Takes of Marine Mammals Incidental to Specified Activities; Low-Energy Marine Geophysical Survey in the Western Tropical Pacific Ocean, November to December, 2011, 45518-45540 [2011-19244]

Agencies

• DEPARTMENT OF COMMERCE
• National Oceanic and Atmospheric Administration

[Federal Register Volume 76, Number 146 (Friday, July 29, 2011)]
[Notices]
[Pages 45518-45540]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 2011-19244]


-----------------------------------------------------------------------

DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

RIN 0648-XA507


Takes of Marine Mammals Incidental to Specified Activities; Low-
Energy Marine Geophysical Survey in the Western Tropical Pacific Ocean, 
November to December, 2011

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

ACTION: Notice; proposed Incidental Harassment Authorization; request 
for comments.

-----------------------------------------------------------------------

SUMMARY: NMFS has received an application from the Scripps Institution 
of Oceanography (SIO) for an Incidental Harassment Authorization (IHA) 
to take marine mammals, by harassment, incidental to conducting a low-
energy marine geophysical (i.e., seismic) survey in the western 
tropical Pacific Ocean, November to December, 2011. Pursuant to the 
Marine Mammal Protection Act (MMPA), NMFS is requesting comments on its 
proposal to issue an IHA to SIO to incidentally harass, by Level B 
harassment only, 19 species of marine mammals during the specified 
activity.

DATES: Comments and information must be received no later than August 
29, 2011.

ADDRESSES: Comments on the application should be addressed to P. 
Michael Payne, Chief, Permits, Conservation and Education Division, 
Office of Protected Resources, National Marine Fisheries Service, 1315 
East-West Highway, Silver Spring, MD 20910. The mailbox address for 
providing e-mail comments is ITP.Goldstein@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.
    All comments received are a part of the public record and will 
generally be posted to https://www.nmfs.noaa.gov/pr/permits/incidental.htm#applications without change. All Personal Identifying 
Information (for example, name, address, etc.) voluntarily submitted by 
the commenter may be publicly accessible. Do not submit confidential 
business information or otherwise sensitive or protected information.
    A copy of the application containing a list of the references used 
in this document may be obtained by writing to the above address, 
telephoning the contact listed here (see FOR FURTHER INFORMATION 
CONTACT) or visiting the Internet at: https://www.nmfs.noaa.gov/pr/permits/incidental.htm#applications.
    The National Science Foundation (NSF) has prepared a draft 
``Environmental Assessment of a Marine Geophysical Survey by the R/V 
Thompson in the western tropical Pacific Ocean November-December 2011 
(EA).'' The draft EA incorporates an ``Environmental Assessment of a 
Low-Energy Marine Geophysical Survey by the R/V Thompson in the Western 
Tropical Pacific Ocean, November-December 2011,'' prepared by LGL Ltd., 
Environmental Research Associates (LGL), on behalf of NSF and SIO, 
which is also available at the same Internet address. Documents cited 
in this notice may be viewed, by appointment, during regular business 
hours, at the aforementioned address.

FOR FURTHER INFORMATION CONTACT: Howard Goldstein or Jolie Harrison, 
Office of Protected Resources, NMFS, 301-427-8401.

SUPPLEMENTARY INFORMATION:

Background

    Section 101(a)(5)(D) of the MMPA (16 U.S.C. 1371 (a)(5)(D)) directs 
the Secretary of Commerce (Secretary) to authorize, upon request, the 
incidental, but not intentional, taking of small numbers of marine 
mammals of a species or population stock, by United States citizens who 
engage in a specified activity (other than commercial fishing) within a 
specified geographical region if certain findings are made and, if the 
taking is limited to harassment, a notice of a proposed authorization 
is provided to the public for review.
    Authorization for the incidental taking of small numbers of marine 
mammals shall be granted if NMFS 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 (where relevant). The authorization must 
set forth the permissible methods of taking, other means of effecting 
the least practicable adverse impact on the species or stock and its 
habitat, and requirements pertaining to the mitigation, monitoring and 
reporting of such takings. 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. 
Section 101(a)(5)(D) of the MMPA 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 small numbers of marine mammals. Within 45 days of the 
close of the public comment period, NMFS must either issue or deny the 
authorization.

[[Page 45519]]

    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].

Summary of Request

    NMFS received an application on June 14, 2011, from SIO for the 
taking by harassment, of marine mammals, incidental to conducting a 
low-energy marine seismic survey in the western tropical Pacific Ocean. 
SIO, a part of the University of California, in collaboration with 
University of Washington (UW), Woods Hole Oceanographic Institution 
(WHOI), Texas A&M University (TAMU), and Kutztown University, plans to 
conduct a magnetic and seismic study of the Hawaiian Jurassic crust 
onboard an oceanographic research vessel in the western tropical 
Pacific Ocean north of the Marshall Islands for approximately 32 days. 
The survey will use a pair of Generator Injector (GI) airguns each with 
a discharge volume of 105 cubic inches (in\3\). SIO plans to conduct 
the proposed survey from approximately November 5 to December 17, 2011. 
The proposed seismic survey will be conducted partly in international 
waters and partly in the Exclusive Economic Zone (EEZ) of Wake Island 
(U.S.), and possibly in the EEZ of the Republic of the Marshall 
Islands.
    SIO plans to use one source vessel, the R/V Thomas G. Thompson 
(Thompson) and a seismic airgun array to collect seismic reflection and 
refraction profiles from the Hawaiian Jurassic crust in the western 
tropical Pacific Ocean. In addition to the proposed operations of the 
seismic airgun array, SIO intends to operate a multibeam echosounder 
(MBES) and a sub-bottom profiler (SBP) continuously throughout the 
survey.
    Acoustic stimuli (i.e., increased underwater sound) generated 
during the operation of the seismic airgun array may have the potential 
to cause a short-term behavioral disturbance for marine mammals in the 
survey area. This is the principal means of marine mammal taking 
associated with these activities and SIO has requested an authorization 
to take 19 species of marine mammals by Level B harassment. Take is not 
expected to result from the use of the MBES or SBP, for reasons 
discussed in this notice; nor is take expected to result from collision 
with the vessel because it is a single vessel moving at a relatively 
slow speed during seismic acquisition within the survey, for a 
relatively short period of time (approximately 39 days). It is likely 
that any marine mammal would be able to avoid the vessel.

