[Federal Register Volume 71, Number 24 (Monday, February 6, 2006)]
[Notices]
[Pages 6041-6055]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 06-1074]
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DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
[I.D. 080905A]
Small Takes of Marine Mammals Incidental to Specified Activities;
Low-Energy Seismic Survey on the Louisville Ridge, Southwest Pacific
Ocean
AGENCY: National Marine Fisheries Service (NMFS), National Oceanic and
Atmospheric Administration (NOAA), Commerce.
ACTION: Notice of issuance of an incidental harassment authorization.
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SUMMARY: In accordance with provisions of the Marine Mammal Protection
Act (MMPA) as amended, notification is hereby given that an Incidental
Harassment Authorization (IHA) to take small numbers of marine mammals,
by harassment, incidental to conducting an oceanographic survey in the
southwestern Pacific Ocean (SWPO) has been issued to the Scripps
Institution of Oceanography (Scripps).
DATES: Effective from January 20, 2006, through January 19, 2007.
ADDRESSES: The authorization and application containing a list of the
references used in this document may be obtained by writing to this
address or by telephoning the contact listed here. The application is
also available at: http://www.nmfs.noaa.gov/pr/permits/incidental.htm.
FOR FURTHER INFORMATION CONTACT: Kenneth Hollingshead, Office of
Protected Resources, NMFS, (301) 713-2289, ext 128.
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 U.S.
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.
An authorization may be granted if NMFS finds that the taking will
have a negligible impact on the species or stock(s) and will not have
an unmitigable adverse impact on the availability of the species or
stock(s) for subsistence uses and that the permissible methods of
taking and requirements pertaining to the 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
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 June 29, 2005, NMFS received an application from Scripps for the
taking, by harassment, of several species of marine mammals incidental
to conducting a low-energy marine seismic survey program during early
2006 in the SWPO. Scripps plans to conduct a seismic survey of several
seamounts on the Louisville Ridge in the SWPO as part of the Integrated
Ocean Drilling Program (IODP). As presently scheduled, the seismic
survey will occur from about January 21 to February 26, 2006.
The purpose of the research program is to conduct a planned
scientific rock-dredging, magnetic, and seismic survey program of six
seamounts of the Louisville seamount chain. The results will be used
to: (1) Test hypotheses about the eruptive history of the submarine
volcanoes, the subsequent formation (by subaerial erosion and
submergence) of its many guyots, and motion of the hotspot plume; and
(2) design an effective IODP cruise (not currently scheduled) to drill
on carefully-selected seamounts. Included in the research planned for
2006 is scientific rock dredging, extensive total-field and three-
component magnetic surveys, the use of multi-beam and Chirp techniques
to map the seafloor, and high-resolution seismic methods to image the
subsea floor. Following the cruise, chemical and geochronologic
analyses will be conducted on rocks from 25 sites.
Description of the Activity
The seismic surveys will involve one vessel. The source vessel, the
R/V Roger Revelle, will deploy a pair of low-energy Generator-Injector
(GI) airguns as an energy source (each with a discharge volume of 45
in\3\), plus a 450-m (1476-ft) long, 48-channel, towed hydrophone
streamer. As the airguns are towed along the survey lines, the
receiving system will receive the returning acoustic signals.
The program will consist of approximately 1840 km (994 nm) of
surveys, including turns. Water depths within the seismic survey areas
are 800-2300 m (2625-7456 ft). The GI guns will be operated on a small
grid (see inset in Figure 1 in Scripps (2006)) for about 28 hours at
each of 6 seamounts between approximately January 28 to February 19,
2006. There will be additional seismic operations associated with
equipment testing, start-up, and repeat coverage of any areas where
initial data quality is sub-standard.
The Revelle is scheduled to depart from Papeete, French Polynesia,
on or about January 21, 2006, and to arrive at Wellington, New Zealand,
on or about February 26, 2006. The GI guns will be used for about 28
hours on each of 6 seamounts between about January 28th to February
19th. The exact dates of the activities may vary by a few days
[[Page 6042]]
because of weather conditions, repositioning, streamer operations and
adjustments, airgun deployment, or the need to repeat some lines if
data quality is substandard. The overall area within which the seismic
surveys will occur is located between approximately 25[deg] and 45[deg]
S., and between 155[deg] and 175[deg] W. The surveys will be conducted
entirely in International Waters.
In addition to the operations of the GI guns, a 3.5-kHz sub-bottom
profiler and passive geophysical sensors to conduct total-field and
three-component magnetic surveys will be operated during seismic
surveys. A Kongsberg-Simrad EM-120 multi-beam sonar will be used
continuously throughout the cruise.
The energy to the airguns is compressed air supplied by compressors
on board the source vessel. Seismic pulses will be emitted at intervals
of 6-10 seconds. At a speed of 7 knots (13 km/h), the 6-10 sec spacing
corresponds to a shot interval of approximately 21.5-36 m (71-118 ft).
The generator chamber of each GI gun, the one responsible for
introducing the sound pulse into the ocean, is 45 in3. The
larger (105 in\3\) injector chamber injects air into the previously-
generated bubble to maintain its shape, and does not introduce more
sound into the water. The two 45/105 in\3\ GI guns will be towed 8 m
(26.2 ft) apart side by side, 21 m (68.9 ft) behind the Revelle, at a
depth of 2 m (6.6 ft).
General-Injector Airguns
Two GI-airguns will be used from the Revelle during the proposed
program. These 2 GI-airguns have a zero to peak (peak) source output of
230.7 dB re 1 microPascal-m (3.4 bar-m) and a peak-to-peak (pk-pk)
level of 235.9B (6.2 bar-m). However, these downward-directed source
levels do not represent actual sound levels that can be measured at any
location in the water. Rather, they represent the level that would be
found 1 m (3.3 ft) from a hypothetical point source emitting the same
total amount of sound as is emitted by the combined airguns in the
airgun array. The actual received level at any location in the water
near the airguns will not exceed the source level of the strongest
individual source and actual levels experienced by any organism more
than 1 m (3.3 ft) from any GI gun will be significantly lower.
Further, the root mean square (rms) received levels that are used
as impact criteria for marine mammals (see Richardson et al., 1995) are
not directly comparable to these peak or pk-pk values that are normally
used to characterize source levels of airgun arrays. The measurement
units used to describe airgun sources, peak or pk-pk decibels, are
always higher than the rms decibels referred to in biological
literature. For example, a measured received level of 160 dB rms in the
far field would typically correspond to a peak measurement of about 170
to 172 dB, and to a pk-pk measurement of about 176 to 178 decibels, as
measured for the same pulse received at the same location (Greene,
1997; McCauley et al., 1998, 2000). The precise difference between rms
and peak or pk-pk values depends on the frequency content and duration
of the pulse, among other factors. However, the rms level is always
lower than the peak or pk-pk level for an airgun-type source.
The depth at which the sources are towed has a major impact on the
maximum near-field output, because the energy output is constrained by
ambient pressure. The normal tow depth of the sources to be used in
this project is 2.0 m (6.6 ft), where the ambient pressure is
approximately 3 decibars. This also limits output, as the 3 decibars of
confining pressure cannot fully constrain the source output, with the
result that there is loss of energy at the sea surface. Additional
discussion of the characteristics of airgun pulses is provided in
Scripps application and in previous Federal Register documents (see 69
FR 31792 (June 7, 2004) or 69 FR 34996 (June 23, 2004)).
Received sound levels have been modeled by Lamont-Doherty Earth
Observatory (L-DEO) for a number of airgun configurations, including
two 45-in\3\ Nucleus G-guns (G guns), in relation to distance and
direction from the airguns. The L-DEO model does not allow for bottom
interactions, and is therefore most directly applicable to deep water.
Based on the modeling, estimates of the maximum distances from the GI
guns where sound levels of 190, 180, 170, and 160 dB microPascal-m
(rms) are predicted to be received are shown in Table 1. Because the
model results are for the G guns, which have more energy than GI guns
of the same size, those distances are overestimates of the distances
for the 45 in\3\ GI guns.
Table 1.--Distances to Which Sound Levels >=190, 180, 170, and 160 dB re 1 [mu]Pa (rms) Might Be Received From
Two 45-in \3\ G Guns, Similar to the Two 45-in \3\ GI Guns That Will Be Used During the Seismic Survey in the SW
Pacific Ocean During January-February 2006. Distances Are Based on Model Results Provided By L-DEO.
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Estimated distances at received levels (m)
Water depth ---------------------------------------------------
190 dB 180 dB 170 dB 160 dB
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100-1000 m.................................................. 15 60 188 525
>1000 m..................................................... 10 40 125 350
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Some empirical data concerning the 180- and 160-dB distances have
been acquired based on measurements during an acoustic verification
study conducted by L-DEO in the northern Gulf of Mexico between May 27
and June 3, 2003 (Tolstoy et al., 2004). Although the results are
limited, the data showed that water depth affected the radii around the
airguns where the received level would be 180 dB re 1 microPa (rms),
NMFS' current injury threshold safety criterion applicable to cetaceans
(NMFS, 2000). Similar depth-related variation is likely in the 190-dB
distances applicable to pinnipeds. Correction factors were developed
for water depths 100-1000 m (328-3281 ft) and less than 100 m (328 ft).
