Revised Outer Continental Shelf Lease Exploration Plan Chukchi Sea, Alaska 

Shell Gulf of Mexico Inc. May 2011 

Appendix C 

Application for National Marine Fisheries Service 

Incidental Harassment Authorization 
Revised Outer Continental Shelf Lease Exploration Plan Chukchi Sea, Alaska 

Shell Gulf of Mexico Inc. May 2011 

THIS PAGE 

INTENTIONALLY 

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Application for Incidental Harassment Authorization for the 

Non-Lethal Taking of Whales and Seals in Conjunction with 

Planned Exploration Drilling Program During 2012 

in the Chukchi Sea, Alaska 

Prepared by: 

Shell Gulf of Mexico Inc. 

3601 C Street, Suite 1000 

Anchorage, Alaska 99503 

 May 2011 

Amended June 2011 

Revised August 2011 

 

Application for Incidental Harassment Authorization for the Non-Lethal Taking of Whales and Seals 

in Conjunction with Planned Exploration Drilling Program During 2012 in the Chukchi Sea, Alaska 

Shell Gulf of Mexico Inc. i Revised August 2011 

Table of Contents 

Page 

Executive Summary ...................................................................................................................................... 1

1. A detailed description of the specific activity or class of activities that can be expected to 

result in incidental taking of marine mammals ................................................................................ 2

2. The dates and duration of such activity and the specific geographic region where it will 

occur ........................................................................................................................................... 14

3. Species and Numbers of Marine Mammals in Area ....................................................................... 15

4. Status, Distribution and Seasonal Distribution of Affected Species or Stocks of Marine 

Mammals ........................................................................................................................................ 16

4.1 Odontocetes ....................................................................................................................... 17

4.2 Mysticetes ......................................................................................................................... 20

4.3 Pinnipeds ........................................................................................................................... 25

5. Type of Incidental Take Authorization Requested ......................................................................... 28

6. Numbers of Marine Mammals That May be Taken ....................................................................... 28

7. The anticipated impact of the activity on the species or stock: ...................................................... 46

7.1 Noise Characteristics and Effects ...................................................................................... 46

7.2 Summary of Potential Effects of Exposure to Underwater Sounds from 

Exploration Drilling .......................................................................................................... 49

7.3 Summary of Potential Effects of Exposure to Underwater Sounds from Airguns ............ 57

8. The anticipated impact of the activity on the availability of the species or stocks of 

marine mammals for subsistence uses............................................................................................ 64

9. Anticipated impact on habitat ........................................................................................................ 66

9.1 Potential Impacts from Seafloor Disturbance (Mooring and MLC Construction) ............ 67

9.2 Potential Impacts on Habitat due to Sound Generation .................................................... 68

9.3 Potential Impacts on Habitat from Drilling Muds and Cuttings Waste............................. 73

9.4 Potential Impacts from Ice Management .......................................................................... 76

9.5 Potential Impacts from Discoverer Presence ..................................................................... 77

10. Anticipated impact of habitat loss or modification ........................................................................ 78

11. The availability and feasibility (economic and technological), methods, and manner of 

conducting such activity or means of effecting the least practicable impact upon affected 

species or stock, their habitat, and of their availability for subsistence uses, paying 

particular attention to rookeries, mating grounds, and areas of similar significance ..................... 78

12. Where the proposed activity would take place in or near a traditional Arctic subsistence 

hunting area and/or may affect the availability of a species or stock of marine mammal 

for Arctic subsistence uses, the applicant must submit a plan of cooperation or 

information that identifies what measures have been taken and/or will be taken to 

minimize any adverse effects on the availability of marine mammals for subsistence uses. 

A plan must include the following ................................................................................................. 78

12.1 A statement that the applicant has notified and provided the affected subsistence 

community with a draft plan of cooperation ..................................................................... 78

12.2 A schedule for meeting with the affected subsistence communities to discuss 

proposed activities and to resolve potential conflicts regarding any aspects of 

either the operation or the plan of cooperation.................................................................. 80
Application for Incidental Harassment Authorization for the Non-Lethal Taking of Whales and Seals 

in Conjunction with Planned Exploration Drilling Program During 2012 in the Chukchi Sea, Alaska 

Shell Gulf of Mexico Inc. ii Revised August 2011 

12.3 A description of what measures the applicant has taken and/or will take to ensure 

that proposed activities will not interfere with subsistence whaling or sealing; ............... 80

13. The suggested means of accomplishing the necessary monitoring and reporting that will 

result in increased knowledge of the species, the level of taking or impacts on the 

population of marine mammals that are expected to be present while conducting activities 

and suggested means of minimizing burdens by coordinating such reporting requirements 

with other schemes already applicable to persons conducting such activity. Monitoring 

plans should include a description of the survey techniques that would be used to 

determine the movement and activity of marine mammals near the activity site(s) 

including migration and other habitat uses, such as feeding .......................................................... 84

14. Suggested means of learning of, encouraging, and coordinating research opportunities, 

plans, and activities relating to reducing such incidental taking and evaluating its effects ........... 85

Cited Literature ........................................................................................................................................... 86

 

Figures 

Figure 1-1 Exploration Drilling Program Location Map ......................................................................... 4

Figure 1-2 Schematic of ZVSP .............................................................................................................. 10

Figure 1-3 Ice Management Vessels Configuration for the Discoverer ................................................. 12

Tables 

Table ES-1 Summary of Incidental Takes of Marine Mammals ............................................................... 2

Table 1-1 Shell Lease Blocks Covered in the Chukchi Sea Exploration Drilling Program 

Starting in 2012 ...................................................................................................................... 3

Table 1-2a Chukchi Sea Exploration Drilling Program – Proposed Vessel List ...................................... 6

Table 1-2b Chukchi Sea Exploration Drilling Program – Proposed Oil Spill Response Vessel 

List .......................................................................................................................................... 7

Table 1-2c Chukchi Sea 2012 Exploration Drilling Program – Proposed Aircraft List ........................... 8

Table 1-3 Sound Source (Airgun Array) Specifications for ZVSP Surveys in the Chukchi Sea 

in 2012 .................................................................................................................................. 10

Table 2-1 Drill Site Locations and Water Depths ................................................................................. 15

Table 4-1 The Habitat, Abundance, and Conservation Status of Marine Mammals Inhabiting 

the Area ................................................................................................................................ 16

Table 6-1 Expected Densities of Cetaceans and Seals in Areas of the Chukchi Sea, Alaska, 

for the Planned Summer (July–August) Period. Species listed under the U.S. ESA 

as Endangered are in italics. ................................................................................................. 33

Table 6-2 Expected Densities of Cetaceans and Seals in Areas of the Chukchi Sea, Alaska, 

for the Fall (September–October) Period. Species listed under the U.S. ESA as 

Endangered are in italics. ..................................................................................................... 35
Application for Incidental Harassment Authorization for the Non-Lethal Taking of Whales and Seals 

in Conjunction with Planned Exploration Drilling Program During 2012 in the Chukchi Sea, Alaska 

Shell Gulf of Mexico Inc. iii Revised August 2011 

Table 6-3 Sound Propagation Modeling Results of Exploration Drilling, Icebreaking, and 

ZVSP Activities at the Burger Prospect in the Chukchi Sea ................................................ 38

Table 6-4 The number of potential exposures of marine mammals to received sound levels in 

the water of ≥120 dB rms during planned exploration drilling activities in Summer 

(July–August) and Fall (September–October) in the Chukchi Sea, Alaska, 2012. .............. 42

Table 6-5 The number of potential exposures of marine mammals to received sound levels in 

the water of ≥120 dB rms during potential icebreaking activities in Summer (July–

August) and Fall (September–October) in the Chukchi Sea, Alaska, 2012. ........................ 43

Table 6-6 The number of potential exposures of marine mammals to received sound levels in 

the water of ≥160 dB rms during planned ZVSP activities in Summer (July–

August) and Fall (September–October) in the Chukchi Sea, Alaska, 2012. ........................ 44

Table 6-7 The total number of potential exposures of marine mammals to received sound 

levels in the water of ≥120 dB or ≥160 dB rms during proposed exploration 

drilling, icebreaking, and ZVSP activities in the Chukchi Sea, Alaska, 2012. ..................... 45

List of Attachments 

Attachment A Equipment Specifications for Discoverer 

Attachment B Ice Management Plan 

Attachment C Marine Mammal Monitoring and Mitigation Plan (4MP) 

Attachment D Plan of Cooperation (POC) Addendum 

Attachment E Analysis of the Probability of an “Unspecified Activity” and Its Impacts: Oil 

Spill 
Application for Incidental Harassment Authorization for the Non-Lethal Taking of Whales and Seals 

in Conjunction with Planned Exploration Drilling Program During 2012 in the Chukchi Sea, Alaska 

Shell Gulf of Mexico Inc. iv Revised August 2011 

List of Acronyms 

~ approximate 

° degrees Fahrenheit 

°C degrees Celsius 

4MP Marine Mammal Monitoring and Mitigation Plan 

μPa micropascal 

ADF&G Alaska Department of Fish and Game 

AEWC Alaska Eskimo Whaling Commission 

AHD acoustic harassment devices 

AISC Alaska Ice Sea Commission 

ASL above sea level 

ATOC Acoustic Thermometry of Ocean Climate 

bbl barrels 

BCB Bering-Chukchi-Beaufort stock (bowheads) 

BOEMRE U.S. Bureau of Ocean Energy Management, Regulation and 

Enforcement 

BOP blowout preventer 

BWASP Bowhead Whale Aerial Survey Program 

CAA Conflict Avoidance Agreement 

CFR Code of Federal Regulations 

CI Confidence Interval 

cm3 cubic centimeters 

CV Coefficient of Variation 

Com Center Communication and Call Center 

COMIDA Chukchi Sea Offshore Monitoring in Drilling Area 

dB decibel 

Discoverer Noble Discoverer 

DNV Det Norske Veritas 

EP Exploration Plan 

ESA Endangered Species Act 

Exploration Drilling program Chukchi Sea Exploration Drilling Program 

EWC Eskimo Walrus Commission 

Fennica Motor Vessel Fennica 

ft foot/feet 

hr hour(s) 

IHA Incidental Harassment Authorization 

IMP ice management plan 

in. inch(es) 

in.3

 cubic inch(es) 

Hz hertz 

IUCN International Union for the Conservation of Nature 

km kilometer(s) 

km2

 square kilometer(s) 

km/hr kilometers per hour 

LC50 lethal concentration 50 percent 

lb pound(s) 
Application for Incidental Harassment Authorization for the Non-Lethal Taking of Whales and Seals 

in Conjunction with Planned Exploration Drilling Program During 2012 in the Chukchi Sea, Alaska 

Shell Gulf of Mexico Inc. v Revised August 2011 

m meter(s) 

mi square miles 

mi statute mile(s) 

min minute(s) 

MLC mudline cellar 

MMPA Marine Mammal Protection Act 

MMO Marine Mammal Observer 

MMS Minerals Management Service 

MONM Marine Operations Noise Model (JASCO) 

M/V Motor Vessel 

NMFS National Marine Fisheries Service 

NMML National Marine Mammal Laboratory 

NPDES National Pollutant Discharge Elimination System 

NSB North Slope Borough 

NWAB Northwest Arctic Borough 

OCS Outer Continental Shelf 

ODPCP Oil Discharge Prevention and Contingency Plan 

OSR Oil Spill Response 

OST Oil Spill Tanker 

OSV offshore supply vessel 

POC Plan of Cooperation 

ppm parts per million 

psi pounds per square inch 

PTD Proposed Total Depth 

PTS Permanent Threshold Shift 

RL Received Level 

rms root mean square 

ROV remotely operated vehicle 

SAR Search and Rescue 

Shell Shell Gulf of Mexico Inc. 

SEL sound exposure level 

TAH total aromatic hydrocarbons 

TTS Temporary Threshold Shift 

TK Traditional Knowledge 

U.S. United States 

USFWS United States Fish and Wildlife Service 

VSI vertical seismic imager 

VSP vertical seismic profile 

ZVSP zero-offset vertical seismic profile 

 
Application for Incidental Harassment Authorization for the Non-Lethal Taking of Whales and Seals 

in Conjunction with Planned Exploration Drilling Program During 2012 in the Chukchi Sea, Alaska 

Shell Gulf of Mexico Inc. vi Revised August 2011 

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Application for Incidental Harassment Authorization for the Non-Lethal Taking of Whales and Seals 

in Conjunction with Planned Exploration Drilling Program During 2012 in the Chukchi Sea, Alaska 

Shell Gulf of Mexico Inc. 1 Revised August 2011 

Executive Summary 

As described herein, during the 2012 exploration drilling season, Shell Gulf of Mexico Inc. 

(Shell) plans to drill up to three exploration wells at three drill sites, and potentially a partial well 

at a fourth drill site in the Chukchi Sea on Outer Continental Shelf (OCS) leases acquired from 

the U.S. Bureau of Ocean Energy Management, Regulation and Enforcement (BOEMRE). Shell 

plans to use the Motor Vessel (M/V) Noble Discoverer (Discoverer) drillship to drill the planned 

wells. The Discoverer will be attended by a minimum of eight support vessels for the purposes 

of ice management, anchor handling, oil spill response (OSR), refueling, and resupply. 

The Discoverer is an industry-standard, ice-strengthened drillship similar to those routinely used 

in the Beaufort and Chukchi Seas since the 1980s. During exploration drilling and associated 

operations, the drillship will emit near continuous non-pulse sounds that ensonify only very 

limited areas of the ocean bottom and intervening water column. Within the timeframe of 

exploration drilling operations, Shell may also conduct a particular type of short-duration vertical 

seismic profile (VSP) survey known as a zero-offset VSP, or ZVSP in each well. The ZVSPs 

emit pulse sounds that also ensonify very limited areas of the ocean bottom and intervening 

water column for only approximately 10-14 hours. Typically, a single ZVSP survey will be 

performed when the well has reached PTD or final depth although, in some instances, a prior 

ZVSP will have been performed at a shallower depth. 

Since the early 1990s, the National Marine Fisheries Service (NMFS) has issued Incidental 

Harassment Authorizations (IHAs) to industry for the non-lethal taking of small numbers of 

marine mammals related to the non-pulse, continuous sounds generated by offshore exploration 

drilling and impulse sounds generated during seismic surveys. Shell requests an IHA pursuant to 

Section 101(a)(5)(D) of the Marine Mammal Protection Act (MMPA), 16 U.S.C. § 1371 (a) (5), 

to allow non-lethal takes of whales and seals incidental to the 2012 exploration drilling program, 

including ZVSP surveys, and related activities. 

Shell has calculated the estimated take of marine mammals from both the low-level continuous 

sound generated during exploration drilling operations, icebreaking, and impulse sound 

generated during a short-duration ZVSP survey likely to occur at or near the end of each well. It 

is assumed that any takes that might result from the proposed operations would be temporary and 

not be of biological significance to marine mammal populations. Any impacts from these sounds 

to whales and seals would be temporary and result in only short-term displacement of seals and 

whales from within ensonified zones produced by such sound sources. 

For example, an impact analysis of underwater sound generated by the drilling vessel and a very 

limited amount of icebreaking activities (see Summary Table ES-1) using the average density 

estimates determined that only 1 bowhead whale and 1 gray whale would be exposed to sounds 

≥120 decibels (dB) re 1 micropascal (μPa) root mean square (rms) equaling <1 percent of the 

population. An even smaller percentage of seal populations in the Chukchi Sea would be 

exposed to underwater sounds in excess of 120 dB re 1 μPa rms. Marginally more numbers of 

marine mammals would be exposed to sounds ≥160 decibels (dB) re 1 μPa for the ZVSP surveys 

(see Table 4-1 for marine mammal populations and Tables 6-4 and 6-7 for estimates of marine 

mammals exposed to sound from the exploration drilling operations, icebreaking, or ZVSPs 

associated with this exploration drilling program). 
Application for Incidental Harassment Authorization for the Non-Lethal Taking of Whales and Seals 

in Conjunction with Planned Exploration Drilling Program During 2012 in the Chukchi Sea, Alaska 

Shell Gulf of Mexico Inc. 2 Revised August 2011 

Table ES-1 Summary of Incidental Takes of Marine Mammals 

Drilling Vessel – Discoverer Icebreaking ZVSP 

1 Bowhead whale 19 Bowhead whales 5 Bowhead whales

0 Beluga whale 4 Beluga whales 1 Beluga whale 

1 Gray whale 14 Gray whales 6 Gray whales 

1 Bearded seals 12 Bearded seals 5 Bearded seals 

17 Ringed seals 343 Ringed seals 132 Ringed seals 

0 Spotted seals 7 Spotted seals 3 Spotted seals 

The small numbers of other whale species and seals that may occur in the Chukchi Sea are 

unlikely to be present around the planned exploration drilling activities. In regard to the 

subsistence harvest of bowhead whale in the Chukchi Sea, as a consequence of Shell’s planned 

mitigation measures, any effects on the bowhead whale as a subsistence resource also will be 

negligible. 

The organization of this request for IHA follows the organization of Chapter 50 Code of Federal 

Regulations (CFR) 216.104 (a). The remainder of this document is organized as to follow 50 

CFR §216.104 (a) (1)-(14). 

Shell relied on guidance in 50 CFR § 216.104, Submission of Requests, to prepare its request for 

this IHA: 

(a) In order for the NMFS to consider authorizing the taking by United States (U.S.) 

citizens of small numbers of marine mammals incidental to a specified activity (other 

than commercial fishing), or to make a finding that incidental take is unlikely to occur, a 

written request must be submitted to the Assistant Administrator. All requests must 

include the following information for their activity: 

1. A detailed description of the specific activity or class of activities that can be 

expected to result in incidental taking of marine mammals 

The specific activities that can be expected to result in incidental taking of marine mammals 

pursuant to the requested IHA are limited to Shell’s exploration drilling program and related 

activities, including ZVSP surveys. Shell has not included the potential impacts arising from a 

hypothetical oil spill in its consideration of “specified activity” in this IHA application for two 

reasons. 

First, oil spill impacts would not be “substantially similar” to the primarily acoustic impacts that 

can be expected to result from exploration drilling and the ZVSP surveys. In identifying the 

“specified activity” at issue in this IHA, Shell has followed the instruction of the U.S. Court of 

Appeals for the Ninth Circuit in Center for Biological Diversity v. Kempthorne, 588 F.3d 701 

(9th Cir. 2009). In that case, the court held that, to be consistent with the purpose of the Marine 

Mammal Protection Act (MMPA), “specified activities” are properly defined so that the 

“anticipated effects are substantially similar.” Id. at 709. The activities specified in this IHA 

application – exploration drilling, ZVSP surveys, and related activities – all have the potential to 
Application for Incidental Harassment Authorization for the Non-Lethal Taking of Whales and Seals 

in Conjunction with Planned Exploration Drilling Program During 2012 in the Chukchi Sea, Alaska 

Shell Gulf of Mexico Inc. 3 Revised August 2011 

cause primarily acoustic impacts and thus are substantially similar. In contrast the potential 

impacts from a spill would be substantially dissimilar from the primarily acoustic impacts for 

which this IHA is sought. 

Second, impacts from speculative events, such as an oil spill, are not properly included in an 

IHA application. The Ninth Circuit instructed that when determining whether an activity will 

have a “negligible impact” on the affected marine mammal population, the analysis should focus 

on “effects that are ‘reasonably expected’ and ‘reasonably likely,’ but not those effects that are 

speculative or uncertain.’” Id. at 710-11. Oil spills are highly unlikely events and are not 

reasonably expected to occur during the course of exploration drilling and ZVSP surveys (See

[Analysis of the Probability of an “Unspecified Activity” and Its Impacts: Oil Spill; Attachment 

E of this application). Thus, an analysis of whether the impacts resulting from the “specified 

activity” will be negligible should not include the impacts from a “speculative” oil spill. 

For these reasons, Shell believes that the MMPA and NMFS’s regulations implementing that 

statute instruct that Shell should not seek “authorization” for an action it does not intend to take, 

and, in fact, has expended substantial resources to prevent. Accordingly, the “specified 

activities” for which Shell seeks this IHA are restricted to exploration drilling, ZVSP surveys, 

and related activities.

Exploration Drilling 

Shell plans to conduct an exploration drilling program on BOEMRE Alaska OCS leases at drill 

sites greater than 64 miles (mi) [103 kilometers (km)] from the Chukchi Sea coast during the 

2012 exploration drilling season (Chukchi Sea Exploration Drilling Program, hereinafter, the

“exploration drilling program”) (Figure 1-1). 

The leases were acquired during the Chukchi Sea Oil and Gas Lease Sale 193 held in February 

2008. During 2012, the initial year of the exploration drilling program, Shell plans to drill up to 

three exploration wells at three drill sites, and potentially a partial well at a fourth drill site at the 

prospect known as Burger (Table 1-1). All wells are planned to be vertical. 

Table 1-1 Shell Lease Blocks Covered in the Chukchi Sea Exploration Drilling Program Starting in 2012 

Prospect Area Protraction Lease Block Shell Lease 

Burger Posey NR03-02 6764 OCS-Y-2280 

Burger Posey NR03-02 6714 OCS-Y-2267 

Burger Posey NR03-02 6912 OCS-Y-2321 

Burger Posey NR03-02 6812 OCS-Y-2294 

Burger Posey NR03-02 6762 OCS-Y-2278 

Burger Posey NR03-02 6915 OCS-Y-2324 
Application for Incidental Harassment Authorization for the Non-Lethal Taking of Whales and Seals 

in Conjunction with Planned Exploration Drilling Program During 2012 in the Chukchi Sea, Alaska Shell Gulf of Mexico Inc. 4 Revised August 2011 Figure 1-1 Exploration Drilling Program Location Map 
Application for Incidental Harassment Authorization for the Non-Lethal Taking of Whales and Seals 

in Conjunction with Planned Exploration Drilling Program During 2012 in the Chukchi Sea, Alaska 

Shell Gulf of Mexico Inc. 5 Revised August 2011 

The ice strengthened drillship Discoverer will be used to drill the wells. Specifications for the 

Discoverer are included in Attachment A. While on location at the drill sites, the Discoverer

will be affixed to the seafloor using eight 7-ton Stevpris anchors arranged in a radial array. The 

underwater fairleads prevent ice fouling of the anchor lines. Turret mooring allows orientation of 

vessel’s bow into the prevailing ice drift direction to present minimum hull exposure to drifting 

ice. The vessel is rotated around the turret by hydraulic jacks. Rotation can be augmented by the 

use of the fitted bow and stern thrusters. The hull has been reinforced for ice resistance. Icestrengthened sponsons have been retrofitted to the ship’s hull. 

The Discoverer is classed by Det Norske Veritas (DNV) as a Mobile Offshore Drilling Unit for 

worldwide service. It is a “1A1 Ship-Shaped Drilling Unit l” and is capable of performing 

exploration drilling operations offshore Alaska. The Discoverer has been issued with a DNV 

Appendix to Class stating: 

“the structural strength and material quality of the ‘Ice Belt’ formed by the sponsons below the 

8950mm A/B level, have been reviewed against the requirements for the DNV ICE-05 Additional 

Class Notation and found to meet those requirements (as contained in DNV Rules for 

Classification of Ships, Pt 5 Ch 1, July 2006) for a design temperature of -15 degrees C.” 

Vessels 

During this exploration drilling program, the Discoverer will be attended by a minimum of eight 

vessels that will be used for ice management, anchor handling, OSR, refueling, resupply, and 

servicing of the exploration drilling operations (Tables 1-2a and 1-2b). In Table 1-2b, the barges 

include an accompanying tow/tug vessel, and in one case potentially an anchor handler that 

together with the barge are counted as one vessel attending the Discoverer. 

The M/V Fennica (Fennica), or a similar vessel, will serve as the ice management vessel in 

support of the Discoverer. This vessel will enter and exit the Chukchi Sea with the Discoverer 

and will remain at a location approximately 25 mi (40 km) upwind and upcurrent of the drillship 

when not in use. Any ice management would be expected to occur at a distance of 3-12 mi (5-19 

km) upwind/upcurrent of the drillship. The M/V Tor Viking (Tor Viking) or a similar vessel will 

serve as the primary anchor handling vessel in support of the Discoverer. The vessel will enter 

and exit the Chukchi Sea with the Discoverer and will remain at a location approximately 25 mi 

(40 km) upwind and upcurrent of the drillship when not in use. Any ice management would be 

expected to occur within 0.6-6.0 mi (1.0-9.6 km) upwind from the Discoverer. 

The planned exploration drilling operations will require two oil spill vessels (OSVs) to resupply 

the Discoverer with exploration drilling materials and supplies from facilities in Dutch Harbor 

and fuel. The vessels may be vessels such as the Harvey Spirit, and the C-Leader, or similar 

offshore supply boats. 
Application for Incidental Harassment Authorization for the Non-Lethal Taking of Whales and Seals 

in Conjunction with Planned Exploration Drilling Program During 2012 in the Chukchi Sea, Alaska 

Shell Gulf of Mexico Inc. 6 Revised August 2011 

Table 1-2a Chukchi Sea Exploration Drilling Program – Proposed Vessel List 

Specification Ice Management Vessel 1 Anchor Handler 2 OSV 3 OSV 4

Length 

380 ft 

116 m 

275 ft 

83.8 m 

280 ft 

85.3 m 

280 ft 

85.3 m 

Width 

85 ft 

26 m 

59 ft 

18 m 

60 ft 

18 m 

60 ft 

18 m 

Draft 

27 ft 

8.2 m 

20 ft 

6.1 m 

15.9 ft 

4.8 m 

19 ft 

5.8 m 

Accommodations 82 berths 64 berths 37 berths 29 berths 

Maximum Speed 

16 knots 

30 km/hr 

16 knots 

30 km/hr 

13 knots 

24 km/hr 

13 knots 

24 km/hr 

Fuel Storage 

11,070 bbl 

1,760 m3 7,484 bbl 1,190 m3

6,233 bbl 

991 m3 7,217 bbl 1,147 m3

1

 Based on Fennica, or similar vessel 2

 Based on Tor Viking, or similar vessel 3

 Based on the Harvey Spirit, or similar vessel 4

 Based on C-Leader, or similar vessel 

Oil Spill Response Vessels 

The OSR vessels supporting the exploration drilling program include a dedicated OSR barge and 

an OSR vessel, both of which have associated smaller workboats, an oil spill tanker (OST), and a 

containment barge (Table 1-2b) . An OSR vessel such as the Nanuq will be staged in the vicinity 

of the drillship when the Discoverer is drilling in liquid hydrocarbon bearing zones to 

immediately respond to a spill and provide containment, recovery, and storage for the initial 

operational period following a spill event. The Nanuq or similar vessel will be paired with an 

OST such as the Mikhail Ulyanov and used to assist refueling the Discoverer and support 

vessels, if necessary. An OSR barge, such as the Klamath, or similar vessel and a tug, such as 

the Crowley Sea Robin, will be staged offshore in the vicinity of the drillship. Together with the 

OSR vessel, it will have sufficient containment, recovery, and storage capacity for the initial 

operational period in the event of a spill. It will carry a 47-ft (14-m) skimming vessel, three 34-ft 

(10-m) workboats, four mini-barges, and boom and duplex skimming units for nearshore 

recovery. An OST such as the Mikhail Ulyanov or similar vessel with a minimum liquid storage 

capacity of 513,000 bbl will be staged such that it would arrive at a recovery site, if needed, 

within 24 hours of departure from their staging location. The purpose of the OST would be to 

provide a place to store large volumes of recovered crude oil, emulsion, and free water in the 

unlikely event of a spill and OSR operations. 

An additional barge housing the oil spill containment system will be stationed offshore, where it 

can be mobilized to a drill site when needed. The barge will be supported by an Invader Class 

Tug and possibly an anchor handler. The tug tending the OSR containment system barge will 

either drift or motor under “slow-steam” movement with the barge. An anchor handler is 

included in this plan only as an additional tending option for the OSR containment system barge, 

if Shell deems it necessary in advance of the season to anchor the OSR containment system 

barge. Shell does not assume the OSR containment system barge will be anchored or that the 

anchor handler is necessary, but includes the option of anchoring the barge and it being also 

tended by an anchor handler in case that option is chosen. 
Application for Incidental Harassment Authorization for the Non-Lethal Taking of Whales and Seals 

in Conjunction with Planned Exploration Drilling Program During 2012 in the Chukchi Sea, Alaska 

Shell Gulf of Mexico Inc. 7 Revised August 2011 

Table 1-2b Chukchi Sea Exploration Drilling Program – Proposed Oil Spill Response Vessel List 

Specification OSR Vessel 1,2

OSR Barge 1

OST 1,4

Containment Barge 1,5

Barge 3 Tug 3 Barge Tug Anchor 

Handler

Length 

301 ft 

91.9 m 

350 ft 

106.7 m 

126 ft 

38.4 m 

853 ft 

260 m 

400 ft 

122 m 

136 ft 

36.5 m 

275 ft 

83.7 m 

Width 

60 ft 

18.3 m 

76 ft 

23.1 m 

34 ft 

10.4 m 

112 ft 

34 m 

100 ft 

30.5 m 

36 ft 

11.1 m 

59 ft 

18.0 m 

Fuel Storage 

6,867 bbl 

(1,092 m3) 

390 bbl 

(62 m3) 

1,786 bbl 

(284 m3) 

221,408 bbl 

(35,200 m3) -- 

3,690 bbl 

(587 m3) 

7,484 bbl 

(1190 m3) 

Liquid Storage 

12,690 bbl 

(2,017 m3) 

76,900 bbl 

(12,226 m3) -- 

543,000 bbl 

(86,328 m3) -- -- -- 

Accommodations 41 -- 6 25 -- 10 64 berths 

Maximum Speed 16 knots -- 5 knots 16 knots -- 10 knots 16 knots 

Workboats 

(3) 34 ft 

work boats 

(1) skim boat 

47 ft (14 m) 

(3) work boats 

34 ft (10 m) 

(4) mini-barges -- -- -- -- -- 1

 Or similar vessel 

2

 Based on the Nanuq 3

 Based on the barge Klamath and the tug Crowley Sea Robin 4

 Based on the Mikhail Ulyanov, the OST will have a minimum storage capacity of 513,000 bbl. 5

 Based on a standard deck barge, Crowley Invader class ocean going tug, and a Vidar, or Tor Viking-style anchor handler 

 
Application for Incidental Harassment Authorization for the Non-Lethal Taking of Whales and Seals 

in Conjunction with Planned Exploration Drilling Program During 2012 in the Chukchi Sea, Alaska 

Shell Gulf of Mexico Inc. 8 Revised August 2011 

Aircraft

Offshore operations will be serviced by helicopters operated out of onshore support base 

locations. The helicopters are not yet contracted. A Sikorsky S-92 or Eurocopter EC225 capable 

of transporting 10 to 12 persons will be used to transport crews between the onshore support base 

and the drillship. The helicopters will also be used to haul small amounts of food, materials, 

equipment, and waste between vessels and the shorebase. The helicopter will be housed at 

facilities at the Barrow airport. Shell will have a second helicopter for Search and Rescue 

(SAR). The SAR helicopter is expected to be a Sikorsky S-61, S-92, Eurocopter EC225, or 

similar model. This aircraft will stay grounded at the Barrow shorebase location except during 

training drills, emergencies, and other non-routine events. 

A fixed wing propeller or turboprop aircraft, such as Saab 340-B 30-seat, Beechcraft 1900, or 

deHavilland Dash8 will be used to routinely transport crews, materials, and equipment between 

the shorebase and hub airports such as Barrow or Fairbanks. A fixed wing aircraft, deHavilland 

Twin Otter (DHC-6) will be used for marine mammal observer (MMO) flights. 

Table 1-2c Chukchi Sea 2012 Exploration Drilling Program – Proposed Aircraft List 

Aircraft Flight Frequency 

Aircraft (or similar)

Sikorsky S-92 or Eurocopter EC225 - crew 

rotation 

Approximately 12 round trips per week between land and offshore 

vessels throughout the 2012 exploration drilling season 

Sikorsky S-61, S-92 or Eurocopter EC225 

helicopter – SAR 

Trips made only in emergency; training flights 

Saab 340-B or Beechcraft 1900 or deHavilland 

Dash8 (Only 1) – onshore crew/supply trips 

Infrequent, up to 4 trips per week from shorebase to hub airports in 

Barrow, Anchorage, or Fairbanks 

deHavilland Twin Otter (DHC-6) – Used for 

4MP 

Daily, beginning 5-7 days before drilling and ending 5-7 days after 

drilling ends 

The ice reinforced drillship Discoverer will move through the Bering Strait and into the Chukchi 

Sea on or about July 1, and then onto the Burger Prospect as soon as ice and weather conditions 

allow. Exploration drilling activities will be curtailed on or before 31 October, and the drillship 

and support vessels will exit the Chukchi Sea at the conclusion of the exploration drilling season. 

