Incidental Takes of Marine Mammals During Specified Activities; Marine Geophysical Surveys in the Eastern Tropical Pacific Ocean in 2007, 11874-11886 [E8-4237]

Agencies

• DEPARTMENT OF COMMERCE
• National Oceanic and Atmospheric Administration

[Federal Register Volume 73, Number 44 (Wednesday, March 5, 2008)]
[Notices]
[Pages 11874-11886]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: E8-4237]


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

DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

RIN 0648-XF15


Incidental Takes of Marine Mammals During Specified Activities; 
Marine Geophysical Surveys in the Eastern Tropical Pacific Ocean in 
2007

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

ACTION: Notice; proposed incidental take authorization; request for 
comments.

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

SUMMARY: NMFS has received an application from the Lamont-Doherty Earth 
Observatory (L-DEO) for an Incidental Harassment Authorization (IHA) to 
take small numbers of marine mammals, by harassment, incidental to 
conducting two marine seismic surveys in the Eastern Tropical Pacific 
Ocean (ETP) during 2008. Under the Marine Mammal Protection Act (MMPA), 
NMFS is requesting comments on its proposed IHA for these activities.

DATES: Comments and information must be received no later than April 4, 
2008.

ADDRESSES: Comments on the application should be addressed to P. 
Michael Payne, 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 PR1.0648-XF15@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: Shane Guan, Office of Protected 
Resources, NMFS, (301) 713-2289, ext 137.

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 certain subsistence uses, and if the permissible methods 
of taking and requirements pertaining to the mitigation, 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

    L-DEO submitted to NMFS an application from L-DEO for the taking, 
by Level B harassment, of several species of marine mammals incidental 
to conducting, with research funding from the National Science 
Foundation (NSF), two marine seismic surveys in the ETP. This project 
would be conducted with L-DEO's new seismic vessel, the R/V Marcus G. 
Langseth (Langseth), which would deploy different configurations of 
airguns and a different bottom-mapping sonar than used previously by L-
DEO. The first survey was planned to be approximately 39 days between 
September and October 2007, and the second one approximately 6 days in 
between November and December 2007. However, due to scheduling issues 
with the vessel, the 39-day survey is rescheduled to June and August 
2008, and the 6-day survey to April and May 2008.

Description of the Specified Activity

    The April-May 6-day survey would examine two important types of 
seismic behavior of the Quebrada, Discovery, and Gofar fault systems 
(QDG) to

[[Page 11875]]

understand better the behavior of earthquakes and faults in general. 
The Discovery and Gofar faults generate more foreshocks in the 1,000 s 
before large earthquakes than anywhere else in the world. Year-long 
Ocean Bottom Seismometer (OBS) deployments during the survey are 
designed to use those foreshock sequences to answer questions about how 
large earthquakes nucleate. Despite accommodating the same amount of 
plate motion (14 cm/year, or 5.5 in/year) and being composed of similar 
oceanic crust, the Discovery and Quebrada faults differ in their 
ability to generate large earthquakes: the Discovery fault routinely 
generates earthquakes >5.5 in magnitude, whereas the Quebrada fault has 
had only one such event in the last 25 years. Refraction images of the 
material properties in both fault zones will show if some subtle 
difference (e.g., in hydrothermal alteration of the rocks) is 
responsible for the difference in seismogenic behavior.
    The June-August 39-day survey would obtain seismic reflection 
imaging of the internal structure of the magmatic-hydrothermal system 
at the fast-spreading mid-ocean ridge of the East Pacific Rise (EPR). 
Much is already known about processes at the EPR, but the proposed 
survey will provide an understanding of how the magmatic system, which 
is known at large spatial scales (1-100 km, or 0.62-62 mi), is coupled 
to volcanic/hydrothermal/biological systems, which are known at 
comparatively small spatial scales (0.001-1 km, or 0.00062-0.62 mi). 
The survey would also provide an understanding of the relationships 
between the temporal variations in subsurface magma systems and highly 
transient phenomena observed at the seafloor like faulting, volcanism, 
and hydrothermal venting.
    The seismic surveys will involve one vessel. The source vessel 
Langseth would deploy a 36-airgun array as an energy source. However, 
for the EPR study, two identical two-string sources will be firing 
alternately, so that no more than 18 airguns will be firing at any 
time, with a maximum discharge volume of 3,300 in\3\. The Langseth 
would also tow the receiving system, which consists of four 6-km (3.73-
mi) hydrophone streamers. For the QDG study, no more than 27 airguns 
would be fired at any time, with a maximum discharge volume of 4,950 
in\3\. The Langseth would also tow the receiving system, a single 8-km 
(4.97-mi) streamer, and would also deploy 40 long-term Ocean Bottom 
Seismometers (OBSs) that would be recovered 1 year after deployment, 
and another 8-10 short-term OBSs on each line that will be retrieved 
after the seismic surveys are completed.
    The EPR and QDG programs would consist of a maximum of 
approximately 7,992 km (4,967 mi) and 654 km (406 mi) of surveys, 
respectively.
    The proposed QDG seismic survey would last for approximately 6 
days, and the proposed EPR seismic survey would last for approximately 
39 days. All activities would be conducted in the period between April 
and August, 2008. The exact dates of the activities will be depend on 
ship scheduling, weather conditions, repositioning, streamer operations 
and adjustments, airgun deployment, or the need to repeat some lines if 
data quality is substandard.
    The QDG seismic survey would also occur in international waters of 
the ETP, approximately 2,265 km (1,408 mi) off the coast of Ecuador and 
approximately 1,300 km (808 mi) west of the Gal[aacute]pagos Islands. 
The overall area within which the seismic survey would occur is located 
between 3[deg] and 5[deg] S, and between 103[deg] and 106[deg] W. Water 
depths in the survey area are more than 3,000 m (9,843 ft) deep. The 
EPR seismic survey would take place in international waters of the ETP, 
offshore from Mexico and Central America at the East Pacific Rise. The 
closest land mass to this survey is Mexico, located approximately 890 
km (553 mi) away. The overall area within which the seismic survey will 
occur is located between 8.3[deg] and 10.2[deg] N, and between 
104.1[deg] and 104.5[deg] W. The survey would take place in water more 
than 2,000 m (6,562 ft) deep.
    In addition to the operations of the airgun array, a multi-beam 
bathymetric sonar would be operated from the source vessel continuously 
throughout the entire cruise, and a lower-energy sub-bottom profiler 
will also be operated during most of the survey.

