[Federal Register Volume 69, Number 109 (Monday, June 7, 2004)]
[Notices]
[Pages 31792-31806]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 04-12810]
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DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
[I.D. 031104B]
Small Takes of Marine Mammals Incidental to Specified Activities;
Marine Seismic Survey on the Blanco Fracture Zone in the Northeastern
Pacific Ocean
AGENCY: National Marine Fisheries Service (NMFS), National Oceanic and
Atmospheric Administration (NOAA), Commerce.
ACTION: Notice of receipt of application and 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), a part of Columbia University, for an Incidental
Harassment Authorization (IHA) to take small numbers of marine mammals,
by harassment, incidental to conducting oceanographic seismic surveys
on the Blanco Fracture Zone in the Northeastern Pacific Ocean. Under
the Marine Mammal Protection Act (MMPA), NMFS is requesting comments on
its proposal to issue an authorization to L-DEO to incidentally take,
by harassment, small numbers of several species of cetaceans and
pinnipeds for a limited period of time within the next year.
DATES: Comments and information must be received no later than July 7,
2004.
[[Page 31793]]
ADDRESSES: Comments on the application should be addressed to P.
Michael Payne, Chief, Marine Mammal Conservation Division, Office of
Protected Resources, National Marine Fisheries Service, 1315 East-West
Highway, Silver Spring, MD 20910-3225, or by telephoning the contact
listed here. The mailbox address for providing email comments is
[email protected] Include in the subject line of the e-mail comment
the following document identifier: 031104B. Comments sent via email,
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 this address or by
telephoning the contact listed here and is also available at: http://www.nmfs.noaa.gov/prot_res/PR2/Small_Take/smalltake_info.htm#applications.
FOR FURTHER INFORMATION CONTACT: Kenneth Hollingshead, Office of
Protected Resources, NMFS, (301) 713-2322, 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.
Permission 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.
Under section 3(18)(A), 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 March 8, 2004, NMFS received an application from L-DEO for the
taking, by harassment, of several species of marine mammals incidental
to conducting a seismic survey program. L-DEO plans to conduct a marine
seismic survey in the Northeastern Pacific Ocean (NPO), off Oregon,
during August, 2004. Up to two seismic surveys are scheduled to take
place in the NPO. The main survey is planned to occur near the
intersection of the Blanco Transform with the Juan de Fuca Ridge. Time
permitting, a second survey may be conducted at Gorda Ridge. The main
seismic survey will take place between 44[deg] 20' and 44[deg] 42' N.
and between 129[deg] 50' and 130[deg] 30' W. or at least 450 km (243
nm) offshore and outside the Exclusive Economic Zone (EEZ) of any
nation. The Gorda Ridge survey is located between 42[deg] 20' and
43[deg] N. and between 126[deg] 30' and 127-157 km, at least 84 nm
(155.6 km) offshore, but within the EEZ of the United States.
The purpose of the seismic survey is to obtain information on the
structure of the oceanic crust created at the Juan de Fuca Ridge. More
specifically, the survey will obtain information on the geologic nature
of boundaries of the earth's crust created at the intermediate-
spreading Juan de Fuca Ridge. Past studies have mapped those boundaries
using manned submersibles, but they have not provided a link between
geologic and seismic structure. This study will provide the seismic
data to assess the geologic nature of the previously mapped areas.
Description of the Activity
The proposed seismic survey will involve one vessel, the R/V
Maurice Ewing (Ewing). The Ewing will deploy a 10- or 12-airgun array
as an energy source, with discharge volumes of 3050 in3 and 3705 in\3\,
respectively. The Ewing will also deploy and retrieve 12 Ocean Bottom
Seismometers (OBSs), plus tow a 6-km (3.2 nm) streamer containing
hydrophones, to receive the returning acoustic signals. As the airguns
are towed along the survey lines, these two systems will receive the
returning acoustic signals.
A total of approximately 150 kilometers (km) (81 nautical miles
(nm)) of OBS surveys using a 12-gun array (24 hours of operation) and
approximately 1017 km (549 nm) of Multi-Channel Seismic (MCS) profiles
using a 10-gun array (6.5 days of operation) are planned to be
conducted during the main survey. These line-kilometer figures include
operations associated with start up, line changes of 10 km (5 nm) for
the 12-gun array and 90 km (49 nm) for the 10-gun array), equipment
testing, contingency profiles, and repeat coverage of any areas where
initial data quality is sub-standard. In the unlikely event that there
are no weather or equipment delays, additional MCS profiles may be
acquired at the northern end of the Gorda Ridge where it intersects the
Blanco Transform. The contingency survey would consist of 220 km (119
nm) of survey lines, plus 63 km (34 nm) for turns and connecting lines,
for a total of 283 km (153 nm). Water depths within the seismic survey
areas are 1600-5000 m (5250-16,405 ft).
During the airgun operations, the vessel will travel at 7.4-9.3 km/
hr (4-5 knots), and seismic pulses will be emitted at intervals of 60-
90 sec (OBS lines) and approximately 20 sec for the Multi-Channel
Seismic profiles (MCS lines). The 20-sec spacing corresponds to a shot
interval of about 50 m (164 ft), while the 60-90 sec spacing
corresponds to a distance of 150 m (492 ft) to 220 m (722 ft),
respectively. The 60-90 sec spacing along OBS lines is to minimize
reverberation from previous shot noise during OBS data acquisition, and
the exact spacing will depend on water depth.
For the 10- and 12-airgun arrays, the sound pressure fields have
been modeled by L-DEO in relation to distance and direction from the
airguns, and in relation to depth. Predicted sound levels are depicted
in Figures 6 and 7 in L-DEO's application. Empirical data concerning
those sound levels have been acquired based on measurements during an
acoustic verification study conducted by L-DEO in the northern Gulf of
Mexico from 27 May to 3 June 2003. L-DEO's analysis of the acoustic
data from that study (Tolstoy et al.,
[[Page 31794]]
2004) provides limited measurements in deep water, such as found at
Blanco Fracture and Gorda Ridge. Those data indicate that, for deep
water, L-DEO's model tends to overestimate the received sound levels at
a given distance. NMFS and L-DEO, therefore, propose that the 180-dB
and 190-dB (re 1 microPascal (root-mean-squared (rms)) sound pressure
fields that will correspond to the proposed safety radii (see
Mitigation) will be the values predicted by L-DEO's model during airgun
operations in deep water, including these planned survey operations.