Description of the Proposed Specified Activity

    SIO's proposed seismic survey in the western tropical Pacific 
Ocean, as part of an integrated magnetic and seismic study of the 
Hawaiian Jurassic crust, will take place for approximately 32 days in 
November to December, 2011 (see Figure 1 of the IHA application). The 
proposed seismic survey will take place in water depths ranging from 
approximately 2,000 to 6,000 meters (m) (6,561.7 to 19,685 feet [ft]) 
and consist of approximately 1,600 kilometers (km) (863.9 nautical 
miles [nmi]) of transect lines in the study area. The survey will take 
place in the area 13[deg] to 23[deg] North, 158[deg] to 172[deg] East, 
just north of the Marshall Islands. The project is scheduled to occur 
from approximately November 5 to December 17, 2011. Some minor 
deviation from these dates is possible, depending on logistics and 
weather.
    The goal of the proposed research is to define the global nature 
and significance of variations in intensity and direction of the 
Earth's magnetic field during the Jurassic time period (approximately 
145 to 180 million years ago), which appears to have been a period of 
sustained low intensity and rapid directional changes or polarity 
reversals compared to other periods in Earth's magnetic field history. 
Access to Jurassic-aged crust with good magnetic signals is very 
limited, with the best continuous records in ocean crust, but only one 
area of the ocean floor has been measured to date: the western Pacific 
Japanese magnetic lineations. To properly assess the global 
significance of the variations and to eliminate local crustal and 
tectonic complications, it is necessary to measure Jurassic magnetic 
signals in a different area of the world. The proposed study will 
attempt to verify the unusual behavior of the Jurassic geomagnetic 
field and test whether it was behaving in a globally coherent way by 
conducting a near-bottom marine magnetic field survey of Pacific 
Hawaiian Jurassic crust located between Hawaii and Guam.
    Widespread, younger, Cretaceous-aged (65 to 140 million years ago) 
volcanism overprinted much of the western Pacific, so it is important 
to know the extent of Cretaceous-aged volcanic crust. This will be 
assessed by carrying out a seismic reflection and refraction survey of 
the Hawaiian Jurassic crust. First, the autonomous underwater vehicle 
(AUV) Sentry and a simultaneously deployed deep-towed magnetometer 
system will acquire two parallel profiles of the near-bottom crustal 
magnetic field 10 km (5.4 nmi) apart and approximately 800 km (432 nmi) 
long. More information on the AUV Sentry is available at https://www.whoi.edu/page.do?pid=38098. Second, the seismic survey will be 
conducted using airguns, a hydrophone streamer, and sonobuoys directly 
over the same profile as the AUV magnetic survey.
    The survey will involve one source vessel, the Thompson. For the 
seismic component of the research program, the Thompson will deploy an 
array of two low-energy Sercel Generator Injector (GI) airguns as an 
energy source (each with a discharge volume of 105 in\3\) at a tow 
depth of 3 m (9.8 ft). The acoustic receiving system will consist of an 
800 m (2,624.7 ft), 48 channel hydrophone streamer and directional, 
passive sonobuoys. Over the course of the seismic operations, 50 Ultra 
Electronics AN/SSQ-53D(3) directional, passive sonobuoys will be 
deployed from the vessel. The sonobuoys consist of a hydrophone, 
electronics, and a radio transmitter. As the airgun is towed along the 
survey lines, the hydrophone streamer and sonobuoys will receive the 
returning acoustic signals and transfer the data to the on-board 
processing system. The seismic signal is measured by the sonobuoy's 
hydrophone and transmitted by radio back to the source vessel. The 
sonobuoys are expendable, and after a pre-determined time (usually 
eight hours), they self-scuttle and sink to the ocean bottom.
    The survey lines will be within the area enclosed by red lines in 
Figure 1 of the IHA application, but the exact locations of the survey 
lines will be determined during transit after observing the location of 
the appropriate magnetic lineation by surface-towed magnetometer. 
Magnetic and seismic data acquisition will alternate on a daily basis; 
seismic surveys will take place while the AUV used to collect magnetic 
data is on deck to recharge its batteries. In addition to the 
operations of the airgun array, a Kongsberg EM300 MBES and ODEC Bathy-
2000 SBP will also be operated from the Thompson continuously 
throughout the cruise. There will be additional seismic operations 
associated with equipment testing, start-up, and possible line changes 
or repeat coverage of any areas where initial data quality is sub-
standard. In SIO's calculations, 25% has

[[Page 45520]]

been added for those contingency operations.
    All planned geophysical data acquisition activities will be 
conducted by technicians provided by SIO, with on-board assistance by 
the scientists who have proposed the study. The Principal Investigators 
are Drs. Masako Tominaga, Maurice A. Tivey, Daniel Lizarralde of WHOI, 
William W. Sager of TAMU, and Adrienne Oakley of Kutztown University. 
The vessel will be self-contained, and the crew will live aboard the 
vessel for the entire cruise.

Vessel Specifications

    The Thompson is operated by the University of Washington under a 
charter agreement with the U.S. Office of Naval Research. The title of 
the vessel is held by the U.S. Navy. The Thompson will tow the two GI 
airgun array, as well as the hydrophone streamer, along predetermined 
lines.
    The vessel has a length of 83.5 m (274 ft); a beam of 16 m (52.5 
ft), and a full load draft of 5.8 m (19 ft). It is equipped with twin 
360[deg] azimuth stern thrusters each powered by a 3,000 horsepower 
(hp) DC motor and a water-jet bow thruster powered by a 1,600 hp DC 
motor. The motors are driven by up to three 1,500 kiloWatt (kW) and 
three 715 kW generators; normal operations use two 1,500 kW and one 750 
kW generator, but this changes with ship speed, sea state, and other 
variables. An operations speed of 7.4 km/hour (hr) (4 knots [kt]) will 
be used during seismic acquisition. When not towing seismic survey 
gear, the Thompson cruises at 22 km/hr (12 kt) and has a maximum speed 
of 26.9 km/hr (14.5 kt). The Thompson has a range of 24,400 km (13,175 
nmi) (the distance the vessel can travel without refueling).
    The vessel will also serve as a platform for which vessel-based 
Protected Species Observers (PSOs) will watch for marine mammals before 
and during the proposed airgun operations.

Acoustic Source Specifications

Seismic Airguns

    The Thompson will deploy and tow an array consisting of a pair of 
45 to 105 in\3\ Sercel GI airgun and a streamer containing hydrophones 
along predetermined lines. Seismic pulses will be emitted at intervals 
of five or ten seconds (s). At speeds of approximately 7.4 km/hr, the 
five to ten s spacing corresponds to shot intervals of approximately 10 
to 20 m (32.8 to 65.6 ft).
    The generator chamber of each GI airgun, the one responsible for 
introducing the sound pulse into the ocean, is either 45 in\3\ or 105 
in\3\, depending on how it is configured. The injector chamber injects 
air into the previously-generated bubble to maintain its shape, and 
does not introduce more sound into the water. The two GI airguns will 
be towed 8 m (26.2 ft) apart side-by-side, 21 m (68.9 ft) behind the 
Thompson, at a depth of 3 m (9.8 ft). Depending on the configuration, 
the total effective volume will be 90 in\3\ or 210 in\3\. As a 
precautionary measure, SIO assumes that the larger volume will be used.
    As the GI airguns are towed along the survey lines, the towed 
hydrophone array in the streamer and the sonobuoys receive the 
reflected signals and transfer the data to the on-board processing 
system. Given the relatively short streamer length behind the vessel, 
the turning rate of the vessel while the gear is deployed is much 
higher than the limit of five degrees per minute for a seismic vessel 
towing a streamer of more typical length (much greater than 1 km [0.5 
nmi]). Thus maneuverability of the vessel is not limited much during 
operations.

