`[Federal Register Volume 69, Number 189 (Thursday, September 30, 2004)]
[Notices]
[Pages 58396-58411]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 04-21973]


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DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

[I.D. 070104A]


Small Takes of Marine Mammals Incidental to Specified Activities; 
Marine Seismic Survey in the Eastern Tropical Pacific Ocean off Central 
America

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

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

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SUMMARY: NMFS has received an application from the Lamont-Doherty Earth 
Observatory (L-DEO), a part of Columbia University, for an Incidental 
Harassment Authorization (IHA) to take small numbers of marine mammals, 
by harassment, incidental to conducting oceanographic seismic surveys 
in the eastern tropical Pacific Ocean (ETPO) off Central America. Under 
the Marine Mammal Protection Act (MMPA), NMFS is requesting comments on 
its proposal to issue an authorization to L-DEO to incidentally take, 
by harassment, small numbers of several species of cetaceans and 
pinnipeds for a limited period of time within the next year.

DATES: Comments and information must be received no later than November 
1, 2004.

ADDRESSES: Comments on the application should be addressed to Steve 
Leathery, Chief, Permits, Conservation and Education Division, Office 
of Protected Resources, National Marine Fisheries Service, 1315 East-
West Highway, Silver Spring, MD 20910-3225, or by telephoning the 
contact listed here. The mailbox address for providing email comments 
is [email protected]. Include in the subject line of the e-mail 
comment the following document identifier: 070104A. 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 this address or by telephoning the contact 
listed here and is also available at: http://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) 713-2322, 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 June 28, 2004, NMFS received an application from L-DEO for the 
taking, by harassment, of several species of marine mammals incidental 
to conducting a marine seismic survey program during a four-week period 
beginning in late November 2004 in the Exclusive Economic Zones of El 
Salvador, Honduras, Nicaragua, and Costa Rica. The purpose of the 
seismic survey is to investigate stratigraphic development in the 
presence of tectonic forcing in the Sandino basin off Nicaragua and 
Costa Rica. Because of the variations in subsidence/uplift histories 
within the Sandino Basin, and the inability to provide whole-basin 
coverage during a research cruise of reasonable length, data will be 
collected in two primary grids in the Sandino Basin and a third, 
smaller grid off Nicoya Peninsula. Grid descriptions are provided in L-
DEO's application.

Description of the Activity

    The seismic survey will involve one vessel. The source vessel, the 
R/V Maurice Ewing, will deploy three low-energy GI airguns as an energy 
source, with a total discharge volume of up to 315 in\3\. As the 
airguns are towed along the survey lines, the towed hydrophone system 
will receive the returning acoustic signals.
    The program will consist of a maximum of 6048 km (3266 nm) of 
surveys. Water depths within the survey area are up to 5000 m (16,400 
ft); most of the survey will be conducted in water depths less than 
2000 m (6560 ft). The area to be surveyed extends from approximately 4 
to 150 km (2 to 80 nm) offshore. The airguns may also be operated 
closer to, and farther from, shore while the ship is maneuvering toward 
or between survey lines.

[[Page 58397]]

    The proposed program will use conventional seismic methodology with 
a small towed array of three GI airguns as the energy source, and a 
towed hydrophone streamer as the receiver system. The energy to the 
airguns is compressed air supplied by compressors on board the source 
vessel. Seismic pulses will be emitted at intervals of 5 seconds. The 
5-sec spacing corresponds to a shot interval of approximately 12.5 m 
(41 ft).
    The generator chamber of each GI gun, the one responsible for 
introducing the sound pulse into the ocean, is 105 in\3\. The injector 
chamber injects air into the previously generated bubble to maintain 
its shape, and does not introduce appreciably more sound into the 
water. The three 105-in\3\ GI guns will be towed behind the Ewing, at a 
depth of 2.5 m (8.2 ft). Operating pressure will be 2000 psi. The GI 
guns will be 7.8 m (25.6 ft) apart and will be towed 37 m (121.4 ft) 
behind the Ewing. The Ewing will also tow a hydrophone streamer that is 
up to 1500 m (4922 ft) long. As the airguns are operated along the 
survey lines, the hydrophone receiving system will receive and record 
the returning acoustic signals.

