Takes of Marine Mammals Incidental to Specified Activities; Taking Marine Mammals Incidental to a Marine Geophysical Survey in the Arctic Ocean, September-October 2011, 41463-41486 [2011-17765]

Agencies

• DEPARTMENT OF COMMERCE
• National Oceanic and Atmospheric Administration

[Federal Register Volume 76, Number 135 (Thursday, July 14, 2011)]
[Notices]
[Pages 41463-41486]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 2011-17765]


-----------------------------------------------------------------------

DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

RIN 0648-XA568


Takes of Marine Mammals Incidental to Specified Activities; 
Taking Marine Mammals Incidental to a Marine Geophysical Survey in the 
Arctic Ocean, September-October 2011

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

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

-----------------------------------------------------------------------

SUMMARY: NMFS has received an application from the University of Alaska 
Geophysics Institute (UAGI) for an Incidental Harassment Authorization 
(IHA) to take marine mammals, by harassment, incidental to conducting a 
marine geophysical seismic survey in the Arctic Ocean during September-
October 2011. Pursuant to the Marine Mammal Protection Act (MMPA), NMFS 
is requesting comments on its proposal to issue an IHA to UAGI to take, 
by Level B harassment only, several species of marine mammals during 
the specified activity.

DATES: Comments and information must be received no later than August 
15, 2011.

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. The mailbox address for 
providing e-mail comments is ITP.Nachman@noaa.gov. NMFS is not 
responsible for e-mail comments sent to addresses other than the one 
provided here. Comments sent via e-mail, 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 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.
    The National Science Foundation (NSF), which is providing funding 
to UAGI to conduct the survey, has prepared a draft ``Environmental 
Assessment of a Marine Geophysical Survey by the R/V Marcus G. Langseth 
in the Arctic Ocean, September-October 2011,'' prepared by LGL Ltd., 
Environmental Research Associates (LGL), on behalf of UAGI and NSF, 
which is also available at the same internet address. 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

[[Page 41464]]

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 March 4, 2011, from UAGI for the 
taking, by harassment, of marine mammals incidental to conducting a 
marine geophysical seismic survey in the Arctic Ocean. NMFS reviewed 
UAGI's application and identified a number of issues requiring further 
clarification. After addressing comments from NMFS, UAGI modified its 
application and submitted a revised application on May 10, 2011. The 
May 10, 2011, application is the one available for public comment (see 
ADDRESSES) and considered by NMFS for this proposed IHA.
    UAGI proposes to conduct a 2D seismic survey in the Arctic Ocean, 
Chukchi Sea, in both international waters and within the U.S. Exclusive 
Economic Zone (EEZ) in water depths ranging from 30-3,800 m (98-12,467 
ft). UAGI plans to conduct the proposed seismic survey from September 5 
through October 9, 2011, which includes vessel transit time from Dutch 
Harbor.
    UAGI plans to use one source vessel, the R/V Marcus G. Langseth 
(Langseth) and a seismic airgun array to collect seismic reflection 
data across the transition from the Chukchi Shelf to the Chukchi 
Borderland to define the apparent change in structure between two large 
continental blocks. In addition to the proposed operations of the 
seismic airgun array, UAGI intends to operate a multibeam echosounder 
(MBES) and a sub-bottom profiler (SBP) continuously throughout the 
survey. A 75-kilohertz (kHz) acoustic Doppler current profiler (ADCP) 
may also be used.
    Acoustic stimuli (i.e., increased underwater sound) generated 
during the operation of the seismic airgun array may have the potential 
to cause a short-term behavioral disturbance for marine mammals in the 
proposed survey area. This is the principal means of marine mammal 
taking associated with these activities, and UAGI has requested an 
authorization to take 11 species of marine mammals by Level B 
harassment. These species are: Bowhead whale; gray whale; humpback 
whale; minke whale; fin whale; beluga whale; killer whale; bearded 
seal; spotted seal; ringed seal; and ribbon seal. Take is not expected 
to result from the use of the MBES or SBP, for reasons discussed later 
in this notice; nor is take expected to result from collision with the 
vessel because it is a single vessel moving at a relatively slow speed 
during seismic acquisition within the survey, for a relatively short 
period of time (approximately 35 days). It is likely that any marine 
mammal would be able to avoid the vessel.

