Small Takes of Marine Mammals Incidental to Specified Activities; Low-Energy Seismic Survey in the Southwest Pacific Ocean, 8768-8783 [05-3442]

Agencies

• DEPARTMENT OF COMMERCE
• National Oceanic and Atmospheric Administration

[Federal Register Volume 70, Number 35 (Wednesday, February 23, 2005)]
[Notices]
[Pages 8768-8783]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 05-3442]


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DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

[I.D. 101204B]


Small Takes of Marine Mammals Incidental to Specified Activities; 
Low-Energy Seismic Survey in the Southwest Pacific Ocean

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 conducting oceanographic seismic surveys 
in the southwestern Pacific Ocean (SWPO) has been issued to the Scripps 
Institution of Oceanography, (Scripps).

DATES: Effective from February 10, 2005, through February 9, 2006.

ADDRESSES: The authorization and application containing a list of the 
references used in this document may be obtained by writing to this 
address or by telephoning the contact listed here. The application is 
also available at: https://www.nmfs.noaa.gov/prot_res/PR2/Small_Take/
smalltake_info.htm#applications.

FOR FURTHER INFORMATION CONTACT: Kenneth Hollingshead, Office of 
Protected Resources, NMFS, (301) 713-2289, ext 128.

SUPPLEMENTARY INFORMATION:

Background

    Sections 101(a)(5)(A) and (D) of the MMPA (16 U.S.C. 1361 et seq.) 
direct the Secretary of Commerce to allow, upon request, the 
incidental, but not intentional, taking of marine mammals by U.S. 
citizens who engage in a specified activity (other than commercial 
fishing) within a specified geographical region if certain findings are 
made and either regulations are issued or, if the taking is limited to 
harassment, a notice of a proposed authorization is provided to the 
public for review.
    Permission may be granted if NMFS finds that the taking will have a 
negligible impact on the species or stock(s) and will not have an 
unmitigable adverse impact on the availability of the species or 
stock(s) for subsistence uses and that the permissible methods of 
taking and requirements pertaining to the monitoring and reporting of 
such takings are set forth. NMFS has defined ``negligible impact'' in 
50 CFR 216.103 as ``...an impact resulting from the specified activity 
that cannot be reasonably expected to, and is not reasonably likely to, 
adversely affect the species or stock through effects on annual rates 
of recruitment or survival.''
    Section 101(a)(5)(D) of the MMPA established an expedited process 
by which citizens of the United States can apply for an authorization 
to incidentally take small numbers of marine mammals by harassment. 
Except with respect to certain activities not pertinent here, the MMPA 
defines ``harassment'' as:
    any act of pursuit, torment, or annoyance which (i) has the 
potential to injure a marine mammal or marine mammal stock in the 
wild [Level A harassment]; or (ii) has the potential to disturb a 
marine mammal or marine mammal stock in the wild by causing 
disruption of behavioral patterns, including, but not limited to, 
migration, breathing, nursing, breeding, feeding, or sheltering 
[Level B harassment].
    Section 101(a)(5)(D) establishes a 45-day time limit for NMFS 
review of an application followed by a 30-day public notice and comment 
period on any proposed authorizations for the incidental harassment of 
marine mammals. Within 45 days of the close of the comment period, NMFS 
must either issue or deny issuance of the authorization.

Summary of Request

    On October 6, 2004, NMFS received an application from Scripps for 
the taking, by harassment, of several species of marine mammals 
incidental to conducting a low-energy marine seismic survey program 
during early 2005 in the SWPO. The overall area within which the 
seismic survey will occur is located between approximately 25[deg] and 
50[deg]S, and between approximately 133[deg] and 162.5[deg]W. The 
survey will be conducted entirely in international waters. The purpose 
of the seismic survey is to collect the site survey data for a second 
Integrated Ocean Drilling Program transect to study the structure of 
the Eocene Pacific from the subtropics into the Southern Ocean. A 
future ocean-drilling program cruise (not currently scheduled) based on 
the data collected in the present program will better document and 
constrain the actual patterns of atmospheric and oceanic circulation on 
Earth at the time of extreme warmth in the early Eocene. Through the 
later ocean drilling program, it is anticipated that marine scientists 
will be able to (1) define the poleward extent of the sub-tropical 
gyre, (2) establish the position of the polar front, (3) determine sea-
surface temperatures and latitudinal temperature gradient, (4) 
determine the width and intensity of the high-productivity zone 
associated with these oceanographic features, (5) characterize the 
water masses formed in the sub-polar region, (6) determine the nature 
of the zonal winds and how they relate to oceanic surface circulation, 
and (7) document the changes in these systems as climate evolves from 
the warm early Eocene to the cold Antarctic of the early Oligocene. As 
presently scheduled, the seismic survey will occur from approximately 
February 11, 2005 to March 21, 2005.

Description of the Activity

    The seismic survey will involve one vessel. The source vessel, the 
R/V Melville, will deploy a pair of low-energy Generator-Injector (GI) 
airguns as an energy source (each with a discharge volume of 45 in\3\), 
plus a 450-meter (m) (1476-ft) long, 48-channel, towed hydrophone 
streamer. As the airguns are towed along the survey lines, the 
receiving system will receive the returning acoustic signals. The 
survey program will consist of approximately 11,000 kilometer (km) 
(5940 nautical mile (nm)) of surveys, including turns. Water depths 
within the seismic survey area are 4000-5000 m (13,123-16,400 ft) with 
no strong topographic features. The GI guns will be operated en route 
between piston-coring sites, where bottom sediment cores will be 
collected. There will be additional operations associated with 
equipment testing, start-

[[Page 8769]]

up, line changes, and repeat coverage of any areas where initial data 
quality is sub-standard.
    The energy to the airguns is compressed air supplied by compressors 
on board the source vessel. Seismic pulses will be emitted at intervals 
of 6-10 seconds. At a speed of 7 knots (about 13 km/h), the 6-10 sec 
spacing corresponds to a shot interval of approximately 21.5-36 m (71-
118 ft).
    The generator chamber of each GI gun, the one responsible for 
introducing the sound pulse into the ocean, is 45 in\3\. 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 45/105 in\3\ GI guns will be towed 8 m (26.2 ft) 
apart side by side, 21 m (68.9 ft) behind the Melville, at a depth of 2 
m (6.6 ft).

