Incidental Takes of Marine Mammals During Specified Activities; Marine Geophysical Survey in the Commonwealth of the Northern Mariana Islands, April to June 2010, 8652-8671 [2010-3869]

Agencies

• DEPARTMENT OF COMMERCE
• National Oceanic and Atmospheric Administration

[Federal Register Volume 75, Number 37 (Thursday, February 25, 2010)]
[Notices]
[Pages 8652-8671]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 2010-3869]


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DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

RIN 0648-XT57


Incidental Takes of Marine Mammals During Specified Activities; 
Marine Geophysical Survey in the Commonwealth of the Northern Mariana 
Islands, April to June 2010

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

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

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SUMMARY: NMFS has received an application from the Lamont-Doherty Earth 
Observatory (L-DEO), a part of

[[Page 8653]]

Columbia University, for an Incidental Harassment Authorization (IHA) 
to take small numbers of marine mammals, by harassment, incidental to 
conducting a marine seismic survey in the Commonwealth of the Northern 
Mariana Islands (CNMI) during April to June 2010. Pursuant to the 
Marine Mammal Protection Act (MMPA), NMFS requests comments on its 
proposal to authorize L-DEO to incidentally take, by Level B harassment 
only, small numbers of marine mammals during the aforementioned 
activity.

DATES: Comments and information must be received no later than March 
29, 2010.

ADDRESSES: Comments on the application should be addressed to P. 
Michael Payne, Chief, Permits, Conservation, and Education Division, 
Office of Protected Resources, National Marine Fisheries Service, 1315 
East-West Highway, Silver Spring, MD 20910. The mailbox address for 
providing e-mail comments is PR1.0648-XT57@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 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 address specified 
above, telephoning the contact listed below (see FOR FURTHER 
INFORMATION CONTACT), or visiting the Internet at: https://www.nmfs.noaa.gov/pr/permits/incidental.htm. 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.

SUPPLEMENTARY INFORMATION:

Background

    Sections 101(a)(5)(A) and (D) of the MMPA (16 U.S.C. 1361 et seq.) 
direct the Secretary of Commerce (Secretary) to allow, upon request, 
the incidental, but not intentional, taking of marine mammals 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 either regulations are issued or, if the taking 
is limited to harassment, a notice of a proposed authorization is 
provided to the public for review.
    An authorization for incidental taking of small numbers of marine 
mammals shall be granted if NMFS finds that the taking will have a 
negligible impact on the species or stock(s), will not have an 
unmitigable adverse impact on the availability of the species or 
stock(s) for subsistence uses, and if the permissible methods of taking 
and requirements pertaining to the mitigation, monitoring and reporting 
of such takings are set forth. NMFS has defined ``negligible impact'' 
in 50 CFR 216.103 as ``* * * an impact resulting from the specified 
activity that cannot be reasonably expected to, and is not reasonably 
likely to, adversely affect the species or stock through effects on 
annual rates of recruitment or survival.'' The authorization must also 
set forth permissible methods of taking, other means of affecting the 
least practicable adverse impact on the species or stock and its 
habitat and requirements for monitoring and reporting such takings.
    Section 101(a)(5)(D) of the MMPA established an expedited process 
by which citizens of the United States can apply for an authorization 
not to exceed one year to incidentally take small numbers of marine 
mammals by harassment. Except with respect to certain activities not 
pertinent here, the MMPA defines ``harassment'' as:

any act of pursuit, torment, or annoyance which (i) has the 
potential to injure a marine mammal or marine mammal stock in the 
wild [``Level A harassment'']; or (ii) has the potential to disturb 
a marine mammal or marine mammal stock in the wild by causing 
disruption of behavioral patterns, including, but not limited to, 
migration, breathing, nursing, breeding, feeding, or sheltering 
[``Level B harassment''].
    16 U.S.C. 1362(18)

    Section 101(a)(5)(D) establishes a 45-day time limit for NMFS' 
review of an application followed by a 30-day public notice and comment 
period for any proposed authorizations for the incidental harassment of 
marine mammals. Within 45 days of the close of the comment period, 
NMFS, on behalf of the Secretary, makes the findings set forth in 
clause 101(a)(5)(D)(i) of the MMPA and must either issue the 
authorization with appropriate conditions to meet the requirements of 
clause 101(a)(5)(D)(ii) or deny it. NMFS will publish notice of 
issuance or denial of the authorization within thirty days of issuance 
or denial.

Summary of Request

    On December 16, 2009, NMFS received an IHA application and an 
Environmental Assessment (EA) from L-DEO for the taking, by Level B 
harassment only, of small numbers of several species of marine mammals 
incidental to conducting, with research funding from the National 
Science Foundation (NSF), a marine seismic survey in the CNMI during 
April to June, 2010. The CNMI is a commonwealth in a political union 
with the U.S. The survey will take place in the Exclusive Economic Zone 
(EEZ) of the U.S. in water depths greater than 2,000 m (6,561.7 ft). 
The seismic study will use a towed array of 36 airguns with a total 
discharge volume of approximately 6,600 in\3\.

Description of the Specified Activity

    L-DEO plans to conduct a seismic survey in the CNMI. The survey 
will occur in the area 16.5[deg] to 19[deg] North, 146.5[deg] to 
150[deg] East within the EEZ (see Figure 1 of L-DEO's application). The 
project is scheduled to occur from April 25 to June 6, 2010. Some minor 
deviation of these dates is possible, depending on logistics and 
weather (i.e., the cruise may depart earlier to be extended due to poor 
weather; there could be extra days (up to three) of seismic operations 
if collected data are of substandard quality.
    L-DEO plans to conduct the seismic survey over the Mariana outer 
forearc, the trench and the outer rise of the subducting and bending 
Pacific plate. The objective is to understand the water cycle within 
subduction-systems. Subduction systems are where the basic building 
blocks of continental crust are made and where Earth's great 
earthquakes occur. Little is known about either of these processes, but 
water cycling through the system is thought to be the primary 
controlling factor in both arc-crust generation and megathrust 
seismicity.
    An important new hypothesis has recently been suggested that, if 
correct, will transform our understanding of the water budget of 
subduction systems. This hypothesis holds that cracking attributable to 
bending of the subducting plate enables water to penetrate through the 
subducting crust into the mantle, where it hydrates the mantle by 
forming the hydrous mineral phase serpentine. This phase is stable to 
greater depths than the hydrous clay minerals of the crust, where most 
of the subducting water was previously believed to be held. Thus, if 
this

