Marine Mammals; Incidental Take During Specified Activities, 35928-35944 [06-5589]

Agencies

• Fish and Wildlife Service
• DEPARTMENT OF THE INTERIOR

[Federal Register Volume 71, Number 120 (Thursday, June 22, 2006)]
[Notices]
[Pages 35928-35944]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 06-5589]


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DEPARTMENT OF THE INTERIOR

Fish and Wildlife Service


Marine Mammals; Incidental Take During Specified Activities

AGENCY: Fish and Wildlife Service, Interior.

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

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SUMMARY: The Fish and Wildlife Service (Service) has received an 
application from the University of Texas at Austin Institute for 
Geophysics (UTIG) for authorization to take small numbers of marine 
mammals by harassment incidental to conducting a marine seismic survey 
in the Arctic Ocean, including the Chukchi Sea, from approximately July 
15 through August 25, 2006. In accordance with provisions of the Marine 
Mammal Protection Act (MMPA), as amended, the Service requests comments 
on its proposed authorization for the applicant to incidentally take, 
by harassment, small numbers of Pacific walrus and polar bears in the 
Chukchi Sea during the seismic survey.

DATES: Comments and information must be received by July 24, 2006.

ADDRESSES: You may submit comments by any of the following methods:
    1. By mail to: Craig Perham, Office of Marine Mammals Management, 
U.S. Fish and Wildlife Service, 1011 East Tudor Road, Anchorage, Alaska 
99503.
    2. By fax to: 907-786-3816.
    3. By electronic mail (e-mail) to: FW7MMM@FWS.gov. Please submit 
comments as an ASCII file avoiding the use of special characters and 
any form of encryption. Please also include your name and return 
address in your message. If you do not receive a confirmation from the 
system that we have received your message, contact us directly at U.S. 
Fish and Wildlife Service, Office of Marine Mammals Management, 907-
786-3810 or 1-800-362-5148.
    4. By hand-delivery to: Office of Marine Mammals Management, U.S. 
Fish and Wildlife Service, 1011 East Tudor Road, Anchorage, Alaska 
99503.

FOR FURTHER INFORMATION CONTACT: Craig Perham, Office of Marine Mammals 
Management, U.S. Fish and Wildlife Service, 1011 East Tudor Road, 
Anchorage, Alaska 99503; telephone 907-786-3810 or 1-800-362-5148; or 
e-mail craig--perham@FWS.gov.

SUPPLEMENTARY INFORMATION:

Background

    Sections 101(a)(5)(A) and (D) of the MMPA, as amended, (16 U.S.C. 
1371(a)(5)(A) and (D)) authorize the Secretary of the Interior to 
allow, upon request, the incidental, but not intentional, taking of 
small numbers of marine mammals by U.S. citizens who engage in a 
specified activity (other than commercial fishing) within a specified 
geographical region provided that 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 
and comment.
    Authorization to incidentally take marine mammals may be granted if 
the Service finds that the taking will have a negligible impact on the 
species or stock(s), and will not have an unmitigable adverse impact on 
the availability of the species or stock(s) for subsistence uses. 
Permissible methods of taking and other means of affecting the least 
practicable impact on the species or stock and its habitat, and 
requirements pertaining to the monitoring and reporting of such 
takings, are prescribed as part of the authorization process.
    The term ``take,'' as defined by the MMPA, means to harass, hunt, 
capture, or kill, or attempt to harass, hunt, capture, or kill any 
marine mammal. Harassment, as defined by the MMPA, means ``any act of 
pursuit, torment, or annoyance which--(i) has the potential to injure a 
marine mammal or marine mammal stock in the wild [the MMPA calls this 
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 [the MMPA calls 
this Level B harassment].''
    The terms ``small numbers,'' ``negligible impact,'' and 
``unmitigable adverse impact'' are defined in 50 CFR 18.27, the 
Service's regulations governing take of small numbers of marine mammals 
incidental to specified activities. ``Small numbers'' is defined as ``a 
portion of a marine mammal species or stock whose taking would have a 
negligible impact on that species or stock.'' ``Negligible impact'' is 
defined 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.'' ``Unmitigable adverse impact'' is defined 
as ``an impact resulting from the specified activity (1) that is likely 
to reduce the availability of the species to a level insufficient for a 
harvest to meet subsistence needs by (i) causing the marine mammals to 
abandon or avoid hunting areas, (ii) directly displacing subsistence 
users, or (iii) placing physical barriers between the marine mammals 
and the subsistence hunters; and (2) that cannot be sufficiently 
mitigated by other measures to increase the availability of marine 
mammals to allow subsistence needs to be met.''
    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 where the take 
will be limited to harassment. Section 101(a)(5)(D)(iii) establishes a 
45-day time limit for Service 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, the Service must

[[Page 35929]]

either issue or deny issuance of the authorization. The Service refers 
to these authorizations as Incidental Harassment Authorizations (IHAs).

Summary of Request

    On March 17, 2006, the Service received an application from UTIG 
for the taking by harassment of Pacific walrus and polar bears 
incidental to conducting, with research funding from the National 
Science Foundation (NSF), a marine seismic survey in the Western Canada 
Basin, Chukchi Borderland, and Mendeleev Ridge of the Arctic Ocean 
during July through August, 2006. The seismic survey will be operated 
in conjunction with a sediment coring project, which will obtain data 
regarding crustal structure, and will take place far north of the 
Chukchi Sea. A description of the coring activities is provided in the 
National Oceanic and Atmospheric Administration's (NOAA) proposed IHA 
for this same research cruise in the Federal Register of May 15, 2006 
(71 FR 27997). Walrus do not occur in the area of the coring activities 
and there is no potential for harassment of walrus. There is a 
potential that coring activities may encounter a very few isolated 
members of the Chukchi Sea polar bear stock; however, the effects to 
those individuals would be no more than minimal. This authorization, 
therefore, assesses the incidental harassment of walrus and polar bear 
resulting from the seismic survey activity in the Chukchi Sea.
    The purpose of the proposed study is to collect seismic reflection 
and refraction data and sediment cores that reveal the crustal 
structure and composition of submarine plateaus in the western Amerasia 
Basin in the Arctic Ocean. Past studies have led many researchers to 
support the idea that the Amerasia Basin opened about a pivot point 
near the Mackenzie Delta. However, the crustal character of the Chukchi 
Borderlands could determine whether that scenario is correct, or 
whether more complicated tectonic scenarios must be devised to explain 
the presence of the Amerasia Basin. These data will assist in the 
determination of the tectonic evolution of the Amerasia Basin and 
Canada Basin, which is fundamental to such basic concerns as sea level 
fluctuations and paleoclimate in the Mesozoic era.

