conservation initiatives: North American Bird 

Conservation Initiative (NABCI) Bird Conservation Regions (BCRs), FWS Regions, and National 

(USDOI, FWS, 2008b).

The NABCI Bird Conservation Regions were developed by a mapping team with members 

from the U.S., Mexico, and Canada to provide a consistent spatial framework for bird conservation in 

North America. The mapping team developed a hierarchical framework of nested ecological units, 

or BCRs (Figure 4.6-2 of this Programmatic EIS). There are four land-based BCRs located adjacent 

to the AOI: BCR 26, Mississippi Alluvial Valley; BCR 27, Southeastern Coastal Plain; BCR 31, 

Peninsular Florida; and BCR 37, Gulf Coastal Prairie (U.S. NABCI Committee, 2000). The FWS 

(USDOI, FWS, 2008b; Tables 24, 25, 33 and 35) listed all birds of conservation concern that may be 

present in BCRs (except for the Red Knot, which has only recently been listed) that include portions 

of the AOI. Shorebirds are, in general, of high conservation concern, with nearly half of the species 

in the U.S. designated as conservation concern (U.S. NABCI Committee, 2009 and 2014).

The BCR 26 (Mississippi Alluvial Valley) has 26 bird species of conservation concern, of 

which 5 species are marine or coastal birds. The BCR 27 (Southeastern Coastal Plain) has 53 bird 

species of conservation concern, of which 19 species are marine and coastal birds. The BCR 31 

(Peninsular Florida) has 49 bird species of conservation concern, of which 18 species are marine 

and coastal birds. The BCR 37 (Gulf Coastal Prairie) has 44 bird species of conservation concern, 

of which 21 species are marine and coastal birds.

6.5 IMPORTANT BIRD AREAS

The Important Bird Area (IBA) Program was developed by the National Audubon Society as 

a global effort to identify and conserve areas that are vital to birds and other biodiversity. The IBAs 

are sites that provide essential habitat for one or more species of birds and include sites for 

breeding, wintering, and migrating birds. By definition (National Audubon Society, 2011), IBAs are 

sites that support
Gulf of Mexico G&G Activities Programmatic EIS E-111

• species of conservation concern (e.g., threatened or endangered species);

• restricted-ranges species (species vulnerable because they are not widely 

distributed);

• species that are vulnerable because their populations are concentrated in one 

general habitat type or biome; and

• species or groups of similar species (such as waterfowl or shorebirds) that are 

vulnerable because they occur at high densities due to congregatory behavior.

The IBAs are located throughout the U.S. including along the coast, in nearshore waters, and 

offshore (Figure 4.6-3 of this Programmatic EIS). Five of the Louisiana IBAs include nearshore 

waters within the AOI: Chenier Plain, Atchafalaya Delta, Barataria Terrebonne, Active Delta, and 

Chandeleur Islands (Figure 4.6-4 of this Programmatic EIS). Additional offshore sites include Dry 

Tortugas National Park, Key West National Wildlife Refuge (NWR), and Great White Heron NWR. 

Furthermore, the GOM includes NWRs (Chapter 4.7.1.2 of this Programmatic EIS), some of which 

include coastal habitat within the AOI. These NWRs (7 in Texas, 2 in Louisiana, 1 in Mississippi, 

1 in Alabama, and 13 in Florida) are primarily managed for the protection and conservation of 

migratory birds (USDOI, FWS, 2013b).

7 MARINE PROTECTED AREAS

Chapter 4.7.1 of this Programmatic EIS provides the succinct description of the affected 

environment for marine protected areas in sufficient detail to support the impact analyses. The 

following descriptions provide additional, expanded information.

A Marine Protected Area (MPA) is defined by Executive Order (EO) 13158 as “any area of 

the marine environment that has been reserved by Federal, State, territorial, Tribal, or local laws or 

regulations to provide lasting protection for part or all of the natural and cultural resources therein.” 

In practice, MPAs are defined areas where natural and cultural resources are given greater 

protection than the surrounding waters. In the U.S., MPAs span a range of habitats, including the 

open ocean, coral reefs, deepwater habitats, coastal areas, intertidal zones, and estuaries, and can 

include freshwater and terrestrial areas. The MPAs are designed to achieve a variety of goals, 

generally falling within six categories: (1) conservation of biodiversity and habitat; (2) fishery 

management; (3) research and education; (4) enhancement of recreation and tourism; 

(5) maintenance of marine ecosystems; and (6) protection of cultural heritage.

Section 5 of EO 13158 specifically states, “In implementing this section, each Federal 

agency shall refer to the MPAs identified under subsection 4(d) of this order.” Section 4(d) states 

that the Secretary of Commerce and the Secretary of the Interior “shall also publish and maintain a 

list of MPAs that meet the definition of MPA for the purposes of this order.” In accordance with 

Section 4(d), a National System of MPAs was established in 2009 for the effective stewardship, 

conservation, restoration, sustainable use, understanding, and appreciation of marine resources. 

The information presented herein was obtained from the Marine Protected Areas Inventory (i.e., the 
E-112 Expanded Affected Environment Information

National System of MPAs) maintained through a partnership between NOAA and the USDOI. For 

the purpose of this analysis, National System MPAs are presented; however, it is recognized in 

Section 5 that additional areas are afforded protection by other management systems (e.g., 

GMFMC) (Simmons et al., 2015) and that specific management areas (e.g., banks and topographic 

features) may be included within boundaries of existing National System MPAs.

It is important to note that the AOI extends beyond the planning areas to account for the 

acoustic energy that could propagate beyond BOEM jurisdictional boundaries; as such, the 

description of MPAs in the AOI include the Florida Keys, Dry Tortugas National Park, Tortugas 

Ecological Reserve, and other sensitive shallow-water habitats within State waters (3 or 9 nmi [5.6 or 

16.7 km; 3.5 or 10.6 mi] from shore). The offshore MPAs within the AOI are listed in Table 4.7-1 of

this Programmatic EIS, and their locations are shown in Figure 4.7-1 of this Programmatic EIS. 

Coastal MPAs are shown in Figure 4.7-2 of this Programmatic EIS and include numerous MPAs 

that, while outside of BOEM’s planning areas, are included to account for potential effects that may 

extend beyond the AOI boundary. Table 4.7-1 of this Programmatic EIS contains sites that are 

currently designated as “members” of the National System of MPAs as well as the sites listed as 

“eligible” for inclusion. All sites listed are afforded some degree of protection based on their 

associated management plans. The following discussion focuses on marine sanctuaries, deepwater 

sites, and fishery management areas within the AOI, followed by a brief summary of coastal MPAs 

completely or partially within the AOI.

Table 4.7-1 of this Programmatic EIS includes the following additional categories of 

information for the respective MPAs:

• government level of management (State or Federal);

• managing agency (a State or Federal agency, and in a few cases, partnerships);

• primary conservation focus;

• areas of MPA within the AOI;

• total area of the MPA; and

• percentage of the MPA falling within the AOI.

7.1 NATIONAL MARINE SANCTUARIES

Two National Marine Sanctuaries have been established in the AOI: the Florida Keys 

National Marine Sanctuary (FKNMS) and the Flower Garden Banks National Marine Sanctuary 

(FGBNMS), the latter of which is located in the northwestern GOM (Figure 4.7-1 of this

Programmatic EIS). They are administered by NOAA’s Office of National Marine Sanctuaries.
Gulf of Mexico G&G Activities Programmatic EIS E-113

7.1.1 Florida Keys National Marine Sanctuary

The FKNMS protects 9,947 km2 (2,900 nmi2) of waters surrounding the Florida Keys, from 

south of Miami west to encompass the Dry Tortugas, excluding Dry Tortugas National Park. This 

FKNMS is administered by NOAA and jointly managed with the State of Florida. It spans a shallowwater interface between the GOM and the Atlantic Ocean and is adjacent to most of the relatively 

shallow estuarine waters of South Florida, including Florida Bay and Biscayne Bay. The sanctuary 

surrounds >1,700 islands, which constitute most of the limestone island archipelago of the Florida 

Keys. This archipelago extends from the Florida peninsula south and westward more than 354 km 

(220 mi), terminating at the islands of Dry Tortugas National Park. The sanctuary contains 

components of five distinct physiographic regions: (1) the Florida Bay, (2) the Southwest 

Continental Shelf, (3) the Florida Reef Tract, (4) the Florida Keys, and (5) the Straits of Florida. The 

regions are environmentally and lithologically unique, and together they form the framework for the 

FKNMS’ diverse terrestrial and aquatic habitats. The oceanic boundary of the FKNMS is the 300-ft 

(91-m) depth contour, beyond which the Florida Straits separate the Florida Keys from Cuba and the 

Bahamas. The waters northwest of the Florida Keys are within the eastern GOM. The FKNMS’ 

GOM region is important as a fisheries resource as the area serves as the nursery grounds for many 

recreationally and commercially important species of fishes and invertebrates, including groupers, 

snappers, pink shrimp, spiny lobster, and stone crab.

The sanctuary supports approximately 6,000 marine species and contains the world’s third 

largest barrier reef, extensive seagrass meadows, and mangrove-fringed islands. A variety of 

plants, invertebrates, fishes, reptiles, birds, and mammals that use or contribute to sanctuary 

resources in the Florida Keys are protected at the Federal or State level. Each species is a valuable 

natural resource that contributes to the ecological balance of the FKNMS. Animal species at risk 

depend on the FKNMS’ diverse habitats, including mangroves, beaches (below high water mark), 

seagrass beds, and coral reefs. State and federally listed threatened and endangered marine and 

aquatic fauna include elkhorn coral, staghorn coral, pillar coral, all five species of sea turtles found in 

the western Atlantic (i.e., loggerhead, green, hawksbill, Kemp’s ridley, and leatherback), American 

alligator (Alligator mississippiensis), American crocodile (Crocodylus acutus), smalltooth sawfish, 

Roseate Tern, Least Tern (Sterna antillarum), and the West Indian manatee. The FKNMS is also in 

the migratory range of three species of whales: humpback whale, fin whale, and North American 

right whale. The FKNMS also protects elements of history such as shipwrecks and other 

archeological treasures, including 669 historic artificial reefs that have been documented to date. As 

of January 2016, 14 shipwrecks and 2 lighthouses within the FKNMS are listed in the National 

Register of Historic Places.

The AOI includes most of the FKNMS (approximately 58% of the total area), from the area 

just south of Long Key to beyond the Dry Tortugas to the southwest.

7.1.2 Flower Garden Banks National Marine Sanctuary

The FGBNMS is located in the northwestern GOM and consists of three distinct areas: the 

East FGB, West FGB, and Stetson Bank. The East FGB covers 65.86 km2 (19.20 nmi2

; 25.43 mi2) 
E-114 Expanded Affected Environment Information

and is located approximately 222 km (120 nmi) south southwest of Cameron, Louisiana. The West 

FGB covers 77.54 km2 (22.61 nmi2

; 29.94 mi2) and is located approximately 200 km (108 nmi; 

124 mi) southeast of Galveston, Texas. Stetson Bank covers 2.18 km2

 (0.64 nmi2; 0.84 mi2) and is 

located approximately 110 km (61 nmi; 68 mi) southeast of Galveston, Texas.

Structurally, the FGB coral reefs are composed of large, closely spaced heads 3 m (10 ft) or 

more in diameter and height. The FGB reefs are the northernmost living coral reefs on the U.S. 

continental shelf. Isolated from other coral reef systems by more than 556 km (300 nmi; 345 mi), the 

East and West FGBs favor hard corals and support at least 21 species. Eight species of coral are 

found on Stetson Bank, where the cooler water temperatures favor non-reef-building corals and 

sponges. The East FGB is also home to the only known oceanic brine seep in GOM continental 

shelf waters. The super-saline water flowing from under the seafloor has created a concentrated 

brine lake and channel in which only salt-tolerant bacteria are able to live. This “lake” and “river” are 

only approximately 25.4 cm (10 in) deep.

The East FGB is a pear-shaped dome capped by 1 km2 (0.4 mi2

) of coral reef, termed “coral 

cap,” that rises to within 17 m (56 ft) of the surface. The West FGB is an oblong-shaped dome that 

includes 0.4 km2 (0.15 mi2

) of coral reef area starting 18 m (59 ft) below the water surface. Brain 

and star corals dominate the coral caps of the East and West FGBs, with a few coral heads 

exceeding 6 m (20 ft) in diameter. On average, 45 to 52 percent of the bottom surfaces of the East 

and West FGBs coral caps are covered by coral species to depths of 30 m (98 ft), and exceeding 

70 percent coral cover in depths of at least 43 m (141 ft) (Hickerson and Schmal, 2005). The coral 

caps do not contain some species commonly found in the Caribbean, such as many of the branching 

corals, sea whips, or sea fans. The deepwater habitat of the FGBs that makes up more than 

98 percent of the area within the FGBNMS boundaries is not as well known. Habitats below 

recreational SCUBA limits (approximately 40 m [131 ft]) include algal-sponge zones, “honeycomb” 

reefs (highly eroded outcroppings), mud flats, mounds, mud volcanoes, and at least one brine seep 

system. Different assemblages of sea life reside in these deeper habitats, including extensive beds 

of coralline algae, pavements and algal nodules, colorful sea fans, sea whips, black corals, deep 

reef fish, batfish, searobins, basket sea stars, and feather stars (USDOI, BOEM, 2012a).

Depths at Stetson Bank range from approximately 17 to 52 m (55 to 170 ft). Environmental 

conditions at Stetson Bank include more extreme fluctuations in temperature and turbidity than at the 

East and West FGBs and do not support the growth of reef-building corals like those found at the 

FGBs. Stetson Bank contains a low-diversity coral community in addition to prominent sponge 

(Phylum porifera) fauna. The outcrops of Stetson Bank are dominated by the branching fire coral 

(Millepora alcicornis) and sponges, with cover exceeding 30 percent (Bernhardt, 2000). There are at 

least nine coral species at Stetson Bank, but most colonies are small and sparsely distributed, with 

the exception of a large area of ten-ray star coral (Hickerson et al., 2008).

Located in the general region of the East and West FGBs are other reefs and banks 

designated through NMFS’ essential fish habitat legislation as HAPCs, including Sonnier Bank, 

McGrail Bank, Bright Bank, Geyer Bank, and Alderdice Bank. These designated deepwater habitats 
Gulf of Mexico G&G Activities Programmatic EIS E-115

contain outcroppings populated with benthic invertebrates, coralline algae, deep coral biota, and a 

variety of fish species. All HAPCs have protective measures from certain fishing operations and 

vessel anchoring and are identified as areas for special consideration during individual species 

assessments.

More than 300 different fish species and 3 species of sea turtles (i.e., hawksbill, leatherback, 

and loggerhead) inhabit FGBNMS waters. Macroalgae, crustaceans, sharks, skates, rays, many 

different types of benthic invertebrates, and a variety of seabirds thrive in the protected waters 

around the FGBs (Showalter and Schiavinato, 2003).

The entirety of the FGBNMS falls within the AOI. Expansion of the FGBNMS is proposed 

following several years of scientific assessment and public input. The proposed expansion was 

determined as one of the top priority issues that emerged during the management plan review 

process completed in 2012. The FGBNMS’ advisory council recommended expanding from 

145.6 km2 (56.2 mi2

) to 725.9 km2 (280.3 mi2) to include up to nine additional reefs and banks, which 

support essential habitat for commercial and recreational fish species (USDOC, NOAA, 2015b).

7.2 OTHER FEDERAL FISHERY MANAGEMENT AREAS

The Pulley Ridge HAPC, the deepest hermatypic (or reef-building) coral reef in the 

continental U.S., is located off the southwest coast of Florida. Pulley Ridge is a drowned barrier 

island approximately 100 km (62 mi) long by 5 km (3.1 mi) wide running parallel to the Florida 

peninsula northwest of the Dry Tortugas. The entirety of the Pulley Ridge HAPC (344 km2

[132.8 mi2

]) is located within the AOI. Live corals dominated by Agaricia sp. have been located 

between the 60- and 70-m (197- and 230-ft) isobaths on the reef along with a diverse assemblage of 

fish species consisting of shallow-water and deepwater species.

Some fishing activities have been restricted in the Pulley Ridge HAPC, but growing concern 

for hermatypic corals in the area may lead to future management options. The GMFMC deepwater 

coral working group has expressed concern over ongoing damage to Pulley Ridge habitat by fishing 

operations and is considering additional protective measures. In May 2015, the Joint Coral Scientific 

and Statistical Committee and Coral Advisory Panel (Coral SSC/AP) recommended extended 

boundaries for the Pulley Ridge HAPC, stating specific concerns over the golden crab fishery (Coral 

SSC/AP, 2015).

While there are substantial areas of cold-water coral habitat in the GOM, it appears to be 

more scattered and less extensive than such habitats in the Atlantic Ocean off the southeastern U.S. 

Much of the research into the cold-water coral communities of the GOM has taken place along the 

northern continental slope. There, several studies have found coral habitat consisting of hermatypic 

coral species such as Lophelia pertusa and zigzag coral (Madrepora oculata). The most extensive 

cold-water coral communities found to date in the GOM occur at the Viosca Knoll, located on the 

upper De Soto Slope, approximately 120 km (65 nmi) south of Mobile Bay, Alabama. The main 

Viosca Knoll site (named the VK 826 Coral Habitat) is an isolated feature that rises 90 m (295 ft) 
E-116 Expanded Affected Environment Information

from the seafloor, providing high relief for an array of suspension feeders, including scleractinian, 

gorgonian, and anthipatharian corals. The VK 862 Lophelia and Black Coral Habitat is located 

approximately 40 km (25 mi) west of the VK 826 Coral Habitat.

Numerous Federal fishery management areas have been designated by the NMFS and 

GMFMC. Other federally protected areas, with different degrees of management and protection, 

include reserves such as the Tortugas Ecological Reserve and the Reef Fish Stressed Area. The 

following MPAs listed in this section are not members of the national system of MPAs but are eligible 

to become members. These areas have restrictions on certain types of fishing activities and are 

briefly discussed here.

The De Soto Canyon Closed Area, located off the east coast of Florida, is a Federal Fishery 

Management Zone and has been managed by the NMFS since its designation in 2000. The MPA is 

closed year-round to all pelagic longline gear in order to protect tunas, swordfish, and other billfish 

and sharks (USDOC, NOAA, n.d.-a). The entire close area (86,854 km2 [33,534.5 mi2

]) falls within 

the AOI.

The East Florida Coast Closed Area, as the name implies, is located primarily along Florida’s 

east coast, but a small portion of it wraps under the southern end of the Florida peninsula. The area 

is closed to fishing gear, such as longline gear, that could indiscriminately catch non-target species. 

This MPA is closed year-round and is primarily focused on alleviating impacts to select species of 

fish and all sea turtles (USDOC, NOAA, n.d.-a). Only a small fraction (0.01%; 12.3 km2 [4.7 mi2

]) of 

the MPA falls within the AOI.

The Florida Middle Grounds are a complex series of carbonate hard bottom outcropping 

located approximately 138 km (86 mi) south of Apalachee Bay, Florida. The outcroppings are 

spread over an area of approximately 1,193 km2 (461 mi2

), with relief of up to 17 m (56 ft). The 

Florida Middle Grounds are the northernmost extent of hermatypic coral growth in the U.S. (Puglise 

and Kelty, 2007), and the fauna most closely resemble a tropical reef. Branching fire coral, elliptical 

star coral, and ten-ray star coral are common, as are octocorals, sea fans of the genus Muricea, and 

the giant barrel sponge (Naar et al., 2007). Other fauna include hydroids, anemones, mollusks, 

crustaceans, echinoderms, polychaetes, and fishes (Hopkins et al., 1977; Coleman et al., 2004a). 

The Florida Middle Grounds are not considered a true coral reef because the lack of abundance of 

hermatypic corals does not allow for the successful accretion of a carbonate reef (USDOI, BOEM, 

2013a). All of the Florida Middle Grounds HAPC (1,159.6 km2 [447.7 mi2

]) falls within the AOI.

Two marine reserves have been established to help manage gag grouper populations in the 

GOM: Madison-Swanson Marine Reserve and Steamboat Lumps Marine Reserve.

Madison-Swanson Marine Reserve is 400 km2 (155 mi2

) of small outcrops and a few higher 

relief pinnacles (up to 9 m [30 ft]) roughly 80 km (50 mi) south of Apalachicola, Florida in water 

depths between 60 and 140 m (197 and 459 ft) (USDOI, BOEM, 2013a). The site is home to 
Gulf of Mexico G&G Activities Programmatic EIS E-117

sponges, sea fans, corals (including bush/tree corals), echinoderms, and crabs (USDOI, BOEM, 

2013a). The entire reserve falls within the AOI.

Steamboat Lumps Marine Reserve is located 161 km (100 mi) south-southwest of Cape San 

Blas, Florida, and approximately 32 km (20 mi) southwest of the Florida Middle Grounds. The 

reserve encompasses approximately 365 km2 (138 mi2

) and comprises a relic reef in 60 to 140 m 

(197 to 459 ft) of water (Hine and Locker, 2008). Fauna in Steamboat Lumps Marine Reserve is 

typical of a deepwater reef, with sponges, sea fans, black corals, bush/tree corals, echinoderms, and 

crustaceans (USDOI, BOEM, 2013a). The entirety of Steamboat Lumps Marine Reserve falls within 

the AOI.

McGrail Bank (formerly known as 18 Fathom Bank) was mentioned but not described in the 

discussion of the FGBNMS. It is one of several named banks found across the continental shelf of 

the northwestern GOM and appears to be biologically and geologically connected to the FGBNMS. 

The top of McGrail Bank lies 46 m (151 ft) beneath the sea surface. Deeper reef habitat includes 

extensive coralline algae and deep coral assemblages at McGrail Bank, which is designated as a 

Coral HAPC. This designation protects the bottom habitat from fish traps and anchoring (USDOC, 

NOAA, National Ocean Service, 2014). McGrail Bank is located approximately 46 km (30 mi) eastnortheast of Geyer Bank and 97 km (60 mi) east-northeast of the East FGB. It consists of a pair of 

ridges separated by a valley. McGrail Bank has the shallowest crest of any of the shelf-edge GOM 

banks west of the Mississippi River Delta, excluding the FGBs. There has been discussion about 

expanding the boundaries of the FGBNMS to include areas such as McGrail Bank (USDOC, NOAA, 

2015b). The entirety of McGrail Bank (48 km2 [18.5 mi2

]) falls within the AOI. Stetson Bank is 

described in Section 7.1, as it is part of the FGBNMS; however, it is also a designated HAPC.

The Pelagic Sargassum Habitat Restricted Area, which extends along the southeast coast of 

the U.S. from Virginia to a narrow region along the Florida Keys. A small portion of this restricted 

area extends into the AOI. This area has seasonal restrictions on the harvest of pelagic Sargassum

(68 FR 18942). Only a fraction of the total restricted area (0.01%; 63 km2 [24 mi2

]) falls within the 

AOI.

The Reef Fish Longline and Buoy Gear Restricted Area extends along all of the Gulf Coast 

States and restricts commercial fishing using longline gear within its boundaries (USDOC, NOAA, 

n.d.-b). The entirety of this restricted area (177, 935 km2 [68,701 mi2

]) falls within the AOI.

The Reef Fish Stressed Area extends along all of the Gulf Coast States and contains 

commercial fishing restrictions within its boundaries (U.S. Government Publishing Office, 2002). The 

entirety of this restricted area (98,557 km2 [38,053 mi2

]) falls within the AOI.

The Tortugas Marine Ecological Reserve, created in 2001, consists of two regions covering a 

total of 151 nmi2 (200 mi2

; 518 km2) at the western extent of the FKNMS. The reserve is closed to 

all consumptive use, including fishing and anchoring, and a portion of it is only open to permitted 
E-118 Expanded Affected Environment Information

marine research (Jeffrey et al., 2012). The entirety of the reserve (229.4 km2 [88.6 mi2]) falls within 

the AOI.

The West and East FGBs HAPC is described in Section 7.1.2. The entirety of the HAPC 

(220.5 km2 [85.1 mi2

]) falls within the AOI.

7.3 COASTAL MARINE PROTECTED AREAS

Coastal MPAs within the AOI include national seashores, NWRs, National Estuarine 

Research Reserves (NERRs), and State-designated MPAs (Figure 4.7-2 and Table 4.7-1 of this

Programmatic EIS).

7.3.1 National Park System (National Seashores)

There are four coastal national parks within the boundary of the AOI that are administered by 

the National Park Service (NPS). The NPS lands along the coast or in coastal areas of the AOI 

include the Dry Tortugas National Park, Everglades National Park, Gulf Islands National Seashore, 

and Padre Island National Seashore (Figure 4.7 2 of this Programmatic EIS).

The Dry Tortugas National Park is located approximately 113 km (70 mi) west of Key West. 

The 261.4-km2 (101-mi2

) park is mostly open water with seven small islands and is accessible only 

by boat or seaplane. The park’s Fort Jefferson is a National Monument, and the designation as a 

National Park protects this monument. Almost 99 percent (258 km2 [99.6 mi2

]) of the park falls within 

the AOI.

The Everglades National Park encompasses nearly 6,216 km2 (2,400 mi2

) and includes the 

southern portion of mainland Florida, Florida Bay, and portions of the upper Florida Keys. The park 

contains approximately 2,280 km2 (880 mi2

) of marine habitat, including open water, shallow waters, 

and mangrove-fringed shorelines and islands. Approximately 12.5 percent (775.3 km2 [299 mi2

]) of 

the park falls within the AOI.

The Gulf Islands National Seashore spans two island chains off the coast of Mississippi and 

the Florida Panhandle. The Gulf Islands consist of seven barrier islands, five in Mississippi and two 

in Florida, making it the Nation’s largest national seashore, covering more than 240 km (150 mi) of 

the Gulf Coast. Two of these islands (Horn and Petit Bois) are designated as Wilderness Areas 

under the Wilderness Act. The park encompasses 526 km2 (203 mi2

) of barrier island and coastal 

waters. Approximately 42.2 percent (775 km2 [299 mi2

]) of the park falls within the AOI.

Padre Island National Seashore lies along the Gulf Coast of Texas and stretches 180 km 

(112 mi), making it the longest barrier island in the U.S. Padre Island separates the GOM from the 

Laguna Madre, one of only a few hypersaline lagoons in the world. The park encompasses 

approximately 529 km2 (204 mi2

). Approximately 12.1 percent (64 km2 [24.7 mi2]) of the park falls 

within the AOI.
Gulf of Mexico G&G Activities Programmatic EIS E-119

7.3.2 National Wildlife Refuges

The National Wildlife Refuge system of U.S. lands and waters is managed by the FWS 

specifically for the enhancement of wildlife. There are 19 NWRs located within the AOI (Table 4.7 1 

and Figure 4.7 2 of this Programmatic EIS).

All terrestrial and aquatic resources within the NWR system are managed with the goals of 

conservation, management, and where appropriate, restoration of the fish, wildlife, and plant 

resources and their habitats within the U.S. for the benefit of present and future generations. 

Management approaches and conservation methods differ among NWRs but typically include 

managing and rehabilitating wildlife habitat, controlling invasive species, and assisting in the 

recovery of rare wildlife species (USDOI, FWS, 2002).

The Anahuac National Wildlife Refuge, established in 1963, borders Galveston Bay in 

southeast Texas and is a region of coastal marsh and prairie. The management focus of the NWR 

is to protect and manage the coastal marsh for migrating, wintering, and breeding waterfowl, 

shorebirds, and waterbirds as well as provide crucial nesting areas for neotropical migratory 

songbirds migrating across the GOM (USDOI, FWS, 2012). Less than 1 km2 (0.4 mi2

) of the 

137 km2 (53 mi2

) of this NWR falls within the AOI.

The Aransas National Wildlife Refuge, established in 1937, includes two upland components 

and the shoreline of Matagorda Island along the Texas coast. Matagorda Island is a significant 

natural area that stretches 61 km (37.9 mi) long and 1.2 to 7.2 km (0.7 to 4.5 mi) wide, covering 

229 km2 (88 mi2

). Approximately 121 km2 (47 mi2) are uplands and the remaining 105 km2 (41 mi2) 

are salt marsh, tidal flats, and beaches. Matagorda Island’s orientation is northeast-southwest with 

the GOM on one side and Espiritu Santo Bay on the other (USDOI, FWS, 2013c). Approximately 

4.6 percent (21.8 km2 [8.4 mi2

]) of this NWR falls within the AOI.

The Breton National Wildlife Refuge, established in 1904, is the second oldest wildlife refuge 

in existence. The NWR consists of barrier islands, including the Chandeleurs, located in the GOM 

off the southeast coast of Louisiana. According to the FWS, this NWR has one of the larger known 

nesting colonies of Royal and Sandwich Terns. This NWR also serves as an important area for 

Reddish Egrets (Egretta rufescens) and provides nesting habitat for various other colonial seabirds. 

This NWR has a large non-breeding concentration of Magnificent Frigatebirds as well as a large 

winter concentration of Redhead Ducks (Aythya americana) with a smaller number of Canvasbacks 

and Lesser Scaups (Aythya affinis). It also serves a large nesting colonies of several thousand 

Eastern Brown Pelicans (Pelecanus occidentalis) and provides wintering migration habitat for Piping 

Plover and other shorebirds (USDOI, FWS, n.d.-a). The entirety of this NWR (30.5 km2 [11.8 mi2

]) 

falls within the AOI.

The Cedar Keys National Wildlife Refuge, established in 1929, is located in coastal Levy 

County, Florida. This NWR is composed of 12 offshore islands around the town of Cedar Key, 

ranging in size from a few acres to 120 ac. This NWR contains one of the largest colonial bird 
E-120 Expanded Affected Environment Information

nesting sites in northern Florida. A wide variety of birds nest on Cedar Key (USDOI, FWS, n.d.-b). 

The entirety of this NWR (3.3 km2 [1.3 mi2

]) falls within the AOI.

The Chassahowitzka National Wildlife Refuge, established in 1941, consists of more than 

125 km2 (48 mi2

) of saltwater bays, estuaries, and brackish marshes at the mouth of the 

Chassahowitzka River, Florida. According to the FWS, this NWR was established primarily to 

protect waterfowl habitat and is home to >250 species of birds, >50 species of reptiles and 

amphibians, and at least 25 different species of mammals, including the endangered West Indian 

Manatee (USDOI, FWS, 2013d). Approximately 48 percent (71.5 km2 [27.6 mi2

]) of this NWR falls 

within the AOI.

The Crystal River National Wildlife Refuge, established in 1983, was specifically created for 

the protection of the endangered Florida manatee (a subspecies of the West Indian Manatee). This

NWR protects important wintering habitat for manatees located in Kings Bay, Florida, which includes 

King Spring and Three Sisters Spring (USDOI, FWS, 2014). Approximately 11.5 percent (3.9 km2

[1.5 mi2

]) of this NWR falls within the AOI.

The Delta National Wildlife Refuge, established in 1935, is composed of marsh habitat 

located just south of Venice, Louisiana, and is part of the Mississippi River Delta. This NWR was 

established as a bird sanctuary and provides wintering habitat and sanctuary for waterfowl and other 

migratory birds (USDOI, FWS, n.d.-c). Approximately 5.2 percent (10.7 km2 [4.1 mi2

]) of this NWR 

falls within the AOI.

The Great White Heron National Wildlife Refuge, established in 1938, is located in the lower 

Florida Keys and consists of approximately 809 km2 (312 mi2

) of open water and islands that are 

north of Marathon Key, and it is part of the Florida Keys National Wildlife Refuges Complex. The 

islands account for approximately 31 km2 (12 mi2

) and consist primarily of mangroves, with some 

larger islands containing pine rockland and tropical hardwood hammock habitats. This NWR 

provides important habitat for migratory birds, sea turtles, and other wildlife (USDOI, FWS, n.d.-d). 

The entirety of this NWR (837.8 km2 [323.5 mi2

]) falls within the AOI.

The J.N. Ding Darling National Wildlife Refuge, established in 1945, is located on Sanibel 

Island, in Lee County, Florida. Approximately 2,800 acres (ac) (1,133 hectares [ha]) of the refuge 

are designated as a Federal Wilderness Area. This NWR is composed of several habitat types: 

estuarine habitat consisting of open water, seagrass beds, mud flats and mangrove islands; and 

interior freshwater habitats consisting of open water ponds, Spartina swales, and West Indian 

hardwood hammocks/ridges. Two brackish water impoundments totaling 800 ac (324 ha) are used 

extensively by wading birds and other water birds (USDOI, FWS, n.d.-e). Approximately 3.4 percent 

(1 km2 [0.4 mi2

]) of this NWR falls within the AOI.

The Key West National Wildlife Refuge, established in 1908, is almost entirely within the 

marine environment and is part of the Florida Keys National Wildlife Refuges Complex. This NWR 

consists of coral reef and seagrass communities as well as mangrove islands with limited sandy 
Gulf of Mexico G&G Activities Programmatic EIS E-121

beach and dune habitat and regions of large sand flats. There are some areas of saltmarsh and 

coastal berm hammocks. This NWR supports critical nesting, roosting, wading, and loafing habitat 

to more than 250 bird species, particularly wading birds (USDOI, FWS, n.d.-f). The entirety of this

NWR, approximately 760 km2 (293.4 mi2

), falls within the AOI.

The Laguna Atascosa National Wildlife Refuge, established in 1946 in southeast Texas, 

includes South Padre Island and the waters of the Bahia Grande. It provides habitat for wintering 

waterfowl and other migratory birds, principally Redhead Ducks as well as endangered species 

conservation and management for shorebirds. This NWR also has the largest population of the 

endangered ocelot (Leopardus pardalis) in the U.S. (USDOI, FWS, 2013e). Less than 1 percent 

(7.5 km2 [2.9 mi2

]) of this NWR falls within the AOI.

The Lower Rio Grande Valley National Wildlife Refuge, established in 1979 in southeastern 

Texas, is a fairly unusual region where four climates (temperate, desert, coastal, and subtropical) 

converge, resulting in a great diversity of plants and wildlife. This NWR was established to protect 

the biodiversity from over development from agriculture (USDOI, FWS, 2013f). This NWR provides 

habitat to 18 federally listed threatened and endangered species. Less than 1 percent (17 km2

[6.5 mi2

]) of this NWR falls within the AOI.

The Lower Suwannee National Wildlife Refuge, established in 1979 in Dixie and Levy 

Counties, Florida, consists of lands located along the lower reaches of the of the Suwanee River, 

beginning at Yellow Jacket and continuing for 20 mi (32 km) until the river flows in the GOM. From 

the mouth of the river, this NWR extends northward along the GOM for 10 mi (16 km). This NWR 

consists of 146 km2 (56 mi2

) of wetlands and 65 km2 (25 mi2) of uplands, providing important habitat 

for wading and shore birds, migratory songbirds, and raptors (USDOI, FWS, n.d.-g). Approximately 

16.3 percent (55.3 km2 [21.4 mi2

]) of this NWR falls within the AOI.

The National Key Deer Refuge, established in 1957 in Monroe County, Florida, consists of 

upland forest, shrub wetland, and wetland marsh habitat, and is part of the Florida Keys National 

Wildlife Refuges Complex. This NWR encompasses the truncated historical range of the 

endangered Key deer (Odocoileus virginianus clavium), including critical habitat. This NWR also 

serves as home to tropical hardwood hammock habitat and 22 federally listed endangered and 

threatened species of plants and animals, 5 of which are unique to the NWR (USDOI, FWS, n.d.-h). 

The entirety of this NWR (557.1 km2

 [215.1 mi2]) falls within the AOI.

The San Bernard National Wildlife Refuge, established in 1969 near Freeport, Texas, 

consists of beaches, dunes, bay estuaries, and salt marsh habitat. Freshwater marsh and 

bottomland hardwood forest habitats of the Brazos and San Bernard River basins are found farther 

inland. This NWR supports a large diversity of coastal wildlife, including 320 species of birds, 

95 species of reptiles and amphibians, and 130 species of butterflies and dragonflies (USDOI, FWS, 

2013g). Less than 1 percent (0.02 km2 [0.007 mi2

]) of this NWR falls within the AOI.
E-122 Expanded Affected Environment Information

The Shell Keys National Wildlife Refuge, established in 1907, consists of a small group of 

dynamic shell fragment islets located south of Marsh Island and west of Greenwich, Louisiana. The 

boundary of the NWR has been interpreted to be the areas in this vicinity that are above mean high 

tide. This NWR is an important area for wading and shore birds. Recent hurricanes and storms 

have eroded the islets to such an extent that no nesting has occurred since 1992 (USDOI, FWS, 

2008c). The entirety of this small NWR (0.02 km2

 [0.007 mi2]) falls within the AOI.

The St. Marks National Wildlife Refuge was established in 1931 along the Florida 

Panhandle. The NWR includes coastal marshes, islands, tidal creeks, and estuaries of seven north 

Florida rivers and is home to a diverse community of plant and animal life. This NWR has more than 

69 km2 (27 mi2

) protected under the Federal Wilderness Act (USDOI, FWS, 2015). Approximately 

24.1 percent (107.6 km2 [41.5 mi2

]) of this NWR falls within the AOI.

The St. Vincent National Wildlife Refuge was established in 1968 in Franklin and Gulf 

Counties, Florida. The NWR is a coastal barrier island consisting of open water, wetlands, forest, 

shrub, and sand dune habitat. This NWR serves as a stop-over for migratory birds, red wolf (Canis 

rufus) propagation, nesting raptors, and nesting loggerhead sea turtles (USDOI, FWS, n.d.-i). Less 

than 1 percent (0.08 km2 [0.03 mi2

]) of this NWR falls within the AOI.

The Ten Thousand Islands National Wildlife Refuge was established in 1996 in Collier 

County, Florida. The NWR consists of a diverse wetland habitat supported by freshwater flow from 

the Fakahatchee Strand and Picayune Strand watersheds. This NWR provides habitat for large 

concentrations of wading birds, shorebirds, waterfowl, and other water birds. Ten percent of 

Florida’s manatee population utilizes the NWR and adjacent waters (USDOI, FWS, n.d.-j). 

Approximately 12.8 percent (18 km2 [6.9 mi2

]) of this NWR falls within the AOI.

7.3.3 National Estuarine Research Reserves

The National Estuarine Research Reserve System (NERRS) is a partnership between NOAA 

and the coastal states that protects more than 1.3 million ac (526,091 ha) of coastal and estuarine 

habitat in a network of 28 reserves located in 22 states and Puerto Rico. The reserves consist of 

relatively pristine estuarine areas that contain key habitat for purposes of long-term research, 

environmental monitoring, education, and stewardship and are protected from significant ecological 

change or developmental impacts (USDOC, NOAA, NERRS, 2011). The NERRs containing 

portions within the AOI are the Apalachicola Bay, the Rookery Bay, and the Mission-Aransas 

Reserves (Table 4.7-1 and Figure 4.7-2 of this Programmatic EIS).

The Apalachicola Bay Reserve is a lagoon and barrier complex consisting of a 99,553-ha 

(246,000-ac) reserve located on the Florida Panhandle. The reserve’s management area includes 

two barrier islands and a portion of a third, the lower 52 mi (84 km) of the Apalachicola River and its 

floodplain, portions of adjoining uplands, and the Apalachicola Bay estuarine, riverine, and floodplain 

systems. Major estuarine habitats found within the reserve include oyster bars, submerged 

vegetation, tidal flats, soft sediment, marshes, and open water (USDOC, NOAA, NERRS, 2009a). 
Gulf of Mexico G&G Activities Programmatic EIS E-123

The reserve supports forage habitat for migratory bird species and for economically important fish 

species.

The Mission-Aransas Reserve, located along western Gulf Coast, consists of a 75,154-ha 

(185,708-ac) contiguous complex of wetland, terrestrial, and marine environments. The wetland 

component consists of riparian habitat and freshwater and salt water marshes. The open water 

component consists of bays with tidal flats, seagrass meadows, mangroves, and oyster reefs 

(USDOC, NOAA, NERRS, 2009b). The reserve supports forage habitat for migratory bird species 

and for economically import fish species.

The Rookery Bay Reserve is located south of Naples along Florida’s Gulf Coast. The 

reserve is a coastal subtropical mangrove forested estuary consisting of approximately 44,516 ha 

(110,000 ac), 28,328 ha (70,000 ac) of which is open water. The remaining 16,188 ha (40,000 ac) 

are primarily composed of mangroves, fresh to brackish water marshes, and upland habitats, 

including upland hammocks and scrub. The reserve provides important habitat to more than 

150 species of birds, economically important fish species, and threatened and endangered species, 

including the Florida panther (USDOC, NOAA, NERRS, 2009c).

7.3.4 State-Designated Marine Protected Areas

There are numerous State-designated coastal MPAs along the coastal boundary of the AOI 

that include State parks, resource conservation areas (e.g., nature preserves, aquatic preserves, 

natural areas, and wildlife management areas), sanctuaries, water quality protection areas, and 

historical areas (Figure 4.7-2 of this Programmatic EIS). In addition, there are areas in Statedesignated MPAs where fishery activities are prohibited or controlled (Table 4.7 1 of this

Programmatic EIS). In total, there are 53 State-designated MPAs within the AOI. The portion of the 

MPA that falls within the AOI is provided in Table 4.7-1 of this Programmatic EIS.

Florida has 48 State-designated eligible MPAs, grouped by managing agency. The Florida 

Department of Environmental Protection (FDEP) manages 36 of these MPAs; the majority were 

designated for protection of natural heritage areas and one was designated for sustainable 

production. The vast majority of these MPAs are Outstanding Florida Waters, although many are 

also State parks and aquatic preserves. Outstanding Florida Waters are water features designated 

by FDEP as worthy of special protection because of their natural attributes and have special 

restrictions on any new activity that would lower water quality or otherwise degrade the body of 

water. Table 4.7-1 of this Programmatic EIS lists the FDEP-managed eligible MPAs, the total area 

that falls within the AOI, and the portion of the MPA that falls within the AOI.

The FWC manages eight MPAs; four are wildlife management areas and the other four are 

designated protection zones for the Florida manatee (Table 4.7-1 of this Programmatic EIS). 

Collectively, the manatee protection areas located within the AOI cover approximately 20.6 km2

(8.0 mi2

), which makes 3.2 percent of the total collective region designated with some form of 
E-124 Expanded Affected Environment Information

manatee protection. The remaining four FWC-managed MPAs have coastal portions of their total 

area that fall within the AOI.

The Florida Division of Historical Resources (FDHR) manage four MPAs that were 

designated to preserve underwater archaeological regions of cultural significance, primarily 

shipwrecks. Table 4.7-1 of this Programmatic EIS lists the FDHR-managed eligible MPAs, the total 

area that falls within the AOI, and the portion of the MPA that falls within the AOI.

Louisiana has five State-designated eligible MPAs, including a refuge and four wildlife 

management areas, three of which are also game preserves. All of these MPAs are managed by 

the Louisiana Department of Wildlife and Fisheries and are listed in Table 4.7-1 of this

Programmatic EIS.

Texas, Alabama, and Mississippi currently do not have any MPAs within the AOI.

8 SARGASSUM AND ASSOCIATED COMMUNITIES

Chapter 4.8.1 of this Programmatic EIS provides the succinct description of the affected 

environment for Sargassum and associated communities in sufficient detail to support the impact 

analyses. The following descriptions provide additional, expanded information.

Sargassum mats comprise two species of brown algae: Sargassum natans and S. fluitans. 

Each species is entirely pelagic, spending its entire life cycle on the ocean surface. Sargassum

reproduces by vegetative fragmentation (LaPoint, 1995), and its movement is controlled by surface 

winds and currents. Sargassum can be found alone or aggregated into large mats or long windrows, 

and it can be randomly spread across the ocean surface or found along current or wind-driven 

boundaries. Sargassum mats also merge with natural and anthropogenic flotsam like terrestrial 

vegetation, seagrass, and trash (Witherington et al., 2012). Sargassum mats can grow to a few 

acres in extent and 1 to 1.5 m (3 to 5 ft) thick. The size of the mats is variable, depending on local 

physical (e.g., currents and winds) and physicochemical (e.g., dissolved oxygen, salinity, and 

temperature) oceanographic conditions (USDOI, BOEM, 2012a). Individual plants can grow up to 

50 cm (20 in) in length and are characterized by a bushy, highly branched thallus (stem) with 

elongated toothed blades containing numerous spherical pneumatocysts (air bladders) (Littler et al., 

1989; Coston-Clements et al., 1991). Pelagic Sargassum mats provide habitat for fauna, including 

more than 100 species of fish; more than 100 species of invertebrates, including crabs, shrimp, and 

mollusks; 4 species of sea turtles; and many species of marine birds (Coston Clements et al., 1991). 

Epiphytic algae (a group of microscopic algae that grow on the surface of marine plants), encrusting 

hydroids, bryozoans, and tube worms are also associated with these communities. Sargassum

provides areas of high biological productivity in otherwise featureless waterbodies, supporting a 

diverse community during all life stages for foraging, protection from predators, and as nursery 

habitat.
Gulf of Mexico G&G Activities Programmatic EIS E-125

8.1 SARGASSUM DISTRIBUTION

Analysis of satellite imagery from 2003 to 2007 suggests that Sargassum grows in the 

northwest GOM during the spring of each year and is then adverted into the Atlantic Ocean during 

fall and winter by the Loop Current and Gulf Stream (Gower and King, 2011). As the Loop Current 

penetrates northward into the GOM, large anticyclonic (clockwise-rotating) eddies (rings) are shed 

(Section 18); these eddies provide the surface energy needed to move the Sargassum to the near 

coastal waters of the Mexico and Texas Gulf Coasts (Webster and Linton, 2013). Models are being 

developed for coastal managers to predict Sargassum mat movement, especially prediction of when 

and where large amounts will come ashore (Webster and Linton, 2013). Estimates suggest that 

0.6 to 6 million tons of Sargassum are present annually in the GOM, with an additional 100 million 

tons or more exported to the Atlantic (Gower and King, 2008 and 2011; Gower et al., 2013). Rapid 

growth of Sargassum ensures that the species are resilient and able to recover rapidly. Frazier et al.

(2015) uses NASA’s Landsat satellite imagery and data from ocean monitoring devices for use in the 

Sargassum Early Advisory predictive model. Frazier et al. (2015) observed the presence and 

abundance of Sargassum through the satellite imagery stating that it can take 2 to 5 months to reach 

the Texas Coast from the Sargasso Sea. 

8.2 FISH HABITAT

The habitat provided by Sargassum mats is important to the life histories of many species of 

pelagic, littoral, and benthic fishes, as the mats provide substrate, protection from predation, and 

access to food in the open sea (Dooley, 1972). Two fish species are endemic to Sargassum, 

spending nearly their entire lives within Sargassum habitat: sargassumfish and Sargassum pipefish 

(Chapter 4.3.2.1 of this Programmatic EIS). Other species, such as the Atlantic tripletail (Lobotes 

surinamensis) and various species of filefish (especially Stephanolepis spp.), appear to completely 

depend on drifting algae for refuge as juveniles (Hemphill, 2005). Some of the large pelagic, 

economically important fish utilizing Sargassum habitats include all life stages of tuna (Thunnus

spp.), dolphinfish, wahoo, and several species of billfish that temporarily associate with Sargassum. 

Wells and Rooker (2004b) documented the abundance of estuarine and pelagic fish species in 

Sargassum mats, indicating that Sargassum may serve as an important means of transport of larval 

and juvenile species between offshore and inshore waters. Larval and juvenile fish have been 

documented within, adjacent to, and below Sargassum, with the highest abundance and greatest 

diversity being documented in waters adjacent to Sargassum mats (Hoffmayer et al., 2005). Eggs 

and larvae of species associated with Sargassum include gray triggerfish, lesser amberjack (Seriola 

fasciata), almaco jack (Seriola rivoliana).

8.3 SEA TURTLE HABITAT

Four species of sea turtles (i.e., loggerhead, green, hawksbill, and Kemp’s ridley) have been 

documented in association with Sargassum in the GOM, specifically post-hatchling and early 

juvenile life stages. The four species of sea turtles have been observed actively foraging within the 

mats, resting and drifting while concealed by the mats, and diving below the mats (Witherington 

et al., 2012). Similar observations of hatchling and juvenile sea turtles’ utilization of Sargassum as 
E-126 Expanded Affected Environment Information

transport via passive drifting and foraging is reported in Carr and Meylan (1980) for green sea turtles 

and in Collard and Ogren (1990) for Kemp’s ridley sea turtles. These observations suggest that sea 

turtles may complete their pelagic developmental life stage within Sargassum communities and then 

transition to neritic zone habitats as subadults.

Sargassum habitat in the offshore waters of the EPA, as well as most of the CPA and WPA,

was designated as critical habitat in July 2014 (79 FR 39856) for hatchling loggerhead sea turtles 

(Figure 4.3-3 of this Programmatic EIS). The designation was established because the survival of 

loggerhead sea turtles, in particular the post-hatchling and small oceanic juvenile stages, depends 

on suitable foraging and shelter habitat, which are provided by Sargassum in the Atlantic and GOM 

(79 FR 39856).

8.4 INVERTEBRATE HABITAT

The invertebrate community that inhabits Sargassum includes motile and sessile species. 

Common invertebrates include hydroids, anthozoans, flatworms, bryozoans, polychaetes, 

gastropods, nudibranchs, bivalves, cephalopods, pycnogonids, isopods, amphipods, copepods, 

decapod crustaceans, insects, and tunicates. Shrimps and crabs make up the bulk of invertebrates 

and are a major food source for Sargassum-associated fishes (Dooley, 1972).

9 COMMERCIAL FISHERIES

Chapter 4.9.1 of this Programmatic EIS provides the succinct description of the affected 

environment for commercial fisheries in sufficient detail to support the impact analyses. The 

following descriptions provide additional, expanded information.

The AOI supports regionally and nationally important commercial fisheries. The NMFS’ 

Fisheries Statistics Division has automated data summary programs that can be used to rapidly and 

easily summarize U.S. commercial fisheries landings (USDOC, NMFS, 2015c). For the purposes of 

this Programmatic EIS, it is not practicable to report specific fisheries landings using the statistics 

queries because data are updated weekly; therefore, this characterization of commercial fisheries is 

primarily summarized from the most recently published Fisheries Economics Report (USDOC, 

NMFS, 2014).

In 2012, the seafood industry in the five coastal states adjacent to the AOI supported nearly 

160,000 jobs (Table 4.9-1 of this Programmatic EIS). Commercial fisheries support numerous 

directly related jobs (fishing crews) as well as many indirectly related industries such as seafood 

distributors, restaurants, and suppliers of commercial fishing gear. Commercial fishing ports often 

support entire coastal fishing communities and local businesses; thus, the fishing industry is an 

important component to the economy of the GOM. In 2012, the GOM region’s seafood industry 

generated a total of approximately $22 billion in sales impacts, with Louisiana generating $1.9 billion 

of that total. Florida generated the largest employment, income, and value added impacts, 

generating 82,000 jobs, $3.1 billion, and $5.5 billion, respectively. Louisiana and Texas had the 
Gulf of Mexico G&G Activities Programmatic EIS E-127

highest landings revenue in the region in 2012, $331 million and $194 million, respectively; the next 

greatest landings revenue came from Florida with $142 million (USDOC, NMFS, 2014). 

9.1 COMMERCIAL LANDINGS

Table 4.9-2 of this Programmatic EIS shows commercial landings in thousands of pounds of 

key species or species groups within the GOM, including blue crab, crawfish, groupers, menhaden, 

mullets, oysters, red snapper, shrimp, stone crab, and tunas (USDOC, NMFS, 2014). Fishers in the 

GOM region landed 1.7 billion lb of finfish and shellfish in 2012. Finfish landings contributed 

82 percent of total landings in the GOM region (1.3 billion lb) in 2012.

Commercial fisheries in the AOI target a variety of fish and invertebrate species in State and 

Federal waters. Landings data do not indicate actual areas where particular species were caught; to 

accurately interpret fishing activity within the AOI from landings data for the coastal states, 

inferences must be made using knowledge of broad habitat use by species represented in the 

dataset. For example, 2012 landings data (Table 4.9-2 of this Programmatic EIS) indicate that blue 

crab is an important fishery species (54.5 million lb in 2012), but blue crabs live primarily in inshore 

waters and would not be part of the fisheries for the AOI. The eastern oyster is a similar example of 

an inshore species making substantial contributions to landings data that should not be used to 

characterize fisheries in the AOI.

9.2 COMMERCIAL FISHING GEARS

The main commercial fishing gears used within the AOI and along the Gulf Coast are bottom 

trawls, purse seines, gill nets, pots/traps, and longlines (bottom and pelagic). Table 4.9-3 of this

Programmatic EIS provides the species sought, seasons, and general areas fished with each gear 

type; a summary of the gear types is provided here.

Bottom trawls are large bag-shaped nets constructed with natural fibers or synthetic 

materials that typically have rectangular mouth openings. Trawls are towed at specific water depths 

(surface, mid water, or bottom), depending on the target species. Trawls are classified by their 

function, bag construction, or method of maintaining the mouth opening (Stevenson et al., 2004). 

Bottom trawls are designed to be towed along the seafloor to catch a variety of demersal fish and 

invertebrate species (e.g., shrimps, Gulf flounder [Paralichthys albigutta], or Atlantic croaker).

Purse seines are a type of net constructed with natural fibers or synthetic materials that are 

used to encircle a school of fish. Once the net has captured a school of fish, it is then cinched 

closed. Purse seines are primarily used to target Gulf menhaden within the inner shelf of the AOI 

during spring and summer months.

Gill nets are constructed of long panels of monofilament netting (mesh size approximately 

3 to 4 in [8 to 10 cm]) with lead line at the bottom and float line at the surface. Nets are set 

perpendicular to shore or encircling a target school of fish. Gill nets are used to catch Spanish 
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mackerel, mullet, black drum, and other coastal species by entanglement in coastal waters offshore 

Alabama, Mississippi, and Louisiana; gill nets are prohibited in Florida and Texas.

Pots/traps are rectangular, square, or cylindrical-enclosed devices with one or more gates 

set on the bottom to target benthic invertebrates (e.g., blue crab, stone crab, spiny lobster, and 

deep-sea red crab). Pots/traps usually are marked at the surface with a buoy that is attached to the 

pot or trap by a rope. This type of gear is usually set in strings near natural or artificial structure or 

hard bottom. Pots are connected by “mainlines” that float or sink to the bottom (Stevenson et al., 

2004). This method is primarily used offshore Florida.

Longlines typically consist of 1.6 to 64.4 km (1 to 40 mi) of monofilament mainline with 

leaders attached to baited hooks (gangions) clipped at regular intervals. The mainline is attached to 

a series of floats equipped with radar reflectors and with radio beacons. Longlines are classified by 

where the gear is set in the water column; longline gear is set at the surface in open waters of the 

GOM or on the seafloor in OCS waters from Florida to Texas on suitable bottom type. Longlines 

drift with the currents or are anchored to the bottom and are used to target benthic (e.g., tilefish and 

large coastal sharks), coastal pelagic (e.g., dolphinfish and wahoo), and pelagic (e.g., tunas, 

swordfish, or pelagic sharks) species (Stevenson et al., 2004).

9.3 TIME AND AREA CLOSURES AND GEAR RESTRICTIONS

One method that FMCs use to control commercial fishing effort or protect specific habitats is 

to designate closed areas or to close fisheries (temporarily, seasonally, or permanently). To notify 

the public of fishery or site closures, the NMFS publishes the regulations, which are usually 

associated with an FMP amendment or management action, in the Federal Register. When a 

closure has been approved, the FMCs, in cooperation with the NMFS, announce these closures by 

posting them to their websites, sending emails and faxes, or holding public meetings. In addition to 

closing fisheries or areas for fish conservation management reasons, regulatory agencies use 

closed areas to protect marine mammals and sea turtles (e.g., from entanglement in discarded 

fishing gear).

Permanent commercial fishing closures can also consist of prohibiting various types of 

commercial fishing gears or fishing techniques. Table 4.9-4 of this Programmatic EIS summarizes 

areas where certain commercial fishing activities are prohibited or where gear restrictions apply 

during all or part of the year; however it is important to note that regulations fluctuate on a regular 

basis and current information on rules must be obtained from the NMFS or GMFMC. Figure 4.9-1 of

this Programmatic EIS shows the locations of most of these closure areas.

10 RECREATIONAL FISHERIES 

Chapter 4.10.1 of this Programmatic EIS provides the succinct description of the affected 

environment for recreational fisheries in sufficient detail to support the impact analyses. The 

following descriptions provide additional, expanded information.
Gulf of Mexico G&G Activities Programmatic EIS E-129

Recreational fishing is an important social and economic activity. Nationally, 8.9 million 

saltwater recreational anglers made 86 million trips and spent $10.3 billion in 2011 (USDOI, FWS 

and USDOC, Census Bureau, 2014). Saltwater recreational fisheries in states adjacent to the AOI 

are among the most valuable in the U.S. In 2012, total fishing trip and durable equipment 

expenditures were $10 billion, and major expenditures included boat expenses ($4.8 billion), fishing 

tackle ($1.4 billion), vehicle expenses ($1.2 billion), second home expenses ($896 million), and other 

equipment ($558 million). In 2012, west Florida ranked first ($9.1 billion) and Louisiana ranked third 

($2 billion) nationally in sales impacts from total expenditures related to recreational fishing 

(USDOC, NMFS, 2014). Among the Gulf Coast States, the number of trips, jobs, sales, income, and 

value-added impacts from recreational fishing were highest in Florida (west coast) in 2012 (Table 

4.10-1 of this Programmatic EIS).

In 2011, Florida ranked first nationally for total expenditures and durable goods expenditures 

related to recreational fishing (Lovell et al., 2013). Among the Gulf Coast States, sales, income, and 

employment impacts created by recreational fishing were highest in Florida (west coast), while the 

impacts generated from shore-based fishing were highest in Texas (Lovell et al., 2013). In 2011, 

Federal taxes generated by angler purchases ranged from $8.5 million (Mississippi) to $661 million 

(Florida), while revenue received by State/local governments ranged from $10.9 million (Mississippi) 

to $534 million (Florida) (Lovell et al., 2013).

In their comprehensive national analysis of recreational fishing, Coleman et al. (2004b) 

estimated that saltwater fishing accounted for approximately 4 percent of the total marine fish landed 

in 2002. However, recreational fishing accounts for a much larger percentage of the total landings 

for populations of concern in the GOM (64%) (Coleman et al., 2004b). Worldwide, increases in 

recreational fishing activity may threaten some already overfished populations (Cooke and Cowx, 

2004); in 2002, recreational fishing activities landed approximately 23 percent of the overfished 

stocks in the U.S. (Coleman et al., 2004b).

10.1 RECREATIONAL FISHING EFFORT

The annual number of recreational angler trips is a measure of recreational fishing effort that 

is monitored by the NMFS via the Marine Recreational Information Program, which is an automated 

data query system that maintains a searchable database of recreational saltwater fishing catch, 

effort, and participation data and statistics. For the purposes of this Programmatic EIS, 

characterization of commercial fisheries is primarily summarized from the most recently published 

Fisheries Economics Report (USDOC, NMFS, 2014).

Recreational fishing effort within the GOM in 2012 consisted of more than 3.1 million 

recreational anglers taking 23 million trips (Table 4.10-1 of this Programmatic EIS); anglers were 

primarily (>91%) residents of the Gulf Coast. Recreational fishing is a year-round activity throughout 

the AOI and can be classified as a nearshore or offshore effort depending on the size of the vessel 

and its fishing location (distance from shore). Nearshore recreational fishing (<4.8 km [3.0 mi]) 

consists of anglers fishing from private vessels and along beaches, marshes, or man-made 
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structures (e.g., jetties, docks, and piers), whereas offshore fishing consists of anglers fishing from 

larger vessels (i.e., private, rental, charter, or party) in offshore waters (>4.8 km [3.0 mi]). According 

to the USDOC, NMFS (2014), recreational fishing trips in the AOI (Louisiana, Mississippi, Alabama, 

and Florida) during 2012 were primarily from private/rental boats (55%), shore (41%), and charter 

vessels (4%). In 2013, the majority of recreational fishing trips were from Florida (60%), while other 

Gulf Coast States accounted for 18 percent (Louisiana), 11 percent (Alabama), 7 percent 

(Mississippi), and 4 percent (Texas) of the total number of trips (USDOC, NMFS, 2014).

10.2 RECREATIONAL FISHING LOCATIONS

Marine fishes depend on and utilize many different types of habitats (e.g., seagrass, salt 

marsh, soft bottom, hard bottom) for feeding, spawning, and nursery grounds. Given the importance 

of these areas to the fish, recreational anglers have many opportunities to target various species in 

these habitats. For example, anglers targeting reef fishes (groupers and snappers) target offshore 

structure (natural and artificial reefs or ledges) (Chapter 4.5.5.2 of this Programmatic EIS), while 

anglers pursuing inshore fishes (spotted seatrout and redfish) target seagrass habitat (Section 20).

10.3 RECREATIONAL CATCH CHARACTERISTICS

Recreational fishing is a year-round activity, but many anglers target specific species at 

certain times, and recreational fishing effort is often weather-dependent; more recreational fishing 

effort occurs during spring through summer when the weather is ideal for anglers fishing from small 

watercraft. The choice of fish species targeted by recreational anglers depends on the season, 

fishing location, and seasonal movement of the target species. For example, one of the best times 

to target pelagic species such as dolphinfish and sailfish in the GOM is during late summer and early 

fall. Bottom fishing for snapper, grunts, and porgies increases during the summer, while grouper 

fishing is best during winter.

The types and numbers of fishes caught by recreational anglers vary by state within the AOI. 

Of the Gulf of Mexico OCS Region’s key species and species groups, spotted seatrout (33 million 

fish), red drum (9 million fish), sand and silver seatrout (7.4 million fish) and Atlantic croaker 

(5.2 million fish) were the most often caught by anglers in 2012 (Table 4.10-3 of this Programmatic 

EIS).

10.4 RECREATIONAL FISHING TOURNAMENTS

Organized saltwater fishing tournaments are held throughout the AOI and are popular 

amateur and professional events that can range in participation from approximately 50 to more than 

2,050 vessels from throughout the U.S. Tournaments can draw large spectator crowds onshore, 

which contributes to the local economy; tournament prizes can be more than $1 million and involve 

corporate sponsors and non-profit beneficiaries. Recreational fishing tournaments are held yearround but most take place in summer. In general, many fishing tournaments are held at the same 

time and place each year; local communities often rely on fishing tournaments to stimulate the local 

economy (e.g., restaurants, hotels, fuel, and supplies). Depending on the fishing tournament and its 
Gulf of Mexico G&G Activities Programmatic EIS E-131

rules, participants have the option to participate in inshore (e.g., red drum, spotted seatrout, snook) 

or offshore (e.g., dolphinfish, wahoo, kingfish) categories, or enter both categories. Every fishing 

tournament has its own set of rules for classes of eligible fish, size limits, time limits, and specific 

geographical boundaries. Based on the tournament’s rules and eligible fish, participant teams 

choose fishing sites and tactics according to their fishing experience and local knowledge. 

Throughout the AOI, there are many fishing tournaments that are annual events; however, it is 

difficult to identify all tournaments given that some are one-time events and sponsorships can 

change from year to year. Overall, saltwater fishing tournaments in the AOI are a traditional 

community-based pastime and important local tradition; there is at least one tournament every 

weekend somewhere between Texas and Florida during the spring/summer months (Table 4.10-4 of

this Programmatic EIS).

11 ARCHAEOLOGICAL RESOURCES

Chapter 4.11.1 of this Programmatic EIS provides the succinct description of the affected 

environment for archaeological resources in sufficient detail to support the impact analyses. The 

following descriptions provide additional, expanded information.

Submerged cultural resources within the AOI include shipwrecks that occurred as early as 

the 16th and 17th centuries during exploration and settlement of North America by Europeans. 

Submerged prehistoric sites dating between 12,000 and 3,500 before present (B.P.) may also be 

present within the AOI, depending on regional landform variation.

The AOI includes State and Federal waters (outside of estuaries) from the Florida Keys in 

the east to the Rio Grande Estuary, Texas, in the west, extending from the coastline to the EEZ, 

200 nmi ( 230 mi; 370 km) seaward from the mean high water line. BOEM’s guidelines state that the 

maximum depth for renewable energy development is 40 m (131 ft) and for marine minerals 

development is 30 m (98 ft). In this discussion, “nearshore” refers to waters from the shoreline to the 

40-m (131-ft) isobath, the maximum limit for G&G activities. “Offshore” refers to the zone extending 

from the 40-m (131-ft) isobath to the outer boundary of the AOI.

11.1 HISTORIC SHIPWRECKS

European explorers have been active in the GOM since the late 16th century, but it was not 

until the second decade of the 17th century that explorers reached the northern GOM within the AOI. 

Shipwrecks within the AOI date from the 16th century until modern times.

The number of shipwrecks and obstructions in the AOI were estimated using information 

from various databases, including the NOAA Automated Wreck and Obstruction Information System 

(AWOIS) (updated January 2015), the NOAA Aids to Navigation (NavAids), the NOAA Electronic 

Navigational Charts (ENC) Direct (updated January 2015), the U.S. Coast Guard (USCG) Hazards 

to Navigation, and the Global GIS Data Services, LLC Global Maritime Wrecks Database (GMWD). 

Information from the AWOIS database includes position (latitude/longitude), feature description, and 

any known historic or descriptive details. Positional accuracy of AWOIS wrecks and obstructions is 
E-132 Expanded Affected Environment Information

highly variable and can have an error of as much as a 1 km (0.5 nmi; 0.6 mi) or more. The NOAA 

NavAids database identifies wreck locations, obstructions, platforms, submerged pilings, 

navigational aids, and light/channel markers. The NOAA ENCDirect contains limited information, 

mainly describing wrecks as dangerous or non-dangerous and identifying source date and chart 

number. The USCG Hazards to Navigation database identifies obstructions, wreck locations, buoys, 

and unidentified object locations. The GMWD provides a range of information for each site, 

including wreck name, wreck nationality, date of sinking, depth of wreck, vessel category, gross 

tons, sinking agent, nominal accuracy of wreck location, source of wreck, nationality of the vessel 

that sunk the wreck if applicable, and more.

A variety of secondary sources with information about shipwrecks in the AOI were reviewed, 

including Berman (1973), Lytle and Holdcamper (1975), and Marx (1987). Lytle and Holdcamper 

(1975) compiled a comprehensive registry (known as the Lytle-Holdcamper List) of most steam 

vessels in the U.S. from 1790 to 1868. This list was originally compiled in 1952 and reprinted in 

1975. The primary sources, collected and compiled by William M. Lytle, include abstracts of 

registers, licenses, and enrollment documents sent or surrendered to the Bureau of Navigation. The 

list also includes a section titled “Losses of United States Merchant Vessels, 1790-1868” that 

provides vessel name, tonnage, year built, nature of wreck, date, place, and lives lost. More than 

3,800 vessels are listed as lost between 1790 and 1868. While the reference is general in nature 

and only covers American steam vessels through the Civil War, it provides an indication of the 

potential number and location of shipwrecks within the AOI. Berman’s work includes approximately 

13,000 shipwrecks within American waters (excluding vessels <50 gross tons). Berman’s 

encyclopedia includes shipwrecks in coastal waters and inland waterways dating from the 

pre-Revolutionary era to modern times.

Many of the shipwreck databases and secondary sources overlap, generating repetitiveness 

in the data. Additionally, these sources are far from comprehensive. They tend to focus on large 

merchant vessels and omit the smaller coastal trading, fishing, and other locally built watercraft that 

may be present as shipwrecks in the nearshore zone of the AOI. Omission of smaller coastal 

watercraft from shipwreck databases would underestimate the number of shipwrecks in the 

nearshore zone.

Review of all databases and secondary sources identified 12,485 known wrecks, 

obstructions, archaeological sites, occurrences, or sites marked as “unknown” in the AOI (Figure 

4.11-1 of this Programmatic EIS). Of these sites, 10,410 (83%) are within the 40-m (131-ft) depth 

contour (nearshore zone) and 2,075 (17%) are in deeper waters (offshore zone). The number of 

offshore zone losses, however, should be considered underrepresented as there were undoubtedly 

many more sinkings that were not recorded because there were no survivors to report the loss. 

Although many obstructions identified as “unknown” are eventually identified through diver 

investigation as modern debris, those that have not been investigated cannot be ruled out as 

potential submerged cultural resources.
Gulf of Mexico G&G Activities Programmatic EIS E-133

Three studies sponsored by the NPS and BOEM included models to identify areas in the 

GOM where shipwrecks may occur. The first of these studies, conducted by Coastal Environments, 

Inc. (CEI) in 1977, estimated that there were 2,500 to 3,000 wrecks within the GOM. The authors 

concluded that approximately two-thirds of those wrecks lie within 1.5 km (0.8 nmi; 0.9 mi) of the 

coast and that most of the remainder could be found within 10 km (5.4 nmi; 6.2 mi) of the coast (CEI, 

1977). The study also concluded that shipwrecks are likely to be concentrated around areas of 

intensive maritime activity such as the approaches and entrances to ports as well as the mouths of 

navigable rivers and straits, and around natural maritime hazards such as reefs and shoals. 

Garrison et al. (1989) expanded upon CEI’s work, utilizing statistical analysis to examine five factors 

that affect shipwreck locations: historic shipping routes; port locations; natural hazards (reefs, 

shoals, etc.); ocean currents and winds; and historic hurricane routes. This study concluded that a 

large percentage of wrecks occurred in the open seas, a reflection of changes in shipping routes 

during the late-19th to early-20th century (Garrison et al., 1989). Garrison et al. (1989) divided the 

GOM into zones ranked by the potential for shipwrecks and the preservation potential of shipwrecks 

to help the MMS (BOEM’s predecessor) identify OCS lease blocks that would require archaeological 

surveys. However, remote-sensing surveys conducted since 1989 and new shipwreck discoveries in 

the GOM have revealed deficiencies in the 1989 model. As a consequence, the MMS authorized an 

additional study to reevaluate and refine the work of that study as well as previous studies.

Pearson et al. (2003) conducted the reevaluation study, utilizing geographic information 

systems (GIS) and nearly 15 years of new data from high-resolution oil and gas shallow hazard 

surveys to refine the previous models of shipwreck distribution and probability of shipwrecks in the 

GOM. By incorporating new variables and quantitative measures in the analysis, Pearson et al. 

(2003) increased the number of OCS lease blocks designated as having a high probability for 

shipwreck resources. Several of the new OCS lease blocks were located in deepwater regions, 

notably in areas of heavy maritime traffic such as the approaches to the Mississippi River. BOEM 

and BSEE have published guidelines (NTL 2005-G07 and NTL 2008-G20 [superseded by NTL 

2011-JOINT-G01]) for performing archaeological surveys and, as a result of the information from the 

cited studies, have revised the guidance and gradually increased the number of OCS lease blocks 

requiring archaeological surveys. As a result of BOEM’s requirements for archaeological surveys in 

the OCS, at least 39 potential historic shipwreck sites have been identified since the implementation 

of the guidelines in 2005. Furthermore, within the last 6 years, a dozen potential shipwrecks have 

been discovered by oil industry surveys in water depths up to 2,987 m (9,800 ft) (USDOI, BOEM, 

2012a). Nine of the potential sites have been visually confirmed as shipwrecks (USDOI, BOEM, 

2012a).

11.2 PREHISTORIC RESOURCES

Submerged cultural resources include prehistoric archaeological sites. Based on previous 

research, sea levels were approximately 90 to 130 m (295 to 427 ft) lower than present at the end of 

the last glacial period approximately 20,000 B.P. and did not reach current levels until approximately 

3,500 B.P. (Pearson et al., 1986). Archaeological evidence indicates that the GOM region was 

occupied by prehistoric people as long ago as 12,000 B.P. Sea-level curves produced by CEI 
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(1977, V1) indicate that sea level was approximately 45 to 60 m (148 to 197 ft) below present level 

at that time. Therefore, the continental shelf shoreward of this range of depth contours has the 

potential for containing prehistoric sites. Due to uncertainties in the rate of sea-level rise and in the 

time of entry of native populations into North America, BOEM has set the 60-m (197-ft) depth 

contour as the seaward extent of potential submerged prehistoric sites on the continental shelf.

Research conducted by CEI (1977, V1) identified several geomorphic features that could 

contain prehistoric sites, including barrier islands, back-barrier embayments, river channels and 

associated floodplains, terraces, and salt domes. The possibility of locating submerged prehistoric 

sites would be greatest in the nearshore zone (<60-m [197-ft] water depth) because portions of this 

area would have been exposed land during the period of human occupation. Survival of sites on the 

OCS is attributed to several factors, including degree of sediment overburden, presence of low wave 

energy environments, and speed of sea-level rise. In the AOI, Holocene deposits are thicker in west 

Texas and the Mississippi River Delta region. Due to its complex of overlapping deltaic lobes, sites 

in the Mississippi River Delta can be buried by up to 91 m (300 ft) of Holocene sediment (USDOI, 

BOEM, 2012a). In western Louisiana and eastern Texas, Holocene sediments generally are thin 

and late Pleistocene deposits lie only a few meters below the seafloor. The McFaddin Beach site 

(Texas Historical Commission site number 41JF50) in Jefferson County, Texas, is an example of a 

site in this region. Artifacts dating between 11,500 and 400 B.P. have been found along the current 

shoreline and are thought to have resulted from redeposition of material from a now-submerged but 

eroding shoreline (Stright et al., 1999, V1). East of the Mississippi River, sediments are sandier and 

the general environment is more energetic. Farther to the east along the western coast of Florida, 

the area is dominated by karst formations, and although located in a relatively low-energy 

environment, the region is sediment starved. Sites in this region typically are found exposed on 

rocky outcrops above karstic river channels (Faught and Gusick, 2011).

Until recently, the earliest material culture that has been identified in the Paleo-Indian period 

in the U.S., called Clovis, is represented by distinctly basal fluted projectile points that date back to 

12,500 B.P. This Paleo-Indian settlement pattern is described as semi-nomadic within a defined 

territory, reliant on reliable freshwater sources and cryptocrystalline raw material sources, exploiting 

large and small game as well as wild plants. As a result of a semi-nomadic settlement pattern, 

Paleo-Indian sites that are most visible in the archaeological record would most likely be located in 

proximity to freshwater sources that would have been visited repeatedly. Clovis culture material can 

be found throughout most of the U.S.

Recently, there have been sites discovered that could pre-date the Clovis culture. Sites such 

as Cactus Hill and Saltville in Virginia show evidence of Clovis and what appears to be pre-Clovis 

occupation. In central Texas, ongoing excavations at the Debra L. Friedkin Site are revealing a 

distinct assemblage of multifaceted flake tools that may indicate a pre-Clovis occupation (Waters 

et al., 2011). Material from the site indicates an occupation from 13,200 to 15,500 B.P. It has been 

hypothesized that the original routes taken by migrants that eventually populated the U.S. might 

have followed a coastal migration.
Gulf of Mexico G&G Activities Programmatic EIS E-135

Conditions necessary for preservation of Paleo-Indian sites along the Gulf of Mexico OCS 

are variable and depend on geomorphological conditions and the rate of sea-level rise. Current 

research on regional geology, relative sea-level change, and marine transgression are providing 

useful data concerning the possibility that there may be intact Paleo-Indian sites submerged along 

the Gulf of Mexico OCS. These submerged Paleo-Indian sites would most likely be found in the 

vicinity of paleochannels or river terraces that offer the highest potential of site preservation.

12 OTHER MARINE USES

Chapter 4.12.1 of this Programmatic EIS provides the succinct description of the affected 

environment for other marine uses in sufficient detail to support the impact analyses. The following 

descriptions provide additional, expanded information.

Other uses of the marine environment in the AOI include shipping and other marine traffic; 

military warning areas that are used for military exercises, training, and other military activities; sand 

and gravel mining; renewable energy development; ocean dredged material disposal; and oil and 

gas exploration and production. Commercial and recreational fishing are described in Sections 9 

and 10, respectively. Recreational resources and tourism are described in Section 15 and human 

resources are described in Section 16. 

The Multipurpose Marine Cadastre, a web-based tool developed by BOEM, NOAA’s Coastal 

Services Center, and other partners, was used to identify the uses of the AOI. The Multipurpose 

Marine Cadastre is an integrated marine information system that provides legal, physical, ecological, 

and cultural information in a common GIS framework. The Multipurpose Marine Cadastre is used by 

Federal agencies and others who are evaluating renewable energy sites and other offshore activities 

as well as others working on regional and State coastal and marine spatial planning efforts. At its 

core, the Multipurpose Marine Cadastre contains the official U.S. marine cadastre and is the only 

utility where users can see all of the official U.S. boundaries on one map. Similar to the Nation’s 

land-based parcel system, a marine cadastre provides information about the spatial extent, rights, 

restrictions, and responsibilities of those wanting access to U.S. waters. All data come from the 

authoritative organizations responsible for data maintenance. In addition to data available from the 

Multipurpose Marine Cadastre, data from BOEM and the Naval Facilities Engineering Command 

(NAVFAC) was used to identify other uses of the marine environment within the AOI.

12.1 SHIPPING AND MARINE TRANSPORTATION 

The USCG designates shipping fairways and establishes traffic separation schemes that 

control movement of vessels as they approach ports (Figure 4.12-1 of this Programmatic EIS) 

(33 CFR part 166). Each port is serviced by a navigation channel maintained and regulated by the 

USACE. Traffic fairways and the buoys and beacons that serve as navigation aids are identified on 

NOAA’s Office of Coast Survey’s navigation charts.

Vessels operating in the AOI include commercial shipping vessels, military vessels, 

commercial business craft (e.g., support vessels, tug boats, fishing vessels, and ferries), commercial 
E-136 Expanded Affected Environment Information

recreational craft (e.g., cruise ships and fishing/sightseeing/diving charters), research vessels, and 

personal craft (e.g., fishing boats, house boats, yachts and sailboats, and other pleasure craft).

Seven deepwater commercial ports that can handle fully laden Panamax ships (pre-Panama 

Canal expansion) are located along the Gulf Coast adjacent to the AOI:

• Houston, Texas;

• Corpus Christi, Texas;

• Beaumont, Texas;

• Galveston, Texas;

• New Orleans, Louisiana;

• Mobile, Alabama; and

• Tampa, Florida.

The Port of Houston ranks first in the U.S. in foreign waterborne tonnage, first in U.S. 

imports, first in U.S. export tonnage, and second in the U.S. in total tonnage. It is also the Nation’s 

leading breakbulk port, handling 65 percent of all major U.S. project cargo (Port of Houston 

Authority, 2015). The Port of South Louisiana located on the Mississippi River ranks first in total 

tonnage. These deepwater ports are discussed further in Section 12.6.1. Large commercial 

vessels (i.e., cargo ships, tankers, and container ships) use these ports to access overland rail and 

road routes to transport goods throughout the U.S. In 2011, Gulf ports (from Brownsville, Texas, to 

Key West, Florida) accounted for 34.1 percent of U.S. vessel calls of oceangoing vessels 

>10,000 deadweight tons (U.S. Department of Transportation, Maritime Administration, 2013). 

Additional information regarding ports within the AOI is provided in Section 16.1. 

Commercial business craft include support vessels, fishing vessels, and ferries. The primary 

types of OCS support vessels include anchor handling, towing, and supply vessels; offshore supply 

vessels; and marine platform supply vessels. The level and locations of activity are irregular, and 

the ports utilized vary based on the activity.

Commercial recreational craft include cruise ships, fishing charters (Section 10), sightseeing 

charters, and diving charters (Section 15). Major cruise ship terminals in the AOI include Galveston, 

Texas; New Orleans, Louisiana; and Tampa, Florida. Numerous coastal cities host smaller charters, 

which typically operate near the coasts.

12.2 MILITARY WARNING AREAS AND OTHER MILITARY USES

Military Warning Areas (MWAs) are established in the AOI to allow military forces to conduct 

training and testing activities. Most of the AOI is within an MWA, as shown in Figure 4.12-2 of this
Gulf of Mexico G&G Activities Programmatic EIS E-137

Programmatic EIS. Military activities can include air-to-air, air-to-surface, and surface-to-surface 

Naval fleet training, submarine and antisubmarine training, and Air Force exercises.

The GOM includes 12 MWAs and 6 Eglin Water Test Areas (EWTAs) (Figure 4.12-2 of this

Programmatic EIS) (NTL 2014-BOEM-G04). Military operations and oil and gas exploration and 

production have coexisted for many years in these multi-use areas. The MWAs and EWTAs 

cumulatively include 75 percent of the total acreage of the WPA, 31 percent of the total acreage of 

the CPA, and 91 percent of the total acreage of the EPA. The U.S. Department of the Navy has 

issued a standard Military Areas Stipulation that is applied to all lessees and operators in the GOM, 

which includes the following provisions:

• Hold and Save Harmless: Lessee assumes all risks of damage or injury to 

persons or property in connection with activity performed by the lessee. 

• Electromagnetic Emissions: Lessee agrees to control its own electromagnetic 

emissions and must coordinate with appropriate military installation command 

headquarters. 

• Operational: Lessee must enter into an agreement with the appropriate military 

command headquarters.

In addition, the following provisions are applied to lessees and operators with activities within 

an EWTA:

• Evacuation Stipulation: Lessee is required to evacuate, upon receipt of a 

directive from BOEM’s Regional Director, all personnel from structures on the 

lease. Lessee must also shut-in and secure all wells and other equipment, 

including pipelines, on the lease.

• Coordination Stipulation: Lessee is required to consult with the appropriate 

military command headquarters regarding the location, density, and planned 

periods of operation of surface structures on the lease, and to maximize 

exploration while minimizing conflicts with U.S. Department of Defense activities 

prior to approval of an exploration plan by BOEM’s Regional Director.

Portions of the AOI are further classified as danger zones, which can be closed or subject to 

limited public access during intermittent periods. Danger zones and restricted areas are defined in 

33 CFR § 334.2 and are described as follows:

• Danger Zone: A defined water area used for target practice, bombing, rocket 

firing, or other especially hazardous operations, normally for the armed forces. 

Danger zones may be closed to the public on a full-time or intermittent basis, as 

stated in the regulations.
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• Restricted Area: A defined water area for the purpose of prohibiting or limiting 

public access to the area. Restricted areas generally provide security for 

government property and protection to the public from the risks of property 

damage or injury arising from the U.S. Government’s use of that area.

Military vessels operating in the AOI are associated with training and testing activities. The 

Naval Surface Warfare Center Panama City Division conducts activities involving a variety of Naval 

assets including vessels, aircraft, and underwater systems that support eight primary research, 

development, test, and evaluation capabilities: air, surface, subsurface, sonar, laser, 

electromagnetic, live ordnance, and projectile firing. Vessel movements will be disclosed following 

standard operating procedures associated with test planning, and a Notice to Mariners will be 

released 24 hours prior to a scheduled test event that requires a secured test area, providing other 

vessels ample time to plan accordingly.

Unexploded Ordnances

The GOM has 26 sites that contain unexploded ordnances, submerged explosives, depth 

charges, torpedoes, or other obstructions, or that are identified as discontinued dump sites for 

explosives or other wastes (Figure 4.12-2 of this Programmatic EIS). These hazard areas, ranging 

in size from approximately 0.006 to 3,877 km2 (0.002 to 1,497 mi2

), are distributed across the AOI, 

cumulatively covering 8,943 km2 (3,453 mi2

) of seafloor.

12.3 SAND AND GRAVEL MINING

BOEM may offer and enter into a noncompetitive negotiated agreement (lease) for sand, 

shell, or gravel resources following the 1994 amendments to the Outer Continental Shelf Lands Act 

(OCSLA) (Public Law [P.L.] 103-426) for certain types of projects funded in whole or part by, or 

authorized by, the Federal Government. The Shore Protection Provisions of the Water Resource 

Development Act of 1999, which amended P.L. 103-426, prohibits charging State and local 

governments a fee for using OCS sand. For all other uses, a competitive bidding process is required 

under Section 8(k)(1) of the OCSLA. The Marine Minerals Program, which is administered by 

BOEM, primarily centers on the identification and use of OCS sand for tax-funded beach 

nourishment and coastal restoration projects (USDOI, BOEM, 2015a). Offshore sand resources in 

the GOM are limited in coastal areas where sand is needed for nourishment and restoration projects. 

Compounding this scarcity of sand is that vast areas of these relatively small offshore sand 

resources are not extractable because of the presence of oil and gas infrastructure, archaeologically 

sensitive areas, and biologically sensitive areas. BOEM’s Marine Minerals Program is implementing 

several measures to help safeguard the most significant OCS sediment resources, reduce multi-use 

conflicts, and minimize interference with oil and gas operations under existing leases and rights-ofway. Figure 4.12-3 of this Programmatic EIS shows the OCS lease blocks with significant sediment 

resources (USDOI, BOEM, 2015b), including those listed in Table E-1. 
Gulf of Mexico G&G Activities Programmatic EIS E-139

Table E-1. OCS Lease Blocks with Significant Sediment Resources

Lease Area OCS Lease Blocks

Breton Sound Area 41, 42, 43, 44, 53, 54, 55, and 56

Chandeleur Area 30 to 34

Main Pass Area 42 to 44, 86 to 90, 92 to 114, and 118 to 120

Main Pass Area, South and East 

Addition 161, 162, 180, and 181

High Island Area 38, 39, 45 to 48, 71 to 76, 88, 89, 114, 199, 200, and 202

Sabine Pass Area 11 to 15

West Cameron Area 20 to 22, 43 to 45, 56 to 58, 90 to 93, 113 to 118, 128 to 

134, 147 to 149, and 168 to 172

West Cameron West Area 155, 156, and 162

Vermilion Area 11, 30, 51 to 54, 68 to 72, 74 to 76, 87 to 96, and 108 to 111

South Marsh Island Area, North 

Addition 207 to 237, 241 to 249, 259, and 260

Eugene Island Area 10, 18 to 35, 37 to 69, and 71 to 93

Ship Shoal Area 64, 71, 84 to 100, and 107 to 110

South Pelto Area 11 to 14 and 17 to 20

West Delta Area 20 to 31, 43 to 50, and 56 to 61

Mobile Area 816 to 821, 856 to 865, and 902 to 909

Table 4.12-1 of this Programmatic EIS provides the recent projects in Florida and Louisiana, 

the cubic yards of sand, and the miles of restored shoreline. Some projects were done on an 

emergency basis, where imminent breaching of barrier islands was prevented by the rapid 

placement of OCS sand. Most projects used sand that was identified by BOEM (USDOI, BOEM, 

2015a) through its cooperative sand evaluation program with coastal states. P.L. 109-234, enacted 

in June 2006, appropriates funds to support coastal restoration efforts in Alabama, Mississippi, 

Louisiana, and Texas to assist in the restoration of the coastal areas damaged by Hurricanes Katrina 

and Rita in 2005. All four states have received funding for surveys, studies, database development, 

or analysis that will be conducted in collaboration with State agencies and universities. Sand 

resource volumes needed to repair the damaged coastlines and barrier islands of the four states is 

estimated to be 191 to 229 million m3 (250 to 300 million yd3

); in Louisiana alone, >518 km2

(200 mi2

) of coastal land was lost due to the hurricanes (USDOI, BOEM, 2015c). Table 4.12-1 of

this Programmatic EIS provides the recent projects in Florida and Louisiana, the cubic yards of sand, 

and the miles of restored shoreline (USDOI, BOEM, 2015d).

