Takes of Marine Mammals Incidental to Specified Activities; Marine Geophysical Survey in the Central Pacific Ocean, November, 2011 Through January, 2012, 57959-57978 [2011-23985]

Agencies

• DEPARTMENT OF COMMERCE
• National Oceanic and Atmospheric Administration

[Federal Register Volume 76, Number 181 (Monday, September 19, 2011)]
[Notices]
[Pages 57959-57978]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 2011-23985]


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DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

RIN 0648-XA584


Takes of Marine Mammals Incidental to Specified Activities; 
Marine Geophysical Survey in the Central Pacific Ocean, November, 2011 
Through January, 2012

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

ACTION: Notice; proposed incidental harassment authorization; request 
for comments.

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SUMMARY: NMFS has received an application from Lamont-Doherty Earth 
Observatory (L-DEO), a part of Columbia University, for an Incidental 
Harassment Authorization (IHA) to take marine mammals, by harassment, 
incidental to conducting a marine geophysical survey in the central 
Pacific Ocean, November through December, 2011. Pursuant to the Marine 
Mammal Protection Act (MMPA), NMFS is requesting comments on its 
proposal to issue an IHA to L-DEO to incidentally harass, by Level B 
harassment only, 20 species of marine mammals during the specified 
activity.

DATES: Comments and information must be received no later than October 
19, 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 20910-3225. The mailbox address 
for providing e-mail comments is ITP.Cody@noaa.gov. NMFS is not 
responsible for e-mail comments send 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.
    An electronic 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 following associated documents are also available at the same 
Internet address: The National Science Foundation's (NSF) draft 
Environmental Analysis (Analysis) Pursuant to Executive Order 12114. 
The Analysis incorporates an ``Environmental Assessment of a Marine 
Geophysical Survey by the R/V Marcus G. Langseth in the Central Pacific 
Ocean, November-December 2011,'' prepared by LGL Limited, on behalf of 
NSF. Documents cited in this notice may be viewed, by appointment, 
during regular business hours, at the aforementioned address.

FOR FURTHER INFORMATION CONTACT: Jeannine Cody, Office of Protected 
Resources, NMFS, (301) 427-8401.

SUPPLEMENTARY INFORMATION: 

Background

    Section 101(a)(5)(D) of the Marine Mammal Protect Act of 1972, as 
amended (MMPA; 16 U.S.C. 1361 et seq.) directs the Secretary of 
Commerce 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. NMFS must publish a notice in the Federal Register 
within 30 days of its determination to issue or deny the authorization.
    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 17, 2011, from L-DEO for the 
taking by harassment, of marine mammals, incidental to conducting a 
marine geophysical survey in the central tropical Pacific Ocean in 
international waters. L-DEO, with research funding from the U.S. 
National Science Foundation (NSF), plans to conduct the proposed survey 
from November 26, 2011, through December 29, 2011. Upon receipt of 
additional information, NMFS determined the application complete and 
adequate on August 26, 2011.
    L-DEO plans to use one source vessel, the R/V Marcus G. Langseth 
(Langseth) and a seismic airgun array to image the structure of the 
oceanic lithosphere (i.e.,

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the Earth's crust and the uppermost mantle) in the Central Pacific 
using three-dimensional (3-D) seismic reflection techniques. The 
Langseth will deploy a single hydrophone streamer and approximately 34 
short-period Ocean Bottom Seismometers (OBS) to collect geophysical 
data. After completion of the seismic survey, the Langseth will recover 
the 34 seismometers and deploy 27 broad-band OBSs and five magneto-
telluric instruments on the seafloor. These instruments will remain on 
the seafloor for 12 months and the scientists will recover these 
instruments on a subsequent cruise in 2012.
    In addition to the proposed operations of the seismic airgun array, 
L-DEO 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 L-DEO has requested 
an authorization to take 20 species of marine mammals by Level B 
harassment. Take is not expected to result from the use of the MBES, 
the SBP, the OBSs, or the magneto-telluric instruments for reasons 
discussed in this notice. Also, NMFS does not expect take to result 
from collision with the Langseth because it is a single vessel moving 
at a relatively slow speeds during seismic acquisition within the 
survey, for a relatively short period of time. It is likely that any 
marine mammal would be able to avoid the vessel.

