Takes of Marine Mammals Incidental to Specified Activities; Physical Oceanographic Studies in the Southwest Indian Ocean, January Through February, 2012, 71940-71958 [2011-30010]

Agencies

• DEPARTMENT OF COMMERCE
• National Oceanic and Atmospheric Administration

[Federal Register Volume 76, Number 224 (Monday, November 21, 2011)]
[Notices]
[Pages 71940-71958]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 2011-30010]


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DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

RIN 0648-XA792


Takes of Marine Mammals Incidental to Specified Activities; 
Physical Oceanographic Studies in the Southwest Indian Ocean, January 
Through February, 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 the United States Navy 
(Navy) for an Incidental Harassment Authorization (IHA) to take marine 
mammals, by harassment, incidental to conducting physical oceanographic 
studies in the southwest Indian Ocean, January through February, 2012. 
Pursuant to the Marine Mammal Protection Act (MMPA), NMFS is requesting 
comments on its proposal to issue an IHA to the Navy to incidentally 
harass, by Level B harassment only, 29 species of marine mammals during 
the specified activity.

DATES: Comments and information must be received no later than December 
21, 2011.

ADDRESSES: Comments on the application should be addressed to P. 
Michael Payne, Chief, Permits and Conservation Division, Office of 
Protected Resources, National Marine Fisheries Service, 1315 East-West 
Highway, Silver Spring, MD 20910. The mailbox address for providing 
email comments is ITP.Magliocca@noaa.gov. NMFS is not responsible for 
email comments sent to addresses other than the one provided here. 
Comments sent via email, 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.
    In accordance with Executive Order 12114, the Navy has prepared a 
draft Overseas Environmental Assessment (OEA), which is also available 
on the Internet. Documents cited in this notice may be viewed, by 
appointment, during regular business hours, at the aforementioned 
address.

FOR FURTHER INFORMATION CONTACT: Michelle Magliocca, 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

[[Page 71941]]

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 August 15, 2011, from the Navy for 
the taking of marine mammals, by Level B harassment, incidental to 
conducting physical oceanographic studies in the southwest Indian 
Ocean. The Navy plans to conduct a seismic oceanographic survey from 
January 23, 2012, through February 8, 2012. Upon receipt of additional 
information, NMFS determined the application complete and adequate on 
September 14, 2011.
    The Navy plans to use one source vessel, the R/V Melville 
(Melville), and a seismic airgun array to obtain high resolution 
imaging of ocean mixing dynamics at the Agulhas Return Current and 
Antarctic Circumpolar Currents (ARC/ACC). The Melville would spend 14 
days on seismic oceanography surveys and three days on acoustic Doppler 
current profiler (ADCP) mooring deployments and recoveries, other 
oceanographic sampling methods, and transit to and from the study site.
    Acoustic stimuli (i.e., increased underwater sound) generated 
during the operation of the 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 the Navy has requested an 
authorization to take 29 species of marine mammals by Level B 
harassment. Take is not expected to result from the use of the 
multibeam echosounder (MBES), subbottom profiler (SBP), or ADCPs, due 
to the narrow and directional acoustic beam field of the MBES, the 
attenuation rate of high-frequency sound in seawater, and the motility 
of free-ranging marine mammals. Take is also not expected to result 
from collision with the Melville because it is a single vessel moving 
at relatively slow speeds during seismic acquisition within the survey, 
for a relatively short period of time.

