Small Takes of Marine Mammals Incidental to Specified Activities; Low-Energy Marine Seismic Survey in the Northeast Pacific Ocean, September 2007, 42045-42058 [E7-14883]

Agencies

• DEPARTMENT OF COMMERCE
• National Oceanic and Atmospheric Administration

[Federal Register Volume 72, Number 147 (Wednesday, August 1, 2007)]
[Notices]
[Pages 42045-42058]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: E7-14883]


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DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

RIN 0648-XB70


Small Takes of Marine Mammals Incidental to Specified Activities; 
Low-Energy Marine Seismic Survey in the Northeast Pacific Ocean, 
September 2007

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 Scripps Institute of 
Oceanography (SIO) for an Incidental Harassment Authorization (IHA) to 
take marine mammals incidental to conducting a low-energy marine 
seismic survey in the northeastern Pacific Ocean during September, 
2007. Pursuant to the Marine Mammal Protection Act (MMPA), NMFS is 
requesting comments on its proposal to issue an IHA to SIO 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 August 
31, 2007.

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: Candace Nachman 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 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 May 4, 2007, NMFS received an application from SIO for the 
taking, by Level B harassment only, of 32 species of marine mammals 
incidental to conducting, with research funding from the National 
Science Foundation (NSF), an ocean-bottom seismograph (OBS) deployment 
and a magnetic, bathymetric, and seismic survey program off the Oregon 
coast in the northeastern Pacific Ocean during September, 2007. The 
purpose of the research program is to record microearthquakes in the 
forearc to determine whether seismicity on the plate boundary is 
characteristic of a locked or a freely slipping fault plane. OBSs will 
be deployed and left in place for a year, and a seismic survey will be 
used to locate the instruments accurately and precisely on the seafloor 
and to characterize the shallow sediment structure around the 
instrument. Seismometers measure movement in the Earth's crust. About 
90 percent of all natural earthquakes occur under water, where great 
pressure and cold make measurements difficult. The OBS was developed 
for this task. Scientists use seismometer data to calculate the energy 
released by earthquakes. Also included in the research is the use of a 
magnetometer and sub-bottom profiler.

Description of the Activity

    The seismic surveys will involve one vessel, the R/V Wecoma 
(Wecoma),

[[Page 42046]]

which is scheduled to depart from Newport, Oregon on September 5, 2007 
and return on September 11, 2007. The exact dates of the activities may 
vary by a few days because of weather conditions, repositioning, OBS 
and streamer operations and adjustments, GI-gun deployment, or the need 
to repeat some lines if data quality is substandard. The seismic 
surveys 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 25-110 km (15.5-68.4 mi) offshore from Oregon 
in water depths between approximately 110 and 3,050 m (361 and 10,007 
ft), entirely within the Exclusive Economic Zone of the U.S.
    The Wecoma will deploy a single low-energy Generator-Injector (GI) 
airgun as an energy source (with a discharge volume of 45 in\3\), 16 
OBSs that will remain in place for a year, and a 300 m-long (984 ft-
long), 16-channel, towed hydrophone streamer. The program will consist 
of approximately 21 km (13 mi) of surveys over each of the 16 OBSs. The 
GI gun will be operated on a small grid for approximately 2 hours at 
each of 16 OBS sites over an approximately 7-day period during 
September, 2007. 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. The OBSs are acoustically 
passive and do not emit any sounds into the ocean.
    In addition to the operations of the GI gun, a 3.5-kHz sub-bottom 
profiler, a Knudsen 320BR sub-bottom profiler, and a magnetometer may 
be run on the transit between OBS locations.

Vessel Specifications

    The Wecoma has a length of 56.4 m (185 ft), a beam of 10.1 m (33.1 
ft), and a maximum draft of 5.6 m (18.4 ft). The ship is powered by a 
single 3,000-hp EMD diesel engine driving a single, controllable-pitch 
propeller through a clutch and reduction gear, and an electric, 350-hp 
azimuthing bow thruster. An operation speed of 11.1 km/h (6 knots) is 
used during seismic acquisition. When not towing seismic survey gear, 
the Wecoma cruises at 22.2 km/h (12 knots) and has a maximum speed of 
26 km/h (14 knots). It has a normal operating range of approximately 
13,300 km (8,264 mi).

