Federal Register, Volume 75, Number 95, May 18, 2010, Pages 27631-27922 Page: 27,712
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Federal Register/Vol. 75, No. 95/Tuesday, May 18, 2010/Notices
the Beaufort Sea in 2007 and 2008.
Ribbon seals do not normally occur in
the Beaufort Sea; however, two ribbon
seal sightings were reported during
vessel-based activities near Prudhoe Bay
in 2008 (Savarese et a]. 2009).
The bowhead and humpback whales
are listed as "endangered" under the
Endangered Species Act (ESA) and as
depleted under the MMPA. Certain
stocks or populations of gray, beluga,
and killer whales and spotted seals are
listed as endangered or proposed for
listing under the ESA; however, none of
those stocks or populations occur in the
proposed activity area. Additionally, the
ribbon seal is considered a "species of
concern" under the ESA, and the
bearded and ringed seals are "candidate
species" under the ESA, meaning they
are currently being considered for
listing.
Shell's application contains
information on the status, distribution,
seasonal distribution, and abundance of
each of the species under NMFS
jurisdiction mentioned in this
document. Please refer to the
application for that information (see
ADDRESSES). Additional information can
also be found in the NMFS Stock
Assessment Reports (SAR). The Alaska
2009 SAR is available at: http://www.
nmfs.noaa.gov/pr/pdfs/sars/ak2009.pd f.
Potential Effects of the Specified
Activity on Marine Mammals
Operating a variety of active acoustic
sources such as airguns, side-scan
sonars, echo-sounders, and sub-bottom
profilers for site clearance and shallow
hazard surveys, ice gouge, and strudel
surveys can impact marine mammals in
a variety of ways.
Potential Effects of Airgun Sounds on
Marine Mammals
The effects of sounds from airgun
pulses might include one or more of the
following: tolerance, masking of natural
sounds, behavioral disturbance, and
temporary or permanent hearing
impairment or non-auditory effects
(Richardson et al. 1995). As outlined in
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) Tolerance
Numerous studies have shown that
pulsed sounds from airguns are often
readily detectable in the water at
distances of many kilometers.
Numerous studies have also shown that
marine mammals at distances more than
a few kilometers from operating seismicvessels 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. Although various baleen whales,
toothed whales, and (less frequently)
pinnipeds have been shown to react
behaviorally to airgun pulses under
some conditions, at other times,
mammals of all three types have shown
no overt reactions. In general, pinnipeds
and small odontocetes seem to be more
tolerant of exposure to airgun pulses
than baleen whales.
(2) Behavioral Disturbance
Marine mammals may behaviorally
react to sound when exposed to
anthropogenic noise. These behavioral
reactions are often shown as: changing
durations of surfacing and dives,
number of blows per surfacing, or
moving direction and/or speed;
reduced/increased vocal activities;
changing/cessation of certain behavioral
activities (such as socializing or
feeding); visible startle response or
aggressive behavior (such as tail/fluke
slapping or jaw clapping); avoidance of
areas where noise sources are located;
and/or flight responses (e.g., pinnipeds
flushing into water from haulouts or
rookeries).
The biological significance of many of
these behavioral disturbances is difficult
to predict, especially if the detected
disturbances appear minor. However,
the consequences of behavioral
modification could be expected to be
biologically significant if the change
affects growth, survival, and
reproduction. Some of these significant
behavioral modifications include:
* Drastic change in diving/surfacing
patterns (such as those thought to be
causing beaked whale stranding due to
exposure to military mid-frequency
tactical sonar);
* Habitat abandonment due to loss of
desirable acoustic environment; and
* Cease feeding or social interaction.
For example, at the Guerreo Negro
Lagoon in Baja California, Mexico,
which is one of the important breeding
grounds for Pacific gray whales,
shipping and dredging associated with a
salt works may have induced gray
whales to abandon the area through
most of the 1960s (Bryant et al. 1984).
After these activities stopped, the
lagoon was reoccupied, first by single
whales and later by cow-calf pairs.
The onset of behavioral disturbance
from anthropogenic noise depends on
both external factors (characteristics of
noise sources and their paths) and thereceiving animals (hearing, motivation,
experience, demography) and is also
difficult to predict (Southall et al. 2007).
Currently NMFS uses 160 dB re 1 pPa
at received level for impulse noises
(such as airgun pulses) as the onset of
marine mammal behavioral harassment.
(3) Masking
Chronic exposure to excessive, though
not high-intensity, noise could cause
masking at particular frequencies for
marine mammals that utilize sound for
vital biological functions. Masking can
interfere with detection of acoustic
signals such as communication calls,
echolocation sounds, and
environmental sounds important to
marine mammals. Since marine
mammals depend on acoustic cues for
vital biological functions, such as
orientation, communication, finding
prey, and avoiding predators, marine
mammals that experience severe
acoustic masking will have reduced
fitness in survival and reproduction.
Masking occurs when noise and
signals (that the animal utilizes) overlap
at both spectral and temporal scales. For
the airgun noise generated from the
proposed site clearance and shallow
hazards surveys, noise will consist of
low frequency (under 1 kHz) pulses
with extremely short durations (in the
scale of milliseconds). Lower frequency
man-made noises are more likely to
affect detection of communication calls
and other potentially important natural
sounds such as surf and prey noise.
There is little concern regarding
masking near the noise source due to
the brief duration of these pulses and
relatively longer silence between airgun
shots (9-12 seconds). However, at long
distances (over tens of kilometers away),
due to multipath propagation and
reverberation, the durations of airgun
pulses can be "stretched" to seconds
with long decays (Madsen et al. 2006).
Therefore it could affect communication
signals used by low frequency
mysticetes when they occur near the
noise band and thus reduce the
communication space of animals (e.g.,
Clark et al. 2009) and cause increased
stress levels (e.g., Foote et al. 2004; Holt
et al. 2009). Nevertheless, the intensity
of the noise is also greatly reduced at
such long distances (for example, the
modeled received level drops below 120
dB re 1 pPa rms at 14,900 m from the
source).
Marine mammals are thought to be
able to compensate for masking by
adjusting their acoustic behavior such as
shifting call frequencies, increasing call
volume and vocalization rates. For
example, blue whales are found to
increase call rates when exposed toseismic survey noise in the St. Lawrence
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United States. Office of the Federal Register. Federal Register, Volume 75, Number 95, May 18, 2010, Pages 27631-27922, periodical, May 18, 2010; Washington D.C.. (https://digital.library.unt.edu/ark:/67531/metadc52676/m1/90/: accessed April 19, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.