[Federal Register Volume 73, Number 228 (Tuesday, November 25, 2008)]
[Notices]
[Pages 71606-71620]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: E8-27895]
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DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
RIN 0648-XK83
Incidental Takes of Marine Mammals During Specified Activities;
Marine Seismic Surveys in the Southwest Pacific Ocean, January-
February, 2009
AGENCY: National Marine Fisheries Service (NMFS), National Oceanic and
Atmospheric Administration (NOAA), Commerce.
ACTION: Notice; proposed incidental take authorization; request for
comments.
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SUMMARY: NMFS has received an application from the Lamont-Doherty
Earth Observatory (L-DEO) for an Incidental Harassment Authorization
(IHA) to take small numbers of marine mammals, by harassment,
incidental to conducting a seismic survey in the southwest Pacific
Ocean. Pursuant to the Marine Mammal Protection Act (MMPA), NMFS
requests comments on its proposal to authorize L-DEO to take, by Level
B harassment only, small numbers of marine mammals incidental to
conducting a marine seismic survey during January through February,
2009.
DATES: Comments and information must be received no later than
December 26, 2008.
ADDRESSES: Comments on the application should be addressed to 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 email comments is [email protected]. Comments sent via
e-mail, including all attachments, must not exceed a 10-megabyte file
size.
A copy of the application containing a list of the references used
in this document may be obtained by writing to the address specified
above, telephoning the contact listed below (see FOR FURTHER
INFORMATION CONTACT), or visiting the internet at: http://www.nmfs.noaa.gov/pr/permits/incidental.htm.
Documents cited in this notice may be viewed, by appointment,
during regular business hours, at the aforementioned address.
FOR FURTHER INFORMATION CONTACT: Jeannine Cody or Ken Hollingshead,
Office of Protected Resources, NMFS, (301) 713-2289.
SUPPLEMENTARY INFORMATION:
Background
Sections 101(a)(5)(A) and (D) of the MMPA (16 U.S.C. 1361 et seq.)
direct the Secretary of Commerce to allow, upon request, the
incidental, but not intentional, taking of marine mammals by United
States citizens who engage in a specified activity (other than
commercial fishing) within a specified geographical region if certain
findings are made and either regulations are issued or, if the taking
is limited to harassment, a notice of a proposed authorization is
provided to the public for review.
Authorization for incidental taking shall be granted if NMFS finds
that the taking will have a negligible impact on the species or
stock(s), will not have an unmitigable adverse impact on the
availability of the species or stock(s) for subsistence uses, and if
the permissible methods of taking and requirements pertaining to the
mitigation, monitoring and reporting of such takings are set forth.
NMFS has defined ``negligible impact'' in 50 CFR 216.103 as ``...an
impact resulting from the specified activity that cannot be reasonably
expected to, and is not reasonably likely to, adversely affect the
species or stock through effects on annual rates of recruitment or
survival.''
Section 101(a)(5)(D) of the MMPA established an expedited process
by which citizens of the United States can apply for an authorization
to incidentally take small numbers of marine mammals by harassment.
Except with respect to certain activities not pertinent here, the MMPA
defines ``harassment'' as:
any act of pursuit, torment, or annoyance which (i) has the
potential to injure a marine mammal or marine mammal stock in the
wild [``Level A harassment'']; or (ii) has the potential to disturb
a marine mammal or marine mammal stock in the wild by causing
disruption of behavioral patterns, including, but not limited to,
migration, breathing, nursing, breeding, feeding, or sheltering
[``Level B harassment'';].
Section 101(a)(5)(D) establishes a 45-day time limit for NMFS'
review of an application followed by a 30-day public notice and comment
period on any proposed authorizations for the incidental harassment of
small numbers of marine mammals. Within 45 days of the close of the
comment period, NMFS must either issue or deny issuance of the
authorization.
Summary of Request
On August 18, 2008, NMFS received an application from L-DEO for the
taking by Level B harassment only, of small numbers of 29 species of
marine mammals incidental to conducting, with
[[Page 71607]]
research funding from the National Science Foundation (NSF), a marine
seismic survey within the Exclusive Economic Zone (EEZ) of Tonga in the
southwest Pacific Ocean during January through February 2009.
L-DEO proposes to tomographically image the crust and uppermost
mantle of the Eastern Lau Spreading Center (ELSC). The survey area is
approximately 42 kilometers (km) offshore from Tonga in water depths
ranging from 1000 - 2600 meters (m). L-DEO chose to survey the ELSC
because it provides the best site to study the complete range of
spreading center processes, magma storage and thermal systems. This
study is part of NSF's RIDGE 2000 program, which was developed to
facilitate the study of mid-ocean ridges and back-arc spreading
centers. These areas mark the boundaries where oceanic plates separate
from one another. Around the mid-ocean ridges, heat from the mantle
drives vast hydrothermal systems that influence ocean water chemistry
and nourish enormous ecosystems. These data are integral to
understanding how mid-ocean ridges influence global climatic conditions
and to understanding plate tectonic processes and their effects on
earthquake occurrence and distribution.
Description of the Specified Activity
The planned survey will involve one source vessel, the R/V Marcus
G. Langseth (Langseth), a seismic vessel owned by the NSF. The proposed
project is scheduled to commence on January 14, 2009, and end on
February 21, 2009. The vessel will depart Nuku'alofa, Tonga on January
14, 2009 for a one-day transit to the study area in the Lau Basin in
the southwest Pacific Ocean (between 19-21[deg] S. and 175-176[deg]
W.).
To obtain high-resolution three-dimensional (3D) structures of the
Lau Basin's magmatic systems and thermal structures, the Langseth will
deploy a towed array of 36 airguns with a total discharge volume of
approximately 6,600 cubic inches (in\3\). The Langseth will also deploy
55 to 64 Ocean Bottom Seismometers (OBS) for the survey. As the airgun
array is towed along the survey lines, the OBS will receive the
returning acoustic signals and record them internally for later
analysis. In addition to the OBS, L-DEO may use a relatively short (up
to 6-km) hydrophone streamer to receive the returning acoustic signals
and transfer the data to the on-board processing system.
The seismic survey effort (e.g., equipment testing, startup, line
changes, repeat coverage of any areas, and equipment recovery) will
require approximately 19 days to complete 42 transects of variable
lengths, totaling 3650 km and will include approximately 456 hours of
airgun operation. Please see L-DEO's application for more detailed
information. The proposed seismic transects will provide a
tomographical image in three dimensions of the physical properties of
the crust and uppermost mantle of this area. The exact dates of the
activities will depend on logistics, weather conditions, and the need
to repeat some lines if data quality is substandard.
Vessel Specifications
The Langseth, operated by L-DEO, was designed as a seismic research
vessel, with a propulsion system designed to be as quiet as possible to
avoid interference with the seismic signals. 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 2925, can accommodate up
to 55 people. The ship is powered by two Bergen BRG-6 diesel engines,
each producing 3550 horsepower (hp), which drive the two propellers
directly. 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
operation speed during seismic acquisition is typically 7.4B9.3 km/h
(4-5 knots). When not towing seismic survey gear, the Langseth can
cruise at 20B24 km/h (11-13 knots). The Langseth has a range of 25,000
km (13,499 nautical miles). The Langseth will also serve as the
platform from which vessel-based marine mammal (and sea turtle)
observers will watch for animals before and during airgun operations.
Acoustic Source Specifications
Seismic Airguns
The full airgun array for the survey consists of 36 airguns (a
mixture of Bolt 1500LL and Bolt 1900LLX airguns ranging in size from 40
to 360 in\3\), with a total volume of approximately 6,600 in\3\ and a
firing pressure of 1900 pounds per square inch (psi). The airgun array
will fire every 400 m or 180 seconds. The dominant frequency component
is 2-188 Hertz (Hz).
The array configuration consists of four identical linear arrays or
strings, with 10 airguns on each string; the first and last airguns
will be spaced 16 m (52 ft) apart. For each operating string, nine
airguns will be fired simultaneously, whereas the tenth is kept in
reserve as a spare, to be turned on in case of failure of another
airgun. The four airgun strings will be distributed across an
approximate area of 24H16 m (79 x 52 ft) behind the Langseth and will
be towed approximately 50-100 m (164-328 ft) behind the vessel at a
tow-depth of 9-12 m (29.5-39.4 ft). The airgun array will fire for a
brief (0.1 second (s)) pulse every 180 s. The array will remain silent
at all other times.
