Small Takes of Marine Mammals Incidental to Specified Activities; Marine Geophysical Survey in the Eastern Tropical Pacific, 3260-3275 [06-532]

Agencies

• DEPARTMENT OF COMMERCE
• National Oceanic and Atmospheric Administration

[Federal Register Volume 71, Number 13 (Friday, January 20, 2006)]
[Notices]
[Pages 3260-3275]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 06-532]


-----------------------------------------------------------------------

DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

[I.D. 112505C]


Small Takes of Marine Mammals Incidental to Specified Activities; 
Marine Geophysical Survey in the Eastern Tropical Pacific

AGENCY: National Marine Fisheries Service (NMFS), National Oceanic and 
Atmospheric Administration (NOAA), Commerce.

ACTION: Notice; receipt of application and proposed incidental take 
authorization; request for comments.

-----------------------------------------------------------------------

SUMMARY: NMFS has received an application from the Scripps Institution 
of Oceanography (SIO) for an Incidental Harassment Authorization (IHA) 
to take small numbers of marine mammals, by harassment, incidental to 
conducting a marine seismic survey in the Eastern Tropical Pacific from 
approximately March 3 to April 1, 2006. Under the Marine Mammal 
Protection Act (MMPA), NMFS is requesting comments on its proposal to 
issue an authorization to SIO to incidentally take, by harassment, 
small numbers of several species of marine mammals during the seismic 
survey.

DATES: Comments and information must be received no later than February 
21, 2006.

ADDRESSES: Comments on the application should be addressed 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. The mailbox address for 
providing e-mail comments is PR1.112505C@noaa.gov. NMFS is not 
responsible for e-mail comments sent to addresses other than the one 
provided here. Comments sent via e-mail, including all attachments, 
must not exceed a 10-megabyte file size.
    A copy of the application containing a list of the references used 
in this document may be obtained by writing to the address specified 
above, telephoning the contact listed below (see FOR FURTHER 
INFORMATION CONTACT), or visiting the Internet at: https://
www.nmfs.noaa.gov/pr/permits/incidental.htm.
    Documents cited in this notice may be viewed, by appointment, 
during regular business hours, at the aforementioned address.

FOR FURTHER INFORMATION CONTACT: Jolie Harrison, Office of Protected 
Resources, NMFS, (301) 713-2289, ext 166.

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.
    Authorization shall be granted if NMFS finds that the taking will 
have a negligible impact on the species or stock(s), 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,

[[Page 3261]]

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 October 2, 2005, NMFS received an application from SIO for the 
taking, by harassment, of several species of marine mammals incidental 
to conducting, with research funding from the National Science 
Foundation (NSF), a marine seismic survey in the Eastern Tropical 
Pacific during March-April, 2006. The purpose of the seismic survey is 
to collect the site survey data for a future Integrated Ocean Drilling 
Program (IODP) drilling transect (not currently scheduled). The 
proposed drilling program will study the structure of the Cenozoic 
equatorial Pacific by drilling an age-transect flowline along the 
position of the paleo-equator in the Pacific, targeting selected time-
slices of interest where calcareous sediments have been preserved best. 
The seismic survey and respective drilling transect will span the early 
Eocene to Miocene equatorial Pacific. Recovered sediments will: (1) 
Contribute towards resolving questions of how and why paleo-
productivity of the equatorial Pacific changed over time, (2) provide 
rare material to validate and extend the astronomical calibration of 
the geological time scale for the Cenozoic, (3) determine sea-surface 
and benthic temperature and nutrient profiles and gradients, (4) 
provide important information about the detailed nature of calcium 
carbonate dissolution (CCD) and changes in the CCD, (5) enhance 
understanding of bio- and magnetostratigraphic datums at the equator, 
as well as (6) provide information about rapid biological evolution and 
turn-over during times of climatic stress. As SIO's strategy also 
implies a paleo-depth transect, they also hope to improve knowledge 
about the reorganization of water masses as a function of depth and 
time. Last, SIO intends to make use of the high level of correlation 
between tropical sediment sections and seismic stratigraphy collected 
on the survey cruise to develop a more complete model of equatorial 
circulation and sedimentation.

Description of the Activity

    The seismic survey will utilize one source vessel, the R/V Roger 
Revelle, which is scheduled to depart from Papeete, French Polynesia, 
on or about March 03, 2006 and will return to port in Honolulu, Hawaii, 
on or about April 01, 2006. The exact dates of the activity may vary by 
a few days because of weather conditions, repositioning, streamer 
operations and adjustments, airgun deployment, or the need to repeat 
some lines if data quality is substandard. The overall area within 
which the seismic survey will occur is located between approx. 20[deg] 
N and 10[deg] S, and between approx. 100[deg] and 155[deg] W. The 
survey will be conducted entirely in International Waters.
    The R/V Roger Revelle will deploy a pair of low-energy Generator-
Injector Guns (GI guns) as an energy source (each with a discharge 
volume of 45 in\3\), plus a 450 m-long, 48-channel, towed hydrophone 
streamer. As the GI guns are towed along the survey lines, the 
receiving system will acquire the returning acoustic signals. The 
program will consist of approximately (approx.) 8,900 km (4,800 nm) of 
survey, including turns. Water depths within the study area are 3,900 
to 5,200 m (12,800 to 16,700 ft). The seismic source will be operated 
along the single track line en route between piston-coring sites, where 
seismic data will be acquired on a small scale grid and cores will be 
collected. There will be additional operations associated with 
equipment testing, start-up, line changes, and repeat coverage of any 
areas where initial data quality is sub-standard.
    All planned geophysical data acquisition activities will be 
conducted by SIO under the direction of the scientists who have 
proposed the study. The scientists are Dr. Mitch Lyle of Boise State 
University, Drs. Neil Mitchell and Carolyn Lear of Cardiff University, 
and Dr. Heiko Palike of University of Southampton. The vessel will be 
self-contained and the crew will live aboard the vessel for the entire 
cruise.
    In addition to the operations of the pair of GI guns, a Kongsberg 
Simrad EM-120 multibeam echosounder, a 3.5 kHz sub-bottom profiler, and 
passive geophysical sensors (gravimeter and magnetometer) will be 
operated continuously throughout the entire cruise.