[[Page 8654]]

hypothesis is correct, it provides a mechanism for transporting water 
far beneath the mantle wedge, where it promotes melting and crust 
formation, and possibly even deeper into the mantle, providing a whole-
earth hydration mechanism that promotes the continued operation of 
plate tectonics, without which our planet would likely be unable to 
support life.
    The scientists involved in this program will test this hypothesis 
by measuring mantle seismic sounds speeds, which vary with degree of 
serpentinization. By comparing these measurements from the Mariana 
system, which is old and cold with the Costa Rica system, which is 
young and warm and where similar measurements have recently been made, 
we should be able to definitively determine whether or not substantial 
water is taken up by the mantle of subducting plates near the outer 
rise of seafloor trenches.
    The planned survey will involve one source vessel, the R/V Marcus 
G. Langseth (Langseth), which will occur in the CNMI. The Langseth will 
deploy an array of 36 airguns (6,600 in\3\) as an energy source at a 
tow depth of 9 m (30 ft). The receiving system will consist of a 6 km 
(3.7 mi) hydrophone streamer and approximately 85 ocean bottom 
seismometers (OBSs). As the airgun array is towed along the survey 
lines, the hydrophone streamer will receive the returning acoustic 
signals and transfer the data to the on-board processing system. The 
OBSs record the returning acoustic signals internally for later 
analysis. The OBSs to be used for the 2010 program will be deployed and 
most (approximately 60) will be retrieved during the cruise, whereas 25 
will be left in place for one year.
    The planned seismic survey will consist of approximately 2,800 km 
(1,739.8 mi) of transect lines within the CNMI (see Figure 1 of L-DEO's 
application). The survey will take place in water depths greater than 
2,000 m (6,561.7 ft). All planned geophysical data acquisition 
activities will be conducted by L-DEO with onboard assistance by the 
scientists who have proposed the study. The scientific team consists of 
Dr. Doug Wiens (Washington University, St. Louis, MO) and Daniel 
Lizarralde (Woods Hole Oceanographic Institution [WHOI], Woods Hole, 
MA). The vessel will be self-contained, and the crew will live aboard 
the vessel for the entire cruise.
    In addition to the operations of the airgun array, a Kongsberg EM 
multibeam echosounder (MBES) and a Knudsen 320B sub-bottom profiler 
(SBP) will be operated from the Langseth continuously throughout the 
CNMI cruise.

Vessel Specifications

    The Langseth will be used as the source vessel. The Langseth will 
tow the 36 airgun array along predetermined lines. The Langseth will 
also tow the hydrophone streamer, retrieve OBSs, and may also deploy 
OBSs. When the Langseth is towing the airgun array as well as the 
hydrophone streamer, the turning rate of the vessel while the gear is 
deployed is limited to five degrees per minute. Thus, the 
maneuverability of the vessel is limited during operations with the 
streamer.
    The Langseth has a length of 71.5 m (234.6 ft), a beam of 17 m 
(55.8 ft), and a maximum draft of 5.9 m (19.4 ft). The ship was 
designed as a seismic research vessel, with a propulsion system 
designed to be as quiet as possible to avoid interference with the 
seismic signals. The ship is powered by two Bergen BRG-6 diesel 
engines, each producing 3,550 horse-power (hp), that drive the two 
propellers directly. Each propeller has four blades, and the shaft 
typically rotates at 750 revolutions per minute (rpm). The vessel also 
has an 800 hp bowthruster, which is not used during seismic 
acquisition. The operation speed during seismic acquisition is 
typically 7.4 to 9.3 km/hr (4 to 5 kt). When not towing seismic survey 
gear, the Langseth can cruise at 20 to 24 km/hr (11 to 13 kt). The 
Langseth has a range of 25,000 km (15,534 mi), which is the distance 
the vessel can travel without refueling. The Langseth will also serve 
as the platform from which vessel-based Protected Species Observers 
(PSOs) will watch for marine animals before and during airgun 
operations. NMFS believes that the realistic possibility of a ship-
strike of a marine mammal by the vessel during research operations and 
in-transit during the proposed survey is discountable.

Acoustic Source Specifications--Seismic Airguns

    During the proposed survey, the airgun array to be used will 
consist of 36 airguns, with a total volume of approximately 6,600 
in\3\. The airgun array will consist of a mixture of Bolt 1500LL and 
1900LL airguns. The airguns array will be configured as four identical 
linear arrays or ``strings'' (see Figure 2 in L-DEO's application). 
Each string will have 10 airguns; the first and last airguns in the 
strings are spaced 16 m (52.5 ft) apart. Nine airguns in each string 
will be fired simultaneously, while the tenth is kept in reserve as a 
spare, to be turned on in case of failure of another airgun. The four 
airgun strings will be distributed across an approximate area of 24 x 
16 m (78.7 x 52.5 ft) behind the Langseth and will be towed 
approximately 140 m (459 ft) behind the vessel. The shot interval will 
be 37.5 m (123.0 ft) or 150 m (492.1 ft) during the study. The shot 
interval will be relatively short (approximately 37.5 m or 
approximately 15 to 18 seconds [s]) for multi-channel seismic surveying 
with the hydrophone streamer, and relatively long (approximately 150 m 
or approximately 58 to 73 s) when recording data on the OBSs. The 
firing pressure of the array is 1,900 pounds per square inch (psi). 
During firing, a brief (approximately 0.1 s) pulse of sound is emitted. 
The airguns will be silent during the intervening periods.
    Because the actual source is a distributed source (36 airguns) 
rather than a single point source, the highest sound levels measurable 
at any location in the water will be less than the nominal source (265 
dB re 1 [mu] Pa[middot]m, peak-to-peak [pk-pk]). 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.