Description of the Specified Activity

    L-DEO's proposed seismic survey is scheduled to commence on 
November 26, 2011, and continue for approximately 35 days ending on 
December 29, 2011. Some minor deviation from these dates is possible, 
depending on logistics, weather conditions, and the need to repeat some 
lines if data quality is substandard. Therefore, NMFS proposes to issue 
an authorization that extends to January 19, 2012.
    Within this time period, the Langseth will conduct seismic 
operations deploying a 36-airgun array, a 6-kilometer (km) hydrophone 
streamer, and 34 OBSs. The Langseth will depart from Honolulu, Hawai'i 
on November 26, 2011 and transit to the survey area in the central 
Pacific Ocean, approximately 1,300 kilometers (km) south of Hawai'i.
    Geophysical survey activities will involve 3-D seismic 
methodologies to define the detailed structure of the oceanic 
lithosphere and to develop a comprehensive theory on its formation and 
evolution. To obtain 3-D images of the lithosphere in the survey area, 
the Langseth will deploy a 36-airgun array as an energy source. The 
receiving system consists of one 6-km-long hydrophone streamer and 
approximately 34 OBSs. As the airgun array is towed along the survey 
lines, the hydrophone streamers will receive the returning acoustic 
signals and transfer the data to the on-board processing system. The 
OBSs will receive the returning acoustic signals and record them for 
internally for later analysis after retrieval from the seafloor.
    The proposed study (e.g., equipment testing, startup, line changes, 
repeat coverage of any areas, and equipment recovery) will take place 
in water depths of approximately 5,000 meters (m) (3.1 miles (mi)). The 
survey will require approximately 11 days (d) to complete approximately 
2,120 km (1,317.3 mi) of transect lines. The Langseth will shoot a 600-
km long transect line twice; once using the hydrophone streamer as the 
receiver and once again using the OBSs. Subsequent seismic operations 
will occur along two semi-circular arcs (180 degrees) centered at the 
mid-point of the 600-km long transect line with radii of 50 and 150 km, 
respectively. The Langseth will conduct additional seismic operations 
in the survey area associated with turns, airgun testing, and repeat 
coverage of any areas where the initial data quality is sub-standard. 
Data acquisition will include approximately 264 hours (hr) of airgun 
operation (11d x 24 hr).
    The scientific team for this survey consists of Drs. J.B. Gaherty 
(L-DEO); D. Lizarralde, J.A. Collins, and R. Evans (Woods Hole 
Oceanographic Institution); and G. Hirth (Brown University).

Vessel Specifications

    The Langseth, owned by NSF, is a seismic research vessel with a 
propulsion system designed to be as quiet as possible to avoid 
interference with the seismic signals emanating from the airgun array. 
The vessel, which has a length of 71.5 m (235 feet (ft)); a beam of 
17.0 m (56 ft); a maximum draft of 5.9 m (19 ft); and a gross tonnage 
of 3,834 pounds, is powered by two 3,550 horsepower (hp) Bergen BRG-6 
diesel engines which drive two propellers. Each propeller has four 
blades and the shaft typically rotates at 750 revolutions per minute. 
The vessel also has an 800-hp bowthruster, which is not used during 
seismic acquisition. The Langseth's operation speed during seismic 
acquisition will be approximately 8.5 km per hr (km/h) (5.3 miles (mi) 
per hr (mph) or 4.6 knots (kts)) and the cruising speed of the vessel 
outside of seismic operations is 18.5 km/h (11.5 mph or 10 kts).
    When the Langseth is towing the airgun array and the hydrophone 
streamer, the turning rate of the vessel is limited to five degrees per 
minute. Thus, the maneuverability of the vessel is limited during 
operations with the streamer.
    The vessel also has an observation tower from which protected 
species visual observers (PSVO) will watch for marine mammals before 
and during the proposed airgun operations. When stationed on the 
observation platform, the PSVO's eye level will be approximately 21.5 m 
(71 ft) above sea level providing the PSVO an unobstructed view around 
the entire vessel.