Vertical Seismic Profile 

Shell may conduct a geophysical survey referred to as a vertical seismic profile or ZVSP at each 

drill site where a well is drilled in 2012. During ZVSP surveys, an airgun array is deployed at a 

location near or adjacent to the drillship, while receivers are placed (temporarily anchored) in the 

wellbore. The sound source (airgun array) is fired repeatedly, and the reflected sonic waves are 

recorded by receivers (geophones) located in the wellbore. The geophones, typically a string of 

them, are then raised up to the next interval in the wellbore and the process is repeated until the 

entire wellbore has been surveyed. The purpose of the ZVSP is to gather geophysical 

information at various depths, which can then be used to tie-in or ground-truth geophysical 

information from the previous seismic surveys with geological data collected within the 

wellbore. 
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Shell will be conducting a particular form of VSP known as the ZVSP, in which the sound 

source is maintained at a constant location near the wellbore (Figure 1-2). A typical sound 

source that likely would be used by Shell in 2012 is the ITAGA eight-airgun array, which 

consists of four 150 cubic inches (in.3) (2,458 cubic centimeters [cm3]) airguns and four 40 in.3

(655 cm3) airguns. These airguns can be activated in any combination and Shell would utilize 

the minimum airgun volume required to obtain an acceptable signal. Current specifications of 

the array are provided in Table 1-3. The airgun array is depicted within its frame or sled, which 

is approximately 6 ft (2 m) x 5 ft (1.5 m) x 10 ft (3 m) (see photograph below). Typical receivers 

would consist of a Schlumberger wireline four level vertical seismic imager (VSI) tool, which 

has four receivers 50-ft (15-m) apart. 

Photograph of the ITAGA 8-airgun array in sled 
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Figure 1-2 Schematic of ZVSP 

 

Table 1-3 Sound Source (Airgun Array) Specifications for ZVSP Surveys in the Chukchi Sea in 2012 

Source 

Type 

No. Sources Maximum Total 

Chamber Size 

Pressure Source Depth Calibrated PeakPeak Vertical 

Amplitude 

Zero-Peak Sound 

Pressure Level 

SLB, 

ITAGA 

Sleeve 

Array 

8 airguns 

4 X 150 in.3

(2458 cm3

) 

4 X 40 in.3

 

(655 cm3

) 

760 in.3

12,454 cm3 2,000 psi 138 bar 

9.8 ft / 3.0 m 

16.4 ft / 5.0 m 

16 bar @1m 

23 bar @1m 

238 dB re1μPa @1m 

241 dB re1μPa @1m 

A ZVSP survey is normally conducted at each well after total depth is reached but may be 

conducted at a shallower depth. For each survey, Shell would deploy the sound source (airgun 

array) over the side of the Discoverer with a crane (sound source will be 50-200 ft (15-61 m) 

from the wellhead depending on crane location), to a depth of approximately 10-23 ft (3-7 m) 

below the water surface. The VSI, with its four receivers will be temporarily anchored in the 

wellbore at depth. The sound source will be pressured up to 2,000 pounds per square inch (psi) 

(138 bar), and activated 5-7 times at approximately 20-second intervals. The VSI will then be 

moved to the next interval of the wellbore and re-anchored, after which the airgun array will 

again be activated 5-7 times. This process will be repeated until the entire wellbore is surveyed 
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in this manner. The interval between anchor points for the VSI usually is between 200-300 ft 

(61-91 m). A normal ZVSP survey is conducted over a period of about 10-14 hours depending 

on the depth of the well and the number of anchoring points. 

Ice Management and Forecasting 

Shell recognizes the exploration drilling program is located in an area that is characterized by 

active sea ice movement, ice scouring, and storm surges. In anticipation of potential ice hazards 

that may be encountered, Shell will implement an IMP (see Attachment B) to ensure real-time 

ice and weather forecasting to identify conditions that might put operations at risk and modify its 

activities accordingly. The IMP also contains ice threat classification levels depending on the 

time available to suspend exploration drilling operations, secure the well and escape from 

advancing hazardous ice. Realtime ice and weather forecasting will be available to operations 

personnel for planning purposes and to alert the fleet of impending hazardous ice and weather 

conditions. Ice and weather forecasting is provided by Shell’s Ice and Weather Advisory Center 

(SIWAC). This center is continuously manned by experienced personnel who rely on a number 

of data sources for ice forecasting and tracking including: 

• Radarsat and Envisat data - satellites with Synthetic Aperture Radar providing allweather imagery of ice conditions with very high resolution; 

• Moderate Resolution Imaging Spectroradiometer - a satellite providing lower resolution 

visual and near infrared imagery; 

• Aerial reconnaissance - provided by specially deployed fixed wing or rotary wing aircraft 

for confirmation of ice conditions and position; 

• Reports from Ice Specialists on the ice management vessel and anchor handler and from 

the Ice Observer on the drillship; 

• Incidental ice data provided by commercial ships transiting the area; and 

• Information from the National Oceanic and Atmospheric Administration ice centers and 

the University of Colorado. 

Drift ice will be actively managed by ice management vessels, consisting of an ice management 

vessel and an anchor handling vessel. Ice management for safe operation of Shell’s planned 

exploration drilling program will occur far out in the OCS, remote from the vicinities of any 

routine marine vessel traffic in the Chukchi Sea, thereby resulting in no threat to public safety or 

services that occur near to shore. Shell vessels will also communicate movements and activities 

through the 2012 North Slope Communications Centers. Management of ice by ice management 

vessels will occur during an exploration drilling season predominated by open water and thus 

will not contribute to ice hazards, such as ridging, override, or pileup in an offshore or nearshore 

environment. 

The ice-management/anchor handling vessels would manage the ice by deflecting any ice floes 

that could affect the Discoverer when it is drilling and would also handle the Discoverer’s 
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anchors during connection to and separation from the seafloor. When managing ice, the Fennica

and Tor Viking will generally be operate a 40o arc up to 3.1 mi (4.9 km) upwind originating at 

the Discoverer (Figure 1-3). 

Figure 1-3 Ice Management Vessels Configuration for the Discoverer

The ice-management/anchor handling vessels would manage any ice floes upwind of the Discoverer by 

deflecting those that could affect the Discoverer when it is on location conducting exploration drilling 

operations. The ice-management/anchor handling vessels would also manage the Discoverer’s anchors 

during connection to and separation from the seafloor. The ice floe frequency and intensity are 

unpredictable and could range from no ice to ice densities that exceed ice-management capabilities, in 

which case exploration drilling operations would be stopped and the Discoverer disconnected from its 

anchors and moved off site. If ice is present, ice management activities may be necessary in early July 

and towards the end of operations in late October, but data regarding historic ice patterns in the area of 

operations indicate that it will not be required throughout the planned exploration drilling season. When 

ice is present at the drill site, ice disturbance will be limited to the minimum needed to allow exploration 

drilling to continue. First-year ice will be the type most likely to be encountered. The ice-management 

vessels will be tasked with managing the ice so that it will flow easily around and past the Discoverer 

without building up in front of it. This type of ice is managed by the ice-management vessel continually 

moving back and forth across the drift line, directly updrift of the Discoverer and making turns at both 

ends. During ice-management, the vessel’s propeller is rotating at approximately 15–20 percent of the 
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vessel’s propeller rotation capacity. Ice management occurs with slow movements of the vessel using 

lower power and therefore slower propeller rotation speed (i.e., lower cavitation), allowing for fewer 

repositions of the vessel, thereby reducing cavitation effects in the water. Occasionally, there may be 

multi-year ice ridges that would be managed at a much slower speed than that used to manage first-year 

ice. 

During Chukchi Sea exploration drilling operations, Shell does not plan to conduct any 

icebreaking activities; rather, Shell will deploy its support vessels to manage ice as described 

herein. As detailed in Shell’s IMP (see Attachment B), actual breaking of ice will occur only in 

the unlikely event that ice conditions in the immediate vicinity of operations create a safety 

hazard for the drilling vessel. In such a circumstance, operations personnel will follow the 

guidelines established in the IMP to evaluate ice conditions and make the formal designation of a 

hazardous, ice alert condition, which would trigger the procedures that govern any actual 

icebreaking operations. Historical data relative to ice conditions in the Chukchi Sea in the 

vicinity of Shell’s planned operations, and during the timeframe for those operations, establish 

that there is a very low probability (e.g., minimal) for the type of hazardous ice conditions that 

might necessitate icebreaking (e.g., records of the National Naval Ice Center archives). This 

probability could be greater at the shoulders of the exploration drilling season (early July or late 

October); therefore, for purposes of evaluating possible impacts of the planned activities, Shell 

has assumed limited icebreaking activities for a very limited period of time, and estimated 

incidental takes of marine mammals (see Section 6) from such activities. 

Planned Mitigation 

NMFS regulations, which require an operator to implement a Plan of Cooperation (POC) to 

mitigate the potential for conflicts between the proposed activity and traditional subsistence 

activities (50 CFR § 18.124(c)(4) and 50 CFR § 216.104(a)(12)). An initial POC was prepared 

and was submitted to NMFS (and BOEMRE) in May 2009 with an initial Chukchi Sea 

Exploration Plan (EP). For this IHA application and the revised Chukchi Sea EP submitted to 

BOEMRE in May 2011, Shell prepared a POC Addendum which updates the initial POC with 

information regarding proposed changes in the proposed exploration drilling program, and 

documentation of meetings undertaken to inform the stakeholders of the revised exploration 

drilling program. The POC Addendum (see Attachment D) builds upon the initial, previous 

POC. 

The Discoverer and all support vessels will operate in accordance with the provisions of the POC 

Addendum and presumed vessel operation mitigation measures included in past IHAs issued to 

Shell for arctic activities. Shell’s POC Addendum will mitigate effects of Shell’s planned 

exploration drilling program where activities would take place in or near a traditional Arctic 

subsistence hunting area and/or may affect the availability of a species or stock of marine 

mammal for Arctic subsistence uses. The initial POC and POC Addendum were prepared based 

upon Shell’s experience (recent and past) since the 1980s in the Alaska OCS and in consultation 

with affected Chukchi Sea communities and marine mammal commissions. During these 

meetings, Shell focused on lessons learned from prior years’ activities and presented mitigation 

measures for avoiding potential conflicts, which are outlined in the POC Addendum. Shell’s 

POC Addendum addresses the issues of vessel transit, drilling, aerial support, and associated 
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onsite vessel activities. The mitigation measures described in Section 12.3 are intended to 

minimize any adverse effects on the availability of marine mammals for subsistence uses. 

2. The dates and duration of such activity and the specific geographic region where it 

will occur 

Anticipated Duration of this Permit 

Shell anticipates that the IHA issued by NMFS for the planned Chukchi Sea exploration drilling 

program will be valid from the date of issuance through the conclusion of the 2012 exploration 

drilling season. 

Timing of Mobilization and Demobilization of the Discoverer 

Shell’s base plan is for the ice management vessel, the Fennica (or similar, primary ice 

management), the anchor handler M/V Tor Viking (or similar, secondary ice management), 

OSVs, and potentially some of the OSR vessels to accompany the Discoverer traveling north 

from Dutch Harbor through the Bering Strait, on or about 1 July 2012, then into the Chukchi Sea, 

before arriving on location approximately 4 July. Exploration drilling is expected to be 

conducted through 31 October 2012. At the end of the exploration drilling season, these support 

vessels, along with various other support vessels will accompany the Discoverer as it travels 

south out of the Chukchi Sea, through the Bering Strait to Dutch Harbor, Alaska. Subject to ice 

conditions, alternate exit routes may be considered. 

Exploration Drilling 

All three, and potentially a forth partial well, will be at Shell’s Burger Prospect (Figure 1) in the 

EP submitted to BOEMRE. Shell has identified a total of six Chukchi Sea EP lease blocks 

(Table 2-1 and Figure 1-1) on the Burger Prospect. All of the six drill sites listed on Table 2-1 

are located more than 64 mi (103 km) off the coast in the Chukchi Sea. During 2012, the 

Discoverer will be used to drill up to three exploration wells and potentially a fourth partial well 

on four of the six possible leases (Table 2-1). For this exploration drilling program, Shell will 

mobilize into the Chukchi Sea on or about July 1, and commence exploration drilling at the 

Burger Prospect as soon as ice, weather, and other conditions allow for safe exploration drilling 

operations. 

Activities associated with the Chukchi Sea exploration drilling program and analyzed herein 

include operation of the Discoverer, associated support vessels, crew change support and 

resupply. The Discoverer will remain at the location of the designated exploration drill sites 

except when mobilizing and demobilizing to and from the Chukchi Sea, transiting between drill 

sites, and temporarily moving off location if it is determined ice conditions require such a move 

to ensure the safety of personnel and/or the environment in accordance to Shell’s IMP. The 

anchor handler and OSR vessels will remain in close proximity to the drillship during 

exploration drilling operations. The ice management vessel will generally be working 

upwind/upcurrent of the drillship from 3-12 mi (5-19 km) away. Crew change/resupply vessels 

will transit to and from the drillship at the estimated frequencies shown in Table 1-2c. 
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Helicopter flight support will provide crew changes. Fixed-wing aircraft will transport crews to 

regional hub airports, and to support aerial surveys for the marine mammal monitoring program. 

Table 2-1 Drill Site Locations and Water Depths

Drill Site 

Approximate 

Distance from shore 

(statute miles) 

Lease 

Block No. 

Surface Location (NAD 83) Water 

Depth 

Latitude (north) Longitude (west) Feet/Meters 

Burger A 75 6764 71° 18' 30.92" 163° 12' 43.17" 150/45.8 

Burger F 76 6714 71° 20' 13.96" 163° 12' 21.75" 149/45.4 

Burger J 69 6912 71° 10' 24.03" 163° 28' 18.52" 144/44.0 

Burger R 75 6812 71° 16' 06.57" 163° 30' 39.44" 143/43.7 

Burger S 78 6762 71° 19' 25.79" 163° 28' 40.84" 147/44.9 

Burger V 65 6915 71° 10' 33.39" 163° 04' 21.23" 147/44.7 

Shell plans to cease drilling on or before 31 October, after which the Discoverer will exit the 

Alaskan Chukchi Sea. Shell anticipates that the exploration drilling program will require 

approximately 32 days per well including mudline cellar (MLC) construction. These estimates 

exclude any downtime for weather or other operational delays. Shell also assumes 

approximately 10 additional days will be needed for transit, drillship mobilization and mooring, 

drillship moves between locations, and drillship demobilization. 

 

3. Species and Numbers of Marine Mammals in Area 

Marine mammals that occur in the area of the planned exploration drilling activities belong to 

three taxonomic groups: odontocetes (toothed cetaceans, such as beluga whale and narwhal), 

mysticetes (baleen whales), and carnivora (pinnipeds and polar bears). Cetaceans and pinnipeds 

(except Pacific walrus) are the subject of this IHA application to NMFS. The Pacific walrus and 

polar bear are managed by the U.S. Fish & Wildlife Service (USFWS) are not discussed further 

in this application. 

Marine mammal species under the jurisdiction of NMFS that are known to or may occur in the 

area of the planned exploration drilling activity include nine cetacean species and four species of 

pinnipeds. Three of these species, the bowhead, humpback and fin whales, are listed as 

“endangered” under the Endangered Species Act (ESA). The bowhead whale is more common 

in the area than the other two species. The fin whale is unlikely to be encountered near the 

planned activities, but a few sightings in the Chukchi Sea have been reported in recent years. 

Similarly, humpback whales are not known to regularly occur in the Chukchi Sea; however 

several humpback sightings were recorded during vessel-based surveys in the Chukchi Sea in 

2007 (Reiser et al. 2009a). Two species of seal (ringed seal and bearded seal) have been 

proposed for listing as “threatened” species under the ESA (NMFS 2010a,b). Both species are 

common and abundant in the Chukchi Sea. 

To avoid redundancy, we have included the required information about the species that are 

known to or may be present and, insofar as they are known, numbers of these species in Section 

4, below. 
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4. Status, Distribution and Seasonal Distribution of Affected Species or Stocks of 

Marine Mammals 

Sections 3 and 4 are integrated here to minimize repetition. 

Marine mammal species under NMFS jurisdiction most likely to occur in the area of the planned 

exploration drilling activities in the Chukchi Sea include four cetacean species (beluga, bowhead 

and gray whales, and harbor porpoise), and three pinniped species (ringed, bearded, and spotted 

seals). Densities of marine mammals in the area of operations are likely to be higher if the ice 

edge occurs nearby. The marine mammal species that is likely to be encountered most widely 

(in space and time) throughout the period of the exploration drilling activities is ringed seal. 

Encounters with bowhead and gray whales are expected to be limited to particular seasons, as 

discussed below. 

Table 4-1 The Habitat, Abundance, and Conservation Status of Marine Mammals Inhabiting the Area 

Species Habitat Abundance ESA1 IUCN2 CITES3

Odontocetes 

Beluga whale 

(Delphinapterus leucas) 

 (Eastern Chukchi Sea Stock) 

Offshore, 

Coastal, Ice edges 3,7104

 Not listed NT – 

Beluga whale 

 (Beaufort Sea Stock) 

Offshore, 

Coastal, Ice edges 39,2575

 Not listed NT – 

Narwhal 

(Monodon monoceros) Offshore, Ice edge Rare6

 Not listed NT – 

Killer whale 

(Orcinus orca) Widely distributed Uncommon Not listed DD – 

Harbor Porpoise 

(Phocoena phocoena) 

 (Bering Sea Stock)

Coastal, inland waters, 

shallow offshore waters 

48,2154 

Common7 Not listed LR-lc – 

Mysticetes 

Bowhead whale 

(Balaena mysticetus) 

Pack ice & 

coastal 

10,5458

12,6319 Endangered LR-lc I 

Gray whale 

(Eschrichtius robustus) 

 (eastern Pacific population) 

Coastal, lagoons, shallow 

offshore waters 

48810 

17,50011 Not listed LR-lc I 

Minke whale 

(Balaenoptera acutorostrata) Shelf, coastal Rare Not listed LR-lc I 

Fin whale 

(Balaenoptera physalus) Slope, mostly pelagic Rare Endangered EN I 

Humpback whale 

(Megaptera novaeangliae) Shelf, coastal Rare Endangered LR-lc I 

Pinnipeds

Bearded seal 

(Erignathus barbatus)

Pack ice, shallow offshore 

waters 

250,000-

300,00012

155,00013

Proposed 

Threatened LR-lc – 

Spotted seal 

(Phoca largha) 

Pack ice, coastal 

haulouts, offshore 59,21414 Arctic pop. 

segments not 

listed 

DD – 

Ringed seal 

(Pusa hispida) 

Landfast & 

pack ice, offshore 

~208,000-

252,00015 Proposed Threatened LR-lc – 

Ribbon seal 

(Histriophoca fasciata) pack ice, offshore 90-100,00016 Not Listed DD – 

1 U.S. Endangered Species Act.
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2

 Red List of Threatened Species (IUCN 2010). Codes for IUCN classifications: CR = Critically Endangered; EN = Endangered; VU 

= Vulnerable; LR = Lower Risk (nt = Near Threatened; lc = Least Concern); DD = Data Deficient 3 Convention on International Trade in Endangered Species of Wild Fauna and Flora (UNEP-WCMC 2004) 

4

 Allen and Angliss (2010) 

5

 Beaufort Sea population (IWC 2000, Allen and Angliss 2010) 

6 Population in Baffin Bay and the Canadian arctic archipelago is ~60,000 (DFO 2004); very few enter the Beaufort Sea 

7

 Vessel-based observations from Industry activities in 2006–2008 (Haley et al. 2010) 

8

 2001 B-C-B Bowhead population estimate (Zeh and Punt 2005) 

9

 2004 B-C-B Bowhead population estimate (Koski et al. 2010) 

10 Southern Chukchi Sea and northern Bering Sea (Clark and Moore 2002) 

11 North Pacific gray whale population (Rugh 2003 in Keller and Gerber 2004) ; see also Rugh et al. (2005) 12 Alaska population (MMS 1996) 

13 Beringia Distinct Population Segment (NMFS 2010a) 

14 Alaska stock based on aerial surveys in 1992 (Allen and Angliss 2010) 

15 Eastern Chukchi Sea population (Bengtson et al. 2005) 

16 Bering Sea, (Burns 1981a) 

Five additional cetacean species—the narwhal, killer whale, minke whale, humpback whale, and 

fin whale—could occur, but each of these species is uncommon or rare in the project area and 

relatively few encounters with these species are expected during the exploration drilling 

program. The narwhal occurs in Canadian waters and occasionally occurs in the Alaskan 

Beaufort Sea and the Chukchi Sea, but is considered extralimital in U.S. waters and is not 

expected to be encountered. 

4.1 Odontocetes 

(a) Beluga (Delphinapterus leucas) 

The beluga whale is an arctic and subarctic species that includes several populations in Alaska 

and northern European waters. It has a circumpolar distribution in the Northern Hemisphere and 

occurs between 50o and 80oN latitude (Reeves et al. 2002). It is distributed in seasonally icecovered seas and migrates to warmer coastal estuaries, bays, and rivers in summer for molting 

(Finley 1982).

Pod structure in beluga groups appears to be along matrilineal lines, with males forming separate 

aggregations. Small groups are often observed traveling or resting together. Belugas often 

migrate in groups of 100 to 600 animals (Braham and Krogman 1977). The relationships 

between whales within groups are not known, although hunters have reported that belugas form 

family groups with whales of different ages traveling together (Huntington 2000). 

In Alaska, beluga whales comprise five distinct stocks: Beaufort Sea, eastern Chukchi Sea, 

eastern Bering Sea, Bristol Bay, and Cook Inlet (O’Corry-Crowe et al. 1997). For the planned 

project, only the Beaufort Sea and eastern Chukchi Sea stocks may be encountered. 

The most recent estimate of the eastern Chukchi Sea population is 3,710 animals (Allen and 

Angliss 2010). This estimate was based on surveys conducted in 1989–1991. Survey effort was 

concentrated on the 106 mi (171 km) long Kasegaluk Lagoon where belugas are found during 

the open-water season. The actual number of beluga whales recorded during the surveys was 

much lower. Correction factors to account for animals that were underwater and for the 

proportion of newborns and yearlings that were not observed due to their small size and dark 

coloration were used to calculate the estimate. The calculation was considered to be a minimum 
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population estimate for the eastern Chukchi Sea stock because the surveys on which it was based 

did not include offshore areas where belugas are also likely to occur. This population is 

considered to be stable. It is assumed that beluga whales from the eastern Chukchi stock winter 

in the Bering Sea (Allen and Angliss 2010). 

Although beluga whales are known to congregate in Kasegaluk Lagoon during summer, 

evidence from a small number of satellite-tagged animals suggests that some of these whales 

may subsequently range into the Arctic Ocean north of the Beaufort Sea. Suydam et al. (2005a) 

put satellite tags on 23 beluga whales captured in Kasegaluk Lagoon in late June and early July 

1998–2002. Five of these whales moved far into the Arctic Ocean and into the pack ice to 79–

80°N latitude. These and other whales moved to areas as far as 685 mi (1,102 km) offshore 

between Barrow and the Mackenzie River Delta spending time in water with 90 percent ice 

coverage. 

During aerial surveys in nearshore areas ~23 mi (~37 km) offshore in the Chukchi Sea in 2006 

and 2007, peak beluga sighting rates were recorded in July. Lowest monthly sighting rates were 

recorded in September (Thomas et al. 2009). When data from the two years were pooled, beluga 

whale sighting rates and number of individuals were highest in the band 16-22 mi (26-35 km) 

offshore. However the largest single groups were sighted at locations near shore in the band 

within 3 mi (5 km) of the shoreline. 

Beluga whales from the eastern Chukchi Sea stock are an important subsistence resource for 

residents of the village of Point Lay, adjacent to Kasegaluk Lagoon, and other villages in 

northwest Alaska. Each year, hunters from Point Lay drive belugas into the lagoon to a 

traditional hunting location. The belugas have been predictably sighted near the lagoon from 

late-June through mid- to late-July (Suydam et al. 2001a). In 2007, approximately 70 belugas 

were also harvested at Kivalina located southeast of Point Hope. 

Belugas of the eastern Chukchi Sea population could occur in the vicinity of the planned 

exploration drilling activities throughout the summer months. Based on the results of satellite 

telemetry data at least some of this stock may also pass the project area during fall migration; 

however, data from Thomas et al. (2009) suggests the highest concentration of belugas may be 

expected to occur much closer to shore than Shell’s planned exploration drilling activities. 

The Beaufort Sea population was estimated to contain 39,257 individuals as of 1992 (Allen and 

Angliss 2010). This estimate was based on the application of a sightability correction factor of 

2× to the 1992 uncorrected census of 19,629 individuals made by Harwood et al. (1996). This 

estimate was obtained from a partial survey of the known range of the Beaufort Sea population 

and may be an underestimate of the true population size. This population is not considered by 

NMFS to be a strategic stock and is believed to be stable or increasing (Allen and Angliss 2010). 

Beluga whales of the Beaufort Sea stock winter in the Bering Sea, summer in the eastern 

Beaufort Sea, and migrate in offshore waters of western and northern Alaska (Allen and Angliss 

2010). The majority of belugas in the Beaufort Sea stock migrate through the Chukchi Sea and 

into the Beaufort Sea in April or May, although some whales may pass Point Barrow as early as 

late-March and as late as July (Braham et al. 1984; Ljungblad et al. 1984; Richardson et al. 

1995b). Beluga whales associated with the Beaufort Sea population would be most likely to 
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occur near the planned exploration drilling activities during fall migration through the Chukchi 

Sea in October. 

(b) Narwhal (Monodon monoceros) 

Narwhals have a discontinuous Arctic distribution (Hay and Mansfield 1989; Reeves et al. 

2002). A large population inhabits Baffin Bay, West Greenland, and the eastern part of the 

Canadian Arctic archipelago, while much smaller numbers inhabit the Northeast Atlantic/East 

Greenland area. The IUCN-World Conservation Union lists the species as “near threatened” 

(IUCN 2010). Aerial surveys of four hunting grounds off the coast of Greenland in 2006 yielded 

abundance estimates of between 6,024 and 8,368 individuals in each area (Heide-Jørgensen et al. 

2010). Innes et al. (2002) estimated a population size of 45,358 narwhals in the Canadian 

Arctic although little of the area was surveyed. More recent surveys of portions of Baffin Bay in 

the Canadian High Arctic resulted in a total population estimate of >60,000 individuals (Richard 

et al. 2010). The Alaskan Beaufort Sea is not defined as a portion of a narwhal population’s 

range and it is considered extralimital in this region (Reeves et al. 2002). However, there are 

scattered records of narwhal in Alaskan waters. Thus, it is possible, but very unlikely, that 

individuals could be encountered in the area of the planned exploration drilling activities in the 

Chukchi Sea. 

(c) Killer Whale (Orcinus orca) 

Killer whales are cosmopolitan and globally fairly abundant. The killer whale is very common 

in temperate waters, but it also frequents the tropics and waters at high latitudes. Killer whales 

appear to prefer coastal areas, but are also found in deep water (Dahlheim and Heyning 1999). 

The greatest abundance is thought to be within 497 mi (800 km) of major continents (Mitchell 

1975) and the highest densities occur in areas with abundant prey. Both resident and transient 

stocks have been described. These are believed to differ in several aspects of morphology, 

ecology, and behavior including dorsal fin shape, saddle patch shape, pod size, home range size, 

diet, travel routes, dive duration, and social integrity of pods (Allen and Angliss 2010). 

Killer whales are known to inhabit almost all coastal waters of Alaska, extending from southeast 

Alaska through the Aleutian Islands to the Bering and Chukchi seas (Allen and Angliss 2010). 

Killer whales probably do not occur regularly in the Beaufort Sea although sightings have been 

reported (Lowry et al. 1987, George and Suydam 1998). George et al. (1994) reported that they 

and local hunters see a few killer whales at Point Barrow each year. Killer whales are more 

common southwest of Barrow in the southern Chukchi Sea and the Bering Sea. Based on 

photographic techniques, ~100 animals have been identified in the Bering Sea (ADFG 1994). 

Killer whales from either the North Pacific resident or transient stock could occur in the Chukchi 

Sea during the summer or fall. The number of killer whales likely to occur in the Chukchi Sea 

during the planned activity is unknown. MMOs onboard industry vessels in the Chukchi Sea 

recorded one killer whale sighting in 2006 and two sightings in 2007 (Reiser et al. 2009a). 

 
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(d) Harbor Porpoise (Phocoena phocoena) 

The harbor porpoise is a small odontocete that inhabits shallow, coastal waters—temperate, 

subarctic, and arctic—in the Northern Hemisphere (Read 1999). Harbor porpoises occur mainly 

in shelf areas where they can dive to depths of at least 722 ft (220 m) and stay submerged for 

more than 5 minutes (Harwood and Wilson 2001) feeding on small schooling fish (Read 1999). 

Harbor porpoises typically occur in small groups of only a few individuals and tend to avoid 

vessels (Richardson et al. 1995a). 

The subspecies Phocoena phocoena vomerina ranges from the Chukchi Sea, Pribilof Islands, 

Unimak Island, and the southeastern shore of Bristol Bay south to San Luis Obispo, California. 

Point Barrow, Alaska, is the approximate northeastern extent of their regular range (Suydam and 

George 1992), though there are extralimital records east to the mouth of the Mackenzie River in 

the Northwest Territories, Canada and recent sightings in the Beaufort Sea in the vicinity of 

Prudhoe Bay during surveys in 2007 and 2008 (Lyons et al. 2009). 

Although separate harbor porpoise stocks for Alaska have not been identified, Alaskan harbor 

porpoises have been divided into three groups for management purposes. These groups include 

animals from southeast Alaska, Gulf of Alaska, and Bering Sea populations. Harbor porpoises 

present in the Chukchi Sea belong to the Bering Sea group, which includes animals from Unimak 

Pass northward. Based on aerial surveys in 1999, the Bering Sea population was estimated at 

66,078 animals, although this estimate is likely conservative as the surveyed area did not include 

known harbor porpoise range near the Pribilof Islands or waters north of Cape Newenhan 

(~55°N latitude; Allen and Angliss 2010). Suydam and George (1992) suggested that harbor 

porpoises occasionally occur in the Chukchi Sea and reported nine records of harbor porpoise in 

the Barrow area in 1985–1991. More recent vessel-based surveys in the Chukchi Sea found that 

the harbor porpoise was commonly encountered during summer and fall from 2006–2008 (Haley 

et al. 2010). 

Based on recent surveys the harbor porpoise is likely to be one of the most abundant cetaceans 

encountered throughout the Chukchi Sea and is likely to occur in the vicinity of the planned 

exploration drilling activities. 

4.2 Mysticetes 

(a) Bowhead Whale (Balaena mysticetus) 

Bowhead whales only occur at high latitudes in the northern hemisphere and have a disjunct 

circumpolar distribution (Reeves 1980). The bowhead is one of only three whale species that 

spend their entire lives in the Arctic. Bowhead whales are found in four areas: the western 

Arctic (Bering, Chukchi, and Beaufort seas) of northeastern Russia, Alaska and northwestern 

Canada; the Canadian High Arctic and West Greenland (Nunavut, Baffin Bay, Davis Strait, and 

Hudson Bay); the Okhotsk Sea (eastern Russia); and the Northeast Atlantic from Spitzbergen 

westward to eastern Greenland. Those four stocks are recognized for management purposes. 

The largest is the Western Arctic or Bering–Chukchi–Beaufort (BCB) stock, which includes 

whales that winter in the Bering Sea, and migrate through the Bering Strait, Chukchi Sea, and 
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Alaskan Beaufort Sea to the Canadian Beaufort Sea, where they feed during the summer. These 

whales migrate west through the Alaskan Beaufort Sea in the fall as they return to wintering 

areas in the Bering Sea. Satellite tracking data reported by the Alaska Department of Fish and 

Game (ADF&G) indicate that most bowhead whales continue migrating west past Barrow and 

through the northern Chukchi Sea to Russian waters before turning south toward the Bering Sea. 

