Small Takes of Marine Mammals Incidental to Specified Activities; Marine Geophysical Survey Across the Arctic Ocean, 24539-24553 [05-9333]

Agencies

• DEPARTMENT OF COMMERCE
• National Oceanic and Atmospheric Administration

[Federal Register Volume 70, Number 89 (Tuesday, May 10, 2005)]
[Notices]
[Pages 24539-24553]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 05-9333]


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DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

[I.D. 040505A]


Small Takes of Marine Mammals Incidental to Specified Activities; 
Marine Geophysical Survey Across the Arctic 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 University of Alaska 
Fairbanks (UAF) for an Incidental Harassment Authorization (IHA) to 
take small numbers of marine mammals, by harassment, incidental to 
conducting a marine seismic survey across the Arctic Ocean from 
northern Alaska to Svalbard. Under the Marine Mammal Protection Act 
(MMPA), NMFS is requesting comments on its proposal to issue an 
authorization to UAF to incidentally take, by harassment, small numbers 
of several species of cetaceans and pinnipeds from August 5 to 
September 30, 2005, during the seismic survey.

DATES: Comments and information must be received no later than June 9, 
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 PR1.040505A@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 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. Documents cited in this notice may be viewed, by 
appointment, during regular business hours, at the aforementioned 
address.

FOR FURTHER INFORMATION CONTACT: Jolie Harrison, Office of Protected 
Resources, NMFS, (301) 713-2289, ext 166.

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 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:
    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

[[Page 24540]]

of the comment period, NMFS must either issue or deny issuance of the 
authorization.

Summary of Request

    On March 30, 2005, NMFS received an application from UAF for the 
taking, by harassment, of several species of marine mammals incidental 
to conducting, with research funding from the National Science 
Foundation (NSF) and the Norwegian Petroleum Directorate (NPD), a 
marine seismic survey across the Arctic Ocean from northern Alaska to 
Svalbard during the period 5 August to 30 September 2005. The purpose 
of the proposed seismic study is to collect seismic reflection and 
refraction data that reveal the structure and stratigraphy of the upper 
crust of the Arctic Ocean. These data will assist in the determination 
of the history of ridges and plateaus that subdivide the Amerasian 
basin in the Arctic Ocean. Past studies have mapped the bottom of the 
Arctic Ocean, but data are needed to describe the boundaries and 
connections between the ridges and plateaus in the Amerasian basin and 
to study the stratigraphy of the smaller basins. This information will 
assist in preparing for future scientific drilling that is crucial to 
reconstructing the tectonic, magmatic, and paleoclimatic history of the 
Amerasian basin.

