Takes of Marine Mammals Incidental to Specified Activities; Marine Geophysical Survey in the Pacific Ocean off Costa Rica, April Through May, 2011, 6430-6448 [2011-2538]

Agencies

• DEPARTMENT OF COMMERCE
• National Oceanic and Atmospheric Administration

[Federal Register Volume 76, Number 24 (Friday, February 4, 2011)]
[Notices]
[Pages 6430-6448]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 2011-2538]


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DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

RIN 0648-XA124


Takes of Marine Mammals Incidental to Specified Activities; 
Marine Geophysical Survey in the Pacific Ocean off Costa Rica, April 
Through May, 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 Lamont-Doherty Earth 
Observatory (L-DEO), a part of Columbia University, for an Incidental 
Harassment Authorization (IHA) to take marine mammals, by harassment, 
incidental to conducting a marine geophysical survey in the eastern 
tropical Pacific (ETP) Ocean off Costa Rica, April through May, 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, 19 species of marine mammals during 
the specified activity.

DATES: Comments and information must be received no later than March 7, 
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.Cody@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

[[Page 6431]]

contact listed here (see FOR FURTHER INFORMATION CONTACT) or visiting 
the Internet at: https://www.nmfs.noaa.gov/pr/permits/incidental.htm#applications.
    The National Science Foundation (NSF), which is providing funding 
for the proposed action, has prepared a draft Environmental Analysis 
which incorporates an ``Environmental Assessment of a Marine 
Geophysical Survey by the R/V Marcus G. Langseth in the Pacific Ocean 
off Costa Rica, April-May, 2011'', prepared by LGL Limited, on behalf 
of NSF 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: Jeannine Cody, Office of Protected 
Resources, NMFS, (301) 713-2289, ext. 113.

SUPPLEMENTARY INFORMATION:

Background

    Section 101(a)(5)(D) of the MMPA (16 U.S.C. 1371(a)(5)(D)) directs 
the Secretary of Commerce to authorize, upon request, the incidental, 
but not intentional, taking of small numbers of marine mammals of a 
species or population stock, by United States citizens who engage in a 
specified activity (other than commercial fishing) within a specified 
geographical region if certain findings are made and, if the taking is 
limited to harassment, a notice of a proposed authorization is provided 
to the public for review.
    Authorization for 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 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 November 12, 2010, from L-DEO for 
the taking by harassment, of marine mammals, incidental to conducting a 
marine geophysical survey in the eastern tropical Pacific Ocean within 
the Exclusive Economic Zone (EEZ) of Costa Rica. L-DEO, with research 
funding from the U.S. National Science Foundation (NSF), plans to 
conduct the proposed survey from April 7, 2011, through May 9, 2011. 
Upon receipt of additional information, NMFS determined the application 
complete and adequate on January 4, 2011.
    L-DEO plans to use one source vessel, the R/V Marcus G. Langseth 
(Langseth) and a seismic airgun array to image the structures along a 
major plate-boundary fault off in the ETP off Costa Rica using three-
dimensional (3-D) seismic reflection techniques. L-DEO will use the 3-D 
seismic reflection data to determine the fault structure and the 
properties of the rocks that lie along the fault zone. 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 19 species 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 32 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 ETP off Costa Rica is 
scheduled to commence on April 7, 2011 and continue for approximately 
32 days ending on May 9, 2011. L-DEO will operate the Langseth to 
deploy a seismic airgun array and hydrophone streamers to complete the 
survey.
    The Langseth will depart from Caldera, Costa Rica on April 7, 2011 
and transit to the survey area offshore from Costa Rica. Some minor 
deviation from these dates is possible, depending on logistics, weather 
conditions, and the need to repeat some lines if data quality is 
substandard. Therefore, NMFS plans to issue an authorization that 
extends to June 6, 2011.
    Geophysical survey activities will involve 3-D seismic 
methodologies to determine the fault structure and the properties of 
the rocks that lie along the fault zone and to assess the property 
changes along the fault and determine where the large stress 
accumulations that lead to large earthquakes occur along the fault 
zone.
    To obtain 3-D images of the fault zone which lies two to nine 
kilometers (km) below the seafloor, the Langseth will deploy a two-
string subarray of nine airguns each as an energy source. The identical 
subarrays will fire alternately, so that no more than 18 airguns will 
fire at any time during the proposed survey. The receiving system will 
consist of four 6-km-long hydrophone streamers. As the airgun subarrays 
are towed along the survey lines, the hydrophone streamers will receive 
the returning acoustic signals and transfer the data to the on-board 
processing system. L-DEO also plans to use two or three small fishing 
vessels around the Langseth to ensure that other vessels do not 
entangle the streamers.
    The proposed study (e.g., equipment testing, startup, line changes, 
repeat coverage of any areas, and equipment recovery) will take place 
in the EEZ of Costa Rica in water depths ranging from less than 100 
meters (m) (328 feet (ft)) to greater than 2,500 m (1.55 miles (mi)). 
The survey will require approximately 32 days (d) to complete 
approximately 19 transects in a racetrack configuration

