Small Takes of Marine Mammals Incidental to Specified Activities; Marine Geophysical Survey in the Gulf of Alaska, September 2008, 45407-45427 [E8-17949]

Agencies

• DEPARTMENT OF COMMERCE
• National Oceanic and Atmospheric Administration

[Federal Register Volume 73, Number 151 (Tuesday, August 5, 2008)]
[Notices]
[Pages 45407-45427]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: E8-17949]



[[Page 45407]]

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DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

RIN 0648-XI15


Small Takes of Marine Mammals Incidental to Specified Activities; 
Marine Geophysical Survey in the Gulf of Alaska, September 2008

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

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

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SUMMARY:  NMFS has received an application from Lamont-Doherty Earth 
Observatory (L-DEO), a part of Columbia University, for an Incidental 
Harassment Authorization (IHA) to take marine mammals incidental to 
conducting a marine seismic survey in the Gulf of Alaska during 
September 2008. Pursuant to the Marine Mammal Protection Act (MMPA), 
NMFS is requesting comments on its proposal to issue an IHA to L-DEO to 
incidentally take, by Level B harassment only, small numbers of several 
species of marine mammals during the aforementioned activity.

DATES:  Comments and information must be received no later than 
September 4, 2008.

ADDRESSES:  Comments on the application should be addressed to P. 
Michael Payne, Chief, Permits, Conservation and Education Division, 
Office of Protected Resources, National Marine Fisheries Service, 1315 
East-West Highway, Silver Spring, MD 20910-3225. The mailbox address 
for providing email comments is PR1.0648-XI15@noaa.gov. Comments sent 
via e-mail, including all attachments, must not exceed a 10-megabyte 
file size.
    A copy of the application containing a list of the references used 
in this document may be obtained by writing to the address specified 
above, telephoning the contact listed below (see FOR FURTHER 
INFORMATION CONTACT), or visiting the internet at: https://
www.nmfs.noaa.gov/pr/permits/incidental.htm#applications.
    Documents cited in this notice may be viewed, by appointment, 
during regular business hours, at the aforementioned address.

FOR FURTHER INFORMATION CONTACT: Howard Goldstein or Ken Hollingshead, 
Office of Protected Resources, NMFS, (301) 713-2289.

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 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 shall be granted if NMFS finds that the taking will 
have a negligible impact on the species or stock(s), will not have an 
unmitigable adverse impact on the availability of the species or 
stock(s) for subsistence uses (where relevant), and if the permissible 
methods of taking and requirements pertaining to the mitigation, 
monitoring and reporting of such takings are set forth. NMFS has 
defined ``negligible impact'' in 50 CFR 216.103 as '' * * * an impact 
resulting from the specified activity that cannot be reasonably 
expected to, and is not reasonably likely to, adversely affect the 
species or stock through effects on annual rates of recruitment or 
survival.''
    Section 101(a)(5)(D) of the MMPA established an expedited process 
by which citizens of the United States can apply for an authorization 
to incidentally take small numbers of marine mammals by harassment. 
Except with respect to certain activities not pertinent here, the MMPA 
defines ``harassment'' as:

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

    Section 101(a)(5)(D) establishes a 45-day time limit for NMFS 
review of an application followed by a 30-day public notice and comment 
period on any proposed authorizations for the incidental harassment of 
marine mammals. Within 45 days of the close of the comment period, NMFS 
must either approve or deny the authorization.

Summary of Request

    On April 10, 2008, NMFS received an application from L-DEO for the 
taking, by Level B harassment only, of small numbers of 21 species of 
marine mammals incidental to conducting, under a cooperative agreement 
with the National Science Foundation (NSF), a seismic survey in the 
northeast Gulf of Alaska (GOA). The proposed cruise will take place in 
the territorial waters and Exclusive Economic Zone (EEZ) of the U.S. 
and is scheduled to occur from 31 August to 23 September 2008.
    The purpose of the proposed seismic survey is to examine crustal 
structure, fault patterns, and tectonic-climate geohistory of the area. 
The proposed program will investigate the interplay of climate and 
tectonics onshore and offshore in an area that includes the world's 
largest strike-slip earthquakes (Magnitude 8.0 Denali Event), largest 
earthquake caused uplift (14.4 m or 47 ft in 1962), largest area of 
seismic uplift (during the 1962 event), highest tsunami (over 200 m or 
656 ft in Latoya Bay in 1958), largest temperate glaciers (the 
Malaspina and Bering Glaciers), and some of the highest sedimentation 
rates (over 1 m or 3.3 ft per year in some places). Nowhere else on the 
planet are tectonics and climate interacting to create this combination 
of mountain building, glacial erosion, strike-slip (California style), 
and subduction (Japan style) earthquakes.
    While affecting a small local population in the past, natural 
seismic activity in the GOA could influence the whole of the North 
Pacific basin, which includes many large population centers. Alaska is 
being directly affected by modern climate change, and new evidence 
suggests that, as climate changes tectonics respond and vice versa. 
This interplay could be fundamental to the way the Earth works as a 
system, and by examining this interplay, the intention of the STEEP 
program is to examine the feedbacks that drive the system.
    The STEEP program is 5 years in length and includes scientists from 
over 10 universities. The study represents the most comprehensive study 
of tectonic and climate interactions ever undertaken in a single 
project. The offshore seismic component is a keystone for the 
experiment. The data obtained from the seismic survey will be used to 
determine the history of tectonic-climate interplay, as well as the 
nature of the Yakutat plate that is causing all of the deformation in 
southern Alaska, built the Saint Elias Mountains, and started the 
aggressive glaciation that continues today.