The proposed survey will occur in depths 800-2300 m (2625-7456 ft), so
only the correction factor for intermediate water depths is relevant
here.
The empirical data indicate that for deep water (>1000 m (3281
ft)), the L-DEO model tends to overestimate the received sound levels
at a given distance (Tolstoy et al., 2004). However, to be
precautionary pending acquisition of additional empirical data, it is
proposed that safety radii during airgun operations in deep water will
be the values predicted by L-DEO's model (Table 1). Therefore, the
assumed 180- and 190-dB radii are 40 m (131 ft) and 10 m (33 ft),
respectively.
[[Page 6043]]
Bathymetric Sonar and Sub-bottom Profiler
The Kongsberg-Simrad EM120 multi-beam sonar operates at 11.25-12.6
kHz, and is mounted in the hull of the Revelle. It operates in several
modes, depending on water depth. In the proposed survey, it will be
used in deep (>800-m) water, and will operate in ``deep'' mode. The
beamwidth is 1[deg] or 2[deg] fore-aft and a total of 150[deg]
athwartship. Estimated maximum source levels are 239 and 233 dB at
1[deg] and 2[deg] beam widths, respectively. Each ``ping'' consists of
nine successive fan-shaped transmissions, each ensonifying a sector
that extends 1[deg] or 2[deg] fore-aft. In the ``deep'' mode, the total
duration of the transmission into each sector is 15 ms. 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. The ``ping''
interval varies with water depth, from approximately 5 sec at 1000 m
(3281 ft) to 20 sec at 4000 m (13123 ft/2.2 nm).
Sub-bottom Profiler--The sub-bottom profiler is normally operated
to provide information about the sedimentary features and the bottom
topography that is simultaneously being mapped by the multi-beam sonar.
The energy from the sub-bottom profiler is directed downward by a 3.5-
kHz transducer mounted in the hull of the Revelle. The output varies
with water depth from 50 watts in shallow water to 800 watts in deep
water. Pulse interval is 1 second (sec) but a common mode of operation
is to broadcast five pulses at 1-s intervals followed by a 5-sec pause.
The beamwidth is approximately 30[deg] and is directed downward.
Maximum source output is 204 dB re 1 microPa (800 watts) while normal
source output is 200 dB re 1 microPa (500 watts). Pulse duration will
be 4, 2, or 1 ms, and the bandwith of pulses will be 1.0 kHz, 0.5 kHz,
or 0.25 kHz, respectively.
Although the sound levels have not been measured directly for the
sub-bottom profiler used by the Revelle, Burgess and Lawson (2000)
measured sounds propagating more or less horizontally from a sub-bottom
profiler similar to the Scripps unit with similar source output (i.e.,
205 dB re 1 microPa m). For that profiler, the 160- and 180-dB re 1
microPa (rms) radii in the horizontal direction were estimated to be,
respectively, near 20 m (66 ft) and 8 m (26 ft) from the source, as
measured in 13 m (43 ft) water depth. The corresponding distances for
an animal in the beam below the transducer would be greater, on the
order of 180 m (591 ft) and 18 m (59 ft) respectively, assuming
spherical spreading. Thus the received level for the Scripps sub-bottom
profiler would be expected to decrease to 160 and 180 dB about 160 m
(525 ft) and 16 m (52 ft) below the transducer, respectively, assuming
spherical spreading. Corresponding distances in the horizontal plane
would be lower, given the directionality of this source (30[deg]
beamwidth) and the measurements of Burgess and Lawson (2000).
Characteristics of Airgun Pulses
Discussion of the characteristics of airgun pulses was provided in
several previous Federal Register documents (see 69 FR 31792 (June 7,
2004) or 69 FR 34996 (June 23, 2004)) and is not repeated here.
Reviewers are encouraged to read these earlier documents for additional
information.
Comments and Responses
A notice of receipt and request for 30-day public comment on the
application and proposed authorization was published on October 17,
2005 (70 FR 60287). During the 30-day public comment period, NMFS
received comments only from the Marine Mammal Commission (Commission).
It is the Commission's view that
(1) Considerable uncertainty exists regarding the effects of sound
on marine mammals;
(2) Better understanding of those effects will require carefully
designed studies, the results of which may not be available for years;
(3) Important activities should not be postponed or delayed until
such results become available; and
(4) Until the results of needed studies become available and
uncertainties are resolved or clarified, it is essential that agencies
take a precautionary approach (as defined in the previous statements
and publications) in authorizing and conducting activities.
Comment 1: The Commission believes that NMFS' preliminary
determinations are reasonable provided NMFS is satisfied that the
proposed mitigation and monitoring activities are adequate to detect
marine mammals in the vicinity of the proposed operations and to ensure
that marine mammals are not being taken in unanticipated ways or
numbers.
Response: For this activity, the radius of the zone of potential
impact ranges from 10 to 60 m (33 to 216.5 ft) depending upon water
depth and whether the sighted mammal is a pinniped, a small cetacean,
or a large cetacean (see Table 1). Considering the very small size of
the conservative shutdown zones, the speed of the vessel when towing
the airgun (7 kts), the length of daylight at this time of the year,
and the marine mammal avoidance measures that are implemented by the
vessel for animals on the vessel's track, it is very unlikely that any
marine mammals would enter the safety zone undetected. If a marine
mammal enters the small safety zone, operational shutdown will be
implemented until the animal leaves the safety zone.
Comment 2: The Commission notes that its April 2004 Beaked Whale
Conference explored issues related to the vulnerability of beaked
whales to anthropogenic sound. Discussions at the workshop appear to
lend support to the hypothesis that beaked whales have unique
characteristics that make them particularly vulnerable to certain
anthropogenic sound sources (e.g., sonars). Preliminary research
findings presented at the workshop suggest that at least some beaked
whales exhibit a unique dive behavior that raises the possibility that
they may live in a physiologic condition of chronic supersaturation
that would increase their susceptibility to received sound levels less
than 180 dB. Workshop participants theorized that the animals'
behavioral response to anthropogenic sound, coupled with their
susceptibility to gas bubble formation may lead to strandings (which in
many cases are lethal). The Commission recognizes that the evidence
with respect to this scenario is preliminary and that other
explanations and scenarios exist. However, the uncertainties concerning
the effects of sound on these species underscore the need for caution.
Response: NMFS notes that the MMC's workshop summary report is
available for reading or downloading at: http://www.mmc.gov/sound/beakedwhalewrkshp/pdf/bwhale_wrkshpsummary.pdf.
Comment 3: The Commission notes that although the proposed study is
not expected to result in injuries or deaths to beaked whales or other
species of marine mammals, observers will conduct monitoring for
injured or dead animals along some recently run transect lines as the
source vessel returns along parallel and perpendicular transect tracks.
In this regard, the Commission would be interested in learning from
NMFS and/or Scripps what the probability is that an injured or dead
beaked whale, other small cetacean, or elephant seal would be sighted
from a ship running transects through an area or retracing recently run
transect lines.
[[Page 6044]]
Response: NMFS is unaware of any scientific studies to demonstrate
efficacy of conducting marine mammal sightings from a moving vessel for
incapacitated or dead marine mammals. However, Scripps notes that the
Revelle will spend approximately 28 hours at each of the 6 seamounts.
As the inset to Figure 1 in the Scripp's application shows, parallel
seismic lines are approximately 2.5 km (1.35 nm) apart, and the
``perpendicular'' lines about twice that distance. Using big-eye
binoculars, injured or dead mammals that are floating should be readily
visible during daytime hours.
Comment 4: The Commission notes that to obtain the best possible
observations prior to initiating full-scale operations, NMFS should
require Scripps not initiate ramp-up after dark and/or to maintain a
low-level output from the airguns if full-scale operations may take
place after dark.
Response: The IHA to Scripps, similar to other seismic IHAs,
requires that ramp-up not commence if the complete safety radii are not
visible for at least 30 minutes prior to ramp-up in either daylight
(rain/fog) or nighttime.
Comment 5: The Commission notes that NMFS' discussion of Scripps'
proposed shut-down procedures in the proposed IHA Federal Register
notice states: ``The mammal has cleared the safety radius if it is
visually observed to have left the safety radius, or if it has not been
seen within the zone for 15 min. (small odontocetes and pinnipeds) or
30 min. (mysticetes and large odontocetes)* * * .'' The Commission
notes that elephant seals can dive for much longer than 15 minutes and,
thus, could be directly below the sound source when it is reactivated.
Response: For elephant seals and other pinnipeds, the safety radius
around the 2-GI airgun seismic source (not the vessel itself) is 10-15
m (33-49 ft) depending upon water depth. When towing seismic airguns,
the Revelle's speed is about 7 knots (nm/hr or 13 km/hr). As a result,
the likelihood of an elephant seal (or any other marine mammal) making
a deep dive and returning to the immediate area of the vessel and its
safety zone, which after 15 minutes of travel will be about 1.75 nm
(3.2 km) away from the elephant seal sighting location, is considered
remote.