Acoustic Source Specifications

Seismic Airguns

    The Langseth will deploy a 36-airgun array, with a total volume of 
approximately 6,600 cubic inches (in\3\) at a tow depth of 9 m (29.5 
ft). The airguns are a mixture of Bolt 1500LL and Bolt 1900LLX airguns 
ranging in size from 40 to 360 in\3\, with a firing pressure of 1,900 
pounds per square inch. The dominant frequency components range from 
zero to 188 Hertz (Hz). The array configuration consists of four 
identical linear or strings, with 10 airguns on each string; the first 
and last airguns will be spaced 16 m (52 ft) apart. Of the 10 airguns, 
nine will fire simultaneously while the tenth airgun will serve as a 
spare and will be turned on in case of failure of one of the other 
airguns. During the multichannel seismic (MCS) survey, each airgun 
array will emit a pulse at approximately 22-second (s) intervals which 
corresponds to a shot interval of approximately 50 m (164 ft). During 
OBS data acquisition, each airgun array will emit a longer pulse at 
approximately 300-s intervals which corresponds to a shot interval of 
approximately 650 m (2,132.5 ft). During firing, the airguns will emit 
a brief (approximately 0.1 s) pulse of sound; during the intervening 
periods of operations, the airguns will be silent.
    L-DEO will tow each array approximately 100 m (328 ft) behind the 
vessel and will distribute the array

[[Page 57961]]

across an area of approximately 24 by 16 m (78.7 by 52.5 ft) behind the 
Langseth.

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 source levels of the airgun array used by L-DEO on the 
Langseth is 236 to 265 dB re: 1 [mu]Pa(p-p) and the rms 
value for a given airgun pulse is typically 16 dB re: 1 [mu]Pa lower 
than the peak-to-peak value. 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, L-DEO has predicted the received sound levels in 
relation to distance and direction from the 36-airgun array and the 
single Bolt 1900LL 40-in\3\ airgun, which will be used during power 
downs. A detailed description of L-DEO's modeling for marine seismic 
source arrays for species mitigation is provided in Appendix A of L-
DEO's application. These are the nominal source levels applicable to 
downward propagation. The effective source levels for horizontal 
propagation are lower than those for downward propagation because of 
the directional nature of the sound from the airgun array.
    Appendix B of L-DEO's environmental analysis discusses the 
characteristics of the airgun pulses. NMFS refers the reviewers to the 
application and environmental analysis documents for additional 
information.

Predicted Sound Levels for the Airguns

    Tolstoy et al., (2009) reported results for propagation 
measurements of pulses from the Langseth's 36-airgun, 6,600 in\3\ array 
in shallow-water (approximately 50 m (164 ft)) and deep-water depths 
(approximately 1,600 m (5,249 ft)) in the Gulf of Mexico in 2007 and 
2008. Results of the Gulf of Mexico calibration study (Tolstoy et al., 
2009) showed that radii around the airguns for various received levels 
varied with water depth and with array tow depth.
    L-DEO used the results from the Gulf of Mexico study to determine 
the algorithm for its model that calculates the exclusion zones (EZ) 
for the 36-airgun array and the single airgun. L-DEO uses these values 
to designate mitigation zones and to estimate take (described in 
greater detail in Section VII of L-DEO's application and Section IV of 
the environmental analysis) for marine mammals.
    Comparison of the Tolstoy et al. calibration study with L-DEO's 
model for the Langseth's 36-airgun array indicated that the model 
represents the actual received levels, within the first few kilometers, 
where the predicted exclusions zones are located. However, the model 
for deep water (greater than 1,000 m; 3,280 ft) overestimated the 
received sound levels at a given distance but is still valid for 
defining exclusion zones at various tow depths. Because the tow depth 
of the array in the calibration study is less shallow (3 m; 9.8 ft) 
than the tow depth array in the proposed survey (9 m; 29.5 ft), L-DEO 
used correction factors for estimating the received levels in deep 
water during the proposed survey. The correction factors used were the 
ratios of the 160- and 180-dB distances from the modeled results for 
the 6,600 in\3\ airgun array towed at 6 m (19.7 ft) versus 9 m (29.5 
ft) from LGL (2008); 1.285 and 1.3381 respectively.
    Table 1 summarizes the predicted distances at which sound levels 
(160- and 180-dB) are expected to be received from the 36-airgun array 
and a single airgun operating in deep water.