General-Injector Airguns

    Three GI-airguns will be used from the Ewing during the proposed 
program. These 3 GI-airguns have a zero to peak (peak) source output of 
240.7 dB re 1 microPascal-m (10.8 bar-m) and a peak-to-peak (pk-pk) 
level of 246 dB (21 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 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 decibels 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 2.5 m (6.7 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 later in 
this document (see Characteristics of Airgun Pulses).
    For the GI-airguns, the sound pressure field has been modeled by L-
DEO in relation to distance and direction from the airguns, and in 
relation to depth. Table 1 shows the maximum distances from the airguns 
where sound levels of 190-, 180-, 170- and 160-dB re 1 microPa (rms) 
are predicted to be received.
    Some empirical data concerning the 180, 170 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 from 27 May to 3 June 
2003 (see Tolstoy et al., 2004). Although the results are limited and 
do not include measurements for three GI-guns, the data for other 
airgun configurations 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. Water depths within the 
survey area are up to 5000 m (16400 ft), but most of the survey will be 
conducted in water depths less than 2000 m (6560 ft), as shown in Table 
1, column 3.

[[Page 58398]]

[GRAPHIC] [TIFF OMITTED] TN30SE04.200

    The empirical data indicate that, for deep water (greater than 1000 
m (3281 ft)), the L-DEO model for the airguns tends to overestimate the 
received sound levels at a given distance (Tolstoy et al., 2004). 
However, to be precautionary pending acquisition of additional 
empirical data, L-DEO and NMFS propose that the mitigation safety radii 
during airgun operations in deep water will be the values predicted by 
L-DEO's model (see Table 1).
    The 180- and 190-dB radii were not measured for three GI- guns 
operating in shallow water (less than 100 m (328 ft)). However, the 
measured 180-dB radius for the 6-airgun array operating in shallow 
water was 6.8x that predicted by L-DEO's model for operation of the 
six-airgun array in deep water. The conservative correction factor is 
applied to the model estimates to predict the radii for the three GI-
guns in shallow water, as shown in Table 1.
    Empirical measurements were not conducted for intermediate depths 
(100-1000 m (328-3281 ft)). On the expectation that results will be 
intermediate between those from shallow and deep water, a 1.5x 
correction factor is applied to the estimates provided by the model for 
deep water situations, as shown in Table 1. This is the same factor 
that was applied to the model estimates during L-DEO cruises in 2003.

Bathymetric Sonar and Sub-bottom Profiler

    In addition to the 3 GI-airguns, a multibeam bathymetric sonar and 
a low-energy 3.5-kHz sub-bottom profiler will be used during the 
seismic profiling and continuously when underway.
    Bathymetric Sonar-Atlas Hydrosweep-The 15.5-kHz Atlas Hydrosweep 
sonar is mounted on the hull of the Maurice Ewing, and it operates in 
three modes, depending on the water depth. There is one shallow water 
mode and two deep-water modes: an Omni mode (similar to the shallow-
water mode but with a source output of 220 dB (rms)) and a Rotational 
Directional Transmission (RDT) mode. The RDT mode is normally used 
during deep-water operation and has a 237-dB rms source output. In the 
RDT mode, each ``ping'' consists of five successive transmissions, each 
ensonifying a beam that extends 2.67 degrees fore-aft and approximately 
30 degrees in the cross-track direction. The five successive 
transmissions (segments) sweep from port to starboard with minor 
overlap, spanning an overall cross-track angular extent of about 140 
degrees, with small (much less than 1 millisec) gaps between the pulses 
for successive 30-degree segments. The total duration of the ``ping,'' 
including all five successive segments, varies with water depth, but is 
1 millisec in water depths less than 500 m and 10 millisec in the 
deepest water. For each segment, ping duration is 1/5 of these values 
or 2/5 for a receiver in the overlap area ensonified by two beam 
segments. The ``ping'' interval during RDT operations depends on water 
depth and varies from once per second in less than 500 m (1640.5 ft) 
water depth to once per 15 seconds in the deepest water. During the 
proposed project, the Atlas Hydrosweep will generally be used in waters 
greater than 800 m (2624.7 ft), but whenever water depths are less than 
400 m (1312 ft) the source output is 210 dB re 1 microPa-m (rms) and a 
single 1-ms pulse or ``ping'' per second is transmitted.
    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 Hydrosweep. The 
energy from the sub-bottom profiler is directed downward by a 3.5-kHz 
transducer mounted in the hull of the Ewing. 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 nominal 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 profilers used by the Ewing, Burgess and Lawson (2000) 
measured sounds propagating more or less horizontally from a sub-bottom 
profiler similar to the L-DEO 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

[[Page 58399]]

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 L-DEO 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 (300 beamwidth) 
and the measurements of Burgess and Lawson (2000).