[[Page 6432]]

that will cover an area of approximately 57 x 12 km (35.4 x 7.5 mi). In 
all, the proposed survey will complete approximately 2,145 km (1,333 
mi) of survey lines with an additional 365 km (227 mi) of turns. Data 
acquisition will include approximately 672 hours (hr) of airgun 
operation (28 d x 24 hr).
    The scientific team consists of Drs. Nathan Bangs, Kirk McIntosh 
(Institute for Geophysics, University of Texas) and Eli Silver 
(University of California at Santa Cruz).

Vessel Specifications

    The Langseth, owned by NSF, is a seismic research vessel with a 
propulsion system designed to be as quiet as possible to avoid 
interference with the seismic signals emanating from the airgun array. 
The vessel, which has a length of 71.5 m (235 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, is 
powered by two 3,550 horsepower (hp) Bergen BRG-6 diesel engines which 
drive two propellers. Each propeller has four blades and the shaft 
typically rotates at 750 revolutions per minute. The vessel also has an 
800-hp bowthruster, which is not used during seismic acquisition. The 
Langseth's operation speed during seismic acquisition will be 
approximately 8.5 km per hr (km/h) (5.3 mi per hr (mph) or 4.6 knots 
(kts)) and the cruising speed of the vessel outside of seismic 
operations is 18.5 km/h (11.5 mph or 10 kts).
    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 (two subarrays with 18 
airguns each) at a tow depth of 7 meters (m) (23 feet (ft)). However, 
the Langseth will fire one subarray at a time, so that no more than 18 
airguns will fire at any time. The maximum discharge volume is 3,300 
cubic inches (in\3\). The airguns are 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 dominant frequency 
components range from zero to 188 Hertz (Hz).
    The subarray configuration consists of two identical linear or 
strings, with 10 airguns on each string; the first and last airguns 
will be spaced 16 m (52 ft) apart. Of the 10 airguns, nine will fire 
simultaneously while the tenth airgun will serve as a spare and will be 
turned on in case of failure of one of the other airguns. Each airgun 
subarray will emit a pulse at approximately 11-second (s) intervals 
which corresponds to a shot interval of approximately 25 m (82 ft). 
During firing, the airguns will emit a brief (approximately 0.1 s) 
pulse of sound; during the intervening periods of operations, the 
airguns will be silent.
    L-DEO will tow each subarray approximately 140 m (459.3 ft) behind 
the vessel and will distribute the subarrays across an area of 
approximately 12 by 16 m (39.4 by 52.5 ft) behind the Langseth, offset 
by 75 m (246 ft).

Metrics Used in This Document

    This section includes a brief explanation of the sound measurements 
frequently used in the discussions of acoustic effects in this 
document. Sound pressure is the sound force per unit area, and is 
usually measured in micropascals ([mu]Pa), where 1 pascal (Pa) is the 
pressure resulting from a force of one newton exerted over an area of 
one square meter. Sound pressure level (SPL) is expressed as the ratio 
of a measured sound pressure and a reference level. The commonly used 
reference pressure level in underwater acoustics is 1 [mu]Pa, and the 
units for SPLs are dB re: 1 [mu]Pa.
    SPL (in decibels (dB)) = 20 log (pressure/reference pressure)
    SPL is an instantaneous measurement and can be expressed as the 
peak, the peak-peak (p-p), or the root mean square (rms). Root mean 
square, which is the square root of the arithmetic average of the 
squared instantaneous pressure values, is typically used in discussions 
of the effects of sounds on vertebrates and all references to SPL in 
this document refer to 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 18-airgun subarray 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 application. 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 environmental analysis discusses the 
characteristics of the airgun pulses. NMFS refers the reviewers to the 
application and environmental analysis 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 empirical values to determine 
exclusion zones for the 18-airgun subarray and the single airgun; to 
designate mitigation zones, and to estimate take (described in greater 
detail in Section VII and Section IV of L-DEO's application and 
environmental analysis, respectively) for marine mammals.
    Results of the Gulf of Mexico calibration study (Tolstoy et al., 
2009) showed that radii around the airguns for various received levels 
varied with water depth. The 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. However, to be conservative, L-DEO has applied the 
modeled distances for the 36-airgun

