Takes of Marine Mammals Incidental to Specified Activities; Marine Geophysical Survey in the Western Gulf of Alaska, June to August, 2011, 26255-26279 [2011-11152]

Agencies

• DEPARTMENT OF COMMERCE
• National Oceanic and Atmospheric Administration

[Federal Register Volume 76, Number 88 (Friday, May 6, 2011)]
[Notices]
[Pages 26255-26279]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 2011-11152]


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DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

RIN 0648-XA343


Takes of Marine Mammals Incidental to Specified Activities; 
Marine Geophysical Survey in the Western Gulf of Alaska, June to 
August, 2011

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 the Lamont-Doherty Earth 
Observatory of Columbia University (L-DEO) for an Incidental Harassment 
Authorization (IHA) to take marine mammals, by harassment, incidental 
to conducting a marine geophysical survey in the western Gulf of Alaska 
(GOA), June to August, 2011. 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, 16 species 
of marine mammals during the specified activity.

DATES: Comments and information must be received no later than June 6, 
2011.

ADDRESSES: Comments on the application should be addressed to P. 
Michael Payne, Chief, Permits, Conservation and Education Division, 
Office of Protected Resources, National Marine Fisheries Service, 1315 
East-West Highway, Silver Spring, MD 20910. The mailbox address for 
providing e-mail comments is ITP.Goldstein@noaa.gov. NMFS is not 
responsible for e-mail comments sent to addresses other than the one 
provided here. Comments sent via e-mail, including all attachments, 
must not exceed a 10-megabyte file size.
    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 L-DEO, with support from the National Science Foundation (NSF), 
has prepared a draft ``Environmental Assessment (EA) of a Marine 
Geophysical Survey by the R/V Marcus G. Langseth in the western Gulf of 
Alaska, July-August 2011,'' prepared by LGL Ltd., Environmental 
Research Associates (LGL), on behalf of L-DEO, which is also available 
at the same internet address. 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 Jolie Harrison, 
Office of Protected Resources, NMFS, (301) 713-2289, ext. 172.

SUPPLEMENTARY INFORMATION:

Background

    Section 101(a)(5)(D) of the MMPA (16 U.S.C. 1371 (a)(5)(D)) directs 
the Secretary of Commerce (Secretary) 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 the 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 (where relevant). 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 requirements pertaining to the mitigation, 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

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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 April 1, 2010, from L-DEO for the 
taking by harassment, of marine mammals, incidental to conducting a 
marine geophysical survey in the western GOA within the U.S. Exclusive 
Economic Zone (EEZ) in depths from approximately 25 meters (m) (82 feet 
[ft]) to greater than 6,000 m (19,685 ft). The cruise was postponed in 
2010 and rescheduled for 2011. NMFS received a revised application on 
March 4, 2011 from L-DEO. L-DEO plans to conduct the proposed survey 
from approximately June 28 to August 4, 2011.
    L-DEO plans to use one source vessel, the R/V Marcus G. Langseth 
(Langseth) and a seismic airgun array to collect seismic reflection and 
refraction profiles from the Shumagin Islands to east of Kodiak Island 
in the GOA. 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 a short-term behavioral disturbance for marine mammals in the 
survey area. This is the principal means of marine mammal taking 
associated with these activities and L-DEO has requested an 
authorization to take 16 species of marine mammals by Level B 
harassment. Take is not expected to result from the use of the MBES or 
SBP, for reasons discussed in this notice; nor is take expected to 
result from collision with the vessel because it is a single vessel 
moving at a relatively slow speed during seismic acquisition within the 
survey, for a relatively short period of time (approximately 38 days). 
It is likely that any marine mammal would be able to avoid the vessel.

