Takes of Marine Mammals Incidental to Specified Activities; Marine Geophysical Survey in the Northwest Pacific Ocean, July Through September 2010, 28568-28587 [2010-12296]

Agencies

• DEPARTMENT OF COMMERCE
• National Oceanic and Atmospheric Administration

[Federal Register Volume 75, Number 98 (Friday, May 21, 2010)]
[Notices]
[Pages 28568-28587]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 2010-12296]


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DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

RIN 0648-XU56


Takes of Marine Mammals Incidental to Specified Activities; 
Marine Geophysical Survey in the Northwest Pacific Ocean, July Through 
September 2010

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

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

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SUMMARY: NMFS has received an application from Lamont-Doherty Earth 
Observatory (L-DEO), a part of Columbia University, for an Incidental 
Harassment Authorization (IHA) to take marine mammals, by harassment, 
incidental to conducting a marine geophysical survey at the Shatsky 
Rise in the northwest Pacific Ocean, July

[[Page 28569]]

through September, 2010. Pursuant to the Marine Mammal Protection Act 
(MMPA), NMFS is requesting comments on its proposal to issue an IHA to 
L-DEO to incidentally harass, by Level B harassment only, 34 species of 
marine mammals during the specified activity.

DATES: Comments and information must be received no later than June 21, 
2010.

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 PR1.0648-XU56@noaa.gov. NMFS is not 
responsible for e-mail comments send to addresses other than the one 
provided here. Comments sent via e-mail, including all attachments, 
must not exceed a 10-megabyte file size.
    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#applications 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 containing a list of the references used 
in this document may be obtained by writing to the above address, 
telephoning the contact listed here (see FOR FURTHER INFORMATION 
CONTACT) or visiting the internet at: https://www.nmfs.noaa.gov/pr/permits/incidental.htm#applications. The following documents associated 
with the application are also available at same internet address: the 
National Science Foundation's (NSF) draft Environmental Assessment (EA) 
and associated report (Report) prepared by LGL Limited Environmental 
Research Associates (LGL) for NSF, titled, ``Environmental Assessment 
of a Marine Geophysical Survey by the R/V Marcus G. Langseth on the 
Shatsky Rise in the Northwest Pacific Ocean, July-September, 2010.'' 
Documents cited in this notice may be viewed, by appointment, during 
regular business hours, at the aforementioned address.

FOR FURTHER INFORMATION CONTACT: Jeannine Cody, Office of Protected 
Resources, NMFS, (301) 713-2289, ext. 113 or Benjamin Laws, Office of 
Protected Resources, NMFS, (301) 713-2289, ext. 159.

SUPPLEMENTARY INFORMATION:

Background

    Section 101(a)(5)(D) of the MMPA (16 U.S.C. 1371 (a)(5)(D)) directs 
the Secretary of Commerce to authorize, upon request, the incidental, 
but not intentional, taking of small numbers of marine mammals of a 
species or population stock, by United States citizens who engage in a 
specified activity (other than commercial fishing) within a specified 
geographical region if certain findings are made and, if the taking is 
limited to harassment, a notice of a proposed authorization is provided 
to the public for review.
    Authorization for incidental taking of small numbers of marine 
mammals shall be granted if NMFS finds that the taking will have a 
negligible impact on the species or stock(s), and will not have an 
unmitigable adverse impact on the availability of the species or 
stock(s) for subsistence uses. The authorization must set forth the 
permissible methods of taking, other means of effecting the least 
practicable adverse impact on the species or stock and its habitat, and 
monitoring and reporting of such takings. 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. 
Section 101(a)(5)(D) of the MMPA 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 small numbers of marine mammals. Within 45 days of the 
close of the public 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 February 2, 2010 from L-DEO for the 
taking by harassment, of marine mammals, incidental to conducting a 
marine geophysical survey in the northwest Pacific Ocean. L-DEO, with 
research funding from the U.S. National Science Foundation (NSF), plans 
to conduct a marine seismic survey in the northwest Pacific Ocean, from 
July through September, 2010.
    L-DEO plans to use one source vessel, the R/V Marcus G. Langseth 
(Langseth), a seismic airgun array, and ocean bottom seismometers (OBS) 
to conduct a geophysical survey at the Shatsky Rise, a large igneous 
plateau in the northwest Pacific Ocean. The proposed survey will 
provide data necessary to decipher the crustal structure of the Shatsky 
Rise; may address major questions of Earth history, geodynamics, and 
tectonics; could impact the understanding of terrestrial magmatism and 
mantle convection; and may obtain data that could be used to improve 
estimates of regional earthquake occurrence and distribution. In 
addition to the proposed operations of the seismic airgun array, L-DEO 
intends to operate a multibeam echosounder (MBES) and a sub-bottom 
profiler (SBP) continuously throughout the survey.
    Acoustic stimuli (i.e., increased underwater sound) generated 
during the operation of the seismic airgun array, may have the 
potential to cause marine mammals in the survey area to be behaviorally 
disturbed in a manner that NMFS considers to be Level B harassment. 
This is the principal means of marine mammal taking associated with 
these activities and L-DEO has requested an authorization to take 
several marine mammals by Level B harassment.