Description of the Specified Activity

    The Navy's proposed physical oceanographic studies are scheduled to 
commence on January 23, 2012, and continue for approximately 17 days 
ending on February 8, 2012. Some minor deviation from these dates is 
possible due to logistics and weather conditions; therefore, the 
authorization would be valid from January 23, 2012 through March 7, 
2012. Within this time period, the Navy would conduct seismic 
oceanography surveys using a towed array of two low-energy 105 in\3\ 
generator-injector (GI) airguns. The Melville would depart from Cape 
Town, South Africa, on January 23, 2012, and transit to the survey area 
near the Agulhas Plateau, off the southern tip of Africa. The exact 
location of the ARC/ACC front in January cannot be predetermined due to 
the natural meander of the currents, but studies would most likely take 
place within the boundaries of 36[deg]S to 43[deg]S and 19[deg]E to 
30[deg]E. The exact locations of the ARC/ACC frontal system would be 
determined on site using high-resolution conductivity-temperature-depth 
measurements. The total area of this region is about 207,500 nautical 
miles\2\ (Nm\2\) (713,000 kilometers\2\ [km\2\]). The proposed study 
would take place in water depths of approximately 1,000 to 5,200 meters 
(m). The survey would require approximately 17 days to complete 
approximately 2,489 km of transect lines, and be comprised of multiple 
transects across and along the ARC/ACC front.

Vessel Specifications

    The Melville, owned by the Navy, 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 97 m (318 feet [ft]); a beam of 14 m 
(46 ft); and a maximum draft of 5 m (16 ft); is powered by two 1,385 
horsepower (hp) Propulsion General Electric motors and a 900 hp 
retracting bow thruster. The Melville's operation speed during seismic 
acquisition would be approximately 7 to 11 km/hour (hr) (4 to 6 knots) 
and the cruising speed of the vessel outside of seismic operations 
would be about 20 km/hr (11 knots). The vessel also has a platform one 
deck below and forward of the bridge, which is positioned 12.5 m (41 
ft) above the waterline and provides a relatively unobstructed 180 
degree view forward. Aft views can be obtained along both the port and 
starboard decks.

Acoustic Source Specifications

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). RMS, 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.

Seismic Airguns

    The Melville would deploy two GI guns, which are stainless steel 
cylinders charged with high pressure air that, when instantaneously 
released into the water column, generate sound. The GI guns would 
operate in harmonic mode (105 in\3\ in each of the generator and 
injector chambers for a total discharge volume of 210 in\3\) with a 
1,200 m long hydrophone streamer. GI guns would be energized 
simultaneously at 2,000 psi every 17 seconds (s). The GI gun array

[[Page 71942]]

would emit sound at a frequency range of 10 to 188 Hertz (Hz) and reach 
a peak source level of 240 dB re 1 [micro]Pa. Seismic oceanography 
studies would be conducted 24 hours (hrs) per day for 14 days (336 hrs) 
and the GI guns would be towed at a depth of 3 to 9 m.

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 sound that travels horizontally toward non-
target areas. The nominal source levels of the airgun array that would 
be used by the Navy on the Melville are 234 dB re: 1 
[mu]Pa(0-p) to 240 dB re: 1 [mu]Pa(p-p).

Predicted Sound Levels for the Airguns

    Lamont-Doherty Earth Observatory (L-DEO) developed a verified model 
that predicts impulsive sound pressure field propagation and accurately 
describes acoustic propagation in marine waters of depths greater than 
1,000 m. These model-generated sound propagation radii are routinely 
used for determination of received sound levels generated by impulsive 
sound sources, and have been previously applied in calculating the 
total ensonified area for use of two low-energy 105 in\3\ GI-guns. 
Modeled sound propagation radii of GI-gun sources that are the same or 
similar to the GI-guns used in this study, in water depths > 1,000 m, 
are given in Table 1. These modeled acoustic propagation distances were 
applied in Environmental Assessments (EAs) and IHAs for seismic surveys 
conducted in the Eastern Tropical Pacific Ocean (ETP) off of Central 
America (NMFS, 2004), the Northern Gulf of Mexico (GOMEX) (L-DEO, 2003; 
NMFS, 2007), and the Arctic Ocean (NMFS, 2006).
    For the ETP, one and three 105 in\3\ GI-gun arrays were modeled, 
with a source output level of 241 dB re 1 [micro]Pa(0-p) and 
247 dB re 1 [micro]Pa(p-p). For the GOMEX survey, GI-gun 
source output levels were (a) 237 dB re 1 [micro]Pa(0-p) and 
243 dB re 1 [micro]Pa(p-p); and (b) 229 dB re 1 
[micro]Pa(0-p) and 236 dB re 1 [micro]Pa(p-p). L-
DEO modeling of a single G-gun has also been applied to a seismic 
survey in the Arctic Ocean. The source level for the 210 in\3\ G-gun 
was 246 dB re 1 [micro]Pa(0-p) and 253 dB re 1 
[micro]Pa(p-p). However, because the G-gun generates more 
energy than a GI-gun of the same size, the distances for received sound 
levels may be an overestimate for the lower energy dual 105 in\3\ GI-
gun source used in the ARC12 research project. The GI-gun is comprised 
of two, independently fired air chambers (the generator and the 
injector) to tune air bubble oscillation and minimize the amplitude of 
the acoustic pulse. In contrast, the G-gun is comprised of one chamber 
and generates a single, less refined injection of air into the water, 
which produces more acoustic energy than that of the GI-gun.