Vessel Specifications

    The R/V Roger Revelle is owned by the U.S. Navy Office of Naval 
Research (ONR) and operated by SIO under a charter agreement. The R/V 
Roger Revelle has a length of 83 m (273 ft), a beam of 16 m (53 ft), 
and a maximum draft of 5.2 m (17 ft). The ship is powered by two 3000 
hp Propulsion General Electric motors and a 1180 hp retracting 
azimuthing bow thruster. Typical operation speed of approx. 13 km/h (7 
knots) is used during seismic acquisition. When not towing seismic 
survey gear, the R/V Roger Revelle cruises at 22 km/h (12 knots) and 
has a maximum speed of 28 km/h (15 knots). It has a normal operating 
range of approx. 27780 km (15,000 nm).
    The R/V Roger Revelle holds 22 crew plus 37 scientists and will 
also serve as the platform from which marine mammal observers will 
watch for marine mammals before and during GI gun operations.

Seismic Source Description

    The R/V Roger Revelle will tow the pair of GI guns and a streamer 
containing hydrophones along predetermined lines. Seismic pulses will 
be emitted at intervals of 6-10 seconds. At a speed of 7 knots (13 km/
h), the 6-10-s spacing corresponds to a shot interval of approx. 22-36 
m (71-118 ft).
    The generator chamber of each GI gun, the one responsible for 
introducing the sound pulse into the water, is 45 in3. The 
larger (105 in\3\) injector chamber injects air into the previously-
generated bubble to maintain its shape, and does not introduce more 
sound into the water. The two 45 in\3\ GI guns will be towed 8 m (26 
ft) apart side by side, 21 m (69 ft) behind the R/V Roger Revelle, at a 
depth of 2 m (7 ft). Specifications for the GI guns are as follows.
    The two GI guns discharge a total volume of approx. 90 in\3\ and 
the dominant frequency components are 1-188 Hz. The source output 
(downward) is 7.2 bar-m (237 dB re 1 microPascal-m) at 0-peak (0-pk) 
and 14.0 bar-m (243 dB re 1 microPascal-m) at peak-peak (pk-pk). The 
nominal downward-directed source levels indicated above 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 
from a hypothetical point source emitting the same total amount of 
sound as is emitted by the combined GI guns. The actual received level 
at any location in the water near the GI guns will not exceed the 
source level of the strongest individual source. In this case, that 
will be about 231 dB re 1 microPa-m peak, or 237 dB re 1 microPa-m pk-
pk. Actual levels experienced by any organism more than 1 m from either 
GI gun will be significantly lower.

[[Page 3262]]

    A further consideration is that the rms (root mean square) received 
levels that are used as impact criteria for marine mammals are not 
directly comparable to the peak or pk-pk values normally used to 
characterize source levels of seismic sources. The measurement units 
used to describe seismic sources, peak or pk-pk decibels, are always 
higher than the rms decibels referred to in biological literature. 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 peak-to-peak measurement of about 176 to 178 decibels, as measured 
for the same pulse received at the same location (Greene, 1997; 
McCauley et al., 1998, 2000a). 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 a seismic source.
    In 1998, scientists convened at the High Energy Seismic Sound 
(HESS) Workshop, reviewed the available science, and agreed on the 
received sound levels above which marine mammals might incur permanent 
tissue damage resulting in a permanent threshold shift (PTS) of 
hearing. Shortly thereafter, a NMFS panel of bioacousticians used the 
information gathered at the HESS workshop to establish the current 
Level A Harassement acoustic criteria for non-explosive sounds, 180 re 
1 microPa-m (rms) for for cetaceans, and 190 re 1 microPa-m (rms) for 
pinnipeds. Since no data existed, linking Permanent Threshold Shift 
(PTS) in marine mammals to any particular sound level to attain these 
thresholds scientists took the level at which Temporary Threshold Shift 
(TTS) was generally predicted to occur (180 dB) and conservatively 
suggested that PTS could occur anywhere above that level. NMFS 
established the acoustic criteria for Level B Harassment (160 re 1 
microPa-m (rms) for impulse noises, 120 re 1 microPa-m (rms) for non-
impulse, continuous, industrial noises) based on the work of Malme et 
al., 1984, who looked at the effects of anthropogenic noise on the 
migration of grey whales. NMFS uses the isopleths of these sound levels 
to estimate Level A Harassment and Level B Harassment take of marine 
mammals and to establish safety zones within which monitoring or 
mitigation measures must be applied.
    Received sound levels have been modeled by the Lamont-Doherty Earth 
Observatory (L-DEO) for two 105 in\3\ GI guns in relation to distance 
and direction from the source. The model does not allow for bottom 
interactions, and is most directly applicable to deep water (such as 
will be ensonified in this survey). Based on the modeling, estimates of 
the maximum distances from the GI guns where sound levels of 160, 180, 
and 190 dB re 1 microPa (rms) are predicted to be received are as 
follows: 160 dB out to 175 m (574 ft); 180 dB out to 54 m (177 ft); and 
190 dB out to 17 m (56 ft). Because the model results are for the 
larger 105 in\3\ GI guns, those distances are overestimates of the 
distances for the two 45 in\3\ GI guns used in this study.
    Empirical data concerning the 160- and 180-dB distances have been 
acquired based on measurements during the acoustic verification study 
conducted by L-DEO in the northern Gulf of Mexico from 27 May to 3 June 
2003 (Tolstoy et al., 2004). Although the results are limited, the data 
showed that radii around the GI guns where the received level would be 
180 dB re 1 microPa (rms) vary with water depth. Similar depth-related 
variation is likely in the 190 dB distances applicable to pinnipeds. 
The empirical data indicate that, for deep water (>1,000 m (3,281 ft)), 
the L-DEO model 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, it is proposed that 
safety radii during seismic operations in the deep water of this study 
will be the values predicted by L-DEO's model. Therefore, the assumed 
180- and 190-dB radii are 54 m (177 ft) and 17 m (56 ft), respectively.