Characteristics of Airgun Pulses

    Airguns function by venting high-pressure air into the water. The 
pressure signature of an individual airgun consists of a sharp rise and 
then fall in pressure, followed by several positive and negative 
pressure excursions caused by oscillation of the resulting air bubble. 
The resulting downward-directed pulse has a duration of only 10 to 20 
ms, with only one strong positive and one strong negative peak pressure 
(Caldwell and Dragoset, 2000). Most energy emitted from airguns is at 
relatively low frequencies. For example, typical high-energy airgun 
arrays emit most energy at 10-120 Hz. However, the pulses contain some 
energy up to 500-1000 Hz and above (Goold and Fish, 1998).
    The pulsed sounds associated with seismic exploration have higher 
peak levels than other industrial sounds to which whales and other 
marine mammals are routinely exposed. As mentioned previously, the pk-
pk source levels of the 2 GI-gun array that will be used for the ETPO 
project are 231 dB re 1 microPa (peak) and 237 dB re 1 microPa (pk-pk). 
However, the effective source level for horizontal propagation will be 
lower and actual levels experienced by any marine mammal more than 1 m 
(3.3 ft) from either GI-gun will be significantly lower.
    Several important factors need to be considered when assessing 
airgun impacts on the marine environment. (1) Airgun arrays produce 
intermittent sounds, involving emission of a strong sound pulse for a 
small fraction of a second followed by several seconds of near silence. 
In contrast, some other acoustic sources produce sounds with lower peak 
levels, but their sounds are continuous or discontinuous but continuing 
for much longer durations than seismic pulses. (2) Airgun arrays are 
designed to transmit strong sounds downward through the seafloor, and 
the amount of sound transmitted in near-horizontal directions is 
considerably reduced. Nonetheless, they also emit sounds that travel 
horizontally toward non-target areas. (3) An airgun array is a 
distributed source, not a point source. The nominal source level is an 
estimate of the sound that would be measured from a theoretical point 
source emitting the same total energy as the airgun array. That figure 
is useful in calculating the expected received levels in the far field 
(i.e., at moderate and long distances). Because the airgun array is not 
a single point source, there is no one location within the near field 
(or anywhere else) where the received level is as high as the nominal 
source level.
    The strengths of airgun pulses can be measured in different ways, 
and it is important to know which method is being used when 
interpreting quoted source or received levels. Geophysicists usually 
quote pk-pk levels, in bar-meters or dB re 1 microPa-m. The peak level 
for the same pulse is typically about 6 dB less. In the biological 
literature, levels of received airgun pulses are often described based 
on the ``average'' or ``root-mean-square'' (rms) level over the 
duration of the pulse. The rms value for a given pulse is typically 
about 10 dB lower than the peak level, and 16 dB lower than the Pk-pk 
value (Greene, 1997; McCauley et al., 1998; 2000). A fourth measure 
that is being used more frequently is the energy level, in dB re 1 
microPa\2\.s. Because the pulses are less than 1 sec in duration, the 
numerical value of the energy is lower than the rms pressure level, but 
the units are different. Because the level of a given pulse will differ 
substantially depending on which of these measures is being applied, it 
is important to be aware which measure is in use when interpreting any 
quoted pulse level. NMFS commonly references the rms levels when 
discussing levels of pulsed sounds that might harass marine mammals.
    Seismic sound received at any given point will arrive via a direct 
path, indirect paths that include reflection from the sea surface and 
bottom, and often indirect paths including segments through the bottom 
sediments. Sounds propagating via indirect paths travel longer 
distances and often arrive later than sounds arriving via a direct 
path. These variations in travel time have the effect of lengthening 
the duration of the received pulse. At the source, seismic pulses are 
about 10 to 20 ms in duration. In comparison, the pulse as received at 
long horizontal distances can have a much longer duration.
    Another important aspect of sound propagation is that received 
levels of low-frequency underwater sounds diminish close to the surface 
because of pressure-release and interference phenomena that occur at 
and near the surface (Urick, 1983, Richardson et al., 1995). Paired 
measurements of received airgun sounds at depths of 3 m (9.8 ft) vs. 9 
or 18 m (29.5 or 59 ft) have shown that received levels are typically 
several decibels lower at 3 m (9.8. ft)(Greene and Richardson, 1988). 
For a mammal whose auditory organs are within 0.5 or 1 m (1.6 or 3.3 
ft) of the surface, the received level of the predominant low-frequency 
components of the airgun pulses would be further reduced.
    Pulses of underwater sound from open-water seismic exploration are 
often detected 50 to 100 km (30 to 54 nm) from the source location 
(Greene and Richardson, 1988; Burgess and Greene, 1999). At those 
distances, the received levels on an approximate rms basis are low 
(below 120 dB re 1 microPa). However, faint seismic pulses are 
sometimes detectable at even greater ranges (e.g., Bowles et al., 1994; 
Fox et al., 2002). Considerably higher levels can occur at distances 
out to several kilometers from an operating airgun array. Additional 
information is contained in the L-DEO application, especially in 
Appendix A (see ADDRESSES).