In addition to the operations of the airgun array, the ocean floor
will be mapped continuously throughout the entire cruise with an Atlas
Hydrosweep DS-2 Multibeam 15.5-kHz bathymetric sonar, and a 3.5-kHz
sub-bottom profiler. Both of these sound sources are commonly operated
simultaneously with the airgun array, but may, on occasion, be utilized
independent of the seismic array.
The Atlas Hydrosweep is mounted on the hull of the Maurice Ewing,
and it operates in three modes, depending on the water depth. There is
one shallow water mode and two deep-water modes: an Omni mode and a
Rotational Directional Transmission (RDT) mode. The RDT mode is
normally used during deep-water operation and has a 237-dB rms source
output. In the RDT mode, each ``ping'' consists of five successive
transmissions, each ensonifying a beam that extends 2.67 degrees fore-
aft and approximately 30 degrees in the cross-track direction. The five
successive transmissions (segments) sweep from port to starboard with
minor overlap, spanning an overall cross-track angular extent of about
140 degrees, with small (<1 millisec) gaps between the pulses for
successive 30-degree segments. The total duration of the ``ping''
including all five successive segments, varies with water depth, but is
1 millisec in water depths less than 500 m and 10 millisec in the
deepest water. For each segment, ping duration is 1/5th of these values
or 2/5th for a receiver in the overlap area ensonified by two beam
segments. The ``ping'' interval during RDT operations depends on water
depth and varies from once per second in less than 500 m (1640.5 ft)
water depth to once per 15 seconds in the deepest water.
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 Hydrosweep. The energy from the sub-
bottom profiler is directed downward by a 3.5 kHz transducer mounted in
the hull of the Ewing. The output varies with water depth from 50 watts
in shallow water to 800 watts in deep water. Pulse interval is 1 second
(s) but a common mode of operation is to broadcast five pulses at 1-s
intervals followed by a 5-s pause. The beamwidth is approximately 30o
and is directed downward. Maximum source output is 204 dB re 1 microPa,
800 watts, while nominal 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.
Sound levels have not been measured directly for the sub-bottom
profiler used by the Ewing, but Burgess and Lawson (2000) measured
sounds propagating more or less horizontally from a similar unit with
similar source output (205 dB re 1 microPa m). 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 or 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), assuming spherical spreading.
The sub-bottom profiler on the Ewing has a stated maximum source
level of 204 dB re 1 microPa. Thus the received level 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
Airguns function by venting high-pressure air into the water. The
pressure signature of an individual airgun consists of a sharp rise and
then fall in pressure, followed by several positive and negative
pressure excursions caused by oscillation of the resulting air bubble.
The resulting downward-directed pulse has a duration of only 10 to 20
ms, with only one strong positive and one strong negative peak pressure
(Caldwell and Dragoset, 2000). Most energy emitted from airguns is at
relatively low frequencies. For example, typical high-energy airgun
arrays emit most energy at 10-120 Hz. However, the pulses contain some
energy up to 500-1000 Hz and above (Goold and Fish, 1998).
The pulsed sounds associated with seismic exploration have higher
peak levels than other industrial sounds to which whales and other
marine mammals are routinely exposed. The peak-to-peak (P-P) source
levels of the 10-gun array and 12-gun arrays that will be used for the
Blanco Fracture project are 255 dB re 1 microPa (55 bar-m) and 257 dB
dB re 1 microPa (68 bar-m), respectively. These are the nominal source
levels applicable to downward propagation. The effective source level
for horizontal propagation is lower.
Several important mitigating factors need to be considered when
assessing airgun impacts on the marine environment: (1) Airgun arrays
produce intermittent sounds, involving emission of a strong sound pulse
for a small fraction of a second followed by several seconds of near
silence. In contrast, some other acoustic sources produce sounds with
lower peak levels, but their sounds are continuous or discontinuous but
continuing for much longer durations than seismic pulses. (2) Airgun
arrays are designed to transmit strong sounds downward through the
seafloor, and the amount of sound transmitted in near-horizontal
directions is considerably reduced. Nonetheless, they also emit sounds
that travel horizontally toward non-target areas. (3) An airgun array
is a distributed source, not a point source. The nominal source level
is an estimate of the sound that would be measured from a theoretical
point source emitting the same total energy as the airgun array. That
figure is useful in calculating the expected received levels in the far
field (i.e., at moderate and long distances). Because the airgun array
is not a single point source, there is no one location within the near
field (or anywhere else) where the received level is as high as the
nominal source level.
The strengths of airgun pulses can be measured in different ways,
and it is important to know which method is being used when
interpreting quoted source or received levels. Geophysicists usually
quote P-P levels, in bar-meters or dB re 1 microPa-m. The peak (zero-
to-peak) level for the same pulse is typically about 6 dB less. In the
biological literature, levels of received airgun pulses are often
described based on the ``average'' or ``root-mean-square'' (rms) level
over the duration of the pulse. The rms value for a given pulse is
typically about 10 dB lower than the peak level, and 16 dB lower than
the P-P value (Greene 1997, McCauley et al. 1998, 2000). A fourth
measure that is being used more frequently is the energy level, in dB
re 1 microPa\2\-s. Because the pulses are less than 1 sec in duration,
the numerical value of the energy is lower than the rms pressure level,
but the units are different. Because the level of a given pulse will
differ substantially depending on which of these measures is being
applied, it is important to be
[[Page 31795]]
aware which measure is in use when interpreting any quoted pulse level.
NMFS commonly references the rms levels when discussing levels of
pulsed sounds that might harass marine mammals.
Seismic sound received at any given point will arrive via a direct
path, indirect paths that include reflection from the sea surface and
bottom, and often indirect paths including segments through the bottom
sediments. Sounds propagating via indirect paths travel longer
distances and often arrive later than sounds arriving via a direct
path. These variations in travel time have the effect of lengthening
the duration of the received pulse. At the source, seismic pulses are
about 10 to 20 ms in duration. In comparison, the pulse duration as
received at long horizontal distances can be much greater.