Description of the Activity

    The seismic survey will involve one source vessel, the R/V Marcus 
G. Langseth (Langseth), which will occur offshore from the Saint Elias 
Mountains. The Langseth will deploy an array of 36

[[Page 45408]]

airguns (6,600 in\3\) as an energy source and, at times, a receiving 
system consisting of one 8-km (3.7-mi) towed hydrophone streamer. The 
streamer will be towed at a depth of 7 m (23 ft) and the airguns at 9 m 
(29.5 ft). The Langseth will also deploy Ocean Bottom Seismometers 
(OBSs) to receive the returning acoustic signals. The OBSs are housed 
in 43-cm diameter glass spheres that have a gross weight of 
approximately 45 kg (99 lbs). As the airgun array is towed along the 
survey lines, the hydrophone streamer and/or OBSs will receive the 
returning acoustic signals and transfer the data to the on-board 
processing system.
    The Langseth is expected to depart Prince Rupert, British Columbia, 
Canada, on approximately 31 August, 2008 for the study area in the GOA 
(see Figure 1 of L-DEO's application). The airgun array is expected to 
operate for a total of ~200-250 hours. With OBS deployment and 
retrieval, the length of the survey will be ~18 days. The overall area 
within which the STEEP survey will take place is located at ~58-
60.5[deg] N, 138-146[deg] W (see Figure 1 of L-DEO's application). The 
proposed survey will be conducted in water depths from <100 m to >3,000 
m (<330 to>9,840 ft) entirely within the territorial waters and 
Exclusive Economic Zone (EEZ) of the United States. The exact dates of 
the activities depend upon logistics, as well as weather conditions 
and/or the need to repeat some lines if data quality is substandard.
    The primary marine seismic survey will consist of two long transect 
lines that will cross each other (Figure 1 of L-DEO's application). For 
the longer line paralleling the shoreline, a seismic reflection-
refraction profile will be shot using the hydrophone streamer as well 
as 25 OBSs deployed on the seafloor and 60 Texan seismometers deployed 
on land across the toe of the Bering Glacier. A reflection-refraction 
profile will also be obtained from the slightly shorter line that is 
perpendicular to the shoreline using the hydrophone streamer as well as 
17 OBSs; this line will be shot twice if time allows. Both of these 
lines will have a shot spacing of 50 m (164 ft, 20 seconds); if the 
onshore-offshore line is shot twice, the shot interval used during the 
second run will be 150 m (492 ft, 60 s). During the reflection-
refraction profiling, the airgun array will be towed at a depth of 9 m. 
In addition, two reflection-only 2-dimensional (2-D) seismic grids will 
be shot; the western grid is located approximately 150 km (93 mi) from 
shore whereas the eastern grid is located nearshore (see Figure 1 in L-
DEO's application). The shot spacing for these grids will be 50 m (164 
ft) and the airgun array will be towed at a depth of 9 m. No OBSs will 
be deployed during reflection-only profiling. There will be additional 
operations associated with equipment testing, startup, line changes, 
and repeat coverage of any areas where initial data quality is sub-
standard. In L-DEO's calculations, 25% has been added to the line total 
for those additional operations.
    The planned seismic survey (excluding the 25 percent contingency) 
will consist of 1909 km of survey lines including turns (see Figure 1 
in L-DEO's application). Most of this effort (923 km or 574 mi) will 
take place in intermediate water depths of 100-1,000 m and in water 
depths >1,000 m deep (812 km or 504 mi), and a smaller portion (174 km 
or 108 mi) will take place in water <100 m deep.
    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 scientific team is headed by Dr. Sean Gullick 
of the University of Texas at Austin Institute for Geophysics (UTIG) 
and also includes Drs. G. Christesen, P. Mann, and H. Van Avendonk of 
UTIG. The vessel will be self-contained, and the crew will live aboard 
the vessel for the entire cruise.
    In addition to the operations of the airgun array, a multibeam 
echosounder (MBES) will be operated from the Langseth continuously 
throughout the STEEP cruise. Also, a sub-bottom profiler (SBP) will be 
operated by the Langseth during most of the survey.

Vessel Specifications

    The Langseth has a length of 71.5 m (234.6 ft), a beam of 17 m 
(55.8 ft), and a maximum draft of 5.9 m (19.4 ft). The ship 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. The ship is powered by two Bergen BRG-6 diesel 
engines, each producing 3,550 hp, that drive the two propellers 
directly. Each propeller has four blades, and the shaft typically 
rotates at 750 rpm. The vessel also has an 800-hp bowthruster. The 
operation speed during seismic acquisition is typically 7.4-9.3 km/h 
(4-5 kt). When not towing seismic survey gear, the Langseth can cruise 
at 20-24 km/h (11-13 kt). The Langseth has a range of 25,000 km (15,534 
mi). The Langseth will also serve as the platform from which vessel-
based marine mammal (and sea turtle) observers (MMOs) will watch for 
animals before and during airgun operations.

Acoustic Source Specifications

Seismic Airguns
    During the proposed survey, the airgun array to be used will 
consist of 36 airguns, with a total volume of approximately 6,600 
in\3\. The airguns will consist of a mixture of Bolt 1500LL and 1900LL 
airguns. The airguns array will be configured as four identical linear 
arrays or ``strings'' (see Figure 2 in L-DEO's application). Each 
string will have ten airguns; the first and last airguns in each string 
are spaced 16 m (52.5 ft) apart. Nine airguns in each string will be 
fired simultaneously, while the tenth is kept in reserve as a spare, to 
be turned on in case of failure of another airgun. The four airgun 
strings will be distributed across an approximate area of 24 x 16 m 
(78.7 x 52.5 ft) behind the Langseth and will be towed approximately 
50-100 m (164-328 ft) behind the vessel at 9-m depth. The firing 
pressure of the array is 2,000 psi. The airgun array will fire in two 
modes: every 50 m (164 ft; 20 s) or every 150 m (492 ft; 60 s). During 
firing, a brief (approximately 0.1 s) pulse of sound is emitted. The 
airguns will be silent during the intervening periods.
    Because the actual source is a distributed sound source (36 
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 (265 dB re 1 microPa.m, peak to peak). 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.
    Sound propagation has been predicted by L-DEO for the 36-airgun 
array operating in deep, intermediate, and shallow water and for a 
single 1900LL 40 in\3\ airgun (which will be used during power downs), 
in relation to distance and direction from the airguns (See Table 1). A 
detailed description of L-DEO's modeling effort is provided in Appendix 
A of the application.
Multibeam Echosounder
    The Simrad EM120 operates at 11.25-12.6 kHz and is hull-mounted on 
the Langseth. The beamwidth is 1[deg] fore-aft and 150[deg] 
athwartship. The maximum source level is 242 dB re 1 microPa (rms; 
Hammerstad, 2005). For deep-water operation, each ``ping'' consists of 
nine successive fan-shaped transmissions, each 15 ms in duration and 
each ensonifying a section that extends 1[deg] fore-aft. The nine 
successive

[[Page 45409]]

transmissions span an overall cross-track angular extent of about 
150[deg], with 16 ms gaps between the pulses for successive sectors. A 
receiver in the overlap area between the two sectors would receive two 
15-ms pulses separated by a 16-ms gap. In shallower water, the pulse 
duration is reduced to 5 or 2 ms, and the number of transmit beams is 
also reduced. The ping interval varies with water depth, from 
approximately 5 s at 1,000 m (3,280 ft) to 20 s at 4,000 m (13,123 ft; 
Kongsberg Maritime, 2005).
Sub-bottom Profiler
    The SBP is normally operated to provide information about the 
sedimentary features and the bottom topography that is simultaneously 
being mapped by the MBES. The energy from the SBP is directed downward 
by a 3.5 kHz transducer in the hull of the Langseth. The output varies 
with water depth from 50 watts in shallow water to 800 watts in deep 
water. The pulse interval is 1 s, but a common mode of operation is to 
broadcast five pulses at 1-s intervals followed by a 5-s pause.