[[Page 6433]]

array in deep water to the 18-airgun subarray when operating in deep-
water areas during the proposed study (Table 1). L-DEO set 2,000 m (1.2 
mi) as the maximum relevant depth as very few, if any, mammals are 
expected to occur below this depth.
    The empirical data for shallow water (< 100 m; 328 ft) indicated 
that the L-DEO model (as applied to the Langseth's 36-airgun array) 
underestimated actual received levels. Accordingly, L-DEO has applied 
correction factors to the distances reported by Tolstoy et al. (2009) 
for shallow depth water. For the 36-airgun array, the distances 
measured in shallow-water to the 160- to 190-dB isopleths ranged from 
1.7 to 5.2 times higher than the distances in deep water (Tolstoy et 
al. 2009). During the proposed cruise, the same factors will be applied 
to derive appropriate shallow-water radii from the modeled deep-water 
radii for the Langseth's 18-airgun subarray (Table 1).
    For intermediate-depths (100-1,000 m; 328-3,280 ft), L-DEO has 
applied a correction factor of 1.5 to the estimates provided by the 
model for the 18-airgun subarray operating in deep-water situations to 
predict safety radii for intermediate-depth sites. L-DEO applied the 
same correction factor to model estimates for an L-DEO cruise in the 
same area in 2003 and 2004.
    Table 1 summarizes the predicted distances at which sound levels 
(160- and 180-dB) are expected to be received from the 18-airgun 
subarray and a single airgun operating in shallow, intermediate and 
deep water depths.

  Table 1--Predicted Distances To Which Sound Levels >= 190, 180, and 160 dB re: 1 [mu]Parms Could Be Received
During the Proposed Survey Using A 18-Airgun Subarray, as Well as a Single Airgun Towed at a Depth Of 7 M in the
                                           Etp During April-May, 2011
                            [Distances are based on model results provided by L-DEO.]
----------------------------------------------------------------------------------------------------------------
                                                                                 Predicted RMS Distances (m)
         Source and volume                        Water depth              -------------------------------------
                                                                                  180 dB             160 dB
----------------------------------------------------------------------------------------------------------------
Single Bolt airgun (40 in\3\).....  Shallow < 100 m.......................                296              1,050
                                    Intermediate..........................                 60                578
                                    100-1,000 m...........................
                                    Deep..................................                 40                385
                                    > 1,000 m.............................
18-Airgun subarray (3,300 in\3\)..  Shallow...............................              1,030           * 19,500
                                    < 100 m...............................
                                    Intermediate..........................                675              5,700
                                    100-1,000 m...........................
                                    Deep..................................                450              3,800
                                    > 1,000 m.............................
----------------------------------------------------------------------------------------------------------------
* This is likely an overestimate, as the measured distance for the 36-airgun array operating in shallow waters
  of the northern Gulf of Mexico was 17,500 m (17.5 km).

    L-DEO conducted modeling for a 2008 survey off Costa Rica using 
site specific data on sound velocity profiles in the water column and 
bottom composition at a depth of 65 m (213.5 ft) in Drake Bay (at the 
proposed survey area) and at a depth of 340 m (1,115 ft) in an area 
approximately 100 km (62 mi) north of the survey area. The modeled 
exclusion zones were smaller than the shallow- and intermediate-depth 
ranges listed in Table 1, suggesting that L-DEO's estimates for the 
proposed survey are overestimates and thus precautionary. Also, the 
estimated 160-dB distance for the 18-airgun subarray in water depths 
less than 100 m (328 ft) (Table 1) is higher than the measured distance 
for the 36-airgun array (17.5 km; Tolstoy et al., 2009), again 
suggesting that these estimates are precautionary. Refer to Appendix A 
of L-DEO's environmental analysis for additional information on L-DEO's 
calculations for the model.