Description of the Activity

    The geophysical survey will involve the United States Coast Guard 
(USCG) cutter Healy. The Healy will rendezvous with the Swedish 
icebreaker Oden near Alpha Ridge. The Oden will be working on a 
separate project, conducting an oceanographic section across the Arctic 
Ocean basin and will coordinate its timing to meet the Healy. The Oden 
will cut a path through the ice as necessary, leading the Healy for the 
remainder of the trans-ocean track past the North Pole and then on 
towards Svalbard. The two icebreakers working in tandem will optimize 
seismic data collection and safety through the heaviest multi-year ice.
    The source vessel, the USCG icebreaker Healy, will use a portable 
Multi-Channel Seismic (MCS) system from the University of Bergen to 
conduct the seismic survey. The Healy will tow two different airgun 
configurations. The primary energy source will be two Generator guns 
(G. guns), each with a discharge volume of 250 in\3\ for a total volume 
of 500 in\3\. The secondary energy source will be a single Bolt airgun 
of 1200 in\3\ that will be used for deeper penetration over three 
ridges (the Alpha, Mendeleev, and Gakkel ridges).
    The Healy will also tow a hydrophone streamer 100-150 m (328-492 
ft) behind the ship, depending on ice conditions. The hydrophone 
streamer will be up to 300 m (984 ft) long. As the airguns are towed 
along the survey lines, the receiving system will receive the returning 
acoustic signals. In addition to the airguns, a multi-beam sonar and 
sub-bottom profiler will be used during the seismic profiling and 
continuously when underway.
    The program will consist of a total of approximately 4060 km (2192 
nautical miles (nm)) of surveys, not including transits when the 
airguns are not operating, plus scientific coring at nine locations. 
The seismic survey will commence >40 km (22 nm) north of Barrow, 
Alaska, and the seismic activities will be completed northwest of 
Svalbard, in Norwegian territorial waters. Water depths within the 
study area are 20 4000 m (66-13123 ft). Little more than 1 percent of 
the survey (approximately 48 km (26 nm)) will occur in water depths 
<100 m (328 ft), 5 percent of the survey (approximately 192 km (104 
nm)) will be conducted in water 100 1000 m (328-3280 ft) deep, and most 
(94 percent) of the survey (approximately 3820 km (2063 nm)) will occur 
in water >1000 m (3280 ft). Additional seismic operations will be 
associated with airgun testing, start up, and repeat coverage of any 
areas where initial data quality is sub-standard.
    Along with the airgun operations, additional acoustical systems 
will be operated during much of, or the entire, cruise. The ocean floor 
will be mapped with a multi-beam sonar, and a sub-bottom profiler will 
be used. These two systems are commonly operated simultaneously with an 
airgun system. An acoustic Doppler current profiler will also be used 
through the course of the project. A 12-kHz pinger will be used during 
the sea-bottom coring operations to monitor the depth of the corer 
relative to the ocean floor. A detailed description of the acoustic 
sources proposed for use during this survey can be found in the UAF 
application, which is available at: https://www.nmfs.noaa.gov/prot_res/
PR1/Small_Take/smalltake_info.htm#applications.
    The coring operations constitute a separate project, which will be 
conducted in conjunction with the seismic study from the Healy. Seismic 
operations will be suspended while the USCG Healy is on site for coring 
at each of nine locations. Depending on water depth and the number of 
cores to be collected, the Healy may be at each site for between 8 and 
36 hours.

Vessel Specifications

    The Healy has a length of 128 m (420 ft), a beam of 25 m (82 ft), 
and a full load draft of 8.9 m (29.2 ft). The Healy is a USCG 
icebreaker, capable of traveling at 5.6 km/h (3 knots) through 1.4 m 
(4.6 ft) of ice. A ``Central Power Plant'', four Sultzer 12Z AU40S 
diesel generators, provides electric power for propulsion and ship's 
services through a 60 Hz, 3-phase common bus distribution system. 
Propulsion power is provided by two electric AC Synchronous, 11.2 MW 
drive motors, fed from the common bus through a Cycloconverter system, 
that turn two fixed-pitch, four-bladed propellers. The operation speed 
during seismic acquisition is expected to be approximately 6.5 km/h 
(3.5 knots). When not towing seismic survey gear or breaking ice, the 
Healy cruises at 22 km/h (12 knots) and has a maximum speed of 31.5 km/
h (17 knots). She has a normal operating range of about 29,650 km 
(16,000 nm) at 23.2 km/hr (12.5 knots).
    The Healy will also serve as the platform from which vessel-based 
marine mammal observers will watch for marine mammals before and during 
airgun operations. The characteristics of the Healy that make it 
suitable for visual monitoring are described in the monitoring section.

Airgun Description and Safety Radii

    The University of Bergen's portable MCS system will be installed on 
the Healy for this cruise. The Healy will tow either two Sodera 250-
in\3\ G. guns (for a total discharge volume of 500 in\3\) or a single 
1200-in\3\ Bolt airgun, along with a streamer containing hydrophones, 
along predetermined lines. Seismic pulses will be emitted at intervals 
of 20 seconds (s) and recorded at a 2 millisecond (ms) sampling rate. 
The 20 s spacing corresponds to a shot interval of approximately 36 m 
(118 ft) at the typical cruise speed.
    The two-G. gun-cluster configuration will be towed below a 
depressor bird at a depth between 7 and 20 m (23 and 66 ft), as close 
to the Healy's stern as possible to minimize ice interference 
(preferred depth is 8 to 10 m (26 to 29 ft)). The two airguns will be 
towed 1 m (3.3 ft) apart, separated by a spreader bar. The G. guns have 
a zero to peak (peak) source output of 236 dB re 1 microPascal-m (6.5 
bar-m) and a peak-to-peak (pk-pk) level of 241 dB (11.7 bar-m). The 
dominant frequency components of these airguns are in the range of 0-
150 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 airgun.