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                                                                                                        Predicted RMS Distances (m)
        Source and Volume              Tow Depth (m)            Water Depth      -----------------------------------------------------------------------
                                                                                          190 dB                  180 dB                  160 dB
--------------------------------------------------------------------------------------------------------------------------------------------------------
Single Bolt airgun                ......................  Deep                    12                      40                      385
                                                         -----------------------------------------------------------------------------------------------
                                  9                       Intermediate            18                      60                      578
                                                         -----------------------------------------------------------------------------------------------
40 in\3\                          ......................  Shallow                 150                     296                     1050
--------------------------------------------------------------------------------------------------------------------------------------------------------
4 strings                         ......................  Deep                    300                     950                     6000
                                                         -----------------------------------------------------------------------------------------------
36 airguns                        9                       Intermediate            450                     1425                    6667
                                                         -----------------------------------------------------------------------------------------------
6600 in\3\                        ......................  Shallow                 2182                    3694                    8000
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Table 1. Predicted distances to which sound levels [gteqt]190, 180, and 160 dB re 1 microPa might be received in shallow (<100 m; 328 ft), intermediate
  (100-1,000 m; 328-3,280 ft), and deep (>1,000 m; 3,280 ft) water during the Central American SubFac and STEEP Gulf of Alaska survey.

    Because the predictions in Table 1 are based in part on empirical 
correction factors derived from acoustic calibration of different 
airgun configurations than those to be used on the Langseth (cf. 
Tolstoy et al., 2004a,b), L-DEO conducted an acoustic calibration study 
of the Langseth's 36-airgun (approximately 6,600 in\3\) array in late 
2007/early 2008 in the Gulf of Mexico (LGL Ltd. 2006). Distances where 
sound levels (e.g., 190, 180, and 160 dB re 1 microPa rms) were 
received in deep, intermediate, and shallow water will be determined 
for various airgun configurations. Acoustic data analysis is ongoing. 
After, analysis, the empirical data from the 2007/2008 calibration 
study will be used to refine the exclusion zones proposed above for use 
during the STEEP cruise, if the data are appropriate and available for 
use at the time of the survey.

Description of Marine Mammals in the Activity Area

    A total of 18 cetacean species, 3 species of pinnipeds, and the sea 
otter are known to or could occur in the GOA study area (see Table 2 of 
the application; Angliss and Outlaw, 2007). Several of the species are 
listed as Endangered under the U.S. Endangered Species Act (ESA), 
including the humpback, sei, fin, blue, North Pacific right, and sperm 
whale, sea otter, and the western stock of Steller sea lions. The 
eastern stock of Steller sea lions is listed as Threatened. The 
southeast Alaska Distinct Population Segment of northern sea otters are 
also listed as Threatened. There is little information on the 
distribution of marine mammals inhabiting the waters offshore of SE 
Alaska or the eastern GOA, although a few reports are available (e.g., 
Buckland et al., 1993; Hobbs and Lerczak, 1993; Straley et al. 1995; 
Calambokidis et al., 1997; MacLean and Koski, 2005; Angliss and Outlaw, 
2007).
    The marine mammals that occur in the proposed survey area belong to 
four taxonomic groups: odontocetes (toothed cetaceans such as 
dolphins), mysticetes (baleen whales), pinnipeds (seals and sea lions), 
and fissipeds (the sea otter). Cetaceans and pinnipeds are managed by 
NMFS and are the subject of this IHA application. Several of the 18 
cetacean species are common in the area (see below). Of the three 
species of pinnipeds that potentially could occur in the study area, 
only the Steller sea lion and harbor seal are likely to be present. The 
northern fur seal inhabits the Bering Sea during the summer, and is 
generally found in SE Alaska in low numbers during the winter and 
during the northward migration in the spring. Sea otters are managed by 
the U.S. Fish and Wildlife Service (USFWS). Informal consultation with 
the USFWS is being sought for sea otters.
    Information on the occurrence, distribution, population size, 
habitat, and conservation status for each of the 21 marine mammal 
species that are likely to occur in the proposed project area is 
presented in Table 5 of L-DEO's application and is reprinted in part 
here as Table 2.
    Based on a compilation of data from 1979 to 2001, many cetaceans 
and pinnipeds occur within the EEZ in both oceanic and coastal waters. 
However, beaked, sperm, dwarf/pygmy sperm, and baleen whales (except 
for the humpback) occur predominantly in oceanic waters (May-Collado et 
al., 2005). Bottlenose and pantropical spotted dolphins, as well as the 
humpback whale, tend to be coastal.
    Table 2 below outlines the cetacean and pinniped species, their 
habitat and abundance in the proposed project area, and the requested 
take levels. Additional information regarding the distribution of these 
species expected to be found in the project area and how the estimated 
densities were calculated may be found in L-DEO's application.

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           Species                   Habitat         Abundance (Alaska)   Regional Abundance        ESA \1\
----------------------------------------------------------------------------------------------------------------
Odontocetes
------------------------------                                                               -------------------

[[Page 45410]]