Multibeam Echosounder

    The Langseth will operate a Kongsberg EM 122 MBES concurrently 
during airgun operations to map characteristics of the ocean floor. The 
hull-mounted MBES emits brief pulses of sound (also called a ping) 
(10.5 to 13 kilohertz (kHz)) in a fan-shaped beam that extends downward 
and to the sides of the ship. The transmitting beamwidth is one or two 
degrees ([deg]) fore-aft and 150[deg] athwartship and the maximum 
source level is 242 dB re: 1 [mu]Pa.
    For deep-water operations, each ping consists of eight (in water 
greater than 1,000 m; 3,280 ft) or four (less than 1,000 m; 3,280 ft) 
successive, fan-shaped transmissions, from two to 15 milliseconds (ms) 
in duration and each ensonifying a sector that extends 1[deg] fore-aft. 
The eight successive transmissions span an overall cross-track angular 
extent of about 150[deg], with 2-ms gaps between the pulses for 
successive sectors.

Sub-Bottom Profiler

    The Langseth will also operate a Knudsen 320B SBP continuously 
throughout the cruise with the MBES to provide information about the 
sedimentary features and bottom topography. The dominant frequency 
component of the SBP is 3.5 kHz which is directed downward in a 30[deg] 
cone by a hull-mounted transducer on the vessel. The maximum output is 
1,000 watts (204 dB re: 1 [mu]Pa), but in practice, the output varies 
with water depth. The pulse interval is one second, but a common mode 
of operation is to broadcast five pulses at 1-s intervals followed by a 
5-s pause.
    NMFS expects that acoustic stimuli resulting from the proposed 
operation of the single airgun or the 18-airgun subarray 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 kts; 8.5 km/h; 5.3 mph) during 
seismic acquisition.

Description of the Specified Geographic Region

    The survey will encompass the area bounded by 8.5-9[deg] N, 83.75-
84.25[deg] W

[[Page 6434]]

offshore from Costa Rica in the Pacific Ocean (see Figure 1 in L-DEO's 
application). The closest that the Langseth will approach the coastline 
is approximately 30 km.

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

    Twenty-eight marine mammal species may occur in the proposed survey 
area, including 20 odontocetes (toothed cetaceans), 6 mysticetes 
(baleen whales) and two pinnipeds. Of these, 19 cetacean species are 
likely to occur in the proposed survey area in the ETP during April 
through May. Five 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 humpback (Megaptera novaeangliae), sei (Balaenoptera 
borealis), fin (Balaenoptera physalus), blue (Balaenoptera musculus), 
and sperm (Physeter macrocephalus) whale.
    The species of marine mammals expected to be most common in the 
survey area (all delphinids) include the short-beaked common dolphin 
(Delphinus delphis), spinner dolphin (Stenella longirostris), 
pantropical spotted dolphin (Stenella attenuata), striped dolphin 
(Stenella coeruleoalba), melon-headed whale (Peponocephala electra), 
and bottlenose dolphin (Tursiops truncatus).
    Two pinnipeds, the California sea lion (Zalophus californianus) and 
the Gal[aacute]pagos sea lion (Zalophus wollebaeki), have the potential 
to transit in the vicinity of the proposed seismic survey, although any 
occurrence would be rare as they are vagrants to the area. Based on 
available data and monitoring reports from previous seismic surveys in 
the area, L-DEO does not expect to encounter these species within the 
proposed survey area and does not present analysis for these species. 
Accordingly, NMFS will not consider these pinniped species in greater 
detail and the proposed IHA will only address requested take 
authorizations for mysticetes and odontocetes.
    Table 2 presents information on the abundance, distribution, 
population status, and conservation status of the marine mammals that 
may occur in the proposed survey area April through May, 2011.

