SC!TM9 C?!AT7g

Coniractor Report

USGS RJJCR-1 999-0005

OC Sttidy MMS 2DOG-002

Cetaceans, Sea Turtles ard Seabirds in the Northern GIf of Mexico;

Distribution, Abundance and Habitat AssociatFons

Volume I: Executive Summary

U.S. DprIment & the In1err US. Gprtmcrt ctthe lnIeror U.S. GIogI Surve Mirirs Mangeren1 Serlc

loçI Resurce Dieisioci Gulf c,1 Mexicc Riri
Contractor Report

USGS/BRD/CR-- 1999-0006

OCS Study IVIMS 2000-002

Cetaceans, Sea Turtles and Seabirds in the Northern Gulf of

Mexico: Distribution, Abundance and Habitat Associations

Volume I: Executive Summary

Editors

Randall W. Davis

William E. Evans

Bernd WUrsig

January 2000

Prepared under

U.S. Geological Survey, Biological Resources Division

Contract Number 1445-CTO9-96-0004 and 1445-1A09-96-0009

by

The GulfCet Program

Department of Marine Biology

Texas A&M University at Galveston

5007 Avenue U

Galveston, Texas 77551

In cooperation with the

U.S. Department of the Interior

Minerals Management Service

Gulf of Mexico OCS Region
PROJECT COOPERATION

This study was procured to meet information needs identified by the Minerals Management

Service (MMS) in concert with the US. Geological Survey, Biological Resources Division

(BRD).

DISCLAINLER

This report was prepared under contract between the U.S. Geological Survey, Biological

Resources Division (BRD), Texas A&M University, and the National Marine Fisheries Service.

This report has been technically reviewed by the BRD and the Minerals Management Service

(MMS), and has been approved for publication. Approval does not signify that the contents

necessarily reflect the views and policies of the BRD or MMS, nor does mention of trade names

or commercial products constitute endorsement or recommendation for use. It is, however,

exempt from review and compliance with the MMS editorial standards.

REPORT AVAILABILITY

Extra copies of this report may be obtained from the Public Information Office at the following

address:

U. S. Department of the Interior

Minerals Management Service

Gulf of Mexico OCS Region

Public Information Office (MS 5034)

1201 Elmwood Park Boulevard

New Orleans, LA 70123-2394

Telephone: (504) 736-2519 or

(800) 200-GULF

CITATION

Davis, R.W., W.E. Evans, and B. Wursig, eds. 2000. Cetaceans, Sea Turtles and Seabirds in the

Northern Gulf of Mexico: Distribution, Abundance and Habitat Associations. Volume I:

Executive Summary. Prepared by Texas A&M University at Galveston and the National

Marine Fisheries Service. U.S. Department of the Interior, Geological Survey, Biological

Resources Division, USGS/BRD/CR-1999-0006 and Minerals Management Service,

Gulf of Mexico OCS Region, New Orleans, LA. OCS Study MMS 2000-002 27 pp.

111
I'REFACE

This study entitled "Cetaceans, Sea Turtles and Seabirds in the Northern Gulf ofMexico:

Distribution, Abundance and Habitat Associations", also known as the GulfCet II study, provides

synoptic data and analyses on the species diversity, abundance, and habitat characteristics for

cetaceans, sea turtles arid seabirds in the northern Gulf of Mexico. Results of the study are

described in three volumes including this volume ("Volume I: Executive Summary"), "Volume

II: Technical Report" and "Volume III: Data Appendix."

This study was sponsored and administered by the U.S. Department of Interior, U.S. Geological

Survey, Biological Resources Division to provide environmental information to the U.S.

Department of Interior, Minerals Management Service. It was managed by Texas A&M

University at Galveston in partnership with the National Marine Fisheries Service at the

Southeast Fisheries Science Center.

V
TABLE OF CONTENTS

List of Figures ix

List of Tables xi

List of Abbreviations and Acronyms xiii

Acknowledgments xv

Contributors xvii

Introduction 1 Background i

GulfCet II Study Area and Objective i

General Oceanography of the Gulf of Mexico 8

Biological Oceanography ii

Visual Surveys of Cetaceans and Sea Turtles 11

Study Area Summaries 12

Overview of Cetacean Distribution 14

Acoustic Surveys of Cetaceans i

Cetacean Habitat is

The Special Case of Sperm Whales: Behavior and Site Fidelity 16

Seabird Ecology 18

Conclusions and Recommendations 19

Cetaceans 20

Sea Turtles 22

Seabirds 23

Potential Effects of Oil and Gas Exploration and Production Activities 23

Recommendations for Future Research 24

Literature Cited 26

vii
LIST OF FIGURES

Figure 1. GulfCet I study area in the western and north-central Gulf between the 100 and

2000-rn isobaths 3

Figure 2. GulfCet II study area including the Minerals Management Service's Eastern Planning Area and the focal study area for cetacean habitat surveys 4

Figure 3. U.S. oceanic northern Gulf of Mexico 6

Figure 4. Contour map of sea surface height for the Gulf of Mexico showing major

hydrographic features of the region 9

ix
LIST OF TABLES

Table 1. Cetaceans of the Gulf of Mexico 2

Table 2. Types of data collected by season arid survey for the GulfCet II Program 7

Table 3. Cetacean abundance in the oceanic northern Gulf of Mexico estimated from Guiftet II

visual survey data, based on the highest estimate for each species from either shipboard or aerial surveys 21

xi
LIST OF ABBREVIATIONS AND ACRONYMS

The following acronyms and abbreviations are used throughout this Executive Summary and the

Technical Report:

ADCP Acoustic Doppler Current Profiler

AVHRR Advanced Very High Resolution Radiometer

BRD Biological Resources Division

CCAR Colorado Center for Astrodynamics Research, University of Colorado

CCR Cold-Core Ring

CHL Chlorophyll

CI Confidence Interval

CON Confluence between ring structures

CTD Conductivity, Temperature, and Depth Profiler

CV Coefficient of Variation

dB rel j.iP Decibels relative to 1 micro Pascal

DCM Deep Chlorophyll Maximum

DFA Discriminant Function Analysis

EPA Eastern Planning Area

GIS Geographic Information System

GPS Global Positioning System

GulfCet I Distribution and Abundance of Cetaceans in the North-Central and

Western Gulf of Mexico (1991-1995)

Gulftet II Cetaceans, Sea Turtles and Seabirds in the Northern Gulf of Mexico:

Distribution, Abundance and Habitat Associations (this study)

HCLS High Chlorophyll, Low Salinity

HPLC High Pressure Liquid Chromatography

IKMT Isaacs Kidd Midwater Trawl

LC Loop Current

LCE Loop Current Eddy

MAR Mississippi-Atchafalaya River

MLD Mixed Layer Depth

MOCNESS Multiple Opening/Closing Net and Environmental Sampling System

MOM Mouth of the Mississippi

MMS Minerals Management Service

NE Northeast

NEGOM Northeastern Gulf of Mexico

NMFS National Marine Fisheries Service

NOAA National Oceanic and Atmospheric Administration

OCS Outer Continental Shelf

PER Periphery of ring structures

PMB Predicted Mean Biomass

PSD Perpendicular Sighting Distance

SAIL Serial ASCII Interface Loop

SD Standard Deviation

SEFSC Southeast Fisheries Science Center, NIvIFS
SSH

SST

Stenellids

Sv

TAMEJ

TAMUG

TOPEX/ERS

TOPEXJPOSEIDON

TS

UC

USGS

WCR

WCWRU

XBT

Sea Surface Height

Sea Surface Temperature

Dolphins of the genus Stenella

Acoustic backseattering strength

Texas A&M University (College Station)

Texas A&M University at Galveston

Topography Experiment Mission/European Research Satellite

Topography Experiment MissionfPoseidon

Temperature-Salinity Relationship

University of Colorado

United States Geological Survey

Warm-Core Ring

Wisconsin Cooperative Wildlife Research Unit

Expendable Bathythermograph

xiv
ACKNOWLEDGMENTS

Many persons contributed to this study, including the crews and graduate students who worked

on the research vessels and aircraft, laboratory technicians, and the data management staff. The

contributors to this report would like to recognize the efforts of Alejanciro Acevedo, Ilona Berk,

Steve Berkowitz, Jose Bersano, Robert Blaylock, Ned Brinkley, British Petroleum, Cheryl

Brown, Carolyn Burks, Shane Collier, Melissa Davis, Brad Dawe, Theia DeLong, Captain Dana

Dyer, Wesley Elsberry, Dagmar Fertl, Michelle Finn, Michael Fliim, Holly Fortenberry, Rachel

Gross, Jeff Hagan, Terry Henwood, Shannon Hesse, Lesley Higgins, Markus Homing, Carrie

Hubard, Clint Jeske, John Lamkin, Kosrow Lashkari, Nicole LeBoeuf, John Longnecker, Steven

Lowder, Kimberly Marks, Greg Marshall, Tony Martinez, Blair Mase, Kathy Maze, National

Geographic Society, Scott Nichols, Steve Nokutis, Dwight Peake, Mike Peccini, Jon Peterson,

Matt Pickett, Robert Pitmari, Todd Pusser, Danielle Raha, Logan Respess, Carol Roden, Diego

Rodriguez, Gerald Scott, Mat-i Smultea, Jon Stern, Sarah Stienessen, Jim Tobias, Erika Vidal,

Melany Wursig, and Mindy Zuschlag.

