Small Takes of Marine Mammals Incidental to Specified Activities; Marine Seismic Survey off the Aleutian Islands in the North Pacific Ocean, 13466-13479 [05-5542]

Agencies

• DEPARTMENT OF COMMERCE
• National Oceanic and Atmospheric Administration

[Federal Register Volume 70, Number 53 (Monday, March 21, 2005)]
[Notices]
[Pages 13466-13479]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 05-5542]


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DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

[I.D. 020405A]


Small Takes of Marine Mammals Incidental to Specified Activities; 
Marine Seismic Survey off the Aleutian Islands in the North Pacific 
Ocean

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

ACTION: Notice of receipt of application and proposed incidental take 
authorization; request for comments.

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SUMMARY: NMFS has received an application from the Lamont-Doherty Earth 
Observatory (L-DEO), a part of Columbia University, for an Incidental 
Harassment Authorization (IHA) to take small numbers of marine mammals, 
by harassment, incidental to conducting a low-energy, shallow-
penetrating seismic survey and scientific rock dredging program around 
the Aleutian Islands. Under the Marine Mammal Protection Act (MMPA), 
NMFS is requesting comments on its proposal to issue an authorization 
to L-DEO to incidentally take, by harassment, small numbers of several 
species of cetaceans and pinnipeds for a limited period of time within 
the next year.

DATES: Comments and information must be received no later than April 
20, 2005.

ADDRESSES: Comments on the application should be addressed to Steve 
Leathery, Chief, Permits, Conservation and Education Division, Office 
of Protected Resources, National Marine Fisheries Service, 1315 East-
West Highway, Silver Spring, MD 20910-3225, or by telephoning the 
contact listed here. The mailbox address for providing email comments 
is PR1.020405A@noaa.gov. Please include in the subject line of the e-
mail comment the following document identifier: 020405A. 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 this address or by telephoning the contact 
listed here and is also available at: https://www.nmfs.noaa.gov/prot_
res/PR2/Small_Take/smalltake_info.htm#applications.

FOR FURTHER INFORMATION CONTACT: Kenneth Hollingshead, Office of 
Protected Resources, NMFS, (301) 713-2289, ext 128.

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.
    Permission may be granted if NMFS finds that the taking will have a 
negligible impact on the species or stock(s), will not have an 
unmitigable adverse impact on the availability of the species or 
stock(s) for subsistence uses, and that the permissible methods of 
taking and requirements pertaining to the 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 United States 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:

[[Page 13467]]

    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 issue or deny issuance of the authorization.

Summary of Request

    On December 23, 2004, NMFS received an application from L-DEO for 
the taking, by harassment, of several species of marine mammals 
incidental to conducting a low-energy, shallow-penetrating seismic 
survey and scientific rock dredging program around the Aleutian 
Islands. The purpose of the proposed study is to examine the east-to-
west change in the angle of the convergence of the Pacific-North 
America plates, which implies systematic westward decreases in the rate 
of subduction and sediment delivery to the Aleutian trench. The 
Aleutian Island Arc is the only island arc where systematic changes in 
physical aspects of the subduction system have been well correlated 
with magma output rates and with the geochemistry of the melts that the 
system produces. Despite its potential importance, studies of volcanism 
in the Aleutians are lacking. In particular, the western Aleutians 
(west of Adak Island) are now playing a key role in the evolving view 
of subduction magma genesis, yet it remains a poorly studied area. Few 
volcanic rock samples are available from that area, and it has not been 
studied substantially at sea.
    In addition to an emphasis on magma genesis and its relationship to 
tectonics, volcanism in the Aleutians and southern Alaska is important 
because it is known to present a hazard to air traffic. However, the 
seismic and geochemical studies proposed by L-DEO are not directly 
hazard-related. They are aimed at understanding the deep-level 
processes that underlie the volcanic eruptions, and are thus relevant 
to the broad goals of understanding volcano behavior and hazard 
assessment in the Aleutians and elsewhere.

Description of the Activity

    The seismic survey will involve one vessel, either the R/V Kilo 
Moana or a similar research vessel. The research vessel will deploy one 
Generator-injector (GI) airgun as an energy source (discharge volume of 
105 in3), plus a towed hydrophone streamer up to 300 m (984 ft) long, 
or possibly as short as 50 m (164 ft). The R/V Kilo Moana has a length 
of 56.5 m (185.3 ft), and a beam of 26.8 m (88 ft). As the GI gun is 
towed along the survey lines, the receiving system will receive the 
returning acoustic signals. The proposed program will consist of 
approximately 4112 km (2220 nm) of seismic survey, and scientific rock 
dredging at 10 locations. The seismic survey will take place in water 
depths from less than 50 m (164 ft) to 3.5 kilometers (km) (1.9 
nautical miles (nm)). More than 99 percent of the survey will be in 
depths greater than 100 m (328 ft), and scientific rock dredging will 
be conducted in water depths 100-1800 m (328-5906 ft), mostly in depths 
greater than 400 m (1312 ft).
    The proposed program will use conventional seismic methodology with 
a single towed GI airgun as the energy source, and a towed hydrophone 
streamer as the receiver system. The energy to the airguns is 
compressed air supplied by compressors on board the source vessel.
    In addition to the GI gun, bathymetric sonars and an echo sounder 
will be used during the seismic profiling and continuously when 
underway. Multi-beam bathymetric and single channel seismic surveys 
will be conducted prior to scientific rock dredging to ensure that 
dredging is done as accurately and productively as possible. The 
surveys will also affect the number of dredges that can be completed. 
While on station for rock dredging, a 12-kHz pinger will be used to 
monitor the depth of the dredge relative to the sea floor. A detailed 
description of the acoustic sources proposed for use during this survey 
can be found in the L-DEO application, which is available at: https://
www.nmfs.noaa.gov/prot_res/PR2/Small_Take/
smalltakeinfo.htm#applications.

