Small Takes of Marine Mammals Incidental to Specified Activities; Low-Energy Marine Seismic Survey in the Northeast Pacific Ocean, June-July 2008, 30076-30093 [E8-11546]

Agencies

• DEPARTMENT OF COMMERCE
• National Oceanic and Atmospheric Administration

[Federal Register Volume 73, Number 101 (Friday, May 23, 2008)]
[Notices]
[Pages 30076-30093]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: E8-11546]


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DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

RIN 0648-XG64


Small Takes of Marine Mammals Incidental to Specified Activities; 
Low-Energy Marine Seismic Survey in the Northeast Pacific Ocean, June-
July 2008

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

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

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SUMMARY:  NMFS has received an application from University of Texas, 
Institute of Geophysics (UTIG) for an Incidental Harassment 
Authorization (IHA) to take marine mammals incidental to conducting a 
low-energy marine seismic survey in the Northeast Pacific Ocean during 
June-July, 2008. Pursuant to the Marine Mammal Protection Act (MMPA), 
NMFS is requesting comments on its proposal to issue an IHA to UTIG to 
incidentally take, by Level B harassment only, several species of 
marine mammals during the aforementioned activity.

DATES:  Comments and information must be received no later than June 
23, 2008.

ADDRESSES:  Comments on the application should be addressed to P. 
Michael Payne, Chief, Permits, Conservation and Education Division, 
Office of Protected Resources, National Marine Fisheries Service, 1315 
East-West Highway, Silver Spring, MD 20910-3225. The mailbox address 
for providing email comments is PR1.0648XB70@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.
    A copy of the application containing a list of the references used 
in this document may be obtained by writing to the address specified 
above, telephoning the contact listed below (see FOR FURTHER 
INFORMATION CONTACT), or visiting the internet at: https://
www.nmfs.noaa.gov/pr/permits/incidental.htm#applications.
    Documents cited in this notice may be viewed, by appointment, 
during regular business hours, at the aforementioned address.

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

SUPPLEMENTARY INFORMATION:

Background

    Sections 101(a)(5)(A) and (D) of the MMPA (16 U.S.C. 1361 et seq.) 
direct the Secretary of Commerce to allow, upon request, the 
incidental, but not intentional, taking of marine mammals by U.S. 
citizens who engage in a specified activity (other than commercial 
fishing) within a specified geographical region if certain findings are 
made and either regulations are issued or, if the taking is limited to 
harassment, a notice of a proposed authorization is provided to the 
public for review.
    Authorization shall be granted if NMFS finds that the taking will 
have a negligible impact on the species or stock(s), will not have an 
unmitigable adverse impact on the availability of the species or 
stock(s) for subsistence uses (where relevant), and if the permissible 
methods of taking and requirements pertaining to the mitigation, 
monitoring, and reporting of such takings are set forth. NMFS has 
defined ``negligible impact'' in 50 CFR 216.103 as ''...an impact 
resulting from the specified activity that cannot be reasonably 
expected to, and is not reasonably likely to, adversely affect the 
species or stock through effects on annual rates of recruitment or 
survival.''
    Section 101(a)(5)(D) of the MMPA established an expedited process 
by which citizens of the U.S. can apply for an authorization to 
incidentally take small numbers of marine mammals by harassment. Except 
with respect to certain activities not pertinent here, the MMPA defines 
``harassment'' as:
    any act of pursuit, torment, or annoyance which (I) has the 
potential to injure a marine mammal or marine mammal stock in the 
wild [Level A harassment]; or (ii) has the potential to disturb a 
marine mammal or marine mammal stock in the wild by causing 
disruption of behavioral patterns, including, but not limited to, 
migration, breathing, nursing, breeding, feeding, or sheltering 
[Level B harassment].
    Section 101(a)(5)(D) establishes a 45-day time limit for NMFS 
review of an application followed by a 30-day public notice and comment 
period on any proposed authorizations for the incidental harassment of 
marine mammals. Within 45 days of the close of the comment period, NMFS 
must either approve or deny the authorization.

Summary of Request

    On March 4, 2008, NMFS received an application from UTIG for the 
taking, by Level B harassment only, of several

[[Page 30077]]

species of marine mammals incidental to conducting, with research 
funding from the National Science Foundation (NSF), a bathymetric and 
seismic survey program approximately 100 km (approximately 62 mi) off 
the Oregon coast in the Northeast Pacific Ocean during June-July, 2008. 
The purpose of the research program is to investigate the methane vent 
systems that exist offshore Oregon. These systems release methane by 
active venting at the seafloor. They can also form relatively high 
concentrations of methane hydrate in the sub seafloor, up to 150 m (492 
ft) below the sea bottom. The goal is to image these systems in detail 
to understand how vent structure directs methane from the subsurface to 
be vented into the oceans, or potentially stored in the subsurface as 
methane hydrate. Methane is a significant greenhouse gas, and methane 
release from vents or from hydrate has a significant potential to 
affect the Earth's climate. Hydrates are also a potentially significant 
source of energy. Also included in the research is the use of a 
multibeam echosounder and sub-bottom profiler.