Special thanks to Paula Canton, Kate deMedeiros, Jenny Ogrodnick, and Mary Beth Rew for

technical editing. The Gulftet Data Management Office also wishes to express its appreciation

to those who served as reviewers of this document.

We gratefully acknowledge the Department of Oceanography, Texas A&M University, the

Texas Institute of Oceanography and the National Marine Fisheries Service for cost-sharing the

use of all research vessels used for the surveys on this project. Two colleagues not on the

GulfCet team provided important help with data reduction: Steve DiMarco (TAMU) carried Out

the initial quality control on the ADCP data from RV Gyre cruises 96G06 and 97G08 to produce

the data sets plotted in Figures 2.8 and 2.10, following protocols developed to support the MMSsponsored Northeast Gulf of Mexico Chemical Oceanography and Hydrography project

(NEGOM-COH). Dr. DiMarco then provided the gridded files of ADCP near surface velocity

that are plotted in Figures 2.9 and 2.11. Peter Hamilton (SAIC) produced the gridded files of

geostrophic velocity at 0 m relative 800 m that are plotted in Figures 2.30 and 2.33.

Special thanks to the Scientific Review Board members Daryl Boness, Roger Hanlon and

Lawrence Pomeroy for their thoughtful review and comments on the goals and results of this

project, and very special thanks to BRD Contracting Officers Technical Representative Gary

Brewer and MMS Contracting Inspectors Robert Avent and Dagmar Fertl for their guidance in

the writing of this report.

This study was funded by the U.S. Department of the Interior, Geological Survey, Biological

Resources Division under contracts 1445-CTO9-96-0004 and 1445-1A09-96-0009.

xv
CONTRIBUTORS

Douglas C. Biggs Department of Oceanography, Texas A&M University, College Station, Texas 77843-3146; dbiggsocean.tamu.edu

Robert B. Cady Department of Oceanography, Texas A&M University, College Station, Texas 77843-3146; robcady@oceaittamu.edu

Randall W. Davis Department of Marine Biology, Texas A&M University, 5007 Avenue U,

Galveston, Texas 77551; davisr@tamug.tamu.edu

William E. Evans Department of Marine Biology, Texas A&M University, 5007 Avenue U,

Galveston, Texas 77551; evansw@tamug.tamu.edu

Elizabeth J. Harris Department of Oceanography, Texas A&M University, College Station,

Texas 77843-3146; lizh@ocean.tamu.edu

Nancy A. Hess Department of Wildlife Ecology, University of Wisconsin, 226 Russell

Labs, 1630 Linden Drive, Madison, Wisconsin 53706-1598;

nahess@students.wjsc.edu

Wayne Hoggard Southeast Fisheries Science Center, National Marine Fisheries Service,

P.O. Drawer 1207, Pascagoula, Mississippi 39568;

whoggardtriton.pas.nmfs.gov

Robert R. Leben Colorado Center for Astrodynamic Research, University of Colorado,

Campus Box 431, Boulder, Colorado 80309-043 1;

leben@orbit.colorado.edu

Spencer K. Lynn GulfCet Program Office, Texas A&M University, 5007 Avenue U,

Galveston, Texas 77551

Keith D. Mullin Southeast Fisheries Science Center, National Marine Fisheries Service,

P.O. Drawer 1207, Pascagoula, Mississippi 39568;

kmullin@triton.pas.nmfs.gov

Jeffrey C. Norris Marine Acoustics Lab, Texas A&M University, 5007 Avenue U,

Galveston, Texas 77551; norrisjtamug.tamu.edu

Joel G. Ortega-Ortiz Marine Mammal Research Program, Texas A&M University, 4700 Avenue

U, Bldg. 303, Galveston, Texas 77551; ortegaj@tamug.tamu.edu

Shannon Rankin Marine Acoustics Lab, Texas A&M University, 5007 Avenue U, Galveston,

Texas 77551

xvii
Patrick H. Ressler

Christine A. Ribic

Andrew J. Schiro

Troy D. Sparks

David W. Weller

John H. Wormuth

Bernd Wursig

Department of Oceanography, Texas A&M University, College Station, Texas 77843-3146; pressler@ocean.tamu.edu

Department of Wildlife Ecology, University of Wisconsin, 226 Russell

Labs, 1630 Linden Drive, Madison, Wisconsin 53706-1598;

caribic@facstaff.wjsc edu

Marine Maminal Research Program, Texas A&M University, 4700 Avenue U, Bldg. 303, Galveston, Texas, 77551

Marine Acoustics Lab, Texas A&M University, 5007 Avenue U,

Galveston, Texas 77551; sparkst@tamug.tamu.edu

Marine Mammal Research Program, Texas A&M University, 4700 Avenue U, Bldg. 303, Galveston, Texas, 77551

Department of Oceanography, Texas A&M University, College Station, Texas 77843-3146; jwormuth@astra.tamu.edu

Marine Mammal Research Program, Texas A&M University, 4700 Avenue

U, Bldg. 303, Galveston, Texas 77551; wursigbtamug.tamuedu

xviii
INTRODUCTION

Background

The mission of the U.S. Geological Survey (USGS) Biological Resources Division (BRD) is to

provide the scientific understanding and technologies needed to support the sound management and conservation of the nation's biological resources. The U.S. Department of the Interior's Minerals Management Service (MMS) is a client agency of the BRD. The IvJIMS has the

responsibility for leasing, minerals exploration and development of submerged Federal lands on

the U.S. Outer Continental Shelf (OCS) under the provisions of the OCS Lands Act

Amendments of 1978. The BRD administered this study, hereafter called the Guiftet II

program. The GulfCet II program was managed by Texas A&M University at Galveston

(TAMUG) in partnership with the National Marine Fisheries Service (NMFS) at the Southeast Fisheries Science Centers (SEFSC).

Until recently, relatively little was known about cetaceans inhabiting deeper waters of the Gulf of Mexico (Table 1) (Fritts et al. 1983, Shane et al. 1986, Scott et al. 1989, Scott and Hansen

1989, Leatherwood and Reeves 1990, Mullin et al. 1994, Jefferson and Schiro 1997). The most

extensive survey of cetaceans in the offshore waters (100-2,000 m deep) of the north-central and

western Gulf of Mexico (Figure 1) was conducted jointly by Texas A&M University and the NIMFS, Southeast Fisheries Science Center beginning in 1992 and called the Guiftet I program

(Davis and Fargion 1996, Baumgartner 1997, Davis et al. 1998). This three-year study provided

synoptic information on the distribution and abundance ofcetaceans using both visual and

acoustic survey techniques. It also provided limited information on cetacean-habitat

associations. In addition to cetaceans, the GulfCet I program provided synoptic information on

the distribution and abundance of sea turtles using aerial survey techniques. Finally, over 30

species of seabirds were sighted during visual shipboard surveys of the study area (Davis and Fargion 1996).

GulfCet II Study Area and Objectives

The GulfCet II program used aerial surveys and shipboard visual and acoustic surveys to

document cetacean, sea turtle and seabird populations. This work was accompanied by data

acquisition designed to further characterize habitat and reveal habitat associations for cetaceans

and seabirds. This study was intended as a spatial and temporal extension of the GulfCet I

program.

The GulfCet II study area included:

(1) The IvfMS Eastern Planning Area (EPA) continental slope from 100-2,000 m deep east of

88°10.O'W and north of 26°00.O'N (70,470 km2) and the EPA continental shelf (12,326 km2)

located from 18.5 km offshore to 100 m deep between 88°10.O'W and 85°55.O'W (Figure 2).

This area was surveyed using both aircraft and ships (RN Oregon II and R/V Gyre).

1
Table 1. Cetaceans of the Gulf of Mexico. The (E) next to the common name indicates that

the species is listed under the Endangered Species Act of 1973 as endangered.