GI-Airgun Description

    The L-DEO portable high-resolution seismic system will be installed 
on the research vessel for this cruise. The seismic vessel will tow the 
single GI-airgun and a streamer containing hydrophones along 
predetermined lines. Seismic pulses will be emitted at intervals of 5-
10 sec. The 5-10 sec spacing corresponds to a shot interval of about 
13-26 m (43-85 ft).
    The GI airgun will have a total discharge volume of up to 105 
in\3\. The gun will be towed 44.3 m (145.3 ft) behind the stern at a 
depth of about 3 m (9.8 ft). The GI-airgun has a zero to peak (peak) 
source output of 231 dB re 1 microPascal-m ( 3.6 bar-m) and a peak-to-
peak (pk-pk) level of 237 dB (7.0 bar-m). The dominant frequency 
components of the airgun are in the range of 0-188 Hz. For a one-gun 
source, the nominal source level represents the actual level that would 
be found about 1 m (3.3 ft) from the GI gun. Actual levels experienced 
by any marine organism more than 1 m (3.3 ft) from the GI gun will be 
significantly lower.
    The rms (root mean square) received levels that are used as impact 
criteria for marine mammals are not directly comparable to the pk or 
pk-pk values normally used to characterize source levels of airguns. 
The measurement units used to describe airgun sources, pk or pk-pk 
decibels, are always higher than the ``root mean square'' (rms) 
decibels referred to in much of the biological literature. For example, 
a measured received level of 160 dB rms in the far field would 
typically correspond to a pk measurement of about 170 to 172 dB, and to 
a pk-pk measurement of about 176 to 178 decibels, as measured for the 
same pulse received at the same location (Greene, 1997; McCauley et 
al., 1998, 2000a). The precise difference between rms and pk or p-pk 
values depends on the frequency content and duration of the pulse, 
among other factors. However, the rms level is always lower than the pk 
or pk-pk level for an airgun-type source.
    The depth at which the source is towed has a major impact on the 
maximum near-field output, because the energy output is constrained by 
ambient pressure. The normal tow depth of the source to be used in this 
project is 3 m (9.8 ft), where the ambient pressure is 3 decibars. This 
also limits output, as the 3 decibars of confining pressure cannot 
fully constrain the source output, with the result that there is loss 
of energy at the sea surface.
    Received sound levels have been modeled by L-DEO for the single GI-
airgun in relation to distance and direction from the gun. This 
publically available model does not allow for bottom interactions, and 
is most directly applicable to deep water. Based on the model, the 
distances from the single GI-airgun where sound levels of 190-, 180-, 
and 160-dB re 1 microPa (rms) are predicted to be received are shown in

[[Page 13468]]

the greater than 1000-m (328 ft) line of Table 1. The rms (root-mean-
square) pressure is an average over the pulse duration. This is the 
measure commonly used in studies of marine mammal reactions to airgun 
sounds. The rms level of a seismic pulse is typically about 10 dB less 
than its peak level (Greene, 1997; McCauley et al., 1998, 2000a).

 Table 1. Estimated distances to which sound levels 190, 180, and 160 dB
 re 1 microPa (rms) might be received from the one 105 in\3\ GI gun that
   will be used during the seismic survey around the Aleutian Islands
   during 2005. The safety radii used during the survey will depend on
                         water depth (see text).
------------------------------------------------------------------------
                 Water Depth                     Estimated Distances at
----------------------------------------------    Received Levels (m)
                                              --------------------------
                                                190 dB   180 dB   160 dB
------------------------------------------------------------------------
                  >1000 m                           10       27      275
                  100-1000 m                        15       41      413
                  <100 m                           125      200      750
------------------------------------------------------------------------

    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., 2004a,b). 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), the safety criterion applicable to 
cetaceans (NMFS 2000), vary with water depth. Similar depth-related 
variation is likely in the 190-dB distances applicable to pinnipeds. 
The 180- and 190-dB distances are typically used as safety radii during 
seismic surveys. For all sea turtle sightings, the 180-dB distance will 
be used as the safety radius. The proposed study area will occur in 
water approximately 30-3000 m (98-9842 ft), although only about 3 
percent of the survey lines are expected to occur in shallow (<1000 m; 
3280 ft) water.
    The empirical data indicate that, for deep water (>1000 m; 3281 
ft), the L-DEO model tends to overestimate the received sound levels at 
a given distance (Tolstoy et al., 2004a,b). However, to be 
precautionary pending acquisition of additional empirical data, L-DEO 
has proposed using safety radii during GI-airgun operations in deep 
water that correspond to the values predicted by L-DEO's model for deep 
water (Table 1). The assumed 190- and 180-dB radii for one GI gun are 
10 m (33 ft) and 27 m (88 ft), respectively.
    Empirical measurements were not conducted for intermediate water 
depths (100-1000 m (328-3281 ft)). On the expectation that results will 
be intermediate between those from shallow and deep water, L-DEO has 
applied a 1.5X correction factor 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 190 and 
180 dB radii in intermediate-depth water are 15 m (49 ft) and 41 m (134 
ft), respectively (Table 1). L-DEO has requested NMFS use these values 
for calculating safety ranges in intermediate-depth waters.
    Empirical measurements were not made for a single small source 
operating in shallow water (<100 m (328 ft)). However, the measured 
180-dB radius for the 6-airgun array operating in shallow water was 
6.8X that predicted by L-DEO's model for operation of the 6-airgun 
array in deep water. This conservative correction factor was used to 
predict the radii for two GI airguns. The radii for one GI-airgun were 
assumed to be half of that predicted for two GI guns. Thus, the 190- 
and 180-dB radii in shallow water are assumed to be 125 m (410 ft) and 
200 m (656 ft), respectively (Table 1) and L-DEO has requested NMFS use 
thse values for establishing safety zones in shallow water.

Characteristics of Airgun Pulses

    Discussion on the characteristics of airgun pulses have been 
provided in the application and in previous Federal Register notices 
(see 69 FR 31792 (June 7, 2004) or 69 FR 34996 (June 23, 2004)). 
Reviewers are referred to those documents for additional information.

Description of Habitat and Marine Mammals Affected by the Activity

    A detailed description of the Aleutian Islands area and its 
associated marine mammals can be found in the L-DEO application and a 
number of documents referenced in the L-DEO application. A total of 18 
cetacean species and 10 species of pinnipeds may occur in the proposed 
study area around the Aleutian Islands. The marine mammals that occur 
in the proposed survey area belong to four taxonomic groups: 
odontocetes (toothed cetaceans, such as dolphins and sperm whales), 
mysticetes (baleen whales), pinnipeds (seals, sea lions, and walrus), 
and fissipeds (sea otter). Of the 18 cetacean species in the area, 
several are common.
    Odontocete whales include the: sperm whale, Cuvier's beaked whale, 
Baird's beaked whale, Stejneger's beaked whale, beluga whale, Pacific 
white-sided dolphin, Risso's dolphin, killer whale, short-finned pilot 
whale, harbor porpoise, and Dall's porpoise;
    Mysticete whales include the: North Pacific right whale, eastern 
North Pacific gray whale, humpback whale, minke whale, sei whale, fin 
whale, and blue whale;
    Pinnipeds include the: northern fur seal, California sea lion, 
Steller sea lion, Pacific walrus, bearded seal, harbor seal, spotted 
seal, ringed seal, ribbon seal, and northern elephant seal. However, 
only four of these species of pinnipeds are likely to occur in the 
western Aleutian Islands: Steller sea lions, harbor seals, northern fur 
seals, and ribbon seals.
    The walrus, California sea lion, and ringed, spotted, bearded, and 
northern elephant seals likely will not be encountered in the study 
area although they are known to occur in the eastern Aleutians. The sea 
otter and the walrus are managed by the U.S. Fish and Wildlife Service 
(USFWS) and are not the subject of this authorization. L-DEO will 
coordinate with the USFWS regarding project operations and sea otters.
    More detailed information on these species is contained in the L-
DEO application.

