Small Takes of Marine Mammals Incidental to Specified Activities; Ocean Bottom Cable Seismic Survey in the Liberty Prospect, Beaufort Sea, Alaska in 2008, 24236-24253 [E8-9682]

Agencies

• DEPARTMENT OF COMMERCE
• National Oceanic and Atmospheric Administration

[Federal Register Volume 73, Number 86 (Friday, May 2, 2008)]
[Notices]
[Pages 24236-24253]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: E8-9682]


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DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

RIN 0648-XH53


Small Takes of Marine Mammals Incidental to Specified Activities; 
Ocean Bottom Cable Seismic Survey in the Liberty Prospect, Beaufort 
Sea, Alaska in 2008

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

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

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SUMMARY: NMFS has received an application from BP Exploration (Alaska), 
Inc. (BPXA) for an Incidental Harassment Authorization (IHA) to take 
marine mammals incidental to a 3D, ocean bottom cable (OBC) seismic 
survey in the Liberty Prospect, Beaufort Sea, Alaska in 2008. Pursuant 
to the Marine Mammal Protection Act (MMPA), NMFS is requesting comments 
on its proposal to issue an IHA to BPXA to incidentally take, by 
harassment, small numbers of several species of marine mammals between 
July and October, 2008, during the aforementioned activity.

DATES:  Comments and information must be received no later than June 2, 
2008.

ADDRESSES:  Comments on the application should be addressed to P. 
Michael Payne, Chief, Permits, Conservation and Education Division, 
Office of Protected Resources, National Marine Fisheries Service, 1315 
East-West Highway, Silver Spring, MD 20910-3225. The mailbox address 
for providing email comments is PR1.0648XH53@noaa.gov. Comments sent 
via e-mail, including all attachments, must not exceed a 10-megabyte 
file size.
    A copy of the application containing a list of the references used 
in this document may be obtained by writing to the address specified 
above, telephoning the contact listed below (FOR FURTHER INFORMATION 
CONTACT), or visiting the internet at: https://www.nmfs.noaa.gov/pr/
permits/incidental.htm#applications.
    Documents cited in this notice may be viewed, by appointment, 
during regular business hours, at the aforementioned address.
    A copy of the 2006 Minerals Management Service's (MMS) Final 
Programmatic Environmental Assessment (PEA) and/or the NMFS/MMS Draft 
Programmatic

[[Page 24237]]

Environmental Impact Statement (DPEIS) are available on the internet 
at: https://www.mms.gov/alaska/.

FOR FURTHER INFORMATION CONTACT: Candace Nachman, Office of Protected 
Resources, NMFS, (301) 713-2289 or Brad Smith, NMFS Alaska Region, 
(907) 271-3023.

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 United States can apply for an authorization 
to incidentally take small numbers of marine mammals by harassment. 
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].
    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.

Summary of Request

    On November 21, 2007, NMFS received an application from BPXA for 
the taking, by Level B harassment only, of small numbers of several 
species of marine mammals incidental to conducting a 3D, OBC seismic 
survey in the Liberty Prospect area of the Alaskan Beaufort Sea in 
2008. The survey would occur over a period of 40-60 days in July and 
August, 2008, with an ``as needed'' extension into September/October 
(in compliance with a Conflict Avoidance Agreement (CAA)) after the 
subsistence whaling season given the uncertainties in ice conditions 
and other factors that can influence the survey. Seismic data 
acquisition is planned to start on July 1 depending on the presence of 
ice. Open water seismic operations can only start when the project area 
is ice free (i.e., less than 10 percent ice coverage), which in this 
area normally occurs around July 20 (+/- 14 days). Limited layout of 
receiver cables might be possible on the mudflats in the Sagavanirktok 
River delta areas before the ice has cleared.
    The Liberty field contains one of the largest undeveloped light-oil 
reservoirs near the North Slope infrastructure, and the development of 
this field could recover an estimated 105 million barrels of oil. The 
field is located in Federal waters of the Beaufort Sea about 8.9 km 
(5.5 mi) offshore in 6.1 m (20 ft) of water and approximately 8 to 13 
km (5 to 8 mi) east of the existing Endicott Satellite Drilling Island 
(SDI; see Figure 1 of BPXA's application). The project area encompasses 
351.8 km\2\ (135.8 mi\2\) in Foggy Island Bay, Beaufort Sea, of which 
one percent is on mudflats, 18.5 percent is in water depths of 0.3-1.5 
m (1-5 ft), 12.5 percent is in water depths of 1.5-3 m (5-10 ft), 43 
percent is in water depths of 3-6.1 m (10-20 ft), and 25 percent is in 
water depths of 6.1-9.1 m (20-30 ft; see Figure 2 of BPXA's 
application). The approximate boundaries of the total surface area are 
between 70[deg] 11' N. and 70[deg] 23' N. and between 147[deg] 10' W. 
and 148[deg] 02' W.
    The Liberty development project design and scope has been changed 
from an offshore stand-alone development (manmade production/drilling 
island and subsea pipeline) to the use of ultra-extended-reach drilling 
from the existing Endicott infrastructure involving an expansion of the 
SDI and use of existing processing facilities. As a result of this 
change in scope, BPXA believes that Liberty can be developed with a 
substantially reduced environmental footprint and impact than the 
originally proposed offshore stand-alone development. The currently 
available seismic data focused primarily on deeper targets and hence 
does not image the shallow overburden sections of the well bore 
optimally.
    The acquisition of additional marine 3D seismic survey data 
increases the probability of successful implementation of the proposed 
ultra-extended-reach drilling techniques by providing higher resolution 
data to assist in imaging for well planning and drilling operations.
    The dataset obtained with the proposed seismic survey will replace 
and augment the data from the Endicott 3D vibroseis survey (1983) and 
NW Badami (Liberty) 3D vibroseis survey (1995). Various seismic 
acquisition methods and sound source reduction technologies have been 
identified and assessed on their technical and environmental 
performance. The 3D, OBC seismic survey method being proposed is the 
most appropriate for the specific survey goal and objectives of the 
current Liberty seismic survey.