Description of the Activity

    The Healy, a U.S. Coast Guard (USCG) Cutter ice-breaker, will 
rendezvous with the science party off Barrow, Alaska, on or around July 
15, 2006. Trained marine mammal observers will also be onboard during 
the cruise. The Healy will sail north and arrive at the beginning of 
the seismic survey, which will start more than 150 kilometers (km) (93 
miles [mi]) north of Barrow. The cruise will last for approximately 40 
days, and it is estimated that the total seismic survey time will be 
approximately 30 days depending on ice conditions. Seismic survey work 
is scheduled to terminate west of Barrow about August 25, 2006. The 
vessel will then sail south to Nome, Alaska, where the science party 
will disembark. In conjunction with the seismic survey, a sediment 
coring project will be conducted in the Arctic Ocean, north of the 
Chukchi Sea. The NOAA's proposed IHA for this same research cruise, 
published in the Federal Register of May 15, 2006, describes the coring 
project activities.
    The majority of seismic survey activities will take place in the 
Arctic Ocean. The Chukchi Sea segment of the survey is approximately 
478 km, located between 75[deg] N and 70.9[deg] N and will occur in 
mid- to late August. The bulk of the seismic survey will not be 
conducted in any country's territorial waters. However, the survey will 
occur within the Exclusive Economic Zone (EEZ) of the United States for 
approximately 563 km.
    The Healy will use a portable Multi-Channel Seismic (MCS) system to 
conduct the seismic survey. A cluster of eight airguns will be used as 
the energy source during most of the cruise, especially in deep water 
areas. The airgun array will have four 500-cubic inches 
(in3) Bolt airguns and four 210-in3 G. guns for a 
total discharge volume of 2,840-in3. In shallow water, 
occurring during the first and last portions of the cruise, a four 105-
in3 GI gun array with a total discharge volume of 420 
in3 will be used. Other sound sources (see below) will also 
be employed during the cruise. The seismic operations during the survey 
will be used to obtain information on the history of the ridges and 
basins that make up the Arctic Ocean.
    The airgun arrays will discharge about once every 60 seconds. The 
compressed air will be supplied by compressors onboard the source 
vessel. The Healy will also tow a hydrophone streamer 100 to 150 meters 
(328 to 492 feet [ft]) behind the ship, depending on ice conditions. 
The hydrophone streamer will be up to 200 m (656 ft) long. As the 
source operates along the survey lines, the hydrophone receiving system 
will receive and record the returning acoustic signals. In addition to 
the hydrophone streamer, sea ice seismometers (SIS) will be deployed on 
ice floes ahead of the ship using a vessel-based helicopter, and then 
retrieved from behind the ship once it has passed the SIS locations.
    The SISs will be deployed as much as 120 km (74 mi) ahead of the 
ship, and recovered when as much as 120 km (74 mi) behind the ship. The 
seismometers will be placed on top of ice floes with a hydrophone 
lowered into the water through a small hole drilled in the ice. These 
instruments will allow seismic refraction data to be collected in the 
heavily ice-covered waters of the region.
    The program will consist of a total of approximately 3,625 km 
(2,252 mi) of surveys, not including transits when the airguns are not 
operating. The area included in this proposal is the southwest leg, 
which extends 478 km into the Chukchi Sea (south of 75[deg] N). Water 
depths within the study area are 40 to 3,858 m (131 to 12,657 ft). 
Little more than 15 percent (approximately 73 km [45 mi]) of the 
Chukchi Sea survey segment will occur in water deeper than 1,000 m 
(3,280 ft); 21 percent (approximately 102 km [63 mi]) will be conducted 
in water 100 to 1,000 m (328 to 3,280 ft) deep. Most of the Chukchi 
survey track, 64 percent (approximately 303 km [188 mi]), will occur in 
water less than 100 m (328 ft). The Principal Investigators (PIs) plan 
to use the larger, 8-airgun array for only 24 km (15 mi) along the 
northernmost reach of the Chukchi survey line in deep water (greater 
than 1,000 m). There will be additional seismic operations associated 
with airgun testing, start up, and repeat coverage of any areas where 
initial data quality is sub-standard. In addition to the airgun array, 
a multibeam sonar and sub-bottom profiler will be used during the 
seismic profiling and continuously when underway.

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 ft). The Healy is capable of 
traveling at 5.6 km/h (3 knots) through 1.4 m (4.6 ft) of ice. A 
Central Power Plant, consisting of 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/hr (hour) (3.5 
knots). When not towing seismic survey gear or breaking ice, the Healy 
cruises at 22 km/hr (12 knots) and has a maximum speed of 31.5 km/hr 
(17 knots). It has a normal operating range

[[Page 35930]]

of about 29,650 km (18,423 mi) at 23.2 km/hr (12.5 knots).

Seismic Source Description

    A portable MCS system will be installed on the Healy for this 
cruise. The source vessel will tow along predetermined lines one of two 
different airgun arrays (an 8-airgun array with a total discharge 
volume of 2,840 in\3\ or a four GI gun array with a total discharge 
volume of 420 in\3\), as well as a hydrophone streamer. Seismic pulses 
will be emitted at intervals of approximately 60 seconds and recorded 
at a 2 millisecond (ms) sampling rate. The 60-second spacing 
corresponds to a shot interval of approximately 120 m (394 ft) at the 
anticipated typical cruise speed.
    As the airgun array is towed along the survey line, the towed 
hydrophone array receives the reflected signals and transfers the data 
to the onboard processing system. The SISs will store returning signals 
on an internal datalogger and also relay them in real-time to the Healy 
via a radio transmitter, where they will be recorded and processed.
    The 8-airgun array will be configured as a four-G. gun cluster with 
a total discharge volume of 840 in\3\ and a four Bolt airgun cluster 
with a total discharge volume of 2,000 in\3\. The source output is from 
246 to 253 dB re 1 [mu]Pa m. The two clusters are four meter apart, 
which will result in less downward directivity than is often present 
during seismic surveys and more horizontal propagation of sound. The 
clusters will be operated simultaneously for a total discharge volume 
of 2,840 in\3\. The 4-GI gun array will be configured the same as the 
four G. gun portion of the 8-airgun array. The energy source (source 
level 239-245 dB re 1 [mu]Pa m) will be towed as close to the stern as 
possible to minimize ice interference. The 8-airgun array will be towed 
below a depressor bird at a depth of 7-20 m (23-66 ft) depending on ice 
conditions; the preferred depth is 8-10 m (26-33 ft).
    The highest sound level measurable at any location in the water 
from the airgun arrays would be slightly less than the nominal source 
level because the actual source is a distributed source rather than a 
point source. The depth at which the 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 a 
relatively deep depth of up to 9 m (30 ft).
    The rms (root mean square) received sound levels that are used as 
impact criteria for marine mammals are not directly comparable to the 
peak or peak-to-peak values normally used to characterize source levels 
of airguns. The measurement units used to describe airgun sources, peak 
or peak-to-peak dB, are always higher than the rms dB referred to in 
much of the biological literature. A measured received level of 160 dB 
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, 2000). The precise 
difference between rms and peak or peak-to-peak 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 
peak-to-peak level for an airgun-type source. Additional discussion of 
the characteristics of airgun pulses is included in Appendix A of 
UTIG's application.