Potential Effects on Marine Mammals

    The effects of noise on marine mammals are highly variable, and can 
be categorized as follows (based on Richardson et al., 1995):
    (1) The noise may be too weak to be heard at the location of the 
animal (i.e., lower than the prevailing ambient noise level, the 
hearing threshold of the animal at relevant frequencies, or both);
    (2) The noise may be audible but not strong enough to elicit any 
overt behavioral response;
    (3) The noise may elicit reactions of variable conspicuousness and 
variable relevance to the well being of the marine mammal; these can 
range from temporary alert responses to active avoidance reactions such 
as vacating an area at least until the noise event ceases;
    (4) Upon repeated exposure, a marine mammal may exhibit diminishing 
responsiveness (habituation), or disturbance effects may persist; the 
latter is most likely with sounds that are highly variable in 
characteristics, infrequent and unpredictable in occurrence, and 
associated with situations that a marine mammal perceives as a threat;
    (5) Any anthropogenic noise that is strong enough to be heard has 
the potential to reduce (mask) the ability of

[[Page 13469]]

a marine mammal to hear natural sounds at similar frequencies, 
including calls from conspecifics, and underwater environmental sounds 
such as surf noise;
    (6) If mammals remain in an area because it is important for 
feeding, breeding or some other biologically important purpose even 
though there is chronic exposure to noise, it is possible that there 
could be noise-induced physiological stress; this might in turn have 
negative effects on the well-being or reproduction of the animals 
involved; and
    (7) Very strong sounds have the potential to cause temporary or 
permanent reduction in hearing sensitivity. In terrestrial mammals, and 
presumably marine mammals, received sound levels must far exceed the 
animal's hearing threshold for there to be any temporary threshold 
shift (TTS) in its hearing ability. For transient sounds, the sound 
level necessary to cause TTS is inversely related to the duration of 
the sound. Received sound levels must be even higher for there to be 
risk of permanent hearing impairment. In addition, intense acoustic or 
explosive events may cause trauma to tissues associated with organs 
vital for hearing, sound production, respiration and other functions. 
This trauma may include minor to severe hemorrhage.

Effects of Seismic Surveys on Marine Mammals

    The L-DEO application provides the following information on what is 
known about the effects on marine mammals of the types of seismic 
operations planned by L-DEO. The types of effects considered in this 
document are (1) tolerance, (2) masking of natural sounds, (2) 
behavioral disturbance, and (3) potential hearing impairment and other 
non-auditory physical effects (Richardson et al., 1995). Given the 
relatively small size of the single airgun planned for the present 
project, its effects are anticipated to be considerably less than would 
be the case with a large array of airguns. L-DEO and NMFS believe it is 
very unlikely that there would be any cases of temporary or permanent 
hearing impairment, or non-auditory physical effects. Also, behavioral 
disturbance is expected to be limited to distances less than 275 m (902 
ft) in deep water, 413 m (1355 ft) for intermediate water depths, and 
750 m (2461 ft) in shallow water, the zones calculated for 160 dB or 
the onset of Level B harassment due to impulse sounds. Additional 
discussion on effects on marine mammal species can be found in the L-
DEO application.
Tolerance
    Numerous studies (referenced in L-DEO, 2004) have shown that pulsed 
sounds from airguns are often readily detectable in the water at 
distances of many kilometers, but that marine mammals at distances more 
than a few kilometers from operating seismic vessels often show no 
apparent response. That is often true even in cases when the pulsed 
sounds must be readily audible to the animals based on measured 
received levels and the hearing sensitivity of that mammal group. 
However, most measurements of airgun sounds that have been reported 
concerned sounds from larger arrays of airguns, whose sounds would be 
detectable farther away than the ones that are planned to be used in 
the proposed survey. Although various baleen whales, toothed whales, 
and pinnipeds have been shown to react behaviorally to airgun pulses 
under some conditions, at other times all three types of mammals 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 small and low-energy GI-airgun source planned for use 
in this proposed project, marine mammals would be expected to tolerate 
being closer to this source than would be the case for a larger airgun 
source typical of most seismic surveys.
Masking
    Masking effects of pulsed sounds on marine mammal calls and other 
natural sounds are expected to be very limited (due in part to the 
small size of the single GI-airgun), although there are very few 
specific data on this. Given the small source planned for use in the 
Aleutian Island survey, there is little potential for masking of baleen 
or sperm whale calls during the proposed research. Seismic sounds are 
short pulses generally occurring for less than 1 sec every 5-10 
seconds. This spacing corresponds to a shot interval of approximately 
13-26 m (43-85 ft).
    Some whales are known to continue calling in the presence of 
seismic pulses. Their calls can be heard between the seismic pulses 
(Richardson et al., 1986; McDonald et al., 1995, Greene et al., 1999). 
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 continued calling in 
the presence of seismic pulses (Madsen et al., 2002). This has also 
been shown during recent research in the Gulf of Mexico (Tyack et al., 
2003). Given the relatively small source planned for use during this 
survey and the intermittent nature of seismic pulses, there is even 
less potential for masking of sperm whale calls during the present 
study than in most seismic surveys. For the same reasons, masking 
effects of seismic pulses also are expected to be negligible in the 
case of the smaller odontocete cetaceans. Also, the sounds important to 
small odontocetes are predominantly at much higher frequencies than are 
airgun sounds.
    Most of the energy in the sound pulses emitted by airguns is at low 
frequencies, with strongest spectrum levels below 200 Hz and 
considerably lower spectrum levels above 1000 Hz. These low frequencies 
are mainly used by mysticetes, but generally not by odontocetes or 
pinnipeds. An industrial sound source will reduce the effective 
communication or echolocation distance only if its frequency is close 
to that of the marine mammal signal. If little or no overlap occurs 
between the frequencies of the industrial noise and the marine mammals, 
as in the case of many marine mammals relative to airgun sounds, 
communication and echolocation are not expected to be disrupted. 
Furthermore, the discontinuous nature of seismic pulses makes 
significant masking effects unlikely even for mysticetes.
    A few cetaceans are known to increase the source levels of their 
calls in the presence of elevated sound levels, or possibly to shift 
their peak frequencies in response to strong sound signals (Dahlheim, 
1987; Au, 1993; Lesage et al., 1999; Terhune, 1999; as reviewed in 
Richardson et al., 1995). These studies involved exposure to other 
types of anthropogenic sounds, not seismic pulses, and it is not known 
whether these types of responses ever occur upon exposure to seismic 
sounds. If so, these adaptations, along with directional hearing, pre-
adaptation to tolerate some masking by natural sounds (Richardson et 
al., 1995) and the relatively low-power acoustic sources being used in 
this survey, would all reduce the importance of masking marine mammal 
vocalizations.
Behavioral Disturbance by Seismic Surveys
    Behavioral disturbance includes a variety of effects, including 
subtle changes in behavior, more conspicuous dramatic changes in 
activities, and displacement. However, there are difficulties in 
defining which marine mammals should be counted as ``taken by 
harassment.'' For many species and