 
Sperm whale (Physeter          Pelagic              159 \4\              24,000 \5\           EN
 macrocephalus)
----------------------------------------------------------------------------------------------------------------
Cuvier's beaked whale          Pelagic              N.A.                 20,000 \6\           N.L.
 (Ziphius cavirostris)
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Baird's beaked whale           Pelagic              N.A.                 6,000 \7\            N.L.
 (Berardius bairdii)
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Stejneger's beaked whale       Likely Pelagic       N.A.                 N.A.                 N.L.
 (Mesoplodon stejnegeri)
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Beluga whale (Delphinapterus   Coastal & Ice Edges  366 \8\              N.A.                 N.L.
 leucas)
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Pacific white-sided dolphin    Pelagic, Shelf,      26,880 \9\           931,000 \10\         N.L.
 (Lagenorhynchus obliquidens)   Coastal
----------------------------------------------------------------------------------------------------------------
Risso's dolphin (Grampus       Pelagic, Shelf,      N.A.                 16,066 \11\          N.L.
 griseus)                       Coastal
----------------------------------------------------------------------------------------------------------------
Killer whale (Orcinus orca)    Pelagic, Shelf,      1,975 \12\           8,500 \13\           N.L.
                                Coastal
----------------------------------------------------------------------------------------------------------------
Short-finned pilot whale       Pelagic, Shelf,      N.A.                 160,200 \6\          N.L.
 (Globicephala macrorhynchus)   Coastal
----------------------------------------------------------------------------------------------------------------
Harbor Porpoise (Phocoena      Coastal              17,076 \14\          202,988 \16\         N.L.
 phocoena)                                          41,854 \15\
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Dall's Porpoise (Phocoenoides  Pelagic & Shelf      83,400 \17\          1,186,000 \18\       N.L.
 dalli)
----------------------------------------------------------------------------------------------------------------
Mysticetes
------------------------------                                                               -------------------
Humpback whale (Megaptera      Coastal & Banks      2,644 \21\           >6,000 \22\          EN
 novaeangliae)
----------------------------------------------------------------------------------------------------------------
Minke whale (Balaenoptera      Coastal & Shelf      1,232 \21\           9,000 \23\           N.L.
 acutorostrata)
----------------------------------------------------------------------------------------------------------------
Gray whale (Eschrichtius       Coastal              N.A.                 18,813 \20\          N.L.
 robustus)
----------------------------------------------------------------------------------------------------------------
Sei whale (Balaenoptera        Pelagic              N.A.                 7,260-12,620 \22\    EN
 borealis)
----------------------------------------------------------------------------------------------------------------
Fin whale (Balaenoptera        Pelagic              1,652 \24\           13,620-18,680 \22\   EN
 physalus)
----------------------------------------------------------------------------------------------------------------
Blue whale (Balaenoptera       Pelagic, Shelf,      N.A.                 1,744 \11\           EN
 musculus)                      Coastal
----------------------------------------------------------------------------------------------------------------
North Pacific right whale      Coastal & Shelf      N.A.                 100-200 \19\         EN
 (Eubalaena japonica)
----------------------------------------------------------------------------------------------------------------
Pinnipeds
------------------------------                                                               -------------------
Northern fur seal              Pelagic, Breeds      N.A.                 721,935 \25\         N.L.
 (Callorhinus ursinus)          Coastally
----------------------------------------------------------------------------------------------------------------
Steller sea lion (Eumetopias   Coastal              47,885 \26\          N.A.                 T
 jubatus)                                           44,780 \27\                               EN
----------------------------------------------------------------------------------------------------------------
Harbor seal (Phoca vitulina    Coastal              180,017 \28\         N.A.                 N.L.
 richardsi)
----------------------------------------------------------------------------------------------------------------
Table 2. The habitat, abundance, and conservation status of marine mammals inhabiting the proposed study area in
  the Gulf of Alaska. Regional abundance estimates are also given, usually for the Northeastern Pacific Ocean or
  the U.S. West Coast.
Note: N.A. = Not available or not applicable.
\1\ U.S. Endangered Species Act. En = Endangered; T = Threatened; N.L. = Not Listed.
\2\ IUCN Red List of Threatened Species (2007). Codes for IUCN classifications: CR = Critically Endangered; EN =
  Endangered; VU = Vulnerable; LR = Lower Risk (-cd = Conservation Dependent; -nt = Near Threatened; -ic = Least
  Concern); DD = Data Deficient; NL = Not Listed.
\3\ Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) (UNEP-WCMC 2007). I
  and II are CITES Appendices; NL = Not Listed.

[[Page 45411]]

 
\4\ Western GOA and eastern Aleutians (Zerbini et al., 2004).
\5\ Eastern temperate North Pacific (Whitehead, 2002).
\6\ Eastern Tropical Pacific (Wade and Gerrodette, 1993).
\7\ Western North Pacific (Reeves and Leatherwood, 1994; Kasuya, 2002).
\8\ Cook Inlet stock (Rugh et al., 2005a).
\9\ GOA (Angliss and Outlaw, 2007).
\10\ North Pacific Ocean (Buckland et al., 1993).
\11\ California/Oregon/Washington (Carretta et al. 2007).
\12\ Minimum abundance in Alaskan waters, includes 1,339 resident and 636 transient (Angliss and Outlaw, 2007).
\13\ Eastern Tropical Pacific (Ford, 2002).
\14\ SE Alaska stock (Angliss and Outlaw, 2007).
\15\ GOA stock (Angliss and Outlaw 2007).
\16\ Western North Pacific Ocean (totals from Carretta et al., 2007 and Angliss and Outlaw, 2007).
\17\ Alaska stock (Angliss and Outlaw, 2007).
\18\ North Pacific Ocean and Bering Sea (Houk and Jefferson, 1999).
\19\ Eastern North Pacific (Wada, 1973).
\20\ Mean of 2000-2001 and 2001-2002 abundance estimates for eastern North Pacific (Angliss and Outlaw, 2007).
\21\ Western GOA and eastern Aleutians (Zerbini et al., 2006).
\22\ North Pacific Ocean (Carretta et al., 2007).
\23\ North Pacific Ocean (Wada, 1976).
\24\ Central waters of western Alaska and eastern and central Aleutian Islands (Angliss and Outlaw, 2007).
\25\ Abundance for Eastern Pacific Stock (Angliss and Outlaw, 2007).
\26\ Eastern U.S. Stock (Angliss and Outlaw, 2007).
\27\ Western U.S. Stock (Angliss and Outlaw, 2007).
\28\ Alaska statewide (Angliss and Outlaw, 2007).
\29\ Abundance estimate for SE Alaska stock (USFWS 2002 in Angliss and Outlaw, 2007).
\30\ Abundance estimate Southcentral Alaska (USFWS 2002 in Angliss and Outlaw, 2007).
\31\ SW Alaska stock (USFWS 2002 in Angliss and Outlaw, 2007).