Description of the Specified Activity

    L-DEO's proposed seismic survey in the western GOA, from the 
Shumagin Islands to east of Kodiak Island, will take place during June 
to August, 2011, in the area 52.5[deg] to 59[deg] North, 147.5[deg] to 
161[deg] West (see Figure 1 of the IHA application). The proposed 
seismic survey will take place in water depths ranging from 25 m (82 
ft) to greater than 6,000 m (82 to 19,685 ft) and consists of 
approximately 2,553 kilometers (km) (1,378.5 nautical miles [nmi]) of 
transect lines in the study area. The project is scheduled to occur 
from approximately June 28 to August 4, 2011. Some minor deviation from 
these dates is possible, depending on logistics and weather.
    The proposed seismic survey will collect seismic reflection and 
refraction data to characterize the subduction zone off southern 
Alaska, which produces large and destructive earthquakes. The data from 
this study will be used to: (1) Estimate the size of the seismogenic 
zone, the portion of the fault that controls the magnitude of 
earthquakes, and (2) provide critical information on how the properties 
of the seismogenic zone change along the subduction zone such that some 
areas produce large earthquakes and others do not. The proposed study 
focuses on the Semidi segment, whose earthquake recurrence interval is 
50 to 75 years and which last ruptured in 1938.
    The survey will involve one source vessel, the Langseth. The 
Langseth will deploy an array of 36 airguns as an energy source at a 
tow depth of 12 m (39.4 ft). The receiving system will consist of two 8 
km (4.3 nmi) long hydrophone streamers and/or 21 ocean bottom 
seismometers (OBSs). As the airgun is towed along the survey lines, the 
hydrophone streamers will receive the returning acoustic signals and 
transfer the data to the on-board processing system. The OBSs record 
the returning acoustic signals internally for later analysis.
    The planned seismic survey (e.g., equipment testing, startup, line 
changes, repeat coverage of any areas, and equipment recovery) will 
consist of approximately 2,553 km of transect lines in the western GOA 
survey area (see Figure 1 of the IHA application). Just over half of 
the survey (1,363 km [736 nmi]) will take place in water deeper than 
1,000 m; 30% or 754 km (407.1 nmi) will be surveyed in intermediate 
depth (100 to 1,000 m) water; and 17% (463 km [250 nmi]) will take 
place in water less than 100 m deep. Approximately 30 km (16.2 nmi) of 
seismic surveying will occur in water less than 40 m deep. A refraction 
survey using OBSs will take place along two lines (lines 3 and 5). 
Following the refraction survey, a multichannel (MCS) survey using two 
hydrophone streamers will take place along all of the transect lines. 
Thus, lines 3 and 5 will be surveyed twice. In addition to the 
operations of the airgun array, a Kongsberg EM 122 MBES and Knudsen 
320B SBP will also be operated from the Langseth continuously 
throughout the cruise. There will be additional seismic operations 
associated with equipment testing, start-up, and possible line changes 
or repeat coverage of any areas where initial data quality is sub-
standard. In L-DEO's calculations, 25% has been added for those 
additional operations.
    All planned geophysical data acquisition activities will be 
conducted by L-DEO, the Langseth's operator, with on-board assistance 
by the scientists who have proposed the study. The Principal 
Investigators are Drs. Donna Shillington, Spahr Webb, and Mladen 
Nedimovic, all of L-DEO. The vessel will be self-contained, and the 
crew will live aboard the vessel for the entire cruise.

Vessel Specifications

    The Langseth, owned by the National Science Foundation, will tow 
the 36 airgun array, as well as the hydrophone streamer, along 
predetermined lines. The Langseth will also deploy and retrieve the 
OBSs. When the Langseth is towing the airgun array and the hydrophone 
streamer, the turning rate of the vessel is limited to five degrees per 
minute. Thus, the maneuverability of the vessel is limited during 
operations with the streamer.
    The vessel has a length of 71.5 m (235 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. 
The Langseth was designed as a seismic research vessel with a 
propulsion system designed to be as quiet as possible to avoid 
interference with the seismic signals emanating from the airgun array. 
The ship is powered by two 3,550 horsepower (hp) Bergen BRG-6 diesel 
engines which drive two propellers directly. Each propeller has four 
blades and the shaft typically rotates at 750 revolutions per minute. 
The vessel also has an 800 hp bowthruster, which is not used during 
seismic acquisition. The Langseth's operation speed during seismic 
acquisition is typically 7.4 to 9.3 km per

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hour (hr) (km/hr) (4 to 5 knots [kts]). When not towing seismic survey 
gear, the Langseth typically cruises at 18.5 km/hr (10 kts). The 
Langseth has a range of 25,000 km (13,499 nmi) (the distance the vessel 
can travel without refueling).
    The vessel also has an observation tower from which protected 
species visual observers (PSVO) will watch for marine mammals before 
and during the proposed airgun operations. When stationed on the 
observation platform, the PSVO's eye level will be approximately 21.5 m 
(71 ft) above sea level providing the PSVO an unobstructed view around 
the entire vessel.

Acoustic Source Specifications

Seismic Airguns

    The Langseth will deploy a 36 airgun array, with a total volume of 
approximately 6,600 cubic inches (in\3\). The airgun array will consist 
of a mixture of Bolt 1500LL and Bolt 1900LLX airguns ranging in size 
from 40 to 360 in\3\, with a firing pressure of 1,900 pounds per square 
inch. The airguns will be configured as four identical linear arrays or 
``strings'' (see Figure 2 of the application). Each string will have 10 
airguns, the first and last airguns in the strings are spaced 16 m (52 
ft) apart. Of the 10 airguns, nine airguns in each string will be fired 
simultaneously, whereas 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 area of approximately 24x16 m (78.7 x 
52.5 ft) behind the Langseth and will be towed approximately 100 m (328 
ft) behind the vessel. The shot interval will be relatively short, 50 m 
(164 ft) or approximately 22 seconds (s), for the MCS survey or 
reflection surveying and relatively longer, 280 m (918.6 ft) or 
approximately 120 s, when recording data on the OBSs during the 
refraction survey. The firing pressure of the array is 1,900 pounds per 
square inch (psi). During firing, a brief (approximately 0.1 s) pulse 
sound is emitted; the airguns will be silent during the intervening 
periods. The dominant frequency components range from two to 188 Hertz 
(Hz).
    The tow depth of the array will be 12 m (39.4 ft) during OBS 
refraction and MCS surveys. Because the actual source is a distributed 
sound source (36 airguns) rather than a single point source, the 
highest sound measurable at any location in the water will be less than 
the nominal source level. In addition, the effective source level for 
sound propagating in near-horizontal directions will be substantially 
lower than the nominal source level applicable to downward propagation 
because of the directional nature of the sound from the airgun array.