Description of the Specified Activity

    UAGI's survey is proposed to occur in the area 72.5-77[deg] N. and 
160-175[deg] W. in international waters and within the U.S. EEZ (see 
Figure 1 in UAGI's application). The project is scheduled to occur from 
September 5-October 9, 2011. Some minor deviation from these dates is 
possible, depending on logistics and weather. Therefore, NMFS is 
proposing to make the IHA valid from September 5-October 23, 2011. The 
vessel will not be able to remain in the area once ice begins to form, 
as the Langseth is not an icebreaker. The Langseth would depart from 
Dutch Harbor on September 5, 2011, and sail northeast to arrive at 
approximately 72.5[deg] N., 162[deg] W., where the seismic survey will 
begin, more than 200 km (124 mi) from Barrow. The entire cruise would 
last for approximately 35 days, and it is estimated that the total 
seismic survey time will be approximately 25 days, depending on ice 
conditions. Seismic survey work is scheduled to terminate near the 
starting point at approximately 72.4[deg] N., 164[deg] W. on October 6; 
the vessel would then sail south to Dutch Harbor for arrival on October 
9. There could be extra days of seismic shooting, if the collected data 
are of substandard quality.
    The proposed survey will include collection of seismic reflection 
data across the transition from the Chukchi Shelf to the Chukchi 
Borderland to define the apparent change in structure between two large 
continental blocks. This study will test existing tectonic models and 
develop new constraints on the development of the Amerasian Basin and 
will substantially advance our understanding of the Mesozoic history of 
this basin. In addition, these data will enable the formulation of new 
tectonic models for the history of this region, which will improve our 
understanding of the surrounding continents.
    The survey will involve one source vessel, the Langseth, which is 
operated by Lamont-Doherty Earth Observatory (L-DEO), a part of 
Columbia University, under a cooperative agreement with NSF. The 
Langseth will deploy an array of 10 airguns (1,830 in\3\) as an energy 
source at a tow depth of 6 m (19.7 ft). The receiving system will 
consist of a 2-km (1.2-mi) long hydrophone streamer. As the airgun 
array is towed along the survey lines, the hydrophone streamer will 
receive the returning acoustic signals and transfer the data to the on-
board processing system. In addition, at least 72 sonobuoys will be 
deployed in order to record seismic refraction data. The Langseth will 
be avoiding the ice edge, and an ice expert will be available to 
provide daily guidance and to predict ice movements.
    The proposed program will consist of a total of approximately 5,502 
km (3,419 mi) of survey lines, not including transits to and from the 
survey area when airguns will not be in use (see Figure 1 in UAGI's 
application). Water depths within the study area range from 
approximately 30-3,800 m (98-12,467). Just over half of the survey 
effort (55%) will occur in water 100-1,000 m (328-3,281 ft) deep, 32% 
will take place in water >1,000 m (3,281 ft) deep, and 13% will occur 
in water depths <100 m (328 ft). There will be additional seismic 
operations in the survey area associated with turns, airgun testing, 
and repeat coverage of any areas where initial data quality is sub-
standard. In addition to the operations of the airgun array, a 
Kongsberg EM 122 MBES and a Knudsen 320B SBP will also be operated from 
the Langseth continuously throughout the cruise. A 75-kHz ADCP may also 
be used.
    All planned geophysical data acquisition activities will be 
conducted by L-DEO with on-board assistance by the scientists who have 
proposed the study. The Principal Investigator is Dr. Bernard Coakley 
of UAGI. The vessel will be self-contained, and the crew will live 
aboard the vessel for the entire cruise.

Vessel Specifications

    The Langseth will tow the 10-airgun array along predetermined 
lines. The vessel will also tow the hydrophone streamer and deploy the 
sonobuoys. When the Langseth is towing the airgun array, as well as the 
hydrophone streamer, the turning rate of the vessel while the gear is 
deployed is limited. Thus, the maneuverability of the vessel is limited 
during operations with the streamer.

[[Page 41465]]

    The vessel has a length of 71.5 m (235 ft); a beam of 17 m (56 ft); 
a maximum draft of 5.9 m (19 ft); and a gross tonnage of 3,834. The 
Langseth was designed as a seismic research vessel with a propulsion 
system designed to be as quiet as possible to avoid interference with 
the seismic signals emanating from the airgun array. The ship is 
powered by two 3,550 horsepower (hp) Bergen BRG-6 diesel engines which 
drive two propellers directly. Each propeller has four blades, and the 
shaft typically rotates at 750 revolutions per minute. The vessel also 
has an 800 hp bowthruster, which is not used during seismic 
acquisition. The Langseth's operation speed during seismic acquisition 
is typically 7.4 to 9.3 km per hour (hr) (km/hr) (4 to 5 knots [kts]). 
When not towing seismic survey gear, the Langseth typically cruises at 
18.5 km/hr (10 kts). The Langseth has a range of 25,000 km (15,534 mi) 
(the distance the vessel can travel without refueling).
    The Langseth is not an ice-strengthened vessel and must especially 
consider safety-of-operations while towing a significant amount of 
equipment behind the vessel; it therefore cannot operate in ice 
conditions that would pose serious hazards to the vessel and crew. 
After consideration of the operational challenges, however, NSF and L-
DEO concluded that the Langseth would be able to support the activity 
if it remained in ice-free waters. An ice expert would be available to 
help provide guidance during any operations.
    The vessel also has an observation tower from which protected 
species visual observers (PSVO) will watch for marine mammals before 
and during the proposed airgun operations. When stationed on the 
observation platform, the PSVO's eye level will be approximately 21.5 m 
(71 ft) above sea level, providing the PSVO an unobstructed view around 
the entire vessel.

Acoustic Source Specifications

(1) Airgun Array

    During the survey, the airgun array to be used will consist of 10 
airguns, with a total volume of approximately 1,830 cubic inches 
(in\3\). The airgun array will consist of a mixture of Bolt 1500LL and 
Bolt 1900LLX airguns, set in a typical configuration of one of the 
Langseth's four linear arrays or ``strings'' (see Figure 2 in UAGI's 
application); the first and last airguns in the strings are spaced 16 m 
(52 ft) apart. The airgun array will be towed approximately 100 m (328 
ft) behind the Langseth. The shot interval will be 15 seconds (s). The 
firing pressure of the array is 1,950 pounds per square inch. During 
firing, a brief (approximately 0.1 s) pulse of sound is emitted. The 
airguns will be silent during the intervening periods.
    The tow depth of the array will be 6 m (19.7 ft). Because the 
actual source is a distributed sound source (10 airguns) rather than a 
single point source, the highest sound levels measurable at any 
location in the water will be less than the nominal source level. In 
addition, the effective source level for sound propagating in near-
horizontal directions will be substantially lower than the nominal 
source level applicable to downward propagation because of the 
directional nature of the sound from the airgun array.

(2) MBES

    The Langseth will operate a Kongsberg EM 122 MBES concurrently 
during airgun operations to map characteristics of the ocean floor. The 
hull-mounted MBES emits brief pulses of sound (also called a ping) 
(10.5 to 13 kHz, usually 12 kHz) in a fan-shaped beam that extends 
downward and to the sides of the ship. The transmitting beamwidth is 
1[deg] fore-aft and 150[deg] athwartship, and the maximum source level 
is 242 dB re 1 [mu]Pa (rms).
    For deep-water operations, each ping consists of eight (in water 
greater than 1,000 m [3,281 ft]) or four (in water less than 1,000 m 
[3,281 ft]) successive, fan-shaped transmissions, each ensonifying a 
sector that extends 1[deg] fore-aft. Continuous-wave pulses increase 
from 2 to 15 milliseconds (ms) long in water depths up to 2,600 m 
(8,530.2 ft), and frequency-modulated chirp pulses up to 100 ms long 
are used in water greater than 2,600 m (8,530.2 ft). The successive 
transmissions span an overall cross-track angular extent of about 
150[deg], with 2 ms gaps between the pulses for successive sectors.