 Table 1--Distances To Which Sound Levels Greater Than or Equal to 190, 180, and 160 dB re 1 [mu]Pa (rms) Could
  be Received in Deep (Greater Than 1,000 m) Water During the Proposed Survey in the CNMI, April 25 to June 6,
                                                      2010
----------------------------------------------------------------------------------------------------------------
                                                                            Predicted RMS distances (m)
       Source and volume         Tow depth (m)     Water depth   -----------------------------------------------
                                                                      190 dB          180 dB          160 dB
----------------------------------------------------------------------------------------------------------------
Single Bolt airgun (40 in3)...               9  Deep (>1,000 m).              12              40             385
4 strings, 36 airguns (6,600                 9  Deep (>1,000 m).             400             940           3,850
 in3).
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[[Page 8655]]

Acoustic Source Specifications--Multibeam Echosounder (MBES) and Sub-
bottom Profiler (SBP)

    Along with the airgun operations, two additional acoustical data 
acquisition systems will be operated during the survey. The ocean floor 
will be mapped with Kongsberg EM 122 MBES and Knudsen 320 SBP. These 
sound sources will be operated from the Langseth continuously 
throughout the cruise.
    The Kongsberg EM 122 MBES operates at 10.5 to 13 (usually 12) kHz 
and is hull-mounted on the Langseth. The transmitting beamwidth is 
1[deg] or 2[deg] fore-aft and 150[deg] athwartship. The maximum source 
level is 242 dB re 1 [mu]Pam (rms). Each ``ping'' consists of eight (in 
water greater than 1,000 m deep) or four (less than 1,000 m) successive 
fan-shaped transmissions, each ensonifying a sector that extends 1[deg] 
fore-aft. Continuous-wave (CW) pulses increase from two to 15 ms long 
in water depths up to 2,600 m (8,530 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 pulses for successive sectors.
    The Knudsen 320B SBP is normally operated to provide information 
about the sedimentary features and the bottom topography that is being 
mapped simultaneously by the MBES. The SBP beam is transmitted as a 27 
degree 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), but 
in practice, the output varies with water depth. The pulse interval is 
1 s, but a common mode of operation is to broadcast five pulses at 1 s 
intervals followed by a 5 s pause.

OBS Description and Deployment

    Approximately 85 OBSs will be deployed by the Langseth before the 
survey, in water depths 3,100 to 8,100 m (10,170.6 to 26,574.8 ft). 
There are three types of OBS deployment:
    (1) Approximately 20 broad-band OBSs located on the bottom in a 
wide two-dimensional (2D) array with a spacing of no more than 100 km 
(62.1 mi);
    (2) Approximately five short-period OBSs tethered in the water 
column above the trench areas deeper than 6 km; and
    (3) Approximately 60 short-period OBSs located on the bottom in a 
2D array with a spacing of about 75 km (46.6 mi).
    The first two types will be left in place for one year for passive 
recording, and the third type will be retrieved after the seismic 
operations. OBSs deployed in water deeper than 5,500 m (18,044.6 ft) 
will require a tether to keep the instruments at a depth of 5,500 to 
6,000 m (18,044.6 to 19,685 ft), as the instruments are rated to a 
maximum depth of 6,000 m. The lengths of the tethers will vary from 65 
to 2,600 m (213.3 to 8,530.2 ft). The tether will fall to the seafloor 
when the OBS is released.
    Two different types of OBSs may be used during the 2010 program. 
The WHOI ``D2'' OBS has a height of approximately 1 m (3.3 ft) and a 
maximum diameter of 50 cm (19.7 in). The anchor is made of hot-rolled 
steel and weighs 23 kg (50.7 lb). The anchor dimensions are 
2.5x30.5x38.1 cm. The LC4x4 OBS from the Scripps Institution of 
Oceanography (SIO) has a volume of approximately 1 m3, with 
an anchor that consists of a large piece of steel grating 
(approximately 1 m2). 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. The anchors will 
remain on the sea floor.

Proposed Dates, Duration, and Specific Geographic Area

    The survey will occur in the following specific geographic area: 
16.5[deg] to 19[deg] North, 146.5[deg] to 150[deg] East within the EEZ 
of the U.S. (see Figure 1 of L-DEO's application). Water depths in the 
survey area range from greater than 2,000 m to greater than 8,000 m 
(26,246.7 ft). The closest that the vessel will approach to any island 
is approximately 50 km (31.1 mi) from Alamagan. The exact dates of the 
activities depend on logistics and weather conditions. The Langseth 
will depart from Guam on April 25, 2010 and return to Guam on June 6, 
2010. Seismic operations will be carried out for 16 days, with the 
balance of the cruise occupied in transit (approximately 2 days) and in 
deployment and retrieval of OBSs and maintenance (25 days).

Description of Marine Mammals in the Proposed Activity Area

    A total of 27 cetacean species, including 20 odontocete (dolphins 
and small- and large-toothed whales) species and nine mysticetes 
(baleen whales) are known to occur in the area affected by the 
specified activities associated with the proposed CNMI marine 
geophysical survey (see Table 2 of L-DEO's application). Cetaceans and 
pinnipeds, which are the subject of this IHA application, are protected 
by the MMPA and managed by NMFS in accordance with its requirements. 
Information on the occurrence, distribution, population size, and 
conservation status for each of the 27 marine mammal species that may 
occur in the proposed project area is presented in the Table 2 of L-
DEO's application as well as here in the table below (Table 2). The 
status of certain marine mammal species as threatened or endangered is 
based on evaluation and listing procedures under the U.S. Endangered 
Species Act (ESA), the International Union for Conservation of Nature 
(IUCN) Red List of Threatened Species, and Convention on International 
Trade in Endangered Species (CITES). Several marine mammal species that 
may be affected by the proposed IHA are listed as Endangered under 
Section 4 of the ESA, including the North Pacific right, sperm, 
humpback, fin, sei, and blue whales.
    There are no reported sightings of pinnipeds in the CNMI (e.g., 
DON, 2005). The dugong (Dugong dugon), also listed under the ESA as 
Endangered, is distributed throughout most of the Indo-Pacific region 
between approximately 27[deg] North and south of the equator (Marsh, 
2002); it seems unlikely that dugongs have ever inhabited the Mariana 
Islands (Nishiwaki et al., 1979). There have been some extralimital 
sightings in Guam, including a single dugong in Cocos Lagoon in 1974 
(Randall et al., 1975) and several sightings of an individual in 1985 
along the southeastern coast (Eldredge, 2003).
    Table 2 below outlines the cetacean species, their habitat and 
abundance in the proposed project area, and the requested take levels. 
Additional information regarding the distribution of these species 
expected to be found in the project area and how the estimated 
densities were calculated may be found in L-DEO's application.