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 the amount of sound 
transmitted in the near horizontal directions is reduced. However, the 
airgun array also emits 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) and the rms value for a 
given airgun pulse is typically 16 dB re 1 [mu]Pa lower than the peak-
to-peak value. However, the difference between rms and peak or peak-to-
peak values for a given pulse depends on the frequency content and 
duration of the pulse, among other factors.
    Accordingly, L-DEO has predicted the received sound levels in 
relation to distance and direction from the 36 airgun array and the 
single Bolt 1900LL 40 in\3\ airgun, which will be used during power-
downs. A detailed description of L-DEO's modeling for marine seismic 
source arrays for species mitigation is provided in Appendix A of L-
DEO's EA. 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 L-DEO's EA discusses the characteristics of the 
airgun pulses. NMFS refers the reviewers to the application and EA 
documents for additional information.

Predicted Sound Levels for the Airguns

    Tolstoy et al., (2009) reported results for propagation 
measurements of pulses from the Langseth's 36 airgun, 6,600 in\3\ array 
in shallow-water (approximately 50 m [164 ft]) and deep-water depths 
(approximately 1,600 m [5,249 ft]) in the Gulf of Mexico in 2007 and 
2008. L-DEO has used these reported and corrected empirical values to 
determine exclusion zones (EZs) for the 36 airgun array and modeled 
measurements for the single airgun; to designate EZs for purposes of 
mitigation, and to estimate take for marine mammals in the GOA.
    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. Empirical measurements from the Gulf of Mexico 
were used for GOA and those measurements were used to determine the 
algorithm for the model. The empirical data for deep water (greater 
than 1,000 m; 3,280 ft) indicated that the L-DEO model (as applied to 
the Langseth's 36 airgun array) overestimated the received sound levels 
at a given distance. For intermediate depths, a correction of the 
empirical measurements for shallow and deep depths were made.
    Using the corrected measurements (airgun array) or model (single 
airgun), Table 1 (below) shows the distances at which three rms sound 
levels are expected to be received from the 36 airgun array and a 
single airgun. The 180 and 190 dB re 1 [mu]Pa (rms) distances are the 
safety criteria for potential Level A harassment as specified by NMFS 
(2000) and are applicable to cetaceans and pinnipeds, respectively. If 
marine mammals are detected within or about to enter the appropriate 
EZ, the airguns will be powered-down (or shut-down, if necessary) 
immediately.
    Table 1 summarizes the predicted distances at which sound levels 
(160,

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180, and 190 dB [rms]) are expected to be received from the 36 airgun 
array and a single airgun operating in deep, intermediate, and shallow 
water depths.

 Table 1--Measured (array) or predicted (single airgun) distances to which sound levels >= 190, 180, and 160 dB
re: 1 [mu]Pa (rms) could be received in various water depth categories during the proposed survey in the western
                                           GOA, June to August, 2011.
----------------------------------------------------------------------------------------------------------------
                                                                             Predicted RMS radii distances  (m)
       Source and volume          Tow depth  (m)      Water depth  (m)    --------------------------------------
                                                                              190 dB       180 dB       160 dB
----------------------------------------------------------------------------------------------------------------
Single Bolt airgun (40 in\3\)..  6 to 12.........  Deep (> 1,000 ).......           12           40          385
                                                   Intermediate (100 to             18           60          578
                                                    1,000).                        150          296        1,050
                                                   Shallow (< 100).......
4 Strings, 36 airguns (6,600     12..............  Deep (> 1,000)........          460        1,100        4,400
 in\3\).                                           Intermediate (100 to            615        1,810       13,935
                                                    1,000).                        770        2,520       23,470
                                                   Shallow (<100)........
----------------------------------------------------------------------------------------------------------------

OBS Description and Deployment

    The study will commence with a refraction survey using OBSs. 
Approximately 21 OBSs will be deployed by the Langseth at the beginning 
of the survey along one transect. After data are collected along this 
transect line, the OBSs will be picked up, and they will be re-deployed 
along the next refraction line. At the end of the refraction survey 
(approximately 3 days of seismic operations), all OBSs will be 
retrieved. OBS deployment is expected to take approximately 3 days, and 
OBS retrieval will take approximately 5 days.
    Scripps Institution of Oceanography LC4x4 OBSs will be used during 
the cruise. This OBS has a volume of approximately 1 m\3\, with an 
anchor that consists of a large piece of steel grating (approximately 1 
m\2\). Once an OBS is ready to be retrieved, an acoustic release 
transponder interrogates the OBS at a frequency of 9 to 11 kHz, and a 
response is received at a frequency of 9 to 13 kHz. The burn-wire 
release assembly is then activated, and the instrument is released from 
the anchor to float to the surface.
    Along with the airgun operations, two additional acoustical data 
acquisition systems will be operated from the Langseth continuously 
during the survey. The ocean floor will be mapped with the Kongsberg EM 
122 MBES and a Knudsen 320B SBP. These sound sources will be operated 
continuously from the Langseth throughout the cruise.