Description of Habitat and Marine Mammals Affected by the Activity

    A detailed description of the ETPO area and its associated marine 
mammals can be found in the L-DEO application and a number of documents 
referenced in the L-DEO application, and is not repeated here. Thirty-
four species of cetaceans are known to occur in the ETPO, belonging to 
two taxonomic groups: odontocetes (sperm whale (Physeter 
macrocephalus), dwarf sperm whale (Kogia sima), pygmy sperm whale (K. 
breviceps), Cuvier's beaked whale (Ziphius cavirostris), Longman's 
beaked whale (Indopacetus pacificus), pygmy beaked whale (Mesoplodon 
peruvianus), gingko-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), short-beaked common 
dolphin (Delphinus delphis), Fraser's dolphin (Lagenodelphis hosei), 
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)); and mysticetes humpback 
whale (Megaptera

[[Page 58400]]

novaeangliae), minke whale (Balaenoptera acutorostrata), sei whale (B. 
borealis), fin whale (B. physalus), Bryde's whale (B. edeni), and blue 
whale (B. musculus). Of these 34 species, L-DEO states that 27 cetacean 
species are likely to occur in the proposed survey area. These 27 
species are shown in Table 2 of this document and are described in L-
DEO (2004)).
    Seven cetacean species (Pacific white-sided dolphin (Lagenorhynchus 
obliquidens), Baird's beaked whale (Berardius bairdii), long-beaked 
common dolphin (Delphinus capensis), dusky dolphin (Lagenorhynchus 
obscurus), southern right whale dolphin (Lissodelphis peronii), 
Burmeister's porpoise (Phocoena spinipinnis), and long-finned pilot 
whale (Globicephala melas)) although present in the wider ETPO, are 
unlikely to be found in L-DEO's proposed survey area (L-DEO, 2004). 
These species are mentioned briefly in L-DEO's application, but are 
unlikely to be taken by incidental harassment and therefore are not 
analyzed further in this document.
    Six species of pinnipeds are known to occur in the ETPO: Guadalupe 
fur seal (Arctocephalus townsendi), California sea lion (Zalophus 
californianus), Galapagos sea lion (Z. wollebaeki), Galapagos fur seal 
(A. galapagoensis), southern sea lion (Otaria flavescens), and South 
American fur seal (A. australis). The last four species could 
potentially occur within the proposed seismic survey area, but they are 
expected to be, at most, uncommon. Ranges of the first two species are 
substantially north of the proposed seismic survey area and, therefore, 
unlikely to be taken by incidental harassment.
    More detailed information on these species is contained in the L-
DEO application, which is available at: http://www.nmfs.noaa.gov/prot_res/PR2/Small_Take/smalltake--info.htm#applications.

Potential Effects on Marine Mammals

    As outlined in several previous NMFS documents, 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 be any temporary threshold 
shift (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 L-DEO application provides the following information on what is 
known about the effects on marine mammals of the types of seismic 
operations planned by L-DEO. 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, 
its effects are anticipated to be considerably less than would be the 
case with a large array of airguns. L-DEO 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 
823 m (2700 ft) in deep water and 2469 m (8100 ft) in shallow water, 
the zones calculated for 160 dB or the onset of Level B harassment. 
Additional discussion on species specific effects can be found in the 
L-DEO application.