Another important aspect of sound propagation is that received
levels of low-frequency underwater sounds diminish close to the surface
because of pressure-release and interference phenomena that occur at
and near the surface (Urick 1983, Richardson et al. 1995). Paired
measurements of received airgun sounds at depths of 3 m (9.8 ft) vs. 9
or 18 m (29.5 or 59 ft) have shown that received levels are typically
several decibels lower at 3 m (9.8. ft)(Greene and Richardson 1988).
For a mammal whose auditory organs are within 0.5 or 1 m (1.6 or 3.3
ft) of the surface, the received level of the predominant low-frequency
components of the airgun pulses would be further reduced.
Pulses of underwater sound from open-water seismic exploration are
often detected 50 to 100 km (30 to 54 nm) from the source location
(Greene and Richardson 1988, Burgess and Greene 1999). At those
distances, the received levels on an approximate rms basis are low
(below 120 dB re 1 microPa). However, faint seismic pulses are
sometimes detectable at even greater ranges (e.g., Bowles et al., 1994,
Fox et al., 2002). Considerably higher levels can occur at distances
out to several kilometers from an operating airgun array. For the
Blanco Fracture survey using 10-gun and 12-gun arrays, the distances at
which seismic pulses are expected to diminish to received levels of 190
dB, 180 dB, 170 dB and 160 dB re 1 microPa rms are as follows:
Table 1. Distances to which sound levels might be received from the airgun arrays planned for use in the Blanco
Fracture Zone.
----------------------------------------------------------------------------------------------------------------
RMS Radii (m/ft)
Airgun Array -------------------------------------------------
190 dB 180 dB 170 dB 160 dB
----------------------------------------------------------------------------------------------------------------
1 airgun...................................................... 13/43 36/118 110/361 350/1148
10 airguns.................................................... 200/656 550/1805 2000/6562 6500/21325
12 airguns.................................................... 200/656 600/1968 2200/1718 7250/23786
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Additional information is contained in the L-DEO application,
especially in Appendix A.
Description of Habitat and Marine Mammals Affected by the Activity
A detailed description of the NPO in the Blanco Fracture/Gorda
Ridge area and its associated marine mammals can be found in the L-DEO
application and a number of documents referenced in the L-DEO
application, and is not repeated here. The main Blanco Transform survey
site, and the Gorda Ridge contingency survey site, are located
approximately 450 and 150 km (243 and 81 nm) offshore from Oregon,
respectively, over water depths of 1600 to 5000 m (5250 to 16405 ft).
Based on their preference for offshore (>2000 m (6560 ft) depth) and/or
slope (200-2000 m or 656-6560 ft) waters, 19 of the 39 marine mammal
species known for Oregon and Washington waters are considered likely to
occur near the survey areas. An additional 14 species could occur, but
are unlikely to do so in the project area because they are rare or
uncommon in slope and offshore waters or they generally do not occur
off Oregon or Washington. While these 14 species are addressed in the
L-DEO application it is unlikely that they will occur in the survey
area. An additional six species are not expected in the project area
because their occurrence off Oregon is limited to coastal/shallow
waters (gray whale (Eschrichtius robustus) and sea otter (Enhydra
lutris)) or they are considered extralimital (beluga whale
(Delphinapterus leucas), ringed seals (Phoca hispida), ribbon seal
(Phoca fasciata), and hooded seal (Cystophora cristata)). As it is
unlikely that these rare, vagrant mammals would occur during the short
time period of this seismic survey, these latter six species are not
addressed further as they are unlikely to be impacted by seismic
signals from this research operation.
The six species of marine mammals expected to be most common in the
deep pelagic or slope waters of the project area include the Pacific
white-sided dolphin (Lagenorhynchus obliquidens), northern right whale
dolphin(Lissodelphis borealis), Risso's dolphin (Grampus griseus),
short-beaked common dolphin (Delphinus delphis), Dall's porpoise
(Phocoenoides dalli), and northern fur seal (Callorhinus ursinus)(Green
et al., 1992, 1993; Buchanan et al., 2001; Carretta et al., 2002;
Barlow, 2003). The sperm whale (Physeter macrocephalus), pygmy sperm
whale (Kogia breviceps), mesoplodont species (Blainville's beaked whale
(Mesoplondon densirostris), Stejneger's beaked whale (M. stejnegeri),
and Hubb's beaked whale (M. carlhubbsi)), Baird's beaked whale
(Berardius bairdii), Cuvier's beaked whale (Ziphius cavirostris), and
northern elephant seals (Mirounga angustirostris) are considered
pelagic species but are generally uncommon in the waters near the
survey area.
Of the five species of pinnipeds known to occur regularly in waters
off Oregon, Washington, or northern California, only the northern fur
seal and northern elephant seal are likely to be present in the pelagic
waters of the proposed project area, located approximately 150-450 km
(243-481 nm) offshore. The Steller sea lion (Eumetopias jubatus) may
also occur there in small numbers. The California sea lion (Zalophus
californianus)and harbor seal (Phoca vitulina) occur in shallow coastal
or shelf waters off Oregon and Washington (Bonnell et al., 1992, Green
et al., 1993, Buchanan et al., 2001), and are not expected to be seen
in the proposed study area. Sea otters were translocated to shallow
coastal waters off the Olympic Peninsula of Washington, but are not
found in the pelagic waters of the project area off Oregon. More
detailed information on these species is contained in the L-DEO
application and additional information is contained in Caretta et al.,
(2002) which are available at: http://www.nmfs.noaa.gov/prot_res/PR2/Small_Take/smalltake_info.htm#applications, and http://
www.nmfs.noaa.gov/prot--res/
[[Page 31796]]
PR2/Stock--Assessment--Program/sars.html, respectively.