[[Page 24541]]

 Actual levels experienced by any marine organism more than 1 m (3.3 
ft) from the airguns will be significantly lower.
    The single Bolt airgun will be towed below a depressor bird at a 
depth of 10 m (29 ft). This airgun has peak source output of 234 dB re 
1 microPascal-m (5 bar-m) and a pk-pk level of 241 dB (11.7 bar-m). The 
dominant frequency components of these airguns are in the range of 8-40 
Hz. Indicated source outputs are for sources at 5 m (16 ft) and for a 
filter bandwidth of approximately 0-250 Hz.
    Received sound levels were modeled by L-DEO for single 1200 in\3\ 
Bolt airgun and for the one and two 250 in3 G. guns in relation to 
distance and direction from the gun. This publically available model 
does not allow for bottom interactions, and, thus, is most directly 
applicable to deep water. For deep water, where most of the present 
project is to occur, the L-DEO model has been shown to be 
precautionary, i.e., it tends to overestimate radii for 190, 180, etc., 
dB re 1 microPa rms (Tolstoy et al. 2004a,b). Based on the models, 
table 1 shows the distances from the planned sources where sound levels 
of 190, 180, and 160 dB re 1 microPa root-mean squared (rms) are 
predicted to be received. The rms pressure is an average over the pulse 
duration. This is the measure commonly used in studies of marine mammal 
reactions to airgun sounds, and in NMFS guidelines concerning levels 
above which ``taking'' might occur. 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 [gteqt]190, 180, and 160 dB re 1 microPa (rms) might be
   received from the 250 in\3\ G. gun(s) and 1200 in3 Bolt airgun that will be used during the seismic survey
   across the Arctic Ocean during 2005. The sound radii used during the survey will depend on water depth (see
    text). Distances are based on model results provided by the Lamont-Doherty Earth Observatory of Columbia
                                                   University.
----------------------------------------------------------------------------------------------------------------
                                                                    Estimated Distances at Received Levels (m)
                                                                 -----------------------------------------------
                                                                     190 dB       180 dB
              Seismic Source Volume                 Water depth     (safety      (safety       160 dB (assumed
                                                                   criterion    criterion    onset of behavioral
                                                                      for          for           harassment)
                                                                   pinnipeds)   cetaceans)
----------------------------------------------------------------------------------------------------------------
                  250 in\3\G. gun                        >1000 m           17           52                   500
                                                      100-1000 m           26           78                   750
                                                          <100 m          213          385                  1364
                  500 in\3\2 G. guns                     >1000 m          100          325                  3300
                                                      100-1000 m          150          500                  5000
                                                          <100 m         1500         2400                  9700
                  1200 in\3\2 Bolt aigun                 >1000 m           25           50                   560
                                                      100-1000 m           38           75                   840
                                                          <100 m          313          370                  1527
----------------------------------------------------------------------------------------------------------------