Tolerance

    Numerous studies (referenced in L-DEO, 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 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 source planned for use in the ETPO, there is even 
less potential for masking of baleen or sperm whale calls during the 
present research than in most seismic surveys (L-DEO, 2004). Seismic 
sounds are short pulses generally occurring for less than 1 sec every 5 
seconds or so. The 5-sec spacing corresponds to a shot interval of

[[Page 58401]]

approximately 12.5 m (41 ft). Sounds from the multibeam sonar are very 
short pulses, occurring for 1-10 msec once every 1 to 15 sec, depending 
on water depth. (During operations in deep water, the duration of each 
pulse from the multibeam sonar as received at any one location would 
actually be only \1/5\ or at most \2/5\ of 1-10 msec, given the 
segmented nature of the pulses.)
    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 ETPO. 
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 
would constitute Level B harassment under the MMPA. Given the many 
uncertainties in predicting the quantity and types of impacts of noise 
on marine mammals, scientists often resort to estimating how many 
mammals may be present within a particular distance of industrial 
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 on pages 35-37 and Appendix A in L-DEO's ETPO 
application.

Hearing Impairment and Other Physical Effects

    Temporary or permanent hearing impairment is a possibility when 
marine mammals are exposed to very strong sounds, but there has been no 
specific documentation of this for marine mammals exposed to airgun 
pulses. Current NMFS policy 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 defining 
the safety (shut-down) radii for seismic surveys. However, those 
criteria were established before there were any data on the minimum 
received levels of sounds necessary to cause auditory impairment in 
marine mammals. As discussed in the L-DEO 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 often considered 
to be a level below which there is no danger of permanent damage.
    Because of the small size of the 3 105 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 3 GI-airguns (and multibeam 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

[[Page 58402]]

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, L-DEO 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 
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. Such sound 
levels would be limited to distances within a few meters of the small 
airguns planned for use during this project.
    There are no data, direct or indirect, on levels or properties of 
sound that are required to induce TTS in any baleen whale. However, TTS 
is not expected to occur during this survey given the small size of the 
source, 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).
    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 3 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, at least in 
waters greater than 100 m (328 ft) deep. 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 L-DEO and other seismic operators, 
should allow cetaceans to move away from the seismic source and to 
avoid being exposed to the full acoustic output of the 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 movement of the vessel and the marine 
mammal. However, 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 bow of the Ewing will be 107 m (351 ft) ahead of the 
airguns and the 205-dB zone would be less than 100 m (328 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.
    Currently, 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 L-DEO during this activity 
are summarized in Table 1 in this document. These sound levels are not 
considered to be the levels at or above which TTS might occur. Rather, 
they are the received levels above which, in the view of a panel of 
bioacoustics specialists convened by NMFS (at a time before TTS 
measurements for marine mammals started to become available), one could 
not be certain that there would be no injurious effects, auditory or 
otherwise, to marine mammals. As noted here, TTS data that are now 
available imply that, at least for dolphins, TTS is unlikely to occur 
unless the dolphins are exposed to airgun pulses substantially stronger 
than 180 dB re 1 microPa (rms).
    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 L-DEO, 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

[[Page 58403]]