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;
(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). 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 L-DEO application provides the following information on what is
known about the effects on marine mammals of the types of seismic
operations planned by L-DEO. The types of effects considered here are
(1) masking, (2) disturbance, and (3) potential hearing impairment and
other physical effects. Additional discussion on species specific
effects can be found in the L-DEO application for taking marine mammals
incidental to this activity.
Masking
Masking effects of pulsed sounds on marine mammal calls and other
natural sounds are expected to be limited, although there are very few
specific data on this. Seismic sounds are short pulses occurring for
less than 1 sec every 20 or 60-90 sec in this project. Sounds from the
multibeam sonar are very short pulses, occurring for 1-10 msec once
every 1 to 15 sec, depending on water depth. (During operations in deep
water, the duration of each pulse from the multibeam sonar as received
at any one location would actually be only 1/5\th\ or at most 2/5\th\
of 1-10 msec, given the segmented nature of the pulses.) 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). 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 that
sounds important to these species 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. These frequencies are
mainly used by mysticetes, but 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
cetacean signal. If little or no overlap occurs between the industrial
noise and the frequencies used, as in the case of many marine mammals
vs. 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 and
preadaptation to tolerate some masking by natural sounds (Richardson et
al., 1995), would all reduce the importance of masking.
Disturbance by Seismic Surveys
Disturbance includes a variety of effects, including subtle changes
in behavior, more conspicuous dramatic changes in 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 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 disruption of a
behavioral pattern. However, if a sound source would displace marine
mammals from an important feeding or breeding area for a prolonged
period, such a disturbance would constitute Level B harassment. 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. This
likely overestimates the numbers of marine mammals that are affected in
some biologically important manner. The sound criteria used to estimate
how many marine mammals might be harassed behaviorally by the seismic
[[Page 31797]]
survey are based on behavioral observations during studies of several
species. However, information is lacking for many species.
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 this for marine mammals exposed to airgun
pulses. Current NMFS policy regarding exposure of marine mammals to
high-level sounds is that cetaceans and pinnipeds should not be exposed
to impulsive sounds [gteqt]180 and 190 dB re 1 microPa (rms),
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 L-DEO 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.
Several aspects of the planned monitoring and mitigation measures
for this project are designed to detect marine mammals occurring near
the airgun array (and multibeam sonar), and to avoid exposing them to
sound pulses that might cause hearing impairment. In addition, 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. 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) notes 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 (Fineran
et al., 2002). Seismic pulses with received levels of 200 205 dB or
more are usually restricted to a radius of no more than 100 m (328 ft)
around a seismic vessel.
There are no data, direct or indirect, on levels or properties of
sound that are required to induce TTS in any baleen whale. 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 (Fineran 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).
A marine mammal within a radius of <=100 m (<= 328 ft) around a
typical array of operating airguns might be exposed to a few seismic
pulses with levels of [gteqt]205 dB, and possibly more pulses if the
mammal moved with the seismic vessel. 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
standard operational protocol for L-DEO and other seismic operators,
should allow cetaceans to move away from the seismic source and to
avoid being exposed to the full acoustic output of the 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, TTS would be more likely in any odontocetes that bow-
ride or otherwise linger near the airguns. While bow-riding,
odontocetes 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. If some
cetaceans did incur TTS through exposure to airgun sounds, this would
very likely be a temporary and reversible phenomenon.
Currently, NMFS believes that, whenever possible 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 L-DEO
during this activity are summarized elsewhere 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 that 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 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.
[[Page 31798]]
Therefore, there is little potential for whales being close enough to
an array to experience TTS. In addition ramping up airgun arrays, which
has become standard operational protocol for many seismic operators
including L-DEO, should allow cetaceans to move away from the seismic
source and to avoid being exposed to the full acoustic output of the
airgun array.
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. Physical damage to a mammal's hearing
apparatus can 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) has 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. Based on existing data, Ketten (1994) has 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 exposure to a series of seismic pulses may be on
the order of 220 dB re 1 microPa (pk-pk) in odontocetes, 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). It 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. 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. However, pinnipeds are
expected to be (at most) uncommon in the Blanco Fracture survey area.
However, although it is unlikely that the planned seismic surveys could
cause PTS in any marine mammals, caution is warranted given the limited
knowledge about noise-induced hearing damage in marine mammals,
particularly baleen whales.
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, and, 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, more recently, an L-DEO seismic
survey has raised the possibility that beaked whales may be especially
susceptible to injury and/or stranding when exposed to strong pulsed
sounds.
In March 2000, several beaked whales that had been exposed to
repeated pulses from high intensity, mid-frequency military sonars
stranded and died in the Providence Channels of the Bahamas Islands,
and were subsequently found to have incurred cranial and ear damage
(NOAA and USN 2001). Based on post-mortem analyses, it was concluded
that an acoustic event caused hemorrhages in and near the auditory
region of some beaked whales. These hemorrhages occurred before death.
They would not necessarily have caused death or permanent hearing
damage, but could have compromised hearing and navigational ability
(NOAA and USN 2001). The researchers concluded that acoustic exposure
caused this damage and triggered stranding, which resulted in
overheating, cardiovascular collapse, and physiological shock that
ultimately led to the death of the stranded beaked whales. During the
event, five naval vessels used their AN/SQS-53C or -56 hull-mounted
active sonars for a period of 16 hours. The sonars produced narrow
(<100 Hz) bandwidth signals at center frequencies of 2.6 and 3.3 kHz (-
53C), and 6.8 to 8.2 kHz (-56). The respective source levels were
usually 235 and 223 dB re 1 micro Pa, but the -53C briefly operated at
an unstated but substantially higher source level. The unusual
bathymetry and constricted channel where the strandings occurred were
conducive to channeling sound. This, and the extended operations by
multiple sonars, apparently prevented escape of the animals to the open
sea. In addition to the strandings, there are reports that beaked
whales were no longer present in the Providence Channel region after
the event, suggesting that other beaked whales either abandoned the
area or perhaps died at sea (Balcomb and Claridge, 2001).
