[Federal Register Volume 69, Number 238 (Monday, December 13, 2004)]
[Notices]
[Pages 72167-72180]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 04-27266]
-----------------------------------------------------------------------
DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
[I.D. 070104A]
Small Takes of Marine Mammals Incidental to Specified Activities;
Marine Seismic Survey in the Eastern Tropical Pacific Ocean off Central
America
AGENCY: National Marine Fisheries Service (NMFS), National Oceanic and
Atmospheric Administration (NOAA), Commerce.
ACTION: Notice of issuance of an incidental harassment authorization.
-----------------------------------------------------------------------
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 oceanographic seismic surveys
in the in the eastern tropical Pacific Ocean (ETPO) off Central America
has been issued to the Lamont-Doherty Earth Observatory (L-DEO), a part
of Columbia University.
DATES: Effective from November 19, 2004 through November 18, 2005.
ADDRESSES: The application and authorization are available by writing
to Steve Leathery, Chief, Permits, Conservation and Education Division,
Office of Protected Resources, National Marine Fisheries Service, 1315
East-West Highway, Silver Spring, MD 20910-3225, by telephoning the
contact listed here and are 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) 713-2289, 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.
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.
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 28, 2004, NMFS received an application from L-DEO for the
taking, by harassment, of several species of marine mammals incidental
to conducting a marine seismic survey program during a 4-week period
beginning in late November 2004 in the Exclusive Economic Zones of El
Salvador, Honduras, Nicaragua, and Costa Rica. The purpose of the
seismic survey is to investigate stratigraphic development in the
presence of tectonic forcing in the Sandino basin off Nicaragua and
Costa Rica. Because of the variations in subsidence/uplift histories
within the Sandino Basin, and the inability to provide whole-basin
coverage during a research cruise of reasonable length, data will be
collected in two primary grids in the Sandino Basin and a third,
smaller grid off Nicoya Peninsula. Grid descriptions are provided in L-
DEO's application.
Description of the Activity
The seismic survey will involve one vessel. The source vessel, the
R/V Maurice Ewing, will deploy three low-energy GI airguns as an energy
source, with a total discharge volume of up to 315 in3. As the airguns
are towed along the survey lines, the towed hydrophone system will
receive the returning acoustic signals.
The program will consist of a maximum of 6048 km (3266 nm) of
surveys. Water depths within the survey area are up to 5000 m (16,400
ft); most of the survey will be conducted in water depths less than
2000 m (6560 ft). The area to be surveyed extends from approximately 4
to 150 km (2 to 80 nm) offshore. The airguns may also be operated
closer to, and farther from, shore while the ship is maneuvering toward
or between survey lines.
The proposed program will use conventional seismic methodology with
a small towed array of three GI airguns as the energy source, and a
towed hydrophone streamer as the receiver system. The energy to the
airguns is compressed air supplied by compressors on board the source
vessel. Seismic pulses will be emitted at intervals of 5 seconds. The
5-sec spacing corresponds to a shot interval of approximately 12.5 m
(41 ft).
The generator chamber of each GI gun, the one responsible for
introducing the sound pulse into the ocean, is 105 in\3\. The injector
chamber injects air into the previously generated bubble to maintain
its shape, and does not introduce appreciably more sound into the
water. The three 105-in\3\ GI guns will be towed behind the Ewing, at a
[[Page 72168]]
depth of 2.5 m (8.2 ft). Operating pressure will be 2000 psi. The GI
guns will be 7.8 m (25.6 ft) apart and will be towed 37 m (121.4 ft)
behind the Ewing. The Ewing will also tow a hydrophone streamer that is
up to 1500 m (4922 ft) long. As the airguns are operated along the
survey lines, the hydrophone receiving system will receive and record
the returning acoustic signals.