[[Page 13470]]

situations, scientists do not have detailed information about their 
reactions to noise, including reactions to seismic (and sonar) pulses. 
Behavioral reactions of marine mammals to sound are difficult to 
predict. 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 does react to an 
underwater sound by changing its behavior or moving a small distance, 
the impacts of the change may not rise to the level of a disruption of 
a behavioral pattern. However, if a sound source would displace marine 
mammals from an important feeding or breeding area, such a disturbance 
may constitute Level B harassment under the MMPA. Given the many 
uncertainties in predicting the quantity and types of impacts of noise 
on marine mammals, scientists often resort to estimating how many 
mammals may be present within a particular distance of industrial 
activities or exposed to a particular level of industrial sound. With 
the possible exception of beaked whales, NMFS believes that this is a 
conservative approach and likely overestimates the numbers of marine 
mammals that may experience a disruption of a behavioral pattern.
    The sound exposure criteria used to estimate how many marine 
mammals might be harassed behaviorally by the seismic survey are based 
on behavioral observations during studies of several species. However, 
information is lacking for many species. Detailed information on 
potential disturbance effects on baleen whales, toothed whales, and 
pinnipeds can be found in Appendix A in L-DEO's Aleutian Islands 
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 airgun 
pulses. Based on current information, NMFS precautionarily sets 
impulsive sounds equal to or greater than 180 and 190 dB re 1 microPa 
(rms) as the exposure thresholds for onset of Level A harassment for 
cetaceans and pinnipeds, respectively (NMFS, 2000). Those criteria have 
been used for several years in setting the safety (shut-down) radii for 
seismic surveys. As discussed in the L-DEO application and summarized 
here,
    1. The 180-dB criterion for cetaceans is probably quite 
precautionary, i.e., lower than necessary to avoid TTS let alone 
permanent auditory injury, at least for delphinids.
    2. 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 TTS.
    3. The level associated with the onset of TTS is often considered 
to be a level below which there is no danger of permanent damage.
    Because of the small size of the single 105 in\3\ GI-airgun, along 
with the planned monitoring and mitigation measures, there is little 
likelihood that any marine mammals would be exposed to sounds 
sufficiently strong to cause even the mildest (and reversible) form of 
hearing impairment. Several aspects of the planned monitoring and 
mitigation measures for this project are designed to detect marine 
mammals occurring near the single GI-airgun (and multibeam bathymetric 
sonar), and to avoid exposing them to airgun sound pulses that might 
(at least in theory) cause hearing impairment. In addition, research 
and monitoring studies on gray whales, bowhead whales and other 
cetacean species indicate that many cetaceans are likely to show some 
avoidance of the area with ongoing seismic operations. In these cases, 
the avoidance responses of the animals themselves will reduce or avoid 
the 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, L-DEO 
and NMFS believe that it is highly unlikely that any of these non-
auditory effects would occur during the proposed survey given the small 
size of the airgun, the brief duration of exposure of any given mammal, 
and the planned mitigation and monitoring measures. The following 
paragraphs discuss the possibility of TTS, permanent threshold shift 
(PTS), and non-auditory physical effects.
TTS
    TTS is the mildest form of hearing impairment that can occur during 
exposure to a strong sound (Kryter, 1985). When an animal experiences 
TTS, its 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. Richardson et al. (1995) note that the magnitude of TTS 
depends on the level and duration of noise exposure, among other 
considerations. For sound exposures at or somewhat above the TTS 
threshold, hearing sensitivity recovers rapidly after exposure to the 
noise ends. Little data on pulsed sound levels and durations necessary 
to elicit mild TTS have been obtained for marine mammals.
    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). Given the 
available data, the received level of a single seismic pulse might need 
to be approximately 210 dB re 1 microPa rms (approx. 221 226 dB pk pk) 
in order to produce brief, mild TTS. Exposure to several seismic pulses 
at received levels near 200 205 dB (rms) 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 (Finneran 
et al., 2002). Seismic pulses with received levels of 200 205 dB or 
more are usually restricted to a zone of no more than 100 m (328 ft) 
around a seismic vessel operating a large array of airguns. Such sound 
levels would be limited to distances within a few meters of the single 
airgun planned for use during this project.
    There are no data, direct or indirect, on levels or properties of 
sound that are required to induce TTS in any baleen whale. However, TTS 
is not expected to occur during this survey given the small size of the 
source, and the strong likelihood that baleen whales would avoid the 
approaching airgun (or vessel) before being exposed to levels high 
enough for there to be any possibility of TTS.
    TTS thresholds for pinnipeds exposed to brief pulses (single or 
multiple) have not been measured, although exposures up to 183 dB re 1 
microPa (rms) have been shown to be insufficient to induce TTS in 
captive California sea lions (Finneran et al., 2003). However, 
prolonged exposures show that some pinnipeds may incur TTS at somewhat 
lower received levels than do small odontocetes exposed for similar 
durations (Kastak et al., 1999; Ketten et al., 2001; Au et al., 2000).
    A marine mammal within a zone of less than 100 m (328 ft) around a 
typical large array of operating airguns might be exposed to a few 
seismic pulses with levels of [gteqt]205 dB, and possibly more