Multibeam Echosounder
The Langseth will operate a Simrad EM120 multibeam echosounder
(MBES) simultaneously during airgun operations to map characteristics
of the ocean floor. The hull-mounted MBES emits brief pulses of mid- or
high-frequency (11.25-12.6 kHz) sound in a fanshaped beam that extends
downward and to the sides of the ship. The beamwidth is 1[deg] fore-aft
and 150[deg] athwartship. The maximum source level is 242 dB re 1
microPam (root mean square (rms)). For deep-water operation,
each ``ping'' consists of nine successive fan-shaped transmissions,
each 15 millisecond (ms) in duration and each ensonifying a sector that
extends 1[deg] foreBaft. The nine successive transmissions span an
overall cross-track angular extent of about 150[deg], with 16 ms gaps
between the pulses for successive sectors. A receiver in the overlap
area between two sectors would receive two 15-ms pulses separated by a
16-ms gap. In shallower water, the pulse duration is reduced to 5 or 2
ms, and the number of transmit beams is also reduced. The ping interval
varies with water depth, from approximately 5 s at 1000 m (3,281 ft) to
20 s at 4000 m (13,124 ft).
Sub-bottom Profiler
The Langseth will operate a sub-bottom profiler (SBP) continuously
throughout the cruise with the MBES. An SBP operates at mid- to high
frequencies and is generally used simultaneously with an MBES to
provide information about the sedimentary features and bottom
topography. SBP pulses are directed downward at typical frequencies of
approximately 3 18 kHz. However, the dominant frequency component of
the SBP is 3.5 kHz which is directed downward in a narrow beam by a
hull-mounted transducer on the vessel. The SBP output varies with water
depth from 50 watts in shallow water to 800 watts in deep water and has
a normal source output (downward) of 200 dB re 1 microPa m and a
maximum source level output (downward) of 204 dB re 1 microPa
m.
[[Page 71608]]
The SBP used aboard the Langseth uses seven beams simultaneously,
with a beam spacing of up to 15 degrees ([deg]) and a fan width up to
30[deg]. Pulse duration is 0.4 100 ms at intervals of 1 s; a common
mode of operation is to broadcast five pulses at 1-s intervals followed
by a 5-s pause.
Characteristics of Airgun Pulses
Discussion of the characteristics of airgun pulses has been
provided in Appendix B of L-DEO=s application and in previous Federal
Register notices (see 69 FR 31792, June 7, 2004; 71 FR 58790, October
5, 2006; 72 FR 71625, December 18, 2007; or 73 FR 52950, September 12,
2008). Reviewers are referred to those documents for additional
information.
Safety Radii
To aid in estimating the number of marine mammals that are likely
to be taken, pursuant to the MMPA, and in developing effective
mitigation measures, NMFS applies certain acoustic thresholds that
indicate the received level at which Level A or Level B harassment
would occur in marine mammals were exposed, see Table 1.
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Predicted RMS Distances (m)
Source and Volume Tow Depth (m) -----------------------------------------------------------
190 dB 180 dB 160 dB
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Single Bolt airgun 40 in\3\ 9-12 12 40 385
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4 strings 36 airguns 6600 in\3\ 9 300 950 6000
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12 340 1120 6850
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Table 1. Predicted distances to which sound levels [gteqt] 190, 180, and 160 dB re 1 micro Pa might be received
in deep (>1000 m; 3280 ft) water from the 36 airgun array during the seismic survey, January - February, 2009.
The distance from the sound source at which an animal would be
exposed to these different received sound levels may be estimated and
is typically referred to as safety radii. These safety radii are
specifically used to help NMFS estimate the number of marine mammals
likely to be harassed by the proposed activity and in deciding how
close a marine mammal may approach an operating sound source before the
applicant will be required to power-down or shut down the sound source.
During this study, all survey efforts will take place in deep
(greater than 1000 m, 3820 ft) water. The L-DEO model does not allow
for bottom interactions, and thus is most directly applicable to deep
water and to relatively short ranges. L-DEO has summarized the modeled
distances for the planned airgun configuration in Table 1 which shows
the distances at which four rms sound levels (190 decibel (dB), 180 dB,
and 160 dB) are expected to be received from the 36-airgun array and a
single airgun operating in water greater than 1000 m (3,820 ft) in
depth.
The calculated distances are expected to overestimate the actual
distances to the corresponding Sound Pressure Levels (SPL), given the
deep-water results of Tolstoy et al. (2004a,b). Additional information
regarding how the safety radii were calculated and how the empirical
measurements were used to correct the modeled numbers may be found in
Section I and Appendix A of L-DEO's application.
The conclusion that the model predictions in Table 1 are
precautionary, relative to actual 180 and 190 dB (rms) radii, is based
on empirical data from the acoustic calibration of different airgun
configurations than those used on the Langseth (cf. Tolstoy et al.,
2004a,b); that sound source verification study was done in the northern
Gulf of Mexico. L-DEO has recently (late 2007/early 2008) conducted a
more extensive acoustic calibration study of the Langseth's 36-airgun
array, also in the northern Gulf of Mexico (LGL Ltd. 2006; Holst and
Beland, 2008). Distances where various sound levels (e.g., 190, 180,
and 160 dB re 1 microPa (rms) were received are being determined for
various airgun configurations and water depths. Those results are not
yet available. However, the empirical data from the 2007/2008
calibration study will be used to refine the exclusion zones proposed
above for use during survey, if the data are appropriate and available
at the time of the survey.
Description of Marine Mammals in the Activity Area
Twenty-nine marine mammal species may occur off the coast of Tonga,
including 21 odontocetes (toothed cetaceans, such as dolphins), and 8
mysticetes (baleen whales). Pinnipeds are unlikely to be encountered in
or near the Lau Basin survey area where seismic operations will occur,
and are, therefore, not addressed further in this document. Five of
these species are listed as endangered under the U.S. Endangered
Species Act (ESA), including the humpback (Megaptera novaeangelae), sei
(Balaenoptera borealis), fin (Balenoptera physalus), blue (Balenoptera
musculus), and sperm (Physeter macrocephalus) whales. This IHA will
only address requested take authorizations for cetaceans as L-DEO does
not expect to encounter pinnipeds that far offshore in the study area.
Thus L-DEO is not requesting any takes for pinnipeds in this IHA.
Table 2 below outlines the species, their habitat and abundance in
the proposed survey area, and the requested number of takes by both
instances and individuals.
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Maximum Estimate of Best Estimate of
Abundance in the SW Occurrence in the Individuals Best Estimate of Exposures Approx. % of
Species Habitat Pacific Survey Area --------------------- Individuals --------------------- Regional Population
Request Instances
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Mysticetes
---------------------------------
Humpback whale* Nearshore waters 6,200 Rare 3 1 3 0.01
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Sei whale* Offshore, pelagic 12,000 Common 3 1 3 0.01
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[[Page 71609]]
Fin whale* Pelagic, continental slope 3,031 Uncommon 3 1 3 0.03
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Blue whale* Pelagic, coastal 756 Uncommon 3 1 3 0.12
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Pygmy right whale Coastal, oceanic 0 Common 3 1 3 N.A.
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Minke whale Pelagic, coastal 155,000 Rare in Jan. 3 1 3 0.001
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Dwarf minke whale Coastal N.A. N.A. 3 1 3 N.A.
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Bryde's whale Pelagic, coastal 16,500 Common 14 4 15 0.02
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Odontocetes
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Sperm whale* Pelagic, deep seas 22,700 Common 22 6 22 0.03
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Pygmy sperm whale Deep waters off the shelf N.A. Common 353 96 358 N.A.
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Dwarf Sperm whale Deep waters off the shelf 11,200 Uncommon 353 96 358 0.85
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Cuvier's beaked whale Pelagic 20,000 Common 40 17 64 0.09
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Southern bottlenose whale Pelagic N.A. Rare 0 0 0 N.A.
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Longman's beaked whale Pelagic N.A. Uncommon 16 7 26 N.A.