As a result of the Deepwater Horizon explosion, oil spill, and response, the Resources and 

Ecosystem Sustainability, Tourist Opportunities, and Revived Economies of the Gulf Coast States 

Act (RESTORE Act) created a trust fund for restoration activities. The Gulf Coast Ecosystem 

Restoration Council is responsible for developing and overseeing implementation of a 

comprehensive plan for ecosystem restoration, economic recovery, and tourism promotion in the 

Gulf Coast region. Currently, the plan outlines the goals, objectives, and evaluation criteria for 

selecting projects for funding but it does not identify specific projects (Gulf Coast Ecosystem 

Restoration Council, 2013); however, it is expected that the major restoration efforts will require the 
E-140 Expanded Affected Environment Information

use of OCS sand resources in order to restore coastal wetlands and barrier islands along the Gulf 

Coast (USDOI, BOEM, 2015a).

12.4 RENEWABLE ENERGY DEVELOPMENT

The Energy Policy Act of 2005 (EPAct) was signed into law by President George W. Bush on 

August 8, 2005. The EPAct authorized the USDOI to grant leases, easements, and rights-of-way in 

the OCS for the development of energy resources other than traditional hydrocarbons on the OCS. 

The Programmatic Environmental Impact Statement for Alternative Energy Development and 

Production and Alternative Use of Facilities on the Outer Continental Shelf, Final Environmental 

Impact Statement was published in 2007 (USDOI, MMS, 2007a) leading the way for BOEM to 

develop an alternative energy program, which was published as a final rule on April 29, 2009 in 

30 CFR part 285.

Wind Energy

Offshore wind energy is seen as the most technologically mature option for a marine 

renewable energy source. As of January 2015, there were 74 operational offshore wind farms, 

including 2,488 turbines in use offshore Europe (European Wind Energy Association, 2015). 

Globally, there is a cumulative capacity of 7,046 megawatts installed in offshore waters as of the end 

of 2013 (Global Wind Energy Council, 2014). Offshore wind energy is a promising renewable 

energy due to its environmental friendliness, renewability, and predictability. Some major hurdles 

remain for widespread use in the U.S., including the following (USDOI, BOEM, 2015e): 

• environmental concerns related to impacts to marine mammals, birds, sea 

turtles, and other species from vessel or turbine strikes, disturbance of nesting 

areas, alteration of key habitat, or low-probability large spills of fuel or lubricating 

oil or dielectric fluids; 

• multiple-use conflicts between wind energy projects and marine transportation, 

fishing, and military activities; and

• cost-effectiveness, and technical challenges regarding turbine installation and 

hook-up to the electrical grid.

As of 2013, there are no operational wind farms within the AOI, and no Wind Energy Areas 

have been identified by the USDOI within the AOI. A licensed wind platform operated by Coastal 

Point Energy is currently the site of a meteorological monitoring tower used to track winds offshore 

Galveston, Texas (Coastal Point Energy, 2015). A 150-megawatt wind farm is scheduled to be built 

on the site, which is located in Texas State waters and also within the AOI.

12.5 OCEAN DREDGED MATERIAL DISPOSAL SITES

Regulated by the U.S. Environmental Protection Agency (USEPA), ocean dredged material 

disposal sites (ODMDSs) are composed of materials from maintenance dredging and are available 
Gulf of Mexico G&G Activities Programmatic EIS E-141

for potential beneficial uses to restore and create habitat, for beach nourishment projects, and for 

industrial and commercial development. There are 19 ODMDSs within the AOI (40 CFR § 228.15), 

ranging in size from 1.4 to 164.8 km2 (0.42 to 48 nmi2

; 0.5 to 63.6 mi2) and located offshore of the 

following areas (Figure 4.12 4 of this Programmatic EIS) (40 CFR § 228.15; USEPA, 2015a):

• Tampa, Florida;

• Pensacola, Florida (nearshore and offshore);

• Mobile, Alabama;

• Pascagoula, Mississippi;

• Gulfport, Mississippi (east and west);

• Mississippi River Gulf Outlet, Louisiana;

• Southwest Pass, Mississippi River, Louisiana;

• Barataria Bay Waterway, Louisiana;

• Houma Navigation Channel, Louisiana;

• Atchafalaya River (east and west) and Bayous Chene, Boeuf, and Black, 

Louisiana (2 sites);

• Calcasieu, Louisiana (3 sites);

• Sabine-Neches, Texas (8 sites);

• Galveston, Texas;

• Freeport Harbor, Texas (2 sites);

• Matagorda Ship Channel, Texas;

• Corpus Christi Ship Channel, Texas;

• Homeport Project, Port Aransas, Texas;

• Port Mansfield, Texas; and

• Brazos Island Harbor, Texas (2 sites).

The USACE is the permitting authority for dredged material disposal. When issuing a permit, 

the USACE must obtain the USEPA’s concurrence, use the USEPA’s developed dumping criteria, 

and use USEPA-designated ODMDSs to the maximum extent feasible. Virtually all ocean dumping 

in the U.S. today is of dredged material (USEPA, 2015a).
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12.6 OIL AND GAS EXPLORATION, PRODUCTION, AND DEVELOPMENT

Under the authority of the OCSLA, BOEM manages the leasing program for the 

1.76 billion ac of the OCS. These Federal lands are organized into 26 planning areas, 

approximately 80 percent of which have been unavailable for leasing because of Congressional 

moratoria and administrative withdrawals. The Gulf of Mexico OCS is divided into the WPA, CPA, 

and EPA, encompassing approximately 159.38 million ac and approximately 29,100 leasable blocks. 

As of June 1, 2016, there were 3,998 active leases in the Gulf of Mexico OCS, covering 

approximately 21.44 million ac (USDOC, BOEM, 2016). The majority of the active leases are 

located in the WPA and CPA; only 46 active leases are located in the EPA. The Gulf of Mexico OCS 

Region currently oversees approximately 3,400 offshore oil and natural gas facilities, accounting for 

nearly 30 percent of the Nation’s domestic oil production and approximately 11 percent of domestic 

natural gas production (USDOI, BSEE, 2014).

The Gulf of Mexico Energy Security Act (GOMESA) was signed into law by President 

George W. Bush on December 20, 2006. Among other provisions, GOMESA banned oil and gas 

leases within 125 mi (201 km) of the Florida coastline in the EPA until at least 2022. The GOMESA 

also banned new oil and gas leases from all areas in the EPA east of the Military Mission Line 

(86°41’ W. longitude) and areas in the CPA within 100 mi (161 km) of the Florida coastline (Figure 

4.12-5 of this Programmatic EIS).

12.6.1 Gas Hydrates

Gas hydrates are an energy-rich but poorly understood class of chemical compounds where 

ice forms an open lattice that encloses methane molecules in a cage-like structure (USDOI, BOEM, 

2012b). Methane hydrates are only stable under high pressure, which makes studying and 

extracting them especially challenging. Several research cruises have been performed in the GOM 

to characterize the presence of gas hydrates, and several test wells have been drilled. The MMS 

(USDOI, MMS, 2008) provided a geological and technical assessment of gas hydrates in the GOM, 

concluding that an estimated mean volume of 607 trillion m3 of methane was present in hydrate 

form. There are no existing plans for gas hydrate mining in the GOM; however, the 2012-2017 

WPA/CPA Multisale EIS (USDOI, BOEM, 2012a) estimated that the first production of gas hydrates 

from U.S. waters could be from the GOM due to the advantageous working environment and existing 

pipeline infrastructure that would make development more efficient.

12.6.2 Offshore Deepwater Ports

According to U.S. Department of Transportation’s Maritime Administration, the Louisiana 

Offshore Oil Port (LOOP) is the only operational offshore deepwater port in the GOM with offshore 

marine terminal facilities. The LOOP has been in operation since 1981 and serves as an unloading 

and distribution center for incoming supertankers for the entire GOM. With a current operating flow 

of approximately 1.2 million bbl of crude oil per day, the LOOP carries 13 percent of all imported oil 

to the U.S. via subsea pipelines transporting it onshore to Lafourche Parish, where it is stored and 

piped to markets throughout the country via onshore pipelines.
Gulf of Mexico G&G Activities Programmatic EIS E-143

Several permits have been issued for deepwater port facilities within the AOI; these permits 

(1) have been approved and then the application for permit withdrawn, (2) have been approved and 

then surrendered, or (3) the facility has been decommissioned. Of the licenses for deepwater port 

facilities in the GOM, one facility is currently operational (LOOP), three licenses (Gulf Landing, Port 

Pelican, and Port Dolphin) were voluntarily surrendered after issuance, two licenses were approved 

but withdrawn prior to license issuance (Bienville and Main Pass), and one facility has been 

decommissioned (Gulf Gateway).

12.6.3 Pipeline and Cable Infrastructure

There is an extensive network of pipelines in the GOM that carry produced oil and gas from 

the offshore field to refineries and terminals onshore (Figure 4.12-6a to c of this Programmatic EIS). 

Most of the pipelines that make landfall along the Gulf Coast were installed in the 1960s and 1970s. 

Thereafter, most new pipelines tied into the existing network of underused pipelines rather than 

making new landfalls in order to minimize cost and environmental impacts (USDOI, MMS, 2007b).

As of 2015, there are 14 OCS-related pipelines that make landfall in Texas and 122 OCSrelated pipelines that make landfall in Louisiana (Smith, official communication, 2015). All gas 

production and >99 percent of OCS oil production is transported to shore through the pipeline 

infrastructure. As drilling has moved into deeper waters in the GOM, methods for laying pipeline in 

deep water have been developed. As of 2012, the deepest pipeline in the Gulf of Mexico OCS was 

in approximately 2,700 m (8,858 ft) of water. More than 500 pipelines are in water depths of >400 m 

(1,312 ft), and 400 of those pipelines are in water depths of >800 m (2,625 ft) (USDOI, BOEM, 

2012a).

In order to provide reliable communications from platforms to shore, British Petroleum (BP) 

started a project in 2005 to engineer and construct a fiber optic communication system in the GOM 

extending to deepwater assets from landing sites in Pascagoula, Mississippi, and Freeport, Texas. 

The fiber optic backbone was laid on the seafloor in 2007 and was operational in 2008, connecting 

seven of BP’s platforms with the BP enterprise. The cable system is 1,216 km (756 mi) long, in 

water depths of almost 2,000 m (6,562 ft). Branching cables (i.e., spurs) extend out perpendicular to 

the main trunk and can be up to 100 km (62 mi) in length (BP, 2008). In addition, there are several 

other submarine power cables and umbilicals associated with oil and gas platforms and field 

development within the GOM (Figure 4.12-7 of this Programmatic EIS).

13 HUMAN RESOURCES AND LAND USE

The onshore portion of the AOI extends along the GOM coastline from the southwestern tip 

of the Florida Keys to the southern coast of Texas. The area encompasses 133 counties/parishes in 

23 BOEM-designated Economic Impact Areas. The G&G activities in the GOM have a concurrent 

impact on the human environment onshore, including land use and coastal infrastructure, 

environmental justice, demographics, and socioeconomic aspects of the communities along the Gulf 

Coast. Activities in the OCS are supported by onshore facilities, which can impact the human 

environment.
E-144 Expanded Affected Environment Information

13.1 LAND USE AND COASTAL INFRASTRUCTURE

The coastal areas of the GOM are not homogenous in terms of physical characteristics or 

socioeconomic attributes; they are divided into counties and parishes, each with unique histories and 

characteristics. Major cities near the study area include Houston, Texas; Baton Rouge and New 

Orleans, Louisiana; Pascagoula, Mississippi; Mobile, Alabama; and Tampa, Florida. Land uses in 

the study area range from urban areas in and around the cities previously mentioned to rural 

agricultural areas. Coastal land uses range from large areas of recreational beaches, wetlands, and 

barrier islands to deepwater ports and oil and gas production infrastructure. In addition, residential, 

commercial, farming/ranching, and other industrial uses are scattered along the coast.

The energy industry has a long history of operating in the GOM and, as a result, coastal 

infrastructure has been built to accommodate and service this sector. The G&G activities have been 

conducted for years in the GOM; therefore, companies that provide goods and services to support 

G&G activities are numerous and well established. For example, companies that provide 

shipbuilding and repair services, ports, and equipment and material suppliers are all part of the 

coastal infrastructure (Table 4.13-2 of this Programmatic EIS).

According to the OCS-Related Infrastructure Fact Book completed in 2011 (Dismukes, 

2011), 28 major shipbuilding yards are located along the GOM, with the majority of these yards 

being topside repair yards. The yards mostly are clustered between New Orleans, Louisiana, and 

Mobile, Alabama (Dismukes, 2011).

Numerous ports and ports facilities that could be used to support G&G activities on the OCS 

are located throughout the GOM region. Ports that support activities on the OCS typically fall into 

one of two categories: (1) smaller facilities that are privately owned and are designed and used to 

support energy development activities in the GOM; or (2) larger facilities that support a wide 

spectrum of maritime activities, including oil and gas exploration, as well as bulk container traffic and 

maritime transportation. The top 50 offshore support ports in the GOM identified in the OCS-Related 

Infrastructure Fact Book are primarily located around the New Orleans/Mobile area or in the Houston 

area (Dismukes, 2011).

The two primary ports that support G&G activities in the GOM are Port Fourchon in 

Lafourche Parish, Louisiana, and the Port of Galveston in Texas, according to G&G permit 

application forms submitted to BOEM. Port Fourchon is the largest port serving oil and gas 

production in the GOM. More than 250 companies utilize the port as a base of operation, and 

>90 percent of the GOM’s deepwater oil production is serviced by Port Fourchon (Greater Lafourche 

Port Commission, n.d.). The Port of Galveston serves cruise ships, cargo ships, research vessel, 

barges, lay barges, and rigs. In 2013, a total of 912 ship calls occurred in the port, including 

317 cargo ships, 85 research vessels, and 179 cruise ships. Pipe-laying vessels and drill rigs 

accounted for 96 ship calls, while pipe-laying barges accounted for an additional 229 ship calls. 

Cargo barges accounted for six ship calls in 2013 (Port of Galveston, n.d.).
Gulf of Mexico G&G Activities Programmatic EIS E-145

13.2 ENVIRONMENTAL JUSTICE

EO 12898 (“Federal Actions to Address Environmental Justice in Minority Populations and 

Low Income Populations”) was signed by President Clinton on February 11, 1994. This EO requires 

each Federal agency to identify and address, as appropriate, disproportionately high and adverse 

human health or environmental impacts of its programs, policies, and activities on minority and lowincome populations, including Native American populations. The USEPA and the Council on 

Environmental Quality emphasize the importance of incorporating environmental justice review in the 

analyses conducted by Federal agencies under NEPA and of developing protective measures that 

avoid disproportionate environmental impacts on minority and low-income populations.

President Clinton issued EO 13045 (“Environmental Health Risks and Safety Risk to 

Children”) on April 21, 1997. This EO requires each Federal agency to “make it a high priority to 

identify and assess environmental health risks and safety risks that may disproportionately affect 

children and shall . . . ensure that its policies, programs, activities, and standards address 

disproportionate risks to children.” This EO was issued because a growing body of scientific 

knowledge demonstrates that children may suffer disproportionately from environmental health and 

safety risks.

The Council on Environmental Quality has issued the following guidance to Federal agencies 

on the terms used in EO 12898:

• Low-Income Population: Low-income populations in an affected area should 

be identified using the annual statistical poverty thresholds from the U.S. Census 

Bureau.

• Minority: An individual who is a member of the following population groups: 

American Indian or Alaskan Native; Asian or Pacific Islander; Black, not of 

Hispanic origin; or Hispanic.

• Minority Population: Minority populations should be identified where (1) the 

minority population of the affected area exceeds 50 percent or (2) the minority 

population percentage of the affected area is meaningfully greater than the 

minority population percentage in the general population or other appropriate unit 

of geographic analysis.

• Children: Individuals under the age of 18.

Table 4.13-3 of this Programmatic EIS shows the percent of the population that are 

considered minorities in the geographic areas around Port Fourchon and the Port of Galveston. 

Totals for the U.S. and for Louisiana and Texas are shown for comparison purposes. Port Fourchon 

is located within the Houma-Bayou Cane-Thibodaux Metropolitan Statistical Area (MSA). The Port 

of Galveston is located in the Houston-Sugar Land-Baytown MSA. As shown in Table 4.13-3 of this

Programmatic EIS, the areas surrounding Port Fourchon have smaller percentages of minorities 

than Louisiana or the U.S. as a whole. In contrast, Galveston and the Houston-Sugar Land-Baytown 
E-146 Expanded Affected Environment Information

MSA have greater percentages of racial minorities than Texas or the U.S. as a whole. The areas 

surrounding the Port of Galveston have smaller percentages of Hispanic or Latino populations than 

the statewide total but larger percentages than the national level (USDOC, Census Bureau, 2012). 

For environmental justice purposes, Galveston and the Houston-Sugar Land-Baytown MSA are 

considered to have meaningfully greater minority populations.

Table 4.13-4 of this Programmatic EIS shows the low-income populations in the same 

geographic areas. As shown in the table, the Houma-Bayou Cane-Thibodaux MSA has a slightly 

greater percentage of residents defined as low income compared with the nationwide average and a 

smaller percentage than the total for Louisiana. In contrast, Lafourche Parish has a smaller 

percentage of residents defined as low income compared to State and national levels. During the 

same time period, 24.7 percent of all residents in the City of Galveston were considered low income 

compared with 18.1 percent in Texas and 15.7 percent in the U.S., making this a difference that was 

meaningfully greater for environmental justice purposes. The Houston-Sugar Land-Baytown MSA 

around the Port of Galveston had a smaller percentage of low-income residents than the State and 

Nation (USDOC, Census Bureau, 2012).

13.3 DEMOGRAPHICS

The population living in the coastal communities along the GOM has experienced a dramatic 

increase over the last 40 years. As of 2010, approximately 24.2 million people lived in communities 

influenced by activities in the GOM, more than double the number of individuals who lived in the 

same communities 40 years ago. In 2010, approximately 7.8 percent of the total population of the 

U.S. lived in communities along the GOM (USDOC, Census Bureau, 2012; USDOC, NOAA, n.d.-c). 

However, this increase in population is not uniformly distributed throughout the region.

Because the GOM region is so diverse, some areas have experienced rapid growth while 

other areas have not kept up with national growth rates. Florida has experienced the most rapid 

population growth in the region, with its total and Gulf Coast populations nearly doubling between 

1970 and 1990. From 1990 to 2010, an additional 3.1 million people moved to the coastal areas of 

the GOM in Florida alone.

In contrast, population growth rates in the coastal areas of Alabama and Louisiana have not 

kept up with national growth rates. Between 1970 and 1990 and from 1990 to 2010, the U.S. 

experienced population growth rates of 22.4 and 24.1 percent, respectively (USDOC, Census 

Bureau, 2002 and 2012), whereas populations in the coastal areas of Louisiana increased by 18.0 

and 7.9 percent, respectively, during the two time periods, and populations in the Alabama coastal 

areas increased by only 20.5 and 19.45 percent, respectively (Table 4.13-1 of this Programmatic 

EIS).

Total population around Port Fourchon and the Port of Galveston is shown in Table 4.13-3 of

this Programmatic EIS. There were 208,178 residents living in the Houma-Bayou Cane-Thibodaux 

MSA and 96,318 residents living in Lafourche Parish in 2010. The area surrounding the Port of 
Gulf of Mexico G&G Activities Programmatic EIS E-147

Galveston is much more populous. In 2010, there were >5.9 million people living in the HoustonSugar Land-Baytown MSA. More than 47,000 residents lived in the City of Galveston (Table 4.13-3

of this Programmatic EIS).

13.4 SOCIOECONOMICS

The communities along the GOM are a diverse group that range from the large urban areas 

like Houston and New Orleans, which have well-integrated economies, to the smaller rural areas that 

are more dependent on a few industries.

The GOM has a great economic impact on the local and regional economies of coastal 

communities from Florida to Texas. In total, approximately 25,100 business enterprises generated 

nearly $161.2 billion in local gross domestic product (GDP) and $33.9 billion in wages and salaries, 

supporting nearly 581,100 jobs in 2012 as a result of activities associated with the GOM. Offshore 

mineral extraction was the largest sector in terms of GDP and wages, accounting for 81.3 percent of 

the total economic activity and 57.5 percent of the total wages and salaries associated with the 

GOM. In contrast, the tourism and recreation sector accounted for >51.4 percent of all jobs 

associated with the GOM but generated only 16.7 percent of the total wages and salaries and only 

7.4 percent of the local GDP tied to activities in the GOM. Marine transportation and shipbuilding 

were large employment sectors as well. The marine construction sector and the living resources 

sector (e.g., commercial fishing) generated the smallest portion of GOM-related employment in 2010 

(Table 4.13-2 of this Programmatic EIS) (USDOC, NOAA, n.d.-c).

The energy industry has a long history in the Gulf Coast States; the industry is mature and it 

is fully integrated into all aspects of the local and regional communities. Numerous companies offer 

G&G services in the GOM. According to an economic study on the oil services contract industry in 

the GOM region completed for BOEM in June 2011, the G&G services’ industry employs between 

5,870 and 6,128 workers in the GOM region and contributes at least $2.94 billion to the regional 

economy. A total of 79 companies were identified as providing G&G prospecting services in the 

GOM and range from large, publicly owned multinational companies to small, privately owned 

companies (Eastern Research Group, Inc., 2011).

A total of 79 companies were identified as providing G&G prospecting services in the GOM 

(Eastern Research Group, Inc., 2011). The firms ranged from large, publicly owned multinational 

companies to small, privately owned companies. Employment at the publicly owned companies 

ranged from 80,000 workers at Schlumberger to only 36 workers at GETECH, Inc. Some of these 

companies perform services in addition to G&G prospecting services; therefore it cannot be 

assumed that all of their employees work in the G&G prospecting field. The majority of the privately 

held companies employed <25 workers. There were, however, a few notable exceptions, including 

Fairfield Industries that employed 400 workers, Paradigm that employed 950 workers, and Willis 

Group that employed 286 workers, which were large privately owned enterprises (Eastern Research 

Group, Inc., 2011).
E-148 Expanded Affected Environment Information

Much of the onshore portion of the G&G industry is located in Harris County, Texas, the 

county that encompasses much of greater Houston. Approximately 68 percent of all firms offering 

G&G services in the GOM are located in Harris County, 84 percent of the total employees working in 

the G&G industry are assigned to offices in Harris County, and 95 percent of the total revenues 

earned in the industry are attributed to companies in Harris County. Other areas with large 

concentrations of personnel engaged in G&G activities included Lafayette Parish, Louisiana, and 

Fort Bend County, Texas (Eastern Research Group, Inc., 2011).

In addition to the oil and gas industry, G&G services and activities in the GOM are utilized by 

a wide variety of scientific, research, educational, governmental, and commercial enterprises. 

Studies into geomorphology, cartology, and climate change; cultural resource surveys; fisheries 

research; military and USCG activities; and BOEM’s Marine Minerals Program all require G&G 

services. As a result, G&G services support these multimillion-dollar industries that employ 

thousands of workers throughout the Gulf Coast.

14 RECREATIONAL RESOURCES AND TOURISM

The GOM has become a popular tourist destination for domestic and foreign travelers. The 

mild climate and coastal waters provide numerous venues for recreation. Beach-going, recreational 

fishing, boating and diving, and nature watching, as well as other water-based activities, are among 

the primary tourist attractions. 

The GOM encompasses 2,625 km (1,631 mi) of coastline. As shown in Table E-2, in a 

typical year, beaches along the Gulf Coast accommodate nearly 22 million visitors during nearly 

207 million annual visitor days. Beaches in Florida account for the vast majority of these visits with 

>15 million visitors annually. Beaches in Texas accounted for nearly 4 million visitors annually, while 

Alabama, Louisiana, and Mississippi each hosted approximately 1 million visitors annually (USDOC, 

NOAA, 2008).

Table E-2. Number of Public Beaches, Number of Visitors, and Number of Visitor Days in Coastal 

Areas of the Gulf of Mexico (From: USDOC, NOAA, 2008)

State/Area Number of Public Beaches 

(2010)

Number of Visitors Annually 

(millions)

Number of Visitor Days 

(millions)

Alabama 25 1.2 11.8

Florida1 556 15.2 177.2

Louisiana 28 0.6 4.0

Mississippi 22 1.0 8.7

Texas 169 3.9 5.2

Total 615 21.9 206.9

1 Florida data include beaches and beach use for both Gulf Coast and Atlantic Coast beaches.

In addition to the beaches, numerous Federal, State, and local parks and wildlife refuges 

(Section 7); public and private boat docks and marinas; boat launches; and equipment rental and 

tour boat companies provide access to the GOM for tourists. The tourism industry has a large 
Gulf of Mexico G&G Activities Programmatic EIS E-149

economic impact on the region. In 2013, >1.7 million workers were employed in the travel and 

tourism industry in the Gulf Coast States. During the same time, total industry spending was 

approximately $165.1 billion, which supported $43.4 billion in wages and salaries. Nearly 

$24.2 billion in tax revenue was generated by this industry (U.S. Travel Association, 2015a-e). 

Table E-3 provides a breakdown of tourism economic statistics by state.

Table E-3. Selected Economic Statistics for the Tourism Industry for 2013 (From: U.S. Travel 

Association, 2015a-e).

State/Area

Travel Industry 

Spending 

(in $ billion)

Employment

Wages and 

Salaries 

(in $ million)

Tax 

Receipts1

 

(in $ billion)

Alabama 8.5 80,050 1,500 0.9

 Gulf Coast Area2 1.9 16,470 285 1

Florida 78.7 826,210 21,200 11.5

 Gulf Coast Area2 28.7 305,892 6,425 1

Louisiana 10.6 107,660 2,100 1.3

 Gulf Coast Area2 8.0 81,643 1,626 1

Mississippi 6.1 85,070 1,800 1.0

 Gulf Coast Area2 1.9 27,587 619 1

Texas 61.2 609,220 16,800 9.5

 Gulf Coast Area2 4.6 43,858 1,027 1

State Total 165.1 1,708,210 43,400 24.2

Gulf Coast Area Total2 45.1 475,450 9,982 1

1

Tax receipt data are only provided at a statewide level.

2

Gulf Coast Area is defined as U.S. Congressional Districts whose boundaries are adjacent to the 

GOM.

In Congressional Districts along the Gulf Coast, total travel industry spending was estimated 

to be $45.1 billion in 2013; during the same year, tourism provided 475,450 jobs with an annual 

payroll of $10.0 billion. Congressional Districts in Florida accounted for the majority of this economic 

impact. In 2013, it was estimated that total travel industry spending in Congressional Districts along 

the Gulf Coast of Florida reached $28.7 billion, while travel industry employment in the same area 

accounted for 305,892 jobs with an associated annual payroll of $6.4 billion. In contrast, during the 

same time period, Gulf Coast Congressional Districts in Alabama accounted for only $1.9 billion in 

travel industry spending, 16,470 travel industry jobs, and $285 million in associated payroll (U.S. 

Travel Association, 2015a-e). Table E-3 above presents Gulf Coast travel industry economic 

statistics broken down by state.

Deepwater Horizon Explosion, Oil Spill, and Response

The Deepwater Horizon explosion, oil spill, and response impacted the GOM tourism 

industry. The impacts of the Deepwater Horizon explosion, oil spill, and response, both real and 

perceived, to recreational resources along the Gulf Coast curtailed tourism spending immediately 

after the explosion and oil spill. According to a study conducted by Oxford Economics (2010) in 

December 2010 for the State of Louisiana, concern that the Deepwater Horizon explosion, oil spill, 
E-150 Expanded Affected Environment Information

and response had impacted water quality, the GOM shoreline, and seafood quality led to a high rate 

of trip cancellations from April to December 2010 by leisure travelers. The Oxford Economics (2010) 

study also found that the influx of media, relief workers, and government officials into the region 

during the response and cleanup phase of the incident helped offset some, but not all, of the lost 

economic activity caused by the reduction in the number of leisure travelers (Oxford Economics, 

2010).

Because most economic data are released after a time lag and, due to restrictions placed on 

the disclosure of data specific to the Deepwater Horizon explosion, oil spill, and response related to 

ongoing litigation, only limited information is currently available to estimate the long-term impacts to 

the tourism industry. The concurrence of the Deepwater Horizon explosion, oil spill, and response 

and the U.S. national economic recession make analysis of the economic impacts of the oil spill to 

specific industries such as tourism more complex. Several ongoing economic studies are being 

conducted to estimate the long-term impacts of the Deepwater Horizon explosion, oil spill, and 

response on tourism in the GOM.

15 AIR QUALITY

The National Ambient Air Quality Standards (NAAQS) were established by the Clean Air Act 

of 1970 (CAA) to serve as the primary standards to protect public health and welfare. Secondary 

standards were created to protect public welfare, including protection of air clarity, and to prevent 

damage to crops and other vegetation. Air quality typically is defined by the concentration of specific 

pollutants established by the USEPA under the NAAQS. The current NAAQS specifically address 

six pollutants considered harmful to public health and the environment: carbon monoxide (CO); lead 

(Pb); nitrogen dioxide (NO2); particulate matter (PM); ozone (O3); and sulfur dioxide (SO2). 

Particulates are divided into two categories: coarse (between 2.5 and 10 μm [PM10]) and fine 

(<2.5 μm [PM2.5]). The USEPA periodically reviews and updates the allowable levels of the 

pollutants covered under the NAAQS. A new 8-hour O3 NAAQS of 0.075 parts per million (ppm) was 

enacted in 2008 by the USEPA. In December 2006, the USEPA reduced the PM2.5 standard from 

65 to 35 micrograms per cubic meter (μg/m3). Other recent changes to the NAAQS include a 

revision of the NO2 NAAQS to a 1-hour standard of 100 parts per billion (ppb), a new 1-hour 

standard of average SO2 of 75 ppb, and the revocation of the 24-hour SO2 NAAQS. The current 

NAAQS are shown in Table E-4. 
Gulf of Mexico G&G Activities Programmatic EIS E-151

Table E-4. USEPA’s National Ambient Air Quality Standards for the Six “Criteria” Pollutants (From: 

USEPA, 2015b) 

Pollutant 

[final rule cite]

Primary/ 

Secondary

Averagin

g Time Level Form

Carbon monoxide (CO) 

[76 FR 54294, Aug 31, 2011]

Primary 8-hour 9 ppm Not to be exceeded more 

1-hour 35 ppm than once per year

Lead (Pb) 

[73 FR 66964, Nov 12, 2008]

Primary and 

Secondary

Rolling 

3-month 

average

0.15 

μg/m3(1) Not to be exceeded

Nitrogen dioxide (NO2) 

[75 FR 6474, Feb 9, 2010] 

[61 FR 52852, Oct 8, 1996]

Primary 1-hour 100 ppb 98th percentile, averaged over 

3 years

Primary and 

Secondary Annual 53 ppb(2) Annual mean

Ozone (O3) 

[73 FR 16436, Mar 27, 2008]

Primary and 

Secondary 8-hour 0.075 

ppm(3)

Annual fourth-highest daily 

maximum 8-hour 

concentration, averaged over 

3 years

Particle pollution 

Dec 14, 2012

PM2.5

Primary Annual 12 μg/m3 Annual mean, averaged over 

3 years

Secondary Annual 15 μg/m3 Annual mean, averaged over 

3 years

Primary and 

Secondary 24-hour 35 μg/m3 98th percentile, averaged over 3 years

PM10

Primary and 

Secondary 24-hour 150 μg/m3

Not to be exceeded more 

than once per year on 

average over 3 years

Sulfur dioxide (SO2) 

[75 FR 35520, Jun 22, 2010]

[38 FR 25678, Sept 14,

1973]

Primary 1-hour 75 ppb(4)

99th percentile of 1-hour daily 

maximum concentrations, 

averaged over 3 years

Secondary 3-hour 0.5 ppm Not to be exceeded more 

than once per year

(1) Final rule signed October 15, 2008. The 1978 lead standard (1.5 μg/m3 as a quarterly average) 

remains in effect until 1 year after an area is designated for the 2008 standard, except in areas 

designated nonattainment for the 1978 standards, in which case the 1978 standard remains in 

effect until implementation plans to attain or maintain the 2008 standard are approved.

(2) The official level of the annual NO2 standard is 0.053 ppm, equal to 53 ppb, which is shown here for 

the purpose of clearer comparison to the 1-hour standard.

(3) Final rule signed March 12, 2008. The 1997 O3 standard (0.08 ppm, annual fourth-highest daily 

maximum 8-hour concentration, averaged over 3 years) and related implementation rules remain in 

place. In 1997, the USEPA revoked the 1-hour O3 standard (0.12 ppm, not to be exceeded more 

than once per year) in all areas, although some areas have continued obligations under that 

standard (“anti-backsliding”). The 1-hour O3 standard is attained when the expected number of 

days per calendar year with maximum hourly average concentrations >0.12 ppm is ≤1 day.

(4) Final rule signed June 2, 2010. The 1971 annual and 24-hour SO2 standards were revoked in the 

same ruling. However, the standards remain in effect until 1 year after an area is designated for the 

2010 standard, except in areas designated nonattainment for the 1971 standards, in which case the 

1971 standards remain in effect until implementation plans to attain or maintain the 2010 standard 

are approved.
E-152 Expanded Affected Environment Information

The OCS sources within 25 mi (40 km) of the States’ seaward boundaries are subject to the 

same Federal and State requirements as those that would apply if the source were located onshore. 

The OCS sources beyond 25 mi (40 km) of the States’ boundaries are subject to Federal 

requirements for Prevention of Significant Deterioration (PSD). The PSD Class I air quality areas 

(where almost no change from current air quality is allowed) are designated under the CAA as areas 

that are protected under strict air quality standards. Incremental standards have been established 

for four pollutants: NO2, SO2, PM10, and PM2.5. The maximum allowable increases over baseline 

concentrations for these pollutants in a PSD Class I area are 2.5 μg/m3 annual arithmetic mean for 

NO2; 25 μg/m3

 3-hour maximum increment, 5 μg/m3 24-hour maximum increment, and 2 μg/m3

annual arithmetic mean for SO2; 8 μg/m3 24-hour maximum increment and 4 μg/m3 annual arthmetic 

mean for PM10; and 2 μg/m3 24-hour maximum increment and 1 μg/m3 annual arthmetic mean for 

PM2.5 (40 CFR § 51.21). Coastal areas of the GOM that are designated as PSD Class I are Breton 

NWR and National Wilderness Area (NWA), Chassahowitzka NWR, St. Marks NWA, Bradwell Bay 

NWA, and Everglades National Park (Figure E-2). A 2008 Agency-funded study showed that 

impacts to the Breton NWR caused by routine OCS activities were well within the PSD Class I 

allowable increment (Wheeler et al., 2008).

BOEM’s Year 2011 Gulfwide Emissions Inventory Study (Wilson et al., 2014) estimated 

emissions for criteria pollutants produced by oil and gas platforms and non-platform sources located 

in the GOM in 2011 (Table E-5). Included in the estimates were emissions from survey vessels in 

reference to non-platform emission sources, total source emissions from OCS oil and gas production 

sources, total emissions for OCS non-platform sources, and overall total emissions from all oil and 

gas sources. In 2011, survey vessels in the GOM were estimated to emit 1,760 tons per year (TPY) 

of CO; 7,851 TPY of nitrogen oxides (NOx); 290 TPY of PM10; 281 TPY of PM2.5; 97 TPY of SO2; and 

105 TPY of volatile organic compounds (VOCs). These numbers were calculated assuming 

238,821 total annual hours of survey vessel operation used in emission calculation formulae.
Gulf of Mexico G&G Activities Programmatic EIS

E-153

Figure E-2. Coastal Areas Designated as PSD Class I and Counties Designated as Nonattainment Areas Adjacent to the Area of 

Interest. 
E-154 Expanded Affected Environment Information

Table E-5. Total Platform and Non-Platform Emission Estimates for Criteria Pollutants

Equipment/Source Category Emission Type (TPY)

CO NOx PM10 PM2.5 SO2 VOCs

Total Platform Emissions 70,753 84,415 760 759 3,197 54,724

Drilling Rigs 6,248 69,135 2,634 2,407 20,863 2,750

Pipelaying Operations 2,124 9,480 350 338 117 128

Support Helicopters 2,163 753 23 22 112 1,624

Support Vessels 35,686 175,558 6,435 6,242 2,157 4,016

Survey Vessels 1,760 7,851 290 281 97 105

Total OCS Oil/Gas Production Source 

Emissions 118,734 347,192 10,492 10,049 26,543 63,347

Total Non-OCS Oil/Gas Production Source 

Emissions 13,008 131,094 4,973 4,569 36,283 37,063

Total Emissions1 131,742 478,287 15,465 14,618 62,827 100,410

1 Totals may not sum due to rounding.

Attainment Status

The CAA, as amended, established classification increments for pollutants based on ongoing 

monitoring of regional air quality. The CAA, as amended, identified timetables and requirements for 

attaining and maintaining air quality criteria. After the USEPA designates primary or secondary 

NAAQS, they must designate areas as “attainment” (meets standards), “nonattainment” (does not 

meet standards), or “unclassifiable” (insufficient data). The attainment statuses are determined after 

air quality monitoring by State or local governments. Once a particular area has a nonattainment 

designation, an implementation plan must be developed by State and local governments to plan how 

the area will achieve attainment status.

The CAA, as amended, does not identify attainment status for OCS waters (similarly, OCS 

waters are not classified as to the presence of criteria pollutants under the NAAQS); only areas 

within State boundaries are classified with an attainment status. Counties with GOM coastline that 

are designated as nonattainment areas (based on the 1997 standards) include Brazoria County, 

Texas (for 8-hour ozone); Galveston County, Texas (for 8-hour ozone); Chambers County, Texas 

(for 8-hour ozone); St. Bernard Parish, Louisiana (for SO2); and Hillsborough County, Florida (for 

lead and SO2) (USEPA, 2015b) (Figure E-2). The CAA also updated jurisdiction for air quality policy 

making and enforcement. The OCS waters east of 87.5° W. longitude fall under the USEPA’s

jurisdiction, while waters west of 87.5° W. longitude fall under BOEM’s jurisdiction.

Deepwater Horizon Explosion, Oil Spill, and Response

After the Deepwater Horizon explosion, oil spill, and response, the USEPA, NOAA, and other 

agencies measured air quality to determine any effects of the oil spill on coastal air quality. These 

measurements indicated that air quality impacts were minor and generally below the health 

standards set by the USEPA (USDOI, BOEM, 2012a). Middlebrook et al. (2011) analyzed air quality 

data acquired after the Deepwater Horizon explosion, oil spill, and response. Along with computer 

modeling, the data indicated that, as a result of the spill, evaporating hydrocarbons were the most 
Gulf of Mexico G&G Activities Programmatic EIS E-155

significant source of air pollution. Ozone pollution was limited to the area immediately downwind of 

the spill, but NOx, CO, and black carbon were emitted from in-situ burning of oil (Middlebrook et al., 

2011). Because the Deepwater Horizon explosion, oil spill, and response was an acute nonrecurring incident, the impact on air quality was limited (Middlebrook et al., 2011). It is unlikely that 

any future data will reveal information that alter conclusions (of minimal air quality impact) caused by 

the Deepwater Horizon explosion, oil spill, and response (USDOI, BOEM, 2012a).

16 WATER QUALITY

Water quality refers to the chemical, physical, biological, and radiological characteristics of 

water. For the purposes of this Programmatic EIS, water quality is discussed as a measure of the 

condition of water relative to the ability of a waterbody to maintain the ecosystems it supports or 

influences. In the case of coastal and marine environments, water quality is influenced by the rivers 

that drain into the area, the quantity and composition of wet and dry atmospheric deposition, and the 

influx of constituents from sediments. In addition to natural inputs, human activity can contribute to 

water quality through discharges, runoff, dumping, air emissions, burning, and spills. Also, mixing or 

circulation of the water can improve water quality through flushing or be the source of factors 

contributing to its decline.

Evaluation of water quality is done by measuring factors considered important to the health 

of an ecosystem. The primary factors influencing coastal and marine environments are temperature, 

salinity, dissolved oxygen, nutrients, pH, oxidation reduction potential (Eh), pathogens, and turbidity 

or suspended load. Trace constituents such as metals and organic compounds can affect water 

quality. Water and sediment quality may be closely linked. Contaminants, which are associated 

with the suspended load, may ultimately reside in the sediments rather than in the water column.

The USEPA (Regions 4 and 6) regulates all waste streams generated from offshore oil and 

gas activities. Section 403 of the Clean Water Act requires that National Pollutant Discharge 

Elimination System (NPDES) permits be issued for discharges to the territorial seas (shore to 3 nmi

[3.5 mi; 5.6 km]), the contiguous zone, and the open ocean in compliance with the USEPA’s 

regulations for preventing unreasonable degradation of the receiving waters. Water quality 

standards consist of the waterbody’s designated uses, water quality criteria to protect those uses 

and determine if they are being attained, and antidegradation policies to help protect high quality 

waterbodies. Discharges from offshore activities within State waters must comply with all applicable 

State water quality standards. In general, waste streams that can be discharged overboard include 

water-based drilling fluids and drill cuttings, synthetic-based fluid-wetted drill cuttings, cement 

slurries, various treated waters (including produced water) and sanitary wastes, and uncontaminated 

freshwater and seawater, provided they meet the criteria of the applicable NPDES permit.

Some areas of the GOM have heavy shipping traffic and may experience localized impacts 

from ships, especially from bilge water, domestic wastewater, and tank washings. Ship discharges 

are regulated under the USEPA’s NPDES vessels program, along with the USCG’s bilge and ballast 

water regulations based on the MARPOL Annex I, Regulations for the Prevention of Pollution by Oil. 
E-156 Expanded Affected Environment Information

The primary means of regulation is the Vessel General Permit, which applies to discharges 

incidental to the normal operation of all non-recreational, non-military vessels 24 m (79 ft) or longer 

that discharge in U.S. waters (USEPA, 2013a).

The AOI is divided into coastal and marine waters for the following water quality discussion. 

Coastal waters include all bays and estuaries from the Rio Grande River to the Florida Bay. 

Offshore water includes both State offshore water and Federal OCS waters extending from outside 

the barrier islands to the EEZ. Marine waters are divided into three regions: the continental shelf 

west of the Mississippi River; the continental shelf east of the Mississippi River; and deep water 

(USDOI, BOEM, 2012b).

Deepwater Horizon Explosion, Oil Spill, and Response

The Deepwater Horizon explosion, oil spill, and response released an estimated 

4.9 million bbl of oil (Operational Science Advisory Team [OSAT], 2010) and 200,000 to 

500,000 tons of hydrocarbon gases (predominantly methane) (Joye et al., 2011a; Reddy et al., 

2011) into the GOM. According to the Federal Interagency Solutions Group’s Oil Budget Calculator 

(2010), of the 4.9 million bbl of oil released from the well, approximately 820,000 bbl were directly 

recovered through a riser insertion tube tool and “top hat,” resulting in approximately 4.1 million bbl 

being released into the environment. Valentine et al. (2010) reported that 2 months after the spill, 

methane, ethane, propane, and butane gases at depth (>799 m [2,621 ft]) were the major gases 

driving rapid respiration by bacteria. An initial report by Kessler et al. (2011a) stated that released 

methane was rapidly consumed by methanotrophic bacteria in GOM deep waters over a 4-month 

period. However, at present, the extent to which the bacteria consumed the methane is under 

dispute (Joye et al., 2011b; Kessler et al., 2011b).

With respect to the spilled oil, 1.4 million bbl were estimated to be naturally or chemically 

dispersed and 1.8 to 2.2 million gal of dispersants were applied to the spill (combined for surface 

and depth) (OSAT, 2010; Allan et al., 2012; Joung and Shiller, 2013; Paul et al., 2013; Spier et al., 

2013) and consequently into the marine environment. The dispersants used contained anionic 

surfactant dioctyl sodium sulfoscuccinate (DOSS) that lowered the interfacial tension between oil 

and water to hamper the formation of large surface oil slicks. The DOSS acts conservatively in the 

water column, is not significantly removed by biodegradation or sedimentation, and has been found 

to be persistent in subsurface waters following the Deepwater Horizon oil spill. Under certain 

conditions, DOSS can persist in the environment for up to 4 years (White et al., 2014).

After the Deepwater Horizon oil spill, the USEPA, NOAA, other agencies, and academic 

institutes collected water quality measurements to determine any effects of the oil spill on coastal 

and deepwater water quality. Results from many of the studies have only recently been published or 

are still in the process of being published; therefore, a summary of available data will be provided.

The OSAT (2010) of the Unified Area Command summarized water and sediment quality 

data measuring concentrations of oil- and dispersant-related chemicals collected from the start of the 
Gulf of Mexico G&G Activities Programmatic EIS E-157

Deepwater Horizon explosion, oil spill, and response through October 2010. The OSAT (2010) 

established a suite of sediment and water quality indicators to determine whether oil- and 

dispersant-related chemicals were in concentrations high enough to cause impacts to human health 

and aquatic life. Samples were collected in nearshore (shoreline to 3 nmi), offshore (3 nmi to 200 m 

[3.5 mi/5.6 km to 656 ft] depth), and deepwater (beyond 200 m [656 ft] depth) environments. 

Results revealed that concentrations of oil- and dispersant-related chemicals in water and sediment 

samples did not exceed the benchmark for impacting human health; <1 percent of water samples 

and approximately 1 percent of sediment samples exceeded concentrations, resulting in impacts to 

aquatic life with respect to oil-related chemicals (e.g., polycyclic aromatic hydrocarbons [PAHs]); 

however, none of the water sample exceedances were consistent with the Deepwater Horizon spill 

signature, and the sediment exceedances were limited to within 3 km (1.6 nmi; 1.7 mi) of the 

wellhead.

Camilli et al. (2010) conducted a subsurface hydrocarbon survey to track the hydrocarbon 

plume associated with the Deepwater Horizon spill. They found a continuous plume of dispersed oil 

at a depth of approximately 1,100 m (3,609 ft) that extended 35 km (19 nmi; 22 mi) from the spill. 

The plume consisted of monoaromatic petroleum hydrocarbon concentrations in excess of 

50 micrograms per liter (μg/L), and the plume persisted for months with no substantial 

biodegradation. Additional water column concentration measurements revealed similarly high 

concentrations of hydrocarbons in the upper 100 m (328 ft) of the water column. Similarly, Diercks 

et al. (2010) reported PAH concentrations reaching 189 mg/L (ppb) at depths between 1,000 and 

1,400 m (3,280 and 4,595 ft) near the wellsite and concentrations considered to be toxic to marine 

organisms in the same depth range up to 13 km (7 nmi; 8 mi) from the spill site.

Allan et al. (2012) monitored bioavailable concentrations of PAHs in coastal waters of 

Louisiana, Mississippi, Alabama, and Florida and observed significant increases following the spill. 

Boehm et al. (2011) reviewed total PAH concentrations in water samples collected through Natural 

Resource Damage Assessment efforts between April and October 2010 in offshore waters ≥4.8 km 

(2.6 nmi; 3.0 mi) from shore. Boehm et al. (2011) found that total PAH concentrations in 85 percent 

of samples were at or near background levels and concentrations attenuated rapidly with distance 

from the wellhead due to dilution and biodegradation. Edwards et al. (2011) reported higher rates of 

microbial respiration within the surface oil slick; however, no increase in microbial abundances or 

biomass was observed within the slick, which was attributed to a lack of available nutrients.

The distribution and chemical composition of hydrocarbons within a 45-km (28-mi) radius of 

the spill were investigated by Spier et al. (2013), who discovered that the distribution of 

hydrocarbons was over a wider area in subsurface waters than previously predicted or reported 

(e.g., Diercks et al., 2010; Valentine et al., 2010). The deepwater hydrocarbon plume predicted by 

models at 1,175 m (3,855 ft) was verified, and additional plumes were identified at water depths of 

25,265 and 865 m (82,889 and 2,838 ft). Furthermore, benzene concentrations were found at 

potentially toxic levels outside of areas previously reported to contain hydrocarbons, and the 

application of subsurface dispersants was found to increase hydrocarbon concentration in 

subsurface waters.
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Paul et al. (2013) collected water samples in the northeast GOM and along the West Florida 

Shelf to measure the general toxicity and mutagenicity of waters in the upper water column. 

Analysis of water samples revealed that 21 percent of samples were toxic to bacteria, 34 percent 

were toxic to phytoplankton, and 43 percent showed DNA-damaging activity. Additionally, the 

degree of toxicity in samples was correlated to total petroleum hydrocarbons (TPH) concentration, 

and mutagenicity persisted for 1.5 years after capping of the well.

Sammarco et al. (2013) examined the geographic extent of petroleum hydrocarbon 

contamination in sediment, seawater, biota, and seafood during and after the Deepwater Horizon 

spill by collecting samples from coastal waters between the Florida Keys and Galveston, Texas. 

Concentrations of TPH in seawater were relatively high and peaked offshore Pensacola, Florida. 

Average concentrations of TPH and PAHs in sediment samples were high throughout the study 

region.

Trace element distributions in the water column near the Macondo well were examined by 

Joung and Shiller (2013). In surface waters, barium, cobalt, copper, iron, manganese, and nickel 

were relatively well correlated with salinity, suggesting mixing with river water was the main influence 

on metal distributions in the area. Conversely, at depths of 1,000 to 1,400 m (3,280 to 4,593 ft) 

within oil/gas plumes, elevated concentrations of cobalt and barium were observed. Cobalt 

concentrations were linked to the Deepwater Horizon oil signature, while barium concentrations were 

attributed to drilling muds used in the attempts to stop the spill.

16.1 COASTAL WATER QUALITY

Including the shore of all barrier islands, wetlands, inland bays, and inland bodies of water, 

the combined coastlines of the Gulf Coast States span more than 75,639 km (47,000 mi) (USDOI, 

BOEM, 2012a). The GOM coastal areas comprise more than 750 bays, estuaries, and sub-estuary 

systems (USEPA, 2012). While the bays and estuaries are outside of the AOI, their influence on 

coastal water quality is not.

More than 60 percent of U.S. drainage, including outlets from 33 major river systems and 

207 estuaries, flows into the GOM (USEPA, 2014). Three major estuarine drainage areas (Texas, 

Mississippi, and West Florida) and three fluvial drainage areas (also Texas, Mississippi, and West 

Florida) have a large influence on water quality in the GOM. Additional freshwater inputs originate in 

Mexico, the Yucatán Peninsula, and Cuba. The river deltas emptying into the GOM bring freshwater 

and sediment into coastal waters, affecting the water quality of receiving waters (Gore, 1992). 

Rivers carry excess nutrients (e.g., nitrogen and phosphorus) and contaminants from industrial 

wastewater discharge, urban runoff, and agriculture to downstream receiving waters.

Population growth in coastal areas can impact water quality. Since 1960, the population of 

the coastal counties of the Gulf Coast States has increased by >100 percent. From 2000 to 2004, 

the population expanded by 6.7 percent. Population growth results in additional land clearing, 

excavation, construction, expansion of paved surface areas, and drainage controls (U.S. 
Gulf of Mexico G&G Activities Programmatic EIS E-159

Commission on Ocean Policy, 2004a and 2004b). These activities alter the quantity, quality, and 

timing of freshwater runoff. Stormwater runoff, which flows across impervious surfaces such as 

parking lots, is more likely to be warmer and to transport contaminants associated with urbanization, 

including suspended solids, heavy metals, pesticides, oil and grease, and nutrients.

In coastal waters of the GOM, water quality is controlled primarily by the anthropogenic 

inputs of land runoff, land point-source discharges, and atmospheric deposition. With increasing 

distance from shore, oceanic circulation patterns play an increasingly larger role in dispersing and 

diluting anthropogenic contaminants and determining water quality. Due primarily to the influence of 

the GOM’s extensive estuary system and input from the Mississippi River, areas of the AOI closer to 

shore show regional variation (USEPA, 2012).

Within the GOM, coastal waters are divided into two biogeographical provinces: 

(1) Louisiana Province and (2) West Indian Province (USEPA, 2012).

Within the AOI, the Louisiana Province extends from the Texas-Mexico border to Anclote 

Key, Florida, and the West Indian Province extends from Tampa Bay to Florida Bay, Florida. The 

overall condition of coastal waters within the AOI is rated as fair with an index score of 2.4 (USEPA, 

2012). This assessment is based on an evaluation of five indices: water quality, sediment, benthic, 

coastal habitat, and fish tissue contaminants. More specifically, the water quality index for the 

GOM’s coastal waters was rated fair, the benthic index was rated fair to poor, the sediment quality 

and coastal habitat indices were rated poor, and the fish tissue contaminants index was rated good 

(USEPA, 2012). Of the evaluation indices listed, sediment quality (ranked as poor) poses an impact 

risk to coastal water quality as contaminants in sediments may be re-suspended into the water by 

anthropogenic activities, storms, or other natural events. Sediments in the GOM coastal region have 

been found to contain pesticides, metals, PCBs, and occasionally PAHs (USEPA, 2012).

Outside of anthropogenic inputs and the GOM’s estuarine and river systems, storm events 

have had a significant impact on the water quality of the coastal waters of the AOI. Hurricanes 

Katrina and Rita in 2005 resulted in impacts on water quality conditions in the GOM from damage 

caused to oil and gas pipelines, oil refineries, manufacturing and storage facilities, sewage treatment 

facilities, and other infrastructure. Hurricane Katrina reportedly damaged 100 pipelines, resulting in 

approximately 211 minor pollution reports; Hurricane Rita damaged 83 pipelines, resulting in 

207 minor pollution reports (USDOI, MMS, 2006). In total, 113 platforms were destroyed and an 

additional 52 platforms incurred extensive damage (Moore, 2006). Furthermore, 50 oil spills were 

reported in the nearshore environment, ranging from 13,000 to 3.78 million gal (Pine, 2006).

16.2 MARINE WATER QUALITY

Marine water composition in the GOM has two primary influences: (1) the configuration of 

the basin, which controls the influx of water from the Caribbean Sea and the output of water through 

the Straits of Florida; and (2) runoff from land masses, which controls the quantity of freshwater input 

into the GOM from the estuarine and fluvial drainage areas. As noted previously, there are three 
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major estuarine drainage areas (Texas, Mississippi, and West Florida) and three fluvial drainage 

areas (also Texas, Mississippi, and West Florida) that together drain a total of 60 percent of the 

continental U.S. and have a large influence on water quality in the GOM. The large amount of 

freshwater runoff mixes into the GOM’s surface water, producing a different composition on the 

continental shelf than that in the open ocean. Marine waters are divided into three regions: the 

continental shelf west of the Mississippi River; the continental shelf east of the Mississippi River; and 

deep water (USDOI, BOEM, 2012b).

16.2.1 Continental Shelf West of the Mississippi River

Water quality on the continental shelf west of the Mississippi River is predominantly 

influenced by the input of sediment, nutrients, and pollutants from the Mississippi and Atchafalaya 

Rivers (USDOI, BOEM, 2012b). There is a surface turbidity layer associated with the freshwater 

plume from the two rivers. During summer months, shelf stratification results in a large hypoxic zone 

on the Louisiana-Texas Shelf in bottom waters (Turner et al., 2005). Hypoxia, the condition of 

having low dissolved oxygen concentration in the water (<2 mg/L), is caused by excessive nutrients 

and other oxygen demanding contaminants. Hypoxia often occurs when the water column becomes 

vertically stratified and mixing between oxygenated surface waters and bottom waters cannot occur. 

Hypoxia is a widespread phenomenon in the AOI (Figure E-3), and the largest hypoxic zone in the 

western Atlantic occurs there (Rabalais et al., 2002; Turner et al., 2005 and 2012; Obenour et al., 

2013). The hypoxic zone in the GOM occurs seasonally and is influenced by the timing of the 

Mississippi and Atchafalaya Rivers discharge, and formation of the zone is attributed to nutrient 

influxes and shelf stratification; the zone persists until wind-driven circulation mixes the water 

column. Recent estimates of the area of low oxygen by the USDOC, NOAA (2015b) as of August 3, 

2015, measured 6,474 mi2 (16,760 km2

), an increase from the size measured in 2014 (5,052 mi2; 

13,085 km2

) and larger than the estimated size (5,838 mi2; 15,120 km2) forecast by the Louisiana 

Universities Marine Consortium (2015) in June 2015. The size of the hypoxic zone has been shown 

to be directly correlated with the flux of nitrogen from the Mississippi River (Turner et al., 2012).
Gulf of Mexico G&G Activities Programmatic EIS E-161

Figure E-3. Distribution of Bottom-Water Dissolved Oxygen July 27-August 1 (West of the 

Mississippi River Delta), 2014. Black line indicates dissolved oxygen level of 2 mg/L. 

(From: USDOC, NOAA, 2015b).

Turner et al. (2003) found trace organic pollutants, including PAHs, PCBs, and trace 

inorganic metals, in shelf sediments offshore Louisiana that were attributed to river discharge. 

Additional input of hydrocarbons associated with natural seeps and oil and gas activity in the region 

were found farther offshore (Turner et al., 2003). Pelagic tar is a common form of hydrocarbon 

contamination present in the offshore environment (Van Vleet et al., 1983a and 1983b; Farrington, 

1987) of the GOM. Higher tar concentrations were closely correlated with proximity to the Loop

Current (Van Vleet et al., 1983b; Farrington, 1987). Van Vleet et al. (1983a) estimated that 

approximately 7,112,323 kg (7,000 tons) of pelagic tar are discharged annually from the GOM into 

the North Atlantic and that approximately half of the oil may be brought into the GOM from the 

Caribbean via the Loop Current, while the remainder appears to originate in the GOM.

16.2.2 Continental Shelf East of the Mississippi River

Water quality on the continental shelf east of the Mississippi River is influenced by river 

discharge, coastal runoff, and the Loop Current and its associated eddies. The Loop Current and its 

associated eddies intrude on the shelf at irregular intervals and mix the water column. Warm-core 

eddies bring clear, low-nutrient water onto the shelf and entrain and transport high turbidity shelf 

waters farther offshore into deeper waters while cold-core eddies introduce nutrient-rich waters onto 

the shelf through upwelling. Waters in the area generally are turbid from the input of fine sediments 

discharged from the Mississippi River, but water clarity improves closer to Florida out of the 

influence of the river outflow.

Multiple studies (Dames & Moore, Inc., 1979; Brooks and Giammona, 1990; Brooks, 1991) 

analyzed water, sediments, and biota for hydrocarbons in the Mississippi, Alabama, and Florida 

area. Results indicated the area showed only minor influence of anthropogenic and petrogenic 
E-162 Expanded Affected Environment Information

hydrocarbons from river sources and natural seeps, and analysis of trace metal contamination 

indicated no contamination sources.

16.2.3 Deep Water

Water quality of the deepwater GOM may be closely tied to sediment quality, and the two 

can affect each other. For example, a contaminant may react with the mineral particles in the 

sediment and be removed from the water column (e.g., adsorption). Thus, under appropriate 

conditions, sediments can serve as sinks for contaminants such as metals, nutrients, and organic 

compounds. However, if sediments are (re)suspended (e.g., due to dredging, a storm event, or in 

conjunction with seasonal mixing and circulation patterns), the resuspension can lead to a temporary 

redox flux, including a localized and temporal release of any formally sorbed metals as well as 

nutrient recycling (USDOI, BOEM, 2012a).

Limited information is available with respect to the deepwater environment of the GOM. Few 

studies analyzing concentrations of trace metals and hydrocarbons in sediments have been 

conducted, and water column measurements have been primarily limited to oxygen, salinity, 

temperature, and nutrients (Trefry, 1981; Gallaway, 1988; Continental Shelf Associates, Inc., 2006; 

Rowe and Kennicutt, 2009). Two studies (Continental Shelf Associates, Inc., 2006; Rowe and 

Kennicutt, 2009) have been completed that measured concentrations of organics, metals, and 

nutrients in sediments in the deepwater zone relative to oil and gas operations and benthic habitats. 

Continental Shelf Associates, Inc. (2006) found that concentrations of barium, mercury, and PAHs 

were elevated in sediment samples near exploratory drilling sites. Rowe and Kennicutt (2009) 

observed elevated PAH and barium concentrations in deepwater sediments at stations in proximity 

to drilling operations. Resuspension of sediments through dredging, trawling, or storm events could 

result in impacts to deepwater water quality, but these events are infrequent.

Deepwater water and sediment quality are most directly impacted by natural hydrocarbon 

seeps, which have been estimated to contribute 1 to 1.4 million bbl of hydrocarbons per year into the 

GOM (Kvenvolden and Cooper, 2003; National Research Council, 2003). Natural seeps are 

extensive throughout the continental slope of the GOM and are the highest contributor of petroleum 

hydrocarbons to the marine environment.

17 GEOGRAPHY AND GEOLOGY 

The AOI encompasses the northern GOM waters along the coasts of Texas, Louisiana, 

Mississippi, Alabama, and Florida from the shoreline (excluding estuaries) out to the maritime 

boundary between the U.S. and Mexico in accordance with the 1978 Treaty on Maritime Boundaries. 

This section provides a regional geologic description, the geologic history, and a characterization of 

sediments of the AOI.
Gulf of Mexico G&G Activities Programmatic EIS E-163

Deepwater Horizon Explosion, Oil Spill, and Response

The Deepwater Horizon explosion, oil spill, and response did not alter or impact the geology 

of the GOM. While the benthic biological resources (Section 5) and the sediments of the GOM may 

have been affected by the spill, the purpose of this document is to analyze the impacts of G&G 

activities to the baseline conditions within the AOI, and geology has been screened out from the 

impacts discussion.

17.1 REGIONAL GEOLOGIC DESCRIPTION

The northern GOM is distinguished by an enormous river delta (Mississippi River), limestone 

islands, expansive and relatively flat continental shelf areas, submarine canyons (De Soto, 

Mississippi, Alaminos, Rio Perdido, and Keathley Canyons), steep escarpments, sea fans, and a 

central flat basin where water depths reach 3,750 to 4,400 m (12,303 to 14,436 ft) (Moretzsohn 

et al., 2013).

The width of the continental shelf in the AOI is variable, ranging from extremely narrow 

(approximately 10 km [6 mi]) near the mouth of the Mississippi River to more than 200 km (124 mi) 

off west Florida (Shepard, 1973) (Figure E-4). The shelf has a gentle gradient (approximately 1°), 

while the gradient of the continental slope ranges from 1° to 4° and extends from the shelf edge at 

20 m (66 ft) water depth off southern Florida to approximately 200 m (656 ft) depth in the northern 

GOM, down to the Sigsbee and Florida Escarpments at approximately 3,000 m (9,842 ft) depth. 

Bathymetry in the GOM is shown in Figure E-4. 

The continental shelf of the northwestern GOM is divided into four physiographic regions: 

the Rio Grande Delta; the south Texas intra-deltaic ramp; the Colorado-Brazos Delta complex; and 

the western Louisiana shelf (Holmes, 2011). The Rio-Grande Delta portion of the inner shelf 

features a northeast trending ridge system formed by faulting; the central shelf is terraced due to 

erosion and deposition, while the shelf break has linear features associated with slumping from 

sediment loading. The south Texas intra-deltaic ramp is gently sloping with a gradient of 2.8 m/km 

(9.2 ft/mi), features carbonate reefs as high as 15 m (49 ft) above the seafloor, and is predominantly 

silty-clay except near the reefs. The Colorado-Brazos Delta complex is characterized by sets of 

linear low ridges and a sediment cover of mud and sand. The western Louisiana shelf is a 

featureless plain. The eastern portion of the shelf is characterized by the presence of four large 

offshore sand shoals (Trinity Shoal, Ship Shoal, Outer Shoal, and St. Bernard Shoal). The shelf 

edge features numerous banks with relief of 3 m (10 ft) or more that are often capped with carbonate 

reefs, the most predominant of which are the FGBs. The majority of the Mississippi-Alabama shelf is 

flat with a gradient of only 40 cm/km (16 in/mi), and the continental shelf and shoreline of the northcentral GOM are the products of fluvial sedimentation and sea-level change (Flocks et al., 2011). 

The Florida shelf ranges from 25 to 250 km (16 to 155 mi) wide and features a broad range of 

seafloor morphologies, bathymetric gradients, sediment types, benthic communities, hard bottom 

exposures, and reef structures with gradients that range from 0.2 to 4 m/km (0.7 to 13 ft/mi) (Hine 

and Locker, 2011).
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Topography of the continental slope off of the Florida panhandle is relatively smooth and 

featureless aside from the De Soto Canyon, whereas the slope off western Florida is distinguished 

by steep gradients and irregular topography (Figure E-4). In the central and western GOM, the 

continental slope is underlain by salt and characterized by canyons, troughs, minibasins, and salt 

structures (e.g., small diapiric domes [domelike rock structures formed beneath Earth’s surface by 

the upward movement of a mass of salt, often associated with oil and gas accumulations]) with 

higher relief than surrounding areas. In the central and western GOM, the Sigsbee Escarpment 

defines the southern limit of the Texas-Louisiana slope and was formed by a large system of salt 

ridges that underlie the region (Figure E-5). In the eastern GOM, the Florida Escarpment 

represents the ancient shelf edge during the Cretaceous Period (Figure E-5).

In addition to De Soto Canyon off the coast of Florida, the AOI contains four canyons on or 

near the Texas-Louisiana continental slope: Mississippi Canyon (Trough) (Figure E-4), located 

southwest of the Mississippi River Delta; Alaminos Canyon (Figure E-5), located on the western end 

of the Sigsbee Escarpment; Keathley Canyon, also located on the western end of the Sigsbee 

Escarpment; and Rio Perdido Canyon, located between the Texas-Louisiana continental slope and 

the East Mexico continental slope.

Located between the Sigsbee Escarpment and Sigsbee Abyssal Plain, the continental rise 

(Figure E 5) is composed of sediments transported to the area from the north. The Sigsbee and 

Florida Escarpments terminate in the Sigsbee and Florida Abyssal Plains. The abyssal plains are 

the deepest portions of the GOM and are characterized as relatively uniform flat areas where the 

Sigsbee Knolls (Figures E-4 and E-5) and other small salt domes represent the only major 

topographical features.
Gulf of Mexico G&G Activities Programmatic EIS E-165

Figure E-4. Bathymetry (shown in meters) in the Gulf of Mexico (From: Maul, 2014).

Figure E-5. Physiographic Provinces in the Gulf of Mexico (From: The Encyclopedia of 

Earth, 2011).
E-166 Expanded Affected Environment Information

17.2 GEOLOGIC HISTORY AND SEDIMENTARY BASINS

The GOM is a passive continental margin (Martin, 1978) that was formed during the TriassicJurassic breaking apart of the supercontinent Pangea approximately 200 million years ago. During 

the Late Triassic, rifting occurred between the North American plate and the African/South American 

and Eurasian plates, the GOM basin was formed as the North American plate separated from the 

South American plate.

The GOM’s geologic history resulted in the development of three distinct geologic provinces: 

a carbonate province, a salt province, and a canyon to deep-sea fan province (ten Brink et al., 2009) 

(Figure E-6). Seawater flowed intermittently into the GOM, evaporated, and deposited a thick 

widespread salt bed (Louann salt) during the Late-Middle Jurassic (Continental Shelf Associates, 

Inc., 2000). During the Late Jurassic, the basin-center crust cooled, subsided, and gradually filled 

with deeper water in which carbonate (i.e., limestone, chalk, and reefs) deposition was dominant 

(Bryant et al., 1991). During the Middle Cretaceous, slow subsidence of the carbonate shelves with 

little elastic input resulted in a reef system being built that extended from southern Texas to southern 

Louisiana, the shelf edge of Florida, and then south to the eastern Campeche Escarpment (Figure 

E-6). In the Late Cretaceous, detrital sediments started to flux into the northern and western GOM 

and accumulate on top of the salt (Continental Shelf Associates, Inc., 2000), causing it to flow 

southward into the northern GOM to the Sigsbee Escarpment (Bryant et al., 1991). Sediments were 

supplied to the deep GOM through submarine canyons and resulted in a series of deepsea fans. 

The GOM was inactive during the Late Eocene; in the Oligocene and Miocene, extensive 

sedimentation occurred and faulting molded the relief that exists presently with the GOM. During the 

mid-late Cenozoic, the total thickness of sediments was estimated to be up to 15 km (9.3 mi) in the 

northwestern GOM (Moretzsohn et al., 2013). In the southern and eastern GOM, carbonate 

deposition remained active since the Late Jurassic-Early Cretaceous, which limited the terrigenous 

influence seen in other areas of the GOM (Gallaway, 1988). Only small amounts of detrital 

sediments were deposited during the Quaternary.
Gulf of Mexico G&G Activities Programmatic EIS E-167

Figure E-6. Primary Geologic Provinces of the Gulf of Mexico as Indicated by the Dashed Lines 

(From: ten Brink et al., 2009). Landslide deposits are marked in red. BC = Bryant 

Canyon; BF = Bryant Fan; EB = East Breaks Landslide; EMF = East Mississippi Fan; 

MC = Mississippi Canyon; MF = Mississippi Fan.

17.3 SEDIMENTS

There are two major sedimentary provinces in the GOM: the younger Cenozoic Province in 

the western and central GOM, and the older Mesozoic Province in the eastern GOM. The Cenozoic 

Province is a clastic regime, characterized by thick deposits of sand, silt, clay, and mud underlain by 

carbonate rocks (i.e., limestone, chalk, and reefs). The Mesozoic Province is a largely carbonate 

(i.e., limestone and reef buildups) regime that extends eastward from the Cretaceous Shelf Edge off 

the coast of Mississippi, Alabama, and Florida towards the coastline of Florida (Salvador, 1991; 

Continental Shelf Associates, Inc., 2000; USDOI, BOEM, 2012a).

The seafloor of the GOM continental shelf consists primarily of muddy to sandy sediments. 

Pequegnat (1983) constructed a GOM sediment distribution map that indicated fine-grained 

sediments dominate in the central and western portions of the northern GOM continental slope, but 

coarser-grained sediments intrude in the eastern portion. More recently, Balsam and Beeson (2003) 

showed that the eastern portion of the shelf is primarily sand to 100 m (328 ft) depth; the western 
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and central shelf consists of a mixture of sand, silt, and clay; and sediments offshore Mississippi and 

Louisiana are silt and clay of terrigenous origin from the Mississippi River (Figure E-7).

Offshore sand resources in the GOM are extremely scarce in coastal areas where sand is 

needed for nourishment and restoration projects. The OCS lease blocks in the GOM with significant 

sediment resources are discussed in Section 12 and are shown in Figure 4.12-3 of this

Programmatic EIS.

Figure E-7. Sediment Distribution Map Showing the Distribution of the Primary Classes of 

Sediment (From: Balsam and Beeson, 2003).

18 PHYSICAL OCEANOGRAPHY 

The GOM is a semi-enclosed, subtropical sea encompassing an area of approximately 

1.5 million km2 (371 million ac) (Moretzsohn et al., 2015) and is the ninth largest waterbody in the 

world. The GOM opens to the Atlantic Ocean through the Straits of Florida and to the Caribbean 

Sea through the Yucatán Channel. The origins of the principal water masses in the GOM include 

Subtropical Underwater, Sargasso Sea Water, Tropical Atlantic Central Water, Antarctic 
Gulf of Mexico G&G Activities Programmatic EIS E-169

Intermediate Water, and a deepwater mixture of water masses (USDOI, BOEM, 2012a). Water 

masses identified in the eastern and western GOM are highly variable and strongly influenced by the 

presence of cyclonic and anticyclonic rings (Nowlin and McLellan, 1967; Vidal et al., 1994).

The GOM is one of the few seas in the world where diurnal tides (single high and low tide per 

day) dominate over semidiurnal tides (two high and low tides per day), resulting in a complex tidal 

regime (Figure E-8). The tidal regime is mixed but dominantly semidiurnal on most of the east coast 

of Florida, becomes dominantly diurnal from the Florida Panhandle through Alabama, is strongly 

diurnal at the Mississippi River Delta, becomes mixed in western Louisiana, and is dominantly 

diurnal through most of south Texas and the Yucatán (Flick et al., 2003). Tidal ranges in the GOM 

are generally microtidal and smaller than those found on the east and west coasts of the U.S. The 

tidal range throughout the GOM varies from approximately 0.5 m (1.6 ft) along the coastline to 

approximately 0.03 m (0.10 ft) or less within coastal bays (Flick et al., 2003; Davis, 2011).

Figure E-8. Tidal Regimes of the Gulf of Mexico (From: Eleuterius and Beaugez, 1979).

Water flow known as the Loop Current enters the GOM through the Yucatán Channel, turns 

clockwise, and then exits the GOM through the Straits of Florida, to become the Florida Current and 

later part of the Gulf Stream (Figure E-9). The Loop Current is the principal current driving 

circulation in the AOI. Position of the current is variable throughout the year; it may be confined to 

the southeastern GOM or it may extend well into the northeastern or north-central GOM, with 
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intrusions of Loop Current water interacting with the shelf edge off Louisiana and the Florida 

Panhandle (Huh et al., 1981; Paluszkiewicz et al., 1983; He and Weisberg, 2003; Vukovich, 2005).

As the Loop Current penetrates northward into the GOM, large (400 km [249 mi] or more in 

diameter) anticyclonic eddies (clockwise-rotating rings) are shed (Wiseman and Sturges, 1999) 

(Figure E-9). These anticyclonic eddies are also called warm-core eddies because they surround a 

central core of warm Loop Current water. The eddies propagate westward or west-southwestward 

across the GOM prior to decaying on the Mexican and Texas shelves. Loop Current penetration into 

the northern GOM and the shedding of eddies occurs at an average rate of once per 11 months. 

The cycle can take as few as 5 months or as long as 19 months (Vukovich, 2005). As the eddies 

interact with the shelves of the western and northern GOM, they entrain water from the shelf and 

generate a cyclonic (counterclockwise-rotating) eddy (also called a cold-core eddy because it 

surrounds a central core of seawater that is cooler and fresher than adjacent waters), resulting in the 

transport of nutrient-rich water off the shelf to deeper waters. Currents within the Loop Current and 

its associated eddies extend to depths of 700 m (2,297 ft) or more. The large anticyclonic ring is a 

semipermanent feature in the western GOM and dominates circulation in the area.

Eddies shed from the Loop Current can persist for a year or longer, and as they decay, they 

generate smaller (30 to 150 km [19 to 93 mi] in diameter) cyclonic and anticyclonic eddies that 

spread throughout the GOM (Hamilton, 1992). Warm-core (anticyclonic) eddies bring clear, low 

nutrient water onto the shelf and entrain and transport high turbidity shelf waters farther offshore into 

deeper waters. Cold-core (cyclonic) eddies introduce nutrient-rich waters onto the shelf through 

upwelling. Both warm-core and cold-core eddies eddies can dominate local circulation in regions 

removed from the direct impacts of the Loop Current and large-scale rings, such as over the 

northeastern slope of the GOM (Hamilton et al., 2000).

Shelf circulation in the GOM is complex and strongly influenced by discharges of the 

Mississippi and Atchafalaya Rivers as well as intrusions of the Loop Current and its eddies. 

Horizontal circulation, water temperature, and salinity on the shelf are affected by season, 

freshwater input, solar heating, wind-induced mixing, and upwelling and downwelling related to Loop 

Current eddies that reach the shelf. Overall, salinity is generally lower near shore due to freshwater 

input from the Mississippi and Atchafalaya Rivers, but the freshwater can extend into deeper waters 

as it is entrained in the Loop Current (Weisberg et al., 2005).

The Louisiana-Texas Shelf is generally dominated by a large cyclonic cell for most of the 

year (Cochrane and Kelly, 1986); however, seasonal reversal of this pattern occurs due to changes 

in wind patterns. Inner-shelf currents on the Louisiana-Texas Shelf flow in the downcoast (south or 

west) direction during non-summer months, reversing to upcoast flow in the summer (Cochrane and 

Kelly, 1986; Nowlin et al., 2005). The Mississippi-Alabama Marine Ecosystems Study (Brooks, 

1991) concluded that four primary forcing mechanisms drive the continental shelf and slope waters 

of that portion of the shelf: synoptic scale wind stress, Loop Current-related intrusions, river 

discharges, and tropical cyclones. Estimates of the flow direction and speed on this portion of the 

shelf indicate a mean cyclonic surface circulation with inner shelf circulation influenced by wind. 
Gulf of Mexico G&G Activities Programmatic EIS E-171

Circulation on the continental shelf of the northeastern GOM tends to follow a cyclonic pattern with 

westward currents prevailing on the inner and middle shelf and eastward flow on the outer shelf 

(Brooks, 1991). Circulation on the West Florida Shelf tends to be to the southeast along the coast 

during the winter and northwest during the summer due to seasonal winds and heat flux forcing. 

The West Florida Shelf circulation is dominated by tides, winds, mesoscale perturbations, and the 

Loop Current. The outer shelf offshore Florida is a transitional area between deepwater currents 

over the continental slope and the shelf regime.

Figure E-9. Strong Loop Current in the Eastern Gulf of Mexico. It can be a short loop (Step 1), or 

stretched very long (Step 2), which often pinches off a spinning body of water called 

an eddy (Step 3). These eddies drift westward over many weeks (Step 4). They 

slowly lose energy in the western GOM. This cycle repeats itself several times a year 

(From: USDOC, NOAA, OER, 2002).
E-172 Expanded Affected Environment Information

Deepwater Horizon Explosion, Oil Spill, and Response

The Deepwater Horizon explosion, oil spill, and response did not alter or impact the physical 

oceanography of the GOM. While the physical oceanography of the GOM influenced the transport, 

distribution, and weathering of the spill, the purpose of this document is to analyze the impacts of 

G&G activities to the baseline conditions within the AOI, and physical oceanography has been 

screened out from the impacts discussion.

19 COASTAL BARRIER ISLAND BEACHES

Coastal restoration projects are often necessary to replace coastal resources impacted by 

natural processes and eroded by human activities (USDOI, BOEM, 2013a and 2015a). Beach 

renourishment projects (described in Section 12.3) are needed to replace eroded sediments along 

coastal beaches and to stabilize the shoreline (Khalil et al., 2013; Sherwood et al., 2014). Table 

4.12-1 of this Programmatic EIS describes recent and future beach renourishment projects and 

estimated yards of sand replaced. Coastal barrier islands are important resources that protect the 

mainland from harsh environmental conditions that may cause shoreline deterioration (Byrnes et al., 

2013; Khalil et al., 2013; State of Louisiana, Coastal Protection and Restoration Authority [CPRA], 

2014; Ford, 2014; USDOI, BOEM, 2015a).

Barrier islands are long narrow islands that usually run parallel to shore and are composed 

largely of sand or other unconsolidated soils (Bagur, 1978; Zhang and Leatherman, 2011). The U.S. 

shoreline in the GOM runs from the Mexican border to southern Florida, approximately 2,623 km 

(1,630 mi) (National Atlas, 2013), and barrier islands are present on more than half of the coastline 

(LaRoe, 1976; USDOI, BOEM, 2015a). Barrier island beaches usually consist of a shoreface, 

foreshore, and backshore (Frey and Howard, 1969; USDOI, BOEM, 2012a; Society for Sedimentary 

Geology, 2013), though this discussion is limited to the shoreface and foreshore up to the mean high 

water line of the barrier island beaches within the AOI. The shoreface consists of the submerged 

substrate seaward of the low tide water line; the foreshore is the unvegetated beach landward of the 

low tide water line up to the beach berm crest (USDOI, BOEM, 2012a).

Wave, wind, and tidal energy are environmental conditions that shape barrier islands and 

create a dynamic system (LaRoe, 1976; Zhang and Leatherman, 2011; USDOI, BOEM, 2012a). 

Storms can have dramatic impacts on low-lying barrier island beaches, often inducing overwash 

events even with small surges (Sherwood et al., 2014; USDOI, BOEM, 2015a). Most of the 

geographic changes experienced by barrier islands are due to storms, subsidence, deltaic influence, 

longshore drift, or anthropogenic stressors (USDOI, BOEM, 2012a). Longshore movements of 

barrier island sand are important due to their role in creating estuarine environments in the lagoons 

between the island and the mainland. Most of the barrier islands in the GOM are migrating laterally 

to some extent (USDOI, BOEM, 2012a), though some of the beaches on the west coast of Florida 

are stable or slowly accreting due to low wave energy and frequent renourishment projects (Morton 

et al., 2005). Most GOM barrier islands are migrating landward, resulting in the accumulation of 

marine sediments on top of terrestrial sediments (Khalil et al., 2013). These transgressive islands 

are usually low-profile, narrow, and sparsely vegetated, and they often have frequent washover 
Gulf of Mexico G&G Activities Programmatic EIS E-173

channels (USDOI, BOEM, 2012a). Landward migration of barrier islands is an inexact and 

discontinuous process that depends on numerous factors, including storm frequency and intensity, 

cold front passage, and the intensity of seasons (Williams et al., 1992).

This discussion briefly describes the barrier island beaches within and adjacent to the AOI. 

The barrier island chain is well developed and nearly continuous from Brownsville to Galveston, 

Texas (Figure E-10). The five major barrier islands of this region (Padre Island, Mustang Island, 

San Jose Island, Matagorda Island, and Galveston Island) are generally narrow, low relief, and 

sediment starved due the localized nature of currents and the resulting sediment transport scheme 

(Paine et al., 2014). As sea level rises, the shorelines along this section of the Gulf Coast have 

been transformed into transgressive landforms, effectively causing erosion and landward movement 

of the sediment (USDOI, BOEM, 2012a; Paine et al., 2014). In eastern Texas and western 

Louisiana, the coastline is dominated by expansive marshlands with inland lakes, left by erosion 

during the last glaciations (USDOI, BOEM, 2012a). This stretch, east to Atchafalaya Bay, Louisiana, 

is primarily marshland with no barrier island beaches.

The barrier islands of the northern GOM stretch from Atchafalaya Bay, Louisiana, to Mobile 

Bay, Alabama (USDOI, BOEM, 2012a and 2013a) (Figure E-11). Beaches along this stretch of 

coast are generally eroding, and deterioration of barrier islands occurs as a result of reduced 

sediment availability and transport, sea-level rise, frequent tropical and winter storms, and 

topographic and geomorphic features (McBride et al., 1992; Otvos and Carter, 2008; USDOI, BOEM, 

2012a and 2013a; Byrnes et al., 2013; Khalil et al., 2013; State of Louisiana, CPRA, 2014). Barrier 

islands off the coast of Louisiana (the Isle Dernieres chain, Timbalier Island, Grand Isle, and the 

Chandeleur Islands) are highly influenced by the Mississippi River Delta (State of Louisiana, CPRA, 

2014). Channelization of the Mississippi River deposits much of the available sediment offshore, 

where it cannot be used to replace eroded beaches (USDOI, BOEM, 2012a). The major barrier 

islands of Mississippi and Alabama are Cat Island, Ship Island, Horn Island, Petit Bois Island, and 

Dauphin Island. These islands generally do not migrate landward as they accrete sediment; instead, 

they are migrating westward by means of shoal-bar accretion due to the dominant westward littoral 

drift in the area (USDOI, BOEM, 2012a). This shoal-bar accretion results in islands with high 

beaches and broad dunes. A noticeable exception is Dauphin Island, Alabama, a 12-km (7.5-mi) 

long, low-profile transgressive island that is slowly migrating landward as a result of frequent storm 

overwash that results in the deposition of sediment on the lee side of the island (Morton, 2008).
E-174 Expanded Affected Environment Information

Figure E-10. Texas Coastal Barrier Island Beaches.
Gulf of Mexico G&G Activities Programmatic EIS E-175

Figure E-11. Louisiana to Alabama Coastal Barrier Island Beaches.
E-176 Expanded Affected Environment Information

The Gulf Coast of Florida has two prominent areas with barrier island beaches (Figure 

E-12). A semicontinuous chain of barrier islands from Perdido Key on the Alabama-Florida State 

line to Panacea, Florida, dominates the coastline of most of the Florida Panhandle. A long stretch of 

coastline without barrier island protection is present from Apalachee Bay near the Big Bend region of 

Florida to Anclote Key just north of Tampa. The Big Bend region of Florida is dramatically different 

than the rest of Florida’s sandy coasts, instead dominated by a marshland made up of black needle 

rush (Juncus roemerianus) and shelly sand beaches (State of Florida, Dept. of Environmental 

Protection, 2010; USDOI, BOEM, 2013a). The barrier island chain continues south along the 

southwest edge of Florida until it ends at Ten Thousand Islands on the edge of the Everglades. The 

barrier island beaches of Florida are low to moderate energy beaches with low relief and small 

dunes composed mostly of quartz sand (Godfrey, 1976). Most of barrier island beaches in the 

region are wider and more stable than the eroding barrier islands of Mississippi, Alabama, and 

Texas (Otvos and Carter, 2008) and include wind dominated and mixed energy islands that reflect 

the diversity of the energy availability on Florida’s coasts (Hine et al., 2001).