Description of the Specified Activity

    L-DEO's proposed seismic survey on the Shatsky Rise is scheduled to 
commence on July 24, 2010 and continue for approximately 17 days ending 
on September 7, 2010. L-DEO will operate the Langseth to deploy an 
airgun array, deploy and retrieve OBS, and tow a hydrophone streamer to 
complete the survey.
    The Langseth will depart from Apra Harbor, Guam on July 19, 2010 
for a six-day transit to the Shatsky Rise, located at 30-37[deg] N, 
154-161[deg] E in international waters offshore from Japan. Some minor 
deviation from these dates is possible, depending on logistics, weather 
conditions, and the need to repeat some lines if data quality is 
substandard. Therefore, NMFS plans to issue an

[[Page 28570]]

authorization that extends to October 21, 2010.
    Geophysical survey activities will involve conventional seismic 
methodologies to decipher the crustal structure of the Shatsky Rise. To 
obtain high-resolution, 3-D structures of the area's magmatic systems 
and thermal structures, the Langseth will deploy a towed array of 36 
airguns as an energy source and approximately 28 OBSs and a 6-kilometer 
(km) long hydrophone streamer. As the airgun array is towed along the 
survey lines, the hydrophone streamers will receive the returning 
acoustic signals and transfer the data to the vessel's onboard 
processing system. The OBSs record the returning acoustic signals 
internally for later analysis.
    The proposed Shatsky Rise study (e.g., equipment testing, startup, 
line changes, repeat coverage of any areas, and equipment recovery) 
will take place in international waters deeper than 1,000 meters (m) 
(3,280 feet (ft)) and will require approximately 17 days (d) to 
complete approximately 15 transects of variable lengths totaling 3,160 
kilometers (km) of survey lines. Data acquisition will include 
approximately 408 hours (hr) of airgun operation (17 d x 24 hr).
    The scientific team consists of Drs. Jun Korenaga (Yale University, 
New Haven, CT), William Sager (Texas A&M University, College Station, 
TX), and John Diebold (L-DEO, Palisades, NY).

Vessel Specifications

    The Langseth, owned by NSF, is 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 vessel, which has a length of 71.5 m (235 feet (ft); a beam of 17.0 
m (56 ft); a maximum draft of 5.9 m (19 ft); and a gross tonnage of 
3,834, can accommodate up to 55 people. The ship is powered by two 
3,550 horsepower (hp) Bergen BRG-6 diesel engines which drive the two 
propellers. 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 
operation speed during seismic acquisition is typically 7.4 to 9.3 km/
hr (3.9 to 5.0 knots (kn)) and the cruising speed of the Langseth 
outside of seismic operations is 18.5 km/hr (9.9 kn).
    The vessel also has an observation tower from which visual 
observers will watch for marine mammals before and during the proposed 
airgun operations. When stationed on the observation platform, the 
observer's eye level will be approximately 18 m (58 ft) above sea level 
providing an unobstructed view around the entire vessel.

Acoustic Source Specifications

Seismic Airguns

    The full airgun array for the proposed survey consists of 36 
airguns (a mixture of Bolt 1500LL and Bolt 1900LLX airguns ranging in 
size from 40 to 360 cubic inches (in\3\)), with a total volume of 
approximately 6,600 in\3\ and a firing pressure of 1,900 pounds per 
square inch (psi). The dominant frequency components range from two to 
188 Hertz (Hz).
    The array configuration consists of four identical linear arrays or 
strings, with 10 airguns on each string; the first and last airguns 
will be spaced 16 m (52 ft) apart. For each operating array or string, 
the Langseth crew will fire the nine airguns simultaneously. They will 
keep the tenth airgun in reserve as a spare, which will be turned on in 
case of failure of one of the other airguns. The crew will distribute 
the four airgun strings across an area measuring approximately 24 by 16 
m (79 by 52 ft) behind the Langseth and will be towed approximately 100 
m (328 ft) behind the vessel at a tow depth of nine to 12 m (29.5 to 
49.2 ft) depending on the transect. The airgun array will fire every 20 
seconds (s) for the multi-channel seismic (MCS) surveying (13 
transects) and will fire every 70 s when recording data on the OBS (2 
transects). The tow depth of the array will be 9 m (29.5 ft) for the 
MCS transects and 12 m (39.3 ft) for the OBS transects. During firing, 
the airguns will emit a brief (approximately 0.1 s) pulse of sound. The 
airguns will be silent during the intervening periods of operations.