Bathymetric Sonar

    Along with the GI-gun operations, two additional acoustical data 
acquisition systems will be operated during much or all of the cruise. 
One of the instruments used to map the ocean floor will be the 
Kongsberg Simrad EM-120 multi-beam echosounder, which is commonly 
operated simultaneously with GI guns.
    The nominal transmit frequency of the Kongsberg Simrad EM-120 is 12 
kHz with an angular coverage sector of up to 150 degrees and 191 beams 
per ping. The transmit fan is split into several individual sectors 
with independent active steering according to vessel roll, pitch and 
yaw. This method places all soundings on a ``best fit'' to a line 
perpendicular to the survey line, thus ensuring a uniform sampling of 
the bottom and 100 percent coverage. The sectors are frequency coded 
(11.25 to 12.60 kHz), and are transmitted sequentially at each ping. 
Pulse length and range sampling rate are variable with depth for best 
resolution, and in shallow waters due care is taken to the near field 
effects. The ping rate is primarily limited by round trip travel time 
in water, up to a ping rate of 5 Hz in shallow water. A pulse length of 
15 ms is typically used in deep water. The transmit fan is split into 
nine different sectors transmitted sequentially within the same ping. 
Using electronic steering, the sectors are individually tilted 
alongtrack to take into account the vessel's current roll, pitch and 
yaw with respect to the survey line heading. The manufacturer provided 
information to show relevant parameters for their multibeam 
echosounders. For the model EM-120, with a one degree beamwidth (BW), 
the pressure levels at a set of fixed distances are as follows: 211 dB 
at 1 m (2.9 ft); 205 dB at 10 m (29 ft); 195 dB at 100 m (287 ft); and 
180 dB at 1,000 m (3,280 ft). Note that the pressure levels are worst 
case, i.e. on-axis and with no defocusing. For our purpose the on-axis 
direction is vertical from the ship to the sea floor. The pressure 
level for sound traveling off-axis will fall rapidly for a narrow beam 
(alongtrack for a multibeam echosounder). The level will reduce by 20 
dB at a little more than twice the beamwidth, which is 1 degree for the 
system installed on R/V Roger Revelle. Acrosstrack, the pressure level 
will typically reduce by 20 dB for angles of more than 75-80[deg] from 
the vertical. For multibeams which use sectorized transmission, such as 
most current Kongsberg Simrad systems, beam defocusing is applied in 
the central sector(s) in shallow waters which results in a more rapid 
reduction in the pressure level. There will be a similar reduction for 
the outer sectors in flat arrays, as used with the EM-120, due to the 
virtual shortening of the array width in these directions.
    The pressure level at 1 m (2.9 ft) is less for the Kongsberg Simrad 
EM-120 multibeam echosounder (211 dB) than it is for the pair of GI 
guns (237 dB) used in this study. However due to the very narrow 
(1[deg]) directivity of the beam, the distance from the transducer at 
which 180 dB re 1 microPa-m is encountered is larger (1,000 m (3,280 
ft)) than that calculated for the GI guns (54 m (177 ft)). Conversely, 
the narrowness of the beam, the short pulse length, the ping rate, and 
the ship's speed during the survey greatly lessens the probability of 
exposing an animal under the ship during one ping of the multibeam 
echosounder, much less for multiple pings. Since the 1[deg] beam of 
sound is directed downward from transducers permanently mounted in the 
ship's hull, the horizontal safety radius of 54 m (177 ft) for 180 dB 
established for the GI guns

[[Page 3263]]

will encompass the entire area ensonified by the multibeam echosounder, 
as well, and marine mammals takes by the echosounder will be avoided 
through the mitigation measures discussed later.

Sub-Bottom Profiler

    A sub-bottom profiler will also be used simultaneously with the GI 
guns to map the ocean floor. The Knudsen Engineering Model 320BR sub-
bottom profiler is a dual frequency transceiver designed to operate at 
3.5 and/or 12 kHz. It is used in conjunction with the multibeam 
echosounder to provide data about the sedimentary features which occur 
below the sea floor. The maximum power output of the 320BR is 10 
kilowatts for the 3.5 kHz section and 2 kilowatts for the 12 kHz 
section (the 12 kHz section is seldom used in survey mode on R/V Roger 
Revelle due to overlap with the operating frequency of the Kongsberg 
Simrad EM-120 multibeam).
    Using the Sonar Equations and assuming 100 percent efficiency in 
the system, the source level for the 320BR is calculated to be 211 dB 
re 1 microPa-m. In practice, the system is rarely operated above 80 
percent power level. The pulse length for the 3.5 kHz section of the 
320BR ranges from 1.5 to 24 ms, and is controlled automatically by the 
system.
    Since the maximum attainable source level of the 320BR sub-bottom 
profiler (211 db re 1 microPa-m) is less than that of the pair of GI 
guns (237 dB re 1 microPa-m) to be used in this study and the sound 
produced by the sub-bottom profiler is directed downward from 
transducers permanently mounted in the ship's hull, the 54 m (177 ft) 
horizontal safety radius established for the GI guns will encompass the 
entire area ensonified by the multibeam echosounder, and marine mammals 
takes by the echosounder will be avoided through the mitigation 
measures discussed later.

Characteristics of Airgun Pulses

    Discussion of the characteristics of airgun pulses has been 
provided in the application and in previous Federal Register notices 
(see 69 FR 31792 (June 7, 2004) or 69 FR 34996 (June 23, 2004)). 
Reviewers are referred to those documents for additional information.