MBES

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

SBP

    The Langseth will also operate a Knudsen 320B SBP continuously 
throughout the cruise simultaneously with the MBES to map and provide 
information about the sedimentary features and bottom topography. The 
beam is transmitted as a 27[deg] cone, which is directed downward by a 
3.5 kHz transducer in the hull of the Langseth. The maximum output is 
1,000 watts (204 dB re 1 [mu]Pa), but in practice, the output varies 
with water depth. The pulse interval is one second, but a common mode 
of operation is to broadcast five pulses at one second intervals 
followed by a five 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 expects these disturbances to be temporary and 
result, at worst, in a temporary modification in behavior and/or low-
level physiological effects (Level B harassment) of small numbers of 
certain species of marine mammals. NMFS does not expect that the 
movement of the Langseth, during the conduct of the seismic survey, has 
the potential to harass marine mammals because of the relatively slow 
operation speed of the vessel (4.6 knots [kts]; 8.5 km/hr; 5.3 mph) 
during seismic acquisition.

Description of the Proposed Dates, Duration, and Specified Geographic 
Region

    The survey will occur in the western GOA in the area 52.5[deg] to 
59[deg] North, 147.5 to 161[deg] West. The seismic survey will take 
place in water depths of 25 m to greater than 6,000 m. The Langseth 
will depart from Kodiak, Alaska on approximately June 28, 2011. The 
program will start with a refraction survey using OBSs. Approximately 
21 OBSs will be deployed along one line; the OBSs will then be 
retrieved and re-deployed along the next refraction line. OBS 
deployment will take approximately three days and recovery will take 
approximately five days; there will be a total of approximately three 
days of refraction shooting. Following the refraction survey, the MCS 
survey will take place using the two streamers. MCS and airgun 
deployment will take approximately three days, and there will be 
approximately 13 days of MCS operations. Upon completion of seismic 
operations, all gear will be picked up and the vessel will travel to 
Dutch Harbor, for arrival on approximately August 4, 2011. Seismic 
operations in the study area will be carried out for approximately 16 
days. Some minor deviation from this schedule is possible, depending on 
logistics and weather (i.e., the cruise may depart earlier or be 
extended due to poor weather; there could be an additional three days 
of seismic operations if collected data are deemed to be of substandard 
quality).

[[Page 26259]]

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

    Twenty-five marine mammal species (18 cetacean, 6 pinniped, and the 
sea otter) are known to or could occur in the GOA study area. Several 
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 (Eubalaena japonica), humpback (Megaptera novaeangliae), 
sei (Balaenoptera borealis), fin (Balaenoptera physalus), blue 
(Balaenoptera musculus), and sperm (Physeter macrocephalus) whales, as 
well as the Cook Inlet distinct population segment (DPS) of beluga 
whales (Dephinapterus leucas) and the western stock of Steller sea 
lions (Eumetopias jubatus). The eastern stock of Steller sea lions is 
listed as threatened, as is the southwest Alaska DPS of the sea otter 
(Enhydra lutris).
    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, sea lions, and 
walrus), and fissipeds (sea otter). Cetaceans and pinnipeds are the 
subject of the IHA application to NMFS. Walrus sightings are rare in 
the GOA. Sea otters generally inhabit nearshore areas inside the 40 m 
(131.2 ft) depth contour (Riedman and Estes, 1990) and could be 
encountered in coastal waters, but likely would not be encountered in 
the deep, offshore waters of the study area. The sea otter and Pacific 
walrus are two marine mammal species mentioned in this document that 
are managed by the U.S. Fish and Wildlife Service (USFWS) and are not 
considered further in this analysis; all others are managed by NMFS. 
The Cook Inlet DPS of beluga whales, California sea lions (Zalophus c. 
californianus), northern fur seals (Callorhinus ursinus), and northern 
elephant seals (Mirounga angustirostris) are not likely to be found in 
the waters of the survey area.
    Table 2 (below) presents information on the abundance, 
distribution, population status, conservation status, and density of 
the marine mammals that may occur in the proposed survey area during 
June to August, 2011.
BILLING CODE 3510-22-P

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BILLING CODE 3510-22-C
    Refer to Section III and IV of L-DEO's application for detailed 
information regarding the abundance and distribution, population 
status, and life history and behavior of these species and their 
occurrence in the proposed project area. The application also presents 
how L-DEO calculated the estimated densities for the marine mammals in 
the proposed survey area. NMFS has reviewed these data and determined 
them to be the best available scientific information for the purposes 
of the proposed IHA.