Other strandings of beaked whales associated with operation of
military sonars have also been reported (e.g., Simmonds and Lopez-
Jurado, 1991; Frantzis, 1998). In these cases, it was
[[Page 31799]]
not determined whether there were noise-induced injuries to the ears or
other organs. Another stranding of beaked whales (15 whales) happened
on 24-25 September 2002 in the Canary Islands, where naval maneuvers
were taking place. Jepson et al. (2003) concluded that cetaceans might
be subject to decompression injury in some situations. If so, this
might occur if the mammals ascend unusually quickly when exposed to
aversive sounds. Previously, it was widely assumed that diving marine
mammals are not subject to the bends or air embolism.
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 hearing 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 Cuviers beaked whales in the Gulf of California
(Mexico) when a seismic survey by the 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 this 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 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.
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. 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.
Long-term exposure to anthropogenic noise may have the potential to
cause physiological stress that could affect the health of individual
animals or their reproductive potential, which could theoretically
cause effects at the population level (Gisner (ed.), 1999). However,
there is essentially no information about the occurrence of noise-
induced stress in marine mammals. Also, it is doubtful that any single
marine mammal would be exposed to strong seismic sounds for
sufficiently long that significant physiological stress would develop.
This is particularly so in the case of broad-scale seismic surveys
where the tracklines are generally not as closely spaced as in many
industry seismic surveys.
Gas-filled structures in marine animals have an inherent
fundamental resonance frequency. If stimulated at this 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 th
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 2002, NMFS held a workshop
(Gentry [ed.], 2002) to discuss whether the stranding of beaked whales
in the Bahamas in 2000 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. Workshop participants did not rule out the possibility
that bubble formation/growth played a role in the stranding and
participants acknowledged that more research is needed in this area.
The only available information on acoustically-mediated bubble growth
in marine mammals is modeling that assumes prolonged exposure to sound.
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.
Possible Effects of Mid-Frequency Sonar Signals
A multi-beam bathymetric sonar (Atlas Hydrosweep DS-2, 15.5-kHz)
and a sub-bottom profiler will be operated from the source vessel
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 Atlas
Hydrosweep, (2) have a longer pulse duration, and (3) are directed
close to horizontally (vs. downward for the Hydrosweep). The area of
possible influence of the Hydrosweep is much smaller - a narrow band
below the source vessel. For the Hydrosweep there is no horizontal
propagation as these signals project at an angle of approximately 45
degrees from the ship. For the deep-water mode, under the ship the 160-
and 180-dB zones are estimated to be 3200 m (10500 ft) and 610 m (2000
ft), respectively. However, the beam width of the Hydrosweep signal is
only 2.67 degrees fore and aft of the vessel, meaning that a marine
mammal diving could receive at most 1-2 signals from the Hydrosweep and
a marine mammal on the surface would be unaffected. Marine
[[Page 31800]]
mammals that do encounter the Hydrosweep 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 Hydrosweep signals
(approximately 10 ms) such sounds 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 be not 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 do not overlap with the
predominant frequencies in the calls, which would avoid significant
masking.
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
beachings 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 sonars were much longer than those of the L-DEO
multibeam sonar, and a given mammal would have received many pulses
from the naval sonars. During L-DEO's operations, the individual pulses
will be very short, and a given mammal would not receive many of the
downward-directed pulses as the vessel passes by.
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 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). 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.
L-DEO and NMFS are not aware of any data on the reactions of
pinnipeds to sonar sounds at frequencies similar to those of the 15.5
kHz frequency of the Ewing's multibeam sonar. Based on observed
pinniped responses to other types of pulsed sounds, and the likely
brevity 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. Finally, the pulsed
signals from the sub-bottom profiler are much weaker than those from
the airgun array and the multibeam sonar. Therefore, behavioral
responses are not expected.
Hearing Impairment and Other Physical Effects
Given recent 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). It is worth noting that the multi-beam sonar proposed
for use by L-DEO is quite different than sonars used for navy
operations. Pulse duration of the multi-beam sonar 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 beamwidth. (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 the 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 Ewing 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 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 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 Blanco Fracture Zone Survey
Although information contained in this document indicates that
injury to marine mammals from seismic sounds potentially occurs at
sound pressure levels higher than 180 and 190 dB, NMFS' current
criteria for onset of Level A harassment of cetaceans and pinnipeds
from impulse sound 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 (Greene, 1997; McCauley et al., 1998, 2000a). The criterion
for Level B harassment onset is 160 dB.
Given the proposed mitigation (see Mitigation later in this
document), all anticipated takes involve a temporary change in behavior
that may constitute Level B harassment. The proposed mitigation
measures will minimize or eliminate the possibility of Level A
harassment. L-DEO has calculated the ``best estimates'' for the numbers
of animals that could be taken by level B harassment during the
proposed Blanco Fracture seismic survey using data on marine mammal
density and abundance from marine mammal surveys in the region, and
estimates of the size of the affected area, as shown in the predicted
RMS radii table (Table 1).
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These estimates are based on a consideration of the number of
marine mammals that might be exposed to sound levels greater than 160
dB, the criterion for the onset of Level B harassment, by operations
with the 10- and 12-gun array planned to be used for this project. The
anticipated radius of influence of the multi-beam sonar is less than
that for the airgun array, so it is assumed that any marine mammals
close enough to be affected by the multi-beam sonar 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.
Table 2 explains the corrected density estimates as well as the
best estimate of the numbers of each species that would be exposed to
seismic sounds greater than 160 dB.
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. Furthermore, if they are
encountered, the numbers of mysticetes estimated to occur within the
160-dB isopleth at the Blanco Fracture and Gorda Ridge survey sites are
expected to be low. In addition, the estimated numbers presented in
Table 2 are considered overestimates of actual numbers for two primary
reasons. First, the number of line kilometers used to estimate the
number of exposures and individuals exposed assumes that both the main
and contingency surveys will be completed; this is highly unlikely
given the likelihood that some inclement weather, equipment
malfunction, and/or implementation of mitigative shut downs or power
downs will occur. Secondly, the estimated 160-dB radii used here are
probably overestimates of the actual 160-dB radii at deep water sites
such as the Blanco Fracture and Gorda Ridge sites (Tolstoy et al.,
2004).
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 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 mitigation measures that are planned,
effects on cetaceans are generally expected to be limited to avoidance
of the area around the seismic operation and short-term changes in
behavior, falling within the MMPA definition of Level B harassment.