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Blainville's beaked whale Pelagic 25,300 Common 40 17 64 0.07
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Ginkgo-toothed beaked whale Pelagic 25,300 Rare 16 7 26 0.03
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Rough-toothed dolphin Deep water 145,900 Uncommon 1,649 857 3,214 0.59
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Bottlenose dolphin Coastal, oceanic 243,500 Common 330 171 643 0.07
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Pantropical spotted dolphin Coastal, pelagic 1,298,400 Uncommon 1,649 857 3,214 0.07
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Spinner dolphin Coastal, pelagic 1,019,300 Rare 3,298 1,714 6,428 0.17
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Striped dolphin Continental shelf 1,918,000 Rare 330 171 643 0.01
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Fraser's dolphin Waters > 1000 m 289,300 Rare 989 514 1,929 0.18
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Short-beaked common dolphin Shelf, pelagic 2,210,900 Common 330 171 643 0.01
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Risso's dolphin Waters > 1000 m 175,800 Common 330 171 643 0.10
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Melon-headed whale Oceanic 45,400 Uncommon 152 43 163 0.10
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Pygmy killer whale Deep, pantropical 38,900 Uncommon 30 9 33 0.02
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False killer whale Pelagic 39,800 Uncommon 91 26 98 0.07
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Killer whale Widely distributed 8,500 Common 61 17 65 0.20
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Short-finned pilot whale Pelagic 160,200 Common 61 17 65 0.01
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[[Page 71610]]
Total 10,173 4,997 18,735 ...................
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Table 2. Abundance, preferred habitat, and commonness of the marine mammal species that may be encountered during the proposed survey within the Lau Basin survey area. The far right columns
indicate the estimated number of each species that will be exposed to 160 dB based on best and maximum density estimates. NMFS believes that, when mitigation measures are taken into
consideration, the activity is likely to result in take of numbers of animals less than those indicated by the column titled Maximum Estimate of Exposures - Request.
* Federally listed endangered species.
Detailed information regarding the status and distribution of these
marine mammals may be found in sections III and IV of L-DEO's
application.
Potential Effects of the Proposed Activity on Marine Mammals
Summary of Potential Effects of Airgun Sounds on Marine Mammals
The effects of sounds from airguns might include one or more of the
following: tolerance, masking of natural sounds, behavioral
disturbance, temporary or permanent hearing impairment, or non-auditory
physical or physiological effects (Richardson et al., 1995; Gordon et
al., 2004; Nowacek et al., 2007; Southall et al., 2007). Permanent
hearing impairment, in the unlikely event that it occurred, would
constitute injury, but temporary threshold shift (TTS) is not an injury
(Southall et al., 2007). Although the possibility cannot be entirely
excluded, it is unlikely that the project would result in any cases of
temporary or permanent hearing impairment, or any significant non-
auditory physical or physiological effects. Some behavioral disturbance
is expected, but is expected to be localized and short-term. These
effects are discussed below, but also in further detail in Appendix B
of L-DEO=s application.
Tolerance
Numerous studies have shown that pulsed sounds from airguns are
often readily detectable in the water at distances of many kilometers.
A summary of the characteristics of airgun pulses, is provided in
Appendix B of L-DEO's application. Several studies have also shown that
marine mammals at distances more than a few kilometers from operating
seismic vessels often show no apparent response (tolerance) (see
Appendix B of L-DEO's application ). That is often true even in cases
when the pulsed sounds must be readily audible to the animals based on
measured received levels and the hearing sensitivity of that mammal
group. Although various baleen whales, toothed whales, and (less
frequently) pinnipeds have been shown to react behaviorally to airgun
pulses under some conditions, at other times mammals of all three types
have shown no overt reactions. In general, pinnipeds usually seem to be
more tolerant of exposure to airgun pulses than cetaceans, with the
relative responsiveness of baleen and toothed whales being variable.
Masking
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, although there are very few specific data on this.
Because of the intermittent nature (one pulse every 180 seconds) and
low duty cycle of seismic pulses, animals can emit and receive sounds
in the relatively quiet intervals between pulses. However, in
exceptional 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). In the
northeastern Pacific Ocean, blue whale calls have been recorded during
a seismic survey off Oregon (McDonald et al., 1995). Among odontocetes,
there has been one report that sperm whales ceased calling when exposed
to pulses from a very distant seismic ship (Bowles et al., 1994), but
more recent studies found that they continued calling in the presence
of seismic pulses (Madsen et al., 2002c; Tyack et al., 2003; Smultea et
al., 2004; Holst et al., 2006; Jochens et al., 2006). 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;
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, masking effects of seismic pulses are expected to be minor,
given the normally intermittent nature of seismic pulses and the
Langseth being the only seismic vessel operating in the area for a
limited time. Masking effects on marine mammals are discussed further
in Appendix B of L-DEO's application.
Disturbance Reactions
Disturbance includes a variety of effects, including subtle to
conspicuous changes in behavior, movement, and displacement. Based on
NMFS (2001, p. 9293), NRC (2005), and Southall et al. (2007), we assume
that simple exposure to sound, or brief reactions that do not disrupt
behavioral patterns in a potentially significant manner, do not
constitute harassment or ``taking''. By potentially significant, we
mean ``in a manner that might have deleterious effects to the well-
being of individual marine mammals or their populations''.
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). 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
al.ne 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. 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
[[Page 71611]]
industrial activities and 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.
Detailed studies have been done on humpback 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. 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 of L-DEO's application, 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. 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 (Eshrichtius robustus), bowhead (Balena
mysticetes), and humpback whales have shown that seismic pulses with
received levels of 160 170 dB re 1 microPa (rms) seem to cause obvious
avoidance behavior in a substantial fraction of the animals exposed
(Richardson et al., 1995). In many areas, seismic pulses from large
arrays of airguns diminish to those levels at distances ranging from 4
15 km (2.5-9.3 mi) 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 of L-DEO's application 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
microPa (rms).
Responses of humpback whales to seismic surveys have been studied
during migration, on summer feeding grounds, and on Angolan winter
breeding grounds; there has also been discussion of effects on the
Brazilian wintering grounds. McCauley et al. (1998, 2000a) studied the
responses of humpback whales off Western Australia to a full-scale
seismic survey with a 16-airgun, 2678-in\3\ array, and to a single 20-
in\3\ airgun with source level 227 dB re 1 microPa m (peak to peak).
McCauley et al. (1998) documented that avoidance reactions began at 5-8
km (3-5 mi) from the array, and that those reactions kept most pods
approximately 3-4 km (1.8-2.5 mi) from the operating seismic boat.
McCauley et al. (2000a) noted localized displacement during migration
of 4-5 km (2.5-3.1 mi) by traveling pods and 7-12 km (4.3-7.5 mi) 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 microPa (rms) for humpback pods containing females, and at
the mean closest point of approach distance the received level was 143
dB re 1 microPa (rms). The initial avoidance response generally
occurred at distances of 5-8 km (3.1-4.9 mi) from the airgun array and
2 km (1.2 mi) from the single airgun. However, some individual humpback
whales, especially males, approached within distances of 100-400 m
(328-1312 ft), where the maximum received level was 179 dB re 1 microPa
(rms).
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). Malme et al.
reported that some of the humpbacks seemed startled at received levels
of 150 169 dB re 1 FPa and concluded that there was no clear evidence
of avoidance, despite the possibility of subtle effects, at received
levels up to 172 re 1 microPa on an approximate rms basis. It has been
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).
Various species of Balaenoptera (blue, sei, fin, and minke whales)
have occasionally been reported in areas ensonified by airgun pulses
(Stone, 2003; MacLean and Haley, 2004; Stone and Tasker, 2006).
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 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 versus 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
vs. 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; Angliss and Outlaw, 2008). 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
[[Page 71612]]
years (Richardson et al., 1987; Angliss and Outlaw, 2008).
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 application have been reported for
toothed whales. However, there are recent systematic studies on sperm
whales (Jochens et al., 2006; Miller et al., 2006), and 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;
Weir, 2008).
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).
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 1 km less, and some individuals
show no apparent avoidance. The beluga (Delphinapterus leucas) is a
species that (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 20 km (6.2-12.4 mi) compared with
20 30 km (12.4-18.6 mi) 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 truncates) 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 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 application 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., 2006).
There are almost no specific data on the behavioral reactions of
beaked whales to seismic surveys. However, northern bottlenose whales
(Hyperoodon ampullatus) continued to produce high-frequency clicks when
exposed to sound pulses from distant seismic surveys (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). Thus, it is likely that 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 ``Strandings and Mortality'' subsection,
later). These strandings are apparently at least in part 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 (see ``Strandings and
Mortality'', below). 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 (refer to Appendix B in L-
DEO's application).