Description of Activity

    OBC seismic surveys are used to acquire seismic data in water that 
is too shallow for large marine-streamer vessels and/or too deep to 
have grounded ice in the winter. This type of seismic survey requires 
the use of multiple vessels for cable deployment/recovery, recording, 
shooting, and utility boats. The planned 3D, OBC seismic survey in the 
Liberty area will be conducted by CGGVeritas. A detailed overview of 
the activities of this survey is provided below, with focus on the 
mobilization procedure, seismic and other sound sources, the deployment 
and retrieval of the receiver cables, and the recording procedure.

Mobilization

    The vessel fleet involved in the seismic survey activities will 
consist of approximately 11 vessels as listed below. Details of these 
vessels (or equivalents) are provided in Appendix A of BPXA's 
application. Vessel usage is subject to availability; however, vessels 
of similar dimensions will be used if those listed below are 
unavailable.
     Two source vessels, the M/V Peregrine (27 x 7 m, 90 x 24 
ft) and the R/V Miss Diane (17 x 5.5 m, 55 x 18 ft).
     One recorder boat/barge, with M/V Alaganik barge (24 x 7 
m, 80 x 24 ft) and Hook Point boat (9.8 x 4.6 m, 32 x 15 ft).
     Four small bow picker vessels to deploy and retrieve the 
receiver cables; these are the F/V Canvasback (9.8 x 4.3 m, 32 x 14 
ft), F/V Cape Fear (9.8 x 3.7

[[Page 24238]]

m, 32 x 12 ft), F/V Rumpleminz (9.8 x 4.3 m, 32 x 14 ft), and F/V Sleep 
Robber (9.8 x 4.3 m, 32 x 14 ft). These vessels can operate in very 
shallow waters up to approximately 0.5 m (18 in) water depth.
     HSE vessel F/V Mariah B (10.4 x 4 m, 34 x 13 ft).
     Crew transport vessel M/V Qayak Spirit (12.8 x 4.3 m, 42 x 
14 ft) and (Northstar's) hovercraft M/V Arctic Hawk (12.8 x 6.1 m, 42 x 
20 ft).
     Crew housing and fuel vessel M/V Arctic Wolf (41 x 11.6 m, 
135 x 38 ft).
    To deploy and retrieve cables in water depths less than those 
accessible by the bow pickers, equipment such as swamp buggies and/or 
Jon boats will be used. For additional mobilization details, refer to 
section 1.2 of BPXA's application.

Seismic Survey Area Details

    The well path is the area of primary interest that needs to be 
fully covered by the seismic data. The size of this zone has been 
reduced to an absolute minimum of 92.1 km\2\ (35.6 mi\2\). To obtain 
full data coverage in this area of interest a larger zone needs to be 
surveyed to account for accurate migration of acoustic reflections. The 
total seismic survey extent is 351.8 km\2\ (135.8 mi\2\) and covers 
some mudflat areas as well.
    Receiver cable lines consist of a hydrophone and a Field Digitizing 
Unit (FDU) placed on the cables at 33.5 m (110 ft) intervals and placed 
on the seafloor according to a predefined configuration to record the 
reflected source signals from the airguns. The cables that will be 
deployed on mudflats and in very shallow water will consist of marsh 
phones and are placed in a similar configuration as those deployed at 
the seabottom. The receiver cables will be oriented in a NE-SW 
direction. A total of approximately 66 NE-SW oriented receiver lines 
will be deployed with increasing line spacing from west to east of 268 
m to 610 m (880 ft to 2,000 ft). Total receiver line length will be 
approximately 788 km (490 mi) of which approximately 16 km (10 mi) will 
be laid on mudflats. The source vessels will travel perpendicular over 
these receiver cables along lines which will have a NW to SE 
orientation and a varying total length of minimum 3.2 and maximum 5.6 
km (2 to 3.5 mi). The total source line length is approximately 3,220 
km (2,000 mi) in water depths varying from 1 to 9.1 m (3 to 30 ft). The 
Liberty seismic survey design is planned such that the most critical 
data along the well path can be acquired as highest priority, before 
time becomes limited.

Seismic Source

    To limit the duration of the total survey, two source vessels (the 
Peregrine and the Miss Dianne) will operate, alternating airgun shots. 
The sources used for seismic data acquisition will be sleeve airgun 
arrays with a total discharge volume of 880 in\3\ divided over two 
arrays. Each source vessel will have two 440 in\3\ arrays comprised of 
four guns in clusters of 2 x 70 in\3\ and 2 x 150 in\3\. The 880 in\3\ 
array has an estimated source level of approximately 250 dB re 1 
microPa.
    The arrays will be towed at a distance of approximately 8-10 m (26-
33 ft) from the source vessel at depths varying from 1-4 m (3-13 ft), 
depending on the water depth. The vessel will travel along 
predetermined lines at approximately 1-5 knots (1.9-9.3 km/hr), mainly 
depending on the water depth. Each source vessel will fire shots every 
8 s, resulting in 4 s shot intervals with two operating source vessels. 
The seismic data acquisition will occur over a 24 hr/day schedule. The 
dominant frequency components for the source are 5-135 Hz. See Appendix 
B of BPXA's application for more details of the 8-airgun array.