Comment 6: The Commission believes NMFS should require that
operations be suspended immediately if a dead or seriously injured
marine mammal is found in the vicinity of the operations, pending
authorization to proceed or issuance of regulations authorizing such
takes under section 101(a)(5)(A) of the MMPA.
Response: A standard condition in all seismic IHAs is for an
emergency shut-down. The IHA states that ``If observations are made or
credible reports are received that one or more marine mammals or sea
turtles are within the area of this activity in an injured or mortal
state, or are indicating acute distress, the seismic airguns will be
immediately shut down and the Chief of the Permits, Conservation and
Education Division, Office of Protected Resources or a staff member
contacted. The airgun array will not be restarted until review and
approval has been given by the Director, Office of Protected Resources
or his designee.'' However, this requirement pertains only to recently
deceased marine mammals, not long-dead ``floaters.''
Description of Habitat and Marine Mammals Affected by the Activity
Forty species of cetacean, including 31 odontocete (dolphin and
small- and large-toothed whale) species and nine mysticete (baleen
whales) species, are believed by scientists to occur in the southwest
Pacific in the proposed seismic survey area. More detailed information
on these species is contained in the Scripps application and the
National Science Foundation (NSF) EA which are available at: http://www.nmfs.noaa.gov/pr/permits/incidental.htm. Table 2 in both the
Scripps application and NSF EA summarizes the habitat, occurrence, and
regional population estimate for these species. The following species
may be affected by this low-intensity seismic survey: Sperm whale,
pygmy and dwarf sperm whales, southern bottlenose whale, Arnoux's
beaked whale, Cuvier's beaked whale, Shepherd's beaked whale,
mesoplodont beaked whales (Andrew's beaked whale, Blainville's beaked
whale, gingko-toothed whale, Gray's beaked whale, Hector's beaked
whale, spade-toothed whale, strap-toothed whale), melon-headed whale,
pygmy killer whale, false killer whale, killer whale, long-finned pilot
whale, short-finned pilot whale, rough-toothed dolphin, bottlenose
dolphin, pantropical spotted dolphin, spinner dolphin, striped dolphin,
short-beaked common dolphin, hourglass dolphin, Fraser's dolphin ,
Risso's dolphin, southern right whale dolphin, spectacled porpoise,
humpback whale, southern right whale, pygmy right whale, common minke
whale, Antarctic minke whale, Bryde's whale, sei whale, fin whale and
blue whale. Because the proposed survey area spans a wide range of
latitudes (25-45[deg] S), tropical, temperate, and possibly polar
species are all likely to be found there. The survey area is all in
deep-water habitat but is close to oceanic island (Kermadec Islands)
habitats, so both coastal and oceanic species might be encountered.
However, abundance and density estimates of cetaceans found there are
provided for reference only, and are not necessarily the same as those
that likely occur in the survey area.
Five species of pinnipeds could potentially occur in the proposed
seismic survey area: Southern elephant seal, leopard seal, crabeater
seal, Antarctic fur seal, and the sub-Antarctic fur seal. All are
likely to be rare, if they occur at all, as their normal distributions
are south of the Scripps survey area. Outside the breeding season,
however, they disperse widely in the open ocean (Boyd, 2002; King,
1982; Rogers, 2002). Only three species of pinniped are known to wander
regularly into the area (Reeves et al., 1999): the Antarctic fur seal,
the sub-Antarctic fur seal, and the leopard seal. Leopard seals are
seen as far north as the Cook Islands (Rogers, 2002).
Potential Effects on Marine Mammals
As outlined in several previous NMFS documents, the effects of
noise on marine mammals are highly variable, and can be categorized as
follows (based on Richardson et al., 1995):
(1) The noise may be too weak to be heard at the location of the
animal (i.e., lower than the prevailing ambient noise level, the
hearing threshold of the animal at relevant frequencies, or both);
(2) The noise may be audible but not strong enough to elicit any
overt behavioral response;
(3) The noise may elicit reactions of variable conspicuousness and
variable relevance to the well being of the marine mammal; these can
range from temporary alert responses to active avoidance reactions such
as vacating an area at least until the noise event ceases;
(4) Upon repeated exposure, a marine mammal may exhibit diminishing
responsiveness (habituation), or disturbance effects may persist; the
latter is most likely with sounds that are highly variable in
characteristics, infrequent and unpredictable in occurrence, and
associated with situations that a marine mammal perceives as a threat;
(5) Any anthropogenic noise that is strong enough to be heard has
the potential to reduce (mask) the ability of a marine mammal to hear
natural sounds at similar frequencies, including calls from
conspecifics, and underwater environmental sounds such as surf noise;
[[Page 6045]]
(6) If mammals remain in an area because it is important for
feeding, breeding or some other biologically important purpose even
though there is chronic exposure to noise, it is possible that there
could be noise-induced physiological stress; this might in turn have
negative effects on the well-being or reproduction of the animals
involved; and
(7) Very strong sounds have the potential to cause temporary or
permanent reduction in hearing sensitivity. In terrestrial mammals, and
presumably marine mammals, received sound levels must far exceed the
animal's hearing threshold for there to be any temporary threshold
shift (TTS) in its hearing ability. For transient sounds, the sound
level necessary to cause TTS is inversely related to the duration of
the sound. Received sound levels must be even higher for there to be
risk of permanent hearing impairment. In addition, intense acoustic or
explosive events may cause trauma to tissues associated with organs
vital for hearing, sound production, respiration and other functions.
This trauma may include minor to severe hemorrhage.
Effects of Seismic Surveys on Marine Mammals
The Scripps' application provides the following information on what
is known about the effects on marine mammals of the types of seismic
operations planned by Scripps. The types of effects considered here are
(1) tolerance, (2) masking of natural sounds, (2) behavioral
disturbance, and (3) potential hearing impairment and other non-
auditory physical effects (Richardson et al., 1995). Given the
relatively small size of the airguns planned for the present project,
its effects are anticipated to be considerably less than would be the
case with a large array of airguns. Scripps and NMFS believe it is very
unlikely that there would be any cases of temporary or especially
permanent hearing impairment, or non-auditory physical effects. Also,
behavioral disturbance is expected to be limited to distances less than
525 m (1722 ft) from the source, the zone calculated for 160 dB or the
onset of Level B harassment. Additional discussion on species-specific
effects can be found in the Scripps application.
Tolerance
Numerous studies (referenced in Scripps, 2005) have shown that
pulsed sounds from airguns are often readily detectable in the water at
distances of many kilometers, but that marine mammals at distances more
than a few kilometers from operating seismic vessels often show no
apparent response. That is often true even in cases when the pulsed
sounds must be readily audible to the animals based on measured
received levels and the hearing sensitivity of that mammal group.
However, most measurements of airgun sounds that have been reported
concerned sounds from larger arrays of airguns, whose sounds would be
detectable farther away than that planned for use in the proposed
survey. Although various baleen whales, toothed whales, and 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 and small odontocetes seem to be
more tolerant of exposure to airgun pulses than are baleen whales.
Given the relatively small, low-energy airgun source planned for use in
this project, mammals are expected to tolerate being closer to this
source than would be the case for a larger airgun source typical of
most seismic surveys.
Masking
Masking effects of pulsed sounds (even from large arrays of
airguns) on marine mammal calls and other natural sounds are expected
to be limited (due in part to the small size of the GI airguns),
although there are very few specific data on this. Given the small
acoustic source planned for use in the SWPO, there is even less
potential for masking of baleen or sperm whale calls during the present
research than in most seismic surveys (Scripps, 2005). GI-airgun
seismic sounds are short pulses generally occurring for less than 1 sec
every 6-10 seconds or so. The 6-10 sec spacing corresponds to a shot
interval of approximately 21.5-36 m (71-118 ft). Sounds from the multi-
beam sonar are very short pulses, occurring for 15 msec once every 5 to
20 sec, depending on water depth.
Some whales are known to continue calling in the presence of
seismic pulses. Their calls can be heard between the seismic pulses
(Richardson et al., 1986; McDonald et al., 1995, Greene et al., 1999).
Although there has been one report that sperm whales cease calling when
exposed to pulses from a very distant seismic ship (Bowles et al.,
1994), a recent study reports that sperm whales continued calling in
the presence of seismic pulses (Madsen et al., 2002). Given the
relatively small source planned for use during this survey, there is
even less potential for masking of sperm whale calls during the present
study than in most seismic surveys. Masking effects of seismic pulses
are expected to be negligible in the case of the smaller odontocete
cetaceans, given the intermittent nature of seismic pulses and the
relatively low source level of the airguns to be used in the SWPO.
Also, the sounds important to small odontocetes are predominantly at
much higher frequencies than are airgun sounds.
Most of the energy in the sound pulses emitted by airgun arrays is
at low frequencies, with strongest spectrum levels below 200 Hz and
considerably lower spectrum levels above 1000 Hz. Among marine mammals,
these low frequencies are mainly used by mysticetes, but generally not
by odontocetes or pinnipeds. An industrial sound source will reduce the
effective communication or echolocation distance only if its frequency
is close to that of the marine mammal signal. If little or no overlap
occurs between the industrial noise and the frequencies used, as in the
case of many marine mammals relative to airgun sounds, communication
and echolocation are not expected to be disrupted. Furthermore, the
discontinuous nature of seismic pulses makes significant masking
effects unlikely even for mysticetes.