Potential Effects on Marine Mammals

    Acoustic stimuli generated by the operation of the airguns, which 
introduce sound into the marine environment, may have the potential to 
cause Level B harassment of marine mammals in the proposed survey area. 
The effects of sounds from airgun operations might include one or more 
of the following: Tolerance, masking of natural sounds, behavioral 
disturbance, temporary or permanent hearing impairment, or non-auditory 
physical or physiological effects (Richardson et al., 1995; Gordon et 
al., 2004; Nowacek et al., 2007; Southall et al., 2007).
    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. 
Based on the available data and studies described here, some behavioral 
disturbance is expected, but NMFS expects the disturbance to be 
localized and short-term.

Tolerance to Sound

    Studies on marine mammals' tolerance to sound in the natural

[[Page 26263]]

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

Masking 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. Because of the intermittent nature and low duty cycle of 
seismic airgun pulses, animals can emit and receive sounds in the 
relatively quiet intervals between pulses. However, in some situations, 
reverberation occurs for much or the entire interval between pulses 
(e.g., Simard et al., 2005; Clark and Gagnon, 2006) which could mask 
calls. Some baleen and toothed whales are known to continue calling in 
the presence of seismic pulses, and their calls can usually be heard 
between the seismic pulses (e.g., Richardson et al., 1986; McDonald et 
al., 1995; Greene et al., 1999; Nieukirk et al., 2004; Smultea et al., 
2004; Holst et al., 2005a,b, 2006; and Dunn and Hernandez, 2009). 
However, Clark and Gagnon (2006) reported that fin whales in the 
northeast Pacific Ocean went silent for an extended period starting 
soon after the onset of a seismic survey in the area. Similarly, there 
has been one report that sperm whales ceased calling when exposed to 
pulses from a very distant seismic ship (Bowles et al., 1994). However, 
more recent studies found that they continued calling in the presence 
of seismic pulses (Madsen et al., 2002; Tyack et al., 2003; Smultea et 
al., 2004; Holst et al., 2006; and Jochens et al., 2008). Dolphins and 
porpoises commonly are heard calling while airguns are operating (e.g., 
Gordon et al., 2004; Smultea et al., 2004; Holst et al., 2005a, b; and 
Potter et al., 2007). The sounds important to small odontocetes are 
predominantly at much higher frequencies than are the 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. 
Refer to Appendix B(4) of L-DEO's EA for a more detailed discussion of 
masking effects on marine mammals.

Behavioral Disturbance

    Disturbance includes a variety of effects, including subtle to 
conspicuous changes in behavior, movement, and displacement. Reactions 
to sound, if any, depend on species, state of maturity, experience, 
current activity, reproductive state, time of day, and many other 
factors (Richardson et al., 1995; Wartzok et al., 2004; Southall et 
al., 2007; Weilgart, 2007). If a marine mammal does react briefly to an 
underwater sound by changing its behavior or moving a small distance, 
the impacts of the change are unlikely to be significant to the 
individual, let alone the stock or population. However, if a sound 
source displaces marine mammals from an important feeding or breeding 
area for a prolonged period, impacts on individuals and populations 
could be significant (e.g., Lusseau and Bejder, 2007; Weilgart, 2007). 
Given the many uncertainties in predicting the quantity and types of 
impacts of noise on marine mammals, it is common practice to estimate 
how many mammals would be present within a particular distance of 
industrial activities and/or exposed to a particular level of 
industrial sound. In most cases, this approach likely overestimates the 
numbers of marine mammals that would be affected in some biologically-
important manner.
    The sound criteria used to estimate how many marine mammals might 
be disturbed to some biologically-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, but for many species there are no data on 
responses to marine seismic surveys.
    Baleen Whales--Baleen whales generally tend to avoid operating 
airguns, but avoidance radii are quite variable (reviewed in Richardson 
et al., 1995). Whales are often reported to show no overt reactions to 
pulses from large arrays of airguns at distances beyond a few kms, even 
though the airgun pulses remain well above ambient noise levels out to 
much longer distances. However, as reviewed in Appendix B (5) of L-
DEO's EA, baleen whales exposed to strong noise pulses from airguns 
often react by deviating from their normal migration route and/or 
interrupting their feeding and moving away. In the cases of migrating 
gray and bowhead whales, the observed changes in behavior appeared to 
be of little or no biological consequence to the animals (Richardson, 
et al., 1995). They simply avoided the sound source by displacing their 
migration route to varying degrees, but within the natural boundaries 
of the migration corridors.
    Studies of gray, bowhead, and humpback whales have shown that 
seismic pulses with received levels of 160 to 170 dB re 1 [mu]Pa (rms) 
seem to cause obvious avoidance behavior in a substantial fraction of 
the animals exposed (Malme et al., 1986, 1988; Richardson et al., 
1995). In many areas, seismic pulses from large arrays of airguns 
diminish to those levels at distances ranging from four 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 L-

