[Federal Register Volume 64, Number 112 (Friday, June 11, 1999)]
[Notices]
[Pages 31548-31553]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 99-14902]
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DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
[I.D. 021699A]
Small Takes of Marine Mammals Incidental to Specified Activities;
Seismic Hazards Investigation in Southern California
AGENCY: National Marine Fisheries Service (NMFS), National Oceanic and
Atmospheric Administration (NOAA), Commerce.
ACTION: Notice of issuance of an incidental harassment authorization.
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SUMMARY: In accordance with provisions of the Marine Mammal Protection
Act (MMPA) as amended, notification is hereby given that an Incidental
Harassment Authorization (IHA) to take small numbers of marine mammals
by harassment incidental to collecting marine seismic-reflection data
offshore from southern California has been issued to the U.S.
Geological Survey (USGS).
DATES: This authorization is effective from June 3, 1999, through July
31, 1999.
ADDRESSES: A copy of the application may be obtained by writing to
Donna Wieting, Acting Chief, Marine Mammal Division, Office of
Protected Resources, National Marine Fisheries Service, 1315 East-West
Highway, Silver Spring, MD 20910-3225, or by telephoning one of the
contacts listed here.
FOR FURTHER INFORMATION CONTACT: Kenneth R. Hollingshead, NMFS, (301)
713-2055, or Christina Fahy, NMFS, 562-980-4023.
SUPPLEMENTARY INFORMATION:
Background
Sections 101(a)(5)(A) and (D) of the MMPA (16 U.S.C. 1361 et seq.)
directs 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.''
Subsection 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. The MMPA now defines ``harassment'' as:
...any act of pursuit, torment, or annoyance which
(a) has the potential to injure a marine mammal or
marine mammal stock in the wild; or (b) 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.
Subsection 101(a)(5)(D) establishes a 45-day time limit for NMFS
review of an application followed by a 30-day public notice and comment
period on any proposed authorizations for the incidental harassment of
small numbers of marine mammals. Within 45 days of the close of the
comment period, NMFS must either issue or deny issuance of the
authorization.
Summary of Request
On January 15, 1999, NMFS received a request from the USGSfor
authorization to take small numbers of several species of marine
mammals by harassment incidental to collecting marine seismic-
reflection data offshore from southern California. Seismic data was
planned to be collected during a 2-week period between May and July
1999 to support studies of the regional landslide and earthquake
hazards and to understand how saltwater invades coastal aquifers. A
revised request was received on February 11, 1999.
Background
The USGS proposes to conduct a high-resolution seismic survey
offshore from Southern California to investigate (1) the hazards posed
by landslides and potential earthquake faults in the nearshore region
from Santa Barbara to San Diego and (2) the invasion of seawater into
freshwater aquifers that are critical to the water supply for people
within the Los Angeles-San Pedro area. Both of these tasks are multi-
year efforts that require using a small airgun.
Coastal Southern California is the most highly populated urban area
along the U.S. Pacific coast. The primary objective of the USGS
research is to provide information to help mitigate the earthquake
threat to this area. The USGS emphasizes that the goal is not
earthquake prediction but rather an assistance in determining what
steps might be taken to minimize the devastation should a large quake
occur. The regional earthquake threat is known to be high, and a major
earthquake could adversely affect the well being of a large number of
people.
Important geologic information that the USGS will derive from this
project's seismic-reflection data concerns how earthquake deformation
is distributed offshore; that is, where the active faults are and what
the history of movement along them has been. This should improve
understanding of the shifting pattern of deformation that occurred
[[Page 31549]]
over both the long term (approximately the last 100,000 years) and
short term (the last few thousand years). The USGS seeks to identify
actively deforming structures that may constitute significant
earthquake threats. The USGS also proposes to locate offshore
landslides that might affect coastal areas. Not only major subsea
landslides might affect the footings of coastal buildings, but also
very large slides can generate local tsunamis. These large sea waves
can be generated by seafloor movement that is produced either by
landslides or by earthquakes. Knowing where large slides have occurred
offshore will help locate areas susceptible to wave inundation.
Some faults that have produced earthquakes lie entirely offshore or
extend into offshore areas where they can be studied using high-
resolution seismic-reflection techniques. An example is the Rose Canyon
fault, which, extending through the San Diego area, is considered to be
the primary earthquake threat. This fault extends northward from La
Jolla, beneath the inner continental shelf, and appears again onshore
in the Los Angeles area. This fault and others like it near shore could
generate moderate (M5-6) to large (M6-7) earthquakes.