    For the two-G. gun source, the highest sound level measurable at 
any location in the water would be slightly less than the nominal 
source level because the actual source is a distributed source rather 
than a point source. However, the two guns would be only 1 m (3.3 ft) 
apart, so the non-point-source effect would be slight. For the single 
Bolt airgun, the source level represents the actual level that would be 
found about 1 m from the energy source. Actual levels experienced by 
any organism more than 1 m from either of the sources will be 
significantly lower.
    The rms received levels that are used by NMFS 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 airguns. The 
measurement units used to describe airgun sources, i.e., peak or pk-pk 
decibels, are always higher than the rms decibels referred to in much 
of the biological literature. A measured received level of 160 decibels 
rms in the far field would typically correspond to a peak measurement 
of about 170 to 172 dB, and to a peak-to-peak 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 peak or pk-pk values for a given pulse 
depends on the frequency content and duration of the pulse, among other 
factors. However, the rms level is always lower than the peak or pk-pk 
level for an airgun-type source.
    The depth at which the sound source is towed has a major impact on 
the maximum near-field output, and on the shape of its frequency 
spectrum. In this case, the source is expected to be towed at 
relatively deep depths of 7 to 20 m (23 to 66 ft).
    Empirical data concerning the 190-, 180-, and 160-dB (rms) 
isopleths in deep and shallow water have been acquired for various 
airgun configurations 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). Those data 
demonstrated that L-DEO's model tends to overestimate the isopleth 
distances applied in deep water. During that study, empirical data were 
not obtained for either the 1200-in3 Bolt airgun or the G. guns that 
will be used during this survey. Although the results were limited, the 
calibration-study results showed that radii around the airguns where 
the received level would be 180 dB re 1 microPa (rms), the safety zone 
radius NMFS uses for cetaceans, (NMFS 2000), vary with water depth. 
Similar depth-related variation is likely in the 190 dB distances used 
for pinnipeds. Although sea turtle sightings are highly unlikely, the 
180-dB distance will also be used as the safety radius for sea turtles, 
as required by NMFS in another recent seismic project (Smultea et al., 
2005). The safety zones are used to trigger mitigation measures, which 
are described below.
    The L-DEO model does not allow for bottom interactions, and thus is 
most directly applicable to deep water and to relatively short ranges. 
In intermediate-depth water a precautionary 1.5x factor will be applied 
to the values predicted by L-DEO's model. In shallow water, larger 
precautionary factors derived from the empirical shallow-water 
measurements will be applied. The proposed study area will occur mainly

[[Page 24542]]

in water 1000 to 4000 m (3280 to 13123 ft) deep, with only 
approximately 1 percent of the survey lines in shallow (<100 m (328 
ft)) water and 5 percent of the survey lines in intermediate water 
depths (100 1000 m (328-3280 ft)).
    The empirical data indicate that, for deep water (>1000 m (3280 
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, UAF has 
proposed using safety radii during airgun operations in deep water that 
correspond to the values predicted by L-DEO's model for deep water 
(Table 1). In deep water, the estimated 190 and 180 dB radii for two 
250-in3 G. guns are 100 and 325 m (328 and 1067 ft), respectively. 
Those for one 1200-in\3\ Bolt airgun are 25 and 50 m (82 and 164 ft), 
respectively.
    Empirical measurements were not conducted for intermediate depths 
(100 1000 m (328-3280 ft)). On the expectation that results would be 
somewhere between those from shallow and deep water, UAF has applied a 
1.5x correction factor to the estimates provided by the model for deep 
water situations. This is the same factor that has been applied to the 
model estimates during L-DEO operations in intermediate-depth water 
from 2003 through early 2005. The estimated 190- and 180-dB radii in 
intermediate-depth water are 150 m (490 ft) and 500 m (1640 ft), 
respectively, for the two G. gun system and 38 and 75 m (125 and 246 
ft), respectively, for the single Bolt airgun (Table 1).
    Empirical measurements were not made for the sources that will be 
employed during the proposed survey operating in shallow water (<100 m 
(328 ft)). The empirical data on operations of two 105 in3 GI guns in 
shallow water showed that modeled values underestimated actual levels 
in shallow water at corresponding distances of 0.5 to 1.5 km (0.3 to 
0.5 nm) by a factor of approximately 3x (Tolstoy et al., 2004b). Sound 
level measurements for the 2 GI guns were not available for distances 
<0.5 km (0.3 nm) from the source. The radii estimated here for two G. 
guns operating in shallow water are derived from L-DEO's deep water 
estimates, with the same adjustments for depth-related differences in 
sound propagation used for 2 GI guns in earlier applications (and 
approximately the same factors as used for L-DEO's 10-airgun array). 
Similarly, the factors for the single airguns are the same as those for 
a single GI gun in earlier applications. Thus, the estimated 190- and 
180-dB radii in shallow water are 1500 and 2400 m (4921 and 7874 ft), 
respectively, for the two G. guns (Table 1). The corresponding radii 
for the single G. gun in shallow water are estimated to be 213 and 385 
m (699 and 1263 ft), respectively. The sound radii for the single Bolt 
airgun in shallow water are estimated to be 313 m (1027 ft) for 190 dB 
and 370 m (1214 ft) for 180 dB.