Furthermore, the estimated numbers of animals potentially exposed to
sound levels sufficient to cause appreciable disturbance are very low
percentages of the population sizes in the NPO generally.
Based on the 160-dB criterion, the best estimates of the numbers of
individual cetaceans that may be exposed to sounds [gteqt]160 dB re 1
microPa (rms) represent 0 to 0.7 percent of the populations of each
species in the NPO. For species listed as endangered under the
Endangered Species Act (ESA), this includes no North Pacific right
whales or sei whales; less than 0.02 percent of the NPO populations of
sperm, humpback and blue whales; and 0.1 percent of the fin whale
population (Table 2). In the cases of mysticetes, beaked whales, and
sperm whales, these potential reactions are expected to involve no more
than very small numbers (0 to 7) of individual cetaceans. Sperm and fin
whales are the endangered species that are most likely to be exposed,
and their NPO populations are approximately 26,053 and 8520,
respectively (Ohsumi and Wada 1974, Carretta et al. 2002).
It is highly unlikely that any right whales will be exposed to
seismic sounds [gteqt]160 dB re 1 microPa (rms). This conclusion is
based on the rarity of this species off Oregon/Washington and in the
NPO generally (less than 100, Carretta et al. 2002), and that the
remnant population of this species apparently migrates to more
northerly areas during the summer. However, L-DEO has requested an
authorization to expose up to two North Pacific right whales to 160 dB,
given the possibility (however unlikely) of encountering one or more of
this endangered species. If a right whale is sighted by the vessel-
based observers, the airguns will be shut down (not just powered down)
regardless of the distance of the whale from the airgun array.
Larger numbers of delphinids may be affected by the proposed main
and contingency seismic studies, but the population sizes of species
likely to occur in the operating area are large, and the numbers
potentially affected are small relative to the population sizes. As
indicated in Table 2, the best estimate of number of individual
delphinids that might be exposed to sounds less than or equal to 160 dB
re 1 microPa (rms) represents a small percentage of the populations of
each species occurring there.
Varying estimates of the numbers of marine mammals that might be
exposed to airgun sounds during the August 2004 seismic surveys off
Oregon have been presented, depending on the specific exposure
criteria, calculation procedures (exposures vs. individuals), and
density criteria used (best vs. maximum). The requested ``take
authorization'' for each species is based on the estimated maximum
number of exposures to [gteqt]160 dB re 1 microPa (rms). That figure
likely overestimates (in most cases by a large margin) the actual
number of animals that will be exposed to these sounds; the reasons for
this are outlined above. Even so, the
[[Page 31803]]
combined estimates for the main and contingency surveys are quite low
percentages of the population sizes. Also, these relatively short-term
exposures are unlikely to result in any long-term negative consequences
for the individuals or their populations.
The many cases of apparent tolerance by cetaceans of seismic
exploration, vessel traffic, and some other human activities show that
co-existence is possible. Mitigation measures such as controlled speed,
course alternation, look outs, non-pursuit, ramp ups, and power downs
or shut downs when marine mammals are seen within defined ranges should
further reduce short-term reactions, and minimize any effects on
hearing sensitivity. In all cases, the effects are expected to be
short-term, with no lasting biological consequence.
In light of the type of take expected and the small percentages of
affected stocks, the action is expected to have no more than a
negligible impact on the affected species or stocks of marine mammals.
In addition, mitigation measures such as controlled vessel speed,
course alteration, look-outs, ramp-ups, and power-downs when marine
mammals are seen within defined ranges (see Mitigation) should further
reduce short-term reactions to disturbance, and minimize any effects on
hearing sensitivity.
Conclusions--Effects on Pinnipeds
Two pinniped species, the northern fur seal and the northern
elephant seal, are likely to be encountered at the survey sites, as
they are associated with pelagic slope and offshore waters off Oregon.
In addition, it is possible (although unlikely) that a small number of
Steller sea lions, California sea lions, and/or harbor seals may also
be encountered, most likely at the Gorda Ridge survey area located
closer to shore in continental slope water; these three species tend to
inhabit primarily coastal and shelf waters. An estimated 79 individual
fur seals and 15 individual elephant seals may be exposed to airgun
sounds with received levels [gteqt]160 dB re 1 microPa (rms). It is
most likely that no California sea lions, Steller sea lions, or harbor
seals will be exposed to such sounds. Similar to cetaceans, the
estimated numbers of pinnipeds that may be exposed to received levels
[gteqt]160 dB are probably overestimates of the actual numbers that
will be significantly affected. This action would therefore have no
more than a negligible impact on the affected species or stocks of
pinnipeds.
Mitigation
For the proposed Blanco Fracture seismic survey, L-DEO will deploy
a 10- or 12-airgun array as an energy source, with discharge volumes of
3050 in3 and 3705 in3, respectively. The airguns in the arrays will be
spread out horizontally so the energy from the array will be directed
mostly downward. The directional nature of the arrays 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. Because the
actual seismic source is a distributed sound source (10-12 airguns)
rather than a single point source, the highest sound levels measurable
at any location in the water will be less than the nominal source
level. Also, the size of the airgun arrays (which are smaller than the
20-gun array used for some other surveys) is another important
mitigation measure that will reduce the potential for effects relative
to those that might occur with a larger array of airguns. This is in
conformance with NMFS' encouraging seismic operators to use the lowest
intensity airguns practical to accomplish research objectives. Also,
that this project is proposed to occur in deep water is also important
as sound levels tend to be lower in deep than in shallow waters at
various distances from the airguns.
Proposed Safety Radii
Received sound levels have been modeled by L-DEO in relation to
distance and direction from the two arrays. The radii around the 10-
airgun array where the received levels would be 180 dB and 190 dB re 1
microPa (rms) were estimated as 550 m (1805 ft) and 200 m (656 ft),
respectively. For the 12-airgun array, the radii around the array where
the received levels would be 180 dB and 190 dB re 1 microPa (rms) were
estimated as 600 m (1969 ft) and 200 m (656 ft), respectively. The 180
and 190 dB shutdown criteria, applicable to cetaceans and pinnipeds,
respectively, are specified by NMFS (2000) and, as mentioned previously
in this document, are considered conservative for protecting marine
mammals from potential injury.