General-Injector Airguns

    Two GI-airguns will be used from the Melville during the proposed 
program. These 2 GI-airguns have a zero to peak (peak) source output of 
237 dB re 1 microPascal-m (7.2 bar-m) and a peak-to-peak (pk-pk) level 
of 243 dB (14.0 bar-m). However, these downward-directed source levels 
do not represent actual sound levels that can be measured at any 
location in the water. Rather, they represent the level that would be 
found 1 m (3.3 ft) from a hypothetical point source emitting the same 
total amount of sound as is emitted by the combined airguns in the 
airgun array. The actual received level at any location in the water 
near the airguns will not exceed the source level of the strongest 
individual source and actual levels experienced by any organism more 
than 1 m (3.3 ft) from any GI gun will be significantly lower.
    Further, the root mean square (rms) received levels that are used 
as impact criteria for marine mammals (see Richardson et al., 1995) are 
not directly comparable to these peak or pk-pk values that are normally 
used by acousticians to characterize source levels of airgun arrays. 
The measurement units used to describe airgun sources, peak or pk-pk 
decibels, are always higher than the rms decibels referred to in 
biological literature. For example, a measured received level of 160 dB 
rms in the far field would typically correspond to a peak measurement 
of about 170 to 172 dB, and to a pk-pk measurement of about 176 to 178 
decibels, as measured for the same pulse received at the same location 
(Greene, 1997; McCauley et al. 1998, 2000). The precise difference 
between rms and peak or pk-pk values depends on the frequency content 
and duration of the pulse, among other factors. However, the rms level 
is always lower than the peak or pk-pk level for an airgun-type source.
    The depth at which the sources are towed has a major impact on the 
maximum near-field output, because the energy output is constrained by 
ambient pressure. The normal tow depth of the sources to be used in 
this project is 2.0 m (6.6 ft), where the ambient pressure is 
approximately 3 decibars. This also limits output, as the 3 decibars of 
confining pressure cannot fully constrain the source output, with the 
result that there is loss of energy at the sea surface. Additional 
discussion of the characteristics of airgun pulses is provided in 
Scripps application and in previous Federal Register documents (see 69 
FR 31792 (June 7, 2004) or 69 FR 34996 (June 23, 2004)).
    Received sound levels have been modeled by L-DEO for two 105 in\3\ 
GI guns, but not for the two 45 in\3\ GI-guns, in relation to distance 
and direction from the airguns. The model does not allow for bottom 
interactions, and is therefore most directly applicable to deep water. 
Based on the modeling, estimates of the maximum distances from the GI 
guns where sound levels of 190, 180, 170, and 160 dB microPascal-m 
(rms) are predicted to be received are shown in Table 1. Because the 
model results are for the larger 105 in\3\ guns, those distances are 
overestimates of the distances for the 45 in\3\ guns.

   TABLE 1. Distances to which sound levels 190, 180, 170, and 160 dB
  microPascal-m (rms) might be received from two 105 in\3\ GI airguns,
   similar to the two 45 in\3\ GI airguns that will be used during the
   seismic survey in the SW Pacific Ocean during February-March 2005.
  Distances are based on model results provided by Lamont-Doherty Earth
                          Observatory (L-DEO).
              Estimated Distances at Received Levels (m/ft)
Water Depth >1000...............   190 dB   180 dB     170 dB     160 dB
                                    17/56   54/177    175/574   510/1673
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    Some empirical data concerning the 180-, and 160-dB distances have 
been acquired for several airgun configurations, including two GI-guns, 
based on measurements during an acoustic verification study conducted 
by L-DEO in the northern Gulf of Mexico (GOM) from 27 May to 3 June 
2003 (Tolstoy et al., 2004). Although the results are limited, the data 
showed that water depth affected the radii around the airguns where the 
received level would be 180 dB re 1 microPa (rms), NMFS' current injury 
threshold safety criterion applicable to cetaceans (NMFS, 2000). 
Similar depth-related variation is likely in the 190-dB distances 
applicable to pinnipeds. Correction factors were developed and 
implemented for previous IHAs for activities with water depths less 
than 1000 m (3281 ft). However, the proposed airgun survey will occur 
in depths 4000-5000 m (13,123-16,400 ft). As a result, NMFS has 
determined correction factors are not necessary here since the L-DEO 
model has been shown to result in more conservative (i.e,. protective) 
impact zones than indicated by the empirical measurements. Therefore, 
the assumed 180- and 190-dB radii are 54 m (177 ft) and 17 m (56 ft), 
respectively. Considering that the 2 GI-airgun array is towed 21 m (69 
ft) behind the Melville and the vessel is 85 m (270 ft) long, the 
forward aspect of the 180-dB isopleth (lines of equal pressure) at its 
greatest depth will not exceed approximately the mid-ship line of the 
Melville. At the water surface, an animal would need to be between the 
vessel and the 450-m (1476 ft) long hydrophone streamer to be within 
the 180-dB isopleth.

Bathymetric Sonar and Sub-bottom Profiler

    In addition to the 2 GI-airguns, a multi-beam bathymetric sonar and 
a low-energy 3.5-kHz sub-bottom profiler will be used during the 
seismic profiling and continuously when underway.
    Sea Beam 2000 Multi-beam Sonar - The hull-mounted Sea Beam 2000 
sonar images the seafloor over a 120[deg]-wide swath to 4600 m (15092 
ft) under the vessel. In ``deep'' mode (400-1000 m

[[Page 8770]]

(1312-3281 ft), it has a beam width of 2[deg], fore-and-aft, uses very 
short (7-20 msec) transmit pulses with a 2-22 s repetition rate and a 
12.0 kHz frequency sweep. The maximum source level is 234 dB microPa 
(rms).
    Sub-bottom Profiler - The sub-bottom profiler is normally operated 
to provide information about the sedimentary features and the bottom 
topography that is simultaneously being mapped by the multi-beam sonar. 
The energy from the sub-bottom profiler is directed downward by a 3.5-
kHz transducer mounted in the hull of the Melville. The output varies 
with water depth from 50 watts in shallow water to 800 watts in deep 
water. Pulse interval is 1 second (s) but a common mode of operation is 
to broadcast five pulses at 1-s intervals followed by a 5-s pause. The 
beamwidth is approximately 30[deg] and is directed downward. Maximum 
source output is 204 dB re 1 microPa (800 watts) while normal source 
output is 200 dB re 1 microPa (500 watts). Pulse duration will be 4, 2, 
or 1 ms, and the bandwith of pulses will be 1.0 kHz, 0.5 kHz, or 0.25 
kHz, respectively.
    Although the sound levels have not been measured directly for the 
sub-bottom profiler used by the Melville, Burgess and Lawson (2000) 
measured sounds propagating more or less horizontally from a sub-bottom 
profiler similar to the Scripps unit with similar source output (i.e., 
205 dB re 1 microPa m). For that profiler, the 160- and 180-dB re 1 
microPa (rms) radii in the horizontal direction were estimated to be, 
respectively, near 20 m (66 ft) and 8 m (26 ft) from the source, as 
measured in 13 m (43 ft) water depth. The corresponding distances for 
an animal in the beam below the transducer would be greater, on the 
order of 180 m (591 ft) and 18 m (59 ft) respectively, assuming 
spherical spreading. Thus the received level for the Scripps sub-bottom 
profiler would be expected to decrease to 160 and 180 dB about 160 m 
(525 ft) and 16 m (52 ft) below the transducer, respectively, assuming 
spherical spreading. Corresponding distances in the horizontal plane 
would be lower, given the directionality of this source (30[deg] 
beamwidth) and the measurements of Burgess and Lawson (2000).