Metrics Used in This Document

    This section includes a brief explanation of the sound measurements 
frequently used in the discussions of acoustic effects in this 
document. Sound pressure is the sound force per unit area, and is 
usually measured in micropascals ([mu]Pa), where 1 pascal (Pa) is the 
pressure resulting from a force of one newton exerted over an area of 
one square meter. Sound pressure level (SPL) is expressed as the ratio 
of a measured sound pressure and a reference level. The commonly used 
reference pressure level in underwater acoustics is 1 [mu]Pa, and the 
units for SPLs are dB re: 1 [mu]Pa. SPL (in decibels [dB]) = 20 log 
(pressure/reference pressure).
    SPL is an instantaneous measurement and can be expressed as the 
peak, the peak-peak (p-p), or the root mean square (rms). Root mean 
square, which is the square root of the arithmetic average of the 
squared instantaneous pressure values, is typically used in discussions 
of the effects of sounds on vertebrates and all references to SPL in 
this document refer to the root mean square unless otherwise noted. SPL 
does not take the duration of a sound into account.

Characteristics of the Airgun Pulses

    Airguns function by venting high-pressure air into the water which 
creates an air bubble. The pressure signature of an individual airgun 
consists of a sharp rise and then fall in pressure, followed by several 
positive and negative pressure excursions caused by the oscillation of 
the resulting air bubble. The oscillation of the air bubble transmits 
sounds downward through the seafloor and the amount of sound 
transmitted in the near horizontal directions is reduced. However, the 
airgun array also emits sounds that travel horizontally toward non-
target areas.
    The nominal downward-directed source levels of the airgun arrays 
used by SIO on the Thompson do not represent actual sound levels that 
can be measured at any location in the water. Rather they represent the 
level that would be found 1 m (3.3 ft) from a hypothetical point source 
emitting the same total amount of sound as is emitted by the combined 
GI airguns. The actual received level at any location in the water near 
the GI airguns will not exceed the source level of the strongest 
individual source. In this case, that will be about 234.4 dB re 1 
[mu]Pam peak, or 239.8 dB re 1 [mu]Pam peak-to-peak. However, the 
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.
    Accordingly, Lamont-Doherty Earth Observatory of Columbia 
University (L-DEO) has predicted the received sound levels in relation 
to distance and direction from the two GI airgun array. A detailed 
description of L-DEO's modeling for marine seismic source arrays for 
species mitigation is provided in Appendix A of SIO's EA. These are the 
nominal source levels applicable to downward propagation. The effective 
source levels for horizontal propagation are lower than those for 
downward propagation when the source consists of numerous airguns 
spaced apart from one another.
    Appendix A of SIO's EA discusses the characteristics of the airgun 
pulses. NMFS refers the reviewers to the application and EA documents 
for additional information.

Predicted Sound Levels for the Airguns

    Received sound levels have been modeled by L-DEO for a number of 
airgun configurations, including two 105 in\3\ GI airguns, in relation 
to distance and direction from the airguns (see Figure 2 of the IHA 
application). The model does not allow for bottom interactions, and is 
most directly applicable to deep water. Based on the modeling, 
estimates of the maximum distances from the GI airguns where sound 
levels of 190, 180, and 160 dB re 1 [mu]Pa (rms) are predicted to be 
received

[[Page 45521]]

in deep water are shown in Table 1 (see Table 1 of the IHA 
application).
    Empirical data concerning the 190, 180, and 160 dB (rms) distances 
were acquired for various airgun arrays based on measurements during 
the acoustic verification studies conducted by L-DEO in the northern 
GOM in 2003 (Tolstoy et al., 2004) and 2007 to 2008 (Tolstoy et al., 
2009). Results of the 36 airgun array are not relevant for the two GI 
airguns to be used in the proposed survey. The empirical data for the 
6, 10, 12, and 20 airgun arrays indicate that, for deep water, the L-
DEO model tends to overestimate the received sound levels at a given 
distance (Tolstoy et al., 2004). Measurements were not made for the two 
GI airgun array in deep water, however, SIO proposes to use the EZ 
predicted by L-DEO's model for the proposed GI airgun operations in 
deep water, although they are likely conservative given the empirical 
proposed GI airgun operations in deep water. Using the L-DEO model, 
Table 1 (below) shows the distances at which three rms sound levels are 
expected to be received from the two GI airgun array. The 180 and 190 
dB re 1 [mu]Pa (rms) distances are the safety criteria for potential 
Level A harassment as specified by NMFS (2000) and are applicable to 
cetaceans and pinnipeds, respectively. If marine mammals are detected 
within or about to enter the appropriate EZ, the airguns will be shut-
down immediately.
    Table 1 summarizes the predicted distances at which sound levels 
(160, 180, and 190 dB [rms]) are expected to be received from the two 
GI airgun array operating in deep water depths.

  Table 1--Distances to Which Sound Levels >= 190, 180, and 160 dB re 1 [mu]Pa (rms) Could be Received in Deep
   Water During the Proposed Seismic Survey in the Western Tropical Pacific Ocean, November to December, 2011.
                             Distances Are Based on Model Results Provided by L-DEO.
----------------------------------------------------------------------------------------------------------------
                                                                                  Predicted RMS radii distances
                                             Tow                                               (m)
            Source and volume               depth         Water depth (m)       --------------------------------
                                             (m)                                   190 dB     180 dB     160 dB
----------------------------------------------------------------------------------------------------------------
Two GI airguns (105 in\3\)...............        3  Deep (> 1,000).............         20         70        670
----------------------------------------------------------------------------------------------------------------

MBES

    The Thompson will operate a Kongsberg EM 300 MBES concurrently 
during airgun operations to map characteristics of the ocean floor. The 
MBES has a hull-mounted transducer within a transducer pod that is 
located amidships. The system's normal operating frequency is 
approximately 30 kHz. The transmit fan-beam is split into either three 
or nine narrower beam sectors with independent active steering to 
correct for vessel yaw. Angular coverage is 36[deg] (in Extra Deep 
Mode, for use in water depths 3,000 to 6,000 m [9,842.5 to 19,685 ft]) 
or 150[deg] (in shallower water). The total angular coverage of 36[deg] 
to 150[deg] consists of the three or nine beams transmitted 
sequentially at each ping. Except in very deep water where the total 
beam is 36[deg] x 1[deg], the composite fan beam is 150[deg] x 1[deg], 
150[deg] x 2[deg] or 150[deg] x 4[deg] depending on water depth. The 
nine beams making up the composite fan will overlap slightly if the 
vessel yaw is less than the fore-aft width of the beam (1, 2, or 
4[deg], respectively). Achievable swath width on a flat bottom will 
normally be approximately five times the water depth. The maximum 
source level is 237 dB re 1 [mu]Pam (rms) (Hammerstad, 2005). In deep 
water (500 to 3,000 m [1,640.4 to 9,842.5 ft]), a pulse length of 5 
milliseconds (ms) is normally used, and the ping rate is mainly limited 
by the round trip travel time in the water.