Description of Habitat and Marine Mammals Affected by the Activity

    A detailed description of the R/V Roger Revelle's track from 
Papeete, French Polynesia to Honolulu, Hawaii and the associated marine 
mammals can be found in the SIO application and a number of documents 
referenced in the SIO application. In the proposed seismic survey 
region during the late winter and early spring months of 2006, 29 
cetacean species are likely to occur including dolphins, small whales, 
tooth and baleen whales. Several of these species are listed under the 
U.S. Endangered Species Act (ESA) as endangered, including sperm 
whales, humpback whales, and blue whales; fin and sei whales may also 
occur in the proposed seismic program area. Information on the 
distribution of these and other species inhabiting the study area and 
the wider Eastern Tropical Pacific (ETP) has been summarized by several 
studies (e.g., Polacheck, 1987; Wade and Gerrodette, 1993; Ferguson and 
Barlow, 2001; Ferguson and Barlow 2003). Four species of pinnipeds 
(Guadelope fur seal (federally listed endangered under the ESA), 
northern elephant seal, South American sea lion, and California sea 
lion) could potentially be encountered during the proposed survey. 
However, impacts to pinnipeds are not anticipated due to the decreased 
likelihood of encountering them in very deep water, the relatively 
small area proposed to be ensonified, and the likely effectiveness of 
the proposed mitigation measures in such a small area. The species that 
may be impacted by this activity and their estimated abundances in the 
ETP are listed in Table 1.
    The marine mammal populations in the proposed seismic survey area 
have not been studied in detail, but the region is included in the 
greater ETP, where several studies of marine mammal distribution and 
abundance have been conducted. The ETP is thought to be a biologically 
productive area (Wyrtki, 1966), and is known to support a variety of 
cetacean species (Au and Perryman, 1985).
    Initial systematic studies of cetaceans in the ETP were prompted by 
the incidental killing of dolphins in the purse-seine fishery for 
yellowfin tuna, Thunnus albacares, in this area (Perrin 1968, 1969; 
Smith 1983; Wahlen, 1986; Wade, 1995). The main cetacean species that 
have been affected by the fishery include pantropical spotted dolphins 
(Stenella attenuata) and spinner dolphins (S. longirostris) (Smith, 
1983). Short-beaked common dolphins (Delphinus delphis), striped 
dolphins (S. coeruleoalba), bottlenose dolphins (Tursiops truncatus), 
Fraser's dolphins (Lagenodelphis hosei), rough-toothed dolphins (Steno 
bredanensis), and short-finned pilot whales (Globicephala 
macrorhynchus) have also been killed in the fishery (e.g., Hall and 
Boyer, 1989). Dolphin mortality was high at the onset of the fishery 
(Allen, 1985). The average annual mortality from 1959 to 1972 was an 
estimated 347,082 dolphins (Wade, 1995). However, between 1973 and 
1980, mortality dropped considerably (Allen, 1985). From 1986 to 1994, 
total annual mortality declined from approximately 130,000 to 4096 
(Lennert and Hall, 1996). By 1995, annual mortality was 3300 (Hall, 
1997), and in 1996, it was 2600 (Hall, 1998).
    The center of the ETP is characterized by warm, tropical waters 
(Reilly and Fiedler, 1994). Cooler water is found along the equator and 
the eastern boundary current waters of Peru and California; this cool 
water is brought to the surface by upwelling (Reilly and Fiedler, 
1994). The two different habitats are generally thought to support 
different cetacean species (Au and Perryman, 1985). Au et al. (1980 in 
Polacheck, 1987) noted an association between cetaceans and the 
equatorial surface water masses in the ETP, which are thought to be 
highly productive. Increased biological productivity has also been 
observed due to upwelling at the Costa Rica Dome (Wyrtki, 1964; Fiedler 
et al.,1991). Several studies have correlated these zones of high 
productivity with concentrations of cetaceans (Volkov and Moroz, 1977; 
Reilly and Thayer, 1990; Wade and Gerrodette, 1993). The ETP is also 
characterized by a shallow thermocline (Wyrtki, 1966) and a pronounced 
oxygen minimum layer (Perrin et al., 1976; Au and Perryman, 1985). 
These features are thought to result in an ``oxythermal floor'' 20-100 
m below the surface, which may cause large groups of cetaceans to 
concentrate in the warm surface waters (Scott and Cattanach, 1998).
    In the application, many references are made to the occurrence of 
cetaceans in the Galapagos; however, for some species, abundance in the 
Galapagos can be quite different from that in the wider ETP (Smith and 
Whitehead, 1999). In addition, references to surveys in the ETP are 
also made. For example, Polacheck (1987) summarized cetacean abundance 
in the ETP for 1977-1980, although the season when surveys were carried 
out was not given. Polacheck (1987) calculated encounter rates as the 
number of schools sighted per 1,000 mi (1,609 km) surveyed. His 
encounter rates do not include any correction factors to account for 
changes in detectability of species with distance from the survey track 
line or the diving behavior of the animals. Wade and Gerrodette (1993) 
also calculated encounter rates for cetaceans (number of schools per 
1,000 km surveyed) in the ETP, based on surveys between late July

[[Page 3264]]

and early December from 1986 to 1990. Their encounter rates include a 
correction factor to account for detectability bias but do not include 
a correction factor to account for availability bias. Ferguson and 
Barlow (2001) calculated cetacean densities in the ETP based on summer/
fall research vessel surveys in 1986-1996. Their densities are 
corrected for both detectability and availability biases. Ferguson and 
Barlow (2003) followed their 2001 report up with an addendum that 
estimated density and abundance with the respective coefficients of 
variation, whereas before some species and groups were pooled. Although 
species encounter rates and densities are generally given for summer/
fall, the proposed seismic survey will be conducted in winter/spring 
2006.

Potential Effects on Marine Mammals

Summary of Potential Effects of GI Gun Sounds

    The effects of sounds from GI guns might include one or more of the 
following: tolerance, masking of natural sounds, behavioral 
disturbance, and at least in theory temporary or permanent hearing 
impairment (Richardson et al., 1995). Given the small size of the GI 
guns planned for the present project, effects are anticipated to be 
considerably less than would be the case with a large array of airguns. 
Both NMFS and SIO believe it very unlikely that there would be any 
cases of temporary or, especially, permanent hearing impairment. Also, 
behavioral disturbance is expected to be limited to animals that are at 
distances less than 510 m (1673 ft). A further review of potential 
impacts of airgun sounds on marine mammals is included in Appendix A of 
SIO's application.
Tolerance
    Numerous studies have shown that pulsed sounds from airguns are 
often readily detectable in the water at distances of many kilometers. 
However, it should be noted that most of the measurements of airgun 
sounds that have been reported concerned sounds from larger arrays of 
airguns, whose sounds would be detectable farther away than those 
planned for use in the present project.
    Numerous studies have shown 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. 
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 GI gun source planned for use in this project, 
mammals are expected to tolerate being closer to this source than might 
be the case for a larger airgun source typical of most seismic surveys.
Masking
    Masking effects of pulsed sounds (even from large arrays of 
airguns) on marine mammal calls and other natural sounds are expected 
to be limited, although there are very few specific data on this. Some 
whales are known to continue calling in the presence of seismic pulses. 
Their calls can be heard between the seismic pulses (e.g., 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 off northern Norway continued 
calling in the presence of seismic pulses (Madsen et al., 2002c). Given 
the small source planned for use here, there is even less potential for 
masking of baleen or 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 GI guns to be used here. Also, the sounds important to 
small odontocetes are predominantly at much higher frequencies than are 
airgun sounds. Further information on masking effects may be found in 
Appendix A(d) of SIO's application.
Disturbance Reactions
    Disturbance includes a variety of effects, including subtle changes 
in behavior, more conspicuous changes in activities, and displacement. 
Disturbance is one of the main concerns in this project. In the 
terminology of the 1994 amendments to the MMPA, seismic noise could 
cause ``Level B'' harassment of certain marine mammals. Level B 
harassment is defined as ``* * * disruption of behavioral patterns, 
including, but not limited to, migration, breathing, nursing, breeding, 
feeding, or sheltering.''
    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, it is difficult to 
know if the impacts of the change are significant to the individual, or 
the stock or the species as a whole. However, if a sound source 
displaces marine mammals from an important feeding or breeding area for 
a prolonged period, impacts on the animals are most likely significant. 
Given the many uncertainties in predicting the quantity and types of 
impacts of noise on marine mammals, it is common practice to estimate 
how many mammals were present within a particular distance of 
industrial activities, or exposed to a particular level of industrial 
sound, and assume that all of the animals within that area may have 
been disturbed.
    The sound criteria used to estimate how many marine mammals might 
be disturbed to some biologically-important degree by a seismic program 
are based on behavioral observations during studies of several species. 
However, information is lacking for many species. Detailed studies have 
been done on humpback, gray, and bowhead whales, and on ringed seals. 
Less detailed data are available for some other species of baleen 
whales, sperm whales, and small toothed whales. Most of those studies 
have concerned reactions to much larger airgun sources than planned for 
use in the present project. Thus, effects are expected to be limited to 
considerably smaller distances and shorter periods of exposure in the 
present project than in most of the previous work concerning marine 
mammal reactions to airguns.
    Baleen Whales--Baleen whales generally tend to avoid operating 
airguns, but avoidance radii are quite variable. Whales are often 
reported to show no overt reactions to pulses from large arrays of 
airguns at distances beyond a few kilometers, even though the airgun 
pulses remain well above ambient noise levels out to much longer 
distances. However, as reviewed in Appendix A of SIO's application, 
baleen whales exposed to strong noise pulses from airguns often react 
by deviating from their normal migration route and/or interrupting 
their feeding and moving away. In the case of the migrating gray and 
bowhead whales, the observed changes in behavior appeared to be of 
little or no biological consequence to the animals. They simply avoided 
the sound source by displacing their migration route to varying 
degrees, but