Potential Effects on Marine Mammals

Potential Effects of Airguns

    The effects of sounds from airguns might include one or more of the 
following: tolerance, masking of natural sounds, behavioral 
disturbances, and 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). With the possible exception of some 
cases of temporary threshold shift in harbor seals, it is unlikely that 
the project would result in any cases of temporary or especially 
permanent hearing impairment, or any significant non-auditory physical 
or physiological effects. Some behavioral disturbance is expected, but 
this would be localized and short-term.
    The rms (root mean square) received levels that are used as impact 
criteria for marine mammals are not directly comparable to the peak or 
peak-to-peak values normally used to characterize source levels of 
airgun arrays. The measurement units used to describe airgun sources, 
peak or peak-to-peak decibels, are always higher than the rms decibels 
referred to in biological literature. A measured received level of 160 
dB rms in the far field would typically correspond to a peak 
measurement of approximately 170 to 172 dB, and to a peak-to-peak 
measurement of approximately 176 to 178 dB, as measured for the same 
pulse received at the same location (Greene, 1997; McCauley et al., 
1998, 2000a). The precise difference between rms and peak or peak-to-
peak values depends on the frequency content and duration of the pulse, 
among other factors. However, the rms level is always lower than the 
peak or peak-to-peak level for an airgun-type source.
Tolerance
    Numerous studies have shown that pulsed sounds from airguns are 
often readily detectable in the water at distances of many kilometers. 
For a summary of the characteristics of airgun pulses, see Appendices B 
) of L-DEO's application. Numerous studies have shown that marine 
mammals at distances more than a few kilometers from operating seismic 
vessels often show no apparent response see Appendix C (e) of the 
application. That is often true even in cases when the pulsed sounds 
must be readily audible to the animals based on measured received 
levels and the hearing sensitivity of the mammal group. Although 
various baleen whales, toothed whales, and (less frequently) pinnipeds 
have been shown to react behaviorally to airgun pulses under some 
conditions, at other times, mammals of all three types have shown no 
overt reactions. In general, pinnipeds usually seem to be more tolerant 
of exposure to airgun pulses than are cetaceans, with relative 
responsiveness of baleen and toothed whales being variable.
Masking
    Obscuring of sounds of interest by interfering sounds, generally at 
similar frequencies, is known as masking. Masking effects of pulsed 
sounds (even from large arrays of airguns) on marine mammal calls and 
other natural sounds are expected to be limited, although there are few 
specific data of relevance. Because of the intermittent nature and low 
duty cycle of seismic pulses, animals can emit and receive sounds in 
the relatively quiet intervals between pulses. Some baleen and toothed 
whales are known to continue calling in the presence of seismic pulses. 
The airgun sounds are pulsed, with quiet periods between the pulses, 
and whale calls often can be heard between the seismic pulses 
(Richardson et al., 1986; McDonald et al., 1995; Greene et al., 1999; 
Nieukirk et al., 2004; Smultea et al., 2004). Although there has been 
one report that sperm whales cease calling when exposed to pulses from 
a very distant seismic ship (Bowles et al., 1994), a more recent study 
reports that sperm whales off northern Norway continued calling in the 
presence of seismic pulses (Madsen et al., 2002). That has also been 
shown during recent work in the Gulf of Mexico and Caribbean Sea 
(Smultea et al., 2004; Tyack et al., 2006). Masking effects of seismic 
pulses are expected to be negligible in the case of the small 
odontocetes given the intermittent nature of seismic pulses. Dolphins 
and porpoises commonly are heard calling while airguns are operating 
(Gordon et al., 2004; Smultea et al., 2004; Holst et al., 2005a,b). 
Also, the sounds important to small odontocetes are predominantly at 
much higher frequencies than the airgun sounds, thus further limiting 
the potential for masking. Masking effects, in general, are discussed 
further in Appendix B (d) of L-DEO's application.

[[Page 45412]]

Disturbance Reactions
    Disturbance includes a variety of effects, including subtle changes 
in behavior, more conspicuous changes in activities, and displacement. 
Reactions to sound, if any, depend on species, state of maturity, 
experience, current activity, reproductive state, time of day, and many 
other factors. If a marine mammal responds to an underwater sound by 
changing its behavior or moving a small distance, the response may or 
may not rise to the level of ``harassment,'' let alone affect the stock 
or the species as a whole. However, if a sound source displaces marine 
mammals from an important feeding or breeding area for a prolonged 
period, impacts on animals or on the stock or species could potentially 
be significant. Given the many uncertainties in predicting the quantity 
and types of impacts of noise on marine mammals, it is common practice 
to estimate how many mammals are likely to be present within a 
particular distance of industrial activities, or exposed to a 
particular level of industrial sound. This practice potentially 
overestimates the numbers of marine mammals that are affected in some 
biologically-important manner.
    The sound exposure thresholds that affect marine mammals 
behaviorally are based on behavioral observations during studies of 
several species. However, information is lacking for many species. 
Detailed studies have been done on humpback, gray, and bowhead whales 
and on ringed seals. Less detailed data are available for some other 
species of baleen whales, sperm whales, and small toothed whales.
    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 (e) of L-DEO's 
application, baleen whales exposed to strong noise pulses from airguns 
often react by deviating from their normal migration route and/or 
interrupting their feeding activities and moving away from the sound 
source. In the case of the migrating gray and bowhead whales, the 
observed changes in behavior appeared to be of little or no biological 
consequence to the animals. They simply avoided the sound source by 
displacing their migration route to varying degrees, but within the 
natural boundaries of the migration corridors.
    Studies of gray, bowhead, and humpback whales have determined that 
received levels of pulses in the 160-170 dB re 1 microPa rms range seem 
to cause obvious avoidance behavior in a substantial fraction of the 
animals exposed. In many areas, seismic pulses from large arrays of 
airguns diminish to those levels at distances ranging from 4.5-14.5 km 
(2.8-9 mi) from the source. A substantial proportion of the baleen 
whales within those distances may show avoidance or other strong 
disturbance reactions to the airgun array. Subtle behavioral changes 
sometimes become evident at somewhat lower received levels.
    Responses of humpback whales to seismic surveys have been studied 
during migration and on the summer feeding grounds, and there has also 
been discussion of effects on the Brazilian wintering grounds. McCauley 
et al. (1998, 2000) 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 a source level 
of 227 dB re 1 microPa m peak-to-peak. McCauley et al. (1998) 
documented that initial 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. McCauley et al. 
(2000) 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 cow-calf pairs. 
Avoidance distances with respect to the single airgun were smaller (2 
km (1.2 mi)) but consistent with the results from the full array in 
terms of received sound levels. Mean avoidance distance from the airgun 
corresponded to a received sound level of 140 dB re 1 microPa (rms); 
that was the level at which humpbacks started to show avoidance 
reactions to an approaching airgun. The standoff range, i.e., the 
closest point of approach of the whales to the airgun, corresponded to 
a received level of 143 dB re 1 microPa (rms). 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 
microPa (rms).
    Humpback whales on their summer feeding grounds in southeast 
summering 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 
150-169 dB re 1 microPa on an approximate rms basis. 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 
microPa on an approximate rms basis.
    It has been 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, 
subject to alternative explanations (IAGC 2004), and not consistent 
with results from 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).
    Results from bowhead whales show that responsiveness of baleen 
whales to seismic surveys can be quite variable depending on the 
activity (migrating vs. feeding) of the whales. 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, where received sound levels were on the order of 
130 dB re 1 microPa (rms) (Miller et al., 1999; Richardson et al., 
1999; see Appendix B (e) of L-DEO's application). However, more recent 
research on bowhead whales (Miller et al., 2005a; Harris et al., 2007) 
corroborates earlier evidence that, during the summer feeding season, 
bowheads are not as sensitive to seismic sources. In summer, bowheads 
typically begin to show avoidance reactions at a received level of 
about 160 170 dB re 1 microPa (rms) (Richardson et al., 1986; Ljungblad 
et al., 1988; Miller et al., 2005a). Nonetheless, statistical analysis 
showed evidence of subtle changes in surfacing, respiration and diving 
cycles when feeding bowheads were exposed to lower-level pulses from 
distant seismic operations (Richardson et al., 1986).
    Reactions of migration 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. Malme et al. (1986, 1988) estimated, based on small sample sizes, 
that 50 percent of feeding gray whales ceased feeding at an average 
received pressure level of 173 dB re 1 microPa on an (approximate) rms 
basis, and that 10 percent of feeding whales interrupted feeding at 
received levels of 163 dB. Those findings were generally consistent 
with the results of experiments conducted on larger numbers of gray 
whales that were