Description of the Proposed Activity

    The seismic survey will involve one vessel, the R/V Thomas G. 
Thompson (Thompson), which is scheduled to depart from Seattle, 
Washington on June 30, 2008 and return on July 19, 2008. The exact 
dates of the activities may vary by a few days because of weather 
conditions, scheduling, repositioning, streamer operations and 
adjustments, GI airguns deployment, or the need to repeat some lines if 
data quality is substandard. The proposed ultra-high resolution 3-
dimensional (3-D) seismic surveys around the methane vent systems of 
Hydrate Ridge, will take place off the Oregon coast in the northeastern 
Pacific Ocean. The overall area within which the seismic surveys will 
occur is located between approximately 44[deg] and 45[deg] N. and 
124.5[deg] and 126[deg] W (Figure 1 in the application). The surveys 
will occur approximately 100 km (approximately 62 mi) offshore from 
Oregon in water depths between approximately 650 and 1,200 m (2,132 and 
3,936 ft), entirely within the Exclusive Economic Zone (EEZ) of the 
U.S.
    The seismic survey will image the subsurface structures that 
control venting. The vent systems control whether the methane is 
directly released into the ocean and atmosphere or stored in methane 
hydrate. Methane hydrate storage has the potential for rapid 
dissociation and release into the ocean or atmosphere. The subsurface 
structure that will be imaged will determine the mechanisms involved in 
methane venting. The results will be applicable to the numerous vent 
systems that exist on continental margins worldwide. The data will also 
be used to design observatories that can monitor and assess the methane 
fluxes and mechanisms of methane release that operate on Hydrate Ridge.
    The Thompson will deploy two low-energy Generator-Injector (GI) 
airguns (guns) as an energy source (with a discharge volume of 40-60 
in\3\ for each gun or a total of 80-120 in\3\) , and a P-Cable system. 
The 12 m (39.5 ft) long P-Cable system is supplied by Northampton 
Oceanographic Center in the U.K. The towed system will consist of at 
least 12 streamers (and possibly up to 24) spaced approximately 12.5 m 
(41 ft) apart and each containing 11 hydrophones, all summed to a 
single channel. The energy to the GI guns is compressed air supplied by 
compressors on board the source vessel. As the GI guns are towed along 
the survey lines, the P-Cable system will receive the returning 
acoustic signals.
    The seismic program will consist of three survey grids: two of the 
surveys each cover a 15 km2 area and the third covers a 25 km\2\ (see 
Figure 1 in UTIG's application). The line spacing within the three 
survey grids will either be 75 m (246 ft) (if 12 streamers are used) or 
150 m (492 ft) (if 24 streamers are used). The total line km to be 
surveyed in the grids at the 75 m spacing is 975 km (605.8 mi), 
including turns. Water depths at the seismic survey locations range 
from 650 to 1,200 m (2132 to 3936 ft). Most (92 percent) of the survey 
will take place over intermediate (100-1,000 m) water depths; the 
remaining 8 percent will be in water deeper than 1,000 m. If time 
permits, an additional 300 line km will be surveyed along the outside 
edges of the three grids. The GI guns are expected to operate for a 
total of approximately 150 hours during the cruise. There will be 
additional seismic operations associated with equipment testing, start-
up, and repeat coverage of any areas where initial data quality is sub-
standard.
    In addition to the operations of the two GI guns and P-cable 
system, a Simrad EM300 30 kHz multibeam echosounder, and a Knudsen 12 
kHz 320BR sub-bottom profiler will be used during the proposed cruise.

Vessel Specifications

    The Thompson has a length of 83.5 m (274 ft), a beam of 16 m (52.5 
ft), and a maximum draft of 5.8 m (19 ft). The ship is powered by twin 
360[deg]-azimuth stern thrusters a single 3,000-hp DC motor and a 
water-jet bow thruster powered by a 1,600-hp motor. The motors are 
driven by up to three 1,500-kW and three 715-kW generators; normal 
operations use two 1,500-kW and one 750-kW generator, but this changes 
with ship speed, sea state, and other variables. An operation speed of 
6.5 km/h (3.5 knots) will be used during seismic acquisition. When not 
towing seismic survey gear, the Thompson cruises at 22.2 km/h (12 
knots) and has a maximum speed of 26.9 km/h (14.5 knots). It has a 
normal operating range of approximately 24,400 km (8,264 mi).

Acoustic Source Specifications

Seismic Airguns
    The vessel Thompson will tow two GI guns and a P-Cable system of 12 
to 24, 12 m long streamers containing hydrophones along predetermined 
survey grids. Seismic pulses will be emitted at intervals of 3.5 s, 
which corresponds to a shot interval of approximately 6.3 m (20.7 ft) 
at a speed of 3.5 knots (6.5 km/h). The generator chamber of a GI gun, 
the one responsible for introducing the sound pulse into the ocean, is 
40-60 in3. The second injector chamber (40-60 in3) injects air into the 
previously-generated bubble to maintain its shape and does not 
introduce more sound into the water. The two 40-60 in3 GI guns will be 
towed 29 m (95.1 ft) behind the Thompson, at a depth of 1.5-3 m (4.9-
9.8 ft). The dominant frequency components are 0-188 Hz.
    The sound pressure field of two 105 in\3\ GI guns has been modeled 
by the Lamont-Doherty Earth Observatory (L-DEO) of Columbia University 
in relation to distance and direction from the GI guns. The model does 
not allow for bottom interactions and is most directly applicable to 
close distances and/or deep water. Because the L-DEO model is for a 
pair of larger GI guns with a total discharge of up to 210 in\3\, the 
values overestimate the distances for two GI guns with a discharge of 
up to 120 in3, as planned for use during the proposed study. This 
source, which is directed downward, was found to have an output (0-
peak) of 237 dB re 1 microPam.
    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

[[Page 30078]]