  Table 2--Habitat, Regional Abundance, and Conservation Status of Marine Mammals That May Occur in or Near the Proposed Seismic Survey Areas Off Costa
                                                       Rica in the Eastern Tropical Pacific Ocean
                            [See text and Tables 2-4 in L-DEO's application and environmental analysis for further details.]
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                                                                            Density
              Species                Occurrence in survey         Habitat             Abundance in the ETP \1\           ESA \2\     -------------------
                                    area during April-May                                                                             Best \3\   Max \4\
--------------------------------------------------------------------------------------------------------------------------------------------------------
Mysticetes
Humpback whale....................  Very rare............  Mainly nearshore       NE Pacific 1392 \6\.............  EN..............      0.25      4.40
                                                            waters and banks.     SE Pacific 2900 \7\.............
Bryde's whale.....................  Uncommon.............  Pelagic and coastal..  13,000 \8\......................  NL..............      0.96      2.52
Sei whale.........................  Very rare............  Mostly pelagic.......  N.A.............................  EN..............      0.01      0.01
Fin whale.........................  Very rare............  Slope, mostly pelagic  2636 \6\........................  EN..............      0.01      0.01
Blue whale........................  Rare.................  Pelagic and coastal..  1415 \9\........................  EN..............      0.13      1.86
Common minke whale................  Very rare............  Coastal..............  N.A.............................  NL..............    < 0.01    < 0.01
Odontocetes
Sperm whale.......................  Uncommon.............  Usually deep pelagic,  26,053 \10\.....................  EN..............      4.19      9.80
                                                            steep topography.
Pygmy sperm whale.................  Very rare............  Deep waters off shelf  N.A. \11\.......................  NL..............      0.03      0.05
Dwarf sperm whale.................  Rare.................  Deep waters off shelf  11,200 \12\.....................  NL..............      0.03      0.05
Cuvier's beaked whale.............  Uncommon.............  Slope and pelagic....  20,000 \9\......................  NL..............      2.47      3.70
Mesoplodon spp....................  Very rare or rare....  Pelagic..............  25,300 \13\.....................  NL..............      0.36      1.00
Rough-toothed dolphin.............  Common...............  Mainly pelagic.......  107,633.........................  NL..............      4.19     11.19
Bottlenose dolphin................  Very common..........  Coastal, shelf,        335,834.........................  NL..............     17.06     90.91
                                                            pelagic.
Pantropical spotted dolphin.......  Very common..........  Coastal and pelagic..  1,575,247 \14\..................  NL..............     76.96    236.66
Spinner dolphin...................  Common...............  Coastal and pelagic..  1,797,716 \14\..................  NL..............     58.43    364.26
Striped dolphin...................  Uncommon.............  Off continental shelf  964,362.........................  NL..............     67.75    154.21
Fraser's dolphin..................  Rare.................  Pelagic..............  289,300 \9\.....................  NL..............    < 0.01    < 0.01
Short-beaked common dolphin.......  Common...............  Shelf, pelagic, high   3,127,203.......................  NL..............    110.89    763.50
                                                            relief.
Risso's dolphin...................  Common...............  Shelf, slope,          110,457.........................  NL..............     12.76     12.76
                                                            seamounts.
Melon-headed whale................  Rare.................  Pelagic..............  45,400 \9\......................  NL..............     11.06     57.70
Pygmy killer whale................  Rare.................  Pelagic..............  38,900 \9\......................  NL..............      1.25      2.30
False killer whale................  Uncommon.............  Pelagic..............  39,800 \9\......................  NL..............      0.01      0.01
Killer whale......................  Rare.................  Widely distributed...  8500 \15\.......................  NL..............      0.19      0.40
Short-finned pilot whale..........  Common...............  Mostly pelagic, high-  589,315 \16\....................  NL..............     11.88     28.22
                                                            relief.
--------------------------------------------------------------------------------------------------------------------------------------------------------
N.A. Not available or not assessed.
\1\ Abundance from Gerrodette et al. (2008) unless otherwise stated.
\2\ U.S. Endangered Species Act: EN = Endangered, T = Threatened, NL = Not listed.
\3\ Best density (/1000km\2\) estimate as listed in Table 3 of the application. Cetecean densities are based on NMFS SWFSC ship transect
  surveys conducted in 1986-2006 from predictive modeling (Barlow et al. 2009; Read et al. 2009) or in 1986-1996 from Ferguson and Barlow (2003).
\4\ Maximum density (/1000km\2\) estimate as listed in Table 3 of the application.
\6\ U.S. west coast (Carretta et al., 2010).
\7\ Southeast Pacific; F[eacute]lix et al. (2005).
\8\ This estimate is mainly for Balaenoptera edeni but may include some B. borealis (Wade and Gerrodette, 1993).
\9\ ETP (Wade and Gerrodette, 1993).
\10\ Eastern temperate North Pacific (Whitehead, 2002).
\11\ California/Oregon/Washington (Carretta et al., 2010).
\12\ This abundance estimate is mostly for K. sima but may also include some K. breviceps (Wade and Gerrodette, 1993).
\13\ This estimate includes all species of the genus Mesoplodon in the ETP (Wade and Gerrodette, 1993).
\14\ For all stocks in ETP.
\15\ ETP (Ford, 2002).

[[Page 6435]]

 
\16\ This estimate is for G. macrorhynchus and G. melas in the ETP (Gerrodette and Forcada, 2002).
\17\ U.S. stock (Carretta et al., 2010).
\18\ Galapagos Islands (Alava and Salazar, 2006).