Deepwater Horizon Explosion, Oil Spill, and Response

The Deepwater Horizon explosion, oil spill, and response influenced barrier islands in the 

GOM. On May 11, 2010, the State of Louisiana requested emergency authorization to build a berm 

barrier seaward of the existing barrier islands to enhance protection of mainland habitats from the 

Deepwater Horizon oil spill (Lavoie et al., 2010). Oil was observed on 50.8 percent of beaches and 

1,773 km (1,102 mi) of shoreline in the GOM (Michel et al., 2013). Oiling was heaviest on the 

islands and marshes of eastern Louisiana near Barataria Bay (USDOI, BOEM, 2012a; Michel et al., 

2013), but the beaches of Mississippi, Alabama, and the Florida Panhandle were also oiled to 

varying degrees (OSAT-2, 2011; Michel et al., 2013; Parham and Gundlach, 2015). On May 23, 

2010, approximately 1 month after the spill began, the Louisiana Department of Environmental 

Quality indicated that oil had been confirmed on the Chandeleur Islands, Whiskey Island, Raccoon 

Island, South Pass, East Fourchon/Elmers Island, Grand Isle, Trinity Island, Brush Island, Pass a 

Loutre, and Marsh Island (USDOI, BOEM, 2012a). Oil was first seen on Dauphin Island and Petit 

Bois Island, Alabama, on June 1, 2010 (Cleveland, 2010); by June 4, 2010, oil was washing ashore 

on the barrier island beaches of the Florida Panhandle as far east as Panama City (Cleveland, 

2010).

In August 2012, Hurricane Isaac occurred in the GOM, causing storm surge, strong winds, 

and rough waves (USDOI, BOEM, 2015a). The extreme weather conditions caused oil buried deep 

in beach sediments to surface and re-mobilize (Michel et al., 2013; USDOI, BOEM, 2015a). After 

Hurricane Isaac, oil was observed on Elmer’s Island and Grand Isle that matched oil from the 

Deepwater Horizon oil spill (USDOI, BOEM, 2013a). Oil and sand mixtures were observed forming 

oil residue mats that were repeatedly buried and exposed along the shoreface and foreshore of 

barrier islands off the coast of Louisiana, Mississippi, Alabama, and Florida (Michel et al., 2013; 

Parham and Gundlach, 2015).
Gulf of Mexico G&G Activities Programmatic EIS EFigure E- 177

12. Florida Coastal Barrier Island Beaches.
E-178 Expanded Affected Environment Information

On October 2, 2014, a plan was finalized for funding early restoration projects in the GOM as 

mentioned in the Final Phase III Early Restoration Plan and Programmatic Environmental Impact 

Statement (USDOI, 2014). More than half of the money was allocated to the restoration of barrier 

islands by restoring beach sediments, dunes, marsh habitats, and bird populations (USDOI, 2014).

20 SEAGRASS 

Seagrasses are a vital component of the GOM’s coastal ecology and economy (Dawes et al., 

2004). Seagrasses provide a variety of ecological services, including sustenance through food webs 

and habitat for marine life (fisheries in particular); critical habitat to other animals; maintenance and 

improvement of water quality; stabilization of sediments; and dampening of wave activity, which in 

turn prevents coastal erosion (Short et al., 2000; Dawes et al., 2004). Seagrasses are also 

economically important. On the Gulf Coast of Florida, seagrass beds are utilized by recreational 

boaters and fishers as well as commercial fishers, directly bringing in millions of dollars to the State 

(Bell, 1993; Dawes et al., 2004).

The seagrass environment of the AOI includes waters of the GOM that lie adjacent to the five 

Gulf Coast States, an area called the Northern Gulf Region (Figure E-13). The region consists of 

2,414 km (1,500 mi) of coastline. Significant additional shoreline is located behind barrier islands or 

in estuarine embayments along the coast (USEPA, 2004); however, these regions of seagrass are 

not included as part of the AOI. The southwestern boundary of the Northern Gulf Region begins 

near Brownsville, Texas (within the WPA), and terminates at the easternmost reaches of Florida 

Bay, including the northern boundary of the Florida Keys and Dry Tortugas (within the southeast 

section of the EPA) (Dawes et al., 2004; USEPA, 2004). Of the Gulf Coast States, the vast majority 

of seagrasses (88%) are found around Florida (Yarbro and Carlson, 2011).

Deepwater Horizon Explosion, Oil Spill, and Response

The U.S. Government has estimated that 4.9 million bbl of oil were released into the GOM 

during the Deepwater Horizon oil spill. Studies in peer-reviewed literature related to direct impacts 

to seagrasses from the spill are scarce. The majority of aquatic vegetation that has been directly 

affected appears to be emergent vegetation associated with wetlands, and this subject is addressed 

in Section 21. Aerial photography was collected on seagrass beds around Breton Island, the 

Chandeleur Islands, and Mississippi Sound (Wells et al., 2012) to assess the condition of seagrass 

beds as part of damage assessment. The results of this effort have not yet been published in a 

peer-reviewed journal.

Indirect impacts to seagrasses occurred from spill response activities and included injuries 

from propeller scarring by response vessels used to deploy and anchor spill boom curtains in 

shallow waters, blowholes from response vessels, and scouring from boom curtains and anchor 

tethers. The USDOC, NOAA (2011) authorized some preliminary restoration work for these indirect 

impacts. Indirect impacts were documented and subsequent restoration efforts were carried out in 

specific regions along the Florida Panhandle.
Gulf of Mexico G&G Activities Programmatic EIS

E-179

Figure E-13. Seagrass Locations Along the Gulf Coast Within the Area of Interest. 
E-180 Expanded Affected Environment Information

The following discussion provides an overview of regions with seagrass communities located 

within the AOI.

20.1 WESTERN PLANNING AREA

Seagrasses in the WPA are widely scattered beds in shallow, high-salinity coastal lagoons 

and bays. Texas coastal waters have the second greatest amount of seagrasses of the Gulf Coast 

States (11%, 92,854 ha [140,066 ac]), the majority of which (74%) are located in the broad shallows

of the Laguna Madre (USDOI, BOEM, 2012b); however, like other coastal bays, the Laguna Madre 

is outside of the AOI.

20.2 CENTRAL PLANNING AREA

Seagrasses are limited off of coastal Louisiana and within its estuaries as a result of turbid 

waters and the soft, highly organic sediments. One offshore area with an established seagrass 

community is located along the Chandeleur Islands. The northern end of the Chandeleur Islands is 

35 km (22 mi) south of Biloxi, Mississippi; the southern end, Breton Island, is 25 km (16 mi) 

northeast of Venice, Louisiana (Poirrier and Handley, 1940). Turtle grass, manatee grass, shoal 

grass (Halodule wrightii), star grass (Halophila engelmannii), and widgeon grass (Ruppia maritima) 

have been documented in this region, with seagrasses mapped on the western side of the 

Chandeleur Island chain. Seagrass beds in Louisiana are often affected by storm events of 

difference severities, with recovery times varying as a function of the size of the disturbance (Franze, 

2002; Fourqurean and Rutten, 2004, as cited in USDOI, BOEM, 2012a). Over a period of 5 years, 

three tropical cyclones made landfall near or on the Louisiana coast: Hurricane Humberto (2007), 

Tropical Storm Edouard (2008), and Hurricane Gustav (2008) (USDOC, NOAA, 2010). The storms 

hit areas that had a small amount of submerged vegetation present. Hurricane Ida (2009) made 

landfall as a weakened tropical mass in Alabama and did not have any documented long-term effect 

on local seagrass communities (USDOC, NOAA, 2010). Some strong storm events resulting in 

significant removal of seagrass beds caused changes to the nekton community structure. Results of 

a study done in Biloxi Marsh following Hurricanes Cindy (2005) and Katrina (2005), which removed 

essentially all of the widgeon grass present, indicated that the post-storm nekton community 

resembled communities that had no vegetation prior to the hurricanes (Maiaro, 2007, as cited in 

USDOI, BOEM, 2012a).

In Mississippi and Alabama, seagrasses are present within Mississippi Sound (USDOI, 

BOEM, 2012b). A study by Byron and Heck (2006), which took place following the passage of 

Hurricane Ivan (2004) through the area, resurveyed a series of stations that were surveyed 

previously by Vittor and Associates (2003) while ground-truthing seagrass areas for aerial imagery 

collected over three zones of interest: Grand Bay, Mobile Bay (including Mississippi Sound east of 

Grand Bay), and Perdido Bay. Byron and Heck (2006) reconfirmed that shoal grass was the most 

common seagrass found at the study sites and additionally noted that widgeon grass was also 

prevalent. Additionally, in 2003, Vittor and Associates reported turtle grass for the first time in Little 

Lagoon, Alabama; Byron and Heck (2006) reconfirmed its presence.
Gulf of Mexico G&G Activities Programmatic EIS E-181

20.3 EASTERN PLANNING AREA

As noted previously, Florida’s coastal waters contain the vast majority of seagrass habitat 

(88%) seen in the Gulf Coast States (Yarbro and Carlson, 2011). Significant seagrass areas with 

portions falling within the AOI are summarized in the following subsections.

20.3.1 Big Bend – Overview

The Big Bend region extends from Anclote Key northwestward to Ochlockonee Point in the 

Panhandle region and includes the coastal waters of Pasco, Hernando, Citrus, Levy, Dixie, Taylor, 

Jefferson, and Wakulla Counties (Dawes et al., 2004). This portion of Florida’s coast is an extensive 

area devoid of offshore barrier islands, with several rivers, creeks, and marshes that discharge 

directly into the GOM (Zieman and Zieman, 1989, as cited in Dawes et al., 2004). The inshore and 

offshore seagrass beds of the region are among the largest in the eastern GOM (Iverson and 

Bittaker, 1986). With regard to ongoing seagrass mapping and monitoring as reported in Yarbro and 

Carlson (2011), the Big Bend region is divided into four monitoring areas described in the following 

sections: (1) the northern region; (2) the southern region; (3) the Suwannee Sound, Cedar Keys, 

and Waccasassa Bay region; and (4) the Springs Coast region, which extends from the mouth of the 

Crystal River south to Anclote Key.

20.3.1.1 Northern Big Bend

The northern region extends from the mouth of the Ochlockonee River in the west to the 

mouth of the Steinhatchee River in the southeast. The northern Big Bend region contained at least 

60,355 ha (149,140 ac) of seagrass in 2006 based on aerial imagery. Seagrass cover in the 

northern Big Bend region is stable, but the recent monitoring assessment noted slight declines 

between the St. Marks and Ochlockonee Rivers (Yarbro and Carlson, 2011). Seagrass species 

composition also appears to be stable; the most recently reported annual monitoring efforts by FWC 

in 2009 saw an upward trend of manatee grass, which occurred >50 percent of the time in almost all 

of sampling locations (Yarbro and Carlson, 2011). Turtle grass, which also showed an increase, 

was seen frequently mixed with manatee grass and was the second most abundant seagrass 

present, occurring at nearly 40 percent of the sites. Shoal grass appears to have declined from 

2004 to 2009. Star grass occurred in 7.5 to 15 percent of all sampling locations in that same period. 

The occurrence of widgeon grass decreased from an already low level (<5 percent). Sampled areas 

with no seagrass present account for 23.5 percent (Yarbro and Carlson, 2011).

The 2001 and 2006, mapping efforts did not extend far enough offshore to capture the deep 

edge of seagrass beds in the northern Big Bend region. The beds probably serve as a corridor for 

grouper and other important fish and shellfish species as they migrate inshore and offshore. Deep 

seagrass beds are present in all Big Bend monitoring areas.

20.3.1.2 Southern Big Bend

The southern Big Bend region extends from the mouth of the Suwannee River north to the 

mouth of the Steinhatchee River. The southern Big Bend region contained 22,721 ha (56,146 ac) of 
E-182 Expanded Affected Environment Information

seagrass cover during its latest assessment in 2006 (Carlson et al., 2010), an almost 6 percent 

decrease since the previous assessment in 2001, when coverage was 24,149 ha (59,674 ac) 

(Yarbro and Carlson, 2011). Considerable bed fragmentation also occurred during the same time 

period, with a 14 percent decrease of continuous seagrass coverage, which measured 20,730 ha 

(51,224 ac) in 2001 and 17,850 ha (44,109 ac) in 2006; it is possible that some of this reduction was 

a result of recent hurricanes (Yarbro and Carlson, 2011). The majority of seagrasses within the 

southern Big Bend region occur south of the Steinhatchee River mouth and the subregion known as 

Horseshoe West, while the areas of least extensive seagrass beds are located near the mouth of the 

Suwannee River (Yarbro and Carlson, 2011).

As of 2009, the FWC noted that approximately 50 percent of the sample locations had no 

seagrass present, which has been a slowly growing trend over the last 5 years, and this could be 

amplified by the storms of 2004 and 2005 (Carlson et al., 2010). Turtle grass is currently the most 

abundant seagrass species at 35 percent occurrence, followed by manatee grass at 28 percent. 

Both of these species had exhibited a 21 to 24 percent decrease as a result of the storms of 2004 

and 2005 (Carlson et al., 2010; Yarbro and Carlson, 2011).

Like its northern counterpart, the southern Big Bend region had extensive but sparse beds of 

paddle grass (Halophila decipiens) located farther offshore that cannot be mapped with conventional 

aerial photography. These likely serve as a corridor for economically important fish and shellfish as 

they migrate inshore and offshore (Yarbo and Carlson, 2011).

20.3.1.3 Suwannee Sound, Cedar Keys, and Waccasassa Bay

The Suwannee Sound, Cedar Keys, and Waccasassa Bay region extends south from the 

mouth of the Suwannee River to just south of the mouth of the Waccasassa River. The latest aerial 

assessment that was analyzed for this region was performed in 2001. Based on that effort, the 

majority (approximately 72%) of the seagrass beds in this region are located in Waccasassa Bay, 

with 9,787 ha (24,184 ac) of seagrass. Of that total, 6,979 ha (17,245 ac; approximately 71%) were 

continuous beds and 2,808 ha (6,939 ac; 29%) were composed of patchy beds. 

Suwannee Sound had the least amount of seagrasses (669 ha [1,652 ac]), but approximately 

55 percent of the beds (366 ha [905 ac]) are continuous. Seagrasses in the Cedar Keys (3,152 ha 

[7,789 ac]) are also predominantly found in continuous beds (79%) (Yarbro and Carlson, 2011).

20.3.1.4 Springs Coast

The Springs Coast region contained at least 153,380 ha (379,010 ac) of seagrass in 2007. 

Seagrass cover in the Springs Coast region appears to be stable or increasing slightly, based on a 

rough comparison of data collected in 1999 and 2007 (Yarbro and Carlson, 2011). It should be 

noted that a recent pilot study (Baumstark et al., 2013), using satellite imagery versus conventional 

aerial imagery, mapped and verified baseline information for the western extent of seagrass along 

the Springs Coast, which reaches nearly 20 mi (32 km) offshore.
Gulf of Mexico G&G Activities Programmatic EIS E-183

20.4 OFFSHORE HALOPHILA BEDS

The vast acreage of offshore and deepwater Halophila decipiens and Halophila engelmanni

beds stretching from the Tortugas Bank to the Florida Panhandle (essentially the entire west coast of 

Florida) is consistently overlooked in seagrass censuses for the eastern GOM. The majority of the 

resource is located in waters 10 m (33 ft) and deeper, mostly beyond the detection limits of standard 

remote-sensing techniques based on reflected light. Most of this habitat lies outside of State waters, 

which is why it is not included in Florida’s totals. Nonetheless, early work supported by the MMS

(BOEM’s predecessor) (Continental Shelf Associates, Inc., 1986 and 1987) found that more than 

1.2 million ac (485,623 ha) of offshore Halophila existed in the area north of Tarpon Springs, 

extending to the eastern end of St. George Bay; approximately 3 million ac (1.2 million ha) existed 

up to 40 to 60 km (25 to 37 mi) offshore and to lesser distances south of Sanibel Island to the Dry 

Tortugas. These surveys did not cover the entire breadth of the Halophila habitat, which in the latter 

area extends out to depths of 30 m (98 ft) (Fonseca et al., 2008). Beyond what was not completely 

covered by these surveys, between the two study areas there exists an approximately 209-km 

(130-mi) alongshore region from offshore of Tampa Bay that apparently has never been surveyed. 

Therefore, the partially documented extent of this habitat exceeds 4 million ac (1.6 million ha) and 

probably exceeds at least 7 million ac (2.8 million ha) (Yarbro and Carlson, 2011). Thus, this poorly 

documented seagrass community, lying as it does mostly in Dederal waters, greatly exceeds the 

entire inshore seagrass acreage of the conterminous U.S. combined (Fonseca, unpublished; 

Fonseca et al., 2001). An issue with documenting these Halophila communities is that they are 

seasonally ephemeral and more variable farther from shore. Depending on the survey, patches of 

Halophila may not be present in the same place or in the same cover.

21 WETLANDS

Wetlands are essentially low-lying habitats where water accumulates long enough to affect 

the condition of the soil or substrate and promotes the growth of water-tolerant plants (LaSalle, 

1998). Because of their importance, wetlands are protected by Federal, State, and occasionally 

local laws. From a regulatory standpoint, a wetland is defined as: “Those areas that are inundated 

or saturated by surface or ground water at a frequency and duration sufficient to support, and that 

under normal circumstances do support, a prevalence of vegetation typically adapted for life in 

saturated soil conditions” (40 CFR § 230.3; 33 CFR § 328.3).

Wetlands are important as they provide several ecological benefits. Wetlands protect water 

quality by filtering out pollutants and excess nutrients (Gosselink et al., 1974). They stabilize 

shorelines from erosion, thereby decreasing the amount of sediments and pollutants entering 

downstream waterbodies (Barbier et al., 2011). Wetlands provide natural storage of water, helping 

prevent downstream flooding from heavy rainfall or storm surges associated with tropical storms and 

hurricanes, which are prevalent occurrences in the GOM. Wetlands can also attenuate associated 

wave and wind energy and protect coastal regions by lessening the damage from these storms 

(Stedman and Dahl, 2008). In terms of wildlife, wetlands provide habitat for a variety of floral and 

faunal species, including some endangered species. Additionally, wetlands are essential to the 

health of commercially and recreationally important fisheries resources. Many economically 
E-184 Expanded Affected Environment Information

important gamefish spend a portion of their life history in or near coastal wetland habitat. From an 

economic standpoint, wetlands provide large-scale opportunities for commercial and recreational 

activities, particularly in the GOM.

There are two broad classifications of wetlands found within the GOM: inland and coastal. 

Inland wetlands typically are found within the floodplains along rivers and streams, in isolated 

depressions surrounded by dry land, and in other low-lying areas. Inland wetlands generally include 

freshwater ecosystems, such as bottomland hardwood forests, swamps, freshwater mangrove 

swamps, and freshwater marshes (Gulf Restoration Network, 2004). Coastal wetlands are primarily 

intertidal habitats, located at the interface between terrestrial and coastal water environments and 

are influenced bidirectionally from forces at their seaward and landward sides (Battaglia et al., 2012; 

USDOI, BOEM, 2012b) (Figure E-14). Across this boundary, plants that characterize this transition 

are positioned based primarily on their tolerances to salinity and inundation gradients as well as to 

sulfide concentrations and substrate stability (Baldwin and Mendelssohn, 1998, as cited in Battaglia 

et al., 2012). The most common coastal wetlands include saltwater mangrove swamps, saltwater 

marshes, and non-vegetated areas such as sand bars, mud flats, and shoals (Gulf Restoration 

Network, 2004). The vegetated coastal wetlands are primarily emergent wetlands, which Cowardin 

et al. (1979) described as “characterized by erect, rooted, herbaceous hydrophytes, excluding 

mosses and lichens, present for most of the growing season in most years”. Coastal emergent 

wetlands along the Gulf Coast include smooth cordgrass (Spartina alterniflora), Gulf cordgrass 

(Spartina spartinae), salt meadow cordgrass (Spartina patens), and saltgrass (Distichlis spicata) 

(Handley et al., 2012). Mangrove swamps are also a common emergent wetland, particularly 

around Florida, which includes one or more additional members of the three mangrove species 

found in the GOM region: red mangroves (Rhizophora mangle), black mangroves (Avicennia 

germinans), and white mangroves (Laguncularia racemosa). Black mangroves have expanded their 

range and become established along the shorelines of the CPA. 

Seagrasses are part of the submerged coastal wetland habitat that can, in some cases, 

significantly extend into marine waters of the GOM (Fonseca et al., 2008). Seagrasses are 

addressed in Section 20. 

The emergent coastal wetlands around the GOM vary topographically and ecologically, and 

have been categorized as different ecoregions: the Western Gulf Coastal Plain; the Mississippi 

Alluvial Plain; and the Southern Coastal Plain (USEPA, 2013b). The Western Gulf Coastal Plain 

comprises the coast of Texas (including Corpus Christi, Nueces Bay, Aransas Bay, and Galveston 

Bay) and the western half of Louisiana’s coast. This region is characterized by flat topography, 

plains, and grasslands, and contains several barrier islands, bays, peninsulas, marshes, lagoons, 

and estuaries (Handley et al., 2012).
Gulf of Mexico G&G Activities Programmatic EIS

E-185

Figure E-14. Wetland Locations Along the Gulf Coast Within the Area of Interest. 
E-186 Expanded Affected Environment Information

The Mississippi Alluvial Plain encompasses the eastern half of Louisiana’s coasts, including 

Barataria Bay, Terrebonne Bay, and the Mississippi River Delta (USDOI, BOEM, 2012b; USEPA, 

2013b). Extensive salt and brackish marshes occur throughout this coastal region, with intermediate 

and freshwater marsh systems occurring farther inland (Handley et al., 2012; USDOI, BOEM, 

2012b). Stands of expanding black mangrove are established in some high-salinity areas within this 

region (Perry and Mendelssohn, 2009; Roth, 2009).

The Southern Coastal Plain extends from the Mississippi coast across Alabama, the Florida 

Panhandle, and along the Gulf Coast of Florida to just south of the Caloosahatchee River, where the 

ecoregion transitions to the Southern Florida Coastal Plain (USEPA, 2013b). The Southern Coastal 

Plain includes Mississippi Sound in Mississippi; Mobile Bay in Alabama; and the Florida Panhandle, 

Tampa Bay, Sarasota Bay, and Charlotte Harbor in Florida. Coastal wetlands in this region are 

composed of salt and brackish marshes as well as extensive mangrove forests (particularly 

alongside the Florida peninsula) located along the many barrier islands and estuaries and lagoons 

positioned along this section of the Gulf Coast (Handley et al., 2012; USEPA, 2013b). The Southern 

Florida Coastal Plain, which consists of the southern quarter of the Florida peninsula, is nearly level 

and subtropical to tropical in its climate, with coastal wetlands comprising freshwater marshes, wet 

prairies, sloughs, swamps, and coastal wetlands (USEPA, 2000).

These various ecoregions of the Gulf Coast share certain defining characteristics, including 

emergent wetland habitats as part of the broader-scale GOM ecosystem. All of these wetlands have 

experienced alteration to varying degrees. Losses of coastal wetlands have been occurring along 

the Gulf Coast for decades, resulting in the conversion of wetland habitats to open water; Louisiana 

has been particularly affected (USDOI, BOEM, 2012b). These changes will likely continue as a 

result of ongoing land development, sea-level rise, induced subsidence, canal construction, and 

tropical storms and hurricanes.

Ongoing and recently initiated coastal habitat protection and restoration efforts are underway 

along the Gulf Coast to address the issue of erosion and land loss. The USDOI, BOEM (2012b), in 

cooperation with State and local agencies as well other Federal entities, has been involved in 

developing habitat restoration projects using OCS sand resources. Other government entities, as 

well as nongovernmental organizations and private partnerships, have assisted and continue to 

assist in a variety of projects to restore coastal wetlands and other important GOM habitats.

Deepwater Horizon Explosion, Oil Spill, and Response

The U.S. Government has estimated that 4.9 million bbl of oil were released in the GOM 

during the Deepwater Horizon oil spill. In spite of that volume, it appears that environmental damage 

to wetlands was limited to marsh shorelines and generally not the marsh interior (Mendelssohn 

et al., 2012). There was an estimated total of 430 mi (692 km) of marsh shoreline that were oiled, 

and a summary by Zengel and Michel (2011) reported that of those marsh shorelines, 41 percent 

(176 mi [283 km]) were heavily or moderately oiled. Silliman et al. (2012) observed that, in some 

heavily oiled Louisiana marshes, shoreline fringes helped contain oil from the interior, but these 
Gulf of Mexico G&G Activities Programmatic EIS E-187

areas underwent extensive mortality to marsh plants from the marsh to 5 to 10 m (16 to 33 ft) inland 

and had sublethal impacts on plants 10 to 20 m (33 to 66 ft) from the shoreline, where oiling was 

less severe.

The primary marsh types affected included salt marshes dominated by smooth cordgrass 

and black needle rush; mangroves, dominated by the black mangrove, which were present on small 

islands and shorelines and as scattered stands within slat marshes; and low- to intermediate-salinity 

marshes, dominated by the common reed (Phragmites aurtalis) along the margin of the Mississippi 

River Birdfoot Delta. Studies following the spill showed variable impacts, depending on oiling 

severity (DeLaune and Wright, 2011; Mendelssohn et al., 2012; Silliman et al., 2012). Nearcomplete mortality of the two dominant species (i.e., smooth cordgrass and black needle rush), 

occurred along heavily oiled shorelines, whereas moderate oiling had no significant effect on 

Spartina despite lowering live aboveground biomass and stem density (Mendelssohn et al., 2012). 

DeLaune and Wright (2011), following extensive review of oil spills literature and related studies in 

the GOM, noted that marsh vegetation under most conditions will recover naturally from oil exposure 

without remediation. The rate of recovery will depend on the degree of oiling, the amount of oil 

penetrating the soil profile, and the plant species’ sensitivity to oil.

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E-246 Expanded Affected Environment Information

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E-248 Expanded Affected Environment Information

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Gulf of Mexico G&G Activities Programmatic EIS E-249

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Gulf of Mexico G&G Activities Programmatic EIS E-251

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E-254 Expanded Affected Environment Information

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APPENDIX F 

G&G SURVEY DESCRIPTIONS

Gulf of Mexico G&G Activities Programmatic EIS F-iii

TABLE OF CONTENTS

Page

LIST OF FIGURES.............................................................................................................................. F-v

LIST OF TABLES................................................................................................................................ F-v

ABBREVIATIONS AND ACRONYMS .............................................................................................. F-vii

1 GEOPHYSICAL SURVEYS......................................................................................................... F-1

1.1 Deep-Penetration Seismic Airgun Surveys........................................................................ F-4

1.1.1 2D (Towed-Streamer) Seismic Surveys ................................................................ F-6

1.1.2 3D (Towed-Streamer) Seismic Surveys ................................................................ F-8

1.1.3 Ocean-Bottom Seismic (Cables and Nodes)....................................................... F-10

1.1.4 Wide Azimuth and Related Multi-Vessel Surveys ............................................... F-16

1.1.5 Borehole Seismic Surveys................................................................................... F-19

1.1.6 Vertical Cable Surveys ........................................................................................ F-24

1.1.7 4D Time-Lapse Surveys ...................................................................................... F-24

1.2 Airgun High-Resolutin Geophysical Surveys ................................................................... F-25

1.3 Non-Airgun Acoustic High-Resolution Geophysical Surveys .......................................... F-27

1.3.1 Subbottom Profiling Surveys ............................................................................... F-28

1.3.2 Side-Scan Sonars................................................................................................ F-29

1.3.3 Echosounders...................................................................................................... F-30

1.4 Non-Acoustic Marine Geophysical Surveys..................................................................... F-30

1.4.1 Marine Gravity Surveys ....................................................................................... F-30

1.4.2 Marine Magnetic Surveys .................................................................................... F-31

1.4.3 Marine Magnetotelluric Surveys .......................................................................... F-31

1.4.4 Marine Controlled Source Electromagnetic Surveys........................................... F-32

1.5 Airborne Remote Surveys ................................................................................................ F-34

1.5.1 Airborne Gravity Surveys..................................................................................... F-34

1.5.2 Airborne Magnetic Surveys ................................................................................. F-34

2 GEOLOGICAL AND GEOTECHNICAL SURVEYS .................................................................. F-35

2.1 Grab and Box Sampling................................................................................................... F-35

2.2 Geologic Coring................................................................................................................ F-35

2.3 Cost and Shallow Test Wells ........................................................................................... F-37

2.4 Cone Penetrometer TestsS .............................................................................................. F-37

3 EMERGING TECHNOLOGIES ................................................................................................. F-38

3.1 Marine Vibroseis (Vibrators)............................................................................................. F-38

3.1.1 Hydraulic Marine Vibrator.................................................................................... F-38

3.1.2 Electric Marine Vibrator ....................................................................................... F-40

3.2 Low-Frequency Acoustic Source (Patented) ................................................................... F-40

3.3 Deep-Towed Acoustics/Geophysics System ................................................................... F-41

3.4 Low-Frequency Passive Seismic Methods for Exploration.............................................. F-42

3.5 Low-Impact Seismic Array ............................................................................................... F-44

3.6 Fiber Optic Receivers....................................................................................................... F-44
F-iv G&G Survey Descriptions

3.7 Airgun Modifications to Lessen Impacts .......................................................................... F-45

3.7.1 Airgun Silencers................................................................................................... F-45

3.7.2 Bubble Curtains ................................................................................................... F-45

3.7.3 eSource Airgun.................................................................................................... F-46

4 OTHER SURVEYS AND EQUIPMENT..................................................................................... F-46

4.1 Acoustic Pingers ............................................................................................................. F-46

4.2 Transponders/Transceivers ........................................................................................... F-47

4.3 Remotely Operated Vehicles and Autonomous Underwater Vehicles....................... F-47

4.4 Water Guns ..................................................................................................................... F-48

5 REFERENCES CITED .............................................................................................................. F-48
Gulf of Mexico G&G Activities Programmatic EIS F-v 

LIST OF FIGURES

Page

Figure F-1. A Marine Seismic Survey Vessel Towing an Airgun Array and a Streamer 

Containing Hydrophones. ............................................................................................ F-4

Figure F-2. The Basic Difference Between 2D and 3D Survey Geometries.................................. F-5

Figure F-3. Three Examples of OBCs. ......................................................................................... F-11

Figure F-4. Five Types of OBNs................................................................................................... F-11

Figure F-5. Layout for a 2D Ocean-Bottom Receiver Seismic Survey......................................... F-12

Figure F-6. (A) Drill Rigs and Platforms in the Gulf of Mexico in a Configuration that Makes 

a Towed-Streamer Seismic Survey Impossible to Conduct; OBCs or OBNs 

Would be Required to Acquire 3D Seismic Data in Such an Obstructed Area.. ....... F-13

Figure F-7. Placement of an OBN or OBC System in a 3D Seismic Survey ............................... F-15

Figure F-8. OBNs Left on the Seafloor for Use in 4D Surveys..................................................... F-16

Figure F-9. The Narrow Range of Source-Receiver Azimuths in Single-Vessel 3D Surveys...... F-17

Figure F-10. New 3D Acoustic Survey Techniques that Provide Improved Data Quality.............. F-18

Figure F-11. The Geometries of the Four Basic Types of 2D VSPs .............................................. F-21

Figure F-12. The Geometry of a 3D VSP Survey........................................................................... F-21

Figure F-13. The Geometry of a Checkshot Survey....................................................................... F-23

Figure F-14. The Equipment Layout for a P-Cable Acquisition Survey ......................................... F-26

Figure F-15. Examples of the Data that the P-Cable Technology can Deliver. ............................. F-27

Figure F-16. The Marine MT Measurement System: (a) Electric and Magnetic Field 

Receiver, (b) Rope, (c) and (d) Anchors, (e) Water Flow Meter, (f) Buoy with a 

Flag, and (g) Survey Vessel....................................................................................... F-32

Figure F-17. (A) CSEM Receiver; (B) CSEM Source..................................................................... F-33

LIST OF TABLES

Page

Table F-1. Types of G&G Activities Included in This Programmatic EIS........................................ F-2

Gulf of Mexico G&G Activities Programmatic EIS F-vii

ABBREVIATIONS AND ACRONYMS ° degrees

2D two-dimensional

3D three-dimensional

4C four-component

4D four-dimensional

AOI area of interest

AUV autonomous underwater vehicle

BOEM Bureau of Ocean Energy Management

CCS carbon capture and storage

CHIRP compressed high-intensity radar pulse

cm centimeter

COST continental offshore strategic test

CPT cone penetrometer test

CSEM controlled source electromagnetic

EIS Environmental Impact Statement

FAZ full azimuth

ft feet

G&G geological and geophysical

GOM Gulf of Mexico

GPS global positioning system

HRG high-resolution geophysical

HSSE health, safety, security, and environment

Hz hertz

in. inch

in

3 cubic inch

IVI Industrial Vehicles International, Inc.

kg kilogram

kHz kilohertz

km kilometer

km

2 square kilometer

kn knot

lb pound m meter

MAZ multi-azimuth

MBES multibeam echosounder

mi mile

mi

2 square mile

mm millimeter

ms millisecond

MT magnetotelluric
F-viii G&G Survey Descriptions

NAZ narrow azimuth

NTL Notice to Lessees and Operators

OBC ocean bottom cable

OBN ocean bottom node

OBS ocean bottom seismic

OCS Outer Continental Shelf

psi pounds per square inch

RAZ rich azimuth

ROV remotely operated vehicle

SBES single-beam echosounder

TMS tether management system

UHR3D ultra-high-resolution 3D

USBL ultra-short baseline

USDOI U.S. Department of the Interior

VSP vertical seismic profile

WAZ wide azimuth
Gulf of Mexico G&G Activities Programmatic EIS F-1 

1 GEOPHYSICAL SURVEYS

A variety of geological and geophysical (G&G) techniques are used to characterize the 

shallow and deep structure of the shelf, slope, and deepwater ocean environments. The G&G 

surveys are conducted to (1) obtain data for hydrocarbon and mineral exploration and production; 

(2) aid in siting of oil and gas structures and facilities, renewable energy structures and facilities, and 

pipelines; (3) locate and monitor use of potential sand and gravel resources for development; 

(4) identify possible seafloor or shallow depth geologic hazards; and (5) locate potential 

archaeological resources and benthic habitats that should be avoided. The selection of a specific 

technique or suite of techniques is driven by data needs and the target of interest. These activities 

include the following: 

• various types of deep-penetration seismic surveys used almost exclusively for oil 

and gas exploration and development;

• other types of surveys and sampling activities used only in support of oil and gas 

exploration and development, including electromagnetic surveys, deep 

stratigraphic and shallow test drilling, and various remote-sensing methods;

• high-resolution geophysical (HRG) surveys used to detect shallow geohazards 

and marine minerals, archaeological resources, and certain types of benthic 

communities; and

• geological and geotechnical bottom sampling used to assess the suitability of 

seafloor sediments for supporting structures (e.g., platforms, pipelines, cables, 

renewable energy facilities such as wind turbines) or to evaluate the quantity and 

quality of marine minerals and sand for beach nourishment or other potential 

marine mineral extraction projects.

Refer to Table F-1 for an overview of G&G activity types that are included in this

Programmatic Environmental Impact Statement (EIS), the applicable program areas in which the 

different types of surveys are used, and their purpose for use in G&G activities.
F-2 G&G Survey Descriptions

Table F-1. Types of G&G Activities Included in This Programmatic EIS. 

Survey Type Applicable Program Areas Purpose(s) O&G REN MMP

Deep-Penetration Airgun Seismic Surveys

Seismic surveys evaluate subsurface geological formations to 

assess potential hydrocarbon reservoirs and optimally site 

exploration and development wells. The 2D surveys provide a 

cross-sectional image of the Earth’s structure while 3D surveys 

provide a volumetric image of underlying geological structures. 

Repeated 3D surveys result in time-lapse, or 4D, surveys that 

assess the depletion of a reservoir. The VSP surveys provide 

information about geologic structure, lithology, and fluids.

2D Seismic – Towed Streamer X X1 --

3D Seismic – Towed Streamer X -- --

2D Seismic – Seafloor Cable or Nodes X X1 --

3D Seismic – Seafloor Cable or Nodes X -- --

Wide Azimuth and Related Multi-Vessel X -- --

Borehole Seismic X -- --

Vertical Cable X -- --

4D (Time-Lapse) X -- --

Airgun HRG Surveys A single airgun used to assess shallow hazards, archaeological 

High-Resolution Seismic X X - resources, and benthic habitats.

Non-Airgun HRG Surveys Assess shallow hazards, potential sand and gravel resources for 

coastal restoration, archaeological resources, and benthic 

habitats. Devices used in subbottom profiling surveys include

• sparkers;

• boomers;

• pingers; and

• CHIRP subbottom profilers.

Subbottom Profiling X X X 

Side-Scan Sonar X X X 

Single Beam and Multibeam Echosounders X X X 

Non-Acoustic Marine Geophysical Surveys

Electromagnetic signals are used to develop a conductivity/

resistivity profile of the seafloor, helping to identify economic 

hydrocarbon accumulations and aid with archaeological surveys.

Marine Gravity X -- --

Marine Magnetic X -- --

Marine Magnetotelluric X -- --

Marine Controlled Source Electromagnetic X -- --

Airborne Remote Surveys

Gravity and magnetic surveys are used to assess structure and 

sedimentary properties of subsurface horizons. Airborne magnetic 

surveys evaluate deep crustal structure, salt-related structure, and 

intra-sedimentary anomalies.

Airborne Gravity X -- --

Airborne Magnetic X -- --
Gulf of Mexico G&G Activities Programmatic EIS

F-3

Table F-1. Types of G&G Activities Included in This Programmatic EIS (continued).

Survey Type Applicable Program Areas Purpose(s) O&G REN MMP

Geological and Geotechnical Surveys Collect surface and near-surface sediment samples to assess 

seafloor properties for siting structures such as platforms, 

pipelines, or cables. Different types of geologic cores include

• gravity corers;

• multicorers;

• piston corers;

• rotary corers;

• ROV push cores; and

• vibracorers.

Geologic coring is also used to assess sediment characteristics for 

use in coastal restoration projects. Shallow test drilling is 

conducted to place test equipment into a borehole to evaluate gas 

hydrates or other properties. The COST wells evaluate 

stratigraphy and hydrocarbon potential without drilling directly into 

oil and gas bearing strata. 

Grab and Box Sampling X X X 

Geologic Coring X X --

Shallow Test Drilling X X --

COST Wells X X --

Cone Penetrometer Tests X X --

Other Surveys and Equipment The devices in this category assist in the execution of surveys, 

either by providing location or facilitating underwater service tasks. 

Additionally, water guns are no longer used as a seismic source 

except in extremely rare instances.

Acoustic Pingers X X --

Transponders, Transceivers, Responders X X --

ROVs and AUVs X X --

2D = two-dimensional; 3D = three-dimensional; 4D = four-dimensional; AUV = autonomous underwater vehicle; CHIRP = compressed highintensity radar pulse; COST = continental offshore stratigraphic test; HRG = high-resolution geophysical; MMP = Marine Minerals Program; O&G = 

Oil and Gas Program; REN = Renewable Energy Program; ROV = remotely operated vehicle; VSP = vertical seismic profile.

1

The renewable energy scenario includes the possibility that a (2D or 3D) deep-penetration seismic survey would be conducted to evaluate 

formation suitability for carbon sequestration. However, given the much greater number and extent of seismic surveys included in the oil and gas 

scenario, a single seismic survey for carbon sequestration is not analyzed separately in this Programmatic EIS.
F-4 G&G Survey Descriptions

1.1 DEEP-PENETRATION SEISMIC AIRGUN SURVEYS

Marine seismic surveys using airgun sources are capable of imaging geological structures to 

several kilometers depth and have become an essential tool for geoscientists studying the Earth’s 

uppermost crust. Deep-penetration seismic surveys are conducted to obtain data on geological 

formations several thousand meters beneath the seafloor. A survey vessel tows an airgun array that 

emits acoustic energy pulses that propagate through water then pass into the seafloor. The acoustic 

signals reflect (or refract) off subsurface layers having acoustic impedance contrasts; upon return 

through the earth, the signals are detected by sensors (i.e., hydrophones, geophones) that may be 

towed in streamer cables behind the vessel (hydrophones) (Figure F-1) or incorporated into cables 

or autonomous nodes and placed on the seafloor (geophones). Receivers may also be placed in 

boreholes or, in rare instances, spaced at various depths in vertically positioned cables in the water 

column.

Figure F-1. A Marine Seismic Survey Vessel Towing an Airgun Array and a Streamer Containing 

Hydrophones (From: Caldwell, 2015).

Data from these surveys can be used to assess potential hydrocarbon structural and 

stratigraphic traps and reservoirs, and also to help locate exploration, development, and production 

wells to optimize extraction and production from a reservoir. Seismic airgun surveys are the only 

commercially proven technology currently available to accurately image the subsurface. Deep 

penetration seismic airgun surveys are also used for scientific and academic research and to detect 

geological fault lines. State-of-the-art computer systems are used to process and analyze seismic 

datasets and to display the subsurface geology in two or three dimensions. Seismic data 

acquisition, processing, and analysis technologies are continuously evolving to provide more 

information about the subsurface. Consequently, regions already surveyed may be resurveyed 

using a new technology to obtain an improved description of subsurface geology, which may lead to 

increased success in the discovery and production of oil and gas resources.
Gulf of Mexico G&G Activities Programmatic EIS F-5 

The types of deep-penetration seismic surveys discussed in this section primarily use 

airguns or airgun arrays as sound sources (Figure F-2). The survey types differ in where the 

receivers that detect the reflected sound source energy are located. The locations for receivers are 

as follows:

• in the water column, integrated into horizontally towed streamers or stationary 

vertical cables;

• in autonomous nodes placed on the seafloor;

• in cables laid on the seafloor; or

• in sensor packages located in wellbores (vertical seismic profiles [VSPs] and 

checkshot surveys).

Figure F-2. The Basic Difference Between 2D and 3D Survey Geometries (From: Caldwell, 2015).
F-6 G&G Survey Descriptions

The different types of deep-penetration seismic surveys have three elements in common: 

(1) a sound source; (2) the means to detect, process, and analyze sound reflected and refracted 

from subsurface geology; and (3) vessels or equipment to deploy the sound source.

The impacts of all survey sound sources are addressed in Chapter 4 of this Programmatic 

EIS. A typical marine seismic source is a sleeve-type airgun array that releases compressed air into 

the water, creating a bubble that generates a pulse of sound sufficiently energetic to penetrate deep 

beneath the seafloor (refer to Chapter 3.4 of this Programmatic EIS for more information about 

airguns, including their source levels). Airguns are broadband acoustic sources that generate 

energy over a wide range of frequencies, from less than 10 hertz (Hz) to more than 5 kilohertz (kHz), 

with industry usable frequencies ranging between 5 and 100 Hz. Most of the energy is concentrated 

at frequencies less than 500 Hz. The acoustic energy produced by an airgun or airgun array 

depends on the following three factors:

(1) firing pressure (2,000 pounds per square inch [psi] for most airguns currently in 

use);

(2) the number of airguns in an array (generally between 20 and 80); and 

(3) the total volume of all the airguns in the array (generally between 1,500 and 

8,460 cubic inches [in3

]).

The output of an airgun array is directly proportional to airgun firing pressure, the number of 

airguns, and the cube root of the total volume of airguns in the array. The geometry of an airgun 

array is designed to project the maximum amount of seismic energy generated by the array vertically 

into the seafloor. However, the acoustic directivity of an airgun array is complex and not uniform in 

all directions. Some energy is emitted in directions that are more horizontal than vertical with the 

directivity of emitted sound, in terms of frequency as well as intensity, being a function of the 

geometry of the airgun array and other factors.

Guard (or chase) vessels are similar to crew boats and range in size from approximately 40 

to 50 meters (m) (130 to 160 feet [ft]) and are responsible for maintaining clearance of the 

streamers, and typically follow within 1 to 2 kilometers (km) (0.6 to 1 mile [mi]) of the array. This 

ensures no interaction with other vessels and minimizes interaction with other marine users in line

with the survey and maintain the appropriate stand-off distance. These vessels are critical to 

maintain array safety. Depending on the size of the survey, one to three guard vessels typically are 

used.

1.1.1 2D (Towed-Streamer) Seismic Surveys

Two-dimensional (2D) surveys provide a cross-sectional image of subsurface geology. A 

single vessel towing an airgun array and a single streamer cable usually conduct 2D seismic 

surveys. The streamer is a polyurethane-jacketed cable containing several hundred to several 

thousand sensors (mostly hydrophones). An integrated navigational system is used to georeference 
Gulf of Mexico G&G Activities Programmatic EIS F-7 

the locations where the airgun array is fired as well as the location and depth of streamer cables. 

Tail buoys at the ends of streamer cables also contain global positioning system (GPS) receivers. 

Radar reflectors usually are placed on the tail buoys so other vessels can detect the ends of 

streamers.

The 2D surveys are primarily used to describe structural and stratigraphic geology, to 

perform reconnaissance surveys in frontier exploration areas, to link known productive areas over 

large geographic areas, and to determine if a three-dimensional (3D) survey is warranted in an area 

of interest (AOI). The 2D towed streamer seismic exploration surveys are conducted on a 

proprietary or a non-exclusive (multi-client) basis. Proprietary surveys usually cover only a few 

Outer Continental Shelf (OCS) lease blocks for an individual client who owns the data and has 

exclusive use of it. In contrast, non-exclusive (multi-client) survey data are owned by the seismic 

surveyor, typically are collected over large multi block areas, and are licensed for use to as many 

clients as possible. Because the survey data are not for the exclusive use of any one client, the 

surveyor’s goal is to license the data multiple times.

Vessels conducting 2D surveys typically are 60 to 90 m (197 to 295 ft) long and tow an 

airgun array 200 to 300 m (656 to 984 ft) behind the ship at a depth of approximately 5 to 10 m 

(16 to 33 ft). The airgun array often consists of 3 subarrays, of 6 to 12 airguns each, and is 

approximately 12.5 to 18 m (41 to 59 ft) long and 16 to 36 m (52 to 118 ft) wide. Following behind 

the airgun array by 100 to 200 m (328 to 656 ft) is a single streamer approximately 5 to 12 km (3.1 to 

7.5 mi) long. The airgun array and streamers are towed at a speed of approximately 4.5 to 5 knots 

(kn) 5.2 to 5.8 miles per hour (mph). Approximately every 10 to 15 seconds, at a separation 

distance of 23 to 35 m (75 to 115 ft) for a vessel traveling at 4.5 kn (5.2 mph), the airgun array is 

fired; the actual time between firings depends on ship speed and data requirements. The airguns 

used for analysis of the proposed action include a small single airgun (90 in3

) and a large airgun 

array (8,000 in3

) as described in Chapter 3.4 of this Programmatic EIS.

In Figure F-2A (left panel), a typical marine 2D seismic survey geometry is shown; in Figure 

F-2B (right panel), a typical marine 3D seismic survey geometry is shown. Both survey geometries 

are presented over contour maps that indicate the structure of a particular horizon (strata) in the 

subsurface. The number of airgun array firings is exactly the same for both surveys. The 

subsurface images of the target strata that are generated by the two survey types are shown in the 

bottom half of Figure F-2. The figure illustrates the difference in the level of detail of the subsurface 

produced by a 3D survey compared to a 2D survey. The ship track spacing shown in the figure is 

500 m (1,640 ft) for both survey types. Typically, spacing between adjacent ship tracks during 

2D surveys will be 1 km (3,280 ft) or more. For 3D surveys, track spacing depends on several 

factors, such as the number of airgun arrays being used (often two) and the number of streamers 

being towed (commonly 8 to 10). In Figure F-2B, the spacing between streamers is 133 m (436 ft). 

The result is that, in the case of this example, data density will be 15 to 50 times greater in the crosstrack dimension for the 3D survey. The data density in the along-track dimension of the figure will be 

approximately the same for both survey types.
F-8 G&G Survey Descriptions

Following ramp-up of the airgun array to full operational output, the 2D survey vessel moves 

along a preset track line until a full line of data is acquired. At the end of a track, the vessel typically 

takes approximately 2 to 6 hours to turn around, realign the airgun array and streamer, and begin 

another survey track. Sometimes it can take much longer to turn between tracks. The spacing 

between track lines and the length of track lines can vary greatly, depending on the objectives of a 

survey. The time required to turn a survey vessel between tracks can vary based on location and 

associated navigational constraints, environmental conditions, and proximity to other vessels. Some 

2D surveys might include only a single long track. Others may have numerous tracks, with track 

spacings as short as 2 to 10 km (1.2 to 6.2 mi). When the survey vessel is operational, data 

acquisition usually is continuous (24 hours per day) and, depending on the size of the survey area, 

may continue for days, weeks, or months. However, data acquisition may be interrupted. A typical 

seismic survey experiences approximately 20 to 30 percent of non-operational downtime due to a 

variety of factors, including technical or mechanical problems, standby for weather or other 

interferences, and performance of mitigation measures (e.g., ramp-up, pre survey visual observation 

periods, and shutdowns) (Caldwell, official communication).

Fewer 2D surveys are conducted than 3D surveys. The 2D surveys usually cover a larger 

area in the same time as 3D surveys do but with lower spatial resolution and also much lower cost. 

Typical spacing between track lines for 2D surveys, which is also the spacing between adjacent 

streamer line positions, is on the order of 1 km (0.6 mi) or more. Geophysical surveyors often have 

proprietary methods for data acquisition depending on the survey target and their data-processing 

capabilities. Such differences can make each surveyor’s dataset for the same area somewhat 

unique, and may prevent a client from combining one surveyor’s dataset for an area with that of 

another surveyor for the same area.

1.1.2 3D (Towed-Streamer) Seismic Surveys

As with 2D towed-streamer seismic surveys, 3D towed-streamer seismic surveys are 

conducted by geophysical surveyors on a proprietary or a non-exclusive multi-client basis. 

Proprietary surveys usually cover only a few OCS lease blocks for an individual client who owns the 

data and therefore will have exclusive use of it. In contrast, for non-exclusive surveys the data are 

owned by the geophysical surveyor, are often collected over large multi block areas, and are 

licensed to as many clients as possible to recover costs, make a profit, and keep the cost to clients 

lower than would be the case for a proprietary survey.

3D seismic surveys provide data that image the subsurface geology with much greater clarity 

and higher resolution than is possible with 2D surveys (Figure F-2). Compared with 2D seismic 

surveys where track spacing is usually 1 km (3,280 ft) or more, the separation between tracks for 

3D surveys depends on several factors such as the number of airgun arrays being used and the 

number of streamers being towed (commonly eight). A common survey design parameter for 

3D surveys is to have the distance between streamer tracks be on the order of 75 to 150 m (246 to 

492 ft). The result is that the data density for any subsurface point will be 15 to 30 times greater in 
Gulf of Mexico G&G Activities Programmatic EIS F-9 

the cross-track direction for 3D surveys than for 2D surveys. The data density in the along-track 

direction will be approximately the same for 2D and 3D towed-streamer surveys.

The 3D survey data can be used to distinguish hydrocarbon-bearing zones from waterbearing zones below the seafloor. The 3D seismic surveys techniques have improved since first 

used in the 1970s, and areas surveyed by older 3D methods may be resurveyed using updated 

methods to provide better characterization of subsurface geology. The 3D surveys also are used in 

areas previously surveyed using 2D techniques that show potential for development. Repeated 3D 

surveys in a single area are used to monitor changes in the structure of producing reservoirs. Such 

surveys, which typically are conducted at 6-month intervals, are called four-dimensional (4D) or timelapse 3D surveys. There are several types of 3D surveys that differ in the number of vessels, sound 

sources, and the location of hydrophones. Conventional, single-vessel 3D surveys are referred to as 

narrow azimuth (NAZ) 3D surveys. Other 3D seismic surveys include wide azimuth (WAZ), multi 

azimuth (MAZ), and rich azimuth (RAZ) surveys, which are discussed in the following sections.

The current state-of-the-art ships used for 3D surveys are purpose-built vessels with much 

greater towing capability than vessels used for 2D surveys. The 3D seismic survey vessels 

generally are 60 to 120 m (197 to 394 ft) long, with the largest vessels more than 120 m (394 ft) in 

length and more than 65 m (213 ft) wide at the stern. The seismic ships typically tow two parallel 

airgun arrays 200 to 300 m (656 to 984 ft) behind them. The arrays contain various numbers and 

sizes of airguns. Streamers containing hydrophones and other sensor are towed 100 to 200 m 

(328 to 656 ft) behind the dual airgun arrays. 

Most 3D ships can tow eight or more streamers, with the total length of streamers (number of 

streamers multiplied by the length of each streamer) exceeding 80 km (49.7 mi). The theoretical 

maximum number of streamers that can be towed by a modern vessel is 24, each of which can be 

up to 12 km (7.5 mi) long, for a total of 288 km (179 mi) of streamers. A 3D seismic vessel usually 

will tow 8 to 14 streamers, each 3 to 8 km (1.9 to 5 mi). The width of the streamer array towed by a 

3D seismic vessel can be quite large. For example, an array of 10 streamers where the streamers 

are 75 to 150 m (246 to 492 ft) apart will have a width of 675 to 1,350 m (2,215 to 4,429 ft), which is 

the swath of ocean surface covered by the survey vessel during each track line. Other streamer 

configurations may result in narrower or wider swaths.

Seismic survey vessels tow their airgun and streamer arrays at a speed of 4 to 5.5 kn (4.6 to 

6.3 mph) during data acquisition. During a 3D seismic survey, one of the two airgun arrays being 

towed is fired approximately every 11 to 15 seconds (i.e., a distance of 25 m [82 ft] for a vessel 

traveling at 4.5 kn [5.2 mph]). The other array is fired 11 to 15 seconds later. To achieve a desired 

distance between airgun firings, the time between firings is a function of survey vessel speed. At the 

end of each track line, which can be 100 to 167 km (62 to 104 mi) long and may take 12 to 20 hours 

to complete, the survey ship turns to begin the next planned track line, an operation that may require 

up to 10 hours to complete, depending on the length of streamers. This procedure runs continuously 

day and night, and may continue for days, weeks, or months depending on the size of the survey 

area. There are survey designs such as coil surveys where turning is continuous, as is data 
F-10 G&G Survey Descriptions

acquisition. Regardless of survey type, data acquisition is almost never continuous. A typical 

seismic survey experiences approximately 20 to 30 percent non-operational downtime due to 

technical or mechanical problems, standby for weather or other interferences, and performance of 

mitigation measures (e.g., ramp up, pre-survey visual observation periods, and shutdowns). The 

airguns used for analysis of the proposed action include a small single airgun (90 in3

) and a large 

airgun array (8,000 in3

) as described in Chapter 3.4 of this Programmatic EIS.

1.1.3 Ocean-Bottom Seismic (Cables and Nodes)

2D Surveys

Ocean-bottom seismic (OBS) surveys can be conducted using ocean-bottom cables (OBCs) 

and/or ocean-bottom nodes (OBNs). The OBC surveys originally were designed to enable seismic 

surveys in shallow water and congested areas such as producing fields with many platforms and 

subsea production structures. The cables contain pairs of hydrophones and geophones to measure 

pressure and very small movements (linear accelerations) of the seafloor. Some seafloor cables are 

used in a retrievable mode of operation, some are used in a permanent installation, and some can 

be used in both modes. Recent innovations in OBS surveys include development of autonomous 

nodes that can be tethered to coated lines and deployed from ships or remotely operated vehicles 

(ROVs), depending on water depth (Figures F-3 and F-4). Current technology can be used in water 

depths to 3,000 m (9,842 ft) or slightly greater. The OBS surveys are most useful to acquire data in 

shallow water and obstructed areas as well as four-component (4C) survey data, which consists of 

pressure and 3D linear acceleration. The 4C data can provide more information than 2D data about 

subsurface fluids and rock characteristics. 

The OBC and autonomous node seismic airgun surveys require the use of several ships. 

One or two ships usually are needed to lay out and pick up cables, one ship is needed to record 

seismic data, one ship tows an airgun array, and two smaller utility boats support survey operations. 

Seismic airgun surveys conducted using recording buoys do not need a recording vessel but still 

need other vessels.

Most 2D OBS surveys use OBCs, with OBNs being a lesser-used alternative. The length of 

a 2D survey line varies from a few to tens of kilometers (miles), depending on the objectives of the 

survey. Because most 2D survey lines are longer than the length of available cables, lines are 

completed in segments that require cables to be picked up and re-laid several times. The distance 

between adjacent 2D lines usually is several hundred meters (a few thousand feet) to a few 

kilometers (a couple of miles). Within survey lines, when autonomous nodes are used, they are 

placed a few hundred meters (several hundred feet) apart; when cables are used, the sensors in the 

cables are usually 50 to 100 m (164 to 328 ft) apart.
Gulf of Mexico G&G Activities Programmatic EIS F-11

Figure F-3. Three Examples of OBCs (From: Caldwell, 2015).

Figure F-4. Five Types of OBNs (From: Caldwell, 2015).
F-12 G&G Survey Descriptions

After OBNs or OBCs are deployed, a vessel towing an airgun array (source vessel) passes 

along the line of sensors (Figure F-5). The spacing between discharges of the airgun array (shots) 

depends on survey objectives. Typical spacing between airgun array shots are 25 m (82 ft), 50 m 

(164 ft), 75 m (246 ft), and 100 m (328 ft). When shot spacing is 25 m (82 ft), a shot is fired every 

11 seconds when the source vessel’s speed is 4.4 kn (5.1 mph). After a survey line is completed, 

the source vessel takes approximately 10 to 15 minutes to turn around then passes along the next 

segment of bottom-deployed sensors. During a survey, OBNs or OBC may remain deployed for a 

couple of days to several weeks, depending on operating conditions and the survey’s design. 

Usually more than one cable, or more than one set of nodes, will be used so that the next receiver 

line segment can be deployed while the previous line segment is being shot.

Figure F-5A shows the layout for a 2D ocean bottom receiver seismic survey with a source 

vessel towing an airgun array and a recording vessel connected to a seismic cable. Figure F-5B

shows the location of OBCs or autonomous nodes relative to a recording vessel and the track line of 

the seismic source vessel. Nodes, while autonomous, may be tethered to a line that is connected to 

a deployment vessel; alternatively, the nodes could be kept autonomous from a surface vessel and 

deployed on the seafloor using an ROV.

Figure F-5. Layout for a 2D Ocean-Bottom Receiver Seismic Survey (From: Caldwell, 2015).

3D Surveys

Newer technology 4C receiving sensors, rather than older 2D sensors (refer to Section 

1.1.2), are used for most ocean bottom receiver 3D surveys. The new 4C technology was 

developed for new types of OBC and autonomous receiving units (nodes) that can be attached to 
Gulf of Mexico G&G Activities Programmatic EIS F-13

coated lines or as autonomous nodes using ROVs. Most 3D ocean-bottom receiver surveys are 

RAZ or in areas where there are structural obstructions on the sea surface or seafloor (Figure F-6). 

Some seafloor surveys are conducted because the receivers are in the quieter environment of the 

seafloor rather than the noisier environment of the sea surface, thereby generally producing better, 

more easily interpreted data than would a streamer survey. Finally, seafloor surveys methods are 

used for some 4D seismic surveys.

Figure F-6. (A) Drill Rigs and Platforms in the Gulf of Mexico in a Configuration that Makes a TowedStreamer Seismic Survey Impossible to Conduct; OBCs or OBNs Would be Required to 

Acquire 3D Seismic Data in Such an Obstructed Area. (B) Schematic of One Possible 

Deployment of Subsea Structures at the Atlantis Field in the Gulf of Mexico; the Acquisition 

of 3D Seismic Data in Such a Situation Might Best be Handled Using an OBN System 

(From: Caldwell, 2015).

Electrical power, command and control signals, and seismic data are transmitted via cable 

to/from a ship, platform, or buoy in seismic surveys that use seafloor cables. In contrast, 

autonomous nodes are equipped with a power source, seismic sensors, and computer processor 

based hardware and software to acquire, pre-process, and store seismic data. Seismic cables are 

laid on the seafloor using special equipment off the back of a vessel that may be designed for that 

purpose. Autonomous nodes generally are deployed from a specially equipped vessel able to lay 

nodes on the seafloor attached to a line or cable, or to individually place nodes on the seafloor using 

a ROV. The deployment method used depends primarily on water depth, but other factors such as 

safety in obstructed areas may be a factor in deployment method selection. The maximum 

deployment depth for new recording systems is approximately 3,000 m (9,842 ft).

Ocean-bottom seismic recording systems may be kept deployed for extended periods of time 

when attached to a buoy or platform at the surface. The power supply of autonomous nodes 

requires periodic replacement or recharging. The service schedule for current autonomous nodes 

for power supply maintenance and data recovery is 120 to 140 days, which is sufficient time to 

complete most surveys.
F-14 G&G Survey Descriptions

A nominally rectangular grid of sensors is laid on the seafloor for 3D OBC or OBN surveys 

(Figure F-7). The spacing between sensor modules on a cable usually is 50 to 200 m (164 to 

328 ft), and the spacing between adjacent cables usually is 200 to 400 m (656 to 1,312 ft). When 

autonomous nodes are used, spacing between nodes often is 300 to 400 m (984 to 1,312 ft) 

measured both parallel and perpendicular to the seismic source vessel’s track lines. The size of the 

receiver grid is usually limited by the amount of equipment the seismic survey contractor has 

available. For example, 961 receiving nodes would be required for a 12- × 12-km (7.5- × 7.5-mi) 

survey area with 400-m (1,312-ft) spacing between nodes, if it was desired to lay out the total grid of 

nodes at the initiation of a survey. The survey could be broken into smaller segments requiring 

fewer nodes; however, to efficiently conduct a survey, approximately 500 nodes or 100 km (62 mi) of 

cable are needed.

Figure F-7A illustrates the layout pattern of an OBN or OBC system (cables and nodes are 

shown side-by-side only for illustrative purposes; generally, only one of the system types would be 

used for a survey) for a 3D survey. The OBC system is connected to a recording vessel or buoy. 

The OBN system would not need a connection to the surface if deployed as individual autonomous 

nodes. A surface connection would be needed if the otherwise autonomous nodes were deployed 

attached to a line or cable. Figure F-7B shows cable systems attached to recording vessels and 

indicates that the track lines of the seismic source vessel may be aligned perpendicular (orthogonal 

or patch geometry) or parallel (parallel or swath geometry) to the receiving array; most surveys are 

shot using orthogonal geometry.

3D ocean-bottom surveys are conducted using the same type of seismic source (airgun 

arrays) used for 2D ocean-bottom and towed-streamer surveys. Once the grid of receiving sensors 

is in place, a seismic source vessel, typically much smaller than a high-end, towed-streamer, 

3D seismic vessel, traverses the area of the grid. A dual-airgun array usually is used, and the 

distance between discharges of the airgun array is 25 to 50 m (82 to 164 ft). The time between 

airgun array discharges corresponding to these distances is 10 to 25 seconds when the source 

vessel’s speed is 4.5 kn (5.2 mph). After a track line is acquired, the seismic source vessel takes 

approximately 10 to 15 minutes to turn around and begin the next survey track line. When data 

acquisition using sets of recording nodes or cable is complete, the nodes or cable are retrieved and 

moved to their next position. A particular set of nodes or cable may remain in place for a couple of 

days to several weeks, depending on operating conditions, survey size, and the logistics of the 

survey. In some cases, nodes or cables may be left on the seafloor for future 4D surveys 

(Figure F-8).

The seafloor topography of the Atlantis Field in the Green Canyon Area of the Gulf of Mexico 

(GOM) is shown in Figure F-8. The inset map shows the BP Atlantis platform and its location. 

Water depth ranges from approximately 1,300 to 2,200 m (4,265 to 7,218 ft). The dots in the figure 

indicate OBN locations for the first of multiple 3D surveys (part of a 4D seismic program) conducted 

in the field. The first survey required two patches of nodes (the pink area and the gray area), each 

patch consisted of approximately 800 nodes and nodes were 426 m (1,398 ft) apart. The total area 
Gulf of Mexico G&G Activities Programmatic EIS F-15

covered by the nodes was 247 square kilometers (km2) (95 square miles [mi2]), and the area 

transected by the sound source vessel was 757 km2 (292 mi2

).

Figure F-7. Placement of an OBN or OBC System in a 3D Seismic Survey (From: Caldwell, 

2015).
F-16 G&G Survey Descriptions

Figure F-8. OBNs Left on the Seafloor for Use in 4D Surveys (Modified from: Beaudoin and 

Ross, 2007).

1.1.4 Wide Azimuth and Related Multi-Vessel Surveys

In conventional 3D seismic surveys involving a single source vessel, only a subset of the 

reflected wave field can be obtained because of the narrow range of source-receiver azimuths, and 

thus are called NAZ surveys (Figure F-9). New techniques such as WAZ, MAZ, RAZ, and full 

azimuth (FAZ) towed streamer acquisition as well as associated data processing have emerged to 

provide better data quality than that achievable using traditional NAZ seismic surveys (Figure F-10). 

The new methods provide seismic data with better illumination, higher signal-to-noise ratios, and 

higher resolution. The various azimuth surveys have been particularly helpful in deepwater locations 

of the GOM and other areas, where breakthroughs have been achieved in imaging subsurface areas 

containing complex geologic structures, particularly those beneath salt bodies with very irregular 

geometries.

Figure F-9 shows offset (the distance between a source and a particular receiver) and 

azimuth (the angles covered by the various directions between a seismic source and individual 

receiving sensors). The two thin green arrows in Figure F-9 show the range of azimuths to the 

farthest offset receivers. The pink rectangle indicates the nominal area imaged by the reflection 

points produced in the subsurface by the recording of energy at all of the receivers in the streamer 

array when the seismic source is fired one time. “Inline” means in the same direction as the vessel 

track, and “crossline” means in the direction perpendicular to the vessel track. With NAZ surveys, 

the width (crossline dimension) of the pink area will be less than half the length (inline dimension). 

The aspect ratio (crossline divided by inline) of the pink area is much less than 0.5 (the inline 

dimension in Figures F-9 and F-10 is shown much less than it is in actuality compared to the 
Gulf of Mexico G&G Activities Programmatic EIS F-17

crossline dimension so as to fit the page). At least one company performs coil surveys that do not 

require any turns, therefore allowing shorter survey durations.

To achieve wider azimuthal coverage, the crossline dimension of the pink areas should be 

greater than that shown in Figure F-9 and should approach the length of the streamers indicated in 

the figure. The thin green arrows in Figure F-10 indicate the azimuthal coverage between the 

source and the farthest receiver, and the heavy short green arrows (Figure F-10D) indicate the 

various azimuths produced by the various passes in the illustrated geometry. Figure F-10A

illustrates one method to acquire WAZ data. This method requires three seismic source vessels, 

only one of which tows receiver streamers, and produces more azimuthal coverage than the NAZ 

geometry but does not generate data for all azimuths. Figure F-10B illustrates another configuration 

used to acquire WAZ data, using the same three vessels shown in Figure F-10A, but in a different 

spatial arrangement. Figure F-10C shows another WAZ data acquisition strategy; it uses two 

source-and-streamer vessels and two source-only vessels. The red arc illustrates that this method 

obtains more than 90° of azimuth. Figure F-10D shows the most basic method used to acquire 

MAZ data. Using this method, a single seismic source and streamer vessel, using conventional 3D 

survey methodology, transects the same area multiple times along different azimuthal directions. 

Figure F-10E illustrates acquisition of RAZ data using multiple passes of one source-and-streamer 

vessel and two source-only vessels, the same vessel configuration shown in Figure F-10B. Making 

two passes at right angles to each other with the vessel configuration shown in Figure F-10C would 

produce FAZ (180° azimuth) coverage. Figure F-10E demonstrates that a combination of WAZ and 

MAZ geometries will produce a RAZ or FAZ geometry. Figure F-10 does not show all of the tested 

survey designs, and new designs will be tested as the seismic industry continues to work to make 

WAZ, MAZ, RAZ, and FAZ shooting more efficient and less costly.

Figure F-9. The Narrow Range of Source-Receiver Azimuths in SingleVessel 3D Surveys (From: Caldwell, 2015).
F-18 G&G Survey Descriptions

Figure F-10. New 3D Acoustic Survey Techniques that Provide Improved Data 

Quality (From: Caldwell, 2015).

The WAZ, MAZ, RAZ, and FAZ seismic survey strategies generally require multiple vessels 

using a variety of vessel operation geometries. Figure F-10 illustrates only some of the survey 

configurations that have been tested or are feasible. The geophysical objectives of a survey, the 

need for high-quality data, data acquisition efficiency, safety, and cost are factors that influence 

survey design. Whatever the design, better azimuthal coverage costs more because some 

combination of more vessels or more vessel passes over the survey area will be required. Seismic 

survey designers continue to create new survey strategies to acquire data more efficiently and at 

less cost. Synchronized discharge of airgun arrays being towed by different vessels is being used in 

some cases because data processing techniques can separate the energy from synchronized 

seismic sources using differences in source-to-receiver offset distances. While this increases the 

level of sound in the ensonified water volume, it also reduces the length of time that the water 

volume is ensonified because the discharge of all the seismic airgun arrays being used for the 

survey occurs at one time. The seismic industry continues to study, design, and refine seismic 

survey designs to increase data quality while reducing survey time, survey costs, and environmental 

impact. Some survey designs have been patented, such as coil survey design where one or more 

seismic source-receiver array vessels follow an overlapping circular path, and there are other 

proprietary and unique designs as well.

The specifications and other elements of the design of MAZ survey airgun arrays are 

developed to obtain the best information possible given the characteristics and depth of geologic 

targets of interest. The energy levels of the airguns used for WAZ, NAZ, and RAZ surveys are the 

same as those discussed in Section 1.1. 
Gulf of Mexico G&G Activities Programmatic EIS F-19

The time required to complete one pass of a transit line for a single NAZ vessel and the time 

required for one pass by multi-vessel conducting a WAZ survey will be essentially the same. Turn 

times will be somewhat longer during multi-vessel surveys to ensure that all vessels are properly 

aligned prior to beginning the next transit line. Turn times depend mostly on the vessels and the 

equipment they are towing (as in conventional 3D surveys); however, the number of vessels towing 

streamers in the entire entourage is the main determinant of the increased time to turn. The MAZ 

technique, where multiple passes are made, increases the time needed for a survey in proportion to 

the number of passes that will be made within an area. The reduction in the number of passes is 

one of the most significant driving factors in continued efforts to design more efficient seismic 

surveys.

1.1.5 Borehole Seismic Surveys

2D VSP Surveys

The placement of seismic sensors in a well or borehole is another way seismic data can be 

acquired. The VSP surveying is conducted by placing seismic receivers, usually three-component 

geophones, at many depths in a wellbore, and recording both direct-arriving and reflection energy 

from an acoustic source (Figure F-11). Thirty years ago, VSP surveys were conducted using a 

single receive sensor. More modern VSP surveys are conducted using strings of 12 to 120 seismic 

sensors. The use of multiple sensor strings shortens acquisition time and helps ensure that the 

airgun source level referenced during data processing is the same for all sensors in a string for each 

airgun discharge. The typical spacing between sensors in strings (tools) is 15 m (49 ft), but it can be 

any distance needed to meet survey requirements. The receiver sensors must be coupled to the 

borehole casing during borehole surveys to obtain high-quality data. There are a variety of methods 

used to couple receive sensors to a borehole casing, including electrically operated locking arms, 

bow springs, magnets, or even just gravity (in deviated wells). Borehole seismic surveys include 

(1) 2D VSPs, (2) 3D VSPs, (3) checkshot surveys, and (4) seismic while drilling. Sensors usually 

are placed at 50 to 200 depths, but this number depends on several factors. The seismic sensors 

usually are spaced equally apart at 15 m (49 ft) so that the total depth covered is a few thousand 

meters (several thousand feet). The seismic source usually is a single airgun or small airgun array 

hung from a platform or deployed from a source vessel. The airguns used for VSPs may be the 

same or similar to those used for 2D and 3D towed-streamer surveys. Normally, the number of 

airguns and the total volume of airguns used are less than those used for towed-streamer surveys 

(Sections 1.1.1 and 1.1.2). Less sound energy is required for VSP surveys because the seismic 

sensors are in a borehole, which is a much quieter environment than that for sensors in a towed 

streamer, and because the VSP sensors are located nearer to the targeted reflecting horizons. The 

total round-trip path for sound from the seismic source to reflector and back to a sensor in a VSP is 

one-half to two-thirds as long as those for seismic surveys where the source and seismic sensor are 

located near the sea surface. VSP survey duration mostly depends on the equipment used for the 

survey, but it also depends partially on survey type and objectives. Some VSP surveys take less 

than a day, and most are completed in a few days. The 2D VSP survey type is defined by seismic 

source location (Figure F-11), and less by the number and depth of sensors. 
F-20 G&G Survey Descriptions

There are four commonly used types of 2D VSP surveys (refer to Figure F-11):

• zero-offset;

• offset (and multiple-offset);

• walkaway; and

• deviated-well (or walk above).

A zero-offset VSP uses a single position for the seismic source that is close to the well 

compared to the depths of the receiving sensors so the sensors mostly receive vertically propagating 

energy. The seismic source usually is an airgun or a small array of airguns hung from a platform. In 

an offset VSP survey, the seismic source is deployed from a small, stationary vessel far enough 

away from the well so that the received seismic waveforms have a significant amount of horizontally 

propagating energy and image some lateral distance away from the borehole. The seismic source 

for a multiple-offset VSP is deployed using a small vessel at multiple locations, typically less than 10, 

where it is held stationary during data acquisition. In some situations, the seismic source locations 

are in a line radiating away from or through the well location. In a walkaway VSP survey, a relatively 

small number of receiving sensors are deployed within the well and the seismic source is moving 

during data acquisition. The walkaway VSP requires a small source vessel capable of accurately 

positioning the seismic source at many positions along a line passing over or near the well. During a 

deviated-well VSP survey, the seismic source, which may be stationary or moving depending on the 

source output level and survey objectives, is fired from a small vessel that is positioned at various 

points above the path of the well. If the number of depth levels at which data are needed to meet 

survey requirements exceeds the number of seismic sensors in a string, then the string is 

repositioned as many times as necessary to obtain data at all desired depths.

The subsurface image obtained from a VSP survey will be a 2D plane defined by the source 

location and the borehole (Figure F-12). In Figure F-11, the black arrows indicate ray paths for 

energy that propagates from the seismic source directly to each sensor in a borehole. The red 

arrows indicate ray paths for energy that is reflected from some point in the subsurface to sensors in 

the borehole. For the deviated-well VSP, the red ray paths show the directly arriving energy paths 

as well as the reflected energy paths. In general, the zero-offset and offset VSPs will have several 

depth levels (typically 50 to 150) in the borehole where sensors are placed, while the walkaway and 

deviated-well VSPs will have fewer depth levels where sensors are placed.

VSP surveys are useful for several reasons: they (1) provide an accurate depth to a seismic 

reflector at the wellbore; (2) provide good rock-velocity information near the well; (3) aid in the 

identification of seismic multiples, such identification being useful in the processing of surface 

seismic data; (4) produce high resolution images of the subsurface near the well; and (5) may be 

used in a time-lapse mode. The VSP surveys provide information about geologic structure, lithology, 

and fluids that is intermediate between that obtained from sea surface seismic surveys and the welllog scale of information. The VSP surveys may be conducted during all stages of oil and gas 
Gulf of Mexico G&G Activities Programmatic EIS F-21

industry activity (i.e., exploration, development, and production), but most are conducted during the 

exploration and development stages.

Figure F-11. The Geometries of the Four Basic Types of 2D VSPs (From: Caldwell, 

2015).

Figure F-12. The Geometry of a 3D VSP Survey (From: Caldwell, 2015).

3D VSP Surveys

The 3D VSPs are relatively new technology made possible by development of multi-level 

sensor strings, with 50 to more than 150 sensors positioned in a well at one time. The distance 

between sensors in a string usually is 15 m (49 ft), but other spacing distances are possible. An 

interval between 1,500 and 3,000 m (4,921 and 9,842 ft) within a well can be instrumented in one or 

two placements of such sensor strings. The time required to conduct a 3D VSP survey depends on 

the number of seismic source positions required to meet data needs and how quickly a seismic 
F-22 G&G Survey Descriptions

source vessel can cover the survey area. The 3D VSP surveys involve many more source positions 

covering some area around a well compared to the relatively few source positions needed for a 

2D VSP survey.

The airguns used for 3D VSP surveys are the same as those used for 3D towed-streamer 

surveys, and the design of the airgun arrays can be quite similar. The data acquisition design (the 

track line of the survey vessel and the schedule for discharge of the airgun arrays) depends on the 

objectives of the survey and can dramatically affect the time required to conduct a survey. Both 

rectangular survey vessel track patterns, as used for 3D towed-streamer surveys, and spiral track 

patterns where the spiral dimensions get larger as the seismic source vessel moves away from the 

well, have been used for 3D VSP surveys (Figure F-12). A rough rule-of-thumb for the design of 

3D VSP surveys is that the distance from the well covered by the seismic source vessel will about 

equal the depth of the well (i.e., for a 3,000-m [9,842-ft] well, the area around the well covered during 

the survey will have a radius of 3,000 m [9,842 ft]).

By completing several seismic source discharge locations around a well, 3D VSP survey 

data will include a substantial number of reflection points around the well. The number of times the 

seismic source is discharged will depend on the objectives of the VSP survey and the number of 

sensors deployed in the borehole at one time. As many as 160 sensors have been deployed in a 

wellbore at one time, which dramatically reduces the number of times the seismic source must be 

discharged to complete a 3D VSP survey. Deployment of several (>50) sensors in a well at one time 

is making the 3D VSP technique economically attractive. Permanent fiber optic, single-fiber sensors 

and a small number of multi-fiber sensors were initially used in 2015 for 3D VSP surveys (Caldwell, 

official communication). Few of these types of sensors are currently employed but their use is likely 

to increase in the future. They are attractive because they are small, easy to install, relatively low 

cost, and can be used to place an unlimited number of sensors in a single well.

Checkshot Surveys

Checkshot surveys are similar to a zero-offset VSP surveys but (1) are less complex and 

require less time to conduct, (2) produce less information, (3) are cheaper, (4) use a less 

sophisticated borehole seismic sensor, and (5) acquire shorter data records at fewer depths. During 

a checkshot survey, a seismic sensor is sequentially placed at a few depths (<20) in a well, and a 

seismic source (almost always an airgun) is hung from the side of the well platform (Figure F-13). 

Only the first energy arriving at the sensor from the seismic source is permanently recorded by the 

sensor and recording unit combination (the black arrow in Figure F-13 indicates a ray path for 

energy propagating from the source directly to a sensor positioned in the borehole). No reflection 

events are recorded, and no sophisticated data processing like that for VSP surveys is required. 

The purpose of a checkshot survey is to estimate the velocity of sound in rocks penetrated by the 

well. Typically, the depths at which the sensors are placed are at, or near, the boundaries of 

prominent lithologic features. Checkshot surveys can be conducted quite quickly, much quicker than 

VSP surveys, but they produce much less information. Because checkshot surveys are much less 
Gulf of Mexico G&G Activities Programmatic EIS F-23

expensive and do not use the wellbore and the drilling rig as long, they are much more common than 

VSP surveys.

In most checkshot surveys, the seismic source is hung from the platform in a fixed location 

within the water column, so a surface vessel is not needed. Because reflection energy does not 

need to be acquired, the seismic source usually is smaller than those used for VSP surveys. On 

occasion, the availability of seismic sources and logistics sometimes makes it operationally and 

financially advantageous to use a VSP type of seismic source array.

Figure F-13. The Geometry of a Checkshot 

Survey (From: Caldwell, 2015).

Seismic While Drilling

The acquisition of seismic while drilling refers to the acquisition of borehole data while there 

is downtime from the actual drilling. There are two different modes of acquisition. One mode 

collects data when a stand of pipe (90 or 135 ft; 27 or 41 m) is being connected to the drill stem. 

These surveys can take days to a month to complete, but they are done intermittently during that 

time period. Airgun arrays are 1,200 to 1,560 in3

. The other mode collects borehole data during the 
F-24 G&G Survey Descriptions

time while round tripping all drill pipe out of the borehole to change the bit. This survey is run 

intermittently for weeks and sometimes up to a month to the well completion depth.

1.1.6 Vertical Cable Surveys

Vertical cable surveys use hydrophones positioned along a cable held vertically in the water 

column between a seafloor anchor and a buoy at the sea surface. The hydrophones record the 

energy produced by an acoustic seismic source, typically an airgun array. The primary energy of 

interest is reflections from subbottom geological features. This technique produces a VSP without 

using a well, but it requires two vessels: one to manage the hydrophone cables and one to manage 

the seismic sources.

The objectives of the survey determine the number and positions of hydrophone cables and 

seismic sources. The hydrophone cables may be left in place for hours or days, depending on the 

size of the survey area and operating conditions. The airgun array is the same as that used for 3D 

towed-streamer surveys. These types of surveys are not common because of the better data 

acquisition techniques available using other types of surveys.

1.1.7 4D Time-Lapse Surveys

The 4D surveys are repeated one or more times after the original baseline survey has been 

completed. The purpose of 4D surveys is to monitor reservoir changes in a producing field. For 

approximately 25 years, the purpose of 4D surveys in the hydrocarbon industry has been to monitor 

changes in oil and gas reservoirs to better manage them. However, in addition to that purpose, 

4D surveys now are being used to monitor changes for environmental and safety reasons. 

Examples of this include monitoring for oil leaks in the seafloor above reservoirs not only for health, 

safety, security, and environment (HSSE) purposes but also for carbon capture and storage (CCS). 

Some of the survey types described in this section can be used in time-lapse mode, including VSP, 

3D towed-streamer, and multibeam bathymetry.

The usefulness and value of 4D surveys is well-established, and such surveys have become 

common. The particular acquisition technique chosen (towed-streamer, temporary OBC or OBNs, or 

permanently emplaced systems on the seafloor) depends on the objectives of the survey, the 

particular geology being addressed, the physical facilities in a given field, and the nature of the 

geophysical response to changes such as reservoir saturation and pressure. The seismic sensors 

used for 4D surveys have been almost exclusively nodal. The seismic survey equipment and 

procedures used for 4D surveys are the same as those described in previous sections. However, 

because these surveys are conducted over producing fields, the survey area is smaller and the 

survey time shorter than needed for most other 3D towed-streamer and 3D OBC or OBN surveys. 

The time lapse between a baseline survey and 4D survey has been as short as 3 months and as 

long as 10 years. Many 4D surveys are repeated every 1 to 2 years. When permanently emplaced 

receiver systems are used, the repeat time generally is on the order of several months because a 

relatively small and inexpensive seismic source vessel is all that is required to conduct additional 

monitoring surveys. A key requirement of 4D surveys is acquisitional repeatability, with emphasis on 
Gulf of Mexico G&G Activities Programmatic EIS F-25

controlling factors that could confound results. This means the monitoring surveys use the same 

seismic source size and depth as well as the same receiver systems, and attempt to duplicate as 

much as possible all other details of the original survey.

1.2 AIRGUN HIGH-RESOLUTION GEOPHYSICAL SURVEYS

The HRG surveys are conducted using several techniques involving airguns and 

electromechanical sources such as side-scan sonars, shallow- and medium-penetration subbottom 

profilers, and single-beam echosounders (SBESs) or multibeam echosounders (MBESs). This 

section discusses shallow-penetration airgun seismic surveys used for HRG surveys. Non-airgun 

acoustic HRG surveys are discussed in Section 1.3. 

The HRG surveys are conducted to investigate the shallow subsurface for geohazards and 

soil conditions over specific locations in one or more OCS lease blocks. Identification of geohazards 

are necessary to avoid drilling and facilities emplacement problems. Geohazards include shallow 

gas, over-pressured zones, shallow water flows, shallow buried channels, gas hydrates, incompetent 

sediments, and mass transport complexes. These surveys also are used to identify potential benthic 

biological communities (or habitats) and archaeological resources. Survey data are used for initial 

site evaluation, drilling rig emplacement, and platform or pipeline design and emplacement. HRG 

surveys and reporting requirements are outlined by Notice to Lessees and Operators (NTL) 2008-

G05 (“Shallow Hazards Program,” extended with NTL 2014 G03) and NTL 2005-G07 

(“Archaeological Resource Surveys and Reports”).

Because the intent of high-resolution, shallow-penetration airgun seismic surveys is to image 

shallow depths (typically 1,000 m [3,280 ft] or less below the seafloor) and to produce highresolution images, the airgun sources used (typically one or two airguns) are smaller (typically 40 to 

400 in3

), the streamers are shorter and towed shallower, the streamer-separation distances are 

smaller (150 to 300 m [492 to 984 ft]), and the firing times between airgun shotpoints are shorter 

than for conventional 2D and 3D airgun seismic surveys. Typical surveys cover one OCS lease 

block, which is usually 4.8 km (3 mi) on a side. The presence of historic archaeological resources 

(e.g., shipwrecks), shallow hazards, or live bottom features can require surveys using a maximum 

line spacing of 300 m (984 ft). Including vessel turns at the end of lines, the time required to survey 

(transect all lines) one OCS lease block is approximately 36 hours. Other activities before and after 

the time spent actively acquiring seismic data, such as streamer and airgun deployment and other 

operations, add to the total survey time. In addition, weather can create conditions that degrade the 

performance of streamer arrays and prevent acquisition of useful data, especially in shallow water 

where streamers are towed close to the sea surface. Sea state conditions caused by weather in the 

GOM can result in operational downtime. Also, in some instances, the time required to conduct a 

survey is affected by needs for tighter line spacing to accomplish survey objectives and data quality 

(USDOI, BOEM, 2012b).

The 3D high-resolution airgun seismic surveys using ships towing multiple streamer cables 

have become more common. These surveys include (1) dual-source acquisition that incorporates 
F-26 G&G Survey Descriptions

better source and streamer positioning accuracies (derived from GPS) that allow for advanced 

processing techniques (pre stack time migration), (2) single-source multi-streamer (up to 

6 streamers maximum in most cases), (3) dual-source multi-streamer, and (4) P-Cable acquisition. 

All of these 3D survey types except P-Cable acquisition have the same surveying practices as highresolution 2D surveying, including shorter streamers (typically 100 to 1,200 m [328 to 3,937 ft]); 

shallower streamer tow depths; more closely spaced shots, often as close as 12.5 m (41 ft); smaller 

airgun arrays (typically 40 to 400 in3); and more closely spaced track lines (generally 25 to 100 m 

[82 to 328 ft]).