Balaenidae

Northern right whale (B)

Balaenopteridae

Blue whale (F)

Fin whale (E)

Sei whale (E)

Bryde's whale

Minke whale

Humpback whale (E)

Physeteridae

Sperm whale (E)

Kogiidae

Pygmy sperm whale

Dwarf sperm whale

Ziphiidae

Delphinidae

Melon-headed whale

Pygmy killer whale

False killer whale

Killer whale

Short-finned pilot whale

Rough-toothed dolphin

Fraser's dolphin

Bottlenose dolphin

Risso's dolphin

Atlantic spotted dolphin

Pantropical spotted dolphin

Striped dolphin

Spinner dolphin

Clymene dolphin

2

Eubalaena glacialis

Balaenoptera musculus

Balaenoptera physalus

Balaenoptera borealis

Balaenoptera edeni

Balaenoptera acutorostrata

Megaptera novaeangliae

Physeter macrocephalus

Kogia breviceps

Kogia siinus

Peponocephala electra

Feresa attenuata

Pseudorca crassidens

Orcinus orca

Globicephala macrorhynchus

Steno bredanensis

Lagenodeiphis hosei

Tursiops truncatus

Grampus griseus

Stenellafrontalis

Stenella attenuata

Stenella coeruleoalba

Stenella longirostris

Stenella clymene

Cuvier's beaked whale Zzphius cavirostris

Blainvifle's beaked whale Mesoplodon densirostris

Sowerby's beaked whale Mesoplodon bidens

Gervais' beaked whale Mesoplodon europaeus
-92 -90 -88 -86 -84 

Longitude West Figure 1. GulfCet I study area in the western and north-central Gulf between 

isobaths.
HOUSTON Longitude West Figure 2. GulfCet II study area including the Minerals Management Services' Eastern 

and the focal study area for cetacean habitat surveys (dashed line). -98 -96 -94 -92 -90 -88 -86 -84 
GulfCet I Study Area (154,621 km2) (Figure 1). U.S. waters from 100-2,000 m deep west of 87°30.O'W. This area is a subset of the oceanic northern Gulf study area (Figure 4) and was

surveyed during spring with the RJV Oregon II.

Oceanic northern Gulf of Mexico (398,960 km2) (Figure 3). Waters within the U.S. Economic Exclusive Zone (EEZ) greater than 100 m deep. This area was surveyed using the

RIV Oregon II during spring.

Focal study area for cetacean habitat surveys (Figure 2). This area was surveyed during

late summer 1996 and mid-summer 1997 by the R/V Gyre to assess the relationship between

cetacean distribution and habitat characteristics (i.e., bathymetry, hydrography and biological oceanography).

Both the EPA slope and Guiftet I study areas are within the boundaries of the oceanic northern

Gulf study area.

The specific objectives of the study were to:

Obtain data on temporal and spatial patterns of distribution and minimum abundance of

cetaceans using line-transect and acoustic survey techniques directly comparable to those used in previous surveys. This included incidental sightings ofsea turtles and seabirds.

Identify possible associations between cetacean and seabird high-use habitats and the

ocean environment, and attempt to explain any relationships that appear to be important to

cetacean distributions.

Objective 1 was a continuation of surveys in the north-central and western Gulf that began during the GulfCet I program and extended into MMS's Eastern Planning Area. To accomplish

this objective, we conducted aerial surveys and simultaneous shipboard visual and acoustic

surveys using line-transect methods.

To characterize cetacean and seabird habitat (Objective 2), we used an integrated approach that

included the analysis of hydrographic and bathymetric features (e.g., anticyclonic and cyclonic

eddies, ocean depth). In addition to physical features, we measured zooplankton and

micronekton biomass derived from both net and acoustic sampling to indicate the amount of

potential food available for higher trophic level foraging by cetaceans and seabirds (Table 2).

Although the diets of most cetaceans and seabirds in the Gulfare poorly known, we

hypothesized that hydrographic regimes in the study area have different levels of potential prey

that influence their distribution. We further hypothesized that these food stocks would be locally

concentrated in nutrient-rich areas offshore from the Mississippi River, within cyclonic eddies, and along the high-shear edges of warm-core eddies.

5
C.' Figure 3. U.S. oceanic northern Gulf of Mexico. Longitude West
Table 2. Types of data collected by season and survey for the GulfCet II Program. Abbreviations

casts; XBT expendable bathythermograph; SST = sea surface temperature; SSS = se

Doppler Current Profiler; MOCNESS = Multiple Opening and Closing Net and Envirohei 'ht. Survey Mammal Surveys C) c,CC) Dates Hydro

H L)

SPRING 1996 RIV Oregon II Cruise 220 Leg I 17 Apr-4 May 1996

Leg 2 8-25 May 1996

I

Leg 3 29May-8 Jun 1996 "/ 

SUMMER 1996 Aerial 9 1l-3lJull996 1/ 

LATE SUMMER 1996 R/V Gyre Cruise Gyre96GO6 11-19 Oct 1996 if

/ I I 

WINTER 1997 Aerial 10 7Feb-2OMar 1997

/

SPRING 1997 RJV Oregon II Cruise 222 Legl l7Apr-5 May 1997

1

Leg2 9-25 May 1997

1

Leg 3 29 May-9 Jun 1997 1 1 1 1

SUMMER 1997 Aerial 11 15 Jul-6 Aug 1997 if 

RN Gyre Cruise Gyre97GO8 6-20 Aug 1997 ii

I I I 

WINTER 1998 Aerial 12 8 Feb-14 Mar 1998

I
THE GULF OF MEXJCO: OCEANOGRAPHY AND BIOLOGY

General Oceanography of the Gulf of Mexico

The Gulf of Mexico is a dynamic body of water dominated by two major circulation features.

The Loop Current, formed by the interconnection of the Yucatan and Florida Currents, governs

the circulation of the eastern Gulf. In the central and western Gulf, a warm-water anticyclonic

eddy with associated cold-water cyclones is the primary circulatory feature. The Loop Current enters the Gulf in a nearly annual cycle. TOPEX/ERS satellites produce sea surface altimetry

maps that show Gulf warm-core eddies originating as pinched-off, northward penetrations of

Loop current meanders (Figure 4). After their separation from the Loop Current, these

anticyclonic eddies drift westward until their progress is eventually constrained by shoaling

topography over the northwestern continental slope of the Gulf. These anticyclonic and cyclonic

eddies remain in the region, slowly decaying or coalescing with another approaching eddy. The

overall resulting circulation of the Gulf of Mexico is remarkable because of its inter-annual

variability and intensity.

The dynamics of the Gulf are made more complex by the large fresh water inflow. Nearly twothirds of the U.S. mainland and half the area of Mexico drains into the Gulf. The Mississippi

River discharges into the northern Gulf through the Balize and Atchafalaya delta regions.

Approximately 30% of the Mississippi River enters the northern Gulf through the Atchafalaya,

and the remaining 70% goes through the Balize bird-foot delta. The Mississippi and other rivers

with their associated pollutants, nutrients, and sediment loads have a great impact on all aspects

of continental shelf oceanography in the northern Gulf. The input ofnutrients ensures high

phytoplankton production and thus higher zooplankton productivity (Lohrenz et al. 1990).

River discharge into the Gulf is distinctly seasonal, with the highest flow occurring from March

through May, and the lowest flow occurring from August through October. Wind forcing and

shelf currents are major factors controlling the distribution of Mississippi River outflow onto the

continental shelf. Loop Current eddies and filaments provide the major control of plume

circulation over the continental slope and into the northern Gulf. The fresh water of the

Mississippi River affects the spatial and temporal distribution ofareas of higher primary and

secondary production that may influence the distribution of cetaceans, sea turtles and seabirds in

the northern Gulf of Mexico.

Four cruises of R/V Oregon II and R/V Gyre (Table 2) were combined with tandem remote

sensing of sea surface height using the TOPEX[POSEIDON and ERS-2 satellite altimeters to

characterize the hydrographic regime of the northeastern Gulf of Mexico for the GulfCet H

program. In May-June (early summer) 1996, October (late summer) 1996, May-June (early

summer) 1997, and August (mid-summer) 1997, the two ships dropped 560 expendable

bathythermographs (XBTs) that profiled the temperature structure of the upper 760 m of the

water colunm. These XBT stations were supplemented with 32 conductivity-temperature-depth

(CTD) stations. The early summer cruises focused on the continental slope of the Eastern

Planning Area (EPA) (Figure 2). The late and mid-summer cruises also surveyed this region of

the slope, but these surveyed farther seaward as well, within a deepwater "focal area" where near

real-time altimetry maps of sea surface height anomaly provided by the University of Colorado

8
30 N

2TN

24 N

21 N

I WN

Figun 4. Ctint..iui mip ti the su suu1Tie& hciht for the thrif o Mexico Iowin rr4or

hydrographic tèature of ihe region. [)att were col keted by inieters aboard the

TOPE.X1'OSE11X)N nd LRS-2 ut1i md used to ohcctivc1y map th height field

lot August 1, 1q97. Th nonliwad penetrudLnl oldie hc'p Currn red in he

eastern Giilf}ias rcsiiltød n the sepmtion of an anticvclone (warm-core eddy),

identified b ih ire region of cked ccriturs in red around a high in the sea Murli1cc

hiht, (\donic. cold-ei,r cddie hhie) arc laws in the sea surface height arid i.ibk

on the periphery ot':he anticckrne. The eddy fic1i n the uestcrn gu'f is made ur of

anticvciones and conpanion cvc1one that are rrmnan i of an older Loop Current eddy

intcrncIin with the continental slope along ihe iexa' and Mexicrn coals. Date for

depths k than 200 rnctcrs have been maed

9

DN

2TN

24N

2

1 3N

c)ErW 93w 3W TW SAW 81W

Lol1ginide

gk- I II - I I 1 L -

I I I I - - - I .30 25 2 IG - 0 5 10 5

Sca surface tei (cm:'

I J 0 2t 30
Center for Astrodynamics Research indicated that there was a mesoscale cyclone (cold-core

eddy) and anticyclone (warm-core eddy) pair.