Hearing Impairment and Other Physical Effects
Temporary or permanent hearing impairment is a possibility when
marine mammals are exposed to very strong sounds, and temporary
threshold shift (TTS) has been demonstrated and studied 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 al.ne permanent hearing damage, i.e.,
permanent threshold shift (PTS), in free-ranging marine mammals exposed
to sequences of airgun pulses during realistic field conditions. To
avoid the potential for injury, NMFS has determined that cetaceans and
pinnipeds should not be exposed to pulsed underwater noise at received
levels exceeding, respectively, 180 and 190 dB re 1
microParms. As summarized above, data that are now available
imply that TTS is unlikely to occur unless odontocetes (and probably
mysticetes as well) are exposed to airgun pulses stronger than 180 dB
re 1 microPa (rms).
Several aspects of the planned monitoring and mitigation measures
for this project are designed to detect marine mammals occurring near
the airgun array, and to avoid exposing them to sound pulses that
might, at least in theory, cause hearing impairment. In addition, many
cetaceans and (to a limited degree) pinnipeds and sea turtles are
likely to show some avoidance or the area with high received levels of
airgun sound. In those cases, the avoidance responses of the animals
themselves will reduce or (most likely) avoid any possibility of
hearing impairment.
Non-auditory physical effects might also occur in marine mammals
exposed to strong underwater pulsed sound. Possible types of non-
auditory physiological effects or injuries that might (in theory) occur
in mammals close to a strong sound source include stress, neurological
effects, bubble
[[Page 71613]]
formation, and other types of organ or tissue damage. It is possible
that some marine mammal species (i.e., beaked whales) may be especially
susceptible to injury and/or stranding when exposed to strong pulsed
sounds. However, as discussed below, there is no definitive evidence
that any of these effects occur even for marine mammals in close
proximity to large arrays of airguns. It is unlikely that any effects
of these types would occur during the proposed project given the brief
duration of exposure of any given mammal, the deep water in the survey
area, and the planned monitoring and mitigation measures (see below).
The following subsections discuss in somewhat more detail the
possibilities of TTS, PTS, and non-auditory physical effects.
Temporary Threshold Shift (TTS)
TTS is the mildest form of hearing impairment that can occur during
exposure to a strong sound (Kryter, 1985). While experiencing TTS, the
hearing threshold rises and a sound must be stronger in order to be
heard. 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).
For toothed whales exposed to single short pulses, the TTS
threshold appears to be, to a first approximation, a function of the
energy content of the pulse (Finneran et al., 2002, 2005). Sound
exposure level (SEL), which takes into account the duration of the
sound, is the metric used to measure energy and uses the units dB re 1
microPa\2\s, as opposed to SPL, which is the pressure metric
used in the rest of this document (units - dB re 1 microPa). Given the
available data, the received energy level of a single seismic pulse
(with no frequency weighting) might need to be approximately 186 dB re
1 microPa\2\s (i.e., 186 dB SEL or approximately 196 201 dB re
1 microPa (rms)) in order to produce brief, mild TTS. Exposure to
several strong seismic pulses that each have received levels near 190
dB re 1 microPa (rms) might result in cumulative exposure of
approximately 186 dB SEL and thus slight TTS in a small odontocete,
assuming the TTS threshold is (to a first approximation) a function of
the total received pulse energy. The distances from the Langseth's
airguns at which the received energy level (per pulse, flat-weighted)
would be expected to be 190 dB re 1 microPa (rms) or above, are shown
in Table 1. Levels 190 dB re 1 microPa (rms) or above are expected to
be restricted to radii no more than 340 m (1115.5 ft) (Table 1) from
the 36-airgun array. For an odontocete closer to the surface, the
maximum radius with 190 dB re 1 microPa (rms) or above, would be
smaller.
The above TTS information for odontocetes is derived from studies
on the bottlenose dolphin and beluga. There is no published TTS
information for other types of cetaceans. However, preliminary evidence
from a harbor porpoise exposed to airgun sound suggests that its TTS
threshold may have been lower (Lucke et al., 2007).
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). In any event,
no cases of TTS are expected given three considerations: (1) the low
abundance of baleen whales in most parts of the planned study area; (2)
the strong likelihood that baleen whales would avoid the approaching
airguns (or vessel) before being exposed to levels high enough for TTS
to occur; and (3) the mitigation measures that are planned.
In pinnipeds, TTS thresholds associated with exposure to brief
pulses (single or multiple) of underwater sound have not been measured.
Initial evidence from more prolonged (non-pulse) exposures suggested
that some pinnipeds (harbor seals in particular) incur TTS at somewhat
lower received levels than do small odontocetes exposed for similar
durations (Kastak et al., 1999, 2005; Ketten et al., 2001). The TTS
threshold for pulsed sounds has been indirectly estimated as being an
SEL of approximately 171 dB re 1 microPa\2\s (Southall et al.,
2007), which would be equivalent to a single pulse with received level
of approximately 181 186 dB re 1 FPa (rms), or a series of pulses for
which the highest rms values are a few dB lower. However, pinnipeds are
not expected to occur in or near the planned study area.
Permanent Threshold Shift (PTS)
When PTS occurs, there is physical damage to the sound receptors in
the ear. In severe cases, there can be total or partial deafness, while
in other cases; the animal has an impaired ability to hear sounds in
specific frequency ranges (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
(Richardson et al., 1995, p. 372ff). Single or occasional occurrences
of mild TTS are not indicative of permanent auditory damage.
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 of
L-DEO's application. 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 6 dB (Southall et al., 2007). On an SEL basis, Southall et
al. (2007:441-4) estimated that received levels would need to exceed
the TTS threshold by at least 15 dB for there to be risk of PTS. Thus,
for cetaceans they estimate that the PTS threshold might be a mammal-
weighted (M-weighted) SEL (for the sequence of received pulses) of
approximately 198 dB re 1 microPa\2\s (15 dB higher than the
TTS threshold for an impulse), where the SEL value is accumulated over
the sequence of pulses. Additional assumptions had to be made to derive
a corresponding estimate for pinnipeds, as the only available data on
TTS-thresholds in pinnipeds pertain to non-impulse sound. Southall et
al. (2007) estimate that the PTS threshold could be a cumulative
Mpw-weighted SEL of approximately 186 dB re 1
microPa2s in the harbor seal exposed to impulse sound. The PTS
threshold for the California sea lion and northern elephant seal the
PTS threshold would probably be higher, given the higher TTS thresholds
in those species.
[[Page 71614]]
Southall et al. (2007) also note that, regardless of the SEL, there
is concern about the possibility of PTS if a cetacean or pinniped
received one or more pulses with peak pressure exceeding 230 or 218 dB
re 1 FPa (peak), respectively. A peak pressure of 230 dB re 1 microPa
(3.2 barm, 0-peak) would only be found within a few meters of
the largest (360 in\3\) airgun in the planned airgun array (Caldwell
and Dragoset, 2000). A peak pressure of 218 dB re 1 microPa could be
received somewhat farther away; to estimate that specific distance, one
would need to apply a model that accurately calculates peak pressures
in the nearfield around an array of airguns.
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 and sea turtles. The planned
monitoring and mitigation measures, including visual monitoring, PAM,
power downs, and shut downs of the airguns when mammals are seen within
or approaching the exclusion zones, will further reduce the probability
of exposure of marine mammals to sounds strong enough to induce PTS.
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 (Gentry, 2002) and direct noise-induced bubble formation
(Crum et al., 2005) are not expected in the case of an impulsive source
like an airgun array. If seismic 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,
some odontocetes, and some pinnipeds, are especially unlikely to incur
non-auditory physical effects. Also, the planned mitigation measures,
including shut downs of the airguns, will reduce any such effects that
might otherwise occur.
Strandings and Mortality
Marine mammals close to underwater detonations of high explosives
can be killed or severely injured, and the auditory organs are
especially susceptible to injury (Ketten et al., 1993; Ketten, 1995).
However, explosives are no longer used for marine seismic research or
commercial seismic surveys, and 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 mass
strandings of beaked whales with naval exercises 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).
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.
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 1 kHz. Typical military mid-frequency sonars emit non-
impulse sounds at frequencies of 2 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; Fernandez 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 (Ziphius
cavirostris) in the Gulf of California, Mexico, when the L-DEO vessel
R/V Maurice Ewing was operating a 20-airgun, 8490-in\3\ airgun 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
[[Page 71615]]
vessel before being exposed to high sound levels; (2) the proposed
monitoring and mitigation measures; and (3) differences between the
sound sources operated by L-DEO and those involved in the naval
exercises associated with strandings.
