Takes of Marine Mammals Incidental to Specified Activities; Taking Marine Mammals Incidental to an Exploration Drilling Program in the Chukchi Sea, Alaska, 69958-70008 [2011-28914]

Agencies

• DEPARTMENT OF COMMERCE
• National Oceanic and Atmospheric Administration

[Federal Register Volume 76, Number 217 (Wednesday, November 9, 2011)]
[Notices]
[Pages 69958-70008]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 2011-28914]



[[Page 69957]]

Vol. 76

Wednesday,

No. 217

November 9, 2011

Part VI





Department of Commerce





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National Oceanic and Atmospheric Administration





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Takes of Marine Mammals Incidental to Specified Activities; Taking 
Marine Mammals Incidental to an Exploration Drilling Program in the 
Chukchi Sea, Alaska; Notice

Federal Register / Vol. 76 , No. 217 / Wednesday, November 9, 2011 / 
Notices

[[Page 69958]]


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DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

RIN 0648-XA811


Takes of Marine Mammals Incidental to Specified Activities; 
Taking Marine Mammals Incidental to an Exploration Drilling Program in 
the Chukchi Sea, Alaska

AGENCY: National Marine Fisheries Service (NMFS), National Oceanic and 
Atmospheric Administration (NOAA), Commerce.

ACTION: Notice; proposed incidental harassment authorization; request 
for comments.

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SUMMARY: NMFS received an application from Shell Offshore Inc. (Shell) 
for an Incidental Harassment Authorization (IHA) to take marine 
mammals, by harassment, incidental to offshore exploration drilling on 
Outer Continental Shelf (OCS) leases in the Chukchi Sea, Alaska. 
Pursuant to the Marine Mammal Protection Act (MMPA), NMFS is requesting 
comments on its proposal to issue an IHA to Shell to take, by Level B 
harassment only, 12 species of marine mammals during the specified 
activity.

DATES: Comments and information must be received no later than December 
9, 2011.

ADDRESSES: Comments on the application should be addressed to Michael 
Payne, Chief, Permits and Conservation Division, Office of Protected 
Resources, National Marine Fisheries Service, 1315 East-West Highway, 
Silver Spring, MD 20910. The mailbox address for providing email 
comments is ITP.Nachman@noaa.gov. NMFS is not responsible for email 
comments sent to addresses other than the one provided here. Comments 
sent via email, including all attachments, must not exceed a 10-
megabyte file size.
    Instructions: All comments received are a part of the public record 
and will generally be posted to https://www.nmfs.noaa.gov/pr/permits/incidental.htm without change. All Personal Identifying Information 
(for example, name, address, etc.) voluntarily submitted by the 
commenter may be publicly accessible. Do not submit Confidential 
Business Information or otherwise sensitive or protected information.
    A copy of the application, which contains several attachments, 
including Shell's marine mammal mitigation and monitoring plan and Plan 
of Cooperation, used in this document may be obtained by writing to the 
address specified above, telephoning the contact listed below (see FOR 
FURTHER INFORMATION CONTACT), or visiting the Internet at: https://www.nmfs.noaa.gov/pr/permits/incidental.htm. Documents cited in this 
notice may also be viewed, by appointment, during regular business 
hours, at the aforementioned address.

FOR FURTHER INFORMATION CONTACT: Candace Nachman, Office of Protected 
Resources, NMFS, (301) 427-8401.

SUPPLEMENTARY INFORMATION:

Background

    Sections 101(a)(5)(A) and (D) of the MMPA (16 U.S.C. 1361 et seq.) 
direct the Secretary of Commerce to allow, upon request, the 
incidental, but not intentional, taking of small numbers of marine 
mammals by U.S. citizens who engage in a specified activity (other than 
commercial fishing) within a specified geographical region if certain 
findings are made and either regulations are issued or, if the taking 
is limited to harassment, a notice of a proposed authorization is 
provided to the public for review.
    Authorization for incidental takings shall be granted if NMFS finds 
that the taking will have a negligible impact on the species or 
stock(s), will not have an unmitigable adverse impact on the 
availability of the species or stock(s) for subsistence uses (where 
relevant), and if the permissible methods of taking and requirements 
pertaining to the mitigation, monitoring and reporting of such takings 
are set forth. NMFS has defined ``negligible impact'' in 50 CFR 216.103 
as ``* * * an impact resulting from the specified activity that cannot 
be reasonably expected to, and is not reasonably likely to, adversely 
affect the species or stock through effects on annual rates of 
recruitment or survival.''
    Section 101(a)(5)(D) of the MMPA established an expedited process 
by which citizens of the U.S. can apply for an authorization to 
incidentally take small numbers of marine mammals by harassment. 
Section 101(a)(5)(D) establishes a 45-day time limit for NMFS review of 
an application followed by a 30-day public notice and comment period on 
any proposed authorizations for the incidental harassment of marine 
mammals. Within 45 days of the close of the comment period, NMFS must 
either issue or deny the authorization.
    Except with respect to certain activities not pertinent here, the 
MMPA defines ``harassment'' as:

any act of pursuit, torment, or annoyance which (i) has the 
potential to injure a marine mammal or marine mammal stock in the 
wild [``Level A harassment'']; or (ii) has the potential to disturb 
a marine mammal or marine mammal stock in the wild by causing 
disruption of behavioral patterns, including, but not limited to, 
migration, breathing, nursing, breeding, feeding, or sheltering 
[``Level B harassment''].