Safety Radii Proposed by UTIG

    Received sound fields have been modeled by Lamont-Doherty Earth 
Observatory (L-DEO) for the 8-airgun and 4-GI gun arrays that will be 
used during this survey. 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, 170, 
160 dB re 1 [mu]Pa rms (Tolstoy et al. 2004a, b).
    Predicted sound fields were modeled using sound exposure level 
(SEL) units (dB re 1 [mu]Pa\2\-s), because a model based on those units 
tends to produce more stable output when dealing with mixed-gun arrays 
like the one to be used during this survey. The predicted SEL values 
can be converted to rms received pressure levels, in dB re 1 [mu]Pa by 
adding approximately 15 dB to the SEL value (Greene 1997; McCauley et 
al. 1998, 2000). 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. The rms level of a seismic pulse is 
typically about 10 dB less than its peak level.
    Empirical data concerning 190, 180, 170, and 160 dB (rms) distances 
in deep and shallow water were acquired for various airgun array 
configurations during the acoustic verification study conducted by L-
DEO in the northern Gulf of Mexico (Tolstoy et al. 2004a, b). The 
proposed Chukchi Sea survey track will occur mainly in shallow water 
with approximately 64 percent of trackline in water depths greater than 
100 m, 21 percent in intermediate water depths (100-1,000 m), and 15 
percent in water deeper than 1,000 meter.
    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 correction 
factor will be applied to the values predicted by L-DEO's model, as has 
been done in other recent NSF-sponsored seismic studies. In shallow 
water, larger precautionary factors derived from the empirical shallow-
water measurements will be applied (see Table 1).

    Table 1.--Estimated Distances to Which Sound Levels (dB re 1[mu] Pa) Might Be Received From Various Gun-Types Used During the Healy Arctic Cruise
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                                                                                                Estimated distances for received levels (m)
                                                                                 -----------------------------------------------------------------------
                                                                                                                           170 dB
                                                                                                                         (alternate
             Seismic source volume                         Water depth              190 dB (shut-     180 dB (shut-      behavioral      160 dB (assumed
                                                                                   down criterion    down criterion      harassment         onset of
                                                                                   for pinnipeds)    for cetaceans)     criterion for      behavioral
                                                                                                                        delphinids &       harassment)
                                                                                                                         pinnipeds)
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105 in\3\ GI gun..............................  >1,000 m........................                10                27                90               275
                                                100-1,000 m.....................                15                41               135               413
                                                <100 m..........................               125               200               375               750
210 in\3\ G. gun..............................  >1,000 m........................                20                78               222               698
                                                100-1,000 m.....................                30               117               333             1,047
                                                <100 m..........................               250               578               925             1,904
420 in\3\ (4-GI gun array)....................  >1,000 m........................                75               246               771             2,441

[[Page 35931]]

 
                                                100-1,000 m.....................               113               369             1,157             3,662
                                                <100 m..........................               938             1,822             3,213             6,657
2,840 in\3\ (8-airgun array)..................  >1,000 m........................               230               716             2,268             7,097
                                                100-1,000 m.....................               *NA               *NA               *NA               *NA
                                                <100 m..........................               *NA               *NA               *NA               *NA
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* The 8-airgun array will only be operated in deep (greater than 1,000 m) water for approximately 24 km at the northern extent of the Chukchi Sea
  portion of the survey.

    The empirical data indicate that, for deep water (greater than 
1,000 m), 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, it is 
proposed that safety radii during airgun operations in deep water will 
be the values predicted by L-DEO's modeling, after conversion from SEL 
to rms (Table 1). The estimated 190 dB (rms) radii for 8-airgun and 4-
GI gun arrays are 230 (745 ft) and 75 m (246 ft), respectively.
    Empirical measurements were not taken for intermediate depths (100-
1,000 m). On the expectation that results would be intermediate between 
those from shallow and deep water, a 1.5x correction factor is applied 
to the estimates provided by the model for deep water situations. This 
is the same factor that has been applied to the model estimates during 
L-DEO operations in intermediate-depth water from 2003 through early 
2005. The assumed 190 dB (rms) radius in intermediate-depth water is 
113 m for the 4-GI gun array (Table 1). The 8-airgun array will only be 
used in deep water, i.e., greater than 1,000 m.
    Empirical measurements were not made for the 4 GI guns that will be 
employed during the proposed survey in shallow water (less than 100 m). 
(The 8-airgun array will not be used in shallow water.) The empirical 
data on operations of two 105 in\3\ GI guns in shallow water showed 
that modeled values underestimated the distance to the actual 160 dB 
sound level radii in shallow water by a factor of approximately 3 
(Tolstoy et al. 2004b). Sound level measurements for the 2 GI guns were 
not available for distances less than 0.5 km (.31 mi) from the source. 
The radii estimated here for the 4-GI guns operating in shallow water 
are derived from the L-DEO model, with the same adjustments for depth-
related differences between modeled and measured sound levels as were 
used for 2-GI guns in earlier applications. Correction factors for the 
different sound level radii are approximately 12x the model estimate 
for the 190 dB radius in shallow water, approximately 7x for the 180 dB 
radius, and approximately 4x for the 170 dB radius (Tolstoy 2004a, b). 
Thus, the 190 dB radius in shallow water is assumed to be 938 m (3,077 
ft) for the 4-GI gun array (Table 1).
    Pursuant to the mitigation measures of this proposed authorization, 
the airguns will be powered down (or shut-down if necessary) 
immediately when walrus or polar bears are detected within or about to 
enter the appropriate radii. The 190 dB safety criteria are consistent 
with guidelines listed for pinnipeds, by the National Marine Fisheries 
Service (NMFS) (2000) and other guidance by NMFS. The UTIG will 
conservatively apply the same 190 dB criterion to polar bears in water 
in this IHA request. Although sound effects on the walrus and polar 
bears have not been studied, the 190 dB criterion was selected because 
walrus, which are pinnipeds, are expected to react similarly to other 
pinnipeds. Polar bears normally swim with their heads above the surface 
and are likely to be less sensitive than pinnipeds to human-caused 
underwater sounds.