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 3 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 
injury, death, or stranding, the association of mass strandings of 
beaked whales with naval exercises and, recently, an L-DEO seismic 
survey have raised the possibility that beaked whales may be especially 
susceptible to injury and/or stranding when exposed to strong pulsed 
sounds.
    In March 2000, several beaked whales that had been exposed to 
repeated pulses from high intensity, mid-frequency military sonars 
stranded and died in the Providence Channels of the Bahamas Islands, 
and were subsequently found to have incurred cranial and ear damage 
(NOAA and USN, 2001). Based on post-mortem analyses, it was concluded 
that an acoustic event caused hemorrhages in and near the auditory 
region of some beaked whales. These hemorrhages occurred before death. 
They would not necessarily have caused death or permanent hearing 
damage, but could have compromised hearing and navigational ability 
(NOAA and USN, 2001). The researchers concluded that acoustic exposure 
caused this damage and triggered stranding, which resulted in 
overheating, cardiovascular collapse, and physiological shock that 
ultimately led to the death of the stranded beaked whales. During the 
event, five naval vessels used their AN/SQS-53C or -56 hull-mounted 
active sonars for a period of 16 hours. The sonars produced narrow 
(<100 Hz) bandwidth signals at center frequencies of 2.6 and 3.3 kHz (-
53C), and 6.8 to 8.2 kHz (-56). The respective source levels were 
usually 235 and 223 dB re 1 micro Pa, but the -53C briefly operated at 
an unstated but substantially higher source level. The unusual 
bathymetry and constricted channel where the strandings occurred were 
conducive to channeling sound. This, and the extended operations by 
multiple sonars, apparently prevented escape of the animals to the open 
sea. In addition to the strandings, there are reports that beaked 
whales were no longer present in the Providence Channel region after 
the event, suggesting that other beaked whales either abandoned the 
area or perhaps died at sea (Balcomb and Claridge, 2001).
    Other strandings of beaked whales associated with operation of 
military sonars have also been reported (e.g., Simmonds and Lopez-
Jurado, 1991; Frantzis, 1998). In these cases, it was not determined 
whether there were noise-induced injuries to the ears or other organs. 
Another stranding of beaked whales (15 whales) happened on 24-25 
September 2002 in the Canary Islands, where naval maneuvers were taking 
place. Jepson et al. (2003) concluded that cetaceans might be subject 
to decompression injury (the bends or air embolism) in some

[[Page 58404]]

situations. If so, this might occur if the mammals ascend unusually 
quickly when exposed to aversive sounds. Previously, it was widely 
assumed that diving marine mammals are not subject to decompression 
injury.
    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 hearing 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 these 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 in conducting seismic surveys in 
areas occupied by beaked whales.

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. 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.
    Long-term exposure to anthropogenic noise may have the potential to 
cause physiological stress that could affect the health of individual 
animals or their reproductive potential, which could theoretically 
cause effects at the population level (Gisner (ed.), 1999). However, 
there is essentially no information about the occurrence of noise-
induced stress in marine mammals. Also, it is doubtful that any single 
marine mammal would be exposed to strong seismic sounds for 
sufficiently long that significant physiological stress would develop. 
This is particularly so in the case of the proposed L-DEO project where 
the airguns are small.
    Gas-filled structures in marine animals have an inherent 
fundamental resonance frequency. If stimulated at this 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). In 2002, NMFS held a workshop 
(Gentry (ed.) 2002) to discuss whether the stranding of beaked whales 
in the Bahamas in 2000 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. Workshop participants did not rule out the possibility 
that bubble formation/growth played a role in the stranding and 
participants acknowledged that more research is needed in this area. 
The only available information on acoustically-mediated bubble growth 
in marine mammals is modeling that assumes prolonged exposure to sound.
    Until recently, it was assumed that diving marine mammals are not 
subject to the bends or air embolism. However, a 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 the proposed L-
DEO survey which involves only three GI-guns.
    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 distances from 
the sound source. However, the available data do not allow for 
meaningful quantitative predictions of the numbers (if any) of marine 
mammals that might be affected in these ways. Marine mammals that show 
behavioral avoidance of seismic vessels, including most baleen whales, 
some odontocetes, and some pinnipeds, are unlikely to incur auditory 
impairment or other physical effects. Also, the planned mitigation and 
monitoring measures are expected to minimize any possibility of serious 
injury, mortality or strandings.

Possible Effects of Mid-frequency Sonar Signals

    A multi-beam bathymetric sonar (Atlas Hydrosweep DS-2 (15.5-kHz) 
and a sub-bottom profiler will be operated from the source vessel 
essentially continuously during the planned survey. Details about these 
sonars were provided previously in this document.
    Navy sonars that have been linked to avoidance reactions and 
stranding of cetaceans generally (1) are more powerful than the Atlas 
Hydrosweep sonars, (2) have a longer pulse duration, and (3) are 
directed close to horizontally (vs. downward for the Atlas Hydrosweep). 
The area of possible influence for the Ewing's sonars is much