Acoustic Source Specifications

Seismic Airguns
    The vessel Wecoma will tow a GI gun and an 300 m-long (984-ft) 
streamer containing hydrophones along predetermined lines. Seismic 
pulses will be emitted at intervals of 10 s, which corresponds to a 
shot interval of approximately 31 m (102 ft) at a speed of 6 knots 
(11.1 km/h). The generator chamber of the GI gun, the one responsible 
for introducing the sound pulse into the ocean, is 45 in\3\. The larger 
(105 in\3\) injector chamber injects air into the previously-generated 
bubble to maintain its shape and does not introduce more sound into the 
water. The 45 in\3\ GI gun will be towed 21 m (69 ft) behind the 
Wecoma, at a depth of 4 m (13 ft). The dominant frequency components 
are 0-188 Hz.
    The sound pressure field of the GI gun variation at a tow depth of 
2.5 m (8.2 ft) has been modeled by the Lamont-Doherty Earth Observatory 
(L-DEO) in relation to distance and direction from the airgun. This 
source, which is directed downward, was found to have an output (0-
peak) of 225.3 dB re 1 microPa m.
    The rms (root mean square) received levels that are used as impact 
criteria for marine mammals are not directly comparable to the peak or 
peak to peak values normally used to characterize source levels of 
airgun arrays. The measurement units used to describe airgun sources, 
peak or peak-to-peak decibels, are always higher than the rms decibels 
referred to in biological literature. A measured received level of 160 
dB rms in the far field would typically correspond to a peak 
measurement of approximately 170 to 172 dB, and to a peak-to-peak 
measurement of approximately 176 to 178 dB, as measured for the same 
pulse received at the same location (Greene 1997; McCauley et al., 
1998, 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 Wecoma will utilize the Knudsen Engineering Model 320BR sub-
bottom profiler, which is a dual-frequency transceiver 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 is 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 mPa-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

[[Page 42047]]

(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 mPa (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 
110-3,050 m (361-10,007 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 23 m and 8 m (75.5 and 26.2 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 35 m and 12 m (115 and 39.4 
ft), respectively.
    The airgun will be shut down immediately when cetaceans or 
pinnipeds are detected within or about to enter the appropriate 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, 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. One 
other species listed as Threatened may occur in the project area: the 
Steller sea lion.
    Gray whales and sea otters (which is under the jurisdiction of the 
U.S. Fish and Wildlife Service) are 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 would be rare at most at the OBS 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 SIO's application.

------------------------------------------------------------------------
                                                                   Rqstd
           Species                   Habitat         Abundance\1\   Take
------------------------------------------------------------------------
Mysticetes
------------------------------                                    ------
North Pacific right whale      Inshore,             N.A.\2\        0
 (Eubalaena japonica) *         occasionally
                                offshore
------------------------------------------------------------------------
Humpback whale (Megaptera      Mainly nearshore     1391           0
 novaeangliae) *                waters and banks
------------------------------------------------------------------------
Minke whale (Balaenoptera      Pelagic and coastal  1015           0
 acutorostrata)
------------------------------------------------------------------------
Sei whale (Balaenoptera        Primarily offshore,  56             0
 borealis) *                    pelagic
------------------------------------------------------------------------
Fin whale (Balaenoptera        Continental slope,   3279           0
 physalus) *                    mostly pelagic
------------------------------------------------------------------------
Blue whale (Balaenoptera       Pelagic and coastal  1744           0
 musculus) *
------------------------------------------------------------------------
Odontocetes
------------------------------                                    ------
Sperm whale (Physeter          Usually pelagic and  1233           0
 macrocephalus) *               deep seas
------------------------------------------------------------------------
Pygmy sperm whale (Kogia       Deep waters off the  247            1
 breviceps)                     shelf
------------------------------------------------------------------------
Dwarf sperm whale (Kogia       Deep waters off the  N.A.           0
 sima)                          shelf
------------------------------------------------------------------------
Cuvier's beaked whale          Pelagic              1884           0
 (Ziphius cavirostris)
------------------------------------------------------------------------
Baird's beaked whale           Pelagic              228            0
 (Berardius bairdii)
------------------------------------------------------------------------

[[Page 42048]]