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 the root mean square unless otherwise noted. SPL 
does not take the duration of a sound into account.

Characteristics of the Airgun Pulses

    Airguns function by venting high-pressure air into the water which 
creates an air bubble. The pressure signature of an individual airgun 
consists of a sharp rise and then fall in pressure, followed by several 
positive and negative pressure excursions caused by the oscillation of 
the resulting air bubble. The oscillation of the air bubble transmits 
sounds downward through the seafloor and sounds that travel 
horizontally toward non-target areas.
    The nominal source levels of the airgun arrays used by L-DEO on the 
Langseth are 236 to 265 dB re: 1 [mu]Pa(p-p). The rms value 
for a given airgun pulse is typically 16 dB re: 1 [mu]Pa lower than the 
peak-to-peak value. Accordingly, L-DEO has predicted the received sound 
levels in relation to distance and direction from the airguns, for the 
36-airgun array and for a single 1900LL 40-in\3\ airgun, which will be 
used during power downs. A detailed description of the modeling effort 
is provided in Appendix A of LGL's Report. These are the nominal source 
levels applicable to downward propagation. The effective source levels 
for horizontal propagation are lower than those for downward 
propagation when the source consists of numerous airguns spaced apart 
from one another.
    Appendix B of LGL's report and previous Federal Register notices 
(see 69 FR 31792, June 7, 2004; 71 FR 58790, October 5, 2006; 72 FR 
71625, December 18, 2007; 73 FR 52950, September 12, 2008, or 73 FR 
71606, November 25, 2008, and 74 FR 42861, August 25, 2009) discuss the 
characteristics of the airgun pulses in detail. NMFS refers the 
reviewers to those documents for additional information.

Predicted Sound Levels for the Airguns

    Tolstoy et al., (2009) recently reported results for propagation 
measurements of pulses from the Langseth's 36-airgun array in two water 
depths, approximately 50 m and 1,600 m (164 and 5,249 ft), in the Gulf 
of Mexico in 2007 and 2008. L-DEO has used these reported empirical 
values to determine exclusion zones (EZ) for the airgun array, 
designate mitigation zones, and estimate take (described in greater 
detail

[[Page 28571]]

in Section VII of the application) for marine mammals.
    L-DEO has summarized the modeled safety radii for the planned 
airgun configuration in Table 1 which shows the measured and predicted 
distances at which sound levels (160-, 180-, and 190-dB) are expected 
to be received from the 36-airgun array and a single airgun operating 
in water greater than 1,000 m (3,820 ft) in depth.

  Table 1--Measured (Array) or Predicted (Single Airgun) Distances to Which Sound Levels >=190, 180, and 160 dB
  re: 1 [mu]Pa Could Be Received in Deep (>1000 m; 3280 ft) Water From the 36-Airgun Array, as well as a Single
Airgun, During the Proposed Shatsky Rise Seismic Survey, July-September, 2010 (Based on L-DEO Models and Tolstoy
                                                  et al., 2009)
----------------------------------------------------------------------------------------------------------------
                                                                                Predicted RMS distances (m)
                    Source and volume                       Tow depth (m) --------------------------------------
                                                                              190 dB       180 dB       160 dB
----------------------------------------------------------------------------------------------------------------
Single Bolt airgun 40 in\3\..............................          9-12 *           12           40          385
4 strings 36 airguns 6600 in\3\..........................               9          400          940         3850
                                                                       12          460         1100         4400
----------------------------------------------------------------------------------------------------------------
* 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 each tow depth.

    Results of the Gulf of Mexico calibration study (Tolstoy et al., 
2009) showed that radii around the airguns for various received levels 
varied with water depth. The tow depth of the airgun array for the 
proposed survey will range from 9 to 12 m (29.5 to 39.4 ft). However, 
in the Gulf of Mexico calibration study, the Langseth towed the airgun 
array at a depth of 6 m (19.6 ft) which is less than the tow depth 
range (9 to 12 m (29.5 to 39.4 ft)) for this proposed seismic survey. 
Accordingly, L-DEO has applied correction factors to the distances 
reported by Tolstoy et al. (2009) for shallow and intermediate depth 
water (i.e., they calculated the ratios between the 160-, 180-, and 
190-dB distances at 6 m versus 9 m (19.6 ft versus 29.5 ft) and the 
ratios between the 160-, 180-, and 190-dB distances at 6 m versus 12 m 
(19.6 ft versus 39.4 ft) from the modeled results for the 6,600-in\3\ 
airgun array). Refer to Appendix A of LGL's Environmental Assessment 
Report for additional information regarding how L-DEO calculated model 
predictions in Table 1 and how the applicant used empirical 
measurements to correct the modeled numbers.