[[Page 3265]]

within the natural boundaries of the migration corridors.
    Studies of gray, bowhead, and humpback whales have determined that 
received levels of pulses in the 160-170 dB re 1 microPa (rms) range 
seem to cause obvious avoidance behavior in a substantial fraction of 
the animals exposed. In many areas, seismic pulses from large arrays of 
airguns diminish to those levels at distances ranging from 4.5-14.5 km 
(2.4-7.8 nm) from the source. A substantial proportion of the baleen 
whales within those distances may show avoidance or other strong 
disturbance reactions to the airgun array. Subtle behavioral changes 
sometimes become evident at somewhat lower received levels, and recent 
studies reviewed in the application have shown that some species of 
baleen whales, notably bowheads and humpbacks, at times show strong 
avoidance at received levels lower than 160-170 dB re 1 microPa (rms). 
Reaction distances would be considerably smaller during the present 
project, in which the 160 dB radius is predicted to be approx. 0.5 km 
(0.27 nm), as compared with several kilometers when a large array of 
airguns is operating.
    Data on short-term reactions (or lack of reactions) of cetaceans to 
impulsive noises do not necessarily provide information about long-term 
effects. It is not known whether impulsive noises affect reproductive 
rate or distribution and habitat use in subsequent days or years. 
However, gray whales continued to migrate annually along the west coast 
of North America despite intermittent seismic exploration and much ship 
traffic in that area for decades (Malme et al., 1984). Bowhead whales 
continued to travel to the eastern Beaufort Sea each summer despite 
seismic exploration in their summer and autumn range for many years 
(Richardson et al., 1987). In any event, the brief exposures to sound 
pulses from the present small GI gun source are highly unlikely to 
result in prolonged effects in baleen whales.
    Toothed Whales--Little systematic information is available about 
reactions of toothed whales to noise pulses. Few studies similar to the 
more extensive baleen whale/seismic pulse work summarized above have 
been reported for toothed whales. However, systematic work on sperm 
whales is underway.
    Seismic operators sometimes see dolphins and other small toothed 
whales near operating airgun arrays, but in general there seems to be a 
tendency for most delphinids to show some limited avoidance of seismic 
vessels operating large airgun systems. However, some dolphins seem to 
be attracted to the seismic vessel and floats, and some ride the bow 
wave of the seismic vessel even when large arrays of airguns are 
firing. Nonetheless, there have been indications that small toothed 
whales sometimes tend to head away, or to maintain a somewhat greater 
distance from the vessel, when a large array of airguns is operating 
than when it is silent (e.g., Goold, 1996a; Calambokidis and Osmek, 
1998; Stone, 2003). Similarly, captive bottlenose dolphins and beluga 
whales exhibit changes in behavior when exposed to strong pulsed sounds 
similar in duration to those typically used in seismic surveys 
(Finneran et al., 2000, 2002). However, the animals tolerated high 
received levels of sound (pk-pk level >200 dB re 1 microPa) before 
exhibiting aversive behaviors. With the presently-planned pair of GI 
guns, such levels would only be found within a few meters of the 
source.
    There are no specific data on the behavioral reactions of beaked 
whales to seismic surveys. However, most beaked whales tend to avoid 
approaching vessels of other types (e.g., Kasuya, 1986; Wursig et al., 
1998). There are increasing indications that some beaked whales tend to 
strand when naval exercises, including sonar operations, are ongoing 
nearby--see Appendix A of SIO's application. The strandings are 
apparently at least in part a disturbance response, although auditory 
or other injuries may also be a factor. Whether beaked whales would 
ever react similarly to seismic surveys is unknown. Seismic survey 
sounds are quite different from those of the sonars in operation during 
the above-cited incidents. There has been a recent (Sept. 2002) 
stranding of Cuvier's beaked whales in the Gulf of California (Mexico) 
when the L-DEO vessel Maurice Ewing was operating a large array of 
airguns (20 guns; 8,490 in3) in the general area. This might 
be a first indication that seismic surveys can have effects similar to 
those attributed to naval sonars. However, the evidence with respect to 
seismic surveys and beaked whale strandings is inconclusive even for 
large airgun sources.
    All three species of sperm whales have been reported to show 
avoidance reactions to standard vessels not emitting airgun sounds, and 
it is to be expected that they would tend to avoid an operating seismic 
survey vessel. There were some limited early observations suggesting 
that sperm whales in the Southern Ocean and Gulf of Mexico might be 
fairly sensitive to airgun sounds from distant seismic surveys. 
However, more extensive data from recent studies in the North Atlantic 
suggest that sperm whales in those areas show little evidence of 
avoidance or behavioral disruption in the presence of operating seismic 
vessels, (McCall Howard 1999; Madsen et al., 2002c; Stone, 2003). An 
experimental study of sperm whale reactions to seismic surveys in the 
Gulf of Mexico has been done recently (Tyack et al., 2003).
    Odontocete reactions to large arrays of airguns are variable and, 
at least for small odontocetes, seem to be confined to a smaller radius 
than has been observed for mysticetes. Thus, behavioral reactions of 
odontocetes to the small GI gun source to be used here are expected to 
be very localized, probably to distances <0.5 km (<0.3 mi).
    Pinnipeds--Pinnipeds are not likely to show a strong avoidance 
reaction to the small GI gun source that will be used. Visual 
monitoring from seismic vessels, usually employing larger sources, has 
shown only slight (if any) avoidance of airguns by pinnipeds, and only 
slight (if any) changes in behavior. Those studies show that pinnipeds 
frequently do not avoid the area within a few hundred meters of 
operating airgun arrays, even for arrays much larger than the one to be 
used here (e.g., Harris et al., 2001). However, initial telemetry work 
suggests that avoidance and other behavioral reactions to small airgun 
sources may be stronger than evident to date from visual studies of 
pinniped reactions to airguns (Thompson et al., 1998). Even if 
reactions of the species occurring in the present study area are as 
strong as those evident in the telemetry study, reactions are expected 
to be confined to relatively small distances and durations, with no 
long-term effects on pinnipeds.
    Additional details on the behavioral reactions (or the lack 
thereof) by all types of marine mammals to seismic vessels can be found 
in Appendix A (e) of SIO's 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 regarding exposure of marine mammals to 
high-level sounds is that in order to avoid hearing impairment, 
cetaceans and pinnipeds should not be exposed to impulsive sounds 
exceeding 180 and 190 dB re1 microPa (rms), respectively (NMFS, 2000). 
Those criteria have been used in defining the safety (shutdown) radii 
planned for this seismic survey. However, those criteria were 
established