Knowing the location and geometry of fault systems is critical to
estimating the location and severity of ground shaking. Therefore, the
results of this project will contribute to decisions involving land
use, hazard zonation, insurance premiums, and building codes.
The proposed work is in collaboration with scientists at the
Southern California Earthquake Center, which analyzes faults and
earthquakes in onshore regions, and with scientists at the Scripps
Institute of Oceanography, who measure strain (incremental movement) on
offshore faults.
The USGS also wants to collect high-resolution seismic- reflection
data to locate the sources and pathways of seawater that intrudes into
freshwater aquifers below San Pedro. Ground water usage in the Los
Angeles basin began in the mid-1800s. Today, more than 44,000 acre-feet
of freshwater each year are extracted from the aquifers that underlie
just the city of San Pedro. Extracting freshwater from coastal aquifers
causes offshore salt water to flow toward areas of active pumping. To
limit this salt-water intrusion, the Water Replenishment District and
water purveyors in San Pedro are investing $2.7 million per year to
inject freshwater underground to establish a zone of high water
pressure in the aquifer. The resulting zone of high pressure will form
a barrier between the invasive saltwater and the productive coastal
aquifers.
USGS scientists in San Diego are working with the Los Angeles
County Department of Public Works and the Water Replenishment District
to develop a ground-water simulation model to predict fluid flow below
San Pedro and nearby parts of the Los Angeles Basin. This model will
eventually be used in managing water resources. The accuracy of the
present model, however, is compromised by a paucity of information
about aquifer geometry and about other geologic factors that might
affect fluid flow. Data the USGS collects will be used to improve
three-dimensional, fluid-flow models to aid in the management of water
resources.
Because noise from seismic airguns and other acoustic instruments
may result in the harassment or injury of marine mammals incidental to
conducting the activity, an IHA under section 101(a)(5)(D) of the MMPA
is warranted.
Fieldwork described here will be the third airgun survey that the
USGS has conducted under close supervision by marine-mammal biologists.
In March 1998, the USGS used a large (6500 in3; 106 liters)
airgun array in and around Puget Sound to study the regional earthquake
hazard. The USGS employed 12 biologists, who worked on two ships
continuously to oversee airgun operations. On several occasions, the
USGS shut off the airguns when marine mammals entered safety zones that
had been stipulated by NMFS under an IHA, and, when mammals left these
zones, the USGS gradually ramped up the array as required to avoid
harming wildlife. Marine mammal biologists reported that, during the
survey, no overt distress was evident among the dense marine mammal
populations, and, afterward, no unexplained marine mammal strandings
occurred. In August 1998, the USGS surveyed offshore from Southern
California, using a small airgun (40 in3; 655
cm3). Marine mammal biologists oversaw this activity, and
the survey the USGS proposes here will be conducted with similar
oversight.
Experimental Design
Marine studies conducted by the USGS focus on areas where natural
hazards have their greatest potential impact on society. In Southern
California, USGS studies will concern four areas. The first area in
priority is the coastal zone and continental shelf between Los Angeles
and San Diego, where much of the hazard appears to be associated with
strike-slip faults, such as the Newport-Inglewood and Palos Verdes
faults. The second study area lies offshore, in the Santa Monica, San
Pedro, and San Diego Trough deeps, where rapid sedimentation has left a
more complete record, relative to shallow-water areas, that the USGS
can use to decipher earthquake history. The third area is the extension
into the Santa Barbara Channel of major elements of onshore geology,
including some large faults. The fourth area is the geologic boundary,
marked generally by the Channel Islands, between the inner California
Borderland (dominated by strike-slip faults) and the Santa Barbara
Channel (dominated by compressional faults). The study proposed here
focuses on the highest priority area, which lies near shore between Los
Angeles and San Diego.
The seismic-reflection survey will last 14 days. From its
experience collecting seismic-reflection data in this general area
during 1998, the USGS proposed to conduct the 1999 survey sometime
within the May through July window. The basis for this decision is its
desire to avoid the gray whale migrations and the peak arrival of other
mysticete whales during late summer.
The USGS has not yet determined the exact tracklines for the
survey, but the USGS does know the areas where airgun use will be
concentrated. Two of these areas are southwest and southeast of Los
Angeles, and the third and largest one is west and northwest of San
Diego. In these areas seismic-reflection data will be collected along a
grid of lines that are about 2 km (1.2 mi) apart.