A few cetaceans are known to increase the source levels of their
calls in the presence of elevated sound levels, or possibly to shift
their peak frequencies in response to strong sound signals (Dahlheim,
1987; Au, 1993; Lesage et al., 1999; Terhune, 1999; as reviewed in
Richardson et al., 1995). These studies involved exposure to other
types of anthropogenic sounds, not seismic pulses, and it is not known
whether these types of responses ever occur upon exposure to seismic
sounds. If so, these adaptations, along with directional hearing, pre-
adaptation to tolerate some masking by natural sounds (Richardson et
al., 1995), and the relatively low-power acoustic sources being used in
this survey, would all reduce the importance of masking marine mammal
vocalizations.
Disturbance by Seismic Surveys
Disturbance includes a variety of effects, including subtle changes
in behavior, more conspicuous dramatic changes in behavioral
activities, and displacement. However, there are difficulties in
defining which marine mammals should be counted as ``taken by
harassment''. For many species and situations, scientists do not have
detailed information about their reactions to noise, including
reactions to seismic (and sonar) pulses. Behavioral reactions of marine
mammals to sound
[[Page 6046]]
are difficult to predict. Reactions to sound, if any, depend on
species, state of maturity, experience, current activity, reproductive
state, time of day, and many other factors. If a marine mammal does
react to an underwater sound by changing its behavior or moving a small
distance, the impacts of the change may not rise to the level of a
disruption of a behavioral pattern. However, if a sound source would
displace marine mammals from an important feeding or breeding area,
such a disturbance would likely constitute Level B harassment under the
MMPA. Given the many uncertainties in predicting the quantity and types
of impacts of noise on marine mammals, scientists often resort to
estimating how many mammals may be present within a particular distance
of industrial activities or exposed to a particular level of industrial
sound. With the possible exception of beaked whales, NMFS believes that
this is a conservative approach and likely overestimates the numbers of
marine mammals that are affected in some biologically important manner.
The sound exposure criteria used to estimate how many marine
mammals might be harassed behaviorally by the seismic survey are based
on behavioral observations during studies of several species. However,
information is lacking for many species. Detailed information on
potential disturbance effects on baleen whales, toothed whales, and
pinnipeds can be found on pages 33-37 and Appendix A in Scripps's SWPO
application.
Hearing Impairment and Other Physical Effects
Temporary or permanent hearing impairment is a possibility when
marine mammals are exposed to very strong sounds, but there has been no
specific documentation of these effects for marine mammals exposed to
airgun pulses. Current NMFS policy precautionarily sets impulsive
sounds equal to or greater than 180 and 190 dB re 1 microPa (rms) as
the exposure thresholds for onset of Level A harassment for cetaceans
and pinnipeds, respectively (NMFS, 2000). Those criteria have been used
in defining the safety (shut-down) radii for seismic surveys. However,
those criteria were established before there were any data on the
minimum received levels of sounds necessary to cause auditory
impairment in marine mammals. As discussed in the Scripps application
and summarized here,
1. The 180-dB criterion for cetaceans is probably quite
precautionary, i.e., lower than necessary to avoid TTS let alone
permanent auditory injury, at least for delphinids.
2. The minimum sound level necessary to cause permanent hearing
impairment is higher, by a variable and generally unknown amount, than
the level that induces barely-detectable TTS.
3. The level associated with the onset of TTS is often considered
to be a level below which there is no danger of permanent damage.
Given the small size of the two 45 in 3 GI-airguns,
along with the proposed monitoring and mitigation measures, there is
little likelihood that any marine mammals will be exposed to sounds
sufficiently strong to cause even the mildest (and reversible) form of
hearing impairment. Several aspects of the planned monitoring and
mitigation measures for this project are designed to detect marine
mammals occurring near the 2 GI-airguns (and bathymetric sonar), and to
avoid exposing them to sound pulses that might (at least in theory)
cause hearing impairment. In addition, research and monitoring studies
on gray whales, bowhead whales and other cetacean species indicate that
many cetaceans are likely to show some avoidance of the area with
ongoing seismic operations. In these cases, the avoidance responses of
the animals themselves will reduce or avoid the possibility of hearing
impairment.
Non-auditory physical effects may also occur in marine mammals
exposed to strong underwater pulsed sound. Possible types of non-
auditory physiological effects or injuries that theoretically might
occur in mammals close to a strong sound source include stress,
neurological effects, bubble formation, resonance effects, 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, Scripps
and NMFS believe that it is especially unlikely that any of these non-
auditory effects would occur during the survey given the small size of
the acoustic sources, the brief duration of exposure of any given
mammal, and the mitigation and monitoring measures. The following
paragraphs discuss the possibility of TTS, permanent threshold shift
(PTS), and non-auditory physical effects.
TTS
TTS is the mildest form of hearing impairment that can occur during
exposure to a strong sound (Kryter, 1985). When an animal experiences
TTS, its hearing threshold rises and a sound must be stronger in order
to be heard. TTS can last from minutes or hours to (in cases of strong
TTS) days. Richardson et al. (1995) note that the magnitude of TTS
depends on the level and duration of noise exposure, among other
considerations. For sound exposures at or somewhat above the TTS
threshold, hearing sensitivity recovers rapidly after exposure to the
noise ends. Little data on sound levels and durations necessary to
elicit mild TTS have been obtained for marine mammals.
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). Given the
available data, the received level of a single seismic pulse might need
to be on the order of 210 dB re 1 microPa rms (approx. 221-226 dB pk-
pk) in order to produce brief, mild TTS. Exposure to several seismic
pulses at received levels near 200-205 dB (rms) might result in slight
TTS in a small odontocete, assuming the TTS threshold is (to a first
approximation) a function of the total received pulse energy (Finneran
et al., 2002). Seismic pulses with received levels of 200-205 dB or
more are usually restricted to a zone of no more than 100 m (328 ft)
around a seismic vessel operating a large array of airguns. Because of
the small airgun source planned for use during this project, such sound
levels would be limited to distances within a few meters directly
astern of the Revelle.
There are no data, direct or indirect, on levels or properties of
sound that are required to induce TTS in any baleen whale. However, TTS
is not expected to occur during this survey given the small size of the
source limiting these sound pressure levels to the immediate proximity
of the vessel, and the strong likelihood that baleen whales would avoid
the approaching airguns (or vessel) before being exposed to levels high
enough for there to be any possibility of TTS.
TTS thresholds for pinnipeds exposed to brief pulses (single or
multiple) have not been measured, although exposures up to 183 dB re 1
microPa (rms) have been shown to be insufficient to induce TTS in
California sea lions (Finneran et al., 2003). However, prolonged
exposures show that some pinnipeds may incur TTS at somewhat lower
received levels than do small odontocetes exposed for similar durations
(Kastak et al., 1999; Ketten et al., 2001; Au et al., 2000). For this
research cruise therefore, TTS is unlikely for pinnipeds.
[[Page 6047]]
A marine mammal within a zone with a radius of <=100 m (<=328 ft)
around a typical large array of operating airguns might be exposed to a
few seismic pulses with levels of >=205 dB, and possibly more pulses if
the mammal moved with the seismic vessel. Also, around smaller arrays,
such as the 2 GI-airgun array proposed for use during this survey, a
marine mammal would need to be even closer to the source to be exposed
to levels greater than or equal to 205 dB. However, as noted
previously, most cetacean species tend to avoid operating airguns,
although not all individuals do so. In addition, ramping up airgun
arrays, which is now standard operational protocol for many U.S. and
some foreign seismic operations, should allow cetaceans to move away
from the seismic source and avoid being exposed to the full acoustic
output of the airgun array. Even with a large airgun array, it is
unlikely that these cetaceans would be exposed to airgun pulses at a
sufficiently high level for a sufficiently long period to cause more
than mild TTS, given the relative movement of the vessel and the marine
mammal. However, with a large airgun array, TTS would be possible in
odontocetes that bow-ride or otherwise linger near the airguns. Bow-
riding odontocetes mostly would be at or above the surface, and thus
not exposed to strong sound pulses given the pressure-release effect at
the surface. However, bow-riding animals generally dive below the
surface intermittently. If they did so while bow-riding near airguns,
they would be exposed to strong sound pulses, possibly repeatedly.
During this project, the anticipated 180-dB radius is less than 60 m
(197 ft), the array is towed about 21 m (69 ft) behind the Revelle, the
bow of the Revelle will be about 104 m (341 ft) ahead of the airguns,
and the 205-dB radius would be less than 50 m (165 ft). Thus, TTS would
not be expected in the case of odontocetes bow riding during airgun
operations, and if some cetaceans did incur TTS through exposure to
airgun sounds, it would very likely be a temporary and reversible
phenomenon.