General-Injector Airguns
Three GI-airguns will be used from the Ewing during the proposed
program. These 3 GI-airguns have a zero to peak (peak) source output of
240.7 dB re 1 microPascal-m (10.8 bar-m) and a peak-to-peak (pk-pk)
level of 246 dB (21 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 decibels 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 2.5 m (6.7 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 later in
this document (see Characteristics of Airgun Pulses).
For the GI-airguns, the sound pressure fields have been modeled by
L-DEO in relation to distance and direction from the airguns, and in
relation to depth. Table 1 shows the maximum distances from the airguns
where sound levels of 190-, 180-, 170- and 160-dB re 1 microPa (rms)
are predicted to be received. Some empirical data concerning the 180,
170 and 160 dB distances have been acquired for several airgun
configurations, including two GI-guns, 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 (see Tolstoy et al., 2004). Although
the results are limited and do not include measurements for three GI-
guns, the data for other airgun configurations showed that water depth
affected the size of 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. Water depths within the survey area are up to
5000 m (16400 ft), but the major part of the survey will be conducted
in water depths less than 1000 m (3281 ft), as shown in Table 1, column
3.
Table 1. Estimated distances to which sound levels [gteqt]190, 180,
170 and 160 dB re 1 microPa (rms) might be received from (A) three 105
in\3\ GI guns and (B) one of those guns, as planned for the seismic
survey off the west coast of Central America during November December
2004. Distance estimates are given for operations in deep,
intermediate, and shallow water. The 180- and 190-dB distances are the
safety radii to be used during the survey. Three GI guns will be used
for the survey and one GI gun will be used during power down.
----------------------------------------------------------------------------------------------------------------
% of Estimated distances at received
seismic levels (m)
Airgun configuration Water depth survey -----------------------------------
conducted 190 dB 180 dB 170 dB 160 dB
----------------------------------------------------------------------------------------------------------------
A. 3 GI guns >1000 m 11.6 26 82 265 823
100-1000 m 57.9 39 123 398 1235
<100 m 30.6 390 574 1325 2469
B. 1 GI gun >1000 m ......... 10 27 90 275
00-1000 m ......... 15 41 135 413
<100 ......... 150 189 450 825
----------------------------------------------------------------------------------------------------------------
The empirical data indicate that, for deep water (greater than 1000
m (3281 ft)), the L-DEO model for the airguns 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, the mitigation safety radii during airgun operations in
deep water will be the values predicted by L-DEO's model (see Table 1).
The 180- and 190-dB radii were not measured for three GI- guns
operating in shallow water (less than 100 m (328 ft)). However, the
measured 180-dB radius for the 6-airgun array operating in shallow
water was 6.8x that predicted by L-DEO's model for operation of the
six-airgun array in deep water. This conservative correction factor is
applied to the model estimates to predict the radii for the three GI-
guns in shallow water, as shown in Table 1.
Empirical measurements were not conducted for intermediate depths
(100-1000 m (328-3281 ft)). On the expectation that results will fall
between those for shallow and deep water, a 1.5x correction factor is
applied to the estimates provided by the model for deep water
situations, as shown in Table 1. This is the same factor that was
applied to the model estimates during L-DEO cruises in 2003.
Bathymetric Sonar and Sub-bottom Profiler
In addition to the 3 GI-airguns, a multibeam bathymetric sonar and
a low-
[[Page 72169]]
energy 3.5-kHz sub-bottom profiler will be used during the seismic
profiling and continuously when underway.
Bathymetric Sonar-Atlas Hydrosweep - The 15.5-kHz Atlas Hydrosweep
sonar 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 (similar to the shallow-
water mode but with a source output of 220 dB (rms)) 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 (much less than 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 1/5 of these values
or 2/5 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. During the
project, the Atlas Hydrosweep will generally be used in waters greater
than 800 m (2624.7 ft), but whenever water depths are less than 400 m
(1312 ft) the source output is 210 dB re 1 microPa-m (rms) and a single
1-ms pulse or ``ping'' per second is transmitted.
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 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 300 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.