The USGS proposes to use a small airgun and 200-m (656-ft) long
streamer to collect seismic-reflection data. The potential effect on
marine mammals is from the airgun; mammals cannot become entangled in
the streamer. The USGS will also use a low-powered, high-resolution
seismic system to obtain detailed information about the very shallow
geology. The seismic- reflection system will be onboard a vessel owned
by a private contractor. Ocean-bottom seismometers will be deployed to
measure the velocity of sound in shallow rocks to help unravel the
recent history of fault motion. These seismometers are passive
recorders and pose no threat to the environment.
Ship navigation will be accomplished using satellites of the Global
Positioning System. The survey ship will be able to report accurate
positions, which is important to mitigating the airgun's effect on
marine mammals and to analyzing what impact, if any, airgun operations
had on the environment.
[[Page 31550]]
The Seismic Sound Sources
During this survey, the USGS will operate two sound sources--an
airgun and a high-resolution Huntec(TM) system. The main
sound source will be a single small airgun of special type called a
generator-injector, or GI-gun (trademark of Seismic Systems, Inc.,
Houston, TX). This type of airgun consists of two small airguns within
a single steel body. The two small airguns are fired sequentially, with
the precise timing required to stifle the bubble oscillations that
typify sound pulses from a single airgun of common type. These
oscillations impede detailed analysis of fault and aquifer structure.
For arrays consisting of many airguns, bubble oscillations are canceled
by careful selection of airgun sizes. The GI-gun is a mini-array that
is carefully adjusted to achieve the desired bubble cancellation.
Airguns and GI-guns with similar chamber sizes have similar peak output
pressures.
The GI-gun for this survey has two equal-sized chambers of 35
in3 (57 mm3), and the gun will be fired every 12
seconds. Compressed air delivered to the GI-gun will have a pressure of
about 3000 psi. The gun will be towed 12 meters (39.4 ft) behind the
vessel and suspended from a float to maintain a depth of about 1 m (3.3
ft).
The manufacturer's literature indicates that a GI-gun of the size
the USGS will use has a sound-pressure level (SPL) of about 220 dB re 1
Pa-m. In comparison, a 40-in3 (65 mm3)
airgun has an SPL of 216 dB re 1 Pa-m (Richardson et al.,
1995). The GI-gun's output sound pulse has a duration of about 10 ms.
The amplitude spectrum of this pulse, as shown by the manufacturer's
data, indicates that most of the sound energy is at frequencies below
500 Hz. Field measurements by USGS personnel indicate that the GI-gun's
emits low sound amplitudes at frequencies above 500 Hz. Thus, high-
amplitude sound from this source is at frequencies that are outside the
main hearing band of odontocetes and pinnipeds (Richardson et al.,
1995).
The high-resolution Huntec(TM) system uses an
electrically powered sound source. In operation, the sound producing
and recording hardware are towed behind the ship near the seabottom.
The unit emits sound about every 0.5 seconds. This system provides
highly detailed information about stratified sediment, so that dates
obtained from fossils in sediment samples can be correlated with
episodes of fault offset. The SPL for this unit is 210 dB re 1
Pa-m. The output-sound bandwidth is 0.5 kHz to 8 kHz, with the
main peak at 4.5 kHz.
Description of Habitat and Marine Mammals Affected by the Activity
The Southern California Bight supports a diverse assemblage of 29
species of cetaceans (whales, dolphins, and porpoises) and 6 species of
pinnipeds (seals and sea lions). The species of marine mammals that are
likely to be present in the seismic research area during the year
include the bottlenose dolphin (Tursiops truncatus), common dolphin
(Delphinus delphis), killer whale (Orcinus orca), Pacific white-sided
dolphin (Lagenorhynchus obliquidens), northern right whale dolphin
(Lissodelphis borealis), Risso's dolphin (Grampus griseus), pilot whale
(Globicephala macrorhynchus), Dall's porpoise (Phocoenoides dalli),
sperm whale (Physeter macrocephalus), humpback whale (Megaptera
novaengliae), gray whale (Eschrichtius robustus), blue whale
(Balaenoptera musculus), minke whale (Balaenoptera acutorostrata), fin
whale (Balaenoptera physalus), harbor seal (Phoca vitulina), elephant
seal (Mirounga angustirostris), northern sea lion (Eumetopias jubatus),
and California sea lion (Zalophus californianus), northern fur seal
(Callorhinus ursinus) and sea otters (Enhydra lutris). General
information on these species can be found in the USGS application and
in Barlow et al. (1997). Please refer to those documents for
information on the biology, distribution, and abundance of these
species.