Characteristics of Airgun Pulses

    Discussion of the characteristics of airgun pulses has 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 Healy's track from north of Barrow, 
through the Arctic ocean to northwest of Svalbard and the associated 
marine mammals can be found in the UAF application and a number of 
documents referenced in the UAF application. A total of 17 cetacean 
species and 10 pinniped species may occur in the proposed study area. 
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 (polar bear).
    Odontocete whales include the sperm whale, northern bottlenose 
whale, beluga whale, narwhal, Atlantic white-beaked dolphin, Atlantic 
white-sided dolphin, killer whale, long-finned pilot whale, and harbor 
porpoise.
    Mysticete whales include the North Atlantic right whale, bowhead 
whale, gray whale, humpback whale, minke whale, sei whale, fin whale, 
and blue whale.
    Pinnipeds include the walrus, bearded seal, harbor seal, spotted 
seal, ringed seal, hooded seal, and harp seal.
    The marine mammal species most likely to be encountered include 
four cetacean species (beluga whale, narwhal, gray whale, bowhead 
whale), five pinniped species (walrus, bearded seal, ringed seal, 
hooded seal, harp seal), and the polar bear. However, most of these 
will occur in low numbers and are most likely to be encountered within 
100 km (54 n.mi) of shore. The most abundant marine mammal likely to be 
encountered throughout the cruise is the ringed seal. The most widely 
distributed marine mammals are expected to be the beluga, ringed seal, 
and polar bear.
    About 13 additional cetacean species could occur in the project 
area, but are unlikely to be encountered along the proposed trackline. 
If encountered at all, those species would be found only near one end 
of the track, either near Svalbard or near Alaska. The following 12 
species, if encountered at all, would be found close to Svalbard: sperm 
whale, northern bottlenose whale, long-finned pilot whale, Atlantic 
white-sided dolphin, Atlantic white-beaked dolphin, harbor porpoise, 
killer whale, North Atlantic right whale, humpback whale, minke whale, 
sei whale, fin whale, and blue whale. Two additional pinniped species, 
the harbor seal and spotted seal, are also unlikely to be encountered.
    Although information on the walrus and polar bear are included 
here, they are managed by the U.S. Fish & Wildlife Service (USFWS) and 
are not the subject of this authorization. UAF will coordinate with the 
USFWS regarding the effects of project operations on walruses and polar 
bears.More detailed information on these species is contained in the 
UAF application (see ADDRESSES).

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 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

[[Page 24543]]

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 UAF application provides the following information on what is 
known about the effects on marine mammals of the types of seismic 
operations planned by UAF. The types of effects considered in here are 
(1) tolerance, (2) masking of natural sounds, (3) behavioral 
disturbance, and (4) potential hearing impairment and other non-
auditory physical effects (Richardson et al., 1995). Because the airgun 
sources planned for use during the present project involve only one or 
two airguns, the effects are anticipated to be considerably less than 
would be the case with a large array. UAF 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 animals that are at distances 
less than 3300 m (10827 ft) in deep water (94 percent of survey), 5000 
m (16404 ft) in intermediate water depths (5 percent of survey), and 
9700 m (31824 ft) in shallow water (1 percent of survey), where the 
received sound levels greater than160 dB are expected to be. This 
corresponds to the value NMFS uses for onset of Level B harassment due 
to impulse sounds. Additional discussion on effects on marine mammal 
species can be found in the UAF 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 low-energy airgun sources planned for use in this 
proposed project, marine mammals would be expected to tolerate being 
closer to these sources than would be the case for a larger airgun 
source typical of most seismic surveys.
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 of relevance. 
Some whales are known to continue calling in the presence of seismic 
pulses. Their calls can be heard between the seismic pulses (e.g., 
Richardson et al., 1986; McDonald et al., 1995; Greene et al., 1999; 
Nieukirk et al., 2004). 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 more recent study reports that sperm 
whales off northern Norway continued calling in the presence of seismic 
pulses (Madsen et al., 2002). That has also been shown during recent 
work in the Gulf of Mexico (Tyack et al. 2003). Given that the airgun 
sources planned for use here involve only 1 or 2 airguns, 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 odontocete 
cetaceans, given the intermittent nature of seismic pulses and the 
relatively low source level of the airgun configurations to be used 
here. Also, the sounds important to odontocetes are predominantly at 
much higher frequencies than are airgun sounds and would not be masked 
by the airguns.
    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's 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 possible adverse impacts of masking 
marine mammal vocalizations.
Behavioral Disturbance by Seismic Surveys
    Disturbance includes a variety of effects, including subtle changes 
in behavior, more conspicuous changes in activities, and displacement. 
Not all behavioral disturbances rise to the level of Level B 
Harassment, which requires a disruption of behavioral patterns of 
biological importance. Exposure to sound alone may not constitute 
harassment or ``taking'' (NMFS 2001, p. 9293). Behavioral reactions of 
marine mammals to sound are difficult to predict. Reactions to sound, 
if any, depend on species, individual variation, state of maturity, 
experience, current activity, reproductive state, time of day,