Although the sound levels have not been measured directly for the
sub-bottom profilers used by the Ewing, Burgess and Lawson (2000)
measured sounds propagating more or less horizontally from a sub-bottom
profiler similar to the L-DEO 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 L-DEO 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.
Additional information is contained in the L-DEO application,
especially in Appendix A.
Comments and Responses
A notice of receipt and request for 30-day public comment on the
application and proposed authorization was published on September 30,
2004 (69 FR 58396). During the 30-day public comment period, NMFS
received one comment which expressed the opinion that marine mammals
should not be killed and that these killings are not small. As noted in
this document, NMFS believes that no marine mammals are likely to be
seriously injured or killed as a result of this L-DEO conducting
seismic surveys.
Description of Habitat and Marine Mammals Affected by the Activity
A detailed description of the ETPO 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. Thirty-
four species of cetaceans are known to occur in the ETPO, belonging to
two taxonomic groups: odontocetes (sperm whale, dwarf sperm whale,
pygmy sperm whale, Cuvier's beaked whale, Longman's beaked whale, pygmy
beaked whale, gingko-toothed beaked whale, Blainville's beaked whale,
rough-toothed dolphin, bottlenose dolphin, pantropical spotted dolphin,
spinner dolphin, striped dolphin, short-beaked common dolphin, Fraser's
dolphin, Risso's dolphin, melon-headed whale, pygmy killer whale, false
killer whale, killer whale, and short-finned pilot whale); and
mysticetes (humpback whale, minke whale, sei whale, fin whale, Bryde's
whale, and blue whale). Of these 34 species, 27 cetacean species are
likely to occur in the survey area. These 27 species are shown in Table
2 of this document and are described in L-DEO (2004)).
Seven cetacean species (Pacific white-sided dolphin, Baird's beaked
whale, long-beaked common dolphin, dusky dolphin, southern right whale
dolphin, Burmeister's porpoise, and long-finned pilot whale) although
present in the wider ETPO, are unlikely to be found in L-DEO's proposed
survey area (L-DEO, 2004). These species are mentioned briefly in L-
DEO's application, but are unlikely to be taken by incidental
harassment and therefore are not analyzed further in this document.
Six species of pinnipeds are known to occur in the ETPO: Guadalupe
fur seal, California sea lion, Galapagos sea lion, Galapagos fur seal,
southern sea lion, and South American fur seal. The last four species
could potentially occur within the proposed seismic survey area, but
they are expected to be, at most, uncommon. Ranges of the first two
species are substantially north of the proposed seismic survey area and
therefore unlikely to be taken by incidental harassment.
More detailed information on these species is contained in the L-
DEO application, which is available at: http://www.nmfs.noaa.gov/prot_res/PR2/Small_Take/smalltake_info.htm#applications.
Potential Effects on Marine Mammals
The effects of sounds from airgun arrays might include one or more
of the following: tolerance, masking of natural sounds, behavioral
disturbance and perhaps temporary or permanent hearing impairment
(Richardson et al. 1995). In addition, intense acoustic 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.
[[Page 72170]]
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) 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. L-DEO 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
823 m (2700 ft) in deep water and 2469 m (8100 ft) in shallow water,
the zones calculated for 160 dB or the onset of Level B harassment.
Additional discussion on species-specific effects can be found in the
L-DEO application.
Tolerance
Numerous studies (referenced in L-DEO, 2004) 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 and 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 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 source planned for use in the ETPO, there is even
less potential for masking of baleen or sperm whale calls during the
present research than in most seismic surveys (L-DEO, 2004). Seismic
sounds are short pulses generally occurring for less than 1 sec every 5
seconds or so. The 5-sec spacing corresponds to a shot interval of
approximately 12.5 m (41 ft). 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 or at most 2/5 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). 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 ETPO.
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. 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 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 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
may 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
[[Page 72171]]
affected in some biologically important manner.