Cable Deployment and Retrieval

    The Peregrine, Miss Dianne, and four bow pickers will be used for 
the deployment and retrieval of the receiver cables. Each of the cable 
vessels will be powered with twin jet diesels and are rigged with 
hydraulically driven deployment and retrieval systems (``Squirters''). 
The Peregrine and Miss Dianne function both as source and cable vessels 
and will be capable of carrying 120 hydrophone stations. The receiver 
cables that will be used are extremely small while still allowing a 
pull of 800 lbs. The smaller bow picker cable vessels will also carry 
120 hydrophone stations and are capable of beach landings. All cable 
vessels will maintain 24-hr operations.
    Part of the receiver cables will be deployed on mudflats to pick up 
reflected source signals and allow for full interpretation of the data 
in the area of interest, i.e., well path (pink line in Figure 2 of 
BPXA's application). The deployment of these receiver cables will be 
conducted by other equipment that can operate in shallow waters and 
marshy conditions (such as swamp buggies or Jon boats).
    The positions of each receiver need to be established. Due to the 
variable bathymetry in the survey area, receiver positioning may 
require more than one technique. A combination of Ocean Bottom Receiver 
Location (OBRL), GPS, and acoustic pingers will be used. For OBRL, the 
source vessel fires a precisely positioned single gun multiple times 
along either side of the receiver cables. Multiple gun locations are 
then calculated at a given receiver to triangulate an accurate position 
for the receiver. In addition, Dyne acoustical pingers will be located 
at predetermined intervals at the receiver lines. The pinger locations 
can be determined using a transponder and allow for interpolation of 
the receiver locations between the acoustical pingers and as 
calibration/verification of the OBRL method. The sonar Dyne pingers 
operate at 19-36 kHz and have a source level of 188-193 dB re 1 microPa 
at 1 m. Because OBRL methods are not accurate in shallow water (< 4.6 
m, 15 ft), the receiver locations at these depths will be recorded as 
``as laid'' positions, which is the GPS location where the receivers 
are deployed.

Recording

    A Sercel 428 FDU will be located at each hydrophone. The system is 
lightweight and robust and rated to 14 m (45 ft) water depth, which 
allows it to operate well in the water depths for this survey. For 
approximately each 30 recorder-hydrophone units, one or two battery 
pack(s) will be deployed at the sea bottom. The battery pack will be 
equipped with a buoy (or acoustic release) and a pinger to ensure that 
the battery packs can be located and retrieved when needed.
    The data received at each FDU will be transmitted through the 
cables to a recorder for further processing. This recorder will be 
installed on a pin-together boat barge combination and positioned close 
to the area where data are being acquired. While recording, the pin-
together boat barge is stationary and is expected to utilize a four 
point anchoring system.

Crew Housing and Transfer

    Both source vessels, the Peregrine and the Miss Dianne, will be 
capable of housing crew, including marine mammal observers (MMOs). The 
Arctic Wolf, Alaganik, and Hook Point will also function as crew 
housing. Crew transfers will occur from the Qayak and the Spirit. For 
more information on crew housing and transfer, refer to Section 1.2 of 
BPXA's application.

Marine Mammals Affected by the Activity

    The Beaufort Sea supports a diverse assemblage of marine mammals, 
including bowhead (Balaena mysticetus), gray (Eschrichtius robustus), 
beluga (Delphinapterus

[[Page 24239]]

leucas), killer (Orcinus orca), minke (Balaenoptera acutorostrata), fin 
(B. physalus), and humpback (Megaptera novaeangliae) whales, harbor 
porpoises (Phocoena phocoena), ringed (Pusa hispida), spotted (Phoca 
largha), and bearded (Erignathus barbatus) seals, polar bears (Ursus 
maritimus), and walruses (Odobenus rosmarus divergens). These latter 
two species are under the jurisdiction of the U.S. Fish and Wildlife 
Service (USFWS) and are not discussed further in this document. A 
separate Letter of Authorization request will be submitted by BPXA for 
this survey to USFWS specific to walruses and polar bears.
    A total of three cetacean species and four pinniped species are 
known to occur or may occur in the Beaufort Sea in or near the Liberty 
area (see Table 1 in BPXA's application for information on habitat and 
abundance). Of these species, only the bowhead whale is listed as 
endangered under the Endangered Species Act (ESA). The narwhal, killer 
whale, harbor porpoise, minke whale, fin whale, and humpback whale 
could occur in the Beaufort Sea, but each of these species is rare or 
extralimital and unlikely to be encountered in the Liberty area.
    The marine mammal species expected to be encountered most 
frequently throughout the seismic survey in the Liberty area is the 
ringed seal. The bearded and spotted seal can also be observed but to a 
far lesser extent than the ringed seal. Presence of beluga, bowhead, 
and gray whales in the shallow water environment within the barrier 
islands is possible but expected to be very limited. Descriptions of 
the biology, distribution, and population status of the marine mammal 
species under NMFS' jurisdiction can be found in BPXA's application, 
the 2007 NMFS/MMS DPEIS on Arctic Seismic Surveys, and the NMFS Stock 
Assessment Reports (SARS). The Alaska SAR is available at: https://
www.nmfs.noaa.gov/pr/pdfs/sars/ak2007.pdf. Please refer to those 
documents for information on these species.