Vessel Specifications

    The Langseth would tow the airgun array and, at times, up to four 
6-km (3.7-mi) streamers containing hydrophones along predetermined 
lines. The operation speed during seismic acquisition is typically 
7.4--9.3 km/h (4--5 kt). When not towing seismic survey gear, the 
Langseth can cruise at 20--24 km/h (11--13 kt).
    The Langseth would also serve as the platform from which vessel-
based visual marine mammal observers will watch for marine mammals 
before and during airgun operations. The characteristics of the Ewing 
that make it suitable for visual monitoring are described under 
Monitoring, later in this document.

Acoustic Source Specifications

Airguns
    The airgun array to be used will consist of 36 airguns, with 
maximum total discharge volume of approximately 6,600 in\3\. The 
airguns will comprise a mixture of Bolt 1500LL and Bolt 1900LLX 
airguns. The array will consist of four identical linear arrays or 
``strings.'' Each string would have ten airguns; the first and last 
airguns in the strings are spaced 16 m (52.5 ft) apart. Nine airguns 
would be fired simultaneously, while the tenth is kept in reserve as a 
spare, to be turned on in case of failure of another airgun. Two of the 
four strings would be fired during the EPR survey (18 airguns), and 
three strings would be fired during the QDG survey (27 airguns). The 
airgun strings would be distributed across an approximate area of 24 x 
16 m (78.7 x 52.5 ft) behind the Langseth and would be towed 
approximately 50-100 m (164-328 ft) behind the vessel. The firing 
pressure of the array is 2,000 psi. During firing, a brief (~0.1 s) 
pulse of sound is emitted. During the EPR survey, the shots would be 
emitted at intervals of ~15 s, corresponding to a shot interval of 
~37.5 m (123 ft). During the QDG survey, the shots would be emitted at 
intervals of ~60 s, corresponding to a shot interval of ~150 m (492 
ft). The airguns would be towed at a depth of 7 m (23 ft) during both 
the QDG and the EPR surveys. The depth at which the source is towed 
affects the maximum near-field output and the shape of its frequency 
spectrum. In deeper water, the effective source level for sound 
propagating in near-horizontal directions is higher than in shallow 
water; however, the nominal source levels of the array at various tow 
depths are nearly identical.
    Because the actual source is a distributed sound source (up to 27 
airguns in these surveys) rather than a single point source, the 
highest sound levels measurable at any location in the water would be 
less than the nominal source level. In addition, the effective source 
level for sound propagating in near-horizontal directions would be 
substantially lower than the nominal source level applicable to 
downward propagation because of the directional nature of the sound 
from the airgun array.
    The specifications of each source planned for use are described in 
Table 1.

[[Page 11876]]



  Table 1.--L-DEO Airgun Configuration and Specification of Each Source
                Planned for Use in the Proposed Projects
------------------------------------------------------------------------
                               18-Airgun array (2    27-Airgun array (3
                                    strings)              strings)
------------------------------------------------------------------------
Energy source...............  18, 2,000 psi Bolt    27, 2,000 psi Bolt
                               airguns of 40-360     airguns of 40-360
                               in\3\.                in\3\.
Source output (downward)....  0-pk: 252 dB re 1     0-pk: 256 dB re 1
                               microPa-m; pk-pk:     microPa-m; pk-pk:
                               259 dB re 1 microPa-  262 dB re 1 microPa-
                               m.                    m.
Air discharge volume........  Approximately 3,300   Approximately 4,950
                               in\3\.                in\3\.
Towing depth of energy        7 m (23 ft).........  7 m (23 ft).
 source.
Dominant frequency            0-188 Hz............  0-188 Hz.
 components.
------------------------------------------------------------------------