(3) SBP

    The Langseth will also operate a Knudsen 320B SBP continuously 
throughout the cruise simultaneously with the MBES to map and provide 
information about the sedimentary features and bottom topography. The 
beam is transmitted as a 27[deg] cone, which is directed downward by a 
3.5 kHz transducer in the hull of the Langseth. The maximum output is 
1,000 watts (204 dB re 1 [mu]Pa), but in practice, the output varies 
with water depth. The pulse interval is 1 s, but a common mode of 
operation is to broadcast five pings at 1-s intervals followed by a 5-s 
pause.

(4) ADCP

    The Ocean Surveyor 75 is an ADCP operating at a frequency of 75 
kHz, producing a ping every 1.4 s. The system is a four-beam phased 
array with a beam angle of 30[deg]. Each beam has a width of 4[deg], 
and there is no overlap. Maximum output is 1 kilowatt, with a maximum 
depth range of 700 m (2,296.6 ft).

Metrics Used in This Document

    This section includes a brief explanation of the sound measurements 
frequently used in the discussions of acoustic effects in this 
document. Sound pressure is the sound force per unit area, and is 
usually measured in micropascals ([mu]Pa), where 1 pascal (Pa) is the 
pressure resulting from a force of one newton exerted over an area of 
one square meter. Sound pressure level (SPL) is expressed as the ratio 
of a measured sound pressure and a reference level. The commonly used 
reference pressure level in underwater acoustics is 1 [mu]Pa, and the 
units for SPLs are dB re: 1 [mu]Pa. SPL (in decibels [dB]) = 20 log 
(pressure/reference pressure).
    SPL is an instantaneous measurement and can be expressed as the 
peak, the peak-peak (p-p), or the root mean square (rms). Root mean 
square, which is the square root of the arithmetic average of the 
squared instantaneous pressure values, is typically used in discussions 
of the effects of sounds on vertebrates, and all references to SPL in 
this document refer to rms unless otherwise noted. SPL does not take 
the duration of a sound into account.

Predicted Sound Levels

    Received sound levels have been predicted by Marine Acoustics, Inc. 
(MAI), in relation to distance and direction from the airguns, for the 
10-airgun array. The MAI model was site specific; sound velocity 
profiles, bathymetry, and bottom composition were used to model 
propagation at seven sites 120-2,727 m (328-8,947 ft) deep in the 
survey area that represented different physiographic provinces 
described by Jakobsson et al. (2003). The source model used was the 
CASS/GRAB model, and propagation was modeled using the Range-Dependent 
Acoustic Model (RAM) (Zingarelli and King, 2005). The detailed modeling 
report can be found in Appendix A1 of the draft EA (see ADDRESSES).
    Received sound levels for a single 40-in\3\ airgun were modeled by 
L-DEO. The tow depth has minimal effect on the maximum near-field 
output and the shape of the frequency spectrum for the

[[Page 41466]]

single airgun; thus, the predicted exclusion zone radii are essentially 
the same at different tow depths. As the L-DEO model does not allow for 
bottom interactions, and thus is most directly applicable to deep water 
and to relatively short ranges, correction factors were used to 
estimate exclusion zone radii in shallow and intermediate-depth water 
as was done for previous L-DEO surveys from the Langseth. A detailed 
description of the L-DEO modeling effort is provided in Appendix A2 of 
the draft EA.
    Table 1 in this document and Table 1 in UAGI's application show the 
distances at which three rms sound levels are expected to be received 
from the 10-airgun array and a single airgun. For the 10-airgun array, 
distances were modeled at seven sites; the distances in Table 1 are the 
averages from the sites in each depth range.

  Table 1--Maximum Predicted Distances to Which Sound Levels >=190, 180, and 160 dB re 1 [mu]Pa (rms) Could Be
Received in Various Water-Depth Categories During the Proposed Survey in the Arctic Ocean. The Distances for the
   10-Airgun Array Are the Averages of Modeled 95% Percentile Distances at Modeling Sites in Each Depth Range
----------------------------------------------------------------------------------------------------------------
                                                                                  Predicted RMS radii (m)
        Source and volume           Tow depth          Water depth        --------------------------------------
                                       (m)                                    190 dB       180 dB       160 dB
----------------------------------------------------------------------------------------------------------------
Single Bolt......................  ...........  Deep (>1000 m)...........           12           40          385
                                             6  Intermediate (100-1000 m)           18           60          578
                                   ...........  Shallow (<100)...........          150          296        1,050
1 string.........................  ...........  Deep (>1000 m)...........          130          425       14,070
10 airguns.......................            6  Intermediate (200-1000 m)          130         1400       13,980
1830 in\3\.......................  ...........  Shallow (<200)...........          190         1870       14,730
----------------------------------------------------------------------------------------------------------------
* The tow depth has minimal effect on the maximum near-field output and the shape of the frequency spectrum for
  the single 40 in\3\ airgun; thus, the predicted safety radii are essentially the same at any tow depth.

    NMFS expects that acoustic stimuli resulting from the proposed 
operation of the single airgun or the 10 airgun array has the potential 
to harass marine mammals, incidental to the conduct of the proposed 
seismic survey. NMFS expects these disturbances to be temporary and 
result, at worst, in a temporary modification in behavior and/or low-
level physiological effects (Level B harassment) of small numbers of 
certain species of marine mammals. NMFS does not expect that the 
movement of the Langseth, during the conduct of the seismic survey, has 
the potential to harass marine mammals because of the relatively slow 
operation speed of the vessel (4-5 kts [7.4 to 9.3 km/hr]) during 
seismic data acquisition.