SBP

    The Thompson will also operate an Ocean Data Equipment Corporation 
Bathy-2000 SBP continuously throughout the cruise simultaneously with 
the MBES to map and provide information about the sedimentary features 
and bottom topography. The SBP has a maximum 7 kilowatt (kW) transmit 
capacity into the underhull array. The energy from the SBP is directed 
downward from a 3 kHz transducer in the transducer array mounted in the 
hull of the vessel. Pulse duration ranges from 1.5 to 24 ms and the 
interval between pulses is controlled automatically by the system or 
manually by an operator depending on water depth and reflectivity of 
the bottom sediments. The system produces one sound pulse and then 
waits for its return before transmitting again. The swept (chirp) 
frequency ranges from 6 to 35 kHz. The maximum source output downward 
is 221 dB re 1 [mu]Pam (rms), but in practice, the system is rarely 
operated above 80% power level.
    NMFS expects that acoustic stimuli resulting from the proposed 
operation of the two GI airgun array has the potential to harass marine 
mammals, incidental to the conduct of the proposed seismic survey. NMFS 
expects these disturbances to be temporary and result, at worst, in a 
temporary modification in behavior and/or low-level physiological 
effects (Level B harassment) of small numbers of certain species of 
marine mammals. NMFS does not expect that the movement of the Thompson, 
during the conduct of the seismic survey, has the potential to harass 
marine mammals because of the relatively slow operation speed of the 
vessel (7.4 km/hr or 4 kt) during seismic acquisition.

Description of the Proposed Dates, Duration, and Specified Geographic 
Region

    The Thompson is expected to depart Honolulu, Hawaii, on November 5, 
2011 and spend approximately 7 days in transit to the proposed survey 
area, 32 days alternating between acquiring magnetic and seismic data, 
and approximately 3 days in transit, arriving at Apra Harbor, Guam, on 
December 17, 2011. Seismic operations will be conducted for a total of 
approximately 16 days. Some minor deviation from this schedule is 
possible, depending on logistics and weather. The survey will encompass 
the area approximately 13[deg] to 23[deg] North, approximately 158[deg] 
to 172[deg] East, just north of the Marshall Islands (see Figure 1 of 
the IHA application). Water depths in the survey area generally range 
from approximately 2,000 to 6,000 m (6,561.7 to 19,685 ft); Wake Island 
is included in the survey area. The seismic survey will be conducted 
partly in international waters and partly in the EEZ of Wake Island 
(U.S.), and possibly in the EEZ of the Republic of the Marshall 
Islands.

Description of the Marine Mammals in the Area of the Proposed Specified 
Activity

    Twenty-six marine mammal species (19 odontocetes, 6 mysticetes, and 
one pinniped) are known to or could occur in the Marshall Islands 
Marine Eco-region (MIME) study area. Several of

[[Page 45522]]

these species are listed as endangered under the U.S. Endangered 
Species Act of 1973 (ESA; 16 U.S.C. 1531 et seq.), including the 
humpback (Megaptera novaeangliae), sei (Balaenoptera borealis), fin 
(Balaenoptera physalus), blue (Balaenoptera musculus), and sperm 
(Physeter macrocephalus) whales, as well as the Hawaiian monk seal 
(Monachus schauinslandi). The North Pacific right whale (Eubalaena 
japonica), listed as endangered under the ESA, was historically 
distributed throughout the North Pacific Ocean north of 35[deg] North 
and occasionally occurred as far south as 20[deg] North. Whaling 
records indicate that the MIME was not part of its range (Townsend, 
1935).
    The dugong (Dugong dugon), also listed as endangered under the ESA, 
is distributed in shallow coastal waters throughout most of the Indo-
Pacific region between approximately 27[deg] North and South of the 
equator (Marsh, 2008). Its historical range extended to the Marshall 
Islands (Nair et al., 1975). However, the dugong is declining or 
extinct in at least one third of its range and no long occurs in the 
MIME (Marsh, 2008). The dugong is managed by the U.S. Fish and Wildlife 
Service (USFWS) and is not considered further in this analysis; all 
others are managed by NMFS.
    The marine mammals that occur in the proposed survey area belong to 
three taxonomic groups: odontocetes (toothed cetaceans, such as 
dolphins), mysticetes (baleen whales), and pinnipeds (seals, sea lions, 
and walrus). Cetaceans are the subject of the IHA application to NMFS.
    Table 2 (below) presents information on the abundance, 
distribution, population status, conservation status, and density of 
the marine mammals that may occur in the proposed survey area during 
November to December, 2011.
BILLING CODE 3510-22-P

[[Page 45523]]

[GRAPHIC] [TIFF OMITTED] TN29JY11.003


[[Page 45524]]


[GRAPHIC] [TIFF OMITTED] TN29JY11.004


[[Page 45525]]


[GRAPHIC] [TIFF OMITTED] TN29JY11.005

BILLING CODE 3510-22-C
    Refer to Section III and IV of SIO's application for detailed 
information regarding the abundance and distribution, population 
status, and life history and behavior of these species and their 
occurrence in the proposed project area. The application also presents 
how SIO calculated the estimated densities for the marine mammals in 
the proposed survey area. NMFS has reviewed these data and determined 
them to be the best available scientific information for the purposes 
of the proposed IHA.

Potential Effects on Marine Mammals

    Acoustic stimuli generated by the operation of the airguns, which 
introduce sound into the marine environment, may have the potential to 
cause Level B harassment of marine mammals in the proposed survey area. 
The effects of sounds from airgun operations might include one or more 
of the following: tolerance, masking of natural sounds, behavioral 
disturbance, temporary or permanent hearing impairment, or non-auditory 
physical or physiological effects (Richardson et al., 1995; Gordon et 
al., 2004; Nowacek et al., 2007; Southall et al., 2007).
    Permanent hearing impairment, in the unlikely event that it 
occurred, would constitute injury, but temporary threshold shift (TTS) 
is not an injury (Southall et al., 2007). Although the possibility 
cannot be entirely excluded, it is unlikely that the proposed project 
would result in any cases of temporary or permanent hearing impairment, 
or any significant non-auditory physical or physiological effects. 
Based on the available data and studies described here, some behavioral 
disturbance is expected, but NMFS expects the disturbance to be 
localized and short-term.

Tolerance to Sound

    Studies on marine mammals' tolerance to sound in the natural 
environment are relatively rare. Richardson et al. (1995) defines 
tolerance as the occurrence of marine mammals in areas where they are 
exposed to human activities or man-made noise. In many cases, tolerance 
develops by the animal habituating to the stimulus (i.e., the gradual 
waning of responses to a repeated or ongoing stimulus) (Richardson, et 
al., 1995; Thorpe, 1963), but because of ecological or physiological 
requirements, many marine animals may need to remain in areas where 
they are exposed to chronic stimuli (Richardson, et al., 1995).
    Numerous studies have shown that pulsed sounds from airguns are 
often readily detectable in the water at distances of many kilometers. 
Malme et al., (1985) studied the responses of humpback whales on their 
summer feeding grounds in southeast Alaska to seismic pulses from a 
airgun with a total volume of 100 in \3\. They noted that the whales 
did not exhibit persistent avoidance when exposed to the airgun and 
concluded that there was no clear evidence of avoidance, despite the 
possibility of subtle effects, at received levels up to 172 dB re 1 
[mu]Pa.
    Weir (2008) observed marine mammal responses to seismic pulses from 
a 24 airgun array firing a total volume of either 5,085 in \3\ or 3,147 
in \3\ in Angolan waters between August 2004 and May 2005. She recorded 
a total of 207 sightings of humpback whales (n = 66), sperm whales (n = 
124), and Atlantic spotted dolphins (n = 17) and reported that there 
were no significant differences in encounter rates (sightings/hr) for 
humpback and sperm whales according to the airgun array's operational 
status (i.e., active versus silent).