[[Page 58405]]

smaller - a narrow band below the source vessel. For the Hydrosweep 
there is no horizontal propagation as these signals project at an angle 
of approximately 45 degrees from the ship. For the deep-water mode, 
under the ship the 160- and 180-dB zones are estimated to be 3200 m 
(10500 ft) and 610 m (2000 ft), respectively. However, the beam width 
of the Hydrosweep signal is only 2.67 degrees fore and aft of the 
vessel, meaning that a marine mammal diving could receive at most 1-2 
signals from the Hydrosweep and a marine mammal on the surface would be 
unaffected. Marine mammals that do encounter the bathymetric sonars at 
close range are unlikely to be subjected to repeated pulses because of 
the narrow fore-aft width of the beam, and will receive only limited 
amounts of pulse energy because of the short pulses and vessel speed. 
Therefore, as harassment or injury from pulsed sound is a function of 
total energy received, the actual harassment or injury threshold for 
the bathymetric sonar signals (approximately 10 ms) would be at a much 
higher dB level than that for longer duration pulses such as seismic 
signals. As a result, NMFS believes that marine mammals are unlikely to 
be harassed or injured from the multibeam sonar.

Masking by Mid-frequency Sonar Signals

    Marine mammal communications will not be masked appreciably by the 
multibeam sonar signals or the sub-bottom profiler given the low duty 
cycle and directionality of the sonars and the brief period when an 
individual mammal is likely to be within its beam. Furthermore, in the 
case of baleen whales, the sonar signals from the Hydrosweep sonar do 
not overlap with the predominant frequencies of the calls, which would 
avoid significant masking.
    For the sub-bottom profiler, marine mammal communications will not 
be masked appreciably because of their relatively low power output, low 
duty cycle, directionality (for the profiler), and the brief period 
when an individual mammal may be within the sonar's beam. In the case 
of most odonotocetes, the sonar signals from the profiler do not 
overlap with the predominant frequencies in their calls. In the case of 
mysticetes, the pulses from the pinger do not overlap with their 
predominant frequencies.

Behavioral Responses Resulting from Mid-Frequency Sonar Signals

    Behavioral reactions of free-ranging marine mammals to military and 
other sonars appear to vary by species and circumstance. Observed 
reactions have included silencing and dispersal by sperm whales 
(Watkins et al., 1985), increased vocalizations and no dispersal by 
pilot whales (Rendell and Gordon, 1999), and the previously-mentioned 
strandings by beaked whales. Also, Navy personnel have described 
observations of dolphins bow-riding adjacent to bow-mounted mid-
frequency sonars during sonar transmissions. However, all of these 
observations are of limited relevance to the present situation. Pulse 
durations from these sonars were much longer than those of the L-DEO 
multibeam sonar, and a given mammal would have received many pulses 
from the naval sonars. During L-DEO's operations, the individual pulses 
will be very short, and a given mammal would not receive many of the 
downward-directed pulses as the vessel passes by.
    Captive bottlenose dolphins and a white whale exhibited changes in 
behavior when exposed to 1-sec pulsed sounds at frequencies similar to 
those that will be emitted by the multi-beam sonar used by L-DEO and to 
shorter broadband pulsed signals. Behavioral changes typically involved 
what appeared to be deliberate attempts to avoid the sound exposure 
(Schlundt et al., 2000; Finneran et al., 2002). The relevance of these 
data to free-ranging odontocetes is uncertain and in any case the test 
sounds were quite different in either duration or bandwidth as compared 
to those from a bathymetric sonar.
    L-DEO and NMFS are not aware of any data on the reactions of 
pinnipeds to sonar sounds at frequencies similar to those of the 15.5 
kHz frequency of the Ewing's multibeam sonar. Based on observed 
pinniped responses to other types of pulsed sounds, and the likely 
brevity of exposure to the bathymetric sonar sounds, pinniped reactions 
are expected to be limited to startle or otherwise brief responses of 
no lasting consequences to the individual animals. The pulsed signals 
from the sub-bottom profiler are much weaker than those from the airgun 
array and the multibeam sonar. Therefore, significant behavioral 
responses are not expected.