The sea surface height anomaly data showed that a broad area of cyclonic circulation was located

in the northeastern Gulf throughout 1996. This appeared in weekly altimetry maps as a

consistent region of negative height anomaly. This cyclonic feature was seen from January to

September in the region of 27-29°N latitude and 89-84°W longitude. By late summer 1996, the

cyclone was centered between 27-28°N latitude and 87-89°W longitude, roughly halfway

between the Mississippi River delta and the northwest edge of the ariticyclone. The R/V Gyre

documented a 62 dyn cm difference in height between the interior of the cyclone and

anticyclone. This created a flow confluence between the two features with an upper layer

geostrophic volume transport of 24 x 106 m3s1 (24 Sverdrups).

In mid-summer 1997, the R/V Gyre again surveyed a deepwater cyclone-anticyclone pair. This

time, the cyclone was centered on the northeast side of the anticyclone and was over the DeSoto

Canyon. The RIV Gyre documented a 84 dyn cm difference in height between the interior of the

cyclone and anticyclone. This created a flow confluence between the two features with an upper

layer geostrophic volume transport of 31 x 106 m3s1 (31 Sverdrups). Continuous shipboard

measurements of sea surface temperature, salinity and chlorophyll concentration showed that low

salinity, high chlorophyll river water was entrained from off the shelf and transported around the periphery of the cyclone.

Bottle sampling at CTD stations showed that there was a significant relationship between water

temperatures less than 22°C and nitrate concentration. As a result, the depth of the 19°C

isotherm provided a good estimation of the depth of the 10 jiM nitrate concentration. Within the

cyclone, the nitracline domed 40-60 m shallower than in the anticyclone. This doming increased

the flux of new nitrogen into surface waters so that the deep chlorophyll maximum (DCM) was

locally shallower and chlorophyll reached higher maximum concentration in the cyclone. The

higher standing stocks of chlorophyll in the upper 100 m of the water column in the cyclones

meant that these were biological "oases" of locally high productivity, while the interior of the

anticyclones were more oligotrophic. During Guiftet II, net trawls and bioacoustic surveys

showed that the cyclones also had locally higher standing stocks of zooplankton and

micronekton. We hypothesized that the higher secondary productivity of the cyclones supported

local aggregations of squid and mid-water fishes that are preyed on by cetaceans.

The four shipboard surveys also found that the depth of the 19°C isotherm was locally shallow at

the shelf-slope break, particularly in the early summer. Unfortunately, no surface chlorophyll

data were available for either of the two early summer cruises, so we do not know whether this

shelf edge upwelling was expressed at the surface as locally high primary production andlor high

surface chlorophyll concentrations. In mid-summer, the shelf-edge doming of the 19°C isotherm

depth was not as strong, and the shelf-slope break was not an area of locally high surface

chlorophyll. In late summer, we found no evidence for shelf edge upwelling from either surface

or subsurface data. However, a 6-10 m thick lens of low salinity river water was transported

completely across the shelf in late summer to be entrained into the deepwater flow confluence

between deepwater cyclone/anticyclone pair. This water of river origin had locally high surface

10
chlorophyll, resulting in more chlorophyll within the confluence than would have been predicted

from DCM characteristics alone.

Biological Oceanography

The goal of the biological oceanography segment of the GulfCet II Program was to estimate the

temporal and spatial distribution of potential cetacean prey. To this end, a series of mostly

nighttime net tows were taken whenever time permitted. A 1 m2 Multiple Opening/Closing Net

and Environmental Sampling System (MOCNESS) was used to sample zooplankton. Tow

speeds were 1.5-2.0 knots. A 14.7 m2 Isaacs Kidd Midwater Trawl was used to sample

micronekton. It was towed at 4-5 knots. These samples can be thought of as discrete

measurements of zooplankton and micronekton biomass. Continuous measurements of

zooplankton and micronekton biomass were made using a 153 kHz Acoustic Doppler Current

Profiler (ADCP). Regression analysis was used to relate the net tow biomass to ADCP

measurements of acoustic volume backscattering strength (Sw). This allowed us to considerably

extend our characterization of the regions transected during late summer 1996 and mid-summer

1997 Gyre cruises.

Both integrated zooplankton biomass and integrated cephalopod paralarvae numbers in the study

area showed higher values in the cyclone and confluence areas than in the anticyclone. Predicted

Mean Biomass (PMI3) estimates, derived from the significant positive relationship between

integrated zooplankton biomass (as determined by direct net sampling and underway

measurements of S using the ADCP), also showed that the cyclone and confluence areas were

enriched in integrated zooplankton and micronekton biomass relative to the anticyclone. In

addition, a statistically significant relationship existed between integrated zooplankton biomass

and integrated cephalopod (a major component of cetacean prey) paralarvae numbers, indicating

that higher zooplankton and micronekton biomass may correlate with higher concentrations of

cetacean prey. Finally, the abundance and diversity of myctophids, another important cetacean

prey group, appeared to be greater in the cyclones and confluence regions than in the

anticyclones. Together, these measurements suggest that the amount of prey for cetaceans and

seabirds may be consistently greater in the cyclone and confluence areas (as opposed to

anticyclone), making these mesoscale features preferential habitats for foraging.

Visual Surveys of Cetaceans and Sea Turtles

The primary objectives of the visual aerial and ship surveys were: 1) obtain a minimum

abundance estimate of each cetacean and sea turtle species in the northeastern Gulf (Figure 2) to

establish a baseline for monitoring trends in abundance over time; 2) study the seasonal

abundance and distribution patterns of cetacean and sea turtle species in the northeastern Gulf; 3)

compare spring abundance estimates of cetaceans in continental slope waters of the north-central

and northwestern Gulf (GulfCet I study area, Figure 1) to previous estimates; and 4) compare

ship-based spring abundance estimates of cetaceans in the oceanic northern Gulf (Figure 3) to

previous estimates.

During all ship surveys, two rotating teams of three observers using 25x binoculars collected

line-transect data. In spring and early summer 1996 and 1997, ship surveys were conducted in

11
three "legs" from the RJV Oregon II (Table 2). Legs 1 and 2 were conducted along transect lines

that were uniformly spaced 60 nautical miles apart throughout the oceanic northern Gulf. Leg 3

focused on the Eastern Planning Area (EPA) shelf and slope. The RIV Gyre was used to conduct

surveys of the EPA shelf and slope and a deepwater focal area during late summer 1996 and

mid-summer 1997.

Aerial surveys were conducted during summer 1996 and 1997, and winter 1997 and 1998

(Table 2). During each season, the goal was to survey 42 transect lines in the EPA slope and

16 transect lines in the EPA shelf. Two observers and a data recorder collected line-transect data

from a DeHavilland DHC-6 Twin-Otter with large convex "bubble" windows on each side of the

fuselage.

Line-transect methods were used to make abundance estimates. For aerial surveys, overall

abundance estimates for cetaceans and sea turtles were made separately for the EPA shelf and

EPA slope. Summer and winter abundance estimates of common species were also made for each study area. For ship surveys, cetacean abundance estimates were made for the spring for

the oceanic northern Gulf and the GulfCet I study areas, and for early summer for the EPA shelf and the EPA slope.

Study Area Summaries

EPA Continental Shelf, Aerial and Ship Surveys- All of the proposed transect lines were

completed during both summer (1,826 km) and winter (1,826 km) aerial surveys. During spring

ship surveys, 449 km were surveyed. Bottlenose dolphins and Atlantic spotted dolphins were

sighted during all seasons surveyed. During aerial surveys, 61 bottlenose dolphin and nine

Atlantic spotted dolphin groups were sighted, and during ship surveys, 31 and 19, respectively.

The overall abundances from early summer ship surveys of bottlenose dolphins and Atlantic

spotted dolphins were 1,056 (CV = 0.33) and 1,827 (0.46), respectively. Overall abundances

from aerial surveys were 1,824 (0.25) and 1,096 (0.50) for bottlenose and Atlantic spotted

dolphins, respectively. The abundance of bottlenose dolphins from aerial surveys during

summer, 3,281 (0.37) was significantly different than the winter estimate, 1,119 (0.30) (p<O.lO).

Too few sightings of Atlantic spotted dolphins were made to examine seasonal differences in

abundance. Both species were widely distributed in the study area.

Three species of sea turtles were sighted during aerial surveys: 85 loggerheads, four leatherbacks

and three Kemp's ridleys. The overall abundance of loggerhead sea turtles was 503 (0.20).

Loggerhead sea turtle abundances were similar during summer and winter with estimates of

480 (0.30) and 524 (0.23), respectively. Loggerhead sea turtles were sighted throughout the EPA

shelf during both summer and winter.