Other Acoustic Devices

    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 multibeam 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 SeaBeam 2112 multibeam 12 kHz bathymetric sonar system will be 
used on the Healy, with a maximum source output of 237 dB re 1 [mu]Pa 
at one meter. The transmit frequency is a very narrow band, less than 
200 Hz, and centered at 12 kHz. Pulse lengths range from less than one 
ms to 12 ms. The transmit interval ranges from 1.5 to 20 seconds, 
depending on the water depth, and is longer in deeper water. The 
SeaBeam system consists of a set of underhull projectors and 
hydrophones. The transmitted beam is narrow (approximately 2[deg]) in 
the fore-aft direction but broad (approximately 132[deg]) in the cross-
track direction. The system combines this transmitted beam with the 
input from an array of receiving hydrophones oriented perpendicular to 
the array of source transducers, and calculates bathymetric data (sea 
floor depth and some indications about the character of the seafloor) 
with an effective 2[deg] by 2[deg] footprint on the seafloor. The 
SeaBeam 2112 system on the Healy produces a useable swath width of 
slightly more than 2 times the water depth. This is narrower than 
normal because of the ice-protection features incorporated into the 
system on the Healy.
    The Knudsen 320BR will provide information on sedimentary layering, 
down to between 20 and 70 m, depending on bottom type and slope. It 
will be operated with the multibeam bathymetric sonar system that will 
simultaneously map the bottom topography.
    The Knudsen 320BR sub-bottom profiler is a dual-frequency system 
with operating frequencies of 3.5 and 12 kHz:
    Low frequency--Maximum output power into the transducer array, as 
wired on the Healy (125 ohms), at 3.5 kHz is approximately 6,000 watts 
(electrical), which results in a maximum source level of 221 dB re 1 
[mu]Pa at 1 m downward. Pulse lengths range from 1.5

[[Page 35932]]

to 24 ms with a bandwidth of 3 kHz (FM sweep from 3 kHz to 6 kHz). The 
repetition rate is range dependent, but the maximum is a 1-percent duty 
cycle. Typical repetition rate is between one-half second (in shallow 
water) to 8 s in deep water.
    High frequency--The Knudsen 320BR is capable of operating at 12 
kHz, but the higher frequency is rarely used because it interferes with 
the SeaBeam 2112 multibeam sonar, which also operates at 12 kHz. The 
calculated maximum source level (downward) is 215 dB re 1 [mu]Pa at 1 m 
(3.28 ft). The pulse duration is typically 1.5 to 5 ms with the same 
limitations and typical characteristics as the low-frequency channel.
    A single 12 kHz transducer and one 3.5 kHz, low-frequency (sub-
bottom) transducer array, consisting of 16 elements in a 4-by-4 array 
will be used for the Knudsen 320BR. The 12 kHz transducer (TC-12/34) 
emits a conical beam with a width of 30[deg], and the 3.5 kHz 
transducer (TR109) emits a conical beam with a width of 26[deg].
    The 150 kHz acoustic Doppler current profiler (ADCPTM) 
has a minimum ping rate of 0.65 ms. There are four beam sectors, and 
each beamwidth is 3[deg]. The pointing angle for each beam is 30[deg] 
off from vertical with one each to port, starboard, forward, and aft. 
The four beams do not overlap. The 150 kHz ADCPTM's maximum 
depth range is 300 m.
    The Ocean Surveyor 75 is an ADCPTM operating at a 
frequency of 75 kHz, producing a ping every 1.4 s. The system is a 
four-beam phased array with a beam angle of 30[deg]. Each beam has a 
width of 4[deg], and there is no overlap. Maximum output power is 1 kW 
with a maximum depth range of 700 m (2,297 ft).

Plan of Cooperation

    The UTIG will consult with representatives of the communities along 
the Chukchi Sea coast to identify any areas or issues of potential 
conflict. These communities are Point Hope, Point Lay, Wainwright, and 
Barrow. A Plan of Cooperation (POC) for the 2006 seismic survey in the 
Chukchi Sea will be developed if identified as warranted during these 
consultations and determined to be necessary by the Service. The POC 
would cover the phases of UTIG's seismic surveys planned in the Chukchi 
Sea when appropriate for the 2006 project. The purpose of the POC will 
be to identify measures that will be taken to minimize any adverse 
effects on the availability of marine mammals for subsistence uses, and 
to ensure good communication between the project scientists and the 
native communities along the coast.
    Subsequent meetings with community representatives and any other 
parties to the POC will be held as necessary to negotiate the terms of 
the plan and to coordinate the planned seismic survey operation with 
subsistence hunting. The POC may address: Operational agreement and 
communications procedures; where and when the agreement becomes 
effective; the general communications scheme; onboard observers; 
conflict avoidance; seasonally sensitive areas; vessel navigation; air 
navigation; marine mammal monitoring activities; measures to avoid 
impacts to marine mammals; measures to avoid conflicts in areas of 
active hunting; emergency assistance; and the dispute resolution 
process.
    In addition, one (or more) Alaska Native knowledgeable about the 
mammals and fish of the area is expected to be included as a member of 
the observer team aboard the Healy. Although the primary 
responsibilities encompass implementing the monitoring and mitigation 
requirements, duties will also include acting as a liaison with hunters 
and fishers if they are encountered at sea. In the unlikely event 
subsistence hunting or fishing is occurring within 5 km (3 mi) of the 
Healy's trackline, the airgun operations will be suspended until the 
Healy is approximately 5 km (3 mi) away.

Description of Habitat and Marine Mammals Affected by the Activity

    A detailed description of the Chukchi Sea ecosystem and the 
associated marine mammals can be found in several documents (Corps of 
Engineers 1999; NMFS 1999; Minerals Management Service (MMS) 2006, 
1996, and 1992). MMS' Programmatic Environmental Assessment (PEA)-
Arctic Ocean Outer Continental Shelf Seismic Surveys 2006--may be 
viewed at: https://www.mms.gov/alaska.
    The marine mammals that occur in the proposed survey area belong to 
three taxonomic groups: odontocetes (toothed cetaceans, such as beluga 
whale and narwhal whale), mysticetes (baleen whales), and carnivora 
(pinnipeds and polar bears). Cetaceans and pinnipeds, with the 
exception of walrus, are managed by the NMFS and are being addressed by 
that agency (71 FR 27997; May 15, 2006). Pacific walrus and polar bear, 
which are managed by the Service, are the subject of this proposed IHA.