[[Page 13471]]

pulses if the mammal moved with the seismic vessel. Around smaller 
arrays, such as the single GI-airgun proposed for use during this 
survey, a marine mammal would need to be even closer to the source to 
be exposed to levels greater than or equal to 205 dB, at least in 
waters greater than 100 m (328 ft) deep. However, as noted previously, 
most cetacean species tend to avoid operating airguns, although not all 
individuals do so. It is unlikely that these cetaceans would be exposed 
to airgun pulses at a sufficiently high level for a sufficiently long 
period to cause more than mild TTS, given the relative movement of the 
vessel and the marine mammal. However, TTS would be more likely in any 
odontocetes that bow-ride or otherwise linger near the airgun array. 
While bow-riding, odontocetes would be at or above the surface, and 
thus not exposed to strong sound pulses given the pressure-release 
effect at the surface. However, bow-riding animals generally dive below 
the surface intermittently. If they did so while bow-riding near the 
airgun(s), they would be exposed to strong sound pulses, possibly 
repeatedly. If some cetaceans did incur TTS through exposure to airgun 
sounds, it would very likely be a temporary and reversible phenomenon. 
However, during this project, the bow of the Kilo Moana will be about 
100 m (328 ft) ahead of the GI-airgun and the 205-dB zone would be 
significantly less than 100 m (328 ft), except when the vessel is 
operating in shallow water (less than 1 percent of the survey time). 
Thus, TTS would not be expected in the case of odontocetes bow riding 
during airgun operations on this vessel.
    NMFS believes that, to avoid Level A harassment, cetaceans should 
not be exposed to pulsed underwater noise at received levels exceeding 
180 dB re 1 microPa (rms). The corresponding limit for pinnipeds is 190 
dB. The predicted 180- and 190-dB distances for the airgun arrays 
operated by L-DEO during this activity are summarized in Table 1 in 
this document.
    It has also been shown that most whales tend to avoid ships and 
associated seismic operations. Thus, whales will likely not be exposed 
to such high levels of airgun sounds. Because of the slow ship speed, 
any whales close to the trackline could move away before the sounds 
become sufficiently strong for there to be any potential for hearing 
impairment. Therefore, there is little potential for whales being close 
enough to an array to experience TTS. In addition, although it is not 
possible to ramp-up the single airgun being used in this survey, 
ramping up multiple airguns in arrays has become standard operational 
protocol for many seismic operators including L-DEO.
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. Although there is no specific evidence that 
exposure to pulses of airgun sounds can cause PTS in any marine 
mammals, even with the largest airgun arrays, physical damage to a 
mammal's hearing apparatus can potentially occur if it is exposed to 
sound impulses that have very high peak pressures, especially if they 
have very short rise times (time required for sound pulse to reach peak 
pressure from the baseline pressure). Such damage can result in a 
permanent decrease in functional sensitivity of the hearing system at 
some or all frequencies.
    Single or occasional occurrences of mild TTS are not indicative of 
permanent auditory damage in terrestrial mammals. However, very 
prolonged exposure to sound strong enough to elicit TTS, or shorter-
term exposure to sound levels well above the TTS threshold, can cause 
PTS, at least in terrestrial mammals (Kryter, 1985). 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. The low-to-moderate levels of TTS that have been induced in 
captive odontocetes and pinnipeds during recent controlled studies of 
TTS have been confirmed to be temporary, with no measurable residual 
PTS (Kastak et al., 1999; Schlundt et al., 2000; Finneran et al., 2002; 
Nachtigall et al., 2003). In terrestrial mammals, the received sound 
level from a single non-impulsive sound exposure must be far above the 
TTS threshold for any risk of permanent hearing damage (Kryter, 1994; 
Richardson et al., 1995). For impulse sounds with very rapid rise times 
(e.g., those associated with explosions or gunfire), a received level 
not greatly in excess of the TTS threshold may start to elicit PTS. The 
rise times for airgun pulses are rapid, but less rapid than for 
explosions.
    Some factors that contribute to onset of PTS are as follows: (1) 
exposure to single very intense noises, (2) repetitive exposure to 
intense sounds that individually cause TTS but not PTS, and (3) 
recurrent ear infections or (in captive animals) exposure to certain 
drugs.
    Cavanagh (2000) has reviewed the thresholds used to define TTS and 
PTS. Based on his review and SACLANT (1998), it is reasonable to assume 
that PTS might occur at a received sound level 20 dB or more above that 
which induces mild TTS. However, for PTS to occur at a received level 
only 20 dB above the TTS threshold, it is probable that the animal 
would have to be exposed to the strong sound for an extended period.
    Sound impulse duration, peak amplitude, rise time, and number of 
pulses are the main factors thought to determine the onset and extent 
of PTS. Based on existing data, Ketten (1994) has noted that the 
criteria for differentiating the sound pressure levels that result in 
PTS (or TTS) are location and species-specific. PTS effects may also be 
influenced strongly by the health of the receiver's ear.
    Given that marine mammals are unlikely to be exposed to received 
levels of seismic pulses that could cause TTS, it is highly unlikely 
that they would sustain permanent hearing impairment. If we assume that 
the TTS threshold for odontocetes for exposure to a series of seismic 
pulses may be on the order of 220 dB re 1 microPa (pk-pk) 
(approximately 204 dB re 1 microPa rms), then the PTS threshold might 
be about 240 dB re 1 microPa (pk-pk). In the units used by 
geophysicists, this is 10 bar-m. Such levels are found only in the 
immediate vicinity of the largest airguns (Richardson et al., 1995; 
Caldwell and Dragoset, 2000). However, as noted previously in this 
document, it is very unlikely that an odontocete would remain within a 
few meters of a large airgun for sufficiently long to incur PTS. The 
TTS (and thus PTS) thresholds of baleen whales and pinnipeds may be 
lower, and thus may extend to a somewhat greater distance from the 
source. However, baleen whales generally avoid the immediate area 
around operating seismic vessels, so it is unlikely that a baleen whale 
could incur PTS from exposure to airgun pulses. Some pinnipeds do not 
show strong avoidance of operating airguns. In summary, it is highly 
unlikely that marine mammals could receive sounds strong enough (and 
over a sufficient period of time) to cause permanent hearing impairment 
during this project. In the proposed project marine mammals are 
unlikely to be exposed to received levels of seismic pulses strong 
enough to cause TTS, and because of the higher level of sound necessary 
to cause PTS, it is even less likely that PTS could occur. This is due 
to the fact that even