Summary of Request

    NMFS received an application on June 30, 2011, from Shell for the 
taking, by harassment, of marine mammals incidental to offshore 
exploration drilling on OCS leases in the Chukchi Sea, Alaska. NMFS 
reviewed Shell's application and identified a number of issues 
requiring further clarification. After addressing comments from NMFS, 
Shell modified its application and submitted a revised application on 
September 12, 2011. NMFS carefully evaluated Shell's application, 
including their analyses, and determined that the application is 
complete. The September 12, 2011, application is the one available for 
public comment (see ADDRESSES) and considered by NMFS for this proposed 
IHA.
    Shell plans to drill up to three exploration wells at three 
possible drill sites and potentially a partial well at a fourth drill 
site on OCS leases offshore in the Chukchi Sea, Alaska, during the 2012 
Arctic open-water season (July through October). Impacts to marine 
mammals may occur from noise produced by the drillship, zero-offset 
vertical seismic profile (ZVSP) surveys, and supporting vessels 
(including icebreakers) and aircraft. Shell has requested an 
authorization to take 13 marine mammal species by Level B harassment. 
However, the narwhal (Monodon monoceros) is not expected to be found in 
the activity area. Therefore, NMFS is proposing to authorize take of 12 
marine mammal species, by Level B harassment, incidental to Shell's 
offshore exploration drilling in the Chukchi Sea. These species 
include: Beluga whale (Delphinapterus leucas); bowhead whale (Balaena 
mysticetus); gray whale (Eschrichtius robustus); killer whale (Orcinus 
orca); minke whale (Balaenoptera acutorostrata); fin whale 
(Balaenoptera physalus); humpback whale (Megaptera novaeangliae); 
harbor porpoise (Phocoena phocoena); bearded seal (Erignathus 
barbatus); ringed seal (Phoca hispida); spotted seal (P. largha); and 
ribbon seal (Histriophoca fasciata).

Description of the Specified Activity and Specified Geographic Region

    Shell plans to conduct an offshore exploration drilling program on 
U.S. Department of the Interior, Bureau of Ocean Energy Management 
(BOEM, formerly the Minerals Management

[[Page 69959]]

Service) Alaska OCS leases located greater than 64 mi (103 km) from the 
Chukchi Sea coast during the 2012 open-water season. The leases were 
acquired during the Chukchi Sea Oil and Gas Lease Sale 193 held in 
February 2008. During the 2012 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. 
See Figure 1-1 in Shell's application for the lease block and drill 
site locations (see ADDRESSES). All drilling is planned to be vertical.

Exploration Drilling

    All of the possible Chukchi Sea offshore drill sites are located 
between 65 and 78 mi (105 and 125.5 km) from the Chukchi coast in water 
depths between 143 and 150 ft (43.7 and 45.8 m). Table 2-1 in Shell's 
application provides the coordinates for the drill sites (see 
ADDRESSES). All of the proposed wells would be at Shell's Burger 
prospect. Shell has identified a total of six lease blocks on this 
prospect where drilling could occur.
(1) Drilling Vessel
    Shell proposes to use the ice strengthened drillship Discoverer to 
drill the wells. The Discoverer is a true drillship and is a largely 
self-contained drillship that offers full accommodations for a crew of 
up to 140 persons. The Discoverer is 514 ft (156.7 m) long with a 
maximum height (above keel) of 274 ft (83.7 m). It is an anchored 
drillship with an 8-point anchored mooring system and would likely have 
a maximum anchor radius of 2,969-2,986 ft (905-910 m) at either the 
Sivulliq or Torpedo drill sites. While on location at the drill sites, 
the Discoverer will be affixed to the seafloor using eight 7,000 kg 
(7.7 ton) Stevpris anchors arranged in a radial array. The underwater 
fairleads prevent ice fouling of the anchor lines. Turret mooring 
allows orientation of the 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. Ice-strengthened sponsons have 
been retrofitted to the ship's hull. Additional details about the 
drillship can be found in Attachment A of Shell's IHA application (see 
ADDRESSES).
(2) Support Vessels
    During the 2012 drilling season, the Discoverer will be attended by 
eight vessels that will be used for ice management, anchor handling, 
oil spill response (OSR), refueling, resupply, and servicing of the 
exploration drilling operations. The ice-management vessels will 
consist of an icebreaker and an anchor handler. 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, and a containment barge. Tables 1-2a 
and 1-2b in Shell's application provide a list of the support and OSR 
vessels that will be used during the drilling program.
    Shell's base plan is for the ice management vessel and the anchor 
handler, or similar vessels, the oil spill vessels (OSVs), and 
potentially some of the OSR vessels to accompany the Discoverer 
traveling north from Dutch Harbor through the Bering Strait, on or 
about July 1, 2012, then into the Chukchi Sea, before arriving on 
location approximately July 4. Exploration drilling is expected to be 
complete by October 31, 2012. At the completion of the drilling season, 
one or two ice-management vessels, along with various support vessels, 
such as the OSR fleet, will accompany the Discoverer as it travels 
south out of the Chukchi Sea and through the Bering Strait to Dutch 
Harbor. Subject to ice conditions, alternate exit routes may be 
considered.
    The M/V Fennica (Fennica), or a similar vessel, will serve as the 
primary ice management vessel, and 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 Fennica and Tor Viking 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 mi (1-9.6 km) upwind from the Discoverer. When 
managing ice, the vessels will generally be confined to a 40[deg] arc 
up to 3.1 mi (4.9 km) upwind originating at the drilling vessel (see 
Figure 1-3 in Shell's application). It is anticipated that the ice 
management vessels will be managing ice for up to 38% of the time when 
within 25 mi (40 km) of the Discoverer. Active ice management involves 
using the ice management vessel to steer larger floes so that their 
path does not intersect with the drill site. Around-the-clock ice 
forecasting using real-time satellite coverage (available through Shell 
Ice and Weather Advisory Center [SIWAC]) will support the ice 
management duties. The proposed exploration drilling operations will 
require two OSVs to resupply the Discoverer with exploration drilling 
materials and supplies from facilities in Dutch Harbor and fuel.
(3) Aircraft
    Offshore operations will be serviced by helicopters operated out of 
onshore support base locations. 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 a 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 
monitoring flights. Table 1-2c in Shell's application presents the 
aircraft planned to support the exploration drilling program.