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; and walruses. The bowhead, humpback, and fin 
whales are listed as endangered, and the polar bear is listed as 
threatened under the U.S. Endangered Species Act of 1973 (ESA; 16 
U.S.C. 1531 et seq.). All of these species are also considered depleted 
under the MMPA. On December 10, 2010, NMFS published a notification of 
proposed threatened status for subspecies of the ringed seal (75 FR 
77476) and a notification 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 species is 
considered depleted under the MMPA.
    The bowhead and beluga whales and the ringed and bearded seals are 
the marine mammal species most likely to be encountered during this 
survey, with the ringed seal being the most likely marine mammal 
species to occur throughout the proposed survey area. Although humpback 
and minke whales are uncommon in the Arctic Ocean, sightings of both 
species have occurred in the Chukchi Sea in recent years (Brueggeman, 
2009; Haley et al., 2010; Clarke et al., 2011).
    There are scattered records of narwhal in Alaskan waters, where the 
species is considered extralimital (Reeves et al., 2002). Harbor 
porpoises occur mainly in shelf areas where they can dive to depths of 
at least 220 m (722 ft) and stay submerged for more than 5 min (Harwood 
and Wilson, 2001). This species prefers shallower waters, making it 
unlikely that harbor porpoises would be encountered during the proposed 
seismic survey. Because of the rarity of these two species in the 
proposed survey area, they are not considered further in this document. 
The polar bear and walrus are managed by the U.S. Fish and Wildlife 
Service (USFWS) and are not considered further in this proposed IHA 
notice.
    Refer to Sections III and IV of UAGI's application for detailed 
information regarding the abundance and distribution, seasonal 
distribution, population status, and life history and behavior of these 
species and their occurrence in the proposed project area. When 
reviewing the application, NMFS determined that the species 
descriptions provided by UAGI correctly characterized the abundance and 
distribution, seasonal distribution, population status, and life 
history and behavior of each species. Additional information can also 
be found in the NMFS Stock Assessment Reports (SAR). The 2010 Alaska 
Marine Mammal SAR is available on the Internet at: https://www.nmfs.noaa.gov/pr/pdfs/sars/ak2010.pdf.
    The application also presents how UAGI calculated the estimated 
densities for the marine mammals in the proposed survey area. NMFS has 
reviewed these data and determined them to be the best available 
scientific information for the purposes of the proposed IHA. UAGI's 
methodology for estimating take is described further in the ``Estimated 
Take by Incidental Harassment'' section found later in this document.

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

[[Page 41467]]

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, 11 marine mammal species 
(seven cetacean and four pinniped species) are likely to occur in the 
proposed survey area. Of the seven cetacean species likely to occur in 
UAGI's propose survey area, five are classified as low frequency 
cetaceans (i.e., bowhead, gray, humpback, minke, and fin whales) and 
two are classified as mid-frequency cetaceans (i.e., beluga and killer 
whales) (Southall et al., 2007).

Potential Effects of the Specified Activity on Marine Mammals

    Acoustic stimuli generated by the operation of the airguns, which 
introduce sound into the marine environment, may have the potential to 
cause Level B harassment of marine mammals in the proposed survey area. 
The effects of sounds from airgun operations might include one or more 
of the following: tolerance, masking of natural sounds, behavioral 
disturbance, temporary or permanent hearing impairment, or non-auditory 
physical or physiological effects (Richardson et al., 1995; Gordon et 
al., 2004; Nowacek et al., 2007; Southall et al., 2007). Takes by 
serious injury or mortality are not anticipated to occur as a result of 
the proposed activities.

Tolerance

    Studies on marine mammals' tolerance to sound in the natural 
environment are relatively rare. Richardson et al. (1995) define 
tolerance as the occurrence of marine mammals in areas where they are 
exposed to human activities or man-made noise. In many cases, tolerance 
develops by the animal habituating to the stimulus (i.e., the gradual 
waning of responses to a repeated or ongoing stimulus) (Richardson, et 
al., 1995; Thorpe, 1963), but because of ecological or physiological 
requirements, many marine animals may need to remain in areas where 
they are exposed to chronic stimuli (Richardson, et al., 1995).
    Numerous studies have shown that pulsed sounds from airguns are 
often readily detectable in the water at distances of many kilometers. 
Malme et al., (1985) studied the responses of humpback whales on their 
summer feeding grounds in southeast Alaska to seismic pulses from an 
airgun with a total volume of 100 in \3\. They noted that the whales 
did not exhibit persistent avoidance when exposed to the airgun and 
concluded that there was no clear evidence of avoidance, despite the 
possibility of subtle effects, at received levels up to 172 dB re 1 
[mu]Pa.
    Weir (2008) observed marine mammal responses to seismic pulses from 
a 24 airgun array firing a total volume of either 5,085 in \3\ or 3,147 
in \3\ in Angolan waters between August 2004 and May 2005. Weir 
recorded a total of 207 sightings of humpback whales (n = 66), sperm 
whales (n = 124), and Atlantic spotted dolphins (n = 17) and reported 
that there were no significant differences in encounter rates 
(sightings/hr) for humpback and sperm whales according to the airgun 
array's operational status (i.e., active versus silent).