The P-Cable acquisition survey technique was first tested in 2007 and utilized in 2014 for the 

first multi-client geohazards ultra-high-resolution 3D (UHR3D) survey in the GOM (Caldwell, official 

communication). In a UHR3D survey, a cable is towed oriented perpendicular to the ship track 

(Figure F-14). Attached to the cable are a series (10 to 20) of short (25 to 300 m [82 to 984 ft]), 

closely spaced (12.5 m [41 ft]) streamers. UHR3D surveying requires accurate geological 

positioning. Figure F-15 shows the level of detail of the seafloor morphology and of the subsurface 

below the seafloor provided by UHR3D technology for five examples of geohazards. It should be 

noted that the subsurface velocities required to process the P Cable (and similar technologies) 

cannot be obtained from this acquisition technique; instead, it must be obtained from borehole 

checkshot surveys (refer to Section 1.1.5) or other methods that measure the appropriate velocities 

(Hill et al., 2015).

Figure F-14. The Equipment Layout for a P-Cable Acquisition Survey (From: Caldwell, 2015).
Gulf of Mexico G&G Activities Programmatic EIS F-27

Figure F-15. Examples of the Data that the P-Cable Technology can Deliver. Diagrams (A) and 

(B) Show the Seafloor Morphology in Two Areas of the Gulf of Mexico and the 

Locations of Features (C) Through (G) Whose Vertical Structures are Shown at 

the Bottom (From: Brookshire and Scott, 2015).

1.3 NON-AIRGUN ACOUSTIC HIGH-RESOLUTION GEOPHYSICAL SURVEYS

As mentioned in Section 1.2, before any operation takes place on the seafloor, there is an 

operational and legal regulatory need to characterize the nature of the seafloor and the geologic 

layers immediately beneath it. In most cases, conventional 2D and 3D deep-penetration seismic 

surveys do not have the resolution to provide the required information. Consequently, in addition to 

high-resolution, shallow-penetration airgun 2D or 3D seismic surveys, non-airgun acoustic surveys 

are conducted (often from the seismic vessel, but sometimes from a vessel dedicated to such 
F-28 G&G Survey Descriptions

surveys). Typical non-airgun HRG surveys may involve one or more types of high-frequency 

acoustic sources such as the following:

• subbottom/sediment profilers (2.5 to 7 kHz);

• pingers (2,000 Hz);

• sparkers (50 to 4,000 Hz); 

• boomers (300 to 3,000 Hz);

• compressed high-intensity radar pulse (CHIRP) subbottom profilers (4 to 

24 kHz);

• side-scan sonar (usually 16 to 1,500 kHz);

• single-beam echosounders (12 to 240 kHz); and

• multibeam echosounders (50 to 400 kHz).

In general, any combination of these techniques, which are employed for both hazard and 

archaeological surveys, may be conducted during a single deployment from the same vessel. 

However, conventional 3D seismic data generally cannot be substituted for HRG survey data for 

pipeline pre-installation surveys. The vessel tow speed during non-airgun HRG surveys may be up 

to 4 to 5 kn (4.6 to 5.8 mph). If a high-resolution airgun survey is required to meet the survey 

objective, it makes operational/economic sense to do everything in a single deployment. For postlease engineering studies used to guide the placement of production facilities and pipelines in deep 

water and to meet archaeological requirements, HRG surveys often are conducted with autonomous 

underwater vehicles (AUVs) equipped with side-scan sonar, an MBES, and a subbottom profiler. 

Geophysical contractors have been using AUVs since 2000 to make detailed maps of the seafloor 

before installing subsea infrastructure.

1.3.1 Subbottom Profiling Surveys

Sparker

A sparker is an acoustic source that uses electricity to vaporize water, creating collapsing 

bubbles that produces a broadband (50 Hz to 4 kHz) omnidirectional pulse of sound that can 

penetrate a few hundred meters (several hundred feet) into the subsurface. Because of the 

sparker’s relatively high frequency compared to deep-penetration seismic, it is used for highresolution shallow imaging. Short hydrophone arrays towed near the sparker receive sound 

reflected from subsurface features. Normally, the sparker is towed on one side of a ship’s wake and 

the hydrophone array is towed on the other side. Some of the operational characteristics of sparker 

surveys are as follows:

• sparker and hydrophone array tow depths are 1 to 1.5 m (3 to 5 ft);

• vessel speed is 3 to 6 kn (3.5 to 6.9 mph) (similar to seismic), but can be faster;
Gulf of Mexico G&G Activities Programmatic EIS F-29

• acquired reflection return length typically is 500 millisecond (ms) (shorter than 

seismic);

• operating rate of two discharges per second (faster than seismic);

• analog-to-digital sampling interval of 0.1 to 0.25 ms (higher than seismic); and

• dominant sound frequency band is 300 to 800 Hz (higher than seismic).

Boomer

A boomer is an acoustic sound source that uses electricity to cause two spring-loaded plates 

to rapidly repel each other, generating an acoustic pulse. The acoustic pulse has a bandwidth of 

300 Hz to 3 kHz. A boomer is commonly mounted on a sled and towed behind a vessel. Short 

hydrophone arrays towed nearby receive sound reflected off subbottom features. Depending on 

subsurface geology, the resolution of the boomer system typically is 0.5 to 1 m (1.6 to 3 ft) and 

penetration is 25 to 50 m (82 to 164 ft). Boomers generate a sound pulse with very repeatable 

characteristics, although wave motion can distort the signal. A boomer often is deployed with other 

higher frequency systems to increase the depth range achieved by the survey.

Pingers and CHIRP Subbottom Profilers

The acoustic pinger is the oldest technology used for bathymetric and subbottom profiling 

surveys. A pinger operates at a single frequency (usually 2 kHz) and is a relatively weak sound 

source, penetrating to a maximum depth of approximately 5 m (16 ft), depending on the composition 

of seafloor sediments.

The CHIRP systems are used for high-resolution subbottom profiling. Instead of operating at 

a single frequency, CHIRP subbottom profilers transmit a pulse consisting of a continuous sweep of 

frequencies ranging from low to high. The CHIRP subbottom profiling technology then processes 

echo returns to achieve high spatial resolution and subbottom penetration equal to or greater than 

equipment previously used for this purpose.

1.3.2 Side-Scan Sonars

Sonar uses reflections of sound pulses to locate, image, and aid in the identification of 

objects in the water and on the seafloor, and to determine water depth. Side-scan sonars transmit 

sound pulses in a beam that is narrow in the direction along the tow vessel’s track and wide 

vertically. The fan-shaped transmit beam sweeps the seafloor from directly under the sound source 

to either side, typically to a distance of 50 to 200 m (164 to 656 ft). The sound pulses do not 

penetrate the subbottom but are reflected off the seafloor and objects lying on the seafloor. As the

vessel moves forward, an image of the seafloor and the relative size and location of objects on the 

seafloor to either side of the vessel is created. Side-scan sonar typically consists of three 

components: a towfish that contains the sound source and receiving transducers; a transmission 

cable; and a topside echo signal processing and display unit. Side-scan sonars often are used in 

conjunction with a SBES or MBES system that covers the part of the seafloor directly under the 
F-30 G&G Survey Descriptions

survey vessel that is not covered by the side-scan sonar. Because these types of sonars are used 

to detect relatively small objects, they operate at higher frequencies (1 to 1,500 kHz), and because 

of the high attenuation of high-frequency sound in the ocean, these sonars have useful ranges of a 

few hundred meters or less. There are hull-mounted and towed side-scan sonars, but because they 

operate at higher frequencies and their range is limited, imaging the seafloor in water depths greater 

than 10 m (33 ft) requires the use of a towed body or an AUV to position the side-scan sound source 

and receiving transducers closer to the seafloor.

1.3.3 Echosounders

Echosounders, also called depth sounders and fathometers, are used to estimate water 

depth. Most seismic and HRG survey vessels have an echosounder, which works by emitting a 

short, usually single frequency, pulse of sound and receives, processes, and displays echo returns 

from the seafloor. If the speed of sound in sea water is known, the device can estimate water depth 

by multiplying the speed of sound by half the time from transmit of a pulse to receipt of an echo. 

Many echosounders also have sensors that detect salinity, temperature, and conductivity, 

measurements that are used to estimate the speed of sound in water.

Single-Beam Echosounders

An SBES transmits a sound pulse aimed vertically below the vessel to estimate the distance 

to the seafloor directly beneath the ship. Typically, higher operating frequencies are used for 

shallow depths and lower frequencies are used for greater depths. For example, an echosounder 

operating at 200 kHz would be used in shallow (<100 m [328 ft]) water, and an echosounder 

operating at 3 kHz would be used in very deep water (3,000 m [9,842 ft]). If a high level of detail 

about seafloor depths is needed, a survey vessel must complete many closely spaced track lines 

because depth is only estimated directly beneath the ship.

Multibeam Echosounders

The MBESs emit multiple sound beams in a fan shape, covering a range of angles beneath 

the ship orthogonal to the ship’s track. Therefore, in one pass of the survey vessel over an area, the 

bathymetry of a swath of the seafloor is estimated, so a larger area can be covered in a shorter time 

and with fewer track lines than is possible using an SBES. The width of the swath depends on the 

number of sound beams, the multibeam operating frequency, and water depth. The MBESs that 

operate at low frequencies (e.g., 12 kHz) are used to survey at depths up to 10,000 m (32,808 ft) 

while others operating at high frequencies (e.g., >300 kHz) are used to survey at depths as shallow 

as 20 m (66 ft) or less.

1.4 NON-ACOUSTIC MARINE GEOPHYSICAL SURVEYS

1.4.1 Marine Gravity Surveys

Measurements of Earth’s gravity field are useful in helping investigate the geologic structure 

of the subsurface. Marine gravity surveys are used in frontier exploration areas and as a 
Gulf of Mexico G&G Activities Programmatic EIS F-31

complement to seismic surveys in well explored areas. There are two basic types of gravity surveys: 

more common conventional gravity surveys and newer gravity gradiometry surveys. While 

conventional gravity surveys measure acceleration due to gravity at each survey point, gravity 

gradiometry measures the spatial rate of change of acceleration due to gravity. Because it is a 

measure of the derivative of Earth’s gravity, gravity gradiometry has a higher signal-to-noise ratio at 

higher frequencies, and therefore higher resolution, than conventional gravity survey data. However, 

conventional gravity survey data have greater sensitivity for deeper geological features.

Both types of marine gravity data can be collected using instruments located on the seafloor, 

in boreholes, on board fixed-wing aircraft, or on helicopters, but most gravity surveys are conducted 

using ships. Conventional shipboard gravity meters are fairly small devices, on the order of 

0.7 × 0.6 × 0.6 m (2.3 × 2 × 2 ft), and weigh approximately 100 kilograms (kg) (220 pounds [lb]). 

Gravity surveys are conducted from dedicated vessels that can operate at speeds of 8 to 10 kn 

(9.2 to 11.5 mph) and can make rapid line changes. Survey transect line spacing typically is 0.5 to 

3 km (0.3 to 1.9 mi), and surveys that cover 500 km2 (193 mi2

) can be completed in a few days. 

Gravity data are now routinely collected by seismic vessels during seismic surveys, but at slower 

seismic vessel speeds. Gravity gradiometry surveys are less common than conventional gravity 

surveys, and the instrumentation for commercial gravity gradiometry is still evolving.

1.4.2 Marine Magnetic Surveys

Marine magnetic surveys measure the Earth’s magnetic field. Magnetic data are used to 

(1) estimate the structure and sedimentary properties of rocks bearing magnetic material; (2) locate 

pipelines, undersea cables, and other offshore structures; and (3) identify archeological sites. 

BOEM requires marine magnetometers for hazard and archaeological surveys in water depths less 

than 200 m (656 ft) (USDOI, BOEM, 2012b). These surveys often are run with acoustic HRG 

surveys. A marine magnetometer sensor is housed in a cylindrical package approximately 1 to 2 m 

(3 to 7 ft) long and 15 to 20 centimeters (cm) (5.9 to 7.9 inches [in]) in diameter, weighing 

approximately 14 kg (31 lb).

Magnetic surveys can be conducted from a ship, where the magnetometer is towed at least 

two and a half ship-lengths behind the ship, so that the ship’s magnetic field does not affect 

measurement of Earth’s magnetic field. Magnetic surveys may be conducted using an AUV as well. 

Magnetic surveys may be conducted in combination with other survey methodologies; if used with an 

airgun survey, the magnetometer package is towed approximately 100 m (328 ft) behind the seismic 

airgun array. The magnetometer typically is towed at a depth of approximately 3 m (10 ft) and 

depth-indicating devices mounted on the tow cable are used to maintain a constant depth. In highresolution magnetic surveys for archaeological resources, the magnetometer must be towed within 

6 m (20 ft) of the seafloor.

1.4.3 Marine Magnetotelluric Surveys

Magnetotelluric (MT) surveys are used to image Earth’s subsurface by measuring natural 

variations in electrical and magnetic fields. Investigation depth ranges from 300 m (984 ft) below the 
F-32 G&G Survey Descriptions

seafloor, by recording higher electromagnetic frequencies, to 10,000 m (32,808 ft) below the 

seafloor, by recording lower electromagnetic frequencies. Natural variations in Earth’s magnetic 

field induce electric currents in the subsurface. By measuring the components of the electrical and 

magnetic fields, a model of the electrical resistivity of the subsurface can be obtained and is often 

combined with seismic data to produce a more complete picture of subsurface structures and 

stratigraphy. This section primarily applies to shallow MT surveys, mostly used for geohydrologic or 

gas hydrate surveys rather than for oil and gas industry activities. Section 1.4.4 describes the 

technique generally used for oil- and gas-related surveys.

2D and 3D MT surveys are common. For marine work, a deployment vessel is required. 

The survey instruments are “V” shaped devices, with the arms of the “V” 5 to 15 m (16 to 49 ft) in 

length; the arms approximately 25 cm (9.8 in.) in diameter; and the weight of the entire unit, 

including the data logger and the sensors, approximately 145 kg (320 lb). The recording unit usually 

will be anchored to the seafloor using one or two anchors and connected to a buoy at the sea 

surface (Figure F-16). The instruments are retrieved using an acoustic release that disconnects the 

anchors from the instrument unit when sent an acoustic command signal, and the instruments are 

then pulled to the surface by recovering the buoy.

Figure F-16. The Marine MT Measurement System: (a) Electric and Magnetic Field Receiver, 

(b) Rope, (c) and (d) Anchors, (e) Water Flow Meter, (f) Buoy with a Flag, and 

(g) Survey Vessel (Modified from: Ueda et al., 2014).

1.4.4 Marine Controlled Source Electromagnetic Surveys

The controlled source electromagnetic (CSEM) method is an offshore geophysical technique 

employed by the commercial offshore oil and gas industry that uses electromagnetic remote-sensing 

technology to estimate the presence and extent of subbottom hydrocarbon accumulations. Electric 

and magnetic field sensors are placed on the seafloor, in a line for a 2D survey or in a grid for a 3D 

survey, commonly 500 to 4,000 m (1,600 to 13,000 ft) apart. The sensors typically record for several 

days to several weeks before being moved to a new line or grid. The complete surveys, therefore, 

can take weeks to months to complete. The sensors are situated in a deployment package that 

weighs approximately 100 kg (220 lb) and is approximately 2.5 × 2.5 × 1 m (8 × 8 × 3 ft) (Figure 
Gulf of Mexico G&G Activities Programmatic EIS F-33

F-17A). The electric dipoles of each receiver station are approximately 10 m (33 ft) long and 1.5 m 

(5 ft) high. The receiver packages use biodegradable anchors for deployment and flotation devices 

for retrieval. The CSEM transmitter employs an active dipole source, typically 50 to 100 m (164 to 

328 ft) long, that is towed approximately 25 to 100 m (82 to 328 ft) above the seafloor (Figure 

F-17B) to transmit a time-varying electromagnetic field into the subsurface. The output of the 

transmitter commonly is 200 to 500 amps, with a maximum for some surveys of 1,000 amps. To 

achieve the penetration needed to detect small hydrocarbon deposits several miles below the 

seafloor, relatively low-base frequencies (0.05 to 50 Hz) are used. This field emitted by the 

transmitter is modified by the presence of subsurface resistive layers, and changes are detected and 

logged by the array of receivers. Because hydrocarbon-bearing formations are highly resistive 

compared to surrounding formations, a CSEM survey can indicate the presence of oil and gas in 

offshore situations. When source transmissions are complete, an acoustic signal commands 

releases to separate the instruments from biodegradable anchors, permitting the sensor packages to 

rise to the surface.

Recent developments have improved the methods and equipment used in towed CSEM 

surveys. The CSEM surveys utilize a source and receivers within towed streamers that can be used 

simultaneously with seismic equipment. While this survey technique has been in development since 

the early 1940s (Srnka, 1986), only recently have receivers been successfully deployed during a 

survey that was using seismic airguns. Similar systems have been used to study subsea geologic 

activity at thermally or magmatically active locations (Sinha et al., 1990). An electromagnetic 

streamer can be deployed and operated in a similar manner to a seismic streamer, but it typically is 

towed at depths up to 100 m (328 ft). An electromagnetic streamer can be up to 10 km (6.2 mi) in 

length and can be towed at the same speed as airgun arrays and seismic streamers (4 to 5 kn

[4.6 to 5.8 mph]). It is likely that this technology will become more widespread and may be 

conducted concurrently with 3D seismic surveys within the next 5 to 10 years.

Figure F-17. (A) CSEM Receiver (From: Electromagnetic Geoservices ASA, 2015a); (B) CSEM 

Source (Modified From: Electromagnetic Geoservices ASA, 2015b).
F-34 G&G Survey Descriptions

1.5 AIRBORNE REMOTE SURVEYS

1.5.1 Airborne Gravity Surveys

In addition to ship-based marine gravity surveys, conventional airborne gravity surveys and 

airborne gravity gradiometry surveys can be conducted using fixed-wing aircraft, though helicopters 

may be used. However, offshore surveys using aircraft are uncommon because of the logistics 

required to keep them in the air for extended periods of time far from shore. The dimensions of the 

gravity instruments and mount are approximately 1 × 1 × 1.5 m (3 × 3 × 5 ft) high and the total 

weight is approximately 150 kg (330 lb). The survey acquisition grid is similar to ship-based surveys, 

generally with flight-line spacing of 0.5 to 3 km (0.3 to 1.9 mi). Surveys of 500 km2 (193 mi2

) can be 

completed in a few hours, with the aircraft flying at an altitude of 70 to 300 m (230 to 984 ft). The 

objectives of the survey will determine the distance between flight lines and the altitude at which the 

survey will be conducted.

1.5.2 Airborne Magnetic Surveys

Measurements of Earth’s magnetic field are useful in helping investigate the geologic 

structures and stratigraphy of the subsurface. Such data are useful in frontier exploration areas and 

as a complement to seismic surveys in well explored areas. There currently are at least five types of 

magnetometers, three of which are commonly used in airborne magnetic surveying. In addition to 

these three different airborne type magnetometers (i.e., proton precession, optically pumped vapor, 

and fluxgate), there are several different configurations that can be used on aircraft, including the 

following:

• a single sensor, typically a tail installation;

• two horizontally separated magnetometers, usually wingtip pod sensors;

• two vertically separated sensors, usually tail-mounted; and

• a total magnetic intensity configuration, typically involving three but potentially 

four magnetic sensors, towed a short distance behind the aircraft.

The sensor pods are cylindrical in shape, usually 1 to 2 m (3 to 7 ft) long and several 

centimeters (several inches) in diameter.

The objectives of a survey (e.g., the size of area to be covered and the desired detail to be 

obtained), the cost, the altitude at which the survey will be conducted, the flight line (transect) 

separation distances, and the flight line orientation are the most important factors to be specified for 

a survey. Recent surveys done in the GOM have been flown at altitudes of 60 to 300 m (197 to 

984 ft), at speeds of 110 kn (126.6 mph), and with flight line spacing of 0.5 to 2 km (0.3 to 1.2 mi) 

(Caldwell, official communication).
Gulf of Mexico G&G Activities Programmatic EIS F-35

2 GEOLOGICAL AND GEOTECHNICAL SURVEYS

Geotechnical surveys are conducted to obtain information about surface and subsurface 

geological and geotechnical features. This information is used to aid siting, design, construction, 

and operation of energy facilities and for the assessment of sediment resources and minerals. 

Geotechnical surveys measure conductivity, pressure, and temperature and also collect geologic 

cores and grab samples. Sediment sampling and testing locations for geotechnical surveys are 

identified using geophysical data and maps developed from HRG survey data.

The principal objectives of geotechnical surveys are (1) to assess the suitability of shallow 

foundation soils to support energy structures and associated infrastructure (i.e., transmission cables, 

pipelines, etc.) under any extreme operational and environmental conditions that might be 

encountered; and (2) to obtain information about soil characteristics needed for design and 

installation of energy structures, support infrastructure, and assessment of sediment resources and 

minerals for non-energy projects. Geotechnical survey data describe the stratigraphic and 

geoengineering properties of sediment that may affect the design of foundations and anchoring 

systems. Geotechnical surveys typically are conducted using a barge or ship approximately 20 to 

100 m (65 to 328 ft) in length.

2.1 GRAB AND BOX SAMPLING

Coring and grab sampling are used to obtain sediment samples for geological and 

geotechnical analyses. Geotechnical sampling and testing are used in engineering studies for 

placement of structures such as platforms and pipelines. Usually, bottom sampling and shallow 

coring are conducted concurrently, using a small marine drilling vessel.

Grab sampling is done using a device with opposing jaws that is dropped onto the seafloor 

and then closed, capturing a small amount of bottom material that is brought to the surface. Grab 

sampling is not ideally suited for collection of coarse sediments because larger pieces of rock tend to 

get caught between the sampler’s jaws, holding them open and causing the contents of the sampler 

to be lost as it is brought to the surface.

A box corer is a large mechanical coring device that takes a large, relatively undisturbed 

sample when lowered to the seafloor by a wire from the vessel. The box corer pushes into the 

sediment by its own weight. As soon as retrieval of the corer is initiated, a rotating spade closes and 

seals the bottom of the box, and the box and materials are brought to the surface with a lower 

chance of loss of contents than with grab samplers. Both techniques are used to obtain samples to 

depths up to 900 m (2,953 ft).

2.2 GEOLOGIC CORING

Gravity Corers, Multicorers, Piston Corers, and Rotary Corers

A gravity corer is a weighted tube mounted within a frame that is lowered from a vessel to 

the seafloor using a cable spooled from a winch. When the corer penetrates the seafloor, the tube 
F-36 G&G Survey Descriptions

fills with sediment. A hydraulically damped gravity corer has a slow rate of penetration into the 

seafloor that is controlled by a water-filled piston. Disturbance of the water-sediment interface is 

minimal, and maximum penetration in mud is approximately 1 m (3 ft). A core-catcher (sliding gate) 

on the bottom of the tube moves into place when retrieval begins, trapping the sediment sample in 

the corer. Operation of a gravity corer requires a ship with a winch powerful enough to lower and 

raise the corer, which can have hundreds to thousands of pounds of weight attached. In addition, 

the winch must have enough wire to reach desired depths. Multicorers are gravity corers with up to 

16 tubes attached to a frame that are used to obtain core samples in shallow water.

A stationary piston corer is a gravity corer that is dropped freefall using a trigger system after 

it has been lowered to a predetermined height above the seafloor. It contains a piston that remains 

stationary at the surface of the seafloor sediment as the core barrel penetrates into the sediment. 

The movement of the coring tube relative to the piston creates a negative pressure in the tube that 

holds the bottom material within the core during retrieval. The operation of a fixed piston gravity 

corer results in better recovery rates and higher quality cores compared to those obtained with a 

standard gravity corer, particularly in soft sediments, because the piston keeps the sediments from 

being disturbed as the corer cuts through them. The piston assembly uses different core barrel 

lengths to obtain cores up to 30 m (98 ft) long and is able to obtain continuous core samples in water 

depths up to several thousand meters (several thousand feet).

Deep geologic cores (cores longer than 30 m [98 ft]) are obtained by standard rotary coring. 

Rotary corers are designed as two- or three-tube devices where the innermost tube acts as a core 

liner; the middle tube, if present, acts as a holder; and the rotating outer tube carries the hollow drill 

bit. As the drill bit cuts through the sediment and rock, the core created passes into the liner in a 

relatively undisturbed state. The cores obtained by this method vary in diameter (3 to 20 cm 

[1.2 to 7.9 in.]) and can penetrate several hundred meters beneath the seafloor.

ROV Push Corers

ROV push cores are used to obtain sediment cores in deepwater environments. 

Traditionally, sediment coring is done remotely from surface vessels; however, use of an ROV 

facilitates the ability to take multiple high-quality cores from locations with specific seafloor types or 

habitats for biological, physical, geological, or chemical analysis. Depending on conditions, ROV 

push samplers can acquire cores up to 1.5 m (5 ft) long. The manipulator arms of a ROV operate a 

push corer. Generally, ROV push corers are used to obtain fairly short small-diameter cores in 

water depths greater than 6,000 m (19,685 ft).

Vibracorers

Vibracorers use a vibratory motor and gravity to cut through seafloor sediments. They have 

a metal frame construction and generally are not used in water depths greater than a few hundred 

meters (several hundred feet). The diameter of the core barrel usually is 8 to 10 cm (3.1 to 3.9 in.), 

and cores up to 15 m (49 ft) long can be obtained using vibracorers. For better penetration and 

recovery rates, the vibratory motor can be run at various frequencies for different types of materials.
Gulf of Mexico G&G Activities Programmatic EIS F-37

Jet Probes

A jet probe is composed of a rigid stainless steel tube with trigger function connected by a 

pressure-rated hose to a high-pressure cylinder. The rod will be marked with graduated increments 

to note the depth of penetration. The jet probe kit is completely self-contained and does not require 

any surface supply lines. Jet probe surveys acquire indirect physical information on subsurface 

lithology by surveying the thickness and stratigraphic layering of sedimentary covers by penetrating 

the sand cover with a jet of water.

2.3 COST AND SHALLOW TEXT WELLS

A continental offshore strategic test (COST) well can be drilled without acquiring a lease on 

the OCS, but it can be drilled in a leased block if it does not interfere with the leaseholder’s activities. 

COST wells are funded by industry consortia; drilled off structure so as not to encounter 

hydrocarbons; and intended to provide information about regional stratigraphy, the existence and 

potential quality of reservoir beds, and the existence of potential hydrocarbon source rocks. The 

data are used to (1) evaluate the interpretation of other data to identify geological structures; 

(2) ground truth interpretation of geophysical survey data by providing samples of subsurface rock 

and geological strata; (3) estimate the age of sediments encounter during drilling; (4) evaluate the 

potential for hydrocarbon accumulations; and (5) determine the presence, absence, or quality of gas 

hydrate deposits. Drilling is done by conventional rotary drilling equipment from a drilling rig. It is 

possible but uncommon that a COST well would be drilled in the GOM during the period of interest 

for this Programmatic EIS.

Shallow test wells can be drilled to allow operators to place wireline testing equipment into a 

borehole to evaluate subsurface properties for the presence of gas hydrates, hazards to drilling, or 

physical structures. Drilling is done by conventional rotary drilling equipment from a vessel such as 

a drilling barge or semisubmersible.

2.4 CONE PENETROMETER TESTS

A cone penetrometer is an instrument consisting of a pointed steel pipe that is forced into the 

seafloor to determine the near-seafloor stratigraphic profile. Penetration is achieved through a 

hydraulic jacking mechanism that pushes the cone into the seafloor, with the depth of penetration on 

the order of 100 m (328 ft). Sensors at the tip take two measurements: the pressure against the 

cone tip (resistance) and the drag on the pipe just behind the cone (friction). The ratio of these two 

numbers is used to map sediment types. A tiny hole near the cone allows pore water pressure to be 

measured, and other sensors can be added to the cone to make additional measurements such as 

gravimetric, electromagnetic, and shear-wave velocities.

In water less than 30 m (98 ft) deep, floating or jack-up barges commonly are used to 

support pushing equipment. In water deeper than 30 m (98 ft), it is common to place cone 

penetrometer test (CPT) equipment on the seafloor. It also is possible to push a cone penetrometer 

from the bottom of a borehole using down-hole equipment. Recently, remotely controlled seafloor 
F-38 G&G Survey Descriptions

drill rigs have been developed that can drill, sample, and push a cone penetrometer into the seafloor 

in water depths up to 3,000 m (9,842 ft).

3 EMERGING TECHNOLOGIES 

Marine vibroseis is considered the most promising alternative to airguns in select settings 

and applications (i.e., shallow water, sensitive habitat, near biological resources). However, marine 

vibroseis may not be a complete replacement for airguns, and there currently is not a vibroseis 

design viable for commercial applications. The attractiveness of marine vibroseis is that it could 

provide the same energy as airguns at lower power levels and in a more contained frequency band 

that would include the fully useable seismic bandwidth.

The oil and gas industry has been developing and testing marine vibroseis technologies 

since the early 1980s, and development is continuing today at an accelerated pace. Limited tests 

have been conducted that show reasonably good technical results. Issues of operational 

effectiveness, reliability, and durability are the key elements confronting the commercial viability of 

marine vibroseis technology at this time, and development work is ongoing to address these areas.

ExxonMobil, Shell, and Total teamed up with the Texas Experimental Engineering Station 

(part of Texas A&M University) to create the Marine Vibroseis Joint Industry Program in order to 

develop and build a full vibrator source array for commercialization. The Marine Vibroseis Joint 

Industry Program used a four-phased approach that began with scoping and development. 

Phase III, which is underway, is pursuing three different technologies and expects that the first 

prototype will be tested and evaluated in 18 months. Phase IV began in late 2014 and was intended 

to build and field test commercial systems from the technologies tested and evaluated in Phase III. 

Phase IV is anticipated to be completed in 2016 (Schostak and Jenkerson, 2015).

Two fundamentally different designs for a marine vibrator currently are under development; 

one vibrator design would use hydraulic activation and the other electrical activation. Both designs 

have passed initial feasibility tests, but both still have technical and operational issues that need to 

be addressed before they are commercially viable.

3.1 MARINE VIBROSEIS (VIBRATORS) 

3.1.1 Hydraulic Marine Vibrator

In 1985, Industrial Vehicles International, Inc. (IVI) offered the first commercial marine 

vibrator. The IVI system consists of a marine vibrator, vibrator controller, and power unit. The IVI 

marine vibrator contains a piston within a housing with power supplied to the electrical, pneumatic, 

and hydraulic subsystems by a power unit. An alternator, air compressor, and two pressure driven 

hydraulic pumps are powered by an air cooled diesel engine. The source is capable of generating 

modulated frequencies between 10 and 250 Hz and can be used in water depths as shallow as 1 m 

(3 ft). The source output is controlled using conventional land vibrator controllers (Industrial Vehicles 

International, Inc., 2010).
Gulf of Mexico G&G Activities Programmatic EIS F-39

The system has been tested in various environments from transition zones to deep water. 

Acoustic performance tests conducted at the Seneca Lake Facility of the Naval Underwater Systems 

Center in 1988 evaluated the system and determined that the marine vibrator was deficient in 

production of low frequencies (Johnston, 1989; Walker et al., 1996). A comparison of the IVI marine 

vibrator, dynamite, and airgun sources in southern Louisiana concluded that the marine vibrator was 

a viable seismic source for environmentally sensitive areas (Potter et al., 1997; Smith and 

Jenkerson, 1998). In transition zones, when coupled with the seafloor, marine vibrators operate like 

a land vibrator (Christensen, 1989). The best performance is on the seafloor, which couple the 

vibrator with the subbottom.

Initial deepwater tests were conducted in the GOM by Geco-Prakla, a subsidiary of 

Schlumberger, using a vibrator with an energy output approximately equivalent to a 1,000-in3 airgun. 

Despite limitations in generation of low-frequency energy, good definition of reflectors down to 

3 seconds indicated that the system was viable (Haldorsen et al., 1985). In 1996, Geco-Prakla 

performed a commercial field test in the North Sea comparing an array of six marine vibrators with a 

single 4,258-in3 airgun; the objectives were to evaluate cost, reliability, production rate, and quality of 

geophysical data. After 2 weeks of data collection, a comparison between marine vibrator and 

airgun data indicated that the marine vibrator generated more sound above 30 Hz and less sound 

below 10 Hz than the airgun, but the seismic data obtained were comparable overall. Marine 

vibrator production rates were slightly lower than those of the airgun, but by the end of the survey, 

the technical downtime of the marine vibrator was similar to that for the airgun (Johnson et al., 

1997).

Geco-Prakla participated in IVI’s marine vibrator program, conducting surveys and tests until 

2000 when the exclusive-use agreement between IVI and Schlumberger expired (Bird, 2003). IVI 

continued to develop the system into the early 2000s. IVI is no longer actively marketing the product 

because there currently is no client base for the system. The significant expense to retrofit marine 

exploration companies’ ships to support marine vibrators is not offset by reduced operation costs or 

better data quality. IVI presently has marine vibrator systems that could be used for seismic data 

collection, but they would require renovation prior to deployment, which could take 3 months to 

1 year (Christensen, official communication, 2010).

Stephen Chelminski, the inventor of the airgun and primary founder of Bolt Technology 

Corporation, also designed a marine vibrator prototype: “seavibe” (Weilgart, 2012). Seavibe is a 

modular, fully functional marine vibratory sound source that is 20 ft long with a 20- to 22-in diameter 

and can be towed at speeds up to 12 kn (13.8 mph) at any depth. The signal can be pulse-coded, a 

frequency swept signal, or a combination of the two without any high frequencies (5 to 100 Hz, 

although the vibrators operating frequency range is 2 to 200 Hz). The signal duration can be 

changed in real time. According to Weilgart (2012), the prototype system is reliable, more efficient 

than airguns, and requires less horsepower to tow than airgun arrays. A significant amount of the 

engineering and design for the Chelminski Research Marine Vibratory Sound Source has been 

completed on the marine vibrator prototype and patents have been applied for, but assembly and 
F-40 G&G Survey Descriptions

testing have not begun. Once financing has been secured, prototypes can be built and testing can 

occur within 1 year (CSA Ocean Sciences Inc., 2014).

3.1.2 Electric Marine Vibrator

The Geokinetics marine vibrator is a collaborative project with Petroleum Geo-Services and 

is a significant design departure from previous marine vibrators. The proof of concept of the 

Geokinetics marine vibrator was demonstrated in water offshore Texas in 1999. The Geokinetics 

marine vibrator design specifications are a frequency range of 6 to 100 Hz and an output level of 

approximately 2 bar meters peak-to-peak. The potential advantages of the marine vibrator include 

lower environmental impacts because of lower source signal amplitude levels, the capability to 

generate specialized frequency sweeps using pseudo-noise technology, and no in-water hydraulics 

with electromechanical drivers and controls. Reduction in overall sound level, specifically at 

frequencies above 100 Hz, which are higher than the useful seismic range, is a major advantage of 

the system. Another advantage is the reduction of peak acoustic power compared to conventional 

seismic sources, which occurs because the source energy is spread over a longer transmission time 

(Tenghamn, 2005 and 2006).

The Geokinetics flextensional shell design minimizes water flow and maximizes pressure 

wave generation that generates low frequencies efficiently. Another design feature of the 

Geokinetics marine vibrator is the two intentional resonances within the seismic bandwidth that help 

the vibrator generate the desired seismic frequency band. The resonant frequencies show up as 

peaks in the generated signal amplitude spectrum. Subtones present have resonant frequencies of 

8 and 24 Hz. The tritons have resonant frequencies of 28 and 80 Hz. If the two spectrums are 

combined, there is an overall high amplitude spectrum completely inside the useable bandwidth for 

seismic surveys.

Currently, the Geokinetics marine vibrator is the electric marine vibrator closest to 

commercialization. Information collected to date suggests that marine vibroseis is less 

environmentally damaging than airguns, but this evaluation needs to be expanded to a full 

environmental assessment to identify and evaluate potential impacts and tradeoffs for the different 

technologies (CSA Ocean Sciences Inc., 2014).

3.2 LOW-FREQUENCY ACOUSTIC SOURCE (PATENTED) 

Originally designed as a ship sound simulator for the Norwegian navy, the low-frequency 

acoustic source (LACS) is being promoted as an alternative source for seismic acquisition (Weilgart, 

2010). The LACS system is a combustion engine with a cylinder, spark plug, two pistons, two lids, 

and a shock absorber. It creates an acoustic pulse when two pistons push lids vertically in opposite 

directions; one wave reflects from the sea surface and combines with the downward moving wave. 

There is no bubble noise from this system as all air is vented and released at the surface, not into 

the underwater environment. The absence of bubble noise allows the system to produce long 

sequences of acoustic pulses at a rate of 11 shots per second; this allows the signal energy to be 

built up in time with a lower amount of energy put into the water (Askeland et al., 2007 and 2009). 
Gulf of Mexico G&G Activities Programmatic EIS F-41

The system design also controls the output signal waveform, which can reduce the amount of nonseismic (>100 Hz) frequencies produced (Spence et al., 2007). The transmitted pulses are recorded 

by a near-field hydrophone and seafloor, and sediment reflections are recorded by a far-field 

streamer (Askeland et al., 2007 and 2009).

Two LACS systems are being offered commercially. The LACS 4A has a diameter of 

400 millimeters (mm) (15.7 in), a height of 600 mm (24 in), and a weight of approximately 100 kg 

(220 lb) in air. Pulse peak peak pressure is 218 dB re 1 μPa at 1 m. Field test results of the LACS 

4A system demonstrate that the system is capable of accurately imaging shallow sediments (~230 m 

[755 ft]) within a fjord environment (Askeland et al., 2008 and 2009). This system is suitable for 

shallow penetration towed streamer seismic surveys or VSPs (Askeland et al., 2008).

The second system, the LACS 8A, theoretically has the potential to compete with a 

conventional deep-penetration airgun seismic array. The LACS 8A system has pulse peak-peak 

pressure of 3 bar meter or 230 dB re 1 μPa at 1 m. The weight is 400 kg (880 lb), and the diameter 

is 800 mm (31.5 in). Several LACS units may be operated together to provide an increased pulse 

pressure (Bjørge Naxys AS, 2010). This system currently does not exist, and the project is presently 

on hold. It would take at least 18 months to build and field test one of these systems if money came 

available to do so (Abrahamsen, official communication, 2010).

The LACS system may be suitable but currently exists only as a design, and there is no 

known interest in further development of this system.

3.3 DEEP-TOWED ACOUSTICS/GEOPHYSICS SYSTEM

The U.S. Department of the Navy developed a deep-towed acoustics/geophysics system 

(DTAGS) to better characterize the geoacoustic properties of abyssal plain and other deepwater 

sediments. The system was tested and modified in the early 1990s and was used in various 

locations around the world until it was lost at sea in 1997 (Gettrust et al., 1991; Wood et al., 2003).

The second generation DTAGS is based on the original design but with more modern 

electronics. It uses the same Helmholtz resonator source consisting of five concentric piezoelectric 

ceramic rings sealed in an oil-filled rubber sleeve to generate a broadband signal greater than 

2 octaves. The optimum frequency performance range is between 220 and 1,000 Hz with a source 

level of 200 dB re 1 μPa @ 1 m, which is a major improvement over the original DTAGS. The 

source is extremely flexible, allowing for changes in waveform and a decrease in sound level to 

produce a source amplitude, waveform, and frequency to suit specific requirements (Wood et al., 

2003; Wood, 2010).

The DTAGS is towed behind a survey vessel usually at a level of 100 m (328 ft) above the 

seafloor and a vessel speed of 2 kn (2.3 mph; 3.7 km/hr); it can operate at full ocean depths (6,000 

m [19,685 ft]). A 450-m (1,476-ft), 48-channel streamer array is towed behind the source to record 

the reflected signals. The DTAGS can also be configured with an aluminum landing plate, which 
F-42 G&G Survey Descriptions

transmits the acoustic energy directly into the seafloor. With this configuration, vertical bottomfounded hydrophone arrays are used to receive reflections (Breland, 2010).

Proximity of the acoustic source to the seafloor is an advantage of the DTAGS. The system 

has a limit of 1 km (0.6 mi) penetration in most marine sediments (Wood et al., 2003). It has been 

used successfully to map gas hydrates in the GOM (Wood et al., 2008), Canadian Pacific (Wood 

and Gettrust, 2000; Wood et al., 2002), and Blake Ridge (Wood and Gettrust, 2000).

There is only one DTAGS in existence at this time. While it has imaged shallow sediments 

and gas hydrate environments extremely well, the current tool design could not replace a deeppenetration airgun array for oil and gas exploration at this time; DTAGS was not designed for this 

purpose. However, there is no physical limitation to designing a resonant cavity source to simulate 

the frequency band of airguns.

According to Weilgart (2012), DTAGS was tested in the GOM in the summer of 2011 and 

was scheduled to undergo another trial off the coast of Oregon in September 2012. Though the 

frequency range of DTAGS is currently 200 to 4,000 Hz, it may be extended down to about 100 Hz 

(Wood, official communication, as cited in Weilgart, 2012).

3.4 LOW-FREQUENCY PASSIVE SEISMIC METHODS FOR EXPLORATION

Low-frequency passive seismic methods utilize microseisms, which are faint tremors caused 

by the natural sounds of the earth, to image the subsurface. A typical survey consists of highly 

sensitive receivers (usually broadband seismometers) placed in the AOI to collect data over a period 

of time. Upon completion of the survey, the data are analyzed and filtered to remove all non-natural 

sounds, which is most efficiently completed using an automated process (Hanssen and Bussat, 

2008).

All of the current methods use one of following three sources of natural sounds: natural 

seismicity; ocean waves; or microseism surface waves.

Natural seismicity uses the earth’s own movements as a source of energy. Two techniques 

have been developed to use this energy source. Daylight imaging (DLI) uses the local seismicity of 

an area to produce reflection seismic profiles, similar to those recorded in active seismic surveys 

(Claerbout, 1968). As in active reflection seismic operations, geophones are deployed; the target 

can be imaged using a regularly spaced 2D line geometry (Hohl and Mateeva, 2006; Draganov 

et al., 2009). The seismicity of the area, geologic complexity, and receiver sensitivity control the 

record length. Daylight imaging can augment active seismic data, where it is difficult to collect data. 

Local earthquake tomography also uses local seismicity of a region to map on the reservoir scale 

(Kapotas et al., 2003). However, it is used to calculate the velocity structure of the subsurface in 3D 

by analyzing each earthquake on multiple receivers and generating ray paths instead of crosscorrelating the recorded signals. This method requires a longer period of data collection than the 

other methods to produce results.
Gulf of Mexico G&G Activities Programmatic EIS F-43

Ocean waves are used as a sound source for the seafloor compliance technique. The 

method requires that ocean-bottom seismometer stations with highly sensitive, broadband 

seismometers and differential or absolute pressure gauges be installed in water several hundred 

meters deep. In the right setting, a coarse one-dimensional (1D) S-wave velocity model of the 

subsurface down to the Moho can be generated using the measured water pressure and vertical 

movement of the seafloor caused by large passing ocean waves (Crawford and Singh, 2008).

Ambient-noise (surface-wave) tomography [AN(SW)T] uses low-frequency (between 0.1 and 

1 Hz) ambient noise records to estimate shear wave velocities and structural information about the 

earth. The ambient noise used consists mainly of microseism surface waves (Rayleigh and Love 

waves) (Bussat and Kugler, 2009). This technique requires the use of broadband seismometers to 

record the low-frequency surface waves, which can penetrate to depths of several kilometers 

(Bensen et al., 2007 and 2008). Because the marine environment produces abundant, high-energy 

surface waves, a few hours or days of acquisition can produce good quality data. The AN(SW)T can 

be used in areas where seismic data are difficult to collect or in environmentally sensitive areas. 

While this technology is new and still in need of further testing, the lateral resolution at several 

kilometer depths may reach a few hundred meters, and the resolution may be better than gravimetric 

or magnetic data, which is promising for oil and gas exploration (Bussat and Kugler, 2009).

Surface-wave amplitudes is a method that images the geological structure of the subsurface 

by analyzing passive acoustic data that have not been geophysically processed. The transformation 

of incoming micro-seismic surface waves, scattered at vertical discontinuities, into body waves may 

produce these data, but the process is not well understood (Gorbatikov et al., 2008).

Low-frequency spectroscopy, also known as LFPS or hydrocarbon microtremor analysis 

(HyMAS), tests for an indication of subsurface hydrocarbon accumulation using spectral signatures 

gathered from the ambient seismic wave field recorded by broadband seismometers. The cause of 

the spectral anomalies, often called direct hydrocarbon indicators (DHI), is presently unknown, but 

the following reasons have been proposed: standing wave resonance; selective attenuation; 

resonant amplification (Graf et al., 2007); and pore fluid oscillations (Frehner et al., 2006; Holzner 

et al., 2009). Energy anomalies in the frequency range between 1 and 6 Hz have been observed in 

known hydrocarbon areas including Mexico (Saenger et al., 2009), Abu Dhabi (Birkelo et al., 2010), 

Brazil and Austria (Graf et al., 2007), and southern Asia (West et al., 2010). However, this 

methodology is highly dependent on the ability to process out all anthropogenic noise and 

topography (Hanssen and Bussat, 2008). This method is still in the early stage of development and 

has not been confirmed in the field during all studies (Ali et al., 2007; Al-Faraj, 2007).

The most successful use of low-frequency passive micro-seismic data has been on land, 

where it is easier to isolate the extraneous noise from the natural signal. The technique is also 

promising in the marine environment. To ensure success of a marine survey, (1) it is imperative that 

the recording instruments are in proper contact with the substrate (the natural signal may not be 

accurately recorded in unconsolidated material) and (2) the increase in both anthropogenic and 
F-44 G&G Survey Descriptions

naturally produced noise in the marine environment is correctly filtered so that it does not mask the 

signal of interest.

Passive seismic surveys cannot replace active seismic acquisition. However, passive 

acoustic data have the potential to enhance oil recovery at a better resolution than magnetic or 

gravimetric methods (Bussat and Kugler, 2009), especially in areas that are environmentally 

sensitive or where active seismic operations are difficult.

3.5 LOW-IMPACT SEISMIC ARRAY

Nedwell (2010) describes the concept of a low-impact seismic array (LISA) based on the use 

of inexpensive but powerful and rugged electromagnetic projectors to replace airgun arrays. The 

prospective benefit was that since the signal could be well controlled, both in frequency content and 

in the direction in which the sound propagated, the possibility existed of undertaking seismic surveys 

in environmentally sensitive areas with little or no collateral environmental impact.

The LISA project embodies the idea of using a large array of small but powerful 

electromagnetic projectors to replace airgun arrays. Initial measurements were made on a small 

(n = 4) array of existing electromagnetic transducers. It was found that a source level of about 

142 dB re 1 μPa per volt @ 1 m was achieved, at a peak frequency of 25 Hz. The operating 

frequency could be reduced to below 10 Hz with reasonable modifications, allowing use of an array 

for seismic exploration. The results indicate that it would be possible to achieve an array source 

level of about 223 dB re 1 μPa @ 1 m, which is adequate for seismic surveying.

3.6 FIBER OPTIC RECEIVERS

Short of replacing seismic airguns, improvements in fiber optic sensing and telemetering 

could allow use of smaller airguns and airgun arrays in the future (Nash and Strudley, 2010). Fiber 

optic receivers are receivers that incorporate optical fibers to transmit the received acoustic signal as 

light. They are most frequently used in the petroleum industry for seismic permanent reservoir 

monitoring, a 4D reservoir evaluation application. The optical receivers are permanently placed on 

the seafloor, ensuring consistency and repeatability of the 4D surveys, better signal-to-noise ratios, 

and quality of subsequently collected data. Fiber optic systems are not new. Fiber optical 

components have been used by the military for years in similar applications for antisubmarine 

warfare and area surveillance and have proven to be highly reliable.

Fiber optic receivers are more sensitive than standard receivers, which allows for smaller 

airgun arrays to be used. While these receivers offer a benefit to the environment through a 

decrease in airgun noise, this technology is not presently available for towed-streamer surveys.

Fiber optic receivers typically are used in areas with large-scale oil and gas production 

requiring 4D monitoring. They would not be expected to be used in the Gulf of Mexico OCS during 

the time period of this Programmatic EIS.
Gulf of Mexico G&G Activities Programmatic EIS F-45

3.7 AIRGUN MODIFICATIONS TO LESSEN IMPACTS

In addition to alternative methods for seismic data collection, industry and the public sector 

have actively investigated the use of technology-based mitigation measures to lessen the impacts of 

airguns in the water.

3.7.1 Airgun Silencers

One such measure, an airgun silencer, which has acoustically absorptive foam rubber on 

metal plates mounted radially around the airgun, has demonstrated 0- to 6-decibel (dB) reductions at 

frequencies above and 0- to 3-dB reductions below 700 Hz. This system has been tested only on 

low pressure airguns and is not a viable mitigation tool because it needs to be replaced after 

100 shots (Spence et al., 2007).

Spence et al. (2007) characterized the airgun silencer as a “proof-of-concept” that would 

require further development to become a commercial product. During a workshop conducted for the 

Spence et al. (2007) report, participants suggested that placing the absorbent material farther from 

the airgun may increase the life of the silencer and allow it to be used for larger airguns and arrays. 

However, a later review by Spence (2009) characterized the airgun silencer treatment as 

“impractical” for the same reasons noted above.

3.7.2 Bubble Curtains

Bubble curtains generally consist of a rubber hose or metal pipe with holes to allow air 

passage and a connector hose attached to an air compressor. They have successfully been tested 

and used in conjunction with pile driving and at construction sites to frighten away fishes and 

decrease the noise level emitted into the surrounding water (Würsig et al., 2000; Sexton, 2007; 

Reyff, 2009). They have also been used as stand-alone units or with light and sound to deflect 

fishes away from dams or keep them out of specific areas (Pegg, 2005; Weiser, 2010).

The use of bubbles as a mitigation for seismic noise has also been pursued. During an initial 

test of the concept, the sound source was flanked by two bubble screens; it demonstrated that 

bubble curtains were capable of attenuating seismic energy up to 28 dB at 80 Hz while stationary in 

a lake. This two bubble curtain configuration was field tested from a moving vessel in Venezuela 

and Aruba where a 12-dB suppression of low-frequency sound and a decrease in the sound level of 

laterally projecting sound was documented (Sixma, 1996; Sixma and Stubbs, 1998). A different 

study in the GOM tested an “acoustic blanket” of bubbles as a method to suppress multiple 

reflections in the seismic data. The results of the acoustic blanket study determined that 

suppression of multiples was not practical using the current technology. However, the acoustic 

blanket measurably suppressed tube waves in boreholes and has the capability of blocking out 

thruster noises from a laying vessel during an ocean bottom cable survey, which would allow closer 

proximity of the shooting vessel and increase productivity (Ross et al., 2004 and 2005).
F-46 G&G Survey Descriptions

A recent study, “Methods to Reduce Lateral Noise Propagation from Seismic Exploration 

Vessels,” was conducted by Stress Engineering Services Inc. under BOEM’s Technology 

Assessment & Research Program (Ayers et al., 2009 and 2010). The first phase of the project was 

spent researching, developing concepts for noise reduction, and evaluating the following three 

concepts: (1) an air bubble curtain; (2) focusing arrays to create a narrower footprint; and 

(3) decreasing noise by redesigning airguns. The air bubble curtain was selected as the most 

promising alternative, which led to more refined studies the second year (Ayers et al., 2009). A 

rigorous 3D acoustic analysis of the preferred bubble curtain design, including shallow-water 

seafloor effects and sound attenuation within the bubble curtain, was conducted during the second 

phase of the study. Results of the model indicated that the bubble curtains performed poorly at 

reducing sound levels and are not a viable option for mitigation of lateral noise propagation during 

seismic operations from a moving vessel (Ayers et al., 2010).

3.7.3 eSource Airgun

Bolt Technology Corporation has engineered a new type of airgun (the eSource airgun) 

designed to abridge the potential impact of seismic survey operations on marine life while also 

conveying optimal bandwidth for subsurface imaging. The eSource airgun optimizes output in the 

seismic band, suppressing the high-frequency components that contribute to acoustic impact, while 

retaining the low-frequency components that are critical to seismic exploration. This new technology 

could be widely available for commercial applications, as only the airguns would have to be changed 

on vessels and all of the handling systems would remain the same. Weilgart (2012) notes that “This 

approach may be too piecemeal and not comprehensive enough, however, as other potentially 

damaging characteristics of airgun pulses remain.”

4 OTHER SURVEYS AND EQUIPMENT

4.1 ACOUSTIC PINGERS

Acoustic positioning systems (i.e., acoustic pingers/transponders/transceivers/responders) 

can yield position estimation accuracy of a few centimeters to tens of meters and can be used over 

operating distances from tens of meters to tens of kilometers. Performance at any particular place 

or time depends on the design of the positioning system, its installed configuration, and the 

characteristics of the underwater acoustic environment. In general, acoustic pingers and 

transponders/transceivers/responders are components used to create underwater positioning 

systems. The operating frequencies of these devices usually is between 8 and 300 kHz. The 

operating frequency selected for a particular system is a function of the design of the system. The 

range over which various devices can be used varies from less than 100 m (328 ft) to more than 

10 km (6.2 mi). The effective range of individual devices depends on the operating environment and 

the characteristics of the device, including its operating frequency.

Acoustic positioning systems are used to keep track of the locations of various components 

of seismic survey systems, including the locations of airgun arrays, streamer positions, OBN and 
Gulf of Mexico G&G Activities Programmatic EIS F-47

OBC locations, and to track ROVs as they operate. Valuable equipment often has a pinger attached 

to facilitate its recovery should it break away from a mooring or otherwise be lost.

4.2 TRANSPONDERS/TRANSCEIVERS

Transponders, like pingers, are a component used in acoustic positioning systems and are 

attached to a mooring, anchor, or other underwater item to be retrieved or located in the future. 

Unlike a pinger, a transponder may remain idle until it is “interrogated” by a transceiver. When the 

transponder is interrogated, it transmits a signal that may include location information. A transceiver 

is used to receive signals from pingers and to transmit signals to interrogate transponders, and in 

both cases aid in locating marine equipment for recovery. Transceivers usually are located on a 

vessel. 

4.3 REMOTELY OPERATED VEHICLES AND AUTONOMOUS UNDERWATER VEHICLES

An AUV is a robot that travels underwater without requiring input from an operator after it is 

released. The AUVs constitute part of a larger group of undersea systems known as autonomous 

underwater vehicles, a classification that includes non-autonomous ROVs that are controlled and 

powered from the surface by an operator/pilot via an umbilical or using a remote control. The ROVs 

are unoccupied, highly maneuverable, and operated by crew on board a vessel. They are linked to 

the ship by a neutrally buoyant tether or, often when working in rough conditions or in deeper water, 

a load-carrying umbilical cable that is used along with a tether management system (TMS). The 

TMS is a garage-like device that contains the ROV during lowering through the splash zone; on 

larger work-class ROVs, the TMS is a separate assembly that sits on top of the ROV. The purpose 

of the TMS is to lengthen and shorten the tether to minimize the effect of cable drag where there are 

underwater currents. The armored umbilical cable contains electrical conductors and fiber optic 

cables that carry electrical power, video, and data signals between the operator and the TMS. The 

TMS then relays the signals and power for the ROV down the tether cable. Once at the ROV, 

electrical power is distributed to the ROV’s components. In high-power applications, most of the 

electrical power drives a high-power electrical motor, which drives a hydraulic pump. The hydraulic 

pump is used for propulsion and to power equipment such as torque tools and manipulator arms 

where electrical motors would be unsuitable for use. Most ROVs are equipped with at least a video 

camera and lights. Additional equipment is commonly added to expand the ROV’s capabilities. 

These may include sonars; magnetometers; a still camera; a manipulator or cutting arm; water and 

sediment samplers; and instruments that measure water clarity, temperature, salinity, sound velocity, 

light penetration, and pressure. The ROVs are classified based on their size, weight, ability, or 

power. The ROVs typically are positioned via acoustic link from the topside vessel, usually in the 

form of an ultra-short baseline (USBL) tracking system. Acoustic transponders also can be placed 

on the seafloor to improve position accuracy for an ROV and other objects.

The ROVs are used to support some G&G surveys, including deploying and retrieving some 

types of seismic sensors, particularly seismic nodes, on the seafloor. Other G&G surveys (such as 

CSEM) use ROVs to do the same with their sensor packages. While AUVs are not as commonly 

used as ROVs, they are used to make detailed maps of the seafloor before construction of subsea 
F-48 G&G Survey Descriptions

infrastructure begins; pipelines and subsea completions can be installed in a cost-effective manner 

with minimum disruption to the environment by using an AUV. An AUV allows survey companies to 

conduct precise surveys of areas where traditional bathymetric surveys would be less effective or 

too costly. Post-lay pipe surveys are possible now as well.

The AUVs now are the preferred method to meet archaeological survey requirements or 

hazard assessment requirements for pipelines in water depths exceeding 200 m (656 ft). Because 

use of magnetometers is waived at these water depths and airguns are not required for pipeline 

surveys, AUVs are used to deploy some of the same sensors as are used during a towed HRG 

survey (Section 1.3), including sonars, subbottom profilers, and MBESs. Although AUVs are 

autonomous, most AUVs are acoustically monitored using a USBL transponder and tracked from a 

mothership in order to ensure accurate positioning.

4.4 WATER GUNS

Water guns are very similar to the airguns used as seismic sound sources for a variety of 

G&G surveys. Water guns use compressed water to produce sound instead of compressed air used 

by airguns. Similar to airguns, water guns produce impulsive signals containing frequencies 

between 20 and 1,500 Hz depending on the size of the water chamber (USDOI, GS, Woods Hole 

Coastal and Marine Science Center, 2015). Water guns are not analyzed separately in this 

Programmatic EIS because the sound they generate is so similar to the sound produced by airguns 

that the analysis would be almost identical. Additionally, the oil and gas industry no longer uses 

water guns as a seismic source except in extremely rare instances.

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APPENDIX G 

SCREENING OUT TEAM REPORT

Gulf of Mexico G&G Activities Programmatic EIS G-iii

TABLE OF CONTENTS

Page

LIST OF TABLES.............................................................................................................................. G-iii

ABBREVIATIONS AND ACRONYMS ............................................................................................... G-v 

1 INTRODUCTION AND PURPOSE............................................................................................... G-1

2 APPROACH USED ...................................................................................................................... G-2

3 RESULTS AND RECOMMENDATIONS...................................................................................... G-8

4 REFERENCES CITED ............................................................................................................... G-10

LIST OF TABLES

Page

Table G-1. Consolidated Acoustic Source and Survey Table. ....................................................... G-7

Gulf of Mexico G&G Activities Programmatic EIS G-v 

ABBREVIATIONS AND ACRONYMS

° degree

2D two-dimensional

AUV autonomous underwater vehicle

BOEM Bureau of Ocean Energy Management

CATEX categorical exclusion

dB decibel

dB re 1 μPa decibel relative to 1 micropascal

EIS Environmental Impact Statement

ft foot

G&G geological and geophysical

GOM Gulf of Mexico

HRG high-resolution geophysical

in3 cubic inch

kHz kilohertz

Mm meter

Mms millisecond

NMFS National Marine Fisheries Service

NOAA National Oceanic and Atmospheric Administration

OCS Outer Continental Shelf

PRR pulse repetition rate

rms root mean square

ScOT Screening Out Team

SEL sound exposure level

SL source level

SME subject matter expert

SPL sound pressure level

U.S. United States

USDOC U.S. Department of Commerce

USDOI U.S. Department of the Interior

VSP vertical seismic profile

WAZ wide azimuth

Gulf of Mexico G&G Activities Programmatic EIS G-1 

1 INTRODUCTION AND PURPOSE 

As part of the planning and drafting of the Programmatic Environmental Impact Statement 

(Programmatic EIS) for geological and geophysical (G&G) activities on the Outer Continental Shelf 

(OCS) of the United States (U.S.) in the Gulf of Mexico (GOM), it was recognized by senior staff of 

Bureau of Ocean Energy Management (BOEM) that there was a need to identify, quantify, and 

analyze all active acoustic source operations that might occur during G&G activities. Ultimately, it 

was desired that this process indicate which sources and activities, based on their potential to affect 

the environment, required a thorough analysis in the Programmatic EIS and which sources and 

activities did not. During the initial meeting on this subject, senior BOEM staff decided to create a 

Screening Out Team (ScOT), which first convened in April 2014, to examine the issue and make 

recommendations. The team consisted of subject-matter experts (SMEs) from BOEM’s Gulf of 

Mexico OCS Region, BOEM’s Headquarters, and CSA Ocean Sciences Inc.

Specifically, the ScOT was assigned the following tasks:

• include for consideration the entire U.S. GOM (e.g., all depth regimes);

• identify all active acoustic G&G sources for the Oil and Gas, Marine Minerals, 

and Renewables Energy Programs currently or in the near future within BOEM’s 

jurisdiction;

• identify all sources regardless of whether they are hull-mounted, towed, or fixed;

• examine all frequency regimes for identified acoustic G&G sources;

• characterize all relevant source operating parameters (e.g., source levels [SLs], 

pulse length, beam patterns, pulse repetition rates);

• identify acoustic G&G sources that may be used simultaneously; and

• consider potential new technology.

The ScOT did not examine non-G&G or non-G&G-related sound sources, including the 

following:

• explosive removal operations;

• construction noises such as pile driving, dredging, etc.;

• production and drilling noise;

• machinery or propulsion noise from vessels or oil platforms;

• local navigation transponders or systems, acoustic communication systems, or 

acoustic releases;
G-2 Screening Out Team Report

• active acoustic sources from geotechnical/geological testing and vessels; and

• vessel traffic.

It should be noted that, even though the charter of the ScOT was very specific (i.e., to 

identify which active acoustic sources/operations that might be or could be screened out from 

extensive and unnecessary analysis), the broad range of the details needed to complete the analysis 

would provide information to the Alternatives’ discussion for the Programmatic EIS. Furthermore, 

the historic and operational data collected to complete the analysis would provide many of the 

technical and operational details for current and future activities that would directly feed into the 

Programmatic EIS acoustic impact modeling. Additionally, the ScOT needed to understand and be 

consistent with ongoing internal BOEM discussions concerning possible future category exclusions 

(CATEXs) for these acoustic systems.

2 APPROACH USED

The ScOT began examination of the task using a “top-down” approach in order to ensure 

that all BOEM programs, survey types, acoustic systems, and overall operations to be addressed in 

the Gulf of Mexico G&G Programmatic EIS were identified and included in the analysis. However, it 

quickly became evident that this approach had a severe disadvantage in identifying and analyzing 

the specific details (e.g., operational frequencies, modes, depths, repetition rates, etc.) of the 

numerous systems and operations that might be used in the GOM. Recognizing this problem and 

having gained a general understanding of the breadth of potential systems and operations that 

needed examination from that first attempt, the ScOT decided to shift to a “bottom-up” approach to 

ensure access to all of the details needed to examine and evaluate those systems. Unfortunately, 

this approach became bogged down in the examination and quantification of the numerous systems 

potentially used; in addition, it was recognized that a large number of permutations and variations 

were possible in how these systems could be deployed together or separately.

After several discussions, the ScOT decided to try a “middle-out” approach. This method 

used the issues encountered in the first two approaches to guide a process that attempted to avoid 

the same pitfalls while maintaining the fidelity needed to complete the desired analyses. In this way, 

the ScOT would be able to group the sources such that those with negligible potential to cause 

impacts could be identified for possible removal from further consideration. At the same time, the 

systems that did not have negligible impact potential could be better characterized and understood 

for subsequent analyses in the Programmatic EIS (e.g., in discussions of alternatives, mitigation, 

etc.). Examples of the steps used in this approach include the following:

• using data from the top-down approach to completely identify all of the surveys 

and active acoustic source system types that needed to be examined;

• using data from the top-down approach to begin grouping and categorizing the 

surveys by characteristics that are operationally significant but not directly related 
Gulf of Mexico G&G Activities Programmatic EIS G-3 

to the systems employed (e.g., operating water depths, durations of operations, 

etc.);

• using historic data and practical experience of the SMEs to identify which 

systems are operated together for which survey types;

• using data from the bottom-up approach to examine each active acoustics 

system type (i.e., single airgun, airgun arrays, boomers, multibeam sonar, side 

scan sonar, subbottom profilers, and echosounder systems) and identify the 

range of the important system parameters present (e.g., frequencies, pulse 

lengths, etc.); and

• utilizing the knowledge of the SMEs to group systems together that have similar 

operating parameters and divide the ranges of the system parameters into 

“natural” divisions based on operational requirements (e.g., what is needed to 

make that system perform well in a given situation) or known biological 

parameters (e.g., frequencies believed to be beyond the hearing range of various 

species).

The ScOT recognized that within the scenarios proposed for the Programmatic EIS, this 

assessment would need to address the projected active acoustic sources activities in the GOM for 

the next 10 years, including changes to the types or specifications for the sources. Furthermore, this 

effort needed to consider currently known technical issues that could affect how the ScOT parses 

the sources. Specifically, the ScOT

• searched for and identified the current trends for source operations in the GOM, 

including the following:

− the trends to increased size and SLs for the numerous variations of wide 

azimuth (WAZ) surveys to better examine areas under subsurface salt 

structures, 

− the relatively new approach in speculation (“spec”) surveys that use a single 

airgun,

− the reduction/absence of vertical cable surveys in recent years,

− a decrease in the number of geophysical surveys conducted on the OCS 

(i.e., water depths less than 200 meters [m]; 656 feet [ft]) and the current 

trend of exploration and production activities moving to deeper water areas 

farther offshore,

− the common use of frequencies above 180 kilohertz (kHz) during marine 

mineral high-resolution geophysical (HRG) surveys to ensure the resolution 

needed for these surveys on the shelf,

− the combinations of HRG survey sources typically used together, and
G-4 Screening Out Team Report

− boomer use in shallow water is rare for the Marine Minerals Program 

because it provides a 0.5- to 1-m (1.6- to 3.3-ft) resolution and typically is 

replaced with subbottom profile systems that have sufficient depth 

penetration and higher resolution (note that it was kept in the analysis 

because it may be used to examine ancient, sediment-filled river channels in 

the future), and that in Renewable Energy Program surveys, it is more 

commonly used;

• recognized the need to be flexible in this discussion to accommodate minor 

variations in source parameters and operational techniques;

• recognized the need to consider new or developmental systems, such as marine 

vibrators or parametric subbottom profilers;

• recognized the potential for changes to the acoustic thresholds or calculation 

techniques that could influence how these sources are perceived; and

• recognized the recent developments or papers that discuss these sources (i.e., 

LGL Ltd., 2010; Martin et al., 2012; Zykov, 2013; Zykov and MacDonnell, 2013; 

Applied Acoustic Engineering, Ltd., 2014a, 2014b, and 2014c; Deng et al., 2014; 

EdgeTech, 2014).

In order to complete the screening process, several specific technical details needed to be 

discussed and resolved by the ScOT. Some of the most important details included the following:

• Using an acoustic metric or suite of metrics that are consistent with existing and 

proposed acoustic thresholds but that also allow appropriate source 

characterization. Typically, root mean square (rms) sound pressure levels 

(SPLs), or SPLrms, and sound exposure levels (SELs) are used. Broadband 

sources like airguns and boomers can use standard metric. However, to capture 

the character of most HRG sources, the SPLrms needs to consider the duration 

of the individual pulses used because they are much shorter than 1 second (e.g., 

microseconds [μs] to milliseconds [ms]). For this analysis, SPLrms has been 

corrected for pulse duration. Thus, if a 200 decibel relative to 1 micropascal 

(dB re 1 μPa) at 1-m source has a 10-ms pulse, it is shown as a 180 dB re 1 μPa 

at 1-m source (e.g., 200 + 10log(0.010 sec) = 200 - 20 = 180 dB).

• Water depths were divided into three categories: shallow or shelf (0 to 20 m; 

0 to 66 ft), slope (20 to 1,100 m; 66 to 3,609 ft), and deep (>1,100 m; 3,609 ft). 

This is consistent with depth zones presented in the Atlantic G&G Programmatic 

EIS (U.S. Department of the Interior [USDOI], BOEM, 2014) and is consistent 

with bathymetric features in the GOM.

• Possible operating frequency bands for multibeam, side-scan, and echosounder 

systems were divided into three groups: <30 kHz, 30 to 180 kHz, and >180 kHz. 

This was done to accommodate the understandings that (1) most mysticetes are 
Gulf of Mexico G&G Activities Programmatic EIS G-5 

believed to have reduced sensitivity above 30 kHz (U.S. Department of 

Commerce [USDOC], National Oceanic and Atmospheric Administration [NOAA], 

2013); (2) odontocetes and pinnipeds have some hearing capability below 

30 kHz but their best sensitivity is between 10 and 120 kHz (estimated by a 

reduced sensitivity of greater than 20 dB from the audiograms in Figure 8.1 of 

Richardson et al. [1995]); and (3) most marine mammals (even high-frequency 

species) are not believed to hear above approximately 180 kHz, but even if they 

do, it is with a very reduced sensitivity level (e.g., more than 40 dB less sensitive 

than for their best frequencies) (Richardson et al., 1995; USDOC, NOAA, 2013).

• SLs for airguns were identified for single airguns and airgun arrays (i.e., multiple 

airguns operated together in an array). These sources were then divided into 

groups using the volume (in cubic inches) of the airgun or array and the 

respective SLrms bands. A simple assessment for the airguns or arrays as 

small, medium, or large resulted in the following bands:

− for single airguns, SLs of <210, 210 to 230, and >230 dB rms (with 

corresponding volumes of <200, 200 to 350, and >350 cubic inches [in3

]); 

and

− for the airgun arrays, SLs <240, 240 to 250, and >250 dB rms, (with 

corresponding volumes of: 2,000 to 3,000; 3,000 to 4,000; and 4,000 to 

8,600 in3

).

• The SMEs identified these as representative of the sources that have been used 

in the GOM since 2010.

• The ScOT understood and was cognizant of the potential influence of pulse 

duration and signal or pulse repetition rates (PRRs) for the various sources. All 

of the sources listed in Table G-1 employ signals with durations of less than 

1 second, and many have signal lengths in the microsecond range. This 

characteristic, when combined with how often that signal is transmitted, directly 

leads to how long an animal could be exposed to the sound source. Neither the 

signal duration nor the PRR were directly used to recommend removal of a 

system from further consideration, but they were considered for sources that 

require further examination.

• Similarly, beam patterns and transmission sequencing by sources (e.g., 

sequential ensonification of different sectors or portions of a full beam with 

different frequencies, such as is often used by multibeam sonar) were not directly 

used in the screening out process, but they may be useful for further analysis. 

However, it should be noted that most of the HRG systems have relatively 

narrow beams which only ensonify small narrow or “pencil-like” volumes of the 

water column (Zykov and MacDonnell, 2013; USDOI, BOEM, 2014). For 

example, most subbottom profilers have a beam that is 15° to 25° wide 

(depending on the frequencies used), while multibeam and side-scan sonar 
G-6 Screening Out Team Report

produce beams or beam fans that are 1° to 2° wide. Various models of the HRG 

systems can be hull-mounted or deployed on a tow body or possibly an 

autonomous underwater vehicle (AUV). When the tow body or AUV is employed, 

these platforms try to maintain a constant height above the seafloor. For 

subbottom profilers, this height may be 3 to 6 m (10 to 20 ft); for side-scan and 

multibeam sonars (in deep tows), it may be 50 to 100 m (164 to 328 ft). For hullmounted systems, with the exception of the more powerful multibeam sonars and 

boomers, there are water depth limitations for optimal use of these systems, 

which limits their operation to shelf waters (i.e., approximately <200 m; 656 ft) or 

reduces their transmission repetition rates. The operation of many of these 

systems in shallow waters or near the seafloor causes the main acoustic beam to 

quickly interact with the bottom and accelerate energy loss. This significantly 

reduces the possibility of adverse effects to nearby marine mammals. For 

example, it would be highly unlikely that a marine mammal would pass through 

the main beam of a subbottom profiler that is being towed 3 m (10 ft) above the 

seafloor. In addition, the acoustic energy that reflects from the seafloor is greatly 

reduced (e.g., 15 to 35 dB) when it interacts with the seafloor, further reducing 

the possibility of impacts.

At the time of the ScOT analysis, the report on the 2008 Madagascar mass stranding of 

melon-headed whales (Southall et al., 2013) was available and one source of concern was 

multibeam sonar systems (or other similar high-frequency HRG system) and their potential for 

adversely affecting marine mammals. Additionally, at the time of the ScOT analysis, the National 

Marine Fisheries Service (NMFS) was in the process of preparing a final version of their Level A 

acoustic threshold criteria for airguns (USDOC, NOAA, 2013). The ScOT was aware of these 

documents and attempted to consider them in their analysis.

Furthermore, results from Deng et al. (2014) had been released and were considered in this 

analysis. Deng et al. (2014) discussed how active acoustic systems such as multibeam and sidescan sonars are designed to produce a signal with a specific frequency content (i.e., in the desired 

frequency band, but also produce a broader range of frequencies. Included in this broader 

frequency band are harmonic and subharmonic signals that nominally display only 40 to 60 dB 

below that produced in the desired band. As an example, while a 240-kHz multibeam sonar has a 

primary (and most powerful) signal above the frequency of an animal’s hearing range, the animal 

may be aware of its presence because it can hear the subharmonics at 120, 80, or 60 kHz 

frequencies, which are within its hearing range. These signals will be present at a reduced SLs and 

are, therefore, significantly less likely to affect an animal; nevertheless, operation of the active 

acoustic systems is not undetectable to that animal.
Gulf of Mexico G&G Activities Programmatic EIS G-7

Table G-1. Consolidated Acoustic Source and Survey Table. 
G-8 Screening Out Team Report

3 RESULTS AND RECOMMENDATIONS

Based on the ScOT discussions outlined previously, the team constructed and refined 

Table G-1. This table is designed to capture the overall nature of the possible surveys that may 

occur during G&G activities. The first major division in this table is the separation of the deep 

penetrating seismic surveys from the HRG-like surveys. This was done to indicate that these two 

categories of surveys typically do not occur together in any coordinated way for any given project 

because the vessels they utilize would physically interfere with the other survey. Furthermore, it is 

highly unlikely that they would occur together for different projects due to the exclusive nature of the 

leasing procedures. Each row or line in the table represents a different type of survey, with the 

columns to the right side of the table identifying which sources would be used for each survey type. 

The two main factors that drive the number of rows in the table are (1) the sources or combinations 

of sources used for each survey type and (2) the depths at which the sources with those critical 

characteristics are employed. Examples of the consequence of these factors can be seen in the 

comparison of the rows for the two-dimensional (2D) and vertical seismic profile (VSP) surveys. 

Because of the differences in the size and power of the sources used (i.e., reduced SL for 

2D surveys in shallow or shelf waters [“S” in the sixth column]), there are two 2D survey rows, one 

for shallow depths (S) and one for slope or deep depths (M or D), while there is only one for the VSP 

surveys. All of the sources for VSP surveys fall into the SL range for a small airgun array, which is 

used for all VSP surveys regardless of the depth in which the survey occurs. A much larger table 

was reduced or concentrated down to this table, while still maintaining the ability to differentiate the 

critical source or operational characteristics of each survey type.

The selection and grouping of the critical characteristics of a source allowed it to be 

represented by a reduced number of cells in Table F-1. For example, the operating frequencies for 

the multibeam sonars commonly used in marine mineral, HRG, and multiple source surveys may 

include 200, 234, 300, and 600 kHz systems. For brevity and tabular clarity, these various systems 

have been contained in the “>180 kHz” cell for this survey type.

Additionally, the cells in the various source columns have been color coded by the ScOT to 

indicate its recommendations concerning whether or not a system can be screened out. The color 

code system is as follows:

• Dark Green identifies sources with operating frequencies above 180 kHz, which 

have been highly recommended to be screened out. Systems that operate at 

these design frequencies are above the hearing range of marine mammals, and 

the portion of their signals that are with the hearing range of marine mammals 

(i.e., the subharmonics and off-design incidental noise components) is 

significantly reduced in level.

• Light Green identifies sources that operate within the marine mammal frequency 

hearing bands but have relatively low SLs (less than 200 dB re 1 μPa at 1 m for a 

single pulse); have a short pulse length (i.e., much less than one second and 

typically 5 to 40 ms); and operate where their main beams quickly interact with 
Gulf of Mexico G&G Activities Programmatic EIS G-9 

the seafloor (i.e., within 20 to 40 m), which significantly reduces their strength. 

Therefore, these sources are recommended to be screened out. There may be a 

very small and narrow volume of the ocean where harassment impacts might 

occur, but it is very unlikely that marine animals would be in these volumes while 

the source is ensonifying them.

• Yellow identifies sources that use dual frequencies (one of which is greater than 

180 kHz) or that use a range of frequencies (part of which is above 180 kHz), 

and are conditionally recommended be screened out for the operations above 

180 kHz and should be further examined for the remaining frequencies. After the 

high frequency systems have been screened out, the remaining systems will 

need to be examined using the approach described in the previous bullet. 

Alternatively, these systems could be directed to only use frequencies above 

180 kHz, which have been highly recommended for screening out.

• Orange identifies sources with medium or high SLs that operate within the 

marine mammal frequency hearing range, and are not recommended for 

screening out. They probably require additional analysis even though many of 

these systems are rarely employed.

• Red identifies most single airgun or airgun array systems that are strongly not 

recommended for screening out and definitely require full analysis. 

• White identifies a small single airgun system that has relatively low power and 

less than frequent use that may be able to be screened out due to the low SL, 

but, for consistency, perhaps all airgun systems should be treated the same. 

Based on the historic acoustic threshold of 160 dB for Level B impacts, the range 

around this source that might impact a marine mammal is approximately 20 m, 

without any weightings applied.

A review of Table G-1 leads to a few overall conclusions about the operation of these 

sources, including the following:

• Due to their strong signal, frequency content, and persistence of operations, 

deep penetrating seismic surveys will require a full analysis of their potential 

acoustic impacts in the Programmatic EIS. Additionally, the use of airgun arrays 

for possible carbon dioxide sequestration surveys will require complete analysis, 

as will use of medium and large single airgun surveys. The small single airguns 

may be eligible for screening out due to their low SL, but it may be simpler to 

treat them the same as other airgun systems.

• The HRG surveys associated with the Oil and Gas Program often need to 

operate off of the OCS. This changes the selected operating systems 

parameters (i.e., lower frequencies, higher SLs, longer signals, higher heights 

above the seafloor, etc.) from those typically used for the Renewable Energy and 
G-10 Screening Out Team Report

Marine Minerals Programs. Therefore, even though Table G-1 seems to indicate 

that these systems may be operated in a fashion similar, they typically are 

operated at the opposite end of the range for that parameter. For example, for a 

dual frequency 120- or 400-kHz multibeam, the 410-kHz system setting may be 

suitable for shallow water, but the 120-kHz setting is used in deeper water to 

reduce signal attenuation in the water column so that it is not above the 180-kHz 

requiring analysis. It is recommended that the HRG operations associated with 

the Oil and Gas Program receive a full analysis in the Programmatic EIS.

• With the exception of the rarely used boomer and the relatively low powered 

subbottom profilers, all systems used for Marine Minerals Program surveys 

should be screened out because they operate above 180 kHz. Discussions with 

the SMEs for those operations identified that this operational selection was 

driven partially by the need for higher resolution in the surveys due to their 

operation in shallow water and by the need to quantify the sediments being 

examined; however, it was a deliberate choice based on potential marine 

mammal impacts.

With the exception of the carbon dioxide sequestration survey, the Renewable Energy HRG 

surveys currently are conducted in a manner similar to the Marine Minerals surveys, but they also 

include some sources that operate below 180 kHz. It is possible that these surveys could use higher 

frequency systems and minimize potential impacts and the need for additional analysis.

4 REFERENCES CITED

Applied Acoustic Engineering, Ltd. 2014a. Sound source, boomers: AA251 boomer plate and 

AA301 boomer plate. Technical specifications. 2 pp. Internet website: 

http://www.appliedacoustics.com/sub-bottom-profiling/sound-source-boomers. Accessed 

August 29, 2014.

Applied Acoustic Engineering, Ltd. 2014b. Delta sparker (technical specification). Internet website: 

http://www.appliedacoustics.com/wp-content/uploads/2015/12/Delta-Sparker.pdf. Accessed 

September 29, 2014.

Applied Acoustic Engineering, Ltd. 2014c. Squid 501, Squid 2000 & Delta Sparker Seismic Sound 

Source, Sparker Assemblies (technical specification). Internet website: 

http://www.appliedacoustics.com/wp-content/uploads/2015/12/Squid-501-and-2000.pdf. 

Accessed September 29, 2014.

Deng, Z.D., B.L. Southall, T.J. Carlson, J. Xu, J.J. Martinez, M.A. Weiland, and J.M. Ingraham. 

2014. 200 kHz commercial sonar systems generate lower frequency side lobes audible to some 

marine mammals. PLoS ONE 9(4):e95315.

EdgeTech. 2014. 4200 Series side scan sonar system. Product brochure. Internet website: 

http://www.edgetech.com/pdfs/ut/4200-Brochure-122012.pdf. Accessed September 29, 2014.
Gulf of Mexico G&G Activities Programmatic EIS G-11

LGL Ltd. 2010. Environmental assessment of a marine geophysical survey by the R/V Marcus G. 

Langseth in the Pacific Ocean off Costa Rica, April-May 2011. Prepared for Lamont-Doherty 

Earth Observatory and National Science Foundation Division of Ocean Sciences by LGL Ltd., 

Environmental Research Associates. Internet website: https://www.nsf.gov/geo/oce/envcomp/

attachment1-bangs-costa-rica-2011-final-ea-6-april2011.pdf. 

Martin, B., J. MacDonnell, N. Chorney, and D. Zeddies. 2012. Sound source verification of Fugro 

Geotechnical Sources. (Appendix A). In: ESS Group, Inc. Renewal application for incidental 

harassment authorization for the non-lethal taking of marine mammals resulting from preconstruction high resolution geophysical survey: Nantucket Sound. 66 pp. Internet website: 

http://www.nmfs.noaa.gov/pr/pdfs/permits/capewind_iha_application_renewal.pdf. Accessed 

October 23, 2013.

Richardson, W.J., C.R. Greene, Jr., C.I. Malme, and D.H. Thomson. 1995. Marine mammals and 

noise. San Diego, CA: Academic Press. 576 pp.

Southall, B.L., T.Rowles, F. Gulland, R.W. Baird, and P.D. Jepson. 2013. Final report of the 

Independent Scientific Review Panel investigating potential contributing factors to a 2008 mass 

stranding of melon-headed whales (Peponocephala electra) in Antsohihy, Madagascar. 75 pp. 

Internet website: http://www.marinemammalcenter.org/assets/pdfs/vetsci-stranding/scientificcontributions/2013/southall-2013-madagascar-mass.pdf. 

U.S. Dept. of Commerce. National Oceanic and Atmospheric Administration. 2013. Draft guidance 

for assessing the effects of anthropogenic sound on marine mammals – acoustic threshold levels 

for onset of permanent and temporary threshold shifts. Posted in the Federal Register on 

December 27, 2013 (78 FR 78822).

U.S. Dept. of the Interior. Bureau of Ocean Energy Management. 2014. Atlantic OCS proposed 

geological and geophysical activities: Mid- and South Atlantic Planning Areas—final 

programmatic environmental impact statement.

Zykov, M. 2013. Underwater sound modeling of low energy geophysical equipment. Operations. 

JASCO Document 00600, Version 1.0. Draft. Technical report by JASCO Applied Sciences for 

CSA Ocean Sciences Inc. 50 pp.

Zykov, M. and J. MacDonnell. 2013. Sound source characterizations for the collaborative baseline 

survey offshore Massachusetts, final report: Side-scan sonar, sub-bottom profiler, and the R/V 

small research vessel experimental. JASCO Document 00413, Version 2.1. Technical report by 

JASCO Applied Sciences for the U.S. Dept. of the Interior, Bureau of Ocean Energy 

Management. 55 pp.

APPENDIX H 

MARINE MAMMAL HEARING 

AND 

SENSITIVITY TO ACOUSTIC IMPACTS

Prepared by

Brandon L. Southall, Ph.D.

SEA, Inc.

9099 Soquel Drive, Suite 8

Aptos, California 95003

Prepared for

CSA Ocean Sciences Inc.

8502 SW Kansas Avenue

Stuart, Florida 34997

Under Contract to

Bureau of Ocean Energy Management

45600 Woodland Road

Sterling, Virginia 20166

Gulf of Mexico G&G Activities Programmatic EIS H-v 

TABLE OF CONTENTS

Page

LIST OF FIGURES............................................................................................................................ H-vii

LIST OF TABLES.............................................................................................................................. H-ix

ABBREVIATIONS AND ACRONYMS .............................................................................................. H-xi

1 INTRODUCTION/OVERVIEW ....................................................................................................... H-1

2 ROLE OF ACOUSTICS IN MARINE MAMMAL ECOLOGY ......................................................... H-2

3 HEARING IN MARINE MAMMALS ............................................................................................... H-3

3.1 Hearing in Mysticetes ......................................................................................................... H-6

3.2 Hearing in Odontocetes...................................................................................................... H-6

3.3 Hearing in Sirenians (Manatees)........................................................................................ H-7

3.4 Marine Mammal Hearing Weighting Functions.................................................................. H-7

4 EFFECTS OF NOISE ON MARINE MAMMAL HEARING AND BEHAVIOR ............................. H-12

4.1 Effects of Noise on Marine Mammal Physiology ............................................................. H-13

4.2 Effects of Noise on Marine Mammal Hearing .................................................................. H-14

4.2.1 Temporary and Permanent Threshold Shift in Marine Mammals ....................... H-14

4.2.2 Auditory Masking ................................................................................................. H-16

4.3 Effects of Noise on Marine Mammal Behavior................................................................. H-17

5 MARINE MAMMAL NOISE EXPOSURE CRITERIA .................................................................. H-19

5.1 Derivation of TTS and PTS Criteria.................................................................................. H-21

5.2 Derivation of Behavioral Effects Criteria .......................................................................... H-24

6 ASSESSMENT OF HEARING INFORMATION FOR SPECIES/ GROUPS IN THE AREA OF 

INTEREST ....................................................................................................................................... H-29

7 REFERENCES CITED ................................................................................................................ H-29

Gulf of Mexico G&G Activities Programmatic EIS H-vii

LIST OF FIGURES

Page

Figure H-1. Example of a Hearing Profile, or Audiogram, for Two Pygmy Killer Whales 

(Feresa attenuata) Using an Electrophysiological Measurement Technique 

(including measurements of background noise).......................................................... H-4

Figure H-2. Measured or Estimated Functional Hearing Ranges for Different Marine 

Mammal Groups Shown Relative to Various Human Noise Sources. ........................ H-5

Figure H-3. Frequency-Weighting Functions for Cetaceans Proposed by Southall et al. 