   Table 1--Measured (Array) or Predicted (Single Airgun) Distances to
    Which Sound Levels Greater Than or Equal to 160 and 180 dB re: 1
 [mu]Parms That Could Be Received in Deep Water Using a 36-Airgun Array,
 as Well as a Single Airgun Towed at a Depth of 9 m (29.5 ft) During the
  Proposed Survey in the Central Pacific Ocean, During November, 2011-
                              January, 2012
        [Distances are based on model results provided by L-DEO.]
------------------------------------------------------------------------
                                                 Predicted RMS distances
                                                           (m)
      Source and volume          Water depth   -------------------------
                                                   160 dB       180 dB
------------------------------------------------------------------------
Single Bolt airgun (40        Deep                      385           40
 in\3\).
�����������������������������
36-Airgun Array.............  (> 1,000 m).....        3,850          940
------------------------------------------------------------------------

    Appendix A of the environmental analysis discusses L-DEO's 
calculations for the model. NMFS refers the reviewers to the 
application and environmental analysis documents for additional 
information.

Ocean Bottom Seismometer

    L-DEO proposes to use the Woods Hole Oceanographic Institution 
(WHOI)

[[Page 57962]]

``D2'' OBS during the cruise. This type of OBS is approximately one 
meter in height and has a maximum diameter of 50 centimeters (cm). The 
anchor (2.5 x 30.5 x 38.1 cm) is made of hot-rolled steel and weighs 23 
kilograms (kg). The acoustic release transponder used to communicate 
with the OBS uses frequencies of 9 to 13 kHz. The source level of the 
release signal is 190 dB re: 1 [mu]Pa.

Multibeam Echosounder

    The Langseth will operate a Kongsberg EM 122 MBES concurrently 
during airgun operations to map characteristics of the ocean floor. The 
hull-mounted MBES emits brief pulses of sound (also called a ping) 
(10.5 to 13 kilohertz (kHz)) in a fan-shaped beam that extends downward 
and to the sides of the ship. The transmitting beamwidth is one or two 
degrees ([deg]) fore-aft and 150[deg] athwartship and the maximum 
source level is 242 dB re: 1 [mu]Pa.
    For deep-water operations, each ping consists of eight (in water 
greater than 1,000 m; 3,280 ft) or four (less than 1,000 m; 3,280 ft) 
successive, fan-shaped transmissions, from two to 15 milliseconds (ms) 
in duration and each ensonifying a sector that extends 1[deg] fore-aft. 
Continuous wave pulses increase from two to 15 milliseconds (ms) long 
in water depths up to 2,600 m (8,530 ft). The MBES uses frequency-
modulated chirp pulses up to 100-ms long in water greater than 2,600 m 
(8,530 ft). The eight successive transmissions span an overall cross-
track angular extent of about 150[deg], with 2-ms gaps between the 
pulses for successive sectors.

Sub-Bottom Profiler

    The Langseth will also operate a Knudsen Chirp 3260 SBP 
concurrently during airgun and MBES operations to provide information 
about the sedimentary features and bottom topography. The SBP is 
capable of reaching depths of 10,000 m (6.2 mi). The dominant frequency 
component of the SBP is 3.5 kHz which is directed downward in a 27[deg] 
cone by a hull-mounted transducer on the vessel. The nominal power 
output is 10 kilowatts (kW), but the actual maximum radiated power is 
three kW or 222 dB re: 1 [mu]Pa. The ping duration is up to 64 ms with 
a pulse interval of one second, but a common mode of operation is to 
broadcast five pulses at 1-s intervals followed by a 5-s pause.
    NMFS expects that acoustic stimuli resulting from the proposed 
operation of the single airgun or the 36-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 in a temporary modification in behavior and/or low-level 
physiological effects (Level B harassment only) of small numbers of 
certain species of marine mammals. NMFS does not expect that the 
movement of the Langseth, during the conduct of the seismic survey, has 
the potential to harass marine mammals because of the relatively slow 
operation speed of the vessel (4.6 kts; 8.5 km/hr; 5.3 mph) during 
seismic acquisition.