[[Page 8656]]



 Table 2--The Habitat, Regional Abundance, Conservation Status, and Best and Maximum Density Estimates of Marine
 Mammals That Could Occur in or Near the Proposed Seismic Survey Area in the CNMI. See Tables 2 to 4 in L-DEO's
                                         Application for Further Detail
----------------------------------------------------------------------------------------------------------------
                                                                                             Density/
                                                               Regional                      1000 km2   Density/
             Species                      Habitat        population size \a\     ESA \b\      (best)    1000 km2
                                                                                               \c\     (max) \d\
----------------------------------------------------------------------------------------------------------------
Mysticetes:
    North Pacific right whale      Pelagic and coastal.  Few 100s...........  EN..........       0.01       0.01
     (Eubalaena japonica).
    Humpback whale (Megaptera      Mainly nearshore      938-1107 \e\.......  EN..........       0.01       0.02
     novaeangliae).                 waters and banks.
    Minke whale (Balaenoptera      Pelagic and coastal.  25,000 \f\.........  NL..........       0.01       0.02
     acutorostrata).
    Bryde's whale Balaenoptera     Pelagic and coastal.  20,000-30,000......  NL..........       0.41       0.62
     brydei).
    Sei whale (Balaenoptera        Primarily offshore,   7,260-12,620 \g\...  EN..........       0.29       0.44
     borealis).                     pelagic.
    Fin whale (Balaenoptera        Continental slope,    13.620-18.680 \h\..  EN..........       0.01       0.02
     physalus).                     mostly pelagic.
    Blue whale (Balaenoptera       Pelagic and coastal.  N.A................  EN..........       0.01       0.02
     musculus).
Odontocetes:
    Sperm whale (Physeter          Usually pelagic and   29,674 \i\.........  EN..........       1.23       1.85
     macrocephalus).                deep seas.
    Pygmy sperm whale (Kogia       Deep waters off       N.A................  NL..........       2.91       4.37
     breviceps).                    shelf.
    Dwarf sperm whale (Kogia       Deep waters off the   11,200 \j\.........  NL..........       7.14      10.71
     sima).                         shelf.
    Cuvier's beaked whale          Pelagic.............  20,000 \j\.........  NL..........       6.21       9.32
     (Ziphius cavirostris).
    Longman's beaked whale         Deep water..........  N.A................  NL..........       0.41       0.62
     (Indopacetus pacificus).
    Blainville's beaked whale      Pelagic.............  25,300 \k\.........  NL..........       1.17       1.76
     (Mesoplodon densirostris).
    Ginkgo-toothed beaked whale    Pelagic.............  N.A................  NL..........       0.01       0.02
     (Mesoplodon ginkgodens).
    Rough-toothed dolphin (Steno   Deep water..........  146,000 ETP \j\....  NL..........       0.29       0.44
     bredanensis).
    Common bottlenose dolphin      Coastal and oceanic,  243,500 ETP \j\....  NL..........       0.21       0.32
     (Tursiops truncatus).          shelf break.
    Pantropical spotted dolphin    Coastal and pelagic.  800,000 ETP \j\....  NL..........      22.60      33.90
     (Stenella attenuata).
    Spinner dolphin (Stenella      Coastal and pelagic.  800,000 ETP \j\....  NL..........       3.14       4.71
     longirostris).
    Striped dolphin (Stenella      Off continental       1,000,000 ETP \j\..  NL..........       6.16       9.24
     coeruleoalba).                 shelf.
    Fraser's dolphin               Waters greater than   289,000 ETP \j\....  NL..........       4.17       6.26
     (Lagenodelphis hosei).         1,000 m.
    Short-beaked common dolphin    Shelf and pelagic,    3,000,000 ETP \j\..  NL..........       0.01       0.01
     (Delphinus delphis).           seamounts.
    Risso's dolphin (Grampus       Waters greater than   175,000 ETP \j\....  NL..........       0.97       1.46
     griseus).                      1,000 m, seamounts.
    Melon-headed whale             Oceanic.............  45,000 ETP \j\.....  NL..........       4.28       6.42
     (Peponocephala electra).
    Pygmy killer whale (Feresa     Deep, pantropical     39,000 ETP \j\.....  NL..........       0.14       0.21
     attenuata).                    waters.
    False killer whale (Pseudorca  Pelagic.............  40,000 \j\.........  NL..........       1.11       0.21
     crassidens).
    Killer whale (Orcinus orca)..  Widely distributed..  8,500 ETP \j\......  NL..........       0.14       0.21
    Short-finned pilot whale       Mostly pelagic, high- 500,000 ETP \j\....  NL..........       1.59       2.39
     (Globicephala macrorhynchus).  relief topography.
Sirenians: Dugong (Dugong dugon).  Coastal.............  N.A................  EN..........       N.A.       N.A.
----------------------------------------------------------------------------------------------------------------
N.A.--Data not available or species status was not assessed,
\a\ North Pacific (Jefferson et al., 2008) unless otherwise indicated.
\b\ U.S. Endangered Species Act: EN = Endangered, NL = Not listed.
\c\ Best estimate as listed in Table 3 of the application.
\d\ Maximum estimate as listed in Table 3 of the application.
\e\ Western North Pacific (Calambokidis et al., 2008).
\f\ Northwest Pacific and Okhotsk Sea (IWC, 2007a).
\g\ North Pacific (Tillman, 1977).
\h\ North Pacific (Ohsumi and Wada, 1974).
\i\ Western North Pacific (Whitehead, 2002b).
\j\ Eastern Tropical Pacific = ETP (Wade and Gerrodette, 1993).
\k\ ETP; all Mesoplodon spp. (Wade and Gerodette, 1993).