EPA Continental Slope, Aerial and Ship Surveys - All of the proposed transect lines were

completed during summer aerial surveys (10,440 km), but due to poor weather, only 80% of the

proposed winter effort was completed. In total, 2,586 km of transects were surveyed during

early summer ship surveys. Combining ship and aerial surveys, 17 cetacean species were sighted

on the EPA slope. Fifteen species were sighted during summer and 14 during winter. In general,

cetaceans were found throughout the study area each season. The most abundant species were

12
the pantropical spotted and spinner dolphins. Abundances of pantropical spotted dolphins were

13,649 (0.26) and 7,432 (0.40) from aerial and ship surveys, respectively, and those of spinner

dolphins were 8,670 (0.48) and 5,319 (0.75), respectively. Other species with abundance

estimates over 1,000 from aerial or ship surveys were bottlenose dolphins, Atlantic spotted

dolphins, Risso's dolphins, striped dolphins and clymene dolphins. Seasonal aerial survey

abundances varied by a factor of two or more for dwarf/pygmy sperm whales (summer peak),

bottlenose dolphins (winter peak), Risso's dolphins (winter peak), and pantropical spotted

dolphins (summer peak), but the difference was only significant for dwarl7pygmy sperm whales

(p<0.10).

Except for the spenn whale, commonly sighted species were widely distributed in the study area,

although at different depth ranges. There was no evidence of seasonal shifts in the distribution

of all cetaceans in general or of any species; however, sightings of many species were too few in

at least one season to speculate about seasonal differences in their spatial distributions. While

there was no evidence of seasonal shifts in distribution within the study area, seasonal abundance

patterns indicated that many individuals might move completely out of the study area during

different seasons.

Two sea turtle species were sighted: 28 leatherbacks and 27 loggerheads. The overall abundance

estimate of leatherbacks was 168 (0.23) turtles. Leatherbacks were about 2.5 times more

abundant in summer than winter with estimates of 230 (0.58) and 90 (0.48), respectively.

However, the difference was not significant (p>0. 10). Leatherbacks were sighted throughout the

EPA slope. The overall abundance estimate of loggerheads was 141 (0.27). Loggerheads were

about 12 times more abundant in winter than summer with estimates of 286 (0.27) and 24 (0.77),

respectively (p<0.10). Loggerheads were sighted throughout the EPA slope with most sightings

near the 100 m isobath.

Oceanic Northern Gulf of Mexico. Ship Surveys - The combined effort from the spring ship

surveys of this area was 8,596 km. Nineteen cetacean species were identified. Pantropical

spotted dolphins were the most abundant species with an estimate of 46,625 (0.24) animals

followed by 11,251(0.66) spinner dolphins and 10,093 (0.40) clymene dolphins Estimates for

bottlenose dolphins, striped dolphins, melon-headed whales, Atlantic spotted dolphins, Risso's

dolphins, and short-finned pilot whales ranged from 5,618 to 1,471. Abundances of all other

species were less than 900. Cetaceans were sighted throughout the study area, but fewer were

sighted in the western Gulf. The abundance estimates of common species were very similar to

those reported by Hansen et al. (1995).

GulfCet I Study Area, Ship Surveys - The combined effort from spring ship surveys of this area

was 3,596 km Fourteen cetacean species were sighted. Pantropical spotted dolphins were the

most abundant species (6,141; CV = 0.37) followed by clymene dolphins (6,557; 0.70), shortfinned pilot whales (2,253; 0.58) and bottlenose dolphins (2,158; 0.76). Estimates for striped

dolphins, Risso's dolphins, and melon-headed whales ranged from 1,000 to 2,000. The

abundances of all other species were less than 1,000. The abundance estimates for commonly

sighted species were generally similar to those reported by Hansen et al. (1996).

13
Overview of Cetacean Distribution

Cetaceans occur throughout the northern Gulf, but each species' distribution appears to be

affected by water depth and/or geographic region. The continental shelf and shelf-edge region

are inhabited almost exclusively by bottlenose dolphins and Atlantic spotted dolphins, and in

oceanic waters, these species do not range beyond the upper continental slope. However, during

GulfCet II, compared to the rest of the northern Gulf, bottlenose dolphins were more widely

distributed on the continental slope in the northeastern Gulf. The oceanic cetacean community in

the northern Gulf is composed of at least 17 species that usually inhabit deep tropical waters.

With few exceptions, Bryde's whales have been found along a narrow corridor near the 100 m

isobath in the northeastern Gulf. Spinner dolphins primarily inhabit the north-central and

northeastern Gulf. Short-finned pilot whales and melon-headed whales have been sighted almost

exclusively in the north-central and northwestern Gulf. Pantropical spotted dolphins and striped

dolphins occur throughout the northern Gulf, but sightings of both species have been rare in the extreme northwestern Gulf. Killer whales range throughout the northern Gulf, but most

sightings occurred in a broad, but distinct, region just southwest of the Mississippi River delta.

Pygmy/dwarf sperm whales have been found throughout the northern Gulf. Sperm whales also

range throughout the northern Gulf, but there has usually been an aggregation of sightings along

the 1,000 m isobath near the Mississippi River delta. Sperm whales were not sighted in the

northwestern Gulf during GulfCet II. Risso's dolphins concentrate in areas along the upper

continental slope, but sightings occur throughout the northern Gulf. False killer whales, pygmy killer whales, and Fraser's dolphins are uncommon but widely distributed. Mesoplodon spp.

and Cuvier's beaked whales are widely distributed in deep water (i.e., usually >1,000 m). In

previous studies, nearly all sightings of rough-toothed dolphins and clymene dolphins were west

of the Mississippi River delta. However, during GulfCet II, all ofthe rough-toothed dolphin

groups were sighted east of the delta, and clymene dolphins were sighted five times in the

northeastern Gulf.

Most of the cetacean species that are routinely sighted in the northern Gulf of Mexico apparently

occur there throughout the year. Including the results of this study, there are sighting records

from three or more seasons of at least 16 cetacean species. The seasonal abundance of several

species (e.g., dwarf/pygmy sperm whale, Risso's dolphin, pantropical spotted dolphin) may vary

in continental slope waters at least regionally; however, the season of a species' maximum or

minimum abundance is not completely consistent among studies.

Acoustic Surveys of Cetaceans

The primary purpose of the acoustic surveys was to describe the distribution and habitat

association of cetaceans in the northeastern Gulf of Mexico based on speciesspecific

vocalizations detected by a towed hydrophone array. In addition, these surveys recorded

man-made noise that could impact cetaceans. This information might prove useful in the

management of future oil and gas development in the Gulf.

Two acoustic surveys were conducted in the EPA (Figure 2 and Table 2) during late summer

1996 (5,228 km of effort) and mid-summer 1997 (2,784 km of effort) as part of the GulfCet II

program. Sperm whales were the most commonly identified cetacean during the late summer

14
cruise, while pantropical spotted dolphins were the most commonly detected species during the

mid-summer cruise. Recordings were made for sperm whales, pantropical spotted dolphins,

clymene dolphins, spinner dolphins, striped dolphins, Atlantic spotted dolphins, false killer

whales, bottlenose dolphins, rough-toothed dolphins and Fraser's dolphins.

The distribution of deep-water cetaceans appeared to be influenced by a cyclone and anticyclone

pair in the northeastern Gulf. Sperm whales in the northeastern Gulf were more closely

associated with the cyclone and the mouth of the Mississippi River (MOM) and less with the

confluence zones than some of the pelagic dolphin species. Almost half of the dolphin contacts

in 1996 were in shallow water north of the influence of the cyclone and anticyclone. Pelagic

dolphin contacts were recorded in the confluence zone. In 1997, dolphins appeared to have three

association patterns relative to hydrographic features. Some contacts appeared to be influenced

by the entrainment of Mississippi River outflow as it was transported seaward by the confluence

zone, while others occurred in the cyclone the strong western current produced by the

geostrophic flow. There were only two dolphins and a single sperm whale contact inside or near

the northern periphery of the anticyclone. This distribution pattern suggests that anticyclones are

not preferred areas for cetaceans in the Gulf of Mexico.

The whistles of nine dolphin species were characterized. There were species-specific patterns to

whistle usage and acoustic structure. Based on these patterns, four unknown contacts were

identified as coming from a pantropical spotted dolphin, Atlantic spotted dolphin, roughtoothed

dolphin and false killer whale.

A diversity of anthropogenic signals was recorded during nearly 17,000 km of acoustic effort

during GulfCet I and II. Many of these were low frequency seismic exploration signals, but

higher frequency signals were also recorded. Bryde's and sperm whales can probably hear these

signals. Cetaceans were exposed to seismic noise, particularly off the MOM and in the eastern

Gulf. Seismic exploration signals were detected during 21% of recordings, ranging from a low

of 10% during the earlier GulfCet I project (encompassing waters from 100-2000 m deep west of

87°30'W) to more than half during the last GulfCet II cruise (encompassing waters from

100-2000 m deep between 84°W and 89°W). There was no significant difference in the cetacean

sighting frequency for low, medium, and high noise levels in different hydrographic features.