Potential Effects of Seismic Surveys on Marine Mammals
General Discussion
Seismic surveys are used to obtain data about rock formations up
to several thousands of feet deep. These surveys are accomplished by
transmitting sound waves into the earth, which are reflected off
subsurface formations and recorded with detectors in the water column.
A typical marine seismic source is an airgun array, which releases
compressed air into the water creating an acoustical energy pulse that
is directed downward toward the seabed. Hydrophones spaced along a
streamer cable just below the surface of the water receive the
reflected energy from the subsurface formations and transmit data to
the seismic vessel. Onboard the vessel, the signals are amplified,
digitized, and recorded on magnetic tape.
Disturbance by seismic noise is the principal means of taking by
this activity. Vessel noise may provide a secondary source. Also, the
physical presence of vessel(s) could lead to some non-acoustic effects
involving visual or other cues.
Depending upon ambient conditions and the sensitivity of the
receptor, underwater sounds produced by open-water seismic operations
may be detectable some distance away from the activity. Any sound that
is detectable is (at least in theory) capable of eliciting a
disturbance reaction by a marine mammal or by masking a signal of
comparable frequency. An incidental harassment take is presumed to
occur when marine mammals in the vicinity of the seismic source (or
vessel) react to the generated sounds or to visual cues.
Seismic pulses are known to cause some species of whales, including
gray whales, to behaviorally respond within a distance of several
kilometers (Richardson et al., 1995). Although some limited masking of
low-frequency sounds is a possibility for those species of whales using
low frequencies for communication, the intermittent nature of seismic
source pulses will limit the extent of masking. Bowhead whales, for
example, are known to continue calling in the presence of seismic
survey sounds, and their calls can be heard between seismic pulses
(Richardson et al., 1986).
When the received levels of noise exceed some behavioral reaction
threshold, cetaceans will show disturbance reactions. The levels,
frequencies, and types of noise that will elicit a response vary
between and within species, individuals, locations and seasons.
Behavioral changes may be subtle alterations in surface-dive-
respiration cycles. More conspicuous responses include changes in
activity or aerial displays, movement away from the sound source, or
complete avoidance of the area. The reaction threshold and degree of
response are related to the activity of the animal at the time of the
disturbance. Whales engaged in active behaviors, such as feeding,
socializing, or mating, are less likely than resting animals to show
overt behavioral reactions, unless the disturbance is directly
threatening.
Hearing damage is not expected to occur during the project. While
it is not known whether a marine mammal very close to the airgun would
be at risk of permanent hearing impairment, temporary threshold shift
(TTS) is a theoretical possibility for animals very close to an airgun.
However, planned monitoring and mitigation measures (described later in
this document) are designed to detect marine mammals occurring near the
seismic source(s) and to avoid, to the greatest extent practicable,
exposing them to sound
[[Page 31551]]
pulses that have any possibility of causing hearing damage, including
TTS.
Maximum Sound-Exposure Levels for Marine Mammals
Loud continuous sounds can damage the hearing of marine mammals.
However, the adverse effects of sound on mammals have been documented
for exposure times that last for tens of seconds or minutes, but
effects have not been documented for the brief pulses typical of the
GI-gun (10 ms) and the Huntec(TM) system (0.3 ms). NMFS has
long considered that the maximum SPLs to which marine mammals should be
exposed from impulse sounds are 180 dB re 1 PaRMS
for mysticetes and sperm whales, and 190 dB re 1
PaRMS for odontocetes and pinnipeds. More recently,
scientists at two workshops on acoustic noise and marine mammals
supported NMFS' determination.
At the time of its application, the USGS lacked detailed
measurement of sound-transmission loss for the southern California
offshore, so, based upon the best science available, the USGS estimated
how SPL varies with distance from the airgun by assuming that sound
decays according to 25Log(R). The coefficient 25 accounts approximately
for the attenuation that is caused by the sound interacting with the
seabottom. The USGS used this procedure to derive safety zone estimates
based on the 220 dB SPL produced by the GI-gun, the larger of the two
sound sources the USGS plans to use.