Potential Effects on Marine Mammals

Potential Effects of Airgun Sounds

    The effects of sounds from airguns might result in one or more of 
the following: tolerance, masking of natural sounds, behavioral 
disturbances, 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 project would result in any 
cases of temporary or especially permanent hearing impairment, or any 
significant non-auditory physical or physiological effects. Some 
behavioral disturbance is expected, but this would be localized and 
short-term. NMFS concurs with this determination.
    The root mean square (rms) received levels that are used as impact 
criteria for marine mammals are not directly comparable to the peak or 
peak-to-peak values normally used to characterize source levels of 
airgun arrays. The measurement units used to describe airgun sources, 
peak or peak-to-peak decibels, are always higher than the rms decibels 
referred to in biological literature. A measured received level of 160 
dB rms in the far field would typically correspond to a peak 
measurement of approximately 170 to 172 dB, and to a peak-to-peak 
measurement of approximately 176 to 178 dB, as measured for the same 
pulse received at the same location (Greene, 1997; McCauley et al., 
1998, 2000a). The precise difference between rms and peak or peak-to-
peak values depends on the frequency content and duration of the pulse, 
among other factors. However, the rms level is always lower

[[Page 8657]]

than the peak or peak-to-peak level for an airgun-type source.

Tolerance

    Numerous studies have shown that pulsed sounds from airguns are 
often readily detectable in the water at distances of many kilometers. 
For a summary of the characteristics of airgun pulses, see Appendix B 
(3) of the EA. Numerous studies have shown that marine mammals at 
distances more than a few kilometers from operating seismic vessels 
often show no apparent response--see Appendix B (5) of L-DEO's 
application. That is often true even in cases when the pulsed sounds 
must be readily audible to the animals based on measured received 
levels and the hearing sensitivity of the mammal group. Although 
various baleen whales, toothed whales, and (less frequently) pinnipeds 
have been shown to react behaviorally to airgun pulses under some 
conditions, at other times, mammals of all three types have shown no 
overt reactions. In general, pinnipeds usually seem to be more tolerant 
of exposure to airgun pulses than are cetaceans, with relative 
responsiveness of baleen and toothed whales being variable.

Masking

    Obscuring of sounds of interest by interfering sounds, generally at 
similar frequencies, is known as masking. Masking effects of pulsed 
sounds (even from large arrays of airguns) on marine mammal calls and 
other natural sounds are expected to be limited, although there are few 
specific data of relevance. Because of the intermittent nature and low 
duty cycle of seismic pulses, animals can emit and receive sounds in 
the relatively quiet intervals between pulses. However in exceptional 
situations, reverberation occurs for much or all of the interval 
between pulses (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. The airgun sounds are 
pulsed, with quiet periods between the pulses, and whale calls often 
can be heard between the seismic pulses (Richardson et al., 1986; 
McDonald et al., 1995; Greene et al., 1999; Nieukirk et al., 2004; 
Smultea et al., 2004; Holst et al., 2005a,b, 2006; Dunn et al., 2009). 
In the northeast Pacific Ocean, blue whale calls have been recorded 
during a seismic survey off Oregon (McDonald et al., 1995). 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 the presence of seismic pulses (Madsen et 
al., 2002; Tyack et al., 2003; Smultea et al., 2004; Holst et al., 
2006; Jochens et al., 2008). Dolphins and porpoises commonly are heard 
calling while airguns are operating (Gordon et al., 2004; Smultea et 
al., 2004; Holst et al., 2005a,b; Potter et al., 2007). The sounds 
important to small odontocetes are predominantly at much higher 
frequencies than the dominant components of airgun sounds, thus 
limiting the potential for masking. In general, masking effects of 
seismic pulses are expected to be minor, given the normally 
intermittent nature of seismic pulses. Masking effects on marine 
mammals are discussed further in Appendix B (4) of the L-DEO EA.

Disturbance Reactions

    Disturbance includes a variety of effects, including subtle changes 
in behavior, more conspicuous changes in activities, and displacement. 
Reactions to sound, if any, depend on species, state of maturity, 
experience, current activity, reproductive state, time of day, and many 
other factors (Richardson et al., 1995; Wartzok et al., 2004; Southall 
et al., 2007; Weilgart, 2007). If a marine mammal does react to an 
underwater sound by changing its behavior or moving a small distance, 
the response may or may not rise to the level of ``harassment'' to the 
individual, or affect the stock or the species population as a whole. 
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 are likely to be present within a 
particular distance of industrial activities, and/or exposed to a 
particular level of industrial sound. In most cases, this practice 
potentially overestimates the numbers of marine mammals that would be 
affected in some biologically-important manner.
    The sound exposure 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 
several species. However, information is lacking for many species. 
Detailed studies have been done on humpback, gray, bowhead, and sperm 
whales. Less detailed data are available for some other species of 
baleen whales, small toothed whales, and sea otters, but for many 
species there are no data on responses to marine seismic surveys.
    Baleen Whales--Baleen whales generally tend to avoid operating 
airguns, but avoidance radii are quite variable. Whales are often 
reported to show no overt reactions to pulses from large arrays of 
airguns at distances beyond a few kilometers, even though the airgun 
pulses remain well above ambient noise levels out to much longer 
distances. However, as reviewed in Appendix B (5) of the L-DEO EA, 
baleen whales exposed to strong noise pulses from airguns often react 
by deviating from their normal migration route and/or interrupting 
their feeding activities and moving away from the sound source. In the 
case of the migrating gray and bowhead whales, the observed changes in 
behavior appeared to be of little or no biological consequence to the 
animals. They simply avoided the sound source by displacing their 
migration route to varying degrees, but within the natural boundaries 
of the migration corridors.
    Studies of gray, bowhead, and humpback whales have demonstrated 
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 (Richardson et al., 1995). In many 
areas, seismic pulses from large arrays of airguns diminish to those 
levels at distances ranging from 4 to 15 km (2.8 to 9 mi) from the 
source. A substantial proportion of the baleen whales within those 
distances may show avoidance or other strong behavioral reactions to 
the airgun array. Subtle behavioral changes sometimes become evident at 
somewhat lower received levels, and studies summarized in Appendix B(5) 
of the L-DEO 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).
    Responses of humpback whales to seismic surveys have been studied 
during migration, on the summer feeding grounds, and on Angolan winter 
breeding grounds; there has also been discussion of effects on the 
Brazilian wintering grounds. McCauley et al. (1998, 2000a) studied the 
responses of humpback whales off Western Australia to a full-scale 
seismic survey with a 16 airgun, 2,678 in\3\ array, and to a single 20 
in\3\ airgun with a source level of 227