Cetacean Habitat

An objective of the GulfCet II program was to characterize cetacean habitat in the eastern Gulf

of Mexico (Figure 2). Correlation of environmental features with sighting data may improve our

understanding of cetacean ecology and indicate which, if any, physical and biological

oceanographic variables influence cetacean distribution. During two of the four GulfCet II

cruises, we conducted visual cetacean surveys and simultaneously collected data on the marine

environment and zooplankton biomass. Cetacean-habitat associations were statistically analyzed

for six physical and biological oceanographic variables. In addition, we retrospectively analyzed

satellite remote sensing data for sea surface height (SSH) anomaly and shipboard cetacean

sightings for the GulfCet I study area (Figure 1). These data were combined with the GulfCet II

data to examine the relationship between cetacean distribution and hydrographic features for the

entire oceanic northern Gulf (Figure 3).

15
Cetaceans in general were concentrated along the continental slope in areas of cyclonic

circulation where chlorophyll was elevated. They were less likely to occur over water deeper

than 2,000 m and in anticyclones. Sperm whales tended to occur along the lower slope and, in

some areas, in cyclonic eddies with elevated predicted mean biomass (PMB) of zooplankton and

micronekton in the depth range of 10-50 m. Squid-eaters (dwarf and pygmy sperm whales, false

killer whales, melon-headed whales, pilot whales, pygmy killer whales, Risso's dolphins, roughtoothed dolphins and all members of the Family Zipbiidae) occurred more frequently along the

upper slope in areas outside of anticyclones. Oceanic stenellids (oceanic dolphins from the

genus Stenella including clymene dolphins, pantropical spotted dolphins, spinner dolphins and

striped dolphins) occurred more often over the lower slope and deepwater regions in areas of

cyclonic or confluence circulation. Finally, bottlenose dolphins and Atlantic spotted dolphins

were seen most frequently on the continental shelf or along the upper slope, but outside of

deepwater hydrographic features such as cyclones and anticyclones.

In the north-central Gulf, an additional factor affecting cetacean distribution may be the narrow

continental shelf south of the Mississippi River delta. Low salinity, nutrient-rich water may

occur over the continental slope near the MOM or be entrained within the confluence of a

cyclone-anticyclone eddy pair and transported beyond the continental slope. This creates a deepwater environment with locally enhanced primary and secondary productivity and may explain

the presence of a resident population of endangered sperm whales within 50 km of the

Mississippi River delta.

In summary, cetaceans in the northeastern and oceanic northern Gulf of Mexico were

concentrated along the continental slope in or near cyclones. These eddies are mesoscale

features with locally concentrated zooplankton and micronekton stocks that appear to develop in

response to increased nutrient-rich water and primary production in the mixed layer. The

exceptions were bottlenose dolphins, Atlantic spotted dolphins and possibly Bryde's whale that

typically occur on the continental shelf or along the shelf break outside of major influences of

eddies. Low salinity, nutrient-rich water from the Mississippi River, which may also contribute

to enhanced primary and secondary productivity in the north-central Gulf, may explain the

presence of a resident population of endangered sperm whales south of the delta. However,

since cyclones in the northern Gulf are dynamic, cetacean distribution will undoubtedly change

in response to the movement of prey associated with these hydrographic features.

The Special Case of Sperm Whales: Behavior and Site Fidelity

The GulfCet II program did not concentrate on behavioral observations of marine mammals.

However, an attempt was made to gather behavioral and other data on sperm whales, due to their

endangered status. Therefore, sperm whales were targeted at limited times when sufficient hours

were available after the major goals of gathering hydrographic and census data had been

obtained. These times were 20-28 August 1994, and again during two half-days on 20 and 28

October 1996. In addition, a non-GulfCet sperm whale focal study occurred from July-August

1995, from an oil production platform near the Mississippi Canyon in the north-central Gulf.

The goal of this latter study was to attach "Crittercam" (Marshall 1998) video/hydrophone

16
systems to whales and thereby record underwater vocalizations during dives. All focal sperm

whale work occurred over or near the Mississippi Canyon.

During focal observation sessions, the general behavior of sperm whales (rafting, travel, social)

was described through 25x pedestal-mounted and hand-held binoculars, within two kilometers of

the research vessel. Group sizes, orientations, lengths of surfacings, number and spacings of

respirations, and types of dives (fluke-up and slip-under) were described. In addition, vocal

repertoire arid click sequences, or coda patterning, were recorded when possible.

Sperm whales were observed at close range by a small inflatable boat when weather and logistics

allowed. As a priority, photographs of naturally varying fluke edge patterns were taken for

photoidentification of individuals, using both still photography and videography. Size

measurements were made by photogranimetry on five whales when an accurate distancemeasuring device, coupled with known focal length of still photo lens, was available.

Sperm whales tended to concentrate between the edges of cyclonic and anticyclonic eddies.

Group sizes were generally two-to-three individuals, and did not change significantly by hour of

day. As many as 12 sperm whales aggregated during an apparent agonistic interaction with pilot

whales on 24 August 1994. It is likely that sperm whales sighted together tend to be subgroupings of larger, probably acoustically-interacting, pods.

A total of 37 sperm whales were individually identified during 1994 and 1996, with four

resightings on multiple days within a year and four others resighted inter-annually. Distance

between resightings ranged from 2.4-9.9 km on the same day; 17.3-24.3 kin between days within

one season; and 36.6-46.2 km between years. These findings indicate remarkable small-range

site fidelity for at least some sperm whales of this population. Body sizes determined from

photogranimetry ranged from 6.6-10.4 m (n=5), and fell within the known sizes of adult females

and immature young of either sex. No large, adult males were sighted in this area.

Rafting was the most common behavior at the surface and accounted for 57.7% of behavior

types. Socializing occurred at low levels and sporadically throughout the day. Orientations of

whales tended to be away from the survey vessel when whales were first sighted, indicating that

they may have reacted to the survey vessel at up to several kilometers. Fluke-up and slip-under

dives appeared to alternate in prevalence by time of day, with more fluke-up dives in morning

and afternoon, but more slip-under dives from 1200 to 1300 hours. Data on this point are

limited, however, and the significance of dive types and diel occurrence has not been ftilly

explored. It is surmised, but not proved, that fluke-out dives relate to steep and deep dives,

presumably for feeding. Mean blow intervals were shorter before fluke-out than slip-under

dives, indicating a faster respiration pattern, possibly related to hyperventilation prior to the

hypothesized steep and deep feeding dives.

Coda patterns of individual sperm whales were recorded during attachment of the "Crittercam"

to three whales; the longest attachment duration was nine minutes. Five distinct coda types were

recorded from about six whales during the first two sessions. Two distinct codas (a four-click

and an eight-click pattern) were recorded from two whales that dove to about 600 m during the 9

minute session. This final session indicated communication between the two whales.

17
Focal sperm whale studies in the Gulf of Mexico have just begun during the GulfCet and

ancillary cruises, and much more behavioral and ecological information needs to be gathered. However, the present "snapshots" of behavior ofendangered sperm whales indicate diel patterns of dive types, surface activity, and respiration patterns. Female-based groups, as has been found

elsewhere, appear to make up the society in and near the Mississippi Canyon, with large males

not yet documented. It is not known whether presumed female societies leave the area to mate,

or whether males come in sporadically. The intra- and inter-year site fidelity of at least some

photoidentified sperm whales suggests that the Mississippi Canyon is important habitat for sperm

whales of the northern Gulf. The affiliation with the edges of cyclonic and anticyclonic eddies

suggests some relationship to distribution and abundance ofprey.

Seabird Ecology

As part of the GulfCet II program, three seabird surveys occurred during cruises conducted in the

northern Gulf of Mexico. From 17 April to 9 June 1996, surveys were conducted from the

NOAA ship Oregon II. The northern slope and oceanic Gulf, and northeast Gulf shelf and slope waters were surveyed during the spring cruise (Figure 3). From 10 to 29 October 1996 and 5 to

21 August 1997, surveys were conducted from the R/V Gyre. The October (late summer) and

August (mid-summer) cruises covered the central pelagic and northeastern continental shelf and

slope regions of the Gulf (Figure 2). Seabird observations on the Oregon II (spring cruise) were

made as time and observer interest allowed during marine mammal observations. Observations

on the IVY Gyre were made with a three- person crew dedicated to counting seabirds.

Seabird groups and species present in the Gulf of Mexico varied by season. The spring cruise data suggest that terns, storm-petrels and gulls were common in the Gulf during May and June.

Jaegers and shearwaters were also present but in lower numbers. Tropicbirds, sulids and

frigatebirds were rarely seen in the Gulf during the spring. The species composition of the late

summer cruise was different from that of the spring cruise, as October reflects a pattern of

migration and winter distribution of seabirds in the Gulf. Two of the three most commonly

identified species (laughing gull and royal tern) were year-round residents of the Gulf. Pomarine

jaegers, a Gulf winter migrant, were the third most commonly identified bird. The mid-summer

cruise sightings included a large number of species. Black terns, the most abundant species

during the mid-summer cruise, were summer migrant pelagic species. The four next most

abundant species were: band-rumped storm-petrels (summer migrant pelagic), magnificent

frigatebirds (permanent residents), Audubon's shearwaters (summer migrant pelagic) and sooty

terns (summer residents).