 
Blainville's beaked whale      Slope, offshore      1247\3\        0
 (Mesoplodon densirostris)
------------------------------------------------------------------------
Hubb's beaked whale            Slope, offshore      1247\3\        0
 (Mesoplodon carlhubbsi)
------------------------------------------------------------------------
Stejneger's beaked whale       Slope, offshore      1247\3\        0
 (Mesoplodon stejnegeri)
------------------------------------------------------------------------
Offshore bottlenose dolphin    Offshore, slope      5,065          0
 (Tursiops truncatus)
------------------------------------------------------------------------
Striped dolphin (Stenella      Off continental      13,934         0
 coeruleoalba)                  shelf
------------------------------------------------------------------------
Short-beaked common dolphin    Shelf and pelagic,   449,846        4
 (Delphinus delphis)            seamounts
------------------------------------------------------------------------
Pacific white-sided dolphin    Offshore, slope      59,274         6
 (Lagenorhynchus obliquidens)
------------------------------------------------------------------------
Northern right whale dolphin   Slope, offshore      20,362         5
 (Lissodelphis borealis)        waters
------------------------------------------------------------------------
Risso's dolphin (Grampus       Shelf, slope,        16,066         3
 griseus)                       seamounts
------------------------------------------------------------------------
False killer whale (Pseudorca  Pelagic,             N.A.           0
 crassidens)                    occasionally
                                inshore
------------------------------------------------------------------------
Killer whale (Orcinus orca)    Widely distributed   466            0
                                                     (Offshore)
------------------------------------------------------------------------
Short-finned pilot whale       Mostly pelagic,      304            0
 (Globicephala macrorhynchus)   high-relief
                                topography
------------------------------------------------------------------------
Harbor porpoise (Phocoena      Coastal and inland   39,586 (OR/    0
 phocoena)                      waters               WA)
------------------------------------------------------------------------
Dall's porpoise (Phocoenoides  Shelf, slope,        99,517         39
 dalli)                         offshore
------------------------------------------------------------------------
Pinnipeds
------------------------------                                    ------
Northern fur seal              Pelagic, offshore    688,028\2\     3
 (Callorhinus ursinus)
------------------------------------------------------------------------
California sea lion (Zalophus  Coastal, shelf       237,000-       0
 californianus californianus)                        244,000
------------------------------------------------------------------------
Steller sea lion (Eumetopias   Coastal, shelf       44,996\2\      0
 jubatus) *                                          Eastern U.S.
------------------------------------------------------------------------
Harbor seal (Phoca vitulina    Coastal              24,732 (OR/    1
 richardsi)                                          WA)
------------------------------------------------------------------------
Northern elephant seal         Coastal, pelagic     101,000 (CA)   0
 (Mirounga angustirostris)      when migrating
------------------------------------------------------------------------
Table 1. Species expected to be encountered (and potentially harassed)
  during SIO's Pacific Ocean cruise.
N.A. - Data not available or species status was not assessed.
* Species are listed as threatened or endangered under the Endangered
  Species Act.

Potential Effects on Marine Mammals

Potential Effects of Airguns

    The effects of sounds from airguns might include one or more of the 
following: tolerance, masking of natural sounds, behavioral 
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 gun planned for 
the present 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 SIO'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 GI gun planned for use in the 
present 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 SIO'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 and low-energy airgun source planned for use in this project, 
NMFS expects mammals (and sea turtles) to tolerate being closer to this 
source than for a larger airgun source typical of most seismic surveys.
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

[[Page 42049]]

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 
SIO'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. If a marine mammal responds to an underwater sound by 
changing its behavior or moving a small distance, the response may or 
may not rise to the level of harassment, let alone affect the stock or 
the species as a whole. 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, small toothed whales, and sea otters. 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 SIO'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 SIO'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.
    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 summering in southeast Alaska did not exhibit 
persistent avoidance when exposed to seismic pulses from a 1.64-L (100 
in\3\) airgun (Malme et al., 1985). Some humpbacks seemed ``startled'' 
at received levels of 150-169 dB re 1 microPa on an approximate rms 
basis. Malme et al. (1985) concluded that there was no clear evidence 
of avoidance, despite the possibility of subtle effects, at received 
levels up to 172 re 1 microPa (approximately rms). Additional effects 
from seismic surveys to wintering humpback whales off Brazil can be 
found in Appendix A (e) of SIO's application.
    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

[[Page 42050]]