Ocean Bottom Seismometer

    The Langseth crew will deploy approximately 28 OBS on the Shatsky 
Rise (see Figure 1 of L-DEO's application) over the course of 
approximately three days. The Langseth crew will retrieve all OBSs 
after seismic operations are completed. L-DEO expects the retrieval to 
last approximately five days.
    L-DEO proposes to use the Woods Hole Oceanographic Institution 
(WHOI) ``D2'' OBS during the cruise. This type of OBS is approximately 
one meter in height and has a maximum diameter of 50 centimeters (cm). 
The anchor (2.5 x 30.5 x 38.1 cm) is made of hot-rolled steel and 
weighs 23 kilograms (kg). The acoustic release transponder used to 
communicate with the OBS uses frequencies of 9 to 13 kHz. The source 
level of the release signal is 190 dB re: 1 [mu]Pa.

Multibeam Echosounder

    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 kilohertz (kHz)) in a fan-shaped beam that extends downward 
and to the sides of the ship. The transmitting beamwidth is one or two 
degrees ([deg]) fore-aft and 150[deg] athwartship and the maximum 
source level is 242 dB re: 1 [mu]Pa.
    For deep-water operations, each ping consists of eight successive 
fan-shaped transmissions, up to 15 milliseconds (ms) in duration and 
each ensonifying a sector that extends 1[deg] fore-aft. The eight 
successive transmissions span an overall cross-track angular extent of 
about 150[deg], with 2 ms gaps between the pulses for successive 
sectors.

Sub-Bottom Profiler

    The Langseth will also operate a Knudsen 320B SBP continuously 
throughout the cruise with the MBES. An SBP operates at mid to high 
frequencies and is generally used simultaneously with an MBES to 
provide information about the sedimentary features and bottom 
topography. SBP pulses are directed downward at typical frequencies of 
approximately three to 18 kHz. However, the dominant frequency 
component of the SBP is 3.5 kHz which is directed downward in a 27[deg] 
cone by a hull-mounted transducer on the vessel. 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 one second, but a common mode 
of operation is to broadcast five pulses at 1-s intervals followed by a 
5-second pause.
    NMFS expects that acoustic stimuli resulting from the proposed 
operation of the single airgun or the 36-airgun array has the potential 
to harass marine mammals, incidental to the conduct of the proposed 
seismic survey. 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 (7.4 to 9.3 km/hr; 3.9 to 5.0 kn).

Description of the Marine Mammals in the Area of the Proposed Specified 
Activity

    Thirty-four marine mammal species may occur in the Shatsky Rise 
survey area, including 26 odontocetes (toothed cetaceans), 7 mysticetes 
(baleen whales) and one pinniped. Six of these species are listed as 
endangered under the U.S. Endangered Species Act of 1973 (ESA; 16 
U.S.C. 1531 et seq.), including the north Pacific right (Eubalena 
japonica), humpback (Megaptera novaeangliae), sei (Balaenoptera 
borealis), fin (Balaenoptera physalus), blue (Balaenoptera musculus), 
and sperm (Physeter macrocephalus) whale.
    The western North Pacific gray whale (Eschrichtius robustus) occurs 
in the northwest Pacific Ocean and is listed as endangered under the 
ESA and as critically endangered by the International Union for 
Conservation of Nature (IUCN). L-DEO does not expect to encounter this 
species within the proposed survey area as gray whales are known to 
prefer nearshore coastal waters. Thus, L-DEO does not present analysis 
for this species nor does the application request take for this 
species.

[[Page 28572]]

    Table 2 presents information on the abundance, distribution, 
population status, and conservation status of marine mammals that may 
occur in the proposed survey area.