[[Page 13472]]

levels immediately adjacent to the single GI-airgun may not be 
sufficient to induce PTS because the mammal would not be exposed to 
more than one strong pulse unless it swam alongside an airgun for a 
period of time.
Strandings and Mortality
    Marine mammals close to underwater detonations of high explosives 
can be killed or severely injured, and the auditory organs are 
especially susceptible to injury (Ketten et al., 1993; Ketten, 1995). 
Airgun pulses are less energetic and have slower rise times than 
underwater detonations. While there is no documented evidence that 
airgun arrays can cause serious injury, death, or stranding, the 
association of mass strandings of beaked whales with naval exercises 
and, recently, an L-DEO seismic survey have raised the possibility that 
beaked whales may be especially susceptible to injury and/or behavioral 
reactions that can lead to stranding when exposed to strong pulsed 
sounds.
    It is important to note that seismic pulses and mid-frequency sonar 
pulses are quite different. Sounds produced by the types of airgun 
arrays used to profile sub-sea geological structures are broadband with 
most of the energy below 1 kHz. Typical military mid-frequency sonars 
operate at frequencies of 2 to 10 kHz, generally with a relatively 
narrow bandwidth at any one time (though the center frequency may 
change over time). Because seismic and sonar sounds have considerably 
different characteristics and duty cycles, 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 hearing damage 
and, indirectly, mortality suggests that caution is warranted when 
dealing with exposure of marine mammals to any high-intensity pulsed 
sound.
    In addition to mid-frequency sonar-related strandings (e.g., for 
additional discussion see 69 FR 74906 (December 14, 2004)), there was a 
September, 2002 stranding of two Cuvier's beaked whales in the Gulf of 
California (Mexico) when a seismic survey by the R/V Maurice Ewing was 
underway in the general area (Malakoff, 2002). The airgun array in use 
during that project was the Ewing's 20-gun 8490-in\3\ array. This might 
be a first indication that seismic surveys can have effects, at least 
on beaked whales, similar to the suspected effects of naval sonars. 
However, the evidence linking the Gulf of California strandings to the 
seismic surveys is inconclusive, and is not based on any physical 
evidence (Hogarth, 2002; Yoder, 2002). The ship was also operating its 
multi-beam bathymetric sonar at the same time but this sonar had much 
less potential than these naval sonars to affect beaked whales. 
Although the link between the Gulf of California strandings and the 
seismic (plus multi-beam sonar) survey is inconclusive, this plus the 
various incidents involving beaked whale strandings associated with 
naval exercises suggests a need for caution in conducting seismic 
surveys in areas occupied by beaked whales.
Non-auditory Physiological Effects
    Possible types of non-auditory physiological effects or injuries 
that might theoretically occur in marine mammals exposed to strong 
underwater sound might include stress, neurological effects, bubble 
formation, resonance effects, and other types of organ or tissue 
damage. There is no evidence that any of these effects occur in marine 
mammals exposed to sound from airgun arrays. However, there have been 
no direct studies of the potential for airgun pulses to elicit any of 
these effects. 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.
    Long-term exposure to anthropogenic noise may have the potential to 
cause physiological stress that could affect the health of individual 
animals or their reproductive potential, which could theoretically 
cause effects at the population level (Gisner (ed.), 1999). However, 
there is essentially no information about the occurrence of noise-
induced stress in marine mammals. Also, it is doubtful that any single 
marine mammal would be exposed to strong seismic sounds for 
sufficiently long that significant physiological stress would develop. 
This is particularly so in the case of the proposed L-DEO project where 
the airgun is small, the ship is moving at 9 knots, and for the most 
part each survey leg does not encompass a large area.
    Gas-filled structures in marine animals have an inherent 
fundamental resonance frequency. If stimulated at this frequency, the 
ensuing resonance could cause damage to the animal. There may also be a 
possibility that high sound levels could cause bubble formation in the 
blood of diving mammals that in turn could cause an air embolism, 
tissue separation, and high, localized pressure in nervous tissue 
(Gisner (ed), 1999; Houser et al., 2001). In 2002, NMFS held a workshop 
(Gentry (ed.) 2002) to discuss whether the stranding of beaked whales 
in the Bahamas in 2000 might have been related to air cavity resonance 
or bubble formation in tissues caused by exposure to noise from naval 
sonar. A panel of experts concluded that resonance in air-filled 
structures was not likely to have caused this stranding. Among other 
reasons, the air spaces in marine mammals are too large to be 
susceptible to resonant frequencies emitted by mid- or low-frequency 
sonar; lung tissue damage has not been observed in any mass, multi-
species stranding of beaked whales; and the duration of sonar pings is 
likely too short to induce vibrations that could damage tissues (Gentry 
(ed.), 2002).
    Opinions were less conclusive about the possible role of gas 
(nitrogen) bubble formation/growth in the Bahamas stranding of beaked 
whales. Workshop participants did not rule out the possibility that 
bubble formation/growth played a role in the stranding and participants 
acknowledged that more research is needed in this area. The only 
available information on acoustically-mediated bubble growth in marine 
mammals is modeling that assumes prolonged exposure to sound.
    Until recently, it was assumed that diving marine mammals are not 
subject to the bends or air embolism. However, a paper concerning 
beaked whales stranded in the Canary Islands in 2002 suggests that 
cetaceans might be subject to decompression injury in some situations 
(Jepson et al., 2003). If so, that might occur if they ascend unusually 
quickly when exposed to aversive sounds. However, the interpretation 
that the effect was related to decompression injury is unproven 
(Piantadosi and Thalmann, 2004; Fernandez et al., 2004). Even if that 
effect can occur during exposure to mid-frequency sonar, there is no 
evidence that this type of effect occurs in response to low-frequency 
airgun sounds. It is especially unlikely in the case of the proposed L-
DEO survey which involves only one GI-airgun.
    In summary, little is known about the potential for seismic survey 
sounds to cause either auditory impairment or other non-auditory 
physical effects in marine mammals. Available data suggest that such 
effects, if they occur at all, would be limited to short distances from 
the sound source. However, the available data do not allow for 
meaningful quantitative predictions of the numbers (if any) of marine 
mammals that might be affected in these ways. Marine mammals that show 
behavioral avoidance of seismic vessels, including most baleen whales, 
some odontocetes, and some pinnipeds,

[[Page 13473]]

are unlikely to incur auditory impairment or other physical effects. 
Also, the planned mitigation and monitoring measures are expected to 
minimize any possibility of serious injury, mortality or strandings.