                               Table 1--Modeled Sound Propagation Radii for Low-Energy Air-Gun Arrays for Depths > 1,000 m
--------------------------------------------------------------------------------------------------------------------------------------------------------
 
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             Air-gun configuration               Water depth   Tow depth                   Received sound levels (dB re 1 [micro]Pa RMS)
                                                     (m)          (m)
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                               190          180          160                     Location
                                                --------------------------------------------------------------------------------------------------------
                                                                      Distance
--------------------------------------------------------------------------------------------------------------------------------------------------------
1 GI-gun 105 in\3\.............................      > 1,000          2.5           10           27          275  ETP.
3 GI-guns 105 in\3\............................      > 1,000          2.5           26           82          823  ETP.
2 GI-guns 105 in\3\ (a)........................      > 1,000            3           20           69          670  GOMEX.
2 GI-guns 105 in\3\ (b)........................      > 1,000            6           15           50          520  GOMEX.
1 G-gun 210 in\3\..............................      > 1,000            9           20           78          698  Arctic.
--------------------------------------------------------------------------------------------------------------------------------------------------------

    Based on extant modeling, the proposed sound propagation radii for 
the two 105 in\3\ GI-guns are 20 m, 70 m, and 670 m for the 190, 180, 
and 160 dB re 1 [micro]Pa RMS isopleths, respectively (Table 2). 
Empirical data indicate that for deep water (> 1,000 m), the L-DEO 
model tends to overestimate the received sound level at a given 
distance (Tolstoy et al., 2004). It follows that the proposed sound 
propagation radii are considered conservative, and the actual distance 
at which received sound levels are 160 dB re 1 uPa RMS or greater are 
expected to be less than that proposed. The proposed sound propagation 
radii are also consistent with recent modeling of sound propagation in 
the Southern Ocean (Breitzke and Bohlen, 2010).

    Table 2--Sound Propagation Radii for the Dual 105 in3 GI-Gun Array Proposed for Use in the ARC12 Research
                                                     Project
----------------------------------------------------------------------------------------------------------------
 
----------------------------------------------------------------------------------------------------------------
           Acoustic source             Frequency    Source level (dB re 1   Received levels (dB re 1 [micro]Pa)
                                          (Hz)            [micro]Pa)
----------------------------------------------------------------------------------------------------------------
                                                                               190          180          160
                                     ---------------------------------------------------------------------------
                                                        Distance (m)
----------------------------------------------------------------------------------------------------------------
2 GI-guns 105 in\3\.................       10-188  ~240(peak-to-peak)....           20           70          670
----------------------------------------------------------------------------------------------------------------

    Considering the circumference of the area ensonified to the 160 dB 
isopleth extends to 1,340 m (twice the 670 m radius); that the GI-gun 
array is towed approximately 2-9 m below the surface at a speed of 4 
knots (7.4 km/hr), and that the seismic oceanographic surveys would be 
conducted for 14 days for 24 hrs/day, the Navy estimates that the

[[Page 71943]]

seismic oceanographic survey distance would encompass 1,344 Nm (2,489 
km). Multiplying the total linear distance of the seismic oceanographic 
survey by the area ensonified to the 160 dB isopleth (1,340 m), yields 
a total ensonified area of approximately 3,335 km \2\.