Potential Effects of Airgun Sounds on Marine Mammals

    The effects of sounds from airguns might include one or more of the 
following: tolerance, masking of natural sounds, behavioral 
disturbance, and temporary or permanent hearing impairment or non-
auditory effects (Richardson et al., 1995). 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., 1995):
    (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;
    (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 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.

Tolerance

    Numerous studies have shown that pulsed sounds from airguns are 
often readily detectable in the water at distances of many kilometers. 
For a summary of the characteristics of airgun pulses, see Appendix C 
of BPXA's application. 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 and small 
odontocetes seem to be more tolerant of exposure to airgun pulses than 
baleen whales.

Masking

    Masking effects of pulsed sounds (even from large arrays of 
airguns) on marine mammal calls and other natural sounds are expected 
to be limited, although there are very few 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). 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 (most probable to be 
present in the area) are not vocal during this period. Masking effects, 
in general, are discussed further in Appendix C of BPXA's application.

Disturbance Reactions

    Disturbance includes a variety of effects, including subtle changes 
in behavior, more conspicuous changes in activities, and displacement. 
Reactions to sound, if any, depend on species,

[[Page 24240]]

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. Given the many uncertainties 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. That 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 a seismic program 
are based on behavioral observations during studies of several species. 
However, information is lacking for many species. Detailed studies have 
been done on humpback, gray, and bowhead whales and ringed seals. Less 
detailed data are available for other species of baleen, sperm, and 
small toothed whales and sea otters.
    Baleen Whales - 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, as reviewed in Appendix C of BPXA's application, 
baleen whales exposed to strong noise pulses from airguns often react 
by deviating from their normal migration route and/or interrupting 
their feeding and moving away. In the case of the migrating gray and 
bowhead whales, the 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.
    Studies of gray, bowhead, and humpback whales have determined that 
received levels of pulses in the 160-170 dB re 1 microPa 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 4.5-14.5 km 
(2.8-9 mi) from the source. For the much smaller airgun array of this 
seismic survey, distances to received levels in the 160-170 dB re 1 
microPa rms range are 1.2-3.5 km (0.7-2.2 mi; Table 3 in BPXA's 
application and Table 1 below). Baleen whales within these shorter 
distances may show avoidance or other strong disturbance reactions to 
the airgun array; however in the Liberty seismic survey area, a limited 
number of baleen whales are expected to occur. Subtle behavioral 
changes sometimes become evident at somewhat lower received levels, and 
recent studies reviewed in Appendix C of BPXA's application 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 microPa rms. Bowhead whales migrating west across the 
Alaskan Beaufort Sea in autumn, in particular, are unusually 
responsive, with avoidance occurring out to distances of 20-30 km 
(12.4-18.6 mi) 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 microPa rms 
(Richardson et al., 1986; Ljungblad et al., 1988; Miller et al., 1999). 
The Liberty seismic project will be conducted in the summer and might 
occur partly in autumn, when the bowheads are commonly involved in 
migration. However, because the survey will be located inshore of the 
barrier islands (where few cetaceans are expected) in shallow water 
(maximum 9.1 m, 30 ft, deep; where high seismic sound propagation loss 
is expected) and with seismic airguns of medium discharge volumes (880 
in3, compared to the 3,000+ in\3\ arrays used offshore), the distance 
of received levels that might elicit avoidance behavior will likely not 
(or barely) reach the main migration corridor and then only through the 
inter-island water passages. Considering that these islands will 
function as a sound barrier beyond which sound will not propagate much, 
the propagation of the sounds generated is expected to be very limited 
offshore of the islands, where most of the baleen whales are expected 
to occur, which will prevent sound propagation into offshore waters 
where cetaceans are expected.
    Malme et al. (1986, 1988) studied the responses of feeding eastern 
gray whales to pulses from a single 100 in\3\ airgun off St. Lawrence 
Island in the northern Bering Sea. They estimated, based on small 
sample sizes, that 50 percent of feeding gray whales ceased feeding at 
an average received pressure level of 173 dB re 1 microPa on an 
(approximate) rms basis, and that 10 percent 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). However, given the infrequent occurrence of 
gray whales in the Beaufort Sea east of Point Barrow, recent MMO 
information from the Beaufort Sea indicating that, at least for bowhead 
whales, sound pressure levels (SPLs) of 160 dB or less did not result 
in abandonment of feeding areas, and the incorporation of mitigation 
and monitoring measures, including the use of MMOs and avoidance of 
concentrated areas of feeding whales, the number of animals exposed to 
sound levels that could cause disturbance of feeding or other behaviors 
should be greatly reduced.
    Data on short-term 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 and bowhead whales 
grew substantially during this time, suggesting that there may be no 
long-term effect from seismic activities. Therefore, the brief 
exposures to sound pulses from the proposed airgun source are highly 
unlikely to result in long-term effects to baleen whales.
    Toothed Whales - Few systematic information is available about 
reactions of toothed whales to noise pulses. Few studies similar to the 
more extensive baleen whale/seismic pulse work summarized above and (in 
more detail) in Appendix C of BPXAs application

[[Page 24241]]