Assuming that the 25Log(R) decay that the USGS used to estimate
safe distances from the airgun is correct, this indicates that an SPL
of 190 dB re 1 Pa is attained about 16 m (52.5 ft) away from
the airgun, and an SPL of 180 dB re 1 Pa is attained at about
40 m (131 ft) away. However, for precautionary reasons during field
operations, the USGS proposes that, at all times, the safe distance for
odontocetes and pinnipeds be 50 m (164 ft) and for mysticetes, 100 m
(328 ft).
Comments and Responses
A notice of receipt of the application and proposed authorization
was published on March 5, 1999 (64 FR 10644), and a 30-day public
comment period was provided on the application and proposed
authorization. Comments were received from the Marine Mammal Commission
(MMC), the California Coastal Commission (CCC), and one individual. The
CCC asked a number of questions; those relevant to the application for
an IHA are included here. Information on the authorization request and
expected impact on marine mammal species, not subject to reviewer
comments, can be found in the proposed authorization notice and is not
repeated here, but is considered part of the record of decision, except
as modified by this notice.
On May 11, 1999, the CCC objected to the USGS project and its
consistency determination, even though the CCC staff had recommended
approval (see CD-32-99). During the May 11, 1999, public hearing, the
USGS modified its project to avoid operating within the 3-mile limit of
State waters and to expand the marine mammal safety radius for
odontocetes to be the same as mysticetes (i.e., 100 m (328 ft) safety
zone) in order to ensure that marine mammals would be exposed to no
greater than 180 dB sound levels. Nevertheless, even with these
modifications, the CCC found the project was not consistent to the
maximum extent practicable with the California Coastal Management Plan
(CCMP).
The CCC further determined that alternative measures exist that
would enable the project to be conducted in a manner consistent to the
maximum extent practicable with the CCMP. One alternative measure
identified by the CCC would require no night-time seismic activities.
The CCC requirements are discussed later in this document. On May 28,
1999, the USGS submitted a letter to NMFS, requesting the CCC suggested
modifications be made to their application for an IHA.
Comment 1: The MMC questions the statement in the USGS application
that NMFS considers that the maximum sound pressure levels (SPLs) to
which marine mammals can be exposed are 180 dB re 1
PaRMS * * * for mysticetes and sperm whales, and
190 dB re 1 PaRMS for odontocetes and pinnipeds. No
citation was provided for this statement and, while the MMC is aware
that the referenced sound levels were judged to be appropriate by the
panel of experts convened by NMFS last September, the MMC was not aware
that NMFS had accepted or made known the panel's findings in this
regard. The MMC requests NMFS' rationale for these determinations.
Response: NMFS notes that the mentioned SPLs have been adopted by
NMFS as the lower bound for Level A harassment authorizations for
impulse sounds, such as from seismic airguns (please refer to 50 CFR
216.3 for a definition of Level A and Level B harassment), and have
relatively long usage in establishing safety zones for marine mammals
in such areas as the U.S. Beaufort Sea (see 61 FR 26501, May 28, 1996;
61 FR 38715, July 25, 1996; 62 FR 38263, July 17, 1997; and 63 FR
40505, July 29, 1998) and Puget Sound (see 62 FR 488817, September 17,
1997, and 63 FR 2213, January 14, 1998). The rationale for using these
levels was provided first in an authorization to the Exxon Corporation
for seismic work in southern California in 1995 (see 60 FR 53753,
October 17, 1995). Because of the length of that discussion, it is not
repeated here. However, since the time of that authorization, NMFS has
questioned the reliability of using data on humans as surrogates for
marine mammal impacts. As a result, until better scientific data on
marine mammals are collected, NMFS has adopted a more precautionary
level of 190 dB as the lower bound for Level A harassment for
odontocetes and pinnipeds, and not the higher levels noted in the Exxon
authorization.
NMFS wishes to clarify that, under section 101(a)(5)(D) of the
MMPA, applicants may apply for a take by acoustic injury (Level A
harassment); however, NMFS limits the use of authorizations for
harassment involving the ``potential to injure'' to takings that may
involve non-serious injury, such as TTS. Serious injury for marine
mammals, such as permanent hearing loss within the species' primary
hearing range, may lead fairly quickly to the animal's death. For
example, if an application indicates that the short-term use of an
acoustic source at its maximum output level has the potential to cause
TTS in a marine mammal's hearing ability, that taking would constitute
a Level A ``harassment'' take, since the animal's hearing ability would
be expected to recover and, therefore, the section 101(a)(5)(D)
application would be appropriate. However, if the acoustic source at
its maximum level has the potential to cause a permanent threshold
shift in a marine mammal's hearing ability or potentially could cause
TTS over a significant period of time on the same animals, that
activity will be considered by NMFS to be capable of causing serious
injury to a marine mammal and, therefore, might not be appropriate for
an IHA, unless effective mitigation was implemented to prevent more
than non-serious injury.