Ocean Surveyor ADCP

    A hull-mounted Teledyne RD Instruments Ocean Surveyor ADCP (TRDI OS 
ADCP) would be operated at 38 kHz with acoustic output pressure of 224 
dB re 1 [micro]Pa. The beamwidth would be 30 degrees off nadir and the 
acoustic pressure along each beam is estimated at 180 dB re 1 [micro]Pa 
at 114 m. The TRDI OS ADCP would operate concurrently with the GI-gun 
array and intermittently to map the distribution of water currents and 
suspended materials in the water column.

Lowered ADCP (L-ADCP)

    A lowered Teledyne RD Instruments ADCP (L-ADCP) would be mounted on 
a rosette with a conductivity-temperature-depth gauge. The beamwidth 
would be 30 degrees off nadir and the output pressure would be 216 dB 
re 1 [micro]Pa at 300 kHz. The L-ADCP would be deployed intermittently 
to collect hydrographic data.

Moored ADCP

    Up to four long-range ADCPs (LR-ADCPs) would be anchored on the 
seafloor using 400 kilograms (kg) of scrap iron (assemblage of four 
scrap locomotive wheels). LR-ADCPs would be moored to the seafloor at 
an estimated 3,000 m, such that they float at a depth of 500 m below 
the sea surface. LR-ADCPs would be suspended from the iron anchorage 
assemblies by a single line comprised of \3/4\-inch (in) nylon line and 
\1/2\-in wire rope. The LR-ADCPs and suspension line would be recovered 
at the close of the study via an acoustic release and the iron 
anchorage assembly would remain on the sea floor. The acoustic source 
frequency would be 75 kHz with an output pressure level of 200 dB re 1 
[micro]Pa at a rate of once per second. The beamwidth would be four 
degrees and directed vertically upward at 20 degrees. LR-ADCPs would be 
moored several kilometers apart, in the area of the ARC/ACC frontal 
system, with exact mooring locations to be determined onsite due to the 
natural meander of the currents and front. LR-ADCPs would operate 
continuously for the estimated 14 days of research before being 
recovered.

Multibeam Echosounder

    The Melville would operate a hull-mounted Kongsberg EM 122 
multibeam echosounder (MBES) at 10.5 to 13 kilohertz (kHz). The MBES 
would generate acoustic pulses in a downward fan-shaped beam, one 
degree fore-aft and 150 degrees athwartship. For deep water operations, 
each ``ping'' is comprised of eight (> 1,000 m depth; 3,280 ft) or four 
(< 1,000 m depth; 3,280 ft) successive acoustic transmissions 2 to 100 
milliseconds (ms) in duration. The maximum sound pressure output level 
would be 242 dB re 1 [micro]Pa.

Sub-Bottom Profiler

    The Melville would also operate a Knudsen 320B/R sub-bottom 
profiler (SBP). The SBP is dual-frequency and operates at 3.5 and 12 
kHz with maximum power outputs of 10 kilowatts (kW) and 2 kW, 
respectively. The pulse length used during this study would be 0.8 to 
24 ms, relative to water depth and sediment characteristics. The pulse 
repetition rates would be between 0.5 and 2 seconds (s) in shallow 
water and up to 8 s in deep water. A common operational mode is 
broadcast of five pulses at 1-s intervals followed by a 5-s delay. 
Maximum acoustic output pressure would be 211 dB re 1 [micro]Pa at 3.5 
kHz; however, systems are typically used at 80 percent capacity. The 
SPB emits a downward conical beam with a width of about 30 degrees.