NMFS believes that, to avoid Level A harassment, cetaceans should
not be exposed to pulsed underwater noise at received levels exceeding
180 dB re 1 microPa (rms). The corresponding limit for pinnipeds has
been set at 190 dB. The predicted 180- and 190-dB distances for the
airgun arrays operated by Scripps during this activity are summarized
in Table 1 in this document. These sound levels are not considered to
be the levels at or above which TTS might occur. Rather, they are the
received levels above which, in the view of a panel of bioacoustics
specialists convened by NMFS (at a time before TTS measurements for
marine mammals started to become available), one could not be certain
that there would be no injurious effects, auditory or otherwise, to
marine mammals. As noted here, TTS data that are now available imply
that, at least for dolphins, TTS is unlikely to occur unless the
dolphins are exposed to airgun pulses substantially stronger than 180
dB re 1 microPa (rms).
It has also been shown that most whales tend to avoid ships and
associated seismic operations. Thus, whales will likely not be exposed
to such high levels of airgun sounds. Because of the relatively slow
ship speed, any whales close to the trackline could move away before
the sounds become sufficiently strong for there to be any potential for
hearing impairment. Therefore, there is little potential for whales
being close enough to an array to experience TTS. In addition, ramping
up the airgun array should allow cetaceans to move away from the
seismic source and avoid being exposed to the full acoustic output of
the GI airguns.
Permanent Threshold Shift (PTS)
When PTS occurs there is physical damage to the sound receptors in
the ear. In some cases there can be total or partial deafness, while in
other cases the animal has an impaired ability to hear sounds in
specific frequency ranges. Although there is no specific evidence that
exposure to pulses of airgun sounds can cause PTS in any marine
mammals, even with the largest airgun arrays, physical damage to a
mammal's hearing apparatus can potentially occur if it is exposed to
sound impulses that have very high peak pressures, especially if they
have very short rise times (time required for sound pulse to reach peak
pressure from the baseline pressure). Such damage can result in a
permanent decrease in functional sensitivity of the hearing system at
some or all frequencies.
Single or occasional occurrences of mild TTS are not indicative of
permanent auditory damage in terrestrial mammals. However, very
prolonged exposure to sound strong enough to elicit TTS, or shorter-
term exposure to sound levels well above the TTS threshold, can cause
PTS, at least in terrestrial mammals (Kryter, 1985). 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. The low-to-moderate levels of TTS that have been induced in
captive odontocetes and pinnipeds during recent controlled studies of
TTS have been confirmed to be temporary, with no measurable residual
PTS (Kastak et al., 1999; Schlundt et al., 2000; Finneran et al., 2002;
Nachtigall et al., 2003). In terrestrial mammals, the received sound
level from a single non-impulsive sound exposure must be far above the
TTS threshold for any risk of permanent hearing damage (Kryter, 1994;
Richardson et al., 1995). For impulse sounds with very rapid rise times
(e.g., those associated with explosions or gunfire), a received level
not greatly in excess of the TTS threshold may start to elicit PTS.
Rise times for airgun pulses are rapid, but less rapid than for
explosions.
Some factors that contribute to onset of PTS are as follows: (1)
Exposure to single very intense noises, (2) repetitive exposure to
intense sounds that individually cause TTS but not PTS, and (3)
recurrent ear infections or (in captive animals) exposure to certain
drugs.
Cavanagh (2000) reviewed the thresholds used to define TTS and PTS.
Based on his review and SACLANT (1998), it is reasonable to assume that
PTS might occur at a received sound level 20 dB or more above that
which induces mild TTS. However, for PTS to occur at a received level
only 20 dB above the TTS threshold, it is probable that the animal
would have to be exposed to the strong sound for an extended period.
Sound impulse duration, peak amplitude, rise time, and number of
pulses are the main factors thought to determine the onset and extent
of PTS. Ketten (1994) noted that the criteria for differentiating the
sound pressure levels that result in PTS (or TTS) are location and
species-specific. PTS effects may also be influenced strongly by the
health of the receiver's ear.
Given that marine mammals are unlikely to be exposed to received
levels of seismic pulses that could cause TTS, it is highly unlikely
that they would sustain permanent hearing impairment. If we assume that
the TTS threshold for odontocetes for exposure to a series of seismic
pulses may be on the order of 220 dB re 1 microPa (pk-pk)
(approximately 204 dB re 1 microPa rms), then the PTS threshold might
be about 240 dB re 1 microPa (pk-pk). In the units used by
geophysicists, this is 10 bar-m. Such levels are found only in the
immediate vicinity of the largest airguns (Richardson et al., 1995;
Caldwell and Dragoset, 2000). However,
[[Page 6048]]
sea Gentryit is very unlikely that an odontocete would remain within a
few meters of a large airgun for sufficiently long to incur PTS. The
TTS (and thus PTS) thresholds of baleen whales and pinnipeds may be
lower, and thus may extend to a somewhat greater distance from the
source. However, baleen whales generally avoid the immediate area
around operating seismic vessels, so it is unlikely that a baleen whale
could incur PTS from exposure to airgun pulses. Some pinnipeds do not
show strong avoidance of operating airguns. In summary, it is highly
unlikely that marine mammals could receive sounds strong enough (and
over a sufficient period of time) to cause permanent hearing impairment
during this project. In this project marine mammals are unlikely to be
exposed to received levels of seismic pulses strong enough to cause
TTS, and because of the higher level of sound necessary to cause PTS,
it is even less likely that PTS could occur. This is due to the fact
that even levels immediately adjacent to the 2 GI-airguns may not be
sufficient to induce PTS because the mammal would not be exposed to
more than one strong pulse unless it swam alongside an airgun for a
period of time.
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).
Airgun pulses are less energetic and have slower rise times. While
there is no documented evidence that airgun arrays can cause serious
injury, death, or stranding, the association of mass strandings of
beaked whales with naval exercises and an L-DEO seismic survey in 2002
have raised the possibility that beaked whales may be especially
susceptible to injury and/or stranding when exposed to strong pulsed
sounds. Information on recent beaked whale strandings may be found in
Appendix A of the Scripps application and in several previous Federal
Register documents (see 69 FR 31792 (June 7, 2004) or 69 FR 34996 (June
23, 2004)). Reviewers are encouraged to read these documents for
additional information.
It is important to note that seismic pulses and mid-frequency sonar
pulses are quite different. Sounds produced by the types of airgun
arrays used to profile sub-sea geological structures are broadband with
most of the energy below 1 kHz. Typical military mid-frequency sonars
operate at frequencies of 2 to 10 kHz, generally with a relatively
narrow bandwidth at any one time (though the center frequency may
change over time). Because seismic and sonar sounds have considerably
different characteristics and duty cycles, 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 pulses can, in special circumstances, lead to physical
damage and, indirectly, mortality suggests that caution is warranted
when dealing with exposure of marine mammals to any high-intensity
pulsed sound.
In addition to the sonar-related strandings, there was a September
2002 stranding of two Cuvier's beaked whales in the Gulf of California
(Mexico) when a seismic survey by the R/V Maurice Ewing was underway in
the general area (Malakoff, 2002). The airgun array in use during that
project was the Ewing's 20-gun 8490-in 3 array. This might
be a first indication that seismic surveys can have effects, at least
on beaked whales, similar to the suspected effects of naval sonars.
However, the evidence linking the Gulf of California strandings to the
seismic surveys is inconclusive, and to date, is not based on any
physical evidence (Hogarth, 2002; Yoder, 2002). The ship was also
operating its multi-beam bathymetric sonar at the same time but this
sonar had much less potential than these naval sonars to affect beaked
whales. Although the link between the Gulf of California strandings and
the seismic (plus multi-beam sonar) survey is inconclusive, this event
plus the various incidents involving beaked whale strandings associated
with naval exercises suggests a need for caution in conducting seismic
surveys in areas occupied by beaked whales. However, the present
project will involve a much smaller sound source than used in typical
seismic surveys. That, along with the monitoring and mitigation
measures planned for this cruise are expected to eliminate any
possibility for strandings and mortality.
Non-Auditory Physiological Effects
Possible types of non-auditory physiological effects or injuries
that might theoretically occur in marine mammals exposed to strong
underwater sound might include stress, neurological effects, bubble
formation, resonance effects, and other types of organ or tissue
damage. There is no evidence that any of these effects occur in marine
mammals exposed to sound from airgun arrays (even large ones). However,
there have been no direct studies of the potential for airgun pulses to
elicit any of these effects. If any such effects do occur, they would
probably be limited to unusual situations when animals might be exposed
at close range for unusually long periods.
It is doubtful that any single marine mammal would be exposed to
strong seismic sounds for sufficiently long that significant
physiological stress would develop. That is especially so in the case
of the present project where the airguns are small, the ship's speed is
relatively fast (6 knots or approximately 11 km/h), and, except while
on a seismic station, the survey lines are widely spaced with little or
no overlap.
Gas-filled structures in marine animals have an inherent
fundamental resonance frequency. If stimulated at that frequency, the
ensuing resonance could cause damage to the animal. There may also be a
possibility that high sound levels could cause bubble formation in the
blood of diving mammals that in turn could cause an air embolism,
tissue separation, and high, localized pressure in nervous tissue
(Gisner (ed), 1999; Houser et al., 2001).
In April 2002, a workshop (Gentry [ed.] 2002) was held to discuss
whether the stranding of beaked whales in the Bahamas in 2000 (Balcomb
and Claridge, 2001; NOAA and USN, 2001) might have been related to air
cavity resonance or bubble formation in tissues caused by exposure to
noise from naval sonar. A panel of experts concluded that resonance in
air-filled structures was not likely to have caused this stranding.