It should also be understood that, while NMFS considers that the
maximum SPLs to which marine mammals should be exposed from impulse
sounds are 180 dB re 1 PaRMS for mysticetes and
sperm whales and 190 dB re 1 PaRMS for odontocetes
and pinnipeds, the definition of ``harassment'' in section 3 of the
MMPA authorizes takes by harassment to include injury (Level A
harassment). As mentioned previously, 180 dB/190 dB SPLs are considered
by NMFS to be the
[[Page 31552]]
lowest level of Level A harassment. This means that safety zones are
established as a mitigation measure to reduce takings to the lowest
level practicable as required by section 101(a)(5)(D)(ii)(I).
Therefore, in accordance with section 101(a)(5)(D)(v), provided the
applicant requested takes that included Level A harassment, the fact
that a marine mammal entered the designated safety zone undetected is
not considered a violation of the MMPA or of the IHA.
In any case, in order to obtain a certificate of compliance
(required of the USGS by the Coastal Zone Management Act) from the CCC,
the USGS must observe the more restrictive 180-dB criterion for both
mysticetes and odontocetes. Accordingly, the USGS, in a letter to NMFS,
amended its application to indicate that a safety zone of 100 m (328
ft) should be established, which is equivalent to 180 dB using 20Log(R)
SPL.
Comment 2: The CCC asked, if the operation includes shallow water,
why 25Log(R) is an appropriate dispersion model? Also, one of the two
sources, the Huntec system, emits sound at or near the bottom (if at
all). Again, is the 25Log(R) the appropriate dispersion model for this
source. If the assumption that 25Log(R) is the correct attenuation
factor, the MMC recommends, in order to protect marine mammals from
serious injury, that a more conservative estimate of the attenuation
rate be used to calculate the safety zones, or that measurements be
made at the beginning of the surveys to confirm the assumed 25Log(R)
within the horizontal distances less than the depth of the water
column.
Response: The USGS notes that it used a 25Log(R) decay in SPL
because acoustic modeling and measurements in the field show that sound
decays quickly in water that overlies a sloping seabottom. In a medium
with no acoustic interfaces, sound spreads spherically and SPL reduces
at 20Log(R). A sloping bottom, however, causes sound to exit the water
layer and beam into the underlying sediment, enhancing the transmission
loss toward a beach (e.g., Jensen and Tindle, 1987; Deane and
Buckingham, 1993; Glegg et al., 1993; Richardson et al., 1994; Jensen
et al., 1994). In fact, a zone of high transmission loss, an ``acoustic
shadow zone,'' lies just offshore from a beach. This argues against the
common misunderstanding that underwater sound intensifies up-slope
toward a beach.
The enhanced transmission loss, relative to 20Log(R), that occurs
over a sloping bottom has been verified by field measurements from
scattered locations. The USGS, in conjunction with its 1997 seismic
survey in Puget Sound (Fisher et al., 1999) measured sound decay with
distance from a 108-liter (L) airgun array (Bain, 1999). A least-
squares, straight-line fit to data from ranges less than 10 km (5.4 nm)
indicates that airgun sound decays at 29Log(R). In water 90 m (295 ft)
deep off Los Angeles Harbor, USGS scientists measured a 26Log(R)
transmission loss, using the same airgun the USGS will deploy this
coming season. Off the Big Sur coast of central California, the SPL of
a single 1.6 L airgun decreased at 25Log(R) decay toward the beach.
Greenridge Sciences, Inc.(1998) measured the transmission loss of
airgun sound at Platform Harmony in the Santa Barbara Channel.
Estimated loss was high, the coefficient of the logarithm is 48 to 60.
Finally, measurements of acoustic thermometry (ATOC) sounds versus
distance, in nearshore water that is 10 m (33 ft) to 80 m (262 ft)
deep, indicate a high transmission loss (TL) of about 43Log(R).