Possible Effects of Multibeam Echosounder (MBES) Signals
The Simrad EM120 12-kHz MBES will be operated from the source
vessel continuously during the planned study. Sounds from the MBES are
very short pulses, occurring for 2 15 ms once every 5 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 microPam (rms). The beam is narrow (1[deg]) in fore-aft
extent and wide (150[deg]) in the cross-track extent. Each ping
consists of nine 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 nine
segments. Also, marine mammals that encounter the Simrad EM120 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 ship (where
the beam is narrowest) are especially unlikely to be ensonified for
more than one 2-15 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 Simrad EM120, and (2) are often directed close to omnidirectionally
versus more downward for the Simrad EM120. The area of possible
influence of the MBES is much smaller a narrow band below the source
vessel. The duration of exposure for a given marine mammal can be much
longer for naval sonar.
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 reactions of free-ranging marine mammals to sonar,
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 and no
dispersal by pilot whales (Globicephala spp.) (Rendell and Gordon,
1999), and the previously-mentioned beachings by beaked whales. During
exposure to a 21 25 kHz sonar with a source level of 215 dB re 1
microPam, gray whales reacted by orienting slightly away from
the source and being deflected from their course by approximately 200 m
(Frankel, 2005). When a 38-kHz echosounder and a 150-kHz acoustic
Doppler current profiler were transmitting during studies in the
Eastern Tropical Pacific, baleen whales showed no significant
responses, while spotted and spinner dolphins were detected slightly
more often and beaked whales less often during visual surveys
(Gerrodette and Pettis, 2005).
Captive bottlenose dolphins exhibited changes in behavior when
exposed to 1-s tonal signals at frequencies similar to those that will
be emitted by the MBES used by L-DEO, and to shorter broadband pulsed
signals. Behavioral changes typically involved what appeared to be
deliberate attempts to avoid the sound exposure (Schlundt et al., 2000;
Finneran et al., 2002; Finneran and Schlundt, 2004). The relevance of
those data to free-ranging odontocetes is uncertain, and in any case,
the test sounds were quite different in duration as compared with those
from an MBES.
Because of the unlikelihood of an animal being exposed to more than
one or two very brief pulses, NMFS does not expect the operation of the
MBES to result in the harassment of any marine mammals.
Possible Effects of the Sub-bottom Profiler Signals
An SBP may be operated from the source vessel at times during the
planned study. Sounds from the sub-bottom profiler are very short
pulses, occurring for 1 4 ms once every second. Most of the energy in
the sound pulses emitted by the SBP is at 3.5 kHz, and the beam is
directed downward in a narrow beam with a spacing of up to 15 and a fan
width up to 30 . The sub-bottom profiler on the Langseth has a maximum
source level of 204 dB re 1 microPam. Kremser et al. (2005)
noted that the probability of a cetacean swimming through the area of
exposure when a bottom profiler emits a pulse is small-even for an SBP
more powerful than that on the Langseth if the animal was in the area,
it would have to pass the transducer at close range and in order to be
subjected to sound levels that could cause TTS.
Marine mammal communications will not be masked appreciably by the
sub-bottom profiler signals given their directionality and the brief
period when an individual mammal is likely to be within its beam.
Furthermore, in the case of most baleen whales, the SBP signals do not
overlap with the predominant frequencies in the calls, which would
avoid significant masking.
Marine mammal behavioral reactions to other pulsed sound sources
are discussed above, and responses to the SBP are likely to be similar
to those for other pulsed sources if received at the same levels.
However, the pulsed signals from the SBP are considerably weaker than
those from the MBES. Therefore, behavioral responses would not be
expected unless marine mammals were to approach very close to the
source. This is not expected to occur because of the mitigation
measures and the likely avoidance behaviors of marine mammals.
It is unlikely that the SBP produces pulse levels strong enough to
cause hearing impairment or other physical injuries even in an animal
that is (briefly) in a position near the source. The SBP is usually
operated simultaneously with other higher-power acoustic sources. Many
marine mammals will move away in response to the approaching higher-
power sources or the vessel itself before the mammals would be close
enough for there to be any possibility of effects from the less intense
sounds from the SBP. In the case of mammals that do not avoid the
approaching vessel and its various sound sources, mitigation measures
that would be applied to minimize effects of other sources would
further reduce or eliminate any minor effects of the SBP.
Possible Effects of the Acoustic Release Signals
The acoustic release transponder used to communicate with the OBS
uses frequencies of 9 13 kHz. Once the OBS is ready to be retrieved, an
acoustic release transponder interrogates the OBS at a frequency of 9
11 kHz, and a response is received at a frequency of 9 13 kHz. These
signals will be used very intermittently. The source level of the
release signal is 190 dB (re 1 microPa at 1 m). An animal would have to
pass by the OBS at close range when the signal is emitted in order to
be exposed to any
[[Page 71616]]
pulses at that level. The sound is expected to undergo a spreading loss
of approximately 40 dB in the first 100 m (328 ft). Thus, any animals
located 100 m (328 ft) or more from the signal will be exposed to very
weak signals (less than 150 dB) that are not expected to have any
effects. The signal is used only for short intervals to interrogate and
trigger the release of the OBS and consists of pulses rather than a
continuous sound. Given the short duration use of this signal and rapid
attenuation in seawater it is unlikely that the acoustic release
signals would significantly affect marine mammals or sea turtles
through masking, disturbance, or hearing impairment. Any effects likely
would be negligible given the brief exposure at presumable low levels.
Proposed Monitoring and Mitigation Measures
Monitoring
L-DEO proposes to sponsor marine mammal monitoring during the
present project, in order to implement the proposed mitigation measures
that require real-time monitoring, and to satisfy the anticipated
monitoring requirements of the IHA. L-DEO's proposed Monitoring Plan is
described below this section. L-DEO understands that this monitoring
plan will be subject to review by NMFS, and that refinements may be
required. The monitoring work described here has been planned as a
self-contained project independent of any other related monitoring
projects that may be occurring simultaneously in the same regions. L-
DEO is prepared to discuss coordination of its monitoring program with
any related work that might be done by other groups insofar as this is
practical and desirable.
Vessel-based Visual Monitoring
Marine mammal observers (MMOs) will be based aboard the seismic
source vessel and will watch for marine mammals and turtles near the
vessel during daytime airgun operations and during any start-ups at
night. The MMOs will also watch for marine mammals and turtles near the
seismic vessel for at least 30 minutes (min) prior to the start of
airgun operations after an extended shut down. When feasible, MMOs will
also observe during daytime periods when the seismic system is not
operating for comparison of sighting rates and behavior with versus
without airgun operations. Based on MMOs' observations, the airguns
will be powered down or shut down when marine mammals are observed
within or about to enter a designated exclusion zone (EZ). The EZ is a
region in which a possibility exists of adverse effects on animal
hearing or other physical effects.
During seismic operations in the Lau Basin, at least three MMOs
will be based aboard the Langseth. MMOs will be appointed by L-DEO with
NMFS' concurrence. At least one MMO, and when practical two MMOs, will
monitor marine mammals and turtles near the seismic vessel during
ongoing daytime operations and nighttime start ups of the airguns. Use
of two simultaneous observers will increase the proportion of the
animals present near the source vessel that are detected. MMOs will be
on duty in shifts of duration no longer than 4 hours (h). Other crew
will also be instructed to assist in detecting marine mammals and
turtles and implementing mitigation requirements (if practical). Before
the start of the seismic survey the crew will be given additional
instruction regarding how to do so.
The Langseth is a suitable platform for marine mammal and turtle
observations. When stationed on the observation platform, the eye level
will be approximately 18 m (59 ft) above sea level, and the observer
will have a good view around the entire vessel. During daytime, the
MMOs will scan the area around the vessel systematically with reticle
binoculars (e.g., 7 50 Fujinon), Big-eye binoculars (25 150), and with
the naked eye. During darkness, night vision devices (NVDs) will be
available (ITT F500 Series Generation 3 binocularimage intensifier or
equivalent), when required. Laser rangefinding binoculars (Leica LRF
1200 laser rangefinder or equivalent) will be available to assist with
distance estimation. Those are useful in training observers to estimate
distances visually, but are generally not useful in measuring distances
to animals directly; that is done primarily with the reticles in the
binoculars.