Masking

    The term masking refers to the inability of a subject to recognize 
the occurrence of an acoustic stimulus as a result of the interference 
of another acoustic stimulus (Clark et al., 2009). 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. Introduced 
underwater sound may, through masking, reduce the effective 
communication distance of a marine mammal species if the frequency of 
the source is close to that used as a signal by the marine mammal, and 
if the anthropogenic sound is present for a significant fraction of the 
time (Richardson et al., 1995). 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., 1995). 
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.
    Masking effects of pulsed sounds (even from large arrays of 
airguns) on marine mammal calls and other natural sounds are expected 
to be limited. Because of the intermittent nature and low duty cycle of 
seismic airgun pulses, animals can emit and receive sounds in the 
relatively quiet intervals between pulses. However, in some situations, 
reverberation occurs for much or the entire interval between pulses 
(e.g., Simard et al., 2005; Clark and Gagnon, 2006), which could mask 
calls. Some baleen and toothed whales are known to continue calling in 
the presence of seismic pulses, and their calls can usually be heard 
between the seismic pulses (e.g., Richardson et al., 1986; McDonald et 
al., 1995; Greene et al., 1999; Nieukirk et al., 2004; Smultea et al., 
2004; Holst et al., 2005a,b, 2006; and Dunn and Hernandez, 2009). 
However, Clark and Gagnon (2006) reported that fin whales in the 
northeast Pacific Ocean went silent for an extended period starting 
soon after the onset of a seismic survey in the area. Similarly, there 
has been one report that sperm whales ceased calling when exposed to 
pulses from a very distant seismic ship (Bowles et al., 1994). However, 
more recent studies found that they continued calling in the presence 
of seismic pulses (Madsen et al., 2002; Tyack et al., 2003; Smultea et 
al., 2004; Holst et al., 2006; and Jochens et al., 2008). Dolphins and 
porpoises commonly are heard calling while airguns are operating (e.g., 
Gordon et al., 2004; Smultea et al., 2004; Holst et al., 2005a,b; and 
Potter et al., 2007). The sounds important to small odontocetes are 
predominantly at much higher frequencies than are the

[[Page 41468]]

dominant components of airgun sounds, thus limiting the potential for 
masking.
    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.
    There is evidence of other marine mammal species continuing to call 
in the presence of industrial activity. For example, bowhead whale 
calls are frequently detected in the presence of seismic pulses, 
although the number of calls detected may sometimes be reduced 
(Richardson et al., 1986; Greene et al., 1999; Blackwell et al., 2009). 
Additionally, 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 more than 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 
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 20 km (12.4 mi) from a human sound source, such as 
that produced during oil and gas industry activities, might hear strong 
calls from other whales within approximately 20 km (12.4 mi), and a 
whale 5 km (3.1 mi) from the source might hear strong calls from whales 
within approximately 5 km (3.1 mi). 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).
    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., 1995). 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., 1995). 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.
    In general, NMFS expects the masking effects of seismic pulses to 
be minor, given the normally intermittent nature of seismic pulses. 
Refer to Appendix B (4) of the draft EA for a more detailed discussion 
of masking effects on marine mammals.

Behavioral Disturbance

    Disturbance includes a variety of effects, including subtle to 
conspicuous changes in behavior, movement, and displacement. Reactions 
to sound, if any, depend on species, state of maturity, experience, 
current activity, reproductive state, time of day, and many other 
factors (Richardson et al., 1995; Wartzok et al., 2004; Southall et 
al., 2007; Weilgart, 2007). 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 population. However, if a sound 
source displaces marine mammals from an important feeding or breeding 
area for a prolonged period, impacts on individuals and populations 
could be significant (e.g., Lusseau and Bejder, 2007; Weilgart, 2007). 
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 would be present within a particular distance of 
industrial activities and/or exposed to a particular level of 
industrial sound. In most cases, this approach likely overestimates the 
numbers of marine mammals that would be affected in some biologically-
important manner.
    The sound criteria used to estimate how many marine mammals might 
be disturbed to some biologically-

[[Page 41469]]