Zero-Offset Vertical Seismic Profile

    At the end of each drill hole, Shell may conduct a geophysical 
survey referred to as 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 drilling vessel, 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 
in a string, 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.
    Shell intends to conduct a particular form of vertical seismic 
profile known as a ZVSP, in which the sound source is maintained at a 
constant location near the wellbore (see Figure 1-2 in Shell's

[[Page 69960]]

application). A typical sound source that would be used by Shell in 
2012 is the ITAGA eight-airgun array, which consists of four 150 in\3\ 
airguns and four 40 in\3\ airguns. These airguns can be activated in 
any combination, and Shell intends to utilize the minimum airgun volume 
required to obtain an acceptable signal. Current specifications of the 
array are provided in Table 1-3 of Shell's application. The airgun 
array is depicted within its frame or sled, which is approximately 6 ft 
x 5 ft x 10 ft (1.8 m x 1.5 m x 3 m) (see photograph in Shell's 
application). Typical receivers would consist of a Schlumberger 
wireline four level Vertical Seismic Imager (VSI) tool, which has four 
receivers 50-ft (15-m) apart.
    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 plans to deploy the 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) and 
activated 5-7 times at approximately 20-second intervals. The VSI will 
then be moved to the next interval of the wellbore and reanchored, 
after which the airgun array will again be activated 5-7 times. This 
process will be repeated until the entire well bore is surveyed in this 
manner. The interval between anchor points for the VSI usually is 
between 200 and 300 ft (61 and 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. Therefore, considering a few 
different scenarios, the airgun array could be fired between 117 and 
245 times during the 10-14 hour period. For example, a 7,000-ft 
(2,133.6-m) well with 200-ft (61-m) spacing and seven activations per 
station would result in the airgun array being fired 245 times to 
survey the entire well. That same 7,000-ft (2,133.6-m) well with 300-ft 
(91-m) spacing and five activations would result in the airgun array 
being fired 117 times to survey the entire well. The remainder of the 
time during those 10-14 hours when the airgun is not firing is used to 
move and anchor the geophone array.

Ice Management and Forecasting

    Shell recognizes that the 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 has developed and will implement an Ice Management 
Plan (IMP; see Attachment B in Shell's IHA application) to ensure real-
time ice and weather forecasting is conducted in order to identify 
conditions that might put operations at risk and will modify its 
activities accordingly. The IMP also contains ice threat classification 
levels depending on the time available to suspend drilling operations, 
secure the well, and escape from advancing hazardous ice. Real-time 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 SIWAC. 
The 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 all-weather 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 and 
anchor handling vessels and from the ice observer on the drillship;
     Incidental ice data provided by commercial ships 
transiting the area; and
     Information from NOAA 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 
causing 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 a drilling season 
predominated by open water and thus is not expected to 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 anchors during 
connection to and separation from the seafloor. When managing ice, the 
ice management and anchor handling vessels will generally be operating 
at a 40[deg] arc up to 3.1 mi (4.9 km) upwind originating at the 
Discoverer (see Figure 1-3 in Shell's application).
    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 sufficiently dense 
that the fleet has insufficient capacity to continue operating, and the 
Discoverer would need to disconnect from its anchors and move 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 it is not 
expected to be needed throughout the proposed drilling season. Shell 
has indicated that when ice is present at the drill site, ice 
disturbance will be limited to the minimum needed to allow drilling to 
continue. First-year ice (i.e., ice that formed in the most recent 
autumn-winter period) 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 or around it. This type of ice is managed by the ice 
management vessel continually moving back and forth across the drift 
line, directly up-drift 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 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 (i.e., ice that has survived at least one summer melt 
season) 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 has 
indicated

[[Page 69961]]

that they do not intend to conduct any icebreaking activities; rather, 
Shell would deploy its support vessels to manage ice as described here. 
As detailed in Shell's IMP (see Attachment B of Shell's IHA 
application), actual breaking of ice would 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 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 from such activities.

Timeframe of Activities

    Shell proposes to mobilize the drillship and its fleet of vessels 
from Dutch Harbor and to travel through the Bering Strait on or about 
July 1, 2012. The vessels would then travel into the Chukchi Sea, 
arriving on location at the Burger prospect in the Chukchi Sea on 
approximately July 4, 2012. Shell proposes to conduct the exploration 
drilling program through October 31, 2012. At the end of the 
exploration drilling season, the Discoverer and its support vessels 
would travel south out of the Chukchi Sea through the Bering Strait to 
Dutch Harbor. Subject to ice conditions, alternate exit routes may be 
considered.
    Shell anticipates that the exploration drilling program will 
require approximately 32 days per well, including mudline cellar 
construction. Therefore, if Shell is able to drill three exploration 
wells during the 2012 open-water season, it would require a total of 96 
days. If Shell is able to drill part of a fourth well, it would add an 
additional 1-32 days to the season but would not extend beyond October 
31, 2012. These estimates do not include any downtime for weather or 
other operational delays. Time to conduct the ZVSP surveys for each 
well is included in the 32 drilling days for each well. Shell also 
assumes approximately 10 additional days will be needed for transit, 
drillship mobilization and mooring, drillship moves between locations, 
and drillship demobilization.
    Activities associated with the 2012 Chukchi Sea exploration 
drilling program include operation of the Discoverer, associated 
support vessels, crew change support, and resupply, ZVSP surveys, and 
icebreaking. 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 with Shell's IMP. The anchor handler and 
OSR vessels will remain in close proximity to the drillship during 
drilling operations.