[[Page 3266]]

before there were any data on the minimum received levels of sounds 
necessary to cause auditory impairment in marine mammals. As discussed 
in Appendix A (f) of the application and summarized here:
     The 180-dB criterion for cetaceans is probably quite 
precautionary, i.e., lower than necessary to avoid TTS, let alone 
permanent auditory injury, at least for delphinids;
     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; and
     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 GI gun source in this project (two 
45 in3 guns), along with the planned monitoring and 
mitigation measures, there is little likelihood that any marine mammals 
will be exposed to sounds sufficiently strong to cause hearing 
impairment. Several aspects of the planned monitoring and mitigation 
measures for this project are designed to detect marine mammals 
occurring near the pair of GI guns (and multibeam echosounder), and to 
avoid exposing them to sound pulses that might cause hearing impairment 
(see Mitigation Measures). In addition, many cetaceans are likely to 
show some avoidance of the area with ongoing seismic operations (see 
above). In those 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 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, as discussed below, it is very unlikely that any 
effects of these types would occur during the present project given the 
small size of the source and the brief duration of exposure of any 
given mammal, especially in view of the planned monitoring and 
mitigation measures.
    Temporary Threshold Shift (TTS)--TTS is the mildest form of hearing 
impairment that can occur during exposure to a strong sound (Kryter 
1985). While experiencing TTS, the 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. For sound exposures at or 
somewhat above the TTS threshold, hearing sensitivity recovers rapidly 
after exposure to the noise ends. Little information on sound levels 
and durations necessary to elicit mild TTS have been obtained for 
marine mammals, and none of the published data concern TTS elicited by 
exposure to multiple pulses of sound.
    Finneran et al. (2002) compared the few available data that exist 
on sound levels and durations necessary to elicit mild TTS and found 
that for toothed whales exposed to single short pulses, the TTS 
threshold appears to be a function of the energy content of the pulse. 
Finneran used the available data to plot known TTS in odontocetes on a 
line depicting sound pressure level versus duration of pulse, and SIO 
used that line to estimate that a single seismic pulse received at 210 
dB re 1 microPa (rms) (approx. 221-226 dB pk-pk) may produce brief, 
mild TTS in Odontocetes. If received sound energy is calculated from 
the sound pressure, a single seismic pulse at 210 dB re 1 microPa (rms) 
equates to several seismic pulses at received levels near 200-205 dB 
(rms). The L-DEO model indicates that seismic pulses with received 
levels of 200-205 dB would be limited to distances within a few meters 
of the small GI gun source to be used in 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. Richardson 
et al. (1995) compiled studies of the reactions of several species of 
baleen whales to seismic sound and found that baleen whales often show 
strong avoidance several kilometers away from an airgun at received 
levels of 150-180 dB. Given the small size of the source, and the 
likelihood that baleen whales will avoid the approaching airguns (or 
vessel) before being exposed to levels high enough to induce TTS, NMFS 
believes it unlikely that the R/V Roger Revelle's airguns will cause 
TTS in any baleen whales.
    TTS thresholds for pinnipeds exposed to brief pulses (single or 
multiple) have not been measured. 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; cf. Au et al., 2000).
    A marine mammal within a radius of 100 m ( 328 ft) around a typical 
large array of operating airguns might be exposed to a few seismic 
pulses with levels of 205 dB, and possibly more pulses if the mammal 
moved with the seismic vessel. As noted above, most cetaceans show some 
degree of avoidance of operating airguns. In addition, ramping up 
airgun arrays, which is standard operational protocol for large airgun 
arrays, should allow cetaceans to move away from the seismic source and 
to avoid being exposed to the full acoustic output of the airgun array. 
Even with a large airgun array, it is unlikely that the cetaceans would 
be exposed to airgun pulses at a sufficiently high level (180 dB) for a 
sufficiently long period (due to the tendency of baleen whales to avoid 
seismic sources) to cause more than mild TTS, given the relative 
movement of the vessel and the marine mammal. The potential for TTS is 
much lower in this project due to the small size of the airgun array 
(past IHA's have authorized take of marine mammals incidental to the 
operation of seismic airguns with a total volume of up to 8,800 
in3 (L-DEO 20-gun array)) . With a large array of airguns, 
TTS would be most likely in any odontocetes that bow-ride or otherwise 
linger near the airguns. While bow riding, odontocetes would be at or 
above the surface, and thus not exposed to strong sound pulses given 
the pressure-release effect at the surface. However, bow-riding animals 
generally dive below the surface intermittently. If they did so while 
bow riding near airguns, they would be exposed to strong sound pulses, 
possibly repeatedly. In this project, the anticipated 180-dB distance 
is <54 m (<155 ft), and the bow of the R/V Roger Revelle will be 106 m 
(304 ft) ahead of the GI guns. As noted above, the TTS threshold (at 
least for brief or intermittent exposures) is likely >180 dB. Thus, TTS 
would not be expected in the case of odontocetes bow riding during the 
planned seismic operations. Furthermore, even if some cetaceans did 
incur TTS through exposure to GI gun sounds, this would very likely be 
mild, temporary, and reversible.
    As mentioned earlier, NMFS has established acoustic criteria to 
avoid permanent physiological damage that indicate that cetaceans and 
pinnipeds should not be exposed to pulsed underwater noise at received 
levels exceeding, respectively, 180 and 190 dB re 1 microPa (rms). The 
predicted 180 and 190 dB distances for the GI guns operated by SIO are 
<54 m (<155 ft) and <17 m (<49 ft), respectively (Those distances 
actually apply to operations with two 105 in3 GI guns, and 
smaller distances would be expected for the two