Characteristics of Airgun Pulses

    Discussion of the characteristics of airgun pulses was provided in 
several previous Federal Register documents (see 69 FR 31792 (June 7, 
2004) or 69 FR 34996 (June 23, 2004)) and is not repeated here. 
Reviewers are referred to those documents for additional information.

Comments and Responses

    A notice of receipt and request for 30-day public comment on the 
application and proposed authorization was published on December 3, 
2004 (69 FR 70236). During the 30-day public comment period, NMFS 
received two comments. One commenter expressed the opinion that marine 
mammals should not be killed and that these killings are not small. As 
noted in this document, NMFS believes that no marine mammals are likely 
to be seriously injured or killed as a result of this L-DEO conducting 
seismic surveys.The concerns of the second commenter, the Center for 
Regulatory Effectiveness (CRE), are discussed here.
    Comment 1: There is no scientific basis for the use of 190, 180, 
170, and 160 dB micro-Pascal (RMS) as criteria for potential injury to 
marine mammals from seismic operations. NMFS uses these criteria along 
with L-DEO (Lamont-Doherty Earth Observatory) modeling, to determine 
the safety (shut-down) radii for seismic surveys. The comment states 
that those criteria are arbitrary and without scientific basis, were 
established without external peer review or published reports, and were 
not based on empirical data.
    Response: NMFS disagrees that there is no factual or scientific 
basis to support the 190, 180, and 160 dB thresholds (we note that 170 
dB is not used by NMFS). At the same time we recognize the limitations 
of these thresholds and, in the interest of transparency, acknowledge 
and disclose them. These limitations largely stem from the data gaps 
for many species of marine mammals, individual intra-species 
variability, and the difficulties inherent in conducting field studies 
in this area of inquiry (both logistic and ethical). NMFS makes its 
data, and the analysis of these data, available to the public and 
solicits public comment. However, there are factual studies that 
support the threshold values used here.
    The 160-dB isopleth for onset of Level B (behavioral) harassment is 
supported by research conducted by Malme et al. (1983, 1984) in their 
study on the California gray whale when exposed to seismic sounds. They 
found that migrating gray whales showed definite avoidance reactions 
and other behavioral changes when exposed to seismic pulses with 
received levels exceeding about 160 dB re 1 micro Pa (rms). The 
received levels at which 10 percent, 50 percent and 90 percent of the 
whales exhibited avoidance were estimated to be 164, 170, and 180 dB 
(Malme et al., 1989; Richardson et al., 1995).
    More recently, McCauley et al. (1998) documented localized 
avoidance by humpback whales of both the seismic array and a single 
airgun (16-gun 2678-in\3\ array and a single 20 in\3\ airgun with a 
source level 227 dB re 1 microPa-m (p-p)). The standoff range (i.e., 
the closest point of approach of the airgun to the whales) corresponded 
to received levels around 140 dB re 1 microPa. The initial avoidance 
response generally occurred at distances of 5 to 8 km (2.7 to 4.3 nm) 
from the airgun array and 2 km (1.0 nm) from the single gun, with 
estimated received levels at 140 dB and 143 dB re 1 microPa rms, 
respectively. However, some individual humpback whales, especially 
males, approached the vessel within distances 100 to 400 m (328 to 1312 
ft), where the maximum received level was 179 dB re 1 microPa rms.
    With respect to the 180 and 190 dB thresholds, data that are now 
available imply that, at least for dolphins, temporary threshold shift 
(TTS)in marine mammals is unlikely to occur unless the dolphins are 
exposed to airgun pulses stronger than 180 dB re 1 microPa (rms). 
However, safety zones must be implemented to protect those species 
believed to be most sensitive to low-frequency seismic noise: mysticete 
whales, sperm whales, and likely beaked whales (although beaked whales' 
best hearing is at significantly higher frequencies than low frequency 
seismic, it is possible that non-auditory injury may occur at lower 
sound pressure levels). As a result, NMFS has established the 180- and 
190-dB safety zones based on the most sensitive species at the 
estimated best hearing frequencies. If information is available that 
sensitive species will not be within the affected area, or empirical 
data are presented that marine mammal stocks within the affected area 
do not have hearing capabilities within the source frequencies, then 
the appropriate safety zones might be reduced in size.
    In some cases mitigation safety zones are perhaps larger than 
necessary to avoid Level A harassment of a particular species or the 
mitigation measures are one-size-fits-all in nature. This reflects the 
different sensitivities of affected species and the lack of data. Where 
different mitigation measures for different species are not practical, 
NMFS manages for the most sensitive species when multiple species are 
present. The safety zone for this seismic survey also affords the 
applicant a set of mitigation measures that can be practically 
implemented and will promote enforceability of the IHA. In this manner 
the applicant can move forward with the project in a timely

[[Page 8771]]