Empirical data concerning these safety radii have been acquired
based on measurements during the acoustic verification study conducted
by L-DEO in the northern Gulf of Mexico from 27 May to 3 June 2003 (see
68 FR 32460, May 30, 2003). L-DEO's analysis of the acoustic data from
that study (Tolstoy et al. 2004) provides limited measurements in deep
water, the situation relevant here. Those data indicate that, for deep
water, the model tends to overestimate the received sound levels at a
given distance. Until additional data become available, it is proposed
that safety radii during airgun operations in deep water, including the
planned operations off Oregon, will be the values predicted by L-DEO's
model. Previously, more conservative (larger) safety radii that are 1.5
times the modeled radii have been used for these surveys. However,
given that these modeled radii are already conservative (i.e.,
overestimates) for deep water situations, even without the X 1.5
factor, these larger radii are not being proposed to be used during
this seismic survey.
Additional Mitigation Measures
The following mitigation measures, as well as marine mammal visual
monitoring (discussed later in this document), are proposed for the
subject seismic surveys, provided that they do not compromise
operational safety requirements: (1) Speed and course alteration; (2)
power-down and shut-down procedures; (3) ramp-up procedures and (4) use
of passive acoustics to detect vocalizing marine mammals. In addition,
special mitigation measures will be implemented for the North Pacific
right whale.
Speed and Course Alteration
If a marine mammal is detected outside the appropriate safety
radius and, based on its position and the relative motion, is likely to
enter the safety radius, the vessel's speed and/or direct course will
be changed if this is practical while minimizing the effects on planned
science objectives. Given the presence of the streamer and airgun array
behind the vessel, the turning rate of the vessel with trailing
streamer and array is no more than five degrees per minute, limiting
the maneuverability of the vessel during operations. 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 radius. If the mammal appears likely to enter the safety radius,
further mitigative actions will be taken, (i.e., either further course
alterations or shutdown of the airguns).
Power-down and Shut-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
[[Page 31804]]
marine mammals are not in the safety zone. A power down may also occur
when the vessel is moving from one seismic line to another, unless the
full airgun array is scheduled to be operated during line changes.
During a power down, one 80 in3 airgun will continue to be operated.
The continued operation of one airgun is intended to alert marine
mammals 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 is detected outside the safety radius but is
likely to enter the safety radius, and if the vessels speed and/or
course cannot be changed to avoid having the mammal enter the safety
radius, the airguns will be powered 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 powered down immediately.
During a power down, at least one airgun (e.g., 80 in\3\) will be
operated. If a marine mammal is detected within or near the smaller
safety radius around that single airgun (Table 1), all airguns will be
shut down.
Following a power 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 min in the case of
mysticetes and large odontocetes, including sperm, pygmy sperm, dwarf
sperm, and beaked whales.
During a power down, the operating airgun will be shut down if a
marine mammal approaches within the modeled safety radius for the then-
operating source, typically a single gun of 80 in3. Because no
calibration measurements have been done to confirm the modeled safety
radii for the single gun, conservative radii may be used (1.5 times the
modeled safety radius). For an 80 in3 airgun, the predicted 180-dB
distance applicable to cetaceans is 36 m (118 ft) and the x1.5
conservative radius is 54 m (177 ft). The corresponding 190-dB radius
applicable to pinnipeds is 13 m (43 ft), with the x1.5 conservative
radius being 20 m (66 ft). If a marine mammal is detected within or
about to enter the appropriate safety radius around the small source in
use during a power down, airgun operations will be entirely shut down.
In addition, the airguns will be shut down if a North Pacific right
whale is sighted anywhere near the vessel, even if it is located
outside the safety radius, because of the rarity and sensitive status
of this species. Resumption of airgun activity will follow procedures
described for power-down operations.
Ramp-up Procedure
When airgun operations commence after a certain period without
airgun operations, the number of guns firing will be increased
gradually, or ``ramped up'' (also described as a ``soft start'').
Operations will begin with the smallest gun in the array (80 in3). Guns
will be added in 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 approximately 18-20 minutes. Throughout the ramp-up
procedure, the safety zone for the full 10- or 12-gun array will be
maintained.
The ``ramp-up'' procedure will be required under the following
circumstances. Under normal operational conditions (vessel speed 4
knots (7.4 km/hr)), a ramp-up would be required after a power-down or
shut-down period lasting more than 4 minutes if the Ewing was towing
the 10- or 12-gun array. At 4 knots, the Ewing would travel 600 m (1969
ft) during a 5-minute period. The 600-m (1969 ft) distance is the
calculated 180-dB safety radius.
If the towing speed is reduced to 3 knots (5.6 km/hr) or less, as
sometimes required when maneuvering in shallow water (not a factor
here), it is proposed that a ramp-up would be required after a ``no
shooting'' period lasting greater than 7 minutes. At towing speeds not
exceeding 3 knots (5.6 km/hr), the source vessel would travel no more
than 600 m (1969 ft) in about 7 minutes. Based on the same calculation,
a ramp-up procedure would be required after a 4-minute period if the
speed of the source vessel was 5 knots (9.3 km/hr).
Ramp-up will not occur if the safety radius has not been visible
for at least 30 minutes prior to the start of ramp-up operations in
either daylight or nighttime. If the safety radius has not been visible
for that 30-minute period (e.g., during darkness or fog), ramp-up will
not commence unless at least one airgun has been firing continuously
during the interruption of seismic activity. That airgun will have a
source level of at least 180 dB re 1 microPa m (rms). It is likely that
the airgun arrays 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
those arrays 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 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 marine mammal is sighted
within or near the applicable safety radii during the day or close to
the vessel at night.
Comments on past proposed IHAs raised the issue of prohibiting
night-time operations as mitigation. However, this is not practicable
due to cost considerations. The daily cost to the Federal Government to
operate vessels such as Ewing is approximately $33,000 to $35,000/day
(Ljunngren, pers. comm. May 28, 2003). If the vessels were prohibited
from operating during nighttime, it is possible that each trip would
require an additional three to five days, or up to $175,000 more,
depending on average daylight at the time of work.