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 not data on reactions of wintering bowhead whales to seismic 
surveys. See Appendix A (e) of SIO's application for more information 
regarding bowhead whale reactions to airguns.
    Malme et al. (1986, 1988) studied the responses of feeding Eastern 
Pacific gray whales to pulses from a single 100 in\3\ airgun off St. 
Lawrence Island in the northern Bering Sea. Malme et al. (1986, 1988) 
estimated, based on small sample sizes, that 50 percent of feeding gray 
whales ceased feeding at an average received pressure level of 173 dB 
re 1 microPa on an (approximate) rms basis, and that 10 percent of 
feeding whales interrupted feeding at received levels of 163 dB. Those 
findings were generally consistent with the results of experiments 
conducted on larger numbers of gray whales that were migrating along 
the California coast and on observations of Western Pacific gray whales 
feeding off Sakhalin Island, Russia (Johnson, 2002).
    We are not aware of any information on reactions of Bryde's whales 
to seismic surveys. However, other species of Balaenoptera (blue, sei, 
fin, and minke whales) have occasionally been reported in areas 
ensonified by airgun pulses. Sightings by observers on seismic vessels 
off the 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 (in press) found only a little or no 
difference in sighting rates and initial sighting distances of 
balaenopterid whales when airguns were operating vs. silent. However, 
there were indications that these whales were more likely to be moving 
away when seen during airgun operations.
    Data on short-term reactions (or lack of reactions) of cetaceans to 
impulsive noises do not necessarily provide information about long-term 
effects. It is not known whether impulsive noises affect reproductive 
rate or distribution and habitat use in subsequent days or years. 
However, gray whales continued to migrate annually along the west coast 
of North America despite intermittent seismic exploration and much ship 
traffic in that area for decades (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, in press).
    Seismic operators 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). 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).
    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 (e) of SIO'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 SIO's application for more information). Behavioral reactions of 
odontocetes to the small GI-gun source to be used here are expected to 
be very localized, probably to distances <0.4 km (0.25 mi).

[[Page 42051]]

    Pinnipeds - Pinnipeds are not likely to show a strong avoidance 
reaction to the GI gun 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 SIO'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-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 SIO'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. 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 SIO'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 (one 
45-in3 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 gun (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 distance from the Wecoma's GI gun 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 
SIO'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 23-35 m 
(75.5-115 ft) around the GI gun. 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 a few meters of the small GI gun 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

[[Page 42052]]

possibility of TTS; and (3) the mitigation measures that are planned.
    In pinnipeds, TTS thresholds associated with exposure to brief 
pulses (single or multiple) of underwater sound have not been measured. 
Initial evidence from prolonged exposures suggested that some pinnipeds 
may incur TTS at somewhat lower received levels than do small 
odontocetes exposed for similar durations (Kastak et al., 1999, 2005; 
Ketten et al., 2001; cf. Au et al., 2000). However, more recent 
indications are that TTS onset in the most sensitive pinniped species 
studied (harbor seal) may occur at a similar sound exposure level as in 
odontocetes (Kastak et al., 2004).
    To avoid injury, NMFS has determined that cetaceans and pinnipeds 
should not be exposed to pulsed underwater noise at received levels 
exceeding, respectively, 180 and 190 dB re 1 microPa (rms). 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 strong 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 SIO'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.
    In the present project employing a single 45-in\3\ GI gun, 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 meters of the GI gun 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 
gun 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 gun for a period longer than the inter-
pulse interval. Baleen whales generally avoid the immediate area around 
operating seismic vessels, as do some other marine mammals. The planned 
monitoring and mitigation measures, including visual monitoring and 
shut downs of the GI gun when mammals are seen within the ``safety 
radii'', 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. 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 impairment or other physical effects in marine 
mammals. Available data suggest that such effects, if they occur at 
all, would be limited to short distances and probably to projects 
involving large arrays of airguns. However, the available data do not 
allow for meaningful quantitative predictions of the numbers (if any) 
of marine mammals that might be affected in those ways. Marine mammals 
that show behavioral avoidance of seismic vessels, including most 
baleen whales, some odontocetes, and some pinnipeds, are especially 
unlikely to incur auditory impairment or other physical effects. Also, 
the planned mitigation measures, including shut downs of the GI gun, 
will reduce any such effects that might otherwise occur.
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). 
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.

[[Page 42053]]

However, the association of mass strandings of beaked whales with naval 
exercises and, in one case, an L-DEO seismic survey, 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. Appendix A (g) of SIO's application provides 
additional details.
    Seismic pulses and mid-frequency sonar pulses are quite different. 
Sounds produced by airgun arrays are broadband with most of the energy 
below 1 kHz. Typical military mid-frequency sonars operate at 
frequencies of 2-10 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 to physical damage and mortality (Balcomb 
and Claridge, 2001; NOAA and USN, 2001; Jepson et al., 2003; Fernandez 
et al., 2004, 2005a; Cox et al., 2006), even if only indirectly, 
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 as a result 
of exposure to seismic surveys. Speculation concerning a possible 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, 2006). In September 2002, there was a stranding of 
two Cuvier's beaked whales in the Gulf of California, Mexico, when the 
L-DEO vessel Maurice Ewing was operating a 20-gun, 8,490-in\3\ array in 
the general area. The link between the stranding and the seismic survey 
was inconclusive and not based on any physical evidence (Hogarth, 2002; 
Yoder, 2002). Nonetheless, the preceding example plus the incidents 
involving beaked whale strandings near naval exercises suggests a need 
for caution in conducting seismic surveys in areas occupied by beaked 
whales. No injuries of beaked whales are anticipated during the 
proposed study because of the proposed monitoring and mitigation 
measures.
    The present project will involve a much smaller sound source than 
used in typical seismic surveys. That, along with the monitoring and 
mitigation measures that are planned, are expected to minimize any 
possibility for strandings and mortality.