    A detailed discussion of the characteristics of airgun pulses has 
been provided in L-DEO's 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.
    Received sound levels have been predicted by L-DEO in relation to 
distance and direction from the airguns for the 36-airgun array with 18 
and 27 airguns firing and for a single 1900LL 40-in\3\ airgun, which 
would be used during power downs.
    The predicted sound contours are shown as sound exposure levels 
(SEL) in decibels (dB) re 1 microPa\2.\-s. SEL is a measure of the 
received energy in the pulse and represents the sound pressure level 
(SPL) that would be measured if the pulse energy were spread evenly 
across a 1-s period. Because actual seismic pulses are less than 1-s in 
duration, this means that the SEL value for a given pulse is lower than 
the SPL calculated for the actual duration of the pulse. The advantage 
of working with SEL is that the SEL measure accounts for the total 
received energy in the pulse, and biological effects of pulsed sounds 
probably depend mainly on pulse energy. SPL for a given pulse depends 
greatly on pulse duration. A pulse with a given SEL can be long or 
short depending on the extent to which propagation effects have 
``stretched'' the pulse duration. The SPL will be low if the duration 
is long and higher if the duration is short, even though the pulse 
energy (and presumably the biological effects) is the same.
    Although SEL may be a better measure than SPL when dealing with 
biological effects of pulsed sound, SPL is the measure that has been 
most commonly used in studies of marine mammal reactions to airgun 
sounds and in NMFS practice concerning levels above which ``taking'' 
might occur. SPL is often referred to as rms or ``root mean square'' 
pressure, averaged over the pulse duration. As noted above, the rms 
received levels that are used as impact criteria for marine mammals are 
not directly comparable to pulse energy (SEL). The SPL (i.e., rms sound 
pressure) for a given pulse is typically 10-15 dB higher than the SEL 
value for the same pulse as measured at the same location (Greene et 
al., 1997; McCauley et al., 1998; 2000). For this project, L-DEO 
assumes that rms pressure levels of received seismic pulses would be 10 
dB higher than the SEL values predicted by L-DEO's model. Thus, the L-
DEO assumes that 170 dB SEL can be viewed as 180 dB rms. NMFS considers 
that this assumption is valid.
    It should be noted that neither the SEL nor the SPL (rms) measure 
is directly comparable to the peak or peak-to-peak pressure levels 
normally used by geophysicists to characterize source levels of 
airguns. Peak and peak-to-peak pressure levels for airgun pulses are 
always higher than the rms dB referred to in much of the biological 
literature (Greene et al., 1997; McCauley et al., 1998; 2000). For 
example, a measured received level of 160 dB rms in the far field would 
typically correspond to a peak measurement of 170-172 dB re 1 microPa, 
and to a peak-to-peak measurement of 176-178 dB, as measured for the 
same pulse received at the same location (Greene et al., 1997; McCauley 
et al., 1998; 2000). The precise difference between rms and peak or 
peak-to-peak values for a given pulse depends on the frequency content 
and duration of the pulse, among other factors. However, the rms level 
is always lower than the peak or peak-to-peak level, and higher than 
the SEL value, for an airgun-type source.
    Empirical data concerning 190, 180, 170, and 160 dB (rms) isopleths 
in deep and shallow water were acquired for various airgun 
configurations during the acoustic calibration study of the Ewing's 20-
airgun, 8,600-in\3\ array in 2003 (Tolstoy et al., 2004a; 2004b). The 
results showed that radii around the airguns where the received level 
was 180 dB re 1 microPa (rms), the onset point for estimating temporary 
hearing threshold shift (TTS) in cetaceans (NMFS, 2000), varied with 
water depth. Similar depth-related variation is likely for 190-dB, the 
onset point used for estimating TTS in pinnipeds, although these were 
not measured. The empirical data indicated that, for deep water (>1,000 
m, or 3,280 ft), the L-DEO model overestimates the received sound 
levels at a given distance (Tolstoy et al., 2004a; 2004b). However, to 
be conservative, the Ewing's modeled distances would be applied to 
deep-water areas during the proposed study. As very few, if any, 
mammals are expected to occur below 2,000 m (6,562 ft), this depth was 
used as the maximum relevant depth.
    For the proposed programs in the ETP, the modeled distances are 
used to estimate deep-water mitigation safety zones; no correction 
factors are necessary because all activities will take place in deep (> 
2,000 m, or 6,562 ft) water. The 180 and 190 dB re 1 microPa (rms) 
distances define the safety criteria, used for mitigation for cetaceans 
and pinnipeds, respectively.
    The predicted distances to which sound levels higher than 190, 180, 
and 160 dB re 1 microPa (rms) could be received, based on the model 
calculation, are shown in Table 2.

[[Page 11877]]



Table 2.--Predicted Distances to Which Sound Levels Higher Than 190, 180, and 160 dB re 1 microPa (rms) Could Be
         Received From the Airgun Array and Single Airgun Planned for Use During the Surveys in the ETP
----------------------------------------------------------------------------------------------------------------
                                                                                  Predicted RMS radii (m)
                      Source and volume                        Min. water --------------------------------------
                                                               depth (m)      190 dB       180 dB       160 dB
----------------------------------------------------------------------------------------------------------------
Single Bolt airgun (40 in\3\)...............................         3000           12           40          385
36-airgun array: 3 strings (4950 in\3\).....................         3000          200          650         4400
36-airgun array: 2 strings (3300 in\3\).....................         2000          140          450         3800
----------------------------------------------------------------------------------------------------------------

Bathymetric Sonar and Sub-Bottom Profiler

    Along with the airgun operations, two additional acoustical data 
acquisition systems would be operated during parts of the Langseth's 
cruises. The ocean floor would be mapped with the 12-kHz Kongsberg 
Simrad EM 120 MBB sonar, and a 2.5-7 kHz sub-bottom profiler would also 
be operated along with the MBB sonar. These sound sources would be 
operated from the Langseth, at times simultaneously with the airgun 
array.
    The Kongsberg Simrad EM 120 operates at 11.25-12.6 kHz and would be 
mounted in a sonar pod hung below the hull of the Langseth. The 
beamwidth is 1[deg] fore-aft and 150[deg] athwartship. The maximum 
source level is 242 dB re 1 microPa at 1 m (rms). For deep-water 
operation, each ``ping'' consists of nine successive fan-shaped 
transmissions, each 15 ms in duration and each ensonifying a sector 
that extends 1[deg] fore-aft. The nine successive transmissions span an 
overall cross-track angular extent of about 150[deg], with 16 ms gaps 
between the pulses for successive sectors. A receiver in the overlap 
area between two sectors would receive two 15-ms pulses separated by a 
16-ms gap. In shallower water, the pulse duration is reduced to 2 ms, 
and the number of transmit beams is also reduced. The ping interval 
varies with water depth, from ~5 s at 1,000 m (3,280 ft) to 20 s at 
4,000 m (13,123 ft).
    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 MBB sonar. The energy from the sub-
bottom profiler is directed downward by a 3.5-kHz transducer in the 
hull of the Langseth. The output varies with water depth from 50 watts 
in shallow water to 800 watts in deep water. Pulse interval is 1 second 
but a common mode of operation is to broadcast five pulses at 1-s 
intervals followed by a 5-s pause.