important degree by a seismic program are based primarily on behavioral 
observations of a few species. Scientists have conducted detailed 
studies on humpback, gray, bowhead, and sperm whales. Less detailed 
data are available for some other species of baleen whales, small 
toothed whales, and sea otters, but for many species there are no data 
on responses to marine seismic surveys.
    Baleen Whales--Baleen whales generally tend to avoid operating 
airguns, but avoidance radii are quite variable (reviewed in Richardson 
et al., 1995). 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 B (5) of NSF's EA, 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 cases of migrating gray and bowhead whales, the observed changes in 
behavior appeared to be of little or no biological consequence to the 
animals (Richardson et al., 1995). 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 shown that 
seismic pulses with received levels of 160 to 170 dB re 1 [mu]Pa (rms) 
seem to cause obvious avoidance behavior in a substantial fraction of 
the animals exposed (Malme et al., 1986, 1988; Richardson et al., 
1995). In many areas, seismic pulses from large arrays of airguns 
diminish to those levels at distances ranging from 4-15 km (2.5-9.3 mi) 
from the source. A substantial proportion of the baleen whales within 
those distances may show avoidance or other strong behavioral reactions 
to the airgun array. Subtle behavioral changes sometimes become evident 
at somewhat lower received levels, and studies summarized in Appendix B 
(5) of NSF's EA have shown that some species of baleen whales, notably 
bowhead and humpback whales, at times, show strong avoidance at 
received levels lower than 160 to 170 dB re 1 [mu]Pa (rms).
    McCauley et al. (1998, 2000a) studied the responses of humpback 
whales off western Australia to a full-scale seismic survey with a 16 
airgun array (2,678 in \3\) and to a single airgun (20 in\3\) with a 
source level of 227 dB re 1 [mu]Pa (p-p). In the 1998 study, they 
documented that avoidance reactions began at 5-8 km (3.1-5 mi) from the 
array, and that those reactions kept most pods approximately 3-4 km 
(1.9-2.5 mi) from the operating seismic boat. In the 2000 study, 
McCauley et al. (2000a) noted localized displacement during migration 
of 4-5 km (2.5-3.1 mi) by traveling pods and 7-12 km (4.3-7.5 mi) by 
more sensitive resting pods of cow-calf pairs. Avoidance distances with 
respect to the single airgun were smaller but consistent with the 
results from the full array in terms of the received sound levels. The 
mean received level for initial avoidance of an approaching airgun was 
140 dB re 1 [mu]Pa for humpback pods containing females, and, at the 
mean closest point of approach distance, the received level was 143 dB 
re 1 [mu]Pa. The initial avoidance response generally occurred at 
distances of 5-8 km (3.1-5 mi) from the airgun array and 2 km (1.2 mi) 
from the single airgun. However, some individual humpback whales, 
especially males, approached within distances of 100-400 m (328-1,312 
ft), where the maximum received level was 179 dB re 1 [mu]Pa.
    Data collected by observers during several seismic surveys in the 
Northwest Atlantic showed that sighting rates of humpback whales were 
significantly greater during periods of no seismic compared with 
periods when a full array was operating (Moulton and Holst, 2010). In 
addition, humpback whales were more likely to swim away and less likely 
to swim towards a vessel during seismic vs. non-seismic periods 
(Moulton and Holst, 2010).
    Humpback whales on their summer feeding grounds in southeast Alaska 
did not exhibit persistent avoidance when exposed to seismic pulses 
from a 100 in \3\ airgun (Malme et al., 1985). Some humpbacks seemed 
``startled'' at received levels of 150 to 169 dB re 1 [mu]Pa. Malme et 
al. (1985) concluded that there was no clear evidence of avoidance, 
despite the possibility of subtle effects, at received levels up to 172 
dB re 1 [mu]Pa (rms).
    Studies have suggested that south Atlantic humpback whales 
wintering off Brazil may be displaced or even strand upon exposure to 
seismic surveys (Engel et al., 2004). The evidence for this was 
circumstantial and subject to alternative explanations (IAGC, 2004). 
Also, the evidence was not consistent with subsequent results from the 
same area of Brazil (Parente et al., 2006) or with direct studies of 
humpbacks exposed to seismic surveys in other areas and seasons. After 
allowance for data from subsequent years, there was no observable 
direct correlation between strandings and seismic surveys (IWC, 
2007:236).
    Studies of the bowhead whale show that their responsiveness to 
seismic surveys can be quite variable depending on their activity 
(migrating vs. feeding). Bowhead whales migrating west across the 
Alaskan Beaufort Sea in autumn, in particular, are unusually 
responsive, with substantial avoidance occurring out to distances of 
20-30 km (12.4-18.6 mi) from a medium-sized airgun source at received 
sound levels of around 120 to 130 dB re 1 [mu]Pa (Miller et al., 1999; 
Richardson et al., 1999; see Appendix B (5) of NSF's EA). However, more 
recent research on bowhead whales (Miller et al., 2005; Harris et al., 
2007) corroborates earlier evidence that, during the summer feeding 
season, bowheads are not as sensitive to seismic sources. Nonetheless, 
subtle but statistically significant changes in surfacing-respiration-
dive cycles were evident upon statistical analysis (Richardson et al., 
1986). In the summer, bowheads typically begin to show avoidance 
reactions at received levels of about 152 to 178 dB re 1 [mu]Pa 
(Richardson et al., 1986, 1995; Ljungblad et al., 1988; Miller et al., 
2005).
    Reactions of migrating and feeding (but not wintering) gray whales 
to seismic surveys have been studied. Malme et al. (1986, 1988) studied 
the responses of feeding eastern Pacific 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% of feeding 
gray whales stopped feeding at an average received pressure level of 
173 dB re 1 [mu]Pa on an (approximate) rms basis, and that 10% of 
feeding whales interrupted feeding at received levels of 163 dB re 1 
[mu]Pa. Those findings were generally consistent with the results of 
experiments conducted on larger numbers of gray whales that were 
migrating along the California coast (Malme et al., 1984; Malme and 
Miles, 1985), and western Pacific gray whales feeding off Sakhalin 
Island, Russia (Wursig et al., 1999; Gailey et al., 2007; Johnson et 
al., 2007; Yazvenko et al., 2007a, b), along with data on gray whales 
off British Columbia (Bain and Williams, 2006).
    Various species of Balaenoptera (blue, sei, fin, and minke whales) 
have occasionally been seen in areas ensonified by airgun pulses 
(Stone, 2003; MacLean and Haley, 2004; Stone and Tasker, 2006), and 
calls from blue and fin whales have been localized in areas with airgun 
operations (e.g., McDonald et al., 1995; Dunn and Hernandez, 2009, 
Castellote et al., 2010). Sightings by observers on seismic vessels off 
the United Kingdom from

[[Page 41470]]