    Refer to Section III 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 of the 
following: tolerance, masking of natural sounds, behavioral 
disturbance, temporary or permanent 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 
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 a 
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 environmental analysis 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

[[Page 6436]]

particular distance of industrial activities and/or exposed to a 
particular level of industrial sound. In most cases, this approach 
likely overestimates the numbers of marine mammals that would be 
affected in some biologically-important manner.
    The sound criteria used to estimate how many marine mammals might 
be disturbed to some biologically-important degree by a seismic program 
are based primarily on behavioral observations of a few species. 
Scientists have conducted detailed studies on humpback, gray, bowhead 
(Balaena mysticetus), and sperm whales. Less detailed data are 
available for some other species of baleen whales, small toothed 
whales, and sea otters (Enhydra lutris), but for many species there are 
no data on responses to marine seismic surveys.
    Baleen Whales--Baleen whales generally tend to avoid operating 
airguns, but avoidance radii are quite variable (reviewed in 
Richardson, et al., 1995). Whales are often reported to show no overt 
reactions to pulses from large arrays of airguns at distances beyond a 
few kilometers, even though the airgun pulses remain well above ambient 
noise levels out to much longer distances. However, as reviewed in 
Appendix B (5) of L-DEO's environmental analysis, 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 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-
DEO's environmental analysis have shown that some species of baleen 
whales, notably bowhead and humpback whales, at times, show strong 
avoidance at received levels lower than 160-170 dB re: 1 [mu]Pa.
    McCauley et al. (1998, 2000) 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 [mu]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 for humpback 
pods containing females, and at the mean closest point of approach 
distance the received level was 143 dB re: 1 [mu]Pa. The initial 
avoidance response generally occurred at distances of 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.
    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.
    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 environmental analysis). 
However, more recent research on bowhead whales (Miller et al., 2005; 
Harris et al., 2007) corroborates earlier evidence that, during the 
summer feeding season, bowheads are not as sensitive to seismic 
sources. Nonetheless, subtle but statistically significant changes in 
surfacing-respiration-dive cycles were evident upon statistical 
analysis (Richardson et al., 1986). In the summer, bowheads typically 
begin to show avoidance reactions at received levels of about 152 to 
178 dB re: 1 [mu]Pa (Richardson et al., 1986, 1995; Ljungblad et al., 
1988; Miller et al., 2005).
    Reactions of migrating and feeding (but not wintering) gray whales 
to seismic surveys have been studied. Malme et al. (1986, 1988) studied 
the responses of feeding eastern Pacific gray whales to pulses from a 
single 100-in\3\ airgun off St. Lawrence Island in the northern Bering 
Sea. They estimated, based on small sample sizes, that 50 percent of 
feeding gray whales stopped feeding at an average received pressure 
level of 173 dB re: 1 [mu]Pa on an (approximate) rms basis, and that 10 
percent of feeding whales interrupted feeding at received levels of 163 
dB re: 1 [mu]Pa. Those findings were generally consistent with the 
results of experiments conducted on larger numbers of gray whales that 
were migrating along the California coast (Malme et al., 1984; Malme 
and Miles, 1985), and western Pacific gray whales feeding off Sakhalin 
Island, Russia (Wursig et al., 1999; Gailey et al., 2007; Johnson et 
al., 2007; Yazvenko et al., 2007a, b), along with data on gray whales 
off British Columbia (Bain and Williams, 2006).
    Various species of Balaenoptera (blue, sei, fin, and minke whales) 
have occasionally been seen in areas ensonified by airgun pulses 
(Stone, 2003; MacLean and Haley, 2004; Stone and Tasker, 2006), and 
calls from blue and fin whales have been localized in areas with airgun 
operations (e.g., McDonald et al., 1995; Dunn and

[[Page 6437]]