Masking of Natural Sounds

    The term masking refers to the inability of a subject to recognize 
the occurrence of an acoustic stimulus as a result of the interference 
of another acoustic stimulus (Clark et al., 2009). Introduced 
underwater sound may, through masking, reduce the effective 
communication distance of a marine mammal species if the frequency of 
the source is close to that used as a signal by the marine mammal, and 
if the anthropogenic sound is present for a significant fraction of the 
time (Richardson et al., 1995).
    Masking effects of pulsed sounds (even from large arrays of 
airguns) on marine mammal calls and other natural sounds are expected 
to be limited. Because of the intermittent nature and low duty cycle of 
seismic airgun pulses, animals can emit and receive sounds in

[[Page 45526]]

the relatively quiet intervals between pulses. However, in some 
situations, reverberation occurs for much or the entire interval 
between pulses (e.g., Simard et al., 2005; Clark and Gagnon, 2006) 
which could mask calls. Some baleen and toothed whales are known to 
continue calling in the presence of seismic pulses, and their calls can 
usually be heard between the seismic pulses (e.g., Richardson et al., 
1986; McDonald et al., 1995; Greene et al., 1999; Nieukirk et al., 
2004; Smultea et al., 2004; Holst et al., 2005a, b, 2006; and Dunn and 
Hernandez, 2009). However, Clark and Gagnon (2006) reported that fin 
whales in the northeast Pacific Ocean went silent for an extended 
period starting soon after the onset of a seismic survey in the area. 
Similarly, there has been one report that sperm whales ceased calling 
when exposed to pulses from a very distant seismic ship (Bowles et al., 
1994). However, more recent studies found that they continued calling 
in the presence of seismic pulses (Madsen et al., 2002; Tyack et al., 
2003; Smultea et al., 2004; Holst et al., 2006; and Jochens et al., 
2008). Dolphins and porpoises commonly are heard calling while airguns 
are operating (e.g., Gordon et al., 2004; Smultea et al., 2004; Holst 
et al., 2005a, b; and Potter et al., 2007). The sounds important to 
small odontocetes are predominantly at much higher frequencies than are 
the dominant components of airgun sounds, thus limiting the potential 
for masking.
    In general, NMFS expects the masking effects of seismic pulses to 
be minor, given the normally intermittent nature of seismic pulses. 
Refer to Appendix A(4) of SIO's EA for a more detailed discussion of 
masking effects on marine mammals.

Behavioral Disturbance

    Disturbance includes a variety of effects, including subtle to 
conspicuous changes in behavior, movement, and displacement. Reactions 
to sound, if any, depend on species, state of maturity, experience, 
current activity, reproductive state, time of day, and many other 
factors (Richardson et al., 1995; Wartzok et al., 2004; Southall et 
al., 2007; Weilgart, 2007). If a marine mammal does react briefly to an 
underwater sound 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 population. However, if a sound 
source displaces marine mammals from an important feeding or breeding 
area for a prolonged period, impacts on individuals and populations 
could be significant (e.g., Lusseau and Bejder, 2007; Weilgart, 2007). 
Given the many uncertainties in predicting the quantity and types of 
impacts of noise on marine mammals, it is common practice to estimate 
how many mammals would be present within a particular distance of 
industrial activities and/or exposed to a particular level of 
industrial sound. In most cases, this approach likely overestimates the 
numbers of marine mammals that would be affected in some biologically-
important manner.
    The sound criteria used to estimate how many marine mammals might 
be disturbed to some biologically-important degree by a seismic program 
are based primarily on behavioral observations of a few species. 
Scientists have conducted detailed studies on humpback, gray, bowhead 
(Balaena mysticetus), and sperm whales, and on ringed seals (Phoca 
hispida). Less detailed data are available for some other species of 
baleen whales, small toothed whales, and sea otters, but for many 
species there are no data on responses to marine seismic surveys.
    Baleen Whales--Baleen whales generally tend to avoid operating 
airguns, but avoidance radii are quite variable (reviewed in Richardson 
et al., 1995). Whales are often reported to show no overt reactions to 
pulses from large arrays of airguns at distances beyond a few kms, even 
though the airgun pulses remain well above ambient noise levels out to 
much longer distances. However, as reviewed in Appendix A (5) of SIO's 
EA, baleen whales exposed to strong noise pulses from airguns often 
react by deviating from their normal migration route and/or 
interrupting their feeding and moving away. In the cases of migrating 
gray and bowhead whales, the observed changes in behavior appeared to 
be of little or no biological consequence to the animals (Richardson, 
et al., 1995). They simply avoided the sound source by displacing their 
migration route to varying degrees, but within the natural boundaries 
of the migration corridors.
    Studies of gray, bowhead, and humpback whales have shown that 
seismic pulses with received levels of 160 to 170 dB re 1 [mu]Pa (rms) 
seem to cause obvious avoidance behavior in a substantial fraction of 
the animals exposed (Malme et al., 1986, 1988; Richardson et al., 
1995). In many areas, seismic pulses from large arrays of airguns 
diminish to those levels at distances ranging from 4.5 to 14.5 km (2.4 
to 7.8 nmi) from the source. A substantial proportion of the baleen 
whales within those distances may show avoidance or other strong 
behavioral reactions to the airgun array. Subtle behavioral changes 
sometimes become evident at somewhat lower received levels, and studies 
summarized in Appendix A (5) of SIO's EA have shown that some species 
of baleen whales, notably bowhead and humpback whales, at times, show 
strong avoidance at received levels lower than 160 to 170 dB re 1 
[mu]Pa (rms).
    McCauley et al. (1998, 2000a) studied the responses of humpback 
whales off western Australia to a full-scale seismic survey with a 16 
airgun array (2,678 in \3\) and to a single airgun (20 in\3\) with 
source level of 227 dB re 1 [micro]Pa (p-p). In the 1998 study, they 
documented that avoidance reactions began at five to eight km (2.7 to 
4.3 nmi) from the array, and that those reactions kept most pods 
approximately three to four km from the operating seismic boat. In the 
2000 study, they noted localized displacement during migration of four 
to five km by traveling pods and seven to 12 km (6.5 nmi) by more 
sensitive resting pods of cow-calf pairs. Avoidance distances with 
respect to the single airgun were smaller but consistent with the 
results from the full array in terms of the received sound levels. The 
mean received level for initial avoidance of an approaching airgun was 
140 dB re 1 [mu]Pa (rms) for humpback pods containing females, and at 
the mean closest point of approach distance the received level was 143 
dB re 1 [mu]Pa (rms). The initial avoidance response generally occurred 
at distances of five to eight km from the airgun array and two km from 
the single airgun. However, some individual humpback whales, especially 
males, approached within distances of 100 to 400 m (328 to 1,312 ft), 
where the maximum received level was 179 dB re 1 [mu]Pa (rms).
    Data collected by observers during several seismic surveys in the 
Northwest Atlantic showed that sighting rates of humpback whales were 
significantly greater during non-seismic periods compared with periods 
when a full array was operating (Moulton and Holst, 2010). In addition, 
humpback whales were more likely to swim away and less likely to swim 
towards a vessel during seismic vs. non-seismic periods (Moulton and 
Holst, 2010).
    Humpback whales on their summer feeding grounds in southeast Alaska 
did not exhibit persistent avoidance when exposed to seismic pulses 
from a 1.64-L (100 in \3\) airgun (Malme et al., 1985). Some humpbacks 
seemed ``startled'' at received levels of 150 to 169 dB re 1 [mu]Pa. 
Malme et al. (1985) concluded that there was no clear evidence of 
avoidance, despite the possibility of subtle effects, at received 
levels up to