1997 to 2000 suggest that, during times of good sightability, sighting 
rates for mysticetes (mainly fin and sei whales) were similar when 
large arrays of airguns were shooting vs. silent (Stone, 2003; Stone 
and Tasker, 2006). However, these whales tended to exhibit localized 
avoidance, remaining significantly further (on average) from the airgun 
array during seismic operations compared with non-seismic periods 
(Stone and Tasker, 2006). In a study off of Nova Scotia, Moulton and 
Miller (2005) found little difference in sighting rates (after 
accounting for water depth) and initial sighting distances of 
balaenopterid whales when airguns were operating vs. silent. However, 
there were indications that these whales were more likely to be moving 
away when seen during airgun operations. Similarly, ship-based 
monitoring studies of blue, fin, sei and minke whales offshore of 
Newfoundland (Orphan Basin and Laurentian Sub-basin) found no more than 
small differences in sighting rates and swim directions during seismic 
versus non-seismic periods (Moulton et al., 2005, 2006a,b). Castellote 
et al. (2010) reported that singing fin whales in the Mediterranean 
moved away from an operating airgun array.
    Ship-based monitoring studies of baleen whales (including blue, 
fin, sei, minke, and humpback whales) in the Northwest Atlantic found 
that, overall, this group had lower sighting rates during seismic vs. 
non-seismic periods (Moulton and Holst, 2010). Baleen whales as a group 
were also seen significantly farther from the vessel during seismic 
compared with non-seismic periods, and they were more often seen to be 
swimming away from the operating seismic vessel (Moulton and Holst, 
2010). Blue and minke whales were initially sighted significantly 
farther from the vessel during seismic operations compared to non-
seismic periods; the same trend was observed for fin whales (Moulton 
and Holst, 2010). Minke whales were most often observed to be swimming 
away from the vessel when seismic operations were underway (Moulton and 
Holst, 2010).
    Data on short-term reactions by cetaceans to impulsive noises are 
not necessarily indicative of long-term or biologically significant 
effects. It is not known whether impulsive sounds affect reproductive 
rate or distribution and habitat use in subsequent days or years. 
However, gray whales have continued to migrate annually along the west 
coast of North America with substantial increases in the population 
over recent years, despite intermittent seismic exploration (and much 
ship traffic) in that area for decades (Appendix A in Malme et al., 
1984; Richardson et al., 1995; Allen and Angliss, 2010). The western 
Pacific gray whale population did not seem affected by a seismic survey 
in its feeding ground during a previous year (Johnson et al., 2007). 
Similarly, bowhead whales have continued to travel to the eastern 
Beaufort Sea each summer, and their numbers have increased notably, 
despite seismic exploration in their summer and autumn range for many 
years (Richardson et al., 1987; Allen and Angliss, 2010).
    Toothed Whales--Little 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 B of NSF's EA have been reported for toothed 
whales. However, there are recent systematic studies on sperm whales 
(e.g., Gordon et al., 2006; Madsen et al., 2006; Winsor and Mate, 2006; 
Jochens et al., 2008; Miller et al., 2009). 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; Bain and Williams, 2006; Holst et al., 
2006; Stone and Tasker, 2006; Potter et al., 2007; Hauser et al., 2008; 
Holst and Smultea, 2008; Weir, 2008; Barkaszi et al., 2009; Richardson 
et al., 2009, Moulton and Holst, 2010).
    Seismic operators and marine mammal observers on seismic vessels 
regularly see dolphins and other small toothed whales near operating 
airgun arrays, but, in general, there is a tendency for most delphinids 
to show some avoidance of operating seismic vessels (e.g., Goold, 
1996a,b,c; Calambokidis and Osmek, 1998; Stone, 2003; Moulton and 
Miller, 2005; Holst et al., 2006; Stone and Tasker, 2006; Weir, 2008; 
Richardson et al., 2009; Barkaszi et al., 2009, Moulton and Holst, 
2010). Some dolphins seem to be attracted to the seismic vessel and 
floats, and some ride the bow wave of the seismic vessel even when 
large arrays of airguns are firing (e.g., Moulton and Miller, 2005). 
Nonetheless, small toothed whales more often tend to head away, or to 
maintain a somewhat greater distance from the vessel, when a large 
array of airguns is operating than when it is silent (e.g., Stone and 
Tasker, 2006; Weir, 2008, Barry et al., 2010, Moulton and Holst, 2010). 
In most cases, the avoidance radii for delphinids appear to be small, 
on the order of 1 km (0.6 mi) or less, and some individuals show no 
apparent avoidance. The beluga whale is a species that (at least at 
times) shows long-distance avoidance of seismic vessels. Aerial surveys 
conducted in the southeastern Beaufort Sea during summer found that 
sighting rates of beluga whales were significantly lower at distances 
10-20 km (6.2-12.4 mi) compared with 20-30 km (12.4-18.6 mi) from an 
operating airgun array, and observers on seismic boats in that area 
rarely saw belugas (Miller et al., 2005; Harris et al., 2007).
    Captive bottlenose dolphins and beluga whales exhibited changes in 
behavior when exposed to strong pulsed sounds similar in duration to 
those typically used in seismic surveys (Finneran et al., 2000, 2002, 
2005). However, the animals tolerated high received levels of sound 
before exhibiting aversive behaviors.
    Results for porpoises depend on species. The limited available data 
suggest that harbor porpoises show stronger avoidance of seismic 
operations than do Dall's porpoises (Stone, 2003; MacLean and Koski, 
2005; Bain and Williams, 2006; Stone and Tasker, 2006). Dall's 
porpoises seem relatively tolerant of airgun operations (MacLean and 
Koski, 2005; Bain and Williams, 2006), although they too have been 
observed to avoid large arrays of operating airguns (Calambokidis and 
Osmek, 1998; Bain and Williams, 2006). This apparent difference in 
responsiveness of these two porpoise species is consistent with their 
relative responsiveness to boat traffic and some other acoustic sources 
(Richardson et al., 1995; Southall et al., 2007).
    Most studies of sperm whales exposed to airgun sounds indicate that 
the sperm whale shows considerable tolerance of airgun pulses (e.g., 
Stone, 2003; Moulton et al., 2005, 2006a; Stone and Tasker, 2006; Weir, 
2008). In most cases the whales do not show strong avoidance, and they 
continue to call (see Appendix B of NSF's EA for a review). However, 
controlled exposure experiments in the Gulf of Mexico indicate that 
foraging behavior was altered upon exposure to airgun sound (Jochens et 
al., 2008; Miller et al., 2009; Tyack, 2009).
    There are almost no specific data on the behavioral reactions of 
beaked whales to seismic surveys. However, some northern bottlenose 
whales remained in the general area and continued to produce high-
frequency clicks when exposed to sound pulses from distant seismic 
surveys (Gosselin and Lawson, 2004; Laurinolli and Cochrane, 2005; 
Simard et al., 2005). Most beaked whales tend to avoid approaching 
vessels of other types (e.g., Wursig et al., 1998). They may also dive