Possible Effects of Mid-frequency Sonar Signals

    A multi-beam bathymetric sonar (Simrad EM120 (for deep water) and 
Simrad EM1002 (for shallow water), and a sub-bottom profiler will be 
operated from the source vessel essentially continuously during the 
planned survey.
    Sounds from the multi-beam are very short pulses, depending on 
water depth. Most of the energy in the sound pulses emitted by the 
multi-beam is at moderately high frequencies, centered at 12 kHz. The 
beam is narrow (1[deg] or 2[deg] ) in fore-aft extent, and wide 
(150[deg]) in the cross-track extent. Each ping consists of nine 
successive transmissions (segments) at different cross-track angles. 
Any given mammal at depth near the trackline would be in the main beam 
for only a fraction of a second. The Simrad EM1002 is a compact high 
resolution multi-beam echo sounder that operates at a frequency of 95 
kHz, down to water depths of 1000 m (3281 ft). The high operational 
frequency of this unit will be beyond the effective audible range of 
all mysticetes and pinnipeds, but the hearing capabilities of many 
odontocetes extend to frequencies this high. The system operates with 3 
different pulse lengths, 0.2, 0.7, and 2 ms, with pulse length 
increasing with increased water depth. The transmitted beam is narrow 
(3[deg]) fore-aft, and wide (150[deg]) across-track. Maximum ping rate 
is 10 per second (in shallow water) with the ping rate decreasing with 
increasing water depth.
    Navy sonars that have been linked to avoidance reactions and 
stranding of cetaceans generally (1) are more powerful than the Simrad 
sonars, (2) have a longer pulse duration, and (3) are directed close to 
horizontally (vs. downward for the Simrad sonars). The area of possible 
influence of the bathymetric sonar is much smaller-a narrow band 
oriented in the cross-track direction below the source vessel. Marine 
mammals that encounter the bathymetric sonar at close range are 
unlikely to be subjected to repeated pulses because of the narrow fore-
aft width of the beam, and will receive only small amounts of pulse 
energy because of the short pulses and ship speed. In assessing the 
possible impacts of the 15.5 kHz Atlas Hydrosweep (similar to the 
Simrad sonar), Boebel et al. (2004) noted that the critical sound 
pressure level at which TTS may occur is 203.2 dB re 1 microPa (rms). 
The critical region included an area of 43 m (141 ft) in depth, 46 m 
(151 ft) wide athwartship, and 1 m (3.3 ft) fore-and-aft (Boebel et 
al., 2004). In the more distant parts of that (small) critical region, 
only slight TTS would be incurred. Therefore, as harassment or injury 
from pulsed sound is a function of total energy received, the actual 
harassment or injury threshold for the bathymetric sonar signals 
(approximately 10 ms) would be at a much higher dB level than that for 
longer duration pulses such as seismic signals. As a result, NMFS 
believes that marine mammals are unlikely to be harassed or injured 
from the Simrad multibeam sonars.
    Sounds from the 12-kHz pinger are very short pulses, occurring for 
1 ms once every second, with source level 193 dB re 1 microPa. The 12-
kHz signal is omnidirectional. The pinger produces sounds that are 
within the range of frequencies used by small odontocetes (killer 
whales, Pacific white-sided dolphins, and Dall's porpoise) and 
pinnipeds (harbor seals and Steller sea lions) that occur or may occur 
in the area of the planned surveys.
Masking by Mid-frequency Sonar Signals
    Marine mammal communications will not be masked appreciably by the 
multibeam sonar signals or the sub-bottom profiler given the low duty 
cycle and directionality of the sonars and the brief period when an 
individual mammal is likely to be within its beam. Furthermore, the 12 
kHz multi-beam will not overlap with the predominant frequencies in 
baleen whale calls, further reducing any potential for masking in that 
group. The approximately 95 kHz pulses from the EM1002 sonar will be 
inaudible to baleen whales and pinnipeds. Furthermore, even to 
odontocetes, 95-kHz sounds would not be audible or cause masking at 
long distances, as they absorb rapidly in seawater, at a rate of 
approximately 33 dB/km over and above normal spreading losses (D. Ross, 
in Malme 1995).
    While the 12-kHz pinger produces sounds within the frequency range 
used by odontocetes that may be present in the survey area and within 
the frequency range heard by pinnipeds, marine mammal communications 
will not be masked appreciably by the pinger signals. This is a 
consequence of the relatively low power output, low duty cycle, and 
brief period when an individual mammal is likely to be within the area 
of potential effects. In the case of mysticetes, the pulses do not 
overlap with the predominant frequencies in the calls, which would 
avoid significant masking.
Behavioral Responses Resulting from Mid-Frequency Sonar Signals
    Behavioral reactions of free-ranging marine mammals to military and 
other sonars appear to vary by species and circumstance. Observed 
reactions have included silencing and dispersal by sperm whales 
(Watkins et al., 1985), increased vocalizations and no dispersal by 
pilot whales (Rendell and Gordon, 1999), and the previously-mentioned 
strandings by beaked whales. Also, Navy personnel have described 
observations of dolphins bow-riding adjacent to bow-mounted mid-
frequency sonars during sonar transmissions. However, all of these 
observations are of limited relevance to the present situation. Pulse 
durations from these sonars were much longer than those of the 
bathymetric sonars to be used during the proposed survey, and a given 
mammal would have received many pulses from the naval sonars. During L-
DEO's operations, the individual pulses will be very short, and a given 
mammal would not receive many of the downward-directed pulses as the 
vessel passes by.
    Captive bottlenose dolphins and a white whale exhibited changes in 
behavior when exposed to 1-sec pulsed sounds at frequencies similar to 
those that will be emitted by the bathymetric sonar to be used by L-DEO 
and to shorter broadband pulsed signals. Behavioral changes typically 
involved what appeared to be deliberate attempts to avoid the sound 
exposure (Schlundt et al., 2000; Finneran et al., 2002). The relevance 
of these data to free-ranging odontocetes is uncertain and in any case 
the test sounds were quite different in either duration or bandwidth as 
compared to those from a bathymetric sonar.
    L-DEO and NMFS are not aware of any data on the reactions of 
pinnipeds to sonar sounds at frequencies similar to those of the 12 kHz 
frequency of the Ewing's multibeam sonar. Based on observed pinniped 
responses to other types of pulsed sounds, and the likely brevity of 
exposure to the bathymetric sonar sounds, pinniped reactions are 
expected to be limited to startle or otherwise brief responses of no 
lasting consequences to the individual animals. The 95-kHz sounds from 
the EM1002 will be inaudible to pinnipeds and to baleen whales, so will 
have no disturbance effects on those groups. The pulsed signals from 
the pinger are much weaker than those from the bathymetric sonars and 
from the GI gun. Therefore,

[[Page 13474]]

behavioral responses are not expected unless marine mammals are very 
close to the source.
Hearing Impairment and Other Physical Effects
    Given recent stranding events that have been associated with the 
operation of naval sonar, there is concern that sonar noise can cause 
serious impacts to marine mammals (for discussion see Effects of 
Seismic Surveys on Marine Mammals). However, the multi-beam sonars 
proposed for use by L-DEO are quite different than sonars used for navy 
operations. Pulse duration of the bathymetric sonars is very short 
relative to the naval sonars. Also, at any given location, an 
individual marine mammal would be in the beam of the multi-beam sonar 
for much less time given the generally downward orientation of the beam 
and its narrow fore-aft beam-width. (Navy sonars often use near-
horizontally-directed sound.) These factors would all reduce the sound 
energy received from the multi-beam sonar rather drastically relative 
to that from the sonars used by the Navy. Therefore, hearing impairment 
by multi-beam bathymetric sonar is unlikely.
    Source levels of the pinger are much lower than those of the GI 
airgun and bathymetric sonars. It is unlikely that the pinger produces 
pulse levels strong enough to cause temporary hearing impairment or 
(especially) physical injuries even in an animal that is (briefly) in a 
position near the source.