Description of the Specified Geographic Region

    The survey will encompass the area bounded by 5-10[deg] N, 150-
156[deg] W in international waters in the central Pacific Ocean (see 
Figure 1 in L-DEO's application). Water depth in the survey area is 
approximately 5,000 m (3.1 mi).

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

    Twenty-six marine mammal species may occur in the proposed survey 
area, including 19 odontocetes (toothed cetaceans), 6 mysticetes 
(baleen whales) and one species of pinniped during November through 
December. Six of 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) whale and the Hawaiian monk seal (Monachus 
schauinslandi).
    Hawaiian monk seals have the potential to transit in the vicinity 
of the proposed seismic survey, although any occurrence would be rare 
as they are vagrants to the area. Based on available data, L-DEO does 
not expect to encounter Hawaiian monk seals within the proposed survey 
area and does not present analysis for these species. Accordingly, NMFS 
will not consider this pinniped species in greater detail and the 
proposed IHA will only address requested take authorizations for 
mysticetes and odontocetes.
    The species of marine mammals expected to be most common in the 
survey area (all delphinids) include the pantropical spotted dolphin 
(Stenella attenuata) and spinner dolphin (Stenella longirostris).
    Table 2 presents information on the abundance, distribution, and 
conservation status of the marine mammals that may occur in the 
proposed survey area November, 2011 through January, 2012.
BILLING CODE 3510-22-P

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[GRAPHIC] [TIFF OMITTED] TN19SE11.006

BILLING CODE 3510-22-C
    Refer to Sections III and IV of L-DEO'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 L-DEO 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 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 an 
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 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

[[Page 57965]]

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 B (4) of L-DEO's environmental analysis 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. Less detailed data are 
available for some other species of baleen whales, small toothed 
whales, and sea otters (Enhydra lutris), 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 kilometers, even though the airgun pulses remain well above ambient 
noise levels out to much longer distances. However, as reviewed in 
Appendix B (5.1) of L-DEO's environmental analysis, 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 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 four to 15 km 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 B (5.1) of L-
DEO's environmental analysis have shown that some species of baleen 
whales, notably bowhead and humpback whales, at times, show strong 
avoidance at received levels lower than 160-170 dB re: 1 [mu]Pa.
    McCauley et al. (1998, 2000) 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 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 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 for humpback pods containing females, and at the mean closest 
point of approach distance the received level was 143 dB re: 1 [mu]Pa. 
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.
    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 172 dB re: 1 [mu]Pa.
    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

[[Page 57966]]

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 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 B (5) of L-DEO's environmental analysis). 
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 [micro]Pa. 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). 
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). In a study off of Nova Scotia, Moulton and 
Miller (2005) found little difference in sighting rates (after 
accounting for water depth) and initial sighting distances of 
balaenopterid whales when airguns were operating vs. silent. However, 
there were indications that these whales were more likely to be moving 
away when seen during airgun operations. Similarly, ship-based 
monitoring studies of blue, fin, sei and minke whales offshore of 
Newfoundland (Orphan Basin and Laurentian Sub-basin) found no more than 
small differences in sighting rates and swim directions during seismic 
versus non-seismic periods (Moulton et al., 2005, 2006a,b). 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; Angliss and Allen, 2009).
    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 B of L-DEO's environmental analysis 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).
    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; see also Barkaszi et al., 2009). 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). 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). In 
most cases, the avoidance radii for delphinids appear to be small, on 
the order of one km 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 (Phocoena phocoena) show stronger 
avoidance of seismic operations than do Dall's porpoises (Phocoenoides 
dalli) (Stone, 2003; MacLean and Koski, 2005; Bain and Williams, 2006; 
Stone and Tasker, 2006). Dall's porpoises seem relatively

[[Page 57967]]

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 B of L-DEO's environmental analysis for 
review). However, controlled exposure experiments in the Gulf of Mexico 
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 (Ziphius cavirostris) 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.
    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 (See Appendix B of L-DEO's 
environmental analysis).