[[Page 41471]]

for an extended period when approached by a vessel (e.g., Kasuya, 
1986), although it is uncertain how much longer such dives may be as 
compared to dives by undisturbed beaked whales, which also are often 
quite long (Baird et al., 2006; Tyack et al., 2006). Based on a single 
observation, Aguilar-Soto et al. (2006) suggested that foraging 
efficiency of Cuvier's beaked whales may be reduced by close approach 
of vessels. In any event, it is likely that most beaked whales would 
also show strong avoidance of an approaching seismic vessel, although 
this has not been documented explicitly. In fact, Moulton and Holst 
(2010) reported 15 sightings of beaked whales during seismic studies in 
the Northwest Atlantic; seven of those sightings were made at times 
when at least one airgun was operating. There was little evidence to 
indicate that beaked whale behavior was affected by airgun operations; 
sighting rates and distances were similar during seismic and non-
seismic periods (Moulton and Holst, 2010). However, no beaked whale 
species are known to occur in the proposed project area.
    Odontocete reactions to large arrays of airguns are variable and, 
at least for delphinids and Dall's porpoises, seem to be confined to a 
smaller radius than has been observed for the more responsive of the 
mysticetes, belugas, and harbor porpoises (see Appendix B of NSF's EA 
for more information).
    Pinnipeds--Pinnipeds are not likely to show a strong avoidance 
reaction to the airgun array. Pinnipeds generally seem to be less 
responsive to exposure to industrial sound than most cetaceans. 
Responses by pinnipeds to underwater sound from some types of 
industrial activities such as seismic exploration appear to be 
temporary and localized (Harris et al., 2001; Reiser et al., 2009).
    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 B(5) of NSF's EA. In the Beaufort 
Sea, some ringed seals avoided an area of 100 m (328 ft) to (at most) a 
few hundred meters around seismic vessels, but many seals remained 
within 100-200 m (328-656 ft) of the trackline as the operating airgun 
array passed by (e.g., Harris et al., 2001; Moulton and Lawson, 2002; 
Miller et al., 2005). Ringed seal sightings averaged somewhat farther 
away from the seismic vessel when the airguns were operating than when 
they were not, but the difference was small (Moulton and Lawson, 2002). 
Similarly, in Puget Sound, sighting distances for harbor seals and 
California sea lions tended to be larger when airguns were operating 
(Calambokidis and Osmek, 1998). Previous telemetry work suggests that 
avoidance and other behavioral reactions may be stronger than evident 
to date from visual studies (Thompson et al., 1998).

Hearing Impairment and Other Physical Effects

    Temporary or permanent hearing impairment is a possibility when 
marine mammals are exposed to very strong sounds. Non-auditory physical 
effects might also occur in marine mammals exposed to strong underwater 
sound. Possible types of non-auditory physical effects or injuries that 
theoretically might occur in mammals close to a strong sound source 
include stress, neurological effects, bubble formation, and other types 
of organ or tissue damage. It is possible that some marine mammal 
species (i.e., beaked whales) may be especially susceptible to injury 
and/or stranding when exposed to strong pulsed sounds. However, as 
discussed later in this document, there is no definitive evidence that 
any of these effects occur even for marine mammals in close proximity 
to industrial sound sources, and beaked whales do not occur in the 
proposed activity area.
    Factors that influence the amount of threshold shift include the 
amplitude, duration, frequency content, temporal pattern, and energy 
distribution of noise exposure. The magnitude of hearing threshold 
shift normally decreases over time following cessation of the noise 
exposure. The amount of threshold shift just after exposure is called 
the initial threshold shift. If the threshold shift eventually returns 
to zero (i.e., the threshold returns to the pre-exposure value), it is 
called temporary threshold shift (TTS) (Southall et al., 2007). 
Researchers have studied TTS in certain captive odontocetes and 
pinnipeds exposed to strong sounds (reviewed in Southall et al., 2007). 
However, there has been no specific documentation of TTS let alone 
permanent hearing damage, i.e., permanent threshold shift (PTS), in 
free-ranging marine mammals exposed to sequences of airgun pulses 
during realistic field conditions. The following subsections discuss in 
somewhat more detail the possibilities of TTS, PTS, and non-auditory 
physical effects.
    Temporary Threshold Shift--TTS is the mildest form of hearing 
impairment that can occur during exposure to a strong sound (Kryter, 
1985). While experiencing TTS, the hearing threshold rises, and a sound 
must be stronger in order to be heard. At least in terrestrial mammals, 
TTS can last from minutes or hours to (in cases of strong TTS) days. 
For sound exposures at or somewhat above the TTS threshold, hearing 
sensitivity in both terrestrial and marine mammals recovers rapidly 
after exposure to the noise ends. Few data on sound levels and 
durations necessary to elicit mild TTS have been obtained for marine 
mammals, and none of the published data concern TTS elicited by 
exposure to multiple pulses of sound. Available data on TTS in marine 
mammals are summarized in Southall et al. (2007). Table 1 (found 
earlier in this document and Table 1 in UAGI's application) presents 
the distances from the Langseth's 10-airgun array at which the received 
energy level (per pulse, flat-weighted) would be expected to be greater 
than or equal to 180 and 190 dB re 1 [mu]Pa (rms). As shown in the 
table, these distances vary with depth.
    Researchers have derived TTS information for odontocetes from 
studies on the bottlenose dolphin and beluga. For the one harbor 
porpoise tested, the received level of airgun sound that elicited onset 
of TTS was lower (Lucke et al., 2009). If these results from a single 
animal are representative, it is inappropriate to assume that onset of 
TTS occurs at similar received levels in all odontocetes (cf. Southall 
et al., 2007). Some cetaceans apparently can incur TTS at considerably 
lower sound exposures than are necessary to elicit TTS in the beluga or 
bottlenose dolphin.
    For baleen whales, there are no data, direct or indirect, on levels 
or properties of sound that are required to induce TTS. The frequencies 
to which baleen whales are most sensitive are assumed to be lower than 
those to which odontocetes are most sensitive, and natural background 
noise levels at those low frequencies tend to be higher. As a result, 
auditory thresholds of baleen whales within their frequency band of 
best hearing are believed to be higher (less sensitive) than are those 
of odontocetes at their best frequencies (Clark and Ellison, 2004), 
meaning that baleen whales require sounds to be louder (i.e., higher dB 
levels) than odontocetes in the frequency ranges at which each group 
hears the best. From this, it is suspected that received levels causing 
TTS onset may also be higher in baleen whales (Southall et al., 2007). 
Since current NMFS practice assumes the same thresholds for the onset 
of hearing impairment in both odontocetes a