 Table 2--Habitat, Regional Population Size, and Conservation Status of Marine Mammals That May Occur in or Near
            the Proposed Seismic Survey Area at the Shatsky Rise Area in the Northwest Pacific Ocean
----------------------------------------------------------------------------------------------------------------
                                                             Regional
            Species                     Habitat          population size     U.S. ESA     IUCN \c\    CITES \d\
                                                               \a\             \b\
----------------------------------------------------------------------------------------------------------------
Mysticetes
    North Pacific right whale.  Pelagic and coastal...  few 100 \e\......           EN           EN            I
    Humpback whale............  Mainly nearshore        938-1107 \f\.....           EN           LC            I
                                 waters and banks.
    Minke whale...............  Pelagic and coastal...  25,000 \g\.......           NL           LC            I
    Bryde's whale.............  Pelagic and coastal...  20,501 \h\.......           NL           DD            I
    Sei whale.................  Primarily offshore,     7260-12,620 \i\..           EN           EN            I
                                 pelagic.
    Fin whale.................  Continental slope,      13,620-18,680 \j\           EN           EN            I
                                 mostly pelagic.
    Blue whale................  Pelagic and coastal...  3500 \k\.........           EN           EN            I
Odontocetes
    Sperm whale...............  Usually pelagic and     29,674 \l\.......           EN           VU            I
                                 deep seas.
    Pygmy sperm whale.........  Deep waters off the     N.A..............           NL           DD           II
                                 shelf.
    Dwarf sperm whale.........  Deep waters off the     11,200 \m\.......           NL           DD           II
                                 shelf.
    Cuvier's beaked whale.....  Pelagic...............  20,000 \m\.......           NL           LC           II
    Baird's beaked whale......  Deep water............  N.A..............           NL           DD           II
    Longman's beaked whale....  Deep water............  N.A..............           NL           DD           II
    Hubb's beaked whale.......  Deep water............  25,300 \n\.......           NL           DD           II
    Ginkgo-toothed beaked       Pelagic...............  25,300 \n\.......           NL           DD           II
     whale.
    Blainville's beaked whale.  Pelagic...............  25,300 \n\.......           NL           DD           II
    Stejneger's beaked whale..  Deep water............  25,300 \n\.......           NL           DD           II
    Rough-toothed dolphin.....  Deep water............  145,900 \m\......           NL           LC           II
    Common bottlenose dolphin.  Coastal and oceanic,    168,000 \o\......           NL           LC           II
                                 shelf break.
    Pantropical spotted         Coastal and pelagic...  438,000 \o\......           NL           LC           II
     dolphin.
    Spinner dolphin)..........  Coastal and pelagic...  801,000 \p\......           NL           DD           II
    Striped dolphin...........  Off continental shelf.  570,000 \o\......           NL           LC           II
    Fraser's dolphin..........  Waters >1000 m........  289,300 \m\......           NL           LC           II
    Short-beaked common         Shelf and pelagic,      2,963,000 \q\....           NL           LC           II
     dolphin.                    seamounts.
    Pacific white-sided         Continental slope and   988,000 \r\......           NL           LC           II
     dolphin.                    pelagic.
    Northern right whale        Deep water............  307,000 \r\......           NL           LC           II
     dolphin.
    Risso's dolphin...........  Waters >1000 m,         838,000 \o\......           NL           LC           II
                                 seamounts.
    Melon-headed whale........  Oceanic...............  45,400 \m\.......           NL           LC           II
    Pygmy killer whale........  Deep, pantropical       38,900 \m\.......           NL           DD           II
                                 waters.
    False killer whale........  Pelagic...............  16,000 \o\.......           NL           DD           II
    Killer whale..............  Widely distributed....  8500 \m\.........           NL           DD           II
    Short-finned pilot whale..  Mostly pelagic, high-   53,000 \o\.......           NL           DD           II
                                 relief topography.
    Dall's porpoise...........  Deep water............  1,337,224 \s\....           NL           LC           II
Pinnipeds
    Northern fur seal.........  Coastal and pelagic...  1.1 million \t\..           NL           VU           --
----------------------------------------------------------------------------------------------------------------
N.A.--Data not available or species status was not assessed.
\a\ Region for population size, in order of preference based on available data, is Western North Pacific, North
  Pacific, or Eastern Tropical Pacific; see footnotes below.
\b\ U.S. Endangered Species Act; EN = Endangered, NL = Not listed.
\c\ Codes for IUCN (2009) classifications; EN = Endangered; VU = Vulnerable; LC = Least Concern; DD = Data
  Deficient.
\d\ Convention on International Trade in Endangered Species of Wild Fauna and Flora (UNEP-WCMC 2009): Appendix I
  = Threatened with extinction; Appendix II = not necessarily now threatened with extinction but may become so
  unless trade is closely controlled.
\e\ North Pacific (Jefferson et al., 2008).
\f\ Western North Pacific (Calambokidis et al., 2008).
\g\ Northwest Pacific and Okhotsk Sea (Buckland et al., 1992; IWC 2009).
\h\ Western North Pacific (Kitakado et al., 2008; IWC 2009).
\i\ North Pacific (Tillman, 1977).
\j\ North Pacific (Ohsumi and Wada, 1974).
\k\ North Pacific (NMFS, 1998).
\l\ Western North Pacific (Whitehead, 2002b).
\m\ Eastern Tropical Pacific (ETP) (Wade and Gerrodette, 1993).
\n\ ETP; all Mesoplodon spp. (Wade and Gerrodette, 1993).
\o\ Western North Pacific (Miyashita, 1993a).
\p\ Whitebelly spinner dolphin in the ETP in 2000 (Gerrodette et al., 2005 in Hammond et al., 2008a).
\q\ ETP (Gerrodette and Forcada 2002 in Hammond et al., 2008b).
\r\ North Pacific (Miyashita, 1993b).
\s\ North Pacific (Buckland et al., 1993).
\t\ North Pacific, 2004-2005 (Gelatt and Lowry, 2008).