The sound exposure levels 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 in L-DEO's ETPO 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 this 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 L-DEO application and summarized
here,
1. The 180-dB criterion for onset of Level A harassment in
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.
Because of the small size of the three 105 in3 GI-airguns, along
with the required 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 monitoring and mitigation
measures for this project are designed to detect marine mammals
occurring near the 3 GI-airguns (and multibeam 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, L-DEO
and NMFS believe that it is especially unlikely that any of these non-
auditory effects would occur during the proposed survey given the small
size of the 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. Such sound
levels would be limited to distances within a few meters of the small
airguns planned for use during this project.
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, 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).
A marine mammal within a zone of less than 100 m (328 ft) around a
typical large 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. Also, around smaller
arrays, such as the three GI-airgun array that will be used 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, at least in
waters greater than 100 m (328 ft) deep. 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 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
[[Page 72172]]
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 bow of the Ewing
will be 107 m (351 ft) ahead of the airguns and the 205-dB zone would
be less than 100 m (328 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.
Currently, 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 L-DEO 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 will 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 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, as mentioned
previously, 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 may 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 frequency, 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 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, 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 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 the subject
seismic survey 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 three 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
[[Page 72173]]
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, recently, an L-DEO seismic survey have 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 microPa, 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 not determined
whether there were noise-induced injuries to the ears or other organs.
Another stranding of 15 beaked whales occurred 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 (the bends or air embolism) 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 decompression injury.
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 Cuvier's 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 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 to affect beaked whales than the naval sonars. 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 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 the proposed L-DEO project where
the airguns are small.
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 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 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.),
[[Page 72174]]
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.
Until recently, it was assumed that diving marine mammals are not
subject to the bends or air embolism. However, a 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, decompression injury might occur if
cetaceans ascend unusually quickly when exposed to aversive sounds.
However, the interpretation that the effect was related to
decompression injury is unproven (Piantadosi and Thalmann, 2004;
Fernandez et al., 2004). Even if that effect can occur during exposure
to mid-frequency 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 the L-DEO survey which involves only three GI-
guns.
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 (Atlas Hydrosweep DS-2 (15.5-kHz)
and a sub-bottom profiler will be operated from the source vessel
essentially continuously during 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 sonars, (2) have a longer pulse duration, and (3) are
directed close to horizontally (vs. downward for the Atlas Hydrosweep).
The area of possible influence for the Ewing's sonars 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 mammals that do encounter the bathymetric sonars 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 (approximately 10 ms) 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 Hydrosweep sonar do
not overlap with the predominant frequencies of the 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 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. The pulsed signals
from the sub-bottom profiler are much weaker than those from the airgun
array and the multibeam sonar. Therefore, significant behavioral
responses are not expected.
[[Page 72175]]
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 on Marine Mammals). However, the multi-beam sonars
proposed for use by L-DEO are quite different than 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 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 ETPO 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 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 and about 16 dB less than its pk-pk level
(Greene, 1997; McCauley et al., 1998; 2000a). The criterion for Level B
harassment onset is 160 dB.
Given the mitigation required under this IHA (see Mitigation later
in this document), all anticipated takes 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. L-DEO has calculated the ``best estimates''
for the numbers of animals that could be taken by level B harassment
during the proposed ETPO 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 (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, the criterion for the onset of Level B harassment, by operations
with the 3 GI-gun array planned to be used for this project. The
anticipated zone of influence of the multi-beam sonar is less than that
for the airguns, 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. A detailed description on the
methodology used by L-DEO to arrive at the estimates of Level B
harassment takes that are provided in Table 2 can be found in L-DEO's
IHA application for the ETPO survey.