Exploratory Drilling Program Sound Characteristics

    Potential impacts to marine mammals could occur from the noise 
produced by the drillship and its support vessels (including the 
icebreakers), aircraft, and the airgun array during ZVSP surveys. The 
drillship produces continuous noise into the marine environment. NMFS 
currently uses a threshold of 120 dB re 1 [mu]Pa (rms) for the onset of 
Level B harassment from continuous sound sources. This 120 dB threshold 
is also applicable for the icebreakers when actively managing or 
breaking ice. The drilling vessel to be used will be the Discoverer. 
The airgun array proposed to be used by Shell for the ZVSP surveys 
produces pulsed noise into the marine environment. NMFS currently uses 
a threshold of 160 dB re 1 [mu]Pa (rms) for the onset of Level B 
harassment from pulsed sound sources.
(1) Drilling Sounds
    Exploratory drilling will be conducted from the Discoverer, a 
vessel specifically designed for such operations in the Arctic. 
Underwater sound propagation results from the use of generators, 
drilling machinery, and the rig itself. Received 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 levels 
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 Hz although tones up to 1,850 
Hz were recorded by Greene (1987a) during drilling operations in the 
Beaufort Sea. At a range of 558 ft (170 m) the 20-1000 Hz band level 
was 122-125 dB for the drillship Explorer I. Underwater sound levels 
were slightly higher (134 dB) during drilling activity from the 
Northern Explorer II at a range of 656 ft (200 m), although tones were 
only recorded below 600 Hz. Underwater sound measurements from the 
Kulluk at 0.62 mi (1 km) were higher (143 dB) than from the other two 
vessels.
    Sound measurements from the Discoverer have not previously been 
conducted 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 Sea 
(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 [micro]Pa at 1 m (rms) 
(Austin and Warner, 2010). Once on location at the drill sites in 
Chukchi Sea, Shell plans to take measurements of the drillship to 
quantify the absolute sound levels produced by drilling and to monitor 
their variations with time, distance, and direction from the drilling 
vessel.
(2) Vessel Sounds
    In addition to the drillship, various types of vessels will be used 
in support of the operations, including ice management vessels, anchor 
handlers, offshore supply vessels, barges and tugs, and OSR 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 (e.g., Aerts et al., 2008; Hauser et al., 2008; 
Brueggeman, 2009; Ireland et al., 2009). For example, Garner and Hannay 
(2009) estimated sound pressure levels of 100 dB at distances ranging 
from approximately 1.5 to 2.3 mi (2.4 to 3.7 km) from various types of 
barges. MacDonald et

[[Page 69962]]

al. (2008) estimated higher underwater sound pressure levels (SPLs) 
from the seismic vessel Gilavar of 120 dB at approximately 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.
    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 [micro]Pa at 1 m (Greene, 1987a; Richardson et al., 1995a).
    Sound levels during ice management activities would not be as 
intense as during icebreaking, and the resulting effects to marine 
species would be less significant in comparison. During ice management, 
the vessel's propeller is rotating at approximately 15-20 percent of 
the vessel's propeller rotation capacity. Instead of actually breaking 
ice, during ice management, the vessel redirects and repositions the 
ice by pushing it away from the direction of the drillship at slow 
speeds so that the ice floe does not slip past the vessel bow. 
Basically, ice management occurs at slower speed, lower power, and 
slower propeller rotation speed (i.e., lower cavitation), allowing for 
fewer repositions of the vessel, thereby reducing cavitation effects in 
the water than would occur during icebreaking. Once on location at the 
drill sites in the Chukchi Sea, Shell plans to measure the sound levels 
produced by vessels operating in support of drilling operations. These 
vessels will include crew change vessels, tugs, ice management vessels, 
and OSR vessels.
(3) Aircraft Sound
    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[deg] cone beneath the aircraft. 
Some of the sound will transmit beyond the immediate area, and some 
sound will enter the water outside the 26[deg] 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 
drillship will generally maintain straight-line routes at altitudes of 
at least 1,500 ft (457 m) above sea level, thereby limiting the 
received levels at and below the surface. Aircraft travel would be 
controlled by Federal Aviation Administration approved flight paths.
(4) Vertical Seismic Profile Sound
    A typical eight airgun array (4 x 40 in\3\ airguns and 4 x 150 
in\3\ airguns, for a total discharge volume of 760 in\3\) would be used 
to perform ZVSP surveys, if conducted after the completion of each 
exploratory well. Typically, a single ZVSP survey will be performed 
when the well has reached proposed total depth or final depth; 
although, in some instances, a prior ZVSP will have been performed at a 
shallower depth. A typical survey will last 10-14 hours, depending on 
the depth of the well and the number of anchoring points, and include 
firings of the full array, plus additional firing of a single 40-in\3\ 
airgun to be used as a ``mitigation airgun'' while the geophones are 
relocated within the wellbore. The source level for the airgun array 
proposed for use by Shell will differ based on source depth. At a depth 
of 9.8 ft (3 m), the SPL is 238 dB re 1 [mu]Pa at 1 m, and at a depth 
of 16.4 ft (5 m), the SPL is 241 dB re 1 [mu]Pa at 1 m, with most 
energy between 20 and 140 Hz.
    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. Typical high-energy airgun 
arrays emit most energy at 10-120 Hz. However, the pulses contain 
significant energy up to 500-1,000 Hz and some energy at higher 
frequencies (Goold and Fish, 1998; Potter et al., 2007).
    Although there will be several support vessels in the drilling 
operations area, NMFS considers the possibility of collisions with 
marine mammals highly unlikely. Once on location, the majority of the 
support vessels will remain in the area of the drillship throughout the 
2012 drilling season and will not be making trips between the shorebase 
and the offshore vessels. When not needed for ice management/
icebreaking operations, the icebreaker and anchor handler will remain 
approximately 25 mi (40 km) upwind and upcurrent of the drillship. Any 
ice management/icebreaking activity would be expected to occur at a 
distance of 0.6-12 mi (1-19 km) upwind and upcurrent of the drillship. 
As the crew change/resupply activities are considered part of normal 
vessel traffic and are not anticipated to impact marine mammals in a 
manner that would rise to the level of taking, those activities are not 
considered further in this document.