Pacific Walrus

    Concentrations of walrus might be encountered in certain areas, 
depending on the location of the edge of the pack ice relative to their 
favored shallow-water foraging habitat. There are two recognized 
subspecies of walrus: the Pacific walrus (Odobenus rosmarus divergens) 
and Atlantic walrus (O. r. rosmarus). Only the Pacific subspecies is 
potentially within the planned seismic survey study area.
    The Pacific walrus is represented by a single stock of animals that 
inhabits the shallow continental shelf waters of the Bering and Chukchi 
Seas, occasionally moving into the East Siberian and Beaufort Seas. The 
population ranges across the international boundaries of the United 
States and Russia, and both nations share common interests with respect 
to the conservation and management of this species.
    Walrus are migratory, moving south with the advancing ice in autumn 
and north as the ice recedes in spring (Fay 1981). In the summer, most 
of the population of Pacific walrus moves to the Chukchi Sea, but 
several thousands aggregate in the Gulf of Anadyr and in Bristol Bay 
(Angliss and Lodge 2004). Limited numbers of walrus inhabit the 
Beaufort Sea during the open water season, and they are considered 
extralimital east of Point Barrow (Sease and Chapman 1988).
    The northeast Chukchi Sea west of Barrow is the northeastern extent 
of the main summer range of the walrus, and only a few are seen farther 
east in the Beaufort Sea (e.g., Harwood et al. 2005). Walrus observed 
in the Beaufort Sea have typically been lone individuals. The reported 
subsistence harvest of walrus by Barrow hunters for the 5-year period 
of 1994-1998 was 99 walrus (USDI 2000a). Most of these were harvested 
west of Point Barrow. In addition, between 1988 and 1998, Kaktovik 
hunters harvested one walrus (USDI 2000b).
    Walrus are most commonly found near the southern margins of the 
pack ice as opposed to deep in the pack where few open leads (polynyas) 
exist to afford access to the sea for foraging (Estes and Gilbert 1978; 
Gilbert 1989; Fay 1982). Walrus are not typically found in areas of 
greater than 80 percent ice cover (Fay 1982). Ice serves as an 
important mobile platform, floating the walrus on to new foraging 
habitat and providing a place to rest and nurse their young.
    This close relationship to the ice largely determines walrus 
distribution and the timing of their migrations. As the pack ice breaks 
up in the Bering Sea and recedes northward in May and June, a majority 
of subadults, females, and calves migrate with it, either by

[[Page 35933]]

swimming or resting on drifting ice sheets. Many males will choose to 
stay in the Bering Sea for the entire year, with concentrations near 
Saint Lawrence Island and further south in Bristol Bay. Two northward 
migration pathways are apparent, either toward the eastern Chukchi Sea 
near Barrow or northwestward toward Wrangel Island. By late June to 
early July, concentrations of walrus migrating northeastward spread 
along the Alaska coast congregating within 200 km of the shore from 
Saint Lawrence Island to southwest of Barrow. In August, largely 
dependent on the retreat of the pack ice, walrus are found further 
offshore with principal concentrations to the northwest of Barrow. By 
October, a reverse migration occurs out of the Chukchi Sea, with 
animals swimming ahead of the developing pack ice, as it is too weak to 
support them (Fay 1982).
    Estimates of the pre-exploitation population of the Pacific walrus 
range from 200,000 to 400,000 animals (USFWS 2000a). Over the past 150 
years, the population has been depleted by overharvesting and then 
periodically allowed to recover (Fay et al. 1989). An aerial survey 
flown in 1990 produced a population estimate of 201,039 animals; 
however, large confidence intervals associated with that estimate 
precluded any conclusions concerning population trend (Gilbert et al. 
1992). The most current minimum population estimate is 188,316 walrus 
(USFWS 2000a). This estimate is conservative, because a portion of the 
Chukchi Sea was not surveyed due to lack of ice. The Service and U.S. 
Geological Survey, in partnership with Russian scientists, will conduct 
a rangewide survey to estimate population size. The results of these 
survey efforts should be available in 2007 (USFWS 2006).
    Pacific walrus feed primarily on benthic invertebrates, 
occasionally fish and cephalopods, and more rarely, some adult males 
may prey on other pinnipeds (reviewed in Riedman 1990). Walrus 
typically feed in depths of 10 to 50 m (Vibe 1950; Fay 1982). Though 
the deepest dive recorded for a walrus was 133 m, they are more likely 
to be found in depths of 80 m or less in coastal or continental shelf 
habitats, where the clams and other mollusks that walrus prefer are 
found (Fay 1982; Fay and Burns 1988; Reeves et al. 2002). In a recent 
study in Bristol Bay, 98 percent of satellite locations of tagged 
walrus were foraging in water depths of 60 m or less (Chadwick and 
Hills 2005).
    Polar bears (Ursus maritimus) are known to prey on walrus calves, 
and killer whales (Orcinus orca) have been known to take all age 
classes of animals. Predation levels are thought to be highest near 
terrestrial haulout sites where large aggregations of walrus can be 
found; however, few observations exist for off-shore environs.
    Pacific walrus have been hunted by coastal Natives in Alaska and 
Chukotka for thousands of years. Exploitation of walrus by Europeans 
has also occurred in varying degrees since first contact. Presently, 
walrus hunting in Alaska and Chukotka is restricted to meet the 
subsistence needs of aboriginal peoples. The Service, in partnership 
with the Eskimo Walrus Commission (EWC) and the Association of 
Traditional Marine Mammal Hunters of Chukotka, administers subsistence 
harvest monitoring programs in Alaska and Chukotka.
    Intraspecific trauma is also a known source of walrus injury and 
mortality. Disturbance events can cause walrus to stampede into the 
water and have been known to result in injuries and mortalities. The 
risk of stampede-related injuries increases with the number of animals 
hauled out. Calves and young animals at the perimeter of these herds 
are particularly vulnerable to trampling injuries.
    Most (64 percent or 303 km) of the proposed Chukchi Sea seismic 
work will take place in water less than 100 m deep. Of those 303 km, 
220 km will be surveyed in water greater then 60 m, where walrus prefer 
to forage (Chadwick and Hills 2005). During a survey through open water 
in the northern Chukchi Sea in early August of 2005, only three walrus 
were sighted south of 72.8[deg] N in water 47 to 69 m deep (Haley and 
Ireland 2006).
    The probability of encountering Pacific walrus along the proposed 
survey line in the Chukchi Sea will depend on the location of the 
southern margin of the pack ice and the timing of spring break-up. If 
the Healy crosses the margin when the ice margin is close to depths 
where walrus prefer to feed, it is likely that walrus will be 
encountered.