manner and NMFS' legal mandate is satisfied.
    NMFS is striving to improve the quality of the information it 
relies upon. We are developing sound exposure guidelines that will 
incorporate the current state of knowledge and take into account 
variations based on sound source, species type, and energy level. These 
guidelines will guide agency decisions and give the regulated 
communities and the public better information for planning, 
enforcement, and understanding. NMFS expects these guidelines to 
reflect the evolving understanding and appreciation of how sound 
affects marine mammals. As part of the process, NMFS has announced its 
intent to prepare an environmental impact statement and initiated 
public scoping to fully involve the public (70 FR 1871 (January 11, 
2005)). The science underlying those guidelines will undergo external 
peer review.
    Comment 2: The comment states there is no basis for correlating the 
effects, if any, on marine mammals of sonar and seismic operations.
    Response: NMFS agrees that the properties of seismic and sonar are 
quite different and will take that into account when developing its 
acoustic guidelines.
    Comment 3: NMFS' reliance on the L-DEO propagation model to 
determine the safety (shut-down) radii for seismic operations is 
unjustified and unsupported. NMFS has stated that for deep water the L-
DEO model overestimates the received sound levels at a given distance. 
The L-DEO model is also inappropriate for use in shallow and 
intermediate depths because it cannot account for bottom interactions 
with sound waves.
    Response: We have previously acknowledged the limitations of the 
model, as has the applicant. The acoustic verification/ calibration 
study in May/June 2003 in the GOM showed that water depth affected 
sound propagation (and, accordingly, the size of the safety radii). As 
a result, correction factors were developed for water depths 100-1000 m 
(328-3281 ft) and less than 100 m (328 ft). Those correction factors 
are not relevant for this survey, which will take place in water depths 
between 4000 and 5000 m (13123 and 16404 ft). Empirical data indicate 
that for water deeper than 1000 m (3281 ft), L-DEO's model tends to 
overestimate the received sound levels at any given distance (Tolstoy 
et al., 2004). Pending acquisition of additional empirical data, 
Scripps' safety radii will be the values predicted by the model. This 
approach will ensure that marine mammals are not inadvertently exposed 
to sound levels greater than what were calculated in the GOM 
verification study.
    Another alternative for estimating propagation would be to conduct 
simple calculations similar to those found in the Minerals Management 
Service's (MMS) Environmental Assessment for Geological and Geophysical 
Seismic Surveys in the GOM. This methodology is illustrated in Appendix 
C of that document (available at https://www.gomr.mms.gov/homepg/
regulate/environ/nepa/2004-054.pdf). NMFS believes this methodology 
would need to be improved prior to use for incidental take 
authorizations because it does not take into account the fact that 
marine mammals dive into deeper water where the sound fields normally 
propagate to greater distances than at the surface. Similarly, using 
simple propagation logarithms (e.g., Lr = Ls- 20 Log R for deep water 
propagation) also has shortcomings, in that they overestimate 
horizontal propagation (seismic airgun arrays project sounds towards 
the bottom and not horizontally). As a result, until improved models 
are developed, NMFS believes that using the L-DEO model, with fully 
explained correction factors where necessary (shallow and intermediate 
water depths) provides a reasonable methodology for calculating the 
zones of impact from vertically propagating seismic arrays.
    Comment 4: According to the abstract of the calibration study 
report (Tolstoy et al., 2004)), ``Received [sound] levels in deep water 
were lower than anticipated based on [L-DEO] modeling, and in shallow 
water they were higher.'' In other words, the L-DEO model is inaccurate 
and unreliable in deep and shallow water.
    Response: The L-DEO model is a general one that does not take into 
account the variation in propagation characteristics for the specific 
water bodies. In the GOM, sound propagation levels in deep water were 
lower and in shallow water were higher than that estimated by the L-DEO 
model. Under the MMPA and ESA, NMFS is charged with using the best 
information available. To the best of NMFS' knowledge, the L-DEO model 
provides a practical alternative to the use of standard propagation and 
attenuation calculations. Therefore, a more accurate statement would be 
that in that part of the GOM received sound levels in deep water were 
lower than anticipated based on the L-DEO model, and in shallow water 
they were higher the L-DEO model. Without making acoustic propagation 
measurements in advance of conducting seismic in each operating area, 
conservative estimates of sound propagation and attenuation were made. 
For this Scripps' seismic survey, the R/V Melville will conduct 
approximately 11,000 kilometers (km) (5940 nautical miles (nm)) of 
straight line seismic transects during the survey. Stopping the vessel 
to calibrate sound speed profiles for a particular water mass body, 
while possible, would result in increased costs through time and 
additional personnel and equipment needed onboard the R/V Melville. As 
an alternative, Scripps erred on the side of marine mammals protection 
and adopted conservative estimates for sound attenuation to the 160-, 
180-, and 190-dB isopleths. For this cruise, NMFS has adopted those 
conservative estimates.
    Comment 5:To the best of CRE's knowledge, the L-DEO model is not 
publically available, and NMFS has not demonstrated that it is 
sufficiently accurate and reliable to use. If NMFS intends to continue 
to use or rely on the L-DEO model, then the Agency should: (1) make the 
model publically available for comment; (2) validate use of the model 
for all contexts in which NMFS uses or relies on it; and (3) document 
use of the model and its results for each specific application in 
question, and make that documentation available for public comment 
along with the application itself in sufficient detail to allow third 
parties to reproduce the model results. If there is some reason why 
NMFS must rely on models that cannot be disclosed, then the agency must 
perform, document and produce the ``especially vigorous robustness 
checks'' that NMFS performed on these models. CRE recommends that NMFS 
adopt the Environmental Protection Agency's (EPA) definition of 
``especially rigorous robustness checks.'' If and when NMFS attempts to 
validate the L-DEO model, CRE recommends that NMFS follow EPA's model 
validation guidance. (EPA draft guidance is available at: https://
www.epa.gov/osp/crem/library/CREM%20Guidance% Draft%2012--03.pdf.
    Response: The L-DEO model is available to the public by contacting 
L-DEO (see the L-DEO application for the address). In addition, the 
model is explained in Diebold (2004, unpublished). A copy of this 
article is available upon request (see ADDRESSES). The 2003 GOM seismic 
airgun calibration study referenced in this document (Tolstoy et al., 
2004) was the result of an IHA issued to L-DEO for seismic work in the 
GOM (68 FR 9991, March 3, 2003). That report has been cited in a number 
of recent authorizations, and Chapter 3 of that

[[Page 8772]]

report has been available since mid-2004 on our homepage where seismic 
incidental take applications are posted. We consider all references 
cited in our Federal Register notices to be part of our administrative 
record. Whenever an article is not generally available publically, we 
strive to make a copy available.
    Chapter 3 of the 2003 GOM 90-day monitoring report was also 
rewritten, submitted for publication, peer-reviewed and finally 
published in the AGU's Geophysical Research Letters (Tolstoy, M., J.B. 
Diebold, S.C. Webb, D.R. Bohnenstiehl, E. Chapp, R.C. Holmes, and M. 
Rawson. 2004. Broadband Calibration of the R/V Ewing Seismic Sources. 
Geophys. Res. Lett., 31, doi:10.1029/ 2004GL020234, 2004). This 
scientific article is publically available through subscription, 
scientific libraries, or Inter-Library loan.
    As to other modeling approaches and software that could be used to 
verify or refute the L-DEO model, there are commercial products 
available, such as Bellhop, PE, and one called Nucleus that produce 
illustrations similar to the L-DEO model, but this latter product 
provides peak levels only, and has several of the same limitations 
contained in the L-DEO model. There are also publically available 
packages that include complex water column velocity structure, and 
seafloor interactions, but most of these have other kinds of 
limitations (e.g., typically, they do not include arrays of sound 
sources, and do not analyze for broadband frequencies).
    Comment 6: The CRE believes that NMFS should be concerned only with 
biologically significant effects on marine mammals, citing as support 
National Research Council reports (NRC 2004, NRC 2000).
    Response: NMFS' decisions are made in accordance with the relevant 
provisions of the MMPA and its implementing regulations. MMPA section 
101(a)(5)(D) requires the Secretary to authorize the taking of marine 
mammals incidental to otherwise lawful activities, provided that the 
activity will have no more than a negligible impact on the affected 
species or stocks of marine mammals. ``Negligible impact'' is defined 
in 50 CFR 216.103 (repeated earlier in this document). This is the 
relevant standard for the Secretary's decision. Although the term 
``biologically significant'' is not used, this concept is captured 
through application of NMFS' definition of ``negligible impact.''