Taking into consideration the additional costs of prohibiting
night-time operations and the likely impact of the activity (including
all mitigation and monitoring), NMFS has preliminarily determined that
the proposed mitigation and monitoring ensures 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 (at least 1 hour in advance), thereby giving
them an opportunity to avoid the approaching array; if ramp-up is
required after an extended power-down, two marine mammal observers will
be required to monitor the safety radii using night vision devices for
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; and ramp-up may occur at night only if
one airgun with a sound pressure level of at least 180 dB has been
maintained during interruption of seismic activity. Therefore it is
likely that the 10-12-airgun array will not be ramped-up from a shut-
down at night.
Marine Mammal Monitoring
L-DEO must have at least three visual observers and two passive
acoustic system biological monitors on board the vessels, and at least
two must be an experienced marine mammal observer that NMFS approves.
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
[[Page 31805]]
nighttime start-ups of the airguns and at night, whenever daytime
monitoring resulted in one or more power-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 an extended power-down or
shut-down.
Use of multiple observers will increase the likelihood that marine
mammals near the source vessel are detected. L-DEO 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. On the bridge of the Maurice Ewing, the observer's
eye level will be 11 m (36 ft) above sea level, allowing for good
visibility within a 210 arc. If observers are stationed on the flying
bridge, the eye level will be 14.4 m (47.2 ft) above sea level. The
observer(s) will systematically scan the area around the vessel with
Big Eyes 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 airguns are powered or
shut down, observers will maintain watch to determine when the animal
is outside the safety radius.
Observers will not be on duty during ongoing seismic operations at
night; bridge personnel will watch for marine mammals during this time
and will call for the airguns to be powered-down if marine mammals are
observed in or about to enter the safety radii. However, an observer
must be on standby at night and available to assist the bridge watch if
marine mammals are detected. If the airguns are ramped-up at night from
a power-down situation, two marine mammal observers will monitor for
marine mammals for 30 minutes prior to ramp-up and during the ramp-up
using night vision equipment that will be available (ITT F500 Series
Generation 3 binocular image intensifier or equivalent). All observer
activity will be assisted by the passive acoustic monitoring (PAM)
system where its use is feasible.
Passive (Acoustic) Monitoring
L-DEO will use the PAM system whenever the vessel is operating in
waters deep enough for the PAM hydrophone array to be towed. Passive
acoustic equipment was first used on the Ewing during the 2003 Sperm
Whale Seismic Study conducted in the Gulf of Mexico and subsequently
was evaluated by L-DEO to determine whether it was practical to
incorporate it into future seismic research cruises. The SEAMAP system
has been used successfully in L-DEO's SE Caribbean study (69 FR 24571,
May 4, 2004). The SEAMAP PAM system has four hydrophones, which allow
the SEAMAP system to derive the bearing toward the a vocalizing marine
mammal. In order to operate the SEAMAP system, the marine mammal
monitoring contingent onboard the Ewing will be increased by 2 to 3
additional biologists who will monitor the SEAMAP system. Verification
of acoustic contacts will then be attempted through visual observation
by the marine mammal observers. However, the PAM system by itself
usually does not determine the distance that the vocalizing mammal
might be from the seismic vessel. It can be used as a cue by the visual
observers as to the presence of an animal and to its approximate
bearing (with some ambiguity). At this time, however, it is doubtful if
PAM can be used as a trigger to initiate power-down of the array.
Perhaps with continued studies the relationship between a signal on a
passive acoustic array and distance from the array can be determined
with sufficient accuracy to be used for this purpose without
complementary visual observations.
Reporting
L-DEO will submit a report to NMFS within 90 days after the end of
the cruise, which is currently predicted to occur during August, 2004.
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
amount and nature of potential take of marine mammals by harassment or
in other ways.
ESA
Under section 7 of the ESA, the National Science Foundation (NSF),
the agency funding L-DEO, has begun consultation on the proposed
seismic survey. NMFS will also consult 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)
The NSF has prepared an EA for the Blanco Fracture Zone
oceanographic seismic surveys. NMFS is reviewing this EA and will
either adopt it or prepare its own NEPA document before making a
determination on the issuance of an IHA. A copy of the NSF EA for this
activity is available upon request (see ADDRESSES).
Preliminary Conclusions
NMFS has preliminarily determined that the impact of conducting the
seismic survey on the Blanco Fracture Zone in the NPO. will 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 preliminary
determination is supported by (1) the likelihood that, given sufficient
notice through slow ship speed and ramp-up, marine mammals are expected
to move away from a noise source that it finds annoying prior to its
becoming potentially injurious; (2) recent research that indicates that
TTS is unlikely (at least in delphinids) at 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 within 100 m (328 ft) of
the vessel; and (4) the likelihood that marine mammal detection ability
by trained observers is close to 100 percent during daytime and remains
high at night to that distance from the seismic vessel. As a result, no
take by injury and/or death is anticipated, and the potential for
temporary or permanent hearing impairment is very low and will be
avoided through the incorporation of the mitigation measures mentioned
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
[[Page 31806]]
harassment takings is estimated to be small. In addition, the proposed
seismic program is not expected to interfere with any 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.
Proposed Authorization
NMFS proposes to issue an IHA to L-DEO for conducting a
oceanographic seismic surveys on the Blanco Fracture Zone in the NPO,
provided the previously mentioned mitigation, monitoring, and reporting
requirements are incorporated. NMFS has preliminarily determined that
the proposed activity would result in the harassment of small numbers
of marine mammals; would have no more than a negligible impact on the
affected marine mammal stocks; and would not have an unmitigable
adverse impact on the availability of species or stocks for subsistence
uses.
Information Solicited
NMFS requests interested persons to submit comments and information
concerning this request (see ADDRESSES).
Dated: May 25, 2004.
Laurie K. Allen,
Director, Office of Protected Resources, National Marine Fisheries
Service.
[FR Doc. 04-12810 Filed 6-4-04; 8:45 am]
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