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 MMOs sometimes see dolphins and 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 airgun arrays are firing. 
There have been indications that small toothed whales sometimes move 
away or maintain a somewhat greater distance from the vessel when a 
large airgun array 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 10-20 km (6.2-12.4 mi) 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 avoid the seismic operations at distances of 10-20 km 
(6.2-12.4 mi; Miller et al., 2005).
    Captive bottlenose dolphins and 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 microPa) before exhibiting aversive behaviors, such 
as reluctance to station at the test site where subsequent exposure to 
impulses would be implemented (Finneran et al., 2002). It is uncertain 
what relevance these observed behaviors in captive, trained marine 
mammals exposed to single sound pulses may have to free-ranging animals 
exposed to multiple pulses. With the presently-planned source, such 
levels would be limited to distances less than 200 m (656 ft) from the 
8-airgun array in shallow water and encounters with beluga whales are 
not likely to occur within these distances. 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 (see Appendix C of BPXA's application).
    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 (see 
Appendix C of BPXA's application). 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 (e.g., some of the individuals ceased foraging 
during seismic activity and only resumed after the sound source 
stopped, and others increased swim speed and/or dive duration; Thompson 
et al., 1998). The effects noted in the study were short-term in nature 
(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 be confined to relatively small 
distances and durations, with no long-term effects on pinniped 
individuals or populations.

Hearing Impairment and Other Physical Effects

    Temporary or permanent hearing impairment is a possibility when 
marine mammals are exposed to very strong sounds, but there has been no 
specific documentation of this for marine mammals exposed to sequences 
of airgun pulses. Current NMFS policy regarding exposure of marine 
mammals to high-level sounds is that cetaceans and pinnipeds should not 
be exposed to impulsive sounds greater than 180 and 190 dB re 1 microPa 
(rms), respectively (NMFS, 2000). Those criteria have been used in 
defining the safety (shutdown) radii planned for the proposed seismic 
survey. 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. As discussed in 
Appendix C and summarized here:
     The 180 dB criterion for cetaceans is precautionary (i.e., 
lower than necessary to avoid TTS, let alone permanent auditory injury, 
at least for belugas and delphinids) as it was established prior to 
empirical research on marine mammals that now indicate that permanent 
auditory injury would not occur until significantly higher SPLs were 
encountered.
     The minimum sound level necessary to cause permanent 
hearing impairment is higher, by a variable and generally unknown 
amount, than the level that induces 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.
    Several aspects of the planned monitoring and mitigation measures 
for this project are designed to detect marine mammals occurring near 
the airguns to avoid exposing them to sound pulses that might cause 
hearing impairment. In addition, many cetaceans are likely to show some 
avoidance of the area with high received levels of airgun sound (see 
above). 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 pulsed 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. 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 large arrays of airguns, and beaked 
whales do not occur in the present study area. It is unlikely that such 
effects would occur during the present project given the brief duration 
of exposure and the planned monitoring and mitigation measures (see 
below). The following sections discuss the possibilities of TTS, 
permanent threshold shift (PTS), and non-auditory physical effects in 
more detail.
    (TTS) - 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

[[Page 24242]]

TTS have been obtained for marine mammals.
    For toothed whales exposed to single short pulses, the TTS 
threshold appears to be, to a first approximation, a function of the 
energy content of the pulse (Finneran et al., 2002, 2005). Given the 
available data, the received level of a single seismic pulse might need 
to be approximately 210 dB re 1 microPa rms (approximately 221 226 dB 
pk-pk) in order to produce brief, mild TTS. Exposure to several seismic 
pulses at received levels near 200-205 dB (rms) might result in slight 
TTS in a small odontocete, assuming the TTS threshold is (to a first 
approximation) a function of the total received pulse energy. Seismic 
pulses with received levels of 200-205 dB or more are usually 
restricted to a radius of no more than 200 m (656 ft) around a seismic 
vessel operating a large array of airguns. For the smaller airgun array 
used in the proposed survey, this radius will be no more than 100 m 
(328 ft).
    There are no data on which to determine the kinds or intensities of 
sound that could cause TTS in baleen whales (NMFS/MMS, 2007). However, 
no cases of TTS are expected given the medium size of the source, the 
strong likelihood that baleen whales (especially migrating bowheads) 
would avoid the approaching airguns (or vessel) before being exposed to 
levels high enough for there to be any possibility of TTS, and the 
proposed mitigation measures.
    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 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 al., 2000). In the harbor seal, which is 
closely related to the ringed seal, TTS onset apparently occurs at 
somewhat lower received energy levels than for odontocetes (see 
Appendix C of BPXA's application).
    A marine mammal within a radius of approximately 60 m (197 ft) 
around the proposed airgun array might be exposed to a few seismic 
pulses with levels greater than 205 dB and possibly more pulses if the 
mammal moved with the seismic vessel. (As noted above, most cetacean 
species tend to avoid operating airguns, although not all individuals 
do so.) However, several of the considerations that are relevant in 
assessing the impact of typical seismic surveys with airgun arrays are 
applicable here:
    (1) ``Ramping up'' (soft start) is standard operational protocol 
during startup of large airgun arrays in many jurisdictions. Ramping up 
involves starting the airguns in sequence, usually commencing with a 
single airgun and gradually adding additional airguns. This practice 
will be employed during the Liberty seismic project when either airgun 
array is operated.
    (2) It is unlikely that cetaceans would be exposed to airgun pulses 
at a high enough level for a long enough period to cause more than mild 
TTS given the relatively small airgun array and the movement of both 
the vessel and the marine mammal. In this project, most of the planned 
seismic survey will be in very shallow water nearshore of the barrier 
islands. The propagation of the sounds generated is expected to be very 
limited offshore of the islands, where most of the baleen whales are 
expected to occur.
    (3) With a large airgun array, TTS would be most likely in 
odontocetes that bow-ride or in odontocetes or pinnipeds that linger 
near the airguns. In the present project, BPXA anticipates the 190 and 
180 dB distances to be 390 m and 880 m (0.24 mi and 0.55 mi), 
respectively, for the 8-gun array (Table 3 in BPXA's application and 
Table 1 below). Only seals could be expected to be potentially close to 
the airguns, and no species that occur within the project area are 
expected to bow-ride.(4) There is a possibility that a small number of 
seals (which often show little or no avoidance of approaching seismic 
vessels) could occur close to the airguns and that they might incur 
slight TTS if no mitigation action (shutdown) were taken.
    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 Pa (rms). The 180- and 190-dB 
distances for the airguns operated by BPXA may be found to vary with 
array depth, however, conservative estimates have been used (390 m and 
880 m, 0.24 mi and 0.55 mi, respectively; see Table 3 in the 
application and Table 1 below) until results from field measurements 
are available (see Section 13.2 of BPXA's application and the 
Monitoring section below). Furthermore, established 190- and 180-dB re 
1 microPa (rms) criteria are not considered to be the levels above 
which TTS might occur. Rather, they are the received levels above 
which, in the view of a panel of bioacoustics specialists convened by 
NMFS before TTS measurements for marine mammals started to become 
available, one could not be certain that there would be no injurious 
effects, auditory or otherwise, to marine mammals. As summarized above, 
data that are now available imply that TTS is unlikely to occur unless 
bow-riding odontocetes are exposed to airgun pulses much stronger than 
180 dB re 1 microPa rms (Southall et al., 2007). Since no bow-riding 
species occur in the study area, it is unlikely such exposures will 
occur.
    (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 empirical evidence that exposure to pulses of airgun 
sound can cause PTS in any marine mammal, even with large arrays of 
airguns (see Southall et al., 2007). However, given the possibility 
that mammals close to an airgun array might incur TTS, there has been 
further speculation about the possibility that some individuals 
occurring very close to airguns 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 if the animal were exposed to the strong sound pulses with very 
rapid rise time see Appendix C of BPXA's application.
    It is highly unlikely that marine mammals could receive sounds 
strong enough (and over a sufficient duration) to cause permanent 
hearing impairment during a project employing the airgun sources 
planned here. In the proposed project, marine mammals are unlikely to 
be exposed to received levels of seismic pulses strong enough to cause 
more than 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 airgun may not be sufficient to 
induce PTS, especially because a mammal would not be exposed to more 
than one strong pulse unless it swam immediately alongside the airgun 
for a period longer than the inter-pulse interval. Baleen whales, and 
belugas as well, generally avoid the immediate area around operating 
seismic vessels. The planned monitoring and mitigation measures, 
including visual monitoring, power- downs, and shutdowns of the airguns 
when mammals are seen within the safety radii, will minimize the 
already-minimal probability of exposure