[[Page 26264]]

DEO's EA have shown that some species of baleen whales, notably bowhead 
and humpback whales, at times, show strong avoidance at received levels 
lower than 160 to 170 dB re 1 [mu]Pa (rms).
    McCauley et al. (1998, 2000a) studied the responses of humpback 
whales off western Australia to a full-scale seismic survey with a 16 
airgun array (2,678 in\3\) and to a single airgun (20 in\3\) with 
source level of 227 dB re 1 [micro]Pa (p-p). In the 1998 study, they 
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. In the 2000 study, they 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 (rms) for 
humpback pods containing females, and at the mean closest point of 
approach distance the received level was 143 dB re 1 [mu]Pa (rms). 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 (328 to 1,312 ft), where the maximum 
received level was 179 dB re 1 [mu]Pa (rms).
    Data collected by observers during several seismic surveys in the 
Northwest Atlantic showed that sighting rates of humpback whales were 
significantly greater during non-seismic periods compared with periods 
when a full array was operating (Moulton and Holst, 2010). In addition, 
humpback whales were more likely to swim away and less likely to swim 
towards a vessel during seismic vs. non-seismic periods (Moulton and 
Holst, 2010).
    Humpback whales on their summer feeding grounds in southeast Alaska 
did not exhibit persistent avoidance when exposed to seismic pulses 
from a 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 dB re 1 [mu]Pa (rms). However, Moulton and Holst 
(2010) reported that humpback whales monitored during seismic surveys 
in the Northwest Atlantic had lower sighting rates and were most often 
seen swimming away from the vessel during seismic periods compared with 
periods when airguns were silent.
    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 L-DEO's EA). However, more recent 
research on bowhead whales (Miller et al., 2005; Harris et al., 2007) 
corroborates earlier evidence that, during the summer feeding season, 
bowheads are not as sensitive to seismic sources. Nonetheless, subtle 
but statistically significant changes in surfacing-respiration-dive 
cycles were evident upon statistical analysis (Richardson et al., 
1986). In the summer, bowheads typically begin to show avoidance 
reactions at received levels of about 152 to 178 dB re 1 [mu]Pa 
(Richardson et al., 1986, 1995; Ljungblad et al., 1988; Miller et al., 
2005).
    Reactions of migrating and feeding (but not wintering) gray whales 
to seismic surveys have been studied. Malme et al. (1986, 1988) studied 
the responses of feeding eastern Pacific gray whales to pulses from a 
single 100 in\3\ airgun off St. Lawrence Island in the northern Bering 
Sea. They estimated, based on small sample sizes, that 50 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 [micro]Pa (rms). Those findings were generally consistent with 
the results of experiments conducted on larger numbers of gray whales 
that were migrating along the California coast (Malme et al., 1984; 
Malme and Miles, 1985), and western Pacific gray whales feeding off 
Sakhalin Island, Russia (Wursig et al., 1999; Gailey et al., 2007; 
Johnson et al., 2007; Yazvenko et al., 2007a, b), along with data on 
gray whales off British Columbia (Bain and Williams, 2006).
    Various species of Balaenoptera (blue, sei, fin, and minke whales) 
have occasionally been seen in areas ensonified by airgun pulses 
(Stone, 2003; MacLean and Haley, 2004; Stone and Tasker, 2006), and 
calls from blue and fin whales have been localized in areas with airgun 
operations (e.g., McDonald et al., 1995; Dunn and Hernandez, 2009; 
Castellote et al., 2010). Sightings by observers on seismic vessels off 
the United Kingdom from 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). Castellote et al. (2010) 
reported that singing fin whales in the Mediterranean moved away from 
an operating airgun array.
    Ship-based monitoring studies of baleen whales (including blue, 
fin, sei, minke, and humpback whales) in the Northwest Atlantic found 
that overall, this group had lower sighting rates during seismic vs. 
non-seismic periods (Moulton and Holst, 2010). Baleen whales as a group 
were also seen significantly farther from the vessel during seismic 
compared with non-seismic periods, and they were more often seen to be 
swimming away from the operating seismic vessel (Moulton and Holst, 
2010). Blue and minke whales were initially sighted significantly 
farther from the vessel during seismic operations compared to non-
seismic periods; the same trend was observed for fin whales (Moulton 
and Holst, 2010). Minke whales were most often observed to be swimming 
away from the vessel when seismic operations were underway (Moulton and 
Holst, 2010).
    Data on short-term reactions by cetaceans to impulsive noises are 
not necessarily indicative of long-term or biologically significant 
effects. It is not known whether impulsive sounds affect reproductive 
rate or distribution and