[[Page 24544]]

season, 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 a 
marine mammal from an important feeding or breeding area, such a 
disturbance may constitute Level B harassment under the MMPA. In 
addition, effects that might not constitute Level B harassment may 
still result in significant displacement of sensitive species, such as 
bowhead whales, thereby affecting subsistence needs. Given the many 
uncertainties in predicting the quantity and types of impacts of noise 
on marine mammals, NMFS estimates the number of marine mammals that may 
be present within a particular distance of industrial activities or 
exposed to a particular level of industrial sound and uses these 
numbers as a proxy. 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 other species. Detailed studies have 
been conducted on humpback, gray, and bowhead whales, and on 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 been on behavioral reactions to much larger 
airgun sources than the airgun configurations 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. Detailed information on potential 
disturbance effects on baleen whales, toothed whales, and pinnipeds can 
be found in the UAF 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 
(injury) 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 UAF 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 lower than levels that may cause permanent hearing damage.
    Because the airgun sources planned for use during this project 
involve only 1 or 2 guns, and with the planned monitoring and 
mitigation measures, there is little likelihood that any marine mammals 
will 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 airgun(s), and 
multi-beam sonar, 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 small area with high 
received levels of airgun sound (see above). In those cases, the 
avoidance responses of the animals themselves will likely reduce or 
prevent any possibility of hearing impairment.
    Non-auditory physical effects might 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 in marine mammals that are in close proximity to 
large arrays of airguns. UAF 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 source, 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, 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, at 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 at 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 that the airgun 
sources involve only 1 or 2 airguns, and the strong likelihood that 
baleen whales would avoid the approaching airgun(s), 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

[[Page 24545]]

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, studies for prolonged 
exposures show that some pinnipeds may incur TTS at somewhat lower 
received levels for prolonged exposures than do small odontocetes 
exposed for similar durations (Kastak et al., 1999; Ketten et al., 
2001; Au et al., 2000). 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).
    A marine mammal within 100 m (<=328 ft) of a typical large array of 
operating airguns might be exposed to a few seismic pulses with levels 
of [gteqt]205 dB, and possibly more pulses if the mammal moved with the 
seismic vessel. (As noted above, most cetacean species tend to avoid 
operating airguns, although not all individuals do so.) However, 
several of the considerations that are relevant in assessing the impact 
of typical seismic surveys with arrays of airguns are not directly 
applicable here:
    (1) The planned airgun sources involve only 1 or 2 airguns, with 
correspondingly smaller radii within which received sound levels could 
exceed any particular level of concern.
    (2) ``Ramping up'' (soft start) is standard operational protocol 
during startup of large airgun arrays in many jurisdictions. Ramping up 
involves starting the airguns in sequence, usually commencing with a 
single airgun and gradually adding additional airguns. This practice 
will be employed when the 2 G. guns are operated.
    (3) Even with a large airgun array, it is unlikely that 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. In this project, 
the airgun sources are much less strong, so the area of influence and 
duration of exposure to strong pulses is much smaller, especially in 
deep and intermediate-depth water.
    (4) With a large array of airguns, TTS would be most likely in any 
odontocetes that bow-ride or otherwise linger near the airguns. In the 
present project, the anticipated 180 dB distances in deep and 
intermediate-depth water are 325 and 500 m (1066 and 1640 ft), 
respectively, for the 2 G. gun system, and 50 and 75 m (164 and 246 
ft), respectively, for the single Bolt airgun (Table 2). The waterline 
at the bow of the Healy will be approximately 123 m (403 ft) ahead of 
the airgun.
    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 UAF 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, ramping up multiple 
airguns in arrays has become standard operational protocol for many 
seismic operators and will occur when the 2 G. guns are operated.
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, based on their similar anatomy and inner ear structures. 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