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, 2000). The precise difference between rms 
and peak or peak-to-peak values depends on the frequency content and 
duration of the pulse, among other factors. However, the rms level is 
always lower than the peak or peak-to-peak level for an airgun-type 
source.
Sub-bottom Profiler
    The Thompson will utilize a Simrad EM300 30-kHz Multibeam 
Echosounder (MBES) as the primary bottom-mapping echosounder during the 
cruise. The Simrad EM300 transducer is hull-mounted within a transducer 
pod that is located midship. The system's normal operating frequency is 
approximately 30 kHz. The transmit fan-beam is split into either three 
or nine narrower beam sectors with independent active steering to 
correct for vessel yaw. Angular coverage is 36 degrees (in Extra Deep 
Mode, for use in water depths 3,000 to 6,000 m) or 150 degrees (in 
shallower water). The total angular coverage of 36 or 150 degrees 
consists of the 3 or 9 beams transmitted at slightly different 
frequencies. The sectors are frequency coded between 30 and 34 kHz and 
they are transmitted sequentially at each ping. Except in very deep 
water where the total beam is 36 x 1, the composite fan beam will 
overlap slightly if the vessel yaw is less than the fore-aft width of 
the beam (1,2, or 4, respectively). Achievable swath width on a flat 
bottom will normally be approximately 5x the water depth. The maximum 
source level is 237 dB re 1 microPam (rms) (Hammerstand, 2005). 
In deep water (500-3,000 m) a pulse length of 5 ms is normally used. At 
intermediate depths (100-1,000 m), a pulse length of 2 ms is used, and 
in shallow water (<300 m), a pulse length of 0.7 ms is used. The ping 
rate is mainly limited by the round trip travel time in the water up to 
a ping rate of 10 pings/s in shallow water.
    The Thompson will also utilize the Knudsen Engineering Model 320BR 
sub-bottom profiler, which is a dual-frequency echosounder designed to 
operate at 3.5 and/or 12 kHz. It is used to provide data about the 
sedimentary features that occur below the sea floor. The energy from 
the sub-bottom profiler is directed downward (in an 80-degree cone) via 
a 12 kHz transducer (EDO 323B) or a 3.5 kHz array of 16 ORE 137D 
transducers in a 4 x 4 arrangement. The maximum power output of the 
320BR is 10 kilowatts for the 3.5 kHz section and 2 kilowatts for the 
12 kHz section.
    The pulse length for the 3.5 kHz section of the 320BR is 0.8-24 ms, 
controlled by the system operator in regards to water depth and 
reflectivity of the bottom sediments, and will usually be 12 or 24 ms 
in this survey. The system produces one sound pulse and then waits for 
its return before transmitting again. Thus, the pulse interval is 
directly dependent upon water depth, and in this survey the interval is 
estimated to be every 4.5-8 sec. Using the Sonar Equations and assuming 
100 percent efficiency in the system (impractical in real world 
applications), the source level for the 320BR is calculated to be 211 
dB re 1 microPa-m. In practice, the system is rarely operated above 80 
percent power level.
Safety Radii
    NMFS has determined that for acoustic effects, using acoustic 
thresholds in combination with corresponding safety radii is the most 
effective way to consistently apply measures to avoid or minimize the 
impacts of an action, and to quantitatively estimate the effects of an 
action. Thresholds are used in two ways: (1) to establish a mitigation 
shut-down or power down zone, i.e., if an animal enters an area 
calculated to be ensonified above the level of an established 
threshold, a sound source is powered down or shut down; and (2) to 
calculate take, in that a model may be used to calculate the area 
around the sound source that will be ensonified to that level or above, 
then, based on the estimated density of animals and the distance that 
the sound source moves, NMFS can estimate the number of marine mammals 
that may be ``taken''. NMFS believes that to avoid permanent 
physiological damage (Level A Harassment), cetaceans and pinnipeds 
should not be exposed to pulsed underwater noise at received levels 
exceeding, respectively, 180 and 190 dB re 1 microPa (rms). NMFS also 
assumes that cetaceans or pinnipeds exposed to levels exceeding 160 dB 
re 1 microPa (rms) may experience Level B Harassment.
    Received sound levels have been modeled by L-DEO for a number of 
airgun configurations, including one 45-in\3\ GI gun, in relation to 
distance and direction from the airgun(s). The model does not allow for 
bottom interactions and is most directly applicable to deep water. 
Based on the modeling, estimates of the maximum distances from the GI 
gun where sound levels of 190, 180, and 160 dB re 1 microPa (rms) are 
predicted to be received in deep (>1000-m, 3280-ft) water are 8, 23, 
and 220 m (26.2, 75.5, and 721.8 ft), respectively and 12, 35, and 330 
m (39.4, 115, and 1,082.7 ft), respectively for intermediate water 
depths (100-1000m, 328-3,280 ft). Because the model results are for a 
2.5-m (8.2-ft) tow depth, the above distances slightly underestimate 
the distances for the 45-in\3\ GI gun towed at 4-m (13-ft) depth.
    Empirical data concerning the 180- and 160- dB distances have been 
acquired based on measurements during the acoustic verification study 
conducted by L-DEO in the northern Gulf of Mexico from 27 May to 3 June 
2003 (Tolstoy et al. 2004). Although the results are limited, the data 
showed that radii around the airguns where the received level would be 
180 dB re 1 microPa (rms) vary with water depth. Similar depth-related 
variation is likely in the 190 dB distances applicable to pinnipeds. 
Correction factors were developed for water depths 100-1,000 m (328-
3,280 ft) and <100 m (328 ft). The proposed survey will occur in depths 
650-1,200 m (2,132-3,936 ft), so the correction factors for the latter 
are not relevant here.
    The empirical data indicate that, for deep water (>1,000 m, 3,280 
ft), the L-DEO model tends to overestimate the received sound levels at 
a given distance (Tolstoy et al., 2004). However, to be precautionary 
pending acquisition of additional empirical data, it is proposed that 
safety radii during airgun operations in deep water will be the values 
predicted by L-DEO's model (above). Therefore, the assumed 180- and 
190-dB radii are 69 m and 20 m (226.3 and 65.6 ft), respectively.
    Empirical measurements were not conducted for intermediate depths 
(100-1,000 m, 328-3,280 ft). On the expectation that results will be 
intermediate between those from shallow and deep water, a 1.5x 
correction factor is applied to the estimates provided by the model for 
deep water situations. This is the same factor that was applied to the 
model estimates during L-DEO cruises in 2003. The assumed 180- and 190-
dB radii in intermediate-depth water are 104 m and 30 m (341.1 and 98.4 
ft), respectively.
    The GI guns will be shut down immediately when cetaceans or 
pinnipeds are detected within or about to enter the measured 180-dB 
(rms) or 190-dB (rms) radius, respectively.

Description of Marine Mammals in the Activity Area

    Thirty-two marine mammal species, including 19 odontocete (dolphins 
and small and large toothed whales) species, seven mysticete (baleen 
whales) species, five pinniped species, and the sea otter,

[[Page 30079]]

may occur or have been documented to occur in the marine waters off 
Oregon and Washington, excluding extralimital sightings or strandings 
(Table 1 here). Six of the species that may occur in the project area 
are listed under the U.S. Endangered Species Act (ESA) as endangered, 
including sperm, humpback, blue, fin, sei, and North Pacific right 
whales. In addition, the southern resident killer whale stock is also 
listed as endangered, but is unlikely to be seen in offshore waters of 
Oregon. The threatened Steller sea lion could also occur in the project 
area. However, the threatened northern sea otter is only known to occur 
in coastal waters and is not expected in the project area (the sea 
otter is under the jurisdiction of the U.S. Fish and Wildlife Service.
    Gray whales are also not expected in the project area because their 
occurrence off Oregon is limited to very shallow, coastal waters. The 
California sea lion, Steller sea lion, and harbor seal are also mainly 
coastal and are not expected at the survey locations. Information on 
habitat and abundance of the species that may occur in the study area 
are given in Table 1 below. Vagrant ringed seals, hooded seals, and 
ribbon seals have been sighted or stranded on the coast of California 
(see Mead, 1981; Reeves et al., 2002) and presumably passed through 
Oregon waters. A vagrant beluga was seen off the coast of Washington 
(Reeves et al., 2002).
    The six species of marine mammals expected to be most common in the 
deep pelagic or slope waters of the project area, where most of the 
survey sites are located, include the Pacific white-sided dolphin, 
northern right whale dolphin, Risso's dolphin, short-beaked common 
dolphin, Dall's porpoise, and northern fur seal (Green et al., 1992, 
1993; Buchanan et al., 2001; Barlow, 2003; Carretta et al., 2006).
    The sperm, pygmy sperm, mesoplodont species, Baird's beaked, and 
Cuvier's beaked whales and the northern elephant seal are considered 
pelagic species, but are generally uncommon in the waters near the 
survey area. 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 UTIG's application.