Visual and satellite tracking data show that many bowhead whales continue migrating west past 

Barrow and through the northern Chukchi Sea to Russian waters before turning southeast toward 

the Bering Sea (Moore et al. 1995; Mate et al. 2000; Quakenbush et al. 2010). Some bowheads 

reach ~75oN latitude during the westward fall migration (Quakenbush et al. 2010). 

The pre-exploitation population of bowhead whales in the Bering, Chukchi, and Beaufort seas is 

estimated to have been 10,400-23,000 whales. Commercial whaling activities in the late-1800s 

and early-1900s may have reduced this population to as few as 3,000 animals (Woodby and 

Botkin 1993). Up to the early 1990s, the population size was believed to be increasing at a rate 

of about 3.2 percent per year (Zeh et al. 1996) despite annual subsistence harvests of 14–74 

bowheads from 1973 to 1997 (Suydam et al. 1995a). A census in 2001 yielded an estimated 

annual population growth rate of 3.4 percent (95 percent confidence interval, 1.7–5 percent) from 

1978 to 2001 and a population size (in 2001) of ~10,470 animals (George et al. 2004, revised to 

10,545 by Zeh and Punt (2005). A photo identification population estimate from data collected 

in 2004 estimated the population (in 2004) to be 12,631 (Koski et al. 2010), which further 

supports the estimated 3.4 percent population growth rate. Assuming a continuing annual 

population growth of 3.4 percent, the 2012 bowhead population may number around 15,232 

animals. The large increases in population estimates that occurred from the late 1970s to the 

early 1990s were partly a result of actual population growth, but were also partly attributable to 

improved census techniques (Zeh et al. 1993). Although apparently recovering well, the BCB 

bowhead population is currently listed as endangered under the ESA and is classified as a 

strategic stock by NMFS and depleted under the MMPA (Allen and Angliss 2010). 

The BCB stock of bowhead whales winters in the central and western Bering Sea and many of 

these whales summer in the Canadian Beaufort Sea (Moore and Reeves 1993). Spring migration 

through the Chukchi Sea occurs through offshore ice leads, generally from March through midJune (Braham et al. 1984; Moore and Reeves 1993), well before the onset of the planned 

exploration drilling activities. 

Some bowheads arrive in coastal areas of the eastern Canadian Beaufort Sea and Amundsen Gulf 

in late May and June, but most may remain among the offshore pack ice of the Beaufort Sea until 

mid- summer. After feeding primarily in the Canadian Beaufort Sea and Amundsen Gulf, 

bowheads migrate westward from late August through mid- or late-October. Fall migration into 

Alaskan waters is primarily during September and October. However, in recent years a small 

number of bowheads have been seen or heard offshore from the Prudhoe Bay region during the 

last week of August (Treacy 1993; LGL and Greeneridge 1996; Greene 1997; Greene et al. 1999; 

Blackwell et al. 2004, 2009a; Greene et al. 2007). Satellite tracking of bowheads has also shown 

that some whales move to the Chukchi Sea prior to September (Quakenbush et al. 2010). 

Bowheads commonly interrupt their migration to feed along the Alaskan Beaufort Sea coast 

(Ljungblad et al. 1986; Lowry 1993; Landino et al. 1994; Würsig et al. 2002; Lowry et al. 2004) 
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and their stop-overs vary in duration from a few hours to a few weeks (Koski et al. 2002). The 

nearest of these known feeding areas to the proposed operations in the Chukchi Sea is just east of 

Pt. Barrow, which is approximately 156 mi (250 km) from the Burger prospect. This location is 

currently under intensive study as part of the BOWFEST program (BOWFEST 2011). 

Westbound bowheads typically reach the Barrow area in mid-September, and remain there until 

late October (e.g., Brower 1996). However, over the years, local residents report having seen a 

small number of bowhead whales feeding off Barrow or in the pack ice off Barrow during the 

summer. Bowhead whales that are thought to be part of the Western Arctic stock may also occur 

in small numbers in the Bering and Chukchi seas during the summer (Rugh et al. 2003). Thomas 

et al. (2009) also reported bowhead sightings in 2006 and 2007 during summer aerial surveys in 

the Chukchi Sea. All sightings were recorded in the northern portion of the study area, north of 

70oN latitude. Autumn bowhead whaling near Barrow normally begins in mid-September to 

early October, but may begin as early as August if whales are observed and ice conditions are 

favorable (USDI/BLM 2005). Whaling near Barrow can continue into October, depending on 

the quota and conditions. 

Most spring-migrating bowhead whales would likely pass through the Chukchi Sea prior to the 

start of the planned exploration drilling activities. However, a few whales that may remain in the 

Chukchi Sea during the summer could be encountered during the exploration drilling activities or 

by transiting vessels. More encounters with bowhead whales would be likely to occur during the 

westward fall migration in late September through October. An ongoing GPS tagging study 

(Quakenbush et al. 2010) has provided information on fall bowhead movements across the 

Chukchi Sea. Most bowheads migrating in September and October appear to transit across the 

northern portion of the Chukchi Sea to the Chukotka coast before heading south toward the 

Bering Sea (Quakenbush et al. 2009). Some of these whales have traveled well north of the 

planned operations, but others have passed near to, or through, the proposed project area. In 

addition to other planned mitigation, Shell will operate in consultation with stakeholders to avoid 

disturbance to subsistence bowhead whaling activities in the Chukchi Sea, should such a 

subsistence bowhead hunt occur during the period of Shell’s planned 2012 exploration drilling 

activities. 

(b) Gray Whale (Eschrichtius robustus) 

Gray whales originally inhabited both the North Atlantic and North Pacific oceans. The Atlantic 

populations are believed to have become extinct by the early 1700s. There are two populations 

in the North Pacific. A relic population, which survives in the Western Pacific, summers near 

Sakhalin Island far from the area of the planned exploration drilling activities. The larger eastern 

Pacific or California gray whale population recovered significantly from commercial whaling 

during its protection under the MMPA (and ESA until 1994) and numbered about 29,758 ±3,122 

in 1997 (Rugh et al. 2005). However, abundance estimates since 1997 indicate a consistent 

decline followed by the population stabilizing or gradually recovering. Rugh et al. (2005) 

estimated the population to be 18,178 ±1,780 in winter 2001-2002 and Rugh et al. (2008) 

estimated the population in winter 2006-2007 to have been 20,110 ±1,766. The eastern Pacific 

stock is not considered by NMFS to be endangered or to be a strategic stock. 
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Eastern Pacific gray whales calve in the protected waters along the west coast of Baja California 

and the east coast of the Gulf of California from January to April (Swartz and Jones 1981; Jones 

and Swartz 1984). At the end of the calving season, most of these gray whales migrate about 

5,000 mi (8,000 km), generally along the west coast of North America, to the main summer 

feeding grounds in the northern Bering and Chukchi seas (Tomilin 1957, Rice and Wolman 

1971, Nerini 1984, Moore et al. 2003, Bluhm et al. 2007). Most gray whales begin the 

southward migration in November with breeding and conception occurring in early December 

(Rice and Wolman 1971). 

Most summering gray whales have historically congregated in the northern Bering Sea, 

particularly off St. Lawrence Island in the Chirikov Basin (Moore et al. 2000), and in the 

southern Chukchi Sea. More recently, Moore et al. (2003) suggested that gray whale use of 

Chirikov Basin has decreased, likely as a result of the combined effects of changing currents 

resulting in altered secondary productivity dominated by lower-quality food. Coyle et al. (2007) 

noted that amplescid amphipod production in the Chirikov Basin had declined by 50 percent 

from the 1980s to 2002-2003 and that as little as 3-6 percent of the current gray whale population 

could consume 10-20 percent of the amplescid amphipod annual production. These data support 

the hypotheses that changes in gray whale distribution may be caused by changes in food 

production and that gray whales may be approaching or have surpassed the carrying capacity of 

their summer feeding areas. Bluhm et al. (2007) noted high gray whale densities along ocean 

fronts and suggested that ocean fronts may play an important role in influencing prey densities in 

eastern North Pacific gray whale foraging areas. The northeastern-most of the recurring feeding 

areas is in the northeastern Chukchi Sea southwest of Barrow (Clarke et al. 1989). 

Gray whales routinely feed in the Chukchi Sea during the summer. Moore et al. (2000) reported 

that during the summer, gray whales in the Chukchi Sea were clustered along the shore primarily 

between Cape Lisburne and Point Barrow and were associated with shallow, coastal shoal 

habitat. In autumn, gray whales were clustered near shore at Point Hope and between Icy Cape 

and Point Barrow, as well as in offshore waters southwest of Point Barrow at Hanna Shoal and 

northwest of Point Hope. The distribution of grays was different during aerial surveys in the 

Chukchi Sea in 2006 and 2007 (Thomas et al. 2009). In 2006, gray whales were most abundant 

along the coast south of Wainwright and offshore of Wainwright (Thomas et al. 2007), and in 

2007, gray whales were most abundant in nearshore areas from Wainwright to Barrow (Thomas 

et al. 2009). Gray whales occur fairly often near Point Barrow, but historically only a small 

number of gray whales have been sighted in the Beaufort Sea east of Point Barrow. 

Although they are most common in portions of the Chukchi Sea close to shore, gray whales may 

also occur in offshore areas of the Chukchi Sea, particularly over offshore shoals. Gray whales 

are likely to be in the vicinity of the planned exploration drilling activities in the Chukchi Sea 

and are likely to be one of the most commonly encountered cetacean species, along with the 

harbor porpoise (Reiser et al. 2011). 

(c) Minke Whale (Balaenoptera acutorostrata) 

Minke whales have a cosmopolitan distribution at ice-free latitudes (Stewart and Leatherwood 

1985), and also occur in some marginal ice areas. Allen and Angliss (2010) recognize two 
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minke whale stocks in U.S. waters: (1) the Alaska stock, and (2) the California/Oregon/ 

Washington stock. There is no abundance estimate for the Alaska stock. Provisional estimates 

of minke whale abundance based on surveys in 1999 and 2000 are 810 and 1003 whales in the 

central-eastern and south-eastern Bering Sea, respectively. These estimates have not been 

corrected for animals that may have been submerged or otherwise missed during the surveys, and 

only a portion of the range of the Alaskan stock was surveyed. Minke whales range into the 

Chukchi Sea, but the level of minke whale use of the Chukchi Sea is unknown. Minke whales 

have been observed from vessels during previous industry activities in the Chukchi Sea (Haley et 

al. 2010) and during aerial surveys conducted by the National Marine Mammal Laboratory 

(NMML) (COMIDA 2011). 

(d) Fin Whale (Balaenoptera physalus) 

Fin whales are widely distributed in all the world's oceans (Gambell 1985), but typically occur in 

temperate and polar regions. Fin whales feed in northern latitudes during the summer where 

their prey include plankton, as well as shoaling pelagic fish, such as capelin Mallotus villosus

(Jonsgård 1966a,b). The North Pacific population’s summering grounds span from the Chukchi 

Sea to California (Gambell 1985). Three fin whale sightings were made in 2008 from industry 

vessels and NMFS/NMML survey aircraft in the northern Chukchi Sea off of Ledyard Bay 

indicating that the range of fin whales may be expanding. Population estimates for the entire 

North Pacific region range from 14,620 to 18,630, however, reliable estimates are not available 

(Allen and Angliss 2010). Provisional estimates of fin whale abundance in the central-eastern 

and southeastern Bering Sea are 3,368 and 683, respectively. No estimates for fin whale 

abundance during the summer in the Chukchi Sea are available. Reiser et al. (2009a) reported a 

fin whale sighting during vessel-based surveys in the Chukchi Sea in 2006. Fin whale is listed as 

“endangered” under the ESA and by the IUCN (2010), and in the North Pacific is classified as a 

strategic stock by NMFS. Fin whales could be encountered in very low numbers during the 

exploration drilling activities in the Chukchi Sea. 

(e) Humpback Whale (Megaptera novaeangliae) 

Humpback whales are distributed in major oceans worldwide but are apparently absent from 

Arctic waters of the North Pacific (Allen and Angliss 2010). In general, humpback whales spend 

the winter in tropical and sub-tropical waters where breeding and calving occur, and migrate to 

higher latitudes for feeding during the summer. 

Humpback whales were hunted extensively during the 20th century and worldwide populations 

may have been reduced to ~10 percent of their original numbers. The International Whaling 

Commission banned commercial hunting of humpback whales in the Pacific Ocean in 1965 and 

humpbacks were listed as “endangered” under the ESA and depleted under the MMPA in 1973. 

Most humpback whale populations appear to be recovering well. 

Humpbacks feed on euphausiids, copepods, and small schooling fish, notably herring, capelin, 

and sandlance (Reeves et al. 2002). As with other baleen whales, the food is trapped or filtered 

when large amounts of water are taken into the mouth and forced out through the baleen plates. 

Individual humpback whales can often be identified by distinctive patterns on the tail flukes. 

They are frequently observed breaching or engaged in other surface activities. Adult male and 
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female humpback whales average 46 and 49 ft (14 and 15 m) in length, respectively (Wynne 

1997). Humpbacks have large, robust bodies and long pectoral flippers, which may reach 1⁄3 of 

their body length. The dorsal fin is variable in shape and located well back toward the posterior 

1⁄3 of the body on a hump which is particularly noticeable when the back is arched during a dive 

(Reeves et al. 2002). 

Allen and Angliss (2010) reported that at least three humpback whale populations have been 

identified in the North Pacific. Two of these stocks may be relevant to the planned exploration 

drilling activities in the Chukchi Sea. The Central North Pacific stock winters in waters near 

Hawaii and migrates to British Columbia, Southeast Alaska, and Prince William Sound to 

Unimak Pass to feed during the summer. The Western North Pacific stock winters off the coast 

of Japan and probably migrates to the Bering Sea to feed during the summer. There may be 

some overlap between the Central and Western North Pacific stocks. 

Humpback whale sightings in the Bering Sea have been recorded southwest of St. Lawrence 

Island, the southeastern Bering Sea, and north of the central Aleutian Islands (Moore et al. 2002, 

Allen and Angliss 2010). Recently there have been sightings of humpback whales in the 

Chukchi Sea and a single sighting in the Beaufort Sea (Green et al. 2007). Reiser et al. (2009a) 

reported four humpback whales during vessel-based surveys in the Chukchi Sea in 2007 and 

Haley et al. (2009) reported one humpback whale sighting during 2008 operations. Green et al. 

(2007) reported and photographed a humpback whale cow/calf pair east of Barrow near Smith 

Bay in 2007. Small numbers of humpback whales could occur within or near the exploration 

drilling activities in the Chukchi Sea. 

4.3 Pinnipeds 

(a) Bearded Seal (Erignathus barbatus) 

Bearded seals are associated with sea ice and have a circumpolar distribution (Burns 1981b). 

They have occasionally been reported to maintain breathing holes in sea ice and broken areas 

within the pack ice, particularly if the water depth is <656 ft (<200 m) (e.g., Harwood et al. 

2005). Bearded seals apparently also feed on ice-associated organisms when they are present, 

and this allows a few bearded seals to live in areas where water depth is considerably greater 

than 656 ft (200 m) (Cameron et al. 2009). During the summer period, bearded seals occur 

mainly in relatively shallow areas because they are predominantly benthic feeders (Burns 

1981b). No reliable estimate of bearded seal abundance is available for the Chukchi Sea (Allen 

and Angliss 2010). The Alaska stock of bearded seals, part of the Beringia distinct population 

segment, has been proposed by NMFS for listing as threatened under the ESA (NMFS 2010a). 

Seasonal movements of bearded seals are directly related to the advance and retreat of sea ice 

and to water depth (Kelly 1988). During winter, most bearded seals in Alaskan waters are found 

in the Bering Sea. In the Chukchi and Beaufort seas, favorable conditions are more limited, and 

consequently, bearded seals are less abundant there during winter. From mid-April to June as 

the ice recedes, some of the bearded seals that overwintered in the Bering Sea migrate northward 

through the Bering Strait. During the summer, they are found near the widely fragmented 
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margin of multi-year ice covering the continental shelf of the Chukchi Sea and in nearshore areas 

of the central and western Beaufort Sea. 

In Alaskan waters, bearded seals occur over the continental shelves of the Bering, Chukchi, and 

Beaufort Seas (Burns 1981b). The Alaska stock of bearded seals may consist of 300,000–

450,000 individuals (MMS 1996). Bengtson et al. (2005) reported bearded seal densities in the 

Chukchi Sea ranging from 0.18 to 0.36 seals/square miles (mi2) (0.07 to 0.14 seals/square 

kilometers [km2]) in 1999 and 2000, respectively. No population estimates could be calculated 

since these densities were not adjusted for haulout behavior. Bearded seals are common in 

offshore pack ice, but there have been high bearded seal numbers observed near the shore south 

of the project area near Kivalina. Haley et al. (2010) reported bearded seal densities ranging 

from 0.03 to 0.23 seals/mi2 (0.01 to 0.09 seals/km2) in the summer and fall, respectively, during 

vessel-based surveys in the Chukchi Sea. These densities were lower than those reported by 

Bengtson et al. (2005) but are not directly comparable since the latter densities were based on 

aerial surveys of seals on sea ice in late May and early June. Bearded seals are likely to be 

encountered during exploration drilling operations, and greater numbers of bearded seals are 

likely to be encountered if the ice edge occurs nearby. 

(b) Spotted Seal (Phoca largha) 

Spotted seals (also known as largha seals) occur in the Beaufort, Chukchi, Bering, and Okhotsk 

Seas, and south to the northern Yellow Sea and western Sea of Japan (Shaughnessy and Fay 

1977). They migrate south from the Chukchi Sea and through the Bering Sea in October (Lowry 

et al. 1998). Spotted seals overwinter in the Bering Sea and inhabit the southern margin of the 

ice during spring (Shaughnessy and Fay 1977). 

An early estimate of the size of the world population of spotted seals was 370,000–420,000, and 

the size of the Bering Sea population, including animals in Russian waters, was estimated to be 

200,000–250,000 animals (Bigg 1981). The total number of spotted seals in Alaskan waters is 

not known (Allen and Angliss 2010), but the estimate is most likely between several thousand 

and several tens of thousands (Rugh et al. 1997). During the summer, spotted seals are found in 

Alaska from Bristol Bay through western Alaska to the Chukchi and Beaufort seas. The 

ADF&G placed satellite transmitters on four spotted seals in Kasegaluk Lagoon and estimated 

that the proportion of seals hauled out was 6.8 percent. Based on an actual minimum count of 

4,145 hauled out seals, Allen and Angliss (2010) estimated the Alaskan population at 59,214 

animals. The Alaska stock of spotted seals is not classified as endangered, threatened, or as a 

strategic stock by NMFS (Allen and Angliss 2010), although the southern distinct population 

segment of spotted seals was recently listed as a threatened species, it occurs entirely outside of 

U.S. waters. 

During spring when pupping, breeding, and molting occur, spotted seals are found along the 

southern edge of the sea ice in the Okhotsk and Bering seas (Quakenbush 1988; Rugh et al. 

1997). In late April and early May, adult spotted seals are often seen on the ice in female-pup or 

male-female pairs, or in male-female-pup triads. Subadults may be seen in larger groups of up to 

200 animals. During the summer, spotted seals are found primarily in the Bering and Chukchi 

seas, but some range into the Beaufort Sea (Rugh et al. 1997; Lowry et al. 1998) from July until 
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September. At this time of year, spotted seals haul out on land part of the time, but also spend 

extended periods at sea. Spotted seals are commonly seen in bays, lagoons and estuaries, but 

also range far offshore as far north as 69–72oN latitude. In summer, they are rarely seen on the 

pack ice, except when the ice is very near shore. As the ice cover thickens with the onset of 

winter, spotted seals leave the northern portions of their range and move into the Bering Sea 

(Lowry et al. 1998). 

In the Chukchi Sea, Kasegaluk Lagoon and Icy Cape are important areas for spotted seals. 

Spotted seals haul out in this region from mid-July until freeze-up in late October or November. 

Lowry et al. (1998) reported a maximum count of about 2,200 spotted seals in the lagoon during 

aerial surveys. No spotted seals were recorded along the shore south of Pt. Lay. Based on 

satellite tracking data, Frost and Lowry (1993) reported that spotted seals tagged at Kasegaluk 

Lagoon spent 94 percent of the time at sea. Extrapolating the count of hauled-out seals to 

account for seals at sea would suggest a Chukchi Sea population of about 36,000 animals. Few 

spotted seals are expected to occur near the planned exploration drilling activities in the Chukchi 

Sea. 

(c) Ringed Seal (Phoca hispida) 

Ringed seals have a circumpolar distribution and occur in all seas of the Arctic Ocean (King 

1983). They are closely associated with ice and, in the summer, they often occur along the 

receding ice edges or farther north in the pack ice. In the North Pacific, they occur in the 

southern Bering Sea and range south to the seas of Okhotsk and Japan. They are found 

throughout the Beaufort, Chukchi, and Bering seas (Allen and Angliss 2010). The Alaska stock, 

part of the Arctic subspecies of ringed seal, has been proposed for listing as threatened under the 

ESA (NMFS 2010b). 

Ringed seals are year-round residents in the Chukchi and Beaufort seas and the ringed seal is the 

most frequently encountered seal species in the area. During winter, ringed seals occupy landfast 

ice and offshore pack ice of the Bering, Chukchi and Beaufort seas. In winter and spring, the 

highest densities of ringed seals are found on stable shorefast ice. However, in some areas where 

there is limited fast ice but wide expanses of pack ice, including the Beaufort Sea, Chukchi Sea 

and Baffin Bay, total numbers of ringed seals on pack ice may exceed those on shorefast ice 

(Burns 1970, Stirling et al. 1982, Finley et al. 1983). Ringed seals maintain breathing holes in 

the ice and occupy lairs in accumulated snow (Smith and Stirling 1975). They give birth in lairs 

from mid-March through April, nurse their pups in the lairs for 5–8 weeks, and mate in late April 

and May (Smith 1973, Hammill et al. 1991, Lydersen and Hammill 1993). 

No estimate for the size of the Alaska ringed seal stock is currently available (Allen and Angliss 

2010). Past ringed seal population estimates in the Bering-Chukchi-Beaufort area ranged from 

1–1.5 million (Frost 1985) to 3.3–3.6 million (Frost et al. 1988). During aerial surveys in 1999, 

Bengtson et al. (2005) reported ringed seal densities offshore from Shishmaref to Barrow ranging 

from 1.0 to 9.6 seals/mi2

 (0.4 to 3.7 seals/km2) and estimated the total Chukchi Sea population at 

245,048 animals in 1999. Densities were higher in nearshore than offshore locations. During 

vessel-based observations from industry activities in the Chukchi Sea, Haley et al. (2010) 

reported seal densities (assumed to be almost entirely ringed seals) from 0.18 to 1.92 seals/mi2
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(0.07 to 0.74 seals/km2) in summer and fall, respectively. Ringed seal will likely be the most 

abundant marine mammal species encountered in the Chukchi Sea during exploration drilling 

operations. 

(d) Ribbon Seal (Histriophoca fasciata) 

Ribbon seals are found along the pack-ice margin in the southern Bering Sea during late winter and 

early spring and they move north as the pack ice recedes during late spring to early summer (Burns 

1970, Burns et al. 1981a). Little is known about their summer and fall distribution, but Kelly (1988) 

suggested that they move into the southern Chukchi Sea, based on a review of sightings during the 

summer. However, ribbon seals appeared to be relatively rare in the northern Chukchi Sea. During 

recent vessel-based surveys in 2006-2008 there were only two ribbon seal sightings among the total 

of 1,390 seal sightings identified to species (Haley et al. 2010). Ribbon seals are expected to be rare 

in the planned project area. 

5. Type of Incidental Take Authorization Requested 

Shell requests an IHA pursuant to Section 101(a)(5)(D) of the MMPA for incidental take by 

harassment of small numbers of cetaceans and pinnipeds during its planned exploration drilling 

activities in the Chukchi Sea during July–October, 2012. 

The operations outlined in sections 1 and 2 have the potential to take marine mammals by “Level 

B” harassment as a result of sound energy introduced to the marine environment. Sounds that 

may “harass” marine mammals will include continuous sounds generated by the exploration 

drilling activities and pulsed sounds generated by the airguns used during the ZVSP activities. 

The effects will depend on the species of cetacean or pinniped, the behavior of the animal at the 

time of reception of the stimulus, as well as the distance and received level of the sound (see 

section 7). Disturbance reactions are likely to vary among some of the marine mammals in the 

general vicinity of the sound source. No “take” by serious injury is reasonably expected or 

reasonably likely, given the nature of the specified activities and the mitigation measures that are 

planned (see Section 11). No lethal takes are expected. 

6. Numbers of Marine Mammals That May be Taken 

Shell seeks authorization for potential “taking” of small numbers of marine mammals under the 

jurisdiction of the NMFS in the planned region of activity. Species most likely to be 

encountered include bowhead and gray whales, beluga, harbor porpoise, and ringed, spotted, and 

bearded seals. Exposure estimates and requests for takes of ribbon seal, fin whale, humpback 

whale, killer whale, minke whale, and narwhal are also included, but are minimal because 

sightings of these species in the Chukchi Sea are rare. 

The only anticipated impacts to marine mammals are associated with underwater sound 

propagation from exploration drilling and ZVSP activities, potential icebreaking activities, and 

associated support vessels. Impacts would consist of temporary displacement of marine 

mammals from within ensonified zones produced by such sound sources. 
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The exploration drilling activities in the Chukchi Sea planned by Shell are not expected to “take” 

more than small numbers of marine mammals, or have more than a negligible effect on their 

populations. Discussions of estimated “takes by harassment” are presented below. 

All anticipated takes would be “takes by harassment”, involving temporary changes in behavior. 

The mitigation measures to be applied will minimize the possibility of injurious takes. However, 

there is no specific information demonstrating that injurious “takes” would occur even in the 

absence of the planned mitigation measures. In the sections below, we describe methods to 

estimate “take by harassment” and present estimates of the numbers of marine mammals that 

might be affected during the planned exploration drilling program in the Chukchi Sea. The 

estimates are based on data obtained during marine mammal surveys in and near the planned 

exploration drilling sites and on estimates of the sizes of the areas where effects could potentially 

occur. Adjustments to reported population or density estimates were made to account for 

seasonal distributions and population increases or declines insofar as possible. 

The main sources of distributional and numerical data used in deriving the estimates are 

described in the next subsection. There is some uncertainty about the representativeness of those 

data and the assumptions used below to estimate the potential “take by harassment”. However, 

the approach used here is the best available at this time. 

Basis for Estimating “Take by Harassment” 

“Take by Harassment” is calculated in this section by multiplying the expected densities of 

marine mammals that may occur near the exploration drilling operations by the area of water 

likely to be exposed to continuous sounds ≥120 dB re 1 μPa rms during exploration drilling 

operations or icebreaking activities, and impulsive sounds ≥160 dB re 1 μPa rms created by 

seismic airguns during ZVSP surveys. 

Marine mammal occurrence near the operation is likely to vary by season and habitat, mostly 

related to the presence or absence of sea ice. This section provides descriptions of the estimated 

densities of marine mammals and areas of water exposed to the indicated sound levels over the 

course of the planned operations. There is no evidence that avoidance at received sound levels 

of ≥120 dB or ≥160 dB rms would have significant biological effects on individual animals or 

that the subtle changes in behavior or movements would “rise to the level of taking” according to 

guidance by the NMFS (NMFS 2001). Any changes in behavior caused by sounds at or near the 

specified received levels would likely fall within the normal variation in such activities that 

would occur in the absence of exploration drilling operations. 

Marine Mammal Density Estimates 

Marine mammal density estimates in the Chukchi Sea have been derived for two time periods, 

the summer period covering July and August, and the fall period including September and 

October. Animal densities encountered in the Chukchi Sea during both of these time periods will 

further depend on the habitat zone within which the operations are occurring: open water or ice 

margin. More ice is likely to be present in the area of operations during the July–August period, 

so summer ice-margin densities have been applied to 50 percent of the area that may be exposed 
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to sounds from exploration drilling and ZVSP activities in those months. Open water densities in 

the summer were applied to the remaining 50 percent of the area. Less ice is likely to be present 

during the September–October period, so fall ice-margin densities have been applied to only 20 

percent of the area that may be exposed to sounds from exploration drilling and ZVSP activities 

in those months. Fall open-water densities were applied to the remaining 80 percent of the area. 

Since icebreaking activities would only occur within ice-margin habitat, the entire area 

potentially ensonified by icebreaking activities has been multiplied by the ice-margin densities in 

both seasons. 

As noted above, there is some uncertainty about the representativeness of the data and 

assumptions used in the calculations. To provide some allowance for the uncertainties, 

“maximum estimates” as well as “average estimates” of the numbers of marine mammals 

potentially affected have been derived. For a few marine mammal species, several density 

estimates were available. In those cases, the mean and maximum estimates were determined 

from the reported densities or survey data. In other cases only one, or no applicable estimate was 

available, so correction factors were used to arrive at “average” and “maximum” estimates. In 

other cases, no applicable estimate (or perhaps a single estimate) was available, so correction 

factors were used to arrive at “average” and “maximum” estimates. These are described in detail 

in the following sections. 

Detectability bias, quantified in part by f(0), is associated with diminishing sightability with 

increasing lateral distance from the survey trackline. Availability bias, g(0), refers to the fact 

that there is <100 percent probability of sighting an animal that is present along the survey 

trackline. Some sources below included these correction factors in the reported densities (e.g. 

ringed seals in Bengtson et al. 2005) and the best available correction factors were applied to 

reported results when they had not already been included (e.g. Moore et al. 2000). 

Cetaceans 

Nine species of cetaceans are known to occur in the planned project area in the Chukchi Sea. 

Only four of these (bowhead and gray whales, beluga, and harbor porpoise) are expected to be 

encountered during the planned exploration drilling activities. Three of the nine species 

(bowhead, fin, and humpback whales) are listed as “endangered” under the ESA. 

Summer densities of belugas in offshore waters are expected to be low, with somewhat higher 

densities in ice-margin and nearshore areas. Aerial surveys have recorded few belugas in the 

offshore Chukchi Sea during the summer months (Moore et al. 2000). Aerial surveys of the 

Chukchi Sea in 2008-2009 flown by the NMML as part of the Chukchi Offshore Monitoring in 

Drilling Area (COMIDA) project have only reported 5 beluga sightings during >8,700 mi 

(>14,000 km) of on-transect effort, only 2 of which were offshore (COMIDA 2009). One of the 

three nearshore sightings was of a large group (~275 individuals on July 12, 2009) of migrating 

belguas along the coastline just north of Peard Bay. Additionally, only one beluga sighting was 

recorded during >37,900 mi (>61,000 km) of visual effort during good visibility conditions from 

industry vessels operating in the Chukchi Sea in September-October of 2006-2008 (Haley et al. 

2010). If belugas are present during the summer, they are more likely to occur in or near the ice 

edge or close to shore during their northward migration. Expected densities have previously 
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been calculated from data in Moore et al. (2000b). However, more recent data from COMIDA 

aerial surveys during 2008-2010 are now available (Clarke and Ferguson in prep.). Effort and 

sightings reported by Clarke and Ferguson (in prep.) were used to calculate the average openwater density estimate. Clarke and Ferguson (in prep) reported two on-transect beluga sightings 

(5 individuals) during 11,985 km of on-transect effort in waters 36-50 m deep in the Chukchi Sea 

during July and August. The mean group size of these two sightings is 2.5. A f(0) value of 

2.841 and g(0) value of 0.58 from Harwood et al. (1996) were also used in the density 

calculation. The CV associated with group size was used to select an inflation factor of 2 to 

estimate the maximum density that may occur in both open-water and ice-margin habitats. 

Specific data on the relative abundance of beluga in open-water versus ice-margin habitat during 

the summer in the Chukchi Sea is not available. However, belugas are commonly associated 

with ice, so an inflation factor of 4 was used to estimate the average ice-margin density from the 

open-water density. Very low densities observed from vessels operating in the Chukchi Sea 

during non-seismic periods and locations in July-August of 2006-2008 (0.0-0.0003/mi2, 0.0-

0.0001/km2

; Haley et al. 2010), also suggest the number of beluga whales likely to be present 

near the planned activities will not be large. 

In the fall, beluga whale densities in the Chukchi Sea are expected to be somewhat higher than in 

the summer because individuals of the eastern Chukchi Sea stock and the Beaufort Sea stock will 

be migrating south to their wintering grounds in the Bering Sea (Allen and Angliss 2010). 