[[Page 45527]]

172 dB re 1 [mu]Pa (rms). However, Moulton and Holst (2010) reported 
that humpback whales monitored during seismic surveys in the Northwest 
Atlantic had lower sighting rates and were most often seen swimming 
away from the vessel during seismic periods compared with periods when 
airguns were silent.
    Studies have suggested that south Atlantic humpback whales 
wintering off Brazil may be displaced or even strand upon exposure to 
seismic surveys (Engel et al., 2004). The evidence for this was 
circumstantial and subject to alternative explanations (IAGC, 2004). 
Also, the evidence was not consistent with subsequent results from the 
same area of Brazil (Parente et al., 2006), or with direct studies of 
humpbacks exposed to seismic surveys in other areas and seasons. After 
allowance for data from subsequent years, there was no observable 
direct correlation between strandings and seismic surveys (IWC, 
2007:236).
    There are no data on reactions of right whales to seismic surveys, 
but results from the closely-related bowhead whale show that their 
responsiveness can be quite variable depending on their activity 
(migrating versus feeding). Bowhead whales migrating west across the 
Alaskan Beaufort Sea in autumn, in particular, are unusually 
responsive, with substantial avoidance occurring out to distances of 20 
to 30 km (10.8 to 16.2 nmi) from a medium-sized airgun source at 
received sound levels of around 120 to 130 dB re 1 [mu]Pa (Miller et 
al., 1999; Richardson et al., 1999; see Appendix A (5) of SIO's EA). 
However, more recent research on bowhead whales (Miller et al., 2005; 
Harris et al., 2007) corroborates earlier evidence that, during the 
summer feeding season, bowheads are not as sensitive to seismic 
sources. Nonetheless, subtle but statistically significant changes in 
surfacing-respiration-dive cycles were evident upon statistical 
analysis (Richardson et al., 1986). In the summer, bowheads typically 
begin to show avoidance reactions at received levels of about 152 to 
178 dB re 1 [mu]Pa (Richardson et al., 1986, 1995; Ljungblad et al., 
1988; Miller et al., 2005).
    Reactions of migrating and feeding (but not wintering) gray whales 
to seismic surveys have been studied. Malme et al. (1986, 1988) studied 
the responses of feeding eastern Pacific gray whales to pulses from a 
single 100 in \3\ airgun off St. Lawrence Island in the northern Bering 
Sea. They estimated, based on small sample sizes, that 50 percent of 
feeding gray whales stopped feeding at an average received pressure 
level of 173 dB re 1 [mu]Pa on an (approximate) rms basis, and that 10 
percent of feeding whales interrupted feeding at received levels of 163 
dB re 1 [mu]Pa (rms). Those findings were generally consistent with the 
results of experiments conducted on larger numbers of gray whales that 
were migrating along the California coast (Malme et al., 1984; Malme 
and Miles, 1985), and western Pacific gray whales feeding off Sakhalin 
Island, Russia (Wursig et al., 1999; Gailey et al., 2007; Johnson et 
al., 2007; Yazvenko et al., 2007a, b), along with data on gray whales 
off British Columbia (Bain and Williams, 2006).
    Various species of Balaenoptera (blue, sei, fin, and minke whales) 
have occasionally been seen in areas ensonified by airgun pulses 
(Stone, 2003; MacLean and Haley, 2004; Stone and Tasker, 2006), and 
calls from blue and fin whales have been localized in areas with airgun 
operations (e.g., McDonald et al., 1995; Dunn and Hernandez, 2009; 
Castellote et al., 2010). Sightings by observers on seismic vessels off 
the United Kingdom from 1997 to 2000 suggest that, during times of good 
sightability, sighting rates for mysticetes (mainly fin and sei whales) 
were similar when large arrays of airguns were shooting vs. silent 
(Stone, 2003; Stone and Tasker, 2006). However, these whales tended to 
exhibit localized avoidance, remaining significantly further (on 
average) from the airgun array during seismic operations compared with 
non-seismic periods (Stone and Tasker, 2006). Castellote et al. (2010) 
reported that singing fin whales in the Mediterranean moved away from 
an operating airgun array.
    Ship-based monitoring studies of baleen whales (including blue, 
fin, sei, minke, and humpback whales) in the Northwest Atlantic found 
that overall, this group had lower sighting rates during seismic vs. 
non-seismic periods (Moulton and Holst, 2010). Baleen whales as a group 
were also seen significantly farther from the vessel during seismic 
compared with non-seismic periods, and they were more often seen to be 
swimming away from the operating seismic vessel (Moulton and Holst, 
2010). Blue and minke whales were initially sighted significantly 
farther from the vessel during seismic operations compared to non-
seismic periods; the same trend was observed for fin whales (Moulton 
and Holst, 2010). Minke whales were most often observed to be swimming 
away from the vessel when seismic operations were underway (Moulton and 
Holst, 2010).
    Data on short-term reactions by cetaceans to impulsive noises are 
not necessarily indicative of long-term or biologically significant 
effects. It is not known whether impulsive sounds affect reproductive 
rate or distribution and habitat use in subsequent days or years. 
However, gray whales have continued to migrate annually along the west 
coast of North America with substantial increases in the population 
over recent years, despite intermittent seismic exploration (and much 
ship traffic) in that area for decades (Appendix A in Malme et al., 
1984; Richardson et al., 1995; Allen and Angliss, 2010). The western 
Pacific gray whale population did not seem affected by a seismic survey 
in its feeding ground during a previous year (Johnson et al., 2007). 
Similarly, bowhead whales have continued to travel to the eastern 
Beaufort Sea each summer, and their numbers have increased notably, 
despite seismic exploration in their summer and autumn range for many 
years (Richardson et al., 1987; Allen and Angliss, 2010).
    Toothed Whales--Little systematic information is available about 
reactions of toothed whales to noise pulses. Few studies similar to the 
more extensive baleen whale/seismic pulse work summarized above and (in 
more detail) in Appendix A of SIO's EA have been reported for toothed 
whales. However, there are recent systematic studies on sperm whales 
(e.g., Gordon et al., 2006; Madsen et al., 2006; Winsor and Mate, 2006; 
Jochens et al., 2008; Miller et al., 2009). There is an increasing 
amount of information about responses of various odontocetes to seismic 
surveys based on monitoring studies (e.g., Stone, 2003; Smultea et al., 
2004; Moulton and Miller, 2005; Bain and Williams, 2006; Holst et al., 
2006; Stone and Tasker, 2006; Potter et al., 2007; Hauser et al., 2008; 
Holst and Smultea, 2008; Weir, 2008; Barkaszi et al., 2009; Richardson 
et al., 2009; Moulton and Holst, 2010).
    Seismic operators and marine mammal observers on seismic vessels 
regularly see dolphins and other small toothed whales near operating 
airgun arrays, but in general there is a tendency for most delphinids 
to show some avoidance of operating seismic vessels (e.g., Goold, 
1996a, b, c; Calambokidis and Osmek, 1998; Stone, 2003; Moulton and 
Miller, 2005; Holst et al., 2006; Stone and Tasker, 2006; Weir, 2008; 
Richardson et al., 2009; Barkaszi et al., 2009; Moulton and Holst, 
2010). Some dolphins seem to be attracted to the seismic vessel and 
floats, and some ride the bow wave of the seismic vessel even when 
large arrays of airguns are firing (e.g., Moulton and Miller, 2005).