Description of Marine Mammals in the Activity Area

    A total of 34 cetacean species and 6 species of pinnipeds are known 
to or may occur in the ETP. Of the 34 cetacean species, 27 are likely 
to occur in the proposed survey area. Five of those 27 cetacean species 
are listed under the U.S. Endangered Species Act (ESA) as endangered: 
Sperm whale (Physeter macrocephalus), humpback whale (Megaptera 
novaeangliae), blue whale (Balaenoptera musculus), fin whale (B. 
physalus), and sei whale (B. borealis).
    The other 22 species that are likely to occur in the proposed 
survey areas are: Minke whale (B. acutorostrata), Bryde's whale (B. 
edeni), Pygmy sperm whale (Kogia breviceps), Dwarf sperm whale (K. 
simus), Cuvier's beaked whale (Ziphius cavirostris), Longman's beaked 
whale (Indopacetus pacificus), Pygmy beaked whale (Mesoplodon 
peruvianus), Ginkgo-toothed beaked whale (M. ginkgodens), Blainville's 
beaked whale (M. densirostris), Rough-toothed dolphin (Steno 
bredanensis), Bottlenose dolphin (Tursiops truncatus), Pantropical 
spotted dolphin (Stenella attenuata), Spinner dolphin (S. 
longirostris), Striped dolphin (S. coeruleoalba), Fraser's dolphin 
(Lagenodelphis hosei), Short-beaked common dolphin (Delphinus delphis), 
Risso's dolphin (Grampus griseus), Melon-headed whale (Peponocephala 
electra), Pygmy killer whale (Feresa attenuata), False killer whale 
(Pseudorca crassidens), Killer whale (Orcinus orca), and Short-finned 
pilot whale (Globicephala macrorhynchus).
    A detailed description of the biology, population estimates, and 
distribution and abundance of these species are provided in the L-DEO's 
IHA application. Additional information regarding the stock assessment 
of these species are be found in NMFS Pacific Marine Mammal Stock 
Assessment Report (Carretta et al., 2007), and can also be accessed via 
the following URL link: https://www.nmfs.noaa.gov/pr/pdfs/sars/
po2006.pdf.
    The most extensive regional distribution and abundance data that 
encompass the entire study area come primarily from multi-year vessel 
surveys conducted in the wider ETP by the NMFS Southwest Fisheries 
Science Center. Information on the distribution of cetaceans inhabiting 
the ETP has been summarized in several studies (e.g., Polacheck, 1987; 
Wade and Gerrodette, 1993; Ferguson and Barlow, 2001), and is also 
described in detail in the L-DEO's IHA application.
    Seven species, although present in the wider ETP, likely would not 
be found in the proposed seismic survey areas. These species are: 
Pacific white-sided dolphins (Lagenorhynchus obliquidens), Baird's 
beaked whales (Berardius bairdii), Long-beaked common dolphins 
(Delphinus capensis), Dusky dolphins (L. obscurus), southern right 
whale dolphins (Lissodelphis peronii), Burmeister's porpoises (Phocoena 
spinipinnis), and long-finned pilot whales (Globicephala melas) 
(Leatherwood et al., 1991; Van Waerebeek et al., 1991; Heyning and 
Perrin, 1994; Brownell and Clapham, 1999; Ferguson and Barlow, 2001; 
Olson and Reilly, 2002). Accordingly, those species are not considered 
any further.
    Six species of pinnipeds are known to occur in the ETP: The 
Guadalupe fur seal (Arctocephalus townsendi), California sea lion 
(Zalophus californianus), Gal[aacute]pagos sea lion (Z. wollebaeki), 
Gal[aacute]pagos fur seal (A. galapagoensis), southern sea lion (Otaria 
flavescens), and South American fur seal (A. australis). However, 
pinnipeds likely would not be encountered during the proposed seismic 
surveys. Therefore, they are not considered further here.

Summary of Potential Effects of Airgun Sounds on Marine Mammals

    The effects of sounds from airguns 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, or non-auditory physical or physiological effects 
(Richardson et al., 1995). These effects are discussed below, but also 
in further detail in Appendix B of L-DEO's application.
    The potential effects of airguns discussed below are presented 
without consideration of the proposed

[[Page 11878]]

mitigation measures described below. When these measures are taken into 
account, it is unlikely that this project would result in temporary, or 
especially, permanent hearing impairment or any non-auditory physical 
or physiological effects.

Tolerance

    Numerous studies have shown that pulsed sounds from airguns are 
often readily detectable in the water at distances of many kilometers. 
A summary of the characteristics of airgun pulses is provided in 
Appendix B of L-DEO's application. Studies have also shown that marine 
mammals at distances more than a few kilometers from operating seismic 
vessels often show no apparent response (tolerance) (Appendix B(e)). 
That is often true even in cases when the pulsed sounds must be readily 
audible to the animals based on measured received levels and the 
hearing sensitivity of that mammal group. Although various baleen 
whales, toothed whales, and (less frequently) pinnipeds have been shown 
to react behaviorally to airgun pulses under some conditions, at other 
times mammals of all three types have shown no overt reactions. In 
general, pinnipeds and small odontocetes seem to be more tolerant of 
exposure to airgun pulses than are baleen whales.

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 of relevance. 
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; 
Nieukirk et al., 2004). Although there has been one report that sperm 
whales ceased calling when exposed to pulses from a very distant 
seismic ship (Bowles et al., 1994), a more recent study reports that 
sperm whales off northern Norway continued calling in the presence of 
seismic pulses (Madsen et al., 2002). That has also been shown during 
recent work in the Gulf of Mexico (Tyack et al., 2003; Smultea et al., 
2004). 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. Dolphins and porpoises commonly are heard 
calling while airguns are operating (e.g., Gordon et al., 2004; Smultea 
et al., 2004; Holst et al., 2005a; 2005b). Also, the sounds important 
to small odontocetes are predominantly at much higher frequencies than 
are airgun sounds. Masking effects, in general, are discussed further 
in LDEO's application Appendix B (d).

Disturbance Reactions

    Disturbance includes a variety of effects, including subtle changes 
in behavior, more conspicuous changes in activities, and displacement.
    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 briefly to an underwater 
sound by slightly changing its behavior or moving a small distance, the 
impacts of the change are unlikely to be significant to the individual, 
let alone the stock or the species as a whole. However, if a sound 
source displaces a marine mammal(s) from an important feeding or 
breeding area for a prolonged period, impacts on the animal(s) could be 
significant.
    There are many uncertainties in predicting the quantity and types 
of impacts of noise on marine mammals. NMFS uses exposures to 180 and 
190 dB re 1 microPa rms to estimate the number of animals that may be 
harassed by a particular sound source in a given area (and also uses 
those SPLs for use in the development of shutdown zones for 
mitigation). These estimates 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.