Description of Habitat and Marine Mammals Affected by the Activity

    A detailed description of the SWPO area and its associated marine 
mammals can be found in the Scripps application and a number of 
documents referenced in that application, and is not repeated here. 
Forty species of cetacean, including 31 odontocete (dolphins and small- 
and large-toothed whales) species and nine mysticete (baleen whales) 
species, are believed by scientists to occur in the southwest Pacific 
in the proposed seismic survey area. Table 2 in the Scripps application 
summarizes the habitat, occurrence, and regional population estimate 
for these species. A more detailed discussion of the following species 
is also provided in the application: Sperm whale, pygmy and dwarf sperm 
whales, southern bottlenose whale, Arnoux's beaked whale, Cuvier's 
beaked whale, Shepherd's beaked whale, Mesoplodont beaked whales 
(Andrew's beaked whale, Blainville's beaked whale, gingko-toothed 
whale, Gray's beaked whale, Hector's beaked whale, spade-toothed whale, 
strap-toothed whale), melon-headed whale, pygmy killer whale, false 
killer whale, killer whale, long-finned pilot whale, short-finned pilot 
whale, rough-toothed dolphin, bottlenose dolphin, pantropical spotted 
dolphin, spinner dolphin, striped dolphin, short-beaked common dolphin, 
hourglass dolphin, Fraser's dolphin, Risso's dolphin, southern right 
whale dolphin, spectacled porpoise, humpback whale, southern right 
whale, pygmy right whale, common minke whale, Antarctic minke whale. 
Bryde's whale, sei whale, fin whale and blue whale. Because the 
proposed survey area spans a wide range of latitudes (25-500 S), 
tropical, temperate, and polar species are all likely to be found 
there. The survey area is all in deep-water habitat but is close to 
oceanic island (Society Islands, Australes Islands) habitats, so both 
coastal and oceanic species might be encountered. However, abundance 
and density estimates of cetaceans found there are provided for 
reference only, and are not necessarily the same as those that likely 
occur in the survey area.
    Five species of pinnipeds could potentially occur in the proposed 
seismic survey area: southern elephant seal, leopard seal, crabeater 
seal, Antarctic fur seal, and the sub-Antarctic fur seal. All are 
likely to be rare, if they occur at all, as their normal distributions 
are south of the Scripps survey area. Outside the breeding season, 
however, they disperse widely in the open ocean (Boyd, 2002; King, 
1982; Rogers, 2002). Only three species of pinniped are known to wander 
regularly into the area (SPREP, 1999): the Antarctic fur seal, the sub-
Antarctic fur seal, and the leopard seal. Leopard seals are seen are 
far north as the Cook Islands (Rogers, 2002).
    More detailed information on these species is contained in the 
Scripps application, which is available at: https://www.nmfs.noaa.gov/
prot_res/PR2/Small_Take/smalltake_info.htm#applications.

Potential Effects on Marine Mammals

    The effects of noise on marine mammals are highly variable, and can 
be categorized as follows (based on Richardson et al., 1995):
    (1) The noise may be too weak to be heard at the location of the 
animal (i.e., lower than the prevailing ambient noise level, the 
hearing threshold of the animal at relevant frequencies, or both);
    (2) The noise may be audible but not strong enough to elicit any 
overt behavioral response;
    (3) The noise may elicit reactions of variable conspicuousness and 
variable relevance to the well being of the marine mammal; these can 
range from temporary alert responses to active avoidance reactions such 
as vacating an area at least until the noise event ceases;
    (4) Upon repeated exposure, a marine mammal may exhibit diminishing 
responsiveness (habituation), or disturbance effects may persist; the 
latter is most likely with sounds that are highly variable in 
characteristics, infrequent and unpredictable in occurrence, and 
associated with situations that a marine mammal perceives as a threat;
    (5) Any anthropogenic noise that is strong enough to be heard has 
the potential to reduce (mask) the ability of a marine mammal to hear 
natural sounds at similar frequencies, including calls from 
conspecifics, and underwater environmental sounds such as surf noise;
    (6) If mammals remain in an area because it is important for 
feeding, breeding or some other biologically important purpose even 
though there is chronic exposure to noise, it is possible that there 
could be noise-induced physiological stress; this might in turn have 
negative effects on the well-being or reproduction of the animals 
involved; and
    (7) Very strong sounds have the potential to cause temporary or 
permanent reduction in hearing sensitivity. In terrestrial mammals, and 
presumably marine mammals, received sound levels must far exceed the 
animal's hearing threshold for there to

[[Page 8773]]

be any TTS in its hearing ability. For transient sounds, the sound 
level necessary to cause TTS is inversely related to the duration of 
the sound. Received sound levels must be even higher for there to be 
risk of permanent hearing impairment. In addition, intense acoustic or 
explosive events may cause trauma to tissues associated with organs 
vital for hearing, sound production, respiration and other functions. 
This trauma may include minor to severe hemorrhage.

Effects of Seismic Surveys on Marine Mammals

    The Scripps' application provides the following information on what 
is known about the effects on marine mammals of the types of seismic 
operations planned by Scripps. The types of effects considered here are 
(1) tolerance, (2) masking of natural sounds, (2) behavioral 
disturbance, and (3) potential hearing impairment and other non-
auditory physical effects (Richardson et al., 1995). Given the 
relatively small size of the airguns planned for the present project, 
the effects are anticipated to be considerably less than would be the 
case with a large array of airguns. Scripps and NMFS believe it is very 
unlikely that there would be any cases of temporary or especially 
permanent hearing impairment, or non-auditory physical effects. Also, 
behavioral disturbance is expected to be limited to distances less than 
500 m (1640 ft), the zone calculated for 160 dB or the onset of Level B 
harassment. Additional discussion on species-specific effects can be 
found in the Scripps application.

Tolerance

    Numerous studies (referenced in Scripps, 2004) have shown that 
pulsed sounds from airguns are often readily detectable in the water at 
distances of many kilometers, but that marine mammals at distances more 
than a few kilometers from operating seismic vessels often show no 
apparent response. That is often true even in cases when the pulsed 
sounds must be readily audible to the animals based on measured 
received levels and the hearing sensitivity of that mammal group. 
However, most measurements of airgun sounds that have been reported 
concerned sounds from larger arrays of airguns, whose sounds would be 
detectable farther away than that planned for use in the proposed 
survey. Although various baleen whales, toothed whales, and pinnipeds 
have been shown to react behaviorally to airgun pulses under some 
conditions, at other times mammals of all three types have shown no 
overt reactions. In general, pinnipeds and small odontocetes seem to be 
more tolerant of exposure to airgun pulses than are baleen whales. 
Given the relatively small and low-energy airgun source planned for use 
in this project, mammals are expected to tolerate being closer to this 
source than would be the case for a larger airgun source typical of 
most seismic surveys.