[[Page 8658]]

dB re 1 [mu]Pam peak-to-peak. McCauley et al. (1998) documented that 
initial avoidance reactions began at 5 to 8 km (3.1 to 5 mi) from the 
array, and that those reactions kept most pods approximately 3 to 4 km 
(1.9 to 2.5 mi) from the operating seismic boat. McCauley et al. 
(2000a) noted localized displacement during migration of 4 to 5 km (2.5 
to 3.1 mi) by traveling pods and 7 to 12 km (4.3 to 7.5 mi) by cow-calf 
pairs. Avoidance distances with respect to the single airgun were 
smaller (2 km [1.2 mi]) but consistent with the results from the full 
array in terms of received sound levels. The mean received level for 
initial avoidance of an approaching airgun was 140 dB re 1 [mu]Pa (rms) 
for humpback whale pods containing females, and at the mean closest 
point of approach (CPA) distance the received level was 143 dB re 1 
[mu]Pa (rms). The initial avoidance response generally occurred at 
distances of 5 to 8 km (3.1 to 5 mi) from the airgun array and 2 km 
(1.2 mi) from the single airgun. However, some individual humpback 
whales, especially males, approached within distances of 100 to 400 m 
(328 to 1,312 ft), where the maximum received level was 179 dB re 1 
[mu]Pa (rms).
    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 on 
an approximate rms basis. Malme et al. (1985) concluded that there was 
no clear evidence of avoidance, despite the possibility of subtle 
effects, at received levels up to 172 re 1 [mu]Pa on an approximate rms 
basis.
    It has been suggested that South Atlantic humpback whales wintering 
off Brazil may be displaced or even strand upon exposure to seismic 
surveys (Engel et al., 2004). The evidence for this was circumstantial 
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 results from direct studies 
of humpbacks exposed to seismic surveys in other areas and seasons. 
After allowance for data from subsequent years, there was ``no 
observable direct correlation'' between strandings and seismic surveys 
(IWC, 2007:236).
    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 the activity 
(migrating vs. feeding). Bowhead whales migrating west across the 
Alaskan Beaufort Sea in autumn, in particular, are unusually 
responsive, with substantial avoidance occurring out to distances of 20 
to 30 km (12.4 to 18.6 mi) from a medium-sized airgun source at 
received sound levels of around 120 to 130 dB re 1 [mu]Pa (rms) (Miller 
et al., 1999; Richardson et al., 1999; see Appendix B (5) of the EA). 
However, more recent research on bowhead whales (Miller et al., 2005a; 
Harris et al., 2007) corroborates earlier evidence that, during the 
summer feeding season, bowheads are not as sensitive to seismic 
sources. Nonetheless, subtle but statistically significant changes in 
surfacing-respiration-dive cycles were evident upon statistical 
analysis (Richardson et al., 1986). In summer, bowheads typically begin 
to show avoidance reactions at a received level of about 152 to 178 dB 
re 1 [mu]Pa (rms) (Richardson et al., 1986, 1995; Ljungblad et al., 
1988; Miller et al., 2005a).
    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. Malme et al. (1986, 1988) estimated, based on small sample sizes, 
that 50 percent of feeding gray whales ceased feeding at an average 
received pressure level of 173 dB re 1 [mu]Pa on an (approximate) rms 
basis, and that 10 percent of feeding whales interrupted feeding at 
received levels of 163 dB dB re 1 [mu]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 with 
observations of Western Pacific gray whales feeding off Sakhalin 
Island, Russia, when a seismic survey was underway just offshore of 
their feeding area (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, Bryde's, and minke 
whales) have occasionally been reported in areas ensonified by airgun 
pulses (Stone, 2003; MacLean and Haley, 2004; Stone and Tasker, 2006), 
and calls from blue and fin whales have been localized in areas with 
airgun operations (e.g. McDonald et al., 1995; Dunn et al., 2009). 
Sightings by observers on seismic vessels off the United Kingdom from 
1997 to 2000 suggest that, during times of good sightability, sighting 
rates for mysticetes (mainly fin and sei whales) were similar when 
large arrays of airguns were shooting and not shooting (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 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 direction during seismic 
vs. non-seismic periods (Moulton et al., 2005, 2006a,b).
    Data on short-term reactions (or lack of reactions) of 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 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 
(see Appendix A in Malme et al., 1984; Richardson et al., 1995; Angliss 
and Outlaw, 2008). The Western Pacific gray whale population did not 
seem affected by a seismic survey in its feeding ground during a prior 
year (Johnson et al., 2007). 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 
Outlaw, 2008).
    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 or the EA have been reported for toothed 
whales. However, recent systematic studies on sperm whales have been 
done (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

[[Page 8659]]