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

    Forty marine mammal species are known to inhabit waters between 
South Africa and Antarctica. 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.) and depleted under the MMPA, including the 
southern right (Eubalaena australis), humpback (Megaptera 
novaeangliae), sei (Balaenoptera borealis), fin (Balaenoptera 
physalus), blue (Balaenoptera musculus), and sperm (Physeter 
macrocephalus) whales. Most of the species occurring in the area spend 
the austral summer in preferred Antarctic habitats, and the austral 
winter in areas northward around the east and west coasts of Africa, 
South America, Australia, and islands of the Indian Ocean. The cape fur 
seal is the only pinniped known to have breeding colonies along the 
southern coast of Africa. It is not listed as threatened or endangered 
under the ESA. Cape fur seals are endemic to South Africa, with 
colonies on islands and patches of mainland along the southern coast.
    Table 3 provides estimates of the average (best) and maximum marine 
mammal population densities in the area of the proposed study during 
the austral summer, anticipated occurrence of each species in the area 
of research during that time, primary habitat(s), and ESA listing 
status.

  Table 3--Habitat, Regional Abundance, and Conservation Status of Marine Mammals That May Occur in or Near the
                 Proposed Seismic Survey Areas Off Southern Africa in the Southwest Indian Ocean
     [See text and Tables 2.0-2.2 in the Navy's application and environmental analysis for further details.]
----------------------------------------------------------------------------------------------------------------
                                     Occurrence in                                                 Density
             Species               survey area during        Habitat            ESA\1\     ---------------------
                                  the Austral  summer                                          Best       Max
----------------------------------------------------------------------------------------------------------------
Mysticetes
    Antarctic minke whale.......  Rare...............  Pelagic and coastal  NL............     < 0.01       0.01
    Blue whale..................  Rare...............  Pelagic and coastal  E.............     < 0.01     < 0.01
    Bryde's whale...............  Common.............  Pelagic and coastal  NL............     < 0.01     < 0.01
    Common minke whale..........  Rare...............  Pelagic and coastal  NL............       0.03       0.05
    Fin whale...................  Rare...............  Continental shelf    E.............     < 0.01       0.01
                                                        and slope and
                                                        pelagic.
    Humpback whale..............  Rare...............  Mainly nearshore     E.............     < 0.01     < 0.01
                                                        waters and banks.
    Sei whale...................  Rare...............  Pelagic............  E.............     < 0.01     < 0.01
Odontocetes
    Arnoux's beaked whale.......  Rare...............  Deep water.........  NL............     < 0.01       0.01

[[Page 71944]]