Masking

    Masking effects of pulsed sounds (even from large arrays of 
airguns) on marine mammal calls and other natural sounds are expected 
to be limited (due in part to the small size of the GI airguns), 
although there are very few specific data on this. Given the small 
acoustic source planned for use in the SWPO, there is even less 
potential for masking of baleen or sperm whale calls during the present 
research than in most seismic surveys (Scripps, 2004). GI-airgun 
seismic sounds are short pulses generally occurring for less than 1 sec 
every 6-10 seconds or so. The 6-10 sec spacing corresponds to a shot 
interval of approximately 21.5-36 m (71-118 ft). Sounds from the multi-
beam sonar are very short pulses, occurring for 7-20 msec once every 2 
to 22 sec, depending on water depth.
    Some whales are known to continue calling in the presence of 
seismic pulses. Their calls can be heard between the seismic pulses 
(Richardson et al., 1986; McDonald et al., 1995, Greene et al., 1999). 
Although there has been one report that sperm whales cease calling when 
exposed to pulses from a very distant seismic ship (Bowles et al., 
1994), a recent study reports that sperm whales continued calling in 
the presence of seismic pulses (Madsen et al., 2002). Given the 
relatively small source planned for use during this survey, there is 
even less potential for masking of sperm whale calls during the present 
study than in most seismic surveys. Masking effects of seismic pulses 
are expected to be negligible in the case of the smaller odontocete 
cetaceans, given the intermittent nature of seismic pulses and the 
relatively low source level of the airguns to be used in the SWPO. 
Also, the sounds important to small odontocetes are predominantly at 
much higher frequencies than are airgun sounds.
    Most of the energy in the sound pulses emitted by airgun arrays is 
at low frequencies, with strongest spectrum levels below 200 Hz and 
considerably lower spectrum levels above 1000 Hz. These low frequencies 
are mainly used by mysticetes, but generally not by odontocetes or 
pinnipeds. An industrial sound source will reduce the effective 
communication or echolocation distance only if its frequency is close 
to that of the marine mammal signal. If little or no overlap occurs 
between the industrial noise and the frequencies used, as in the case 
of many marine mammals relative to airgun sounds, communication and 
echolocation are not expected to be disrupted. Furthermore, the 
discontinuous nature of seismic pulses makes significant masking 
effects unlikely even for mysticetes.
    A few cetaceans are known to increase the source levels of their 
calls in the presence of elevated sound levels, or possibly to shift 
their peak frequencies in response to strong sound signals (Dahlheim, 
1987; Au, 1993; Lesage et al., 1999; Terhune, 1999; as reviewed in 
Richardson et al., 1995). These studies involved exposure to other 
types of anthropogenic sounds, not seismic pulses, and it is not known 
whether these types of responses ever occur upon exposure to seismic 
sounds. If so, these adaptations, along with directional hearing, pre-
adaptation to tolerate some masking by natural sounds (Richardson et 
al., 1995) and the relatively low-power acoustic sources being used in 
this survey, would all reduce the importance of masking marine mammal 
vocalizations.

Disturbance by Seismic Surveys

    Disturbance includes a variety of effects, including subtle changes 
in behavior, more conspicuous dramatic changes in activities, and 
displacement. However, there are difficulties in defining which marine 
mammals should be counted as taken by harassment. For many species and 
situations, scientists do not have detailed information about their 
reactions to noise, including reactions to seismic (and sonar) pulses. 
Behavioral reactions of marine mammals to sound are difficult to 
predict. Reactions to sound, if any, depend on species, state of 
maturity, experience, current activity, reproductive state, time of 
day, and many other factors. If a marine mammal does react to an 
underwater sound by changing its behavior or moving a small distance, 
the impacts of the change may not rise to the level of a disruption of 
a behavioral pattern. However, if a sound source would displace marine 
mammals from an important feeding or breeding area, such a disturbance 
may constitute Level B harassment under the MMPA. Given the many 
uncertainties in predicting the quantity and types of impacts of noise 
on marine mammals, it is appropriate to resort to estimating how many 
mammals may be present within a particular distance of industrial

[[Page 8774]]

activities or exposed to a particular level of industrial sound. With 
the possible exception of beaked whales, NMFS believes that this is a 
conservative approach and likely overestimates the numbers of marine 
mammals that are affected in some biologically important manner.
    The sound exposure criteria used to estimate how many marine 
mammals might be harassed behaviorally by the seismic survey are based 
on behavioral observations during studies of several species. However, 
information is lacking for many species. Detailed information on 
potential disturbance effects on baleen whales, toothed whales, and 
pinnipeds can be found in Scripps's SWPO application and its Appendix 
A.

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. Based on current information, NMFS precautionarily sets 
impulsive sounds equal to or greater than 180 and 190 dB re 1 microPa 
(rms) as the exposure thresholds for onset of Level A harassment for 
cetaceans and pinnipeds, respectively (NMFS, 2000). Those criteria have 
been used in setting the safety (shut-down) radii for seismic surveys. 
As discussed in the Scripps application and summarized here.
    1. 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.
    2. The minimum sound level necessary to cause permanent hearing 
impairment is higher, by a variable and generally unknown amount, than 
the level that induces barely-detectable TTS.
    3. The level associated with the onset of TTS is considered to be a 
level below which there is no danger of permanent damage.
    Because of the small size of the two 45 in\3\ GI-airguns, 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 even the mildest (and reversible) form of 
hearing impairment. Several aspects of the planned monitoring and 
mitigation measures for this project are designed to detect marine 
mammals occurring near the 2 GI-airguns (and bathymetric sonar), and to 
avoid exposing them to sound pulses that might (at least in theory) 
cause hearing impairment. In addition, research and monitoring studies 
on gray whales, bowhead whales and other cetacean species indicate that 
many cetaceans are likely to show some avoidance of the area with 
ongoing seismic operations. In these cases, the avoidance responses of 
the animals themselves will reduce or avoid the possibility of hearing 
impairment.
    Non-auditory physical effects may also occur in marine mammals 
exposed to strong underwater pulsed sound. Possible types of non-
auditory physiological effects or injuries that theoretically might 
occur in mammals close to a strong sound source include stress, 
neurological effects, bubble formation, resonance effects, and other 
types of organ or tissue damage. It is possible that some marine mammal 
species (i.e., beaked whales) may be especially susceptible to injury 
and/or stranding when exposed to strong pulsed sounds. However, Scripps 
and NMFS believe that it is especially unlikely that any of these non-
auditory effects would occur during the proposed survey given the small 
size of the acoustic sources, the brief duration of exposure of any 
given mammal, and the planned mitigation and monitoring measures. The 
following paragraphs discuss the possibility of TTS, permanent 
threshold shift (PTS), and non-auditory physical effects.