However, there were no beluga sightings reported during >11,200 mi (>18,000 km) of vessel 

based effort in good visibility conditions during 2006-2008 industry operations in the Chukchi 

Sea (Haley et al. 2010). Densities derived from survey results in the northern Chukchi Sea in 

Clarke and Ferguson (in prep) were used as the average density for open-water fall season 

estimates (see Table 6-2). Clarke and Ferguson (in prep) reported 3 beluga sightings (6 

individuals) during 10,036 km of on-transect effort in water depths 36–50 m. The mean group 

size of those three sightings is 2. A f(0) value of 2.841 and g(0) value of 0.58 from Harwood et 

al. (1996) were used in the calculation. The same inflation factor of 2 used for summer densities 

was used to estimate the maximum density that may occur in both open-water and ice-margin 

habitats in the fall. Moore et al. (2000) reported lower than expected beluga sighting rates in 

open-water during fall surveys in the Beaufort and Chukchi seas, so an inflation value of 4 was 

used to estimate the average ice-margin density from the open-water density. Based on the lack 

of any beluga sightings from vessels operating in the Chukchi Sea during non-seismic periods 

and locations in September-October of 2006-2008 (Haley et al. 2010), the relatively low 

densities shown in Table 6-2 are consistent with what is likely to be observed form vessels 

during the planned operations. 

By July, most bowhead whales are northeast of the Chukchi Sea, within or migrating toward 

their summer feeding grounds in the eastern Beaufort Sea. No bowheads were reported during 

6,640 mi (10,686 km) of on-transect effort in the Chukchi Sea by Moore et al. (2000). Aerial 

surveys in 2008-2010 by the NMML as part of the COMIDA project reported only 6 sightings 

during >16,020 mi (>25,781 km) of on-transect effort (Clarke and Ferguson in prep). Two of the 

six sightings were in waters ≤35 m deep and the remaining four sightings were in waters 51-200 

m deep. Bowhead whales were also rarely sighted in July-August of 2006-2008 during aerial 

surveys of the Chukchi Sea coast (Thomas et al. 2010). This is consistent with movements of 

tagged whales (see ADFG 2010), all of which moved through the Chukchi Sea by early May 
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2009, and tended to travel relatively close to shore, especially in the northern Chukchi Sea. The 

estimate of bowhead whale density in the Chukchi Sea was calculated by assuming there was 

one bowhead sighting during the 7,447 mi (11,985 km) of survey effort in waters 36-50 m deep 

in the Chukchi Sea during July-August reported in Clarke and Ferguson (in prep), although no 

bowheads were actually observed during those surveys. The mean group size from September–

October sightings reported in Clarke and Ferguson (in prep) is 1.1, and this was also used in the 

calculation of summer densities. The group size value, along with a f(0) value of 2 and a g(0)

value of 0.07, both from Thomas et al. (2002) were used to estimate a summer density of 

bowhead whales (Table 6-1). The CV of group size and standard errors reported in Thomas et al 

(2002) for f(0) and g(0) correction factors suggest that an inflation factor of 2 is appropriate for 

estimating the maximum density from the average density. Bowheads are not expected to be 

encountered in higher densities near ice in the summer (Moore et al. 2000), so the same density 

estimates are used for open-water and ice-margin habitats. Densities from vessel based surveys 

in the Chukchi Sea during non-seismic periods and locations in July-August of 2006-2008 

(Haley et al. 2010) ranged from 0.0003-0.0018/mi2

 (0.0001-0.0007/km2) with a maximum 95 

percent confidence interval (CI) of 0.0075/mi2

 (0.0029/km2). This suggests the densities used in 

the calculations and shown in Table 6-1 are somewhat higher than are likely to be observed from 

vessels near the area of planned operations. 

During the fall, bowhead whales that summered in the Beaufort Sea and Amundsen Gulf migrate 

west and south to their wintering grounds in the Bering Sea making it more likely that bowheads 

will be encountered in the Chukchi Sea at this time of year. Moore et al. (2002; Table 8) 

reported 34 bowhead sightings during 27,560 mi (44,354 km) of on-transect survey effort in the 

Chukchi Sea during September-October. Thomas et al. (2010) also reported increased sightings 

on coastal surveys of the Chukchi Sea during September and October of 2006-2008. GPS 

tagging of bowheads appear to show that migration routes through Chukchi Sea are more 

variable than through the Beaufort Sea (Quakenbush et al. 2010). Some of the routes taken by 

bowheads remain well north of the planned exploration drilling activities while others have 

passed near to or through the area. Kernel densities estimated from GPS locations of whales 

suggest that bowheads do not spend much time (e.g. feeding or resting) in the north-central 

Chukchi Sea near the area of planned activities (Quakenbush et al. 2010). Clarke and Ferguson 

(in prep) reported 14 sightings (15 individuals) during 10,036 km of on transect aerial survey 

effort in 2008-2010. The mean group size of those sightings is 1.1. The same f(0) and g(0)

values that were used for the summer estimates above were used for the fall estimates (Table 6-

2). As with the summer estimates, an inflation factor of 2 was used to estimate the maximum 

density from the average density in both habitat types. Moore et al. (2000) found that bowheads 

were detected more often than expected in association with ice in the Chukchi Sea in SeptemberOctober, so a density of twice the average open-water density was used as the average icemargin density. Densities from vessel based surveys in the Chukchi Sea during non-seismic 

periods and locations in July-August of 2006-2008 (Haley et al. 2010) ranged from 0.0008 to 

0.0114/mi2 (0.0003-0.0044/km2) with a maximum 95 percent confidence interval (CI) of 

0.1089/mi2 (0.0419/km2). This suggests the densities used in the calculations and shown in 

Table 6-2 are somewhat higher than are likely to be observed from vessels near the area of 

planned operations. 

 
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Table 6-1 Expected Densities of Cetaceans and Seals in Areas of the Chukchi Sea, Alaska, for the Planned Summer 

(July–August) Period. Species listed under the U.S. ESA as Endangered are in italics. 

Gray whale densities are expected to be much higher in the summer months than during the fall. 

Moore et al. (2000) found the distribution of gray whales in the planned operational area was 

scattered and limited to nearshore areas where most whales were observed in water less than 114 

ft (35 m) deep. Thomas et al. (2010) also reported substantial declines in the sighting rates of 

gray whales in the fall. The average open-water summer density (Table 6-1) was calculated 

from 2008–2010 aerial survey effort and sightings in Clarke and Ferguson (in prep) for water 

depths 118-164 ft (36-50 m) including 54 sightings (73 individuals) during 7,447 mi (11,985 km) 

of on-transect effort. The average group size of those sightings is 1.35. Correction factors f(0) = 

2.49 (Forney and Barlow 1998) and g(0) = 0.30 (Forney and Barlow 1998, Mallonee 1991) were 

also used in the density calculation. Similar to beluga and bowhead whales, an inflation factor of 

2 was used to estimate the maximum densities from average densities in both habitat types and 

seasons. Gray whales are not commonly associated with sea ice, but may be present near it, so 

the same densities were used for ice-margin habitat as were derived for open-water habitat 

during both seasons. Densities from vessel based surveys in the Chukchi Sea during non-seismic 

periods and locations in July-August of 2006-2008 (Haley et al. 2010) ranged from 0.0055/mi2

 to 

0.0208/mi2

 (0.0021/km2 to 0.0080/km2) with a maximum 95 percent CI of 0.0874 mi2 (0.0336 

km2

). 

Average Maximum Average Maximum

Density Density Density Density

Species (# / km2

) (# / km2) (# / km2) (# / km2)

Odontocetes

Monodontidae

Beluga 0.0010 0.0020 0.0040 0.0080

Narwhal 0.0000 0.0000 0.0000 0.0001

Delphinidae

Killer whale 0.0001 0.0004 0.0001 0.0004

Phocoenidae

Harbor porpoise 0.0011 0.0015 0.0011 0.0015

Mysticetes

Bowhead whale 0.0013 0.0026 0.0013 0.0026

Fin whale 0.0001 0.0004 0.0001 0.0004

Gray whale 0.0258 0.0516 0.0258 0.0516

Humpback whale 0.0001 0.0004 0.0001 0.0004

Minke whale 0.0001 0.0004 0.0001 0.0004

Pinnipeds

Bearded seal 0.0107 0.0203 0.0142 0.0270

Ribbon seal 0.0005 0.0020 0.0005 0.0020

Ringed seal 0.3668 0.6075 0.4891 0.8100

Spotted seal 0.0073 0.0122 0.0098 0.0162

Open Water Ice Margin
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In the fall, gray whales may be dispersed more widely through the northern Chukchi Sea (Moore 

et al. 2000), but overall densities are likely to be decreasing as the whales begin migrating south. 

A density calculated from effort and sightings (15 sightings [19 individuals] during 6,236 mi 

(10,036 km) of on-transect effort) in water 118-164 ft (36-50 m) deep during September–October 

reported by Clarke and Ferguson (in prep) was used as the average estimate for the Chukchi Sea 

during the fall period. The corresponding group size value of 1.26, along with the same f(0) and 

g(0) values described above were used in the calculation. Densities from vessel based surveys in 

the Chukchi Sea during non-seismic periods and locations in July-August of 2006-2008 (Haley 

et al. 2010) ranged from 0.0068/mi2 to 0.0109/mi2 (0.0026/km2 to 0.0042/km2) with a maximum 

95 percent CI of 0.0720 mi2 (0.0277 km2). 

Harbor Porpoise densities were estimated from industry data collected during 2006-2008 

activities in the Chukchi Sea. Prior to 2006, no reliable estimates were available for the Chukchi 

Sea and harbor porpoise presence was expected to be very low and limited to nearshore regions. 

Observers on industry vessels in 2006–2008, however, recorded sightings throughout the 

Chukchi Sea during the summer and early fall months. Density estimates from 2006-2008 

observations during non-seismic periods and locations in July-August ranged from 0.0021/mi2

 to 

0.0039/mi2

 (0.0008/km2 to 0.0015/km2) with a maximum 95 percent CI of 0.0205/mi2

(0.0079/km2) (Haley et al. 2010). The average density from the summer season of those three 

years (0.0029/mi2, 0.0011/km2) was used as the average open-water density estimate while the 

high value (0.0039/mi2

, 0.0015/km2) was used as the maximum estimate (Table 6-1). Harbor 

porpoise are not expected to be present in higher numbers near ice, so the open-water densities 

were used for ice-margin habitat in both seasons. Harbor porpoise densities recorded during 

industry operations in the fall months of 2006-2008 were slightly lower and ranged from 

0.0075/mi2

 to 0.0029/mi2 (0.0029/km2 to 0.0011/km2) with a maximum 95 percent CI of 

0.0242/mi2

 (0.0093/km2). The average of those three years (0.0018/mi2, 0.0007/km2) was again 

used as the average density estimate and the high value 0.0029/mi2 (0.0011/km2) was used as the 

maximum estimate (Table 6-2). 

 
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Table 6-2 Expected Densities of Cetaceans and Seals in Areas of the Chukchi Sea, Alaska, for the Fall (September–

October) Period. Species listed under the U.S. ESA as Endangered are in italics.

The remaining five cetacean species that could be encountered in the Chukchi Sea during Shell’s 

planned exploration drilling program include the humpback whale, killer whale, minke whale, 

fin whale, and narwhal. Although there is evidence of the occasional occurrence of these 

animals in the Chukchi Sea, it is unlikely that more than a few individuals will be encountered 

during the planned exploration drilling program. Clarke et al. (2011) and Haley et al. (2010) 

reported humpback whale sightings; George and Suydam (1998) reported killer whales; 

Brueggeman et al. (1990), Haley et al. (2010) and COMIDA (2011) reported minke whales; and 

Clarke et al. (2011) and Haley et al. (2010) reported fin whales. Narwhal sightings in the 

Chukchi Sea have not been reported in recent literature, but subsistence hunters occasionally 

report observations near Barrow, and Reeves et al. (2002) indicated a small number of 

extralimital sightings in the Chukchi Sea. 

Pinnipeds 

Three species of pinnipeds under NMFS jurisdiction are likely to be encountered in the Chukchi 

Sea during Shell’s planned exploration drilling program: ringed seal, bearded seal, and spotted 

seal. Each of these species, except for the spotted seal, is associated with both the ice margin 

Average Maximum Average Maximum

Density Density Density Density

Species (# / km2

) (# / km2) (# / km2) (# / km2)

Odontocetes

Monodontidae

Beluga 0.0015 0.0030 0.0060 0.0120

Narwhal 0.0000 0.0000 0.0000 0.0001

Delphinidae

Killer whale 0.0001 0.0004 0.0001 0.0004

Phocoenidae

Harbor porpoise 0.0007 0.0011 0.0007 0.0011

Mysticetes

Bowhead whale 0.0219 0.0438 0.0438 0.0876

Fin whale 0.0001 0.0004 0.0001 0.0004

Gray whale 0.0080 0.0160 0.0080 0.0160

Humpback whale 0.0001 0.0004 0.0001 0.0004

Minke whale 0.0001 0.0004 0.0001 0.0004

Pinnipeds

Bearded seal 0.0107 0.0203 0.0142 0.0270

Ribbon seal 0.0005 0.0020 0.0005 0.0020

Ringed seal 0.2458 0.4070 0.3277 0.5427

Spotted seal 0.0049 0.0081 0.0065 0.0108

Open Water Ice Margin
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and the nearshore area. The ice margin is considered preferred habitat (as compared to the 

nearshore areas) for ringed and bearded seals during most seasons. Spotted seals are often 

considered to be predominantly a coastal species except in the spring when they may be found in 

the southern margin of the retreating sea ice. However, satellite tagging has shown that they 

sometimes undertake long excursions into offshore waters during summer (Lowry et al. 1994, 

1998). Ribbon seals have been reported in very small numbers within the Chukchi Sea by 

observers on industry vessels (Patterson et al. 2007, Haley et al. 2010). 

Ringed seal and bearded seals “average” and “maximum” summer ice-margin densities (Table 

6-1) were available in Bengtson et al. (2005) from spring surveys in the offshore pack ice zone 

(zone 12P) of the northern Chukchi Sea. However, corrections for bearded seal availability, 

g(0), based on haulout and diving patterns were not available. Densities of ringed and bearded 

seals in open water are expected to be somewhat lower in the summer when preferred pack ice 

habitat may still be present in the Chukchi Sea. Average and maximum open-water densities 

have been estimated as 3/4 of the ice margin densities during both seasons for both species. The 

fall density of ringed seals in the offshore Chukchi Sea has been estimated as 2/3 the summer 

densities because ringed seals begin to reoccupy nearshore fast ice areas as it forms in the fall. 

Bearded seals may also begin to leave the Chukchi Sea in the fall, but less is known about their 

movement patterns so fall densities were left unchanged from summer densities. For 

comparison, the ringed seal density estimates calculated from data collected during summer 

2006-2008 industry operations ranged from 0.0411/mi2

 to 0.1786/mi2 (0.0158/km2 to 

0.0687/km2

) with a maximum 95 percent CI of 0.3936/mi2 (0.1514/km2) (Haley et al. 2010). 

These estimates are lower than those made by Bengtson et al. (2005) which is not surprising 

given the different survey methods and timing. 

Little information on spotted seal densities in offshore areas of the Chukchi Sea is available. 

Spotted seal densities in the summer were estimated by multiplying the ringed seal densities by 

0.02. This was based on the ratio of the estimated Chukchi populations of the two species (Table 

4-1). Chukchi Sea spotted seal abundance was estimated by assuming that 8 percent of the 

Alaskan population of spotted seals is present in the Chukchi Sea during the summer and fall 

(Rugh et al. 1997), the Alaskan population of spotted seals is 59,214 (Allen and Angliss 2010), 

and that the population of ringed seals in the Alaskan Chukchi Sea is ~208,000 animals 

(Bengtson et al. 2005). In the fall, spotted seals show increased use of coastal haulouts so 

densities were estimated to be 2/3 of the summer densities. 

Two ribbon seal sightings were reported during industry vessel operations in the Chukchi Sea in 

2006-2008 (Haley et al. 2010). The resulting density estimate of 0.0013/mi2

 (0.0005/km2) was 

used as the average density and 4 times that was used as the maximum for both seasons and 

habitat zones. 

As described in earlier sections, the assumed start date of exploration drilling in the Chukchi Sea 

using the drillship Discoverer and associated support vessels is 4 July. Up to four wells (three 

wells, and one partial well) may be drilled in a drilling season, with an assumed average of 32 

days at each drill site (including the partial well drill site, including 7.5 days of MLC excavation 

at all four drill sites. All four drill sites will be at the Burger Prospect. Exploration drilling 

operations are expected to be conducted through 31 October 2012.
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in Conjunction with Planned Exploration Drilling Program During 2012 in the Chukchi Sea, Alaska 

Shell Gulf of Mexico Inc. 37 Revised August 2011 

Area Potentially Exposed to Sounds ≥120 dB or ≥160 dB re 1μPa rms 

Estimated Area Exposed to Continuous Sounds ≥120 dB re 1μPa rms from Exploration 

Drilling Activities 

Sounds from the Discoverer have not previously been measured in the Arctic. However, 

measurements of sounds produced by the Discoverer were made in the South China Sea in 2009 

(Austin and Warner 2010). The results of those measurements were used to model the sound 

propagation from the Discoverer (including a nearby support vessel) at planned exploration 

drilling locations in the Chukchi and Beaufort seas (Warner and Hannay 2011). Broadband 

source levels of sounds produced by the Discoverer varied by activity and direction from the 

ship, but were generally between 177 and 185 dB re 1 μPa 1 m (rms) (Austin and Warner 2010). 

Propagation modeling at the Burger Prospect resulted in an estimated distance of 0.814 mi (1.31 

km) to the point at which exploration drilling sounds would likely fall below 120 dB. The 

estimated 1.31 km distance was multiplied by 1.5 (= 1.22 mi [1.97 km]) as a further 

precautionary measure before calculating the total area that may be exposed to continuous 

sounds ≥120 dB re 1 μPa rms by the Discoverer at each drill site on the Burger Prospect (Table 

6-3). Given this distance or radius, he total area of water ensonified to ≥120 dB rms during 

exploration drilling at each drill site was estimated to be 4.6 mi2

 (12 km2). 

The acoustic propagation model used to estimate the sound propagation from Discoverer in the 

Chukchi Sea is JASCO Research’s Marine Operations Noise Model (MONM). MONM 

computes received sound levels in rms units when source levels are specified also in those units. 

MONM treats sound propagation in range-varying acoustic environments through a wide-angled 

parabolic equation solution to the acoustic wave equation. The specific parabolic equation code 

in MONM is based on the Naval Research Laboratory’s Range-dependent Acoustic Model. This 

code has been extensively benchmarked for accuracy and is widely employed in the underwater 

acoustics community (Collins 1993). 

Changes in the water column of the Chukchi Sea through the course of the exploration drilling 

season will likely affect the propagation of sounds produced by exploration drilling activities, so 

the modeling of exploration drilling sounds was run using expected oceanographic conditions in 

October which are expected to support greater sound propagation (Warner and Hannay 2011). 

Results of sound propagation modeling that were used in the calculations of areas exposed to 

various levels of received sounds are summarized in Table 6-3. 

Distances shown in Table 6-3 were used to estimate the area ensonified to ≥120 dB rms around 

the drillship. As noted above, all exploration drilling activities will occur at the Burger Prospect. 

The exploration drill sites assumed for the summer of 2012 at the Burger Prospect (Burger A, F, 

J, and V) are 3.4 to 13 mi (5.5 km to 21 km) from each other and wells will not be drilled 

simultaneously. Therefore, the area exposed to continuous sounds ≥120 dB at each drill site is 

not expected to overlap with any other drill site. The total area of water potentially exposed to 

received sound levels ≥120 dB rms by exploration drilling operations during July–August at two 

locations is therefore estimated to be 9.42 mi2

 (24.4 km2). Activities at two additional locations 

in September–October may expose an additional 9.42 mi2

 (24.4 km2) to continuous sounds ≥120 

dB rms. 
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Sound propagation measurements will be performed on the Discoverer and support vessels in 

2012, once these are on location in Chukchi Sea. The results of those measurements will be used 

during the season to implement mitigation measures as required by the IHA. 

Table 6-3 Sound Propagation Modeling Results of Exploration Drilling, Icebreaking, and ZVSP Activities at the 

Burger Prospect in the Chukchi Sea 

Estimated Area Exposed to Continuous Sounds ≥120 dB re 1μPa rms from Icebreaking 

Activities 

Measurements of the icebreaking supply ship Robert Lemeur pushing and breaking ice during 

exploration drilling operations in the Beaufort Sea in 1986 resulted in an estimated broadband 

source level of 193 dB re 1 μPa · m (Greene 1987a; Richardson et al. 1995a). Measurements of 

the icebreaking sounds were made at 5 different distances and those were used to generate a 

propagation loss equation [RL=141.4–1.65R–10Log(R) where R is range in kilometers (Greene 

1987a); converting R to meters results in the following equation: R=171.4–10log(R)–0.00165R]. 

Using that equation, the estimated distance to the 120 dB threshold level for continuous sounds 

from icebreaking is 4.74 mi (7.63 km). Since the measurements of the Robert Lemeur were 

taken in the Beaufort Sea under presumably similar conditions as would be encountered in the 

Chukchi Sea in 2012, an inflation factor of 1.25 was selected to arrive at a precautionary 120 dB 

distance of 5.9 mi (9.5 km) for icebreaking sounds. Additionally, measurements of identical 

sound sources at the Burger and Camden Bay prospects in 2008 yielded similar results, 

suggestion that sound propagation at the two locations is likely to be similar (Hannay and 

Warner 2009). 

If ice is present, icebreaking activities may be necessary in early July and towards the end of 

operations in late October, but it is not expected to be needed throughout the proposed 

exploration drilling season. Icebreaking activities would likely occur in a 40o

 arc up to 3.1 mi (5 

km) upwind of the drilling vessel (see Section 1, Figure 1-3 and Attachment B of this application 

for additional details). This activity area plus a 5.9 mi (9.5 km) buffer around it results in an 

estimated total area of 162 mi2

 (420 km2) that may be exposed to sounds ≥120 dB from 

icebreaking activities in each season. 

Estimated Area Exposed to Impulse Sounds ≥160 dB re 1μPa rms from ZVSP Activities 

A typical sound source that would be used by Shell in 2012 is an ITAGA eight-airgun array, 

which consists of four 150 in.3

 (2,458 cm3) airguns and four 40 in.3 (655 cm3) airguns. The ≥160 

dB re 1 μPa rms radius for this source was estimated from measurements of a similar airgun 

source used in the region in 2008 during the BP Liberty seismic survey in the Beaufort Sea. 

Received Level Modeling Used in

Source (dB re 1 μPa) Results (km) Calculations (km)

Discoverer 120 1.31 1.97

Icebreaking 120 7.63 9.50

ZVSP 160 3.67 5.51
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Preseason estimates of the propagation of airgun sounds from the ITAGA VSP sound source 

have therefore been estimated based on the measurements of the seismic source reported in BP’s 

90-day report (Aerts et al. 2008). The BP liberty source was also an eight-airgun array, but had a 

slightly larger total volume of 880 in.3 (14,421 cm3). Because the number of airguns is the same, 

and the difference in total volume only results in an estimated 0.4 dB decrease in the source level 

of the ZVSP source, the 100th percentile propagation model from the measurements of the BP 

Liberty source is almost directly applicable. However, the BP Liberty source was towed at a 

depth of 5.9 ft (1.8 m), while the ZVSP source will be lowered to a target depth of 13 ft (4 m 

[from 10-23 ft (3-7 m)]). The deeper depth of the ZVSP source has the potential to increase the 

source strength by as much as 6 dB. Thus, the constant term in the propagation equation from 

the BP Liberty airgun source has been increased from 235.4 to 241.4 while the remainder of the 

equation (–18*LogR – 0.0047*R) has been left unchanged. This equation results in the 

following estimated distances to maximum received levels: 190 dB = 1719 ft (524 m); 180 dB = 

4068 ft (1240 m); 160 dB = 12,041 ft (3670 m); 120 dB = 34,449 ft (10,500 m). The ≥160 dB 

distance was multiplied by 1.5 (Table 6-3) for use in estimating the area ensonified to ≥160 dB 

rms around the drillship during ZVSP activities. Therefore, the total area of water potentially 

exposed to received sound levels ≥160 dB rms by ZVSP operations at two exploration drill sites 

during each season (summer and fall) is estimated to be 73.67 mi2

 (190.8 km2). 

Potential Number of “Takes by Harassment” 

This subsection provides estimates of the number of individuals potentially exposed to 

continuous sound levels ≥120 dB re 1 μPa rms from exploration drilling and icebreaking 

activities and pulsed sound levels ≥160 dB re 1 μPa rms by ZVSP activities. The estimates are 

based on a consideration of the number of marine mammals that might be disturbed appreciably 

by operations in the Chukchi Sea and the anticipated area exposed to those sound levels. 

The number of individuals of each species potentially exposed to received levels of continuous 

drilling related sounds ≥120 dB or to pulsed airguns sounds ≥160 dB within each season 

(summer and fall) and habitat zone was estimated by multiplying 

– the anticipated area to be ensonified to the specified level in each season (summer and 

fall) and habitat zone to which that density applies, by 

– the expected species density. 

The numbers of individuals potentially exposed were then summed for each species across the 

two seasons and habitat zones. Some of the animals estimated to be exposed, particularly 

migrating bowhead whales, might show avoidance reactions before being exposed to pulsed 

airgun sounds ≥160 dB. Thus, these calculations actually estimate the number of individuals 

potentially exposed to the specified sounds levels that would occur if there were no avoidance of 

the area ensonified to that level. 

The exploration drilling program is planned to occur from July 4 through October 31 as 

described in the previous section. We have assumed that ZVSP activities may occur at each well 

drilled. Additionally, we have assumed that more ice is likely to be present in the area of 

operations during the July–August period, so summer ice-margin densities have been applied to 

50 percent of the area that may be exposed to sounds from exploration drilling and ZVSP 
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activities in those months. Open water densities in the summer were applied to the remaining 50 

percent of the area. Less ice is likely to be present during the September–October period, so fall 

ice-margin densities have been applied to only 20 percent of the area that may be exposed to 

sounds from exploration drilling and ZVSP activities in those months. Fall open-water densities 

were applied to the remaining 80 percent of the area. Since icebreaking activities would only 

occur within ice-margin habitat, the entire area potentially ensonified by icebreaking activities 

has been multiplied by the ice-margin densities in both seasons. 

Species with an estimated average number of individuals exposed equal to zero are included 

below for completeness, but are not likely to be encountered. 

Exploration Drilling Activities 

Estimates of the average and maximum number of individual marine mammals that may be 

exposed to continuous sound levels ≥120 dB by exploration drilling activities are shown by 

season and habitat in Table 6-4. Due to the relatively small estimated ≥120 dB radius around the 

exploration drilling activities, only a few individuals of any species are estimated to be exposed 

based on average densities. However, chance encounters with individuals of any species are 

possible as all listed species are known to occur in the Chukchi Sea. Minimal estimates have 

therefore been included in the Total (Max) column to account for chance encounters or where 

greater numbers may be encountered than calculations suggested. 

Icebreaking Activities 

Estimates of the average and maximum number of individual marine mammals that may be 

exposed to continuous sound levels ≥120 dB by exploration drilling activities are shown by 

season and habitat in Table 6-5. Should icebreaking be necessary, it would ensonify a larger area 

of water to ≥120 dB than the exploration drilling activities or to ≥160 dB by ZVSP surveys and 

therefore results in the highest number of potential estimated individual exposed to such sounds. 

The average and maximum estimates of the number of individual bowhead whales exposed to 

received sound levels ≥120 dB are 19 and 38, respectively. The average estimates for beluga and 

gray whales are 4 and 14, respectively (Table 6-5). Few other cetaceans are likely to be exposed 

to icebreaking sounds ≥120 dB, but maximum estimates have been included to account for 

chance encounters. 

Ringed seals are expected to be the most abundant animal in the Chukchi Sea and the average 

and maximum estimates of the number exposed to ≥120 dB by potential icebreaking activities 

are 343 and 568, respectively (Table 6-5). Estimated exposures of other seal species are 

substantially less than those for ringed seals (Table 6-5). 

 
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ZVSP Activities 

Estimates of the average and maximum number of individual marine mammals that may be 

exposed to pulsed airgun sounds at received levels ≥160 dB during ZVSP activities are shown by 

season and habitat in Tables 6-6. The estimates are somewhat greater than for exploration 

drilling activities because of the larger ≥160 dB radius around the airguns compared to the 

estimated ≥120 dB radius around exploration drilling activities (Table 6-3). 

The average and maximum estimates of the number of individual bowhead whales potentially 

exposed to received sound levels ≥160 dB are 5 and 11, respectively. The average estimates for 

beluga and gray whales are 1 and 6, respectively (Table 6-6). Few other cetaceans are likely to 

be exposed to airgun sounds ≥160 dB, but maximum estimates have been included to account for 

chance encounters. 

The average and maximum estimated number of ringed seals potentially exposed to ≥160 dB by 

ZVSP activities are 132 and 218, respectively (Table 6-6). Estimated exposures of other seal 

species are substantially below those for ringed seals (Table 6-6). 
Application for Incidental Harassment Authorization for the Non-Lethal Taking of Whales and Seals 

in Conjunction with Planned Exploration Drilling Program During 2012 in the Chukchi Sea, Alaska Shell Gulf of Mexico Inc. 42 Revised August 2011 Table 6-4 The number of potential exposures of marine mammals to received sound levels in the water of 

≥120 dB rms during planned exploration drilling 

activities in Summer (July–August) and Fall (September–October) in the Chukchi Sea, Alaska, 2012. 

Avg. Max. Avg. Max.

Avg. Max.

Avg. Max. Avg. Max.

Avg. Max.

Avg. Max.

Odontocetes

Monodontidae

Beluga 0 0 0 0 0 0 00 00 0 0 0 5

Narwhal 0 0 0 0 0 0 00 00 0 0 0 5

Delphinidae

Killer whale 0 0 0 0 0 0 00 00 0 0 0 5

Phocoenida

e

Harbor porpoise 0 0 0 0 0 0 00 00 0 0 0 5

Mysticetes

Bowhead whale 0 0 0 0 0 0 01 00 1 1 1 5Fin whale 0 0 0 0 0 0 00 00 0 0 0 5Gray whale 0 1 0 1 1 1 00 00 0 0 1 5Humpback Whale 0 0 0 0 0 0 00 00 0 0 0 5Minke whale 0 0 0 0 0 0 00 00 0 0 0 5

Pinnipeds

Bearded seal 0 0 0 0 0 1 00 00 0 1 1 5Ribbon seal 0 0 0 0 0 0 00 00 0 0 0 5Ringed seal 4 7

6 10 10 17 5 8 2 3

6 11 17 28

Spotted seal 0 0 0 0 0 0 00 00 0 0 0 5

Number of Individuals Potentially Exposed to Drilling Sounds 

≥ 120 dB

Summer

Total Ice Margin Open Water Open Water

Fall

Grand Total Total Ice Margin
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in Conjunction with Planned Exploration Drilling Program During 2012 in the Chukchi Sea, Alaska Shell Gulf of Mexico Inc. 43 Revised August 2011 Table 6-5 The number of potential exposures of marine mammals to received sound levels in the water of 

≥120 dB rms during potential icebreaking activities in 

Summer (July–August) and Fall (September–October) in the Chukchi Sea, Alaska, 2012. 

Avg. Max. Avg. Max. Avg. Max. Avg. Max. Avg. Max. Avg. Max. Avg. Max.