Therefore, on the basis of abundant, numerical acoustic modeling
and some field measurements, the USGS and NMFS believe that 25Log(R) is
a conservative estimate of sound TL for airgun sounds over a sloping
seabottom, like that offshore from southern California. In particular,
sound that propagates into shallow water near and within the 3-mile
(4.8 km) limit should decay sharply toward shore. However, the CCC will
require the USGS to observe a 100-m (328-ft) safety radius around the
airgun, which distance is consistent with the source level of the
airgun and a 20Log(R) TL model. At this distance, received SPL would be
180 dB using a 20Log(R) TL model. Because a more conservative estimate
of the attenuation rate has been used to calculate the safety zones
measurements, NMFS does not consider it necessary for measurements to
be made at the beginning of the surveys to confirm the TL.
The Huntec instrument is deployed at varying depths beneath the sea
surface to avoid noise from large ships and ocean waves, but no attempt
is made to maintain this instrument at a close distance to the sea
floor. For safety reasons, the Huntec vehicle remains at least 50 m
(164 ft) above the seafloor, except in water that is shallower than 100
m (328 ft), where the Huntec will be at a depth of about 10 m (33 ft).
The maximum deployment is 150 m (492 ft). The maximum SPL of the Huntec
is about 25 percent of the G-I gun's maximum SPL, and mitigation zones
were calculated to account for the GI-gun. These zones, therefore, are
even more conservative for Huntec.
Comment 3: The CCC asked how will marine mammals be observed and
avoided during low-visibility times (such as night-time and fog)? Will
there only be visual monitoring or is acoustic monitoring included as
well.
Response: The USGS proposes to rely on visual monitoring; there
will not be any aerial surveys or acoustic monitoring. At night,
biologists proposed to use light-amplification scopes to improve
visibility and detection of the animals. However, in order for the USGS
to be consistent to the greatest extent practicable with the CCMP, the
USGS will not conduct GI-gun seismic surveys during nighttime.
Comment 4: The MMC notes that marine mammal observers aboard the
seismic vessels will need to work 6 hour shifts if seismic operations
continue around the clock. The MMC questions whether two observers will
be able to effectively monitor and detect marine mammals approaching
the designated safety zones, particularly at night and after the first
few days working the alternating 6-hour shifts. The MMC recommends that
NMFS consult with the applicant to better determine the rationale for
using two observers as proposed.
Response: Three biological observers will be employed with two on
watch at all times. According to restrictions placed on the USGS by the
CCC, the USGS will be unable to use the airgun for 8 hours overnight,
so all observers will benefit from a full, 8-hour sleep, and off-watch
periods during the day offer additional rest.
Comment 5: The CCC asks who will be conducting the marine mammal
monitoring?
Response: Employees of researchers at the Cascadia Research in
Olympia, WA, will likely oversee monitoring.
Comment 6: The CCC asks why a 35-in3 airgun is louder
than a 45-in3 airgun? Is that because it contains two
chambers?
Response: The GI-gun uses 3000-psi pressure, while most airguns
use 2000-psi pressure. This likely accounts for the greater source
strength of the GI-gun.
Estimated Number of Potential Harassments of Marine Mammals
The zone of influence for the GI-gun is defined to be the circle
whose radius is the distance from the gun where the SPL reduces to 160
dB re 1 Parms for those marine mammals that can
hear either the low frequency sound from seismic airguns or the mid-
frequency Huntec system. For 25Log(R) TL, the zone of influence is
estimated to be a
[[Page 31553]]
circle with a radius of 250 m (820 ft); for 20Log(R), the zone of
influence would be 1,000 m. Based solely on estimated marine mammal
populations within the survey area and on the number of individuals
that were observed during the 1998 USGS survey and not on the expected
number of animals that may be harassed by the GI-gun and Huntec system,
the USGS estimates that up to 5 killer whales, 10 minke whales, 50
northern sea lions, 100 northern fur seals, 100 northern elephant
seals, 100 Dall's porpoise, 100 Risso's dolphins, 100 northern right-
whale dolphins, 100 Pacific white-sided dolphins, 100 bottlenosed
dolphins, 200 California sea lions, 200 Pacific harbor seals, and 6,000
common dolphins may be harassed incidental to the USGS survey. No
mysticetes (except possibly minke whales) or sperm whales are expected
to be in the area at the time of the survey and, therefore, would not
be subject to incidental harassment, and no marine mammals will be
seriously injured or killed as a result of the seismic survey. In
addition, because the Huntec system will be towed near the seabottom
and because the attenuation of mid-frequency sources is greater than
low frequency sources, it is likely that few to no marine mammals at or
near the surface will be affected by this acoustic instrument.