TTS

    TTS is the mildest form of hearing impairment that can occur during 
exposure to a strong sound (Kryter, 1985). When an animal experiences 
TTS, its hearing threshold rises and a sound must be stronger in order 
to be heard. TTS can last from minutes or hours to (in cases of strong 
TTS) days. Richardson et al. (1995) note that the magnitude of TTS 
depends on the level and duration of noise exposure, among other 
considerations. For sound exposures at or somewhat above the TTS 
threshold, hearing sensitivity recovers rapidly after exposure to the 
noise ends. Little data on sound levels and durations necessary to 
elicit mild TTS have been obtained for marine mammals.
    For toothed whales exposed to single short pulses, the TTS 
threshold appears to be, to a first approximation, a function of the 
energy content of the pulse (Finneran et al., 2002). Given the 
available data, the received level of a single seismic pulse might need 
to be on the order of 210 dB re 1 microPa rms (approx. 221 226 dB pk 
pk) in order to produce brief, mild TTS. Exposure to several seismic 
pulses at received levels near 200 205 dB (rms) might result in slight 
TTS in a small odontocete, assuming the TTS threshold is (to a first 
approximation) a function of the total received pulse energy (Finneran 
et al., 2002). Seismic pulses with received levels of 200 205 dB or 
more are usually restricted to a zone of no more than 100 m (328 ft) 
around a seismic vessel operating a large array of airguns. Because of 
the small airgun source planned for use during this project, such sound 
levels would be limited to distances within a few meters directly 
astern of the Melville.
    There are no data, direct or indirect, on levels or properties of 
sound that are required to induce TTS in any baleen whale. However, TTS 
is not expected to occur during this survey given the small size of the 
source limiting these sound pressure levels to the immediate proximity 
of the vessel, and the strong likelihood that baleen whales would avoid 
the approaching airguns (or vessel) before being exposed to levels high 
enough for there to be any possibility of TTS.
    TTS thresholds for pinnipeds exposed to brief pulses (single or 
multiple) have not been measured, although exposures up to 183 dB re 1 
microPa (rms) have been shown to be insufficient to induce TTS in 
California sea lions (Finneran et al., 2003). However, prolonged 
exposures show that some pinnipeds may incur TTS at somewhat lower 
received levels than do small odontocetes exposed for similar durations 
(Kastak et al., 1999; Ketten et al., 2001; Au et al., 2000). For this 
research cruise therefore, TTS is unlikely for pinnipeds.
    A marine mammal within a zone of less than 100 m (328 ft) around a 
typical large array of operating airguns might be exposed to a few 
seismic pulses with levels of [gteqt]205 dB, and possibly more pulses 
if the mammal moved with the seismic vessel. Also, around smaller 
arrays, such as the 2 GI-airgun array proposed for use during this 
survey, a marine mammal would need to be even closer to the source to 
be exposed to levels greater than or equal to 205 dB. However, as noted 
previously, most cetacean species tend to avoid operating airguns, 
although not all individuals do so. In addition, ramping up airgun 
arrays, which is now standard operational protocol for U.S. and some 
foreign seismic operations, 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 these cetaceans would be exposed to airgun pulses at a 
sufficiently high level for a sufficiently long period to cause more 
than mild TTS, given the relative

[[Page 8775]]

movement of the vessel and the marine mammal. However, with a large 
airgun array, TTS would be more 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. During this project, the anticipated 
180-dB distance is less than 54 m (177 ft), the array is towed 21 m (69 
ft) behind the Melville and the bow of the Melville will be 106 m (348 
ft) ahead of the airguns and the 205-dB zone would be less than 50 m 
(165 ft). Thus, TTS would not be expected in the case of odontocetes 
bow riding during airgun operations and if some cetaceans did incur TTS 
through exposure to airgun sounds, it would very likely be a temporary 
and reversible phenomenon.
    NMFS believes that, to avoid Level A harassment, cetaceans should 
not be exposed to pulsed underwater noise at received levels exceeding 
180 dB re 1 microPa (rms). The corresponding limit for pinnipeds has 
been set at 190 dB. The predicted 180- and 190-dB distances for the 
airgun arrays operated by Scripps during this activity are summarized 
in Table 1 in this document. It has also been shown that most whales 
tend to avoid ships and associated seismic operations. Thus, whales 
will likely not be exposed to such high levels of airgun sounds. 
Because of the slow ship speed, any whales close to the trackline could 
move away before the sounds become sufficiently strong for there to be 
any potential for hearing impairment. Therefore, there is little 
potential for whales being close enough to an array to experience TTS. 
In addition, as mentioned previously, ramping up the airgun array, 
which has become standard operational protocol for many seismic 
operators including Scripps, should allow cetaceans to move away from 
the seismic source and to avoid being exposed to the full acoustic 
output of the GI airguns.

Permanent Threshold Shift (PTS)

    When PTS occurs there is physical damage to the sound receptors in 
the ear. In some cases there can be total or partial deafness, while in 
other cases the animal has an impaired ability to hear sounds in 
specific frequency ranges. Although there is no specific evidence that 
exposure to pulses of airgun sounds can cause PTS in any marine 
mammals, even with the largest airgun arrays, physical damage to a 
mammal's hearing apparatus can potentially occur if it is exposed to 
sound impulses that have very high peak pressures, especially if they 
have very short rise times (time required for sound pulse to reach peak 
pressure from the baseline pressure). Such damage can result in a 
permanent decrease in functional sensitivity of the hearing system at 
some or all frequencies.
    Single or occasional occurrences of mild TTS are not indicative of 
permanent auditory damage in terrestrial mammals. However, very 
prolonged exposure to sound strong enough to elicit TTS, or shorter-
term exposure to sound levels well above the TTS threshold, can cause 
PTS, at least in terrestrial mammals (Kryter, 1985). Relationships 
between TTS and PTS thresholds have not been studied in marine mammals 
but are assumed to be similar to those in humans and other terrestrial 
mammals. The low-to-moderate levels of TTS that have been induced in 
captive odontocetes and pinnipeds during recent controlled studies of 
TTS have been confirmed to be temporary, with no measurable residual 
PTS (Kastak et al., 1999; Schlundt et al., 2000; Finneran et al., 2002; 
Nachtigall et al., 2003). In terrestrial mammals, the received sound 
level from a single non-impulsive sound exposure must be far above the 
TTS threshold for any risk of permanent hearing damage (Kryter, 1994; 
Richardson et al., 1995). For impulse sounds with very rapid rise times 
(e.g., those associated with explosions or gunfire), a received level 
not greatly in excess of the TTS threshold may start to elicit PTS. 
Rise times for airgun pulses are rapid, but less rapid than for 
explosions.
    Some factors that contribute to onset of PTS are as follows: (1) 
exposure to single very intense noises, (2) repetitive exposure to 
intense sounds that individually cause TTS but not PTS, and (3) 
recurrent ear infections or (in captive animals) exposure to certain 
drugs.
    Cavanagh (2000) has reviewed the thresholds used to define TTS and 
PTS. Based on his review and SACLANT (1998), it is reasonable to assume 
that PTS might occur at a received sound level 20 dB or more above that 
which induces mild TTS. However, for PTS to occur at a received level 
only 20 dB above the TTS threshold, it is probable that the animal 
would have to be exposed to the strong sound for an extended period.
    Sound impulse duration, peak amplitude, rise time, and number of 
pulses are the main factors thought to determine the onset and extent 
of PTS. Based on existing data, Ketten (1994) has noted that the 
criteria for differentiating the sound pressure levels that result in 
PTS (or TTS) are location and species-specific. PTS effects may also be 
influenced strongly by the health of the receiver's ear.
    Given that marine mammals are unlikely to be exposed to received 
levels of seismic pulses that could cause TTS, it is highly unlikely 
that they would sustain permanent hearing impairment. If we assume that 
the TTS threshold for odontocetes for exposure to a series of seismic 
pulses may be on the order of 220 dB re 1 microPa (pk-pk) 
(approximately 204 dB re 1 microPa rms), then the PTS threshold might 
be about 240 dB re 1 microPa (pk-pk). In the units used by 
geophysicists, this is 10 bar-m. Such levels are found only in the 
immediate vicinity of the largest airguns (Richardson et al., 1995; 
Caldwell and Dragoset, 2000). However, it is very unlikely that an 
odontocete would remain within a few meters of a large airgun for 
sufficiently long to incur PTS. The TTS (and thus PTS) thresholds of 
baleen whales and pinnipeds may be lower, and thus may extend to a 
somewhat greater distance from the source. However, baleen whales 
generally avoid the immediate area around operating seismic vessels, so 
it is unlikely that a baleen whale could incur PTS from exposure to 
airgun pulses. Some pinnipeds do not show strong avoidance of operating 
airguns. In summary, it is highly unlikely that marine mammals could 
receive sounds strong enough (and over a sufficient period of time) to 
cause permanent hearing impairment during this project. In the proposed 
project marine mammals are unlikely to be exposed to received levels of 
seismic pulses strong enough to cause TTS, and because of the higher 
level of sound necessary to cause PTS, it is even less likely that PTS 
could occur. This is due to the fact that even levels immediately 
adjacent to the 2 GI-airguns may not be sufficient to induce PTS 
because the mammal would not be exposed to more than one strong pulse 
unless it swam alongside an airgun for a period of time.