Odontocetes

Monodontidae

Beluga 0 0 2 3 2 3 0 0 3 5 3 5 4 5Narwhal 0 0 0 0 0 0 0 0 0 0 0 0 0 5

Delphinidae

Killer whale 0 0 0 0 0 0 0 0 0 0 0 0 0 5

Phocoenidae

Harbor porpoise 0 0 0 1 0 1 0 0 0 0 0 0 1 5

Mysticetes

Bowhead whale 0 0 1 1 1 1 0 0 18 37 18 37 19 38Fin whale 00 00 00 00 00 00 05Gray whale 0 0 11 22 11 22 0 0 3 7 3 7 14 28Humpback Whale 00 00 00 00 00 00 05Minke whale 0 0 0 0 0 0 0 0 0 0 0 0 0 5

Pinnipeds

Bearded seal 0 0 6 11 6 11 0 0 6 11 6 11 12 23Ribbon seal 0 0 0 1 0 1 0 0 0 1 0 1 0 5Ringed seal 0 0 205 340 205 340 0 0 138 228 138 228 343 568Spotted seal 0 0 4 7 4 7 0 0 3 5 3 5 7 11

Number of Individuals Potentially Exposed to Icebreaking Sounds 

≥120 dB

Summer Fall

Open Water Ice Margin Total Open Water Ice Margin Total Grand Total
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in Conjunction with Planned Exploration Drilling Program During 2012 in the Chukchi Sea, Alaska Shell Gulf of Mexico Inc. 44 Revised August 2011 Table 6-6 The number of potential exposures of marine mammals to received sound levels in the water of ≥160 dB rms during planned ZVSP 

 activities in Summer (July–August) and Fall (September–October) in the Chukchi Sea, Alaska, 2012. 

Avg. Max. Avg. Max. Avg. Max. Avg. Max. Avg. Max. Avg. Max. Avg. Max.

Odontocetes

Monodontidae

Beluga 0 0 0 1 0 1 00 00 0 1 1 5

Narwhal 0 0 0 0 0 0 00 00 0 0 0 5

Delphinidae

Killer whale 0 0 0 0 0 0 00 00 0 0 0 5

Phocoenidae

Harbor porpoise 0 0 0 0 0 0 00 00 0 0 0 5

Mysticetes

Bowhead whale 0 0 0 0 0 0 37 23 5 10 5 11Fin whale 0 0 0 0 0 0 00 00 0 0 0 5

Gray whale 2 5 2 5 5 10 1 2 0 1 2 3 6 13

Humpback Whale 0 0 0 0 0 0 00 00 0 0 0 5

Minke whale 0 0 0 0 0 0 00 00 0 0 0 5

Pinnipeds

Bearded seal 1 2 1 3 2 5 23 11 2 4 5 9

Ribbon seal 0 0 0 0 0 0 00 00 0 0 0 5Ringed seal 35 58 47 77 82 135 38 62 13 21 50 83 132 218Spotted seal 1 1 1 2 2 3 11 00 1 2 3 5

Number of Individuals Potentially Exposed to VSP Sounds ≥160 dB

Fall Summer

Open Water Ice Margin Total Open Water Ice Margin Total Grand Total
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in Conjunction with Planned Exploration Drilling Program During 2012 in the Chukchi Sea, Alaska Shell Gulf of Mexico Inc. 45 Revised August 2011 Table 6-7 The total number of potential exposures of marine mammals to received sound levels in the water of 

≥120 dB or 

≥160 dB rms during proposed exploration 

drilling, icebreaking, and ZVSP activities in the Chukchi Sea, Alaska, 2012. 

Species Average MaximumOdontocetes

Monodontidae

Beluga 5 15Narwhal 0 15

Delphinidae

Killer whale 0 15

Phocoenidae

Harbor porpoise 1 15

Mysticetes

Bowhead whale 25 53Fin whale 0 15Gray whale 21 46Humpback Whale 0 15Minke whale 0 15

Pinnipeds

Bearded seal 17 36Ribbon seal 1 15Ringed seal 492 814Spotted seal 10 21

Total Number of Individuals Potentially 

Exposed to Sounds 

≥120 dB or 

≥160 dB
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Conclusions 

Effects on marine mammals are generally expected to be restricted to avoidance of the area 

around the planned activities and short-term changes in behavior, falling within the MMPA 

definition of “Level B harassment”. 

Cetaceans 

Overall, few cetaceans are expected to be exposed to continuous sounds ≥120 dB rms or impulse 

sounds ≥160 dB rms in the Chukchi Sea during the exploration drilling program, should they 

show no avoidance of the activities. This is largely a result of the relatively small area expected 

to be exposed to sounds at these levels. The average estimates suggest 25 bowhead whales may 

be exposed to sounds at or above the specified levels (Table 6-7). This number is <1 percent of 

the BCB population of >15,232 assuming 3.4 percent annual population growth from the 2001 

estimate of >10,545 animals (Zeh and Punt 2005) which is supported by a 2004 population 

estimate of 12,631 by Koski et al. (2010). Similarly small numbers of beluga and gray whales 

may also be exposed to sounds from the exploration drilling program if they do not avoid the 

area of operations. The small numbers of other whales that may occur in the Chukchi Sea are 

unlikely to be present around the planned operations but chance encounters may occur. The few 

individuals would represent a very small proportion of their respective populations. 

Pinnipeds 

Ringed seal is by far the most abundant species expected to be encountered during the planned 

operations. The best (average) estimate of the numbers of ringed seals exposed to sounds at the 

specified received levels during the exploration drilling program is 492 ringed seals which 

represents <1 percent of the estimated Chukchi Sea population. Fewer individuals of other 

pinniped species are estimated to be exposed to sounds at the specified received levels, also 

representing small proportions of their populations. Pinnipeds are unlikely to react to continuous 

sounds or impulsive sounds until received levels are much stronger than 120 dB rms and 160 dB, 

respectively. So it is probable that a smaller number of these animals would actually be 

disturbed. 

7. The anticipated impact of the activity on the species or stock: 

The reasonably expected or reasonably likely impacts of the specified activities (planned 

offshore exploration drilling program and brief ZVSP surveys) on marine mammals will be 

related primarily to acoustic effects. Petroleum development and associated activities in marine 

waters introduce sound into the environment. The acoustic sense of marine mammals probably 

constitutes their most important distance receptor system, and underwater sounds could (at least 

in theory) have several types of effects on marine mammals. Potential acoustic effects relate to 

sound produced by exploration drilling activity, vessels and aircraft. 

7.1 Noise Characteristics and Effects 

The effects of sound on marine mammals are highly variable, and can be categorized as follows 

(based on Richardson et al. 1995a): 
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1. The sound may be too weak to be heard at the location of the animal, i.e. lower than the 

prevailing ambient noise level, the hearing threshold of the animal at relevant 

frequencies, or both. 

2. The sound may be audible but not strong enough to elicit any overt behavioral response. 

This has been demonstrated upon exposure of bowhead whales to low levels of seismic, 

drilling, dredge, or icebreaker sounds (Richardson et al. 1986; 1990; 1995a,b,). 

3. The sound may elicit reactions of variable conspicuousness and variable relevance to the 

well being of the animal. These can range from subtle effects on respiration or other 

behaviors (detectable only by statistical analysis) to active avoidance reactions. 

4. Upon repeated exposure, animals may exhibit diminishing responsiveness (habituation), 

or disturbance effects may persist. The latter is most likely with sounds that are highly 

variable in characteristics, unpredictable in occurrence, and associated with situations that 

the animal perceives as a threat. 

5. Any man made sound that is strong enough to be heard has the potential to reduce (mask) 

the ability of marine mammals to hear natural sounds at similar frequencies, including 

calls from conspecifics, echolocation sounds of odontocetes, and environmental sounds 

such as ice or surf noise. 

6. Very strong sounds have the potential to cause temporary or permanent reduction in 

hearing sensitivity. Effects of non-explosive sounds on hearing thresholds of some 

marine mammals have been studied. Data are available for two species of odontocetes 

exposed to a single strong noise pulse lasting one second (Ridgway et al. 1997 and pers. 

comm.) and for three species of pinnipeds exposed to moderately strong sound for 20-22 

minutes (Kastak et al. 1999). Received sound levels must far exceed the animal's hearing 

threshold for any temporary threshold shift (TTS) to occur. The TTS threshold depends 

on duration of exposure; the sound level necessary to cause TTS is higher for short sound 

exposures than for long sound exposures. Received levels must be even higher to risk 

permanent hearing impairment (probably at least 10 dB above the TTS threshold). 

Exploration Drilling Sounds 

Exploration drilling will be conducted from a drillship designed for such operations in the Arctic. 

Underwater sound propagation during the activities results from the use of generators, drilling 

machinery, and the rig itself. Sound levels during vessel-based operations may fluctuate 

depending on the specific type of activity at a given time and aspect from the vessel. Underwater 

sound levels may also depend on the specific equipment in operation. Lower sound levels have 

been reported during well logging than during drilling operations (Greene 1987b), and 

underwater sound appeared to be lower at the bow and stern aspects than at the beam (Greene 

1987a). 

Most drilling sounds generated from vessel-based operations occur at relatively low frequencies 

below 600 hertz (Hz) although tones up to 1,850 Hz were recorded by Greene (1987a) during 

drilling operations in the Beaufort Sea. At a range of 0.1 mi (0.17 km) the 20-1000 Hz band 

level was 122-125 dB re 1μPa for the drillship Explorer I. Underwater sound levels were 
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slightly higher (134 db re 1μPa) during drilling activity from the Explorer II at a range of 0.12 mi 

(0.20 km) although tones were only recorded below 600 Hz. Underwater sound measurements 

from the Kulluk at 0.61 mi (0.98 km) were higher (143 dB re 1μPa) than from the other two 

vessels. 

Airgun Sounds 

A typical eight airgun array used to perform ZVSP surveys in each exploration well would 

consist of 4×40 in.3 (655 cm3) airguns and 4×150 in.3 (2,458 cm3) airguns. Typically, a single 

ZVSP survey will be performed when the well has reached PTD or final depth although, in some 

instances, a prior ZVSP will have been performed at a shallower depth. A typical survey, would 

last 10–14 hours, depending on the depth of the well and the number of anchoring points, and 

include firings of up to the full array, plus additional firing of a single 40 in.3 (655 cm3) airgun to 

be used as a “mitigation airgun” while the geophones are relocated within the wellbore. The 

estimated source level used to model sound propagation from the airgun array is ~241 dB re 

1μPa · m rms. 

Airguns function by venting high-pressure air into the water. The pressure signature of an 

individual airgun consists of a sharp rise and then fall in pressure, followed by several positive 

and negative pressure excursions caused by oscillation of the resulting air bubble. The sizes, 

arrangement, and firing times of the individual airguns in an array are designed and synchronized 

to suppress the pressure oscillations subsequent to the first cycle. A typical high-energy airgun 

arrays emit most energy at 10–120 Hz. However, the pulses contain significant energy up to 

500–1000 Hz and some energy at higher frequencies (Goold and Fish 1998; Potter et al. 2007). 

Aircraft Noise 

Helicopters may be used for personnel and equipment transport to and from the drillship. Under 

calm conditions, rotor and engine sounds are coupled into the water within a 26°(degree) cone 

beneath the aircraft. Some of the sound will transmit beyond the immediate area, and some 

sound will enter the water outside the 26o area when the sea surface is rough. However, 

scattering and absorption will limit lateral propagation in the shallow water. 

Dominant tones in noise spectra from helicopters are generally below 500 Hz (Greene and 

Moore 1995). Harmonics of the main rotor and tail rotor usually dominate the sound from 

helicopters; however, many additional tones associated with the engines and other rotating parts 

are sometimes present. 

Because of doppler shift effects, the frequencies of tones received at a stationary site diminish 

when an aircraft passes overhead. The apparent frequency is increased while the aircraft 

approaches and is reduced while it moves away. 

Aircraft flyovers are not heard underwater for very long, especially when compared to how long 

they are heard in air as the aircraft approaches an observer. Helicopters flying to and from the 
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drillship will generally maintain straight-line routes at altitudes of 1,500 ft (457 m) above sea 

level (ASL), thereby limiting the received levels at and below the surface. 

Vessel Noise 

In addition to the drillship, various types of vessels will be used in support of the operations 

including ice management vessels, an anchor handler, OSVs, and oil-spill response vessels. 

Sounds from boats and vessels have been reported extensively (Greene and Moore 1995; 

Blackwell and Greene 2002, 2005, 2006). Numerous measurements of underwater vessel sound 

have been performed in support of recent industry activity in the Chukchi and Beaufort seas. 

Results of these measurements were reported in various 90-day and comprehensive reports since 

2007. For example, Garner and Hannay (2009) estimated sound pressure levels of 100 db re 1 

μPa at distances ranging from ~1.5 to 2.3 mi (~2.4 to 3.7 km) from various types of barges. 

MacDonnell et al. (2008) estimated higher underwater sound pressure levels from the seismic 

vessel Gilavar of 120 db re 1 μPa at ~13 mi ( ~21 km) from the source, although the sound level 

was only 150 dB at 85 ft (26 m) from the vessel. Like other industry-generated sound, 

underwater sound from vessels is generally at relatively low frequencies. 

The primary sources of sounds from all vessel classes are propeller cavitation, propeller singing, 

and propulsion or other machinery. Propeller cavitation is usually the dominant noise source for 

vessels (Ross 1976). Propeller cavitation and singing are produced outside the hull, whereas 

propulsion or other machinery noise originates inside the hull. There are additional sounds 

produced by vessel activity, such as pumps, generators, flow noise from water passing over the 

hull, and bubbles breaking in the wake. Icebreakers contribute greater sound levels during icebreaking activities than ships of similar size during normal operation in open water (Richardson 

et al. 1995a). This higher sound production results from the greater amount of power and 

propeller cavitation required when operating in thick ice. 

7.2 Summary of Potential Effects of Exposure to Underwater Sounds from Exploration 

Drilling 

The potential effects of sounds from the proposed exploration drilling activities might include 

one or more of the following: tolerance, masking of natural sounds, behavioral disturbance, and 

at least in theory, temporary or permanent hearing impairment, or non-auditory physical effects 

(Richardson et al. 1995a). It is unlikely that there would be any cases of temporary or especially 

permanent hearing impairment, or non-auditory physical effects. 

Tolerance 

Numerous studies have shown that underwater sounds from industry activities are often readily 

detectable in the water at distances of many kilometers. Numerous studies have also shown that 

marine mammals at distances more than a few kilometers away often show no apparent response 

to industry activities of various types. This is often true even in cases when the sounds must be 

readily audible to the animals based on measured received levels and the hearing sensitivity of 

that mammal group. Although various baleen whales, toothed whales, and (less frequently) 

pinnipeds have been shown to react behaviorally to underwater sound such as airgun pulses 

under some conditions, at other times mammals of all three types have shown no overt reactions. 
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In general, pinnipeds, small odontocetes, and sea otters seem to be more tolerant of exposure to 

some types of underwater sound than are baleen whales. 

Disturbance Reactions 

Disturbance includes a variety of effects, including subtle changes in behavior, more 

conspicuous changes in activities, and displacement. Based on NMFS (2001, p. 9293), we 

assume that simple exposure to sound, or brief reactions that do not disrupt behavioral patterns in 

a potentially significant manner, do not constitute harassment or “taking”. By potentially 

significant, we mean “in a manner that might have deleterious effects to the well-being of 

individual marine mammals or their populations”. 

Reactions to sound, if any, depend on species, state of maturity, experience, current activity, 

reproductive state, time of day, and many other factors. If a marine mammal does react briefly to 

an underwater sound by changing its behavior or moving a small distance, the impacts of the 

change are unlikely to be significant to the individual, let alone the stock or the species as a 

whole. However, if a sound source displaces marine mammals from an important feeding or 

breeding area for a prolonged period, impacts on the animals could be significant. In predicting 

the quantity and types of impacts of noise on marine mammals, it is common practice to estimate 

how many mammals were present within a particular distance of industrial activities, or exposed 

to a particular level of industrial sound. This practice, however, likely overestimates the 

numbers of marine mammals that are affected in some biologically-important manner. 

The sound criteria used to estimate how many marine mammals might be disturbed to some 

biologically important degree by industrial sounds are based on behavioral observations during 

studies of several species. Detailed studies have been done on humpback, gray, and bowhead 

whales, and on ringed seals. Less detailed data are available for some other species of baleen 

whales, sperm whales, small toothed whales, and sea otters. 

Baleen Whales—Richardson et al. (1995b) reported changes in surfacing and respiration 

behavior, and the occurrence of turns during surfacing in bowhead whales exposed to playback 

of underwater sound from exploration drilling activities. These subtle behavioral effects were 

temporary and localized, and occurred at distances up to 1.2-2.5 mi (2-4 km). Safety radii for the 

proposed exploration drilling activities are expected to be small and are not expected to result in 

significant disturbance to baleen whales. 

Some bowheads appeared to divert from their migratory path after exposure to projected 

icebreaker sounds. Other bowheads however, tolerated projected icebreaker sound at levels 20 

dB and more above ambient sound levels. The source level of the projected sound however, was 

much less than that of an actual icebreaker, and reaction distances to actual ice breaking may be 

much greater than those reported here for projected sounds. 

Brewer et al. (1993) and Hall et al. (1994) reported numerous sightings of marine mammals 

including bowhead whales in the vicinity of offshore exploration drilling operations in the 

Beaufort Sea. One bowhead whale sighting was reported within ~400 m of a drilling vessel 

although most other bowhead sightings were at much greater distances. Few bowheads were 

recorded near industrial activities by aerial observers. After controlling for spatial 
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autocorrelation in aerial survey data from Hall et al. (1994) using a Mantel test, Schick and 

Urban (2000) found that the variable describing straight line distance between the rig and 

bowhead whale sightings was not significant, but that a variable describing threshold distances 

between sightings and the rig was significant. Thus, although the aerial survey results suggested 

substantial avoidance of the operations by bowhead whales, observations by vessel-based 

observers indicate that at least some bowheads may have been closer to industrial activities than 

was suggested by results of aerial observations. 

Richardson et al. (2008) reported a slight change in the distribution of bowhead whale calls in 

response to operational sounds on BP’s Northstar Island. The southern edge of the call 

distribution ranged from 0.47 to 1.46 mi (0.76 to 2.35 km) farther offshore, apparently in 

response to industrial sound levels. This result however, was only achieved after intensive 

statistical analyses, and it is not clear that this represented a biologically significant effect. 

Patenaude et al. (2002) reported fewer behavioral responses to aircraft overflights by bowhead 

compared to beluga whales. Behaviors classified as reactions consisted of short surfacings, 

immediate dives or turns, changes in behavior state, vigorous swimming, and breaching. Most 

bowhead reaction resulted from exposure to helicopter activity and little response to fixed-wing 

aircraft was observed. Most reactions occurred when the helicopter was at altitudes ≤492 ft 

(≤150 m) and lateral distances ≤820 ft (≤250 m). Restriction on aircraft altitude will be part of 

the mitigation measures during the proposed exploration drilling activities and likely to have 

little or no disturbance effects on baleen whales. Any disturbance that did occur would likely be 

temporary and localized. 

 

Southall et al. (2007 Appendix C) reviewed a number of papers describing the responses of 

marine mammals to non-pulsed sound. In general, little or no response was observed in animals 

exposed at received levels from 90-120 dB rms. Probability of avoidance and other behavioral 

effects increased when received levels were 120-160 dB rms. Some of the relevant reviews of 

Southall et al. (2007) are summarized below. 

Baker et al. (1982) reported some avoidance by humpback whales to vessel noise when received 

levels were 110-120 dB rms, and clear avoidance at 120-140 dB (sound measurements were not 

provided by Baker but were based on measurements of identical vessels by Miles and Malme 

1983). 

Malme et al. (1983, 1984) used playback of sound from helicopter overflight and drilling rigs 

and platforms to study behavioral effects on migrating gray whales. Received levels exceeding 

120 dB induced avoidance reactions. Malme et al. (1984) calculated 10%, 50%, and 90% 

probabilities of gray whale avoidance reactions at received levels of 110, 120, and 130 dB re 1 

μPa, respectively. 

Malme et al. (1986) observed the behavior of feeding gray whales during four experimental 

playbacks of drilling sounds (50 to 315 Hz; 21-minutes (min) overall duration and 10% duty 

cycle; source levels 156 to 162 dB re 1 μPa-m). In two cases for received levels of 100 to 110 dB 

re 1 μPa, no behavioral reaction was observed. Avoidance behavior was observed in two cases 

where received levels were 110 to 120 dB re 1 μPa. 
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Richardson et al. (1990) performed 12 playback experiments in which bowhead whales in the 

Alaskan Arctic were exposed to drilling sounds. Whales generally did not respond to exposures 

in the 100 to 130 dB re 1 μPa range, although there was some indication of minor behavioral 

changes in several instances. 

McCauley et al. (1996) reported several cases of humpback whales responding to vessels in 

Hervey Bay, Australia. Results indicated clear avoidance at received levels between 118 to 124 

dB re 1 μPa in three cases for which response and received levels were observed/measured. 

Palka & Hammond (2001) analyzed line transect census data in which the orientation and 

distance off transect line were reported for large numbers of Minke whales. Minor changes in 

locomotion speed, direction, and/or diving profile were reported at ranges from 1,847 to 2,352 ft 

(563 to 717 m) at received levels (RLs) of 110 to 120 dB re 1 μPa. 

Frankel & Clark (1998) conducted playback experiments with wintering humpback whales using 

a single speaker producing a low-frequency “M-sequence” (sine wave with multiple-phase 

reversals) signal in the 60 to 90 Hz band with output of 172 dB re 1 μPa at 1 m. For 11 

playbacks, exposures were between 120 and 130 dB re 1 μPa and included sufficient information 

regarding individual responses. During eight of the trials, there were no measurable differences 

in tracks or bearings relative to control conditions, whereas on three occasions, whales either 

moved slightly away from (n = 1) or towards (n = 2) the playback speaker during exposure. The 

presence of the source vessel itself had a greater effect than did the M-sequence playback. 

Finally, Nowacek et al. (2004) used controlled exposures to demonstrate behavioral reactions of 

northern right whales to various nonpulse sounds. Playback stimuli included ship noise, social 

sounds of conspecifics, and a complex, 18-min “alert” sound consisting of repetitions of three 

different artificial signals. Ten whales were tagged with calibrated instruments that measured 

received sound characteristics and concurrent animal movements in three dimensions. Five out 

of six exposed whales reacted strongly to alert signals at measured received levels between 130 

and 150 dB re 1 μPa (i.e., ceased foraging and swam rapidly to the surface). Two of these 

individuals were not exposed to ship noise and the other four were exposed to both stimuli. 

These whales reacted mildly to conspecific signals. Seven whales, including the four exposed to 

the alert stimulus, had no measurable response to either ship sounds or actual vessel noise. 

Toothed Whales—Most toothed whales have the greatest hearing sensitivity at frequencies much 

higher than that of baleen whales and may be less responsive to low-frequency sound commonly 

associated with industry activities. Richardson et al. (1995a) reported that beluga whales did not 

show any apparent reaction to playback of underwater drilling sounds at distances greater than 

656–1,312 ft (200-400 m). Reactions included slowing down, milling, or reversal of course after 

which the whales continued past the projector, sometimes within 164-328 ft (50-100 m). The 

authors concluded (based on a small sample size) that playback of drilling sound had no 

biologically significant effects on migration routes of beluga whales migrating through pack ice 

and along the seaward side of the nearshore lead east of Pt. Barrow in spring. 
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At least six of 17 groups of beluga whales appeared to alter their migration path in response to 

underwater playbacks of icebreaker sound (Richardson et al. 1995b). Received levels from the 

icebreaker playback were estimated at 78-84 dB re 1 μPa in the 1/3-octave band centered at 

5,000 Hz, or 8-14 dB above ambient. If beluga whales reacted to an actual icebreaker at received 

levels of 80 dB, reactions would be expected to occur at distances on the order of 6 mi (10 km). 

Finley et al. (1990) also reported beluga avoidance of icebreaker activities in the Canadian High 

Arctic at distances of 22 to 31 mi (35 to 50 km). In addition to avoidance, changes in dive 

behavior and pod integrity were also noted. Beluga whales have also been report to avoid active 

seismic vessels at distances of 6-12 mi (10-19 km) (Miller et al. 2005). It is likely that at least 

some beluga whales may avoid the vicinity of the proposed activities thus reducing the potential 

for exposure to high levels of underwater sound. 

Patenaude et al. (2002) reported that beluga whales appeared to be more responsive to aircraft 

overflights than bowhead whales. Changes were observed in diving and respiration behavior, 

and some whales veered away when a helicopter passed at ≤820 ft (≤250 m) lateral distance at 

altitudes up to 492 ft (150 m). However, some belugas showed no reaction to the helicopter. 

Belugas appeared to show less response to fixed-wing aircraft than to helicopter overflights. 

In reviewing responses of cetaceans with best hearing in mid-frequency ranges, which includes 

toothed whales, Southall et al. (2007) reported that combined field and laboratory data for midfrequency cetaceans exposed to nonpulse sounds did not lead to a clear conclusion about 

received levels coincident with various behavioral responses. In some settings, individuals in the 

field showed profound (significant) behavioral responses to exposures from 90 to 120 dB re 1 

μPa, while others failed to exhibit such responses for exposure to received levels from 120 to 150 

dB re 1 μPa. Contextual variables other than exposure received level, and probable species 

differences, are the likely reasons for this variability. Context, including the fact that captive 

subjects were often directly reinforced with food for tolerating noise exposure, may also explain 

why there was great disparity in results from field and laboratory conditions—exposures in 

captive settings generally exceeded 170 dB re 1 μPa before inducing behavioral responses. 

Below we summarize some of the relevant material reviewed by Southall et al. (2007). 

LGL and Greeneridge (1986) and Finley et al. (1990) documented belugas and narwhals 

congregated near ice edges reacting to the approach and passage of icebreaking ships. Beluga 

whales responded to oncoming vessels by (1) fleeing at speeds of up to 20 kilometers per hour 

(km/hr) from distances of 12 to 50 mi (19 to 80 km), (2) abandoning normal pod structure, and 

(3) modifying vocal behavior and/or emitting alarm calls. Narwhals, in contrast, generally 

demonstrated a “freeze” response, lying motionless or swimming slowly away (as far as 23 

mi/37 km down the ice edge), huddling in groups, and ceasing sound production. There was 

some evidence of habituation and reduced avoidance 2 to 3 days after onset. 

The 1982 season observations by LGL & Greeneridge (1986) involved a single passage of an 

icebreaker with both ice-based and aerial measurements on 28 June 1982. Four groups of 

narwhals (n = 9 to 10, 7, 7, and 6) responded when the ship was 4.0 mi (6.4 km away) with 

received levels of ~100 dB re 1 μPa in the 150- to 1,150-Hz band. At a later point, observers 

sighted belugas moving away from the source at >12.4 mi (> 20 km) with received levels of ~90 

dB re 1 μPa in the 150- to 1,150-Hz band. The total number of animals observed fleeing was 
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about 300, suggesting approximately 100 independent groups (of three individuals each). No 

whales were sighted the following day, but some were sighted on 30 June, with ship noise 

audible at spectrum levels of approximately 55 dB re 1 μPa/Hz (up to 4 kHz). 

Observations during 1983 (LGL & Greeneridge 1986) involved two icebreaking ships with aerial 

survey and ice-based observations during seven sampling periods. Narwhals and belugas 

generally reacted at received levels ranging from 101 to 121 dB re 1 μPa in the 20- to 1,000-Hz 

band and at a distance of up to 65 km. Large numbers (100s) of beluga whales moved out of the 

area at higher received levels. As noise levels from icebreaking operations diminished, a total of 

45 narwhals returned to the area and engaged in diving and foraging behavior. During the final 

sampling period, following an 8-hour quiet interval, no reactions were seen from 28 narwhals 

and 17 belugas (at received levels ranging up to 115 dB re 1 μPa). 

The final season (1984) reported in LGL & Greeneridge (1986) involved aerial surveys before, 

during, and after the passage of two icebreaking ships. During operations, no belugas and few 

narwhals were observed in an area approximately 17 mi (27 km) ahead of the vessels, and all 

whales sighted over 12-50 mi (19 to 80 km) from the ships were swimming strongly away. 

Additional observations confirmed the spatial extent of avoidance reactions to this sound source 

in this context. 

Gordon et al. (1992) conducted opportunistic visual and acoustic monitoring of sperm whales in 

New Zealand exposed to nearby whale-watching boats (within 1,476 ft/450 m). Sperm whales 

respired significantly less frequently, had shorter surface intervals, and took longer to start 

clicking at the start of a dive descent when boats were nearby than when they were absent. Noise 

spectrum levels of whalewatching boats ranged from 109 to 129 dB re 1 μPa/Hz. Over a 

bandwidth of 100 to 6,000 Hz, equivalent broadband source levels were ~157 dB re 1 μPa-m; 

received levels at a range of 1,476 ft (450 m) were ~104 dB re 1 μPa. 

Buckstaff (2004) reported elevated dolphin whistle rates with received levels (RLs) from 

oncoming vessels in the 110 to < 120 dB re 1 μPa. These hearing thresholds were apparently 

lower than those reported by a researcher listening with towed hydrophones. 

Morisaka et al. (2005) compared whistles from three populations of Indo-Pacific bottlenose 

dolphins (Tursiops aduncus). One population was exposed to vessel noise with spectrum levels 

of ~85 dB re 1 μPa/Hz in the 1- to 22-kHz band (broadband received levels ~128 dB re 1 μPa) as 

opposed to ~65 dB re 1 μPa/Hz in the same band (broadband RL ~108 dB re 1 μPa) for the other 

two sites. Dolphin whistles in the noisier environment had lower fundamental frequencies and 

less frequency modulation, suggesting a shift in sound parameters as a result of increased 

ambient noise. 

Morton and Symonds (2002) used census data on killer whales in British Columbia to evaluate 

avoidance of nonpulse acoustic harassment devices (AHDs). Avoidance ranges were about 2.5 

mi (4 km). Also, there was a dramatic reduction in the number of days “resident” killer whales 

were sighted during AHD-active periods compared to pre- and post-exposure periods and a 

nearby control site. 
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Monteiro-Neto et al. (2004) studied avoidance responses of tucuxi (Sotalia fluviatilis) to 

Dukane® Netmark acoustic deterrent devices. In a total of 30 exposure trials, ~5 groups each 

demonstrated significant avoidance compared to 20 pinger off and 55 no-pinger control trials 

over two quadrats of about 0.2 mi2 (0.5 km2). Estimated exposure received levels were ~115 dB 

re 1 μPa. 

Awbrey & Stewart (1983) played back semi-submersible drillship sounds (source level: 163 dB 

re 1 μPa-m) to belugas in Alaska. They reported avoidance reactions at 985 ft and 4,921 ft (300 

m and 1,500 m) and approach by groups at a distance of 3,927 yd (3,500 m) with received levels 

~110 to 145 dB re 1 μPa over these ranges assuming a 15 log R transmission loss. Similarly, 

Richardson et al. (1990) played back drilling platform sounds (source level: 163 dB re 1 μPa-m) 

to belugas in Alaska. They conducted aerial observations of eight individuals among ~100 spread 

over an area several hundred meters to several kilometers from the sound source and found no 

obvious reactions. Moderate changes in movement were noted for three groups swimming within 

656 ft (200 m) of the sound projector. 

Finally, two recent papers deal with important issues related to changes in marine mammal vocal 

behavior as a function of variable background noise levels. Foote et al. (2004) found increases in 

the duration of killer whale calls over the period 1977 to 2003, during which time vessel traffic 

in Puget Sound, and particularly whale-watching boats around the animals, increased 

dramatically. Scheifele et al. (2005) demonstrated that belugas in the St. Lawrence River 

increased the levels of their vocalizations as a function of the background noise level (the 

“Lombard Effect”). 

Several researchers conducting laboratory experiments on hearing and the effects of nonpulse 

sounds on hearing in mid-frequency cetaceans have reported concurrent behavioral responses. 

Nachtigall et al. (2003) reported that noise exposures up to 179 dB re 1 μPa and 55-min duration 

affected the trained behaviors of a bottlenose dolphin participating in a TTS experiment. 

Finneran & Schlundt (2004) provided a detailed, comprehensive analysis of the behavioral 

responses of belugas and bottlenose dolphins to 1-s tones (received levels 160 to 202 dB re 1 

μPa) in the context of TTS experiments. Romano et al. (2004) investigated the physiological 

responses of a bottlenose dolphin and a beluga exposed to these tonal exposures and 

demonstrated a decrease in blood cortisol levels during a series of exposures between 130 and 

201 dB re 1 μPa. Collectively, the laboratory observations suggested the onset of behavioral 

response at higher received levels than did field studies. The differences were likely related to 

the very different conditions and contextual variables between untrained, free-ranging 

individuals vs. laboratory subjects that were rewarded with food for tolerating noise exposure. 

Pinnipeds—Pinnipeds generally seem to be less responsive to exposure to industrial sound than 

most cetaceans. Pinniped responses to underwater sound from some types of industrial activities 

such as seismic exploration appear to be temporary and localized (Harris et al. 2001, Reiser et al. 

2009b). 