Mitigation of Potential Environmental Impact
To avoid potential TTS injury to marine mammals, a safety zone will
be established and monitored continuously by biologists, and the USGS
must shut off the airguns whenever the ship and a marine mammal
converge closer than 100 m (328 ft). However, because no authorization
was requested to incidentally harass mysticetes (except minke whales)
or sperm whales (since they're not expected to be in the area), a
safety zone of 250 m (820 ft) will need to be monitored for these
species.
The USGS plans to have marine biologists aboard the ship who will
have the authority to stop airgun operations when a mammal enters the
safety zone.
During seismic-reflection surveying, the ship's speed will be only
4 to 5 knots, so that, when the airgun is being discharged, nearby
marine mammals will have gradual warning of the vessel's approach and
can move away. Finally, NMFS will coordinate with the local stranding
network during the time of the survey to determine whether strandings
can be related to the seismic operation.
Additionally, in accordance with the May 28, 1999, request from the
USGS, airgun activities will not be conducted during nighttime. This
will decrease the potential that a marine mammal might enter the safety
zone undetected.
Monitoring and Reporting
Biologists, affiliated with the Cascadia Research Collective in
Olympia, Washington, will monitor marine mammals at all times while the
airguns are active. Three trained marine mammal observers will be
aboard the seismic vessel to mitigate the potential environmental
impact from airgun use and to gather data on the species, number, and
reaction of marine mammals to the airgun. To ensure that no marine
mammals are within the safety zone, monitoring will begin no later than
30 minutes prior to the acoustic sources being turned on. Each observer
will work shifts that limit on-watch times to no more than 4
consecutive hours. Observers will use 7x50 binoculars with internal
compasses and reticules to record the horizontal and vertical angle to
sighted mammals. Monitoring data to be recorded during airgun
operations include the observer on duty and weather conditions (such as
Beaufort sea state, wind speed, cloud cover, swell height,
precipitation, and visibility). For each mammal sighting, the observer
will record the time, bearing and reticule readings, species, group
size, and the animal's surface behavior and orientation. Observers will
instruct geologists to shut off the airgun array whenever a marine
mammal enters its respective safety zone.
Consultation
Under section 7 of the Endangered Species Act, NMFS has completed
consultation on the issuance of an IHA. NMFS finds this action to be
unlikely to adversely affect listed marine mammals because the
endangered whales are expected to be in offshore waters outside the
Channel Islands at the time of the year that the activity will take
place and northern sea lions, which are expected to be in more
northerly waters during the summer, are not known to be affected by low
frequency seismic sources unless close to the source.
Conclusions
NMFS has determined that the short-term impact of conducting marine
seismic-reflection data in offshore southern California may result, at
worst, in a temporary modification in behavior by certain species of
pinnipeds and cetaceans. While behavioral modifications may be made by
certain species of marine mammals to avoid the resultant noise from the
seismic airgun, this behavioral change is expected to have no more than
a negligible impact on the animals.
In addition, no take by serious injury or death is anticipated, and
takes will be at the lowest level practicable due to the incorporation
of the mitigation measures previously mentioned. No known rookeries,
mating grounds, areas of concentrated feeding, or other areas of
special significance for marine mammals occur within or near the
planned area of operations during the season of operations.
Since NMFS is assured that the taking would not result in more than
the incidental harassment (as defined by the MMPA) of small numbers of
certain species of marine mammals, would have only a negligible impact
on these stocks, and would result in the least practicable impact on
the stocks, NMFS has determined that the requirements of section
101(a)(5)(D) of the MMPA have been met and the authorization can be
issued.
Authorization
Accordingly, NMFS has issued an IHA to the USGS for the possible
harassment of small numbers of several species of marine mammals
incidental to collecting marine seismic-reflection data offshore from
southern California during the period from June 3 through July 31,
provided the mitigation, monitoring and reporting requirements
described in the authorization are undertaken.
Dated: June 3, 1999.
Hilda Diaz-Soltero,
Director, Office of Protected Resources, National Marine Fisheries
Service.
[FR Doc. 99-14902 Filed 6-10-99; 8:45 am]
BILLING CODE 3510-22-F