[[Page 72176]]
[GRAPHIC] [TIFF OMITTED] TN13DE04.000
[[Page 72177]]
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 ETPO (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 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 three GI-guns 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, 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 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 0 to approximately 0.4 percent (except for
approximately 2.4 percent for dwarf sperm whales) of the regional ETPO
species populations (Table 2). L-DEO also estimates that approximately
0.1 percent of the estimated (corrected) regional ETPO population of
approximately 26,053 sperm whales (Table 2) would be exposed to sounds
>160 dB re 1 microPa (rms). In the case of endangered balaenopterids,
it is most likely that no humpback, sei, or fin whales will be exposed
to seismic sounds > 160 dB re 1 microPa (rms), based on the reported
(corrected) densities of those species in the survey region. However,
L-DEO has requested an authorization to expose up to 2 individuals of
each of those species to seismic sounds of [gteqt] 160 dB during the
proposed survey given the possibility of encountering one or more
groups. Best estimates of blue whales are 3 individuals that might be
potentially exposed to seismic pulses with received levels [gteqt] 160
dB re 1 microPa (rms), representing approximately 0.2 percent of the
estimated regional ETP population of approximately 1400 blue whales
(Table 2).
Larger 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). The best estimates of the
numbers of individual delphinids that will potentially be exposed to
sounds > 160 dB re 1 microPa (rms) represent less than 0.1 percent of
the approximately 10,000,000 dolphins estimated to occur in the ETPO,
and less than 0.3 percent of the bottlenose dolphin population
occurring there (Table 2).
Mitigation measures such as controlled speed, course alteration,
observers, use of the PAM system, 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. 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 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
It is unlikely that any pinnipeds will be encountered during the
proposed survey. However, to ensure that the L-DEO project remains in
compliance with the MMPA in the event that a few pinnipeds are
encountered, L-DEO has requested an authorization to expose up to 10
individuals of each of four pinniped species to seismic sounds with rms
levels > 160 dB re 1 microPa. If pinnipeds are encountered, they will
be stray individuals outside of their normal range. The proposed 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 three 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
passing 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
microPa (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
[[Page 72178]]
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
proposed surveys would have little impact on the abilities of marine
mammals to feed in the area where seismic work is planned. Some of the
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 legal subsistence hunting for marine mammals in the
ETPO off Central America, so the proposed L-DEO 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 ETPO off Central America, L-
DEO will deploy three GI-airguns as an energy source, with a total
discharge volume of 315 in\3\. The energy from the airguns will be
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 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)
power-down and shut-down procedures; (3) ramp-up procedures, (4) use of
passive acoustics to detect vocalizing marine mammals and (5)
incorporation of a protocol that seismic lines will be run from shallow
water towards deeper water whether the lines are being run parallel to
shore or perpendicular to shore. This last mitigation measure would
mitigate potential takings of beaked whales. Some of these mitigation
measures will also be implemented to protect sea turtles.
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 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).
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 marine mammals are not in the safety zone. During a power
down, one GI-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 vessel's speed and/or
course cannot be changed to avoid having the mammal enter the safety
radius, the GI-guns 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, one GI-airgun (i.e., 105 in\3\) will be operated.
If a marine mammal is detected within or near the smaller safety radius
around that single GI-gun (Table 1), all guns 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 airgun operations following a power-down whose duration has
exceeded these specified limits, the airgun array will be ramped-up
gradually. Ramp-up is described later in this document.
During a power-down, the operating GI-airgun will be shut down if a
marine mammal approaches and is about to enter the modeled safety
radius for the operating single GI gun. For a 105 in3 GI gun, the
predicted 180-dB distances applicable to cetaceans are 27-189 m (89-620
ft), depending on water depth, and the corresponding 190-dB radii
applicable to pinnipeds are 10-150 m (33-492 ft), depending on depth
(Table 1). Airgun activity will not resume until the marine mammal has
cleared the safety radius, as described for power-down situations.