Description of Marine Mammals in the Area of the Specified Activity

    The Chukchi Sea supports a diverse assemblage of marine mammals, 
including: bowhead, gray, beluga, killer, minke, humpback, and fin 
whales; harbor porpoise; ringed, ribbon, spotted, and bearded seals; 
narwhals; polar bears (Ursus maritimus); and walruses (Odobenus 
rosmarus divergens; see Table 4-1 in Shell's application). The bowhead, 
humpback, and fin whales are listed as ``endangered'' under the 
Endangered Species Act (ESA) and as depleted under the MMPA. Certain 
stocks or populations of gray, beluga, and killer whales and spotted 
seals are listed as endangered or are proposed for listing under the 
ESA; however, none of those stocks or populations occur in the proposed 
activity area. On December 10, 2010, NMFS published a notice of

[[Page 69963]]

proposed threatened status for subspecies of the ringed seal (75 FR 
77476) and a notice of proposed threatened and not warranted status for 
subspecies and distinct population segments of the bearded seal (75 FR 
77496) in the Federal Register. Neither of these two ice seal species 
is considered depleted under the MMPA. Additionally, the ribbon seal is 
considered a ``species of concern'' under the ESA. Both the walrus and 
the polar bear are managed by the U.S. Fish and Wildlife Service 
(USFWS) and are not considered further in this proposed IHA notice.
    Of these species, 12 are expected to occur in the area of Shell's 
proposed operations. These species include: The bowhead, gray, 
humpback, minke, fin, killer, and beluga whales; harbor porpoise; and 
the ringed, spotted, bearded, and ribbon seals. Beluga, bowhead, and 
gray whales, harbor porpoise, and ringed, bearded, and spotted seals 
are anticipated to be encountered more than the other marine mammal 
species mentioned here. The marine mammal species that is likely to be 
encountered most widely (in space and time) throughout the period of 
the proposed drilling program is the ringed seal. Encounters with 
bowhead and gray whales are expected to be limited to particular 
seasons, as discussed later in this document. Where available, Shell 
used density estimates from peer-reviewed literature in the 
application. In cases where density estimates were not readily 
available in the peer-reviewed literature, Shell used other methods to 
derive the estimates. NMFS reviewed the density estimate descriptions 
and articles from which estimates were derived and requested additional 
information to better explain the density estimates presented by Shell 
in its application. This additional information was included in the 
revised IHA application. The explanation for those derivations and the 
actual density estimates are described later in this document (see the 
``Estimated Take by Incidental Harassment'' section).
    The narwhal occurs in Canadian waters and occasionally in the 
Alaskan Beaufort Sea and the Chukchi Sea, but it is considered 
extralimital in U.S. waters and is not expected to be encountered. 
There are scattered records of narwhal in Alaskan waters, including 
reports by subsistence hunters, where the species is considered 
extralimital (Reeves et al., 2002). Due to the rarity of this species 
in the proposed project area and the remote chance it would be affected 
by Shell's proposed Chukchi Sea drilling activities, this species is 
not discussed further in this proposed IHA notice.
    Shell's application contains information on the status, 
distribution, seasonal distribution, abundance, and life history of 
each of the species under NMFS jurisdiction mentioned in this document. 
When reviewing the application, NMFS determined that the species 
descriptions provided by Shell correctly characterized the status, 
distribution, seasonal distribution, and abundance of each species. 
Please refer to the application for that information (see ADDRESSES). 
Additional information can also be found in the NMFS Stock Assessment 
Reports (SAR). The Alaska 2010 SAR is available at: https://www.nmfs.noaa.gov/pr/pdfs/sars/ak2010.pdf.

Brief Background on Marine Mammal Hearing

    When considering the influence of various kinds of sound on the 
marine environment, it is necessary to understand that different kinds 
of marine life are sensitive to different frequencies of sound. Based 
on available behavioral data, audiograms have been derived using 
auditory evoked potentials, anatomical modeling, and other data, 
Southall et al. (2007) designate ``functional hearing groups'' for 
marine mammals and estimate the lower and upper frequencies of 
functional hearing of the groups. The functional groups and the 
associated frequencies are indicated below (though animals are less 
sensitive to sounds at the outer edge of their functional range and 
most sensitive to sounds of frequencies within a smaller range 
somewhere in the middle of their functional hearing range):
     Low frequency cetaceans (13 species of mysticetes): 
functional hearing is estimated to occur between approximately 7 Hz and 
22 kHz (however, a study by Au et al. (2006) of humpback whale songs 
indicate that the range may extend to at least 24 kHz);
     Mid-frequency cetaceans (32 species of dolphins, six 
species of larger toothed whales, and 19 species of beaked and 
bottlenose whales): functional hearing is estimated to occur between 
approximately 150 Hz and 160 kHz;
     High frequency cetaceans (eight species of true porpoises, 
six species of river dolphins, Kogia, the franciscana, and four species 
of cephalorhynchids): functional hearing is estimated to occur between 
approximately 200 Hz and 180 kHz; and
     Pinnipeds in Water: functional hearing is estimated to 
occur between approximately 75 Hz and 75 kHz, with the greatest 
sensitivity between approximately 700 Hz and 20 kHz.
    As mentioned previously in this document, 12 marine mammal species 
(four pinniped and eight cetacean species) are likely to occur in the 
proposed drilling area. Of the eight cetacean species likely to occur 
in Shell's project area, five are classified as low frequency cetaceans 
(i.e., bowhead, gray, humpback, minke, and fin whales), two are 
classified as mid-frequency cetaceans (i.e., beluga and killer whales), 
and one is classified as a high-frequency cetacean (i.e., harbor 
porpoise) (Southall et al., 2007).
    Underwater audiograms have been obtained using behavioral methods 
for four species of phocinid seals: the ringed, harbor, harp, and 
northern elephant seals (reviewed in Richardson et al., 1995a; Kastak 
and Schusterman, 1998). Below 30-50 kHz, the hearing threshold of 
phocinids is essentially flat down to at least 1 kHz and ranges between 
60 and 85 dB re 1 [mu]Pa. There are few published data on in-water 
hearing sensitivity of phocid seals below 1 kHz. However, measurements 
for one harbor seal indicated that, below 1 kHz, its thresholds 
deteriorated gradually to 96 dB re 1 [mu]Pa at 100 Hz from 80 dB re 1 
[mu]Pa at 800 Hz and from 67 dB re 1 [mu]Pa at 1,600 Hz (Kastak and 
Schusterman, 1998). More recent data suggest that harbor seal hearing 
at low frequencies may be more sensitive than that and that earlier 
data were confounded by excessive background noise (Kastelein et al., 
2009a,b). If so, harbor seals have considerably better underwater 
hearing sensitivity at low frequencies than do small odontocetes like 
belugas (for which the threshold at 100 Hz is about 125 dB).
    Pinniped call characteristics are relevant when assessing potential 
masking effects of man-made sounds. In addition, for those species 
whose hearing has not been tested, call characteristics are useful in 
assessing the frequency range within which hearing is likely to be most 
sensitive. The four species of seals present in the study area, all of 
which are in the phocid seal group, are all most vocal during the 
spring mating season and much less so during late summer. In each 
species, the calls are at frequencies from several hundred to several 
thousand hertz--above the frequency range of the dominant noise 
components from most of the proposed oil exploration activities.
    Cetacean hearing has been studied in relatively few species and 
individuals. The auditory sensitivity of bowhead, gray, and other 
baleen whales has not been measured, but relevant anatomical