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 sequences 
of airgun pulses. NMFS's incidental take authorizations generally 
protect against exposure to impulsive sounds greater than 180 and 190 
dB re 1 microPa (rms), for cetaceans and pinnipeds, respectively (NMFS, 
2000). Those criteria have been used in defining the safety (shut down) 
radii planned for the proposed seismic surveys.
    Several aspects of the monitoring and mitigation measures proposed 
for this project are designed to detect marine mammals occurring near 
the airguns to avoid exposing them to sound pulses that might, at least 
in theory, cause hearing impairment (see Mitigation and Monitoring 
section below). In addition, many cetaceans are likely to show some 
avoidance of the area with high received levels of airgun sound. In 
those cases, the avoidance responses of the animals themselves will 
reduce or (most likely) avoid any 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, and other types of organ or 
tissue damage. It is possible that some marine mammal species (e.g., 
beaked whales) may be especially susceptible to injury and/or stranding 
when exposed to strong pulsed sounds. However, there is no definitive 
evidence that any of these effects occur even for marine mammals in 
close proximity to large arrays of airguns. It is unlikely that any 
effects of these types would occur during the proposed project given 
the brief duration of exposure of any given mammal, and the planned 
monitoring and mitigation measures (see below).

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 involving mid-
frequency sonar 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.
    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 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; Fernandez et al., 2005a), even if only 
indirectly,

[[Page 11879]]

suggests that caution is warranted when dealing with exposure of marine 
mammals to any high-intensity pulsed sound.
    In September, 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 airgun, 8,490 in\3\ airgun array in the 
general area. The link between the stranding and the seismic surveys 
was inconclusive and not based on any physical evidence (Hogarth, 2002; 
Yoder, 2002). Nonetheless, that together with the incidents involving 
beaked whale strandings near naval exercises suggests a need for 
caution in conducting seismic surveys in areas occupied by beaked 
whales. No injuries of beaked whales are anticipated during the 
proposed study, due to the proposed monitoring and mitigation measures.

Possible Effects of Multibeam Bathymetric (MBB) Sonar Signals

    The Kongsberg Simrad EM 120 12-kHz sonar will be operated from the 
source vessel at some times during the planned study. As discussed 
above, sounds from the MBB sonar are very short pulses, occurring for 
15 ms once every 5-20 s, depending on water depth. Most of the energy 
in the sound pulses emitted by this MBB sonar is at frequencies 
centered at 12 kHz. The beam is narrow (1[deg]) in fore-aft extent and 
wide (150[deg]) in the cross-track extent. Each ping consists of nine 
successive fan-shaped transmissions (segments) at different cross-track 
angles. Any given mammal at depth near the trackline would be in the 
main beam for only one or two of the nine segments. Also, marine 
mammals that encounter the Kongsberg Simrad EM 120 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. Animals close to the ship (where the beam is 
narrowest) are especially unlikely to be ensonified for more than one 
15 ms pulse (or two pulses if in the overlap area). Similarly, Kremser 
et al. (2005) noted that the probability of a cetacean swimming through 
the area of exposure when an MBB sonar emits a pulse is small. The 
animal would have to pass the transducer at close range and be swimming 
at speeds similar to the vessel in order to be subjected to sound 
levels that could cause TTS.
    Navy sonars that have been linked to avoidance reactions and 
stranding of cetaceans (1) generally have a longer pulse duration than 
the Kongsberg Simrad EM 120, and (2) are often directed close to 
horizontally vs. downward for the Kongsberg Simrad EM 120. The area of 
possible influence of the EM 120 is much smaller-a narrow band below 
the source vessel. The duration of exposure for a given marine mammal 
can be much longer for a Navy sonar. Possible effects of sonar on 
marine mammals are outlined below.

Possible Effects of Sub-Bottom Profiler Signals

     A sub-bottom profiler would be operated from the source vessel 
during the planned study. As discussed before, sounds from the sub-
bottom profiler are very short pulses, occurring for 1, 2, or 4 ms once 
every second. Most of the energy in the sound pulses emitted by this 
sub-bottom profiler is at mid frequencies, centered at 3.5 kHz. The 
beam width is approximately 30[deg] and is directed downward.
    Sound levels have not been measured directly for the sub-bottom 
profiler used by the Langseth, 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 at 1[deg] m). The 160 and 
180 dB re 1 microPa (rms) radii, in the horizontal direction, were 
estimated to be, respectively, near 20 m (65.6 ft) and 8 m (26.2 ft) 
from the source, as measured in 13 m (42.7 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.
    The sub-bottom profiler on the Langseth has a stated maximum source 
level of 204 dB re 1 microPa at 1 m. Thus, the received level would be 
expected to decrease to 160 and 180 dB about 160 m (525 ft) and 16 m 
(53 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] beam width) and 
the measurements of Burgess and Lawson (2000).

Numbers of Marine Mammals Estimated to be Taken

    All anticipated takes would be takes by Level B harassment, 
involving temporary changes in behavior. The proposed mitigation 
measures will prevent the possibility of injurious takes. The estimates 
of take are based on consideration of the number of marine mammals that 
might be disturbed by approximately 654 km (406 mi) of seismic surveys 
at the QDG study site and approximately 7,992 km (4,967 mi) of seismic 
surveys at the EPR study site in the ETP.
    The anticipated radii of influence of the MBB sonar are less than 
those for the airgun array. It is assumed that, during simultaneous 
operations of the airgun array and sonar, any marine mammals close 
enough to be affected by the sonar would already be affected by the 
airguns. However, whether or not the airguns are operating 
simultaneously with the sonar, marine mammals are not expected to be 
``taken'' by the sonar given its characteristics (e.g., narrow 
downward-directed beam) and other considerations described above. 
Therefore, no additional allowance is included for animals that might 
be affected by sound sources other than airguns.
    There is some uncertainty about how representative the data are for 
the QDG survey because of the time of year and the validity of the 
assumptions used below to estimate the potential take by harassment. 
The data derived from marine mammals surveys that were conducted from 
the time of year that is different from the proposed QDG seismic 
surveys. However, the approach used here is based on the best available 
data. To provide some allowance for those uncertainties, ``best 
estimates'' and ``maximum estimates'' of the numbers potentially 
affected have been derived based on the average and maximum estimates 
of densities reported by Ferguson and Barlow (2001) for the survey 
blocks encompassing each project study area as presented in Tables 3 
and 4 of L-DEO's application.