[[Page 45528]]

Nonetheless, small toothed whales more often tend to head away, or to 
maintain a somewhat greater distance from the vessel, when a large 
array of airguns is operating than when it is silent (e.g., Stone and 
Tasker, 2006; Weir, 2008; Barry et al., 2010; Moulton and Holst, 2010). 
In most cases, the avoidance radii for delphinids appear to be small, 
on the order of one km or less, and some individuals show no apparent 
avoidance. The beluga whale (Delphinapterus leucas) is a species that 
(at least at times) shows long-distance avoidance of seismic vessels. 
Aerial surveys conducted in the southeastern Beaufort Sea during summer 
found that sighting rates of beluga whales were significantly lower at 
distances 10 to 20 km compared with 20 to 30 km from an operating 
airgun array, and observers on seismic boats in that area rarely see 
belugas (Miller et al., 2005; Harris et al., 2007).
    Captive bottlenose dolphins (Tursiops truncatus) and beluga whales 
exhibited changes in behavior when exposed to strong pulsed sounds 
similar in duration to those typically used in seismic surveys 
(Finneran et al., 2000, 2002, 2005). However, the animals tolerated 
high received levels of sound before exhibiting aversive behaviors.
    Results for porpoises depend on species. The limited available data 
suggest that harbor porpoises show stronger avoidance of seismic 
operations than do Dall's porpoises (Stone, 2003; MacLean and Koski, 
2005; Bain and Williams, 2006; Stone and Tasker, 2006). Dall's 
porpoises seem relatively tolerant of airgun operations (MacLean and 
Koski, 2005; Bain and Williams, 2006), although they too have been 
observed to avoid large arrays of operating airguns (Calambokidis and 
Osmek, 1998; Bain and Williams, 2006). This apparent difference in 
responsiveness of these two porpoise species is consistent with their 
relative responsiveness to boat traffic and some other acoustic sources 
(Richardson et al., 1995; Southall et al., 2007).
    Most studies of sperm whales exposed to airgun sounds indicate that 
the sperm whale shows considerable tolerance of airgun pulses (e.g., 
Stone, 2003; Moulton et al., 2005, 2006a; Stone and Tasker, 2006; Weir, 
2008). In most cases the whales do not show strong avoidance, and they 
continue to call (see Appendix A of SIO's EA for review). However, 
controlled exposure experiments in the GOM indicate that foraging 
behavior was altered upon exposure to airgun sound (Jochens et al., 
2008; Miller et al., 2009; Tyack, 2009).
    There are almost no specific data on the behavioral reactions of 
beaked whales to seismic surveys. However, some northern bottlenose 
whales (Hyperoodon ampullatus) remained in the general area and 
continued to produce high-frequency clicks when exposed to sound pulses 
from distant seismic surveys (Gosselin and Lawson, 2004; Laurinolli and 
Cochrane, 2005; Simard et al., 2005). Most beaked whales tend to avoid 
approaching vessels of other types (e.g., Wursig et al., 1998). They 
may also dive for an extended period when approached by a vessel (e.g., 
Kasuya, 1986), although it is uncertain how much longer such dives may 
be as compared to dives by undisturbed beaked whales, which also are 
often quite long (Baird et al., 2006; Tyack et al., 2006). Based on a 
single observation, Aguilar-Soto et al. (2006) suggested that foraging 
efficiency of Cuvier's beaked whales may be reduced by close approach 
of vessels. In any event, it is likely that most beaked whales would 
also show strong avoidance of an approaching seismic vessel, although 
this has not been documented explicitly. In fact, Moulton and Holst 
(2010) reported 15 sightings of beaked whales during seismic studies in 
the Northwest Atlantic; seven of those sightings were made at times 
when at least one airgun was operating. There was little evidence to 
indicate that beaked whale behavior was affected by airgun operations; 
sighting rates and distances were similar during seismic and non-
seismic periods (Moulton and Holst, 2010).
    There are increasing indications that some beaked whales tend to 
strand when naval exercises involving mid-frequency sonar operation are 
ongoing nearby (e.g., Simmonds and Lopez-Jurado, 1991; Frantzis, 1998; 
NOAA and USN, 2001; Jepson et al., 2003; Hildebrand, 2005; Barlow and 
Gisiner, 2006; see also the Stranding and Mortality section in this 
notice). These strandings are apparently a disturbance response, 
although auditory or other injuries or other physiological effects may 
also be involved. Whether beaked whales would ever react similarly to 
seismic surveys is unknown. Seismic survey sounds are quite different 
from those of the sonar in operation during the above-cited incidents.
    Odontocete reactions to large arrays of airguns are variable and, 
at least for delphinids and Dall's porpoises, seem to be confined to a 
smaller radius than has been observed for the more responsive of the 
mysticetes, belugas, and harbor porpoises (Appendix A of SIO's EA).
    Pinnipeds--Pinnipeds are not likely to show a strong avoidance 
reaction to the airgun array. Visual monitoring from seismic vessels 
has shown only slight (if any) avoidance of airguns by pinnipeds, and 
only slight (if any) changes in behavior, see Appendix A(5) of SIO's 
EA. In the Beaufort Sea, some ringed seals avoided an area of 100 m to 
(at most) a few hundred meters around seismic vessels, but many seals 
remained within 100 to 200 m (328 to 656 ft) of the trackline as the 
operating airgun array passed by (e.g., Harris et al., 2001; Moulton 
and Lawson, 2002; Miller et al., 2005). Ringed seal sightings averaged 
somewhat farther away from the seismic vessel when the airguns were 
operating than when they were not, but the difference was small 
(Moulton and Lawson, 2002). Similarly, in Puget Sound, sighting 
distances for harbor seals and California sea lions tended to be larger 
when airguns were operating (Calambokidis and Osmek, 1998). Previous 
telemetry work suggests that avoidance and other behavioral reactions 
may be stronger than evident to date from visual studies (Thompson et 
al., 1998).