[[Page 69964]]

and behavioral evidence is available. These whales appear to be 
specialized for low frequency hearing, with some directional hearing 
ability (reviewed in Richardson et al., 1995a; Ketten, 2000). Their 
optimum hearing overlaps broadly with the low frequency range where 
exploration drilling activities, airguns, and associated vessel traffic 
emit most of their energy.
    The beluga whale is one of the better-studied species in terms of 
its hearing ability. As mentioned earlier, the auditory bandwidth in 
mid-frequency odontocetes is believed to range from 150 Hz to 160 kHz 
(Southall et al., 2007); however, belugas are most sensitive above 10 
kHz. They have relatively poor sensitivity at the low frequencies 
(reviewed in Richardson et al., 1995a) that dominate the sound from 
industrial activities and associated vessels. Nonetheless, the noise 
from strong low frequency sources is detectable by belugas many 
kilometers away (Richardson and Wursig, 1997). Also, beluga hearing at 
low frequencies in open-water conditions is apparently somewhat better 
than in the captive situations where most hearing studies were 
conducted (Ridgway and Carder, 1995; Au, 1997). If so, low frequency 
sounds emanating from drilling activities may be detectable somewhat 
farther away than previously estimated.
    Call characteristics of cetaceans provide some limited information 
on their hearing abilities, although the auditory range often extends 
beyond the range of frequencies contained in the calls. Also, 
understanding the frequencies at which different marine mammal species 
communicate is relevant for the assessment of potential impacts from 
manmade sounds. A summary of the call characteristics for bowhead, 
gray, and beluga whales is provided next.
    Most bowhead calls are tonal, frequency-modulated sounds at 
frequencies of 50-400 Hz. These calls overlap broadly in frequency with 
the underwater sounds emitted by many of the activities to be performed 
during Shell's proposed exploration drilling program (Richardson et 
al., 1995a). Source levels are quite variable, with the stronger calls 
having source levels up to about 180 dB re 1 [mu]Pa at 1 m. Gray whales 
make a wide variety of calls at frequencies from < 100-2,000 Hz (Moore 
and Ljungblad, 1984; Dalheim, 1987).
    Beluga calls include trills, whistles, clicks, bangs, chirps and 
other sounds (Schevill and Lawrence, 1949; Ouellet, 1979; Sjare and 
Smith, 1986a). Beluga whistles have dominant frequencies in the 2-6 kHz 
range (Sjare and Smith, 1986a). This is above the frequency range of 
most of the sound energy produced by the proposed exploratory drilling 
activities and associated vessels. Other beluga call types reported by 
Sjare and Smith (1986a,b) included sounds at mean frequencies ranging 
upward from 1 kHz.
    The beluga also has a very well developed high frequency 
echolocation system, as reviewed by Au (1993). Echolocation signals 
have peak frequencies from 40-120 kHz and broadband source levels of up 
to 219 dB re 1 [mu]Pa-m (zero-peak). Echolocation calls are far above 
the frequency range of the sounds produced by the devices proposed for 
use during Shell's Chukchi Sea exploratory drilling program. Therefore, 
those industrial sounds are not expected to interfere with 
echolocation.