[[Page 28573]]

    Refer to Section IV of L-DEO's application for detailed information 
regarding the status and distribution of these marine mammals and to 
Section III of the application for additional information regarding how 
L-DEO estimated the regional population size for the marine mammals in 
Shatsky Rise area.

Potential Effects on Marine Mammals

Summary of Potential Effects of Airgun Sounds

    Level B harassment of cetaceans and pinnipeds has the potential to 
occur during the proposed seismic survey due to acoustic stimuli caused 
by the firing of a single airgun or the 36-airgun array which 
introduces sound into the marine environment. The effects of sounds 
from airguns 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). Permanent hearing impairment, in the 
unlikely event that it occurred, would constitute injury, but temporary 
threshold shift (TTS) is not an injury (Southall et al., 2007). 
Although the possibility cannot be entirely excluded, it is unlikely 
that the proposed project would result in any cases of temporary or 
permanent hearing impairment, or any significant non-auditory physical 
or physiological effects. Some behavioral disturbance is expected, but 
NMFS expects the disturbance to be localized and short-term.

Tolerance

    Numerous studies have shown that pulsed sounds from airguns are 
often readily detectable in the water at distances of many kilometers. 
For a brief summary of the characteristics of airgun pulses, see 
Appendix B of L-DEO's application.
    Several studies have also shown that marine mammals at distances 
more than a few kilometers from operating seismic vessels often show no 
apparent response (tolerance) (see Appendix B (3) LGL's Report). 
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 usually seem to be more 
tolerant of exposure to airgun pulses than cetaceans, with the relative 
responsiveness of baleen and toothed whales being variable (see 
Appendix B (5) of LGL's Report).

Masking of Natural Sounds

    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). 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).
    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 specific data on this. 
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 et al., 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 dominant components of airgun sounds, 
thus limiting the potential for masking.
    In general, NMFS expects the masking effects of seismic pulses to 
be minor, given the normally intermittent nature of seismic pulses. 
Masking effects on marine mammals are discussed further in Appendix 
B(4) of LGL's Report.

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-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 
(Balaena mysticetus), and sperm whales. Less detailed data are 
available for some other species of baleen whales, small toothed 
whales, and sea otters (Enhydra lutris), 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. 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 the LGL report, 
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

[[Page 28574]]

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 shown that 
seismic pulses with received levels of 160 to 170 dB re: 1 [mu]Pa seem 
to cause obvious avoidance behavior in a substantial fraction of the 
animals exposed (Richardson et al., 1995). In many areas, seismic 
pulses from large arrays of airguns diminish to those levels at 
distances ranging from 4 to 15 km 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 the EA 
have shown that some species of baleen whales, notably bowhead and 
humpback whales, at times show strong avoidance at received levels 
lower than 160-170 dB re: 1 [mu]Pa.
    Researchers have studied the responses of humpback whales to 
seismic surveys during migration, feeding during the summer months, 
breeding while offshore from Angola, and wintering offshore from 
Brazil. McCauley et al. (1998, 2000a) studied the responses of humpback 
whales off western Australia to a full-scale seismic survey with a 16-
airgun, 2,678-in\3\ array, and to a single 20-in\3\ airgun with source 
level 227 dB re: 1 [mu]Pa(p-p). McCauley et al. (1998) 
documented that avoidance reactions began at five to eight km from the 
array, and that those reactions kept most pods approximately three to 
four km from the operating seismic boat. McCauley et al. (2000a) noted 
localized displacement during migration of four to five km by traveling 
pods and seven to 12 km 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 
(CPA) distance the received level was 143 dB re: 1 [mu]Pa. The initial 
avoidance response generally occurred at distances of five to eight km 
from the airgun array and two km from the single airgun. However, some 
individual humpback whales, especially males, approached within 
distances of 100 to 400 m, where the maximum received level was 179 dB 
re: 1 [mu]Pa.
    Humpback whales on their summer feeding grounds in southeast Alaska 
did not exhibit persistent avoidance when exposed to seismic pulses 
from a 1.64-L (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 re: 1 [mu]Pa.
    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).
    There are no data on reactions of right whales to seismic surveys, 
but results from the closely-related bowhead whale show that their 
responsiveness can be quite variable depending on their activity 
(migrating versus 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 
to 30 km 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 LGL's report). 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 percent 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 
percent 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 et al., 2009). Sightings 
by observers on seismic vessels off the United Kingdom from 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).
    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.