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 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 presents the 
distances from the Langseth's airguns at which the received energy 
level (per pulse, flat-weighted) that would be expected to be greater 
than or equal to 180 dB re: 1 [mu]Pa.
    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. 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. The 180-dB level is a shutdown 
criterion applicable to cetaceans, as specified by NMFS (2000); these 
levels were used to establish the EZs. NMFS also assumes that cetaceans 
exposed to levels exceeding 160 dB re: 1 [mu]Pa (rms) may experience 
Level B harassment.
    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, L-DEO expects no cases of TTS given: (1) The low 
abundance of baleen whales in the planned study area at the time of the 
survey; and (2) the strong likelihood that baleen whales would avoid 
the approaching airguns (or vessel) before

[[Page 57968]]

being exposed to levels high enough for TTS to occur.
    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 decibels above that inducing mild TTS if the animal were 
exposed to strong sound pulses with rapid rise time-see Appendix B (6) 
of L-DEO's environmental analysis. 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 B (6) of L-DEO's environmental 
analysis 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
    (4) Tissue damage directly from sound exposure, such as through 
acoustically-mediated bubble formation and growth or acoustic resonance 
of tissues. Some of these mechanisms are unlikely to apply in the case 
of impulse sounds. However, there are increasing indications that gas-
bubble disease (analogous to the bends), induced in supersaturated 
tissue by a behavioral response to acoustic exposure, could be a 
pathologic mechanism for the strandings and mortality of some deep-
diving cetaceans exposed to sonar. However, the evidence for this 
remains circumstantial and associated with exposure to naval mid-
frequency sonar, not seismic surveys (Cox et al., 2006; Southall et 
al., 2007).
    Seismic pulses and mid-frequency sonar signals are quite different, 
and some mechanisms by which sonar sounds have been hypothesized to 
affect beaked whales are unlikely to apply to airgun pulses. Sounds 
produced by airgun arrays are broadband impulses with most of the 
energy below one kHz. Typical military mid-frequency sonar emits non-
impulse sounds at frequencies of two to 10 kHz, generally with a 
relatively narrow bandwidth at any one time. A further difference 
between seismic surveys and naval exercises is that naval exercises can 
involve sound sources on more than one vessel. Thus, it is not 
appropriate to assume that there is a direct connection between the 
effects of military sonar and seismic surveys on marine mammals. 
However, evidence that sonar signals can, in special circumstances, 
lead (at least indirectly) to physical damage and mortality (e.g., 
Balcomb and Claridge, 2001; NOAA and USN, 2001; Jepson et al., 2003; 
Fern[aacute]ndez et al., 2004, 2005; Hildebrand 2005; Cox et al., 2006) 
suggests that caution is warranted when dealing with exposure of marine 
mammals to any high-intensity ``pulsed'' sound.
    There is no conclusive evidence of cetacean strandings or deaths at 
sea as a result of exposure to seismic surveys, but a few cases of 
strandings in the general area where a seismic survey was ongoing have 
led to speculation concerning a possible link between seismic surveys 
and strandings. Suggestions that there was a link between seismic 
surveys and strandings of humpback whales in Brazil (Engel et al., 
2004) were not well founded (IAGC, 2004; IWC, 2007). In September 2002, 
there was a stranding of two Cuvier's beaked whales in the Gulf of 
California, Mexico, when the L DEO vessel R/V Maurice Ewing was 
operating a 20-airgun (8,490 in\3\) array in the general area. The link 
between the stranding and the seismic surveys was inconclusive and not 
based on any physical evidence (Hogarth, 2002; Yoder, 2002). 
Nonetheless, the Gulf of California incident plus the beaked whale 
strandings near naval exercises involving use of mid-frequency sonar 
suggests a need for caution in conducting seismic surveys in areas 
occupied by beaked whales until more is known about effects of seismic 
surveys on those species (Hildebrand, 2005). No injuries of beaked 
whales are anticipated during the proposed study because of:
    (1) The high likelihood that any beaked whales nearby would avoid 
the approaching vessel before being exposed to high sound levels,
    (2) Differences between the sound sources operated by L-DEO and 
those involved in the naval exercises associated with strandings.
    Non-auditory Physiological Effects--Non-auditory physiological 
effects or injuries that theoretically might occur in marine mammals 
exposed to strong underwater sound include stress, neurological 
effects, bubble formation, resonance, and other types of organ or 
tissue damage (Cox et al., 2006; Southall et al., 2007). Studies 
examining such effects are limited. However, resonance effects (Gentry, 
2002) and direct noise-induced bubble formations (Crum et al., 2005) 
are implausible in the case of exposure to an impulsive broadband 
source like an airgun array. If seismic