Ramp-up Procedure
When airgun operations commence after a specified period without
airgun operations, the number of guns firing will be increased
gradually, or ``ramped up'' (also described as a ``soft start''). The
specified period of time for the GI-airguns varies depending on the
speed of the source vessel. Under normal operational conditions (vessel
speed 4.9 knots or 9 km/h), the Ewing would travel 574 m (1476 ft) in
about 4 minutes. The 574-m distance is the calculated 180-dB safety
radius for the three GI-gun array operating in shallow water. Thus, a
ramp-up would be required after a power-down or shut-down period
lasting about 4 minutes or longer if the Ewing was traveling at 4.9
knots and was towing the three GI-airgun array. Ramp up will begin with
one of the 105-in\3\ GI guns. The other two GI-guns will be added at 5
min intervals. During ramp up, the safety radius for the full gun array
will be maintained.
[[Page 72179]]
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). However, ramp-up may occur from a power down in heavy fog
or high sea states, as long as at least one GI gun has been maintained
during the interruption of seismic activity.
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. However, lights and NVDs will probably not be very
effective as a basis for monitoring the larger safety radii around the
three GI-guns operating in shallow water. It is an IHA requirement
that, in shallow water, nighttime start ups of the airguns will not be
authorized. However, ramp-up may occur from a power-down at night, as
long as at least one GI-gun has been maintained during the interruption
of the seismic signal. Also, if the airgun array has been operational
before nightfall, it can remain operational throughout the night, even
though the entire safety radius may not be visible.
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. The
daily cost to operate vessels such as Ewing is approximately $33,000-
$35,000/day (Ljunngren, pers. comm. May 28, 2003). If the vessels were
prohibited from operating during nighttime, each trip could require an
additional three to five days to complete, or up to $175,000 more,
depending on average daylight at the time of work.
If a seismic survey vessel is limited to daylight seismic
operations, efficiency would also be much reduced. Without commenting
specifically on how that 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
L-DEO must have at least three visual observers on board the Ewing,
and at least two must be an experienced marine mammal observer that
NMFS has approved in advance of the start of the ETPO 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. 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 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 GI-airguns are powered-
down 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 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. If the airguns are
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 Ewing returns
along a parallel transect track and when the Ewing runs seismic lines
perpendicular to previously run seismic lines. A final post-survey
transect will be conducted by the Ewing as it retrieves the towed
hydrophone array. 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)
L-DEO has agreed to use the PAM system whenever the Ewing 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 additional biologists/acousticians 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. NMFS encourages L-DEO to continue to study the relationship
between a signal on a passive acoustic array and distance from the
array can be determined with
[[Page 72180]]
sufficient accuracy to be used for this purpose without complementary
visual observations.
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 requirements 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 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.
Therefore as mentioned earlier, it is likely that the 3 GI-airgun array
will not be ramped-up from a shut-down at night when in waters
shallower than 100 m (328 ft).
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 November and
December, 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.
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 June 24, 2004, based on
information contained within its EA, that implementation of the subject
action is not a major Federal action having significant effects on the
environment within the meaning of NEPA. NSF determined, therefore, that
an environmental impact statement would not be prepared. On September
30, 2004 (69 FR 58396), NMFS noted that the NSF had prepared an EA for
the ETPO surveys and made this EA was available upon request. 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 (see ADDRESSES).
Determinations
NMFS has determined that the impact of conducting the seismic
survey in the ETPO off Central America 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 sufficient notice
through slow ship speed and ramp-up, marine mammals are expected to
move away from a noise source that is annoying prior to its becoming
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 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 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 harassment
takings is estimated to be small. In addition, the proposed seismic
program will not interfere with any 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
NMFS has issued an IHA to L-DEO to take marine mammals, by
harassment, incidental to conducting seismic surveys in the ETPO for a
1-year period, provided the mitigation, monitoring, and reporting
requirements are undertaken.
Dated: December 7, 2004.
Stephen L. Leathery,
Acting Director, Office of Protected Resources, National Marine
Fisheries Service.
[FR Doc. 04-27266 Filed 12-10-04; 8:45 am]
BILLING CODE 3510-22-S