Potential Effects of the Specified Activity on Marine Mammals

    The likely or possible impacts of the proposed exploratory drilling 
program in the Chukchi Sea on marine mammals could involve both non-
acoustic and acoustic effects. Potential non-acoustic effects could 
result from the physical presence of the equipment and personnel. 
Petroleum development and associated activities introduce sound into 
the marine environment. Impacts to marine mammals are expected to 
primarily be acoustic in nature. Potential acoustic effects on marine 
mammals relate to sound produced by drilling activity, vessels, and 
aircraft, as well as the ZVSP airgun array. The potential effects of 
sound from the proposed exploratory drilling program might include one 
or more of the following: tolerance; masking of natural sounds; 
behavioral disturbance; non-auditory physical effects; and, at least in 
theory, temporary or permanent hearing impairment (Richardson et al., 
1995a). However, for reasons discussed later in this document, it is 
unlikely that there would be any cases of temporary, or especially 
permanent, hearing impairment resulting from these activities. As 
outlined in previous NMFS documents, the effects of noise on marine 
mammals are highly variable, and can be categorized as follows (based 
on Richardson et al., 1995a):
    (1) The noise 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 noise may be audible but not strong enough to elicit any 
overt behavioral response;
    (3) The noise may elicit reactions of variable conspicuousness and 
variable relevance to the well being of the marine mammal; these can 
range from temporary alert responses to active avoidance reactions such 
as vacating an area at least until the noise event ceases but 
potentially for longer periods of time;
    (4) Upon repeated exposure, a marine mammal may exhibit diminishing 
responsiveness (habituation), or disturbance effects may persist; the 
latter is most likely with sounds that are highly variable in 
characteristics, infrequent, and unpredictable in occurrence, and 
associated with situations that a marine mammal perceives as a threat;
    (5) Any anthropogenic noise that is strong enough to be heard has 
the potential to reduce (mask) the ability of a marine mammal to hear 
natural sounds at similar frequencies, including calls from 
conspecifics, and underwater environmental sounds such as surf noise;
    (6) If mammals remain in an area because it is important for 
feeding, breeding, or some other biologically important purpose even 
though there is chronic exposure to noise, it is possible that there 
could be noise-induced physiological stress; this might in turn have 
negative effects on the well-being or reproduction of the animals 
involved; and
    (7) Very strong sounds have the potential to cause a temporary or 
permanent reduction in hearing sensitivity. In terrestrial mammals, and 
presumably marine mammals, received sound levels must far exceed the 
animal's hearing threshold for there to be any temporary threshold 
shift (TTS) in its hearing ability. For transient sounds, the sound 
level necessary to cause TTS is inversely related to the duration of 
the sound. Received sound levels must be even higher for there to be 
risk of permanent hearing impairment. In addition, intense acoustic or 
explosive events may cause trauma to tissues associated with organs 
vital for hearing, sound production, respiration and other functions. 
This trauma may include minor to severe hemorrhage.

Potential Acoustic Effects From Exploratory Drilling Activities

(1) Tolerance
    Numerous studies have shown that underwater sounds from industry 
activities are often readily detectable by marine mammals 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

[[Page 69965]]

of various types (Miller et al., 2005; Bain and Williams, 2006). 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 or vessels 
under some conditions, at other times mammals of all three types have 
shown no overt reactions (e.g., Malme et al., 1986; Richardson et al., 
1995; Madsen and Mohl, 2000; Croll et al., 2001; Jacobs and Terhune, 
2002; Madsen et al., 2002; Miller et al., 2005). In general, pinnipeds 
and small odontocetes seem to be more tolerant of exposure to some 
types of underwater sound than are baleen whales. Richardson et al. 
(1995a) found that vessel noise does not seem to strongly affect 
pinnipeds that are already in the water. Richardson et al. (1995a) went 
on to explain that seals on haul-outs sometimes respond strongly to the 
presence of vessels and at other times appear to show considerable 
tolerance of vessels, and Brueggeman et al. (1992, cited in Richardson 
et al., 1995a) observed ringed seals hauled out on ice pans displaying 
short-term escape reactions when a ship approached within 0.25-0.5 mi 
(0.4-0.8 km).
(2) Masking
    Masking is the obscuring of sounds of interest by other sounds, 
often at similar frequencies. Marine mammals are highly dependent on 
sound, and their ability to recognize sound signals amid other noise is 
important in communication, predator and prey detection, and, in the 
case of toothed whales, echolocation. Even in the absence of manmade 
sounds, the sea is usually noisy. Background ambient noise often 
interferes with or masks the ability of an animal to detect a sound 
signal even when that signal is above its absolute hearing threshold. 
Natural ambient noise includes contributions from wind, waves, 
precipitation, other animals, and (at frequencies above 30 kHz) thermal 
noise resulting from molecular agitation (Richardson et al., 1995a). 
Background noise also can include sounds from human activities. Masking 
of natural sounds can result when human activities produce high levels 
of background noise. Conversely, if the background level of underwater 
noise is high (e.g., on a day with strong wind and high waves), an 
anthropogenic noise source will not be detectable as far away as would 
be possible under quieter conditions and will itself be masked.
    Although some degree of masking is inevitable when high levels of 
manmade broadband sounds are introduced into the sea, marine mammals 
have evolved systems and behavior that function to reduce the impacts 
of masking. Structured signals, such as the echolocation click 
sequences of small toothed whales, may be readily detected even in the 
presence of strong background noise because their frequency content and 
temporal features usually differ strongly from those of the background 
noise (Au and Moore, 1988, 1990). The components of background noise 
that are similar in frequency to the sound signal in question primarily 
determine the degree of masking of that signal.
    Redundancy and context can also facilitate detection of weak 
signals. These phenomena may help marine mammals detect weak sounds in 
the presence of natural or manmade noise. Most masking studies in 
marine mammals present the test signal and the masking noise from the 
same direction. The sound localization abilities of marine mammals 
suggest that, if signal and noise come from different directions, 
masking would not be as severe as the usual types of masking studies 
might suggest (Richardson et al., 1995a). The dominant background noise 
may be highly directional if it comes from a particular anthropogenic 
source such as a ship or industrial site. Directional hearing may 
significantly reduce the masking effects of these noises by improving 
the effective signal-to-noise ratio. In the cases of high-frequency 
hearing by the bottlenose dolphin, beluga whale, and killer whale, 
empirical evidence confirms that masking depends strongly on the 
relative directions of arrival of sound signals and the masking noise 
(Penner et al., 1986; Dubrovskiy, 1990; Bain et al., 1993; Bain and 
Dahlheim, 1994). Toothed whales, and probably other marine mammals as 
well, have additional capabilities besides directional hearing that can 
facilitate detection of sounds in the presence of background noise. 
There is evidence that some toothed whales can shift the dominant 
frequencies of their echolocation signals from a frequency range with a 
lot of ambient noise toward frequencies with less noise (Au et al., 
1974, 1985; Moore and Pawloski, 1990; Thomas and Turl, 1990; Romanenko 
and Kitain, 1992; Lesage et al., 1999). A few marine mammal species are 
known to increase the source levels or alter the frequency of their 
calls in the presence of elevated sound levels (Dahlheim, 1987; Au, 
1993; Lesage et al., 1993, 1999; Terhune, 1999; Foote et al., 2004; 
Parks et al., 2007, 2009; Di Iorio and Clark, 2009; Holt et al., 2009).
    These data demonstrating adaptations for reduced masking pertain 
mainly to the very high frequency echolocation signals of toothed 
whales. There is less information about the existence of corresponding 
mechanisms at moderate or low frequencies or in other types of marine 
mammals. For example, Zaitseva et al. (1980) found that, for the 
bottlenose dolphin, the angular separation between a sound source and a 
masking noise source had little effect on the degree of masking when 
the sound frequency was 18 kHz, in contrast to the pronounced effect at 
higher frequencies. Directional hearing has been demonstrated at 
frequencies as low as 0.5-2 kHz in several marine mammals, including 
killer whales (Richardson et al., 1995a). This ability may be useful in 
reducing masking at these frequencies. In summary, high levels of noise 
generated by anthropogenic activities may act to mask the detection of 
weaker biologically important sounds by some marine mammals. This 
masking may be more prominent for lower frequencies. For higher 
frequencies, such as that used in echolocation by toothed whales, 
several mechanisms are available that may allow them to reduce the 
effects of such masking.
    Masking effects of underwater sounds from Shell's proposed 
activities on marine mammal calls and other natural sounds are expected 
to be limited. For example, beluga whales 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, as cited in Shell, 2009). 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, as cited in Shell, 2009). At distances greater than 660-
1,300 ft (200-400 m), recorded sounds from drilling 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 minor 
changes are not expected to affect the beluga whale population 
(Richardson et al., 1991; Richard et al., 1998). Brewer et al. (1993) 
observed belugas within 2.3 mi (3.7 km) of the drilling unit Kulluk 
during drilling; however, the authors do