----------------------------------------------------------------------------------------------------------------
               Species                             Habitat                  Abundance\1\          Rqstd Take
----------------------------------------------------------------------------------------------------------------
Mysticetes                             ...............................  ....................  ..................
 
North Pacific right whale (Eubalaena   Inshore, occasionally offshore   N.A.\2\               0
 japonica) *
----------------------------------------------------------------------------------------------------------------
Humpback whale (Megaptera              Mainly nearshore waters and      1391                  1
 novaeangliae) *                        banks
----------------------------------------------------------------------------------------------------------------
Minke whale (Balaenoptera              Pelagic and coastal              1015                  1
 acutorostrata)
----------------------------------------------------------------------------------------------------------------
Sei whale (Balaenoptera borealis) *    Primarily offshore, pelagic      56                    0
----------------------------------------------------------------------------------------------------------------
Fin whale (Balaenoptera physalus) *    Continental slope, mostly        3279                  1
                                        pelagic
----------------------------------------------------------------------------------------------------------------
Blue whale (Balaenoptera musculus) *   Pelagic and coastal              1744                  0
----------------------------------------------------------------------------------------------------------------
Odontocetes                            ...............................  ....................  ..................
 
Sperm whale (Physeter macrocephalus)   Usually pelagic and deep seas    1233                  2
 *
----------------------------------------------------------------------------------------------------------------
Pygmy sperm whale (Kogia breviceps)    Deep waters off the shelf        247                   2
----------------------------------------------------------------------------------------------------------------
Dwarf sperm whale (Kogia sima)         Deep waters off the shelf        N.A.                  0
----------------------------------------------------------------------------------------------------------------
Cuvier's beaked whale (Ziphius         Pelagic                          1884                  0
 cavirostris)
----------------------------------------------------------------------------------------------------------------
Baird's beaked whale (Berardius        Pelagic                          228                   1
 bairdii)
----------------------------------------------------------------------------------------------------------------
Blainville's beaked whale (Mesoplodon  Slope, offshore                  1247 \3\              0
 densirostris)
----------------------------------------------------------------------------------------------------------------
Hubb's beaked whale (Mesoplodon        Slope, offshore                  1247 \3\              0
 carlhubbsi)
----------------------------------------------------------------------------------------------------------------
Stejneger's beaked whale (Mesoplodon   Slope, offshore                  1247 \3\              0
 stejnegeri)
----------------------------------------------------------------------------------------------------------------
Mesoplodon sp. (Unidentified)          Slope, offshore                  1247                  1
----------------------------------------------------------------------------------------------------------------
Offshore bottlenose dolphin (Tursiops  Offshore, slope                  5,065                 0
 truncatus)
----------------------------------------------------------------------------------------------------------------
Striped dolphin (Stenella              Off continental shelf            13,934                0
 coeruleoalba)
----------------------------------------------------------------------------------------------------------------
Short-beaked common dolphin            Shelf and pelagic, seamounts     449,846               7
 (Delphinus delphis)
----------------------------------------------------------------------------------------------------------------
Pacific white-sided dolphin            Offshore, slope                  59,274                6
 (Lagenorhynchus obliquidens)
----------------------------------------------------------------------------------------------------------------
Northern right whale dolphin           Slope, offshore waters           20,362                5
 (Lissodelphis borealis)
----------------------------------------------------------------------------------------------------------------
Risso's dolphin (Grampus griseus)      Shelf, slope, seamounts          16,066                3
----------------------------------------------------------------------------------------------------------------
False killer whale (Pseudorca          Pelagic, occasionally inshore    N.A.                  0
 crassidens)
----------------------------------------------------------------------------------------------------------------
Killer whale (Orcinus orca)            Widely distributed               466 (Offshore)        1
----------------------------------------------------------------------------------------------------------------

[[Page 30080]]

 
Short-finned pilot whale               Mostly pelagic, high-relief      304                   0
 (Globicephala macrorhynchus)           topography
----------------------------------------------------------------------------------------------------------------
Harbor porpoise (Phocoena phocoena)    Coastal and inland waters        39,586 (OR/WA)        0
----------------------------------------------------------------------------------------------------------------
Dall's porpoise (Phocoenoides dalli)   Shelf, slope, offshore           99,517                47
----------------------------------------------------------------------------------------------------------------
Pinnipeds                              ...............................  ....................  ..................
 
Northern fur seal (Callorhinus         Pelagic, offshore                688,028 \2\           19
 ursinus)
----------------------------------------------------------------------------------------------------------------
California sea lion (Zalophus          Coastal, shelf                   237,000-244,000       NA
 californianus californianus)
----------------------------------------------------------------------------------------------------------------
Northern elephant seal (Mirounga       Coastal, pelagic when migrating  101,000 (CA)          2
 angustirostris)
----------------------------------------------------------------------------------------------------------------
Table 1. Species expected to be encountered (and potentially harassed) during UTIG's NE Pacific Ocean cruise.
N.A. B Data not available or species status was not assessed.
* Species are listed as threatened or endangered under the Endangered Species Act.
\1\ Abundance given for U.S., Eastern North Pacific, or California/Oregon/Washington Stock, whichever is
  included in the 2005 U.S. Pacific Marine Mammal Stock Assessments (Carretta et al. 2006), unless otherwise
  stated.
\2\ Angliss and Outlaw (2005).
\3\ All mesoplodont whales