Among other reasons, the air spaces in marine mammals are too large to
be susceptible to resonant frequencies emitted by mid-or low-frequency
sonar; lung tissue damage has not been observed in any mass, multi-
species stranding of beaked whales; and the duration of sonar pings is
likely too short to induce vibrations that could damage tissues (Gentry
[ed.], 2002). Opinions were less conclusive about the possible role of
gas (nitrogen) bubble formation/growth in the Bahamas stranding of
beaked whales.
Until recently, it was assumed that diving marine mammals are not
subject to decompression injury (the bends) or air embolism. However, a
short paper concerning beaked whales stranded in the Canary Islands in
2002 suggests that cetaceans might be subject to decompression injury
in some situations (Jepson et al., 2003). If so, that might occur if
they ascend unusually quickly when exposed to aversive sounds. However,
the interpretation that strandings are related to decompression injury
is unproven (Piantadosi and Thalmann, 2004; Fern[aacute]ndez et al.,
2004). Even if that effect can occur during exposure to mid-frequency
[[Page 6049]]
sonar, there is no evidence that this type of effect occurs in response
to low-frequency airgun sounds. It is especially unlikely in the case
of this project involving only two small, low-intensity GI-airguns.
In summary, little is known about the potential for seismic survey
sounds to cause either auditory impairment or other non-auditory
physical effects in marine mammals. Available data suggest that such
effects, if they occur at all, would be limited to short distances from
the sound source. However, the available data do not allow for
meaningful quantitative predictions of the numbers (if any) of marine
mammals that might be affected in these ways. Marine mammals that show
behavioral avoidance of seismic vessels, including most baleen whales,
some odontocetes, and some pinnipeds, are unlikely to incur auditory
impairment or other physical effects. Also, the planned mitigation and
monitoring measures are expected to minimize any possibility of serious
injury, mortality or strandings.
Possible Effects of Mid-frequency Sonar Signals
A multi-beam bathymetric sonar (Simrad EM120, 11.25-12.6 kHz) and a
sub-bottom profiler will be operated from the source vessel essentially
continuously during much of the planned survey. Details about these
sonars were provided previously in this document.
Navy sonars that have been linked to avoidance reactions and
stranding of cetaceans generally: (1) Are more powerful than the Simrad
EM120 sonar; (2) have a longer pulse duration; and (3) are directed
close to horizontally (vs. downward for the Simrad EM120). The area of
possible influence of the Simrad EM120 is much smaller--a narrow band
oriented in the cross-track direction below the source vessel. Marine
mammals that encounter the Simrad EM120 at close range 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 and vessel speed. Therefore, as harassment or
injury from pulsed sound is a function of total energy received, the
actual harassment or injury threshold for the bathymetric sonar signals
would be at a much higher dB level than that for longer duration pulses
such as seismic signals. As a result, NMFS believes that marine mammals
are unlikely to be harassed or injured from the multibeam sonar.
Masking by Mid-Frequency Sonar Signals
Marine mammal communications will not be masked appreciably by the
multibeam sonar signals or the sub-bottom profiler given the low duty
cycle and directionality of the sonars and the brief period when an
individual mammal is likely to be within its beam. Furthermore, in the
case of baleen whales, the sonar signals from the Simrad EM120 do not
overlap with the predominant frequencies of their calls, which would
avoid significant masking.
For the sub-bottom profiler, marine mammal communications will not
be masked appreciably because of their relatively low power output, low
duty cycle, directionality (for the profiler), and the brief period
when an individual mammal may be within the sonar's beam. In the case
of most odonotocetes, the sonar signals from the profiler do not
overlap with the predominant frequencies in their calls. In the case of
mysticetes, the pulses from the pinger do not overlap with their
predominant frequencies.
Behavioral Responses Resulting From Mid-Frequency Sonar Signals
Behavioral reactions of free-ranging marine mammals to military and
other sonars 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 (Rendell and Gordon, 1999), and the previously-mentioned
strandings by beaked whales. Also, Navy personnel have described
observations of dolphins bow-riding adjacent to bow-mounted mid-
frequency sonars during sonar transmissions. However, all of these
observations are of limited relevance to the present situation. Pulse
durations from these military tactical sonars were much longer than
those of the Scripps multibeam sonar, and a given mammal would have
received many pulses from the naval sonars. During Scripps' operations,
the individual pulses will be very short, and a given mammal would not
receive many of the downward-directed pulses as the vessel passes by.
Captive bottlenose dolphins and a white whale exhibited changes in
behavior when exposed to 1-sec pulsed sounds at frequencies similar to
those that will be emitted by the multi-beam sonar used by Scripps 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). The relevance
of these data to free-ranging odontocetes is uncertain and in any case
the test sounds were quite different in either duration or bandwidth as
compared to those from a bathymetric sonar.
Scripps and NMFS are not aware of any data on the reactions of
pinnipeds to sonar sounds at frequencies similar to those of the 12.0
kHz frequency of the Revelle's multibeam sonar. Based on observed
pinniped responses to other types of pulsed sounds, and the likely
short duration of exposure to the bathymetric sonar sounds, pinniped
reactions are expected to be limited to startle or otherwise brief
responses of no lasting consequences to the individual animals. The
pulsed signals from the sub-bottom profiler are much weaker than those
from the multibeam sonar and somewhat weaker than those from the 2 GI-
airgun array. Therefore, significant behavioral responses are not
expected.
Hearing Impairment and Other Physical Effects
Given stranding events that have been associated with the operation
of naval sonar, there is much concern that sonar noise can cause
serious impacts to marine mammals (for discussion see Effects of
Seismic Surveys on Marine Mammals). However, the multi-beam sonars
proposed for use by Scripps are quite different than tactical sonars
used for navy operations. Pulse duration of the bathymetric sonars is
very short relative to the naval sonars. Also, at any given location,
an individual marine mammal would be in the beam of the multi-beam
sonar for much less time given the generally downward orientation of
the beam and its narrow fore-aft beam-width. (Navy sonars often use
near-horizontally directed sound.) These factors would all reduce the
sound energy received from the multi-beam sonar rather drastically
relative to that from the sonars used by the Navy. Therefore, hearing
impairment by multi-beam bathymetric sonar is unlikely.
Source levels of the sub-bottom profiler are much lower than those
of the airguns and the multi-beam sonar. Sound levels from a sub-bottom
profiler similar to the one on the Revelle were estimated to decrease
to 180 dB re 1 microPa (rms) at 8 m (26 ft) horizontally from the
source (Burgess and Lawson, 2000), and at approximately 18 m (59 ft)
downward from the source. Furthermore, received levels of pulsed sounds
that are necessary to cause temporary or especially permanent hearing
impairment in marine mammals appear to be higher than 180 dB (see
earlier discussion). Thus, it is unlikely
[[Page 6050]]
that the sub-bottom profiler 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 sub-bottom profiler 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 sub-bottom
profiler. 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 the higher-power sources would further
reduce or eliminate any minor effects of the sub-bottom profiler.
Estimates of Take by Harassment for the SWPO Seismic Survey
Although information contained in this document indicates that
injury to marine mammals from seismic sounds potentially occurs at
sound pressure levels significantly higher than 180 and 190 dB, NMFS'
current criteria for where onset of Level A harassment of cetaceans and
pinnipeds from impulse sound might occur are, respectively, 180 and 190
re 1 microPa rms. The rms level of a seismic pulse is typically about
10 dB less than its peak level and about 16 dB less than its pk-pk
level (Greene, 1997; McCauley et al., 1998; 2000a). The criterion for
where onset of Level B behavioral harassment occurs is 160 dB.
Given the mitigation (see Mitigation later in this document), all
anticipated effects involve a temporary change in behavior that may
constitute Level B harassment. The mitigation measures will minimize or
eliminate the possibility of Level A harassment or mortality. Scripps
has calculated the ``best estimates'' for the numbers of animals that
could be taken by level B harassment during the proposed SWPO seismic
survey using data on marine mammal density (numbers per unit area) and
estimates of the size of the affected area, as shown in the predicted
RMS radii table (see Table 1).
These estimates are based on a consideration of the number of
marine mammals that might be exposed to sound levels greater than 160
dB by operations with the 2 GI-gun array planned to be used for this
project. The anticipated zones of influence of the multi-beam sonar and
sub-bottom profiler are less than that for the airguns, so it is
assumed that during simultaneous operations of these instruments that
any marine mammals close enough to be affected by the multi-beam and
sub-bottom profiler sonars would already be affected by the airguns.
Therefore, no additional incidental takings are included for animals
that might be affected by the multi-beam sonar. Given their
characteristics (described previously), Level B harassment takings are
considered unlikely when the multibeam and sub-bottom profiler are
operating but the airguns are silent.
Table 2 provides the best estimate of the numbers of each species
that would be exposed to seismic sounds greater than 160 dB and the
number of marine mammals requested to be taken by Level B harassment. A
detailed description on the methodology used by Scripps to arrive at
the estimates of Level B harassment takes that are provided in Table 2
can be found in Scripps's IHA application for the SWPO survey.