 
    Cuvier's beaked whale.......  Common.............  Pelagic............  NL............     < 0.01     < 0.01
    Dwarf sperm whale...........  Indeterminate......  Continental shelf    NL............     < 0.01     < 0.01
                                                        an deep water.
    Gray's beaked whale.........  Rare...............  Deep water.........  NL............     < 0.01     < 0.01
    Hector's beaked whale.......  Rare...............  Deep water.........  NL............     < 0.01     < 0.01
    Pygmy right whale...........  Indeterminate......  Continental shelf..  NL............     < 0.01     < 0.01
    Pygmy sperm whale...........  Indeterminate......  Continental shelf    ..............     < 0.01     < 0.01
                                                        and deep water.
    Southern bottlenose whale...  Rare...............  Deep water.........  NL............       0.01       0.01
    Southern right whale........  Common.............  Coastal and pelagic  E.............     < 0.01     < 0.01
    Sperm whale.................  Common.............  Pelagic and deep     E.............       0.01       0.01
                                                        water.
    Strap-toothed whale.........  Common.............  Deep water.........  NL............     < 0.01     < 0.01
    True's beaked whale.........  Common.............  Deep water.........  NL............     < 0.01     < 0.01
    Common bottlenose dolphin...  Common.............  Coastal and pelagic  ..............       0.04       0.10
    Dusky dolphin...............  Rare...............  Coastal and pelagic  NL............     < 0.01     < 0.01
    False killer whale..........  Indeterminate......  Pelagic............  NL............     < 0.01     < 0.01
    Fraser's dolphin............  n/a................  Deep water.........  NL............        n/a        n/a
    Heaviside's dolphin.........  Rare...............  Coastal and deep     NL............     < 0.01       0.01
                                                        water.
    Hourglass dolphin...........  Rare...............  Coastal and pelagic  NL............     < 0.01     < 0.01
    Indo-pacific bottlenose       n/a................  Coastal and          NL............        n/a        n/a
     dolphin.                                           continental shelf.
    Indo-pacific hump-backed      n/a................  Coastal............  NL............        n/a        n/a
     dolphin.
    Killer whale................  Common.............  Ubiquitous.........  NL............       0.01       0.01
    Long-beaked common dolphin..  Common.............  Coastal and          NL............     < 0.01     < 0.01
                                                        continental shelf.
    Long-finned pilot whale.....  Rare...............  Continental shelf    NL............       0.05       0.10
                                                        and slope and
                                                        pelagic.
    Pantropical spotted dolphin.  Indeterminate......  Coastal and pelagic  NL............       0.01       0.01
    Pygmy killer whale..........  Rare...............  Deep water.........  NL............     < 0.01     < 0.01
    Risso's dolphin.............  Common.............  Deep water.........  NL............       0.06       0.10
    Rough-toothed dolphin.......  Rare...............  Deep water.........  NL............     < 0.01     < 0.01
    Short-beaked common dolphin.  Common.............  Continental shelf    NL............       0.24       0.38
                                                        and slope and
                                                        pelagic.
    Short-finned pilot whale....  Rare...............  Pelagic............  NL............       0.03       0.04
    Southern right whale dolphin  Common.............  Deep water.........  NL............       0.01       0.02
    Spinner dolphin.............  Common.............  Coastal and pelagic  NL............     < 0.01       0.01
    Striped dolphin.............  Common.............  Continental shelf    NL............       0.19       0.31
                                                        and slope and
                                                        pelagic.
Pinnipeds
    Cape fur seal...............  Rare...............  Islands and          NL............       0.04        n/a
                                                        mainland.
----------------------------------------------------------------------------------------------------------------
n/a Not available or not assessed.
\1\ U.S. Endangered Species Act: EN = Endangered, T = Threatened, NL = Not listed.
\18\ Galapagos Islands (Alava and Salazar, 2006).

    Refer to section 2.0 of the Navy'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 the Navy calculated the estimated densities for the marine mammals 
in the proposed survey area. While Table 3 lists all 40 species known 
to inhabit the proposed survey area, the Navy is only requesting take 
authorization for 29 species. The Navy does not anticipate take, nor is 
NMFS proposing to authorize take, for the following species: Blue 
whale, Bryde's whale, dwarf sperm whale, pygmy right whale, pygmy sperm 
whale, dusky dolphin, Fraser's dolphin, heaviside's dolphin, Indo-
Pacific bottlenose dolphin, Indo-Pacific hump-backed dolphin, and Cape 
fur seal. This is based on population density estimates for cetaceans 
and the total ensonified area of the proposed activity. Cape fur seals 
are not expected to be harassed because their primary habitat is among 
the bays of the South African coastline, more than 30 Nm away from the 
proposed survey activities.