[[Page 45413]]

migrating along the California coast (Malme et al., 1984; Malme and 
Miles, 1985), and with observations of Western Pacific gray whales 
feeding off Sakhalin Island, Russia, when a seismic survey was underway 
just offshore of their feeding area (Gailey et al., 2007; Johnson et 
al., 2007; Yazvenko et al. 2007a,b).
    Various species of Balaenoptera (blue, sei, fin, and minke whales) 
have occasionally been reported in areas ensonified by airgun pulses. 
Sightings by observers on seismic vessels off the United Kingdom from 
1997 to 2000 suggest that, at times of good sightability, numbers of 
rorquals seen are similar when airguns are shooting and not shooting 
(Stone, 2003; Stone and Tasker, 2006). Although individual species did 
not show any significant displacement in relation to seismic activity, 
all baleen whales combined were found to remain significantly further 
from the airguns during shooting compared with periods without shooting 
(Stone, 2003; Stone and Tasker, 2006). In a study off Nova Scotia, 
Moulton and Miller (in press) found only a little or no difference in 
sighting rates 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.
    Data on short-term reactions (or lack of reactions) of cetaceans to 
impulsive noises do not necessarily provide information about long-term 
effects. It is not known whether impulsive noises affect reproductive 
rate or distribution and habitat use in subsequent days or years. 
However, gray whales continued to migrate annually along the west coast 
of North America despite intermittent seismic exploration and much ship 
traffic in that area for decades (see Appendix A in Malme et al., 
1984). The western Pacific gray whale population did not seem affected 
by a seismic survey in its feeding ground during a prior year (Johnson 
et al., 2007). Bowhead whales continued to travel to the eastern 
Beaufort Sea each summer despite seismic exploration in their summer 
and autumn range for many years (Richardson et al., 1987). In any 
event, brief exposures to sound pulses from the proposed airgun source 
are highly unlikely to result in prolonged effects.
    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 have 
been reported for toothed whales. However, a systematic study on sperm 
whales has been done ( Jochens and Biggs, 2003; Tyack et al., 2003; 
Jochens et al., 2006; Miller et al., 2006), and there is an increasing 
amount of information about responses of various odontocetes to seismic 
surveys based on monitoring studies (e.g., Stone, 2003; Smultea et al., 
2004; Moulton and Miller, 2005; Bain and Williams, 2006; Holst et al., 
2006; Stone and Tasker, 2006).
    Seismic operators and marine mammal observers sometimes see 
dolphins and other small toothed whales near operating airgun arrays, 
but in general there seems to be a tendency for most delphinids to show 
some limited avoidance of seismic vessels operating large airgun 
systems. However, some dolphins seem to be attracted to the seismic 
vessel and floats, and some ride the bow wave of the seismic vessel 
even when large airgun arrays are firing. Nonetheless, there have been 
indications that small toothed whales sometimes 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., Goold, 
1996a,b,c; Calambokidis and Osmek, 1998; Stone, 2003; Stone and Tasker, 
2006). In most cases, the avoidance radii for delphinids appear to be 
small, on the order of 1 km (0.62 mi) or less. The beluga may be a 
species that (at least at times) shows long-distance avoidance of 
seismic vessels. Aerial surveys during seismic operations in the 
southeastern Beaufort Sea recorded much lower sighting rates of beluga 
whales within 10-20 km (6.2-12.4 mi) of an active seismic vessel. These 
results were consistent with the low number of beluga sightings 
reported by observers aboard the seismic vessel, suggesting that some 
belugas might be avoiding the seismic operations at distances of 10-20 
km (6.2-12.4 mi) (Miller et al., 2005a).
    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; Finneran and Schlundt, 2004). The animals tolerated high received 
levels of sound (pk-pk level >200 dB re 1 microPa) before exhibiting 
aversive behaviors. For pooled data at 3, 10, and 20 kHz, sound 
exposure levels during sessions with 25, 50, and 75 percent altered 
behavior were 180, 190, and 199 dB re 1 microPa\2\, respectively 
(Finneran and Schlundt, 2004).
    Results for porpoises depend on species. Dall's porpoises seem 
relatively tolerant of airgun operations (MacLean and Koski, 2005) and, 
during a survey with a large airgun array, tolerated higher noise 
levels than did harbor porpoises and gray whales (Bain and Williams, 
2006). However, Dall's porpoises do respond to the approach of large 
airgun arrays by moving away (Calambokidis and Osmek, 1998; Bain and 
Williams, 2006). The limited available data suggest that harbor 
porpoises show stronger avoidance (Stone, 2003; Bain and Williams, 
2006; Stone and Tasker, 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 
in general (Richardson et al., 1995; Southall et al. 2007).
    Most studies of sperm whales exposed to airgun sounds indicate that 
this species shows considerable tolerance of airgun pulses. In most 
cases, the whales do not show strong avoidance and continue to call 
(see Appendix B of L-DEO's application). However, controlled exposure 
experiments in the Gulf of Mexico indicate that foraging effort is 
somewhat reduced upon exposure to airgun pulses from a seismic vessel 
operating in the area, and there may be a delay in diving to foraging 
depth (Miller et al., 2006; Tyack et al., 2006).
    There are no specific data on the behavioral reactions of beaked 
whales to seismic surveys. Most beaked whales tend to avoid approaching 
vessels of other types (Wursig et al., 1998). They may also dive for an 
extended period when approached by a vessel (Kasuya, 1986). It is 
likely that these beaked whales would normally show strong avoidance of 
an approaching seismic vessel, but this has not been documented 
explicitly.
    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 L-DEO's 
application).
    Pinnipeds - Pinnipeds are not likely to show a strong avoidance 
reaction to the airgun sources that will be used. Visual monitoring 
from seismic vessels, usually employing larger sources, has shown only 
slight (if any) avoidance of airguns by pinnipeds, and only slight (if 
any) changes in behavior (see Appendix B(e) of L-DEO's application). 
Ringed seals frequently do not avoid the area within a few hundred 
meters of operating airgun arrays (Harris et al., 2001; Moulton and 
Lawson, 2002; Miller et al., 2005a). However, initial telemetry work 
suggests that avoidance and other behavioral reactions by two