[[Page 28575]]

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; Angliss and Allen, 2009). 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; Angliss and Allen, 2009).
    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 the LGL report 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).
    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; see also Barkaszi et al., 2009). 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). In 
most cases the avoidance radii for delphinids appear to be small, on 
the order of one km less, and some individuals show no apparent 
avoidance. The beluga whale (Delphinapterus leucas) 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 to 20 km compared with 20 to 30 km from an operating 
airgun array, and observers on seismic boats in that area rarely see 
belugas (Miller et al., 2005; Harris et al., 2007).
    Captive bottlenose dolphins (Tursiops truncatus) 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 (Phocoena phocoena) show stronger 
avoidance of seismic operations than do Dall's porpoises (Phocoenoides 
dalli) (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 the LGL report for 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 (Hyperoodon ampullatus) 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 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.
    There are increasing indications that some beaked whales tend to 
strand when naval exercises involving mid-frequency sonar operation are 
ongoing nearby (e.g., Simmonds and Lopez-Jurado, 1991; Frantzis, 1998; 
NOAA and USN, 2001; Jepson et al., 2003; Hildebrand, 2005; Barlow and 
Gisiner, 2006; see also the Strandings and Mortality subsection in this 
notice). These strandings are apparently a disturbance response, 
although auditory or other injuries or other physiological effects may 
also be involved. Whether beaked whales would ever react similarly to 
seismic surveys is unknown (see the Strandings and Mortality subsection 
in this notice). Seismic survey sounds are quite different from those 
of the sonar in operation during the above-cited incidents. 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 (Appendix B of the LGL 
Report).

Hearing Impairment and Other Physical Effects

    Temporary or permanent hearing impairment is a possibility when 
marine mammals are exposed to very strong sounds. TTS has been 
demonstrated and studied 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.
    L-DEO has included exclusion (i.e., shut-down) zones for the 
proposed

[[Page 28576]]

seismic survey on the Shatsky Rise to minimize the exposure of marine 
mammals to levels of sound associated with hearing impairment.
    Several aspects of the planned monitoring and mitigation measures 
for this project are designed to detect marine mammals occurring near 
the airgun array, and to avoid exposing them to sound pulses that 
might, at least in theory, cause hearing impairment (see below this 
section). In addition, many cetaceans show some avoidance of the area 
where received levels of airgun sound are high enough such that hearing 
impairment could potentially occur. 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 may also occur in marine mammals 
exposed to strong underwater pulsed sound. Possible types of non-
auditory physiological effects or injuries that might (in theory) 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 transient sounds. However, as discussed below this section, 
there is no definitive evidence that any of these effects occur even 
for marine mammals in close proximity to large arrays of airguns. It is 
unlikely that any effects of these types would occur during the present 
project given the brief duration of exposure of any given mammal, the 
deep water in the study area, and the planned monitoring and mitigation 
measures. 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). The distances from 
the Langseth's airguns at which the received energy level (per pulse, 
flat-weighted) that would be expected to be greater than or equal to 
180 dB re: 1 [micro]Pa are estimated in Table 1.
    The above TTS information for odontocetes is derived 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). 
From this, it is suspected that received levels causing TTS onset may 
also be higher in baleen whales (Southall et al., 2007). For this 
proposed study, L-DEO expects no cases of TTS given three 
considerations: (1) The low abundance of baleen whales in the planned 
study area at the time of the survey; (2) the strong likelihood that 
baleen whales would avoid the approaching airguns (or vessel) before 
being exposed to levels high enough for TTS to occur; and (3) the 
mitigation measures that are planned.
    Permanent Threshold Shift--When PTS occurs, there is physical 
damage to the sound receptors in the ear. In severe 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 (Kryter, 
1985). There is no specific evidence that exposure to pulses of airgun 
sound can cause PTS in any marine mammal, even with large arrays of 
airguns. However, given the possibility that mammals close to an airgun 
array might incur at least mild TTS, there has been further speculation 
about the possibility that some individuals occurring very close to 
airguns might incur PTS (e.g., Richardson et al., 1995, p. 372ff; 
Gedamke et al., 2008). Single or occasional occurrences of mild TTS are 
not indicative of permanent auditory damage, but repeated or (in some 
cases) single exposures to a level well above that causing TTS onset 
might elicit PTS.
    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 strong sound pulses with rapid rise time--see Appendix B(6) 
of LGL's Report. Based on data from terrestrial mammals, a 
precautionary assumption is that the PTS threshold for impulse sounds 
(such as airgun pulses as received close to the source) is at least 6 
dB higher than the TTS threshold on a peak-pressure basis, and probably 
greater than six dB (Southall et al., 2007).
    Given the higher level of sound necessary to cause PTS as compared 
with TTS, it is considerably less likely that PTS would occur. Baleen 
whales generally avoid the immediate area around operating seismic 
vessels, as do some other marine mammals. The planned monitoring and 
mitigation measures, including visual monitoring, passive acoustic 
monitoring (PAM) to complement visual observations (if practicable), 
power downs, and shut downs of the airguns when mammals are seen within 
or approaching the ``exclusion zones,'' will further reduce the 
probability of exposure of marine mammals to sounds strong enough to 
induce PTS.
    Stranding and Mortality--Marine mammals close to underwater 
detonations of high explosives can be killed or severely injured, and 
the auditory organs are especially susceptible to injury (Ketten et 
al., 1993; Ketten, 1995). However, explosives are no longer used for 
marine waters for commercial seismic surveys or (with rare exceptions) 
for seismic research; they have been replaced entirely by airguns or 
related non-explosive pulse generators. Airgun pulses are less 
energetic and have slower rise times, and there is no specific evidence 
that they can cause serious injury, death, or stranding even in the 
case of large airgun arrays. However, the association of strandings of 
beaked whales with naval exercises involving mid-frequency active sonar 
and, in one case, an L-DEO seismic survey (Malakoff, 2002; Cox et al., 
2006), 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 (e.g., Hildebrand, 
2005; Southall et al., 2007).