[[Page 24243]]

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. 
However, studies examining such effects are very limited. 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. That is especially so in the case 
of the proposed project where the airgun configuration focuses most 
energy downward and the source vessels are moving at 4-5 knots (7.4-9.3 
km/hr). The faster a seismic vessel moves, the less time an individual 
marine mammal would be exposed to the noise source. Only individuals 
swimming close to, parallel to, and at the same speed as the vessel 
would incur a number of high intensity sounds. This medium airgun array 
would only have 190 and 180 dB distances of 390 and 880 m (0.24 and 
0.55 mi), respectively.
    In general, little is known about the potential for seismic survey 
sounds to cause auditory impairment or other physical effects in marine 
mammals. Available data suggest that such effects, if they occur at 
all, would be limited to short distances or more likely to projects 
involving large airgun arrays. 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 seismic vessels, including most 
baleen whales, some odontocetes (including belugas), and some 
pinnipeds, are especially unlikely to incur auditory impairment or 
other physical effects. Also, the planned monitoring and mitigation 
measures include shutdowns of the airguns, which will reduce any such 
effects that might otherwise occur.

Stranding and Mortality

    Marine mammals close to underwater detonations of high explosives 
can be killed or severely injured, and their auditory organs are 
especially susceptible to injury (Ketten et al., 1993; Ketten, 1995). 
Airgun pulses are less energetic and have slower rise times, and there 
is no evidence that they can cause serious injury, death, or stranding 
even in the case of large airgun arrays. However, the association of 
mass strandings of beaked whales with naval exercises, and, in one 
case, a 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 (more details 
are provided in Appendix C of BPXA's application). However, no beaked 
whales are found within this project area. Due to the shallow water 
environment, medium airgun arrays, and planned monitoring and 
mitigation measures of the proposed survey, the mortality of marine 
mammal species is not expected.

Potential Effects of Pinger Signals on Marine Mammals

    A pinger system (Dyne Acoustical Pingers) and acoustic release/
transponders (Benthos) will be used during seismic operations to 
position the receivers and locate and retrieve the batteries. Sounds 
from these pingers are very short pulses. The Dyne pinger has a source 
level ranging from approximately 188-193 dB re 1 microPa at 1 m in a 
frequency range of 19-36 kHz, and the benthos has sources levels of 
approximately 192 dB re 1 microPa at 1 m in a frequency range of 7-15 
kHz. Pulses are emitted on command from the operator aboard the source 
vessel.

Masking

    The pinger produces sounds within the frequency range that could be 
detected by some seals and baleen whales, as they can hear sounds at 
frequencies up to 36 kHz. However, marine mammal communications will 
not be masked appreciably by the pinger signals. This is a consequence 
of the relatively low power output, low duty cycle, and brief period 
when an individual mammal is likely to be within the area of potential 
effects.