[[Page 45414]]

other species of seals to small airgun sources may at times be stronger 
than evident to date from visual studies of pinniped reactions to 
airguns (Thompson et al., 1998). Even if reactions of any pinnipeds 
that might be encountered in the present study area are as strong as 
those evident in the telemetry study, reactions are expected to be 
confined to relatively small distances and durations, with no long-term 
effects on pinniped individuals or populations.
    Additional details on the behavioral reactions (or the lack 
thereof) by all types of marine mammals to seismic vessels can be found 
in Appendix B (e) of L-DEO's application.
Hearing Impairment and Other Physical Effects
    Temporary or permanent hearing impairment is a possibility when 
marine mammals are exposed to very strong sounds, but there has been no 
specific documentation of this for marine mammals exposed to sequences 
of airgun pulses.
    NMFS will be developing new noise exposure criteria for marine 
mammals that take account of the now-available scientific data on TTS, 
the expected offset between the TTS and permanent threshold shift (PTS) 
thresholds, differences in the acoustic frequencies to which different 
marine mammal groups are sensitive, and other relevant factors. 
Detailed recommendations for new science-based noise exposure criteria 
were published in early 2008 (Southall et al., 2007).
    Several aspects of the planned monitoring and mitigation measures 
for this project (see below) are designed to detect marine mammals 
occurring near the airguns to avoid exposing them to sound pulses that 
might, at least in theory, cause hearing impairment. In addition, many 
cetaceans are likely to show some avoidance of the area with high 
received levels of airgun sound (see above). In those cases, the 
avoidance responses of the animals themselves will reduce or (most 
likely) avoid any possibility of hearing impairment.
    Non-auditory physical effects may also occur in marine mammals 
exposed to strong underwater pulsed sound. Possible types of non-
auditory physiological effects or injuries that theoretically might 
occur in mammals close to a strong sound source include stress, 
neurological effects, bubble formation, resonance effects, and other 
types of organ or tissue damage. It is possible that some marine mammal 
species (i.e., beaked whales) may be especially susceptible to injury 
and/or stranding when exposed to strong pulsed sounds. However, as 
discussed below, there is no definitive evidence that any of these 
effects occur even for marine mammals in close proximity to large 
arrays of airguns. It is especially unlikely that any effects of these 
types would occur during the present project given the brief duration 
of exposure of any given mammal and the proposed monitoring and 
mitigation measures (see below). The following subsections discuss in 
somewhat more detail the possibilities of Temporary Threshold Shift 
(TTS), Permanent Threshold Shift (PTS), and non-auditory physical 
effects.
    Temporary Threshold Shift - TTS is the mildest form of hearing 
impairment that can occur during exposure to a strong sound (Kryter, 
1985). While experiencing TTS, the hearing threshold rises and a sound 
must be stronger in order to be heard. At least in terrestrial mammals, 
TTS can last from minutes or hours to (in cases of strong TTS) days. 
For sound exposures at or somewhat above the TTS threshold, hearing 
sensitivity in both terrestrial and marine mammals recovers rapidly 
after exposure to the noise ends. Few data on sound levels and 
durations necessary to elicit mild TTS have been obtained for marine 
mammals, and none of the published data concern TTS elicited by 
exposure to multiple pulses of sound. Available data on TTS in marine 
mammals are summarized in Southall et al. (2007).
    For toothed whales exposed to single short pulses, the TTS 
threshold appears to be, to a first approximation, a function of the 
energy content of the pulse (Finneran et al., 2002, 2005). Given the 
available data, the received level of a single seismic pulse (with no 
frequency weighting) might need to be approximately 186 dB re 1 
microPa\2.\s (i.e., 186 dB SEL or approximately 221-226 dB pk-pk) in 
order to produce brief, mild TTS. Exposure to several strong seismic 
pulses that each have received levels near 175-180 dB SEL might result 
in slight TTS in a small odontocete, assuming the TTS threshold is (to 
a first approximation) a function of the total received pulse energy. 
The distance from the Langseth's airguns at which the received energy 
level (per pulse) would be expected to be [gteqt]175-180 dB SEL are the 
distances shown in the 190 dB re 1 microPa (rms) column in Table 3 of 
L-DEO's application and Table 1 above (given that the rms level is 
approximately 10-15 dB higher than the SEL value for the same pulse). 
Seismic pulses with received energy levels [gteqt]175-180 dB SEL (190 
dB re 1 microPa (rms)) are expected to be restricted to radii no more 
than 140-200 m (459-656 ft) around the airguns. The specific radius 
depends on the number of airguns, the depth of the water, and the tow 
depth of the airgun array. For an odontocete closer to the surface, the 
maximum radius with [gteqt]175-180 dB SEL or [gteqt]190 dB re 1 microPa 
(rms) would be smaller.
    The above TTS information for odontocetes is derived from studies 
on the bottlenose dolphin and beluga. There is not published TTS 
information for other types of cetaceans. However, preliminary evidence 
from harbor porpoise exposed to airgun sound suggests that its TTS 
threshold may have been lower (Lucke et al. 2007).
    For baleen whales, there are no data, direct or indirect, on levels 
or properties of sound required to induce TTS. The frequencies to which 
baleen whales are most sensitive are lower than those for odontocetes, 
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. In any 
event, no cases of TTS are expected given three considerations: (1) the 
relatively low abundance of baleen whales expected in the planned study 
areas; (2) the strong likelihood that baleen whales would avoid the 
approaching airguns (or vessel) before being exposed to levels high 
enough for there to be any possibility of TTS; and (3) the mitigation 
measures that are planned.
    In pinnipeds, TTS thresholds associated with exposure to brief 
pulses (single or multiple) of underwater sound have not been measured. 
Initial evidence from prolonged (non-pulse) exposures suggested that 
some pinnipeds may incur TTS at somewhat lower received levels than do 
small odontocetes exposed for similar durations (Kastak et al., 1999, 
2005; Ketten et al., 2001; Au et al., 2000). The TTS threshold for 
pulsed sounds has been indirectly estimated as being an SEL of 
approximately 171 dB re 1 microPa\2.\ s (Southall et al., 2007), which 
would be equivalent to a single pulse with received level approximately 
181-186 re 1 microPa (rms), or a series of pulses for which the highest 
rms values are a few dB lower. Corresponding values for California sea 
lions and northern elephant seals are likely to be higher (Kastak et 
al., 2005).
    A marine mammal within a radius of less than 100 m (328 ft) around 
a typical