(2007)........................................................................................................................... H-9

Figure H-4. Frequency Weighting Filters (“Type 2”) for Low-Frequency (LF), Mid-Frequency 

(MF), and High-Frequency (HF) Cetaceans Derived by Finneran and Jenkins 

(2012)......................................................................................................................... H-10

Figure H-5. “Merged” Auditory Filters for Mid-Frequency (MF) and High-Frequency (HF) 

Cetaceans Proposed by the National Oceanic and Atmospheric Administration ..... H-11

Figure H-6. Modified Auditory Filters for Low-Frequency (LF) Cetaceans Proposed by the 

National Oceanic and Atmospheric Administration ................................................... H-11

Figure H-7. Auditory Filters for Seals (Phocids) and Sea Lions (Otariids) Proposed by the 

National Oceanic and Atmospheric Administration ................................................... H-12

Figure H-8. Time Series Plot Showing a Calling Blue Whale (Balaenoptera musculus) and 

the Increasing Noise (and masking) in the Same Low-Frequency Band from an 

Approaching Vessel ................................................................................................... H-17

Gulf of Mexico G&G Activities Programmatic EIS H-ix

LIST OF TABLES

Page

Table H-1. Marine Mammal Functional Hearing Groups and Estimated Functional Hearing 

Ranges Proposed by Southall et al. (2007) .................................................................. H-8

Table H-2. Sound Source Categories, Acoustic Characteristics, and Examples Proposed 

by Southall et al. (2007)............................................................................................... H-20

Table H-3. Marine Mammal Noise Exposure Criteria for Injury for Different Marine Mammal 

Functional Hearing Groups Proposed by Southall et al. (2007) ................................. H-22

Table H-4. Revised Marine Mammal Noise Exposure Criteria for TTS and PTS Onset 

Proposed by the National Oceanic and Atmospheric Administration ......................... H-24

Table H-5. Marine Mammal Noise Exposure Criteria for Behavior for Different Marine 

Mammal Functional Hearing Groups Proposed by Southall et al. (2007) .................. H-25

Table H-6. Southall et al. (2007) Assessment of Individual Behavioral Responses of 

Low-Frequency Cetaceans to Multiple-Pulse Exposure for Various Received 

Levels........................................................................................................................... H-26

Table H-7. Probabilistic Disturbance (rms) Sound Pressure Level Thresholds (M-weighted) 

Proposed by Wood et al. (2012) based on Southall et al. (2007) Severity Scaling 

to Predict a Level B Behavioral Response.................................................................. H-28

Gulf of Mexico G&G Activities Programmatic EIS H-xi

ABBREVIATIONS AND ACRONYMS

dB decibel

dB re 1 μPa decibels relative to 1 micropascal

EIS Environmental Impact Statement

FR Federal Register

G&G geological and geophysical

GOM Gulf of Mexico

HESS High Energy Seismic Survey (team)

Hz hertz

kHz kilohertz

NMFS National Marine Fisheries Service

NOAA National Oceanic and Atmospheric Administration

NRC National Research Council

PTS permanent threshold shift

rms root mean square

SEL sound exposure level

TTS temporary threshold shift

USDOC U.S. Department of Commerce

Gulf of Mexico G&G Activities Programmatic EIS H-1 

1 INTRODUCTION/OVERVIEW 

Marine mammals rely on sound to live, producing and receiving it to perform various life 

functions. The ocean is naturally noisy, but humans add a myriad of sounds that are increasingly 

impinging on the underwater soundscape. There is clear evidence that certain sounds can 

negatively affect marine life under certain conditions, but the type and magnitude of these impacts 

for different species and sound types remain poorly understood. Recently, there have been 

significant advances in scientific knowledge, at least in some conditions, on hearing systems, the 

effects of noise on hearing, and behavioral responses to various sounds. The scientific community 

is discovering group (e.g., species, taxonomic) and species-specific differences in hearing and how it 

may be affected as well as the overarching relevance of sound exposure context in driving the 

probability, severity, and consequences of behavioral response. New ways of assessing and 

mitigating potential impacts emerged from this evolution in understanding.

The initial focus on how anthropogenic noise might affect marine mammals centered on 

potential injurious types of sound impacts. This was driven largely by concerns over direct hearing 

or tissue damage and isolated marine mammal mass stranding events; these have primarily involved 

beaked whales exposed to military sonar but recently have included melon-headed whales 

(Peponocephala electra) exposed to military and commercial sonar systems. Largely due to various 

research (discussed in Section 4.2) indicating that direct physical injury from noise is limited for 

some species except when quite close to sound sources, there is increasing interest in biologically 

significant behavioral changes from noise within a broader ecological context. While the zones 

around sounds in which species from different marine mammal groups may be physically harmed 

appear to be small, the areas over which animals may be disturbed in significant ways that may 

impact vital life functions (e.g., foraging, reproduction, or even survival if reactions increase risk of 

predation or stranding) may be significantly larger. These considerations and the underlying 

complexity of understanding and assessing their probability of occurrence have become more 

central in developing noise exposure criteria and other means of assessing the probability of 

negative effects from noise exposure. A key challenge in establishing and updating exposure 

criteria and conducting environmental assessments given the rapidly evolving science revealing 

these complexities is establishing an appropriately precautionary yet tractable approach. Many of 

these issues and the underlying science are considered in detail in a major comprehensive review 

and application of science in the context of noise exposure criteria (Southall et al., 2007). Selected 

recent studies that have provided additional important findings are also summarized here, and 

subsequent efforts to synthesize and apply more recent scientific findings and evolve exposure 

criteria for various sound sources by Finneran and Jenkins (2012); the U.S. Department of 

Commerce, National Marine Fisheries Service (Federal Register, 2013); and Tougaard et al. (2014) 

are discussed also.

This appendix summarizes the current state of scientific knowledge about the importance of 

sound and the effects of noise on marine mammals. Most attention is given to species typically 

present in the Gulf of Mexico (GOM), primarily odontocetes (toothed whales and dolphins), with 

some discussion of mysticetes (baleen whales), and sirenians (manatees). The potential effects of 
H-2 Marine Mammal Hearing and Sensitivity to Acoustic Impacts

noise exposure on marine mammal physiology, hearing, communication, and behavior from 

continuous and pulsed (impulsive) sound source types (e.g., longer continuous signals versus brief 

transient impulsive signals) are discussed. Additionally, evolving noise exposure criteria and 

operational mitigation measures are building on historical approaches, with attention to the types of 

acoustic sources present in the proposed geological and geophysical (G&G) operations proposed 

within the Area of Interest.

2 ROLE OF ACOUSTICS IN MARINE MAMMAL ECOLOGY 

The underwater acoustic environment can be noisy, with sounds from a host of natural and 

anthropogenic sources. Some natural sounds are biological (e.g., fishes, marine mammals, some 

invertebrates) and others are environmental (e.g., waves, earthquakes, rain). Among the 

anthropogenic sources, many produce noise as an unwanted by-product of normal operations (e.g., 

shipping, drilling, tidal turbines), whereas others (e.g., sonars, airguns, underwater communications 

systems) are produced for a specific remote-sensing or data transfer purpose (Hildebrand, 2009). 

Detailed measurements have been made for many of these sources, but how they interact and 

cause or contribute to adverse effects on acoustically oriented marine life remains poorly 

understood.

For most marine vertebrates, the production and reception of sound serves critical biological 

functions, including communication, foraging, navigation, and predator avoidance (Schusterman, 

1981; Watkins and Wartzok, 1985; Richardson et al., 1995; Tyack, 1998; Wartzok and Ketten, 1999; 

National Research Council [NRC], 2003, 2005; Clark and Ellison, 2004; Southall et al., 2007). All 

marine mammals that have been observed and studied at even a very basic level are known to 

produce sounds in a variety of inter- and intra-individual contexts, most associated with the vital life 

functions of foraging, reproduction, and survival (NRC, 2005). As described in detail in previous 

summaries of marine mammal vocalizations (Wartzok and Ketten, 1999), it is evident that different 

species groups use different frequency ranges in the sounds they typically produce, including social 

communication and (for odontocetes) echolocation sounds. These broad relationships reveal some 

general conclusions regarding the potential interference, which is driven largely by frequency 

overlap, of human noise with marine mammal vocal signals. While the frequencies of vocalizations 

do not always completely overlap with the best frequencies of species-typical hearing, these 

comparisons reveal a greater potential for interference between low-frequency shipping and seismic 

survey noise and low-frequency calls of mysticetes than with the moderate to very high frequencies 

(ultrasonic) produced by odontocetes (dolphins and porpoises).

Odontocetes have developed sophisticated biosonar capabilities involving high-frequency 

(ultrasonic) impulsive clicks to feed and navigate (Au, 1993) and use a variety of whistles and other 

calls to communicate in social interactions. These animals make sounds across some of the widest 

frequency bands that have been measured in any animal group. Communicative sounds generally 

range from a few hundreds of hertz to several tens of kilohertz, but echolocation clicks can extend 

above 100 kilohertz (kHz).
Gulf of Mexico G&G Activities Programmatic EIS H-3 

Mysticetes have developed moderate to long-range communication capabilities for 

reproductive and social interactions and to orient themselves in the underwater world (Clark, 1990; 

Popper and Edds-Walton, 1997). These whales generally produce low-frequency sounds in the tens 

of hertz to several kilohertz band, with a few signals extending above 10 kHz, most notably in 

humpback whales (Megaptera novaeangliae) (Au et al., 2006).

Other non-cetacean marine mammals, including manatees (sirenians) and pinnipeds, make 

and listen to sounds for a variety of communicative and spatial orientation functions, but like the 

large whales, they appear to lack specialized echolocation capabilities (Schusterman, 1981; Wartzok 

and Ketten, 1999; Schusterman et al., 2000; Nowacek et al., 2003). These sounds can extend 

above those used by mysticetes but occur over a narrower frequency band than those used by 

odontocetes and are from approximately 100 hertz (Hz) to several tens of kilohertz.

3 HEARING IN MARINE MAMMALS

Hearing has been measured using behavioral and electrophysiological methods in 

approximately 25 percent of the known marine mammal species, although with a disproportional 

representation of species commonly found in captivity, and some entire groups (e.g., mysticetes) 

remain untested. For detailed reviews, refer to Southall et al. (2007), Mooney et al. (2012), and 

Reichmuth et al. (2013); key subsequent findings are discussed here. The focus of this appendix is 

on marine mammal hearing, but other marine vertebrates can be affected by human sounds as well. 

For a discussion of hearing and the effects of noise on sea turtle hearing, refer to Appendix I. For a 

discussion of hearing and the effects of noise on fish hearing, refer to Appendix J. 

In terms of the physical morphology of hearing structures for the primary taxa of concern in 

the GOM (cetaceans), a detailed review is given in Mooney et al. (2012). Broadly speaking, 

cetacean ears include many of the same features present in terrestrial mammals, including an 

external opening (outer ear); a tympanic membrane, Eustacian tube, and ossicles (middle ear 

elements); and a cochlea and semicircular canals (inner ear). There are clear differences, however, 

including the fact that the outer ear does not include an external ear appendage (pinna) and the 

auditory meatus (ear canal) is an elongated and mostly collapsed structure winding through the 

tissues of the head. The bony portions of the ear are extremely dense and are not as directly 

integrated into the skull as in terrestrial mammals. The exact pathways of sound into the cochlea 

are not completely understand and may differ among species and sound frequencies. However, for 

some species (and especially odontocetes that are the primary focus here), there are specialized 

fats present in the lower jaw and modifications of the bony structures that appear to provide a sound 

transduction path via a fundamentally different route that the conventional external to middle to inner 

ear path common in terrestrial mammals (refer to Mooney et al. [2012] for a review). These auditory 

conduction pathways (first proposed by Norris [1964] for dolphins) have been fairly well studied 

recently in other odontocetes and appear to be important if not the primary sound transmission 

pathways for these species; the extent to which these specializations extend to mysticetes is an area 

of current research, although there are some similarities known. Most of the structures of the inner 

ear (within the cochlea) for transducing sound into neural signals are common to terrestrial 
H-4 Marine Mammal Hearing and Sensitivity to Acoustic Impacts

mammals; the cochlea is in fact one of the most conserved structures across all mammals. 

However, there are known differences across taxa, including relatively large and limber basilar 

membranes supporting the sensory cells in low-frequency cetaceans (mysticetes) and narrower and 

stiffer basilar membranes in the mid- and high-frequency cetaceans (odontocetes).

In terms of measuring hearing capabilities directly, auditory sensitivity generally is quantified 

by determining the quietest possible sound that is detectable by an animal (via a behavioral 

response or by quantifying an electrical response) on some signal presentations. By testing such 

responses across a range of frequencies, a measure of the animal’s overall hearing capability 

(typically called an “audiogram”) may be obtained; an example is given in Figure H-1. 

Figure H-1. Example of a Hearing Profile, or Audiogram, for Two Pygmy Killer 

Whales (Feresa attenuata) Using an Electrophysiological Measurement 

Technique (including measurements of background noise) (From: 

Montie et al., 2011).

Where detection threshold levels are lower, hearing sensitivity is greater (i.e., the animal can 

hear better at frequencies where detection thresholds are lower), and vice versa. This sensitivity 

usually follows a U-shaped curve with regions of relatively good sensitivity at the bottom of the 

curve, and sensitivity is greatly reduced in regions above and below. The region of lowest overall 

average hearing is called the range of best hearing sensitivity. Similarly, the region where hearing 

thresholds are within some range from the lowest overall threshold (e.g., 80 decibels [dB] in Southall 

et al. [2007]) is often referred to as the overall range of functional hearing.
Gulf of Mexico G&G Activities Programmatic EIS H-5 

Given the available direct measurements of hearing (such as those used to create 

audiograms, as shown in Figure H-1), the extrapolations based on taxonomy, and the predictions 

based on auditory morphology, vocalizations, or behavior, it is clear that not all marine mammals 

have equal hearing frequency ranges or best hearing sensitivity (Richardson et al., 1995; Wartzok 

and Ketten, 1999; Southall et al., 2007). This is particularly true within the odontocetes, which are 

the primary focus here given their relatively common occurrence in the GOM (refer to Mooney et al., 

2012).

Most marine mammals have measured or estimated (in the case of mysticetes) functional 

hearing capabilities in frequency ranges that are similar to where their vocalizations occur (Figure 

H-2). However, for some species, there can be substantial differences in auditory capabilities 

relative to vocal parameters (Ladich and Yan, 1998); specifically, hearing may occur over broader 

ranges than those associated with species-typical vocalizations (Luther and Wiley, 2009). This can 

be important as vocal frequency ranges may be particularly important with regard to potential 

interference of communication from noise (masking), whereas hearing sensitivity is an important 

consideration with regard to direct auditory impacts such as temporary or permanent threshold shift 

(TTS or PTS, respectively).

Figure H-2. Measured or Estimated Functional Hearing Ranges for Different Marine Mammal 

Groups Shown Relative to Various Human Noise Sources.

While vocalizations and functional hearing for marine mammals as a whole cover a wide 

frequency band (refer to Southall et al., 2007; Mooney et al., 2012; Reichmuth et al., 2013), 

mysticetes likely hear into very low frequencies, while odontocetes hear over a very broad range, 

extending well into the ultrasonic (for humans) range. Specific hearing characteristics for different 

marine mammal groups are described in the following sections.
H-6 Marine Mammal Hearing and Sensitivity to Acoustic Impacts

3.1 HEARING IN MYSTICETES

Because of the lack of captive subjects and logistical challenges of bringing experimental 

subjects into the laboratory, direct measurements of hearing in mysticetes are unavailable, although 

there was an unsuccessful attempt to directly measure hearing in a stranded gray whale 

(Eschrichtius robustus) calf by Ridgway and Carder (2001). Consequently, hearing in mysticetes is 

estimated based on other means such as vocalizations (Wartzok and Ketten, 1999), anatomy 

(Houser et al., 2001; Parks et al., 2007; Tubelli et al., 2012a), behavioral responses to sound 

(Frankel, 2005; Reichmuth, 2007), and nominal natural background noise conditions in the likely 

frequency ranges of hearing (Clark and Ellison, 2004).

The combined information from these and other sources strongly suggests that mysticetes 

are likely most sensitive to sound from tens of hertz to approximately 10 kHz. However, humpback 

whales produce sounds with harmonics extending above 24 kHz (Au et al., 2006). Additionally, 

Ketten et al. (2007), Ketten and Mountain (2009), and Tubelli et al. (2012a,b) suggested, based on 

anatomical data, that some mysticetes could hear frequencies up to 30 kHz. Southall et al. (2007) 

estimated the lower and upper frequencies for functional hearing in mysticetes, collectively, to be 

7 Hz and 22 kHz, respectively; however, based on the previous information, this may be a slight 

underestimate on the high-frequency cutoff. Nevertheless, the cited studies support the conclusion 

that mysticetes operate primarily in the very low- and low-frequency ranges.

3.2 HEARING IN ODONTOCETES

Because of the presence of specialized high-frequency biosonar and lower frequency 

communication systems in odontocetes (including dolphins and porpoises), it is almost certain that 

they hear over an extremely wide frequency range, spanning 12 octaves in some species. Hearing 

has been directly measured in controlled conditions with behavioral or electrophysiological 

techniques for more than a dozen odontocete species (refer to Mooney et al., 2012). Southall et al. 

(2007) reviewed the available literature and (like Wartzok and Ketten [1999]) identified two functional 

hearing groups within the odontocetes, which they referred to as mid-frequency cetaceans (with 

functional hearing between 150 Hz and 160 kHz) and high-frequency cetaceans (functional hearing 

estimated between 200 Hz and 180 kHz).

Subsequent to the Southall et al. (2007) publication, additional data have been obtained on a 

number of species that had been tested previously, including bottlenose dolphin (Tursiops truncatus) 

(Popov et al., 2007; Houser et al., 2008) and harbor porpoise (Phocoena phocoena) (Kastelein et al., 

2012a). Additionally, direct behavioral measurements, electrophysiological measurements, or 

anatomical modeling results have been obtained for a number of new species, including whitebeaked dolphin (Lagenorhynchus albirostris) (Nachtigall et al., 2008), Cuvier’s beaked whale 

(Ziphius cavirostris) (Cranford et al., 2008a,b), Gervais’ beaked whale (Mesolodon europaeus) 

(Finneran et al., 2009), long-finned pilot whale (Globicephala melas) (Pacini et al., 2010), shortfinned pilot whale (Globicephala macroorhynchus) (Schlundt et al., 2011), Blainville’s beaked whale 

(Mesoplodon densirostris) (Pacini et al., 2011), false killer whale (Pseudorca crassidens) (Montie 

et al., 2011), and Indo-Pacific humpback dolphin (Sousa chinensis) (Li et al., 2011). While there are 
Gulf of Mexico G&G Activities Programmatic EIS H-7 

slight species-specific differences, the combined results expand the overall understanding of 

cetacean hearing and suggest that these additional species have basic hearing ranges and 

functional capabilities similar to those of other cetaceans. These and other studies have contributed 

to an increased understanding of hearing in odontocetes, but they are fundamentally consistent with 

the Southall et al. (2007) assessment for these species in terms of the broad range and highfrequency extension of functional hearing in odontocetes.

3.3 HEARING IN SIRENIANS (MANATEES) 

Hearing has been tested in terms of absolute and masked hearing capabilities in the 

sirenians that occur in the GOM, which are West Indian manatees (Trichechus manatus) (Gerstein 

et al., 1999; Mann et al., 2005; Gaspard et al., 2012). The combined data suggest that they have 

hearing capabilities similar to phocid seals except perhaps at the lowest frequencies, with functional 

hearing between approximately 250 Hz and 80 kHz. Based on these data, the extrapolation of data 

from some pinnipeds (phocid seals) to manatees, where information is lacking, would seem 

reasonable. This is particularly important in terms of the assessment of potential noise effects on 

hearing because there is little direct data for manatees but a comparatively larger amount of data for 

seals. Thus, pinnipeds are discussed here in the context of extrapolating results to manatees 

despite almost exclusively not occurring in the GOM.

Pinnipeds are amphibious mammals and have functional hearing above and below water, 

although they have broader functional hearing ranges in water (refer to Kastak and Schusterman 

[1998] for a more detailed discussion). Direct measurements of hearing using behavioral and 

electrophysiological methods have been obtained in nearly 10 different species of seals and sea 

lions (Southall et al., 2007; Mulsow and Reichmuth, 2010; Mulsow et al., 2011; Reichmuth et al., 

2013). Southall et al. (2007) estimated functional hearing across all pinnipeds as extending between 

75 Hz and 75 kHz underwater and between 75 Hz and 30 kHz in air. However, they also noted that 

there appears to be a segregation in functional hearing within pinniped taxa, as there is with 

odontocetes, with phocids (seals lacking external ear pinnae that are less mobile on land, such as 

harbor seals [Phoca vitulina]) extending to much higher frequencies, especially in water, than 

otariids (sea lions and fur seals that have distinct external ear pinnae and are more agile on land). 

This would be a logical additional segregation in terms of functional hearing within marine mammals, 

as proposed by the National Oceanic and Atmospheric Administration (USDOC, NOAA, 2013) in 

expanding on the Southall et al. (2007) functional hearing groups. As described previously, 

manatees appear most similar to phocid seals, and the effects of noise on their hearing is 

considered based on this extrapolation.

3.4 MARINE MAMMAL HEARING WEIGHTING FUNCTIONS

Because marine mammals, like most animals, do not hear equally well at all frequencies, 

frequency-weighting functions are often used as a means of quantitatively assessing and accounting

for differential frequency responses for different species. The functions are commonly applied in 

calculating the potential for the detection of a sound at a specific frequency and for assessing 

potential noise impacts. The frequency-weighting functions derived by Southall et al. (2007), as well 
H-8 Marine Mammal Hearing and Sensitivity to Acoustic Impacts

as subsequent proposed variants, are described briefly here (Finneran and Jenkins, 2012; USDOC, 

NOAA, 2013); newer versions of frequency-weighting functions’ (Finneran, 2015) and NOAA’s 

proposed acoustic guidelines (USDOC, NOAA, 2015) were released and are in review, but they 

were not available for analysis in this Programmatic Environmental Impact Statement (EIS). Several 

recent iterations of noise exposure criteria are discussed in greater detail in Section 4. As noted 

previously, subsequent results largely support the segregation of marine mammals into these 

general functional hearing categories with some minor modifications, including the extrapolation of 

results from seals to manatees.

Table H-1 shows the five functional hearing groups and estimated functional hearing ranges 

for marine mammals proposed in the Southall et al. (2007) noise exposure criteria. Using the 

estimated lower and upper frequency cut-off limits as 6-dB down points on an exponential roll-off for 

the frequency-weighting functions (as is done in human C-weighting), Southall et al. (2007) 

developed frequency-weighting filters for each of the five functional hearing groups as shown in 

Figure H-3. 

Table H-1. Marine Mammal Functional Hearing Groups and Estimated Functional Hearing Ranges 

Proposed by Southall et al. (2007). 

Functional 

Hearing Group

Estimated 

Auditory 

Bandwidth

Genera Represented

Number of 

Species/ 

Subspecies

FrequencyWeighting 

Network

Low-frequency 

(lf) cetaceans 7 Hz to 22 kHz* Balaena, Caperea, Eschrichtius, 

Megaptera, Balaenoptera 13 Mlf

Mid-frequency 

(mf) cetaceans 150 Hz to 160 kHz

Steno, Sousa, Sotalia, Tursiops, 

Stenella, Delphinus, Lagenodelphis, 

Lagenorhynchus, Lissodelphis, 

Grampus, Peponocephala, Feresa, 

Pseudorca, Orcinus, Globicephala, 

Orcacella, Physeter, Delphinapterus, 

Monodon, Ziphius, Berardius, 

Tasmacetus, Hyperoodon, 

Mesoplodon

57 Mmf

Highfrequency (hf) 

cetaceans

200 Hz to 180 kHz

Phocoena, Neophocaena, 

Phocoenoides, Platanista, Inia, 

Kogia, Lipotes, Pontoporia, 

Cephalorhynchus

19 Mhf

Pinnipeds in 

water (pw)** 75 Hz to 75 kHz Trichecus manatus 1 Mpw

* As described in the text, more recent modeling work would suggest that the upper frequency end of 

the estimated auditory bandwidth may be slightly higher (approximately 30 kHz), at least for some 

species.

** Pinniped functional hearing values are given here for the purposes of applicability to manatees, 

given the limited data on noise impacts on manatees and general similarities in at least the 

functional hearing bandwidth between manatees and phocid seals (for which the Southall et al. 

[2007] functional hearing group for pinnipeds was based).
Gulf of Mexico G&G Activities Programmatic EIS H-9 

Figure H-3. Frequency-Weighting Functions for Cetaceans Proposed by Southall et al. (2007).

Considerable subsequent research supporting modifications to these initial frequencyweighting functions has been conducted. Finneran and Schlundt (2011) conducted subjective equal 

loudness measurements with a bottlenose dolphin from which frequency-weighting functions were 

derived. Finneran and Schlundt (2010, 2013) conducted frequency-specific TTS measurements that 

demonstrated a high degree of frequency-specificity in the susceptibility of dolphins to TTS. Based 

on these results, Finneran and Jenkins (2012) proposed a modification of the Southall et al. (2007) 

auditory weighting functions that represents relatively increased susceptibility to noise-induced 

threshold shifts at intermediate sound frequencies of greater hearing sensitivity. These hybrid 

functions (called Type 2 filters) were extrapolated to frequencies where data currently exist 

(Finneran and Jenkins, 2012) (Figure H-4). Tougaard et al. (2014) noted the importance of sound 

frequency in the potential effects of noise, with specific reference to relatively recent data on harbor 

porpoises. They built on earlier arguments related to the use of narrower frequency-weighting

functions than the original M-weighting functions pioneered by Southall et al. (2007). The 

considerable recent experimental hearing data clearly supports the use of narrower frequencyweighting filters and potentially additional functional hearing groups, although considerable scientific 

debate about the nature of these modifications remains.
H-10 Marine Mammal Hearing and Sensitivity to Acoustic Impacts

Figure H-4. Frequency Weighting Filters (“Type 2”) for Low-Frequency (LF), Mid-Frequency 

(MF), and High-Frequency (HF) Cetaceans Derived by Finneran and Jenkins 

(2012).

Within their draft acoustic guidelines, NOAA (USDOC, NOAA, 2013) proposed the use of the 

mid- and high-frequency cetacean weighting functions in regulatory contexts, given the supporting 

data from odontocetes described previously. These proposed functions were available at the time of 

this Programmatic EIS preparation; NOAA’s (USDOC, NOAA, 2015) modified proposed guidelines 

have further modifications that are not explicitly discussed in this appendix. Figure H-5 shows these 

frequency-weighting functions and the components derived from the Southall et al. (2007) 

M-weighting and subsequent hearing data.
Gulf of Mexico G&G Activities Programmatic EIS H-11

Figure H-5. “Merged” Auditory Filters for Mid-Frequency (MF) and High-Frequency

(HF) Cetaceans Proposed by the National Oceanic and Atmospheric 

Administration (From: USDOC, NOAA, 2013).

However, NOAA (USDOC, NOAA, 2013) took a different approach regarding low-frequency 

cetacean weighting functions, given the considerable uncertainty regarding all aspects of hearing in 

these taxa. Because there are no direct measurements of hearing in mysticetes, this function was 

based on auditory anatomy and characteristics of vocalization parameters for different mysticete 

species (Figure H-6).

Figure H-6. Modified Auditory Filters for Low-Frequency (LF) Cetaceans 

Proposed by the National Oceanic and Atmospheric Administration 

(From: USDOC, NOAA, 2013).
H-12 Marine Mammal Hearing and Sensitivity to Acoustic Impacts

Additionally, NOAA (USDOC, NOAA, 2013) proposed a segregation of the Southall et al. 

(2007) functional hearing groups within pinnipeds, separating phocids (seals) from otariids (sea lions 

and fur seals) (Figure H-7). While there are more limited equal loudness and frequency-specific 

TTS data for pinnipeds than those now available for dolphins, NOAA (USDOC, NOAA, 2013) 

proposed retaining the M-weighting concept from Southall et al. (2007) and also segregating the two 

groups based on what is known about frequency ranges of hearing. Given the extrapolation 

suggested from seals to manatees, the phocid weighting function would be the more appropriate 

based on information currently available.

The scientific understanding of hearing and perceptual processes relevant to deriving sound 

frequency-weighting functions are areas of active research and deliberation. There are clear 

functional differences in hearing sensitivity across broad groups of marine mammals, but there is 

incomplete information with which to unequivocally derive some of these functions. More data are 

available for odontocetes than for mysticetes or sirenians. The series of quantitative methods 

derived to express these differences in terms of the relative perception and sensitivity of different 

marine mammal groups to noise exposure reflects some of the progress made in this challenging 

area, including approaches proposed by NOAA (USDOC, NOAA, 2013).

Figure H-7. Auditory Filters for Seals (Phocids) and Sea Lions (Otariids) Proposed 

by the National Oceanic and Atmospheric Administration (From: 

USDOC, NOAA, 2013).

4 EFFECTS OF NOISE ON MARINE MAMMAL HEARING AND 

BEHAVIOR 

Around loud noise sources or where there is an overlap between more distant sources and 

the frequencies of sound used by marine mammals, noise may interfere with important biological 

functions. Although there may be no effect of exposure, noise (natural or anthropogenic) can affect 
Gulf of Mexico G&G Activities Programmatic EIS H-13

marine life in various ways, inducing alteration of behavior, reduction of acoustic communication, 

reduced navigation or orientation capability, temporary or permanent damage to the auditory or other 

systems, and in extreme cases, habitat avoidance or even death (Richardson et al., 1995; NRC, 

2003, 2005; Nowacek et al., 2007; Southall et al., 2007). Noise impacts may be synergistic with 

those of other human stressors. While determining the biological significance of noise exposure 

impacts remains challenging (refer to NRC [2005] and Southall et al. [2007, 2009]), significant 

strides have been made in quantifying the effects of noise on marine mammals. The potential and 

measured effects of noise on physiology, hearing, and behavior are reviewed here, with attention to 

findings subsequent to the Southall et al. (2007) review and assessment of noise impacts on marine 

mammals.

4.1 EFFECTS OF NOISE ON MARINE MAMMAL PHYSIOLOGY

Noise can result in direct physiological impacts on marine mammals, even in cases where 

hearing impacts or behavioral responses may be lacking. These may include stress responses and 

direct physical injury (e.g., tissue damage). Stress responses can range from an acute startle 

response to more chronic effects and can vary widely across individuals in type and magnitude

according to a host of factors (refer to Busch and Hayward [2009] for a recent review). Stress 

reactions in humans and other vertebrates include various physiological changes to pulmonary, 

respiratory, cardiac, metabolic, neuro-endocrine, immune, and reproductive functions; these can 

vary from relatively benign to very detrimental or fatal in some conditions.

Direct measurements of physical stress responses in marine mammals from sound exposure 

are relatively limited but increasing (Thomas et al., 1990; Miksis et al., 2001; Romano et al., 2004; 

Rolland et al., 2012). A greater amount of data is available for terrestrial mammals and other 

animals and, in some cases, may be useful where direct information is lacking (Wright et al., 

2007a,b). The available literature for marine mammals indicates endocrine secretions of 

glucocorticoids and altered cardiovascular function following relatively intense noise exposure in 

some cases.

Direct physical injury can occur from exposure to high levels of sound or, more commonly, to 

shock wave pulses associated with high-intensity events such as explosions. These pulses are 

typically short peak pressures that may damage internal organs or air-filled body cavities such as 

lungs (Yelverton et al., 1973; Goertner, 1982; Young, 1991). Data on direct physical injury are 

limited to anecdotal or forensic investigations after accidental events because ethical considerations 

typically have limited direct empirical methods to measure such impacts in marine mammals. 

However, such observations (e.g., Todd et al., 1996) and modeling based on impact data for the 

human vestibular system, as well as other organs (e.g., lungs), for underwater sound exposures 

(Cudahy and Ellison, 2002) suggest that marine mammals could be susceptible to direct physical 

injury to particular organ systems and tissues following intense exposure, particularly where high 

particle motion events occur.
H-14 Marine Mammal Hearing and Sensitivity to Acoustic Impacts

Other forms of physiological damage that have been investigated and in some cases seen in 

marine mammals include the formation of gas bubble lesions and fat emboli similar to those 

associated with human decompression sickness; these have been observed in beaked whale 

species that stranded near naval mid-frequency sonar training exercises (Jepson et al., 2003; 

Fernández et al., 2005). Currently, these tissue impacts are thought to result from a behavioral 

response that changes diving patterns in some way and subsequently causes lesion/emboli 

formation, rather than as a direct physical effect of sound exposure (Cox et al., 2006; Zimmer and 

Tyack, 2007). These kinds of emboli have not been definitively shown in other marine mammals 

exposed to natural or anthropogenic sound to date.

4.2 EFFECTS OF NOISE ON MARINE MAMMAL HEARING

Much of the scientific and regulatory attention on the impacts of noise on marine life has 

centered on the issue of how sound affects hearing in marine mammals. While the available 

literature on the underlying issues remains quite limited compared to that available for terrestrial 

species, considerable progress has been made in these areas, particularly in the last decade, for 

marine mammals. There have been numerous reviews of the available data on these issues 

(Richardson et al., 1995; Wartzok and Ketten, 1999; NRC, 2003, 2005), the most recent 

comprehensive assessment being the Southall et al. (2007) review and application of the available 

science in the context of proposing noise exposure criteria. A summary description of temporary 

and permanent hearing losses and auditory masking is provided here, with reference to these 

reviews and some discussion of more recent literature on each issue (refer also to Finneran and 

Jenkins, 2012; USDOC, NOAA, 2013).

4.2.1 Temporary and Permanent Threshold Shift in Marine Mammals

Noise-induced threshold shifts are increases in hearing thresholds within a certain frequency 

range (Yost, 2000). Following exposure, the magnitude of the threshold shift normally decreases 

over time after cessation of noise exposure. Threshold shifts can be temporary (TTS) or permanent 

(PTS) and can consist of a variety of physiological, chemical, and neural phenomena that may or 

may not recover following noise exposure. Several important factors relate to the type and 

magnitude of hearing loss, including exposure level, frequency content, duration, and temporal 

pattern of exposure. A range of mechanical stress or damage (e.g., supporting cell structure fatigue) 

and metabolic (e.g., inner ear hair cell metabolism, such as energy production, protein synthesis, 

and ion transport) processes within the auditory system underlie TTS and PTS (Kryter, 1994; Ward, 

1997; Yost, 2000). Intense sound exposure often results in changes in mechanical processes, 

whereas prolonged exposure typically results in metabolic changes (e.g., Saunders et al., 1985).

The TTS is a relatively short-term reversible loss of hearing, often resulting from cellular 

fatigue and metabolic changes. For marine mammal TTS studies, a threshold shift of 6 dB is 

commonly considered the minimum threshold shift that is statistically larger than typical day-to-day

or session-to-session variation in a subject’s baseline threshold at a particular frequency (Kastak 

et al., 2005; as in Southall et al., 2007). Conversely, PTS is an irreversible loss of hearing 

(permanent damage) that commonly results from inner ear hair cell loss or severe damage to 
Gulf of Mexico G&G Activities Programmatic EIS H-15

auditory tissues (e.g., Saunders et al., 1985; Henderson et al., 2008). Southall et al. (2007) 

reviewed the available terrestrial literature and concluded that 40 dB of TTS was a reasonable and 

conservative approximation of PTS onset for marine mammals (refer to Henderson et al. [2008] for a 

consideration of the human literature in this regard). The PTS data typically are not collected in 

marine mammals owing to ethical and permitting considerations, but an earlier TTS experiment was 

found to unintentionally induce PTS in a harbor seal (Kastak et al., 2008). In this experiment, which 

involved exposure to tonal fatiguing noise of increasing exposure level, initial experiments failed to 

induce measurable TTS on multiple trials, but following subsequent exposure at similar levels, an 

initially large TTS of at least 30 dB was measured and decreased over a period of months but 

remained a measurable PTS at the exposure frequency of approximately 5 dB for years following the 

experiment.

The TTS data on different exposures with impulsive and continuous noise have been 

obtained in four odontocetes, including two mid-frequency cetaceans (bottlenose dolphin and beluga 

whale [Delphinapterus leucas]) and two high-frequency cetaceans (harbor porpoise and Yangtze 

finless porpoise [Neophocaena asiaeorientalis]). Similar measurements have been obtained for 

three pinniped species (two phocids: harbor seal and elephant seal [Mirounga lionina]; one otariid: 

California sea lion); these are considered here relative to potential noise effects on manatees in the 

GOM. Much of the data was reviewed in detail by Southall et al. (2007), but there are some notable 

new data that change some of the conclusions reached in that assessment (Finneran, 2013; 

USDOC, NOAA, 2013). In general, it appears that marine mammal auditory systems for most 

species are relatively resilient to noise exposure and that relatively intense sounds are required to 

cause TTS (Finneran and Schlundt, 2010, 2013) and, given some simplifying assumptions to 

extrapolate to 40 dB TTS, PTS as well. However, there are clear differences in the sound exposure 

types and noise exposure frequency as well as between species. As in terrestrial mammals, marine 

mammals experience TTS at relatively lower onset levels for impulsive noise than for non-impulsive 

noise. The relative TTS onset levels for different marine mammal groups from the Southall et al. 

(2007) criteria are discussed in the following section regarding exposure criteria. However, some 

modifications to these criteria are now appropriate based on subsequent information.

New data are available demonstrating much lower (>20 dB) TTS onset exposure levels for 

harbor porpoises exposed to impulse noise (airguns) than has been measured in other odontocetes 

(Lucke et al., 2009). These data are significant because they are the only TTS measurements 

available for any individual in the high-frequency cetacean functional hearing group for the kinds of 

impulse noise involved in seismic surveys. Additional measurements with harbor porpoise using 

pile-driving noise (Kastelein et al., 2012b) and non-impulse bands of noise for harbor porpoises 

(Kastelein et al., 2013a) and finless porpoises (Popov et al., 2011a,b, 2013) similarly indicate much 

lower TTS onset in high-frequency cetaceans. This argues for use of direct measurements for TTS 

onset in these animals rather than using the extrapolated (though much more expansive) data for 

mid-frequency cetaceans in predicting auditory fatigue (refer also to Tougaard et al., 2014).

Several studies have contributed to an expanded understanding of TTS onset and growth at 

a range of sound frequencies in odontocetes and pinnipeds. Mooney et al. (2009a,b) demonstrated 
H-16 Marine Mammal Hearing and Sensitivity to Acoustic Impacts

conditions where equal energy assumptions about exposure of different durations and levels fail to 

accurately predict TTS onset and growth. Finneran and Schlundt (2013) provided additional 

measurements across a wide range of frequencies (3 to 80 kHz) for examining relationships 

between frequency and growth rates. Kastelein et al. (2012b,c, 2013b) provide TTS onset data for 

several sound types, including impulse noise for harbor seals; these are generally consistent with 

the conclusions derived by Southall et al. (2007) from the earlier pinniped data from Kastak et al. 

(1998, 2001, 2005). Finneran and Schlundt (2010; 2013) and Finneran et al. (2010a,b) provided 

additional TTS data for bottlenose dolphins, demonstrating a greater sensitivity (10 to 20 dB) to 

noise exposure (lower absolute TTS onset levels) and a more rapid growth of TTS with increasing 

noise exposure level at higher frequencies within their range of best sensitivity than had been tested 

when the Southall et al. (2007) criteria were published. These data suggest that the exposure level 

relative to the subject’s absolute hearing sensitivity (referred to as the sensation level) is particularly 

important in determining TTS onset. They also suggest that exposure levels in the region of best 

hearing sensitivity should be used as generic TTS onset values against which frequency-weighting

functions could be applied to account for frequency-specific hearing. The importance of frequency 

relationships between noise sources and potential high-level auditory effects such as TTS-onset has 

been demonstrated in odontocetes; the recent demonstration of very high absolute received levels 

with little or no TTS measured low-frequency noise from a seismic airgun in odontocetes that hear 

poorly at these frequencies (Finneran et al., 2015). These overall findings for odontocetes provide 

some insight into potential effects for mysticetes because no mysticete TTS values are or, for the 

foreseeable future, will be available). However, caution should be taken in directly applying absolute 

exposure levels for TTS onset from one group to another where large differences in frequencyspecific hearing likely exist.

4.2.2 Auditory Masking

In addition to potential effects on hearing from relatively high levels of sound exposure that 

would occur relatively close to anthropogenic sound sources in the field, noise interference 

(“masking”) effects can, and likely do, occur over much greater distances from real sound sources. 

Noise can affect hearing and partially or completely reduce an individual’s ability to effectively 

communicate; detect important predator, prey, and conspecific signals; and detect important 

environmental features associated with spatial orientation (refer to Clark et al. [2009] for a review). 

Spectral, temporal, and spatial overlap between the masking noise and the sender/receiver 

determines the extent of interference; the greater the spectral and temporal overlap, the greater the 

potential for masking.

Southall et al. (2007) considered auditory masking issues and realized the much greater 

relative areas over which this phenomena could occur relative to TTS and PTS, but they did not 

propose explicit exposure criteria for marine mammals, owing in part to the very divergent conditions 

in which masking can occur and a lack of clear understanding about defining an “onset” for masking 

that would be statistically definable and biologically meaningful. Largely for the same reasons,

masking effects generally have been considered only qualitatively in planning of activities and 

regulatory decisions related to noise impacts. Subsequent data have demonstrated vocal 
Gulf of Mexico G&G Activities Programmatic EIS H-17

modifications in marine mammals exposed to noise that are presumably the result of anthropogenic 

masking noise (Holt et al., 2009). Additionally, Clark et al. (2009) provided a quantitative means of 

determining the relative loss of acoustic communication range for marine mammals using specific 

calls in conditions where they are exposed to specific anthropogenic noise sources. While Clark 

et al. (2009) included a metric for individual processing gain that accounts for the individual ability to 

segregate signals from masking noise based on spatial differences between signals and noise as 

well as other cues, more recent measurements of masked hearing in various kinds of masking noise, 

including co-modulated noise, suggest that this processing gain may be considerably greater than 

previously considered (Branstetter and Finneran, 2008; Branstetter et al., 2013).

There is particular concern that low-frequency anthropogenic noise may mask 

communication in mysticetes, which can communicate over long distances and within the same 

frequency band (Payne and Webb, 1971; Clark et al., 2009). An example of mysticete calling 

behavior that may be increasingly masked by nearby ship noise is shown in Figure H-8. 

Figure H-8. Time Series Plot Showing a Calling Blue Whale (Balaenoptera 

musculus) and the Increasing Noise (and masking) in the Same 

Low-Frequency Band from an Approaching Vessel (Image courtesy of 

C. Clark).

4.3 EFFECTS OF NOISE ON MARINE MAMMAL BEHAVIOR

Behavioral responses to sound are highly variable and critically depend on the context of 

sound exposure, as much or more than the level-duration-frequency characteristics that determine 

the probability of auditory effects (Wartzok et al., 2004; Southall et al., 2007). There is a wide range 

of possible behavioral responses to sound exposure, given that the sound is audible to the particular 

animal, including the following, in approximate order of increasing severity but decreasing likelihood:

5 10 15 20

time, minutes

20

40

60

80

100

120

0

frequency, Hz

Blue

Whale
H-18 Marine Mammal Hearing and Sensitivity to Acoustic Impacts

• none observable – animals can become less sensitive over repeated exposures 

(habituation) and this does not preclude the occurrence of physiological stress 

responses;

• looking or increased alertness;

• minor behavioral responses such as vocal modifications associated with 

masking;

• cessation of feeding or social interactions;

• temporary avoidance behavior (emerging as one of the more common 

responses);

• modification of group structure or activity state;

• habitat abandonment; and

• injury or death via direct response or possibly exacerbated by physiological 

factors. 

These effects clearly have differing probabilities to affect marine mammal vital rates (NRC, 

2005), but it has proven (and remains) exceedingly difficult to establish a generally accepted 

definition and criterion for biologically meaningful behavioral disturbance. Assessing the severity of 

behavioral effects of anthropogenic sound exposure on marine mammals presents unique 

challenges associated with the inherent complexity of behavioral responses and the contextual 

factors affecting them, within and between individuals and species. Severity of responses depends 

on characteristics of the sound source (e.g., moving or stationary, number and spatial distribution of 

sound source[s], similarity to predator sounds, and other relevant factors) (Richardson et al., 1995; 

NRC, 2005; Southall et al., 2007; Wirsing et al., 2008; Bejder et al., 2009; Barber et al., 2010). 

Ellison et al. (2012) reviewed these and other studies demonstrating the context-specificity of marine 

mammal behavioral responses and proposed a new context-based approach to the assessment of 

behavioral responses in marine mammals.

Southall et al. (2007) reviewed the considerable amount of available literature on the effects 

of noise on marine mammal hearing but (other than for single impulse exposures where TTS onset 

was used as a threshold value for behavioral disturbance) did not find a single metric or identifiable 

exposure level that was broadly applicable as a benchmark for behavioral effects. Several general 

observations were made, including that many of the responses observed across taxa were 

temporary avoidance behavior. Additionally, certain species (e.g., harbor porpoises, beaked whales) 

appear to be categorically more sensitive to noise than other species observed, and certain 

behavioral states (e.g., migrating) can make species such as bowhead whales (Balaena mysticetus) 

more sensitive to exposure. Subsequent data have demonstrated and quantified behavioral 

responses of various species, including some of the Endangered Species Act-listed marine 

mammals being considered in this Programmatic EIS, to seismic exploration using airguns (Weir, 

2008a,b; Miller et al., 2009). Additional data have demonstrated behavioral responses of cetaceans 
Gulf of Mexico G&G Activities Programmatic EIS H-19

to vessels associated with whale-watching activities (e.g., Bejder and Lusseau, 2008; Visser et al., 

2010), seismic surveys (Thompson et al., 2013), mid-frequency military sonar with blue whales 

(Goldbogen et al., 2013), and to the construction of offshore energy installations (Tougaard et al., 

2009, 2013; Thompson et al., 2010; Dähne et al., 2013). Additionally, a recent report (Southall et al., 

2013) concluded that multibeam echosounders used in offshore energy development projects may 

have played a role in a mass stranding of melon-headed whales, most likely by affecting their 

behavior. Finally, there has been considerable new information, using both controlled exposure 

experiments and opportunistic observations of anthropogenic noise source operations, on the 

behavioral responses of particularly sensitive marine mammals, including harbor porpoises 

(Kastelein et al., 2008a,b, 2012b; Gilles et al., 2009) and beaked whales (Caretta et al., 2008; 

McCarthy et al., 2011; Southall et al., 2011; Tyack et al., 2011; DeRuiter et al., 2013). The findings 

of these studies support and amplify the conclusions of Southall et al. (2007) that these are 

particularly sensitive species, although it remains unclear whether any additional species should be 

added to this general category.

5 MARINE MAMMAL NOISE EXPOSURE CRITERIA

Beginning in the 1980s with regulations on oil and gas exploration, sound-producing entities 

and regulatory agencies have been grappling with how to quantitatively predict and operationally 

mitigate the effects of human noise from industrial activities on marine life. While the marine noise 

issue is an increasingly global one, many of the developments on exposure criteria for marine 

mammals have involved U.S. regulatory processes.

In June 1997, the High Energy Seismic Survey (HESS, 1999) team convened a panel of 

experts to assess existing data on marine mammals exposed to seismic pulses and to predict 

exposures at which physical injury could occur. With the limited available data at that time, exposure 

to airgun pulses with received levels above 180 dB re 1 μPa (decibels relative to 1 micropascal) (root 

mean square [rms] – averaged over the pulse duration) was determined to have a high potential for 

“serious behavioral, physiological, and hearing effects.”

Based on the HESS (1999) panel conclusions, the National Marine Fisheries Service 

(NMFS) established a 180-dBrms (received level) threshold criterion for injury from impulse sound 

and continuous (non-impulsive) sound exposure for cetaceans and a 190-dBrms threshold criterion 

for pinnipeds (Federal Register, 2003). Additionally, behavioral response criteria were developed as 

step-function (all-or-none) thresholds based solely on the rms value of received levels and have 

been used by NMFS, although not entirely consistently. Thresholds for behavioral response from 

impulse sounds are 160 dBrms (received level) for all marine mammals based on behavioral 

response data for marine mammals exposed to seismic airgun operations (Malme et al., 1983, 1984; 

Richardson et al., 1986). The threshold for behavioral response for continuous sounds has been 

120 dBrms (for some but not all sound sources) based on the results of Malme et al. (1984) and 

Richardson et al. (1990).
H-20 Marine Mammal Hearing and Sensitivity to Acoustic Impacts

These acoustic thresholds for seismic sounds and sounds other than those associated with 

U.S. Navy activities are based exclusively on dB rms measurements and the 1980s estimates of 

such levels associated with hearing impact as opposed to the direct measurements that have been 

made subsequent to establishment of the thresholds. The duration over which the rms is calculated 

can vary significantly for impulsive sounds, and the use of this metric for characterizing impulse 

noise has been questioned (Madsen et al., 2006). In addition, the duration and impulsive nature of 

the sound also determine the potential level of PTS. Therefore, thresholds based on rms values 

alone are not very predictive of the likelihood of PTS onset.

Recognizing that the available data on hearing and noise impacts were rapidly evolving and 

that a more comprehensive and scientifically robust method of assessment would be required than 

these simplistic threshold estimates, NMFS supported an expert working group to develop more 

comprehensive and current marine mammal noise exposure criteria. This process ultimately 

resulted in the Southall et al. (2007) marine mammal noise exposure criteria. Within this process, 

several important segregations were made. First, the marine mammals were segregated into 

functional hearing groups (not entirely taxonomy-based), as described previously. All cetacean 

criteria are discussed here, but the relatively low probability of occurrence of both low- and highfrequency cetacean species in the GOM is noted. Additionally, criteria for seals are discussed given 

the relevance of extrapolation to manatees given the lack of such supporting data. Second, sound 

sources were categorized into functional categories based on their acoustic and repetitive properties 

(Table H-2).

Table H-2. Sound Source Categories, Acoustic Characteristics, and Examples Proposed by Southall 

et al. (2007). 

Sound 

Type Acoustic Characteristics (at source) Examples

Single 

Pulse

Single acoustic event; >3 dB 

difference between received level 

using impulse versus equivalent 

continuous time constant

Single explosion; sonic boom; single airgun, 

watergun, pile strike, or sparker pulse; single ping of 

certain sonars, depth sounders, and pingers

Multiple 

Pulse

Multiple discrete acoustic events 

within 24 hours; >3 dB difference 

between received level using 

impulse versus equivalent 

continuous time constant

Serial explosions; sequential airgun, watergun, pile 

strikes, or sparker pulses; certain active sonar 

(IMAPS); some depth sounder signals

NonPulse

Single or multiple discrete acoustic 

events within 24 hours; <3 dB 

difference between received level 

using impulse versus equivalent 

continuous time constant

Vessel/aircraft passes; drilling; many construction or 

other industrial operations; certain sonar systems 

(LFA; tactical mid-frequency); acoustic 

harassment/deterrent devises; acoustic tomography 

sources (ATOC); some depth sounder signals

ATOC = acoustic thermometry of ocean climate; IMAPS = Integrated Marine Mammal Monitoring and 

Protection System; LFA = low-frequency active.

The potential for hearing and behavioral effects for noise exposures of these different 

categories was assessed for each of the different functional hearing groups according to a wider and 

more applicable set of acoustic exposure metrics. Using an alternate threshold such as sound 
Gulf of Mexico G&G Activities Programmatic EIS H-21

energy (sound exposure level [SEL]) that incorporates amplitude level and duration as well as peak 

sound pressure into the noise metric is considered to be more biologically realistic. Consequently, 

Southall et al. (2007) suggested SEL thresholds for TTS onset and the predicted PTS onset levels 

they estimated. As has been observed for humans (Kryter et al., 1966), recent work in marine 

mammals demonstrates that TTS onset is not perfectly correlated with received SELs either; rather, 

duration appears to have a larger impact on TTS onset than predicted by SELs, and recovery time 

between noise exposure also has an impact on the levels of TTS (Mooney et al., 2009b; Finneran 

and Schlundt, 2010). At this point, SEL remains a better metric for the prediction of injury onset than 

rms, but with some demonstrated limitations similar to those observed in predicting TTS dependence 

on sounds of different exposure level and duration in terrestrial mammals; these threshold metrics 

will need to be reevaluated regularly as new data are reported. For behavioral effects, the 

conventional rms levels for sound exposure were considered, in part because this typically is all of 

the information available regarding available studies.

5.1 DERIVATION OF TTS AND PTS CRITERIA

Southall et al. (2007) estimated PTS onset as noise exposures estimated to result in 40 dB 

of TTS for different sound types, using both a peak pressure and an SEL criterion; the SEL threshold 

is ultimately the functional criteria for most realistic exposure scenarios. For all cetacean functional 

hearing groups, estimated TTS onset levels for impulse and non-impulse noise were based on data 

obtained from a few individuals of two mid-frequency species (bottlenose dolphins and beluga 

whales). For pinnipeds, some data were available on non-impulsive noise but extrapolations to PTS 

onset for impulsive noise (such as that associated with seismic airguns) also included extrapolations 

involving data from bottlenose dolphins.

Based on data available at the time, Southall et al. (2007) proposed explicit numerical 

exposure level values for injury from sound exposure for each of the marine mammal functional 

hearing groups. Received level threshold values were determined using measured TTS onset levels 

where possible (or extrapolating them from related species where not), a series of extrapolation 

procedures to estimate the growth of TTS, and a reasonably conservative estimate of physical injury 

(40 dB TTS). For SEL values, the frequency-weighting functions described previously would be 

applied to the received sound to account for differential frequency sensitivity among the different 

marine mammal groups. The resulting thresholds for injury from sound exposure for different marine 

mammal groups, obtained via these general methods and using all available relevant data as 

proposed by Southall et al. (2007), are summarized in Table H-3. 

While the Southall et al. (2007) exposure criteria represented a major step forward in the 

assessment of potential noise effects on marine mammals, subsequent data have resulted in 

modification and re-evaluation of exposure criteria. A variety of modifications to exposure criteria 

have been proposed.

Notably, for high-frequency cetaceans (e.g., harbor porpoises), subsequent data are 

available from Lucke et al. (2009). The data indicate a lower TTS onset value in terms of SEL and 
H-22 Marine Mammal Hearing and Sensitivity to Acoustic Impacts

peak pressure. In this analysis, these directly relevant data form the basis for estimating TTS onset 

and potential for injury in harbor porpoises and other high-frequency cetaceans, rather than the 

extrapolated predictions of Southall et al. (2007); refer to also Tougaard et al. (2014). Consequently, 

a PTS onset threshold for impulse noise of 179 dB re 1 μPa2

•s is used for this functional hearing 

group, based on Lucke et al. (2009) TTS onset levels and the Southall et al. (2007) extrapolation 

procedure to PTS as proposed by Wood et al. (2012).

Table H-3. Marine Mammal Noise Exposure Criteria for Injury for Different Marine Mammal Functional 

Hearing Groups Proposed by Southall et al. (2007). 

Marine Mammal Group Sound Type

Single Pulses Multiple Pulses Non-Pulses

Low-Frequency Cetaceans Cell 1 Cell 2 Cell 3

Sound Pressure Level (flat*) 230 230 230

Sound Exposure Level (Mlf) 198 198 215

Mid-Frequency Cetaceans Cell 4 Cell 5 Cell 6

Sound Pressure Level (flat) 230 230 230

Sound Exposure Level (Mmf) 198 198 215

High-Frequency Cetaceans Cell 7 Cell 8 Cell 9

Sound Pressure Level (flat) 230 230 230

Sound Exposure Level (Mhf) 198 198 215

Pinnipeds (in water) Cell 10 Cell 11 Cell 12

Sound Pressure Level (flat) 218 218 218

Sound Exposure Level (Mpw) 186 186 203

* “Flat” for peak sound pressure level indicates no frequency-weighting is applied.

Sound pressure levels are expressed in units of dBpeak re μPa. Sound exposure levels are expressed 

in units of dB re 1 μPa2•s.

An additional consideration regards the assessment of potential auditory effects of impulse 

noise on low-frequency cetaceans (mysticetes). There are no direct measurements of TTS/PTS in 

low-frequency mysticetes because of the inability to test their hearing in the wild. Some TTS data for 

mid-frequency cetaceans in regions of best sensitivity (Finneran and Schlundt, 2010) may be

applicable when considering the appropriate TTS onset value to extrapolate to mysticetes, which are 

highly unlikely to be tested in a controlled hearing study to measure auditory fatigure. Gedamke 

et al. (2011) modeled the potential for TTS onset for mysticetes. Their model does suggest that TTS 

(and possibly PTS) onset from seismic surveys is plausible over ranges of several kilometers; 

however, the uncertainty of the inputs to the model (i.e., the extrapolations of noise impacts and 

hearing in other species), as well as individual variation, can have a large impact on the estimates, 

which must at this point be considered speculative (as the authors themselves state). In addition, 

much of the cumulative SEL is due to the loudest airgun pulses when the animal is closest to the 

airgun array. In the absence of direct measurements of hearing or noise impacts in any mysticete 

species, subsequent data on TTS in other cetaceans calls into question the hearing group 

extrapolation proposed by Southall et al. (2007). Specifically, Finneran and Schlundt (2010, 2013) 

recently demonstrated greater sensitivity to non-impulse noise exposure for mid-frequency

cetaceans at higher frequencies (within their region of best sensitivity) than had been tested when 
Gulf of Mexico G&G Activities Programmatic EIS H-23

the Southall et al. (2007) criteria were published. Given the measurements of lower TTS onset 

values in the region of best hearing sensitivity for mid-frequency cetaceans and the low-frequency

nature of seismic airgun impulses, a more conservative extrapolation of results to low-frequency

cetaceans was considered justified (refer to Southall et al., 2007). For reasons relating to the much 

higher natural ambient background levels at low frequencies and presumed adaptations in basic 

hearing capabilities of these species than for other cetacean species (Wartzok and Ketten, 1999), 

rather than a direct application of the high-frequency cetacean TTS onset values, a more 

conservative extrapolation of the mid-frequency TTS onset data for impulse noise than that 

proposed by Southall et al. (2007) was suggested by Wood et al. (2012). In this assessment, given 

the results from odontocetes and a reasonable interpretation that such frequency-specific effects 

would likely occur at low frequencies for mysticetes, a modification of the PTS onset level was 

derived by subtracting 6 dB (half the magnitude in terms of sound pressure) from the original 

Southall et al. (2007) level, for a resulting PTS onset threshold for mysticetes of 192 dB re 1 μPa2

•s. 

Newer TTS measurements in mid- and high-frequency cetaceans (Finneran and Schlundt, 

2010; Finneran et al., 2010a,b) will require reanalysis of the appropriate TTS onset (and thus injury 

onset) point for this category as well. For example, onset of TTS from pulsed watergun/airgun noise 

has been tested in three species of cetaceans. Finneran et al. (2002) exposed a beluga whale and 

bottlenose dolphin to watergun noise. The beluga whale showed TTS onset at 186 dB re 1 μPa2

•s 

(equivalent to 183 dB M-weighted), but the bottlenose dolphin did not show indication of TTS at the 

levels this experiment was able to produce. The level for the beluga whale was therefore used in the 

initial Southall et al. (2007) threshold for all cetaceans (198 = 183 + 15). However, Lucke et al. 

(2009) found a TTS onset in a harbor porpoise exposed to airgun noise at 164 dB re 1 μPa2

•s, 

considerably lower than reported by Finneran et al. (2002) for beluga whales. Whether this 

difference is due to species or individual difference or a combination of the two is difficult to say. 

Onset of TTS in pinnipeds in water has been tested for several species (e.g., Kastak et al., 2005), 

but only with non-pulsed sounds (Southall et al., 2007). As a result, Southall et al. (2007) used the 

relationship between TTS onset from non-pulsed sounds in beluga whales and harbor seals 

(approximately 12 dB) to estimate TTS onset levels for pinnipeds in water exposed to pulsed 

sounds.

Improvements based on additional data were envisioned, and in most cases specifically 

called for in terms of experimental approaches and priorities, and the conclusions and threshold 

values will continue to evolve over time. Despite the expected requisite re-thinking based on new 

data, the Southall et al. (2007) approach to marine mammal noise exposure represented a major 

evolution in the complexity and scientific basis for predicting the effects of noise on hearing in marine 

mammals over the simplistic historical NMFS thresholds for injury. Within their recently proposed 

acoustic guidelines, NOAA (USDOC, NOAA, 2013) considered the earlier Southall et al. (2007) 

criteria, modifications based on Finneran and Jenkins (2012), and the subsequent scientific data 

described previously and summarized modified onset thresholds for TTS and PTS. These values 

are summarized in Table H-4, and there is an extensive discussion of derivation of these criteria in 

USDOC, NOAA (2013).
H-24 Marine Mammal Hearing and Sensitivity to Acoustic Impacts

Table H-4. Revised Marine Mammal Noise Exposure Criteria for TTS and PTS Onset Proposed by the 

National Oceanic and Atmospheric Administration (From: USDOC, NOAA, 2013). 

Hearing Group PTS Onset (Received Level) TTS Onset (Received Level)

Impulsive Non-Impulsive Impulsive Non-Impulsive

Low-Frequency 

Cetaceans

Cell 1 

230 dBpeak; 

187 dB SELcum

Cell 2 

230 dBpeak; 

198 dB SELcum

Cell 11 

224 dBpeak; 

172 dB SELcum

Cell 12 

224 dBpeak; 

178 dB SELcum

Mid-Frequency 

Cetaceans

Cell 3 

230 dBpeak; 

187 dB SELcum

Cell 4 

230 dBpeak; 

198 dB SELcum

Cell 13 

224 dBpeak; 

172 dB SELcum

Cell 14 

224 dBpeak; 

178 dB SELcum

High-Frequency 

Cetaceans

Cell 5 

201 dBpeak; 

161 dB SELcum

Cell 6 

201 dBpeak; 

180 dB SELcum

Cell 15 

195 dBpeak; 

146 dB SELcum

Cell 16 

195 dBpeak; 

160 dB SELcum

Phocid Pinnipeds 

(Underwater)

Cell 7 

235 dBpeak; 

192 dB SELcum

Cell 8 

235 dBpeak; 

197 dB SELcum

Cell 17 

229 dBpeak; 

177 dB SELcum

Cell 18 

229 dBpeak; 

183 dB SELcum

Otariid Pinnipeds 

(Underwater)

Cell 9 

235 dBpeak;

215 dB SELcum

Cell 10 235 

dBpeak; 

220 dB SELcum

Cell 19 

229 dBpeak;

200 dB SELcum

Cell 20 

229 dBpeak;

206 dB SELcum

dB = decibel; PTS = permanent threshold shift; SEL = sound exposure level; and TTS = temporary 

threshold shift.

5.2 DERIVATION OF BEHAVIORAL EFFECTS CRITERIA

In terms of behavioral impacts, the Southall et al. (2007) noise exposure criteria took a dual 

approach that was dependent on the sound type. For exposure to single impulses (e.g., explosions), 

the acoustic component of the event was considered sufficiently intense to constitute behavioral 

harassment at levels consistent with TTS onset (Table H-5). The logic for this was that these events 

are so brief and transient that any responses other than those affecting hearing would likely be 

similarly transient in nature and thus not affect the long-term health or fitness of animals. It was 

noted, however, that startle responses can trigger stress and other physiological responses, the 

biological significance of which remains poorly understood.

For all other sound types (which are the majority), Southall et al. (2007) did not propose 

explicit threshold criteria for the reasons of context-dependence and other complexities in the nature 

of behavioral responses and available literature described previously. It was concluded that 

significant behavioral effects would likely occur at exposure levels below those required for TTS and 

PTS but that simple step-function thresholds for behavior (such as the historical NMFS values) were 

inconsistent with the best available science. While an overarching exposure level approach for 

behavior, as seems reasonable for injury, is perhaps more convenient from an assessment 

standpoint, the underlying reasons behind the type and magnitude of behavioral response involve a 

multitude of factors and require a multivariate assessment method to adequately describe.
Gulf of Mexico G&G Activities Programmatic EIS H-25

Table H-5. Marine Mammal Noise Exposure Criteria for Behavior for Different Marine Mammal

Functional Hearing Groups Proposed by Southall et al. (2007). 

Marine Mammal 

Group

Sound Type

Single Pulses Multiple Pulses Non-Pulses

Low-Frequency 

Cetaceans Cell 1 Cell 2 Cell 3

Sound Pressure 

Level 224 dBpeak re 1 μPa (flat*) See Tables 6 and 7 in Southall et al. (2007)

See Tables 14 and 15 

in Southall et al. (2007)

Sound Exposure 

Level 183 dB re 1 μPa2

•s (Mlf) N/A N/A

Mid-Frequency 

Cetaceans Cell 4 Cell 5 Cell 6

Sound Pressure 

Level 224 dBpeak re 1 μPa (flat) See Tables 8 and 9 in Southall et al. (2007)

See Tables 16 and 17 

in Southall et al. (2007)

Sound Exposure 

Level 183 dB re 1 μPa2

•s (Mmf) N/A N/A

High-Frequency 

Cetaceans Cell 7 Cell 8 Cell 9

Sound Pressure 

Level

224 dBpeak re 1 μPa (flat) 

Southall et al. (2007)

See Tables 18 and 19 in 

Southall et al. (2007)

See Tables 18 and 19 

in Southall et al. (2007)

Sound Exposure 

Level 183 dB re 1 μPa2•s (Mhf) N/A N/A

Pinnipeds 

(in water) Cell 10 Cell 11 Cell 12

Sound Pressure 

Level 212 dBpeak re 1 μPa (flat) See Tables 10 and 11 in Southall et al. (2007)

See Tables 20 and 21 

in Southall et al. (2007)

Sound Exposure 

Level 171 dB re 1 μPa2

•s (Mpw) N/A N/A

* “Flat” for peak sound pressure level indicates no frequency-weighting is applied. N/A = not 

applicable.

Southall et al. (2007) reviewed the available marine mammal literature and proposed a 

severity scaling for behavioral response applied to the available data but did not present explicit 

step-function thresholds for behavioral response. This was because of the lack of convergence in 

the data on broadly applicable exposure levels resulting in significant behavioral responses.

The Southall et al. (2007) severity scaling attempted for the first time to put some reasonable 

bounds on the likely significance of observed responses, highlighting the importance of responses 

with the potential to affect vital rates and survivorship (as in NRC, 2005). An ordinal ranking of 

behavioral response severity (refer to Table 4 in Southall et al. [2007]) was developed to delineate 

behaviors that are relatively minor or brief from those considered more likely to affect vital rates. 

The observed behavioral responses in all 10 conditions for multiple pulses and continuous noise for 

each of the five functional hearing groups were reviewed in detail, and individual responses were 

assessed according to this severity scaling and measured or reasonably estimated exposure levels. 

An example of this severity scaling of the observed behavioral literature in one of these conditions 

(low-frequency cetaceans exposed to impulse noise, predominantly airguns) that may be particularly 

relevant to this assessment is shown in Table H-6. Blank cells in this table indicate the lack of data 
H-26 Marine Mammal Hearing and Sensitivity to Acoustic Impacts

regarding a measured response rather than a known lack of response for these received sound 

levels and response categories; an overarching conclusion of Southall et al. (2007) was the striking 

lack of data in most exposure conditions for marine mammals.

Table H-6. Southall et al. (2007) Assessment of Individual Behavioral Responses of Low-Frequency 

Cetaceans to Multiple-Pulse Exposure for Various Received Levels. (Individual 

observations are weighted to account for statistical considerations.) 

Response 

Score 

Received Exposure Level (dBrms re 1 μPa)

80 to 

<90

90 to 

<100

100 to 

<110

110 to 

<120

120 to 

<130

130 to 

<140

140 to 

<150

150 to 

<160

160 to 

<170

170 to 

<180

180 to 

<190

190 to 

<200

9

8

7 1

(6)

6 9.5

(3,7)

47.4

(3,7)

2.2

(3,7)

1.4

(4)

2

(1,2)

5.5

(1,2,4,6)

9.3

(1,2,4,6,8)

5 1

(3,7)

1

(4)

1 

(1,2)

4

3 1 

(1,2)

1

(1,2)

2

1 5

(3,7)

6 

(3,7)

1

(3,7)

2

(1,2)

3

(5)

0 59.8

(3,7)

17.7

(3,7)

1.1

(3,7,8)

0.1

(8)

0.1

(8)

6.8

(1,2,8)

6.3

(1,2,8)

1

Malme et al. (1983); 2Malme et al. (1984); 3Richardson et al. (1986); 4Ljungblad et al. (1988); 5Todd 

et al. (1996); 6McCauley et al. (1998); 7Richardson et al. (1999); and 8Miller et al. (2005).

This severity scaling, as evident in Table H-6, did not reveal broadly applicable patterns of 

response in most cases, i.e., where no response occurs below some specific received level and a 

high probability of response occurs above some point (as step-functions would presume). Certain 

observations were made, including the behavioral context-dependence of response for different 

received levels in migrating bowhead whales and the particular sensitivity of harbor porpoises both 

in field and laboratory experiments. But the primary advances made in the Southall et al. (2007) 

criteria in terms of behavioral response were to very clearly demonstrate that step-function 

thresholds for response using a single received level and no other considerations related to 

behavioral context are overly simplistic and outdated, and to develop at least a qualitative means of 

addressing behavioral response severity issues.

The Southall et al. (2007) review found that contextual factors of sound exposure relating to 

different animal groups, sound types, and exposure conditions as well as differing activity states 

complicate efforts to derive simple step-function thresholds for all species (refer also to Ellison et al., 

2011). A recent modified approach proposed by Wood et al. (2012) sought to account for both 

species and contextual differences and is discussed here as an example of the derivation and broad 

application of the Southall et al. (2007) severity scaling to behavioral response criteria. Within this 

process, for the majority of marine mammal species, a method similar to the NMFS step-function 
Gulf of Mexico G&G Activities Programmatic EIS H-27

threshold (160 dB re 1 μPa [rms]) for impulse noise was used. As reviewed in detail in Appendix II 

(“Studies Involving Marine Mammal Behavioral Responses to Multiple Pulses”) of Southall et al. 

(2007), most marine mammals exposed to impulse noise demonstrate responses of varying 

magnitude in the 140 to 180 dB re 1 μPa (rms) exposure range, including the mysticetes in the 

Malme et al. (1983, 1984) studies on which the NMFS threshold is based. Potential disturbance 

levels at SPLs above 140 dB re 1 μPa (rms) were also highlighted in HESS (1999). Within the Wood 

et al. (2012) analysis of a proposed seismic survey off California, based on the integrated 

conclusions of Southall et al. (2007) using the severity scaling approach across different marine 

mammal groups, a probabilistic approach was applied at which 10 percent, 50 percent, and 

90 percent of individuals exposed are assumed to produce a behavioral response at exposures of 

140, 160, and 180 dB re 1 μPa (rms), respectively. Finally, in this analysis, the M-weighting 

functions of Southall et al. (2007) were applied to these exposure estimates. 

As noted by Southall et al. (2007) and supported by subsequent data, certain marine 

mammal species and (within some species) individuals in specific behavioral modes appear to be 

significantly more sensitive to noise exposure. For instance, migrating bowhead whales are much 

more likely than other mysticetes (including feeding bowhead whales) to respond clearly to seismic 

airgun noise at much lower (120 to 140 dB re 1 μPa [rms]) received sound levels (Richardson et al., 

1999).

Finally, certain species including harbor porpoises and beaked whales, appear to have a 

categorically different level of response than other marine mammals to much lower received levels. 

As reviewed in Southall et al. (2007), for harbor porpoises this appears to be consistent across 

sound types and laboratory and field settings. As demonstrated by Tyack et al. (2011) and DeRuiter 

et al. (2013), beaked whales appear to share this particular sensitivity, which may in part explain 

their disproportionate representation in marine mammal stranding events associated with sound 

exposure. Based on the initial assessment of Southall et al. (2007) and considering the more recent 

supporting evidence for beaked whales specifically, a particularly sensitive behavioral response 

category for these species and porpoises is assessed here. NMFS also recognizes species and 

contextual factors in setting behavioral response thresholds, the most obvious being the use of a 

120 dB re 1 μPa threshold for behavioral response of harbor porpoise to Navy acoustic sources with 

a wide range of activities (U.S. Dept. of the Navy, 2008). Thus, for these species, independent of 

behavioral state, Wood et al. (2012) applied the conclusions of Southall et al. (2007) severity scaling 

assessments for these species to derive 50 percent and 90 percent behavioral response 

probabilities calculated for M-weighted exposure levels of 120 and 140 dB re 1 μPa (rms), 

respectively; the 10 percent probability was not modeled in this case, but the 50 percent criterion is 

used as a step-function. Table H-7 provides a synopsis of the thresholds and the probability of a 

Level B behavioral response. Probabilities provided here from Wood et al. (2012) are not additive; 

that is, they reflect the probability of disturbance for a range of received sound levels along a 

theoretical response curve.
H-28 Marine Mammal Hearing and Sensitivity to Acoustic Impacts

Table H-7. Probabilistic Disturbance (rms) Sound Pressure Level Thresholds (M-weighted) Proposed 

by Wood et al. (2012) based on Southall et al. (2007) Severity Scaling to Predict a Level B 

Behavioral Response. (For comparison, the National Marine Fisheries Commission 

threshold for behavioral response for all marine mammals is 160 dB re 1 μPa (rms, 

unweighted. Probabilities are not additive and reflect the probability of disturbance for a 

range of received sound levels along a theoretical response curve.) 

Marine Mammal Group

Probabilistic Disturbance rms Thresholds

(M-weighted dB re 1 μPa [rms])

120 140 160 180

Behavioral Response Probability (percent)

Porpoises/beaked whales 50 90 -- --

Migrating mysticetes 10 50 90 --

All other species/behaviors -- 10 50 90

Note: Behavior Response Probability is based on low (10%), moderate (50%), and high (90%) 

categories of probability for different response levels in different contexts. Cells with dashes 

indicate probabilities less than 10% or more than 90%.

The Southall et al. (2007) criteria for behavior are a starting point to develop a rudimentary 

framework in moving toward a more multivariate and biologically meaningful way of assessing the 

type and magnitude of behavioral responses of marine mammals to noise than historical thresholds 

(refer to Ellison et al., 2012; Wood et al., 2012). As evidenced by the absence of data in many 

exposure level and response types, significant data gaps exist in almost all areas, and many of the 

available studies lack key information about the nature of exposure in which behavioral responses 

were observed (which is why many studies were excluded from the Southall et al. [2007] analysis). 

This is an active area of research, and subsequent studies (some described previously) have begun 

to report additional information on background noise, various exposure metrics, and behavioral 

contexts. 

Broad application of the Southall et al. (2007) criteria for injury and behavior has been 

relatively slow in evolving, in part due to the increased complexity of the recommendations over 

previous simplistic approaches, such as step-functions used by NMFS. However, NMFS has used 

exposure criteria consistent with the Southall et al. (2007) thresholds for injury from sound exposure 

for assessing potential impacts of U.S. Navy active sonar operations (Federal Register, 2009a and 

2009b) for a host of species, including large whales and pinnipeds; subsequent derivations of the 

Southall et al. (2007) criteria based on some of the subsequent data described previously are given 

in Finneran and Jenkins (2012). In fact, these regulations actually include higher exposure values 

for certain species for which higher TTS onset values were directly measured than the more 

conservative values used in Southall et al. (2007). Additionally, recent NMFS regulations (Federal 

Register, 2009a,b) have begun to use a more graduated dose-function based approach to 

behavioral response rather than the historical step-function thresholds. NMFS is preparing acoustic 

exposure guidelines that are expected to increasingly consider the complexity and contextdependence of responses of marine mammals to sound.
Gulf of Mexico G&G Activities Programmatic EIS H-29

6 ASSESSMENT OF HEARING INFORMATION FOR SPECIES/ 

GROUPS IN THE AREA OF INTEREST

Specific sound sources that will be used in G&G exploration activities in the GOM, as 

discussed in Chapter 3 of this Programmatic EIS, include impulsive (e.g., two- and threedimensional seismic exploration surveys using conventional airguns) and continuous noise sources 

such as, vessel propulsion systems, drilling, dredging, sediment sampling, and electromagnetic 

surveys.

Most of the marine mammals likely to be present in the Area of Interest, as discussed in 

Chapter 4.2.2 of this Programmatic EIS, are mid-frequency cetaceans and manatees with some 

mysticetes (Bryde’s whales) and high-frequency cetaceans (dwarf and pygmy sperm whales). For 

some of these species (e.g., bottlenose dolphins), relatively good information exists about hearing 

and behavioral responses to some types of sounds (e.g., Nowacek et al., 2001), though not for 

seismic exploration specifically. For most of the mid-frequency cetacean species, including the 

endangered sperm whale, the injury criteria proposed by Southall et al. (2007) and general 

conclusions on behavioral response would be expected to be applicable; direct recent information on 

behavioral responses in sperm whales to seismic airguns are available as well (e.g., Miller et al., 

2009).

For West Indian manatees, direct measurements of hearing are available (Gerstein et al., 

1999; Mann et al., 2005) as well as responses to vessel presence and noise (Nowacek et al., 2004). 

From the perspective of hearing injury, the use of pinniped exposure criteria from the Southall et al. 

(2007) criteria would seem reasonable, as described previously. These animals generally are very 

coastal-oriented, meaning they likely would encounter G&G activities only in nearshore waters.

For the mysticetes that could occur in the area (limited to Bryde’s whales), as for all lowfrequency cetaceans, no direct information regarding hearing is available. As described previously, 

the Southall et al. (2007) exposure criteria for injury are based on assumptions and extrapolations 

from mid-frequency cetacean data that may need to be reassessed to some degree based on the 

subsequent measurements of lower onset TTS levels in bottlenose dolphins within their range of 

best hearing sensitivity (Finneran and Schlundt, 2010), although there is limited direct available data 

with which to support such extrapolation.

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APPENDIX I 

SEA TURTLE HEARING 

AND 

SENSITIVITY TO ACOUSTIC IMPACTS

Prepared by

Soraya Moein Bartol, Ph.D.

1584 Wesleyan Drive

Norfolk, Virginia 23502

Prepared for

CSA Ocean Sciences Inc.

8502 SW Kansas Avenue

Stuart, Florida 34997

Under contract to

Bureau of Ocean Energy Management

45600 Woodland Road 

Sterling, Virginia 20166

Gulf of Mexico G&G Activities Programmatic EIS I-v 

TABLE OF CONTENTS

Page

LIST OF FIGURES............................................................................................................................... I-v

LIST OF TABLES................................................................................................................................. I-v

ABBREVIATIONS AND ACRONYMS ............................................................................................... I-vii

1 INTRODUCTION ............................................................................................................................ I-1

2 MORPHOLOGY.............................................................................................................................. I-2

3 ELECTROPHYSIOLOGICAL RESPONSE TO SOUND................................................................ I-4

4 BEHAVIORAL RESPONSES TO SOUND..................................................................................... I-5

5 EFFECTS OF ANTHROPOGENIC NOISE.................................................................................... I-7

6 REFERENCES CITED ................................................................................................................. I-10

LIST OF FIGURES

Page

Figure I-1. Middle Ear Anatomy of a Juvenile Loggerhead Sea Turtle.............................................I-3

Figure I-2. Typical Range of Frequencies that Contain Maximum Acoustic Energy 

from Seismic Airgun Signals Compared to Frequency Ranges of Hearing 

in Sea Turtles...................................................................................................................I-9

LIST OF TABLES

Page

Table I-1. Relative Risk of Injury to Sea Turtles Exposed to Seismic Airgun Sounds at 

Three Distances from the Sound Source ........................................................................I-8

 

Gulf of Mexico G&G Activities Programmatic EIS I-vii

ABBREVIATIONS AND ACRONYMS

ABR auditory brainstem response

AEP auditory evoked potential

cm

3 cubic centimeter

CT computed tomography

dB re 1 μPa decibels relative to 1 micropascal

Hz hertz

in

3 cubic inch

MRI magnetic resonance imaging

ms millisecond

PTS permanent threshold shift

TTS temporary threshold shift

Gulf of Mexico G&G Activities Programmatic EIS I-1 

1 INTRODUCTION

There is growing concern over anthropogenic sound in the world’s oceans and its potentially 

harmful effects on protected marine organisms, including sea turtles. There are seven extant 

species of sea turtle: green (Chelonia mydas); hawksbill (Eretmochelys imbricata); loggerhead 

(Caretta caretta); olive ridley (Lepidochelys olivacea); Kemp’s ridley (Lepidochelys kempii); flatback 

sea turtle (Natator depressus); and leatherback (Dermochelys coriacea). All sea turtles share a 

similar body form, although shell morphology is different in leatherback turtles compared to the hardshelled species. Similar to other migratory marine species, sea turtles occupy different ecological 

niches throughout ontogeny (refer to the review by Bolton, 2003), each characterized by unique 

acoustic conditions. Sea turtles spend the majority of their lives in the ocean; their only land-linked 

behaviors are egg deposition and hatching. Once hatchlings reach the sea, they are pelagic, 

moving primarily with ocean currents. After a period of years, the number of which varies among 

species and populations, a critical ontogenetic habitat shift occurs whereby most sea turtles actively 

recruit to a demersal, neritic habitat and are considered juveniles. Upon reaching maturity, sea 

turtles maintain a discrete foraging area (this region frequently overlaps with the juveniles’ habitat), 

migrating only to return to their natal nesting beach. The exception to this life history model is in the 

North Atlantic leatherback turtle populations, which remain pelagic as juveniles and adults and return 

to the neritic zone only for reproduction (Bolton, 2003).

Few studies have examined the role acoustic cues play in the ecology of sea turtles 

(Mrosovsky, 1972; Cook and Forrest, 2005; Samuel et al., 2005). There is evidence that sea turtles 

may use sound to communicate; the few vocalizations described for sea turtles are restricted to the 

grunts and gular pumps of nesting females (Mrosovsky, 1972; Cook and Forrest, 2005) and four 

types of sounds within the nest environment of leatherback turtles (Ferrara et al., 2014). These 

noises are low-frequency sounds and have been described as relatively loud compared to ambient 

noise, leading to speculation that the sounds are not just a result of nesting and hatching activity but 

that nesting females and hatchlings may use sound to communicate with conspecifics (Mrosovsky, 

1972; Cook and Forrest, 2005; Ferrara et al., 2014). Very little is known about the extent to which 

sea turtles use their auditory environment (“soundscape”) for navigation, environmental assessment, 

or identification of predators and prey. However, the passive acoustic environment for sea turtles 

changes with each ontogenetic habitat shift. In the inshore environment where juvenile and adult 

sea turtles generally reside, the ambient biotic environment is noisier than the open ocean 

environment of the hatchlings and is dominated by low-frequency sound (Hawkins and Myrberg, 

1983). In highly trafficked inshore areas, nearly constant low-frequency noises from shipping, 

recreational boating, and seismic surveys compound the potential for acoustic impact (Hildebrand, 

2005) and might prevent an animal from hearing signals from biologically important stimuli (Fay, 

2009).

The focus of this appendix is on sea turtle hearing, but other marine vertebrates can be 

affected by human sounds as well. For a discussion of hearing and the effects of noise on marine 

mammal hearing, refer to Appendix H. For a discussion of hearing and the effects of noise on fish 

hearing, refer to Appendix J. 
I-2 Sea Turtle Hearing and Sensitivity to Acoustic Impacts

2 MORPHOLOGY 

Much of the early research on the hearing capacity of sea turtles is limited to gross 

morphological dissections (Wever, 1978; Lenhardt et al., 1985). More recently, researchers have 

been describing the middle ear cavity using x-ray computed tomography (CT) and magnetic 

resonance imaging (MRI) (Ketten et al., 1999; Willis et al., 2013). The tympanum is a continuation of 

the facial tissue and is distinguishable only by palpation of the area. Beneath the tympanum is a 

thick layer of subtympanal fat (Figure I-1), a feature that distinguishes sea turtles from terrestrial and 

semi-aquatic turtles. The fats appear to differ bilaterally within an animal and vary considerably 

between animals. With the difference in fat levels, a variation in middle ear air space is observed 

also (Willis et al., 2013). Recent imaging data suggest that this layer of fat is similar to the fats found 

in the jaws of odontocetes and may function as a low-impedance channel for sounds to the ear 

(Ketten et al., 1999). The middle ear cavity lies posterior to the tympanum, and the Eustachian tube 

connects the middle ear with the throat (Wever, 1978; Lenhardt et al., 1985). As with most turtles, 

the middle ear is small and encased by bone. The ossicular mechanism consists of two elements: 

the extracolumella and the columella (stapes). The extracolumella is a cartilaginous disk under the 

tympanic membrane attached to the columella by ligaments. The columella, a long rod with the 

majority of its mass concentrated at each end, extends medially from the middle ear cavity through a 

narrow bony channel and expands within the oval window to form a funnel-shaped end. The 

columella is free to move only longitudinally within this channel so that when the tympanum is 

depressed directly above the middle of the extracolumella, the columella moves readily in and out of 

the oval window without any flexion of the columella. The stapes and oval window are connected to

the saccular wall by fibrous strands. It is thought that these stapedo-saccular strands relay 

vibrational energy from the stapes to the saccule (Wever and Vernon, 1956; Wever, 1978; Lenhardt 

et al., 1985). For semi-aquatic turtles, the columella is the main pathway for sound input to the inner 

ear; when the columella is clipped but the tympanum is intact, a test animal displayed an extreme 

decrease in hearing sensitivity (Wever and Vernon, 1956).
Gulf of Mexico G&G Activities Programmatic EIS I-3 

Figure I-1. Middle Ear Anatomy of a Juvenile Loggerhead Sea Turtle (From: Moein, 1994).