In terms of hydrographic environments, the cyclone had the greatest species diversity of the

hydrographic enviromnents. Additionally, the confluence and Loop Current eddy during midsummer had a greater species diversity than the continental shelf. We found species-specific

habitat relationships with hydrographic environments for several species. Pomarine jaegers were

more likely to be present in the MOM during late sunmier. Audubon's shearwaters during midsummer were more likely to be encountered inside the cyclone, while band-rumped storm-petrels

were more likely present in the other margin areas. Black terns, also during mid-summer, were

encountered more frequently in the MOM. An interesting result for the mid-summer cruise was

18
that while the MOM was higher overall in chlorophyll concentration, many pelagic species were

not seen at all inside transects in the MOM (Audubon's shearwater, band-rumped storm-petrel,

bridled tern and sooty tern).

In terms of specific habitat variables, indicators of plankton standing stock (measured by surface

chlorophyll and predicted mean biomass {PMB] of zooplankton and micronekton integrated from

10-50 m depth) best predicted (or was tied with another model as best model) seabird presence

for five of the seven species analyzed. Sea surface properties of temperature and salinity best

predicted presence for black tern, sooty tern, and laughing gull (tied with plankton standing

stock). Sea surface height and bathymetry explained pomarine jaeger and Audubon's shearwater

presence, respectively. Sea surface salinity and temperature best predicted the presence of black

and sooty terns.

Laughing gull presence in October was predicted by two competing sets of habitat variables:

plankton standing stock and sea surface properties. Laughing gulls were predicted in transects of

increased PMB and increased concentrations of chlorophyll by the plankton standing stock

model. The sea surface properties model predicted laughing gulls in intermediate ranges of

temperature.

In October, pomarine jaegers were predicted to be encountered in transects with higher

geostrophic flow arid intermediate sea surface height ranges. This suggests that pomarine jaegers

may have been attracted to regions such as the confluence or the edge of the Loop Current eddy.

However, in the analysis considering species presence and absence in the hydrographic

environments, pornarine jaegers were more likely encountered in the MOM. This suggests that

pomarine j aegers may not be attracted to one particular environment during October.

Surface chlorophyll and PMB best predicted Audubon's shearwater and band-rumped stormpetrel presence in August. Both species were predicted to be present at lower chlorophyll

concentrations (generally less than 0.2 mg/rn3). This finding is consistent with the observation

that neither species was present in transects in the MOM, which is where the majority of the high

chlorophyll transects occurred.

CONCLUSIONS AND RECOMMENDATIONS

The Gulf of Mexico is a semi-enclosed, intercontinental sea with a total area of about 1.5 million

square kilometers. As a large marine ecosystem, it has a unique bathymetry, hydrography and

productivity. Cetaceans, sea turtles and seabirds are upper trophic level predators that play an

important role in the pelagic marine ecosystem of the Gulf of Mexico. These are highly valued

taxa, protected by national laws and international agreements, and knowledge of their

distribution, abundance and ecology is vital to their protection. GulfCet II was planned to help

resolve issues concerning the potential impacts of various oil and gas activities on cetaceans, sea

turtles and seabirds that inhabit the northern and eastern regions of the Gulf of Mexico,

emphasizing the continental slope where water depths range from 100 to 2,000 m.

An integrated methodology was used that included visual surveys from ships and aircraft, and

acoustic recordings and hydrographic collections from ships. Near real-time sea surface

19
altimetry from the TOPEX/POSIEIDON and ERS satellites was used during ship surveys to

determine the location of hychographic features (e.g., cyclones, anticyclones and confluence

zones). Archival satellite sea surface altimetry data were used to retrospectively determine the

location of hydrographic features for analysis with cetacean sightings collected during GulfCet I.

We measured zooplankton and micronekton biomass derived from both net and acoustic

sampling to indicate the amount of potential food available for higher trophic level foraging by

cetaceans and seabirds.

Cetaceans

Nineteen cetacean species were identified in the oceanic northern Gulf of Mexico (398,960 km2,

Figure 3) during GulfCet II surveys. Total abundance estimates ranged from 86,705 (based on

shipboard surveys) to 94,182 (based on highest estimate for each species from either shipboard

or aerial surveys) animals (Table 3). Cetaceans were sighted throughout the study area, but

fewer were sighted in the western Gulf. There are now sighting records during three or more

seasons for at least 16 cetacean species. The seasonal abundance of several species (e.g.,

dwarf/pygmy sperm whale, Risso's dolphin, pantropical spotted dolphin) may vary regionally in

continental slope waters.

Seventeen cetacean species were sighted in the Minerals Management Service's Eastern

Planning Area (EPA, 70,470 km2, Figure 3). The abundance estimate based on aerial surveys

(which were more extensive than the ship surveys in the EPA) was 38,184 total animals. In

general, cetaceans were found throughout the EPA each season. The most abundant species

were pantropical spotted dolphins (13,649) and spinner dolphins (8,670). Other species with

abundance estimates over 1,000 based on aerial surveys were bottlenose dolphins, Atlantic

spotted dolphins, Risso's dolphins, striped dolphins and clymene dolphins.

Cetaceans in the northeastern and oceanic northern Gulf of Mexico were concentrated along the

continental slope in or near cyclones and confluence zones. Cyclonic eddies are mesoscale

features with locally concentrated zooplankton and micronekton stocks that appear to develop in

response to increased nutrient-rich water and primary production in the mixed layer. In the

north-central Gulf, an additional factor affecting cetacean distribution may be the narrow

continental shelf south of the Mississippi River delta. Low salinity, nutrient-rich water may

occur over the continental slope near the MOM or be entrained within the confluence of a

cyclone-anticyclone eddy pair and transported beyond the continental slope. This creates a deepwater environment with locally enhanced primary and secondary productivity arid may explain

the presence of a resident, breeding population of endangered sperm whales within 50 km of the

Mississippi River delta. We suggest that this area may be essential habitat for sperm whales in

the northern Gulf. Overall, the results suggest that the amount of potential prey for cetaceans

(and seabirds) may be consistently greater in the cyclone, confluence areas, and south of the

MOM, making them preferential areas for foraging. Since cyclones in the northern Gulf are

dynamic and usually associated with westward moving cyclone-anticyclone pairs, cetacean

distribution will be dynamic. However, with near real-time satellite remote sensing of sea

surface altimetry, these features can be tracked and used to predict where pelagic cetaceans in

general may be concentrated. The exceptions are bottlenose dolphins, Atlantic spofted dolphins

20
Table 3. Annual cetacean abundance in the oceanic northern Gulf of Mexico estimated from

GulfCet II visual survey data.

21

Species Abundance

Pantropical spotted dolphin 46,625

Spinner dolphin 11,251

Clymene dolphin 10,093

Bottlenose dolphin 5,618

Striped dolphin 4,858

Melon-headed whale 3,965

Atlantic spotted dolphin 3,213

Risso's dolphin 3,040

Short-finned pilot whale 1,471

Rough-toothed dolphin 852

False killer whale 817

Dwarf/pygmy sperm whale 733

Sperm whale 530

Pygmy killer whale 518

Killer whale 277

Cuvier's beaked whale 159

Fraser's dolphin 127

Bryde's whale 35

Total 94,182
and possibly Bryde's whales that typically occur on the continental shelf or along the shelf break

outside of major influences of eddies.

Although cetaceans were commonly observed throughout the GulfCet study area during all four

seasons, we could not determine whether animals were in transit or resident in the study area for

extended periods. It is possible that the oceanic northern Gulf encompasses only a portion of the

home range for many of the species observed. Without additional information on daily

movement patterns and feeding behavior, significant uncertainties remain in our understanding

of cetacean association with mesoscale hydrographic features. The seasonal movements of

cetaceans may be affected by reproductive and migratory behavior, although we currently have

little information on the behavior of pelagic species. The exception is sperm whales south of the

MOM, which appear to reside along the lower slope throughout the year. We suggest that this

area may be essential habitat for sperm whales in the northern Gulf, although additional

information on population structure, seasonal movements and behavior is needed.

To obtain a better understanding of the seasonal and annual distribution, abundance and habitatassociations of cetaceans, a survey of the entire Gulf with simultaneous satellite and

conventional radio tracking and photo-identification of the predominant species (e.g., pantropical

dolphins, sperm whales) is needed. Skin biopsies and skin swabbing (Harlin et al. 1999) for

genetic analysis of population structure and blubber biopsies for assessing diet (based on fatty

acid profiles that can be used to identify prey) should be taken. In addition to tracking the

movements of cetaceans at sea, animal-borne satellite telemeters can record information on

diving behavior. When combined with dietary information from blubber fatty acid profiles,

diving behavior can provide new and much needed information on foraging areas, prey species

and resource partitioning among cetaceans (Evans 1971, Tanaka 1987, Mate 1989, Merrick et al.