Blackwell et al. (2004) reported little or no reaction of ringed seals in response to pile-driving 

activities during construction of a man-made island in the Beaufort Sea. Ringed seals were 

observed swimming as close as 150 ft (46 m) from the island and may have been habituated to 
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the sounds which were likely audible at distances <1.9 mi (<3.0 km) underwater and 0.3 mi (0.5 

km) in air. Moulton et al. (2003) reported that ringed seal densities on ice in the vicinity of a 

man-made island in the Beaufort Sea did not change significantly before and after construction 

and drilling activities. 

Southall et al. (2007) reviewed literature describing responses of pinnipeds to non-pulsed sound 

and reported that the limited data suggest exposures between ~90 and 140 dB re 1 μPa generally 

do not appear to induce strong behavioral responses in pinnipeds exposed to nonpulse sounds in 

water; no data exist regarding exposures at higher levels. It is important to note that among these 

studies of pinnipeds responding to nonpulse exposures in water, there are some apparent 

differences in responses between field and laboratory conditions. In contrast to the midfrequency odontocetes, captive pinnipeds responded more strongly at lower levels than did 

animals in the field. Again, contextual issues are the likely cause of this difference. 

Jacobs & Terhune (2002) observed harbor seal reactions to AHDs (source level in this study was 

172 dB re: 1 μPa-m) deployed around aquaculture sites. Seals were generally unresponsive to 

sounds from the AHDs. During two specific events, individuals came within 43 and 44 m of 

active AHDs and failed to demonstrate any measurable behavioral response; estimated received 

levels based on the measures given were ~120 to 130 dB re 1 μPa. 

Costa et al. (2003) measured received noise levels from an Acoustic Thermometry of Ocean 

Climate (ATOC) program sound source off northern California using acoustic data loggers 

placed on translocated elephant seals. Subjects were captured on land, transported to sea, 

instrumented with archival acoustic tags, and released such that their transit would lead them 

near an active ATOC source (at 3,081 ft [939-m] depth; 75-Hz signal with 37.5- Hz bandwidth; 

195 dB re 1 μPa-m max. source level, ramped up from 165 dB re 1 μPa-m over 20 min) on their 

return to a haulout site. Received exposure levels of the ATOC source for experimental subjects 

averaged 128 dB re 1 μPa (range 118 to 137) in the 60- to 90-Hz band. None of the instrumented 

animals terminated dives or radically altered behavior upon exposure, but some statistically 

significant changes in diving parameters were documented in nine individuals. Translocated 

northern elephant seals exposed to this particular nonpulse source began to demonstrate subtle 

behavioral changes at ~120 to 140 dB re 1 μPa exposure RLs. 

Kastelein et al. (2006) exposed nine captive harbor seals in a ~80 x 100 ft (~24 × 30 m) 

enclosure to nonpulse sounds used in underwater data communication systems (similar to 

acoustic modems). Test signals were frequency modulated tones, sweeps, and bands of noise 

with fundamental frequencies between 8 and 16 kHz; 128 to 130 [± 3] dB re 1 μPa-m source 

levels; 1- to 2-s duration (60-80% duty cycle); or 100% duty cycle. They recorded seal positions 

and the mean number of individual surfacing behaviors during control periods (no exposure), 

before exposure, and in 15-min experimental sessions (n = 7 exposures for each sound type). 

Seals generally swam away from each source at received levels of ~107 dB re 1 μPa, avoiding it 

by ~5 m, although they did not haul out of the water or change surfacing behavior. Seal reactions 

did not appear to wane over repeated exposure (i.e., there was no obvious habituation), and the 

colony of seals generally returned to baseline conditions following exposure. The seals were not 

reinforced with food for remaining in the sound field. 
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7.3 Summary of Potential Effects of Exposure to Underwater Sounds from Airguns 

Tolerance 

Numerous studies have shown that pulsed sounds from airguns are often readily detectable in the 

water at distances of many kilometers. Numerous studies have shown that marine mammals at 

distances more than a few kilometers from operating seismic vessels often show no apparent 

response. That is often true even in cases when the pulsed sounds must be readily audible to the 

animals based on measured received levels and the hearing sensitivity of that mammal group. 

Although various baleen whales, toothed whales, and (less frequently) pinnipeds have been 

shown to react behaviorally to airgun pulses under some conditions, at other times mammals of 

all three types have shown no overt reactions. In general, pinnipeds, small odontocetes, and sea 

otters seem to be more tolerant of exposure to airgun pulses than are baleen whales. 

Masking 

Masking effects of underwater sounds on marine mammal calls and other natural sounds are 

expected to be limited. Masking effects of pulsed sounds (even from larger arrays of airguns 

than proposed in this project) on marine mammal calls and other natural sounds are expected to 

be limited, although there are very few specific data of relevance. Some whales are known to 

continue calling in the presence of seismic pulses. Their calls can be heard between the seismic 

pulses (e.g., Richardson et al. 1986; McDonald et al. 1995; Greene et al. 1999; Nieukirk et al. 

2004). Although there has been one report that sperm whales cease calling when exposed to 

pulses from a very distant seismic ship (Bowles et al. 1994), a more recent study reports that 

sperm whales off northern Norway continued calling in the presence of seismic pulses (Madsen 

et al. 2002). That has also been shown during recent work in the Gulf of Mexico (Tyack et al. 

2003). Bowhead whale calls are frequently detected in the presence of seismic pulses, although 

the number of calls detected may sometimes be reduced in the presence of airgun pulses 

(Richardson et al. 1986; Greene et al. 1999; Blackwell et al. 2009a). Bowhead whales in the 

Beaufort Sea may decrease their call rates in response to seismic operations, although movement 

out of the area might also have contributed to the lower call detection rate (Blackwell et al. 

2009a,b). Additionally, there is increasing evidence that, at times, there is enough reverberation 

between airgun pulses such that detection range of calls may be significantly reduced. In 

contrast, Di Iorio and Clark (2009) found evidence of increased calling by blue whales during 

operations by a lower-energy seismic source, a sparker. Masking effects of seismic pulses are 

expected to be negligible given the low number of cetaceans expected to be exposed, the 

intermittent nature of seismic pulses and the fact that ringed seals (the most abundant species in 

the area) are not typically vocal during this period. 

Disturbance Reactions 

Baleen Whales— Baleen whale responses to pulsed sound have been studied more thoroughly 

than responses to continuous sound. Baleen whales generally tend to avoid operating airguns, but 

avoidance radii are quite variable. Whales are often reported to show no overt reactions to 

pulses from large arrays of airguns at distances beyond a few kilometers, even though the airgun 

pulses remain well above ambient noise levels out to much longer distances. However, baleen 

whales exposed to strong noise pulses from airguns may react by deviating from their normal 
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migration route. In the case of the migrating gray and bowhead whales, observed changes in 

behavior appeared to be of little or no biological consequence to the animals. They simply 

avoided the sound source by displacing their migration route to varying degrees, but within the 

natural boundaries of the migration corridors. Baleen whale responses to pulsed sound however, 

may depend on the type of activity in which the whales are engaged. Some evidence suggests 

that feeding bowhead whales may be more tolerant of underwater sound than migrating 

bowheads (Miller et al. 2005; Lyons et al. 2009; Christie et al. 2010). 

Studies of gray, bowhead, and humpback whales have determined that received levels of pulses 

in the 160–170 dB re 1 μPa rms range seem to cause obvious avoidance behavior in a substantial 

fraction of the animals exposed. In many areas, seismic pulses from large arrays of airguns 

diminish to those levels at distances ranging from 2.8 to 9.0 mi (4.5 to 14.5 km) from the source. 

For the much smaller airgun array used during the ZVSP survey, distances to received levels in 

the 160–170 dB re 1 μPa rms range are estimated to be 1.44-2.28 mi (2.31-3.67 km). Baleen 

whales within those distances may show avoidance or other strong disturbance reactions to the 

airgun array. Subtle behavioral changes sometimes become evident at somewhat lower received 

levels, and studies have shown that some species of baleen whales, notably bowhead and 

humpback whales, at times show strong avoidance at received levels lower than 160–170 dB re 1 

μPa rms. Bowhead whales migrating west across the Alaskan Beaufort Sea in autumn, in 

particular, are unusually responsive, with avoidance occurring out to distances of 12-19 mi (20–

30 km) from a medium-sized airgun source (Miller et al. 1999; Richardson et al. 1999). 

However, more recent research on bowhead whales (Miller et al. 2005) corroborates earlier 

evidence that, during the summer feeding season, bowheads are not as sensitive to seismic 

sources. In summer, bowheads typically begin to show avoidance reactions at a received level of 

about 160–170 dB re 1 μPa rms (Richardson et al. 1986; Ljungblad et al. 1988; Miller et al. 

1999). 

Malme et al. (1986, 1988) studied the responses of feeding eastern gray whales to pulses from a 

single 100 in.3

 (1,639 cm3) airgun off St. Lawrence Island in the northern Bering Sea. They 

estimated, based on small sample sizes, that 50% of feeding gray whales ceased feeding at an 

average received pressure level of 173 dB re 1 μPa on an (approximate) rms basis, and that 10% 

of feeding whales interrupted feeding at received levels of 163 dB. Those findings were 

generally consistent with the results of experiments conducted on larger numbers of gray whales 

that were migrating along the California coast, and on observations of the distribution of feeding 

Western Pacific gray whales off Sakhalin Island, Russia during a seismic survey (Yazvenko et al. 

2007). 

Data on short-term reactions (or lack of reactions) of cetaceans to impulsive noises do not 

necessarily provide information about long-term effects. It is not known whether impulsive 

noises affect reproductive rate or distribution and habitat use in subsequent days or years. 

However, gray whales continued to migrate annually along the west coast of North America 

despite intermittent seismic exploration and much ship traffic in that area for decades (Appendix 

A in Malme et al. 1984). Bowhead whales continued to travel to the eastern Beaufort Sea each 

summer despite seismic exploration in their summer and autumn range for many years 

(Richardson et al. 1987). Populations of both gray whales and bowhead whales grew 
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in Conjunction with Planned Exploration Drilling Program During 2012 in the Chukchi Sea, Alaska 

Shell Gulf of Mexico Inc. 59 Revised August 2011 

substantially during this time. In any event, the brief exposures to sound pulses from the 

proposed airgun source are highly unlikely to result in prolonged effects. 

Toothed Whales—Few systematic data are available about reactions of toothed whales to noise 

pulses. Few studies similar to the more extensive baleen whale/seismic pulse work summarized 

above have been reported for toothed whales. However, systematic work on sperm whales is 

underway (Tyack et al. 2003), and there is an increasing amount of information about responses 

of various odontocetes to seismic surveys based on monitoring studies (e.g., Stone 2003; Smultea 

et al. 2004; Moulton and Miller 2005). 

Seismic operators and marine mammal observers sometimes see dolphins and other small 

toothed whales near operating airgun arrays, but in general there seems to be a tendency for most 

delphinids to show some limited avoidance of seismic vessels operating large airgun systems. 

However, some dolphins seem to be attracted to the seismic vessel and floats, and some ride the 

bow wave of the seismic vessel even when large arrays of airguns are firing. Nonetheless, there 

have been indications that small toothed whales sometimes move away, or maintain a somewhat 

greater distance from the vessel, when a large array of airguns is operating than when it is silent 

(e.g., Goold 1996a,b,c; Calambokidis and Osmek 1998; Stone 2003). The beluga may be a 

species that (at least at times) shows long-distance avoidance of seismic vessels. Aerial surveys 

during seismic operations in the southeastern Beaufort Sea recorded much lower sighting rates of 

beluga whales within 6-12 mi (10–20 km) of an active seismic vessel. These results were 

consistent with the low number of beluga sightings reported by observers aboard the seismic 

vessel, suggesting that some belugas might be avoiding the seismic operations at distances of 

6-12 mi (10–20 km) (Miller et al. 2005). 

Captive bottlenose dolphins and (of more relevance in this project) beluga whales exhibit 

changes in behavior when exposed to strong pulsed sounds similar in duration to those typically 

used in seismic surveys (Finneran et al. 2002, 2005). However, the animals tolerated high 

received levels of sound (pk–pk level >200 dB re 1 μPa) before exhibiting aversive behaviors. 

 

Reactions of toothed whales to large arrays of airguns are variable and, at least for delphinids, 

seem to be confined to a smaller radius than has been observed for mysticetes. A ≥170 dB 

disturbance criterion (rather than ≥160 dB) is considered appropriate for delphinids (and 

pinnipeds), which tend to be less responsive than other cetaceans. However, based on the limited 

existing evidence, belugas should not be grouped with delphinids in the “less responsive” 

category. 

Pinnipeds—Pinnipeds are not likely to show a strong avoidance reaction to the airgun sources 

that will be used. Visual monitoring from seismic vessels has shown only slight (if any) 

avoidance of airguns by pinnipeds, and only slight (if any) changes in behavior. Ringed seals 

frequently do not avoid the area within a few hundred meters of operating airgun arrays (Harris 

et al. 2001; Moulton and Lawson 2002; Miller et al. 2005). However, initial telemetry work 

suggests that avoidance and other behavioral reactions by two other species of seals to small 

airgun sources may at times be stronger than evident to date from visual studies of pinniped 

reactions to airguns (Thompson et al. 1998). Even if reactions of the species occurring in the 

present study area are as strong as those evident in the telemetry study, reactions are expected to 
Application for Incidental Harassment Authorization for the Non-Lethal Taking of Whales and Seals 

in Conjunction with Planned Exploration Drilling Program During 2012 in the Chukchi Sea, Alaska 

Shell Gulf of Mexico Inc. 60 Revised August 2011 

be confined to relatively small distances and durations, with no long-term effects on pinniped 

individuals or populations. As for delphinids, a ≥170 dB disturbance criterion is considered 

appropriate for pinnipeds, which tend to be less responsive than many cetaceans. 

Hearing Impairment and Other Physical Effects 

Temporary or permanent hearing impairment is a possibility when marine mammals are exposed 

to very strong sounds. Current NMFS policy regarding exposure of marine mammals to highlevel sounds is that cetaceans and pinnipeds should not be exposed to impulsive sounds 180 and 

≥190 dB re 1 μPa (rms), respectively (NMFS 2000). Those criteria have been used in defining 

the safety (shut down) radii during seismic survey activities in the Arctic in recent years. 

However, those criteria were established before there were any data on the minimum received 

levels of sounds necessary to cause temporary auditory impairment in marine mammals. In 

summary, 

• the 180 dB criterion for cetaceans is probably quite precautionary, i.e., lower than 

necessary to avoid TTS, let alone permanent auditory injury, at least for belugas and 

delphinids. 

• the minimum sound level necessary to cause permanent hearing impairment is higher, by 

a variable and generally unknown amount, than the level that induces barely-detectable 

TTS. 

• the level associated with the onset of TTS is often considered to be a level below which 

there is no danger of permanent damage. 

NMFS is presently developing new noise exposure criteria for marine mammals that account for 

the now-available scientific data on TTS and other relevant factors in marine and terrestrial 

mammals (NMFS 2005b; D. Wieting in Orenstein et al. 2004). New science-based noise 

exposure criteria are also proposed by a group of experts in this field, based on an extensive 

review and syntheses of available data on the effect of noise on marine mammals (Southall et al., 

2007) and this review seems to confirm that the current 180 dB and 190 dB are conservative. 

Several aspects of the planned monitoring and mitigation measures for this project are designed 

to detect marine mammals occurring near the exploration drilling activities to avoid exposing 

them to underwater sound levels that might, at least in theory, cause hearing impairment. In 

addition, many cetaceans are likely to show some avoidance of the proposed activities. In those 

cases, the avoidance responses of the animals themselves will reduce or (most likely) avoid any 

possibility of hearing impairment. 

Non-auditory physical effects might also occur in marine mammals exposed to strong 

underwater sound. Possible types of non-auditory physiological effects or injuries that 

theoretically might occur in mammals close to a strong sound source include stress, neurological 

effects, bubble formation, and other types of organ or tissue damage. It is possible that some 

marine mammal species (i.e., beaked whales) may be especially susceptible to injury and/or 

stranding when exposed to strong pulsed sounds. However, as discussed below, there is no 

definitive evidence that any of these effects occur even for marine mammals in close proximity 

to industrial sound sources and beaked whales do not occur in the proposed study area. It is 

unlikely that any effects of these types would occur during the proposed project given the brief 
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in Conjunction with Planned Exploration Drilling Program During 2012 in the Chukchi Sea, Alaska 

Shell Gulf of Mexico Inc. 61 Revised August 2011 

duration of exposure of any given mammal, and the planned monitoring and mitigation measures 

(see below). The following subsections discuss in somewhat more detail the possibilities of 

TTS, permanent threshold shift (PTS), and non-auditory physical effects. 

Temporary Threshold Shift - TTS is the mildest form of hearing impairment that can occur 

during exposure to a strong sound (Kryter 1985). While experiencing TTS, the hearing threshold 

rises and a sound must be stronger in order to be heard. At least in terrestrial mammals, TTS can 

last from minutes or hours to (in cases of strong TTS) days. For sound exposures at or somewhat 

above the TTS threshold, hearing sensitivity in both terrestrial and marine mammals recovers 

rapidly after exposure to the noise ends. Few data on sound levels and durations necessary to 

elicit mild TTS have been obtained for marine mammals, and none of the published data concern 

TTS elicited by exposure to multiple impulses of sound. [There are, however, recent data on 

TTS in dolphins caused by multiple pulses of sonar sound―Mooney et al. (2009).] 

The distinction between TTS and PTS is not absolute. Although mild TTS is fully reversible and 

is not considered to be injury, exposure to considerably higher levels of sound causes more 

“robust” TTS, involving a more pronounced temporary impairment of sensitivity that takes 

longer to recover. There are very few data on recovery of marine mammals from substantial 

degrees of TTS, but in terrestrial mammals there is evidence that “robust” TTS may not be fully 

recoverable, i.e., TTS can grade into PTS (Le Prell in press). 

The received energy level of a single seismic pulse that caused the onset of mild TTS in the 

beluga, as measured without frequency weighting, was ~186 dB re 1 μPa2 · s or 186 dB sound 

exposure level (SEL) (Finneran et al. 2002).1

 The rms level of an airgun pulse (in dB re 1 μPa 

measured over the duration of the pulse) is typically 10–15 dB higher than the SEL for the same 

pulse when received within a few kilometers of the airguns. Thus, a single airgun pulse might 

need to have a received level of ~196–201 dB re 1 μPa rms in order to produce brief, mild TTS. 

Exposure to several strong seismic pulses that each has a flat-weighted received level near 190 

dB rms (175–180 dB SEL) could result in cumulative exposure of ~186 dB SEL (flat-weighted) 

or ~183 dB SEL (Mmf-weighted), and thus slight TTS in a small odontocete. That assumes that 

the TTS threshold upon exposure to multiple pulses is (to a first approximation) a function of the 

total received pulse energy, without allowance for any recovery between pulses. 

For baleen whales, there are no data, direct or indirect, on levels or properties of sound that are 

required to induce TTS. However, no cases of TTS are expected given the moderate size of the 

source, and the likelihood that baleen whales (especially migrating bowheads) would avoid the 

exploration drilling and vessel activities before being exposed to levels high enough for there to 

be any possibility of TTS. 

In pinnipeds, TTS thresholds associated with exposure to brief pulses (single or multiple) of 

underwater sound have not been measured. Initial evidence from prolonged exposures to sound 

suggested that some pinnipeds may incur TTS at somewhat lower received levels than do small 

odontocetes exposed for similar durations (Kastak et al. 1999, 2005; Ketten et al. 2001; cf. Au et 

 

1

 If the low-frequency components of the watergun sound used in the experiments of Finneran et al. (2002) are 

downweighted as recommended by Southall et al. (2007) using their Mmf-weighting curve, the effective exposure 

level for onset of mild TTS was 183 dB re 1 μPa2 · s (Southall et al. 2007). 
Application for Incidental Harassment Authorization for the Non-Lethal Taking of Whales and Seals 

in Conjunction with Planned Exploration Drilling Program During 2012 in the Chukchi Sea, Alaska 

Shell Gulf of Mexico Inc. 62 Revised August 2011 

al. 2000). For harbor seal, which is closely related to the ringed seal, TTS onset apparently 

occurs at somewhat lower received energy levels than for odontocetes. 

NMFS (1995, 2000) concluded that cetaceans and pinnipeds should not be exposed to pulsed 

underwater noise at received levels exceeding, respectively, 180 and 190 dB re 1 μPa (rms). 

NMFS is in the process of developing an EIS to establish new sound exposure criteria for marine 

mammals (NMFS 2005b). New criteria are likely to include a time component in addition to 

sound pressure level which has been the only metric used previously when developing mitigation 

measures for industrial sound exposure for marine mammals. Due to the relatively small sound 

radii expected to result from the proposed exploration drilling and support activities, marine 

mammals would be unlikely to incur TTS without remaining very near the activities for some 

unknown time period. Given the proposed mitigation and the likelihood that many marine 

mammals are likely to avoid the proposed activities, exposure sufficient to produce TTS is 

unlikely to occur. 

Permanent Threshold Shift (PTS) - When PTS occurs, there is physical damage to the sound 

receptors in the ear. In some cases, there can be total or partial deafness, whereas in other cases, 

the animal has an impaired ability to hear sounds in specific frequency ranges. 

There is no specific evidence that exposure to underwater industrial sound associated with oil 

exploration can cause PTS in any marine mammal. However, given the possibility that 

mammals might incur TTS, there has been further speculation about the possibility that some 

individuals occurring very close to such activities might incur PTS. Single or occasional 

occurrences of mild TTS are not indicative of permanent auditory damage in terrestrial 

mammals. Relationships between TTS and PTS thresholds have not been studied in marine 

mammals, but are assumed to be similar to those in humans and other terrestrial mammals. PTS 

might occur at a received sound level at least several decibels above that inducing mild TTS. 

It is highly unlikely that marine mammals could receive sounds strong enough (and over a 

sufficient duration) to cause permanent hearing impairment during the proposed exploration 

drilling program. Marine mammals are unlikely to be exposed to received levels strong enough 

to cause even slight TTS. Given the higher level of sound necessary to cause PTS, it is even less 

likely that PTS could occur. In fact, even the levels immediately adjacent to the drillship may 

not be sufficient to induce PTS, even if the animals remain in the immediate vicinity of the 

activity. The planned monitoring and mitigation measures, including measurement of sound 

radii and visual monitoring when mammals are seen within “safety radii”, will minimize the 

already-minimal probability of exposure of marine mammals to sounds strong enough to induce 

PTS. 

Non-auditory Physiological Effects - Non-auditory physiological effects or injuries that 

theoretically might occur in marine mammals exposed to strong underwater sound include stress, 

neurological effects, bubble formation, and other types of organ or tissue damage. If any such 

effects do occur, they probably would be limited to unusual situations when animals might be 

exposed at close range for unusually long periods. It is doubtful that any single marine mammal 

would be exposed to strong seismic sounds for sufficiently long that significant physiological 

stress would develop. 
Application for Incidental Harassment Authorization for the Non-Lethal Taking of Whales and Seals 

in Conjunction with Planned Exploration Drilling Program During 2012 in the Chukchi Sea, Alaska 

Shell Gulf of Mexico Inc. 63 Revised August 2011 

Until recently, it was assumed that diving marine mammals are not subject to the bends or air 

embolism. This possibility was first explored at a workshop (Gentry [ed.] 2002) held to discuss 

whether the stranding of beaked whales in the Bahamas in 2000 (Balcomb and Claridge 2001; 

NOAA and USN 2001) might have been related to bubble formation in tissues caused by 

exposure to noise from naval sonar. However, the opinions were inconclusive. Jepson et al. 

(2003) first suggested a possible link between mid-frequency sonar activity and acute and 

chronic tissue damage that results from the formation in vivo of gas bubbles, based on the 

beaked whale stranding in the Canary Islands in 2002 during naval exercises. Fernández et al. 

(2005a) showed those beaked whales did indeed have gas bubble-associated lesions as well as fat 

embolisms. Fernández et al. (2005b) also found evidence of fat embolism in three beaked 

whales that stranded 62 mi (100 km) north of the Canaries in 2004 during naval exercises. 

Examinations of several other stranded species have also revealed evidence of gas and fat 

embolisms (e.g., Arbelo et al. 2005; Jepson et al. 2005a; Méndez et al. 2005). Most of the 

afflicted species were deep divers. There is speculation that gas and fat embolisms may occur if 

cetaceans ascend unusually quickly when exposed to aversive sounds, or if sound in the 

environment causes the destabilization of existing bubble nuclei (Potter 2004; Arbelo et al. 2005; 

Fernández et al. 2005a; Jepson et al. 2005b). Even if gas and fat embolisms can occur during 

exposure to mid-frequency sonar, there is no evidence that that type of effect occurs in response 

to the types of sound produced during the proposed exploratory activities. Also, most evidence 

for such effects has been in beaked whales, which do not occur in the proposed survey area. 

Available data on the potential for underwater sounds from industrial activities to cause auditory 

impairment or other physical effects in marine mammals suggest that such effects, if they occur 

at all, would be temporary and limited to short distances. However, the available data do not 

allow for meaningful quantitative predictions of the numbers (if any) of marine mammals that 

might be affected in those ways. Marine mammals that show behavioral avoidance of the 

proposed activities, including most baleen whales, some odontocetes (including belugas), and 

some pinnipeds, are especially unlikely to incur auditory impairment or other physical effects. 

Strandings and Mortality 

Marine mammals close to underwater detonations of high explosive can be killed or severely 

injured, and the auditory organs are especially susceptible to injury (Ketten et al. 1993; Ketten 

1995). Underwater sound from exploration drilling and support activities are less energetic and 

have slower rise times, and there is no proof that they can cause serious injury, death, or 

stranding. However, the association of mass strandings of beaked whales with naval exercises 

and, in one case, an L-DEO seismic survey, has raised the possibility that beaked whales exposed 

to strong pulsed sounds may be especially susceptible to injury and/or behavioral reactions that 

can lead to stranding. The potential for stranding to result from exposure to strong pulsed sound 

suggests that caution be used when exposing marine mammals to pulsed or other underwater 

sound. Most of the stranding events associated with exposure of marine mammals to pulsed 

sound however, have involved beaked whales, which do not occur in the proposed area. 

Additionally, the sound produced from the proposed activities will be at much lower levels than 

those reported during stranding events. 

 
Application for Incidental Harassment Authorization for the Non-Lethal Taking of Whales and Seals 

in Conjunction with Planned Exploration Drilling Program During 2012 in the Chukchi Sea, Alaska 

Shell Gulf of Mexico Inc. 64 Revised August 2011 

8. The anticipated impact of the activity on the availability of the species or stocks of 

 marine mammals for subsistence uses 

Subsistence hunting continues to be an essential aspect of Inupiat Native life, especially in rural 

coastal villages. The Inupiat participate in subsistence hunting activities in and around the 

Chukchi Sea. The animals taken for subsistence provide a significant portion of the food that 

will last the community through the year. Marine mammals represent on the order of 60-80 

percent of the total subsistence harvest. Along with the nourishment necessary for survival, the 

subsistence activities strengthen bonds within the culture, provide a means for educating the 

young, provide supplies for artistic expression, and allow for important celebratory events. In 

this IHA application, Shell specifically discusses the potential impact from the exploration 

drilling program to subsistence use of the bowhead whale, beluga, and seals, which are the 

primary marine mammals harvested for subsistence that are also covered under this authorization 

of incidental take by NMFS.

Bowhead Whale. Most activities associated with Shell’s planned exploration drilling program 

would have no or negligible effects on bowhead whales or on subsistence hunts for bowheads. 

Sound energy and general activity associated with exploration drilling and operation of vessels 

and aircraft have the potential to temporarily affect the behavior of bowhead whales. However, 

as noted above in Section 7, though temporary diversions of the swim path of migrating whales 

have been documented, the whales have generally been observed to resume their initial 

migratory route within a distance of 6-20 mi (10-32 km) (Davis 1987; Brewer et al. 1993; Hall et 

al. 1994). Drilling noise has not been shown to block or impede migration even in narrow ice 

leads (Davis 1987; Richardson et al. 1991). Any effects on the bowhead whale as a subsistence 

resource would be negligible. 

Observed behavioral effects from sound energy produced by drilling, such as avoidance, 

deflection, and changes in surface/dive ratios, have generally been restricted to the area 

ensonified to >160 dB or more although effects have infrequently been observed out to distance 

ensonified to 120 dB. As indicated above in Table 6-3, areas ensonified to >160 dB or more are 

limited to the areas within 0.06 mi (0.1 km) of the drillship, and areas expected to be ensonified 

to >120 dB would be expected to be limited to the areas within 0.913 mi (1.47 km) of the 

drillship. Shell’s proposed drill sites are located more than 64 mi (103 km) from the Chukchi 

Sea coastline, whereas available mapping of subsistence use areas indicates bowhead hunts are 

conducted within about 30 mi (48 km) of shore. There is therefore little or no opportunity for the 

proposed exploration drilling activities to affect bowhead hunts. 

Planned vessel traffic between the drill sites and marine support facilities in Wainwright would 

traverse areas used during bowhead harvests by Wainwright crews. However, bowhead hunts by 

residents of Wainwright, Point Hope and Point Lay takes place almost exclusively in the spring 

and are typically curtailed prior to the date Shell would commence the proposed exploration 

drilling program. From 1984 through 2009, bowhead harvests by these Chukchi Sea villages 

occurred only between April 14 and June 24 (George and Tarpley 1986; George et al. 1987, 1988 

1990, 1992, 1995, 1998, 1999, 2000; Philo et al. 1994; Suydam et al. 1995b, 1996, 1997, 2001b, 

2002, 2003, 2004, 2005b, 2006, 2007, 2008, 2009, 2010), while Shell will not enter the Chukchi 

Sea prior to July 1. Fall whaling by Chukchi Sea villages may occur in the future, particularly if 

bowhead quotas are not completely filled during the spring hunt, and fall weather is 
Application for Incidental Harassment Authorization for the Non-Lethal Taking of Whales and Seals 

in Conjunction with Planned Exploration Drilling Program During 2012 in the Chukchi Sea, Alaska 

Shell Gulf of Mexico Inc. 65 Revised August 2011 

accommodating. A Wainwright whaling crew harvested the first fall bowhead in 90 years or 

more on October 8, 2010. Shell's mitigation measures, which include a system of subsistence 

advisors, community liaisons, and Communication and Call Centers (Com Centers), will be 

implemented to avoid any effects from vessel traffic on fall whaling in the Chukchi. 

Aircraft traffic (helicopters and small fixed wing airplanes) between the drill sites and facilities 

in Wainwright and Barrow would also traverse these subsistence areas. Again, flights to and 

from Wainwright would take place after the date on which bowhead whaling out of Point Hope, 

Point Lay, and Wainwright is typically finished for the year. Barrow crews hunt bowheads 

during the spring and the fall, although most commonly east of Barrow along the Beaufort Sea 

coast. Aircraft flights between the Barrow air support facilities and Shell's drill sites located 

approximately 140 mi (227 km) to the west/southwest would traverse areas sometimes used 

during spring and fall whaling by Barrow crews. Spring whaling by Barrow crews is normally 

finished before the date that such flights would commence. From 1984 through 2009 whales 

were harvested in the spring by Barrow crews only between April 23 and June 15 (George and 

Tarpley 1986; George et al. 1987, 1988, 1990, 1992, 1995, 1998, 1999, 2000; Philo et al. 1994; 

Suydam et al. 1995b, 1996, 1997, 2001b, 2002, 2003, 2004, 2005b, 2006, 2007, 2008, 2009, 

2010), while Shell operations would not commence until early July. During these same years 

fall bowheads were harvested between August 31 and October 29, so some flights could traverse 

areas hunted in the fall. However, in the past 35 years, Barrow whaling crews have harvested 

almost all whales in the Beaufort Sea to the east of Point Barrow (Suydam et al. 2008), 

indicating that relatively little fall hunting occurs to the west where the flight corridor is located. 

The most commonly observed reactions of bowheads to aircraft traffic are hasty dives, but 

changes in orientation, dispersal, and changes in activity are sometimes noted. Such reactions 

could potentially affect subsistence hunts if the flights occurred near and at the same time as the 

hunt. Shell has developed and proposes to implement a number of mitigation measures to ensure 

that any effects on the bowhead whale as a subsistence resource, or effects on bowhead 

subsistence hunts would be negligible. These mitigation measures, which include minimum 

flight altitudes, employment of subsistence advisors in the villages, and implementation of a 

Communications Plan (with operation of Com Centers), are described below in Section 12.3. 