Behavioral Responses

    Marine mammal behavioral reactions to other pulsed sound sources 
are discussed above, and responses to the pinger are likely to be 
similar to those for other pulsed sources if received at the same 
levels. However, the pulsed signals from the pinger are much weaker 
than those from the airgun. Therefore, behavioral responses are not 
expected unless marine mammals are very close to the source. The 
maximum reaction that might be expected would be a startle reaction or 
other short-term response. NMFS (2001) has concluded that momentary 
behavioral reactions ``do not rise to the level of taking.''

Hearing Impairment and Other Physical Effects

    Source levels of the pinger are much lower than those of the 
airguns (see above). It is unlikely that the pinger produces pulse 
levels strong enough to cause temporary hearing impairment or physical 
injuries even in an animal that is (briefly) in a position near the 
source.

Estimated Take of Marine Mammals by Incidental Harassment

    The anticipated harassments from the activities described above may 
involve temporary changes in behavior. There is no evidence that the 
planned activities could result in serious injury or mortality, for 
example due to collisions with vessels or strandings. Disturbance 
reactions, such as avoidance, are very likely to occur amongst marine 
mammals in the vicinity of the source vessel. The mitigation and 
monitoring measures proposed to be implemented (see below) during this 
survey are based on Level B harassment criteria and will minimize any 
potential risk to injury.
    The methodology used by BPXA to estimate incidental take by 
harassment by seismic and the numbers of marine mammals that might be 
affected in the proposed seismic acquisition activity area in the 
Beaufort Sea is presented here. The density estimates for the species 
covered under this proposed IHA are based on the estimates by Moore et 
al. (2000b) for beluga whales, Miller et al. (2002) for bowhead whales, 
and Moulton et al. (2003) and Frost et al. (2003) for ringed seals. The 
estimates for the number of marine mammals that might be affected 
during the proposed OBC seismic survey in the Liberty area are based on 
expected marine mammal density and anticipated area ensonified by 
levels of greater than 170 and 160 dB re 1 microPa.
    In its application, BPXA provides estimates of the number of 
potential ``exposures'' to sound levels greater than 160 dB re 1 
microPa (rms) and greater than 170 dB. BPXA states that while the 160-
dB criterion applies to all species of cetaceans and pinnipeds, BPXA 
believes that a 170-dB criterion should be considered appropriate for 
delphinids and pinnipeds, which tend to be less responsive, whereas the 
160-dB criterion is considered appropriate for other cetaceans (LGL, 
2007). However, NMFS has noted in the past that it is unaware of any 
empirical evidence to indicate that some delphinid species do not 
respond at the lower level (i.e., 160 dB). As a result, NMFS will 
estimate Level B harassment takes based on the 160-dB criterion.

[[Page 24244]]

    Expected density of marine mammals in the survey area of operation 
and area of influence are based on best available data. Density data 
derived from studies conducted in or near the proposed survey area are 
used for calculations, where available. When estimates were derived 
from data collected in regions, habitats, or seasons that differ from 
the proposed seismic survey, adjustments to reported population or 
density estimates were made to account for these differences insofar as 
possible (see Section 6.1 of BPXA's application).
    The anticipated area to be ensonified by levels of greater than 160 
dB re 1 microPa is a combination of the area covered by the 
approximately 3,219 km (2,000 mi) survey lines and the estimated safety 
radii. The close spacing of neighboring vessel tracklines within the 
planned seismic survey area results in a limited area exposed to sounds 
of 160 dB or greater, while much of that area is exposed repeatedly.