1994, Davis et al. 1998). We believe that the diet of many cetaceans found in the Gulf is

dominated by cephalopods and mesopelagic fishes associated with the vertically migrating

acoustic deep scattering layer (Perrin et al. 1973, Clarke 1996). However, there is little direct

dietary information for pelagic cetaceans in the Gulf. Future studies should increase acoustic

and net sampling of zooplankton and micronekton in different hydrographic features so that we

can develop stronger statistical correlations between cetacean distribution and their potential

prey. Behavioral data are also needed to determine whether animals use certain areas for specific

activities, such as social/sexual behavior, foraging, resting, or transiting.

Sea Turtles

GulfCet II aerial surveys provided the first assessment of sea turtle abundance and distribution

over a large area of the oceanic northeastern Gulf of Mexico. Three sea turtle species occurred

in the EPA study area: loggerhead, Kemp's ridley, and leatherback sea turtles. The leatherback

and Kemp's ridley sea turtles are listed as endangered, and loggerhead sea turtles are listed as

threatened. The overall density of loggerhead sea turtles in the EPA shelf was 20 times that of

the EPA slope. The majority of loggerheads in the EPA slope were sighted during winter.

While many winter sightings were near the 100 m isobath, there were sightings of loggerheads

over very deep waters (i.e., >1000 m). It is not clear why adult loggerheads would occur in

oceanic waters unless they were traveling between foraging sites. Leatherbacks were sighted

throughout the EPA slope and were about 12 times more abundant in winter than summer. The

22
nearly disjunct summer arid winter distributions of leatherbacks indicates that specific areas may

be important to this species either seasonally or for short periods of time.

Seabirds

Seabird species present in the Gulf of Mexico varied by season. The species composition of the

sightings during late summer reflected a pattern of migration and transition to a winter

distribution. Two of the three most commonly identified species (laughing gull and royal tern) in

late summer are considered to be year-round residents in the Gulf. Pomarine jaegers, a wintering

marine species in the Gulf, were the third most commonly identified species. During midsummer, the black tern was the most abundant species, followed by band-rumped storm-petrels

(summer migrant pelagic), frigatebirds (permanent resident), Audubon's shearwaters (summer

migrant pelagic) and sooty terns (summer resident).

Cyclones had the greatest diversity of seabird species, although habitat use varied among

species. Pomarine jaegers were more likely to be present in the MOM area during late summer.

Audubon's shearwaters were more likely to be encountered inside a cyclone, while band-rumped

storm-petrels were more likely to be present in the areas other than cyclones, anticyclones or

confluence zones during mid-summer. Black terns were encountered more frequently in the

MOM area during mid-summer Generalized additive models incorporating indicators of

plankton standing stock (surface chlorophyll and predicted mean biomass of zooplankton and

micronekton) best predicted seabird presence for five of the seven species analyzed. Other

predictive models were: sea surface properties of temperature and salinity for black tern, sooty

tern, and laughing gull; sea surface height for pomarine jaeger; and bathymetry for Audubon's

shearwater. Seasonal surveys are needed to better assess community structure and seabirdhabitat associations.

Potential Effects of Oil and Gas Exploration and Production Activities

Eighty-three percent of the crude oil and 99% of the gas production in United States federal

waters occurs in the Gulf of Mexico, primarily along the Texas-Louisiana continental shelf and

slope (Cranswick and Regg 1997). By 2003, oil production in the Gulf is projected to increase

43%. Production from deepwater fields (depth >305 m) will account for about 59% of the daily

oil production and 27% of the daily gas production in the Gulf (Melancon and Baud 1999). In

addition to oil and gas exploration and production, this area has considerable commercial

shipping traffic that enters the northern Gulf ports. The long-term forecast for petroleum

transportation is for the total volume to increase into the next century. The cumulative impact of

these human activities on cetaceans in the northern Gulf cannot be predicted with certainty.

However, it can be anticipated that cetaceans along the continental slope will encounter

increasing oil and gas exploration and production activities. There are significant uncertainties

in our understanding of short and long-term effects of seismic and other loud industrial sounds

on the behavior and distribution of Gulf cetaceans. Against the background of growing oil and

gas exploration and development, continued research and monitoring are needed to assess the

potential impacts of these activities on pelagic cetaceans, sea turtles and seabirds in the Gulf of

Mexico.

23
Recommendations for Future Research

In light of the current expansion of oil and gas activities into deep-water regions of the Gulf,

more detailed information on the population biology, ecology, behavior and potential industryrelated impacts is needed for cetaceans, sea turtles and seabirds. The following are research

recommendations in approximate order of priority for the northern Gulf ofMexico:

Information is needed on the movements, diving behavior and site fidelity of endangered sperm

whales along the continental slope southeast of the Mississippi River delta. Satellite telemeters

should be attached to sperm whales to examine seasonal movements and diving behavior in

relation to mesoscale hydrographic features and estimates of potential prey abundance. Skin

biopsies and skin swabbing should be conducted to determine how closely related Gulf sperm

whales are to those from the adjacent Atlantic Ocean and Caribbean Sea. Blubber biopsies

should be taken to assess diet (based on fatty acid profiles that indicate dietary preferences). A

photo-identification study in this region should be conducted to assess the site fidelity of

individual whales.

Monitoring of cetacean and sea turtle distribution and abundance in the northern oceanic Gulf

during the NMFS ichthyoplankton surveys should continue. These surveys can be conducted at

relatively low cost because they occur simultaneously with ongoing cruises. Research on

cetacean habitat-associations using satellite remote sensing and shipboard measurements should

continue. Although progress was made during the Gulftet II study, much remains to be learned

about cetacean habitat in the western and southern Gulf. If shifts in a species' distribution occur, a better understanding of habitat will be needed.

A GulfCet III Program for the southern Gulf of Mexico (south of the U.S. Economic Exclusive

Zone including the Straits of Florida) should be initiated in cooperation with Mexico (this could

be accomplished through U.S. and Mexico university cooperative research programs already in

existence). Research objectives should be similar to those of GulfCet II (i.e., cetacean, sea turtle

and seabird seasonal distribution and abundance surveys and habitat studies). This would

complement studies of northern Gulf waters where oil and gas activities already occur.

We recommend controlled experiments on the effects of seismic sounds and other industrial

sounds on cetaceans. In addition, researchers should monitor the effects of seismic ship activity

on the behavior and distribution of cetaceans. Potential changes in sperm whale behavior,

movements, and vocalizations during geophysical exploration should be examined. This may

necessitate an experimental approach, with access to scaled-down or real-time industrial activity

under investigator control. Finally, a retrospective analysis should be conducted of GulfCet

cetacean distribution data relative to seismic vessel location, signal characteristics, and source

level. This research wwould require the cooperation of the geophysical survey industry.

Specifically, we would need information on when and where seismic survey activities occur and

the types of seismic signals produced. Trained observers might be placed directly on seismic

vessels to monitor cetacean behavior.

Research on genetic stock structure should be given added emphasis. The Marine Mammal

Protection Act mandates that stocks of cetaceans be protected. Stocks can be defined in a

24
number of ways, but genetic analyses can provide the clearest indication of divisions. Questions

of interest for each species include: (1) Are cetaceans in the Gulf of Mexico separate stocks

from the adjacent Atlantic/Caribbean? (2) Is there more than one Gulf of Mexico stock? (3) Are

there seasonal differences in occurrence patterns? Genetic analysis of skin samples collected

during vessel surveys both in the Gulf and adjacent waters could begin to answer these questions.

Of particular interest is Biyde's whale. Bryde's whales have displayed considerable local

variation world-wide, and analysis of skin biopsy samples could determine whether the northern

Gulf stock of Bryde's whales is restricted geographically and genetically isolated from animals

in the Atlantic Ocean.

Seasonal seabird surveys should continue to better assess community patterns and understand

how patterns change within a season in response to varied marine environments, such as the

presence of eddies. In the present study, we found that seabirds responded to different

conditions created by the outflow of the Mississippi River and hydrographically defined

mesoscale features.

Taxonomic analyses of the Multiple Opening/Closing Net and Environmental Sampling System

and Isaacs Kidd Midwater Trawl samples collected during this study could allow us to identify

indicator species for the hycirographic features and extend the usefulness of the Acoustic Doppler

Current Profiler data. In future studies, we should increase our sampling intensity in the major

hydrographic features so that we can develop stronger statistical correlations.

In conclusion, the continental slope in the northern Gulf of Mexico is an area that supports a

diverse cetacean community, but one whose density does not equal areas such as the continental

slope in the northeastern United States and the eastern tropical Pacific. We now have a better

understanding of the mesoscale features that influence cetacean distribution, and the use of

satellite remote sensing of sea surface altimetry is increasing our ability to predict where

cetaceans may be concentrated. Against the background of growing oil and gas exploration and

development, continued research and monitoring are needed to assess the potential impacts of

these activities on pelagic cetaceans, sea turtles and seabirds in the Gulf of Mexico. The GulfCet

program has demonstrated that any future monitoring programs would have to be long-term, with

an intensive sampling effort to detect significant changes in the density and distribution of

cetaceans.

25
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26
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27
: USGS

science fora changing world

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