The vessel-based monitoring will provide data to estimate the
numbers of marine mammals exposed to various received sound levels, to
document any apparent disturbance reactions or lack thereof, and thus
to estimate the numbers of mammals potentially ``taken'' by harassment.
It will also provide the information needed in order to power down or
shut down the airguns at times when mammals and turtles are present in
or near the safety radii. When a sighting is made, the following
information about the sighting will be recorded:
1. Species, group size, age/size/sex categories (if determinable),
behavior when first sighted and after initial sighting, heading (if
consistent), bearing and distance from seismic vessel, sighting cue,
apparent reaction to the airguns or vessel (e.g., none, avoidance,
approach, paralleling, etc.), and behavioral pace.
2. Time, location, heading, speed, activity of the vessel, sea
state, visibility, and sun glare.
The data listed under (2) will also be recorded at the start and
end of each observation watch, and during a watch whenever there is a
change in one or more of the variables.
All observations and power-downs or shut downs will be recorded in
a standardized format. Data will be entered into a custom database
using a notebook computer. The accuracy of the data entry will be
verified by computerized validity data checks as the data are entered
and by subsequent manual checking of the database. Preliminary reports
will be prepared during the field program and summaries forwarded to
the operating institution's shore facility and to NSF weekly or more
frequently.
Results from the vessel-based observations will provide:
1. The basis for real-time mitigation (airgun power-down or shut-
down).
2. Information needed to estimate the number of marine mammals
potentially taken by harassment, which must be reported to NMFS per
terms of MMPA authorizations or regulations.
3. Data on the occurrence, distribution, and activities of marine
mammals and turtles in the area where the seismic study is conducted.
4. Data on the behavior and movement patterns of marine mammals and
turtles seen at times with and without seismic activity.
Passive Acoustic Monitoring
Passive acoustic monitoring (PAM) will take place to complement the
visual monitoring program. Visual monitoring typically is not effective
during periods of bad weather or at night, and even with good
visibility, is unable to detect marine mammals when they are below the
surface or beyond visual range. Acoustical monitoring can be used in
addition to visual observations to improve detection, identification,
localization, and tracking of cetaceans. The acoustic monitoring will
serve to alert visual observers (if on duty) when vocalizing cetaceans
are detected. It is only useful when marine mammals call, but it can be
effective either by day or by night, and does not depend on good
visibility. It will be monitored in real time so that the visual
observers can be advised when cetaceans are detected. When bearings
(primary and mirror-
[[Page 71617]]
image) to calling cetacean(s) are determined, the bearings will be
relayed to the visual observer to help him/her sight the calling
animal(s).
The PAM system consists of hardware (i.e., hydrophones) and
software. The ``wet end'' of the system consists of a low-noise, towed
hydrophone array that is connected to the vessel by a ``hairy'' faired
cable. The array will be deployed from a winch located on the back
deck. A deck cable will connect from the winch to the main computer lab
where the acoustic station and signal conditioning and processing
system will be located. The lead-in from the hydrophone array is
approximately 400 m (1312 ft) long, and the active part of the
hydrophone array is approximately 56 m (184 ft) long. The hydrophone
array is typically towed at depths less than 20 m (66 ft).
The towed hydrophones will be monitored 24 h per day while at the
seismic survey area during airgun operations, and during most periods
when the Langseth is underway while the airguns are not operating. One
MMO will monitor the acoustic detection system at any one time, by
listening to the signals from two channels via headphones and/or
speakers and watching the real-time spectrographic display for
frequency ranges produced by cetaceans. MMOs monitoring the acoustical
data will be on shift for 1 6 h at a time. Besides the visual MMOs, an
additional MMO with primary responsibility for PAM will also be aboard.
All MMOs are expected to rotate through the PAM position, although the
most experienced with acoustics will be on PAM duty more frequently.
When a vocalization is detected while visual observations are in
progress, the acoustic MMO will contact the visual MMO immediately, to
alert him/her to the presence of cetaceans (if they have not already
been seen), and to allow a power down or shut down to be initiated, if
required. The information regarding the call will be entered into a
database. The data to be entered include an acoustic encounter
identification number, whether it was linked with a visual sighting,
date, time when first and last heard and whenever any additional
information was recorded, position and water depth when first detected,
bearing if determinable, species or species group (e.g., unidentified
dolphin, sperm whale), types and nature of sounds heard (e.g., clicks,
continuous, sporadic, whistles, creaks, burst pulses, strength of
signal, etc.), and any other notable information. The acoustic
detection can also be recorded for further analysis.
Mitigation
L-DEO's mitigation procedures are based on protocols used during
previous L-DEO seismic research cruises as approved by NMFS, and on
best practices recommended in Richardson et al. (1995), Pierson et al.
(1998), and Weir and Dolman (2007). The measures are described in
detail below this section.
Proposed Safety Zones
As noted earlier, L-DEO modeled received sound levels for the 36-
airgun array and for a single 1900LL 40-in\3\ airgun (which will be
used during power downs), in relation to distance and direction from
the airguns. Based on the modeling for deep water, the distances from
the source where sound levels are predicted to be 190, 180, and 160 dB
re 1 FPa (rms) were determined (Table 1). The 180- and 190-dB radii
vary with tow depth of the airgun array and range up to 1120 m and 340
m, respectively. The 180- and 190-dB levels are shut-down criteria
applicable to cetaceans and pinnipeds, respectively, as specified by
NMFS (2000); these levels were used to establish the safety zones. If
the MMO detects marine mammal(s) or turtle(s) within or about to enter
the appropriate safety radii, the airguns will be powered down (or shut
down if necessary) immediately (see below).
Mitigation During Operations
Mitigation measures that will be adopted during the L-DEO survey
include: (1) speed or course alteration, provided that doing so will
not compromise operational safety requirements; (2) power-down
procedures; (3) shut-down procedures; (4) ramp-up procedures; and (5)
special procedures for species of particular concern.
Speed or Course Alteration - If a marine mammal or sea turtle is
detected outside the safety zone and, based on its position and the
relative motion, is likely to enter the safety zone, the vessel's speed
and/or direct course may be changed. This would be done if practicable
while minimizing the effect on the planned science objectives. The
activities and movements of the marine mammal or sea turtle (relative
to the seismic vessel) will then be closely monitored to determine
whether the animal is approaching the applicable safety zone. If the
animal appears likely to enter the safety zone, further mitigative
actions will be taken, i.e., either further course alterations or a
power down or shut down of the airguns. Typically, during seismic
operations that use hydrophone streamers, the source vessel is unable
to change speed or course and one or more alternative mitigation
measures (see below) will need to be implemented.
Power-down Procedures - A power-down involves decreasing the number
of airguns in use such that the radius of the 180-dB (or 190-dB) zone
is decreased to the extent that marine mammals or turtles are no longer
in or about to enter the safety zone. A power-down of the airgun array
can also occur when the vessel is moving from one seismic line to
another. During a power-down for mitigation, one airgun will be
operated. The continued operation of one airgun is intended to alert
marine mammals and turtles to the presence of the seismic vessel in the
area. In contrast, a shut-down occurs when all airgun activity is
suspended.
If a marine mammal or turtle is detected outside the safety zone
but is likely to enter the safety radius, and if the vessel's speed
and/or course cannot be changed to avoid having the animal enter the
safety radius, the airguns will be powered down before the animal is
within the safety radius. Likewise, if a mammal or turtle is already
within the safety zone when first detected, the airguns will be powered
down immediately. During a power-down of the airgun array, the 40-in\3\
airgun will be operated. If a marine mammal or turtle is detected
within or near the smaller safety radius around that single airgun
(Table 1), it will be shut down (see next subsection).
Following a power-down, airgun activity will not resume until the
marine mammal or turtle has cleared the safety zone. The animal will be
considered to have cleared the safety zone if it: (1) is visually
observed to have left the safety zone; or (2) has not been seen within
the zone for 15 min in the case of small odontocetes; or (3) has not
been seen within the zone for 30 min in the case of mysticetes and
large odontocetes, including sperm, pygmy sperm, dwarf sperm, and
beaked whales; or (4) the vessel has moved outside the safety zone for
turtles, i.e., approximately 5 to 20 min, depending on the sighting
distance, vessel speed, and tow-depth.