The auditory sense organ within the inner ear of the sea turtle cochlea is the basilar papilla 

(basilar membrane). This membrane is large and composed of dense connective tissue in sea 

turtles (compared to the thin basilar membrane found in terrestrial turtles) (Wever, 1978; 

Hetherington, 2008). The basilar papilla is positioned opposite the round window and lies within the 

pathway of fluid displacement due to columella motion. In most reptiles, and presumably in sea 

turtles as well, the tectorial membrane lays over the hair cells of the basilar papilla. For sea turtles, 

the innervations of the hair cells may be accomplished through the movement of the overlying 

tectorial membrane rather than the movement of the papillae (Hetherington, 2008).

Based on the functional morphology of the ear, it appears that sea turtles receive sound 

through the standard vertebrate tympanic middle ear path. The sea turtle ear morphology, however, 

is adapted to underwater sound not aerial sound. For the terrestrial vertebrate, the middle ear is an 

impedance transformer between sound in air (environment) and sound in fluid (inner ear). This 

impedance mismatch can be overcome by having a high convergence ratio between the tympanic 

membrane and the oval window (thus amplifying the force acting on the inner ear) or by having a 

multiple bone ossicular mechanism that acts as a lever system to amplify force. The convergence 

ratio of the tympanic membrane to the oval window in sea turtles is reported to be lower than semi-
I-4 Sea Turtle Hearing and Sensitivity to Acoustic Impacts

aquatic turtles (Lenhardt et al., 1985), and sea turtles lack an ossicular mechanism that acts as an 

effective lever (having only a single straight columella). Thus, the sea turtle ear appears to be poorly 

adapted to receive aerial sounds. However, the ear is well adapted to sound conducted in water. 

The dense layer of fat under the tympanum may act as a low-impedance channel for underwater 

sound (similar to the pathway found in odontocetes [Ketten et al., 1999]). Furthermore, the retention 

of air in the middle ear of sea turtles suggests that they are able to detect sound pressures 

(Hetherington, 2008).

3 ELECTROPHYSIOLOGICAL RESPONSE TO SOUND

Electrophysiological studies on hearing have been conducted on juvenile and subadult green 

turtles (Ridgway et al., 1969; Bartol and Ketten, 2006; Dow Piniak et al., 2012a); juvenile Kemp’s 

ridley turtles (Bartol and Ketten, 2006); post-hatchling, juvenile, and adult loggerhead turtles (Bartol 

et al., 1999; Lavender et al., 2012, 2014; Martin et al., 2012); and hatchling leatherback turtles (Dow 

Piniak et al., 2012b). Electrophysiological responses, specifically auditory evoked potentials (AEPs), 

are the most widely accepted technique for measuring hearing when normal behavioral testing is 

impractical. AEPs reflect the synchronous discharge of large populations of neurons within the 

auditory pathway and thus are useful for monitoring the functionality of the auditory system. Some 

AEP research has concentrated the responses occurring within the first 10 milliseconds (ms) 

following presentation of click or brief tone burst stimuli. This response has been termed the 

auditory brainstem response (ABR) and consists of a series of five to seven patterned and 

identifiable waves. These techniques are noninvasive and often performed on conscious subject 

animals (Bullock, 1981; Corwin et al., 1982; Bartol et al., 1999).

Green Sea Turtle

Ridgway et al. (1969) measured auditory cochlear potentials of green turtles using aerial and 

vibrational stimuli. Thresholds were not measured; instead, cochlear response curves of 

0.1 microvolt potential were plotted for frequencies ranging from 50 to 2,000 hertz (Hz). Green 

turtles’ best sensitivity fell within a limited frequency range for aerial stimuli (200 to 700 Hz) and 

vibrational stimuli (300 to 500 Hz). Though this investigation examined two separate modes of 

sound reception (i.e., air and bone conduction), sensitivity curves were relatively similar, suggesting 

that the inner ear is the main structure for determining frequency sensitivity. More recently, Bartol 

and Ketten (2006) collected underwater ABRs from juvenile and subadult green turtles. For these 

experiments, a speaker was suspended in air while the sea turtle’s tympanum remained submerged 

underwater. All sea turtles tested responded to sounds in the low-frequency range, from at least 

100 Hz (lowest frequency tested) to no greater than 800 Hz. Interestingly, hearing sensitivity of 

green turtles varied with size; smaller green turtles had a broader range of hearing (100 to 800 Hz; 

greatest sensitivity at 600 to 700 Hz at 95 decibels relative to 1 micropascal (dB re 1 μPa) than that 

detected in larger subadult subjects (100 to 500 Hz, greatest sensitivity 200 to 400 Hz at 93 to 

97 dB re 1 μPa). Dow Piniak et al. (2012a) recorded both in-air and in-water AEP responses from 

juvenile green turtles. The AEP signature recorded from green turtles was similar to that seen in 

studies of fish evoked potentials, with a frequency-doubling response (i.e., where response waves 

oscillate at twice the stimulus frequency). Juvenile green turtles responded to stimuli between 
Gulf of Mexico G&G Activities Programmatic EIS I-5 

50 and 1,600 Hz in water and 50 and 800 Hz in air. Ranges of maximum sensitivity were between 

50 and 400 Hz in water and 300 and 400 Hz in air. Although these animals responded to an 

expanded range of frequencies, sensitivity decreased sharply for frequencies above 400 Hz in both 

media.

Loggerhead Sea Turtle

Hearing has been studied on multiple size classes of loggerhead sea turtles. Bartol et al. 

(1999) collected ABRs from juvenile loggerhead turtles by delivering vibratory stimuli directly to the 

dermal plates over the tympanum. Thresholds were recorded for both tonal and click stimuli. Best 

sensitivity was found in the low-frequency region of 250 to 1,000 Hz. The decline in sensitivity was 

rapid above 1,000 Hz, and the most sensitive threshold tested was at 250 Hz. Lavender et al. 

(2012, 2014) recorded underwater AEPs from post-hatchling to juvenile loggerhead turtles. These 

experiments involved submerging a restrained, fully conscious sea turtle just below the water 

surface and presenting sound using an underwater speaker. Under these conditions, post-hatchling 

and juvenile loggerhead turtles were found to respond to frequencies between 50 and 1,100 Hz. 

Post-hatchlings responded with the greatest sensitivity at 200 Hz (116 dB re 1 μPa) while juveniles 

were most sensitive at 50, 100, and 400 Hz (117 to 118 dB re 1 μPa). Martin et al. (2012) acquired 

AEPs from a single submerged adult loggerhead turtle using an underwater pool speaker and 

reported thresholds between 100 and 1,131 Hz, with highest sensitivity occurring at 100 to 400 Hz 

(threshold levels were approximately 109 dB re 1 μPa).

Leatherback Sea Turtle

Only one study has addressed the hearing of leatherback sea turtles (Dow Piniak et al., 

2012b). This study measured the hearing of hatchlings (immediately after emergence from the nest) 

in water and in air. For these recordings, the animals were sedated then fully submerged and 

presented with stimuli from an underwater speaker or placed on a foam pad and stimulated with an 

aerial speaker. The animals reacted to low-frequency sounds, responding to stimuli between 50 and 

1,600 Hz in air and 50 and 1,200 Hz in water (lowest sensitivity recorded was 93 dB re 1 μPa at 

300 Hz).

Kemp’s Ridley Sea Turtle

Bartol and Ketten (2006) recorded hearing from Kemp’s ridley turtles using the same 

methods described for juvenile and subadult green sea turtles. The two juveniles tested had a 

restricted hearing range (100 to 500 Hz) with their most sensitive hearing falling between 100 and 

200 Hz (110 dB re 1 μPa) (Bartol and Ketten, 2006).

4 BEHAVIORAL RESPONSES TO SOUND

Multiple studies have attempted to examine the behavioral responses of juvenile loggerhead 

turtles to sound in their natural environment, both in controlled settings (O’Hara and Wilcox, 1990; 

Moein et al., 1995; McCauley et al., 2000; Lavender et al., 2012; 2014; Martin et al., 2012) and as 

observed in situ (Holst et al., 2007; Weir, 2007; DeRuiter and Doukara, 2012). 
I-6 Sea Turtle Hearing and Sensitivity to Acoustic Impacts

Behavioral Audiograms

Behavioral audiograms have been collected from post-hatchling, juvenile, and adult 

loggerhead turtles (Lavender et al., 2012, 2014; Martin et al., 2012) and required the animal to 

perform a task in the presence of auditory stimuli. Though time consuming (it can take months to 

train a sea turtle to sound), behavioral audiograms are a more sensitive measure of hearing 

threshold than electrophysiological responses (Kastak and Schusterman, 1998; Szymanski et al., 

1999; Nachtigall et al., 2000; Casper et al., 2003; Wolski et al., 2003) and ascribe a critical 

behavioral component to hearing trials. Lavender et al. (2012, 2014) recorded audiograms using a 

two-response, forced-choice approach, whereby the sea turtles were required to vary behavior 

according to the presence or absence of sound. Post-hatchling and juvenile loggerhead turtles 

responded to similar frequencies as found in their previous AEP studies (50 to 1,000 Hz); however, 

their threshold levels were more sensitive than reported using the electrophysiological approach. 

Post-hatchling turtles responded with the greatest sensitivity at 200 Hz (85 dB re 1 μPa) while 

juveniles were most sensitive at 800 Hz (76 dB re 1 μPa). This study reported no difference in 

threshold levels between the two ontogenetic stages. Martin et al. (2012) recorded a behavioral 

audiogram from one adult loggerhead turtle using a go/no-go paradigm and found the animal 

responded to sounds between 50 and 800 Hz with best sensitivity at 100 Hz (98 dB re 1 μPa).

Behavioral Responses in Controlled Settings

Several sea turtle behavioral studies have been initiated to assist in the development of an 

acoustic repelling device for sea turtles. O’Hara and Wilcox (1990) attempted to create a sound 

barrier for loggerhead turtles at the end of a canal using seismic airguns (Bolt Technology Model 

600B, 165 cubic centimeters [cm3

] and Model 542, 13 cm3). The test results indicated that airguns 

were effective as a deterrent for a distance of approximately 30 meters (98 feet) when the sound 

output of the system was approximately 220 dB re 1 μPa at 1 m in the 25- to 1,000-Hz range. 

However, this study did not account for the reflection of sound by the canal walls, and the stimulus 

frequency and intensity levels are ambiguous. Moein et al. (1995) investigated the use of airguns 

(Bolt Technology Par 2800, 20-cubic inch [in3

] chamber) to repel juvenile loggerhead turtles from 

hopper dredges. A net enclosure was erected in the York River, Virginia to contain the sea turtles, 

and an airgun was stationed at each end of the net. Sound frequencies of the airguns ranged from 

100 to 1,000 Hz at three decibel levels (175, 177, and 179 dB re 1 μPa at 1 m). Avoidance of the 

airguns was observed upon first exposure. However, after three separate exposures to the airguns, 

the sea turtles habituated to the stimuli. This termination of response to stimuli could indicate 

damage to the sea turtles’ ears and a temporary or permanent shift in their threshold levels. 

McCauley et al. (2000) examined the response of sea turtles (one green turtle and one loggerhead 

turtle) to an airgun signal (Bolt Technology Model 600B, 20-in3 chamber). For these trials, the sea 

turtles were placed in cages and behavior was monitored as a single airgun approached and 

departed. The sea turtles showed a noticeable increase in swimming behavior when the received 

airgun level was higher than 166 dB re 1 μPa at 1 m, and they became erratic and increasingly 

agitated when the received level was higher than 175 dB re 1 μPa at 1 m. Because these animals 

were caged, avoidance behavior could not be monitored. However, the researchers speculated that 
Gulf of Mexico G&G Activities Programmatic EIS I-7 

avoidance would occur at 175 dB re 1 μPa at 1 m, the point at which the animals were acutely 

agitated (McCauley et al., 2000).

Behavioral Responses In Situ

Researchers have attempted to monitor sea turtle avoidance to sound during active seismic 

surveys (Holst et al., 2007; Weir, 2007; DeRuiter and Doukara, 2012). Weir (2007) observed 

240 animals during a 10-month seismic survey off the coast of Angola (source levels of 220 to 

248 dB re 1 μPa, peak energy between 10 and 200 Hz). Behaviors were recorded at the first 

sighting and as the vessel and towed equipment moved in relation to the sea turtle. Fewer sea 

turtles were observed near the airguns as they were firing (compared to the shutdown state). 

However, the source of agitation for the sea turtle could not be identified; the sea turtle could have 

reacted to the ship and towed equipment rather than specifically to the airgun (Weir, 2007). 

DeRuiter and Doukara (2012) observed sea turtles (mainly loggerhead turtles) during active 

operation of an airgun array (252 dB re 1 μPa [peak]) and found a startle response (rapid dive) to the 

airgun as it approached. Though the researchers did not perform a control with the airguns off and 

thus could not rule out if these responses were due to visual cues, the timing of the sea turtles’ 

responses to the firing of the sounds indicates a reaction to the airgun (DeRuiter and Doukara, 

2012). Holst et al. (2007) looked at sea turtle monitoring data during seismic surveys. This report 

included data from visual observations and passive acoustic monitoring. Displacement of the sea 

turtles during the surveys was apparent for large- and small-source surveys.

5 EFFECTS OF ANTHROPOGENIC NOISE

Anthropogenic noise levels are increasing in the oceans (Hildebrand, 2009); however, very 

little is known about the effects anthropogenic noise may have on marine species, especially sea 

turtles. Anthropogenic noises can originate from several sources, including shipping traffic, seismic 

surveys for petroleum exploration, military sonar operations, and pile driving. These sounds have 

the potential to impact an animal in several ways, including trauma to hearing (temporary or 

permanent), trauma to non-hearing tissue (barotraumas), alteration of behavior, and masking of 

biologically significant sounds (McCarthy, 2004).

Hearing damage usually is categorized as a temporary or permanent injury. Temporary 

threshold shifts (TTSs) are recoverable injuries to the hearing structure and can vary in intensity and 

duration. Normal hearing abilities return over time; however, animals often lack the ability to detect 

prey and predators or assess their environment effectively during the recovery period. In contrast, 

permanent threshold shifts (PTSs) are the permanent loss of hearing through loss of sensory hair 

cells (Clark, 1991). Few studies have looked at hair cell damage in reptiles, and it is unknown if sea 

turtles are able to regenerate hair cells (Warchol, 2011). There are almost no data on the effects of 

intense sounds on sea turtles; thus, it is difficult to predict the level of damage to hearing structures. 

Clear avoidance reactions to seismic signals at levels between 166 and 179 dB re 1 μPa have been 

observed (Moein et al., 1995; McCauley et al., 2000); however, both studies were done in a caged 

environment, so the extent of avoidance could not be monitored. Moein et al. (1995) observed a 

habituation effect to airguns; the animals stopped responding to the signal after three presentations. 
I-8 Sea Turtle Hearing and Sensitivity to Acoustic Impacts

This lack of behavioral response could be an indication of TTS or PTS brought on by exposure to 

airguns.

Currently, data gaps prevent the development of science-based quantitative exposure 

criteria and guidelines. Based on the available literature, qualitative sound exposure guidelines for 

sea turtles have been developed for five classes of sounds: (1) explosions; (2) seismic airguns; 

(3) pile driving; (4) active sonar; and (5) continuous sound sources (Popper et al., 2014). In the 

guidelines, sea turtles are placed in moderate-to-high levels of risk for physical impairment when 

near the source for all G&G source categories except mid-frequency sonar that operates at 

frequencies outside of the hearing range of sea turtles (Table I-1) (Popper et al., 2014). For 

example, there is an overlap in the frequency range of output from seismic airguns sounds and 

hearing ranges of sea turtles (Figure I-2). The frequency overlap can be seen when the sound 

energy of an acoustic signal (i.e., seismic) is distributed across the frequency domain. In Figure I-2, 

only the frequencies with the maximum (highest) sound energy for airguns are illustrated and range 

from 20 to 200 Hz (Popper et al., 2014). Furthermore, while physiological data on the adverse 

effects of seismic airguns on sea turtles are not available, it can be inferred that if the received levels 

are high enough, exposure could cause injury (TTS or PTS).

Table I-1. Relative Risk of Injury to Sea Turtles Exposed to Seismic Airgun Sounds at Three Distances 

from the Sound Source (From: Popper et al., 2014). 

Type of Animal Impairment Behavior Recoverable Injury TTS Masking

Sea Turtles

(N) High 

(I) Low 

(F) Low

(N) High 

(I) Low 

(F) Low

(N) Low 

(I) Low 

(F) Low

(N) High 

(I) Moderate 

(F) Low

F = far (thousands of meters from source); I = intermediate (hundreds of meters from source); 

N = near (tens of meters from source); TTS = temporary threshold shift.
Gulf of Mexico G&G Activities Programmatic EIS I-9 

Figure I-2. Typical Range of Frequencies that Contain Maximum Acoustic Energy from 

Seismic Airgun Signals Compared to Frequency Ranges of Hearing in Sea 

Turtles. (Hearing data have not been collected from sea turtles to 

frequencies lower than 50 Hz [Data from: Bartol et al., 1999; Bartol and 

Ketten, 2006; Dow Piniak et al., 2012a,b; Martin et al., 2012; Lavender et al., 

2014]).

Anthropogenic noises below injury levels could provoke annoyance responses and mask 

relevant sounds in an animal’s environment. Ideally, when studying the behavioral responses of wild 

animals, multiple individuals should be observed in situ and under natural conditions. These data 

are difficult to collect and even more difficult to interpret. Avoidance and startle responses to seismic 

airguns have been demonstrated for sea turtles in a few studies (O’Hara and Wilcox, 1990; Moein 

et al., 1995; Holst et al., 2007; Weir, 2007; DeRuiter and Doukara, 2012) and these behavioral 

avoidance reactions could interfere with sea turtles’ normal behaviors. For example, DeRuiter and 

Doukara (2012) speculated that the observed startle response prevented sea turtles from basking 

and could result in decline in their metabolic activity. Furthermore, masking sounds (i.e., signals that 

can reduce the detectability of another sound) can interfere with a sea turtle’s ability to acquire prey, 

to find a mate, to avoid predators, and to identify an appropriate nesting site (Nunny et al., 2008). 

Sea turtles appear to be low-frequency specialists; thus, potential masking noises would fall within at 

least 50 to 1,000 Hz. However, there are no quantitative data demonstrating masking effects for sea 

turtles.

More research on the behavioral and physiological responses to sounds needs to be 

conducted on sea turtles before appropriate noise exposure criteria can be developed for reduced 

fitness, injury, and death. While the research community is making progress in determining the 

frequency range of hearing for sea turtles, there are few data on hearing loss/damage, hair cell 

regeneration, masking, and behavioral responses. Inner ear research on hair cell population needs 
I-10 Sea Turtle Hearing and Sensitivity to Acoustic Impacts

to be conducted on multiple species and age classes by using histology/imaging techniques to 

analyze variations in auditory anatomy among stages and species. The critical point at which noise 

disrupts scene analysis and masks signals should be explored, and quantitative data on masking 

need to be collected for sea turtles. When looking at behavioral responses, research beyond the 

startle response must be conducted. Controlled experiments in the natural environment need to be 

conducted to document and classify reactions to sound as either nuisance (i.e., causing the animal 

to move away, changing the animals’ behavior to another acceptable consequence) or injurious (i.e., 

preventing the animal from completing essential behavior). The results of these research studies 

could provide new data on the hearing ability and response to sound for sea turtles, and serve as a 

quantitative base for assessing potential impacts of man-made sound sources on multiple species of 

sea turtles across habitats and developmental stages.

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Casper, B.M., P.S. Lobel, and H.Y. Yan. 2003. The hearing sensitivity of the little skate, Raja 

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Clark, W.W. 1991. Recent studies of temporary threshold shift (TTS) and permanent threshold shift 

(PTS) in animals. Journal of the Acoustical Society of America 90(1):155-163.

Cook, S.L. and T.G. Forrest. 2005. Sounds produced by nesting leatherback sea turtles 

(Dermochelys coriascea). Herpetological Review 36(4):387-390.

Corwin, J.T., T.H. Bullock, and J. Schweitzer. 1982. The auditory brain stem response in five 

vertebrate classes. Electroencephalography and Clinical Neurophysiology 54(6):629-641.

DeRuiter, S.L. and K.L. Doukara. 2012. Loggerhead turtles dive in response to airgun sound 

exposure. Endangered Species Research 16:55-63.

Dow Piniak, W.E., D.A. Mann, S.A. Eckert, and C.A. Harms. 2012a. Amphibious hearing in sea 

turtles. In: Popper, A.N. and A. Hawkins, eds. The effects of noise on aquatic life. Advances in 

Experimental Medicine and Biology. Pp. 83-87. 
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Dow Piniak, W.E., S.A. Eckert, C.A. Harms, and E.M. Stringer. 2012b. Underwater hearing 

sensitivity of the leatherback sea turtle (Dermochelys coriacea): Assessing the potential effect of 

anthropogenic noise. U.S. Dept. of the Interior, Bureau of Ocean Energy Management, 

Headquarters, Herndon, VA. OCS Study BOEM 2012-01156. 35 pp.

Fay, R.R. 2009. Soundscape and the sense of hearing in fish. Integrative Zoology 4:26-32.

Ferrara, C.R., R.C. Vogt, M.R. Harfush, R.S. Sousa-Lima, E. Albavera, and A. Tavera. 2014. First

evidence of leatherback turtle (Dermochelys coriacea) embryos and hatchlings emitting sounds. 

Chelonian Conservation and Biology 13(1):110-114.

Hawkins, A.D. and A.A. Myrberg, Jr. 1983. Hearing and sound communication under water. In: 

Lewis. B. ed. Bioacoustics: A comparative approach. London: Academic Press. Pp. 347-405.

Hetherington, T. 2008. Comparative anatomy and function of hearing in aquatic amphibians, 

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Hildebrand, J.A. 2005. Man-made noise. In: Richardson, W.J., C.R. Greene, Jr., C.I. Malme, and 

D.H. Thomson, eds. Marine mammals and noise. San Diego, CA: Academic Press. 

Pp. 101-158.

Hildebrand, J.A. 2009. Anthropogenic and natural sources of ambient noise in the ocean. Marine 

Ecology Progress Series 395:5-20.

Holst, M., W.J. Richardson, W.R. Koski, M.A. Smultea, B. Haley, M.W. Fitzgerald, and M. Rawson. 

2007. Effects of large and small-source seismic surveys on marine mammals and sea turtles. 

American Geophysical Union, Abstract #OS42A-01.

Kastak, D. and R.J. Schusterman. 1998. Low-frequency amphibious hearing in pinnipeds: 

Methods, measurements, noise, and ecology. Journal of the Acoustical Society of America

103:2,216-2,228.

Ketten, D.R., C. Merigo, E. Chiddick, and H. Krum. 1999. Acoustic fatheads: parallel evolution of 

underwater sound reception mechanisms in dolphins, seals, turtles, and sea birds. Journal of 

the Acoustical Society of America 105:1,110.

Lavender, A.L., S.M. Bartol, and I.K. Bartol. 2012. Hearing capabilities of loggerhead sea turtles 

(Caretta caretta) throughout ontogeny. In: Popper, A.N. and A. Hawkins, eds. The effects of 

noise on aquatic life. New York, NY: Springer. Pp. 89-92.

Lavender, A.L., S.M. Bartol, and I.K. Bartol. 2014. Ontogenetic investigation of underwater hearing 

capabilities in loggerhead sea turtles Caretta caretta using a dual testing approach. Journal of

Experimental Biology 217:2,580-2,589.

Lenhardt, M.L., R.C. Klinger, and J.A. Musick. 1985. Marine turtle middle-ear anatomy. Journal of

Auditory Research 25(1):66-72.
I-12 Sea Turtle Hearing and Sensitivity to Acoustic Impacts

Martin, K.J., S.C. Alessi, J.C. Gaspard, A.D. Tucker, G.B. Bauer, and D.A. Mann. 2012. 

Underwater hearing in the loggerhead turtle (Caretta caretta): A comparison of behavioral and 

auditory evoked potential audiograms. Journal of Experimental Biology 215:3,001-3,009.

McCarthy, E. 2004. International regulation of underwater sound: Establishing rules and standards 

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Sea Turtle Research Program: Summary report. Technical Report CERC-95. Pp. 90-93.

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29(3):256-258.

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whale hearing. In: Au, W.W.L., R.R. Fay, and A.N. Popper, eds. Hearing by whales and 

dolphins. New York, NY: Springer-Verlag. Pp. 330-363.

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low frequency sound. Copeia 2:564-567.

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APPENDIX J 

FISH HEARING AND THE SENSITIVITY OF FISH 

TO HEARING LOSS AND INJURY 

FROM EXPOSURE TO ANTHROPOGENIC SOUND

Prepared by

Thomas J. Carlson, Ph.D.

ProBioSound LLC

Holmes Beach, Florida 34217

Prepared for

CSA Ocean Sciences Inc.

8502 SW Kansas Avenue

Stuart, Florida 34997

Under Contract to

Bureau of Ocean Energy Management

381 Elden Street, MS 4040

Herndon, Virginia 20170

Gulf of Mexico G&G Activities Programmatic EIS J-v 

TABLE OF CONTENTS

Page

ABBREVIATIONS AND ACRONYMS .............................................................................................. J-vii

1 INTRODUCTION .......................................................................................................................... J-1

2 THE PHYSICS OF UNDERWATER SOUND............................................................................... J-1

3 THE MECHANICS OF FISH HEARING....................................................................................... J-3

4 SOURCES OF ANTHROPOGENIC SOUND AND SOUND METRICS ...................................... J-4

5 MECHANISMS OF HEARING LOSS AND INJURY .................................................................... J-8

5.1 Hearing Loss ....................................................................................................................... J-8

5.2 Injury ................................................................................................................................. J-9

5.3 Concussion.......................................................................................................................... J-9

5.4 Decompression.................................................................................................................... J-9

6 EXPOSURE CRITERIA AND GUIDELINES.............................................................................. J-11

7 REFERENCES CITED ............................................................................................................... J-12

Gulf of Mexico G&G Activities Programmatic EIS J-vii

ABBREVIATIONS AND ACRONYMS

dB re 1 μPa decibels relative to 1 micropascal

dB re 1 μPa2

•s decibels relative to 1 micropascal squared second

EIS Environmental Impact Statement

g gram

G&G geological and geophysical

GOM Gulf of Mexico

Hz hertz

kHz kilohertz

m/s meters per second

nm/s nanometers per second

PTS permanent threshold shift

rms root mean square

SEL sound exposure level

SPD sound pressure difference

SPL sound pressure level

TTS temporary threshold shift

Gulf of Mexico G&G Activities Programmatic EIS J-1 

1 INTRODUCTION

One of the objectives of the Gulf of Mexico (GOM) Programmatic Environmental Impact 

Statement (EIS) is to determine or estimate the potential impacts of sound generated by geological 

and geophysical (G&G) survey activities on fish populations in the northern part of the GOM. Over 

millions of years, fishes have evolved hearing systems that utilize sound to perform a wide range of 

important life functions, including finding food and mates, communicating with conspecifics, and 

avoiding predators (Clack and Allin, 2004). Evolutionary processes that have resulted in the 

adaptations exhibited by the more than 32,000 species of fish (Helfman et al., 2009) have only had 

to contend with high levels of anthropogenic sound within the last few decades (Hildebrand, 2009).

The basics of hearing in fishes are known even though the hearing of only a very small 

number of species (approximately 50) has been studied (Fay, 1988; Popper et al., 2003; Lovell 

et al., 2005; Wysocki et al., 2009; Meyer et al., 2012). The study of fish hearing has, from necessity, 

involved studying the physics of underwater sound.

This appendix reviews the physics of underwater sound, mechanics of fish hearing, sources 

of anthropogenic sound and sound metrics, mechanisms of injury to fish from exposure to 

anthropogenic sound, and criteria for the protection of fish from exposure to injurious levels of G&G 

survey sounds. References cited in the appendix include technical reports as well as peer-reviewed 

literature. This appendix is not intended to be a comprehensive review of fish hearing, fish 

physiology, and the physics of sound but an overview of the elements of these subject areas that 

relate directly to the assessment of risk of hearing loss and injury to fish from exposure to 

anthropogenic sound. For a discussion of hearing and the effects of noise on marine mammal 

hearing, refer to Appendix H. For a discussion of hearing and the effects of noise on sea turtle 

hearing, refer to Appendix I. 

2 THE PHYSICS OF UNDERWATER SOUND

Sound is a mechanical disturbance that propagates as a longitudinal wave through 

compressible media. The acoustic energy propagated in a sound wave consists of very small 

molecular vibrations that travel at a rate dependent upon the density of the medium. In water, the 

speed of sound is approximately 1,500 meters per second (m/s) (4,921 feet per second) and is 

slightly faster in saltwater than in freshwater. The speed of sound increases with temperature, 

salinity, and depth (hydrostatic pressure). The propagated mechanical energy in a sound wave is in 

the kinetic energy of water particle motion and the potential energy of the pressure (stress) 

component of a sound wave. When water molecules are closer together, the fluid is compressed 

and pressure is higher; when water molecules are farther apart, the fluid is rarefied and pressure is 

lower. In this appendix, cited works will be those that consider these topics within the context of 

bioacoustics. 

Because of the relative ease of measuring pressure (a scalar quantity), it is the most 

commonly measured component of sound. Water particle velocity (a vector quantity with both 

magnitude and direction) is more difficult to measure under field conditions and therefore is 
Gulf of Mexico G&G Activities Programmatic EIS J-2 

infrequently measured. The difficulty in measuring water particle velocity in the field poses a 

considerable challenge in the study of fish hearing impacts. While all fish can detect the water 

particle velocity component of a sound wave, only those with swim bladders, which may be 

associated with specialized structures connected to or in close proximity to their ears, can utilize the 

pressure component of a sound wave in order to hear. This is a particular problem when studying 

fish hearing within the near field of a sound source.

The definition of “near” for a sound source is complicated by many factors. Near a sound 

source, the particle motion component of the acoustic field has the characteristics of incompressible 

hydrodynamic flow. This means that the ratio of particle velocity and acoustic pressure amplitudes is 

much higher than when farther from the source. The rate of change in particle motion in the region 

near the source is a function of the characteristics of the source. The rate of decrease with range of 

acoustic particle motion near a source is on the order of 1/r2 to 1/r3, where r is the range from the 

source. This decreases to 1/r in the propagation of a far field sound wave where the ratio of the 

amplitudes of particle velocity and acoustic pressure equals the specific acoustic impedance (Clay 

and Medwin, 1977; Kalmijn, 1988; Uric, 1983; Au and Hastings, 2008). As the distance from an 

acoustic source increases, the ratio of pressure to particle velocity approaches the value expected 

for a plane wave, where the majority of energy in the propagating sound wave is in the form of 

pressure, and far field conditions are satisfied (Kalmijn, 1988; Au and Hastings, 2008).

In the far field, as sound propagates away from its source, a number of factors, including 

geometric spreading, attenuation, reflection, scattering, and refraction, interact to affect the level of 

sound and other characteristics of the sound wave. For the low frequencies at which the vast 

majority of fish species hear (frequencies <1 kilohertz [kHz]), attenuation is not a major factor 

(Rogers and Cox, 1988). More important are other propagation effects that reduce the intensity 

(energy per unit time) of the sound wave and modify features of the signal that may change its 

information content. In general, from the perspective of the receiver, as distance from a source 

increases, the various factors affecting propagation make the sound harder to detect and 

significantly affect the quality of information it carries (Rogers and Cox, 1988).

Because of the various factors that influence sound as it travels from its source, the resulting 

sound field has considerable complexity in space and time. As a rule, single measurements made at 

a point in the volume cannot be used to describe conditions in the sound field at other locations 

(nearer or farther from the source). Consequently, when an estimate of sound field characteristics 

for a large volume are needed, sound propagation models are used to estimate the intensity in the 

sound wave at points distant from the source. Such models may be used to estimate amplitude and 

frequency features of the propagating sound wave. There are several sound propagation models in 

use at any time, each designed to satisfy a particular sound propagation simulation need (Etter, 

2012).

Sound propagation is complex as it needs to consider propagation through the water column 

as well as through the seafloor. Sound introduced into the seafloor through activities such as pile 

driving, some types of geophysical sound sources, and explosions from buried explosive material or 
Gulf of Mexico G&G Activities Programmatic EIS J-3 

in structures connected to the seafloor can result in sound being transmitted long distances through 

the earth and reintroduced into the water column some distance from the source (Jackson et al., 

1994).

3 THE MECHANICS OF FISH HEARING

Fish use light and sound to sense their environment. Because of the rapid attenuation of 

light, particularly in the portion of the electromagnetic spectrum visible to humans and most fish, 

sound is very important to fish to obtain information about their environment as it attenuates much 

more slowly than light. Fish are believed to use sound to sense their environment (acoustic scene 

assessment), communicate with conspecifics, detect prey, navigate, and perform other lifesustaining functions (Bregman, 1990; Fay and Popper, 2000; Lewis and Fay, 2004; Bass and 

Ladich, 2008).

There is considerable literature covering the morphology and physiology of fish ears as well 

as fish hearing. Popper et al. (2014) reviewed literature addressing the elements of fish hearing 

related to sensitivity to man-made sound. This appendix addresses the basic mechanics of the fish 

ear, swim bladder, and specialized structures that enhance hearing and may contribute to the 

susceptibility of fish to hearing loss or injury when exposed to anthropogenic sound.

The basic elements of a fish’s inner ear are three orthogonal, semicircular canals and their 

associated otolith organs. More detailed descriptions of the morphology of fishes’ ears and their 

function can be found in Popper et al. (1988, 2003). In addition to hearing, the vestibular system of 

the inner ears of fish enable them to sense gravity and function as six degrees of freedom sensors; 

this permits fish to sense tri axial linear (x, y, and z or forward-backward, side-to-side, and up-anddown) and angular (pitch, roll, and yaw) accelerations of their bodies (Fay and Popper, 2000; Platt, 

1988).

The inner ear of fish is stimulated by the water particle motion component of a sound wave. 

The fish, which is nearly neutrally buoyant, moves with the oscillatory motion of the water particles in 

the sound wave whereas the otolithic masses, because they are approximately three times the 

density of the fish, lag behind the motion of the sensory epithelia of the fish’s ear. The resulting 

differential motion between the otolithic masses and the otolithic sensory epithelia bends hair cell 

stereocilia, which causes the fish to hear the sound wave. Fish without swim bladders, which 

includes many teleost species and all elasmobranchs, only hear sounds when the level of particle 

motion in the sound is high enough to cause the sequence of events described above. 

Consequently, these fish are considered to have poor hearing and can only hear (detect a source) 

when they are close to a sound source with sufficient energy to cause particle motion above their 

hearing thresholds (Kalmijn, 1988; Rogers and Cox, 1988; Fay and Popper, 2000).

Fish with swim bladders have the potential to extend the frequency range and sensitivity of 

their hearing. The extent to which this happens depends on the location of the swim bladder relative 

to the ear or structures that would pair the swim bladder to the ear. However, the mere presence of 
Gulf of Mexico G&G Activities Programmatic EIS J-4 

a swim bladder without further specialization appears to offer minimal hearing enhancement over 

that of fish without swim bladders (Braun and Grande, 2008). Braun and Grande (2008) described

the known specializations that have evolved in fishes to enhance hearing. The hearing 

specializations include swim bladder rostral extensions, auditory bullae, suprabranchial chambers 

(does not involve the swim bladder), and Weberian apparatus (Braun and Grande, 2008).

The hypothesis that the presence of a swim bladder or other hearing specialization is the 

basis for the observed differences in hearing sensitivity between fish species and that hearing 

function at the level of hair cells (particle motion) is similar among vertebrates continues to gain 

scientific support (Popper and Fay, 1997; Radford et al., 2012).

There are three listed fish species in the portion of the GOM covered by this Programmatic 

EIS: Gulf sturgeon (Acipenser oxyrichus desotoi); smalltooth sawfish (Pristis pectinata); and 

largetooth sawfish (Pristis perotteti). The Gulf sturgeon has a swim bladder but no hearing 

specializations. The sawfish are elasmobranchs and do not have swim bladders. The species of 

fish taken by commercial and recreational fishers within the GOM are identified by the Gulf of Mexico 

Fishery Management Council (2012). The majority of the managed fish species within the GOM 

have swim bladders such as snappers (Lutjanus, Etelis, Ocyurus, Pristipomoides, Rhomboplites), 

groupers (Epinephelus, Mycteroperca), tilefishes (Caulolatilus, Lopholatilus), jacks (Seriola), 

triggerfishes (Balistes), wrasses (Lachnolaimus), cobia (Rachycentron canadum) (a migratory 

pelagic fish), and bluefish (Pomatomus saltatrix) (a species that is not managed but is taken by 

fishers). Managed fish species without swim bladders include mackerel (Scomberomorus spp.), 

cero (Scomberomorus regalis), and little tunny (Euthynnus alletteratus). Dolphinfish (Coryphaena 

hippurus), which also do not have a swim bladder, are not managed but are taken in commercial and 

recreational fisheries. The relationship between the morphology of the swim bladder and inner ears 

and the hearing of some species of fish within the families listed above have been investigated and 

found to vary between species (Barun and Grande, 2008; Horodysky et al., 2008; Wright et al., 

2011).

4 SOURCES OF ANTHROPOGENIC SOUND AND SOUND METRICS

There is considerable interest in anthropogenic (human made) underwater sound driven by a 

better understanding of the importance of sound to aquatic animals and the potential impacts of 

sound on the health of aquatic animals. Anthropogenic sound can be assigned to one of two 

general categories: continuous and pulsed (or impulsive). Pulsed sounds can be single (e.g., an 

underwater explosion) or multiple (e.g., a seismic sound source or pile driving).

Continuous sounds include ship noise or noises from drilling or operation of pumps. At 

locations far from a seismic survey or in cases where more than one seismic survey is underway in a 

part of an ocean, seismic sounds that are pulsed sounds near the source may appear continuous 

depending on several factors that affect the propagation of sound over long distances (Greene and 

Richardson, 1988). Continuous sound may vary in amplitude with time, and the sound sources may 

be narrow band with dominant discrete frequencies (tonal) or have a continuous distribution of sound 
Gulf of Mexico G&G Activities Programmatic EIS J-5 

over a broad frequency range (broadband). Continuous sound sources such as ship engines can 

have signatures that permit individual vessels to be identified (Hildebrand, 2009; Ogden et al., 2011). 

Shipping noise has spectra that are lower in frequency with highest levels in the 20 to 50 hertz (Hz) 

range, which overlaps the range of best hearing for most species of fish (Rogers and Cox, 1988). 

The same is true of seismic sources. Many sources of continuous anthropogenic sound have not 

been measured so information about their characteristics is not available.

Pulsed sounds typically are short in duration and generated by a large number of sources 

(e.g., seismic sound sources, pile driving, explosions, commercial and recreational sonars and 

echosounders, and subbottom profilers). Such sounds are impulsive in nature in that they are short 

(typically less than 100 milliseconds [ms] in duration), have a relatively rapid onset, a relatively high 

peak amplitude, and a gradual decline to ambient sound levels at which time they may appear 

almost continuous in nature. Because of the shorter rise times and other features, transient sounds 

tend to have a relatively broad frequency range. A complete characterization of transient sounds 

that are repeated, as is the case for pile driving and seismic exploration, need to include the time 

period over which the sounds are generated and the time between sounds. Explosions are an 

example of an impulsive sound source. If an explosion occurs in the water column, it will likely have 

a very rapid rise time and high amplitude typical of a shock wave. Impulsive sound from single 

charge explosions tend to have durations similar to that of seismic and pile driving sounds but much 

higher peak pressures and much shorter rise times. However, if the explosion results from several 

time-delayed charges, the resulting sound may have considerable duration and will not have the 

distinctive features of the impulsive sound generated by a single explosive charge (Continental Shelf 

Associates, Inc., 2004). Impulsive sounds generated by seismic sources, pile driving, and 

explosions have part of their energy at low frequencies that can be heard by fish and can create 

overpressures capable of physically injuring fish.

A wide range of navigation, military, commercial, and recreational sonars generate impulsive 

sounds. Such sound-producing instruments are very common and are used by almost every vessel 

on the water. Military sonars are designed to detect submarines; surface vessels and other military 

targets typically operate at frequencies less than 20 kHz and may generate complex transmissions 

that can be up to 100 seconds in duration. The military uses other sonars with characteristics similar 

to that of commercial sonars for other detection tasks. Commercial sonars are used to locate targets 

(fish) in the water column, map the seafloor, and perform some subbottom characterization 

objectives. Except for a small number of clupeid species that can hear at ultrasonic frequencies 

(Mann et al., 1997, 2001, 2005; Popper et al., 2004; Wilson et al., 2009), the impulsive sounds 

generated by high-frequency sound sources cannot be heard by fish and will not pose a threat of 

physical injury or affect behavior.

Hildebrand (2009) grouped anthropogenic and natural sources of sound into three frequency 

bands. According to Hildebrand (2009), the lowest band (10 to 500 Hz) is dominated by shipping 

sound with additions from seismic exploration being conducted in deeper water. Because of low 

attenuation, low-frequency sound may propagate very long distances affecting entire ocean basins. 

The middle band (0.5 to 25 kHz) is produced primarily by natural sources with contributions from 
Gulf of Mexico G&G Activities Programmatic EIS J-6 

some commercial and military sonars and small vessels. Because of higher attenuation, midfrequency band sound affects more local areas, on the order of tens of kilometers, around sound 

sources. The highest frequency band (>25 kHz) contains anthropogenic sound produced by various 

commercial and recreational sources. However, at high frequencies, sound attenuation is very high 

and the characteristics of some sources, such as high directivity, limit their effect to small areas very 

near the source. Most types of G&G sound sources other than vessels and airguns produce sound 

within the mid- and high-frequency bands described by Hildebrand (2009).

Sound may be described by several metrics depending on the needs of the target analysis 

(Hastings, 2008). In the case of this appendix, the focus is on metrics that are used to evaluate the 

potential for a sound to affect fish hearing or to cause injury to fish. Fish differ from marine mammals 

in that their hearing is sensitive to both the particle motion and pressure components of a sound. 

The hearing of marine mammals is discussed in Appendix H. Some impacts to fish hearing are 

thought to be related to the energy in an exposure. The energy related metric currently used is a 

measure proportional to the energy of an exposure in the far field of a sound source. For transient 

impulsive sound, this metric is sound exposure level (SEL). SEL is expressed in decibels relative to

1 micropascal squared second (dB re 1 μPa2

•s) and is computed from observed pressures in a 

transient sound signal as shown in Equation 1. SEL can be expressed as an index of the energy in 

an exposure from a single impulsive sound or of the cumulative energy in an exposure from multiple 

impulsive sounds. If cumulative SEL is used to index the energy in a multiple event sound exposure, 

then information about the number of events and their distribution in time should be part of the 

metric. SEL for a single impulsive sound event is expressed as SELss, where “ss” stands for “single 

strike” (Equation 1). SEL for the cumulative energy in multiple impulsive sound events is SELcum 

(Equation 2), where “cum” stands for cumulative.

SSSSSSssss = 10llllll10(∫ pp(tt)2 dd ) (1)

SSSSSScccccc = 10 llllll10 ∑ 10 nn �SSSSSSssss,ii⁄10� ii=1 (2)

The SEL metrics for impulsive sounds with durations less than 1 second are derived from a 

more general measure of sound energy than those for sounds longer in duration; this is the 

equivalent continuous sound pressure level (SPL). Equation 3 shows the computation for the 

commonly used equivalent continuous SPL using standard terminology and units. In Equation 3, 

T is in seconds and po is the reference sound pressure in μPa.

eeeeSSSSSSeeee = 10 llll 10 �

1

TT ∫ pp(tt)2

pp0

2

TT

0 dd � (3)

Current practice is to characterize continuous sound using the SPL, which is the level of the 

root mean square (rms) pressure in all or segments of an exposure. This metric is computed as 

shown in Equation 4, where T is in seconds. It is presented as SPLrms referenced to 1 μPa.
Gulf of Mexico G&G Activities Programmatic EIS J-7 

SSSSSSrr = 20 llllll10 ��1

TT ∫ pp(tt)2 dd � (4)

The SPLrms also is used as a measure of the rms pressure in transient sounds. When used 

for this purpose, it is computed differently than for continuous sounds. Because of the very short 

duration of most transient sound signals, inclusion of background noise in the computation can bias 

the metric. To avoid this bias, the current convention is to only include the central 90 percent of the 

signal in the computation, excluding the first and last 5 percent of the signal. In this case, the metric 

is computed as shown in Equation 5 and is referenced to 1 μPa.

SSSSSSrr ,90 = 20 llllll10 �� 1

TT90

∫ pp(tt)2 dd � (5)

A third commonly used metric to report SPLs is SPLpeak, which can take several forms. 

Common forms include the levels of the peak positive and negative pressure (zero to peak; or peak) 

or the level of the absolute peak pressure (p-p). In all cases, the reference for the levels is 1 μPa. 

Because of the increasing importance of peak negative pressure as an explanatory variable for 

evaluation of potential decompressive injury to fish and the historical use of peak positive pressure in 

regulatory practice, it is suggested that both peak positive and peak negative pressure levels be 

reported for impulsive sounds. Equation 6 shows how these metrics are computed.

SSSSSSpp pppp = 20 llllll10(max(±pp(tt))) (6)

It has been known for some time that all fish “hear” the particle motion component of sound 

(Ladich and Popper, 2004). As in the case of pressure, particle motion measurements are reported 

as levels relative to a reference value. The ANSI S1.1 1992(R2004) standard is a sound particle 

velocity reference, with the units nanometers per second (nm/s). In ISO/DIS 1683, the International 

Organization for Standardization recommends the use of 1 nm/s as the reference for sound particle 

velocity. Because particle velocity is a vector, both magnitude and direction need to be considered. 

Equation 7 shows the computation to reduce tri-axial particle velocity measurements over the 

duration of a sound event to a single particle velocity magnitude time history.

vv(tt) = ⌈vv(tt)⌉ = �vvxx(tt)2 + vvyy(tt)2 + vvyy(tt)2 (7)

The result of the operation described in Equation 7 is a series of particle velocity vector 

magnitude values at the digital sampling frequency of the particle velocity measurement system over 

the duration of the sound event. This set of particle velocity amplitudes can be summarized in 

several ways. Equation 8 is used to compute the level (L), referenced to 1 nm/s, of the peak 

particle velocity in the sound event. Equation 9 is the particle velocity analog of SPLrms for 

pressure. This computation returns the decibel level for the rms of particle velocity amplitude over 

the central 90 percent of the duration of an impulsive sound event.

VVVV = 20 llllll10�vvpp pppp� (8)
Gulf of Mexico G&G Activities Programmatic EIS J-8 

vv90 = 20 llllll10 �� 1

TT90

∫ vv(tt)2dd � (9)

To date, regulatory authorities have not used particle velocity as an element of exposure 

criteria for fish.

5 MECHANISMS OF HEARING LOSS AND INJURY

High levels of anthropogenic sound can affect hearing in or cause injury to fishes. The 

mechanisms of hearing loss and injury differ, and the susceptibility across species and age groups, 

at least for the species tested to date, is quite variable.

5.1 HEARING LOSS

Hearing loss in animals, in general, is a function of the intensity, frequency content, and 

duration of exposure. Hearing loss is the result of overstimulation of hair cells. For fish, the 

overstimulation may result in loss of hair cells and temporary hearing loss (i.e., temporary threshold 

shift [TTS]). Permanent hearing loss (i.e., permanent threshold shift [PTS]) has not been 

demonstrated in fish because fish are known to regenerate hair cells and increase the number of 

hair cells in their ears over their life (Popper and Fay, 1999). The TTS has been observed in fish 

exposed to continuous and transient sound (Popper and Schilt, 2008). The occurrence of hair cell 

loss and TTS is a function of the species of fish as well as the characteristics of the sound exposure 

(Popper and Schilt, 2008; Au and Hastings, 2008). The recovery time from TTS varies with the 

magnitude of TTS, species, and likely other factors not identified in studies performed to date 

(Popper and Hastings, 2009). For example, Popper et al. (2005) found that northern pike (Esox 

lucius) and lake chub (Couesius plumbeus) experienced TTS following exposure to seismic sound 

but recovered within 24 hours. Broad whitefish (Coregonus nasus) exposed to the same levels of 

seismic sound did not experience TTS. No damage was found to the structure of the ears of these 

fish (Song et al., 2008).

The question when evaluating the likely effect of exposure to G&G sound sources on hearing 

in fish is the SEL (the level of sound the fish receive) at which TTS is likely to occur. It has been 

shown for mammals that asymptotic TTS is a linear function of the difference between the SPL of an 

exposure noise and a baseline-hearing threshold (Carder and Miller, 1972). Based on an analysis of 

data, Hastings et al. (1996) suggested that sound levels 90 to 140 decibels (dB) above the baselinehearing threshold of fish could injure their inner ears. Smith et al. (2004) tested the hypothesis of 

linear threshold shift (LINTS) where the TTS in fish is a linear function of the difference (in dB) 

between the level of noise exposure and baseline hearing threshold. The linear function fit to data 

indicated that a TTS of 6 dB would be experienced at a sound pressure difference (SPD) of 40 dB 

and a TTS of 20 dB would be experienced at an SPD of 100 dB. The data also suggested that fish 

are more susceptible to TTS at lower sound frequencies where hearing tends to be most sensitive. 

Even though limited in the number of species tested, the studies completed to date provide initial 

estimates of the level of noise that may lead to TTS in fish.
Gulf of Mexico G&G Activities Programmatic EIS J-9 

5.2 INJURY

Injury to fish from exposure to anthropogenic sound is from barotrauma. Barotraumas are 

tissue injuries resulting from rapid changes in pressure. Depending on the sound source and the 

receiving distance from a source, barotrauma may be caused by concussion or decompression.

5.3 CONCUSSION

Concussion injuries are caused by high amplitude positive overpressures typified by an initial 

positive pressure pulse with a very rapid rise time and high peak pressure. Well-known examples of 

a high-energy concussive overpressure pulse are the shock waves produced by in-water detonation 

of explosives with the chemical dynamics (rapid burn rate) of dynamite (Cole, 1948).

Concussion is most likely not a significant source of mortality for fish exposed to sound 

generated by G&G sources such as airguns in open field conditions. Falk and Lawrence (1973) 

found that while linear and point source explosions killed fish, exposure to a seismic airgun did not. 

Recent studies of exposure of fish to seismic airguns did not observe barotrauma injuries (Hastings 

et al., 2008; Popper et al., 2005; McCauley and Kent, 2012). McCauley et al. (2003) observed hair 

cell damage in pink snapper (Pagrus auratus) and erratic behavior of exposed fish that may have 

indicated vestibular disruption; however, immediate or delayed mortality of exposed fish resulting 

from injuries to tissues other than ear tissue was not reported.

5.4 DECOMPRESSION

Decompression injuries are caused by negative overpressures such as the negative 

pressure resulting from pulsations of a gas bubble created by an explosion or airgun discharge. The 

high positive overpressures generated by sources that can cause concussion injuries at short 

distances from the source become a negative overpressure and a cause of decompression injuries 

when they are inverted, by reflection from the water surface (Cole, 1948). The negative 

overpressures that result from airguns may be sufficiently large at shorter ranges from a source pose 

the risk of decompressive injuries to fish with swim bladders. Decompressive injuries have been 

observed in fish exposed to sounds generated by pile driving, which are very similar to the sounds 

generated by airguns (Halvorsen et al., 2011) and similar enough to serve as a primary data source 

for guidelines on the exposure of fish to seismic survey sounds (Popper et al., 2014). Seismic 

exploration devices such as water guns produce, by implosion rather than a bubble, a negative 

overpressure pulse (Hutchinson and Detrick, 1984).

Injuries caused by decompression were first noticed and described during investigations of 

injuries to fish caused by explosions. Investigators expecting to find primarily concussive injuries 

found instead evidence that the swim bladder seemed to explode in fish immediately killed by 

explosions and that mortally injured fish had injuries to swim bladders and other internal organs 

suggestive of decompression rather than concussion. Decompression has become the focus of 

injury to fish from exposure to sound and other events where the pressure that fish are exposed to 

changes quickly.
Gulf of Mexico G&G Activities Programmatic EIS J-10

There are two primary sources of decompression injuries to fish, one involving fishes’ swim 

bladders and the other involving gases dissolved in the blood and tissues of fish. Boyles’ and 

Henry’s Laws describe the basic mechanics of these decompression injury mechanisms (Chang, 

2005).

Boyles’ Law describes the response of gas-filled bodies, such as a fish’s swim bladder and 

bubbles that may exist in the digestive track or elsewhere, to changes in pressure. It can be 

expressed as shown in Equation 9, where P stands for pressure and V for volume.

P1•V1 = P2•V2 (9)

In Equation 9, P1 is the pressure acting on a fish prior to exposure and, for swim bladder 

fish, this is assumed to be their acclimation pressure. Here, acclimation refers to buoyancy and it is 

assumed that when acclimated, a fish’s swim bladder is filled to volume V1 and that the fish is 

neutrally buoyant. Pressure is absolute pressure and, after allowing for atmospheric pressure, is 

proportional to the depth of the fish. The P2 is the pressure of exposure and it is the instantaneous 

pressure that exists during passage of a sound wave. The V2 is the volume of the fish’s swim 

bladder in response to the change in pressure acting on the fish. When the compressive portion of 

the sound wave is at the fish, then V2 < V1; antithetically, when the decompressive (rarefaction) 

portion of the sound wave is at the fish, V2 > V1.

Scientists investigating the effect of explosions on fish estimated that a 60 percent reduction 

in pressure was sufficient to rupture the swim bladder (Simenstad, 1974). Development of criteria 

for the design of hydroturbines included the specification that the pressure drop (which is essentially 

instantaneous) through the turbine runner should not exceed 60 percent of the pressure at the 

acclimation depth of the fish passing through the turbines (Cada et al., 1997). The susceptibility of 

fish to injury when decompressed is determined by the ratio of the acclimation pressure and 

exposure pressure (Yelverton et al., 1975; Goertner, 1978a; Brown et al., 2009, 2012), meaning the 

risk of decompression injury from sound is depth dependent. Rogers and Zeddies (2008) extended 

consideration of the effect of depth on the ability of a fish’s swim bladder to enhance hearing. They 

noted that due to an increase in the density of air in the swim bladder with depth, the swim bladder 

volume fluctuations from an incident sound wave would become increasing smaller with depth. This 

effect would, while resulting in decreased hearing sensitivity, reduce the risk of hearing loss due to 

overstimulation of ear hair cells.

Fish acclimate to the concentration of dissolved gas in the water they occupy. Gas 

exchange through gills maintains gas tensions in the blood at the levels that exist in the water fish 

occupy, provides oxygen for bodily functions, and removes carbon dioxide (Perry and McDonald, 

1993). Henry’s Law defines the relationship between the concentration of gas in solution in a fish’s 

blood and the pressure acting on the fish. Henry’s Law states that there is a constant of 

proportionality between the pressure acting on a fluid and the concentration of gas in the fluid. This 

relationship is shown in Equations 10 and 11, where P stands for pressure, C for concentration, 

and kg is a gas-specific solubility coefficient (Chang, 2005).
Gulf of Mexico G&G Activities Programmatic EIS J-11

P = kgC (10)

Or for a particular gas,

P1C1 = P2C2 (11)

The primary causes of death, both immediate and delayed, in decompressed swim bladder 

fish are various combination injuries resulting from bubbles in the gills, hemorrhaging in internal 

organs, and frothy blood in the heart (Gaspin, 1975; Yelverton et al., 1975; Christian, 1973; 

Goertner, 1978b; Brown et al., 2009, 2012; Rummer and Bennett, 2005). It appears that the 

combination of swim bladder expansion and change in the gaseous state from dissolved to free, at 

decompression (Equation 11) has effects that injure and kill fish. Two examples are as follows: 

(1) the release of gas from the blood and formation of bubbles in the gills blocks oxygen exchange; 

and (2) increased internal pressure in the caudal vein causes increases in intra-vein pressure, a 

rupture of the vein, and hemorrhaging in the kidney (Brown et al., 2009). The change in relative 

pressure drives changes in the state of gas carried by a fish’s blood, and fish at depth (higher 

pressure) are relatively less at risk of injury from decompressive pressure exposure. Unlike the case 

for swim bladder rupture and related decompressive injuries, no thresholds for injury or response 

functions have been derived for the risk of injury from changes in the state of gas at decompression.

6 EXPOSURE CRITERIA AND GUIDELINES

At present, there are no standardized or widely accepted criteria to gauge the exposure of 

fish to anthropogenic sound. Interim criteria for the onset of injury have been proposed for pile 

driving (Woodbury and Stadler, 2008; Stadler and Woodbury, 2009). These are dual criteria that 

also consider the size of fish. The criteria are expressed as levels for the allowable peak pressure 

(SPLpeak = 206 dB re 1 μPa) and an index for the total energy of exposure over the time required to 

drive a pile (SELcum = 187 dB re 1 μPa2

•s for fish weighing ≥2 grams [g] and 183 dB re 1 μPa2•s for 

fish weighing <2 g). Additional information about these interim criteria can be found in Popper et al. 

(2006) and Carlson et al. (2007).

Popper et al. (2014) presented guidelines for the exposure of fish to seismic sound. The 

guidelines resulted from consideration of data available through mid-2013 for impacts to hearing and 

physiological injury to fish from exposure to anthropogenic sound by a working group initially 

convened in 2004 by the U.S. Department of Commerce’s National Oceanic and Atmospheric 

Administration. In 2006, the working group was reorganized under the ANSI-Accredited Standards 

Committee S3/SC 1, Animal Bioacoustics, sponsored by the Acoustical Society of America. The 

guidelines for exposure of fish to sound produced by seismic airguns are presented in Table 7.4 of 

Popper et al. (2014).

Exposure guidelines are presented for mortality and potential mortal injury, recoverable 

injury, TTS, masking, and behavior in Popper et al. (2014). The guidelines for injury and TTS are 

presented as sound levels and those for masking and behavior as a relative risk of effect (high, 
Gulf of Mexico G&G Activities Programmatic EIS J-12

moderate, or low) in zones near (tens of meters), intermediate to (hundreds of meters), and far from 

(thousands of meters) a seismic source. Exposure guidelines for injury include an index of the total 

sound energy of exposure (SELcum) as well as the peak pressure (SPLpeak) of exposure. In the 

case of TTS, the exposure guideline is limited to an index of total energy of exposure. Numerical 

values are not given for masking and behavior guidelines. In all cases where numerical values are 

given the values are for the level of sound received by a fish.

For fish without swim bladders, exposure guidelines for mortality and potential mortal injury, 

recoverable injury, and TTS are >219 dB SELcum or >213 dB SPLpeak, >216 dB SELcum or 

213 dB SPLpeak, and >186 dB SELcum, respectively. The guidelines for relative risk of masking 

are low for all distances from an airgun source, while for behavior the relative risks are high, 

medium, and low for zones near, intermediate, and far from a seismic source.

Exposure guidelines for fish with swim bladders not involved in hearing are 210 dB SELcum 

or >207 dB SPLpeak for mortality and mortal injury, 203 dB SELcum or >207 dB SPLpeak for 

recoverable injury, and >186 dB SELcum for TTS. For this class of fishes, the relative risks for 

masking are low at all distances from a seismic source and are high, moderate, and low for risk of 

effect on behavior at near, intermediate, and far zones respectively from a seismic source.

Exposure guidelines for fish with swim bladders involved in hearing are 207 dB SELcum or 

>207 dB SPLpeak for mortality and mortal injury, 203 dB SELcum or >207 dB SPLpeak for 

recoverable injury, and >186 dB SELcum for TTS. For this class of fishes, the relative risks for 

masking are low for near and intermediate zones from a seismic source and moderate for the far 

zone from a source. The risk for effects on behavior are high in near and intermediate zones from a 

seismic source and are moderate in the far zone from a source.

No exposure criteria or guidelines are available for G&G sources other than airguns.

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APPENDIX K

CUMULATIVE AND CHRONIC EFFECTS 

IN THE GULF OF MEXICO

Cumulative and Chronic Effects in the Gulf of Mexico

Estimating Reduction of Listening Area and Communication Space 

due to Seismic Activities in Support of the BOEM Geological and 

Geophysical Activities Draft Programmatic Environmental Impact 

Statement 

Submitted to:

Jolie Harrison

National Marine Fisheries Service

Contract: EA-133F-15-SE-1591

6 June 2016

P001296-001

Document # 01073

Version 1.0

JASCO Applied Sciences (Canada) Ltd.

2305–4464 Markham Street

Victoria, BC V8Z 7X8 Canada

Tel: +1-250-483-3300

Fax: +1-250-483-3301

www.jasco.com

. 
K-ii Cumulative and Chronic Effects in the Gulf of Mexico

Document Version Control

Version Date Name Change

1.0 2015 Dec 18 D. Hannay Version 1.0 submitted to client

Suggested citation:

Matthews, M.-N.R., A. Schlesinger, and D. Hannay. 2015. Cumulative and Chronic Effects in the Gulf of 

Mexico: Estimating Reduction of Listening Area and Communication Space due to Seismic Activities in 

Support of the BOEM Geological and Geophysical Activities Draft Programmatic. Environmental Impact 

Statement. JASCO Document # 01073, Version 1.0. Technical report by JASCO Applied Sciences for 

National Marine Fisheries Service. 
Gulf of Mexico G&G Activities Programmatic EIS K-iii

Contents

EXECUTIVE SUMMARY........................................................................................................ 1

1. INTRODUCTION .............................................................................................................. 2

1.1. Acoustic Metrics ................................................................................................................................ 5

1.1.1. Root-Mean-Square Sound Pressure Level............................................................................ 5

1.1.2. Sound Exposure Level........................................................................................................... 6

1.1.3. Energy Equivalent Sound Pressure Level ............................................................................. 7

1.2. Marine Species and Auditory Bands................................................................................................. 7

1.3. Chronic and Cumulative Effects........................................................................................................ 7

2. METHODOLOGY ............................................................................................................. 8

2.1. Acoustic Source Models.................................................................................................................... 8

2.2. Transmission Loss Models................................................................................................................ 8

2.3. Chronic and Cumulative Exposure (CCE) Calculator..................................................................... 10

2.3.1. Survey Distribution............................................................................................................... 10

2.3.2. Removal of Top 10% of Pulse Exposures ........................................................................... 13

2.4. Baseline Levels ............................................................................................................................... 13

2.5. Listening Area ................................................................................................................................. 15

2.6. Bryde’s Whale Communication Space............................................................................................ 17

3. MODELED PARAMETERS............................................................................................... 19

3.1. Acoustic Environment ..................................................................................................................... 19

3.2. Acoustic Sources ............................................................................................................................ 19

3.3. Transmission Loss and CCE Calculator ......................................................................................... 19

3.4. Bryde’s Whale Communication Space............................................................................................ 20

4. RESULTS..................................................................................................................... 21

4.1. Cumulative Sound Exposure Levels ............................................................................................... 22

4.2. Time-Averaged Equivalent Sound Pressure Levels ....................................................................... 24

4.3. Listening Area ................................................................................................................................. 28

4.4. Bryde’s Whale Communication Space............................................................................................ 32

5. DISCUSSION AND CONCLUSION ..................................................................................... 41

5.1. Site-Specific Results ....................................................................................................................... 41

ACKNOWLEDGMENTS ....................................................................................................... 43

LITERATURE CITED .......................................................................................................... 44

Gulf of Mexico G&G Activities Programmatic EIS K-v 

Figures

Figure 1. G&G EIS project area with ten modeled receiver sites (yellow dots), project management 

zones (grey shaded areas), activity zones (1–6), and closure areas (hashed arears). .......................... 3

Figure 2. The N×2-D and maximum-over-depth modeling approach used by MONM................................. 9

Figure 3. Location of the modeled survey cells (purple dots) and receiver (yellow dots)........................... 12

Figure 4. Summed levels for frequency bands of 10 Hz to 10 kHz for all sites at 5 m receiver depth. ...... 14

Figure 5. Summed levels for frequency bands of 10 Hz to 10 kHz for nine sites at 30 m receiver............ 14

Figure 6. Summed levels for frequency bands of 10 Hz to 10 kHz for seven sites at 500 m receiver 

depth. ..................................................................................................................................................... 15

Figure 7. Schematic representation of changes in listening area around a marine mammal..................... 16

Tables 

Table 1. Modeled receiver site locations and water depths.......................................................................... 2

Table 2. Survey types and sources used to represent the modeled activities.............................................. 4

Table 3. Description of survey activity levels for G&G EIS Alternatives. ...................................................... 4

Table 4. Survey lengths (km) associated with each alternative for each activity zone................................. 5

Table 5. Maximum average pulse density (annual number of pulses per km2; Alternative C) per 

airgun array in each activity zone. ......................................................................................................... 10

Table 6. Eastern Slope: Geoacoustic properties of the sub-bottom sediments as a function of depth, 

in meters below the seafloor.................................................................................................................. 19

Table 7. Broadband (10–5000 Hz) baseline (Alternative A; no activity) SPL (dB re 1 μPa) for each 

receiver site and depth........................................................................................................................... 21

Table 8. Alternative C: Cumulative SEL (dB re 1 μPa2s) at each receiver site with M-weighting for 

low- , mid-, and high-frequency cetaceans and without weighting. ....................................................... 22

Table 9. Alternative E (25% reduction): Cumulative SEL (dB re 1 μPa2s) at each receiver site with Mweighting for low- , mid-, and high-frequency cetaceans and without weighting................................... 22

Table 10. Alternative F1 (area closures): Cumulative SEL (dB re 1 μPa2s) at each receiver site with 

M-weighting for low- , mid-, and high-frequency cetaceans and without weighting. ............................. 23

Table 11. Alternative F2 (area closures and 25% reduction): Cumulative SEL (dB re 1 μPa2s) at each 

receiver site with M-weighting for low- , mid-, and high-frequency cetaceans and without 

weighting................................................................................................................................................ 23

Table 12. Alternative C: Time-averaged equivalent sound pressure levels (Leq) at each receiver site 

with M-weighting for low- , mid-, and high-frequency cetaceans and without weighting....................... 24

Table 13. Alternative C: Time-averaged equivalent sound pressure levels (Leq) above ambient at 

each receiver site with M-weighting for low- , mid-, and high-frequency cetaceans and without 

weighting................................................................................................................................................ 24

Table 14. Alternative E (25% reduction): Time-averaged equivalent sound pressure levels (Leq) at 

each receiver site with M-weighting for low- , mid-, and high-frequency cetaceans and without 

weighting................................................................................................................................................ 25

Table 15. Alternative E (25% reduction): Time-averaged equivalent sound pressure levels (Leq) 

above ambient at each receiver site with M-weighting for low- , mid-, and high-frequency 

cetaceans and without weighting........................................................................................................... 25

Table 16. Alternative F1 (area closures): Time-averaged equivalent sound pressure levels (Leq) at 

each receiver site with M-weighting for low- , mid-, and high-frequency cetaceans and without 

weighting................................................................................................................................................ 26
K-vi Cumulative and Chronic Effects in the Gulf of Mexico

Table 17. Alternative F1 (area closures): Time-averaged equivalent sound pressure levels (Leq) 

above ambient at each receiver site with M-weighting for low- , mid-, and high-frequency 

cetaceans and without weighting........................................................................................................... 26

Table 18. Alternative F2 (area closures and 25% reduction): Time-averaged equivalent sound 

pressure levels (Leq) at each receiver site with M-weighting for low- , mid-, and high-frequency 

cetaceans and without weighting........................................................................................................... 27

Table 19. Alternative F2 (area closures and 25% reduction): Time-averaged equivalent sound 

pressure levels (Leq) above ambient at each receiver site with M-weighting for low- , mid-, and 

high-frequency cetaceans and without weighting.................................................................................. 27

Table 20. Alternative C relative to Alternative A (no activity): Remainder of listening area (%) at each 

receiver site with M-weighting for low- , mid-, and high-frequency cetaceans and without 

weighting................................................................................................................................................ 28

Table 21. Alternative E (25% reduction) relative to Alternative A (no activity): Remainder of listening 

area (%) at each receiver site with M-weighting for low- , mid-, and high-frequency cetaceans and 

without weighting. .................................................................................................................................. 28

Table 22. Alternative F1 (area closures) relative to Alternative A (no activity): Remainder of listening 

area (%) at each receiver site with M-weighting for low- , mid-, and high-frequency cetaceans and 

without weighting. .................................................................................................................................. 29

Table 23. Alternative F2 (area closures and 25% reduction) relative to Alternative A (no activity): 

Remainder of listening area (%) at each receiver site with M-weighting for low- , mid-, and highfrequency cetaceans and without weighting.......................................................................................... 29

Table 24. Alternative E (25% reduction) relative to Alternative C: Remainder of listening area (%) at 

each receiver site with M-weighting for low- , mid-, and high-frequency cetaceans and without 

weighting................................................................................................................................................ 30

Table 25. Alternative F1 (area closures) relative to Alternative C: Remainder of listening area (%) at 

each receiver site with M-weighting for low- , mid-, and high-frequency cetaceans and without 

weighting................................................................................................................................................ 30

Table 26. Alternative F2 (area closures and 25% reduction) relative to Alternative E (25% reduction): 

Remainder of listening area (%) at each receiver site with M-weighting for low- , mid-, and highfrequency cetaceans and without weighting.......................................................................................... 31

Table 27. Alternative F2 (area closures and 25% reduction) relative to Alternative F1 (area closures): 

Remainder of listening area (%) at each receiver site with M-weighting for low- , mid-, and highfrequency cetaceans and without weighting.......................................................................................... 31

Table 28. Baseline (Alternative A; no activity) SPL (dB re 1 μPa) for 100 Hz for each receiver site 

and depth. .............................................................................................................................................. 32

Table 29. Alternative C relative to Alternative A (no activity): Bryde’s whale communication space at 

all receiver sites. .................................................................................................................................... 33

Table 30. Alternative E (25% reduction) relative to Alternative A (no activity): Bryde’s whale 

communication space at all receiver sites. ............................................................................................ 34

Table 31. Alternative F1 (area closures) relative to Alternative A (no activity): Bryde’s whale 

communication space at all receiver sites. ............................................................................................ 35

Table 32. Alternative F2 (area closures and 25% reduction) relative to Alternative A (no activity): 

Bryde’s whale communication space at all receiver sites...................................................................... 36

Table 33. Alternative E (25% reduction) relative to Alternative C: Bryde’s whale communication 

space at all receiver sites....................................................................................................................... 37

Table 34. Alternative F1 (area closures) relative to Alternative C (no activity): Bryde’s whale 

communication space at all receiver sites. ............................................................................................ 38

Table 35. Alternative F2 (area closures and 25% reduction) relative to Alternative E (25% reduction): 

Bryde’s whale communication space at all receiver sites...................................................................... 39

Table 36. Alternative F2 (area closures and 25% reduction) versus Alternative F1 (area closures): 

Bryde’s whale communication space at all receiver sites...................................................................... 40
Gulf of Mexico G&G Activities Programmatic EIS K-1 

Executive Summary 

This report presents a chronic and cumulative effects assessment of noise exposures caused by oil and 

gas exploration activities in the United States (U.S.)–managed areas of the Gulf of Mexico by assessing

changes in listening area, applicable to all marine mammal species, and communication space for

Bryde’s whale (Balaenoptera edeni). This assessment considers four levels of activity, which correspond 

to the alternatives defined in Chapter 2 of the Gulf of Mexico Geological and Geophysical Activities Draft 

Programmatic Environmental Impact Statement (G&G EIS) (NOAA 2016). 

The two relatively new methods of assessing changes in listening area and communication space are 

explained in detail in Sections 2.5 and 2.6 of this report. The change in listening area method follows an 

approach applied to an effects assessment for in-air sounds to birds (Barber et al. 2009), but it had not 

previously been applied to underwater noise and marine fauna. To our knowledge, this study, and a 

related assessment of chronic and cumulative effects of noise in arctic waters, are the first applications of 

the listening area method to underwater sounds. The communication space assessment implemented the 

methods previously used for assessing anthropogenic noise effects on blue (Balaenoptera musculus) and 

fin (Balaenoptera physalus) whales by Clark et al. (2009). 

The term “listening area” refers to the region of ocean over which sources of sound can be detected by an 

animal at the center of a space. Sound sources considered by this method can be the same species 

(such as calls from conspecifics), a different species (such as a predator or prey species), natural sounds 

(such as breaking surface waves), and anthropogenic sounds. The change in listening area method 

applied by Barber et al. (2009) calculates a fractional reduction in listening area due to an addition of 

anthropogenic noise to the environment. It does not provide absolute areas or volumes as does the

communication space method; however, a benefit of the change in listening area method is that it does 

not require the signal source levels. The method only depends on the rate of sound transmission loss.

Changes in listening space can be related to the effects of anthropogenic noise on marine fauna. 

This communication space assessment considers the region within the ocean surrounding a calling 

Bryde’s whale, in which other Bryde’s whales can detect its calls. The relationship between 

communication space and the well-being of Bryde’s whales is presently unknown, but it is reasonable to 

assume that Bryde’s communications serve an important purpose, as it does in other marine mammals, 

(e.g., attracting mates, identifying and tracking offspring, and maintaining group structure) that could 

affect an individual’s and possibly a population’s health. Bryde’s whale communication space is limited by 

the masking of their calls due to natural ambient sounds and/or anthropogenic noise. Communication 

space is larger for louder calls. Adding ambient and especially anthropogenic noise to the environment 

surrounding the Bryde’s whales leads to a decrease in communication space. Hence, the possible effects 

of anthropogenic noise on Bryde’s whales can be inferred by examining the reduction in communication 

space.
K-2 Cumulative and Chronic Effects in the Gulf of Mexico

1. Introduction

This study evaluates potential chronic and cumulative effects to marine mammals from noise exposures 

caused by oil and gas exploration activities in the Gulf of Mexico in support of the Bureau of Ocean 

Energy Management (BOEM) Geological and Geophysical Activities Draft Programmatic Environmental 

Impact Statement (G&G EIS). In this assessment, the methods for calculating a change in listening area 

by Barber et al. (2009) and communication space by Clark et al. (2009) were applied. Both of these 

methods require knowledge of ambient and anthropogenic noise levels at receiver positions. JASCO 

developed a framework to calculate cumulative sound exposure levels (SEL) produced by large numbers 

of geographically distributed acoustic sources, such as the seismic pulses from multiple seismic surveys 

using airgun arrays. SELs were calculated for several scenarios for one full year of exploration activities 

in the Gulf at ten receiver sites (Table 1 and Figure 1). The framework was implemented using scripted 

Excel spreadsheets, which incorporated acoustic transmission loss tables from sound propagation

modeling of an 8000 in3 airgun array and single 90 in3 airgun. The same source types (Table 2) were 

considered in a previous modeling assessment of marine mammal exposures (G&G EIS, Appendix D; 

NOAA 2016). 

BOEM divided the study area into three project management zones (Western, Central, and Eastern Gulf–

grey areas, Figure 1). For the purpose of this assessment, we subdivided these zones into six activity 

zones based on the water depth. The 200 m isobaths was chosen as the divider of coastal and offshore 

areas.

Table 1. Modeled receiver site locations and water depths.

Site Receiver Site Latitude Longitude Water Depth (m)

1 Western Gulf 27.01606 −95.7405 842

2 Florida Escarpment 25.95807 −84.6956 693

3 Midwestern Gulf 27.43300 −92.1200 830

4 Sperm Whale Site 24.34771 −83.7727 1053

5 Deep Offshore 27.64026 −87.0285 3050

6 Mississippi Canyon 28.15455 −89.3971 1106

7 Bryde’s Whale Site 28.74043 −85.7302 212

8 De Soto Canyon 29.14145 −87.1762 919

9 

Flower Garden Banks 

National Marine 

Sanctuary

27.86713 −93.8259 88

10 Bottlenose Dolphin Site 29.40526 −93.3247 12
Gulf of Mexico G&G Activities Programmatic EIS

K-3

Figure 1. G&G EIS project area with ten modeled receiver sites (yellow dots), project management zones (grey shaded areas), activity 

zones (1–6), and closure areas (hashed arears). The inset shows a zoom into the Flower Gardens closure area. 
K-4 Cumulative and Chronic Effects in the Gulf of Mexico

Table 2. Survey types and sources used to represent the modeled activities.

Survey Type Representative Airgun Array Pulse Spacing (m)

2-D seismic 1 × 8000 in3 50

3-D NAZ seismic 2 × 8000 in3 37.5

3-D WAZ seismic 4 × 8000 in3 37.5

3-D Coil seismic 4 × 8000 in3 50

Geotechnical 1 × 90 in3 (single airgun) 0.7*

* Assumes 3 pulses per second and a tow speed of 4 knots, which is a surrogate for boomer-type sources.

Chapter 2 of G&G EIS (NOAA 2016) describes a number of alternatives that represent different survey 

activity levels in the Gulf of Mexico. For this analysis, Alternatives, C, E, and F were chosen to represent 

a range of activity levels; the content of each of these alternatives is summarized in Table 3. For the 

purpose of this assessment Alternative F was split into two sub-alternatives, F1 and F2. The later reflects 

the addition of closure areas (as for F1) and a 25% reduction of the activity level in all activity zones (as 

for E). Additionally, calculations of change in listening area and communication space require baseline 

noise levels for reference. We refer to this condition as Alternative A. It is defined by commercial shipping 

noise and noise from natural sounds produced mainly by wind and breaking waves. It therefore does not 

include seismic survey activity. 

Table 3. Description of survey activity levels for G&G EIS Alternatives.

G&G EIS Alternatives Description

A No seismic survey activities. Noise consists of natural sounds and commercial vessel noise. 

C All activities uniformly distributed throughout the project area, over 12 months, except for 

coastal water closures (Figure 1) beginning of February to end of May. 

E Same as Alternative C, with a 25% reduction of the activity level in all activity zones. 

F1 Same as Alternative C, with the addition of closure areas (Flower Gardens, Central Planning, 

De Soto, and Dry Tortugas closure areas; Figure 1) and 25% of the activity that would have 

occurred in the closure areas redistributed in non-closure areas of the same activity zone. 

F2 Same as Alternative F1, with a 25% reduction of the activity levels in all activity zones. 

In addition to the survey and source types (Table 2), BOEM provided the anticipated annual (2017–2026) 

survey lengths (km) for each type of activity and project management zone. The survey lengths were 

annually averaged for each type of activity, in each activity zone, and for all alternatives (Table 4). These 

lengths were used to calculate the survey distributions across the study area.
Gulf of Mexico G&G Activities Programmatic EIS K-5 

Table 4. Survey lengths (km) associated with each alternative for each activity zone. A dash 

means no survey of this type is expected within the activity zone.

Activity

Zone

Alternative C Alternative E

2-D 3-D NAZ 3-D WAZ 3-D Coil Geotechnical 2-D 3-D NAZ 3-D WAZ 3-D Coil Geotechnical

1 - 5,391 - - 154 - 4,043 - - 116

2 - 25,698 9,995 4,284 237 - 19,274 7,496 3,213 178

3 - 53,921 7,695 3,297 3,176 - 40,441 5,771 2,473 2,382

4 12,038 112,190 - 28,031 12,149 9,029 84,143 - 21,023 9,112

5 - - - - 505 - - - - 379

6 10,001 23,706 7,260 3,111 2,528 7,501 17,780 5,445 2,333 1,896

Activity

Zone

Alternative F1 Alternative F2

2-D 3-D NAZ 3-D WAZ 3-D Coil Geotechnical 2-D 3-D NAZ 3-D WAZ 3-D Coil Geotechnical

1 - 5,344 - - 150 - 4,008 - - 113

2 - 25,663 9,981 4,278 236 - 19,247 7,486 3,209 177

3 - 53,719 7,666 3,285 3,134 - 40,289 5,750 2,463 2,351

4 9,191 85,659 - 21,402 9,256 6,893 64,244 - 16,052 6,942

5 - - - - 444 - - - - 333

6 8,982 21,290 6,520 2,794 2,186 6,736 15,968 4,890 2,095 1,639

1.1. Acoustic Metrics

Underwater sound pressure amplitude is commonly measured in decibels (dB) relative to a fixed 

reference pressure of pο = 1 μPa. Because the loudness and other exposure effects of impulsive (pulsed) 

noise, e.g., shots from seismic airguns, are not generally proportional to the instantaneous acoustic 

pressure, several sound level metrics are commonly used to evaluate impulsive sound effects on marine 

life. 

1.1.1. Root-Mean-Square Sound Pressure Level

The root-mean square (rms) SPL (Lp, dB re 1 μPa) is the rms pressure level in a stated frequency band 

over a time window (T, s) containing the pulse:















 = ∫ ο

2 2

10 )( 1 log10 pdttp T

L

T

p (1) 

The rms SPL can be thought of as a measure related to the average sound intensity or as the effective

pressure intensity over the duration of an acoustic event, such as the emission of one acoustic pulse. 

Because the time window length, T, is a divisor, pulses having the same total acoustic energy, but more 

spread out in time, will have a lower rms SPL. The value of T for the purpose of the rms SPL calculation 

can be selected using different approaches. According to one, T is defined as the 90% energy pulse 

duration, containing the central 90% (from 5% to 95% of the total) of the cumulative square pressure (or 

sound exposure level) of the pulse, rather than over a fixed time window (Malme et al. 1986, Greene 

1997, McCauley et al. 1998). The 90% rms SPL (Lp90, dB re 1 μPa) in a stated frequency band is 

calculated over this 90% energy time window, T90: 
K-6 Cumulative and Chronic Effects in the Gulf of Mexico















 = ∫ ο

2 2

90

90 10

90

)( 1 log10 pdttp TL

T

p (2) 

The other approach for rms SPL calculation of a pulse is to use fixed time window. In this study, a sliding 

window was used to calculate rms SPL values for a series of fixed window lengths within the pulse. The 

maximum value of rms SPL over all time window positions is taken to represent the rms SPL of the pulse.

1.1.2. Sound Exposure Level

The sound exposure level (SEL) (LE, dB re 1 μPa2·s) is the time integral of the squared pressure in a

stated frequency band over a stated time interval or event. The per-pulse SEL is calculated over the time 

window containing the entire pulse (i.e., 100% of the acoustic energy), T100: 















 = ∫ οο

2 2

10

100

L )(log10 pTdttp

T

E (3) 

where Tο is a reference time interval of 1 s by convention. The per-pulse SEL, with units of dB re 

1 μPa·√s, or equivalently dB re 1 μPa2

·s, is related, at least numerically, to the total acoustic energy flux 

density delivered over the duration of the acoustic event at a receiver location. SEL, unlike energy flux 

density, neglects the acoustic impedance of the medium (here water), which depends on density,sound 

speed, and on proximity to reflective surfaces and position within refractive environments. SEL is a 

measure of sound exposure through time rather than just sound pressure. 

SEL is a cumulative metric; it can be accumulated over a single pulse, or calculated over periods 

containing multiple pulses. To accumulate multiple pulse cumulative SEL (LEc), the single pulse SELs are 

summed. If there are N such pulses having individual SELs of (LEi), then: 















 = ∑=

N

i

Ei L

LE

1

10 c 10 og10 10l (4) 

The SEL is related to the total acoustic energy flux density delivered over the duration of the set period of 

time, i.e., 24 h. It is a representation of the accumulated SEL delivered by multiple acoustic events, e.g., 

multiple pulses of a single acoustic source. 

Because the rms SPL and SEL of a single pulse are computed from the same time integral of square 

pressure, these metrics are related numerically by a simple expression, which depends only on the 

duration of the 90% energy time window T90: 

log10 ( ) 458.0 LL pE 90 += T9010 + (5) 

where the factor of 0.458 dB accounts for the missing 10% of SEL due to consideration of just 90% of the 

cumulative square pressure in the Lp90 calculation. It is important to note that the decibel reference units 

of LE and Lp90 are not the same, so this expression must be interpreted only in a numerical sense. No 

similar relationship exists when SPL is calculated using fixed time windows shorter than the full pulse 

duration, T100; however, if the window length T is equal to or greater than T100 then the relationship is 

simply:

LL pE += log10 10 ( ) T (6) 
Gulf of Mexico G&G Activities Programmatic EIS K-7 

1.1.3. Energy Equivalent Sound Pressure Level

Energy equivalent SPL (dB re 1 μPa, denoted Leq) is the measure of the average amount of energy 

carried by a time-dependent pressure wave, p(t), over a period of time T. It is defined as the rms SPL

over a fixed duration time window:















 = ∫ 2 2

eq 10 )( 1 log10 pdttp o T

L

T

 (7) 

The Leq is numerically equal to the rms SPL of a steady sound that has the same total energy as the 

sound measured over the given time window. The expressions for Lp and Leq are numerically identical; 

conceptually, the difference between the two metrics is that the former is computed over short time 

periods, usually one second or less, and tracks the fluctuations of a non-steady acoustic signal, whereas 

the latter reflects the average SPL of an acoustic signal over tens of seconds or longer. The integration 

time should be specified for both Lp and Leq.

1.2. Marine Species and Auditory Bands

Within this assessment, a number of species were considered, with a variety of hearing acuities and 

frequency-dependent sensitivities. Twenty-one cetacean species are listed in Appendix D in the G&G EIS 

(NOAA 2016). These include low-, mid-, and high-frequency cetaceans. Hence, the corresponding Mweighting filters defined by Southall et al. (2007) were applied in the assessment of change in listening 

area. Because Bryde’s whales are the only low-frequency cetacean, the most common mysticete in the 

Gulf, and appear to be present year-round (G&G EIS, Appendix E; NOAA 2016), this species was 

selected for the communication space assessment.