[[Page 45415]]

large array of operating airguns might be exposed to a few seismic 
pulses with levels of greater than or equal to 205 dB, and possibly 
more pulses if the mammal moved with the seismic vessel. (As noted 
above, most cetacean species tend to avoid operating airguns, although 
not all individuals do so.) In addition, ramping up airgun arrays, 
which is standard operational protocol for large airgun arrays, should 
allow cetaceans to move away form the seismic source and to avoid being 
exposed to the full acoustic output of the airgun array. Even with a 
large airgun array, it is unlikely that the cetaceans would be exposed 
to airgun pulses at a sufficiently high level for a sufficiently long 
period to cause more than mild TTS, given the relative movement of the 
vessel and the marine mammal. The potential for TTS is much lower in 
this project. With a large array of airguns, TTS would be most likely 
in any odontocetes that bow-ride or otherwise linger near the airguns. 
While bow-riding, odontocetes would be at or above the surface, and 
thus not exposed to strong pulses given the pressure-release effect at 
the surface. However, bow-riding animals generally dive below the 
surface intermittently. If they did so while bow-riding near airguns, 
they would be exposed to strong sound pulses, possibly repeatedly. If 
some cetaceans did incur TTS through exposure to airgun sounds, this 
would very likely be mild, temporary, and reversible.
    To avoid the potential for injury, NMFS has determined that 
cetaceans and pinnipeds should not be exposed to pulsed underwater 
noise at received levels exceeding, respectively, 180 and 190 dB re 1 
microPa (rms). As summarized above, data that are now available imply 
that TTS is unlikely to occur unless odontocetes (and probably 
mysticetes as well) are exposed to airgun pulses stronger than 180 dB 
re 1 microPa (rms).
    Permanent Threshold Shift - When PTS occurs, there is physical 
damage to the sound receptors in the ear. In some cases, there can be 
total or partial deafness, while in other cases, the animal has an 
impaired ability to hear sounds in specific frequency ranges.
    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 TTS, there has been further speculation about the 
possibility that some individuals occurring very close to airguns might 
incur PTS. Single or occasional occurrences of mild TTS are not 
indicative of permanent auditory damage in terrestrial mammals. 
Relationships between TTS and PTS thresholds have not been studied in 
marine mammals, but are assumed to be similar to those in humans and 
other terrestrial mammals. PTS might occur at a received sound level at 
least several decibels above that inducing mild TTS if the animal were 
exposed to strong sound pulses with rapid rise time (see Appendix B (f) 
of L-DEO's application). The specific difference between the PTS and 
TTS thresholds has not been measured for marine mammals exposed to any 
sound type. However, 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.
    On an SEL basis, Southall et al. (2007) estimated that received 
levels would need to exceed the TTS threshold by at least 15 dB for 
there to be risk of PTS. Thus, for cetaceans they estimate that the PTS 
threshold might be a cumulative SEL (for the sequence of received 
pulses) of approximately 198 dB re 1 microPa\2.\s. Additional 
assumptions had to be made to derive a corresponding estimate for 
pinnipeds. Southall et al. (2007) estimate that the PTS threshold could 
be a cumulative SEL of approximately 186 dB 1 Pa2 s in the harbor seal; 
for the California sea lion and northern elephant seal the PTS 
threshold would probably be higher. Southall et al. (2007) also note 
that, regardless of the SEL, there is concern about the possibility of 
PTS if a cetacean or pinniped receives one or more pulses with peak 
pressure exceeding 230 or 218 dB re 1 microPa (3.2 bar\.\ m, 0-pk), 
which would only be found within a few meters of the largest (360-
in\3\) airguns in the planned airgun array (Caldwell and Dragoset, 
2000). A peak pressure of 218 dB re 1 microPa could be received 
somewhat farther away; to estimate that specific distance, one would 
need to apply a model that accurately calculates peak pressures in the 
near-field around an array of airguns.
    Given the higher level of sound necessary to cause PTS as compared 
with TTS, it is considerably less likely that PTS could occur. In fact, 
even the levels immediately adjacent to the airguns may not be 
sufficient to induce PTS, especially because a mammal would not be 
exposed to more than one strong pulse unless it swam immediately 
alongside the airgun for a period longer than the inter-pulse interval. 
Baleen whales 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), power downs, and shut downs of the 
airguns when mammals are seen within the EZ will minimize the already 
minimal probability of exposure of marine mammals to sounds strong 
enough to induce PTS.
    Non-auditory Physiological Effects - Non-auditory physiological 
effects or injuries that theoretically might occur in marine mammals 
exposed to strong underwater sound include stress, neurological 
effects, bubble formation, resonance effects, and other types of organ 
or tissue damage (Cox et al., 2006.; Southall et al., 2007). However, 
studies examining such effects are limited. If any such effects do 
occur, they would probably be limited to unusual situations when 
animals might be exposed at close range for unusually long periods, 
when sound is strongly channeled with less-than-normal propagation 
loss, or when dispersal of the animals is constrained by shorelines, 
shallows, etc. Airgun pulses, because of their brevity and 
intermittence, are less likely to trigger resonance or bubble formation 
than are m