Potential Effects of Airguns

    The effects of sounds from airguns might include one or more of the 
following: tolerance, masking of natural sounds, behavioral 
disturbance, and temporary or permanent hearing impairment or non-
auditory physical or physiological effects (Richardson et al., 1995; 
Gordon et al., 2004). Given the small size of the GI guns planned for 
the proposed project, effects are anticipated to be considerably less 
than would be the case with a large array of airguns. It is very 
unlikely that there would be any cases of temporary or, especially, 
permanent hearing impairment or any significant non-auditory physical 
or physiological effects. Also, behavioral disturbance is expected to 
be limited to relatively short distances.
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 A 
of UTIG's application. However, it should be noted that most of the 
measurements of airgun sounds that have been reported concerned sounds 
from larger arrays of airguns, whose sounds would be detectable 
considerably farther away than the two GI guns planned for use in the 
proposed project.
    Numerous other studies have shown that marine mammals at distances 
more than a few kilometers from operating seismic vessels often show no 
apparent response (see Appendix A (e) of UTIG's application). That is 
often true even in cases when the pulsed sounds appear to be readily 
audible to the animals based on measured received levels and the 
hearing sensitivity of that 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 and small odontocetes seem to be more tolerant of 
exposure to airgun pulses than are baleen whales. Given the relatively 
small, low-energy airgun source planned for use in this project, NMFS 
expects mammals to tolerate being closer to this source than for a 
larger airgun source typical of most seismic surveys. Mysticetes, 
odontocetes, pinnipeds and sea otters have all been seen commonly by 
observers aboard vessels conducting small-source seismic surveys, 
indicating some degree of tolerance of sounds from small airgun sources 
(e.g., Calambokidis et al., 2002; Haley and Koski, 2004; Holst et al., 
2005a; Ireland et al., 2005; MacLean and Koski, 2005; see also ``site 
survey'' portions of Stone, 2003 and Stone and Tasker, 2006).
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 
very few specific data on this matter. Some whales are known to 
continue calling in the presence of seismic pulses. Their calls can 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). Although there has been one report that sperm 
whales cease calling when exposed to pulses from a very distant seismic 
ship (Bowles et al., 1994), a recent study reports that sperm whales 
off northern Norway continued calling in the presence of seismic pulses 
(Madsen et al., 2002c). Similar reactions have also been shown during 
recent work in the Gulf of Mexico (Tyack et al., 2003; Smultea et al., 
2004). Given the small source planned for use here, there is even less 
potential for masking of baleen or sperm whale calls during the present 
study than in most seismic surveys. Masking effects of seismic pulses 
are expected to be negligible in the case of the smaller odontocete 
cetaceans, given the intermittent nature of seismic pulses and the 
relatively low source level of the airgun to be used here. Dolphins and 
porpoises are commonly heard calling while airguns are operating 
(Gordon et al., 2004; Smultea et al., 2004; Holst et al., 2005a,b). 
Also, the sounds important to small odontocetes are predominantly at 
much higher frequencies than are airgun sounds. Masking effects, in 
general, are discussed further in Appendix A (d) of UTIG's application.
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). If a marine mammal responds to an underwater sound by 
changing its behavior or moving a small

[[Page 30081]]

distance, the response may or may not rise to the level of harassment, 
let alone affect the stock or the species as a whole. Alternatively, if 
a sound source displaces marine mammals from an important feeding or 
breeding area, effects on the stock or species could potentially be 
more than negligible. Given the many uncertainties in predicting the 
quantity and types of impacts of noise on marine mammals, it is common 
practice to estimate how many mammals are likely to be present within a 
particular distance of industrial activities, or exposed to a 
particular level of industrial sound. This practice potentially 
overestimates the numbers of marine mammals that are affected in some 
biologically-important manner.
    The sound criteria used to estimate how many marine mammals might 
be disturbed to some biologically-important degree by a seismic program 
are based on behavioral observations during studies of several species. 
However, information is lacking for many species. Detailed studies have 
been done on humpback, gray, and bowhead whales and ringed seals. Less 
detailed data are available for some other species of baleen whales, 
sperm whales, and small toothed whales. Most of those studies have 
focused on the impacts resulting from the use of much larger airgun 
sources than those planned for use in the present project. Thus, 
effects are expected to be limited to considerably smaller distances 
and shorter periods of exposure in the present project than in most of 
the previous work concerning marine mammal reactions to airguns.
    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 A (e) of UTIG's 
application, baleen whales exposed to strong noise pulses from airguns 
often react by deviating from their normal migration route and/or 
interrupting their feeding activities and moving away from the sound 
source. In the case of the migrating gray and bowhead whales, the 
observed changes in behavior appeared to be of little or no biological 
consequence to the animals. They simply avoided the sound source by 
displacing their migration route to varying degrees, but within the 
natural boundaries of the migration corridors.
    Studies of gray, bowhead, and humpback whales have determined that 
received levels of pulses in the 160-170 dB re 1 microPa (rms) range 
seem to cause obvious avoidance behavior in a substantial fraction of 
the animals exposed. In many areas, seismic pulses from large arrays of 
airguns diminish to those levels at distances ranging from 4.5-14.5 km 
(2.8-9 mi) from the source. A substantial proportion of the baleen 
whales within those distances may show avoidance or other strong 
disturbance reactions to the airgun array. Subtle behavioral changes 
sometimes become evident at somewhat lower received levels, and recent 
studies, reviewed in Appendix A (e) of UTIG's application, have shown 
that some species of baleen whales, notably bowheads and humpbacks, at 
times show strong avoidance at received levels lower than 160-170 dB re 
1 microPa (rms). Reaction distances would be considerably smaller 
during the present project, in which the 160-dB radius is predicted to 
be approximately 0.22 or 0.33 km (0.14 or 0.21 mi), as compared with 
several kilometers when a large array of airguns is operating.
    Responses of humpback whales to seismic surveys have been studied 
during migration and on the summer feeding grounds, and there has also 
been discussion of effects on the Brazilian wintering grounds. McCauley 
et al. (1998, 2000) studied the responses of humpback whales off 
Western Australia to a full-scale seismic survey with a 16-airgun, 
2,678-in\3\ array, and to a single 20-in\3\ airgun with a source level 
of 227 dB re 1 microPa m. McCauley et al. (1998) documented that 
avoidance reactions began at 5-8 km (3.1-5 mi) from the array, and that 
those reactions kept most pods approximately 3-4 km (1.9-2.5 mi) from 
the operating seismic boat. McCauley et al. (2000) noted localized 
displacement during migration of 4-5 km (2.5-3.1 mi) by traveling pods 
and 7-12 km (4.3-7.5 mi) by cow-calf pairs. Avoidance distances with 
respect to the single airgun were smaller but consistent with the 
results from the full array in terms of received sound levels. Mean 
avoidance distance from the airgun corresponded to a received sound 
level of 140 dB re 1 microPa (rms); that was the level at which 
humpbacks started to show avoidance reactions to an approaching airgun. 
The standoff range, i.e., the closest point of approach of the whales 
to the airgun, corresponded to a received level of 143 dB re 1 microPa 
(rms). The initial avoidance response generally occurred at distances 
of 5-8 km (3.1-5 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 100-400 m (328-1,312 ft), where 
the maximum received level was 179 dB re 1 microPa (rms).
    Humpback whales on their summer feeding grounds in southeast Alaska 
did not exhibit persistent avoidance when exposed to seismic pulses 
from a 1.64-L (100 in\3\) airgun (Malme et al., 1985). Some humpbacks 
seemed ``startled'' at received levels of 150-169 dB re 1 microPa on an 
approximate rms basis. Malme et al. (1985) conclude that there was no 
clear evidence of avoidance, despite the possibility of subtle effects, 
at received levels up to 172 re 1 microPa (approximately rms).
    It has been suggested that South Atlantic humpback whales wintering 
off Brazil may be displaced or even strand upon exposure to seismic 
surveys (Engel et al., 2004). The evidence for this was circumstantial, 
subject to alternative explanations (IAGC 2004), and not consistent 
with results from direct studies of humpbacks exposed to seismic 
surveys in other areas and seasons. After allowance for data from 
subsequent years, there was ``no observable direct correlation'' 
between strandings and seismic surveys (IWC 2007:236).
    Results from bowhead whales show that responsiveness of baleen 
whales to seismic surveys can be quite variable depending on the 
activity (migrating vs. feeding) of the whales. Bowhead whales 
migrating west across the Alaskan Beaufort Sea in autumn, in 
particular, are unusually responsive, with substantial avoidance 
occurring out to distances of 20 30 km (12.4-18.6 mi) from a medium-
sized airgun source, where received sound levels were on the order of 
130 dB re 1 microPa (rms) (Miller et al., 1999; Richardson et al., 
1999). However, more recent research on bowhead whales (Miller et al., 
2005a) corroborates earlier evidence that, during the summer feeding 
season, bowheads are not as sensitive to seismic sources. In summer, 
bowheads typically begin to show avoidance reactions at a received 
level of about 160-170 dB re 1 microPa (rms) (Richardson et al., 1986; 
Ljungblad et al., 1988; Miller et al., 1999). There are no data on the 
reactions of wintering bowhead whales to seismic surveys. See Appendix 
A (e) of UTIG's application for more information regarding bowhead 
whale reactions to airguns.
    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