[[Page 3267]]

45 in3 GI guns to be used here.). These sound levels 
represent the received levels above which one could not be certain that 
there would be no injurious effects, auditory or otherwise, to marine 
mammals. As mentioned previously in the toothed whale section, Finneran 
et al.'s (2000 and 2002) TTS data indicate that a small number of 
captive dolphins have been exposed to more 200 dB re 1 microPa (rms) 
without suffering from TTS, though NMFS believes that the sound levels 
represented by these studies of small numbers of captive animals may 
not accurately represent the predicted reactions of wild animals under 
the same circumstances. Scientists at NMFS are currently compiling and 
reanalyzing available information on the reactions of marine mammals to 
sound in an effort to eventually establish new acoustic criteria. 
However, NMFS currently considers the 160, 180, and 190 dB thresholds 
to be the appropriate sound pressure level criteria for non-explosive 
sounds.
    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.
    There is no specific evidence that exposure to pulses of airgun 
sound can cause PTS in any marine mammal, even with large arrays of 
airguns. However, given the possibility that mammals close to an airgun 
array might incur TTS, there has been further speculation about the 
possibility that some individuals occurring very close to airguns might 
incur PTS. Single or occasional occurrences of mild TTS are not 
indicative of permanent auditory damage in terrestrial mammals. 
Relationships between TTS and PTS thresholds have not been studied in 
marine mammals, but NMFS assumes they are probably similar to those in 
humans and other terrestrial mammals. PTS might occur at a received 
sound level 20 dB or more above that inducing mild TTS if the animal 
were exposed to the strong sound for an extended period, or to a strong 
sound with rather rapid rise time (Cavanaugh, 2000).
    It is highly unlikely that marine mammals could receive sounds 
strong enough to cause permanent hearing impairment during a project 
employing two 45 in\3\ GI guns. In the present project, marine mammals 
are unlikely to be exposed to received levels of seismic pulses strong 
enough to cause TTS, as they would probably need to be within a few 
meters of the GI guns for this to occur. Given the higher level of 
sound necessary to cause PTS, it is even less likely that PTS could 
occur. In fact, even the levels immediately adjacent to the GI guns may 
not be sufficient to induce PTS, especially since a mammal would not be 
exposed to more than one strong pulse unless it swam immediately 
alongside a GI gun for a period longer than the inter-pulse interval 
(6-10 s). Also, baleen whales generally avoid the immediate area around 
operating seismic vessels. Furthermore, the planned monitoring and 
mitigation measures, including visual monitoring, ramp ups, and shut 
downs of the GI guns when mammals are seen within the ``safety radii,'' 
will minimize the already-minimal probability of exposure of marine 
mammals to sounds strong enough to induce PTS.
    Non-auditory Physiological Effects--Non-auditory physiological 
effects or injuries that theoretically might 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 proof that any of these effects occur in 
marine mammals exposed to sound from airgun arrays (even large ones), 
but there have been no direct studies of the potential for airgun 
pulses to elicit any of those 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.
    It is doubtful that any single marine mammal would be exposed to 
strong seismic sounds for sufficiently long that significant 
physiological stress would develop. That is especially so in the case 
of the present project where the GI guns are small, the ship's speed is 
relatively fast (7 knots (13 km/h)), and for the most part the survey 
lines are widely spaced with little or no overlap.
    Gas-filled structures in marine animals have an inherent 
fundamental resonance frequency. If stimulated at that frequency, the 
ensuing resonance could cause damage to the animal. A workshop (Gentry 
[ed.], 2002) was held to discuss whether the stranding of beaked whales 
in the Bahamas in 2000 (Balcomb and Claridge, 2001; NOAA and USN, 2001) 
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. Opinions were less conclusive 
about the possible role of gas (nitrogen) bubble formation/growth in 
the Bahamas stranding of beaked whales.
    Until recently, it was assumed that diving marine mammals are not 
subject to the bends or air embolism. However, a short 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, that might occur if they ascend unusually 
quickly when exposed to aversive sounds. Even if that can occur during 
exposure to mid-frequency sonar, there is no evidence that that type of 
effect occurs in response to airgun sounds. It is especially unlikely 
in the case of this project involving only two small GI guns.
    In general, little is known about the potential for seismic survey 
sounds to cause auditory impairment or other physical effects in marine 
mammals. Available data suggest that such effects, if they occur at 
all, would be limited to short distances and probably to projects 
involving large arrays of airguns. However, the available data do not 
allow for meaningful quantitative predictions of the numbers (if any) 
of marine mammals that might be affected in those ways. Marine mammals 
that show behavioral avoidance of seismic vessels, including most 
baleen whales, some odontocetes, and some pinnipeds, are especially 
unlikely to incur auditory impairment or other physical effects. Also, 
the planned mitigation measures, including shut downs, will reduce any 
such effects that might otherwise occur.

Strandings and Mortality

    Marine mammals close to underwater detonations of high explosive 
can be killed or severely injured, and the auditory organs are 
especially susceptible to injury (Ketten et al., 1993; Ketten, 1995). 
Airgun pulses are less energetic and have slower rise times, and there 
is no proof that they can cause serious injury, death, or stranding 
even in the case of large airgun arrays. However, the association of 
mass strandings of beaked whales with naval exercises and, in one case, 
an L-DEO seismic survey, has raised the possibility that beaked whales 
exposed to strong pulsed sounds may be especially susceptible to injury 
and/or behavioral reactions that can lead to stranding. Additional 
details may be found in Appendix A (g) of SIO's application.
    Seismic pulses and mid-frequency sonar pulses are quite different. 
Sounds produced by airgun arrays are broadband with most of the energy 
below 1 kHz. Typical military mid-frequency sonars operate at 
frequencies

[[Page 3268]]

of 2-10 kHz, generally with a relatively narrow bandwidth at any one 
time. Thus, 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 physical damage and mortality NOAA and USN, 
2001; Jepson et al., 2003), even if only indirectly, suggests that 
caution is warranted when dealing with exposure of marine mammals to 
any high-intensity pulsed sound.
    In Sept. 2002, there was a stranding of two Cuvier's beaked whales 
in the Gulf of California, Mexico, when the L-DEO vessel Maurice Ewing 
was operating a 20-gun 8490 in3 array in the general area. 
The link between this stranding and the seismic surveys was 
inconclusive and not based on any physical evidence (Hogarth, 2002; 
Yoder, 2002). Nonetheless, that plus the incidents involving beaked 
whale strandings near naval exercises suggests a need for caution in 
conducting seismic surveys in areas occupied by beaked whales. The 
present project will involve a much smaller sound source than used in 
typical seismic surveys. That, along with the monitoring and mitigation 
measures that are planned, are expected to minimize any possibility for 
strandings and mortality.