Potential Effects of the Specified Activity on Marine Mammals

    Acoustic stimuli generated by the operation of 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 considered an injury but rather a type of Level B harassment 
(Southall et al., 2007). Although the possibility cannot be entirely 
excluded, it is unlikely that the

[[Page 71945]]

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 mammal 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). Marine mammals are 
highly dependent on sound, and their ability to recognize sound signals 
amid other noise is important in communication, predator and prey 
detection, and, in the case of toothed whales, echolocation. 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). Even in the absence of manmade sounds, 
the sea is usually noisy. Background ambient noise often interferes 
with or masks the ability of an animal to detect a sound signal even 
when that signal is above its absolute hearing threshold. Natural 
ambient noise includes contributions from wind, waves, precipitation, 
other animals, and (at frequencies above 30 kHz) thermal noise 
resulting from molecular agitation (Richardson et al., 1995). 
Background noise can also include sounds from human activities. Masking 
of natural sounds can result when human activities produce high levels 
of background noise. Conversely, if the background level of underwater 
noise is high, (e.g., on a day with strong wind and high waves), an 
anthropogenic noise source will not be detectable as far away as would 
be possible under quieter conditions and will itself be masked.
    Masking effects of pulsed sounds 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 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.
    Although some degree of masking is inevitable when high levels of 
manmade broadband sounds are introduced into the sea, marine mammals 
have evolved systems and behavior that function to reduce the impacts 
of masking. Structured signals, such as the echolocation click 
sequences of small toothed whales, may be readily detected even in the 
presence of strong background noise because their frequency content and 
temporal features usually differ strongly from those of the background 
noise (Au and Moore, 1988, 1990). The components of background noise 
that are similar in frequency to the sound signal in question primarily 
determine the degree of masking of that signal.
    There is evidence of other marine mammal species continuing to call 
in the presence of industrial activity. For example, bowhead whale 
calls are frequently detected in the presence of seismic pulses, 
although the number of calls detected may sometimes be reduced 
(Richardson et al., 1986; Greene et al., 1999; Blackwell et al., 2009). 
Additionally, annual acoustical monitoring near BP's Northstar 
production facility during the fall bowhead migration westward through 
the Beaufort Sea has recorded thousands of calls each year (for 
examples, see Richardson et al., 2007; Aerts and Richardson, 2008). 
Construction, maintenance, and operational activities have been 
occurring from this facility for more than 10 years. To compensate and 
reduce masking, some mysticetes may alter the frequencies of their 
communication sounds (Richardson et al., 1995a; Parks et al., 2007). 
Masking processes in baleen whales are not amenable to laboratory 
study, and no direct measurements on hearing sensitivity are available 
for these species. It is not currently possible to determine with 
precision the potential consequences of temporary or local background 
noise levels. However, Parks et al. (2007) found that right whales 
altered their vocalizations, possibly in response to background noise 
levels. For species that can hear over a relatively broad frequency 
range, as is presumed to be the case for mysticetes, a narrow band 
source may only cause partial masking. Richardson et al. (1995a) note 
that a bowhead whale

[[Page 71946]]