[[Page 30082]]

northern Bering Sea. Malme et al. (1986, 1988) estimated, based on 
small sample sizes, that 50 percent of feeding gray whales ceased 
feeding at an average received pressure level of 173 dB re 1 microPa on 
an (approximate) rms basis, and that 10 percent of feeding whales 
interrupted feeding at received levels of 163 dB. Those findings were 
generally consistent with the results of experiments conducted on 
larger numbers of gray whales that were migrating along the California 
coast and on observations of Western Pacific gray whales feeding off 
Sakhalin Island, Russia (Johnson et al., 2007).
    Various species of Balaenoptera (blue, fin, sei, and minke whales) 
have occasionally been reported in areas ensonified by airgun pulses. 
Sightings by observers on seismic vessels off the U.K. from 1997 to 
2000 suggest that, at times of good sightability, numbers of rorquals 
seen are similar when airguns are shooting and not shooting (Stone, 
2003). Although individual species did not show any significant 
displacement in relation to seismic activity, all baleen whales 
combined were found to remain significantly further from the airguns 
during shooting compared with periods without shooting (Stone, 2003; 
Stone and Tasker, 2006). In a study off Nova Scotia, Moulton and Miller 
(2005) found little or no difference in sighting rates and initial 
sighting distances of balaenopterid whales when airguns were operating 
vs. silent. However, there were indications that these whales were more 
likely to be moving away when seen during airgun operations.
    Data on short-term reactions (or lack of reactions) of cetaceans to 
impulsive noises do not necessarily provide information about long-term 
effects. It is not known whether impulsive noises affect reproductive 
rate or distribution and habitat use in subsequent days or years. 
However, gray whales continued to migrate annually along the west coast 
of North America despite intermittent seismic exploration and much ship 
traffic in that area for decades (Appendix A in Malme et al., 1984). 
Bowhead whales continued to travel to the eastern Beaufort Sea each 
summer despite seismic exploration in their summer and autumn range for 
many years (Richardson et al., 1987). In any event, the brief exposures 
to sound pulses from the present small airgun source are highly 
unlikely to result in prolonged effects.
    Toothed Whales - Little systematic information is available about 
reactions of toothed whales to noise pulses. Few studies similar to the 
more extensive baleen whale/seismic pulse work summarized above have 
been reported for toothed whales. However, a systematic study on sperm 
whales has been done (Jochens and Biggs, 2003; Tyack et al., 2003; 
Miller et al., 2006), and there is an increasing amount of information 
about responses of various odontocetes to seismic surveys based on 
monitoring studies (Stone, 2003; Smultea et al., 2004; Bain and 
Williams, 2006; Holst et al., 2006; Stone and Tasker, 2006; Moulton and 
Miller, 2005).
    Seismic operators and marine mammal observers sometimes see 
dolphins and other small toothed whales near operating airgun arrays, 
but in general there seems to be a tendency for most delphinids to show 
some limited avoidance of seismic vessels operating large airgun 
systems. However, some dolphins seem to be attracted to the seismic 
vessel and floats, and some ride the bow wave of the seismic vessel 
even when large arrays of airguns are firing. Nonetheless, there have 
been indications that small toothed whales sometimes tend to head away, 
or to maintain a somewhat greater distance from the vessel, when a 
large array of airguns is operating than when it is silent (Goold, 
1996; Calambokidis and Osmek, 1998; Stone, 2003). In most cases, the 
avoidance radii for delphinids appear to be small, on the order of 1 km 
(0.62 mi) or less.
    The beluga may be a species that (at least at times) shows long-
distance avoidance of seismic vessels. Aerial surveys during seismic 
operations in the southeastern Beaufort Sea recorded much lower 
sighting rates of beluga whales within 10-20 km (6.2-12.4 mi) of an 
active seismic vessel. These results were consistent with the low 
number of beluga sightings reported by observers aboard the seismic 
vessel, suggesting that some belugas might be avoiding the seismic 
operations at distances of 10-20 km (6.2-12.4 mi) (Miller et al., 
2005a). Similarly, captive bottlenose dolphins and beluga whales 
exhibit 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 (pk-pk 
level >200 dB re 1 microPa) before exhibiting aversive behaviors.
    Results for porpoises depend on species. Dall's porpoises seem 
relatively tolerant of airgun operations (MacLean and Koski, 2005; Bain 
and Williams, 2006), whereas the limited available data suggest that 
harbor porpoises show stronger avoidance (Stone, 2003; Bain and 
Williams, 2006; Stone and Tasker, 2006). This apparent difference in 
responsiveness of these two porpoise species is consistent with their 
relative responsiveness to boat traffic in general (Richardson et al., 
1995; Southall et al., 2007).
    Most studies of sperm whales exposed to airgun sounds indicate that 
this species shows considerable tolerance of airgun pulses. In most 
cases, the whales do not show strong avoidance, and they continue to 
call (see Appendix A of UTIG's application for review). However, 
controlled exposure experiments in the Gulf of Mexico indicate that 
foraging effort is apparently somewhat reduced upon exposure to airgun 
pulses from a seismic vessel operating in the area, and there may be a 
delay in diving to foraging depth.
    There are no specific data on the behavioral reactions of beaked 
whales to seismic surveys. Most beaked whales tend to avoid approaching 
vessels of other types (Wursig et al., 1998). They may also dive for an 
extended period when approached by a vessel (Kasuya, 1986). It is 
likely that these beaked whales would normally show strong avoidance of 
an approaching seismic vessel, but this has not been documented 
explicitly.Odontocete reactions to large arrays of airguns are variable 
and, at least for delphinids and some porpoises, seem to be confined to 
a smaller radius than has been observed for mysticetes (see Appendix A 
of UTIG's application for more information). Behavioral reactions of 
most odontocetes to the small GI gun source to be used here are 
expected to be very localized.
    Pinnipeds - Pinnipeds are not likely to show a strong avoidance 
reaction to the two GI guns that will be used. Visual monitoring from 
seismic vessels, usually employing larger sources, has shown only 
slight (if any) avoidance of airguns by pinnipeds, and only slight (if 
any) changes in behavior (see Appendix A (e) of UTIG's application). 
Ringed seals frequently do not avoid the area within a few hundred 
meters of operating airgun arrays (Harris et al., 2001; Moulton and 
Lawson, 2002; Miller et al., 2005a). However, initial telemetry work 
suggests that avoidance and other behavioral reactions by two other 
species of seals to small airgun sources may at times be stronger than 
evident to date from visual studies of pinniped reactions to airguns 
(Thompson et al., 1998). Even if reactions of any pinnipeds that might 
be encountered in the present study area are as strong as those evident 
in the telemetry study, reactions are expected to be confined to 
relatively small distances and durations, with no long-