Polar Bear

    Polar bears have a circumpolar distribution throughout the northern 
hemisphere (Amstrup et al. 1986) and occur in relatively low densities 
throughout most ice-covered areas (DeMaster and Stirling 1981). Polar 
bears are divided into six major populations and many sub-populations 
based on mark-and-recapture studies (Lentfer 1983), radio telemetry 
studies (Amstrup and Gardner 1994), and morpho-metrics (Manning 1971; 
Wilson 1976). Polar bears are common in the Chukchi and Beaufort Seas 
north of Alaska throughout the year, including the late summer period 
(Harwood et al. 2005). They also occur throughout the East Siberian, 
Laptev, and Kara Seas of Russia and the Barent's Sea of northern 
Europe. They are found in the northern part of the Greenland Sea, and 
are common in Baffin Bay, which separates Canada and Greenland, as well 
as through most of the Canadian Arctic Archipelago.
    In Alaska, they have been observed as far south in the eastern 
Bering Sea as St. Matthew Island and the Pribilof Islands, but they are 
most commonly found within 180 miles of the Alaskan coast of the 
Chukchi and Beaufort Seas, from the Bering Strait to the Canadian 
border. Two stocks occur in Alaska: (1) The Chukchi/Bering Seas stock; 
and (2) the Southern Beaufort Sea stock. The Chukchi/Bering Seas stock 
is defined as polar bears inhabiting the area as far west as the 
eastern portion of the Eastern Siberian Sea, as far east as Point 
Barrow, and extending into the Bering Sea, with its southern boundary 
determined by the extent of annual ice.
    The world population estimate of polar bears ranges from 20,000-
25,000 individuals (ICUN, in prep). Amstrup (1995) estimated the 
minimum population of polar bears for the Beaufort Sea to be 
approximately 1,500 to 1,800 individuals, with an average density of 
about one bear per 38.6 to 77.2 square miles (100 to 200 km\2\). 
Previous population estimates have put the Chukchi/Bering Seas 
population at 2,000 to 5,000; however, there are no reliable data on 
the population status of polar bears in the Bering/Chukchi Seas. An 
estimate was derived by subtracting the total estimated Alaska polar 
bear population from the Beaufort Sea population, thus yielding an 
estimate of 1,200-3,200 animals (Amstrup 1995).
    The Alaskan polar bear population is considered to be stable or 
increasing slightly (USFWS 2000b, c). Polar bear populations located in 
the Southern Beaufort Sea have been estimated to have an annual growth 
rate of 2.2 to 2.4 percent with an annual harvest of only 1.9 percent 
(Amstrup 1995). The Southern Beaufort Sea population ranges from the 
Baillie Islands, Canada, in the east to Point Hope, Alaska, in the 
west. The Chukchi/Bering Seas population ranges from Point Barrow, 
Alaska, in the east to the Eastern Siberian Sea in the west. These two 
populations overlap between Point Hope and Point Barrow, Alaska, 
centered near Point Lay (Amstrup 1995). Both of these populations have 
been extensively studied by tracking the movement of tagged females 
(Garner et al. 1990). Radio-tracking studies indicate significant 
movement within

[[Page 35934]]

populations and occasional movement between populations (Garner et al. 
1990; Amstrup 1995).
    Although insufficient data exist to accurately quantify polar bear 
denning along the Alaskan Chukchi Sea coast, dens in the area are less 
concentrated than for other areas in the Arctic. The majority of 
denning of Chukchi Sea polar bears occurs on Wrangel Island, Herald 
Island, and certain locations on the northern Chukotka coast. Females 
without dependent cubs breed in the spring, and pregnant females enter 
maternity dens by late November; the young are usually born in late 
December or early January. Female bears can be quite sensitive to 
disturbances during this denning period.
    Greater than 90 percent of a polar bear's diet is ringed (Phoca 
hispida) and bearded (Erignathus barbatus) seals; walrus calves are 
hunted occasionally. Polar bears hunt in areas where there are high 
concentrations of ringed and bearded seals (Larsen 1985; Stirling and 
McEwan 1975). This includes areas of land-fast ice, as well as moving 
pack ice. They hunt along leads and other areas of open water, or by 
waiting at a breathing hole, or by breaking through the roof of a 
seal's lair. Lairs are excavated in snow drifts on top of the ice. 
Bears also stalk seals in the spring when they haul out on the ice in 
warm weather. The relationship between ice type and bear distribution 
is as yet unknown, but it is suspected to be related to seal 
availability. Polar bears are opportunistic feeders and feed on a 
variety of foods and carcasses, including other marine mammals, 
reindeer, arctic cod, and geese and their eggs (Smith 1985; Jefferson 
et al. 1993; Smith and Hill 1996; Derocher et al. 2000). Polar bears 
are also known to eat nonfood items including styrofoam, plastic, 
antifreeze, and hydraulic and lubricating fluids.
    The most significant source of mortality is man. Before the MMPA 
was passed, polar bears were taken by sport hunters and residents. 
Between 1925 and 1972, the mean reported kill was 186 bears per year. 
Since 1972, only Alaska Natives have been allowed to hunt polar bears 
for their subsistence uses or for handicraft and clothing items for 
sale. From 1980 to 2005, the total annual harvest for Alaska averaged 
101 bears: 64 percent from the Chukchi Sea and 36 percent from the 
Beaufort Sea.
    MMS bowhead whale aerial surveys since 1979 have documented an 
increase, starting in 1992, in the proportion of polar bears associated 
with land vs. sea-ice in the fall season (Monnett et al. 2005). In 
2004, a large number of bears were observed swimming more than 2 km 
offshore, and a number of polar bear carcasses were subsequently 
observed offshore. Monnett et al. (2005) suggest that, as the pack ice 
edge moves northward, drowning deaths of polar bears may increase. The 
number of polar bears encountered in open water may, therefore, be 
slightly higher than previously reported.
    Polar bears typically range as far north as 88[deg] N (Ray 1971; 
Durner and Amstrup 1995); at about 88[deg] N their population thins 
dramatically. However, polar bears have been observed across the 
Arctic, including close to the North Pole (van Meurs and Splettstoesser 
2003). Stirling (1990) reported that, of 181 sightings of bears, only 3 
were above 82[deg] N. Three polar bears were observed from the Healy in 
the northern Chukchi Sea during a survey through this area in August of 
2005 (Haley and Ireland 2006). These three sightings occurred along 
2,401 km of observed trackline over 14 days between 70[deg] N and 
81[deg] N.
    Historically, polar bears have preferred the pack ice over coastal 
areas during the summer (Stirling 1988; Amstrup 1995). However, since 
the late 1980s, polar bears have been observed in greater numbers near 
coastal areas during late summer and fall in the central Beaufort Sea 
(Schliebe et al. 2004). This recent observation of bear behavior may be 
related to the 30-year moratorium on polar bear hunting and the recent 
success of subsistence whale harvests, the scraps of which appear to 
have become a reliable, annual food source for polar bears (Schliebe et 
al. 2004). The Healy is likely to encounter polar bears when it enters 
the pack ice, and small numbers of bears could be encountered anywhere 
along the entire trackline, as well as in the course of coring 
activities.

Potential Impacts of Activities on Pacific Walrus and Polar Bear

Potential Effects of Airguns

    The effects of sounds from airguns might include one or more of the 
following: noise, behavioral disturbance, and, at least in theory, 
temporary or permanent hearing impairment, or non-auditory physical 
effects (Richardson et al. 1995). Because the airgun sources planned 
for use during the present project involve only 4 or 8 airguns, the 
effects are anticipated to be less than would be the case with a large 
array of airguns. It is very unlikely that there would be any cases of 
temporary or especially permanent hearing impairment, or non-auditory 
physical effects. Also, behavioral disturbance is expected to be 
limited to relatively short distances.