[[Page 26265]]

habitat use in subsequent days or years. However, gray whales have 
continued to migrate annually along the west coast of North America 
with substantial increases in the population over recent years, despite 
intermittent seismic exploration (and much ship traffic) in that area 
for decades (Appendix A in Malme et al., 1984; Richardson et al., 1995; 
Allen and Angliss, 2010). The western Pacific gray whale population did 
not seem affected by a seismic survey in its feeding ground during a 
previous year (Johnson et al., 2007). Similarly, bowhead whales have 
continued to travel to the eastern Beaufort Sea each summer, and their 
numbers have increased notably, despite seismic exploration in their 
summer and autumn range for many years (Richardson et al., 1987; Allen 
and Angliss, 2010).
    Toothed Whales--Little systematic information is available about 
reactions of toothed whales to noise pulses. Few studies similar to the 
more extensive baleen whale/seismic pulse work summarized above and (in 
more detail) in Appendix B of L-DEO's EA have been reported for toothed 
whales. However, there are recent systematic studies on sperm whales 
(e.g., Gordon et al., 2006; Madsen et al., 2006; Winsor and Mate, 2006; 
Jochens et al., 2008; Miller et al., 2009). There is an increasing 
amount of information about responses of various odontocetes to seismic 
surveys based on monitoring studies (e.g., Stone, 2003; Smultea et al., 
2004; Moulton and Miller, 2005; Bain and Williams, 2006; Holst et al., 
2006; Stone and Tasker, 2006; Potter et al., 2007; Hauser et al., 2008; 
Holst and Smultea, 2008; Weir, 2008; Barkaszi et al., 2009; Richardson 
et al., 2009; Moulton and Holst, 2010).
    Seismic operators and marine mammal observers on seismic vessels 
regularly see dolphins and other small toothed whales near operating 
airgun arrays, but in general there is a tendency for most delphinids 
to show some avoidance of operating seismic vessels (e.g., Goold, 
1996a,b,c; Calambokidis and Osmek, 1998; Stone, 2003; Moulton and 
Miller, 2005; Holst et al., 2006; Stone and Tasker, 2006; Weir, 2008; 
Richardson et al., 2009; Barkaszi et al., 2009; Moulton and Holst, 
2010). Some dolphins seem to be attracted to the seismic vessel and 
floats, and some ride the bow wave of the seismic vessel even when 
large arrays of airguns are firing (e.g., Moulton and Miller, 2005). 
Nonetheless, small toothed whales more often tend to head away, or to 
maintain a somewhat greater distance from the vessel, when a large 
array of airguns is operating than when it is silent (e.g., Stone and 
Tasker, 2006; Weir, 2008; Barry et al., 2010; Moulton and Holst, 2010). 
In most cases, the avoidance radii for delphinids appear to be small, 
on the order of one km or 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 show stronger avoidance of seismic 
operations than do Dall's porpoises (Stone, 2003; MacLean and Koski, 
2005; Bain and Williams, 2006; Stone and Tasker, 2006). Dall's 
porpoises seem relatively tolerant of airgun operations (MacLean and 
Koski, 2005; Bain and Williams, 2006), although they too have been 
observed to avoid large arrays of operating airguns (Calambokidis and 
Osmek, 1998; Bain and Williams, 2006). This apparent difference in 
responsiveness of these two porpoise species is consistent with their 
relative responsiveness to boat traffic and some other acoustic sources 
(Richardson et al., 1995; Southall et al., 2007).
    Most studies of sperm whales exposed to airgun sounds indicate that 
the sperm whale shows considerable tolerance of airgun pulses (e.g., 
Stone, 2003; Moulton et al., 2005, 2006a; Stone and Tasker, 2006; Weir, 
2008). In most cases the whales do not show strong avoidance, and they 
continue to call (see Appendix B of L-DEO's EA 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. In fact, Moulton and Holst 
(2010) reported 15 sightings of beaked whales during seismic studies in 
the Northwest Atlantic; seven of those sightings were made at times 
when at least one airgun was operating. There was little evidence to 
indicate that beaked whale behavior was affected by airgun operations; 
sighting rates and distances were similar during seismic and non-
seismic periods (Moulton and Holst, 2010).
    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 Stranding and Mortality section 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. 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 L-DEO's EA).
    Pinnipeds--Pinnipeds are not likely to show a strong avoidance 
reaction to the airgun array. Visual monitoring from seismic vessels 
has shown only slight (if any) avoidance of airguns by pinnipeds, and 
only slight (if any) changes in behavior, see Appendix B(5) of L-DEO's 
EA. In the Beaufort Sea, some ringed

[[Page 26266]]

seals avoided an area of 100 m to (at most) a few hundred meters around 
seismic vessels, but many seals remained within 100 to 200 m (328 to 
656 ft) of the trackline as the operating airgun array passed by (e.g., 
Harris et al., 2001; Moulton and Lawson, 2002; Miller et al., 2005). 
Ringed seal sightings averaged somewhat farther away from the seismic 
vessel when the airguns were operating than when they were not, but the 
difference was small (Moulton and Lawson, 2002). Similarly, in Puget 
Sound, sighting distances for harbor seals and California sea lions 
tended to be larger when airguns were operating (Calambokidis and 
Osmek, 1998). Previous telemetry work suggests that avoidance and other 
behavioral reactions may be stronger than evident to date from visual 
studies (Thompson et al., 1998).