Shut-down Procedures - During a power down, the operating airgun(s)
will be shut down if a marine mammal or turtle is seen within or
approaching the exclusion zone for a single airgun. Shut-downs will be
implemented (1) if an animal enters the exclusion zone of the single
airgun after a power-down has been initiated, or (2) if an animal is
initially seen within the exclusion zone of a single airgun when more
than one airgun (typically the full array) is
[[Page 71618]]
operating. Airgun activity will not resume until the marine mammal or
turtle has cleared the EZ, or until the visual marine mammal observer
(MMVO) is confident that the animal has left the vicinity of the
vessel. Criteria for judging that the animal has cleared the EZ will be
as described in the preceding subsection.
Ramp-up Procedures - A ramp-up procedure will be followed when the
airgun array begins operating after a specified period without airgun
operations or when a power-down has exceeded that period. It is
proposed that, for the present cruise, this period would be
approximately 9 min. This period is based on the largest modeled 180-dB
radius for the 36-airgun array (see Table 1) in relation to the planned
speed of the Langseth while shooting the airguns. Similar periods
(approximately 8 10 min) were used during previous L-DEO surveys.
Ramp-up will begin with the smallest gun in the array (40 in\3\).
Airguns will be added in a sequence such that the source level of the
array will increase in steps not exceeding 6 dB per 5-min period over a
total duration of about 35 min. During ramp-up, the MMOs will monitor
the safety zone and if marine mammals or turtles are sighted, a course/
speed change, power down, or shut down will be implemented as though
the full array were operational.
If the complete safety zone has not been visible for at least 30
min prior to the start of operations in either daylight or nighttime,
ramp-up will not commence unless at least one airgun (40 in\3\ or
similar) has been operating during the interruption of seismic survey
operations. Given these provisions, it is likely that the airgun array
will not be ramped up from a complete shut-down at night or in thick
fog, because the outer part of the safety zone for that array will not
be visible during those conditions. If one airgun has operated during a
power-down period, ramp-up to full power will be permissible at night
or in poor visibility, on the assumption that marine mammals and
turtles will be alerted to the approaching seismic vessel by the sounds
from the single airgun and could move away if they choose. Ramp-up of
the airguns will not be initiated if a sea turtle or marine mammal is
sighted within or near the applicable safety zones during the day or
close to the vessel at night.
Shutdown if Injured or Dead Whale is Found - In the unanticipated
event that any cases of marine mammal injury or mortality are found and
are judged likely to have resulted from these activities, L-DEO will
cease operating seismic airguns and report the incident to the Office
of Protected Resources, NMFS immediately.
Reporting
L-DEO will submit a report to NMFS within 90 days after the end of
the cruise. The report will describe the operations that were conducted
and sightings of marine mammals and turtles near the operations. The
report will provide full documentation of methods, results, and
interpretation pertaining to all monitoring. The 90-day report will
summarize the dates and locations of seismic operations, and all marine
mammal and turtle sightings (dates, times, locations, activities,
associated seismic survey activities). The report will also include
estimates of the number and nature of exposures that could result in
``takes'' of marine mammals by harassment or in other ways.
All injured or dead marine mammals (regardless of cause) must be
reported to NMFS as soon as practicable. Report should include species
or description of animal, condition of animal, location, time first
found, observed behaviors (if alive) and photo or video, if available.
Estimated Take by Incidental Harassment
Because of the mitigation measures that will be required and the
likelihood that some cetaceans will avoid the area around the operating
airguns of their own accord, NMFS does not expect any marine mammals to
approach the sound source close enough to be injured (Level A
harassment). All anticipated takes would be ``takes by Level B
harassment'', as described previously, involving temporary behavioral
modifications or low-level physiological effects.
Estimates of the numbers of marine mammals that might be affected
are based on consideration of the number of marine mammals that could
be disturbed appreciably by approximately 3,650 km of seismic surveys
during the proposed seismic program in the Lau Basin, Tonga. Few
systematic aircraft- or ship-based surveys have been conducted for
marine mammals in offshore waters of the South Pacific Ocean, and the
species of marine mammals that occur there are not well known. L-DEO's
estimates are based on species accounts in part derived from Reeves et
al. (1999), who summarized distribution information from the area
served by the South Pacific Regional Environment Programme (SPREP). The
SPREP region covers a vast area of the Pacific Ocean between the Tropic
of Capricorn and the Equator from Papua New Guinea (140[deg] E) to
Pitcairn Island (130[deg] W).
It should be noted that the estimates of exposures to various sound
levels assume that the surveys will be completed; in fact, the planned
number of line-kilometers has been increased by 25 percent to
accommodate lines that may need to be repeated, equipment testing, etc.
Furthermore, any marine mammal sightings within or near the designated
safety zone will result in the power or shut down of seismic operations
as a mitigation measure. Thus, the following estimates of the numbers
of marine mammals potentially exposed to 160-dB sounds are
precautionary, and probably overestimate the actual numbers of marine
mammals that might be involved. These estimates assume that there will
be no weather, equipment, or mitigation delays, which is highly
unlikely.
The anticipated radii of influence of the MBES and SBP are less
than those for the airgun array. It is assumed that, during
simultaneous operations of the airgun array and the other sources, any
marine mammals close enough to be affected by the MBES or SBP would
already be affected by the airguns. However, whether or not the airguns
are operating simultaneously with the other sources, marine mammals are
expected to exhibit no more than short-term and inconsequential
responses to the MBES and SBP given their characteristics (e.g., narrow
downward-directed beam) and other considerations (see Possible Effects
of Multibeam Echosounder Signals and Possible Effects of the Sub-bottom
Profiler Signals). Such reactions are not considered to constitute
``taking'' (NMFS 2001). Therefore, no additional allowance is included
for animals that might be affected by sound sources other than airguns.
Density Estimates
The basis for estimating the densities of marine mammals in the
proposed study area is discussed in section VII of L-DEO's application.
The density estimates used in this assessment are from one of
Longhurst's (2007) biogeographic provinces north of the survey area
that is oceanographically similar to the province in which the seismic
activities will take place. Some of the surveys conducted by Ferguson
and Barlow (2001) in the Eastern Tropical Pacific (ETP) during 1986
1996 are in Longhurst's (2007) North Pacific Tropical Gyre Province,
which is similar to the South Pacific Subtropical Gyre (SPSG), in which
the proposed seismic survey will occur. The similarities are: (1) they
are both low-nitrate, low-
[[Page 71619]]
chlorophyll regions of the oceans with numerous coral reefs, and (2)
upwelled nutrients by islands are used by corals and do not increase
pelagic productivity. The species assemblages that occur in the
southwest Pacific Ocean will be different than those sighted during the
surveys in the ETP. However, the overall abundance of species groups
with generally similar habitat requirements are expected to be roughly
similar.
Potential Number of Exposures to Sound Levels at or above 160 dB
L-DEO's ``best estimate'' of the potential number of exposures of
cetaceans, absent any mitigation measures, to seismic sounds with
received levels at or above 160 dB re 1 microPa (rms) is 18,735 (Table
2). L-DEO's ``maximum estimate'' of the potential number of exposures
of cetaceans, with mitigation measures, to seismic sounds with received
levels at or above 160 dB re 1 microPa(rms) is 10,173 (Table 2). It is
assumed that marine mammals exposed to airgun sounds this strong might
change their behavior sufficiently to be considered ``taken by
harassment''.
The number of potential exposures to sound levels at or above 160
dB re 1 microPa (rms) were calculated by multiplying the expected
average species density (see section VII of L-DEO's application) times
the anticipated minimum area (17,525 km\2\, 10,889 mi2) to be
ensonified to that level during airgun operations including overlap.
The area expected to be ensonified was determined by entering the
planned survey lines into a MapInfo Geographic Information System
(GIS), using the GIS to identify the relevant areas by ``drawing'' the
applicable 160-dB buffer around each seismic line, and then calculating
the total area within the buffers. Areas where overlap occurred
(because of closely-spaced lines) were included when estimating the
number of exposures.
Number of Individual Cetaceans Exposed to Sound Levels at or above 160
dB
L-DEO's ``best estimate'' of the potential number of different
individuals that could be exposed to airgun sounds with received levels
at or above 160 dB re 1 microPa (rms) on one or more occasions is
4,997. That total includes 11 baleen whales, four of which are
considered endangered under the ESA: one humpback whale, one blue
whale, one sei whale, and one fin whale, which would represent small
numbers of the regional populations (Table 2). In addition, six sperm
whales (also listed as endangered under the ESA) could be exposed
during the survey, as well as 48 beaked whales (Table 2).