[[Page 28577]]

Appendix B(6) of the LGL report provides additional details.
    Specific sound-related processes that lead to strandings and 
mortality are not well documented, but may include:
    (1) Swimming in avoidance of a sound into shallow water;
    (2) a change in behavior (such as a change in diving behavior) that 
might contribute to tissue damage, gas bubble formation, hypoxia, 
cardiac arrhythmia, hypertensive hemorrhage or other forms of trauma;
    (3) a physiological change such as a vestibular response leading to 
a behavioral change or stress-induced hemorrhagic diathesis, leading in 
turn to tissue damage; and
    (4) tissue damage directly from sound exposure, such as through 
acoustically-mediated bubble formation and growth or acoustic resonance 
of tissues. Some of these mechanisms are unlikely to apply in the case 
of impulse sounds. However, there are increasing indications that gas-
bubble disease (analogous to the bends), induced in supersaturated 
tissue by a behavioral response to acoustic exposure, could be a 
pathologic mechanism for the strandings and mortality of some deep-
diving cetaceans exposed to sonar. The evidence for this remains 
circumstantial and associated with exposure to naval mid-frequency 
sonar, not seismic surveys (Cox et al., 2006; Southall et al., 2007).
    Seismic pulses and mid-frequency sonar signals are quite different, 
and some mechanisms by which sonar sounds have been hypothesized to 
affect beaked whales are unlikely to apply to airgun pulses. Sounds 
produced by airgun arrays are broadband impulses with most of the 
energy below one kHz. Typical military mid-frequency sonar emits non-
impulse sounds at frequencies of two to 10 kHz, generally with a 
relatively narrow bandwidth at any one time. A further difference 
between seismic surveys and naval exercises is that naval exercises can 
involve sound sources on more than one vessel. Thus, it is not 
appropriate to assume that there is a direct connection between the 
effects of military sonar and seismic surveys on marine mammals. 
However, evidence that sonar signals can, in special circumstances, 
lead (at least indirectly) to physical damage and mortality (e.g., 
Balcomb and Claridge, 2001; NOAA and USN, 2001; Jepson et al., 2003; 
Fern[aacute]ndez et al., 2004, 2005; Hildebrand 2005; Cox et al., 2006) 
suggests that caution is warranted when dealing with exposure of marine 
mammals to any high-intensity ``pulsed'' sound.
    There is no conclusive evidence of cetacean strandings or deaths at 
sea as a result of exposure to seismic surveys, but a few cases of 
strandings in the general area where a seismic survey was ongoing have 
led to speculation concerning a possible link between seismic surveys 
and strandings. Suggestions that there was a link between seismic 
surveys and strandings of humpback whales in Brazil (Engel et al., 
2004) were not well founded (IAGC, 2004; IWC, 2007). In September 2002, 
there was a stranding of two Cuvier's beaked whales (Ziphius 
cavirostris) in the Gulf of California, Mexico, when the L DEO vessel 
R/V Maurice Ewing was operating a 20-airgun (8,490 in \3\) in the 
general area. The link between the stranding and the seismic surveys 
was inconclusive and not based on any physical evidence (Hogarth, 2002; 
Yoder, 2002). Nonetheless, the Gulf of California incident plus the 
beaked whale strandings near naval exercises involving use of mid-
frequency sonar suggests a need for caution in conducting seismic 
surveys in areas occupied by beaked whales until more is known about 
effects of seismic surveys on those species (Hildebrand, 2005). No 
injuries of beaked whales are anticipated during the proposed study 
because of:
    (1) The high likelihood that any beaked whales nearby would avoid 
the approaching vessel before being exposed to high sound levels,
    (2) the proposed monitoring and mitigation measures, and
    (3) differences between the sound sources operated by L-DEO and 
those involved in the naval exercises associated with strandings.
    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, resonance, and other types of organ or 
tissue damage (Cox et al., 2006; Southall