Hearing Impairment and Other Physical Effects

    Exposure to high intensity sound for a sufficient duration may 
result in auditory effects such as a noise-induced threshold shift--an 
increase in the auditory threshold after exposure to noise (Finneran, 
Carder, Schlundt, and Ridgway, 2005). Factors that influence the amount 
of threshold shift include the amplitude, duration, frequency content, 
temporal pattern, and energy distribution of noise exposure. The 
magnitude of hearing threshold shift normally decreases over time 
following cessation of the noise exposure. The amount of threshold 
shift just after exposure is called the initial threshold shift. If the 
threshold shift eventually returns to zero (i.e., the threshold returns 
to the pre-exposure value), it is called temporary threshold shift 
(TTS) (Southall et al., 2007).
    Researchers have studied TTS in certain captive odontocetes and 
pinnipeds exposed to strong sounds (reviewed in Southall et al., 2007). 
However, there has been no specific documentation of TTS let alone 
permanent hearing damage, i.e., permanent threshold shift (PTS), in 
free-ranging marine mammals exposed to sequences of airgun pulses 
during realistic field conditions.
    Temporary Threshold Shift--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. At least in terrestrial mammals, 
TTS can last from minutes or

[[Page 45529]]

hours to (in cases of strong TTS) days. For sound exposures at or 
somewhat above the TTS threshold, hearing sensitivity in both 
terrestrial and marine mammals 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. Available data on TTS in marine mammals are summarized in 
Southall et al. (2007). Table 1 (above) presents the distances from the 
Thompson's airguns at which the received energy level (per pulse, flat-
weighted) would be expected to be greater than or equal to 190 dB re 1 
[mu]Pa (rms).
    Researchers have derived TTS information for odontocetes from 
studies on the bottlenose dolphin and beluga. For the one harbor 
porpoise tested, the received level of airgun sound that elicited onset 
of TTS was lower (Lucke et al., 2009). If these results from a single 
animal are representative, it is inappropriate to assume that onset of 
TTS occurs at similar received levels in all odontocetes (cf. Southall 
et al., 2007). Some cetaceans apparently can incur TTS at considerably 
lower sound exposures than are necessary to elicit TTS in the beluga or 
bottlenose dolphin.
    For baleen whales, there are no data, direct or indirect, on levels 
or properties of sound that are required to induce TTS. The frequencies 
to which baleen whales are most sensitive are assumed to be lower than 
those to which odontocetes are most sensitive, and natural background 
noise levels at those low frequencies tend to be higher. As a result, 
auditory thresholds of baleen whales within their frequency band of 
best hearing are believed to be higher (less sensitive) than are those 
of odontocetes at their best frequencies (Clark and Ellison, 2004). 
From this, it is suspected that received levels causing TTS onset may 
also be higher in baleen whales (Southall et al., 2007). For this 
proposed study, SIO expects no cases of TTS given the low abundance of 
baleen whales in the proposed survey area at the time of the proposed 
survey, and the strong likelihood that baleen whales would avoid the 
approaching airguns (or vessel) before being exposed to levels high 
enough for TTS to occur.
    In pinnipeds, TTS thresholds associated with exposure to brief 
pulses (single or multiple) of underwater sound have not been measured. 
Initial evidence from more prolonged (non-pulse) exposures suggested 
that some pinnipeds (harbor seals in particular) incur TTS at somewhat 
lower received levels than do small odontocetes exposed for similar 
durations (Kastak et al., 1999, 2005; Ketten et al., 2001). The TTS 
threshold for pulsed sounds has been indirectly estimated as being an 
SEL of approximately 171 dB re 1 [micro]Pa\2\[middot]s (Southall et 
al., 2007) which would be equivalent to a single pulse with a received 
level of approximately 181 to 186 dB re 1 [micro]Pa (rms), or a series 
of pulses for which the highest rms values are a few dB lower. 
Corresponding values for California sea lions and northern elephant 
seals are likely to be higher (Kastak et al., 2005).
    To avoid the potential for injury, NMFS (1995, 2000) concluded that 
cetaceans should not be exposed to pulsed underwater noise at received 
levels exceeding 180 dB re 1 [mu]Pa (rms) and pinnipeds should not be 
exposed to pulsed underwater noise at received levels exceeding 190 dB 
re 1 [mu]Pa (rms). NMFS believes that to avoid the potential for 
permanent physiological damage (Level A harassment), cetaceans should 
not be exposed to pulsed underwater noise at received levels exceeding 
180 dB re 1 [mu]Pa (rms) and pinnipeds should not be exposed to pulsed 
underwater noise at received levels exceeding 190 dB re 1 [mu]Pa (rms). 
The 180 dB and 190 dB levels are the shutdown criterion applicable to 
cetaceans and pinnipeds, respectively, as specified by NMFS (2000); 
these levels were used to establish the EZs. NMFS also assumes that 
marine mammals exposed to levels exceeding 160 dB re 1 [mu]Pa (rms) may 
experience Level B harassment.
    Permanent Threshold Shift--When PTS occurs, there is physical 
damage to the sound receptors in the ear. In severe cases, there can be 
total or partial deafness, whereas in other cases, the animal has an 
impaired ability to hear sounds in specific frequency ranges (Kryter, 
1985). 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 at least mild TTS, there has been further speculation 
about the possibility that some individuals occurring very close to 
airguns might incur PTS (e.g., Richardson et al., 1995, p. 372ff; 
Gedamke et al., 2008). Single or occasional occurrences of mild TTS are 
not indicative of permanent auditory damage, but repeated or (in some 
cases) single exposures to a level well above that causing TTS onset 
might elicit PTS.
    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 dBs above that inducing mild TTS if the animal were 
exposed to strong sound pulses with rapid rise time--see Appendix A (6) 
of SIO's EA. Based on data from terrestrial mammals, a precautionary 
assumption is that the PTS threshold for impulse sounds (such as airgun 
pulses as received close to the source) is at least 6 dB higher than 
the TTS threshold on a peak-pressure basis, and probably greater than 
six dB (Southall et al., 2007).
    Given the higher level of sound necessary to cause PTS as compared 
with TTS, it is considerably less likely that PTS would occur. Baleen 
whales generally avoid the immediate area around operating seismic 
vessels, as do some other marine mammals.
    Stranding 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). However, explosives are no longer used for 
marine waters for commercial seismic surveys or (with rare exceptions) 
for seismic research; they have been replaced entirely by airguns or 
related non-explosive pulse generators. Airgun pulses are less 
energetic and have slower rise times, and there is no specific evidence 
that they can cause serious injury, death, or stranding even in the 
case of large airgun arrays. However, the association of strandings of 
beaked whales with naval exercises involving mid-frequency active sonar 
and, in one case, an L-DEO seismic survey (Malakoff, 2002; Cox et al., 
2006), has raised the possibility that beaked whales exposed to strong 
``pulsed'' sounds may be especially susceptible to injury and/or 
behavioral reactions that can lead to stranding (e.g., Hildebrand, 
2005; Southall et al., 2007). Appendix A (6) of SIO's EA provides 
additional details.
    Specific sound-related processes that lead to strandings and 
mortality are not well documented, but may include:
    (1) Swimming in avoidance of a sound into shallow water;
    (2) A change in behavior (such as a change in diving behavior) that 
might contribute to tissue damage, gas bubble formation, hypoxia, 
cardiac arrhythmia, hypertensive hemorrhage or other forms of trauma;
    (3) A physiological change such as a vestibular response leading to 
a behavioral change or stress-induced hemorrhagic diathesis, leading in 
turn to tissue damage; and

[[Page 45530]]

    (4) Tissue damage directly from sound exposure, such as through 
acoustically-mediated bubble formation and growth or acoustic resonance 
of tissues. Some of these mechan