Beluga. Beluga typically do not represent a large proportion of the subsistence harvests by 

weight in the communities of Wainwright and Barrow, the nearest communities to Shell’s 

planned exploration drilling program. Barrow residents hunt beluga in the spring (normally after 

the bowhead hunt) in leads between Point Barrow and Skull Cliffs in the Chukchi Sea – 

primarily in April-June, and later in the summer (July-August) on both sides of the barrier island 

in Elson Lagoon / Beaufort Sea (MMS 2008), but harvest rates indicate the hunts are not 

frequent. Wainwright residents hunt beluga in April-June in the spring lead system, but this hunt 

typically occurs only if there are no bowheads in the area. Communal hunts for beluga are 

conducted along the coastal lagoon system later in July-August. 

Belugas typically represent a much greater proportion of the subsistence harvest in Point Lay and 

Point Hope. Point Lay’s primary beluga hunt occurs from mi-June through mid-July, but can 

sometimes continue into August if early success is not sufficient. Point Hope residents hunt 

beluga primarily in the lead system during the spring (late March to early June) bowhead hunt, 

but also in open water along the coastline in July and August. Beluga are harvested in coastal 
Application for Incidental Harassment Authorization for the Non-Lethal Taking of Whales and Seals 

in Conjunction with Planned Exploration Drilling Program During 2012 in the Chukchi Sea, Alaska 

Shell Gulf of Mexico Inc. 66 Revised August 2011 

waters near these villages, generally within a few miles from shore. Shell’s proposed drill sites 

are located more than 60 mi (97 km) offshore, therefore proposed exploration drilling in the 

Burger Prospect would have no or negligible effect on beluga hunts. Aircraft and vessel traffic 

between the drill sites and support facilities in Wainwright, and aircraft traffic between the drill 

sites and air support facilities in Barrow would traverse areas that are sometimes used for 

subsistence hunting of belugas. 

 Disturbance associated with vessel and aircraft traffic could therefore potentially affect beluga 

hunts. However, all of the beluga hunt by Barrow residents in the Chukchi Sea, and much of the 

hunt by Wainwright residents would likely be completed before Shell activities would 

commence. Additionally, vessel and aircraft traffic associated with Shell’s planned exploration 

drilling program will be restricted under normal conditions to designated corridors that remain 

onshore or proceed directly offshore thereby minimizing the amount of traffic in coastal waters 

where beluga hunts take place. The designated traffic corridors do not traverse areas indicated in 

recent mapping as utilized by Point Lay, or Point Hope for beluga hunts, and avoids important 

beluga hunting areas in Kasegaluk Lagoon. Shell has developed and proposes to implement a 

number of mitigation measures to ensure that any effects on the beluga whale as a subsistence 

resource, or effects on beluga subsistence hunts would be negligible. These mitigation measures, 

which include minimum flight altitudes, employment of subsistence advisors in the villages, and 

implementation of a Communications Plan (with operation of Com Centers), are described below 

in Section 12.3. Therefore, any behavioral responses of avoidance of activity areas by beluga in 

the Chukchi Sea would have no or negligible effect on the subsistence resource or subsistence 

hunts for beluga. 

Seals. Seals are an important subsistence resource and ringed seals make up the bulk of the seal 

harvest. Most ringed and bearded seals are harvested in the winter or in the spring before Shell’s 

exploration drilling program would commence, but some harvest continues during open water 

and could possibly be affected by Shell’s planned activities. Spotted seals are also harvested 

during the summer. Most seals are harvested in coastal waters, with available maps of recent and 

past subsistence use areas indicating seal harvests have occurred only within 30-40 mi (48-64 

km) of the coastline. Shell planned drill sites where exploration activities would occur are 

located more than 64 statute mi (103 km) offshore, so activities within the Burger Prospect, such 

as drilling, would have no impact on subsistence hunting for seals. Helicopter traffic between 

land and the offshore exploration drilling operations could potentially disturb seals and, 

therefore, subsistence hunts for seals, but any such effects would be minor due to the small 

number of flights and the altitude at which they typically fly, and the fact that most seal hunting 

is done during the winter and spring. Any effects on subsistence hunts for seals would be 

negligible and temporary lasting only minutes after the flight has passed. Any effects on the 

seals as a subsistence resource, or effects on subsistence hunts for seals would be negligible. 

These mitigation measures, which include minimum flight altitudes, employment of subsistence 

advisors in the villages, and implementation of a Communications Plan (with operation of Com 

Centers), are described below in Section 12.3. 

9. Anticipated impact on habitat 

Shell’s planned exploration drilling program will not result in any permanent impact on habitats 

used by marine mammals, or to their prey sources. With regard to migrating cetaceans and seals, 
Application for Incidental Harassment Authorization for the Non-Lethal Taking of Whales and Seals 

in Conjunction with Planned Exploration Drilling Program During 2012 in the Chukchi Sea, Alaska 

Shell Gulf of Mexico Inc. 67 Revised August 2011 

any effects would be temporary and of short duration at any one place. The primary potential 

impacts to all marine mammals that are reasonably expected or reasonably likely are associated 

with elevated sound levels from exploration drilling operations, its support vessels, and aircraft. 

The effects to habitat of marine mammals by sounds from the planned exploration drilling 

program are expected to be negligible. 

Although evaluation of speculative events such as oil spills is not properly included in the 

“negligible impacts” analysis, Shell recognizes the agency’s interest in these remote risks. 

Therefore, [as a courtesy] Shell includes with this IHA application an analysis of the highly 

unlikely, unanticipated impact of a crude oil spill event during this exploration drilling program 

(Attachment E). This is an analysis of the impacts from a hypothetical, site-specific, very large 

oil spill scenario created for Shell’s regional oil spill response plan (Chukchi Sea Regional Oil 

Discharge Prevention and Contingency Plan [ODPCP] – revised April 2011) which was 

submitted to BOEMRE contemporaneously with Shell’s Chukchi Sea Exploration Plan. Under 

30 CFR 254. 26(d) (1) Shell’s oil spill response plan must envision a crude oil spill scenario 

from a worst case discharge lasting 30 days. Attachment E analyzes the impacts from such a sitespecific scenario, and presents this analysis in light of the very large crude oil spill impact 

analyses already conducted for oil and gas exploration activities in the arctic by NMFS (NMFS 

2008) and BOEMRE’s on-going effort in the Supplemental Environmental Impact Statement for 

Chukchi Sea Lease Sale 193 (BOEMRE in print). Given that a very large oil spill is a highly 

unlikely and unanticipated result of Shell’s planned exploration drilling program, the analysis is 

not included within Section 9 of this IHA application which assesses the anticipated impacts of 

this activity, but provided separately as Attachment E. 

9.1 Potential Impacts from Seafloor Disturbance (Mooring and MLC Construction) 

There will be some seafloor disturbance or temporary increased turbidity in the seabed sediments 

during anchoring and emplacement of the MLCs. The amount and duration of disturbed or 

turbid conditions will depend on sediment material and consolidation and specific activity. The 

Discoverer would be stabilized and held in place with a system of eight 15,400 pounds (lb) 

(7,000 kg) Stevpris anchors during operations. The anchors from the Discoverer are designed to 

embed into the seafloor. Prior to setting, the anchors will penetrate the seafloor and drag two or 

three times their length. Both the anchor and anchor chain will disturb sediments and create an 

“anchor scar” which is a depression in the seafloor caused by the anchor embedding. Anchor 

depressions commonly exceed the dimensions of the anchor itself. 

 

Each Stevpris anchor may impact an area of 2,027 ft2

 (188 m2) of the seafloor. Minimum impact 

estimates from each well or mooring the Discoverer by its eight anchors is 16,216 ft2 (1,507 m2

) 

of seafloor. This estimate assumes that the anchors are set only once. Shell plans to pre-set 

anchors at each drill site for whichever drillship is used for exploration drilling. Unless moved 

by an outside force such as sea current, anchors should only need to be set once per drill site. 

Once the Discoverer ends operation, the anchors will be retrieved. Over time the anchor scars 

will be filled through natural movement of sediment. The duration of the scars depends upon the 

energy of the system, water depth, ice scour, and sediment type. Anchor scars were visible under 

low energy conditions in the North Sea for five to ten years after retrieval. Scars typically do not 
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form or persist in sandy mud or sand sediments but may last for nine years in hard clays (Centaur 

Associates, Inc. 1984). Surficial sediments in Shell's Burger Prospect consist of soft sandy mud 

(silt and clay) with lesser amounts of gravel (Battelle Memorial Institute 2010; Blanchard et al. 

2010a,b). The energy regime, plus possible effects of ice gouge in the Chukchi Sea suggests that 

anchor scars would be refilled faster than in the North Sea. 

Excavation of each MLC by the Discoverer will displace about 17,128 ft3 (485 m3) of seafloor 

sediments and directly disturb approximately 314 ft2 (29 m2) of seafloor. Material will be 

excavated from the MLCs using a large diameter drillbit. Pressurized air and seawater (no 

drilling mud used) will be used to assist in the removal of the excavated materials from the MLC. 

Some of the excavated sediments will be displaced to adjacent seafloor areas and some will be 

removed via the air lift system and discharged on the seafloor away from the MLC. These 

excavated materials will also have some indirect effects as they are deposited on the seafloor in 

the vicinity of the MLCs. Direct and indirect effects would include slight changes in seafloor 

relief and sediment consistency. 

9.2 Potential Impacts on Habitat due to Sound Generation 

Marine Mammals

Shell does not expect any significant or lasting impacts to marine mammals from sound energy 

created by exploration drilling activities in the Chukchi Sea. Sound is crucial to marine 

mammals because they use it to navigate, communicate, find open water, avoid predators, and 

find food. There are a variety of sounds in the Chukchi Sea, especially during the “open water” 

exploration drilling season, when the area is exposed to the peak level of man-made sound from 

oil and gas exploration activities and biological research surveys. Sound sources from Shell’s 

exploration activities that could be heard by marine mammals include the drillship, marine 

vessels, and support vessels. Sounds that are natural in the marine environment of the Chukchi 

Sea include sound from ice, surf, subsea landslides, and other animals. Concern has been 

expressed regarding the presence and intensity of impacts from sound energy on marine 

mammals. Concerns are mainly aimed at deflection of whales from hunting and migration areas, 

masking of natural sounds, and physiological damage to marine mammals’ hearing. Based on 

previous studies regarding sound energy and effects on marine mammals, as well as the 

preventive mitigation measures planned for the project, Shell does not expect any significant or 

lasting impacts to marine mammals from sound energy resulting from exploration drilling 

activities in the Chukchi Sea. 

Avoidance behavior in response to sound energy by marine mammals, such as temporary 

deflection, is the most likely behavioral response expected as a result of Shell’s exploration 

drilling activities in the Chukchi Sea. Depending upon the sound source, different mitigation 

measures will be implemented. Mitigation measures have been included in the 4MP that is 

included as an appendix of this IHA application. That discussion and analysis of Shell’s sound 

energy mitigation measures is incorporated here by reference. 

MMOs will be stationed on all drilling and support vessels to survey inside the exclusion zone 

(areas within isopleths of certain sound levels for different species) for marine mammals. For 
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support vessels in transit, if a marine mammal is sighted from a vessel within its respective 

safety radius, the Shell vessel will reduce activity (e.g. reduce speed) and sound energy level to 

ensure that the animal(s) are not exposed to sound above their respective safety level. Full 

activity will not be resumed until all marine mammals are outside of the vessel’s exclusion zone 

and there are no other marine mammals likely to enter the exclusion zone. Regular overflight 

surveys and support vessel surveys for marine mammals will be conducted to further monitor 

exploration drilling areas. 

Anchored vessels, including the drillship, will remain at anchor and continue ongoing operations 

if approached by a marine mammal. An approaching animal, not exhibiting avoidance behavior, 

is likely curious and not regarded as harassed. The anchored vessel will remain in place and 

continue ongoing operations to avoid possibly causing avoidance behavior by suddenly changing 

sound conditions. Moving vessels will avoid groups of whales by a distance of 1,500 ft (457 m), 

and will reduce speed if within 900 ft (274 m) of other marine mammals. MMOs use distance as 

an indicator of the safety radii, which is anticipated to be much smaller than 900 ft (274 m). 

These measures will reduce the sound energy received by the mammals. Shell will not be 

operating during the sensitive times such as pupping and molting. These important activities will 

be over by the time Shell activities start. If seals are hauled out on ice in the vicinity of 

operations temporary deflection is expected. 

While observing the response of beluga whales to icebreakers, Finley and Davis (1984) reported 

avoidance behavior when ice breaker vessels approached at distances of 22-31 mi (35-50 km). 

Belugas are thought to have poor hearing below one Hz, the range of most exploration drilling 

activities, but have shown some behavioral reactions to the sounds. Brewer et al. (1993) 

observed belugas within 2.3 mi (3.7 km) of the drilling unit Kulluk during exploration drilling. 

Seals are not expected to be impacted by sound energy from Shell vessel traffic or exploration 

drilling. This was demonstrated during a study designed to assess ringed seals’ reactions to 

drilling activity (Brewer et al. 1993). After observing the seals approach within 33 ft (10 m) of 

the drilling unit Kulluk, the scientists concluded that they are not disturbed by drilling activity. 

The same conclusion was reached concerning bearded seals that approached within 656 ft (200 

m) of ice breakers (Brewer et al. 1993). In another study involving the drillship Explorer II, 

seals were observed within 115 ft (35 m) of the ship during drilling (Gallagher et al. 1992). 

Sound energy introduced into the environment of marine mammals could cause masking (the 

covering of sound that would otherwise have been heard). Masking can interfere with the 

detection of important natural sources. Underwater sound could possibly mask environmental 

sounds (Terhune 1981) or communication between marine mammals (Perry and Renouf 1987). 

However, in a study conducted by Cummings et al. (1984) in which breeding ringed seals were 

subjected to recordings of industrial sounds and there were no documented effects on ringed seal 

vocalizations. 

Belugas primarily use high-frequency sounds to communicate and locate prey; therefore, 

masking by low-frequency sounds associated with drilling activities is not expected to occur 

(Gales 1982). If the distance between communicating whales does not exceed their distance 

from the drilling activity, the likelihood of potential impacts from masking would be low (Gales 

1982). At distances greater than 660-1,300 ft (200-400 m), recorded sounds from drilling 
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activities did not affect behavior of beluga whales even though the sound energy level and 

frequency were such that it could be heard several kilometers away (Richardson et al. 1995b). 

This exposure resulted in whales being deflected from the sound energy and changing behavior. 

These brief changes are expected to be temporary and are not expected to affect whale 

population (Richardson et al. 1991; Richard et al. 1998). 

Threatened and Endangered Species

Sound is important to bowhead whales because they use it to navigate, communicate, find open 

water, avoid predators, and find areas of food abundance. Bowhead whales, along with being 

endangered, are a key subsistence resource of the Inupiat Eskimos of the North Slope. There is 

concern regarding potential impacts on the whales due to sound energy produced by exploration 

drilling activities. Potentially, sounds created by exploration drilling activities could affect 

behavior, mask whale communication and other environmental sounds, or damage hearing 

mechanisms. There have been no conclusive studies on the sensitivity of bowhead whale hearing 

(Richardson et al. 1995b). It is likely that the range of hearing includes the frequency range used 

in their calls. Most frequencies used by bowhead whales are low (less than 1,000 Hz) 

(Richardson et al. 1995b). Mitigation measures are in place to minimize or eliminate impacts to 

the whales and, by extension, subsistence uses of the whales. Shell does not expect any lasting 

impacts on marine mammals from sound energy created during exploration drilling activities in 

the Chukchi Sea. 

In order to limit the whales’ close contact with ice management and other support vessels, 

MMOs will be stationed on all support vessels to survey inside the exclusion zone (areas within 

isopleths of certain sound levels for different species) for marine mammals. If a marine mammal 

is sighted from a vessel in transit within its respective safety radius, the Shell vessel will reduce 

activity (e.g. reduce speed) and sound energy level to ensure that the animal is not exposed to 

sound above its respective safety levels. Full activity will not be resumed until all marine 

mammals are outside of the exclusion zone and there are no other marine mammals likely to 

enter the exclusion zone before the next overflight survey. Regular overflight surveys and 

support vessel surveys for marine mammals will be conducted to further monitor exploration 

drilling areas. Anchored vessels, including the drilling unit, will remain at anchor and continue 

ongoing operations if approached by a marine mammal. An approaching animal, not exhibiting 

avoidance behavior, is likely curious and not regarded as harassed. The anchored vessel will 

remain in place and continue ongoing operations to avoid possibly causing avoidance behavior 

by suddenly changing sound energy conditions. 

Avoidance behavior in response to sound by marine mammals such as temporary deflection from 

migration corridors is the most likely behavioral response expected as a result of Shell’s 

exploration activities in the Chukchi Sea. Bowhead whales, likely due to their hearing range, 

have been reported to react more to low frequency sounds than higher frequency sounds 

(Richardson et al. 1995b). Davis (1987) studied the responses exhibited by bowhead whales to 

drilling sound. The only response he saw was avoidance behavior in some whales. Davis (1987) 

concluded that avoidance behavior was temporary and sound energy from drilling did not 

impede migration of the whales. Recordings from the drilling ship Explorer II were projected in 

the Canadian Beaufort Sea during the drilling season (Richardson et al. 1985). Changes in 
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behavior in response to the sounds were observed. Some whales showed avoidance behavior, 

but the deflection away from the sound was considered weak (Richardson et al. 1985). During 

the same study, Richardson et al. (1985) observed whales between 2.5 mi and 12.4 mi (4 and 20 

km) while drilling activity was occurring, and he concluded that the whales were undisturbed. In 

a similar study where recordings from the drilling unit Kulluk were projected, no deflection was 

seen until sound pressure levels reached 120 dB or higher (Wartzok et al. 1989). 

Concern has been expressed that sound energy levels produced by exploration drilling and ice 

management could cause masking. Masking can interfere with the detection of important natural 

sound sources. Underwater sound could possibly mask environmental sounds (Terhune 1981) or 

communication between marine mammals (Perry and Renouf 1987). Effects of sound energy 

from exploration drilling and ice management will be temporary and localized, and are not 

expected to significantly impact marine mammals. 

Loud sound (higher than 180 dB) could cause temporary (the duration would depend upon the 

level and duration of noise exposure) or permanent damage to hearing ability (Kryter 1985; 

Richardson and Malme 1993). Since bowhead whales have been shown to exhibit avoidance 

behaviors in the presence of lower level sound (115 dB) (Richardson et al. 1990), it is unlikely 

that they would approach such sound sources close enough to be exposed to sound levels that 

could be injurious (Richardson and Malme 1993). 

Zooplankton

Sound energy generated by exploration drilling activities will not negatively impact the diversity 

and abundance of zooplankton. The primary generators of sound energy are the drillship and 

marine vessels. Ice management vessels are likely to be the most intense sources of sound 

associated with the exploration drilling program (Richardson et al. 1995a). Ice management 

vessels, during active ice management, may have to adjust course forward and astern while 

moving ice and thereby create greater variability in propeller cavitation than other vessels that 

maintain course with less adjustment. The drillship maintains station during exploration drilling 

without activation of propulsion propellers. Richardson (et al.1995a) reported that the noise 

generated by an icebreaker pushing ice was 10-15 dB greater than the noise produced by the ship 

underway in open water. It is expected that the lower level of sound produced by the drillship, 

ice management vessels conducting icebreaking, or other vessels would have less impact on 

zooplankton than would 3D seismic (survey) sound. 

No appreciable adverse impact on zooplankton populations will occur due in part to large 

reproductive capacities and naturally high levels of predation and mortality of these populations. 

Any mortality or impacts on zooplankton as a result of Shell’s operations is insignificant as 

compared to the naturally-occurring reproductive and mortality rates of these species. This is 

consistent with previous conclusions that crustaceans (such as zooplankton) are not particularly 

sensitive to sound produced by seismic sounds (Wiese 1996). Impact from sound energy 

generated by an ice breaker, other marine vessels, and drill ships would have less impact, as 

these activities produce lower sound energy levels (Burns et al. 1993). Historical sound 

propagation studies performed on the Kulluk by Hall et al. (1994) also indicate the Kulluk and 

similar drilling units would have lower sound energy output than three-dimensional seismic 

sound sources (Burns et al. 1993). The drillship Discoverer would emit sounds at a lower level 
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than the Kulluk and therefore the impacts due to exploration drilling noise would be even lower 

than the Kulluk. Therefore, zooplankton organisms would not likely be affected by sound energy 

levels by the vessels to be used during Shell’s exploration drilling activities in the Chukchi Sea. 

Benthos

There was no indication from benthic biomass or density that previous drilling activities at the 

Hammerhead Prospect have had a measurable impact on the ecology of the immediate local area. 

To the contrary, the abundance of benthic communities in the Sivulliq area would suggest that 

the benthos were actually thriving there (Dunton et al. 2008). 

Sound energy generated by exploration drilling activities will not appreciably affect diversity and 

abundance of plants or animals on the seafloor. The primary generators of sound energy are the 

drillship and marine vessels. Ice management vessels are likely to be the most intense sources of 

sound associated with the exploration drilling program (Richardson et al. 1995a). Ice 

management vessels, during active ice management, may have to adjust course forward and 

astern while moving ice and thereby create greater variability in propeller cavitation than other 

vessels that maintain course with less adjustment. The drillship maintains station during 

exploration drilling without activation of propulsion propellers. Richardson et al.(1995a) 

reported that the noise generated by an icebreaker pushing ice was 10-15 dB greater than the 

noise produced by the ship underway in open water. The lower level of sound produced by the 

drillship, ice management vessels conducting icebreaking, or other vessels will have less impact 

on bottom-dwelling organisms than would 3D seismic (survey) sound. 

No appreciable adverse impacts on benthic populations would be expected due in part to large 

reproductive capacities and naturally high levels of predation and mortality of these populations. 

Any mortalities or impacts that might occur as a result of Shell’s operations is insignificant 

compared to the naturally-occurring high reproductive and mortality rates. This is consistent 

with previous BOEMRE conclusions that the effect of seismic exploration on benthic organisms 

probably would be immeasurable (USDI/MMS 2007). Impacts from sound energy generated by 

ice breakers, other marine vessels, and drillship would have less impact, as these activities 

produce much lower sound energy levels (Burns et al. 1993). 

 

Fish

Fish react to sound and use sound to communicate (Tavolga et al. 1981). Experiments have 

shown that fish can sense both the intensity and direction of sound (Hawkins 1981). Whether or 

not fish can hear a particular sound depends upon its frequency and intensity. Wavelength and 

the natural background sound also play a role. The intensity of sound in water decreases with 

distance as a result of geometrical spreading and absorption. Therefore, the distance between the 

sound source and the fish is important. Physical conditions in the sea, such as temperature 

thermoclines and seabed topography, can influence transmission loss and thus the distance at 

which a sound can be heard. 
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The impact of sound energy from exploration drilling and ice management activities will be 

negligible and temporary. Fish typically move away from sound energy above a level that is at 

120dB or higher (Ona 1988). 

Drillship sound source levels during drilling can range from 90 dB within 31 mi (50 km) of the 

drillship to 138 dB within a distance of 0.06 mi (0.01 km) from the drillship (Greene 

1985,1987b). These are predicted sound levels at various distances based on modeled 

transmission loss equations in the literature (Greene 1987b). Ice management vessel sound 

source levels can range from 174-184 dB. At these intensity levels, fish may avoid the drilling 

unit, ice management vessels, or other large support vessels. This avoidance behavior is 

temporary and limited to periods when a vessel is underway or drilling. 

There have been no studies of the direct effects of ice management vessel sounds on fish. 

However, it is known that the ice management vessels produce sounds generally 10-15 dB higher 

when moving through ice rather than open water (Richardson et al. 1995b). In general, fish show 

greater reactions to a spike in sound energy levels, or impulse sounds, rather than a continuous 

high intensity signal (Blaxter et al. 1981). 

Fish sensitivity to impulse sound varies depending on the species of fish. Cod, herring and other 

species of fish with swim bladders have been found to be relatively sensitive to sound, while 

mackerel, flatfish, and many other species that lack swim bladders have been found to have poor 

hearing (Hawkins 1981, Hastings and Popper 2005). An alarm response in these fish is elicited 

when the sound signal intensity rises rapidly compared to sound rising more slowly to the same 

level (Blaxter et al. 1981). 

9.3 Potential Impacts on Habitat from Drilling Muds and Cuttings Waste 

General 

The National Pollutant Discharge Elimination System (NPDES) General Permit establishes 

discharge limits for drilling fluids (at the end of a discharge pipe) to a minimum 96-hr Lethal 

Concentration 50 percent (LC50) of 30,000 parts per million (ppm). Both modeling and field 

studies have shown that discharged drilling fluids are diluted rapidly in receiving waters (Ayers 

et al. 1980a, 1980b; Brandsma et al. 1980; NRC 1983; O’Reilly et al. 1989; Nedwed et al. 2004; 

Smith et al. 2004; Neff 2005). The dilution rate is strongly affected by the discharge rate; the 

NPDES General Permit limits the discharge of cuttings and fluids to 750 bbl/hr (89 m3

/hr). For 

example, the EPA modeled hypothetical 750 bbl/hr (89 m3/hr) discharges of drilling fluids in 

water depths of 66 ft (20 m) in the Beaufort and Chukchi Sea and predicted a minimum dilution 

of 1,326:1 at 330 ft (100 m). 

Modeling of similar discharges offshore of Sakhalin Island predicted a 1,000-fold dilution within 

10 minutes and 330 ft (100 m) of the discharge. In a field study (O’Reilly et al. 1989) of a 

drilling waste discharge offshore of California, a 270 bbl (43 m3) discharge of drilling fluids was 

found to be diluted 183-fold at 33 ft (10 m) and 1,049-fold at 330 ft (100 m). Neff (2005) 
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concluded that concentrations of discharged drilling fluids drop to levels that would have no 

effect within about two minutes of discharge and within 16 ft (5 m) of the discharge location. 

Marine Mammals

The levels of drill cuttings and drilling mud discharges are regulated by the EPA’s NPDES 

General Permit. The impact of the limited amount of drilling mud and cuttings discharges would 

be localized to the drill sites and temporary. Drilling mud and cuttings discharges could displace 

marine mammals a short distance from an exploration drilling location. 

Gray whales will more than likely avoid exploration drilling activities and not come into close 

contact with drilling mud or cuttings. However, gray whales are benthic feeders and the area of 

seafloor that will be covered by discharge will be unavailable to the whales for foraging 

purposes. This is not expected to impact individual whales or the population, because the areas 

of disturbance are insignificant compared to the area covered by the whales for foraging. 

Impacts on beluga whales from the discharge of drilling mud and cuttings are not likely. 

It is anticipated that drilling mud and cuttings will only dispense up to 330 ft (100 m) from the 

drillship in beluga feeding areas. Therefore, it is highly unlikely that beluga whales will come 

into contact with any drilling discharge and impacts are not expected. 

Seals are not expected to be impacted by drilling mud or cuttings. If seals remain within 330 ft 

(100 m) of the discharge source for an extended period of time, it is possible that physiological 

effects due to toxins could impact the animal. However, it is highly unlikely that a seal would 

remain within 330 ft (100 m) of the discharge source for any extended period of time. 

Threatened and Endangered Species

Negative effects on endangered whales from drilling discharges are not expected. Baleen 

whales, such as bowheads, tend to avoid drilling rigs at distances up to 12 mi (20 km). 

Therefore, it is highly unlikely that the whales will swim or feed in close enough proximity of 

discharges to be affected. 

The levels of drilling mud and cuttings discharges are regulated by the EPA’s NPDES General 

Permit. The impact of drilling mud and cuttings discharges would be localized and temporary. 

Drilling mud and cuttings discharges could displace endangered whales (bowhead and humpback 

whales) a short distance from an exploration drilling location. Effects on the whales present 

within a few meters of the discharge point would be expected, primarily due to sedimentation. 

However, endangered whales are not likely to have long-term exposures to drilling mud and 

cuttings because of the episodic nature of discharges (typically only a few hours in duration). 

Seals, including the proposed for threatened listing ringed and bearded seals, are not expected to 

be impacted by drilling mud and cuttings. If seals remain within 330 ft (100 m) of the discharge 

source for an extended period of time, it is possible that physiological effects due to toxins could 

impact the animal. However, it is highly unlikely that a seal would remain within 330 ft (100 m) 

of the discharge source for any extended period of time. 
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It is expected that any toxic effects on fish and fish larvae present within a few feet of the 

discharge point would be negligible and ephemeral. 

Zooplankton

Studies by the EPA (2006) and Neff (2005) indicate that though planktonic organisms are 

extremely sensitive to environmental conditions (e.g., temperature, light, availability of nutrients, 

and water quality), there is little or no evidence of effects from drilling mud and cuttings 

discharges on plankton. 

More than 30 OCS well sites have been drilled in the Beaufort Sea. The Warthog well was 

drilled in Camden Bay in 35 ft (11 m) of water (Thurston et al. 1999). The BOEMRE routinely 

monitored that well site for contaminants and found that it had no accumulated petroleum 

hydrocarbons or heavy metals (Brown et al. 2001). 

The levels of drilling mud and cuttings discharges are regulated by the EPA’s NPDES General 

Permit. The impact by drilling mud and cuttings discharges would be localized and temporary. 

Effects on zooplankton present within a few meters of the discharge point would be expected, 

primarily due to sedimentation. However, zooplankton are not likely to have long-term 

exposures to drilling mud and cuttings because of the episodic nature of discharges (typically 

only a few hours in duration). Results of a recent study on a historical drill site in Camden Bay 

(HH-2) showed that movement of drilling mud and cuttings were restricted to within 330 ft (100 

m) of the discharge site (Trefry and Trocine 2009). 

Fine-grained particulates and other solids in drilling mud and cuttings could cause sublethal 

effects to organisms in the water column. The responses observed following exposure to drilling 

mud include alteration of respiration and filtration rates and altered behavior. Zooplankton in the 

immediate area of discharge from exploration drilling operations could potentially be adversely 

impacted by sediments in the water column, which could clog respiratory and feeding structures, 

and they could suffer abrasions. This impact would likely not have more than a short-term 

impact and not affect population levels of zooplankton. 

Benthos

Drilling mud and cuttings discharges are regulated by the EPA’s NPDES General Permit. The 

impact of drilling mud and cuttings discharges would be localized and temporary. Effects on 

benthic organisms present within a few meters of the discharge point would be expected, 

primarily due to sedimentation. However, benthic animals are not likely to have long-term 

exposures to drilling mud and cuttings because of the episodic nature of discharges (typically 

only a few hours in duration). 

Significant heavy metal contamination of sediments and resulting effects on benthic organisms is 

not expected. The general NPDES permit contains stringent limitations on the concentrations of 

mercury, cadmium, chromium, silver, and thallium allowed in discharged drilling fluids and 

cuttings. Additional limitations are placed on free oil, diesel oil, and total aromatic hydrocarbons 

(TAH) allowed in discharged drilling fluids and cuttings. Discharge rates are also controlled by 

the permit. Baseline studies at the 1985 Hammerhead drill site (Trefry and Trocine 2009) 
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detected background levels Al, Fe, Zn, Cd and Hg in all surface and subsurface sediment 

samples. Considering the relatively small area that drilling mud and cuttings sediment will be 

deposited, no significant impacts on sediment are expected to occur. The expected increased 

concentrations of Zn, Cd, and Cr in sediments near the drill site due to the discharge are in the 

range where no or low effects would result. 

Studies in the 1980s, 1999, 2000, and 2002 (Brown et al. 2001 in USDI/MMS 2003) also found 

that benthic organism near drilling sites in the Beaufort have accumulated neither petroleum 

hydrocarbon nor heavy metals. In 2008 Shell investigated the benthic communities (Dunton et 

al. 2008) and sediments (Trefry and Trocine 2009) around the Sivulliq Prospect including the 

location of the historical Hammerhead drill site that was drilled in 1985. Benthic communities at 

the historical Hammerhead drill site were found not to differ statistically in abundance, 

community structure, or diversity, from benthic communities elsewhere in this portion of the 

Beaufort Sea, indicating that there was no long term effect. Because discharges from drilling 

mud and cuttings are composed of seawater, impacts to benthic organisms will be negligible and 

restricted to a very small area of the seafloor in the Chukchi Sea. 