Strandings and Mortality

    Marine mammals close to underwater detonations of high explosives 
can be killed or severely injured, and the auditory organs are 
especially susceptible to injury (Ketten et al., 1993; Ketten, 1995). 
Airgun pulses are less energetic and have slower rise times. While 
there is no documented evidence that airgun arrays can cause serious

[[Page 8776]]

injury, death, or stranding, the association of strandings of beaked 
whales with naval exercises and an L-DEO seismic survey in 2002 have 
raised the possibility that beaked whales may be especially susceptible 
to injury and/or stranding when exposed to strong pulsed sounds. 
Information on recent beaked whale strandings may be found in Appendix 
A of the Scripps application and in several previous Federal Register 
documents (see 69 FR 31792 (June 7, 2004) or 69 FR 34996 (June 23, 
2004)).
    It is important to note that seismic pulses and mid-frequency sonar 
pulses are quite different. Sounds produced by the types of airgun 
arrays used to profile sub-sea geological structures are broadband with 
most of the energy below 1 kHz. Typical military mid-frequency sonars 
operate at frequencies of 2 to 10 kHz, generally with a relatively 
narrow bandwidth at any one time (though the center frequency may 
change over time). Because seismic and sonar sounds have considerably 
different characteristics and duty cycles, it is not appropriate to 
assume that there is a direct connection between the effects of 
military sonar and seismic surveys on marine mammals. However, evidence 
that sonar pulses can, in special circumstances, lead to physical 
damage and, indirectly, mortality suggests that caution is warranted 
when dealing with exposure of marine mammals to any high-intensity 
pulsed sound.
    In addition to the sonar-related strandings, there was a September, 
2002 stranding of two Cuvier's beaked whales in the Gulf of California 
(Mexico) when a seismic survey by the Ewing was underway in the general 
area (Malakoff, 2002). The airgun array in use during that project was 
the Ewing's 20-gun 8490-in\3\ array. This might be a first indication 
that seismic surveys can have effects, at least on beaked whales, 
similar to the suspected effects of naval sonars. However, the evidence 
linking the Gulf of California strandings to the seismic surveys is 
inconclusive, and to date is not based on any physical evidence 
(Hogarth, 2002; Yoder, 2002). The ship was also operating its multi-
beam bathymetric sonar at the same time but this sonar had much less 
potential than naval sonars to affect beaked whales. Although the link 
between the Gulf of California strandings and the seismic (plus multi-
beam sonar) survey is inconclusive, this plus the various incidents 
involving beaked whale strandings associated with naval exercises 
suggests a need for caution when conducting seismic surveys in areas 
occupied by beaked whales. However, the present project will involve a 
much smaller sound source than used in typical seismic surveys. 
Considering this and the required monitoring and mitigation measures, 
any possibility for strandings and mortality is expected to be 
eliminated.

Non-auditory Physiological Effects

    Possible types of non-auditory physiological effects or injuries 
that might theoretically occur in marine mammals exposed to strong 
underwater sound might include stress, neurological effects, bubble 
formation, resonance effects, and other types of organ or tissue 
damage. There is no evidence that any of these effects occur in marine 
mammals exposed to sound from airgun arrays (even large ones). However, 
there have been no direct studies of the potential for airgun pulses to 
elicit any of these effects. If any such effects do occur, they would 
probably be limited to unusual situations when animals might be exposed 
at close range for unusually long periods.
    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 airguns are small, the ship's speed is 
relatively fast (7 knots or approximately 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. There may also be a 
possibility that high sound levels could cause bubble formation in the 
blood of diving mammals that in turn could cause an air embolism, 
tissue separation, and high, localized pressure in nervous tissue 
(Gisner (ed), 1999; Houser et al., 2001).
    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. 
Among other reasons, the air spaces in marine mammals are too large to 
be susceptible to resonant frequencies emitted by mid- or low-frequency 
sonar; lung tissue damage has not been observed in any mass, multi-
species stranding of beaked whales; and the duration of sonar pings is 
likely too short to induce vibrations that could damage tissues (Gentry 
(ed.), 2002). 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. However, the interpretation 
that the effect was related to decompression injury is unproven 
(Piantadosi and Thalmann, 2004; Fernandez et al., 2004). Even if that 
effect can occur during exposure to mid-frequency sonar, there is no 
evidence that this type of effect occurs in response to low-frequency 
airgun sounds. It is especially unlikely in the case of this project 
involving only two small GI-airguns.
    In summary, little is known about the potential for seismic survey 
sounds to cause either auditory impairment or other non-auditory 
physical effects in marine mammals. Available data suggest that such 
effects, if they occur at all, would be limited to short distance