20 km (12.4 mi) from a human sound source, such as that produced during 
oil and gas industry activities, might hear strong calls from other 
whales within approximately 20 km (12.4 mi), and a whale 5 km (3.1 mi) 
from the source might hear strong calls from whales within 
approximately 5 km (3.1 mi). Additionally, masking is more likely to 
occur closer to a sound source, and distant anthropogenic sound is less 
likely to mask short-distance acoustic communication (Richardson et 
al., 1995a).
    Redundancy and context can also facilitate detection of weak 
signals. These phenomena may help marine mammals detect weak sounds in 
the presence of natural or manmade noise. Most masking studies in 
marine mammals present the test signal and the masking noise from the 
same direction. The sound localization abilities of marine mammals 
suggest that, if signal and noise come from different directions, 
masking would not be as severe as the usual types of masking studies 
might suggest (Richardson et al., 1995). The dominant background noise 
may be highly directional if it comes from a particular anthropogenic 
source such as a ship or industrial site. Directional hearing may 
significantly reduce the masking effects of these noises by improving 
the effective signal-to-noise ratio. In the cases of high-frequency 
hearing by the bottlenose dolphin, beluga whale, and killer whale, 
empirical evidence confirms that masking depends strongly on the 
relative directions of arrival of sound signals and the masking noise 
(Penner et al., 1986; Dubrovskiy, 1990; Bain et al., 1993; Bain and 
Dahlheim, 1994). Toothed whales, and probably other marine mammals as 
well, have additional capabilities besides directional hearing that can 
facilitate detection of sounds in the presence of background noise. 
There is evidence that some toothed whales can shift the dominant 
frequencies of their echolocation signals from a frequency range with a 
lot of ambient noise toward frequencies with less noise (Au et al., 
1974, 1985; Moore and Pawloski, 1990; Thomas and Turl, 1990; Romanenko 
and Kitain, 1992; Lesage et al., 1999). A few marine mammal species are 
known to increase the source levels or alter the frequency of their 
calls in the presence of elevated sound levels (Dahlheim, 1987; Au, 
1993; Lesage et al., 1993, 1999; Terhune, 1999; Foote et al., 2004; 
Parks et al., 2007, 2009; Di Iorio and Clark, 2009; Holt et al., 2009).
    These data demonstrating adaptations for reduced masking pertain 
mainly to the very high frequency echolocation signals of toothed 
whales. There is less information about the existence of corresponding 
mechanisms at moderate or low frequencies or in other types of marine 
mammals. For example, Zaitseva et al. (1980) found that, for the 
bottlenose dolphin, the angular separation between a sound source and a 
masking noise source had little effect on the degree of masking when 
the sound frequency was 18 kHz, in contrast to the pronounced effect at 
higher frequencies. Directional hearing has been demonstrated at 
frequencies as low as 0.5-2 kHz in several marine mammals, including 
killer whales (Richardson et al., 1995). This ability may be useful in 
reducing masking at these frequencies. In summary, high levels of noise 
generated by anthropogenic activities may act to mask the detection of 
weaker biologically important sounds by some marine mammals. This 
masking may be more prominent for lower frequencies. For higher 
frequencies, such as that used in echolocation by toothed whales, 
several mechanisms are available that may allow them to reduce the 
effects of such masking.
    In general, NMFS expects the masking effects of seismic pulses to 
be minor, given the normally intermittent nature of seismic pulses, the 
frequency and output pressure of the dual GI-guns, and the likelihood 
that marine mammals may avoid the sound source.

Behavioral Disturbance

    Behavioral disturbance includes a variety of effects, including 
subtle to conspicuous changes in behavior, movement, and displacement. 
Marine mammal 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 proximity to activities and/or exposed to a particular level 
of 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 and small toothed 
whales, 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, 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 altering 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.
    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

[[Page 71947]]

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 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 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

[[Page 71948]]

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). Similarly, recent 
empirical observations indicate that delphinids have been frequently 
observed within the 160 dB isopleth during seismic survey operations 
(LGL 2009, 2010b). 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.
    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. 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 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, seem to be confined to a smaller radius than 
has been observed for the more responsive of the mysticetes and other 
odontocetes.

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, 
can be limited to a particular frequency range, and can be in varying 
degrees (i.e., a loss of a certain number of dBs of sensitivity). 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). As illustrated 
previously in Table 2, the Melville's airguns are expected to reach or 
exceed 180 dB re: 1 [micro]Pa at 70 m (230 ft).
    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. The established 180-dB re 1 
[micro]Pa (rms) criterion is the received level above which, in the 
view of a panel of bioacoustics specialists convened by NMFS before 
additional TTS measurements for marine mammals became available, one 
could not be certain that there would be no injurious effects, auditory 
or otherwise, to marine mammals. TTS is considered by NMFS to be a type 
of Level B (non-injurious) harassment. The 180-dB level is a shutdown 
criterion applicable to cetaceans, as specified by NMFS (2000) and is 
used to establish an exclusion zone (EZ), as appropriate. NMFS also 
assumes that cetaceans exposed to levels exceeding 160 dB re: 1 [mu]Pa 
(rms) may experience Level B harassment.

[[Page 71949]]

    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, 
auditor