Species Perception of Sound and Masking Effects

    The underwater hearing of a walrus has been measured at frequencies 
from 13 Hz to 1,200 Hz. The range of best hearing was from 1 to 12 kHz, 
with maximum sensitivity (67 dB re 1 [mu]Pa) occurring at 12 kHz 
(Kastelein et al. 2002). Most of the energy in the sound pulses emitted 
by airgun arrays is at low frequencies, with the strongest spectrum 
levels below 200 Hz and considerably lower spectrum levels above 1,000 
Hz. These low frequencies are not generally used by Pacific walrus. 
Masking effects of pulsed sound (even from large arrays of airguns) on 
Pacific walrus calls and other natural sounds are expected to be 
limited, and given the intermittent nature of these seismic pulses, 
masking effects are expected to be negligible. Any sound levels 
received by polar bears in the water would be attenuated because polar 
bears generally swim with their heads out of the water or at the 
surface and polar bears do not dive much below 4.5 m. Received levels 
of airgun sounds are reduced near the surface because of the pressure 
release effect at the water's surface (Greene and Richardson 1988; 
Richardson et al. 1995). Walrus and polar bears on the ice would be 
unaffected by underwater sound.

Disturbance Reactions

    Disturbance includes a variety of effects, including subtle changes 
in behavior, more conspicuous changes in activities, and displacement. 
Reactions to sound depend on species, state of maturity, experience, 
current activity, reproductive state, time of day, and many other 
factors. If a marine mammal does react briefly to a disturbance by 
changing its behavior or moving a small distance, the impacts of the 
change are unlikely to be significant to the individual, let alone the 
stock or the species as a whole. Alternatively, if a sound source 
displaces marine mammals from an important area for a prolonged period, 
impacts on the animals are most likely significant.
    Numerous studies have shown that pulsed sounds from airguns are 
often readily detectable in the water at distances of many kilometers; 
however, numerous studies have shown 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

[[Page 35935]]

hearing sensitivity of that mammal group.
    Seismic operations are expected to create significantly more noise 
than general vessel and icebreaker traffic; however, data specific to 
the potential response of walrus to seismic operations is limited. 
Therefore, we rely on observations of walrus and other pinniped 
reactions to similar activities and apply these conservatively to 
determine expected reactions. Potential effects of prolonged or 
repeated disturbances to Pacific walrus include displacement from 
preferred feeding areas, increased stress levels, increased energy 
expenditure, masking of communication, and impairment of 
thermoregulation of neonates that spend too much time in the water. 
There are some uncertainties in predicting the quantity and types of 
impacts of noise on marine mammals; however, appropriate mitigation 
measures minimize the potential for displacement.
    The response of walrus to sound sources may be either avoidance or 
tolerance. It is possible that noises produced by the icebreaking or 
seismic activities may cause avoidance behavior in walrus. Walrus on 
ice have been observed to become alert and dive into the water when 
icebreakers passed over 2 km (1.2 mi) away (Fay et al. 1984; Brueggeman 
et al. 1990, 1991, 1992). In addition, Brueggeman et al. (1990) suggest 
that walrus on ice floes may avoid icebreakers by 10 to 15 km (6.2 to 
9.3 mi). Anecdotal observations by walrus hunters and researchers 
suggest that males tend to be more tolerant of disturbances than 
females and individuals tend to be more tolerant than groups. Females 
with dependent calves are considered least tolerant of disturbances.
    Pacific walrus are not likely to show a strong avoidance reaction 
to the medium-sized airgun sources that will be used. Studies in the 
Beaufort Sea based on visual monitoring from seismic vessels has shown 
only slight (if any) avoidance of airguns by pinnipeds in general, and 
only slight (if any) changes in behavior. These studies have shown that 
pinnipeds frequently do not avoid the area within a few hundred meters 
of operating airgun arrays (e.g., Miller et al. 2005, Harris et al. 
2001). However, visual studies have their limitations, and initial 
telemetry work suggests that avoidance and other behavioral reactions 
to small airgun sources may at times be stronger than evident to date 
from visual studies of pinniped reactions to airguns (Thompson et al. 
1998). Even if reactions of the species occurring in the present study 
area are as strong as those evident in the telemetry study, reactions 
are expected to be confined to relatively small distances and 
durations, with no long-term effects on pinniped individuals or 
populations.
    Quantitative research on the sensitivity of walrus to noise has 
been limited because no audiograms (a test to determine the range of 
frequencies and minimum hearing threshold) have been done on walrus. 
Hearing range is assumed to be within the 13 Hz and 1,200 Hz range of 
their own vocalizations, with maximum hearing sensitivity in the 1 to 
12 kHz range (Kastelein et al. 2002). Walrus hunters and researchers 
have also noted that walrus tend to react to the presence of humans and 
machines at greater distances from upwind approaches than from downwind 
approaches, suggesting that odor may also be a stimulus for a flight 
response. The visual acuity of walrus is thought to be less than for 
other species of pinnipeds. The reaction of walrus to vessels is highly 
dependent on distance, vessel speed, and possibly vessel smell 
(Richardson et al. 1995; Fay et al. 1984), as well as previous exposure 
to hunting (D.G. Roseneau In Malme et al. 1989). Walrus in the water 
appear to be less readily disturbed by vessels than walrus hauled out 
on land or ice (Fay et al. 1984).
    Seismic activities may affect polar bears in a number of ways. 
Seismic ships and icebreakers may be physical obstructions to polar 
bear movements, although these impacts are of short-term and localized 
effect. Noise, sights, and smells produced by exploration activities 
may repel or attract bears, either disrupting their natural behavior or 
endangering them by threatening the safety of seismic personnel.
    In the Chukchi Sea, during the open-water season, polar bears spend 
the majority of their time on pack ice, which limits the chance of 
impacts from seismic activities. Occasionally, polar bears can be found 
in open water, miles from the ice edge or ice floes.
    Vessel traffic could result in short-term behavioral disturbance to 
polar bears. During the open-water season, most polar bears remain 
offshore in the pack ice and are not typically present in the area of 
vessel traffic. If a ship is surrounded by ice, it is more likely that 
curious bears will approach. Any on-ice activities create the 
opportunity for bear-human interactions. In relatively ice-free waters, 
polar bears are less likely to approach ships, although bears may be 
encountered on ice floes.
    Ships and icebreakers may act as physical obstructions in the 
spring if they transit through a restricted lead system, such as the 
Chukchi Polynya. Polynyas are important habitat for marine mammals, 
which makes them important hunting areas for polar bears. Ship traffic 
in these ice conditions may intercept or alter movements of bears. A 
similar situation could occur in the fall when the pack ice begins to 
expand.
    Little research has been conducted on the effects of noise on polar 
bears. Polar bears are curious and tend to investigate novel sights, 
smells, and possibly noises. Noise produced by seismic activities could 
elicit several different responses in polar bears. It may act as a 
deterrent to bears entering an area of operation, or potentially 
attract curious bears. Underwater noises are probably not a relevant 
form of disturbance because bears spend most of their time on the ice 
or at the surface of the water.