1.3. Chronic and Cumulative Effects

Historically, studies focused on short-term effects from high-intensity sounds (e.g., the near-field sounds 

from seismic airguns, sonars, and pile driving) when researching the effects of anthropogenic noise on 

marine mammals. More recently, focus has shifted to effects of long-term exposure that affect marine 

mammals over larger spatial and temporal extents (Clark et al. 2009, Hatch et al. 2012). These long-term 

exposures, or chronic effects, may in some cases be more relevant to marine animals than short-term 

acute effects, especially for communication between conspecifics (e.g. Hatch et al. 2012). 
K-8 Cumulative and Chronic Effects in the Gulf of Mexico

2. Methodology

2.1. Acoustic Source Models

The source levels and directivity of the airgun array were predicted with JASCO’s Airgun Array Source 

Model (AASM; MacGillivray 2006). This model is based on the physics of oscillation and radiation of 

airgun bubbles described by Ziolkowski (1970). The model solves the set of parallel differential equations 

that govern bubble oscillations. AASM also accounts for nonlinear pressure interactions between airguns, 

port throttling, bubble damping, and generator-injector (GI) gun behavior that are discussed by Dragoset 

(1984), Laws et al. (1990), and Landro (1992). AASM includes four empirical parameters that were tuned 

so model output matches observed airgun behavior. The model parameters fit to a large library of 

empirical airgun data using a “simulated annealing” global optimization algorithm. These airgun data are 

measurements of the signatures of Bolt 600/B guns ranging in volume from 5 to 185 in3

 (Racca and 

Scrimger 1986). 

AASM produces a set of “notional” signatures for each array element based on: 

• Array layout

• Volume, tow depth, and firing pressure of each airgun

• Interactions between different airguns in the array

These notional signatures are the pressure waveforms of the individual airguns at a standard reference 

distance of 1 m; they account for the interactions with the other airguns in the array. The signatures are 

summed with the appropriate phase delays to obtain the far-field source signature of the entire array in all

directions. This far-field array signature is filtered into 1/3-octave-bands to compute the source levels of 

the array as a function of frequency band and azimuthal angle in the horizontal plane (at the source 

depth), after which it is considered a directional point source in the far field.

A seismic array consists of many sources and the point-source assumption is invalid in the near field 

where the array elements add incoherently. The maximum extent of the near field of an array (Rnf) is: 

λ

<

4

2

nf

l R

(8) 

where λ is the sound wavelength and l is the longest dimension of the array (Lurton 2002, §5.2.4). For 

example, an airgun array length of l = 16 m yields a near-field range of 85 m at 2 kHz and 17 m at 

100 Hz. Beyond this Rnf range, the array is assumed to radiate like a directional point source and is 

treated as such for propagation modeling.

The interactions between individual elements of the array create directionality in the overall acoustic 

emission. Generally, this directionality is prominent mainly at frequencies in the mid-range between tens 

of hertz to several hundred hertz. At lower frequencies, with acoustic wavelengths much larger than the 

inter-airgun separation distances, the directionality is small. At higher frequencies, the pattern of lobes is 

too finely spaced to be resolved and the effective directivity is less. 

2.2. Transmission Loss Models

The acoustic fields at the receiver sites were modeled at frequencies from 10 Hz to 5 kHz, for sources up 

to 500 km away, using JASCO’s Marine Operations Noise Model (MOMN; Racca et al. 2015). MONM 

computes received per-pulse SEL for directional impulsive sources at a specified source depth. 

MONM computes acoustic propagation from 10 Hz to 1 kHz via a wide-angle parabolic equation solution 

to the acoustic wave equation (Collins 1993) based on a version of the U.S. Naval Research Laboratory’s 
Gulf of Mexico G&G Activities Programmatic EIS K-9 

Range-dependent Acoustic Model (RAM), which has been modified to account for a solid seabed (Zhang 

and Tindle 1995). It computes acoustic propagation above 1 kHz via the BELLHOP Gaussian beam 

acoustic ray-trace model (Porter and Liu 1994). 

The parabolic equation method has been extensively benchmarked and is widely employed in the 

underwater acoustics community (Collins et al. 1996). MONM accounts for the additional reflection loss at 

the seabed due to partial conversion of incident compressional waves to shear waves at the seabed and 

sub-bottom interfaces, and it includes wave attenuations in all layers. At frequencies above 1 kHz, MONM 

also accounts for sound attenuation due to energy absorption through ion relaxation and viscosity of 

water in addition to acoustic attenuation due to reflection at the medium boundaries and internal layers 

(Fisher and Simmons 1977). The version of MONM used in this assessment was validated with real data 

from marine seismic survey projects near Sakhalin Island (Racca et al. 2015) that used large airgun 

arrays similar to the ones considered in this report.

MONM incorporates the following site-specific environmental properties: a bathymetric grid of the 

modeled area, underwater sound speed as a function of depth, and a geoacoustic profile based on the 

overall stratified composition of the seafloor.

MONM computes acoustic fields in three dimensions by modeling transmission loss within twodimensional (2-D) vertical planes aligned along radials covering a 360° swath from the source, an 

approach commonly referred to as N×2-D. These vertical radial planes are separated by an angular step 

size of ∆θ, yielding N = 360°/∆θ number of planes (Figure 2).

Figure 2. The N×2-D and maximum-over-depth modeling approach used by MONM.

MONM treats frequency dependence by computing acoustic transmission loss at the center frequencies 

of 1/3-octave-bands. Sufficiently many 1/3-octave-bands, starting at 10 Hz, are modeled to include the 

majority of acoustic energy emitted by the source. At each center frequency, the transmission loss is 

modeled within each of the N vertical planes as a function of depth and range from the source. The 

1/3-octave-band received per-pulse SELs are computed by subtracting the band transmission loss values 
K-10 Cumulative and Chronic Effects in the Gulf of Mexico

from the directional source level in that frequency band. Composite broadband received SELs are then 

computed by summing the received 1/3-octave-band levels.

The received per-pulse SEL sound field within each vertical radial plane is sampled at various ranges 

from the source, generally with a fixed radial step size. At each sampling range along the surface, the 

sound field is sampled at various depths, with the step size between samples increasing with depth below 

the surface. 

2.3. Chronic and Cumulative Exposure (CCE) Calculator 

A Chronic and Cumulative Exposure (CCE) calculator was developed to assist with assessing chronic 

seismic exploration noise received by marine mammals at the 10 receiver sites. This calculator is 

implemented as Microsoft Excel spreadsheets with scripting to provide a flexible tool for evaluating 

cumulative SELs generated by scenarios of seismic activity distributed over wide areas. The modeling 

geometry implemented in the CCE calculator makes use of acoustic reciprocity, whereby the model was 

run with the source and receiver positions interchanged—an efficient approach when there are more 

potential source sites than receiver sites. 

The acoustic transmission loss results and the modeled source levels for each activity type are stored in 

the spreadsheets of the CCE calculator. The CCE calculator contains sets of marine mammal hearing 

frequency weighting filter coefficients that can be applied to the received levels. For change in listening 

space calculations, we applied filters for low-, mid-, and high-frequency cetaceans as defined by Southall 

et al. (2007). The CCE calculator also contains baseline (ambient) level spectrum for all receiver sites and 

depths (Section 2.4). 

The CCE calculator computes three values: cumulative SELs, Leq, and Leq above ambient at the selected 

receiver site resulting from all pulses from the seismic surveys specified for each alternative.

2.3.1. Survey Distribution

Since the activity locations were unknown, the survey source pulses were uniformly distributed 

throughout each activity zone according to the respective survey line lengths within the activity zones 

(Table 4) and pulse intervals. Rather than modeling every pulse position throughout each activity zone, 

the seismic surveys were divided into several survey cells, each representing a portion of the overall 

project area. The number of pulses contained within each cell was based on the average pulse density in 

each activity zone (Table 5) and the cell areas. The cumulative levels estimated using this approach are 

accurate when the cell dimensions are small, relative to the source-receiver separation.

Table 5. Maximum average pulse density (annual number of pulses per km2

; Alternative C) per 

airgun array in each activity zone.

Representative 

Airgun Array Zone 1 Zone 2 Zone 3 Zone 4 Zone 5 Zone 6

8000 in3 5.5 43.9 57.5 42.2 0 20.0

90 in3 14.1 58.2 67.3 88.4 1.6 2.9

The coordinates of the center of each cell were entered in the CCE calculator with the number of pulses 

represented by the corresponding cell. The calculator assumed this number of pulses occurred at the 

cell’s geometric center. The error in cumulative SEL due to approximating all shot locations within the cell 

by the cell’s center location is expected to be negligible.

To minimize the number of cells throughout the project area and to minimize the error in the cumulative 

level estimates, the cell dimensions were defined so that the distances of the closest side to the most 

distant side of a cell from any receiver had a ratio of less than 1.5. This approach limited the difference in 
Gulf of Mexico G&G Activities Programmatic EIS K-11

transmission loss between any point in the cell and its center to less than ~ 2 dB assuming 20×log(R) 

transmission loss. Thus, cells closest to a receiver represented smaller areas than more distant cells. The 

entire project area was divided into 1706 cells (Figure 3). The coordinates of the center of each cell were 

entered in the CCE calculator with the number of pulses contained within the cell.

The number of pulses in each cell in activity zones along the coast accounted for a 4-month coastal-water 

closure area (orange hashed; Figure 3). Alternatives F1 and F2 include additional closure areas also 

shown in Figure 3. For these alternatives, we removed activity from areas consisting of the actual closure 

areas and from a surrounding spatial buffer designed to maintain sound pressure levels (SPL) below 

160 dB re 1 μPa (90% rms) at the closure area boundaries. The effect on activities due to closures might 

be the redistribution of a fraction of the excluded surveying activity. To account for this possibility, 25% of 

the survey pulses excluded from a closure area were redistributed outside the closure area, but within the 

same activity zone. The spatial buffer widths varied from 4.8 to 8.4 km for the 8000 in3 airgun array, 

depending on the closure area (grey line around closure areas in Figures 1 and 3). No buffers were 

applied for the 90 in3 airgun source since its 160 dB re 1 μPa (rms) distance was estimated at less than 

100 m for the modeled receiver depths.
K-12 Cumulative and Chronic Effects in the Gulf of Mexico

Figure 3. Location of the modeled survey cells (purple dots) and receiver (yellow dots). Survey source pulses were uniformly 

distributed throughout each activity zone according to the respective survey line lengths within the activity zones. Each modeled 

survey cell location is associated with a number of pulses proportional to the cell area (not shown here).
Gulf of Mexico G&G Activities Programmatic EIS K-13

2.3.2. Removal of Top 10% of Pulse Exposures

A feature of underwater sound propagation is that nearby sources generally contribute substantially more 

SEL than more distant sources of the same type, since the exposure levels decay approximately with the 

square of distance from the source. This causes cumulative SEL received from spatially distributed and 

moving seismic sources to be dominated by the source pulses generated closest to a receiver. However, 

the time period of exposures from nearby sources is typically quite short. While exposures from nearby 

sources are important for assessing acute effects, their inclusion in a chronic effects assessment can be 

unrepresentative. To avoid this problem, this analysis neglected the highest seismic pulse exposures 

received during a fraction (10%) of the year-long analysis period. 

The specific method for removing the highest pulse contributions first involved sorting cells based on their 

received per-pulse SEL. Since the pulses were uniformly distributed through each activity zone, the time 

required to survey each cell was assumed proportional to the number of pulses in the cell. The SELordered cells corresponding to 10% of the 1-year study duration (36.5 days) were neglected prior to 

calculating cumulative SEL, Leq and Leq above ambient. 

2.4. Baseline Levels 

To estimate changes in listening area and communication space for various levels of seismic activities, 

we calculated a baseline noise level containing mainly commercial shipping noise and noise from natural 

sounds produced mainly by wind and breaking waves. The commercial shipping noise levels were 

obtained from the SoundMap mapping tool (SoundMap Working Group 2015). SoundMap produces 

commercial shipping noise levels over the Gulf of Mexico region in 1/3-octave frequency bands between 

50 and 800 Hz. Natural ambient noise levels were calculated from the formulas of Wenz (1962) and Cato 

(2008) for a wind speed of 8.5 knots. The natural noise levels were added to all available vessel noise 

levels to generate composite 1/3-octave-band baseline levels between 10 Hz and 5000 Hz. Since no data 

for commercial shipping noise were available outside the frequency range of the SoundMap results, 

shipping noise outside the 50-800 Hz bands was excluded (Figures 4–6).

Broadband baseline levels varied between 94.3 and 102.3 dB re 1 μPa, depending on the receiver 

location and depth. Third-octave band baseline levels were entered in the CCE calculator. Leq and Leq

above ambient were then calculated in 1/3-octave bands using low-, mid-, and high-frequency cetacean

filters and without frequency weighting. Baseline levels in the 100 Hz 1/3-octave band, which varied 

between 76.1 and 86.7 dB re 1 μPa, were used to calculate Bryde’s whale communication space under 

Alternative A.
K-14 Cumulative and Chronic Effects in the Gulf of Mexico

Figure 4. Summed levels for frequency bands of 10 Hz to 10 kHz for all sites at 5 m receiver depth.

The natural interpolated sound levels (blue line; Wenz (1962), Cato (2008)) and SoundMap data 

were summed for frequency bands between 50 and 800 Hz. Beyond these limits the interpolated 

natural levels were used. 

Figure 5. Summed levels for frequency bands of 10 Hz to 10 kHz for nine sites at 30 m receiver.

The natural interpolated sound levels (blue line; Wenz (1962), Cato (2008)) and SoundMap data 

were summed for frequency bands between 50 and 800 Hz. Beyond these limits the interpolated 

natural levels were used. Note that not all sites have water depth reaching this receiver depth. 
Gulf of Mexico G&G Activities Programmatic EIS K-15

Figure 6. Summed levels for frequency bands of 10 Hz to 10 kHz for seven sites at 500 m receiver 

depth. The natural interpolated sound levels (blue line; Wenz (1962), Cato (2008)) and SoundMap 

data were summed for frequency bands between 50 and 800 Hz. Beyond these limits the 

interpolated natural levels were used. Note that not all sites have water depth reaching this

receiver depth.

2.5. Listening Area

The term listening area refers to the area associated with the maximum detection distance of a signal by 

an animal. A listening area assessment considers the region of ocean where marine fauna can detect 

sound from conspecifics, as well as from predators and prey (Figure 7). The introduction of noise in the 

same frequency band as the signal may reduce an animal’s ability to detect the signal, and therefore 

decreases the maximum detection distance and reduces the listening area. 
K-16 Cumulative and Chronic Effects in the Gulf of Mexico

Figure 7. Schematic representation of changes in listening area around a marine mammal. Under 

ambient conditions, an animal may be able to listen to conspecifics, as well as predators and 

prey. When the noise level increases, the listening area is reduced. (Figure adapted from NPS 

2010.) 

The remaining fraction of the listening area after an increase in noise level can be calculated without prior 

knowledge of the signal source level and detection distance by approximating the transmission loss (TL) 

as: 

TL = log10 ( ) RN . (9) 

The maximum detection distance of the signal (Ro), associated with a source level SL, will result in a 

received level RLo: 

( ) RLo 10 RNSL o −= log . (10) 

The maximum detection distance (R) associated with an increase in noise level will result in a received 

level (RL): 

RL −= log10 ( ) RNSL . (11) 
Gulf of Mexico G&G Activities Programmatic EIS K-17

The remaining fraction of listening area after an increase in noise level is therefore: 

N

N

RL SL

N

RL SL

o o R

R

∆−

−

−

=

=

2

)(2

)(2

2

2

10

10

10

π

π

. (12) 

Where ∆ is equal to the increase in noise level, in dB. Results are presented in fractions (percentage) of 

the listening area that is left, relative to the original, after an increase in noise level.

This concept was applied by Barber et al. (2009) to terrestrial organisms. To our knowledge, this concept 

has not previously been applied to marine animals. Unlike the assessment of communication space 

(Section 2.6), the assessment of change in listening area does not require prior knowledge parameters 

such as the signal source levels, detection thresholds based on the receiver perception capabilities, 

signal directivity, noise and signal duration, and band-specific (spectral) noise levels. This assessment 

can be done for specific frequency bands, or by taking into consideration the animal’s auditory system 

and applying a relevant filter to the noise level.

This equation is expected to overestimate the reduction in listening area at most sites, where the TL is 

better estimated by an equation of the form: 

TL = log10 ( )−αRRN . (13) 

In this study, we estimated N at each of the receiver sites by curve fitting the modeled TL from the 

receiver at ranges ≤ 75 km. The noise level increase, ∆, is the difference between the estimated ambient 

level and Leq or between two alternatives being compared. The approach considers the additive nature of 

ambient noise to Leq in decibel space (for example, if Leq and ambient level were equal, then ∆ would be 

3 dB). While that may seem counterintuitive, recall that the decibel sum of two equal sound levels is their 

individual value plus 3 dB. Changes in listening area were calculated for unfiltered broadband (10–

5000 Hz) noise levels, as well as by applying low-, mid-, and high-frequency cetaceans weighting to the 

noise levels.

2.6. Bryde’s Whale Communication Space

A communication space assessment considers the region of ocean within marine fauna can detect calls 

from conspecifics. Masking can be defined as a reduction in communication space (active acoustic 

space) that an individual experiences due to an increase in background noise (ambient and 

anthropogenic) in the frequency bands relevant for communicating. Reduction in communication space 

due to anthropogenic sounds cannot be determined based on the broadband cumulated sound exposure 

level, because the effect depends on the spectral noise level within the frequency band of the sounds in 

question and therefore varies dynamically with receiver distance from the sound (noise) source. To 

estimate the communication space quantitatively, it is necessary to account for parameters such as call 

source levels, detection thresholds based on the receiver perception capabilities, signal directivity, bandspecific (spectral) noise levels, and noise and signal duration.

The communication space for Bryde’s whales was estimated using a similar approach to that employed 

by Clark et al. (2009). This approach calculates the horizontal area in square kilometers over which a call 

can be detected, recognizing that the true call could originate within a 3-D volume of ocean. The primary 

difference between our approach and Clark et al.’s is that we a applied the analysis in a single 

representative 1/3-octave-band rather than to broadband levels. This approach is based on a form of the 

sonar equation that considers the maximum distance an animal can detect a signal in the presence of 

masking noise. The form of the sonar equation employed here was:

SLSE TL NL DIDT ++−−−= SG . (14) 
K-18 Cumulative and Chronic Effects in the Gulf of Mexico

The signal excess (SE) is the signal excess above detectability. The source level (SL) is the animal call 

source level. TL is the acoustic transmission loss between the calling and listening Bryde’s whales (a 

function of the distance of their separation). NL is the noise level in the same frequency band as the 

source level. DT is the detection threshold of the animal, representing the amount above ambient level

the sound must be in order for it to be detected. The directivity index (DI) represents the animal’s ability to 

discriminate sounds coming from a specific direction, in the presence of masking noise arriving uniformly

from all directions. SG is the signal gain that indicates the ability of the animal to use its knowledge of the 

time-frequency structure of the call to differentiate it from background noise.

 
Gulf of Mexico G&G Activities Programmatic EIS K-19

3. Modeled Parameters 

3.1. Acoustic Environment

The environmental parameters used by the transmission loss model (MONM; Section 2.2) were the same 

ones used in the 2016–2025 Annual Acoustic Exposure Estimates for Marine Mammals (Appendix D of 

the G&G EIS; NOAA 2016). Water depths throughout the modeled area were obtained from the National 

Geophysical Data Center’s U.S. Coastal Relief Model l (NGDC 2014). Sound speed profiles for February

for each receiver site were used to estimate the transmission loss for the entire year. This adds a level of 

conservativeness since the winter profiles include an isovelocity layer and, at some sites, a surface sound 

channel; both can enhance sound propagation for the near-surface sources considered here. Three of the 

four sets of geoacoustic parameters (Center-West Shelf, Slope, and Deep) from the G&G EIS, 

Appendix D (NOAA 2016) were used in this assessment. A fourth set of parameters (Table 6) was 

developed to model transmission loss at receiver sites on the eastern slope (offshore Florida), based on 

the information previously acquired (G&G EIS, Appendix D; NOAA 2016). 

Table 6. Eastern Slope: Geoacoustic properties of the sub-bottom sediments as a function of 

depth, in meters below the seafloor (mbsf). Within each depth range, each parameter varies 

linearly within the stated range.

Depth below 

seafloor (m) Material Density (g/cm3) 

P-wave speed 

(m/s)

P-wave 

attenuation 

(dB/λ)

S-wave speed 

(m/s)

S-wave 

attenuation

(dB/λ)

0–20

Silt

φ=6

1.44 1532 0.41

200 0.22

20–50 1.7 1725 1.00

50–200 1.7 1826 1.30

200–600 1.87 2105 1.75

> 600 2.04 2466 2.11

3.2. Acoustic Sources

The source levels and directivity of the two types of airgun arrays were predicted with AASM 

(Section 2.1). Source levels in 1/3-octave frequency bands for each source were determined and input in

the acoustic propagation model. Directivity was purposely removed by averaging the direction-dependent 

levels modeled with AASM because here we assumed randomly oriented surveys. The averaging 

preserved total acoustic energy emitted.

The acoustic source levels used in the CCE calculator (Section 2.3) were derived from the Appendix D of 

the G&G EIS (NOAA 2016). 

3.3. Transmission Loss and CCE Calculator

Sixteen vertical planes were modeled around each receiver site, providing an angular spacing of 

22.5 degrees. The modeled radial lengths were limited to 500 km. Seismic pulses originating more than 

500 km from a specified receiver were estimated to have little influence on the cumulative sound field and 

were excluded. Receiver depths were modeled at 5, 30, and 500 m. The surrogate sources (90 in3 and 

8000 in3 arrays) were modeled at 4 and 8 m depths. 

The Leq was based on the accumulation period of 1 year, and T was 31.45 × 106 seconds.
K-20 Cumulative and Chronic Effects in the Gulf of Mexico

3.4. Bryde’s Whale Communication Space

A representative source level was estimated from the median Bryde’s whale source level reported by

Širović et al. (2014). Under the assumption that the call bandwidth spanned two 1/3-octave-bands, a 

source level of 152 dB re 1 μPa at 1 m was specified for the 100 Hz band based on the broadband source 

level for Bryde’s moans of 155 dB re 1 μPa at 1 m. All communication space calculations were performed 

in the single 1/3-octave frequency band centered at 100 Hz. 

A 1/3-octave-band analysis is relevant for assessing audibility of a signal, as it is often used to 

approximate the critical bandwidth of the mammalian ear. We used a signal excess of SE = 0, to 

represent the onset of detectability. Transmission loss was obtained at each receiver site from the 

transmission loss model results. The noise levels were calculated with the CCE calculator as described in 

Section 2.3. The detection threshold was assumed to be 10 dB and the detection index was assumed to 

be zero (Clark et al. 2009). The signal processing gain (SG = 10log(TW)), which accounts for the animal’s 

ability to detect and recognize a signal from conspecifics, was estimated as 12.36 dB, based on a median 

frequency bandwidth (W) of 43 Hz and call length (T) of 0.4 seconds (Širović et al. 2014). 
Gulf of Mexico G&G Activities Programmatic EIS K-21

4. Results 

This section presents the modeled results of cumulative sound exposure levels (Tables 8–11) and timeaveraged equivalent sound pressure levels (Tables 12–19) for all modeled scenarios. Scenario estimates 

are then compared to each other, as well as to baseline noise level. Relative differences are calculated 

and ranked. Results are then presented as changes in listening area (Tables 20–27) and changes in 

communication space for Bryde’s whales (Tables 28–36). Communication space and listening area 

calculations use baseline noise levels (Alternative A) for reference (Table 7). Alternative A is comprised of

commercial shipping noise and natural sounds produced mainly by wind and breaking waves. 

Table 7. Broadband (10–5000 Hz) baseline (Alternative A; no activity) SPL (dB re 1 μPa) for each 

receiver site and depth.

Hearing 

Group

Receiver 

Depth (m) Site 1 Site 2 Site 3 Site 4 Site 5 Site 6 Site 7* Site 8 Site 9* Site 10*

LowFrequency 

Cetaceans

5 96.1 95.9 96.9 95.9 95.9 95.9 96.3 96.3 97.2 102.2

30 96.1 95.9 96.3 95.9 96.0 95.9 96.6 96.3 97.2

500 96.1 96.0 98.3 96.5 96.5 95.9 96.4

MidFrequency 

Cetaceans 

5 94.6 94.6 94.7 94.6 94.6 94.6 94.7 94.7 94.7 100.3

30 94.6 94.6 94.7 94.6 94.6 94.6 94.7 94.6 94.7

500 94.6 94.6 94.8 94.7 94.7 94.6 94.7

HighFrequency 

Cetaceans 

5 94.3 94.3 94.4 94.3 94.3 94.3 94.4 94.3 94.3 99.6

30 94.3 94.3 94.4 94.3 94.3 94.3 94.4 94.3 94.4

500 94.3 94.3 94.4 94.4 94.4 94.3 94.3

Unweighted

5 96.3 96.1 97.1 96.1 96.1 96.1 96.5 96.5 97.3 102.3

30 96.3 96.1 96.5 96.1 96.2 96.1 96.8 96.5 97.4

500 96.3 96.2 98.5 96.7 96.7 96.1 96.6

* Cells without values correspond to receiver depths that do not exist at shallow sites.
K-22 Cumulative and Chronic Effects in the Gulf of Mexico

4.1. Cumulative Sound Exposure Levels

Tables 8–11 present the results for cumulative SELs (dB re 1 μPa2s) for each receiver site and depth for 

all modeled alternatives. These levels were filtered for low-, mid-, and high-frequency cetaceans. These

results are based on the total number of pulses (shots) for a one-year duration.

Table 8. Alternative C: Cumulative SEL (dB re 1 μPa2

s) at each receiver site with M-weighting for 

low- , mid-, and high-frequency cetaceans and without weighting. 

Hearing 

Group

Receiver 

Depth (m) Site 1 Site 2 Site 3 Site 4 Site 5 Site 6 Site 7* Site 8 Site 9* Site 10* 

LowFrequency 

Cetaceans

5 173.8 170.8 169.1 164.8 189.6 165.1 123.7 164.8 175.8 157.0

30 176.8 179.4 174.8 174.6 193.8 168.6 138.8 167.9 174.3

500 180.9 179.8 178.2 173.8 191.9 174.8 170.9

MidFrequency 

Cetaceans 

5 173.2 160.3 167.1 158.3 186.5 163.6 102.3 161.5 175.7 156.9

30 172.3 162.4 159.6 161.0 185.1 149.7 113.5 149.3 174.2

500 164.7 164.4 163.4 160.2 180.9 155.3 152.0

HighFrequency 

Cetaceans

5 172.7 158.1 166.7 156.6 185.9 163.5 99.1 160.9 175.5 156.8

30 172.0 160.3 157.2 158.2 184.3 146.7 109.6 146.3 174.0

500 162.4 162.6 161.0 157.9 179.1 152.7 149.3

Unweighted

5 173.8 171.2 169.3 165.0 189.6 165.2 125.1 165.1 175.9 157.0

30 177.6 180.4 175.3 175.2 194.1 169.5 140.0 168.9 174.4

500 182.0 181.0 179.2 174.7 193.1 176.2 172.1

* Cells without values correspond to receiver depths that do not exist at shallow sites.

Table 9. Alternative E (25% reduction): Cumulative SEL (dB re 1 μPa2s) at each receiver site with 

M-weighting for low- , mid-, and high-frequency cetaceans and without weighting. 

Hearing 

Group

Receiver 

Depth (m) Site 1 Site 2 Site 3 Site 4 Site 5 Site 6 Site 7* Site 8 Site 9* Site 10* 

LowFrequency 

Cetaceans

5 172.5 169.5 167.9 163.5 188.3 163.9 122.5 163.6 174.6 155.7

30 175.6 178.2 173.5 173.4 192.5 167.3 137.6 166.6 173.1

500 179.6 178.6 177.0 172.6 190.7 173.6 169.7

MidFrequency 

Cetaceans 

5 171.9 159.0 165.8 157.1 185.3 162.3 101.1 160.2 174.4 155.7

30 171.1 161.2 158.4 159.8 183.9 148.5 112.2 148.1 172.9

500 163.5 163.1 162.1 159.0 179.6 154.0 150.7

HighFrequency 

Cetaceans 

5 171.5 156.8 165.5 155.4 184.7 162.2 97.8 159.6 174.3 155.6

30 170.8 159.1 156.0 157.0 183.1 145.5 108.4 145.1 172.8

500 161.2 161.3 159.8 156.6 177.8 151.4 148.0

Unweighted

5 172.6 169.9 168.1 163.8 188.4 164.0 123.8 163.9 174.6 155.8

30 176.4 179.1 174.1 174.0 192.8 168.3 138.8 167.7 173.2

500 180.8 179.7 177.9 173.5 191.9 174.9 170.9

* Cells without values correspond to receiver depths that do not exist at shallow sites.
Gulf of Mexico G&G Activities Programmatic EIS K-23

Table 10. Alternative F1 (area closures): Cumulative SEL (dB re 1 μPa2s) at each receiver site with 

M-weighting for low- , mid-, and high-frequency cetaceans and without weighting. 

Hearing 

Group

Receiver 

Depth (m) Site 1 Site 2 Site 3 Site 4 Site 5 Site 6 Site 7* Site 8 Site 9* Site 10* 

LowFrequency 

Cetaceans

5 174.8 171.4 171.3 165.0 193.4 163.2 123.1 160.3 176.5 158.3

30 178.9 179.4 177.4 174.9 197.1 166.2 138.1 164.2 175.2

500 182.2 179.9 180.9 174.1 195.0 173.3 166.7

MidFrequency 

Cetaceans

5 174.2 160.8 169.1 158.5 188.9 161.8 101.1 157.5 176.3 158.2

30 173.3 162.7 162.4 161.2 188.9 142.4 112.1 144.2 174.9

500 166.6 165.1 165.5 159.3 184.9 149.1 145.6

HighFrequency 

Cetaceans 

5 173.8 158.7 168.6 156.8 187.0 161.7 98.3 156.9 176.2 158.2

30 173.1 160.5 160.0 158.4 187.4 138.9 108.3 140.7 174.8

500 164.7 162.9 163.6 157.1 183.4 146.3 142.9

Unweighted

5 174.9 171.5 171.5 165.2 193.5 163.4 124.5 160.6 176.6 158.4

30 179.5 180.5 178.2 175.5 197.4 167.0 139.6 165.2 175.2

500 183.3 181.0 182.5 175.0 195.6 173.6 168.0

* Cells without values correspond to receiver depths that do not exist at shallow sites.

Table 11. Alternative F2 (area closures and 25% reduction): Cumulative SEL (dB re 1 μPa2s) at 

each receiver site with M-weighting for low- , mid-, and high-frequency cetaceans and without 

weighting. 

Hearing 

Group

Receiver 

Depth (m) Site 1 Site 2 Site 3 Site 4 Site 5 Site 6 Site 7* Site 8 Site 9* Site 10* 

LowFrequency 

Cetaceans

5 173.6 170.2 170.1 163.7 192.2 162.0 121.9 159.1 175.3 157.1

30 177.7 178.2 176.1 173.6 195.8 165.0 136.9 163.0 173.9

500 181.0 178.7 179.6 172.8 193.8 172.0 165.4

MidFrequency 

Cetaceans

5 172.9 159.5 167.8 157.3 187.7 160.6 99.9 156.2 175.1 157.0

30 172.0 161.5 161.2 160.0 187.7 141.2 110.8 143.0 173.7

500 165.3 163.9 164.3 158.1 183.6 147.8 144.3

HighFrequency 

Cetaceans 

5 172.5 157.4 167.4 155.6 185.8 160.4 97.1 155.6 174.9 156.9

30 171.8 159.3 158.8 157.2 186.1 137.6 107.1 139.4 173.5

500 163.5 161.6 162.3 155.9 182.1 145.1 141.6

Unweighted

5 173.6 170.3 170.3 164.0 192.2 162.1 123.3 159.3 175.3 157.1

30 178.2 179.3 176.9 174.2 196.2 165.7 138.4 164.0 174.0

500 182.0 179.7 181.3 173.7 194.3 172.3 166.8

* Cells without values correspond to receiver depths that do not exist at shallow sites.
K-24 Cumulative and Chronic Effects in the Gulf of Mexico

4.2. Time-Averaged Equivalent Sound Pressure Levels

Tables 12–19 present the time-averaged equivalent SPLs for each receiver site and depth for all modeled

alternatives. The time-averaged equivalent SPLs were calculated by applying the cumulative SELs and 

the filtered baseline noise levels (Table 7) with a time average of 31.45 × 106 seconds. The values in the 

tables represent time-averaged equivalent SPLs above and below the baseline levels (Alternative A - 

Table 7).

Table 12. Alternative C: Time-averaged equivalent sound pressure levels (Leq) at each receiver site 

with M-weighting for low- , mid-, and high-frequency cetaceans and without weighting. 

Hearing 

Group

Receiver 

Depth (m) Site 1 Site 2 Site 3 Site 4 Site 5 Site 6 Site 7* Site 8 Site 9* Site 10* 

LowFrequency 

Cetaceans

5 100.7 98.9 98.8 96.8 114.6 96.9 96.3 97.2 102.4 102.3

30 102.9 105.0 101.4 101.2 118.8 97.9 96.6 98.0 101.4

500 106.3 105.4 104.5 100.8 117.0 101.3 99.2

MidFrequency 

Cetaceans 

5 99.8 95.1 96.6 94.9 111.6 95.6 94.7 95.3 101.7 100.4

30 99.2 95.4 95.1 95.2 110.3 94.7 94.7 94.7 100.5

500 95.9 95.8 95.7 95.1 106.2 94.8 94.7

HighFrequency 

Cetaceans

5 99.4 94.6 96.3 94.6 111.0 95.3 94.4 94.9 101.5 99.6

30 98.9 94.8 94.6 94.7 109.5 94.3 94.4 94.4 100.3

500 95.1 95.2 95.0 94.7 104.5 94.4 94.4

Unweighted

5 100.8 99.1 99.0 97.1 114.7 97.1 96.5 97.4 102.5 102.3

30 103.5 105.9 101.9 101.7 119.1 98.4 96.8 98.4 101.5

500 107.4 106.5 105.2 101.5 118.2 102.4 99.9

* Cells without values correspond to receiver depths that do not exist at shallow sites.

Table 13. Alternative C: Time-averaged equivalent sound pressure levels (Leq) above ambient at 

each receiver site with M-weighting for low- , mid-, and high-frequency cetaceans and without 

weighting. 

Hearing 

Group

Receiver 

Depth (m) Site 1 Site 2 Site 3 Site 4 Site 5 Site 6 Site 7* Site 8 Site 9* Site 10* 

LowFrequency 

Cetaceans

5 4.5 3.0 1.8 1.0 18.7 1.0 0 0.9 5.2 0

30 6.7 9.1 5.1 5.2 22.9 2.0 0 1.6 4.2

500 10.2 9.4 6.1 4.4 20.5 5.4 2.8

MidFrequency 

Cetaceans 

5 5.1 0.5 1.9 0.3 17.0 1.0 0 0.6 7.0 0.1

30 4.6 0.8 0.4 0.6 15.6 0 0 0 5.8

500 1.2 1.1 0.9 0.5 11.5 0.2 0.1

HighFrequency 

Cetaceans 

5 5.1 0.3 1.9 0.2 16.7 1.0 0 0.6 7.1 0.1

30 4.6 0.5 0.3 0.3 15.1 0 0 0 6.0

500 0.8 0.8 0.6 0.3 10.2 0.1 0

Unweighted

5 4.4 3.1 1.8 1.0 18.6 1.0 0 0.9 5.1 0

30 7.2 9.8 5.3 5.5 23.0 2.3 0 1.9 4.2

500 11.1 10.2 6.7 4.8 21.5 6.2 3.3

* Cells without values correspond to receiver depths that do not exist at shallow sites.
Gulf of Mexico G&G Activities Programmatic EIS K-25

Table 14. Alternative E (25% reduction): Time-averaged equivalent sound pressure levels (Leq) at 

each receiver site with M-weighting for low- , mid-, and high-frequency cetaceans and without 

weighting. 

Hearing 

Group

Receiver 

Depth (m) Site 1 Site 2 Site 3 Site 4 Site 5 Site 6 Site 7* Site 8 Site 9* Site 10* 

LowFrequency 

Cetaceans

5 99.9 98.3 98.4 96.6 113.4 96.7 96.3 97.0 101.6 102.2

30 101.9 104.0 100.6 100.4 117.6 97.5 96.6 97.6 100.7

500 105.2 104.3 103.5 100.1 115.8 100.5 98.6

MidFrequency 

Cetaceans 

5 99.0 95.0 96.2 94.8 110.4 95.4 94.7 95.1 100.7 100.3

30 98.4 95.2 95.0 95.0 109.0 94.6 94.7 94.7 99.6

500 95.6 95.5 95.5 95.0 105.0 94.7 94.7

HighFrequency 

Cetaceans 

5 98.6 94.6 95.9 94.5 109.8 95.1 94.4 94.8 100.5 99.6

30 98.1 94.7 94.6 94.6 108.3 94.3 94.4 94.4 99.4

500 95.0 95.0 94.9 94.6 103.4 94.4 94.4

Unweighted

5 100.0 98.6 98.6 96.8 113.5 96.9 96.5 97.2 101.6 102.3

30 102.6 104.8 101.0 100.8 117.9 97.9 96.8 98.0 100.8

500 106.3 105.3 104.3 100.7 116.9 101.5 99.3

* Cells without values correspond to receiver depths that do not exist at shallow sites.

Table 15. Alternative E (25% reduction): Time-averaged equivalent sound pressure levels (Leq) 

above ambient at each receiver site with M-weighting for low- , mid-, and high-frequency 

cetaceans and without weighting. 

Hearing 

Group

Receiver 

Depth (m) Site 1 Site 2 Site 3 Site 4 Site 5 Site 6 Site 7* Site 8 Site 9* Site 10* 

LowFrequency 

Cetaceans

5 3.8 2.4 1.4 0.7 17.5 0.8 0 0.7 4.4 0

30 5.8 8.1 4.2 4.4 21.6 1.6 0 1.3 3.5

500 9.1 8.3 5.2 3.6 19.3 4.5 2.2

MidFrequency 

Cetaceans 

5 4.3 0.4 1.5 0.2 15.8 0.7 0 0.5 6.0 0

30 3.8 0.6 0.3 0.4 14.4 0 0 0 4.9

500 0.9 0.9 0.7 0.4 10.4 0.1 0.1

HighFrequency 

Cetaceans

5 4.2 0.2 1.5 0.2 15.5 0.8 0 0.4 6.2 0.1

30 3.8 0.4 0.2 0.2 13.9 0 0 0 5.1

500 0.6 0.6 0.5 0.2 9.1 0.1 0

Unweighted

5 3.7 2.5 1.4 0.7 17.4 0.8 0 0.7 4.3 0

30 6.2 8.7 4.5 4.7 21.7 1.8 0 1.5 3.4

500 10.0 9.1 5.8 4.0 20.3 5.3 2.7

* Cells without values correspond to receiver depths that do not exist at shallow sites.
K-26 Cumulative and Chronic Effects in the Gulf of Mexico

Table 16. Alternative F1 (area closures): Time-averaged equivalent sound pressure levels (Leq) at 

each receiver site with M-weighting for low- , mid-, and high-frequency cetaceans and without 

weighting. 

Hearing 

Group

Receiver 

Depth (m) Site 1 Site 2 Site 3 Site 4 Site 5 Site 6 Site 7* Site 8 Site 9* Site 10* 

LowFrequency 

Cetaceans

5 101.4 99.2 99.7 96.9 118.4 96.6 96.3 96.6 102.9 102.3

30 104.6 105.0 103.3 101.3 122.1 97.2 96.6 97.1 102.0

500 107.6 105.5 106.6 101.0 120.1 100.3 97.7

MidFrequency 

Cetaceans 

5 100.5 95.1 97.4 94.9 114.0 95.3 94.7 94.9 102.2 100.4

30 99.9 95.4 95.4 95.2 114.0 94.6 94.7 94.7 101.1

500 96.4 96.0 96.2 95.1 110.0 94.7 94.7

HighFrequency 

Cetaceans 

5 100.1 94.7 97.0 94.6 112.1 95.0 94.4 94.6 102.0 99.6

30 99.6 94.9 94.8 94.7 112.5 94.3 94.4 94.3 100.9

500 95.6 95.2 95.4 94.6 108.6 94.3 94.4

Unweighted

5 101.5 99.3 99.9 97.1 118.5 96.8 96.5 96.8 103.0 102.3

30 105.1 106.0 104.0 101.9 122.5 97.5 96.8 97.4 102.1

500 108.6 106.4 108.0 101.6 120.6 100.5 98.2

* Cells without values correspond to receiver depths that do not exist at shallow sites.

Table 17. Alternative F1 (area closures): Time-averaged equivalent sound pressure levels (Leq) 

above ambient at each receiver site with M-weighting for low- , mid-, and high-frequency 

cetaceans and without weighting. 

Hearing 

Group

Receiver 

Depth (m) Site 1 Site 2 Site 3 Site 4 Site 5 Site 6 Site 7* Site 8 Site 9* Site 10* 

LowFrequency 

Cetaceans

5 5.2 3.3 2.7 1.0 22.6 0.7 0 0.3 5.7 0.1

30 8.5 9.1 7.0 5.4 26.1 1.3 0 0.8 4.8

500 11.5 9.4 8.2 4.5 23.6 4.3 1.3

MidFrequency 

Cetaceans 

5 5.9 0.5 2.7 0.3 19.4 0.7 0 0.3 7.5 0.1

30 5.2 0.8 0.8 0.6 19.4 0 0 0 6.4

500 1.7 1.3 1.4 0.4 15.3 0 0

HighFrequency 

Cetaceans

5 5.8 0.4 2.7 0.2 17.8 0.7 0 0.2 7.7 0.1

30 5.3 0.5 0.5 0.3 18.1 0 0 0 6.5

500 1.3 0.9 1.0 0.3 14.2 0 0

Unweighted

5 5.2 3.2 2.7 1.0 22.5 0.7 0 0.3 5.6 0.1

30 8.8 9.9 7.5 5.7 26.3 1.4 0 0.9 4.7

500 12.3 10.2 9.5 5.0 24.0 4.4 1.6

* Cells without values correspond to receiver depths that do not exist at shallow sites.
Gulf of Mexico G&G Activities Programmatic EIS K-27

Table 18. Alternative F2 (area closures and 25% reduction): Time-averaged equivalent sound 

pressure levels (Leq) at each receiver site with M-weighting for low- , mid-, and high-frequency 

cetaceans and without weighting. 

Hearing 

Group

Receiver 

Depth (m) Site 1 Site 2 Site 3 Site 4 Site 5 Site 6 Site 7* Site 8 Site 9* Site 10* 

LowFrequency 

Cetaceans

5 100.6 98.6 99.1 96.7 117.2 96.4 96.3 96.6 102.0 102.3

30 103.6 103.9 102.4 100.5 120.9 96.9 96.6 96.9 101.2

500 106.4 104.4 105.5 100.2 118.8 99.6 97.4

MidFrequency 

Cetaceans 

5 99.6 95.0 96.9 94.9 112.8 95.1 94.7 94.8 101.2 100.4

30 99.0 95.2 95.2 95.1 112.8 94.6 94.7 94.7 100.2

500 96.0 95.7 95.9 95.0 108.8 94.6 94.7

HighFrequency 

Cetaceans 

5 99.2 94.6 96.5 94.5 110.9 94.9 94.4 94.5 101.0 99.6

30 98.8 94.7 94.7 94.6 111.2 94.3 94.4 94.3 100.0

500 95.3 95.0 95.2 94.5 107.4 94.3 94.4

Unweighted

5 100.7 98.7 99.3 96.9 117.3 96.6 96.5 96.8 102.1 102.3

30 104.0 104.9 103.0 101.0 121.2 97.2 96.8 97.2 101.3

500 107.4 105.3 107.0 100.8 119.4 99.8 97.8

* Cells without values correspond to receiver depths that do not exist at shallow sites.

Table 19. Alternative F2 (area closures and 25% reduction): Time-averaged equivalent sound 

pressure levels (Leq) above ambient at each receiver site with M-weighting for low- , mid-, and 

high-frequency cetaceans and without weighting. 

Hearing 

Group

Receiver 

Depth (m) Site 1 Site 2 Site 3 Site 4 Site 5 Site 6 Site 7* Site 8 Site 9* Site 10* 

LowFrequency 

Cetaceans

5 4.4 2.7 2.2 0.8 21.3 0.5 0 0.3 4.9 0

30 7.4 8.0 6.0 4.6 24.9 1.0 0 0.6 4.0

500 10.3 8.4 7.2 3.7 22.3 3.6 1.0

MidFrequency 

Cetaceans 

5 5.0 0.4 2.2 0.2 18.2 0.5 0 0.2 6.5 0.1

30 4.4 0.6 0.6 0.4 18.1 0 0 0 5.5

500 1.4 1.0 1.1 0.3 14.1 0 0

HighFrequency 

Cetaceans

5 4.9 0.3 2.1 0.2 16.5 0.5 0 0.2 6.7 0.1

30 4.4 0.4 0.4 0.3 16.9 0 0 0 5.6

500 1.0 0.7 0.8 0.2 13.0 0 0

Unweighted

5 4.3 2.6 2.2 0.8 21.2 0.5 0 0.3 4.8 0

30 7.7 8.8 6.5 4.8 25.1 1.1 0 0.7 3.9

500 11.1 9.1 8.4 4.2 22.7 3.6 1.2

* Cells without values correspond to receiver depths that do not exist at shallow sites.
K-28 Cumulative and Chronic Effects in the Gulf of Mexico

4.3. Listening Area

Tables 20–27 present the calculated change in listening area for each receiver site and depth for all 

modeled alternatives. 

Table 20. Alternative C relative to Alternative A (no activity): Remainder of listening area (%) at 

each receiver site with M-weighting for low- , mid-, and high-frequency cetaceans and without 

weighting. 

Hearing 

Group

Receiver 

Depth (m) Site 1 Site 2 Site 3 Site 4 Site 5 Site 6 Site 7* Site 8 Site 9* Site 10* 

LowFrequency 

Cetaceans

5 22.1 43.7 55.7 76.0 0.6 72.2 100 75.5 17.7 98.6

30 13.6 7.7 22.9 21.6 0.2 55.0 100 61.2 29.7 -

500 6.2 7.1 17.6 29.9 0.3 21.9 - 45.8 - -

MidFrequency 

Cetaceans 

5 18.0 87.5 54.4 91.3 0.9 73.5 100 82.2 9.9 97.9

30 25.8 80.7 88.7 84.8 1.2 98.7 100 98.8 18.8 -

500 71.8 72.3 77.4 87.8 4.1 95.7 - 98.0 - -

HighFrequency 

Cetaceans

5 18.5 91.6 54.6 93.6 1.0 72.5 100 83.1 9.4 97.6

30 25.8 86.4 92.7 90.9 1.4 99.3 100 99.4 18.1 -

500 80.3 78.9 84.5 92.0 5.9 97.4 - 98.8 - -

Unweighted

5 22.7 42.6 55.8 75.7 0.6 72.6 100 75.0 18.4 98.6

30 11.9 6.4 21.2 19.7 0.2 50.4 100 56.2 30.3 -

500 4.9 5.5 14.7 26.3 0.3 17.2 - 39.9 - -

* Cells without values correspond to receiver depths that do not exist at shallow sites.

Table 21. Alternative E (25% reduction) relative to Alternative A (no activity): Remainder of 

listening area (%) at each receiver site with M-weighting for low- , mid-, and high-frequency 

cetaceans and without weighting. 

Hearing 

Group

Receiver 

Depth (m) Site 1 Site 2 Site 3 Site 4 Site 5 Site 6 Site 7* Site 8 Site 9* Site 10* 

LowFrequency 

Cetaceans

5 28.5 51.3 63.1 80.9 0.8 77.8 100 80.6 23.3 99.0

30 18.1 10.4 29.1 27.5 0.2 62.4 100 68.1 36.7 -

500 8.4 9.6 22.7 36.7 0.5 27.8 - 53.4 - -

MidFrequency 

Cetaceans 

5 23.7 90.3 61.9 93.4 1.3 78.9 100 86.1 13.7 98.4

30 32.5 84.9 91.3 88.2 1.7 99.0 100 99.1 24.2 -

500 77.4 77.8 82.1 90.6 5.6 96.7 - 98.5 - -

HighFrequency 

Cetaceans 

5 24.4 93.6 62.0 95.1 1.4 78.0 100 86.8 13.1 98.2

30 32.4 89.5 94.5 93.1 2.0 99.5 100 99.5 23.4 -

500 84.5 83.3 87.9 93.9 8.1 98.0 - 99.1 - -

Unweighted

5 29.2 50.1 63.2 80.7 0.8 78.2 100 80.2 24.1 99.0

30 15.9 8.7 27.1 25.4 0.2 58.0 100 63.5 37.4 -

500 6.7 7.6 19.3 32.8 0.4 22.3 - 47.4 - -

* Cells without values correspond to receiver depths that do not exist at shallow sites.
Gulf of Mexico G&G Activities Programmatic EIS K-29

Table 22. Alternative F1 (area closures) relative to Alternative A (no activity): Remainder of 

listening area (%) at each receiver site with M-weighting for low- , mid-, and high-frequency 

cetaceans and without weighting. 

Hearing 

Group

Receiver 

Depth (m) Site 1 Site 2 Site 3 Site 4 Site 5 Site 6 Site 7* Site 8 Site 9* Site 10* 

LowFrequency 

Cetaceans

5 17.4 39.9 41.9 75.1 0.2 80.3 100 89.9 15.0 98.1

30 8.2 7.8 13.0 20.6 0.1 68.2 100 79.1 25.4 -

500 4.5 6.9 9.6 28.6 0.1 29.2 - 70.1 - -

MidFrequency 

Cetaceans 

5 14.2 86.1 42.0 91.0 0.5 80.8 100 92.1 8.3 97.2

30 21.3 79.6 80.4 84.2 0.4 99.8 100 99.6 16.0 -

500 62.3 68.7 67.4 89.8 1.4 98.9 - 99.5 - -

HighFrequency 

Cetaceans 

5 14.6 90.4 42.7 93.3 0.7 80.3 100 92.7 7.9 96.8

30 20.9 85.9 86.9 90.5 0.6 99.9 100 99.8 15.4 -

500 70.5 77.7 75.0 93.2 1.9 99.4 - 99.7 - -

Unweighted

5 17.9 40.5 41.9 74.8 0.2 80.4 100 89.8 15.6 98.2

30 7.5 6.2 11.2 18.8 0.1 65.4 100 75.8 26.2 -

500 3.6 5.6 6.6 25.2 0.1 28.8 - 64.1 - -

* Cells without values correspond to receiver depths that do not exist at shallow sites.

Table 23. Alternative F2 (area closures and 25% reduction) relative to Alternative A (no activity): 

Remainder of listening area (%) at each receiver site with M-weighting for low- , mid-, and highfrequency cetaceans and without weighting. 

Hearing 

Group

Receiver 

Depth (m) Site 1 Site 2 Site 3 Site 4 Site 5 Site 6 Site 7* Site 8 Site 9* Site 10* 

LowFrequency 

Cetaceans

5 23.0 47.4 49.7 80.2 0.3 84.6 100 92.3 20.1 98.6

30 11.2 10.5 17.3 26.4 0.1 74.3 100 83.5 31.9 -

500 6.1 9.4 12.9 35.4 0.2 36.1 - 75.9 - -

MidFrequency 

Cetaceans 

5 19.1 89.2 49.9 93.1 0.7 85.0 100 94.0 11.6 97.9

30 27.3 83.9 84.6 87.7 0.6 99.8 100 99.7 20.9 -

500 69.0 74.7 73.5 92.2 2.0 99.2 - 99.6 - -

HighFrequency 

Cetaceans

5 19.6 92.7 50.6 94.9 1.0 84.5 100 94.4 11.1 97.5

30 26.8 89.1 89.9 92.7 0.8 99.9 100 99.9 20.1 -

500 76.2 82.3 80.1 94.9 2.7 99.5 - 99.8 - -

Unweighted

5 23.6 48.0 49.8 80.0 0.3 84.6 100 92.2 20.8 98.6

30 10.2 8.4 15.0 24.3 0.1 71.8 100 80.8 32.8 -

500 4.9 7.6 9.1 31.5 0.2 35.7 - 70.6 - -

* Cells without values correspond to receiver depths that do not exist at shallow sites.
K-30 Cumulative and Chronic Effects in the Gulf of Mexico

Table 24. Alternative E (25% reduction) relative to Alternative C: Remainder of listening area (%) at 

each receiver site with M-weighting for low- , mid-, and high-frequency cetaceans and without 

weighting. 

Hearing 

Group

Receiver 

Depth (m) Site 1 Site 2 Site 3 Site 4 Site 5 Site 6 Site 7* Site 8 Site 9* Site 10* 

LowFrequency 

Cetaceans

5 129.1 117.4 113.3 106.5 140.7 107.7 100 106.7 131.8 100.3

30 132.5 135.3 127.0 127.7 142.0 113.4 100 111.2 123.5 -

500 135.2 136.0 129.5 123.1 141.0 127.1 - 116.5 - -

MidFrequency 

Cetaceans 

5 131.8 103.3 113.8 102.2 140.3 107.3 100 104.8 137.7 100.5

30 125.6 105.1 102.9 104.0 140.7 100.3 100 100.3 129.0 -

500 107.7 107.6 106.1 103.2 137.6 101.1 - 100.5 - -

HighFrequency 

Cetaceans 

5 131.4 102.2 113.7 101.6 140.2 107.7 100 104.5 138.2 100.6

30 125.7 103.5 101.9 102.3 140.5 100.2 100 100.2 129.3 -

500 105.2 105.7 104.1 102.1 136.2 100.7 - 100.3 - -

Unweighted

5 128.8 117.8 113.3 106.6 140.6 107.6 100 106.9 131.4 100.3

30 133.7 136.2 127.9 128.7 142.0 115.1 100 113.0 123.2 -

500 136.1 137.1 131.1 124.7 141.1 129.6 - 118.9 - -

* Cells without values correspond to receiver depths that do not exist at shallow sites.

Table 25. Alternative F1 (area closures) relative to Alternative C: Remainder of listening area (%) at 

each receiver site with M-weighting for low- , mid-, and high-frequency cetaceans and without 

weighting. 

Hearing 

Group

Receiver 

Depth (m) Site 1 Site 2 Site 3 Site 4 Site 5 Site 6 Site 7* Site 8 Site 9* Site 10* 

LowFrequency 

Cetaceans

5 78.7 91.3 75.2 98.8 34.7 111.2 100 119.1 84.8 99.5

30 60.0 100.9 57.0 95.4 39.9 124.0 100 129.1 85.6 -

500 72.1 97.4 54.6 95.9 42.7 133.8 - 153.1 - -

MidFrequency 

Cetaceans 

5 78.9 98.4 77.3 99.6 51.7 110.0 100 112.2 84.1 99.3

30 82.6 98.6 90.6 99.2 34.9 101.1 100 100.8 85.0 -

500 86.8 95.0 87.0 102.3 34.5 103.4 - 101.6 - -

HighFrequency 

Cetaceans

5 78.6 98.7 78.3 99.7 74.2 110.8 100 111.6 84.0 99.1

30 81.1 99.4 93.7 99.5 42.8 100.6 100 100.5 84.8 -

500 87.8 98.5 88.8 101.4 32.8 102.0 - 100.9 - -

Unweighted

5 78.7 95.1 75.2 98.8 34.4 110.7 100 119.7 84.9 99.5

30 62.9 96.9 52.9 95.3 38.9 129.7 100 134.9 86.2 -

500 72.7 100.7 45.0 95.6 50.5 167.6 - 160.9 - -

* Cells without values correspond to receiver depths that do not exist at shallow sites.
Gulf of Mexico G&G Activities Programmatic EIS K-31

Table 26. Alternative F2 (area closures and 25% reduction) relative to Alternative E (25% 

reduction): Remainder of listening area (%) at each receiver site with M-weighting for low- , mid-, 

and high-frequency cetaceans and without weighting. 

Hearing 

Group

Receiver 

Depth (m) Site 1 Site 2 Site 3 Site 4 Site 5 Site 6 Site 7* Site 8 Site 9* Site 10* 

LowFrequency 

Cetaceans

5 80.6 92.4 78.8 99.1 34.8 108.7 100 114.5 86.0 99.6

30 61.7 100.9 59.5 95.8 39.9 119.2 100 122.6 87.0 -

500 72.8 97.5 56.6 96.3 42.8 130.0 - 142.2 - -

MidFrequency 

Cetaceans 

5 80.5 98.8 80.6 99.7 51.9 107.8 100 109.2 85.0 99.4

30 84.1 98.9 92.6 99.4 35.1 100.8 100 100.6 86.0 -

500 89.2 96.0 89.5 101.8 35.1 102.6 - 101.2 - -

HighFrequency 

Cetaceans 

5 80.3 99.0 81.5 99.8 74.3 108.4 100 108.8 84.8 99.3

30 82.8 99.5 95.1 99.6 43.1 100.4 100 100.4 85.9 -

500 90.2 98.8 91.1 101.0 33.5 101.5 - 100.7 - -

Unweighted

5 80.6 95.8 78.8 99.1 34.5 108.3 100 115.0 86.2 99.6

30 64.4 97.0 55.4 95.7 39.0 123.8 100 127.3 87.6 -

500 73.2 100.7 46.8 96.1 50.5 160.0 - 149.1 - -

* Cells without values correspond to receiver depths that do not exist at shallow sites.

Table 27. Alternative F2 (area closures and 25% reduction) relative to Alternative F1 (area 

closures): Remainder of listening area (%) at each receiver site with M-weighting for low- , mid-, 

and high-frequency cetaceans and without weighting. 

Hearing 

Group

Receiver 

Depth (m) Site 1 Site 2 Site 3 Site 4 Site 5 Site 6 Site 7* Site 8 Site 9* Site 10* 

LowFrequency 

Cetaceans

5 132.2 118.9 118.7 106.8 141.1 105.3 100 102.6 133.7 100.5

30 136.3 135.2 132.6 128.3 142.1 108.9 100 105.6 125.5 -

500 136.4 136.1 134.3 123.6 141.3 123.5 - 108.3 - -

MidFrequency 

Cetaceans 

5 134.5 103.6 118.7 102.3 140.8 105.2 100 102.0 139.2 100.7

30 128.0 105.5 105.3 104.2 141.6 100.1 100 100.1 130.6 -

500 110.7 108.7 109.2 102.6 139.9 100.3 - 100.1 - -

HighFrequency 

Cetaceans

5 134.2 102.5 118.4 101.7 140.5 105.3 100 101.9 139.5 100.8

30 128.2 103.7 103.4 102.4 141.4 100 100 100 130.9 -

500 108.1 106.0 106.8 101.7 139.4 100.2 - 100.1 - -

Unweighted

5 131.9 118.6 118.7 106.9 141.1 105.3 100 102.6 133.3 100.5

30 136.9 136.3 133.8 129.3 142.1 109.8 100 106.6 125.2 -

500 137.1 137.1 136.4 125.2 141.3 123.7 - 110.2 - -

* Cells without values indicate that the site was too shallow to place a receiver at the specified depth.
K-32 Cumulative and Chronic Effects in the Gulf of Mexico

4.4. Bryde’s Whale Communication Space

Tables 29–36 present the relative changes in Bryde’s whale communication space for all modeled

alternatives based on communication in the 1/3-octave band centered at 100 Hz. The baseline levels 

(SPLs for Alternative A; Table 28) used in these comparisons were calculated for the same frequency 

band.

Table 28. Baseline (Alternative A; no activity) SPL (dB re 1 μPa) for 100 Hz for each receiver site 

and depth.

Receiver 

Depth (m) Site 1 Site 2 Site 3 Site 4 Site 5 Site 6 Site 7* Site 8 Site 9* Site 10*

5 79.18 76.18 80.21 76.26 76.27 76.13 79.93 79.98 80.70 86.66

30 78.15 76.20 78.95 76.44 76.59 76.19 81.66 79.05 80.59

500 78.12 77.63 83.46 80.66 80.71 76.86 79.75

* Cells without values correspond to receiver depths that do not exist at shallow sites.
Gulf of Mexico G&G Activities Programmatic EIS K-33

Table 29. Alternative C relative to Alternative A (no activity): Bryde’s whale communication space 

at all receiver sites. 

Site Receiver 

Depth (m)

Alternative A Alternative C 

∆ area (km2) % of original 

area area (km2) area (km2) 

1 

5 98.2 49.4 48.8 50

30 190.9 31.5 159.4 16

500 182.2 19.2 163.1 11

2 

5 186.8 40.9 145.9 22

30 286.7 51.7 235.0 18

500 232.1 28.0 204.1 12

3 

5 108.4 76.2 32.2 70

30 186.7 82.7 104.0 44

500 81.5 26.3 55.1 32

4 

5 164.5 77.0 87.6 47

30 252.3 55.5 196.9 22

500 135.1 30.9 104.2 23

5 

5 0.8 0 0.8 5

30 4.3 0.2 4.1 4

500 26.3 0 26.3 0

6 

5 186.1 173.1 13.0 93

30 290.1 244.4 45.6 84

500 271.3 117.3 154.0 43

7* 5 60.4 60.4 0 100

30 110.1 110.1 0 100

8 

5 81.9 79.4 2.5 97

30 195.3 167.9 27.4 86

500 159.3 116.6 42.7 73

9* 5 34.1 34.0 0 100

30 97.8 97.5 0.3 100

10* 5 3.5 3.5 0 100

* Sites 7, 9, and 10 are located in areas too shallow to place a receiver at the 500 m depth, and Site 10 is located in an area too shallow to 

place a receiver at the 30 or 500 m depths. 
K-34 Cumulative and Chronic Effects in the Gulf of Mexico

Table 30. Alternative E (25% reduction) relative to Alternative A (no activity): Bryde’s whale 

communication space at all receiver sites.

Site Receiver 

Depth (m)

Alternative A Alternative E 

∆ area (km2) % of original 

area area (km2) area (km2) 

1 

5 98.2 57.9 40.3 59

30 190.9 43.0 148.0 23

500 182.2 23.9 158.3 13

2 

5 186.8 53.1 133.7 28

30 286.7 70.6 216.1 25

500 232.1 37.1 195.0 16

3 

5 108.4 83.1 25.3 77

30 186.7 97.6 89.1 52

500 81.5 30.8 50.7 38

4 

5 164.5 91.3 73.2 55

30 252.3 77.3 175.0 31

500 135.1 41.6 93.5 31

5 

5 0.8 0 0.8 5

30 4.3 0.2 4.1 5

500 26.3 0 26.3 0

6 

5 186.1 176.1 10.0 95

30 290.1 254.9 35.2 88

500 271.3 141.7 129.6 52

7* 5 60.4 60.4 0 100

30 110.1 110.1 0 100

8 

5 81.9 80.1 1.9 98

30 195.3 174.3 21.1 89

500 159.3 125.3 34.0 79

9* 5 34.1 34.1 0 100

30 97.8 97.6 0.2 100

10* 5 3.5 3.5 0 100

* Sites 7, 9, and 10 are located in areas too shallow to place a receiver at the 500 m depth, and Site 10 is located in an area too shallow to 

place a receiver at the 30 or 500 m depths. 
Gulf of Mexico G&G Activities Programmatic EIS K-35

Table 31. Alternative F1 (area closures) relative to Alternative A (no activity): Bryde’s whale 

communication space at all receiver sites.

Site Receiver 

Depth (m)

Alternative A Alternative F1

∆ area (km2) % of original 

area area (km2) area (km2) 

1 

5 98.2 34.4 63.7 35

30 190.9 19.9 171.0 10

500 182.2 12.9 169.3 7

2 

5 186.8 27.3 159.5 15

30 286.7 57.5 229.2 20

500 232.1 24.0 208.2 10

3 

5 108.4 49.7 58.6 46

30 186.7 51.8 134.9 28

500 81.5 19.7 61.8 24

4 

5 164.5 74.3 90.3 45

30 252.3 51.9 200.4 21

500 135.1 30.3 104.8 22

5 

5 0.8 0 0.8 3

30 4.3 0.1 4.2 3

500 26.3 0 26.3 0

6 

5 186.1 180.2 5.9 97

30 290.1 276.8 13.2 95

500 271.3 176.6 94.7 65

7* 5 60.4 60.4 0 100

30 110.1 110.1 0 100

8 

5 81.9 81.2 0.8 99

30 195.3 188.6 6.7 97

500 159.3 146.4 12.9 92

9* 5 34.1 34.1 0 100

30 97.8 97.4 0.4 100

10* 5 3.5 3.5 0 100

* Sites 7, 9, and 10 are located in areas too shallow to place a receiver at the 500 m depth, and Site 10 is located in an area too shallow to 

place a receiver at the 30 or 500 m depths. 
K-36 Cumulative and Chronic Effects in the Gulf of Mexico

Table 32. Alternative F2 (area closures and 25% reduction) relative to Alternative A (no activity): 

Bryde’s whale communication space at all receiver sites.

Site Receiver 

Depth (m)

Alternative A Alternative F2

∆ area (km2) % of original 

area area (km2) area (km2) 

1 

5 98.2 41.4 56.8 42

30 190.9 27.4 163.6 14

500 182.2 17.5 164.7 10

2 

5 186.8 34.9 151.9 19

30 286.7 77.5 209.2 27

500 232.1 31.6 200.5 14

3 

5 108.4 57.4 50.9 53

30 186.7 65.8 120.9 35

500 81.5 22.6 58.9 28

4 

5 164.5 88.8 75.8 54

30 252.3 74.1 178.3 29

500 135.1 40.8 94.3 30

5 

5 0.8 0 0.8 3

30 4.3 0.2 4.1 4

500 26.3 0 26.3 0

6 

5 186.1 181.6 4.5 98

30 290.1 280.1 9.9 97

500 271.3 195.5 75.8 72

7* 5 60.4 60.4 0 100

30 110.1 110.1 0 100

8 

5 81.9 81.4 0.6 99

30 195.3 190.3 5.1 97

500 159.3 149.4 9.9 94

9* 5 34.1 34.0 0 100

30 97.8 97.5 0.3 100

10* 5 3.5 3.5 0 100

* Sites 7, 9, and 10 are located in areas too shallow to place a receiver at the 500 m depth, and Site 10 is located in an area too shallow to 

place a receiver at the 30 or 500 m depths. 
Gulf of Mexico G&G Activities Programmatic EIS K-37

Table 33. Alternative E (25% reduction) relative to Alternative C: Bryde’s whale communication 

space at all receiver sites.

Site Receiver 

Depth (m)

Alternative C Alternative E 

∆ area 

(km2)

% of original 

area

area (km2) area (km2) 

1 

5 49.4 57.9 −8.5 117

30 31.5 43.0 −11.5 136

500 19.2 23.9 −4.7 125

2 

5 40.9 53.1 −12.3 130

30 51.7 70.6 −18.9 137

500 28.0 37.1 −9.1 132

3 

5 76.2 83.1 −6.9 109

30 82.7 97.6 −14.9 118

500 26.3 30.8 −4.5 117

4 

5 77.0 91.3 −14.3 119

30 55.5 77.3 −21.8 139

500 30.9 41.6 −10.7 135

5 

5 0.038 0.043 −0.005 113

30 0.182 0.212 −0.030 116

500 0 0 0

6 

5 173.1 176.1 −3.0 102

30 244.4 254.9 −10.4 104

500 117.3 141.7 −24.4 121

7* 5 60.4 60.4 0 100

30 110.1 110.1 0 100

8 

5 79.4 80.1 −0.6 101

30 167.9 174.3 −6.4 104

500 116.6 125.3 −8.7 107

9* 5 34.0 34.1 0 100

30 97.5 97.6 −0.1 100

10* 5 3.5 3.5 0 100

* Sites 7, 9, and 10 are located in areas too shallow to place a receiver at the 500 m depth, and Site 10 is located in an area too shallow to 

place a receiver at the 30 or 500 m depths. 
K-38 Cumulative and Chronic Effects in the Gulf of Mexico

Table 34. Alternative F1 (area closures) relative to Alternative C (no activity): Bryde’s whale 

communication space at all receiver sites.

Site Receiver 

Depth (m)

Alternative C Alternative F1

∆ area (km2) % of original 

area

area (km2) area (km2) 

1 

5 49.4 34.4 15.0 70

30 31.5 19.9 11.6 63

500 19.2 12.9 6.2 67

2 

5 40.9 27.3 13.6 67

30 51.7 57.5 −5.9 111

500 28.0 24.0 4.0 86

3 

5 76.2 49.7 26.4 65

30 82.7 51.8 30.9 63

500 26.3 19.7 6.7 75

4 

5 77.0 74.3 2.7 96

30 55.5 51.9 3.5 94

500 30.9 30.3 0.6 98

5 

5 0.038 0.023 0.015 61

30 0.182 0.123 0.059 68

500 0 0 0

6 

5 173.1 180.2 −7.1 104

30 244.4 276.8 −32.4 113

500 117.3 176.6 −59.3 151

7* 5 60.4 60.4 0 100

30 110.1 110.1 0 100

8 

5 79.4 81.2 −1.7 102

30 167.9 188.6 −20.7 112

500 116.6 146.4 −29.8 126

9* 5 34.0 34.1 0 100

30 97.5 97.4 0 100

10* 5 3.5 3.5 0 100

* Sites 7, 9, and 10 are located in areas too shallow to place a receiver at the 500 m depth, and Site 10 is located in an area too shallow to 

place a receiver at the 30 or 500 m depths. 
Gulf of Mexico G&G Activities Programmatic EIS K-39

Table 35. Alternative F2 (area closures and 25% reduction) relative to Alternative E (25% 

reduction): Bryde’s whale communication space at all receiver sites.

Site Receiver 

Depth (m)

Alternative E Alternative F2

∆ area (km2) % of original 

area

area (km2) area (km2) 

1 

5 57.9 41.4 16.5 71

30 43.0 27.4 15.6 64

500 23.9 17.5 6.4 73

2 

5 53.1 34.9 18.2 66

30 70.6 77.5 −6.9 110

500 37.1 31.6 5.5 85

3 

5 83.1 57.4 25.6 69

30 97.6 65.8 31.9 67

500 30.8 22.6 8.2 73

4 

5 91.3 88.8 2.5 97

30 77.3 74.1 3.3 96

500 41.6 40.8 0.8 98

5 

5 0.043 0.028 0.015 65

30 0.212 0.151 0.061 71

500 0 0 0

6 

5 176.1 181.6 −5.5 103

30 254.9 280.1 −25.3 110

500 141.7 195.5 −53.8 138

7* 5 60.4 60.4 0 100

30 110.1 110.1 0 100

8 

5 80.1 81.4 −1.3 102

30 174.3 190.3 −16.0 109

500 125.3 149.4 −24.1 119

9* 5 34.1 34.0 0 100

30 97.6 97.5 0.1 100

10* 5 3.5 3.5 0 100

* Sites 7, 9, and 10 are located in areas too shallow to place a receiver at the 500 m depth, and Site 10 is located in an area too shallow to 

place a receiver at the 30 or 500 m depths. 
K-40 Cumulative and Chronic Effects in the Gulf of Mexico

Table 36. Alternative F2 (area closures and 25% reduction) versus Alternative F1 (area closures): 

Bryde’s whale communication space at all receiver sites.

Site Receiver 

Depth (m)

Alternative F1 Alternative F2

∆ area (km2) % of original 

area

area (km2) area (km2) 

1 

5 34.4 41.4 −6.9 120

30 19.9 27.4 −7.4 137

500 12.9 17.5 −4.6 135

2 

5 27.3 34.9 −7.6 128

30 57.5 77.5 −20.0 135

500 24.0 31.6 −7.6 132

3 

5 49.7 57.4 −7.7 115

30 51.8 65.8 −14.0 127

500 19.7 22.6 −2.9 115

4 

5 74.3 88.8 −14.5 120

30 51.9 74.1 −22.1 143

500 30.3 40.8 −10.6 135

5 

5 0.023 0.028 −0.005 122

30 0.123 0.151 −0.028 123

500 0 0 0

6 

5 180.2 181.6 −1.5 101

30 276.8 280.1 −3.3 101

500 176.6 195.5 −18.9 111

7* 5 60.4 60.4 0 100

30 110.1 110.1 0 100

8 

5 81.2 81.4 −0.2 100

30 188.6 190.3 −1.7 101

500 146.4 149.4 −3.0 102

9* 5 34.1 34.1 0 100

30 97.4 97.5 −0.1 100

10* 5 3.5 3.5 0 100

* Sites 7, 9, and 10 are located in areas too shallow to place a receiver at the 500 m depth, and Site 10 is located in an area too shallow to 

place a receiver at the 30 or 500 m depths. 
Gulf of Mexico G&G Activities Programmatic EIS K-41

5. Discussion and Conclusion

This assessment applied acoustic modeling to determine changes to Bryde’s whale communication space 

and changes in listening area (all species), caused by the introduction of various seismic survey activities

in the Gulf of Mexico. Ten receiver sites were modeled (Table 1, Figure 1) for five alternatives of seismic 

survey activity (Table 3), representing possible levels of annual survey activity across six geographic 

activity zones comprising the project area (Figure 1). The assessment results for change in listening area 

are presented in Tables 20–27, and results for Bryde’s whale communication space are presented in 

Tables 28–36. 

The key findings of this acoustic effects assessment are: 

• Communication space and listening area decreased for all alternatives relative to the no-activity 

Alternative A, except at Site 7. Change in listening area was generally greater for low-frequency 

cetaceans than for mid- and high-frequency cetaceans. 

• The largest decreases, by up to 99.9% of listening area (low-frequency cetaceans) and up to 100% of 

Bryde’s whale communication space, occurred at Site 5 for reasons outlined below. The decreases in 

communication space and listening area at other sites were highly variable (between 0.1% and 95%). 

The amount of change depended on the location, receiver depth, and marine mammal frequency 

weighting filter used. 

• Bryde’s whale communication space and low-frequency cetacean listening area reductions were 

greater at the 500 m receiver depth than at the shallower receiver depths (5 and 30 m). That was 

attributed to the downward refracting sound speed profile near the surface, caused by the thermocline 

steering sound to deeper depths. It was also influenced by surface interactions that increase 

transmission loss (lower anthropogenic levels) at shallow depths for low frequencies. 

• Listening area reductions for mid- and high-frequency cetaceans were substantially lower than for 

low-frequency cetaceans at most sites. Change in listening areas were generally small (> 75% 

remaining) except at Sites 1, 5, and 9. The listening area reductions were not systematically greater 

at depth, and in fact in some cases were less. 

5.1. Site-Specific Results 

• Site 1 (Western Gulf, 842 m water depth) experienced decreased listening area of up to 93.8% (6.2% 

remaining) for low-frequency cetaceans. Bryde’s whale communication space was decreased by up 

to 89% (11% remaining), for Alternative C. The proposed area closures and reduced activity 

alternatives did not appreciably change these results. 

• Site 2 (Florida Escarpment, 693 m water depth) experienced decreased listening area of up to 92.9% 

(7.1% remaining) for low-frequency cetaceans. Bryde’s whale communication space was decreased 

up to 88% (12% remaining), for Alternative C. The proposed area closures and reduced activity

alternatives did not appreciably change these results. 

• Site 3 (Midwestern Gulf, 830 m water depth) experienced decreased listening area of up to 82.4% 

(17.6% remaining) for low-frequency cetaceans. Bryde’s whale communication space was decreased 

up to 88% (12% remaining) for Alternative C. The proposed area closures Alternative F1 actually lead 

to increased noise at Site 3 due to the redistribution of 25% of the activity inside the central planning 

area into the rest of Zone 4. This resulted in a decreased listening area of 90.4%. 

• Site 4 (Sperm Whale Site, 1053 m water depth) experienced decreased listening area of up to 70.1% 

(29.9% remaining) for low-frequency cetaceans. Bryde’s whale communication space was decreased 

by up to 77% (23% remaining) for Alternative C. The proposed area closures Alternative F1 did not 

appreciably affect this site even though it lies near the Dry Tortugas closure area. 
K-42 Cumulative and Chronic Effects in the Gulf of Mexico

• Site 5 (Deep Offshore, 3050 m water depth) experienced the largest change to communication space 

and had the greatest relative reduction in listening area for all alternatives. Communication space was 

decreased by more than 95% (to less than 5% remaining) for all activity alternatives relative to the noactivity alternative (Alternative A). Listening area was reduced to less than 1% for low-frequency 

cetaceans and to less than 8% for mid-frequency and high-frequency cetaceans for all alternatives 

relative to Alternative A. This site experienced the highest anthropogenic noise levels because: 

1. Receiver 5 was located in Zone 4, which has the highest density of seismic pulses. 

2. This receiver site lies in deep water that supports longer-range low-frequency sound propagation 

than shallower sites. As a result, a larger number of seismic pulses contributed to its accumulated 

acoustic energy. 

• Site 6 (Mississippi Canyon, 1106 m water depth) experienced decreased listening area of up to 

78.1% (21.9% remaining) for low-frequency cetaceans. Bryde’s whale communication space 

decreased up to 77% (23% remaining) for Alternative C. Site 6 lies inside the central planning closure 

area and consequently Alternative F1 led to improved noise conditions, with listening area loss at 

70.8% (29.2% remaining) for low-frequency cetaceans compared to the no-activity alternative

(Alternative A). This is an increase of the listening area by 7.3% compared to that for Alternative C.

• Site 7 (Bryde’s Whale Site, 212 m water depth) experienced the lowest anthropogenic sound levels 

(Leq) for all alternatives. These Leq were in fact below baseline levels (Alternative A) even for the full 

activity level described in Alternative C. Consequently, no changes to communication space or 

listening area were experienced for any of the alternatives. There are three primary reasons for low 

anthropogenic noise levels at this site: 

1. The ocean sound speed profile is downward refracting and steers sound energy from distant 

sources into the seabed, where it is absorbed by softer, non-reflective sediments. 

2. Only geotechnical surveys are performed in Zone 5 (Florida shelf), adjacent to this receiver site. 

The geotechnical surveys are represented by a single small airgun source that produces 

substantially less acoustic energy than the 3-D airgun array used in other activity zones (see 

Table 5). 

3. The 2-D and 3-D survey activity levels in Zone 6, in which this receiver resides, are low relative to 

other sites. 

• Site 8 (De Soto Canyon, 919 m water depth) experienced decreased listening area of up to 54.2% 

(45.8% remaining) for low-frequency cetaceans. Bryde’s whale communication space decreased up 

to 27% (73% remaining) for Alternative C. The proposed area closures for Alternative F1 further 

improved the noise conditions at this site since it lies on the eastern edge of the central planning 

closure area. This led to a change in listening area of 24.1% (75.9% remaining) compared to the noactivity alternative (Alternative A).This is an increase of listening area by 30.1% compared to 

Alternative C. 

• Site 9 (Flower Garden Banks National Marine Sanctuary, 88 m water depth) experienced decreased 

listening area of up to 54.2% (17.7% remaining) for low-frequency cetaceans and up to 90.6% (9.4% 

remaining) for high-frequency cetaceans. Interestingly, the Bryde’s whale communication space 

decreases did not show this loss and indicated no loss in space for Alternative C. This result was 

likely due to noise outside of the Bryde’s whale call band affecting listening area, but not the Bryde’s 

communication space. The proposed area closures for Alternative F1 did not appreciably change 

these results even though the site lies in the Flower Garden closure area. 

• Site 10 (Bottlenose Dolphin Site, 12 m water depth) was inside the coastal closure area and 

experienced little low-frequency seismic survey noise and only marginal higher-frequency noise. Its 

decrease in listening area was by up to 2.4% (97.6% remaining) for high-frequency cetaceans with 

even smaller decreases for low-frequency cetaceans and mid-frequency cetaceans. The Bryde’s 

whale communication space was unaffected. 
Gulf of Mexico G&G Activities Programmatic EIS K-43

Acknowledgments 

With much appreciation, we thank Erin Dunable for her help on the interpretation and editorial review of 

this report, and Jolie Harrison and Leila Hatch for their insights and contributions to developing the

analysis approaches. 

 
K-44 Cumulative and Chronic Effects in the Gulf of Mexico

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APPENDIX L 

PANEL REPORTS

Gulf of Mexico G&G Activities Programmatic EIS L-iii 

TABLE OF CONTENTS 

Page 

LIST OF FIGURES ........................................................................................................................... L-v

LIST OF TABLES ............................................................................................................................. L-v

ABBREVIATIONS AND ACRONYMS ............................................................................................ L-vii

1 LOWEST PRACTICABLE SOUND SOURCE PANEL REPORT ................................................. L-1

1.1 Introduction .......................................................................................................................... L-1

1.2 Internal Expert Panel ........................................................................................................... L-1

1.3 Subject-Matter Experts ........................................................................................................ L-3

1.4 History of Marine Seismic Surveys ...................................................................................... L-4

1.5 Technology and Parameters ................................................................................................ L-5

1.6 Key Points ............................................................................................................................ L-6

1.7 Discussion............................................................................................................................ L-6

1.7.1 Number of Elements in an Array ................................................................................ L-6

1.7.2 Operating Pressure of an Array ................................................................................. L-8

1.7.3 Volume of an Array, Including Individual Element Volumes ....................................... L-8

1.7.4 Array Dimensions ...................................................................................................... L-8

1.8 Summary ............................................................................................................................. L-9

1.9 Conclusions ....................................................................................................................... L-10

2 DUPLICATIVE PANEL REPORT ............................................................................................... L-11

2.1 Introduction ........................................................................................................................ L-11

2.2 Internal Expert Panel ......................................................................................................... L-11

2.3 Subject-Matter Experts ...................................................................................................... L-13

2.4 Acknowledgement .............................................................................................................. L-14

2.5 Definition of Duplicative Survey ......................................................................................... L-14

2.6 Background and History of Seismic Surveys ..................................................................... L-14

2.7 Environmental and Regulatory Concerns .......................................................................... L-15

2.8 Data Aquisition ................................................................................................................... L-16

2.8.1 Differences between Multi-Client and Proprietary Data Acquisition ......................... L-16

2.8.2 Why Multi-Client Seismic Data? ............................................................................... L-16

2.9 Gulf of Mexico Seismic Acquisition Review – Mississippi Canyon Protraction Area .......... L-17

2.9.1 Comparison of the Generational Events in Highlighted Area A ............................... L-22

2.9.2 Comparison of Generational Events in Highlighted Area B ..................................... L-24

2.9.3 Comparison of Generational Events in Highlighted Area C ..................................... L-26

2.9.4 Comparison of Generational Events in Highlighted Area D ..................................... L-28

2.9.5 Comparison of Generational Events in Highlighted Area E ..................................... L-30

2.9.6 Comparison of Generational Events in Highlighted Area F ...................................... L-32

2.10 Overall Analysis ................................................................................................................. L-34

2.11 Geophysical Hardware Advancements .............................................................................. L-35

2.12 Acquisition Geometry Advancements ................................................................................ L-36

2.13 Potential Metrics to Determine Duplicative Surveys ........................................................... L-37

2.14 Summary ........................................................................................................................... L-38

2.14.1Panel Determination ................................................................................................ L-39

3 LITERATURE CITED ................................................................................................................. L-39

 
L-iv Panel Reports

ATTACHMENT 1: GLOSSARY OF GEOPHYSICAL TERMS AND COMMON 

ABBREVIATIONS.............................................................................................. L-41

ATTACHMENT 2: DIFFERENCES BETWEEN MULTI-CLIENT AND EXCLUSIVE SURVEYS.... L-44

ATTACHMENT 3: ENLARGED VERSIONS OF COMPOSITE GENERATIONAL LINES ............. L-45
Gulf of Mexico G&G Activities Programmatic EIS L-v 

LIST OF FIGURES

Page

Figure L-1. Generations 1-4 Composite 2D Seismic Lines Built from Multiple Company 

3D Datasets. ................................................................................................................. L-20

Figure L-2. Orientation of Traverse Lines for Generations 1 through 4 .......................................... L-21

Figure L-3. Generational Comparison of Highlighted Area A. ........................................................ L-22

Figure L-4. Generational Comparison of Highlighted Area B. ........................................................ L-24

Figure L-5. Generational Comparison of Highlighted Area C......................................................... L-26

Figure L-6. Generational Comparison of Highlighted Area D......................................................... L-28

Figure L-7. Generational Comparison of Highlighted Area E. ........................................................ L-30

Figure L-8. Generational Comparison of Highlighted Area F. ........................................................ L-32

Figure L-9. Schematic Comparison of Narrow-Azimuth vs. Multi-Azimuth vs. Wide-Azimuth 

Streamer Acquisition..................................................................................................... L-36

LIST OF TABLES

Page

Table L-1. Mississippi Canyon Seismic Surveys Acquisition Parameters..................................... L-19

Table L-2. Summary of Significant Parameters............................................................................. L-35

Gulf of Mexico G&G Activities Programmatic EIS L-vii

ABBREVIATIONS AND ACRONYMS

2D two dimensional

3D three dimensional

4D four dimensional

BOEM Bureau of Ocean Energy Management

dB decibel

E&P exploration and production

EIS environmental impact statement

e.g. for example

et al. and others

FAZ full azimuth

ft foot

G&G geological and geophysical

GOM Gulf of Mexico

GOMR Gulf of Mexico OCS Region

i.e. that is

in3 cubic inch

m meter

MMS Minerals Management Service

NAZ narrow azimuth

OCB ocean bottom cable

OCS Outer Continental Shelf

PGS Petroleum Geo-Services, Inc.

psi pounds per square inch

RAZ rich azimuth

SEL 

S/N signal-to-noise

SPLrms 

U.S. United States

USGS U.S. Department of the Interior, Geological Survey

WAZ wide azimuth

Gulf of Mexico G&G Activities Programmatic EIS L-1 

1 LOWEST PRACTICABLE SOUND SOURCE PANEL REPORT

Submitted by Lowest Practical Sound Source Panel (8/12/2016) 

1.1 INTRODUCTION

The Natural Resource Defense Council, Inc. et al., as Plaintiffs in a lawsuit against the U.S. 