[[Page 69966]]

not describe any behaviors that may have been exhibited by those 
animals. Please refer to the Arctic Multiple-Sale Draft Environmental 
Impact Statement (USDOI MMS, 2008), available on the Internet at: 
https://www.mms.gov/alaska/ref/EIS%20EA/ArcticMultiSale_209/_DEIS.htm, 
for more detailed information.
    There is evidence of other marine mammal species continuing to call 
in the presence of industrial activity. Annual acoustical monitoring 
near BP's Northstar production facility during the fall bowhead 
migration westward through the Beaufort Sea has recorded thousands of 
calls each year (for examples, see Richardson et al., 2007; Aerts and 
Richardson, 2008). Construction, maintenance, and operational 
activities have been occurring from this facility for over 10 years. To 
compensate and reduce masking, some mysticetes may alter the 
frequencies of their communication sounds (Richardson et al., 1995a; 
Parks et al., 2007). Masking processes in baleen whales are not 
amenable to laboratory study, and no direct measurements on hearing 
sensitivity are available for these species. It is not currently 
possible to determine with precision the potential consequences of 
temporary or local background noise levels. However, Parks et al. 
(2007) found that right whales (a species closely related to the 
bowhead whale) altered their vocalizations, possibly in response to 
background noise levels. For species that can hear over a relatively 
broad frequency range, as is presumed to be the case for mysticetes, a 
narrow band source may only cause partial masking. Richardson et al. 
(1995a) note that a bowhead whale 12.4 mi (20 km) from a human sound 
source, such as that produced during oil and gas industry activities, 
might hear strong calls from other whales within approximately 12.4 mi 
(20 km), and a whale 3.1 mi (5 km) from the source might hear strong 
calls from whales within approximately 3.1 mi (5 km). Additionally, 
masking is more likely to occur closer to a sound source, and distant 
anthropogenic sound is less likely to mask short-distance acoustic 
communication (Richardson et al., 1995a).
    Although some masking by marine mammal species in the area may 
occur, the extent of the masking interference will depend on the 
spatial relationship of the animal and Shell's activity. Almost all 
energy in the sounds emitted by drilling and other operational 
activities is at low frequencies, predominantly below 250 Hz with 
another peak centered around 1,000 Hz. Most energy in the sounds from 
the vessels and aircraft to be used during this project is below 1 kHz 
(Moore et al., 1984; Greene and Moore, 1995; Blackwell et al., 2004b; 
Blackwell and Greene, 2006). These frequencies are mainly used by 
mysticetes but not by odontocetes. Therefore, masking effects would 
potentially be more pronounced in the bowhead and gray whales that 
might occur in the proposed project area. If, as described later in 
this document, certain species avoid the proposed drilling locations, 
impacts from masking are anticipated to be low.
(3) Behavioral Disturbance Reactions
    Behavioral responses to sound are highly variable and context-
specific. Many different variables can influence an animal's perception 
of and response to (in both nature and magnitude) an acoustic event. An 
animal's prior experience with a sound or sound source affects whether 
it is less likely (habituation) or more likely (sensitization) to 
respond to certain sounds in the future (animals can also be innately 
pre-disposed to respond to certain sounds in certain ways; Southall et 
al., 2007). Related to the sound itself, the perceived nearness of the 
sound, bearing of the sound (approaching vs. retreating), similarity of 
a sound to biologically relevant sounds in the animal's environment 
(i.e., calls of predators, prey, or conspecifics), and familiarity of 
the sound may affect the way an animal responds to the sound (Southall 
et al., 2007). Individuals (of different age, gender, reproductive 
status, etc.) among