Hearing Impairment and Other Physical Effects

    Temporary or permanent hearing impairment is a possibility when 
marine mammals are exposed to very strong sounds, but there has been no 
specific documentation of this for marine mammals exposed to sequences 
of airgun pulses. Currently, the Service does not have specific 
guidelines regarding ``allowable'' received sound levels for either 
walrus or polar bears; however, we have adopted the NMFS criterion for 
Pacific walrus that pinnipeds should not be exposed to impulsive sounds 
greater or equal to 190 dB re 1 [mu]Pa (rms) (NMFS 2000). As a 
conservative measure, this criterion is also applied to polar bear. 
This criterion defines the safety (shut-down) radii planned for the 
proposed seismic survey.
    Several aspects of the planned monitoring and mitigation measures 
for this project are designed to detect animals occurring near the 
airguns (and multi-beam bathymetric sonar), and to avoid exposing them 
to sound pulses that might cause hearing impairment. Marine mammal 
observers will be on watch during seismic operations. In addition, 
walrus and polar bears are likely to show some avoidance of the area 
with high received levels of airgun sound. In those cases, the 
avoidance responses of the animals themselves will reduce or (most 
likely) avoid any possibility of hearing impairment.
    Temporary Threshold Shift (TTS): TTS is the mildest form of hearing 
impairment that can occur during exposure to a strong sound (Kryter 
1985). While experiencing TTS, the hearing threshold rises and a sound 
must be stronger in order to be heard. TTS can last from minutes or 
hours to (in cases of strong TTS) days. For sound

[[Page 35936]]

exposures at or somewhat above the TTS threshold, hearing sensitivity 
recovers rapidly after exposure to the noise ends. Few data on sound 
levels and durations necessary to elicit mild TTS have been obtained 
for marine mammals, and none of the published data concern TTS elicited 
by exposure to multiple pulses of sound. In Pacific walrus, TTS 
thresholds associated with exposure to brief pulses (single or 
multiple) of underwater sound have not been measured.
    A marine mammal within a radius of 100 m around a typical large 
array of operating airguns might be exposed to a few seismic pulses 
with levels of 205 dB, and possibly more pulses if the mammal moved 
with the seismic vessel. However, based on the implementation of the 
mitigation measures required by this proposed authorization, several of 
the considerations that are relevant in assessing the impact of typical 
seismic surveys with arrays of airguns are not directly applicable 
here. These considerations include the effects on polar bear and walrus 
of:
    Ramping up (soft start), which 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, 
which will be employed when the airgun array is operated, requires that 
the safety radius be visible for 30 minutes prior to the start of 
operations and that no walrus or polar bear has been sighted within or 
near the safety radius during the final 15 minutes, thereby avoiding 
exposure of walrus and polar bears to potential effects of ramping up.
    Longer term exposure to airgun pulses at a sufficiently high level 
for a sufficiently long period to cause more than mild TTS. Because the 
mitigation measures require that the operation of airguns either shut-
down or power-down (which procedure is followed depends on the 
circumstances as described in the section on Mitigation) if a walrus or 
polar bear approaches or nears the safety radius, long term exposure to 
airgun pulses at high levels will be avoided.
    The predicted 190 dB distances for the airguns operated by UTIG 
vary with water depth. They are estimated to be 230 m in deep water for 
the 8-airgun system, and 75 m in deep water for the 4-GI gun system. In 
intermediate depths, this distance is predicted to increase to 113 m 
for the 4-GI gun system. The 8-airgun array will only be used in deep 
water (greater than 1,000 m). The predicted 190 dB distance for the 4-
GI gun system in shallow water is 938 m (Table 1). Shallow water (less 
than 100 m) will occur along 303 km (64 percent) of the planned 
trackline in the Chukchi Sea. Those sound levels are not considered to 
be the levels above which TTS might occur.
    Permanent Threshold Shift (PTS): When PTS occurs, there is physical 
damage to the sound receptors in the ear. In some cases, there can be 
total or partial deafness; in other cases, the animal has an impaired 
ability to hear sounds in specific frequency ranges.
    There is no specific evidence that exposure to pulses of airgun 
sound can cause PTS in any marine mammal, even with large arrays of 
airguns. However, given the possibility that mammals close to an airgun 
array might incur TTS, there has been further speculation about the 
possibility that some individuals occurring very close to airguns might 
incur PTS. Single or occasional occurrences of mild TTS are not 
indicative of permanent auditory damage in terrestrial mammals. 
Relationships between TTS and PTS thresholds have not been studied in 
marine mammals, but are assumed to be similar to those in humans and 
other terrestrial mammals. PTS might occur at a received sound level at 
least several decibels above that inducing mild TTS if the animal were 
exposed to the strong sound pulses with very rapid rise time.
    It is unlikely that walrus or polar bears could receive sounds 
strong enough (and over a sufficient duration) to cause permanent 
hearing impairment during a project employing the medium-sized airgun 
sources planned here. In the proposed project, walrus or bears are 
unlikely to be exposed to received levels of seismic pulses strong 
enough to cause TTS, as they would probably need to be within 100 to 
200 m of the airguns for that to occur. Given the higher level of sound 
necessary to cause PTS, it is even less likely that PTS could occur. In 
fact, even the levels immediately adjacent to the airgun may not be 
sufficient to induce PTS, especially because an animal would not be 
exposed to more than one strong pulse unless it swam immediately 
alongside the airgun for a period longer than the inter-pulse interval. 
The planned monitoring and mitigation measures, including visual 
monitoring, power-downs, and shut-downs of the airguns when walrus and 
bears are seen within the safety radii, will minimize the already 
minimal probability of exposure of animals to sounds strong enough to 
induce PTS.
    Non-auditory Physiological Effects: Non-auditory physiological 
effects or injuries that theoretically might occur in Pacific walrus or 
polar bears exposed to strong underwater sound include stress, 
neurological effects, and other types of organ or tissue damage. 
However, studies examining such effects are very limited. If any such 
effects do occur, they probably would be limited to unusual situations 
when animals might be exposed at close range for unusually long 
periods. It is doubtful that any single walrus or bear would be exposed 
to strong seismic sounds long enough for significant physiological 
stress to develop. That is especially so in the case of the proposed 
project where the airgun configuration is moderately sized, the ship is 
moving at 3 to 4 knots (5.5 to 7.4 km/hr), and for the most part, the 
tracklines will not double back through the same area.
    In general, little is known about the potential for seismic survey 
sounds to cause auditory impairment or other physical effects in 
Pacific walrus or polar bears. Available data suggest that such 
effects, if they occur at all, would b