Basis for Take Estimates

    As discussed above, several extensive marine mammal surveys have 
been conducted in the ETP over numerous years. The most comprehensive 
data available for the regions encompassing the proposed survey areas 
are the Ferguson and Barlow (2001) data collected from late July to 
early December 1986-1996.
    Because the proposed QDG survey is planned for April-May 2008, data 
collected by Ferguson and Barlow (2001) in July-December may not be as 
representative for the QDG survey. Again, however, it is the best 
available information. For some species, the densities derived from 
past surveys may not be representative of the densities that would be 
encountered during the actual proposed seismic studies. For example, 
the density of cetaceans sighted during L-DEO's 2003 Hess Deep survey 
was considerably lower (only one sighting) than the densities 
anticipated to occur there based on the Ferguson and Barlow (2001) 
data. The Hess Deep survey occurred in mid-July, and was apparently not 
well

[[Page 11880]]

represented by the Ferguson and Barlow (2001) data collected during the 
fall, beginning just after the Hess Deep survey.
    Despite the above caveats, the Ferguson and Barlow (2001) data 
still represent the best available data for estimating numbers of 
animals potentially exposed to the proposed seismic sounds. Average and 
maximum densities for marine mammals from Ferguson and Barlow (2001) 
were calculated for each of the project areas based on encompassing and 
adjacent survey blocks. Maximum densities were either the highest 
estimated density in any of the blocks or, if that number was zero, the 
average group size for that species. The densities reported in Ferguson 
and Barlow (2001) were corrected for both detectability [f(0)] and 
availability [g(0)] biases, and therefore, are relatively unbiased.

Estimated Number of Takes by Harassment

    The number of individuals that may be exposed to airgun sounds with 
received levels higher than 160 dB re 1 microPa (rms) on one or more 
occasions can be estimated by considering the total marine area that 
would be within the 160-dB radius around the operating airgun array on 
at least one occasion. In the QDG survey, the proposed seismic lines do 
not run parallel to each other in close proximity, and only one 
transect line might be surveyed a second time, which minimizes the 
number of times an individual mammal may be exposed during the survey. 
In the EPR survey, the seismic lines are parallel and in close 
proximity, and the entire grid may be surveyed more than twice, which 
may result in individuals being exposed on two or more occasions. It is 
not known how much time will pass between the first and the second 
transit along each line, so it is also possible that different marine 
mammals could occur in the area during the second pass. Thus, the best 
estimates in this section are based on a single pass of all survey 
lines (including turns), and maximum estimates are based on maximum 
densities, i.e., the highest single-block density among all of the 
blocks used in the calculations. Tables 3 and 4 show the best and 
maximum estimates of the number of marine mammals that could 
potentially be affected during the EPR and QDG seismic surveys, 
respectively.
    The number of individuals potentially exposed to 160 dB re 1 
microPa (rms) or higher in each area was calculated by multiplying the 
expected species density, either ``mean'' (i.e., best estimate) or 
``maximum'' (maximum estimate) times by the anticipated minimum area to 
be ensonified to that level during airgun operations.

 Table 3.--Estimates of the Numbers of Different Individual Marine Mammals That Might Be Exposed to Sound Levels
> 160 dB re 1 microPa (rms) During L-DEO's Proposed EPR Seismic Program in the ETP. The Proposed Sound Source Is
                             an 18-Airgun Array With a Total Volume of 3,300 in \3\
 [``NA'' indicates that no percentage of population data were available due to the lack of population estimate]
----------------------------------------------------------------------------------------------------------------
                        Number of individuals exposed to SPL > 160 dB re 1 microPa (rms)
-----------------------------------------------------------------------------------------------------------------
                                                                                Percent of
                                                                                 regional
                        Species                            Best estimate     population based  Maximum  estimate
                                                                            on best  estimate
----------------------------------------------------------------------------------------------------------------
Humpback whale.........................................                  0               0.00                  2
Minke whale............................................                  0                 NA                  1
Bryde's whale..........................................                  3               0.02                  7
Sei whale..............................................                  0                 NA                  2
Fin whale..............................................                  0               0.00                  2
Blue whale.............................................                  0               0.03                  1
Sperm whale............................................                  2               0.01                  4
Pygmy sperm whale......................................                  0                 NA                  1
Dwarf sperm whale......................................                 66               0.59                 87
Cuvier's beaked whale..................................                 16               0.08                 30
Longman's beaked whale.................................                  0               0.00                  4
Pygmy beaked whale.....................................                  0                 NA                  4
Blainville's beaked whale..............................                  0                 NA                  4
Mesoplodon sp..........................................                  8               0.03  .................
Rough-toothed dolphin..................................                 27               0.02                109
Bottlenose dolphin.....................................                 18               0.01                 38
Spotted dolphin........................................                697               0.03               1327
Spinner dolphin........................................                342               0.02                695
Striped dolphin........................................                303               0.02                792
Fraser's dolphin.......................................                  5               0.00                 47
Short-beaked common dolphin............................                  7               0.00                835
Risso's dolphin........................................                 18               0.01                 53
Melon-headed whale.....................................                  5               0.01                 30
Pygmy killer whale.....................................                  9               0.02                 46
False killer whale.....................................                  3               0.01                  8
Killer whale...........................................                  1               0.01                  3
Short-finned pilot whale...............................                 20               0.01                 41
----------------------------------------------------------------------------------------------------------------


[[Page 11881]]