[[Page 30083]]

term effects on pinniped individuals or populations.
    Additional details on the behavioral reactions (or the lack 
thereof) by all types of marine mammals to seismic vessels can be found 
in Appendix A (e) of UTIG's application.

Hearing Impairment and Other Physical Effects

    Temporary or permanent hearing impairment is a possibility when 
marine mammals are exposed to very strong sounds, but there has been no 
specific documentation of this for marine mammals exposed to sequences 
of airgun pulses. Current NMFS policy regarding exposure of marine 
mammals to high-level sounds is that cetaceans and pinnipeds should not 
be exposed to impulsive sounds of 180 and 190 dB re 1 microPa (rms), 
respectively (NMFS, 2000). Those criteria have been used in defining 
the safety (shut-down) radii planned for the proposed seismic survey. 
The precautionary nature of these criteria is discussed in Appendix A 
(f) of UTIG's application, including the fact that the minimum sound 
level necessary to cause permanent hearing impairment is higher, by a 
variable and generally unknown amount, than the level that induces 
barely-detectable temporary threshold shift (TTS) (which NMFS' criteria 
are based on) and the level associated with the onset of TTS is often 
considered to be a level below which there is no danger of permanent 
damage. NMFS is presently developing new noise exposure criteria for 
marine mammals that take account of the now-available scientific data 
on TTS, the expected offset between the TTS and permanent threshold 
shift (PTS) thresholds, differences in the acoustic frequencies to 
which different marine mammal groups are sensitive, and other relevant 
factors.
    Because of the small size of the airgun source in this project (two 
40-60 in\3\ GI gun), alongwith the planned monitoring and mitigation 
measures, there is little likelihood that any marine mammals will be 
exposed to sounds sufficiently strong to cause hearing impairment. 
Several aspects of the planned monitoring and mitigation measures for 
this project are designed to detect marine mammals occurring near the 
GI guns (and multibeam echosounder and sub-bottom profiler), and to 
avoid exposing them to sound pulses that might, at least in theory, 
cause hearing impairment. In addition, many cetaceans are likely to 
show some avoidance of the area with high received levels of airgun 
sound (see above). In those cases, the avoidance responses of the 
animals themselves will reduce or (most likely) avoid any possibility 
of hearing impairment.
    Non-auditory physical effects may also occur in marine mammals 
exposed to strong underwater pulsed sound. Possible types of non-
auditory physiological effects or injuries that theoretically might 
occur in mammals close to a strong sound source include stress, 
neurological effects, bubble formation, resonance effects, and other 
types of organ or tissue damage. It is possible that some marine mammal 
species (i.e., beaked whales) may be especially susceptible to injury 
and/or stranding when exposed to strong pulsed sounds. However, as 
discussed below, there is no definitive evidence that any of these 
effects occur even for marine mammals in close proximity to large 
arrays of airguns. It is especially unlikely that any effects of these 
types would occur during the present project given the small size of 
the source, the brief duration of exposure of any given mammal, and the 
planned 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) - 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. 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 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.
    For toothed whales exposed to single short pulses, the TTS 
threshold appears to be, to a first approximation, a function of the 
energy content of the pulse (Finneran et al. 2002, 2005). Given the 
available data, the received level of a single seismic pulse (with no 
frequency weighting) might need to be approximately 186 dB re 1 
microPa\2\s (i.e., 186 dB SEL or approximately 221-226 dB pk-
pk) in order to produce brief, mild TTS. Exposure to several strong 
seismic pulses that each have received levels near 175-180 dB SEL might 
result in slight TTS in a small odontocete, assuming the TTS threshold 
is (to a first approximation) a function of the total received pulse 
energy. The distances from the Thompson's GI guns at which the received 
energy level (per pulse) would be expected to be [gteqt]175-180 dB SEL 
are the distances shown in the 190 dB re 1 microPa (rms) column in 
Table 1 of UTIG's application (given that the rms level is 
approximately 10-15 dB higher than the SEL value for the same pulse). 
Seismic pulses with received energy levels [gteqt]175-180 dB SEL (190 
dB re 1 microPa (rms)) are expected to be restricted to radii no more 
than 69-104 m (226.3-341.1 ft) around the two GI guns. The specific 
radius depends on the depth of the water. For an odontocete closer to 
the surface, the maximum radius with [gteqt]175-180 dB SEL or 
[gteqt]190 dB re 1 microPa (rms) would be smaller. Such levels would be 
limited to distances within tens of meters of the small GI guns source 
to be used in this project.
    For baleen whales, direct or indirect data do not exist on levels 
or properties of sound thatare required to induce TTS. The frequencies 
to which baleen whales are most sensitive are 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. In any event, no cases of TTS are expected 
given three considerations: (1) the 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 proposed to be 
implemented.
    In pinnipeds, TTS thresholds associated with exposure to brief 
pulses (single or multiple) of underwater sound have not been measured. 
Initial evidence from prolonged exposures suggests that some pinnipeds 
may incur TTS at somewhat lower received levels than do small 
odontocetes exposed for similar durations (Kastak et al., 1999, 2005; 
Ketten et al., 2001; cf. Au et al., 2000). The TTS threshold for pulsed 
sounds has been indirectly estimated as being an SEL of about 171 dB re 
microPa\2\s (Southall et al., 2007), which would be equivalent 
to about 181-186 dB re 1 microPa (rms). Corresponding values for 
California sea lions and northern elephant seals are likely to be 
higher (Kastak et al., 2005).
    To avoid injury, NMFS has determined that cetaceans and pinnipeds 
should not be exposed to