Possible Effects of Bathymetric Sonar Signals

    A multibeam bathymetric echosounder (Kongsberg Simrad EM-120, 12 
kHz) will be operated from the source vessel during much of the planned 
study. Sounds from the multibeam echosounder are very short pulses, 
occurring for 5-15 ms at up to 5 Hz, depending on water depth. As 
compared with the GI guns, the sound pulses emitted by this multibeam 
echosounder are at moderately high frequencies, centered at 12 kHz. The 
beam is narrow (1[deg]) in fore-aft extent, and wide (150[deg]) in the 
cross-track extent.
    Navy sonars that have been linked to avoidance reactions and 
stranding of cetaceans (1) generally are more powerful than the 
Kongsberg Simrad EM-120, (2) have a longer pulse duration, and (3) are 
directed close to horizontally, vs. downward, as for the multibeam 
echosounder. The area of possible influence of the Kongsberg Simrad EM-
120 is much smaller--a narrow band oriented in the cross-track 
direction below the source vessel. Marine mammals that encounter the 
EM-120 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.
Masking
    Marine mammal communications will not be masked appreciably by the 
multibeam echosounder signals given the low duty cycle of the system 
and the brief period when an individual mammal is likely to be within 
its beam. Furthermore, in the case of baleen whales, the signals do not 
overlap with the predominant frequencies in the calls, which would 
avoid significant masking.
Behavioral Responses
    Behavioral reactions of free-ranging marine mammals to military and 
other sonars appear to vary by species and circumstance. Observed 
reactions have included silencing and dispersal by sperm whales 
(Watkins et al., 1985), increased vocalizations and no dispersal by 
pilot whales (Rendell and Gordon, 1999), and the previously-mentioned 
beachings by beaked whales. However, all of those observations are of 
limited relevance to the present situation. Pulse durations from those 
sonars were much longer than those of the SIO multibeam echosounder, 
and a given mammal would have received many pulses from the naval 
sonars. During SIO's operations, the individual pulses will be very 
short, and a given mammal would not be likely to receive more than a 
few of the downward-directed pulses as the vessel passes by unless it 
were swimming in the same speed and direction as the ship in a fixed 
position underneath the ship.
    Captive bottlenose dolphins and a white whale exhibited changes in 
behavior when exposed to 1 s pulsed sounds at frequencies similar to 
those that will be emitted by the multibeam echosounder used by SIO, 
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 those data to free-ranging odontocetes is uncertain, and in any 
case, the test sounds were quite different in either duration or 
bandwidth as compared with those from a bathymetric echosounder.
    NMFS is not aware of any data on the reactions of pinnipeds to 
sonar sounds at frequencies similar to those of the R/V Roger Revelle's 
multibeam echosounder. Based on observed pinniped responses to other 
types of pulsed sounds, and the likely brevity of exposure to the 
multibeam sounds, pinniped reactions are expected to be limited to 
startle or otherwise brief responses of no lasting consequence to the 
animals. NMFS (2001) concluded that momentary behavioral reactions ``do 
not rise to the level of taking.'' Thus, brief exposure of cetaceans or 
pinnipeds to small numbers of signals from the multibeam bathymetric 
echosounder system are not expected to result in a ``take'' by 
harassment.

Hearing Impairment and Other Physical Effects

    Given recent stranding events that have been associated with the 
operation of naval sonar, there is concern that mid-frequency sonar 
sounds can cause serious impacts to marine mammals (see above). 
However, the multibeam echosounder proposed for use by SIO is quite 
different than sonars used for navy operations. Pulse duration of the 
multibeam echosounder is very short relative to the naval sonars. Also, 
at any given location, an individual marine mammal would be exposed to 
the multibeam sound signal for much less time given the generally 
downward orientation of the beam and its narrow fore-aft beamwidth. 
(Navy sonars often use near-horizontally-directed sound.) Those factors 
would all reduce the sound energy received from the multibeam 
echosounder rather drastically relative to that from the sonars used by 
the Navy.

Possible Effects of Sub-Bottom Profiler Signals

    A sub-bottom profiler will be operated from the source vessel much 
of the time during the planned study. Sounds from the sub-bottom 
profiler are short pulses of 1.5-24 ms duration. The triggering rate is 
controlled automatically so that only one pulse is in the water column 
at a time. Most of the energy in the sound pulses emitted by this sub-
bottom profiler is at mid frequencies, centered at 3.5 kHz. The 
beamwidth is approx. 30[deg] and is directed downward. Sound levels 
have not been measured directly for the sub-bottom profiler used by the 
R/V Roger Revelle, but Burgess and Lawson (2000) measured sounds 
propagating more or less horizontally from a similar unit with similar 
source output (205 dB re 1 microPa-m). The 160 and 180 dB re 1 microPa 
(rms) radii, in the horizontal direction, were estimated to be, 
respectively, near 20 m (66 ft) and 8 m (26 ft) from the source, as 
measured in 13 m (43 ft) water depth. The corresponding distances for 
an animal in the beam below the transducer would be greater, on the 
order of 180 m (591 ft) and 18 m (59 ft), assuming spherical spreading.

[[Page 3269]]

    The sub-bottom profiler on the R/V Roger Revelle has a stated 
maximum source level of 211 dB re 1 microPa-m and a normal source level 
of 200 dB re 1 microPa-m. Thus the received level would be expected to 
decrease to 160 and 180 dB about 160 m (525 ft) and 16 m (52 ft) below 
the transducer, respectively, again assuming spherical spreading. 
Corresponding distances in the horizontal plane would be lower, given 
the directionality of this source (30[deg] beamwidth) and the