Potential Effects of Other Acoustic Devices

Sub-bottom Profiler Signals
    A sub-bottom profiler will be operated from the source vessel at 
all times during the planned study. Sounds from the sub-bottom profiler 
are very short pulses, occurring for 12 or 24 ms once every 4.5-8 
seconds. Most of the energy in the sound pulses emitted by this sub-
bottom profiler is at mid frequencies, centered at 3.5 kHz. The beam 
width is approximately 80o (cone-shaped) and is directed downward.
    The sub-bottom profiler on the Wecoma has a stated maximum source 
level of 211 dB re 1 microPa m (see section II of SIO's application). 
Thus, the received level would be expected to decrease to 180 dB and 
160 dB approximately 35 m (115 ft) and 350 m (1,148.3 ft) below the 
transducer, respectively, assuming spherical spreading. Corresponding 
distances in the horizontal plane would be substantially lower, given 
the directionality of this source. Kremser et al. (2005) noted that the 
probability of a cetacean swimming through the area of exposure when a 
bottom profiler emits a pulse is small, and if the animal was in the 
area, it would have to pass the transducer at close range in order to 
be subjected to sound levels that could cause TTS.
    Marine mammal communications will not be masked appreciably by the 
sub-bottom profiler signals given their directionality and the brief 
period when an individual mammal is likely to be within its beam. 
Furthermore, in the case of most odontocetes, the sonar signals do not 
overlap with the predominant frequencies in the calls, which would 
avoid significant masking.
    Marine mammal behavioral reactions to other pulsed sound sources 
are discussed above, and responses to the sub-bottom profiler are 
likely to be similar to those for other pulsed sources if received at 
the same levels. Behavioral responses are not expected unless marine 
mammals are very close to the source.
    Source levels of the sub-bottom profiler are much lower than those 
of the airguns and the multi-beam sonar, which are discussed above. 
Sounds from the sub-bottom profiler are estimated to decrease to 180 dB 
re 1 microPa (rms) at approximately 35 m (115 ft) downward from the 
source. Furthermore, received levels of pulsed sounds that are 
necessary to cause temporary or especially permanent hearing impairment 
in marine mammals appear to be higher than 180 dB (see earlier). Thus, 
it is unlikely that the sub-bottom profiler produces pulse levels 
strong enough to cause hearing impairment or other physical injuries 
even in an animal that is (briefly) in a position near the source.
    The sub-bottom profiler is usually operated simultaneously with 
other higher-power acoustic sources. Many marine mammals will move away 
in response to the approaching higher-power sources or the vessel 
itself before the mammals would be close enough for there to be any 
possibility of effects from the less intense sounds from the sub-bottom 
profiler. In the case of mammals that do not avoid the approaching 
vessel and its various sound sources, mitigation measures that would be 
applied to minimize effects of the higher-power sources would further 
reduce or eliminate any minor effects of the sub-bottom profiler.

Estimated Take by Incidental Harassment

    All anticipated takes would be ``takes by harassment'', involving 
temporary changes in behavior. The proposed mitigation measures are 
expected to minimize the possibility of injurious takes. (However, as 
noted earlier, there is no specific information demonstrating that 
injurious ``takes'' would occur even in the absence of the planned 
mitigation measures.) In the sections below, we describe methods to 
estimate ``take by harassment'', and present estimates of the numbers 
of marine mammals that might be affected during the proposed seismic 
survey in the northeast Pacific Ocean. The estimates are based on data 
concerning marine mammal densities (numbers per unit area) obtained 
during surveys off Oregon and Washington during 1996 and 2001 by NMFS 
Southwest Fisheries Science Center (SWFSC) and estimates of the size of 
the area where effects potentially could occur.
    The following estimates are based on a consideration of the number 
of marine mammals that might be disturbed appreciably by operations 
with the GI gun to be used during approximately 340 line-km of surveys 
at 16 sites off the coast of Oregon in the northeastern Pacific Ocean. 
The anticipated radii of influence of the sub-bottom profiler are less 
than those for the