Hernandez, 2009). Sightings by observers on seismic vessels off the 
United Kingdom from 1997 to 2000 suggest that, during times of good 
sightability, sighting rates for mysticetes (mainly fin and sei whales) 
were similar when large arrays of airguns were shooting vs. silent 
(Stone, 2003; Stone and Tasker, 2006). However, these whales tended to 
exhibit localized avoidance, remaining significantly further (on 
average) from the airgun array during seismic operations compared with 
non-seismic periods (Stone and Tasker, 2006). In a study off of Nova 
Scotia, Moulton and Miller (2005) found little difference in sighting 
rates (after accounting for water depth) and initial sighting distances 
of balaenopterid whales when airguns were operating vs. silent. 
However, there were indications that these whales were more likely to 
be moving away when seen during airgun operations. Similarly, ship-
based monitoring studies of blue, fin, sei and minke whales offshore of 
Newfoundland (Orphan Basin and Laurentian Sub-basin) found no more than 
small differences in sighting rates and swim directions during seismic 
versus non-seismic periods (Moulton et al., 2005, 2006a,b).
    Data on short-term reactions by cetaceans to impulsive noises are 
not necessarily indicative of long-term or biologically significant 
effects. It is not known whether impulsive sounds affect reproductive 
rate or distribution and habitat use in subsequent days or years. 
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; Angliss and Allen, 2009).
    Toothed Whales--Little systematic information is available about 
reactions of toothed whales to noise pulses. Few studies similar to the 
more extensive baleen whale/seismic pulse work summarized above and (in 
more detail) in Appendix B of L-DEO's environmental analysis have been 
reported for toothed whales. However, there are recent systematic 
studies on sperm whales (e.g., Gordon et al., 2006; Madsen et al., 
2006; Winsor and Mate, 2006; Jochens et al., 2008; Miller et al., 
2009). There is an increasing amount of information about responses of 
various odontocetes to seismic surveys based on monitoring studies 
(e.g., Stone, 2003; Smultea et al., 2004; Moulton and Miller, 2005; 
Bain and Williams, 2006; Holst et al., 2006; Stone and Tasker, 2006; 
Potter et al., 2007; Hauser et al., 2008; Holst and Smultea, 2008; 
Weir, 2008; Barkaszi et al., 2009; Richardson et al., 2009).
    Seismic operators and marine mammal observers on seismic vessels 
regularly see dolphins and other small toothed whales near operating 
airgun arrays, but in general there is a tendency for most delphinids 
to show some avoidance of operating seismic vessels (e.g., Goold, 
1996a,b,c; Calambokidis and Osmek, 1998; Stone, 2003; Moulton and 
Miller, 2005; Holst et al., 2006; Stone and Tasker, 2006; Weir, 2008; 
Richardson et al., 2009; see also Barkaszi et al., 2009). Some dolphins 
seem to be attracted to the seismic vessel and floats, and some ride 
the bow wave of the seismic vessel even when large arrays of airguns 
are firing (e.g., Moulton and Miller, 2005). Nonetheless, small toothed 
whales more often tend to head away, or to maintain a somewhat greater 
distance from the vessel, when a large array of airguns is operating 
than when it is silent (e.g., Stone and Tasker, 2006; Weir, 2008). In 
most cases, the avoidance radii for delphinids appear to be small, on 
the order of one km less, and some individuals show no apparent 
avoidance. The beluga whale (Delphinapterus leucas) is a species that 
(at least at times) shows long-distance avoidance of seismic vessels. 
Aerial surveys conducted in the southeastern Beaufort Sea during summer 
found that sighting rates of beluga whales were significantly lower at 
distances 10 to 20 km compared with 20 to 30 km from an operating 
airgun array, and observers on seismic boats in that area rarely see 
belugas (Miller et al., 2005; Harris et al., 2007).
    Captive bottlenose dolphins (Tursiops truncatus) and beluga whales 
exhibited changes in behavior when exposed to strong pulsed sounds 
similar in duration to those typically used in seismic surveys 
(Finneran et al., 2000, 2002, 2005). However, the animals tolerated 
high received levels of sound before exhibiting aversive behaviors.
    Results for porpoises depend on species. The limited available data 
suggest that harbor porpoises (Phocoena phocoena) show stronger 
avoidance of seismic operations than do Dall's porpoises (Phocoenoides 
dalli) (Stone, 2003; MacLean and Koski, 2005; Bain and Williams, 2006; 
Stone and Tasker, 2006). Dall's porpoises seem relatively tolerant of 
airgun operations (MacLean and Koski, 2005; Bain and Williams, 2006), 
although they too have been observed to avoid large arrays of operating 
airguns (Calambokidis and Osmek, 1998; Bain and Williams, 2006). This 
apparent difference in responsiveness of these two porpoise species is 
consistent with their relative responsiveness to boat traffic and some 
other acoustic sources (Richardson et al., 1995; Southall et al., 
2007).
    Most studies of sperm whales exposed to airgun sounds indicate that 
the sperm whale shows considerable tolerance of airgun pulses (e.g., 
Stone, 2003; Moulton et al., 2005, 2006a; Stone and Tasker, 2006; Weir, 
2008). In most cases the whales do not show strong avoidance, and they 
continue to call (see Appendix B of L-DEO's environmental analysis for 
review). However, controlled exposure experiments in the Gulf of Mexico 
indicate that foraging behavior was altered upon exposure to airgun 
sound (Jochens et al., 2008; Miller et al., 2009; Tyack, 2009).
    There are almost no specific data on the behavioral reactions of 
beaked whales to seismic surveys. However, some northern bottlenose 
whales (Hyperoodon ampullatus) remained in the general area and 
continued to produce high-frequency clicks when exposed to sound pulses 
from distant seismic surveys (Gosselin and Lawson, 2004; Laurinolli and 
Cochrane, 2005; Simard et al., 2005). Most beaked whales tend to avoid 
approaching vessels of other types (e.g., Wursig et al., 1998). They 
may also dive for an extended period when approached by a vessel (e.g., 
Kasuya, 1986), although it is uncertain how much longer such dives may 
be as compared to dives by undisturbed beaked whales, which also are 
often quite long (Baird et al., 2006; Tyack et al., 2006). Based on a 
single observation, Aguilar-Soto et al. (2006) suggested that foraging 
efficiency of Cuvier's beaked whales may be reduced by close approach 
of vessels. In any event, it is likely that most beaked whales would 
also show strong avoidance of an approaching seismic vessel, although 
this has not been documented explicitly.
    There are increasing indications that some beaked whales tend to 
strand when naval exercises involving mid-frequency sonar operation are 
ongoing nearby (e.g., Simmonds and Lopez-Jurado, 1991; Frantzis, 1998; 
NOAA and