Estimates of Take by Harassment for the Aleutian Islands Seismic Survey

    Given the proposed mitigation (see Mitigation later in this 
document), all anticipated takes involve a temporary change in behavior 
that may constitute Level B harassment. The proposed mitigation 
measures will minimize or eliminate the possibility of Level A 
harassment or mortality. L-DEO has calculated the ``best estimates'' 
for the numbers of animals that could be taken by Level B harassment 
during the proposed Aleutian Islands seismic survey using data on 
marine mammal density and abundance from marine mammal surveys in the 
region by Brueggeman et al. (1987, 1988), Troy and Johnson (1989), 
Dahlheim et al.(2000), Waite et al. (2002), Doroff et al. (2003), Wade 
et al.(2003), and Tynan (2004), and estimates of the size of the 
affected area, as shown in the predicted RMS radii table (see Table 1).
    These estimates are based on a consideration of the number of 
marine mammals that might be exposed to sound levels greater than 160 
dB, the criterion for the onset of Level B harassment, by operations 
with the single GI-airgun planned to be used for this project. No 
animals are expected to exhibit responses to the sonars or pinger given 
their characteristics (e.g., narrow, downward-directed beam) described 
previously. Therefore, no additional incidental takings are included 
for animals that might be affected by the multi-beam sonars or 12-kHz 
pinger.
    Table 2 incorporates the corrected density estimates and provides 
the best estimate of the numbers of each species that would be exposed 
to seismic sounds greater than 160 dB. A detailed description on the 
methodology used by L-DEO to arrive at the estimates of Level B 
harassment takes that are provided in
    Table 2 can be found in L-DEO's IHA application for the Aleutian 
Islands survey.

BILLING CODE 0-5542-S

[[Page 13475]]

[GRAPHIC] [TIFF OMITTED] TN21MR05.413

Conclusions

Effects on Cetaceans

    Strong avoidance reactions by several species of mysticetes to 
seismic vessels have been observed at ranges up to 6-8 km (3.2-4.3 nm) 
and occasionally as far as 20-30 km (10.8-16.2 nm) from the source 
vessel. However, reactions at the longer distances appear to be 
atypical of most species and situations, particularly when feeding 
whales are involved (Miller et al. in press). Fewer than 150 mysticetes 
are expected to be encountered during the proposed survey in the 
Aleutian Islands (Table 2) and disturbance effects would be confined to 
shorter distances given the low-energy acoustic source to be used 
during this project. In addition, the estimated numbers presented in 
Table 2 are considered overestimates of actual numbers that may be 
harassed.
    Odontocete reactions to seismic pulses, or at least the reactions 
of dolphins, are expected to extend to lesser distances than are those 
of mysticetes. Odontocete low-frequency

[[Page 13476]]

hearing is less sensitive than that of mysticetes, and dolphins are 
often seen from seismic vessels. In fact, there are documented 
instances of delphinids and Dall's porpoise approaching active seismic 
vessels. However, dolphins as well as some other types of odontocetes 
sometimes show avoidance responses and/or other changes in behavior 
when near operating seismic vessels.
    Taking into account the small size and the relatively low sound 
output of the single GI-airgun to be used, and the mitigation measures 
that are planned, effects on cetaceans are generally expected to be 
limited to avoidance of a small area around the seismic operation and 
short-term changes in behavior, falling within the MMPA definition of 
Level B harassment. Furthermore, the estimated numbers of animals 
potentially exposed to sound levels sufficient to cause appreciable 
disturbance are very low percentages of the affected populations.
    Based on the 160-dB criterion, the best estimates of the numbers of 
individual odontocete cetaceans that may be exposed to sounds 
[gteqt]160 dB re 1 microPa (rms) represent 0 to approximately 0.4 
percent (except for approximately 3.1 percent for killer whales) of the 
regional species populations (Table 2).
    Mitigation measures such as controlled speed, course alteration, 
observers, and shut downs when marine mammals are seen within defined 
ranges should further reduce short-term reactions, and minimize any 
effects on hearing. In all cases, the effects are expected to be short-
term, with no lasting biological consequence. In light of the type of 
take expected and the small percentages of affected stocks of 
cetaceans, the action is expected to have no more than a negligible 
impact on the affected species or stocks of cetaceans.

Effects on Pinnipeds

    Two pinniped species (the Steller sea lion and the harbor seal) and 
the sea otter are likely to be encountered in the study area. Also, it 
is possible that a small number of northern fur seals may be 
encountered, and possible (but very unlikely) that a few ribbon seals 
may be encountered. An estimated 56 individual harbor seals and 34 
individual Steller sea lions (<0.1 percent and 0.2 percent of their 
northeast Pacific Ocean populations, respectively) may be exposed to GI 
gun sounds at received levels greater than or equal to 160 dB re 1 
microPa (rms) during the seismic survey. It is probable that only a 
small percentage of those would actually be disturbed. It is most 
likely that only 3 northern fur seals and no ribbon seals will be 
exposed to sounds greater than or equal to 160 dB. Effects are expected 
to be limited to short-term and localized behavioral changes falling 
within the MMPA definition of Level B harassment. As is the case for 
cetaceans, the short-term exposures to sounds from the single GI-airgun 
is not expected to result in any long-term consequences for the 
individuals or their populations and the activity is expected to have 
no more than a negligible impact on the affected species or stocks of 
pinnipeds.

Potential Effects on Habitat

    The proposed seismic survey will not result in any permanent impact 
on habitats used by marine mammals, or to the food sources they 
utilize. The main impact issue associated with the proposed activity 
will be temporarily elevated noise levels and the associated direct 
effects on marine mammals.
    One of the reasons for the adoption of airguns as the standard 
energy source for marine seismic surveys was that they (unlike the 
explosives used in the distant past) do not result in any appreciable 
fish kill. Various experimental studies showed that airgun discharges 
cause little or no fish kill, and that any injurious effects were 
generally limited to the water within a meter or so of an airgun. 
However, it has recently been found that injurious effects on captive 
fish, especially on fish hearing, m