[[Page 30084]]

pulsed underwater noise at received levels exceeding, respectively, 180 
and 190 dB re 1 microPa (rms). Those sound levels were not considered 
to be the levels above which TTS might occur. Rather, they were 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 marine mammals. As 
summarized above, data that are now available imply that TTS is 
unlikely to occur unless odontocetes (and probably mysticetes as well) 
are exposed to airgun pulses stronger than 180 dB re 1 microPa (rms).
    Permanent Threshold Shift (PTS) - When PTS occurs, there is 
physical damage to the sound receptors in the ear. In some cases, there 
can be total or partial deafness, while in other cases, the animal has 
an impaired ability to hear sounds in specific frequency ranges.
    There is no specific evidence that exposure to pulses of airgun 
sound can cause PTS in any marine mammal, even with large arrays of 
airguns. However, given the possibility that mammals close to an airgun 
array might incur TTS, there has been further speculation about the 
possibility that some individuals occurring very close to airguns might 
incur PTS. Single or occasional occurrences of mild TTS are not 
indicative of permanent auditory damage in terrestrial mammals. 
Relationships between TTS and PTS thresholds have not been studied in 
marine mammals, but are assumed to be similar to those in humans and 
other terrestrial mammals. PTS might occur at a received sound level at 
least several decibels above that inducing mild TTS if the animal were 
exposed to strong sound pulses with rapid rise time (see Appendix A (f) 
of UTIG's application). The specific difference between the PTS and TTS 
thresholds has not been measured for marine mammals exposed to any 
sound type. However, based on data from terrestrial mammals, a 
precautionary assumption is that the PTS threshold for impulse sounds 
(such as airgun pulses as received close to the source) is at least 6 
dB higher than the TTS threshold on a peak-pressure basis and probably 
more than 6 dB.
    On an SEL basis, Southall et al. (2007) estimate 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 SEL of about 198 dB re 1 microPa\2\.s. Additional 
assumptions had to be made to derive a corresponding estimate for 
pinnipeds. Southall et al. (2007) estimate that the PTS threshold could 
be an SEL of about 186 dB re 1 microPa\2\s in the harbor seal; 
for the California sea lion and northern elephant seal the PTS 
threshold would probably be higher. Southall et al. (2007) also not 
that, regardless of the SEL, there is concern about the possibility of 
PTS if a cetacean or pinniped received one or more pulses with peak 
pressure exceeding 230 or 218 dB 1 microPa (peak).
    In the proposed project employing two 40 to 60-in\3\ GI guns, 
marine mammals are highly unlikely to be exposed to received levels of 
seismic pulses strong enough to cause TTS, as they would probably need 
to be within a few tens of meters of the GI guns for that to occur. 
Given the higher level of sound necessary to cause PTS, it is even less 
likely that PTS could occur. In fact, even the levels immediately 
adjacent to the GI guns may not be sufficient to induce PTS, especially 
since a mammal would not be exposed to more than one strong pulse 
unless it swam immediately alongside the GI guns for a period longer 
than the inter-pulse interval. Baleen whales generally avoid the 
immediate area around operating seismic vessels, as do some other 
marine mammals and sea turtles. The planned monitoring and mitigation 
measures, including visual monitoring and shut downs of the GI guns 
when mammals are seen within or about to enter the ``safety radii'' or 
exclusion zone (EZ), will minimize the already-minimal probability of 
exposure of marine mammals to sounds strong enough to induce PTS.
    Non-auditory Physiological Effects - Non-auditory physiological 
effects or injuries that theoretically might occur in marine mammals 
exposed to strong underwater sound include stress, neurological 
effects, bubble formation, resonance effects, and other types of organ 
or tissue damage. However, studies examining such effects are limited. 
If any such effects do occur, they would probably be limited to unusual 
situations when animals might be exposed at close range for unusually 
long periods, when the sound is strongly channeled with less-than-
normal propagation loss, or when dispersal of the animals is 
constrained by shorelines, shallows, etc. Airgun pulses, because of 
their brevity and intermittence, are less likely to trigger resonance 
or bubble formation than are more prolonged sounds. It is doubtful that 
any single marine mammal would be exposed to strong seismic sounds for 
time periods long enough to induce physiological stress.
    Until recently, it was assumed that diving marine mammals are not 
subject to the bends or air embolism. This possibility was first 
explored at a workshop (Gentry [ed.], 2002) held to discuss whether the 
stranding of beaked whales in the Bahamas in 2000 (Balcomb and 
Claridge, 2001; NOAA and USN, 2001) might have been related to bubble 
formation in tissues caused by exposure to noise from naval sonar. 
However, this link could not be confirmed. Jepson et al. (2003) first 
suggested a possible link between mid-frequency sonar activity and 
acute chronic tissue damage that results from the formation in vivo of 
gas bubbles, based on the beaked whale stranding in the Canary Islands 
in 2002 during naval exercises. Fernandez et al. (2005a) showed those 
beaked whales did indeed have gas bubble-associated lesions, as well as 
fat embolisms. Fernandez et al. (2005b) also found evidence of fat 
embolism in three beaked whales that stranded 100 km (62 mi) north of 
the Canaries in 2004 during naval exercises. Examinations of several 
other stranded species have also revealed evidence of gas and fat 
embolisms (Arbelo et al., 2005; Jepson et al., 2005a; Mendez et al., 
2005). Most of the afflicted species were deep divers. There is 
speculation that gas and fat embolisms may occur if cetaceans ascend 
unusually quickly when exposed to aversive sounds, or if sound in the 
environment causes the destablization of existing bubble nuclei 
(Potter, 2004; Arbelo et al., 2005; Fernandez et al., 2005a; Jepson et 
al., 2005b; Cox et al., 2006). Even if gas and fat embolisms can occur 
during exposure to mid-frequency sonar, there is no evidence that that 
type of effect occurs in response to airgun sounds.
    In general, little is known about the potential for seismic survey 
sounds to cause auditory imp