[[Page 6438]]

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 
environmental analysis).

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 presents the 
distances from the Langseth's airguns at which the received energy 
level (per pulse, flat-weighted) that would be expected to be greater 
than or equal to 180 dB re: 1 [mu]Pa.
    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. 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. 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: (1) The low 
abundance of baleen whales in the planned study area at the time of the 
survey; and (2) the strong likelihood that baleen whales would avoid 
the approaching airguns (or vessel) before being exposed to levels high 
enough for TTS to occur. Permanent Threshold Shift--When PTS occurs, 
there is physical damage to the sound receptors in the ear. In severe 
cases, there can be total or partial deafness, whereas in other cases, 
the animal has an impaired ability to hear sounds in specific frequency 
ranges (Kryter, 1985). There is no specific evidence that exposure to 
pulses of airgun sound can cause PTS in any marine mammal, even with 
large arrays of airguns. However, given the possibility that mammals 
close to an airgun array might incur at least mild TTS, there has been 
further speculation about the possibility that some individuals 
occurring very close to airguns might incur PTS (e.g., Richardson et 
al., 1995, p. 372ff; Gedamke et al., 2008). Single or occasional 
occurrences of mild TTS are not indicative of permanent auditory 
damage, but repeated or (in some cases) single exposures to a level 
well above that causing TTS onset might elicit PTS.
    Relationships between TTS and PTS thresholds have not been studied 
in marine mammals, but are assumed to be similar to those in humans and 
other terrestrial mammals. PTS might occur at a received sound level at 
least several decibels above that inducing mild TTS if the animal were 
exposed to strong sound pulses with rapid rise time-see Appendix B (6) 
of L-DEO's environmental analysis. Based on data from terrestrial 
mammals, a precautionary assumption is that the PTS threshold for 
impulse sounds (such as airgun pulses as received close to the source) 
is at least 6 dB higher than the TTS threshold on a peak-pressure 
basis, and probably greater than six dB (Southall et al., 2007).
    Given the higher level of sound necessary to cause PTS as compared 
with TTS, it is considerably less likely that PTS would occur. Baleen 
whales generally avoid the immediate area around operating seismic 
vessels, as do some other marine mammals.
    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,

[[Page 6439]]

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 environmental analysis provides additional 
details.
    Specific sound-related processes that lead to strandings and 
mortality are not well documented, but may include:
    (1) Swimming in avoidance of a sound into shallow water;
    (2) a change in behavior (such as a change in diving behavior) that 
might contribute to tissue damage, gas bubble formation, hypoxia, 
cardiac arrhythmia, hypertensive hemorrhage or other forms of trauma;
    (3) a physiological change such as a vestibular response leading to 
a behavioral change or stress-induced hemorrhagic diathesis, leading in 
turn to tissue damage; and
    (4) tissue damage directly from sound exposure, such as through 
acoustically-mediated bubble formation and growth or acoustic resonance 
of tissues. Some of these mechanisms are unlikely to apply in the case 
of impulse sounds. However, there are increasing indications that gas-
bubble disease (analogous to the bends), induced in supe