 Table 4.--Estimates of the Numbers of Different Individual Marine Mammals That Might Be Exposed to Sound Levels
> 160 dB re 1 microPa (rms) During L-DEO's Proposed QDG Seismic Program in the ETP. The Proposed Sound Source is
                              a 27-Airgun Array With a Total Volume of 4,950 in \3\
 [``NA'' indicates that no percentage of population data were available due to the lack of population estimate]
----------------------------------------------------------------------------------------------------------------
                        Number of individuals exposed to SPL > 160 dB re 1 microPa (rms)
-----------------------------------------------------------------------------------------------------------------
                                                                                Percent of
                                                                                 regional
                        Species                            Best estimate     population based  Maximum  estimate
                                                                            on best  estimate
----------------------------------------------------------------------------------------------------------------
Humpback whale.........................................                  0               0.00                  1
Minke whale............................................                  0                 NA                  1
Bryde's whale..........................................                  6               0.05                 24
Sei whale..............................................                  0                 NA                  2
Fin whale..............................................                  0               0.00                  2
Blue whale.............................................                  1               0.04                  3
Sperm whale............................................                  4               0.01                 13
Pygmy sperm whale......................................                  0                 NA                  1
Dwarf sperm whale......................................                  0               0.00                  2
Cuvier's beaked whale..................................                 48               0.24                 81
Longman's beaked whale.................................                  0               0.00                  3
Pygmy beaked whale.....................................                  0                 NA                  3
Blainville's beaked whale..............................                  0                 NA                  3
Mesoplodon sp..........................................                  7               0.03  .................
Rough-toothed dolphin..................................                 24               0.02                166
Bottlenose dolphin.....................................                 17               0.01                 48
Spotted dolphin........................................                468               0.02               1236
Spinner dolphin........................................                226               0.01                431
Striped dolphin........................................                482               0.03                599
Fraser's dolphin.......................................                 43               0.01                151
Short-beaked common dolphin............................                 30               0.00               2089
Risso's dolphin........................................                 16               0.01                 68
Melon-headed whale.....................................                  7               0.01                 38
Pygmy killer whale.....................................                  3               0.01                 16
False killer whale.....................................                 11               0.03                 47
Killer whale...........................................                  1               0.01                  2
Short-finned pilot whale...............................                 35               0.02                105
----------------------------------------------------------------------------------------------------------------

    The area expected to be ensonified was determined by entering the 
planned survey lines into a MapInfo Geographic Information System 
(GIS), using the GIS to identify the relevant areas by ``drawing'' the 
applicable 160-dB buffer around each seismic line and then calculating 
the total area within the buffers. Areas where overlap occurred 
(because of intersecting lines) were included only once to determine 
the minimum area expected to be ensonified to higher than 160 dB re 1 
microPa at least once.
    Applying the approach described above, 2,492 km\2\ (923 mi\2\) 
would be within the 160-dB isopleth on one or more occasions during the 
EPR survey, and 2,911 km\2\ (1,224 mi\2\) would be ensonified on one or 
more occasions during the QDG survey. This approach does not allow for 
turnover in the marine mammal populations in the study areas during the 
course of the studies. That might underestimate actual numbers of 
individuals exposed, although the conservative distances used to 
calculate the area may offset this. In addition, the approach assumes 
that no cetaceans would move away or toward the trackline as the 
Langseth approaches in response to increasing sound levels prior to the 
time the levels reach 160 dB. Another way of interpreting the estimates 
that follow is that they represent the number of individuals that are 
expected (in the absence of a seismic program) to occur in the waters 
that will be exposed to 160 dB re 1 microPa (rms) or higher.
    The ``best estimate'' of the number of individual marine mammals 
that might be exposed to seismic sounds with received levels of 160 dB 
re 1 microPa (rms) or higher during the EPR survey includes 2 
endangered whales (both sperm whales), 24 beaked whales, and 3 Bryde's 
whales. Pantropical spotted, spinner, and striped dolphins are 
estimated to be the most common species exposed; the best estimates for 
those species are 697, 342, and 303, respectively. Estimates for other 
species are lower (Table 3).
    The ``best estimate'' of the number of individual marine mammals 
that might be exposed to seismic sounds with received levels of 160 dB 
re 1 microPa (rms) or higher during the QDG survey includes 5 
endangered whales (4 sperm whales and 1 blue whale), 55 beaked whales, 
and 6 Bryde's whales. Striped, spotted, and spinner dolphins are 
estimated to be the most common species exposed; the best estimates for 
those species are 482, 468, and 226, respectively. Estimates for other 
species are lower (Table 4).
    The ``best estimate'' of the total number of individual marine 
mammals that might be exposed to seismic sounds with received levels of 
160 dB re 1 microPa (rms) or higher for both surveys, along with the 
percentage of regional population, is listed in Table 5. It includes 
two ESA-listed species (6 sperm whales and 1 blue whale), 79 beaked 
whales, and 9 Bryde's whales. Striped, spotted, and spinner dolphins 
are estimated to be the most common species exposed; the best estimates 
for those species are 785, 1,165, and 568, respectively. Estimates for 
other species are lower (Table 5).

[[Page 11882]]



    Table 5.--Estimates of the Numbers of Different Individual Marine
   Mammals That Might Be Exposed to Sound Levels > 160 dB re 1 microPa
      (rms) During L-DEO's Two Proposed Seismic Program in the ETP
 [``NA'' indicates that no percentage of population data were available
                 due to the lack of population estimate]
------------------------------------------------------------------------
 Total number of individuals exposed to SPL > 160 dB re 1 microPa (rms)
-------------------------------------------------------------------------
                                                            Percent of
                                                             regional
                 Species                  Best  estimate    population
                                                           based on best
                                                             estimate
------------------------------------------------------------------------
Humpback whale..........................               0            0.00
Minke whale.............................               0              NA
Bryde's whale...........................               9            0.07
Sei whale...............................               0              NA
Fin whale...............................               0            0.00
Blue whale..............................               1            0.04
Sperm whale.............................               6            0.02
Pygmy sperm whale.......................               0              NA
Dwarf sperm whale.......................              66            0.59
Cuvier's beaked whale...................              64            0.32
Longman's beaked whale..................               0            0.00
Pygmy beaked whale......................               0              NA
Blainville's beaked whale...............               0              NA
Mesoplodon sp...........................              15            0.06
Rough-toothed dolphin...................              51            0.04
Bottlenose dolphin......................              35            0.02
Spotted dolphin.........................           1,165            0.05
Spinner dolphin.........................             568            0.03
Striped dolphin.........................             785            0.05
Fraser's dolphin........................              48            0.01
Short-beaked common dolphin.............              37            0.00
Risso's dolphin.........................              34            0.02
Melon-headed whale......................              12            0.02
Pygmy killer whale......................              12            0.03
False killer whale......................              14            0.04
Killer whale............................               2            0.02
Short-finned pilot whale................              55            0.03
------------------------------------------------------------------------