Fish 

The levels of drilling mud and cuttings discharges are regulated by the EPA’s NPDES General 

Permit. The impact of drilling mud and cuttings discharges would be localized and temporary. 

Drilling mud and cuttings discharges could displace fish a short distance from an exploration 

drilling location. Effects on fish and fish larvae present within a few meters of the discharge 

point would be expected, primarily due to sedimentation. However, fish and fish larvae that live 

in the water column are not likely to have long-term exposures to drilling mud and cuttings 

because of the episodic nature of discharges (typically only a few hours in duration). 

Although unlikely at deeper offshore exploration drilling locations, demersal fish eggs could be 

smothered if discharges occur in a spawning area during the period of egg production. No 

specific demersal fish spawning locations have been identified at the Burger well locations. The 

most abundant and trophically important marine fish, the Arctic cod, spawns with planktonic 

eggs and larvae under the sea ice during winter and will therefore have little exposure to 

discharges. 

Habitat alteration concerns apply to special or relatively uncommon habitats, such as those 

important for spawning, nursery, or overwintering. Important fish overwintering habitats are 

located in coastal rivers and nearshore coastal waters, but are not found in the proposed 

exploration drilling areas. Important spawning areas have not been identified in the Chukchi 

Sea. 

9.4 Potential Impacts from Ice Management 

Ice-management activities include the physical pushing or moving of ice in the proposed 

exploration drilling area and to prevent ice floes from striking the drilling unit. Ringed, bearded, 

and spotted seals (along with the ribbon seal and walrus) are dependent on sea ice for at least part 

of their life history. Sea ice is important for life functions such as resting, breeding, and molting. 
Application for Incidental Harassment Authorization for the Non-Lethal Taking of Whales and Seals 

in Conjunction with Planned Exploration Drilling Program During 2012 in the Chukchi Sea, Alaska 

Shell Gulf of Mexico Inc. 77 Revised August 2011 

These species are dependent on two different types of ice: pack ice and landfast ice. Shell does 

not expect to have to manage pack ice during the majority of the exploration drilling season. The 

majority of the pack ice management should occur in the early and latter portions of the 

exploration drilling season. Landfast ice would not be present during Shell’s proposed 

operations. 

The ringed seal is the most common pinniped species in the Chukchi Sea project area. While 

ringed seals use ice year-round, they do not construct lairs for pupping until late winter/early 

spring on the landfast ice. Therefore, since Shell plans to conclude exploration drilling on or 

before October 31, Shell’s activities would not impact ringed seal lairs or habitat needed for 

breeding and pupping in the Chukchi Sea. Ringed seals can be found on the pack ice surface in 

the late spring and early summer in the Chukchi Sea, the latter part of which may overlap with 

the start of Shell’s planned exploration drilling activities. If an ice floe is managed into one that 

contains hauled out seals, the animals may become startled and enter the water when the two ice 

floes meet. 

Bearded seals breed in the Bering and Chukchi Seas, but would not be plentiful in the area of the 

Chukchi Sea exploration drilling program. 

Spotted seals are even less common in the Chukchi Sea project area. The ice used by bearded 

and spotted seals needed for life functions such as breeding and molting would not be impacted 

as a result of Shell’s exploration drilling program since it is unlikely these life functions would 

occur in the proposed project area, during the time in which drilling activities will take place. 

For ringed seals, ice-management would occur during a time when life functions such as 

breeding, pupping, and molting do not occur in the proposed activity area. Additionally, these 

life functions normally occur on landfast ice, which will not be impacted by Shell’s activity. 

Therefore, it is determined that Shell’s planned exploration drilling program in the Chukchi Sea 

is not expected to have any habitat-related effects that could cause significant or long-term 

consequences for individual marine mammals or on the food sources that they utilize. 

9.5 Potential Impacts from Discoverer Presence 

The length of the Discoverer (514 ft [156.7 m]) is not significant enough to cause large-scale 

diversions from the animals’ normal swim and migratory paths. The Discoverer’s physical 

footprint is small relative to the size of the geographic region either would occupy, and will 

likely not cause marine mammals to deflect greatly from their typical migratory routes. 

Any deflection of bowhead whales or other marine mammal species due to the physical presence 

of the Discoverer or its support vessels would be very minor. Even if animals may deflect 

because of the presence of the drillship, the Chukchi Sea’s migratory corridor is much larger in 

size than the length of the drillship and animals would have other means of passage around the 

drillship. In sum, the physical presence of the drillship is not likely to cause a significant 

deflection to migrating marine mammals. 
Application for Incidental Harassment Authorization for the Non-Lethal Taking of Whales and Seals 

in Conjunction with Planned Exploration Drilling Program During 2012 in the Chukchi Sea, Alaska 

Shell Gulf of Mexico Inc. 78 Revised August 2011 

10. Anticipated impact of habitat loss or modification 

The effects of the planned exploration drilling program are expected to be negligible. It is 

estimated that only a small portion of the animals utilizing the areas of the planned program 

would be temporarily displaced. During the period of the exploration drilling program (July 4-

October 31st), most marine mammals would be dispersed throughout the area. The peak of the 

bowhead whale migration through the Chukchi Sea typically occurs in September and October. 

Again, some bowheads might be temporarily displaced around the exploration drilling operation 

during this time. The numbers of cetaceans and seals subject to displacement, if any, would be 

extremely few in relation to abundance estimates for the mammals addressed under this IHA. 

In addition, feeding does not appear to be an important activity by bowheads migrating through 

the Chukchi Sea in most years. In the absence of important feeding areas, the potential diversion 

of a small number of bowheads is not expected to have any significant or long-term 

consequences for individual bowheads or their population. Bowheads, gray, or beluga whales 

are not predicted to be excluded from any habitat, nor are any seals predicted to be excluded 

from any habitat by the offshore exploration drilling program. 

The planned exploration drilling program is not expected to have any habitat-related effects that 

would produce long-term affects to marine mammals or their habitat due to the limited extent of 

the acquisition areas and timing of the program. 

11. The availability and feasibility (economic and technological), methods, and manner 

of conducting such activity or means of effecting the least practicable impact upon 

affected species or stock, their habitat, and of their availability for subsistence uses, 

paying particular attention to rookeries, mating grounds, and areas of similar 

significance 

Details of the planned mitigations are discussed in the Marine Mammal Monitoring and 

Mitigation Plan (4MP; Attachment C). 

12. Where the proposed activity would take place in or near a traditional Arctic 

subsistence hunting area and/or may affect the availability of a species or stock of 

marine mammal for Arctic subsistence uses, the applicant must submit a plan of 

cooperation or information that identifies what measures have been taken and/or 

will be taken to minimize any adverse effects on the availability of marine mammals 

for subsistence uses. A plan must include the following 

12.1 A statement that the applicant has notified and provided the affected subsistence 

community with a draft plan of cooperation 

Shell has prepared and will implement a POC pursuant to BOEMRE Lease Sale Stipulation No. 

5, which requires that all exploration operations be conducted in a manner that prevents 

unreasonable conflicts between oil and gas activities and the subsistence activities and resources 

of residents of the North Slope. This stipulation also requires adherence to, and USFWS and 
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in Conjunction with Planned Exploration Drilling Program During 2012 in the Chukchi Sea, Alaska 

Shell Gulf of Mexico Inc. 79 Revised August 2011 

NMFS regulations, which require an operator to implement a POC to mitigate the potential for 

conflicts between the proposed activity and traditional subsistence activities (50 CFR 

§ 18.124(c)(4) and 50 CFR § 216.104(a)(12)). A POC was prepared and submitted with the 

initial Chukchi Sea EP that was submitted to BOEMRE in May 2009, and approved on 7 

December 2009. Shell has prepared a POC Addendum (Attachment D) which updates the POC 

with information regarding proposed changes to the proposed exploration drilling program as 

compared to the initial Chukchi Sea EP. The POC Addendum includes documentation of 

meetings undertaken to specifically to inform the stakeholders of the revised exploration drilling 

program and obtain their input. The POC Addendum builds upon the previous POC. 

The POC Addendum identifies the measures that Shell has developed in consultation with North 

Slope subsistence communities to minimize any adverse effects on the availability of marine 

mammals for subsistence uses and will implement during its planned Camden Bay and Chukchi 

Sea exploration drilling programs planned to begin in the summer of 2012. In addition, the POC 

Addendum details Shell’s communications and consultations with local subsistence communities 

concerning its planned exploration drilling program, potential conflicts with subsistence 

activities, and means of resolving any such conflicts (50 CFR § 18.128(d) and 50 CFR 

§ 216.104(a) (12) (i), (ii), (iv)). Shell has documented its contacts with the North Slope 

subsistence communities, as well as the substance of its communications with subsistence 

stakeholder groups. 

The leases within the Burger Prospect were acquired during the Chukchi Sea Oil and Gas Lease 

Sales 193 held in February 2008. During the 2012 exploration drilling program Shell plans to 

drill up to three exploration wells, and potentially a fourth partial well, on four leases (Table 1-

1). 

Shell’s Chukchi Sea exploration drilling program is planned for the Burger Prospect in the 

Chukchi Sea (Figure 1-1). This program is set-out in detail in a revised Chukchi Sea EP 

submitted to BOEMRE in May 2011 and the impacts of the project, as well as the measures Shell 

will implement to mitigate those impacts, are analyzed in the Chukchi Sea Environmental Impact 

Analysis Shell submitted to BOEMRE (Appendix F to the revised Chukchi Sea EP). Shell will 

implement this POC Addendum, and the mitigation measures set-forth herein, for its Chukchi 

Sea exploration drilling program. 

 

The potentially affected subsistence communities, identified in BOEMRE Lease Sale Stipulation 

No. 5, that were consulted regarding Shell’s exploration drilling activities include: Barrow, 

Wainwright, Point Lay and Point Hope. Shell presented its POC for the Chukchi Sea exploration 

drilling program to these potentially affected subsistence communities during these 

consultations. Additionally, Shell met with subsistence groups including the AEWC, Inupiat 

Community of the Arctic Slope (ICAS), and the Native Village of Barrow, and presented 

information regarding the proposed activities to the North Slope Borough (NSB) and Northwest 

Arctic Borough (NWAB) Assemblies, and NSB and NWAB Planning Commissions. Several 

one-on-one meetings were also held throughout the villages. 

Beginning in early January 2009 and continuing into 2011, the one-on-one meetings Shell held 

included representatives from the NSB and NWAB, subsistence-user group leadership, and 
Application for Incidental Harassment Authorization for the Non-Lethal Taking of Whales and Seals 

in Conjunction with Planned Exploration Drilling Program During 2012 in the Chukchi Sea, Alaska 

Shell Gulf of Mexico Inc. 80 Revised August 2011 

Village Whaling Captain Association representatives. These meetings took place at the 

convenience of the community leaders and in various venues. Meetings were held starting on the 

12 January 2009 and have continued to date. Shell’s primary purpose in holding individual 

meetings was to inform key leaders, prior to the public meetings, so that they would be prepared 

to give appropriate feedback on planned activities. 

Shell continues to meet each year with the commissioners and committee heads of Alaska 

Beluga Whale Committee, the Nanuuq Commission, Eskimo Walrus Commission (EWC), and 

Alaska Ice Seal Commission (AISC) jointly in co-management meetings. Shell held individual 

consultation meetings with representatives from the various marine mammal commissions to 

discuss the planned Chukchi exploration drilling program. Following the exploration drilling 

season, Shell will have a post-season co-management meeting with the commissioners and 

committee heads to discuss results of mitigation measures and outcomes of the preceding season. 

The goal of the post-season meeting is to build upon the knowledge base, discuss successful or 

unsuccessful outcomes of mitigation measures, and possibly refine plans or mitigation measures 

if necessary. 

Shell also attended the 2011 Conflict Avoidance Agreement (CAA) negotiation meetings in 

support of a limited program of marine environmental baseline activities in 2011 surveys taking 

place in the Beaufort and Chukchi seas. Shell is committed to a CAA process and will 

demonstrate this by making a good-faith effort to negotiate an agreement every year it has 

planned activities. 

12.2 A schedule for meeting with the affected subsistence communities to discuss proposed 

activities and to resolve potential conflicts regarding any aspects of either the operation 

or the plan of cooperation 

 

In the POC Addendum report (Attachment D), Table 4.2-1 provides a list of public meetings 

attended by Shell since January 2009 to develop the POC and the POC Addendum. Attachment 

D, updated to April 2011, also includes sign-in sheets and presentation materials used at the POC 

meetings held in 2011 to present the revised Chukchi Sea EP. Comment analysis tables for 

numerous meetings held during 2011 summarize feedback from the communities on Shell 

planned activities beginning in the summer of 2012. These comments analysis tables, with 

responses from Shell and corresponding mitigation measures pertinent to the comment are 

included in Attachment D. 

12.3 A description of what measures the applicant has taken and/or will take to ensure that 

proposed activities will not interfere with subsistence whaling or sealing; 

The following mitigation measures, plans and programs, are integral to this POC and were 

developed during consultation with potentially affected subsistence groups and communities. 

These measures, plans, and programs to monitor and mitigate potential impacts to subsistence 

users and resources will be implemented by Shell during its exploration drilling operations in the 

Chukchi Sea. The mitigation measures Shell has adopted and will implement during its Chukchi 

Sea exploration drilling operations are listed and discussed below. These mitigation measures 

reflect Shell’s experience conducting exploration activities in the Alaska arctic OCS since the 
Application for Incidental Harassment Authorization for the Non-Lethal Taking of Whales and Seals 

in Conjunction with Planned Exploration Drilling Program During 2012 in the Chukchi Sea, Alaska 

Shell Gulf of Mexico Inc. 81 Revised August 2011 

1980s and its ongoing efforts to engage with local subsistence communities to better understand 

their concerns and develop appropriate and effective mitigation measures to address those 

concerns. This most recent version of Shell’s planned mitigation measures was presented to 

community leaders and subsistence user groups starting in January 2009 and has evolved since in 

response to information learned during the consultation process. 

Subsistence Mitigation Measures 

To minimize any cultural or resource impacts from its exploration operations, Shell will 

implement the following additional measures to ensure coordination of its activities with local 

subsistence users to minimize further the risk of impacting marine mammals and interfering with 

the subsistence hunt: 

Communication 

• Shell has developed a Communication Plan and will implement this plan before initiating 

exploration drilling operations to coordinate activities with local subsistence users, as 

well as Village Whaling Captains’ Associations, to minimize the risk of interfering with 

subsistence hunting activities, and keep current as to the timing and status of the bowhead 

whale hunt and other subsistence hunts. The Communication Plan includes procedures 

for coordination with Com Centers to be located in coastal villages along the Chukchi 

and Beaufort Seas during Shell’s proposed exploration drilling activities. 

• Shell will employ local SAs from the Beaufort and Chukchi Sea villages that are 

potentially impacted by Shell’s exploration drilling activities. The SAs will provide 

consultation and guidance regarding the whale migration and subsistence activities. 

There will be one per village, working approximately 8-hours per day and 40-hours per 

week during the exploration drilling season. The subsistence advisor will use local 

knowledge (Traditional Knowledge) to gather data on subsistence lifestyle within the 

community and to advise in ways to minimize and mitigate potential negative impacts to 

subsistence resources during the exploration drilling season. Responsibilities include 

reporting any subsistence concerns or conflicts; coordinating with subsistence users; 

reporting subsistence-related comments, concerns, and information; coordinating with the 

Com Center personnel; and advising how to avoid subsistence conflicts. SAs will have a 

handbook that will specify work tasks in more detail. 

Aircraft Travel 

• Aircraft shall not operate below 1,500 ft (457 m) unless the aircraft is engaged in marine 

mammal monitoring, approaching, landing or taking off, in poor weather (fog or low 

ceilings), or in an emergency situation, while over land or sea to minimize disturbance to 

mammals and birds. Aircraft engaged in marine mammal monitoring shall not operate 

below 1,500 ft (457 m) in areas of active whaling; such areas to be identified through 

communications with the Com Centers. 

• Aircraft will not operate within 0.5 mi (0.8 km) of walrus or polar bears when observed 

on land or ice. 
Application for Incidental Harassment Authorization for the Non-Lethal Taking of Whales and Seals 

in Conjunction with Planned Exploration Drilling Program During 2012 in the Chukchi Sea, Alaska 

Shell Gulf of Mexico Inc. 82 Revised August 2011 

• Shell will also implement non-MMO flight restrictions prohibiting aircraft from flying 

within 1,000 ft (300 m) of marine mammals or below 1,500 ft (457 m) altitude (except 

during takeoffs and landings or in emergency situations) while over land or sea. This 

flight will also help avoid disturbance of and collisions with birds. 

Vessel Travel 

• The Discoverer and support vessels will enter the Chukchi Sea through the Bering Strait 

on or after July 1, minimizing effects on marine mammals and birds that frequent open 

leads and minimizing effects on spring and early summer bowhead whale hunting. 

• All vessels transit routes will avoid known fragile ecosystems, including the Ledyard Bay 

Critical Habitat Unit, and will include coordination through Com Centers. 

• To minimize impacts on marine mammals and subsistence hunting activities, the drillship 

and support fleet will transit through the Chukchi Sea along a route that lies offshore of 

the polynya zone. In the event the transit outside of the polynya zone results in Shell 

having to break ice (as opposed to managing ice by pushing it out of the way), the 

drillship and support vessels will enter into the polynya zone far enough so that ice 

breaking is not necessary. If it is necessary to move into the polynya zone, Shell will 

notify the local communities of the change in the transit route through the Com Centers. 

As soon as the fleet transits past the ice, it will exit the polynya zone and continue a path 

in the open sea toward the drill sites. 

• MMOs will be aboard the Discoverer and all support vessels. 

• Vessels will not operate within 0.5 mi (0.8 km) of walrus or polar bears when observed 

on land or ice. 

• When within 900 ft (274 m) of marine mammals, vessels will reduce speed, avoid 

separating members from a group and avoid multiple changes of direction. 

• Vessel speed is to be reduced during inclement weather conditions in order to avoid 

collisions with marine mammals. 

• Shell will communicate and coordinate with the Com Centers regarding all vessel transit. 

• Lighting on the drilling vessel will be shaded and has been replaced with ClearSky 

lighting. ClearSky lighting is designed to minimize the disorientation and attraction of 

birds to the lighted drilling vessel to reduce the possibility of a bird collision (see Bird 

Strike Avoidance and Lighting Plan, Appendix I, revised Chukchi Sea EP). 

Exploration Drilling Operations 

• Drilling mud will be cooled to mitigate any potential permafrost thawing or thermal 

dissociation of any methane hydrates encountered during exploration drilling, if such 

materials are present at the drill site. 

• Drilling muds will be recycled to the extent practicable based on operational 

considerations (e.g., whether mud properties have deteriorated to the point where they 

cannot be used further) so that the volume of the spent mud is reduced. 
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in Conjunction with Planned Exploration Drilling Program During 2012 in the Chukchi Sea, Alaska 

Shell Gulf of Mexico Inc. 83 Revised August 2011 

• Critical operations will not be started if potential hazards (ice floe, inclement weather, 

etc.) are in the vicinity and there is not sufficient time to complete the critical operation 

before the arrival of the hazard at the drill site. 

• All casing and cementing programs will be certified by a registered professional 

engineer. 

• The blowout prevention program will be enhanced through the use of two sets of 

blind/shear rams, increased frequency of BOP performance tests from 14 to 7 days, a 

remotely operated vehicle (ROV) control panel on the seafloor with sufficient pressured 

water-based fluid to operate the BOP, a containment system that includes both capping 

stack equipment and, treatment and flaring capabilities, a fully-designed relief well 

drilling plan and provisions for a second relief well drilling vessel (Kulluk) to be 

available to drill the relief well if the primary drilling vessel is disabled and not capable 

of drilling its own relief well. 

ZVSPs 

• Airgun arrays will be ramped up slowly to the required level during ZVSPs to warn 

cetaceans and pinnipeds in the vicinity of the airguns and provide time for them to leave 

the area and avoid potential injury or impairment of their hearing abilities. Ramp-ups 

from a cold start when no airguns have been firing will begin by firing a single airgun in 

the array. A ramp up to the required level will not begin until there has been a minimum 

of 30 minutes of observation of the safety zone by MMOs to assure that no marine 

mammals are present. The safety zone is the extent of the 180 dB radius for cetaceans 

and 190 dB for pinnipeds. The entire safety zone must be visible during the 30-minute 

lead-in to an array ramp up. If a marine mammal(s) is sighted within the safety zone 

during the 30-minute watch prior to ramp up, ramp up will be delayed until the marine 

mammal(s) is sighted outside of the safety zone or the animal(s) is not sighted for at least 

15-30 minutes: 15 minutes for small odontocetes and pinnipeds, or 30 minutes for baleen 

whales and large odontocetes. 

Ice Management 

• Ice management will involve preferentially redirecting, rather than breaking, ice floes 

while the floes are well away from the drill site. 

• Real time ice and weather forecasting will be from the Shell Ice and Weather Advisory 

Center (SIWAC). 

Oil Spill Response 

• The primary OSR vessel will be on standby at all times when drilling into zones 

containing oil to ensure that oil spill response capability is available within one hour, if 

needed. 

• Shell will deploy an OSR fleet that is capable of collecting oil on the water up to the 

planning scenario which is greater than the calculated WCD flowrate of a blowout in the 

unlikely event that one should occur. The primary OSR vessel will be on standby when 

drilling into zones containing oil to ensure that oil spill response capability is available 
Application for Incidental Harassment Authorization for the Non-Lethal Taking of Whales and Seals 

in Conjunction with Planned Exploration Drilling Program During 2012 in the Chukchi Sea, Alaska 

Shell Gulf of Mexico Inc. 84 Revised August 2011 

within one hour, if needed. The remainder of the OSR fleet will be fully engaged within 

72 hours. 

• In addition to the OSR fleet, oil spill containment equipment will be available for use in 

the unlikely event of a blowout. The containment barge will be centrally located in the 

Beaufort Sea and supported by an Invader Class Tug and possibly an anchor handler. The 

containment equipment will be designed for conditions found in the Arctic including ice 

and cold temperatures. This equipment will also be designed for maximum reliability, 

ease of operation, flexibility and robustness so it could be used for a variety of blowout 

situations. 

• Capping stack equipment will be stored as equipment aboard one of the ice management 

vessels and will be available for immediate deployment in the unlikely event of a 

blowout. Capping stack equipment consist of subsea devices assembled to provide direct 

surface intervention capability with the following priorities: 

1. Attaching a device or series of devices to the well to affect a seal capable of 

withstanding the maximum anticipated wellhead pressure and closing the 

assembly to completely seal the well against further flows (commonly called 

“capping and killing”) 

2. Attaching a device or series of devices to the well and diverting flow to surface 

vessel(s) equipped for separation and disposal of hydrocarbons (commonly called 

“capping and diverting”) 

• A polar bear culvert trap has been constructed in anticipation of OSR needs and will be 

available prior to exploration drilling. 

• Pre-booming is required for all fuel transfers between vessels. 

13. The suggested means of accomplishing the necessary monitoring and reporting that 

will result in increased knowledge of the species, the level of taking or impacts on 

the population of marine mammals that are expected to be present while conducting 

activities and suggested means of minimizing burdens by coordinating such 

reporting requirements with other schemes already applicable to persons 

conducting such activity. Monitoring plans should include a description of the 

survey techniques that would be used to determine the movement and activity of 

marine mammals near the activity site(s) including migration and other habitat 

uses, such as feeding 

The planned marine mammal monitoring and mitigation program for the Chukchi Sea 

exploration drilling program is included as Attachment C and this document addresses the issues 

in item 13. 
Application for Incidental Harassment Authorization for the Non-Lethal Taking of Whales and Seals 

in Conjunction with Planned Exploration Drilling Program During 2012 in the Chukchi Sea, Alaska 

Shell Gulf of Mexico Inc. 85 Revised August 2011 

14. Suggested means of learning of, encouraging, and coordinating research 

opportunities, plans, and activities relating to reducing such incidental taking and 

evaluating its effects 

Various agencies and programs may undertake marine mammal studies in the Chukchi Sea 

during the course of the exploration drilling season. It is unclear if these studies might be 

relevant to Shell’s planned exploration drilling program. Shell is prepared to share information 

obtained during implementation of our marine mammal monitoring and mitigation program with 

a variety of groups who may find the data useful in their research. A suggested list of recipients 

includes: 

• The NSB Department of Wildlife Management (T. Hepa) 

• The USFWS Office of Marine Mammal Management (C. Perham and J. Garlic-Miller) 

• The BOEMRE’s Bowhead Whale Aerial Survey Program (C. Monnett) 

• National Oceanic and Atmospheric Administration, National Marine Mammal 

Laboratory (Robyn Angliss) 

• The Kuukpik Subsistence Oversight Panel 

• Alaska Eskimo Whaling Commission (H. Brower -Barrow) 

• Beluga Whale Committee (W. Goodwin -Kotzebue) 

• Inupiat Community of the Arctic Slope (Martha Ipalook Faulk -Barrow) 

• North Slope Science Initiative (J. Payne) 

• BOEMRE Field Supervisor (J. Walker) 

• Alaska Department of Natural Resources (S. Longan) 

• Alaska Department of Fish and Game 
Application for Incidental Harassment Authorization for the Non-Lethal Taking of Whales and Seals 

in Conjunction with Planned Exploration Drilling Program During 2012 in the Chukchi Sea, Alaska 

Shell Gulf of Mexico Inc. 86 Revised August 2011 

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in Conjunction with Planned Exploration Drilling Program During 2012 in the Chukchi Sea, Alaska 

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in Conjunction with Planned Exploration Drilling Program During 2012 in the Chukchi Sea, Alaska 

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Attachment A 

Equipment Specifications for Discoverer
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in Conjunction with Planned Exploration Drilling Program During 2012 in the Chukchi Sea, Alaska 

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Discoverer Specifications 

DISCOVERER OPERATING WATER DEPTH 

MAX WATER DEPTH 1,000 ft with present equipment (can be outfitted to 2,500 ft) 

MAX DRILLING DEPTH 20,000 ft 

DISCOVERER DRILLING PACKAGE 

DRAW WORKS EMSCO E-2,100 - 1,600 horsepower (hp) 

ROTARY National C-495 with 49-1/2-in. opening 

MUD PUMPS 2 ea Continental Emsco Model FB-1600 Triplex Mud Pumps 

DERRICK Pyramid 170 ft with 1,300,000 lb nominal capacity 

PIPE RACKING BJ 3-arm system 

DRILL STING COMPENSATOR Shaffer 400,000 lb with 18-ft stroke 

RISER TENSIONS 8 ea 80,000 lb Shaffer 50-ft stroke tensioners 

CROWN BLOCK Pyramid with 9 ea 60-in. diameter sheaves rated at 1,330,000 lb 

TRAVELING BLOCK Continental - Emsco RA60-6 

BOP Cameron Type U 18.75-in. x 10,000 pounds per square inch (psi) 

RISER Cameron RCK type 

TOP DRIVE Varco TDS-3S, with GE-752 motor, 500 ton 

BOP HANDLING Hydraulic skid based system, drill floor 

DISCOVERER SPECIFICATIONS

TYPE-DESIGN Drillship - Sonat Offshore Drilling Discoverer Class 

SHAPE Monohull with sponsons added for ice-resistance1

SHIP BUILDERS & YEAR Namura Zonshno Shipyard, Osaka, Japan - hull number 355 

YEAR OF HULL CONSTRUCTION 1965 

YEAR OF CONVERSION 1976 

DATE OF LAST DRY-DOCKING 2010 

DISCOVERER DIMENSIONS 

LENGTH 514 ft 156.7 m 

LENGTH BETWEEN PERPENDICULARS 

(LBP) 486 ft 148.2 m 

BREADTH (MOULDED) OVER SPONSONS 85.3 ft 26.0 m 

MAX HEIGHT (ABOVE KEEL) 274 ft 83.7 m 

HEIGHT OF DERRICK ABOVE RIG 

FLOOR 175 ft 53.3 m 

DISCOVERER MOORING EQUIPMENT 

Anchor pattern symmetric 8 points system. The unit is fitted with Sonat Offshore Drilling patented roller turret mooring 

system giving the unit the ability to maintain favorable heading without an interruption of the drilling operations 

ANCHORS 

Stevpris New Generation 7,000 kilograms (kg) each (ea) 15,400 

pounds (lb) ea 

ANCHOR LINES Chain Wire Combination 

SIZE/GRADE 2.75-inch (in.) wire 3-in. ORQ Chain 

LENGTH 2,750 ft (838 m) wire + 1,150 ft (351 m) chain (useable) per anchor 

 

DISCOVERER DISPLACEMENT 

FULL LOAD 20,253 metric tons (mt) 

DRILLING 18,780 mt (Drilling, max load, deep hole, deep water) 
Application for Incidental Harassment Authorization for the Non-Lethal Taking of Whales and Seals 

in Conjunction with Planned Exploration Drilling Program During 2012 in the Chukchi Sea, Alaska 

Shell Gulf of Mexico Inc. A-2 Revised August 2011 

 

1

 Sponsons designed and constructed to meet requirements of Det Norske Veritas (DNV) Additional Class Notation ICE-05. 

DISCOVERER DRAFT 

DRAFT AT LOAD LINE 27 ft 8.20 m 

TRANSIT 27 ft (fully loaded, operating , departure) 8.20 m 

DRILLING 25.16 ft 7.67 m 

DISCOVERER HELIDECK 

MAXIMUM HELICOPTER SIZE Sikorsky S-92N 

FUEL STORAGE 2 ea 720-gallon (gal) tanks 

DISCOVERER ACCOMODATIONS 

NUMBER OF BEDS 140 

SEWAGE TREATMENT UNIT Hamworthy ST-10 

DISCOVERER PROPULSION EQUIPMENT 

PROPELLER 1 each 15 ft 7-in. (4.75 m) diameter, fixed blade 

PROPULSION DRIVE UNIT Marine Diesel, 6 cylinder, 2 cycle, Crosshead type 

HORSEPOWER 7,200 hp @ 135 RPM 

TRANSIT SPEED 8 knots max 

GENERAL STORAGE CAPACITIES 

SACK STORAGE AREA 33,000 ft3 (934 m3) 

BULK STORAGE 

Bentonite / Barite 1,132 bbl (180 m3) - 4 tanks 

Bulk Cement 1,132 bbl (180 m3) - 4 tanks 

LIQUID MUD 

Active 1,200 bbl (191 m3) 

Reserve 1,200 bbl (191 m3) 

Total 2,400 bbl (382 m3) 

POTABLE WATER 1,670 bbl / 265.5 m3 (aft peak can be used as additional pot water tank) 

DRILL WATER 5,798 bbl / 921.7 m3 

FUEL OIL 6,497 bbl / 1,033 m3 
Application for Incidental Harassment Authorization for the Non-Lethal Taking of Whales and Seals 

in Conjunction with Planned Exploration Drilling Program During 2012 in the Chukchi Sea, Alaska 

Shell Gulf of Mexico Inc. May 2011 

 

Attachment B 

Ice Management Plan 

(Refer to Appendix K of the Revised Chukchi Sea EP) 
Application for Incidental Harassment Authorization for the Non-Lethal Taking of Whales and Seals 

in Conjunction with Planned Exploration Drilling Program During 2012 in the Chukchi Sea, Alaska 

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Attachment C 

Marine Mammal Monitoring and Mitigation Plan (4MP) 

(Refer to Appendix D of the Revised Chukchi Sea EP) 
Application for Incidental Harassment Authorization for the Non-Lethal Taking of Whales and Seals 

in Conjunction with Planned Exploration Drilling Program During 2012 in the Chukchi Sea, Alaska 

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Attachment D 

Plan of Cooperation (POC) Addendum 

(Refer to Appendix H of the Revised Camden Bay EP) 
Application for Incidental Harassment Authorization for the Non-Lethal Taking of Whales and Seals 

in Conjunction with Planned Exploration Drilling Program During 2012 in the Chukchi Sea, Alaska 

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Revised Outer Continental Shelf Lease Exploration Plan Chukchi Sea, Alaska 

Shell Gulf of Mexico Inc. May 2011 

Attachment E 

Analysis of the Probability of an “Unspecified Activity” 

and Its Impacts: Oil Spill 

(Refer to Section 4.3 of Appendix F of the Revised Chukchi Sea EP) 

 
Application for Incidental Harassment Authorization for the Non-Lethal Taking of Whales and Seals 

in Conjunction with Planned Exploration Drilling Program During 2012 in the Chukchi Sea, Alaska 

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