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 observers on seismic vessels regularly see 
dolphins and other small toothed whales near operating airgun arrays, 
but in general there seems to be a tendency for most delphinids to show 
some avoidance of operating seismic vessels (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). However, some dolphins seem to be 
attracted to the seismic vessel and floats, and some ride the bow wave 
of the seismic vessel even when large airgun arrays are firing (Moulton 
and Miller, 2005). Nonetheless, there have been indications that 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 (Stone and Tasker, 2006; Weir, 2008). 
In most cases, the avoidance radii for delphinids appear to be small, 
on the order of 1 km (0.62 mi) or less, and some individuals show no 
apparent avoidance. The beluga is a species that (at least at times) 
shows long-distance avoidance of seismic vessels. Aerial surveys during 
seismic operations in the southeastern Beaufort Sea during summer found 
that sighting rates of beluga whales were significantly lower at 
distances 10 to 20 km (6.2 to 12.4 mi) compared with 20 to 30 km (mi) 
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 and beluga whales exhibited changes in 
behavior when exposed to strong pulsed sounds similar in duration to 
those typically used in seismic surveys (Finneran et al., 2000, 2002, 
2005; Finneran and Schlundt, 2004). 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; 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 operations 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 in general (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 (Stone, 
2003; Moulton et al., 2005, 2006a; Stone and Tasker, 2006; Weir, 2008). 
In most cases, the whales do not show strong avoidance and continue to 
call (see Appendix B in the L-DEO EA). However, controlled exposure 
experiments in the Gulf of Mexico indicate that foraging behavior was 
altered upon exposure to airgun sounds (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, northern bottlenose whales 
(Hyperodon ampullatus) continued to produce high-frequency clicks when 
exposed to sound pulses from distant seismic surveys (Laurinolli and 
Cochrane, 2005; Simard et al., 2005). Most beaked whales tend to avoid 
approaching vessels of other types (Wursig et al., 1998). They may also 
dive for an extended period when approached by a vessel (Kasuya, 1986), 
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). It is likely that these 
beaked whales would normally show strong avoidance of an approaching 
seismic vessel, but this has not been documented explicitly.
    Odontocete reactions to large arrays of airguns are variable and, 
at least for delphinids and Dall's porpoises, seem to be confined to a 
smaller radius than has been observed for the more responsive of the 
mysticetes, belugas, and harbor porpoises (Appendix B of the L-DEO EA).

Hearing Impairment and Other Physical Effects

    Temporary or permanent hearing impairment is a possibility when 
marine mammals are exposed to very strong sounds, but there has been no 
specific documentation of this for marine mammals exposed to sequences 
of airgun pulses.
    NMFS will be developing new noise exposure criteria for marine 
mammals that take account of the now-available scientific data on 
temporary threshold shift (TTS), the expected offset between the TTS 
and permanent threshold shift (PTS) thresholds, differences in the 
acoustic frequencies to which different marine mammal groups are 
sensitive, and other relevant factors. Detailed recommendations for new 
science-based noise exposure criteria were published in late 2007 
(Southall et al., 2007).
    Several aspects of the planned monitoring and mitigation measures 
for this project (see below) are designed to detect marine mammals 
occurring near the airguns to avoid exposing them to sound pulses that 
might, at least in theory, cause hearing impairment. In addition, many 
cetaceans are likely to show some avoidance of the area where received 
levels of airgun sound are high enough such that hearing impairment 
could potentially occur. In those cases, the avoidance responses of the 
animals themselves will reduce or (most likely) avoid any possibility 
of hearing impairment.
    Non-auditory physical effects may also occur in marine mammals 
exposed to strong underwater pulsed sound. Possible types of non-
auditory physiological effects or injuries that might (in theory) occur 
in mammals close to a strong sound source include stress, neurological 
effects, bubble formation, and other types of organ or tissue damage. 
It is possible that some marine mammal species (i.e., beaked whales) 
may be especially susceptible to injury and/or stranding when exposed 
to strong pulsed sounds. However, as discussed below, there is no 
definitive evidence that any of these effects occur even for marine 
mammals in close proximity to large arrays of airguns. It is especially 
unlikely that any effects of these types would occur during the present 
project given the brief duration of exposure of any given mammal, the 
deep water in the study area, and the proposed monitoring and 
mitigation measures (see below). The following subsections discuss in 
somewhat more detail the possibilities of TTS, PTS, and non-auditory 
physical effects.
    Temporary Threshold Shift--TTS is the mildest form of hearing 
impairment that can occur during exposure to a strong sound (Kryter, 
1985). While experiencing TTS, the hearing threshold rises and a sound 
must be stronger in order to be heard. At least in terrestrial mammals, 
TTS can last from minutes or hours to (in cases of strong TTS) days. 
For sound exposures at or somewhat above the TTS threshold, hearing 
sensitivity in both terrestrial and marine mammals recovers rapidly 
after exposure to the noise ends. Few data on sound levels and 
durations necessary to elicit mild TTS have been obtained for

[[Page 8660]]