[[Page 24546]]

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, during this project, it is highly unlikely that marine 
mammals could receive sounds strong enough and over a sufficient period 
of time to cause permanent hearing impairment. 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 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, in one case, 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 
military 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 (see 69 FR 
74906 (December 14, 2004) for additional discussion), 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 event, in 
addition to 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.
    The present project will involve lower-energy sound sources than 
used in typical seismic surveys. That, along with the monitoring and 
mitigation measures that are planned, and the infrequent occurrence of 
beaked whales in the project area, will minimize any possibility for 
strandings and mortality.

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 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. 
That is especially so in the case of the present project which will 
deploy only 1 or 2 airguns, the ship is moving 3 4 knots, and for the 
most part the tracklines will not ``double back'' through the same 
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.
    A short 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

[[Page 24547]]

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 survey, involving only 1 or 2 
airguns that will operate in any one location only briefly.
    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, 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 SeaBeam 2112 multi-beam 12-kHz bathymetric sonar system and a 
sub-bottom profiler will be operated from the source vessel nearly 
continuously during the planned study. A pinger will be operated during 
all coring.
    Sounds from the SeaBeam 2112 multi-beam sonar system 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 (approximately 2 ) in fore-aft 
extent and wide (approximately 130[deg]) in the cross-track extent. Any 
given mammal at depth near the trackline would be in the main beam for 
only a fraction of a second. Navy sonars that have been linked to 
avoidance reactions and stranding of cetaceans generally: (1) are more 
powerful than the SeaBeam 2112 sonar, (2) have a longer pulse duration, 
and (3) are directed close to horizontally (vs. downward for the 
SeaBeam 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 SeaBeam 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 SeaBeam multibeam sonars.
    Sounds from the sub-bottom profiler are very short pulses; pulse 
duration ranges from 0.5 to 25 milliseconds, and the interval between 
pulses can range between 0.25 s and 10 s, depending upon water depth. A 
3.5-kHz transducer emits a conical beam with a width of 26[deg] and the 
12 kHz transducer emits a conical beam with a width of 30[deg]. The 
swept (chirp) frequency ranges from 2.75 kHz to 6 kHz. Most of the 
energy from the sub-bottom profiler is directed downward from the 
transducer array. Sound levels have not been measured directly for the 
sub-bottom profiler used by the Healy, but Burgess and Lawson (2000) 
measured sounds propagating more or less horizontally from a similar 
unit with similar source output (205 dB re 1 microPa m). The 160- and 
180- dB re 1 microPa rms radii, in the horizontal direction, were 
estimated to be, respectively, near 20 m (66 ft) and 8 m (26 ft) from 
the source, as measured in 13 m or 43 ft water depth. The corresponding 
distances for an animal in the beam below the transducer would be 
greater, on the order of 180 m (591 ft) and 18 m (59 ft), assuming 
spherical spreading.
    Sounds from the 12-kHz pinger are very short pulses, occurring for 
0.5, 2, or 10 ms once every second, with source level approximately 192 
dB re 1 microPa at a one pulse per second rate. The 12-kHz signal is 
omnidirectional. The pinger produces sounds that are within the range 
of frequencies used by small odontocetes and pinnipeds that occur or 
may occur in the area of the planned survey.
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.
    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 
UAF'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-s pulsed sounds at frequencies similar to 
those that will be emitted by the bathymetric

[[Page 24548]]

sonar to be used by