The spinner dolphin is estimated to be the most common species in
the area, with a best estimate of 1,714 spinner dolphins exposed to
sound levels at or above 160 dB re 1 microPa(rms).
Based on numbers of animals encountered during previous L-DEO
seismic surveys, the likelihood of the successful implementation of the
required mitigation measures, and the likelihood that some animals will
avoid the area around the operating airguns, NMFS believes that L-DEOs
airgun seismic testing program may result in the Level B harassment of
some lower number of individual marine mammals (a few times each) than
is indicated by the column titled, Maximum Estimate of Exposures -
Request, in Table 2. L-DEO has asked for authorization for take of
their ``maximum estimate'' of numbers for each species. Though NMFS
believes that take of the requested numbers is unlikely, we still find
these numbers small relative to the population sizes.
Potential Effects on Habitat
The proposed seismic survey will not result in any permanent impact
on habitats used by marine mammals, or to the food sources they use.
The main impact issue associated with the proposed activity will be
temporarily elevated noise levels and the associated direct effects on
marine mammals.
The Langseth will deploy and retrieve approximately 55-64 OBS. The
OBS anchors will remain upon equipment recovery. Although OBS placement
will disrupt a very small area of seafloor habitat and may disturb
benthic invertebrates, the impacts are expected to be localized and
transitory. The vessel will deploy the OBS in such a way that creates
the least disturbance to the area. Thus, it is not expected that the
placement of OBS would have adverse effects beyond naturally occurring
changes in this environment, and any effects of the planned activity on
marine mammal habitats and food resources are expected to be
negligible.
Effects on Fish and Invertebrates - One reason for the adoption of
airguns as the standard energy source for marine seismic surveys is
that, unlike explosives, they have not been associated with large-scale
fish kills. However, existing information on the impacts of seismic
surveys on marine fish and invertebrate populations is very limited.
There are three types of potential effects of exposure to seismic
surveys: (1) pathological, (2) physiological, and (3) behavioral.
Pathological effects involve lethal and temporary or permanent
sublethal injury. Physiological effects involve temporary and permanent
primary and secondary stress responses, such as changes in levels of
enzymes and proteins. Behavioral effects refer to temporary and (if
they occur) permanent changes in exhibited behavior (e.g., startle and
avoidance behavior). The three categories are interrelated in complex
ways. For example, it is possible that certain physiological and
behavioral changes could potentially lead to an ultimate pathological
effect on individuals (i.e., mortality).
The specific received sound levels at which permanent adverse
effects to fish potentially could occur are little studied and largely
unknown. Furthermore, the available information on the impacts of
seismic surveys on marine fish is from studies of individuals or
portions of a population; there have been no studies at the population
scale. The studies of individual fish have often been on caged fish
that were exposed to airgun pulses in situations not representative of
an actual seismic survey. Thus, available information provides limited
insight on possible real-world effects at the ocean or population
scale. This makes drawing conclusions about impacts on fish problematic
because, ultimately, the most important issues concern effects on
marine fish populations, their viability, and their availability to
fisheries.
The existing body of information on the impacts of seismic survey
sound on marine invertebrates is also very limited. However, benthic
invertebrates in the Lau Basin are not expected to be affected by
seismic operations, as sound levels from the airguns will diminish
dramatically by the time the sound reaches the ocean floor at a depth
of approximately 2250 m (7382 ft).
There is some unpublished and very limited evidence of the
potential for adverse effects on invertebrates. Based on the physical
structure of their sensory organs, marine invertebrates appear to be
specialized to respond to particle displacement components of an
impinging sound field and not to the pressure component (Popper et al.,
2001). The only information available on the impacts of seismic surveys
on marine invertebrates involves studies of individuals; there have
been no studies at the population scale. Thus, available information
provides limited insight on possible real-world effects at the regional
or ocean scale. The most important aspect of potential impacts concerns
how exposure to seismic survey sound ultimately affects invertebrate
populations and their
[[Page 71620]]
viability, including availability to fisheries. More detailed
information on studies of potential impacts of sounds on fish and
invertebrates is provided in Appendix E of L-DEO's application.
Negligible Impact Determination
NMFS has preliminarily determined, provided that the aforementioned
mitigation and monitoring measures are implemented, that the impact of
conducting a seismic program in the southwest Pacific Ocean may result,
at worst, in a temporary modification in behavior and/or low-level
physiological effects (Level B Harassment) of small numbers of certain
species of marine mammals. While behavioral and avoidance reactions may
be made by these species in response to the resultant noise from the
airguns, these behavioral changes are expected to have a negligible
impact on the affected species and stocks of marine mammals.
While the number of potential incidental harassment takes will
depend on the distribution and abundance of marine mammals in the area
of seismic operations, the number of potential harassment takings is
estimated to be relatively small in light of the population size (see
Table 2). NMFS anticipates the actual take of individuals to be lower
than the numbers depicted in the table, because those numbers do not
reflect either the implementation of the mitigation numbers or the fact
that some animals will avoid the sound at levels lower than those
expected to result in harassment. Additionally, mitigation measures
require that the Langseth avoid any areas where marine mammals are
concentrated.
In addition, no take by death and/or serious injury is anticipated,
and the potential for temporary or permanent hearing impairment will be
avoided through the incorporation of the required mitigation measures
described in this document. This conclusion is supported by: (1) the
likelihood that, given sufficient notice through slow ship speed and
ramp-up of the seismic array, marine mammals are expected to move away
from a noise source that it is annoying prior to its becoming
potentially injurious; (2) TTS is unlikely to occur, especially in
odontocetes, until levels above 180 dB re 1 microPa (rms) are reached;
(3) the fact that injurious levels of sound are only likely very close
to the vessel; and (4) the monitoring program developed to avoid injury
will be sufficient to detect (using visual detection and PAM), with
reasonable certainty, all marine mammals within or entering the
identified safety zones.
Endangered Species Act (ESA)
Under section 7 of the ESA, the National Science Foundation (NSF)
has begun consultation on this proposed seismic survey. NMFS will also
consult internally on the issuance of an IHA under section 101(a)(5)(D)
of the MMPA for this activity. Consultation will be concluded prior to
a determination on the issuance of an IHA.
National Environmental Policy Act (NEPA)
On September 22, 2005 (70 FR 55630), NSF published a notice of
intent to prepare a Programmatic Environmental Impact Statement/
Overseas Environmental Impact Statement (EIS/OES) to evaluate the
potential environmental impacts associated with the use of seismic
sources in support of NSF-funded research by U.S. academic scientists.
NMFS agreed to be a cooperating agency in the preparation of the EIS/
OEIS. This EIS/OEIS has not been completed. Therefore, in order to meet
NSF's and NMFS' NEPA requirements for the proposed activity and
issuance of an IHA to L-DEO, the NSF has prepared an Environmental
Assessment of a Marine Geophysical Survey by the Langseth in the
southwest Pacific Ocean off the coast of Tonga. NMFS is reviewing that
document and will either adopt NSF's EA or conduct a separate NEPA
analysis, as necessary, prior to making a determination of the issuance
of the IHA. NMFS has posted NSF's EA on its website at http://www.nmfs.noaa.gov/pr/permits/incidental.htm#applications.
Preliminary Conclusions
Based on the preceding information, and provided that the proposed
mitigation and monitoring are incorporated, NMFS has preliminarily
concluded that the proposed activity will incidentally take, by level B
behavioral harassment only, small numbers of marine mammals. The
provision requiring that the activities not have an unmitigable adverse
impact on the availability of the affected species or stock for
subsistence uses does not apply for this proposed action. No take by
Level A harassment (injury) or death is anticipated and harassment
takes should be at the lowest level practicable due to incorporation of
the mitigation measures proposed in this document.
Proposed Authorization
NMFS proposes to issue an IHA to L-DEO for a marine seismic survey
in the southwest Pacific Ocean during January February, 2009, provided
the previously mentioned mitigation, monitoring, and reporting
requirements are incorporated.
Dated: November 18, 2008.
James H. Lecky,
Director, Office of Protected Resources, National Marine Fisheries
Service.
[FR Doc. E8-27895 Filed 11-25-08; 8:45 am]
BILLING CODE 3510-22-S