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Conclusions
Effects on Cetaceans
Strong avoidance reactions by several species of mysticetes to
seismic vessels have been observed at ranges up to 6-8 km (3.2-4.3 nm)
and occasionally as far as 20-30 km (10.8-16.2 nm) from the source
vessel. However, reactions at the longer distances appear to be
atypical of most species and situations, particularly when feeding
whales are involved. Few mysticetes are expected to be encountered
during the proposed survey in the SWPO (Table 2) and disturbance
effects would be confined to shorter distances given the low-energy
acoustic source to be used during this project. In addition, the
estimated numbers presented in Table 2 are considered overestimates of
actual numbers that may be harassed.
Odontocete reactions to seismic pulses, or at least the reactions
of dolphins, are expected to extend to lesser distances than are those
of mysticetes. Odontocete low-frequency hearing is less sensitive than
that of mysticetes, and dolphins are often seen from seismic vessels.
In fact, there are
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documented instances of dolphins approaching active seismic vessels.
However, dolphins as well as some other types of odontocetes sometimes
show avoidance responses and/or other changes in behavior when near
operating seismic vessels.
Taking into account the small size and the relatively low sound
output of the 2 GI-gun array to be used, and the mitigation measures
that are planned, effects on cetaceans are generally expected to be
limited to avoidance of a small area around the seismic operation and
short-term changes in behavior. Furthermore, the estimated numbers of
animals potentially exposed to sound levels sufficient to cause
appreciable disturbance are very low percentages of the affected
populations.
Based on the 160-dB criterion, the best estimates of the numbers of
individual cetaceans that may be exposed to sounds >= 160 dB re 1
microPa (rms) represent from 0 to approximately 0.04 percent of the
regional SWPO species populations (Table 2). In the case of endangered
balaenopterids, it is most likely that no more than 1 humpback, sei, or
fin whale will be exposed to seismic sounds >= 160 dB re 1 microPa
(rms), based on estimated densities of those species in the survey
region. Therefore, Scripps has requested an authorization to expose up
to 1 individual of each of those species to seismic sounds of >= 160 dB
during the proposed survey. Best estimates of blue whales are that no
individuals would be potentially exposed to seismic pulses with
received levels >= 160 dB re 1 microPa (rms) (Table 2).
Higher numbers of delphinids may be affected by the proposed
seismic surveys, but the population sizes of species likely to occur in
the survey area are large, and the numbers potentially affected are
small relative to population sizes (Table 2).
Mitigation measures such as controlled speed, course alteration,
observers, ramp ups, and shut downs when marine mammals are seen within
defined ranges should further reduce short-term reactions, and minimize
any effects on hearing. In all cases, the effects are expected to be
short-term, with no lasting biological consequence. In light of the
type of effects expected and the small percentages of affected stocks
of cetaceans, the action is expected to have no more than a negligible
impact on the affected species or stocks of cetaceans.
Effects on Pinnipeds
Five pinniped species may be encountered at the survey sites, but
their distribution and numbers have not been documented in the proposed
survey area. In all likelihood, these species will be in southern
feeding areas during the period for this survey. However, to ensure
that the Scripps project remains in compliance with the MMPA in the
event that a few pinnipeds are encountered, Scripps has requested an
authorization to expose up to 3-5 individuals of each of the five
pinniped species to seismic sounds with rms levels >= 160 dB re 1
[mu]Pa. Therefore, the survey would have, at most, a short-term effect
on their behavior and no long-term impacts on individual pinnipeds or
their populations. Responses of pinnipeds to acoustic disturbance are
variable, but usually quite limited. Effects are expected to be limited
to short-term and localized behavioral changes falling within the MMPA
definition of Level B harassment. As is the case for cetaceans, the
short-term exposures to sounds from the two GI-guns are not expected to
result in any long-term consequences for the individuals or their
populations and the activity is expected to have no more than a
negligible impact on the affected species or stocks of pinnipeds.
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
utilize. The main impact issue associated with the proposed activity
will be temporarily elevated noise levels and the associated direct
effects on marine mammals.
One of the reasons for the adoption of airguns as the standard
energy source for marine seismic surveys was that they (unlike the
explosives used in the distant past) do not result in any appreciable
fish kill. Various experimental studies showed that airgun discharges
cause little or no fish kill, and that any injurious effects were
generally limited to the water within a meter or so of an airgun.
However, it has recently been found that injurious effects on captive
fish, especially on fish hearing, may occur at somewhat greater
distances than previously thought (McCauley et al., 2000a,b; 2002;
2003). Even so, any injurious effects on fish would be limited to short
distances from the source. Also, many of the fish that might otherwise
be within the injury-zone are likely to be displaced from this region
prior to the approach of the airguns through avoidance reactions to the
approaching seismic vessel or to the airgun sounds as received at
distances beyond the injury radius.
Fish often react to sounds, especially strong and/or intermittent
sounds of low frequency. Sound pulses at received levels of 160 dB re 1
[mu]Pa (peak) may cause subtle changes in behavior. Pulses at levels of
180 dB (peak) may cause noticeable changes in behavior (Chapman and
Hawkins, 1969; Pearson et al., 1992; Skalski et al., 1992). It also
appears that fish often habituate to repeated strong sounds rather
rapidly, on time scales of minutes to an hour. However, the habituation
does not endure, and resumption of the disturbing activity may again
elicit disturbance responses from the same fish.
Fish near the airguns are likely to dive or exhibit some other kind
of behavioral response. This might have short-term impacts on the
ability of cetaceans to feed near the survey area. However, only a
small fraction of the available habitat would be ensonified at any
given time, and fish species would return to their pre-disturbance
behavior once the seismic activity ceased. Thus, the surveys would have
little impact on the abilities of marine mammals to feed in the area
where seismic work is planned. Fish that do not avoid the approaching
airguns (probably a small number) may be subject to auditory or other
injuries.
Zooplankton that are very close to the source may react to the
airgun's shock wave. These animals have an exoskeleton and no air sacs;
therefore, little or no mortality is expected. Many crustaceans can
make sounds and some crustacea and other invertebrates have some type
of sound receptor. However, the reactions of zooplankton to sound are
not known. Some mysticetes feed on concentrations of zooplankton. A
reaction by zooplankton to a seismic impulse would only be relevant to
whales if it caused a concentration of zooplankton to scatter. Pressure
changes of sufficient magnitude to cause this type of reaction would
probably occur only very close to the source, so few zooplankton
concentrations would be affected. Impacts on zooplankton behavior are
predicted to be negligible, and this would translate into negligible
impacts on feeding mysticetes.
Potential Effects on Subsistence Use of Marine Mammals
There is no known legal subsistence hunting for marine mammals in
the SWPO, so the proposed Scripps activities will not have any impact
on the availability of these species or stocks for subsistence users.
Mitigation
For the proposed seismic survey in the SWPO, Scripps will deploy 2
GI-airguns as an energy source, each with a discharge volume of 45
in3. The
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energy from the airguns is directed mostly downward. The directional
nature of the airguns to be used in this project is an important
mitigating factor. This directionality will result in reduced sound
levels at any given horizontal distance as compared with the levels
expected at that distance if the source were omnidirectional with the
stated nominal source level. Also, the small size of these airguns is
an inherent and important mitigation measure that will reduce the
potential for effects relative to those that might occur with large
airgun arrays. This measure is in conformance with NMFS policy of
encouraging seismic operators to use the lowest intensity airguns
practical to accomplish research objectives.
The following mitigation measures, as well as marine mammal visual
monitoring (discussed later in this document), will be implemented for
the subject seismic surveys: (1) Speed and course alteration (provided
that they do not compromise operational safety requirements); (2) shut-
down procedures; and (3) ramp-up procedures.
Speed and Course Alteration
If a marine mammal is detected outside its respective safety zone
(180 dB for cetaceans, 190 dB for pinnipeds) 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, when practical and safe, be
changed to avoid the mammal in a manner that also minimizes the effect
to the planned science objectives. The marine mammal activities and
movements relative to the seismic vessel will be closely monitored to
ensure that the marine mammal does not approach within the safety zone.
If the mammal appears likely to enter the safety zone, further
mitigative actions will be taken (i.e., either further course
alterations or shut down of the airguns).
Shut-down Procedures
Although power-down procedures are often standard operating
practice for seismic surveys, power-down will not be used for this
activity because powering down from two guns to one gun would make only
a small difference in the 180- or 190-dB radius--probably not enough to
allow continued one-gun operations if a mammal came within the safety
radius for two guns.
If a marine mammal is detected outside the safety radius but is
likely to enter the safety radius, and if the vessel's speed and/or
course cannot be changed to avoid having the mammal enter the safety
radius, the GI-guns will be shut down before the mammal is within the
safety radius. Likewise, if a mammal is already within the safety zone
when first detected, the airguns will be shut down immediately.
Following a shut-down, airgun activity will not resume until the
marine mammal 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 and pinnipeds, or
(3) has not been seen within the zone for 30 minutes in the case of
mysticetes and large odontocetes, including sperm, pygmy sperm, dwarf
sperm, beaked and bottlenose whales.
