Small Takes of Marine Mammals Incidental to Specified Activities; Seismic Hazards Investigation in Southern California

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

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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