Potential Impacts to Subsistence Harvest of Marine Mammals

    The proposed activities will not have any impact on the 
availability of the species or stocks for subsistence use described in 
section 101(a)(5)(D)(i)(II).

Potential Impacts on Habitat and Prey

    The proposed seismic survey would not result in any permanent or 
significant impact on habitats used by marine mammals, or to the food 
sources they use. The main impact issue associated with the proposed 
activity would be temporarily elevated noise levels and the associated 
direct effects on marine mammals, as discussed above. The following 
sections briefly review effects of airguns on fish and invertebrates, 
and more details are included in Appendices C and D of the L-DEO's IHA 
application, respectively.

Effects on Fish

    There are three types of potential effects of exposure to seismic 
surveys: (1) Pathological, (2) physiological, and (3) behavioral. 
Pathological effects involve lethal and temporary or permanent sub-
lethal injury. Physiological effects involve temporary and permanent 
primary and secondary stress responses, such as changes in levels of 
enzymes and proteins. Behavioral effects refer to temporary and (if 
they occur) permanent changes in exhibited behavior (e.g., startle and 
avoidance behavior). The three categories are interrelated in complex 
ways. For example, it is possible that certain physiological and 
behavioral changes could potentially lead to an ultimate pathological 
effect on individuals (i.e., mortality).
    The potential for pathological damage to hearing structures in fish 
depends on the energy level of the received sound and the physiology 
and hearing capability of the species in question. For a given sound to 
result in hearing loss, the sound must exceed, by some specific amount, 
the hearing threshold of the fish for that sound (Popper, 2005). The 
consequences of temporary or permanent hearing loss in individual fish 
on a fish population is unknown; however, it likely depends on the 
number of individuals affected and whether critical behaviors involving 
sound (e.g. predator avoidance, prey capture, orientation and 
navigation, reproduction, etc.) are adversely affected. McCauley et al. 
(2003) found that exposure to airgun sound caused observable anatomical 
damage to the auditory maculae of ``pink snapper'' (Pagrus auratus). 
This damage in the ears had not been repaired in fish sacrificed and 
examined almost two months after exposure. On the other hand, Popper et 
al. (2005) found that received sound exposure levels of 177 dB re 1 
microPa\2\-s caused no hearing loss in broad whitefish (Coreogonus 
nasus) . During both studies, the repetitive exposure to sound was 
greater than would have occurred during a typical seismic survey. 
However, the substantial low-frequency energy produced by the airgun 
arrays (less than 400 Hz in the study by McCauley et al. (2003) and 
less than 200 Hz in Popper et al. (2005)) likely did not propagate to 
the fish because the water in the study areas was very shallow 
(approximately 9 m (29.5 ft) in the former case and less than 2 m (6.6 
ft) in the latter). Water depth sets a lower limit on the lowest sound 
frequency that will propagate at about one-quarter wavelength (Urick, 
1983; Rogers and Cox, 1988).

[[Page 11883]]

    Except for these two studies, at least with airgun-generated sound 
treatments, most contributions rely on rather subjective assays such as 
fish ``alarm'' or ``startle response'' or changes in catch rates by 
fishers. These observations are important in that they attempt to use 
the levels of exposures that are likely to be encountered by most free-
ranging fish in actual survey areas. However, the associated sound 
stimuli are often poorly described, and the biological assays are 
varied (Hastings and Popper, 2005).
    According to Buchanan et al. (2004), for the types of seismic 
airguns and arrays involved with the proposed program, the pathological 
(mortality) zone for fish would be expected to be within a few meters 
of the seismic source. Numerous other studies provide examples of no 
fish mortality upon exposure to seismic sources (Falk and Lawrence, 
1973; Holliday et al., 1987; La Bella et al., 1996; Santulli et al., 
1999; McCauley et al., 2000a; 2000b; 2003; Bjarti, 2002; Hassel et al., 
2003; Popper et al., 2005).
    Some studies have reported, some equivocally, that mortality of 
fish, fish eggs, or larvae can occur close to seismic sources 
(Kostyuchenko, 1973; Dalen and Knutsen, 1986; Booman et al., 1996; 
Dalen et al., 1996). Some of the reports claimed seismic effects from 
treatments quite different from actual seismic survey sounds or even 
reasonable surrogates. Saetre and Ona (1996) applied a ``worst-case 
scenario'' mathematical model to investigate the effects of seismic 
energy on fish eggs and larvae. They concluded that mortality rates 
caused by exposure to seismic surveys are so low, as compared to 
natural mortality rates, that the impact of seismic surveying on 
recruitment to a fish stock must be regarded as insignificant.
    Physiological effects refer to cellular and/or biochemical 
responses of fish to acoustic stress. Such stress potentially could 
affect fish populations by increasing mortality or reducing 
reproductive success. Primary and secondary stress responses of fish 
after exposure to seismic survey sound appear to be temporary in all 
studies done to date (Sverdrup et al., 1994; McCauley et al., 2000a; 
2000b). The periods necessary for the biochemical changes to return to 
normal are variable, and depend on numerous aspects of the biology of 
the species and of the sound stimulus.
    Behavioral effects include changes in the distribution, migration, 
mating, and catchability