[[Page 57969]]

surveys disrupt diving patterns of deep-diving species, this might 
perhaps result in bubble formation and a form of the bends, as 
speculated to occur in beaked whales exposed to sonar. However, there 
is no specific evidence of this upon exposure to airgun pulses.
    In general, very little is known about the potential for seismic 
survey sounds (or other types of strong underwater sounds) to cause 
non-auditory physical effects in marine mammals. Such effects, if they 
occur at all, would presumably be limited to short distances and to 
activities that extend over a prolonged period. The available data do 
not allow identification of a specific exposure level above which non-
auditory effects can be expected (Southall et al., 2007), or any 
meaningful quantitative predictions of the numbers (if any) of marine 
mammals that might be affected in those ways. Marine mammals that show 
behavioral avoidance of seismic vessels, including most baleen whales 
and some odontocetes, are especially unlikely to incur non-auditory 
physical effects.

Potential Effects of Other Acoustic Devices

MBES
    L-DEO will operate the Kongsberg EM 122 MBES from the source vessel 
during the planned study. Sounds from the MBES are very short pulses, 
occurring for two to 15 ms once every five to 20 s, depending on water 
depth. Most of the energy in the sound pulses emitted by this MBES is 
at frequencies near 12 kHz, and the maximum source level is 242 dB re: 
1 [mu]Pa. The beam is narrow (1 to 2[ordm]) in fore-aft extent and wide 
(150[ordm]) in the cross-track extent. Each ping consists of eight (in 
water greater than 1,000 m deep) or four (less than 1,000 m deep) 
successive fan-shaped transmissions (segments) at different cross-track 
angles. Any given mammal at depth near the trackline would be in the 
main beam for only one or two of the segments. Also, marine mammals 
that encounter the Kongsberg EM 122 are unlikely to be subjected to 
repeated pulses because of the narrow fore-aft width of the beam and 
will receive only limited amounts of pulse energy because of the short 
pulses. Animals close to the vessel (where the beam is narrowest) are 
especially unlikely to be ensonified for more than one 2- to 15-ms 
pulse (or two pulses if in the overlap area). Similarly, Kremser et al. 
(2005) noted that the probability of a cetacean swimming through the 
area of exposure when an MBES emits a pulse is small. The animal would 
have to pass the transducer at close range and be swimming at speeds 
similar to the vessel in order to receive the multiple pulses that 
might result in sufficient exposure to cause TTS.
    Navy sonars that have been linked to avoidance reactions and 
stranding of cetaceans: (1) Generally have longer pulse duration than 
the Kongsberg EM 122; and (2) are often directed close to horizontally 
versus more downward for the MBES. The area of possible influence of 
the MBES is much smaller--a narrow band below the source vessel. Also, 
the duration of exposure for a given marine mammal can be much longer 
for naval sonar. During L-DEO's operations, the individual pulses will 
be very short, and a given mammal would not receive many of the 
downward-directed pulses as the vessel passes by. Possible effects of 
an MBES on marine mammals are outlined below.
    Masking--Marine mammal communications will not be masked 
appreciably by the MBES signals given the low duty cycle of the 
echosounder and the brief period when an individual mammal is likely to 
be within its beam. Furthermore, in the case of baleen whales, the MBES 
signals (12 kHz) do not overlap with the predominant frequencies in the 
calls, which would avoid any significant masking.
    Behavioral Responses--Behavioral reactions of free-ranging marine 
mammals to sonars, echosounders, and other sound sources appear to vary 
by species and circumstance. Observed reactions have included silencing 
and dispersal by sperm whales (Watkins et al., 1985), increased 
vocalizations