Department of the Interior as Defendant, have expressed concern that marine offshore seismic 

surveys should use the lowest sound intensity level that would not only illuminate subsurface targets 

but also minimize horizontal propagation that may have physical and/or behavioral effects on marine 

mammal populations. As per condition VII.A., the “Order Granting Joint Motion for Approval of 

Settlement Agreement and Stay of Proceedings” (June 24, 2013), the Bureau of Ocean Energy 

Management (BOEM) agreed to convene an internal expert panel to determine whether it would be 

feasible to develop standards to determine a lowest practicable source level. The panel has 

determined that it would not be reasonable or practicable to develop these metrics. 

1.2 INTERNAL EXPERT PANEL

The internal BOEM Panel who formulated this document consisted of the following 

personnel:

Tamara S. Arzt, J.D, M.P.A. is an Environmental Protection Specialist and the 

Endangered Species Act Lead for BOEM’s Headquarters. She has worked for 

BOEM since 2011. Ms. Arzt received her B.A. from Smith College with a major in 

Government and her M.P.A from the University of Massachusetts, Amherst with a 

specific focus on environmental policy and endangered species. Ms. Arzt then 

worked for an alternative dispute resolution firm in Boulder, Colorado, where she 

focused on resolving multiple Federal environmental issues. In 2003, Ms. Arzt 

received her J.D. from Vermont Law School concentrating on environmental law. 

Upon graduation, she was accepted into the Presidential Management Fellowship 

program and worked for the Bureau of Land Management with the U.S. Department 

of the Interior in Washington, DC and Colorado. Ms. Arzt continued her career in 

public service, working for county and municipal government on the Northfork of 

Long Island, New York, with a continued emphasis on the environment, in particular 

coastal and wetlands issues. In addition to being the Endangered Species Act Lead 

in BOEM’s Headquarters’ Office, Ms. Arzt works extensively with Marine Mammal 

Protection Act and National Environmental Policy Act, as well as Coastal Zone 

Management Act and National Historic Preservation Act, issues associated with both 

traditional and renewable energy development on the Outer Continental Shelf (OCS). 

Ronald (Ron) Brinkman currently serves as BOEM’s Senior Staff Geophysicist for 

the Gulf of Mexico OCS Region’s Office of Resource Evaluation. He has worked as 

a geophysical interpreter, permitting and acquisition specialist, and geophysical 

subject-matter expert in the preparation of the Atlantic and Gulf of Mexico Geological 
L-2 Panel Reports

and Geophysical Programmatic Environmental Statements (EISs), as well as 

subject-matter advisor to the OKEANOS and CETSOUND working groups. Ron has 

B.S. degrees in Mathematics and Geology from the Louisiana State University (New 

Orleans) and has been employed with the U.S. Department of the Interior for over 

39 years. He has been an active member of the Society of Exploration 

Geophysicists since 1992.

Ty Collins is a Geophysicist at in BOEM’s Gulf of Mexico OCS Region’s Office of 

Resource Evaluation. Prior to working at BOEM, he worked in commercial 

geophysical survey acquisition in the United States (U.S.) OCS, including the Gulf of 

Mexico, Beaufort Sea, and Chukchi Sea. He has experience in commercial survey 

design, acquisition, processing, and interpretation of geophysical data. At BOEM, 

Mr. Collins interprets geophysical and geological data to evaluate the “fair market 

value” of lease blocks related to OCS lease sales. Mr. Collins holds a Professional 

Geoscientist License from the Louisiana Board of Professional Geoscientists and a 

B.S. degree in Geophysics from the University of New Orleans. He is a graduate of 

the Daniel J. Tearpock Geoscience Certification Program and is an active member of 

the Society of Exploration Geophysicists.

Patrick Hart is a geophysicist with the U.S. Department of the Interior’s Geological 

Survey (USGS), working at the Pacific Coastal and Marine Science Center in Santa 

Cruz, California. Mr. Hart obtained a B.S. and M.S. in Geophysics from Stanford 

University in 1980. After working in the exploration industry for 6 years in various 

seismic data acquisition and processing positions, he joined the USGS Branch of 

Pacific Marine Geology in Menlo Park, California, as a marine seismic data analyst. 

Over the last 30 years, he has worked on a wide variety of projects utilizing marine 

seismic data, including gas hydrate characterization, marine geohazard analysis, and 

sound source verification. Mr. Hart is an active member of the Society of Exploration 

Geophysicists and the American Geophysical Union.

John Johnson is a supervisory geologist with the BOEM’s Gulf of Mexico OCS 

Region (GOMR) in New Orleans, Louisiana. He received his B.S. and M.S. degrees 

in Geology from the University of Florida prior to starting work as a geologist with the 

USGS’ Conservation Division (the predecessor of MMS) in 1981. Mr. Johnson 

evaluated offshore lease prospects for fair market value determination for over 

15 years and served as Staff Geologist. Since 2007, he has been supervisor of 

BOEM’s Gulf of Mexico OCS Region, Office of Resource Evaluation’s Data 

Acquisition and Special Projects Unit. This group is responsible for geological and 

geophysical (G&G) permitting in the Gulf of Mexico and for the purchasing, loading, 

and managing (including archiving and public release) of digital seismic data for the 

GOMR.
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Stanley (Stan) Labak works in BOEM’s Division of Environmental Science in 

Sterling, Virginia. Mr. Labak has been with BOEM for about 3 years, where he is a 

Physical Scientist (Marine Acoustician) in the Physical & Chemical Sciences Branch. 

His specific areas of experience and expertise include modeling, analysis, and 

evaluation of underwater acoustic source and propagation, especially with regards to 

its potential impact to marine species. Stan received his B.S. in Ocean Engineering 

at the U.S. Naval Academy and his M.S. in Ocean Engineering at the Massachusetts 

Institute of Technology, where he was a Draper Fellow. He is a retired Naval 

Reservist.

Dr. Carolyn Ruppel is a geophysicist who obtained all of her degrees at the 

Massachusetts Institute of Technology. After a stint as a Postdoctoral Scholar at 

Woods Hole Oceanographic Institution, she spent 12 years as a professor (tenured 

2000) at Georgia Tech. From 2003-2006, she was a program manager at the 

National Science Foundation, Division of Ocean Sciences as a faculty rotator. She 

moved to a senior position in USGS in 2006 and is now Chief Scientist of the USGS’ 

Gas Hydrates Project and the informal contact for environmental compliance issues 

within the Coastal and Marine Geology Program at USGS. Dr. Ruppel has served on 

the U.S. Department of Energy’s Federal Advisory Committee for gas hydrates, 

several editorial boards, and numerous national/international committees in marine 

science; has been a Distinguished Lecturer for the Ocean Drilling Program; and has 

testified to several National Research Council panels. She is a Fellow of the 

Geological Society of America.

1.3 SUBJECT-MATTER EXPERTS

The Panel would also like to knowledge and thank the following subject-matter experts who, 

while not official Panel Members, contributed their individual expertise in the document’s

development:

Tom Neugebauer is the Director of Project Management and Execution Western 

Hemisphere for TGS-NOPEC Geophysical Company. He received his B.S. in 

oceanographic technology from Florida Tech and A.S. in electrical engineering 

technology from HCC. Over the past 36 years Tom has worked in marine seismic 

acquisition, marine/land data processing, processing management, seismic sales 

and project development with GSI, Seismograph Services, Geco-Prakla and TGS. 

Since 2014, Tom has held the position of Director of marine projects for the Western 

Hemisphere region at TGS.

Detlef Ross is a Geophysical Advisor at Petroleum Geo-Services, Inc. (PGS), 

located in Houston, Texas. He received his Pre-Diploma (equal B.S.) in Physical 

Oceanography and Diploma (M.S.) in Geophysics from the University of Kiel, 

Germany, prior to starting work for PGS Geophysical AS in Oslo, Norway, in 1998. 
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Over the last 18 years, Mr. Ross has held various positions as a geophysicist, field 

engineer, supervisor, and project manager, working onshore and offshore. Since 

2013, he has assumed the role of geophysical advisor.

We would also like to acknowledge special technical assistance provided to the panel by

Mr. Steven Fishburn who is the former Vice President GOM Multi-Client, Petroleum 

Geo-Services, Inc.

1.4 HISTORY OF MARINE SEISMIC SURVEYS

In the summer of 1921, a small team of physicists and geologists performed a historical 

experiment near the Vines Branch area in south-central Oklahoma. Using a dynamite charge as a 

seismic source and a special instrument called a seismograph, the team recorded seismic waves 

that had traveled through the subsurface of the earth. Analysis of the recorded data showed that 

seismic reflections from a boundary between two underground rock layers had been detected. 

Further analysis of the data produced an image of the subsurface—called a seismic reflection 

profile—that agreed with a known geologic feature. That result is widely regarded as the first proof 

that an accurate image of the earth’s subsurface could be made using reflected waves. However, 

because of the economics of that time, it wasn’t until 1929 when improvements in technology and 

economics converged to make seismic reflections an accepted method of prospecting for oil

(Dragoset, 2005). 

In the 1950s, marine seismic imaging became the foremost exploration method as 

companies looked to expand drilling provinces into the marine environment. Marine seismic 

acquisition faced the same fundamental geological challenges as land surveys did with some 

additional physical challenges brought about by the water column. Dynamite was still the preferred 

acoustic source, and charges were detonated in the water column at depths ranging from a few feet 

to tens of feet. The size of the charges and the depths at which they were exploded were 

determined by the local geology, the nature of ambient noise in the area, and the desired depth of 

seismic wave penetration in the earth.

However, explosives were not an ideal seismic source when used underwater. The bubble 

of gases created by an underwater explosion oscillates in the water and produced a source wavelet 

that consisted of a long sequence of impulses. Seismic records produced with such a source 

wavelet were then unsuitable for interpretation. The digital filtering technology used to collapse the 

train of impulses would not become available until the 1960s; therefore, companies tried to detonate 

the charges at shallow depths so that the gas bubble would reach the surface before any oscillations 

would occur.

Explosives became obsolete in the 1970s because of the concern for potential damage to 

marine life, as well as dangers to the crews deploying it. These concerns lead to the development of 

the marine airgun by Bolt Technologies and Texas Instruments in the 1970s.
Gulf of Mexico G&G Activities Programmatic EIS L-5 

The design of the airgun created a pulsed sound by the sudden electro-mechanical release 

of highly compressed air through a vented port. The airgun also created source wavelets, but this 

problem was overcome by the tuned airgun array concept. The tuning of airguns involves the 

simultaneous deployment of different-sized airguns where the initial pulses sum coherently, thereby 

increasing the strength of the combined source and also minimizing the bubble pulses that do not 

sum coherently. This maximizes the signal-to-noise ratio of a source.

1.5 TECHNOLOGY AND PARAMETERS

It should be noted that airgun acoustic sources are not exclusively used in commercial oil 

and gas exploration but are also used for scientific research. Some current scientific uses include, 

but are not limited to the following: (1) hazard identification, such as earthquake faulting, aquifer 

exploitation, and submarine slides; (2) historical issues, such as review of large-scale plate 

tectonics; (3) national security; and (4) the delineation of U.S. territorial waters and delineation of the 

extended continental shelf.

During recent years, the idea that seismic surveys could be adjusted to “lowest practicable 

source levels” for a particular site or survey has garnered increasing attention. This is despite the 

fact that source volumes do not correspond linearly with source output levels (in fact, it is a cube root 

relationship).

Briefly, the key parameters considered, and their impacts on sound levels generated by 

source arrays, include the following: 

(1) Number of Elements: There is a linear relationship between the number of 

identical elements and array loudness expressed as peak pressure (SPLpeak), 

i.e., half as many identical elements would make the array half as loud or 

6 decibels (dB) quieter in the direction of the downward looking beam. 

(2) Operating Pressure: There is a 3⁄4 proportional relationship between operating 

air pressure and loudness expressed as SPLpeak, i.e., an array pressurized at 

2,000 pounds per square inch (psi) would be about 4 to 5 dB louder than an 

array pressurized at 1,000 psi. 

(3) Air Volume: For both the individual source elements and the total array, 

loudness is proportional to the cube root of the ratio of different volumes; 

therefore, a 6-dB reduction in loudness from a 240-cubic inch (in3

) element 

would require replacement by a 30-in3 element, and a 6-dB reduction in 

loudness from an 8,000-in3 array would require reduction of total array air 

volume to 1,000 in3

. When comparing array output from different sizes and 

combinations of sources and source pressures, we use the peak pressure as 

the metric of loudness because that is the primary output parameter of interest 

for the array’s intended purpose. Measurements that sum the energy from 

multiple pressure oscillations over time, such as SPLrms or SEL, are more 
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appropriate for far-field measurements away from the array where multi-path 

and other effects contribute to the received sound field.

(4) Array Dimensions: This is the most complicated aspect of the array. The 

simplest statement that can be made about array geometry is that it is optimized 

for geophysical imaging and any changes are likely to reduce array 

effectiveness.

1.6 KEY POINTS

(1) A reduction in source air volume has a relatively minimal influence on source 

level. 

(2) The modeled or theoretical source levels often quoted for seismic source arrays 

are not directly predictive of the received levels at distance in the water column 

because of the effect of the element separation in the array.

1.7 DISCUSSION

Setting aside the use of non-equivalent acoustic terminology, these statements have been 

generally interpreted to mean a goal of reducing the level of sound exposure to marine life, without 

losses to data quality that would jeopardize the goals of the survey and that may possibly lead to the 

need for more or lengthier surveys to compensate for any lost data quality.

“Sound intensity level” is not equivalent to “sound pressure level” averaged over some time 

period (RMS), nor is it equivalent to the cumulative energy within some time period (e.g., SEL). The 

metric of greatest interest in discussing the source array is peak pressure of the primary pulse, 

whereas the measures of biological interest away from the source array are typically measures of 

averaged pressure across the pulse (dB SPLrms), which is usually referenced to 90 percent of the 

energy in the pulse or Sound Exposure Level (dB SEL) averaged across the multi-path propagation 

of a single pulse or multiple pulses.

Factors to be considered in the arrays are described in Chapters 1.7.1-1.7.4 below.

1.7.1 Number of Elements in an Array

Sound pressure (amplitude) is linearly proportional to the number of elements in the array. 

This only holds true, however, if all of the elements occupy the same location, which is physically 

impossible. This property is normally discussed as the near-field or far-field of a source or receiver 

array. For typical airgun arrays, the far-field is not reached until about 200 to 300 meters (m) (656 to 

984 feet [ft]). 

The difference between point and distributed sources needs to be clarified. Some sources 

that are physically smaller (e.g., completely contained within a sphere with a 1-m [3-ft] diameter) can 

be considered point sources. However, most other sources (e.g., an airgun array, which could be 
Gulf of Mexico G&G Activities Programmatic EIS L-7 

tens of meters in width and length) are distributed sources. For a distributed source, a receiver must 

be some distance away from the source to perceive it acoustically as a single, or point, source. 

Closer to the source, a receiver gathers many signals from all separate components of the source. 

The receiver then is considered in the “near-field.” Once a receiver is beyond this range and can 

interpret the signal as a point source, it is considered in the source’s “far-field.” This problem is 

visually analogous to viewing an illuminated 100-story building at night and attempting to 

characterize the lighting intensity around it. One would need to be miles away from that building to 

see it as a single light source. Anywhere closer, individual floors could be seen, and how they are 

perceived would strongly influence the level of light received. If the observer was only 10 m (33 ft) 

from the ground floor, higher floors would be partially seen and the overall light being produced by 

such a structure could be greatly underestimated.

This distinction between near-field and far-field is a particularly important one for distributed 

sources such as airgun arrays. This is because the most severe potential impacts on animals 

generally occur near the source, and an understanding and assessment of these impacts requires a 

correct understanding of the sound field in the near-field. If a receiver (i.e., animal) is in the nearfield of an airgun array, it will receive energy from all individual sources (e.g., individual airguns) in 

that array (just as the observer of the building would receive some light from the many floors in the 

example above). However, the closest individual source (i.e., a floor for the building example) will 

tend to be the dominant source, with other individual sources in the array making smaller 

contributions to the overall received sound level. Because these additional contributions will be 

delayed in time (due to the physical geometry and the time differences required for sound travel from 

individual sources to the receiver) and might not be in phase (i.e., peak pressures might not arrive 

simultaneously or “in-phase”), these contributions will seldom sum to the maximum energy of the 

overall signal and could actually result in diminishing some of the signal. In this way, near-field 

sound of the real array would always be less than that modeled for a theoretical point source. In 

effect, estimating the near-field sound field around an assumed point source is conservative 

because it will always be greater than the actual values in the near-field.

The use of the theoretical point source is useful and valid in the far-field, but extreme care 

needs to be exercised with using it to approximate an airgun array when not in the far-field. The 

actual received level in the main beam in the near-field can be expected to be 20 to 30 dB less than 

that approximated by a point source, which can be further reduced outside of that beam, especially 

in the horizontal directions.

Additionally, the extent and shape of the far-field and the details of the sound field closer 

than the far-field are highly dependent on the configuration of the airgun array. Reductions in the 

size and number of airguns in that array will generally reduce the far-field point source level, but it 

will have a lesser impact to the near-field, sound-field structure and can actually cause increased 

levels in some of the volume if the main beam is allowed to widen. The existing models can and do 

predict these effects, but it is very difficult to generalize these trends into a simple and easily 

understood result.
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1.7.2 Operating Pressure of an Array

Based on supplied BOEM geophysical permit application data, the source arrays used by the 

seismic industry almost exclusively operate at a pressure of approximately 2,000 psi. There is very 

little practical opportunity of varying source levels by varying the operating pressure used. 

Generally, increasing the pressure requires greater compressor capacity on the seismic vessel 

(which is already significant) and decreasing the pressure can potentially lead to water leakage into 

the compression chambers, but perhaps more importantly it can lead to unwanted “auto-firing” when 

insufficient pressure in the chamber results in a premature release of air in one or more array 

elements and in “polluting” the overall output signal with energy outside the signal of interest.

1.7.3 Volume of an Array, Including Individual Element Volumes

The sound pressure (peak amplitude) is proportional to the cube root of the ratio between 

two source volumes (Caldwell and Dragoset, 2000). Thus, an 8,000-in3 array produces only about 

twice the loudness of a 1,000- in3 array with all things being equal (such as the number of elements 

and the spatial dimensions of the array). This volume to loudness ratio holds for the sizes of single 

elements, e.g., a 240-in3 element only generates twice the peak pressure level of a 30-in3 element

and not eight times the level as some might assume. It is mainly the frequency components of the 

source signals that differ with size, i.e., larger elements produce more low-frequency sound. A 

single 800-in3 element would be required to double the source output of a 100 cubic inch element. 

However, if we were to create an array of four 100-in3 elements, we would produce twice the 

acoustic output in the array pressure peak compared with a single 800-in3 element. In other words, 

we get twice the output from only half the volume because we have enabled the output from the four 

elements to be synchronized so that their peaks align. That is why we have noted that the output 

sound pressure level for a seismic array is more closely related to the total number of elements in 

the array than to the total array volume and that is why source geometry is so important. Achieving 

greater peak pressure outputs from an array of smaller elements than would be achieved by a single 

element of the same combined volume is only possible if the pressure pulses line up, and since they 

cannot line up in all directions, the additive gain cannot be achieved equally in all directions.

1.7.4 Array Dimensions

The dimensions of a source array and the number and different volume of elements it 

contains are very important in reducing the effect of the “bubble trains” to achieve a seismic signal 

that is optimum for imaging the geological objectives. Furthermore, the distance between the 

individual elements in the array have a significant influence on the resultant source level generated 

by the array since acoustic energy is dissipated as it travels the distance needed to align with pulses 

from the other elements. The alignment of the pulses from the individual elements adds to the peak 

amplitude of the primary pulse, but it tends to create destructive interference between the 

subsequent pressure oscillations of the individual bubbles, reducing the number of “confusing 

echoes” that can interfere with the quality of the resulting geophysical images. 
Gulf of Mexico G&G Activities Programmatic EIS L-9 

An array is typically 10 by 15 m (33 by 49 ft) (or more) for the purpose of enabling the timing 

of air bubble releases from the different elements to produce a downward beam of the lower 

frequencies most useful to seismic surveys (usually between 2 and 250 hertz). Actual maximum 

source levels of arrays in the direction of the downward beam are generally 10 to 20 dB lower than 

the theoretical source levels predicted by the number of elements alone, and even lower in the more 

horizontal or lateral aspects where the additive effect from the individual elements is even less. The 

actual source levels will be lower because the contributions of acoustic energy from each individual 

element attenuate before joining the pressure pulses from other elements in the array. A significant 

amount of attenuation occurs over very short separation distances between elements. As the 

distance from the source doubles, the sound pressure level halves (think of the sound from an 

individual element radiating in all directions and getting thinner and thinner, like the skin of a balloon 

as it is inflated). The dimensions of the source array can have more influence on the resultant 

output than the number of elements in the array, with output dependent on the way the elements are 

laid out in the source array. Increasing the number of elements in the array is done primarily to 

remove unwanted components such as “bubble trains” that reduce the clarity of the resulting returns 

from the rock layers below, as well as providing directionality. Significantly reducing the number of 

elements in an array will, therefore, be undesirable from the perspective of the resultant seismic data 

quality.

In the horizontal or lateral direction, the interaction between the elements is complex, 

depending on their alignment in space and time. Since the elements are activated to achieve 

maximum coherence downward, there will be much less coherence in other directions, typically 15 to 

30 dB less peak pressure and less suppression of bubble oscillations.

1.8 SUMMARY

An examination of the aspects of a seismic array that can be adjusted demonstrates the 

following:

(1) the total volume of an array does not have a major influence on the source level 

of the array because the source level is proportional to the cube root of the 

volume;

(2) the design of any specific array has to account for acoustic response to specific 

subsurface geological variations, survey target depths, and length of receivers 

(offsets) to illuminate geologic anomalies;

(3) the main influences on the source level of an array are not the volumes but

(a) the operating pressure in which there is not much scope for variation; 

(b) the number of elements in an array; 

(i) the reason for multiple elements is mainly to attenuate the bubble train 

that is the characteristic of single elements and to maximize output in 

the downward looking signal. (Multiple elements boost the nominal 
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source level of the primary pulse but still fall 10 to 30 dB peak short of 

the theoretical maximum predicted by the number and size of the 

elements alone, due to the spatial separation of array elements.); and

(c) the dimensions of the array (or separation distances of the elements within 

the array), which is part of achieving the signal from the multiple elements 

as described above.

1.9 CONCLUSIONS

• There is minimal scope for reducing the source level of an acoustic array by 

modifying the operating pressure or the total air volume of the array. Changing 

the source level by modifying the number of elements or the dimensions of the 

array would result in an undesirable accentuation of high frequencies and would

compromise the quality of seismic data with a loss of low frequencies. A goal of 

achieving reductions in horizontally propagated sound will need to take into 

account the contributions of the environment in propagating the array output. 

The array is designed to optimize a relatively short down and back propagation 

through water and many layers of rock of varying thickness and density. 

Alterations of that design to achieve reduced lateral propagation will be difficult 

and will most certainly reduce image quality. A solution that might produce 

marginal decreases in laterally propagated energy, at best, in one area would 

likely not work under different ocean conditions, a different geology below, or 

different depth profiles across the track lines, to highlight only a few of the 

environmental variables that can affect propagation of sound through the water 

column.

• The idea of a simple set of standards for a universal solution to limit or reduce 

array output without loss of data quality and that would yield any measureable 

benefit to the marine environment is impracticable and not supported by current 

best available scientific data. A regulatory attempt to establish standards and/or 

metrics would not be practical or even feasible.

• The panel has determined that it would not be reasonable or practicable to 

develop metrics.
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2 DUPLICATIVE PANEL REPORT 

Submitted by Duplicative Seismic Survey Panel (8/12/2016)

2.1 INTRODUCTION

The Natural Resource Defense Council, Inc. et al., as Plaintiffs in a lawsuit against the U.S. 

Department of the Interior as Defendant, have expressed concern that certain marine offshore areas 

have been repeatedly subjected to unnecessary seismic surveys and that these surveys contribute 

to chronic and unwarranted noise that may have physical and behavioral effects on marine mammal 

populations. As per condition VII.A., the “Order Granting Joint Motion for Approval of 

Settlement Agreement and Stay of Proceedings” (June 24, 2013), BOEM agreed to convene an 

internal expert panel to determine whether it would be feasible to develop standards to determine 

whether a deep-penetration seismic survey, as defined in the Agreement, is unnecessarily 

duplicative. The panel has determined that it would be feasible to develop these standards prior to 

development of a Programmatic EIS and that BOEM will include and evaluate these standards in the 

Programmatic EIS.

2.2 INTERNAL EXPERT PANEL

The internal BOEM Panel who formulated the document consisted of the following 

personnel:

Tamara S. Arzt, J.D, M.P.A. is an Environmental Protection Specialist and the 

Endangered Species Act Lead for BOEM’s Headquarters. She has worked for 

BOEM since 2011. Ms. Arzt received her B.A. from Smith College with a major in 

Government and her M.P.A from the University of Massachusetts, Amherst with a 

specific focus on environmental policy and endangered species. Ms. Arzt then 

worked for an alternative dispute resolution firm in Boulder, Colorado, where she 

focused on resolving multiple Federal environmental issues. In 2003, Ms. Arzt 

received her J.D. from Vermont Law School concentrating on environmental law. 

Upon graduation, she was accepted into the Presidential Management Fellowship 

program and worked for the Bureau of Land Management with the U.S. Department 

of the Interior in Washington, DC and Colorado. Ms. Arzt continued her career in 

public service, working for county and municipal government on the Northfork of 

Long Island, New York, with a continued emphasis on the environment, in particular 

coastal and wetlands issues. In addition to being the Endangered Species Act Lead 

in BOEM’s Headquarters’ Office, Ms. Arzt works extensively with Marine Mammal 

Protection Act and National Environmental Policy Act, as well as Coastal Zone 

Management Act and National Historic Preservation Act, issues associated with both 

traditional and renewable energy development on the OCS.

Ronald (Ron) Brinkman currently serves as BOEM’s Senior Staff Geophysicist for 

the Gulf of Mexico OCS Region’s Office of Resource Evaluation. He has worked as 
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a geophysical interpreter, permitting and acquisition specialist, and geophysical 

subject-matter expert in the preparation of the Atlantic and Gulf of Mexico Geological 

and Geophysical Programmatic EISs, as well as subject-matter advisor to the 

OKEANOS and CETSOUND working groups. Ron has B.S. degrees in Mathematics 

and Geology from the Louisiana State University (New Orleans) and has been 

employed with the U.S. Department of the Interior for over 39 years. He has been an 

active member of the Society of Exploration Geophysicists since 1992.

Ty Collins is a Geophysicist at in BOEM’s Gulf of Mexico OCS Region’s Office of 

Resource Evaluation. Prior to working at BOEM, he worked in commercial 

geophysical survey acquisition in the United States’ OCS, including the Gulf of 

Mexico, Beaufort Sea, and Chukchi Sea. He has experience in commercial survey 

design, acquisition, processing, and interpretation of geophysical data. At BOEM, 

Mr. Collins interprets geophysical and geological data to evaluate the “fair market 

value” of lease blocks related to OCS lease sales. Mr. Collins holds a Professional 

Geoscientist License from the Louisiana Board of Professional Geoscientists and a 

B.S. degree in Geophysics from the University of New Orleans. He is a graduate of

the Daniel J. Tearpock Geoscience Certification Program and is an active member of 

the Society of Exploration Geophysicists.

John Johnson is a supervisory geologist with the BOEM’s Gulf of Mexico OCS 

Region in New Orleans, Louisiana. He received his B.S. and M.S. degrees in 

Geology from the University of Florida prior to starting work as a geologist with the 

USGS’ Conservation Division (the predecessor of MMS) in 1981. Mr. Johnson 

evaluated offshore lease prospects for fair market value determination for over 

15 years and served as Staff Geologist. Since 2007, he has been supervisor of 

BOEM’s Gulf of Mexico OCS Region, Office of Resource Evaluation’s Data 

Acquisition and Special Projects Unit. This group is responsible for G&G permitting 

in the Gulf of Mexico and for the purchasing, loading, and managing (including 

archiving and public release) of digital seismic data for the GOMR.

Stanley (Stan) Labak works in BOEM’s Division of Environmental Science in 

Sterling, Virginia. Mr. Labak has been with BOEM for about 3 years, where he is a 

Physical Scientist (Marine Acoustician) in the Physical & Chemical Sciences Branch. 

His specific areas of experience and expertise include modeling, analysis, and 

evaluation of underwater acoustic source and propagation, especially with regards to 

its potential impact to marine species. Stan received his B.S. in Ocean Engineering 

at the U.S. Naval Academy and his M.S. in Ocean Engineering at the Massachusetts 

Institute of Technology, where he was a Draper Fellow. He is a retired Naval 

Reservist.

Gary Watkins is a staff geophysicist for BOEM’s Gulf of Mexico OCS Region’s

Geology and Geophysics Section in New Orleans, Louisiana. He received his 
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Bachelor of Geophysical Engineering (1971), Masters of Science Geophysics (1982)

degrees from Colorado School of Mines. After a 5-year tour as an officer with the 

U.S. Navy, he worked with the Seismograph Service Company in Denver, Colorado

(1977); Energy Reserves Group in Denver, Colorado (1981); Union Oil of California 

in Midland, Texas (1983) and Lafayette, Louisiana (1987); Kansas Department of 

Health and Environment Bureau of Remediation in Topeka, Kansas (1993); and 

MMS (BOEM’s predecessor) in New Orleans, Louisiana (1997). With BOEM, Mr. 

Watkins has evaluated offshore lease prospects for fair market value determination 

for over 19 years and has served as the Geology and Geophysics Section’s staff 

geophysicist since 2008.

2.3 SUBJECT-MATTER EXPERTS

The Panel would also like to knowledge and thank the following subject-matter experts who, 

while not official Panel Members, contributed their individual expertise in the document’s

development:

Victoria Cornish is Energy Policy Analyst for the Marine Mammal Commission, an 

independent U.S. Government agency located in Bethesda, Maryland. At the 

Commission, Ms. Cornish is focused on the effects of offshore oil and gas and 

renewable energy activities on marine mammals and their environment, as well as 

the enhancement of policies and programs to better understand and minimize those 

effects. Ms. Cornish holds a B.S. in Biology from the University of California at San 

Diego and an M.S. in Biological Oceanography from the University of Miami. Prior to 

joining the Commission, Ms. Cornish worked for the National Oceanic and 

Atmospheric Administration’s National Marine Fisheries Service (1991-2007) and for 

Ocean Conservancy, a not-for-profit environmental organization (2007-2010).

Detlef Ross is a Geophysical Advisor at Petroleum Geo-Services, Inc., located in 

Houston, Texas. He received his Pre-Diploma (equal B.S.) in Physical 

Oceanography and Diploma (M.S.) in Geophysics from the University of Kiel, 

Germany, prior to starting work for PGS Geophysical AS in Oslo, Norway, in 1998. 

Over the last 18 years, Mr. Ross has held various positions as a geophysicist, field 

engineer, supervisor, and project manager, working onshore and offshore. Since 

2013, he has assumed the role of geophysical advisor.

We would also like to acknowledge special technical assistance provided to the 

panel by

Mr. Steven Fishburn who is the former Vice President GOM Multi-Client, Petroleum 

Geo-Services, Inc.
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2.4 ACKNOWLEDGEMENT

BOEM would also like to acknowledge and thank the following geophysical companies that 

have allowed us to display their data used in construction of the composite lines used in this report: 

Petroleum Geo-Services, Inc. (PGS), Compagnie Generale de Geophysique (CGG), and TGS 

Geophysical Company (TGS).

2.5 DEFINITION OF DUPLICATIVE SURVEY

The Panel agreed upon the following definition:

Duplicative Seismic Survey – A duplicative seismic survey is a deep-penetration 

geophysical survey, as defined in Section I.A. of the initial “Settlement” (Civil Action 

No. 2:10-cv-01882), whose acquisition parameters, design, technology, and 

geospatial surface location metrics make it essentially the same as an existing 

seismic survey. Acquisition parameters that should be considered in any duplicative 

characterization include, but are not limited to, the following: (1) survey geometry 

(surface orientation, line, and/or shot point orientation); (2) increase in azimuthal 

imaging for subsalt illumination; (3) source array composition, sequencing, and 

architecture; (4) spatial sampling and received frequency content; and (5) record 

length and sample rate.

Note: This definition excludes any reservoir monitoring, time-lapse (4-dimensional 

[4D]) surveys whose actual intent is to duplicate existing surveys as closely 

as possible for comparative purposes, any overlap of individual shot points 

that may occur as a result of resumption of acquisition after an interruption to 

any initial acquisition, and other survey types excluded in the initial 

Settlement Agreement.

2.6 BACKGROUND AND HISTORY OF SEISMIC SURVEYS

The collection of marine seismic exploration data in the U.S. began in the mid-1940s with 

dynamite used as the acoustic source. Subsequent to complaints from sport and commercial fishing 

that the use of dynamite killed too many fish, geophysical contractors began to use a slower 

detonating nitro-carbonitrate in marine shooting beginning in the early 1950s. At sea, seismic data 

collection required that these sources have the capability to be towed and activated at frequent, 

regular intervals in a series of high-energy releases, or in the industry vernacular, “shots.” By the 

mid-1970s, the most common, reliable, and more environmentally friendly marine source became an 

acoustic “air gun.” It was, and still is, essentially a steel container charged with high-pressure air 

from a towing vessel that releases the air rapidly through a portal to form a pressure pulse in the 

water column. The pressure wave produced by this air bubble is transmitted through the 

surrounding water before it penetrates the ocean bottom boundary and is subsequently reflected and 

refracted from geologic interfaces in the earth. The reflected signals from these interfaces then 

return to the water column where they are then recorded by receivers (hydrophones) positioned and 
Gulf of Mexico G&G Activities Programmatic EIS L-15

towed by the source vessel or by nodal receivers (geophones) that have been geospatially 

positioned on the ocean bottom. Simplistically, the recorded velocity responses are then processed 

to provide the geophysical interpreter with a geological illumination of the subsurface.

This process was initially used in the collection of 2-dimensional (2D) data where data were 

acquired using a single vessel, single source array and one cable of towed receivers. Single lines of 

data or linear grids were used to create individual planar views that were then used by interpreters to 

“map” specific areas. In the early 1980s, the process evolved into 3-dimensional (3D) acquisition 

where the source vessel would tow multiple parallel cables of narrowly spaced receivers, called 

streamers, that allow for the acquisition of data volumes instead of lines. Technologically, this is 

analogous to a (3D) medical ultrasound versus a (2D) x-ray.

Coincident to the technological evolution, the architecture of the leasing program in the Gulf 

of Mexico changed from a process where specific company-nominated blocks were bid on for lease 

sales (until 1982) to one where the newly formed Minerals Management Service (MMS) offered for 

leasing all blocks that were not leased at the time of the lease sale. This transition occurred in 1982 

and the new process became known as “areawide leasing,” which still exists today. This became a 

seminal moment in the Gulf of Mexico multi-client, seismic acquisition industry in all U.S waters in 

that it allowed large areas of acreage to be acquired by single seismic contractors who would then 

license all or parts of those surveys to potential bidders.

The emphasis on deeper water surveys and the illumination of targets below subsurface salt 

structures deep in the earth led to further technological advances in the acquisition of 3D data. 

Multiple vessels with longer cables, coil geometry surveys, and increased computer capacities have 

contributed to the acquisition of wide-, rich-, and multi-azimuthal datasets to produce more robust 

subsalt geologic illumination.

In Attachment 1, we have included a list of geophysical terms with definitions and common 

abbreviations to refer to as part of the following discussion.

2.7 ENVIRONMENTAL AND REGULATORY CONCERNS

The concern of noise in the oceans is a topic of recent discussions among marine scientists. 

Our Panel was tasked specifically to look at the feasibility to develop standards or metrics to 

determine whether any future proposed survey is unnecessarily duplicative to previous seismic data 

acquisition. This could have the effect to minimize or eliminate any unnecessary noise in the marine 

environment that could be chronically disruptive to marine mammals and other affected species in 

the marine environment.

There were discussions within the Panel regarding possible scenarios where geophysical 

contractors may collaborate on survey acquisition to acquire a single survey in specific areas rather 

than compete against each other in specific areas. It was felt that this is outside of the range of this 

Panel and that this could have other regulatory implications. While it was pointed out that 
L-16 Panel Reports

exploration and production (E&P) companies in other countries have collaborated on acquisition 

projects, it should be noted that the leasing architecture in those countries do not allow for areawide 

leasing, as is currently prescribed in the United States’ OCS areas, but are restricted to specific 

predefined areas only. Prior to OCS areawide leasing, these types of collective company 

acquisitions were conducted in U.S. waters and were called “group shoots.” These acquisitions 

were limited to the specific companies who agreed to pool resources for that acquisition.

2.8 DATA AQUISITION

2.8.1 Differences between Multi-Client and Proprietary Data Acquisition

After the advance of areawide leasing, the prevalent business model of multi-client surveys 

evolved. It had the premise of multiple companies having access to the same geophysical 

contractor-acquired dataset,but allows any E&P company to have equal access to that data via a 

license to any or all data collected in that given survey. The geophysical contractors assume the risk 

of acquisition but retain the ownership of the data and sell licenses for data usage to multiple E&P 

companies to recoup their investment and make a profit.

Both 2D and 3D seismic exploration surveys are conducted by geophysical contractors either 

on a proprietary or non-exclusive (multi-client) basis. Proprietary surveys usually cover only a few 

blocks for an individual E&P client who would then retain the data and therefore would have 

exclusive use of it. In contrast, non-exclusive survey data are owned by the geophysical contractor, 

are generally collected over large multi-block areas, and are licensed to as many E&P clients as 

possible to recover costs and produce profits for the contractor. Because the survey data are not for 

the exclusive use of any one E&P client, the contractor’s goal is to license the data to multiple E&P 

clients. 

Geophysical contractors use proprietary, patented, trade-secret survey acquisition and data 

processing methods that make their surveys and data unique. While different surveys for different 

purposes may cover the same general area, these can be done over several years and represent 

technological shifts that produce better subsurface illumination in specific areas. Geophysical 

surveys, whether multi-client or proprietary, are temporary and transitory. Seismic source vessels 

are constantly in motion. The movement of both the vessel and the animals, coupled with the way 

sound energy decays with time and distance, results in short durations of exposure to sound from 

operations for marine animals. A survey is in any one location for about 3 minutes, covering 8 to 

9 kilometers (5 to 6 miles) at 3 to 5 knots (4 to 6 miles per hour) in a 60-minute period).

Note: We have tried to highlight the differences between multi-client and proprietary 

surveys in Attachment 2. 

2.8.2 Why Multi-Client Seismic Data?

Industry estimates of proven oil reserves have doubled since 1980 as a result of better 

3D seismic imaging to pinpoint reservoirs, especially in deep water and below thick salt formations
Gulf of Mexico G&G Activities Programmatic EIS L-17

(Aylor, 1997). As seismic acquisition technology and processing techniques continue to advance, 

geophysical companies often reacquire data over the same area in order to provide greater 

illumination of the subsurface for their geological evaluations. The technology and techniques of 

acquisition have improved over time, ultimately improving the illumination the subsurface structural 

features and giving E&P companies a clearer understanding of the subsurface geology by 

delineating reservoir boundaries and reducing risks to the E&P companies. Absent this 

technological advancement, the latest Gulf of Mexico subsalt deepwater discoveries would not have 

been possible and U.S. production offshore would have been stymied. The E&P companies want 

the latest and best seismic data to better evaluate prospective acreage prior to OCS lease sales and 

to substantiate their bid bonus to BOEM. BOEM also benefits from the latest seismic data, enabling 

BOEM to provide better resource estimates, better estimates for potential worst-case spill 

discharges, and to determine fair market value of the resources (i.e., oil and gas) when evaluating 

lease bids and bonuses.

The business model outlined makes use of collective economics by spreading the costs of 

data acquisition and processing over time among multiple E&P customers who desire to make use 

of the data. Under this model, the seismic contractor initiates and conducts projects of general 

industry interest at its own financial risk. Restricted non-transferable data user licenses are then 

sold to individual E&P companies for a fraction of the cost of acquiring and processing the entire 

dataset.

This business model also reduces the potential for multiple E&P companies to individually 

contract specific proprietary surveys to be collected on their behalf, many of which would be 

considered duplicative by our definition. However, the possibility still exists that a contractor, or E&P 

company, could attempt to re-survey a given geographic area using the same acquisition 

parameters.

2.9 GULF OF MEXICO SEISMIC ACQUISITION REVIEW – MISSISSIPPI CANYON 

PROTRACTION AREA

The Duplicative Survey Panel was asked to address the issue of previous overlapping 

surveys in the Gulf of Mexico (GOM) and their potential for historical seismic acquisition duplication. 

Recognizing the impractical nature of examining all datasets in the GOM, the Panel decided to focus 

on the Mississippi Canyon protraction area. This area was chosen for several reasons. First, there 

have been numerous major oil and gas discoveries over time in the Mississippi Canyon area, 

yielding an extensive GOM database where multiple datasets had been acquired over the years. 

Second, the 2002-2006 Sperm Whale Seismic Study managed by Texas A&M University, was 

conducted primarily near the 200-m (656-ft) isobath in the Mississippi Canyon area. Third, the welldocumented Deepwater Horizon explosion at the Macondo well was also located within the 

Mississippi Canyon protraction area (i.e., Mississippi Canyon Block 252).

Panel members were able to discern four discrete “generations” of 3D seismic data. 

BOEM’s geophysical interpreters created a composite 2D line from the 3D volumes for each of the 
L-18 Panel Reports

four generations over approximately the same geospatial area to demonstrate the quality changes 

for each generation. The processing scheme used were Kirchhoff 3D prestack time-migrated 

versions, except for Generation 4, in which the prestack depth-migrated version was used (Note: No 

time-migrated versions were available; therefore, the vertical scale is in depth and not time).

In an attempt to further define the generations of surveys, the Panel members then looked at 

acquisition parameters that were available and captured those metrics in Table L-1. These 

parameters were evaluated for similarities and differences. The significant parameters with 

significant generational differences were azimuth (narrow or wide), streamer length (total length of 

towed receivers), record length (time to record seismic return after a shot occurred), shot point 

interval (spacing between source activation), nominal fold (number of recorded rays at a specific 

point), group interval (spacing of individual receivers on the towed cable), and processed cell size 

(the bin size from which traces are summed to create the fold). The differences in these acquisition 

parameter metrics appeared to correspond with the previously identified four generations of data 

quality.

The four generations of surveys shown in Figure L-1 (“Generations 1-4 Composite 2D 

Seismic Lines Built from Multiple Company 3D Datasets”) are defined below.

• The first generation was acquired from 1992 to 1998. In this time period, seismic 

data acquired in the Mississippi Canyon area used a single vessel, narrowazimuth (NAZ) methodology, with streamer lengths between 4,800 and 6,000 m 

(15,748 and 19,685 ft). These had a nominal fold of 48 to 60, record lengths 9 to 

12 seconds in length, and a predominant bin size of 12.5 x 20 m (41 x 66 ft).

• The second generation was acquired from 1998 to 2002. The most noticeable 

change in acquisition was the increase in streamer length to between 7,200 and 

8,000 m (232,622 and 26,246 ft). The increase in streamer length allowed for 

recovery of complexity in the seismic record lost using shorter streamer length. 

This allowed for an increase in fold to range from 57.6 to 64, but bin size 

remained the same.

• The third generation was acquired from 2003 to 2005. The main change was the 

acquisition of smaller group intervals that resulted in smaller bin sizes of 

approximately 6.25 x 20 m (20.5 x 66 ft). These smaller bin sizes allowed for 

better imagery in the processing of the data that was temporally complemented 

by greater storage capacity due to computer technology. This allowed for the 

increase of complex data used for the construction of subsalt velocity models.

• The fourth generation was acquired from 2004 to 2012. This acquisition method 

involved wide-azimuth (WAZ) technology that employed multiple source/receiver 

vessels using long cable offsets (7,000 to 8,100 m; 22,966 to 26,575 ft) and 

resulted in greater nominal fold. The end product of processing was portrayed in 
Gulf of Mexico G&G Activities Programmatic EIS L-19

depth (as opposed to time) since no time-migrated versions were produced by 

the contractors. These provided a huge increase in fold of 186 to 216.

Table L-1. Mississippi Canyon Seismic Surveys Acquisition Parameters

Source: Brinkman, official communication, 2016. 

Type Acquisition 

Date

Airgun Source 

(cu in)

Shotpoint 

Interval 

(m)

Streamer 

Length 

(m)

Record 

Length 

(s)

Nominal 

Fold

Group 

Interval 

(m)

Processed 

cell Size 

(M)

NAZ 1991 5400 40 4800 10 60 NA

26.6 x 26 

13.3 x 26.6

NAZ 1993 3000 25 4800 9 48 NA 12.5 x 25

NAZ 1993 3000 25 4800 9 48 NA 26.6 x 26.6

NAZ 1995 4720 31.25 6000 10.5 48 25 12.5 x 20

NAZ 1996 5400 25 5200 9 52 NA 12.5 x 20

NAZ 1996 3000 25 6000 12 48 NA 12.5 x 20

NAZ 1997 3000 25 6000 12 48 NA 12.5 x 20

NAZ 1997 3000 25 6000 9 60 NA 12.5 x 20

NAZ 1998 8100 40 4800 10 60 NA

26.6 x 26 

13.3 x 26.6

NAZ 1998 4720 31.25 6000 10.5 48 25 12.5 x 20

NAZ 1998 5580 50 6000 13 60 NA 12.5 x 20

NAZ 1999 5400 62.5 8000 12.288 64 25 12.5 x 20

NAZ 1999 5400 62.5 8000 12.288 64 25 12.5 x 20

NAZ 1999 5400 62.5 8000 12.288 64 25 12.5 x 20

NAZ 1999 4180/5400 31.25m - 

62.5m 7200/8000 12.288 57.6/64 25 12.5 x 20 & 12.5 x 40

NAZ 1999 4180 75 7200 12.288 57.6 25 12.5 x 22.5

NAZ 1999 5400 62.5 8000 12.288 64 25 12.5 x 20

NAZ 2002 3960 37.5 8100 13 54 12.5 12.5 x 20

NAZ 2004 3040 62.5 8100 10 64 NA 12.5 x 12.5

NAZ 2002 5085 31.25 8000 12 64 12.5 6.25 x 25

NAZ 2002 5085 31.25 8000 12 64 12.5 6.25 x 25

NAZ 2002 3040 62.5 8100 13 64 12.5 12.5 x 12.5

NAZ 2003 5085 25 8000 12 80 12.5 6.25x20

OBC & 

NAZ

2003 3040 to 8475 62.5-75 9000 13

60-120 & 

71-144

12.5 -50

6.25 x 40 & 

25 x 40

WAZ 2009 8475 37.5 7000 14 186 12.5 6.25 x 60

WAZ 2009 10,170 42 7000 14 186 12.5 6.25 x 60

WAZ 2010 8475 37.5 7000 14 186 12.5 6.25 x 60

WAZ 2010 8475 37.5 7000 14 186 12.5 6.25 x 60

WAZ 2012 8475 37.5 8100 14 216 12.5 m 6.25 x 60

NA= Not Available Generation 1 Generation 3

Generation 2 Generation 4
L-20 Panel Reports

Figure L-1. Generations 1-4 Composite 2D Seismic Lines Built from Multiple Company 3D Datasets. 
Gulf of Mexico G&G Activities Programmatic EIS L-21

If these surveys with different acquisition technology would be considered duplicative, then 

they w ould have identical or no improvement in data quality. Using the four generations of seismic 

data, multi-survey traverses were constructed for each generation, with the data linearly constructed 

from the southwest to northeast corners of Mississippi Canyon and the construct matching 

geographically as close as possible (Figure L-2).

We have juxtaposed the four generations of data in Figures 1-4 of Figure L-1 and have 

highlighted specific areas identified as Areas A-F to further analyze the improvements in data quality 

attributed to acquisition improvements. The first three-generational datasets were processed in the 

time domain (pre-stack time migration), while the fourth generation was in depth (pre-stack depth 

migration). There were no time datasets available in the construction of Generation 4 since the 

companies now go directly to depth with no intermediate step for time.

Figure L-2. Orientation of Traverse Lines for Generations 1 through 4 (USDOI, BOEM, 2016).
L-22 Panel Reports

2.9.1 Comparison of the Generational Events in Highlighted Area A

A comparison of the generational events highlighted in Area A is shown in Figure L-3. 

Figure L-3. Generational Comparison of Highlighted Area A.
Gulf of Mexico G&G Activities Programmatic EIS L-23

Analysis of Improvements to Highlighted Area A

The dashed red circle areas of Figures A1, A2, and A4 of Figure L-3 are an enlargement of 

the improved seismic data examples of Area A in Figures 1, 2, and 4 of Figure L-1. The examples 

are described below. 

• The identification of salt bodies in deep seismic data is important as salt plays an 

important role in how oil and gas traps develop, especially along the base (1) and 

sides of salt (2), 

• The identification of faults (3) in deep seismic data is critical not only to 

potentially trap oil and gas but to also identify shallow drilling hazards.

The improvements in the definition of the salt body and faults are attributed to longer offsets 

or streamer lengths, increased fold, and a change from NAZ to WAZ acquisition methods. Specific 

changes are described below.

• Streamer length was increased from 4,800 m (15,748 ft) (most commonly used 

from 1993 to 2000) for Generation 1 to 8,000 m (26,246 ft) (most commonly used 

from 2000 to 2005) for Generation 2. Generations 3 and 4 also mostly used 

8,000-m (26,246-ft) streamer lengths. The reduction of maximum streamer 

lengths from Generation 3 is attributed to a change in azimuthal methodology.

• Fold was steadily increased from 48 (most common) for Generation 1 to 64 (most 

common) for Generations 2 and 3, and to 184 (most common) for Generation 4. 

The increase in fold contributed to more live traces contributing to a stacked 

trace, which in turn improved the imagery of and around the salt body.

The advancement in survey geometry and azimuthal (NAZ-WAZ) coverage from 1993 to 

2014 allowed for more complex seismic ray paths not previously recorded to be captured, 

contributing to the increase of fold and number of subsurface image points. 
L-24 Panel Reports

2.9.2 Comparison of Generational Events in Highlighted Area B

A comparison of the generational events highlighted in Area B is shown in Figure L-4. 

Figure L-4. Generational Comparison of Highlighted Area B. 
Gulf of Mexico G&G Activities Programmatic EIS L-25

Analysis of Improvements to Highlighted Area B

The dashed red circle areas of Figures B1, B2, and B4 of Figure L-4 are an enlargement of 

the improved seismic data examples of Area B in Figures 1, 2, and 4 of Figure L-1. The examples 

are described below. 

• The outlined salt body top (1) and base (2) of salt changed with each generation 

of seismic data. Reflector continuity on the side of salt (3) also improved with 

later generations of seismic data.

• Faults (4) are associated with the salt body, which potentially could cause a trap 

for oil and gas. The faults are similarly positioned in Figures B1, B2, and B4 of 

Figure L-4, but the ability to recognize faults improved with each generation of 

data. 

• Along the left side of the salt body, Figures B1 and B2 of Figure L-4 have

reflectors with a gentle to low angle dip to the left (5); however, in Figure B4 of 

Figure L-4, the dip (5) is much steeper with a low spot developing before they 

start to rise steeply.

• Below the base of salt (2) is a seismic reflector with a downward arc (i.e., 

closure) appearance (6, the yellow highlight) and is suggestive of a potential oil 

trap. In Figures B1 and B2 of Figure L-4, this features could be extended 

farther to the left. In Figure B4 of Figure L-4, the arc ends against a salt weld 

(i.e., a salt weld is caused by the movement of salt, which leaves the sediments 

on top or sides against the sediments that were below the base of salt). Figure 

B4 of Figure L-4 also has reflectors on the left of the salt weld, which dips 

steeply to the left; while on the right, the reflectors have a significantly less dip.

The improvements in the definition of the salt body, the improved recognition of faults, and 

clearer seismic reflectors along the side and below the salt body are attributed to longer offsets or 

streamer lengths, increased fold, a change to WAZ acquisition, and longer record lengths. Specific 

changes are described below.

• Like at Area A, the increase in streamer length from 4 800 to 8,000 m (15,748 to 

26,246 ft) between generations allowed for complex seismic data ray paths from 

the source to the deep geologic beds and then back to the receiver cable to be 

captured.

• The steady increase in fold between the generations contributed to more seismic 

receiver data summed, which improved the imagery of and around the salt body.

• The advancement in survey geometry and azimuthal coverage between 

generations allowed for more complex seismic ray paths to be captured, which 

contribute to improved deep-subsurface imaging, especially below salt bodies.
L-26 Panel Reports

2.9.3 Comparison of Generational Events in Highlighted Area C

A comparison of the generational events highlighted in Area C is shown in Figure L-5. 

Figure L-5. Generational Comparison of Highlighted Area C. 
Gulf of Mexico G&G Activities Programmatic EIS L-27

Analysis of Improvements to Highlighted Area C

The dashed red circle areas of Figures C1, C2, and C4 of Figure L-5 are an enlargement of 

the improved seismic data examples of Area C on Figures 1, 2, and 4 of Figure L-1. The examples 

are described below. 

• In Figures C1 and C2 of Figure L-5, at about the “7.0 Sec” timeline (1) are a 

series of darker seismic reflectors that are easier to see. In addition, these 

reflectors are less broken up (i.e., more continuous). In Figure C4 of Figure 

L-5, these reflectors dip (2) from the right side of the figure into the center, but 

Figures C1 and C2 of Figure L-5 do not have a similar dip.

• At about the “6.0 Sec” timeline, in the center of Figures C1, C2, and C4 of 

Figure L-5, is a low area (3) with dips by seismic reflectors on the left and right 

into the low area. The low area is better defined with each generation of seismic 

data.

• On Figures C1 and C2 of Figure L-5, on the left side of the previously noted low 

area (3) at about the “7.0 Sec” timeline, the seismic reflectors (4) have a 

predominate, gentle dip into the low area in the center of the figures, with just a 

slight suggestion of dip to the left; in Figure C4 of Figure L-5, the corresponding 

area (about 27,500 ft [8,382 m]) has reflectors with an obvious dip to the left and 

right.

• At about the “8.0 Sec” timeline in the center of Figures C1 and C2 of Figure L-5

(5), the data are broken up within this deep low area (refer to the highlighted 

line); however, on Figure C4 of Figure L-5, the corresponding area no longer 

has reflectors that are broken up and hard to follow.

The improvements in the definition of the low area and deeper reflectors are attributed 

mainly to longer offsets or streamer lengths, increased fold, and longer record lengths. Specific 

changes were:

• As in previous areas, the increase in streamer length between generations has 

allowed for more complex seismic data ray paths from the source, to the deeper 

geologic beds, and reflected back to the surface where they are captured. This 

is especially critical for very deep seismic reflectors to be clearly displayed.

• The steady increase in fold between the generations contributed to more seismic 

receiver data summed within a specific area into one trace which improved how 

the data are displayed.

• The use of longer recording time or record length allowed for the deeper data to 

be captured. The capture of deeper data can enable a better understanding of 

why and where shallow oil and gas traps occur regionally by changes in the 

deeper geology. 
L-28 Panel Reports

2.9.4 Comparison of Generational Events in Highlighted Area D

A comparison of the generational events highlighted in Area D is shown in Figure L-6. 

Figure L-6. Generational Comparison of Highlighted Area D. 
Gulf of Mexico G&G Activities Programmatic EIS L-29

Analysis of Improvements to Highlighted Area D

The dashed red circle areas of Figures D1-D4 of Figure L-6 are an enlargement of the 

improved seismic data examples of Area D on Figures 1-4 of Figure L-1. The examples are 

described below. 

• The salt body outlined top (1) and base (2) changed with each generation of 

seismic data, especially along the left side and base of salt. These two areas 

changed from no definable edge of salt to a clearer edge of salt. As noted in 

Area A, the ability to define where salt is located helps to identify the type and 

location of oil and gas traps. It is also important when designing a drilling 

program near salt.

• Associated with this salt body are several faults (3); however, the ability to 

identify the faults improve with each generation.

• The seismic data at the base of salt and below (about the “4.0 Sec” line) has no 

clear definition in Figures D1-D3 of Figure L-6. In these figures, the deeper 

seismic reflectors all dip away from this undefined area below salt, which imply 

the salt may extend deeper. In Figure D4 of Figure L-6, the area under the 

well-defined base of salt (5) has improved clarity and suggests the existence of a 

vertical salt weld (i.e., a vertical salt weld is an area where salt has evacuated 

upward. As the salt moved up, the sediments on opposite sides collapsed 

inward against each other to form a vertical weld. It is represented by the vertical 

dash line with two black circles on either side. Identification of vertical salt welds 

allow for larger, older fault systems to occur, which have the potential to have 

deep oil and gas traps away from the salt body. Two such cases are the faults 

between 15,000 and 20,000 ft (4,572 and 6,096 m) located on the right of the salt 

weld.

The improvements in the definition of the salt body’s left side and base, as well as the 

deeper seismic data below the base of salt, are attributed mainly to the larger air gun source used in 

Generation 4, an increase in fold, and longer record lengths. Specific changes are described below.

• The increase in fold was due to a combined reduction in shot point interval, 

receiver group intervals, and the processed cell size. The smaller shot and 

receiver intervals allowed for more data to be recorded, which allowed for 

seismic processing to have more data in which to enhance the clarity of the 

deeper geology.

• The larger source size employed in Generation 4 allowed for greater energy to 

be returned from the deeper geologic beds. This in turn enhanced the seismic 

reflections above the background noise recorded in the acquisition program.
L-30 Panel Reports

2.9.5 Comparison of Generational Events in Highlighted Area E

A comparison of the generational events highlighted in Area E is shown in Figure L-7. 

Figure L-7. Generational Comparison of Highlighted Area E. 
Gulf of Mexico G&G Activities Programmatic EIS L-31

Analysis of Improvements to Highlighted Area E

The dashed red circle areas of Figures E1-E4 of Figure L-7 are an enlargement of the 

improved seismic data examples of Area E on Figures 1-4 of Figure L-1. The examples are 

described below. 

• Within Area E is a salt body whose size changes with each generation of seismic 

data. Figure E1 of Figure L-7 suggests the salt is divided into a top (1) and 

bottom (2) segment with a vertical weld (3) in between. Figures E2 and E3 of 

Figure L-7 are similar to Figure E1 of Figure L-7, but the two salt segments 

appear to be closer. Figure E4 suggests a continuous narrow salt column (4) is 

present to the deeper portion of the data. Knowing if a salt body or a salt weld is 

present is beneficial because a salt body will always trap oil and gas while a salt 

weld may not.

• On the right side of Figures E1-E4 of Figure L-7 are two colored (red) seismic 

reflectors, one shallow and one deep. The shallow reflector (5) shows a change 

from a dip to the left (into the salt column) and right in Figure E1 of Figure L-7. 

In Figure E2 of Figure L-7, the reflector has mainly left dip into salt. Figure E3

of Figure L-7 has the shallow reflector with dip to the left and right, but the dips 

are gentler. However, in Figure E4 of Figure L-7, the shallow reflector has just 

a steep left dip into salt.

• The second, deeper seismic reflector (6) on the right side has a left dip into the 

deeper portion of the salt column; however, the steepness of the dip changes 

with each generation. Additionally, the display clarity of the reflector changes 

between generations, with Figure E4 of Figure L-7 the easiest display to follow 

the reflector. 

The improvements in the definition of the salt’s outline, as well as changes in the dip of 

seismic reflectors, are attributed mainly to an increase in fold, streamer length, and record. Specific 

changes are described below.

• The increase in fold was due to a combined reduction in shot point interval, 

receiver group intervals, and the processed cell size. The smaller shot and 

receiver intervals allowed for more data to be recorded, which allowed for 

seismic processing to have more data in which to enhance the clarity of the 

deeper geology.

• The increase in streamer length, combined with longer records, allows for deeper 

reflected seismic energies to be captured by the surface receivers. Without the 

capture of deeper data, the inaccurate interpretation of the critical structures, 

such as the salt body in Figures E1-E4 of Figure L-7, can cause a wrong 

geologic interpretation that could result in a poorly planned well and/or needless 

drilled well.
L-32 Panel Reports

2.9.6 Comparison of Generational Events in Highlighted Area F

A comparison of the generational events highlighted in Area F is shown in Figure L-8. 

Figure L-8. Generational Comparison of Highlighted Area F. 
Gulf of Mexico G&G Activities Programmatic EIS L-33

Analysis of Improvements to Highlighted Area F

The dashed red circle areas of Figures F1-F4 of Figure L-8 are an enlargement of the 

improved seismic data examples of Area F on Figures 1, 2, and 4 of Figure L-1. The examples are 

described below. 

• At the top left is a shallow salt body (1) on Figures F1-F4 of Figure L-8 whose 

base is attached to a salt weld (2), which is attached to the top of a deeper salt 

body (3). The shape and size of the upper salt (1) and lower salt (3) changed 

with each generation, but its presence did not change. The clarity of this area did 

increase somewhat with each generation.

• On the right side of Figures F1-F4 of Figure L-8 is a fault (4) that extends from 

the “2.0 Sec/5000 ft” markers to the top of the deeper salt near “6.0 Sec/20,000 

ft.” markers. This fault was most likely created by geologic forces as the deeper 

salt (3) flowed upward. The removal of salt caused a lower area to develop, 

which allowed more sediment (seismic markers 5, 6, and 7) to be deposited into 

the low. These types of low areas typically have greater amounts of sand 

deposited within them. In these figures, the seismic reflectors (5, 6, and 7) all 

climb up to and end at the salt weld (2), which suggests any deposited sands 

would do the same and provides for the potential of oil and gas to be trapped. 

The clarity of these reflectors, as well as the salt weld, improved with each 

generation.

• In the bottom right (8) of Figures F1-F4 of Figure L-8, the lower salt body (3) 

base is not imaged at all. The full-scale displays of Area F on Figures 1-4 of 

Attachment 3 show seismic data below Area F to be poor to the bottom of 

Figure 4 of Attachment 3. Current belief is that this deeper area should be 

approximately equivalent geologically to oil- and gas-producing intervals onshore 

in Mississippi and Alabama; however, current seismic data clarity is not good 

enough to determine if the potential exists for this producing interval to extend 

into Area F or beyond.

The improvements in the definition of the location of salt are attributed streamer length, 

airgun source, and fold; however, the lack of clarity of extremely deep seismic reflectors is attributed 

to insufficient streamer length, array geometry, and fold. Specific acquisition elements that impacted 

seismic data in Area F are described below.

• The increase of streamer length allowed for greater clarity of the deeper seismic 

reflectors and top of the lower salt. Generation 4, Figure F4 of Attachment 3, 

has the best display clarity of the deeper portion of the seismic data.

• The decrease in shot point and group intervals, along with a decrease in cell 

size, cause greater detail clarity in the shallow portion (2.0 to 4 seconds and

5,000 to 10,000 ft [1,524 and 3,048 m). As these elements were decreased in 
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size, it allowed for thinner geologic beds to be imaged (i.e., an increase in 

shallow seismic frequency content). Increased shallow geologic detail allows for 

greater identification of shallow drilling hazards and shallow gas traps.

• The increase in fold was due to greater streamer lengths combined with and 

increase in airgun energy and a decrease in group intervals. It allowed for 

seismic processing to improve display clarity of seismic reflectors below and 

adjacent to the shallow salt and salt weld. The increase in fold also improved the 

strength and clarity of seismic reflectors away from salt and greater confidence in 

placement of the fault.

• While the seismic reflectors in Area F improved with each generation of seismic 

data acquisition, one area did not improve enough that the data can be used for 

any geologic evaluation. This was the area at the base of the deep salt body (3). 

The data below the outlined salt is useless and to obtain useable seismic data 

will require changes to the acquisition parameters used in Figures F1-F4 of 

Figure L-8. Should petroleum companies want to look at the deeper geology, 

the most likely improvement necessary could be longer streamer lengths, 

increased fold, and possibly shorter group intervals. It will also probably require 

new instrumentation, such as hydrophones, as well as new array methods/design 

for both the source and receivers.

2.10 OVERALL ANALYSIS

The six areas outlined in Figures 1-4 of Attachment 3 demonstrated improved subsurface 

imagery with advances in acquisition methodology and technical advancement. From this 

observation, it is implied that, at least within the Mississippi Canyon protraction area, spatially 

duplicative 3D time or depth surveys have occurred, but the surveys cannot be considered as 

duplicative with the improved subsurface imagery. The improved subsurface images can be 

contributed to a few acquisition parameters that also allowed for the improved processing of complex 

seismic ray paths to identify, enhance, and image deep subsurface seismic data of geologic 

structures. 

The earlier acquisition did not provide adequate subsalt imagery to fully define the flanks and 

base of the shallow salt bodies. The use of NAZ, combined with the shorter streamer lengths 

(offsets) and record lengths, reduced the fold of the data that hurt imaging of the subsurface. The 

importance of longer offsets and fold is well documented within geophysical literature. Rekdal and 

Long (2006) noted, “Longer offsets may benefit imaging quality of very deep targets.”.

The lower fold also contributed to a lower signal-to-noise ratio (S/N), which reduced the 

continuity of the salt’s surrounding reflectors. A high S/N ratio impacts the seismic imaging. Hegna 

et al. (2001) commented, “Fold is one of the most important parameter that is evaluated. If the area 

suffers from low S/N, high fold is desirable in order to improve the data quality.” Table L-2 shows 

that the increase in fold from Generation 1 to Generation 4 is manifested in the improved imagery of 
Gulf of Mexico G&G Activities Programmatic EIS L-35

Areas A-F in Figures 1-4 of Attachment 3. An increase in fold is achieved by a reduction in the 

shot and/or receiver intervals or by an increase in streamer length, but it is not the only method 

available to increase the S/N to improve imagery of the subsurface. Other parameters to consider 

are areal shape/orientation of shot and/or receiver array.

The change in areal shape/orientation of shot or receiver array allows for areas within the 

subsurface to have more traces to image a specific area that would otherwise be lost to due complex 

ray paths of the returned energy to the hydrophones. The complex ray paths were caused by abrupt 

changes in shallow and intermediate salt body thicknesses, combined with complex geologic 

structures above and below the salt. Brice et al. (2013) commented, “In the presence of complex 

geology, ray bending can leave portions of the subsurface untouched by seismic waves when only a 

narrow range of source-receiver azimuths (NAZ) is recorded. Attempts to solve this problem have 

led to the development of wide-azimuth (WAZ), rich-azimuth (RAZ), full-azimuth (FAZ), and multiazimuth (MAZ) acquisition configurations.” The use of different acquisition methodology of NAZ, 

WAZ, MAZ, RAZ, and FAZ (refer to Chapter 2.12, “Acquisition Geometry Advances,” below) 

provides improved event continuity, higher S/N, and improved imagery of surfaces above and below 

salt bodies, as well as the salt itself. This is demonstrated in Figures 1-4 of Attachment 3 by Areas 

A-F with WAZ acquisition geometry. 

The apparent significant acquisition parameters are shown below in Table L-2. Table L-2

also shows that, as the group interval decreased, air gun source increased, and record length 

increased, the fold increased. As observed in Figures 1-4 of Attachment 3 and Figures L-3 

through L-8 for Areas A-F, as the fold increased, the imagery quality also increased. Each of the 

parameters played a part in the improved imagery singly or in tandem with other parameter changes. 

The Panel also acknowledges that these are currently significant parameters in data acquisition. 

However, as technology changes, so may the emphasis of other parameters that may contribute to 

future significant data quality.

Table L-2. Summary of Significant Parameters

Source: Brinkman, official communication, 2016.

2.11 GEOPHYSICAL HARDWARE ADVANCEMENTS

The geophysical industry continuously undertakes research to develop new hardware in an 

attempt to improve the sub-surface seismic imagery. These proprietary accomplishments allow for 

Generation Type

Streamer 

Length 

(meter)

Airgun Source 

(cu in)

Shotpoint 

Interval 

(meter)

Record 

Length 

(seconds)

Nominal 

Fold

Group 

Interval 

(meter)

1 NAZ 4800-6000 3000-5400 25-40 9 to 12 48 to 60 25

2 NAZ 6000-8100 3960-5580 31.25-75 12.8 to 13 57.6-64 12.5-25

3 NAZ & OBC 8000-9000 3040-8475 25-62.5 10 to 13 64 to 144 12.5-50

4 WAZ 7000-8100 8475-10170 37.5-42 14 186-216 12.5
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the seismic service companies to hold a competitive advantage over their competitors and foster 

further research as competitors attempt to gain the competitive edge. Below is a partial list of 

streamer technology advancements literature dated from 2005 to 2013. The list emphasizes the 

effort seismic contractors and hardware manufacturers put into research and development.

• Hoogeveen et al. (2005) discuss the use of the solid streamer by PGS to 

overcome the unwanted low-frequency noise bursts caused by swell noise.

• Tenghamn et al. (2007) discuss dual-sensor streamers by PGS to eliminate 

spectral notches caused by ghost reflections at the receivers. Dual sensors also 

allow for increased flexibility in streamer towing depth to permit continued 

recording in rough seas and increase the potential bandwidth of the data.

• Proprietary hardware advancements have allowed geophysical service 

companies to collect seismic data that are unique and not replicated by any of 

their competitors.

2.12 ACQUISITION GEOMETRY ADVANCEMENTS

Figure L-9 shows the progression and differences in 3D marine seismic acquisition in areas 

of sub-salt illumination. Narrow-azimuth (conventional NAZ) seismic acquisition shows how a single 

vessel acquires a volume of data by towing multiple streamers. Multi-azimuth (MAZ) consists of 

several acquisitions of data in an area from different orientations. These distinct datasets are 

merged into one multi-azimuth dataset. Wide-azimuth (WAZ) data involve multiple sources and 

acquisitions that provide wider ranges of azimuths. Figure L-9 is just one of several types of multivessel designs for WAZ surveys. Rich azimuth (RAZ, not shown) requires several traverses of WAZ 

surveys in different orientations.

Figure L-9. Schematic Comparison of Narrow-Azimuth vs. Multi-Azimuth vs. WideAzimuth Streamer Acquisition (Wide-azimuth presents the most aggressive 

scenario and necessitates more than one vessel. Multi-azimuth uses two or 

more shooting directions using one vessel.) (Rekdal and Long, 2006). 
Gulf of Mexico G&G Activities Programmatic EIS L-37

2.13 POTENTIAL METRICS TO DETERMINE DUPLICATIVE SURVEYS

BOEM’s geoscientists examined historical datasets and looked at all acquisition criteria. The 

list, while not in any order of importance, have all been determined to be the significant factors in 

determining whether surveys would be deemed duplicative.

(1) Geospatial Location – This is the first and most obvious metric to review. A 

potential survey’s spatial extent can be viewed as a polygon. This polygon can 

be compared with existing survey polygons to determine where overlap of the 

proposed survey and existing survey(s) would occur, and it is the starting point 

to determining duplication.

• Overlap with Current Datasets and Extent of that Overlap

• Surface Orientation/Geometry

(2) Survey Acquisition Design – A survey’s potential for advanced imagery in 

complex regimes are dependent upon the richness of its azimuthal acquisition. 

Generally, higher azimuthal richness results in a better quality signal acquired.

• Acquisition Geometry

• Azimuthal Imaging

• Line/Shot Pint Orientation

(3) Receiver Criteria – An increase in receivers tends to lead to an increase in 

azimuth, fold, and S/N. This is achieved by the lengthening of streamers or 

from towing more streamers. Individual geophysical contractors use proprietary 

streamers that enhance the received signal and give them a competitive 

advantage.

• Streamer Type

• Number of Receiver (Streamer) Boats

• Number of Streamers per Boat

• Location (Ocean Bottom Cable [OBC]/Vessel Towed)

• Length

• In-line/Crossline Offsets

• Streamer Separation

• Number of Channels

• Streamer Depth

(4) Source Criteria – The source is designed to optimize the harmonics of the 

produced wavelet by taking advantage of constructive and destructive 
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interference in the wave train. The source is carefully planned for that specific 

survey with geology, water depth, and other factors in mind to optimize a 

particular zone or multiple zones of interest. An increase in source size does 

not always lead to better geologic penetration.

• Source Type

• Array Size

• Array Architecture/Composition

• Source Arrays per Vessel

• Firing Sequence

• Gun Depth

• Number of Source Vessels

(5) Data Sampling – This criteria focuses on the density of the seismic data. 

Generally, the denser the data, the more signal is generated in acquisition, but it 

is more labor and cost intensive.

• Spatial

− Fold of Coverage

− Shot-Point Interval

− Group Interval

− Recorded Bin Size

• Temporal

− Sample Rate

− Record Length

• Frequency Content

2.14 SUMMARY

As demonstrated in the Mississippi Canyon case study provided in this report, a comparison 

of the spatial polygons of seismic survey coverage acquired in the Gulf of Mexico, in and of itself, is 

not adequate to determine whether duplicative seismic acquisition has occurred in the past or might 

result from a new survey. The polygons represent only one portion of the potential metrics needed 

to determine if a survey is unnecessarily duplicative or not. The case study demonstrated additional 

criteria that could be considered during the permitting process. These criteria could be, but are not 

limited to, geospatial location, survey acquisition design, receiver and source criteria, and data 

sampling. All of the previously mentioned metrics, jointly and individually, play a role to determine 

whether a survey would be deemed unnecessarily duplicative. Any evaluation of a proposed survey 
Gulf of Mexico G&G Activities Programmatic EIS L-39

will require an in-depth evaluation of how its metrics compare with existing surveys. Sound 

environmental stewardship is critical to BOEM’s mission, and the suggested metrics outlined in this 

report can help BOEM achieve its mission by the reduction and/or prevention of unnecessary 

seismic survey acquisition.

2.14.1 Panel Determination

The Panel has determined the following: 

(1) It is feasible to determine whether or not a newly proposed seismic survey is 

unnecessarily duplicative when compared with previous surveys in an area 

(2) This determination can be accomplished under the current laws and regulations 

governing G&G activities on the OCS. However, the additional information 

required from the companies may necessitate reviewing any additional burden 

placed upon them to ensure the requirements of the Paperwork Reduction Act 

of 1995 are met.

3 LITERATURE CITED

Aylor, W.K. 1997. The role of 3-D seismic in a world-class turnaround. The Leading Edge 

17(12):1678-1681.

Brice, T., M. Buia, A. Cooke, D. Hill, E. Paler, N. Khaled, S. Tchikanha, E. Zamboni, E. Kotochigov, 

and N. Moldoveanu. 2013. Developments in full azimuth marine seismic imaging. Oilfield 

Review (Spring 2013), pp. 42-55. 

Brinkman, R. 2016. Official communication. U.S. Dept. of the Interior, Bureau of Ocean Energy 

Management, Gulf of Mexico OCS Region, New Orleans, LA.

Caldwell, J. and W. Dragoset. 2000. A brief overview of seismic air-gun arrays. The Leading Edge 

(August 2000) pp. 898-902.

Dragoset, B. 2005. A historical reflection on reflections. The Leading Edge 

24(Supplement 46):1-31.

Hegna, S., B. Krokan, and E. Selbekk. 2001. Single source 3D acquisition – a high quality and cost 

– effective alternative. SEG Technical Program Expanded Abstracts 2001, pp. 48-51. 

doi:10.1190/1.1816654.

Hoogeveen, J.H., S. Hegna, R. Tenghan, A. Stenzel, and C. Borresen. 2005. Practical aspects of 

an innovative solid streamer concept. SEG Technical Program Expanded Abstracts 2005, 

pp. 76-80.

Rekdal, T. and A. Long. 2006. Recent advances in marine seismic acquisition and processing 

technology. CSEG Recorder 31 (Special), 11 pp. 
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Tenghamn, R., S. Vaage, and C. Borresen. 2007. A dual-sensor, towed marine streamer; its viable 

implementation and initial results. SEG Technical Program Expanded Abstracts 2007, 

pp. 989-993.

U.S. Dept. of the Interior. Bureau of Ocean Energy Management. 2016. Seismic data used by 

BOEM to evaluate duplicate surveys within the Mississippi Canyon Protraction Area.
Gulf of Mexico G&G Activities Programmatic EIS L-41

ATTACHMENT 1: GLOSSARY OF GEOPHYSICAL TERMS AND COMMON 

ABBREVIATIONS 

Glossary of Geophysical Terms

Acquisition Density – the density of source emissions or receiver recording density. 

Aliasing – frequency uncertainty resulting from having less than two samples per cycle (refer to 

Spatial Sampling) 

Azimuth – the horizontal angle measured from true north. 

Bin Size – the theoretical sample interval determined by source and receiver spacing for grouping of 

traces that sample the same sub-surface point or area

Channels – receiver groups; one or more receivers can compose one channel. 

Common Depth Point (CDP) – the CDP with a given bin size as defined above. 

Energy Source Type – the type of source or method used to produce a signal directed into the 

earth to record seismic events such as reflections or refractions, e.g., compressed air used in 

air guns. 

Firing Sequence – pattern in which individual/groups of arrays are fired, i.e., popcorn sequencing or 

alternate sequencing. 

Fold – the number of traces that sample a given location in a survey (referred to as common 

mid-point) that are stacked together during an imaging sequence. 

Frequency Content – refers to the bandwidth of a signal that is produced by the source or the 

bandwidth that is retrieved by the receivers. 

Group Interval – the horizontal distance between streamer components that represents one 

receiver group (channel); multiple receivers are grouped (summed) into one channel; the 

distance each of these groups span is referred to as the group interval. 

Line Spacing – the spacing between adjacent lines traversed during the acquisition of a survey and

can be sail line spacing, surface receiver (cable) spacing, or sub-surface line spacing. 

Listening Window – refer to Record Length. 

Location (OBC/vessel towed) – describes whether receivers are towed behind a vessel or 

semi-permanently positioned on the seafloor. 

Offset – distance between source/receiver pairs, either in the parallel (in-line) or perpendicular 

(crossline) direction. 

Overlap – the same spatial area over which two or more surveys have acquired data. 

Receiver – a sensor designed to record signals, such as reflections or refractions, generated by a 

seismic energy source. 

Receiver Boats (cable) – acquisition vessels that tow streamers. 

Receiver Depth – depth below water surface in which streamers are being towed. 

Record Length – the amount of time in milliseconds that is recorded for each source excitation 

during the acquisition of a survey. 

Sample Interval – the time between readings recorded during seismic acquisition or the time or 

depth interval between sequential samples of a seismic trace. 
L-42 Panel Reports

Sample Rate – the inverse of the sample interval, the time in micro or milliseconds between sample 

points recorded by a recording system during seismic acquisition. 

Separation – the distance between receiver locations, source point locations, streamers, or source 

arrays that dictate the nominal geometry of a survey design. 

Sequential Sourcing – the individual source emission pattern in an operation that utilizes multiple 

energy sources. 

Simultaneous Sourcing – the emission of multiple sources at or near the same tie in the recording 

sequence. 

Source – a device that releases energy used to generate a seismic pulse that is directed into the 

earth, reflected, refracted, and recorded during seismic acquisition. 

Source Array – the total arrangement of source elements or sub-arrays that comprises a seismic 

source. 

Source Depth – depth below water surface in which sources are being towed. 

Source Point – the location where seismic energy is released and where arrays are used; this

usually refers to the geometric center of the arrays. 

Source Spacing – the distance between sequential source points along a line of a survey. 

Spatial Sampling – measurements taken only at discrete locations. 

St Streamer Length – total length of streamers measured from a position on the vessel to the tail 

buoy; this includes active and inactive sections. 

Streamer – towed cable containing receivers. 

Streamer Length – total length of streamers measured from a position on the vessel to the tail 

buoy; this length includes active and inactive sections. 

Streamer Separation – distance between streamers towed by the same vessel. 

Sub-array (source) – composed of individual airgun elements; multiple sub-arrays compose an air 

gun array; sub-arrays are designed to optimize harmonics. 

Survey Geometry – the relationships of source spacing, line spacing, receiver spacing, and offset 

ranges that a particular deployment of in-field equipment produces.

Survey Orientation – the primary orientation of survey lines or primary azimuth of source and 

receiver relationships, typically related to NAZ acquisition, that can affect the imaging quality 

of a survey due to geological orientations of the subsurface events. 

Syncline – a fold in stratified rocks in which the rocks dip toward a central depression, i.e., the 

attitude of the rocks is concave upward; opposite of anticline. 

Trace – a record of data from one seismic channel. 

Tow Depth – the depth, below the surface of the water, at which a source or receiver array is towed 

behind a seismic vessel (typically 5 to 30 m; 16 to 98 ft). 

Common Abbreviations

FAZ (Full-Azimuth Acquisition) – a survey that, by design, combines elements of NAZ, WAZ, and 

RAZ to generate azimuths that sample the sub-surface from all directions.
Gulf of Mexico G&G Activities Programmatic EIS L-43

MAZ (Multi-Azimuth Acquisition) – a survey that, by design, produces multiple narrow ranges of 

azimuths through acquisition of NAZ in multiple directions (refer to Figure L-9, “Acquisition 

Geometry Advancements,” in Chapter 2.12 for a diagram).

NAZ (Narrow Azimuth Acquisition) – a survey that, by design, produces only a narrow range of 

azimuths related to the travel paths between source and receiver locations, typically single 

vessel (refer to Figure L-9, “Acquisition Geometry Advancements,” in Chapter 2.12 for a 

diagram).

OBC (Ocean Bottom Cable) – sources towed behind a source vessel while the receiver arrays 

(assembled in cables) are placed on the seabed, deployed, and recovered/repositioned for a 

cable-laying (recording) vessel. 

OBN (Ocean Bottom Node) – same as OBC only receivers are deployed as individual units and 

recovered/repositioned via a remotely operated vehicle from the recording vessel. 

RAZ (Rich-Azimuth Acquisition) – a survey that, by design, combines elements of either or both 

NAZ and WAZ to produce a large range of azimuths, typically multiple vessels and multiple 

acquisition directions.

TS (Towed Streamer) – receiver and airgun (source) cables (streamers) are towed through the 

water at a given depth (typically between 5 and 30 m [16 and 98 ft] below the sea surface) 

behind a seismic source vessel.

TS 2D (Two-Dimensional Towed Streamer) – a TS survey where the seismic vessel only tows one 

source and one streamer to record a single CDP line of the sub-surface (1 horizontal 

direction, i.e., in-line and depth, hence 2D). 

TS 3D (Three-Dimensional Towed Streamer) – a TS survey where the seismic vessel tows 

multiple sources and streamers to record multiple CDP lines of the sub-surface in a single 

pass (in-line and cross-line, i.e., perpendicular to the in-line direction and depth, hence 3D). 

TS 4D (Four-Dimensional [or Time Lapse] Towed Streamer) –, TS 3D surveys acquired 

repeatedly with the same survey geometry over the same survey area; the difference 

between two of these surveys then represents the changes in the sub-surface (e.g., due to a 

producing oil or gas field) over a given time period, typically a couple of years. 

VC (Vertical Cable) – same as OBC only the cables are positioned vertically in the water column 

with an anchor at the seabed and buoys at/near the sea surface.

VSP (Vertical Seismic Profiling) – the receiver is placed from a production or drill rig at different 

depths inside a well while the sources are positioned in a given pattern at the sea surface.

WAZ (Wide-Azimuth Acquisition) – a survey that, by design, produces a wider range of azimuths 

related to the travel paths between sources and receivers, and uses multiple vessels (refer to 

Figure L-9, “Acquisition Geometry Advancements,” in Chapter 2.12 for a diagram). 
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ATTACHMENT 2: DIFFERENCES BETWEEN MULTI-CLIENT AND 

EXCLUSIVE SURVEYS 

Multi-Client Surveys Exclusive Surveys

Multi-client acquisition develops a product – 

seismic data available for licensing to multiple 

E&P companies

Proprietary acquisition provides a service – 

seismic data only available to the E&P company

Seismic contractor designs a survey that E&P 

companies (the market) have asked for; E&P 

companies use the information to develop 

prospects and delineate reservoirs, as well as for 

use in the preparation of an upcoming lease sale. 

Covers large areas – in the Gulf of Mexico, a 

multi-client acquisition project would likely cover 

hundreds of OCS blocks. 

Seismic company and E&P company enter into 

agreement for acquisition of seismic data over a predetermined area (e.g., possibly acreage under 

lease). The proprietary model is used often to “fine 

tune” an E&P company’s exploration and 

development plan(s) (e.g., where to drill the initial 

well and subsequent wells) to sufficiently and 

efficiently identify gas hydrocarbon reservoirs. This 

includes time-lapse surveys to better understand the 

reservoir and how well the current wells are 

recovering oil and/or gas.

Seismic contractor bears the risk – i.e., pays the 

cost of acquisition (with some pre-commitment 

money furnished by E&P companies), obtains all 

necessary permits and approvals, and develops, 

manages and conducts projects.

Seismic contractor provides the vessel and crew to 

acquire data; E&P company pays the full cost of 

acquisition.

Seismic contractor owns the seismic data. E&P company owns the seismic data.

Contractor license use of the seismic data to E&P 

companies – either all of the data acquired or 

some subset. License agreement will determine 

how E&P company can use the data.

E&P company can use and share the data with other 

E&P companies without restrictions.

The E&P company can license to use the data at 

a fraction of the project cost of what an E&P 

company would pay for acquisition of seismic 

data on much less acreage (fewer OCS blocks).

On a per acre basis, cost of seismic data acquisition 

is much higher than if only licensed from the 

contractor. Cost of acquisition is dependent on 

supply/demand of vessel and crew.

E&P = exploration and production.

OCS = Outer Continental Shelf.
Gulf of Mexico G&G Activities Programmatic EIS L-45

ATTACHMENT 3: ENLARGED VERSIONS OF COMPOSITE GENERATIONAL LINES
L-46 Panel Reports

****
Gulf of Mexico G&G Activities Programmatic EIS L-47
L-48 Panel Reports

The Department of the Interior Mission

The Department of the Interior protects and manages the Nation’s natural 

resources and cultural heritage; provides scientific and other information 

about those resources; and honors the Nation’s trust responsibilities or 

special commitments to American Indians, Alaska Natives, and affiliated 

island communities.

The Bureau of Ocean Energy Management Mission

The Bureau of Ocean Energy Management (BOEM) is responsible for 

managing development of U.S. Outer Continental Shelf energy and mineral 

resources in an environmentally and economically responsible way.