During airgun operations following a shut-down whose duration has
exceeded these specified limits, the airgun array will be ramped-up
gradually. Ramp-up is described later in this document.
Ramp-up Procedure
A ramp-up procedure will be followed when the airguns begin
operating after a period without airgun operations. The two GI guns
will be added in sequence 5 minutes apart. During ramp-up procedures,
the safety radius for the two GI guns will be maintained.
During the day, ramp-up cannot begin from a shut-down unless the
entire 180-dB safety radius has been visible for at least 30 minutes
prior to the ramp up (i.e., no ramp-up can begin in heavy fog or high
sea states).
During nighttime operations, if the entire safety radius is visible
using vessel lights and night-vision devices (NVDs) (as may be the case
in deep and intermediate waters), then start up of the airguns from a
shut down may occur, after completion of the 30-minute observation
period.
Comments on past IHAs raised the issue of prohibiting nighttime
operations as a practical mitigation measure. However, this is not
practicable due to cost considerations and ship time schedules. If the
Revelle was prohibited from operating during nighttime, each trip could
require an additional several days to complete.
If a seismic survey vessel is limited to daylight seismic
operations, efficiency would also be much reduced. Without commenting
specifically on how that limitation would affect the present project,
for seismic operators in general, a daylight-only requirement would be
expected to result in one or more of the following outcomes:
cancellation of potentially valuable seismic surveys; reduction in the
total number of seismic cruises annually due to longer cruise
durations; a need for additional vessels to conduct the seismic
operations; or work conducted by non-U.S. operators or non-U.S. vessels
when in waters not subject to U.S. law.
Marine Mammal Monitoring
Scripps must have at least three visual observers on board the
Revelle, and at least two must be experienced marine mammal observers
that NMFS has approved in advance of the start of the SWPO cruise.
These observers will be on duty in shifts of no longer than 4 hours.
The visual observers will monitor marine mammals and sea turtles
near the seismic source vessel during all daytime airgun operations,
during any nighttime start-ups of the airguns, and at night whenever
daytime monitoring resulted in one or more shut-down situations due to
marine mammal presence. During daylight, vessel-based observers will
watch for marine mammals and sea turtles near the seismic vessel during
periods with shooting (including ramp-ups), and for 30 minutes prior to
the planned start of airgun operations after a shut-down.
Use of multiple observers will increase the likelihood that marine
mammals near the source vessel are detected. Revelle bridge personnel
will also assist in detecting marine mammals and implementing
mitigation requirements whenever possible (they will be given
instruction on how to do so), especially during ongoing operations at
night when the designated observers are on stand-by and not required to
be on watch at all times.
The observer(s) will watch for marine mammals from the highest
practical vantage point on the vessel, which is either the bridge or
the flying bridge. The observer(s) will systematically scan the area
around the vessel with Big Eye binoculars, reticle binoculars (e.g., 7
x 50 Fujinon) and with the naked eye during the daytime. Laser range-
finding binoculars (Leica L.F. 1200 laser rangefinder or equivalent)
will be available to assist with distance estimation. The observers
will be used to determine when a marine mammal or sea turtle is in or
near the safety radii so that the required mitigation measures, such as
course alteration and power-down or shut-down, can be implemented. If
the GI-airguns are shut down, observers will maintain watch to
determine when the animal is outside the safety radius.
Observers may not be on duty during ongoing seismic operations at
night; bridge personnel will watch for marine mammals during this time
and will call
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for the airguns to be powered-down or shut-down if marine mammals are
observed in or about to enter the safety radii. However, a biological
observer must be on standby at night and available to assist the bridge
watch if marine mammals are detected at any distance from the Revelle.
If the 2 GI-airgun is ramped-up at night (see previous section), two
marine mammal observers will monitor for marine mammals for 30 minutes
prior to ramp-up and during the ramp-up using either deck lighting or
NVDs that will be available (ITT F500 Series Generation 3 binocular
image intensifier or equivalent).
Post-Survey Monitoring
In addition, the biological observers will be able to conduct
monitoring of most recently-run transect lines as the Revelle returns
along parallel and perpendicular transect tracks (see inset of Figure 1
in the Scripps application). This will provide the biological observers
with opportunities to look for injured or dead marine mammals (although
no injuries or mortalities are expected during this research cruise).
Passive Acoustic Monitoring (PAM)
Because of the very small zone for potential Level A harassment,
Scripps has not proposed to use the PAM system during this cruise.
Summary
Taking into consideration the additional costs of prohibiting
nighttime operations and the likely impact of the activity (including
all mitigation and monitoring), NMFS has determined that the mitigation
and monitoring measures ensure that the activity will have the least
practicable impact on the affected species or stocks. Marine mammals
will have sufficient notice of a vessel approaching with operating
seismic airguns, thereby giving them an opportunity to avoid the
approaching array; if ramp-up is required, two marine mammal observers
will be required to monitor the safety radii, in daylight or night-
time, using shipboard lighting or NVDs for at least 30 minutes before
ramp-up begins and verify that no marine mammals are in or approaching
the safety radii; ramp-up may not begin unless the entire safety radii
are visible.
Reporting
Scripps will submit a report to NMFS within 90 days after the end
of the cruise, which is currently predicted to occur during January and
February, 2006. The report will describe the operations that were
conducted and the marine mammals that were detected. The report must
provide full documentation of methods, results, and interpretation
pertaining to all monitoring tasks. The report will summarize the dates
and locations of seismic operations, marine mammal sightings (dates,
times, locations, activities, associated seismic survey activities),
and estimates of the numbers of affected marine mammals and a
description of their reactions.
Endangered Species Act (ESA)
NMFS has issued a biological opinion regarding the effects of this
action on ESA-listed species and critical habitat under the
jurisdiction of NMFS. That biological opinion concluded that this
action is not likely to jeopardize the continued existence of listed
species or result in the destruction or adverse modification of
critical habitat. A copy of the Biological Opinion is available upon
request (see ADDRESSES).
National Environmental Policy Act (NEPA)
The NSF made a FONSI determination on November 3, 2005 (70 FR
68102, November 9, 2005), based on information contained within its EA
(see 70 FR 39346, July 7, 2005 for public availability), that
implementation of the subject action is not a major Federal action
having significant effects on the environment within the meaning of
NEPA. The NSF determined, therefore, that an environmental impact
statement would not be prepared.
NMFS noted that the NSF had prepared an EA for the SWPO surveys and
made this EA available upon request (October 17, 2005, 70 FR 60287). In
accordance with NOAA Administrative Order 216-6 (Environmental Review
Procedures for Implementing the National Environmental Policy Act, May
20, 1999), NMFS has reviewed the information contained in NSF's EA and
determined that the NSF EA accurately and completely describes the
proposed action alternative, and the potential impacts on marine
mammals, endangered species, and other marine life that could be
impacted by the preferred alternative and the other alternatives.
Accordingly, NMFS adopted the NSF EA under 40 CFR 1506.3 and made its
own FONSI. The NMFS FONSI also takes into consideration additional
mitigation measures required by the IHA that are not in NSF's EA.
Therefore, it is not necessary to issue a new EA, supplemental EA or an
environmental impact statement for the issuance of an IHA to L-DEO for
this activity. A copy of the EA and the NMFS FONSI for this activity is
available upon request.
Determinations
NMFS has determined that the impact of conducting the seismic
survey on the Louisville Ridge in the SWPO may result, at worst, in a
temporary modification in behavior by certain species of marine
mammals. This activity is expected to result in no more than a
negligible impact on the affected species or stocks.
For reasons stated previously in this document, this determination
is supported by: (1) The likelihood that, given advance notice through
relatively slow ship speed and ramp-up, marine mammals are expected to
move away from a noise source that is annoying before it becomes
potentially injurious; (2) recent research that indicates that TTS is
unlikely (at least in delphinids) until levels closer to 200-205 dB re
1 microPa are reached rather than 180 dB re 1 microPa; (3) the fact
that 200-205 dB isopleths would be well within 100 m (328 ft) of the
vessel even in shallow water; and (4) the likelihood that marine mammal
detection in the safety zone by trained observers is close to 100
percent during daytime and remains high at night to the short distance
from the seismic vessel. As a result, no take by injury or death is
anticipated, and the potential for temporary or permanent hearing
impairment is very low and would be avoided through the incorporation
of the mitigation measures described in this document.
While the number of potential incidental harassment takes will
depend on the distribution and abundance of marine mammals in the
vicinity of the survey activity, the number of potential harassment
takings is estimated to be small. In addition, the proposed seismic
program will not interfere with any known legal subsistence hunts,
since seismic operations will not take place in subsistence whaling and
sealing areas and will not affect marine mammals used for subsistence
purposes.
Authorization
On January 20, 2006, NMFS has issued an IHA to Scripps to take
marine mammals, by harassment, incidental to conducting seismic surveys
in the SWPO for a 1-year period, provided the mitigation, monitoring,
and reporting requirements are undertaken.
Dated: January 31, 2006.
James H. Lecky,
Director, Office of Protected Resources, National Marine Fisheries
Service.
[FR Doc. 06-1074 Filed 2-3-06; 8:45 am]
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