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). Based on these data, 
the received energy level of a single seismic pulse (with no frequency 
weighting) might need to be approximately 186 dB re 1 
[mu]Pa\2\[middot]s (i.e., 186 dB SEL or approximately 196 to 201 re 1 
[mu]Pa [rms]) in order to produce brief, mild TTS. Exposure to several 
strong seismic pulses that each have received levels near 190 re 1 
[mu]Pa (rms) might result in cumulative exposure of approximately 186 
dB SEL and thus slight TTS in a small odontocete, assuming the TTS 
threshold is (to a first approximation) a function of the total 
received pulse energy; however, this `equal energy' concept is an 
oversimplification. The distance 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 190 dB re 1 [mu]Pa (rms) are estimated 
in Table 1 of L-DEO's application and above. Levels greater than or 
equal to 190 dB re 1 [mu]Pa (rms) are expected to be restricted to 
radii no more than 400 m. For an odontocete closer to the surface, the 
maximum radius with greater than or equal to 190 dB re 1 [mu]Pa (rms) 
would be smaller.
    The above TTS information for odontocetes is derived from studies 
on the bottlenose dolphin and beluga. For the one harbor porpoise 
tested, the received level of airgun sound that elicited onset of TTS 
was lower (Lucke et al., 2009). If these results from a single animal 
are representative, it is inappropriate to assume that onset of TTS 
occurs at similar received levels in all odontocetes (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 required to induce TTS. The frequencies to which 
baleen whales are most sensitive are lower than those to which 
odontocetes are more 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). In any event, no 
cases of TTS are expected given three considerations:
    (1) The relatively low abundance of baleen whales expected in the 
planned study areas;
    (2) The strong likelihood that baleen whales would avoid the 
approaching airguns (or vessel) before being exposed to levels high 
enough for there to be any possibility of TTS; and
    (3) The mitigation measures that are planned.
    To avoid the potential for injury, NMFS (1995, 2000) concluded that 
cetaceans and pinnipeds should not be exposed to pulsed underwater 
noise at received levels exceeding 180 and 190 dB re 1 [mu]Pa (rms), 
respectively. This sound level is not considered to be the level above 
which TTS might occur. Rather, it was the received levels above which, 
in the view of a panel of bioacoustics specialists convened by NMFS 
before TTS measurements for marine mammals started to become available, 
one could not be certain that there would be no injurious effects, 
auditory or otherwise, to cetaceans. As summarized above and in 
Southall et al. (2007), data that are now available imply that TTS is 
unlikely to occur in most odontocetes (and probably mysticetes as well) 
unless they are exposed to a sequence of several airgun pulses stronger 
than 190 dB re 1 [mu]Pa (rms).
    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 (Richardson et al., 1995; 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 the L-DEO 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, and probably 
greater than 6 dB (Southall et al., 2007). On an SEL basis, Southall et 
al. (2007) estimated that received levels would need to exceed the TTS 
threshold by at least 15 dB for there to be risk of PTS. Thus, for 
cetaceans they estimate that the PTS threshold might be an M-weighted 
SEL (for the sequence of received pulses) of approximately 198 dB re 1 
[mu]Pa2[middot]s (15 dB higher than the Mmf -
weighted TTS threshold, in a beluga, for a watergun impulse), where the 
SEL value is cumulated over the sequence of pulses.
    Southall et al. (2007) also note that, regardless of the SEL, there 
is concern about the possibility of PTS if a cetacean or pinniped 
receives one or more pulses with peak pressure exceeding 230 or 218 dB 
re 1 [mu]Pa (peak), respectively. Thus PTS might be expected upon 
exposure of cetaceans to either SEL greater than or equal to 198 dB re 
1 [mu]Pa2[middot]s or peak pressure greater than or equal to 
230 dB re 1 [mu]Pa. Corresponding proposed dual criteria for pinnipeds 
(at least harbor seals) are greater than or equal to 186 dB SEL and 
greater than or equal to 218 dB peak pressure (Southall et al., 2007). 
These estimates are all first approximations, given the limited 
underlying data, assumptions, species differences, and evidence that 
the ``equal energy'' model may not be entirely correct. A peak pressure 
of 230 dB re 1 [mu]Pa (3.2 bar [middot] m, 0-pk), which would only be 
found within a few meters of the largest (360 in3) airguns 
in the planned airgun array (Caldwell and Dragoset, 2000). A peak 
pressure of 218 dB re 1 [mu]Pa could be received somewhat farther away; 
to estimate that specific distance, one would need to apply a model 
that accurately calculates peak pressures in the near-field around an 
array of airguns.
    Given the higher level of sound necessary to cause PTS as compared 
with TTS, it is considerably less likely that PTS could occur. Baleen 
whales generally avoid the immediate area around operating seismic 
vessels, as do some other marine mammals. The planned monitoring and 
mitigation measures, including visual monitoring, passive acoustic 
monitoring (PAM) to complement visual observations (if practicable), 
power-downs, and shut-downs of the airguns when mammals are seen within 
or approaching the EZs will further reduce the probability of exposure 
of marine mammals to sounds strong enough to induce PTS.

[[Page 8661]]

    Strandings and Mortality--Marine mammals close to underwater 
detonations of high explosives can be killed or severely injured, and 
their 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 proof that they 
can cause serious injury, death, or stranding even in the case of large 
airgun arrays. However, the association of mass strandings of beaked 
whales with naval exercises 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 (Hildebrand, 2005; Southall et al., 2007). Appendix B(6) of 
the L-DEO 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 vetibular response leading to 
a behavioral change or stress-induced hemorrhagic diathesis, leading in 
turn to tissue damage; and
    (4) Tissue damage directly from sound exposure, such as through 
acoustically mediated bubble formation and growth or acoustic resonance 
of tissues.
    Some of these mechanisms are unlikely to apply in the case of 
impulse sounds. However, there are increasing indications that gas-
bubble disease (analogous to ``the bends''), induced in supersaturated 
tissue by a behavioral response to acoustic exposure, could be a 
pathologic mechanism for the strandings and mortality of some deep-
diving cetaceans exposed to sonar. The evidence for this remains 
circumstantial and associated with exposure to naval mid-frequency 
sonar, not seismic surveys (Cox et al., 2006; Southall et al., 2007).
    Seismic pulses and mid-frequency sonar signals are quite different, 
and some mechanisms by which sonar sounds have been hypothesized to 
affect beaked whales are unlikely to apply to airgun pulses. Sounds 
produced by airgun arrays are broadband impulses with most of the 
energy below 1 kHz. Typical military mid-frequency sonars operate at 
frequencies of 2 to 10 kHz, generally with a relatively narrow 
bandwidth at any one time. Thus, it is not appropriate to assume that 
there is a direct connection between the effects of military sonar and 
seismic surveys on marine mammals. However, evidence that sonar pulses 
can, in special circumstances, lead (at least indirectly) to physical 
damage and mortality (Balcomb and Claridge, 2001; NOAA and USN, 2001; 
Jepson et al., 2003; Fern[aacute]ndez et al., 2004, 2005a; Cox et al., 
2006) suggests that caution is warranted when dealing with exposure of 
marine mammals to any high-intensity pulsed sound.
    There is no conclusive evidence of cetacean strandings or deaths at 
sea as a result of exposure to seismic surveys, but a few cases of 
strandings in the general area where a seismic survey was ongoing have 
led to speculation concerning a possible link between seismic surveys 
and strandings. Suggestions that there was a link between seismic 
surveys and strandings of humpback whales in Brazil (Engel et al., 
2004) was not well founded based on available data (IAGC, 2004; IWC, 
2007b). In September 2002, there wa