Hearing Impairment and Other Physical Effects

    Exposure to high intensity sound for a sufficient duration may 
result in auditory effects such as a noise-induced threshold shift--an 
increase in the auditory threshold after exposure to noise (Finneran, 
Carder, Schlundt, and Ridgway, 2005). Factors that influence the amount 
of threshold shift include the amplitude, duration, frequency content, 
temporal pattern, and energy distribution of noise exposure. The 
magnitude of hearing threshold shift normally decreases over time 
following cessation of the noise exposure. The amount of threshold 
shift just after exposure is called the initial threshold shift. If the 
threshold shift eventually returns to zero (i.e., the threshold returns 
to the pre-exposure value), it is called temporary threshold shift 
(TTS) (Southall et al., 2007).
    Researchers have studied TTS in certain captive odontocetes and 
pinnipeds exposed to strong sounds (reviewed in Southall et al., 2007). 
However, there has been no specific documentation of TTS let alone 
permanent hearing damage, i.e., permanent threshold shift (PTS), in 
free-ranging marine mammals exposed to sequences of airgun pulses 
during realistic field conditions.
    Temporary Threshold Shift--TTS is the mildest form of hearing 
impairment that can occur during exposure to a strong sound (Kryter, 
1985). While experiencing TTS, the hearing threshold rises and a sound 
must be stronger in order to be heard. At least in terrestrial mammals, 
TTS can last from minutes or hours to (in cases of strong TTS) days. 
For sound exposures at or somewhat above the TTS threshold, hearing 
sensitivity in both terrestrial and marine mammals recovers rapidly 
after exposure to the noise ends. Few data on sound levels and 
durations necessary to elicit mild TTS have been obtained for marine 
mammals, and none of the published data concern TTS elicited by 
exposure to multiple pulses of sound. Available data on TTS in marine 
mammals are summarized in Southall et al. (2007). Table 1 (above) 
presents the distances from the Langseth's airguns at which the 
received energy level (per pulse, flat-weighted) would be expected to 
be greater than or equal to 180 dB re 1 [micro]Pa (rms).
    To avoid the potential for injury, NMFS (1995, 2000) concluded that 
cetaceans should not be exposed to pulsed underwater noise at received 
levels exceeding 180 dB re 1 [mu]Pa (rms). NMFS believes that to avoid 
the potential for permanent physiological damage (Level A harassment), 
cetaceans should not be exposed to pulsed underwater noise at received 
levels exceeding 180 dB re 1 [mu]Pa (rms). The 180 dB level is a 
shutdown criterion applicable to cetaceans, as specified by NMFS 
(2000); these levels were used to establish the EZs. NMFS also assumes 
that cetaceans exposed to levels exceeding 160 dB re 1 [mu]Pa (rms) may 
experience Level B harassment.
    Researchers have derived TTS information for odontocetes from 
studies on the bottlenose dolphin and beluga. For the one harbor 
porpoise tested, the received level of airgun sound that elicited onset 
of TTS was lower (Lucke et al., 2009). If these results from a single 
animal are representative, it is inappropriate to assume that onset of 
TTS occurs at similar received levels in all odontocetes (cf. Southall 
et al., 2007). Some cetaceans apparently can incur TTS at considerably 
lower sound exposures than are necessary to elicit TTS in the beluga or 
bottlenose dolphin.
    For baleen whales, there are no data, direct or indirect, on levels 
or properties of sound that are required to induce TTS. The frequencies 
to which baleen whales are most sensitive are assumed to be lower than 
those to which odontocetes are most sensitive, and natural background 
noise levels at those low frequencies tend to be higher. As a result, 
auditory thresholds of baleen whales within their frequency band of 
best hearing are believed to be higher (less sensitive) than are those 
of odontocetes at their best frequencies (Clark and Ellison, 2004). 
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 the strong 
likelihood that baleen whales would avoid the approaching airguns (or 
vessel) before being exposed to levels high enough for TTS to occur.
    In pinnipeds, TTS thresholds associated with exposure to brief 
pulses (single or multiple) of underwater sound have not been measured. 
Initial evidence from more prolonged (non-pulse) exposures suggested 
that some pinnipeds (harbor seals in particular) incur TTS at somewhat 
lower received levels than do small odontocetes exposed for similar 
durations (Kastak et al., 1999, 2005; Ketten et al., 2001). The TTS 
threshold for pulsed sounds has been indirectly estimated as being an 
SEL of approximately 171 dB re 1 [mu]Pa\2\[middot]s (Southall et al., 
2007) which would be equivalent to a single pulse with a received level 
of approximately 181 to 186 dB re 1 [micro]Pa (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).
    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 dBs above that inducing mild TTS if the animal were 
exposed to strong sound pulses with rapid rise time--see Appendix B(6) 
of L-DEO's EA. 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,

[[Page 26267]]

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.
    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). Appendix B(6) of L-DEO's EA 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 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. However, 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