Marine Mammal Density Estimates

    The duration of the seismic data acquisition in the Liberty area is 
estimated to be approximately 40 days, based on a continuous 24-hr 
operation. This can extend to a maximum of 60 days taking into account 
unpredictable delays. It is expected that the data acquisition can be 
completed during the months of July and August. However, if further 
data acquisition is required after August, the seismic activities may 
resume in September and/or October after completion of the whaling 
season and in accordance with a CAA. Therefore, the nearshore marine 
mammal densities for the summer period have been applied to 95 percent 
of the total trackline kilometers. The fall densities have been applied 
to the remaining 5 percent.
    Most marine mammals in the Alaskan Beaufort Sea are migratory, 
occupying different habitats and/or locations during the year. The 
densities can therefore vary greatly within seasons and for different 
locations. For the purpose of this IHA request, different densities 
have been derived for the summer (late July through August) and the 
fall (September through early October). In addition to seasonal 
variation in densities, spatial differentiation is also an important 
factor for marine mammal densities, both in latitudinal and 
longitudinal gradient. Taking into account the size and location of the 
proposed seismic survey area and the associated area of influence, only 
the nearshore zone (defined as the area between the shoreline and the 
50 m, 164 ft, line of bathymetry) in the western part of the Beaufort 
Sea (defined as the area west of 141[deg] W.) is relevant for the 
density calculations. If the best available density data cover other 
zones than the nearshore zone or areas outside the western part of the 
Beaufort Sea, densities were derived based on expert judgment.
    Ideally, when calculating densities from marine mammal distribution 
survey data, two correction factors need to be taken into account: (1) 
detectability bias [f(0)] and (2) availability bias [g(0)]. The 
detectability bias is associated with the diminishing sightability when 
the distance between the observation point and marine mammal increases. 
The availability bias refers to the fact that marine mammals may be 
present in the area but are not available to the observer to be sighted 
(i.e., beneath the water surface). The uncorrected number of marine 
mammals observed is therefore always lower than the actual numbers 
present. For most density data not enough information is available of 
the survey specifics or of marine mammal behavior and movement patterns 
to calculate these two correction factors. The density estimates 
provided here are based on uncorrected data, except for the beluga and 
bowhead whale densities. Correction factors were applied to the data 
from Moore et al. (2000b) and Miller et al. (2002) derived from Harwood 
et al. (1996).
    Because the available density data are not always representative 
for the area of interest, and correction factors were not always known, 
there is some uncertainty in the data and assumptions used in the 
density calculations. To provide allowance for these uncertainties, 
maximum estimates of the numbers potentially affected have been 
provided in addition to average densities. The marine mammal densities 
presented are believed to be close to, and in most cases, higher than 
the densities that are expected to be encountered during the survey.
Cetaceans
    The densities of beluga and bowhead whales present in the Beaufort 
Sea are expected to vary by season and location. During the early and 
mid-summer, most belugas and bowheads are found in the Canadian 
Beaufort Sea or adjacent areas. During fall, both species migrate 
through the Alaskan Beaufort Sea, sometimes interrupting their 
migration to feed.
    Beluga Whales - Beluga density estimates for the Alaskan Beaufort 
Sea are derived from aerial survey data obtained by Moore et al. 
(2000b). The overall beluga whale density (i.e., total sightings from 
all depth regimes) was calculated with these data, and this density was 
assumed to represent the average offshore density for the summer season 
in the eastern Beaufort Sea. During the summer season, beluga whales 
are far more abundant in the offshore area, and so the densities for 
the nearshore area were estimated to be 10 percent of the offshore 
densities.
    During the summer season, most beluga whales are found in offshore 
waters of the eastern Beaufort Sea and few are expected to be 
encountered in the western part of the Beaufort Sea, especially in the 
inshore waters of the barrier islands (Davis and Evans, 1982; Harwood 
et al., 1996; Richard et al., 2001). The average density of beluga 
whales for the proposed survey was therefore estimated to be 10 percent 
of the density of the eastern Beaufort Sea (see Table 2 in BPXA's 
application).
    In fall, during the westward migration, the offshore density is 
expected to be roughly equal across the eastern and western regions of 
the Alaskan Beaufort Sea. Also the depth distribution of migrating 
beluga whales is expected to be more equally distributed. For the 
autumn period, the density of beluga whales in the western Beaufort Sea 
was estimated to be 10 percent of the highest fall density calculated 
from Moore et al. (2000b; see Table 2 of the application). The maximum 
density estimates of beluga whales were calculated as 4x the average 
estimates.
    Bowhead Whales - Bowhead sightings in the Alaskan Beaufort become 
more common as the whales start their westward migration in late 
August. Peak sighting rates occur near Kaktovik (east of the Liberty 
area) in September. The density data used in this IHA request are 
derived from Miller et al. (2002) who calculated the seasonal 
distribution and numbers of bowheads observed in the eastern Alaskan 
Beaufort Sea and adjacent Canadian waters from aerial surveys conducted 
by various researchers during the late summer and autumn of 1979-2000. 
Correction factors (Thomas et al., 2002) were applied to these density 
estimates.Bowheads in the eastern Alaskan Beaufort Sea and Canada occur 
in offshore habitats in summer. From late August-early September 
shallower habitats are selected during years with moderate and light 
ice-cover and deeper waters in years with heavy ice-cover. In the 
western Beaufort Sea during the period July-August very few bowhead 
whales are expected to be present in the nearshore zone because spring 
migration normally ends by mid-June (Braham et al., 1984; Moore and 
Reeves,

[[Page 24245]]

1993), and the fall westward migration usually does not begin until 
late August or early September (Braham et al., 1980; Moore and Reeves, 
1993). The densities calculated from 14 surveys in August in water 
depths of >50 m (164 ft) in the eastern Alaskan and Canadian Beaufort 
Sea were used as the basis for the summer density calculations in this 
IHA request. Because bowheads mainly occur in offshore waters during 
the summer season with decreasing abundance from east to west, density 
estimates for the proposed survey were estimated to be 10 percent of 
the reported densities by Miller et al. (2002; see Table 2 in BPXA's 
application).
    Many of the bowhead whales will be migrating westward during the 
fall period, mostly in the nearshore and continental habitat zones. So, 
the fall densities of bowhead whales provided for the eastern Alaskan 
and Canadian Beaufort Sea are considered to be similar as those for the 
western Beaufort Sea. Average and maximum densities for the autumn 
period were based on calculated densities of 79 surveys conducted in 
the period September October for the combined nearshore and continental 
zones (Miller et al., 2002). Because the whale density during the fall 
migration is generally higher in the nearshore area (<50m, 164 ft), the 
estimates provided were multiplied by two to obtain nearshore fall 
densities (see Table 2 in the application). For the proposed survey, 10 
percent of these estimates were used.
    Both the summer and autumn densities are assumed to be conservative 
given that the proposed survey takes place entirely inside the barrier 
islands.
Pinnipeds
    Pinnipeds in the polar regions are mostly associated with sea ice 
and most census methods count pinnipeds when they are hauled out on the 
ice. To account for the proportion of animals present but not hauled 
out (availability bias) or seals present on the ice but missed 
(detection bias), a correction factor should be applied to the ``raw'' 
counts. This correction factor is very dependent on the behavior of 
each species. To estimate the proportion of ringed seals visible 
resting on the ice surface, radio tags were placed on seals during the 
spring months during 1999-2003 (Kelly et al., 2006). Applying the 
probability that seals were visible to the data from past aerial 
s