Hearing Impairment and Other Physical Effects

    Given recent stranding events that have been associated with the 
operation of naval sonar, there is much concern that sonar noise can 
cause serious impacts to marine mammals (for discussion see Effects of 
Seismic Surveys on Marine Mammals). However, the multi-beam sonars 
proposed for use by L-DEO are quite different than sonars used for navy 
operations. Pulse duration of the bathymetric sonars is very short 
relative to the naval sonars. Also, at any given location, an 
individual marine mammal would be in the beam of the multi-beam sonar 
for much less time given the generally downward orientation of the beam 
and its narrow fore-aft beam-width. (Navy sonars often use near-
horizontally-directed sound.) These factors would all reduce the sound 
energy received from the multi-beam sonar rather drastically relative 
to that from the sonars used by the Navy. Therefore, hearing impairment 
by multi-beam bathymetric sonar is unlikely.
    Source levels of the sub-bottom profiler are much lower than those 
of the airguns and the multi-beam sonar. Sound levels from a sub-bottom 
profiler similar to the one on the Ewing were estimated to decrease to 
180 dB re 1 microPa (rms) at 8 m (26 ft) horizontally from the source 
(Burgess and Lawson, 2000), and at approximately 18 m downward from the 
source. Furthermore, received levels of pulsed sounds that are 
necessary to cause temporary or especially permanent hearing impairment 
in marine mammals appear to be higher than 180 dB (see earlier 
discussion). Thus, it is unlikely that the sub-bottom profiler produces 
pulse levels strong enough to cause hearing impairment or other 
physical injuries even in an animal that is (briefly) in a position 
near the source.
    The sub-bottom profiler is usually operated simultaneously with 
other higher-power acoustic sources. Many marine mammals will move away 
in response to the approaching higher-power sources or the vessel 
itself before the mammals would be close enough for there to be any 
possibility of effects from the less intense sounds from the sub-bottom 
profiler. In the case of mammals that do not avoid the approaching 
vessel and its various sound sources, mitigation measures that would be 
applied to minimize effects of the higher-power sources would further 
reduce or eliminate any minor effects of the sub-bottom profiler.

Estimates of Take by Harassment for the ETPO Seismic Survey

    Although information contained in this document indicates that 
injury to marine mammals from seismic sounds potentially occurs at 
sound pressure levels significantly higher than 180 and 190 dB, NMFS' 
current criteria for onset of Level A harassment of cetaceans and 
pinnipeds from impulse sound are, respectively, 180 and 190 re 1 
microPa rms. The rms level of a seismic pulse is

[[Page 58406]]

typically about 10 dB less than its peak level and about 16 dB less 
than its pk-pk level (Greene, 1997; McCauley et al., 1998; 2000a). The 
criterion for Level B harassment onset is 160 dB.
    Given the proposed mitigation (see Mitigation later in this 
document), all anticipated takes involve a temporary change in behavior 
that may constitute Level B harassment. The proposed mitigation 
measures will minimize or eliminate the possibility of Level A 
harassment or mortality. L-DEO has calculated the ``best estimates'' 
for the numbers of animals that could be taken by level B harassment 
during the proposed ETPO seismic survey using data on marine mammal 
density and abundance from marine mammal surveys in the region, and 
estimates of the size of the affected area, as shown in the predicted 
RMS radii table (see Table 1).
    These estimates are based on a consideration of the number of 
marine mammals that might be exposed to sound levels greater than 160 
dB, the criterion for the onset of Level B harassment, by operations 
with the 3 GI-gun array planned to be used for this project. The 
anticipated zone of influence of the multi-beam sonar is less than that 
for the airguns, so it is assumed that any marine mammals close enough 
to be affected by the multi-beam sonar would already be affected by the 
airguns. Therefore, no additional incidental takings are included for 
animals that might be affected by the multi-beam sonar.
    Table 2 explains the corrected density estimates as well as the 
best estimate of the numbers of each species that would be exposed to 
seismic sounds greater than 160 dB. A detailed description on the 
methodology used by L-DEO to arrive at the estimates of Level B 
harassment takes that are provided in Table 2 can be found in L-DEO's 
IHA application for the ETPO survey.
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Conclusions

Effects on Cetaceans

    Strong avoidance reactions by several species of mysticetes to 
seismic vessels have been observed at ranges up to 6-8 km (3.2-4.3 nm) 
and occasionally as far as 20-30 km (10.8-16.2 nm) from the source 
vessel. However, reactions at the longer distances appear to be 
atypical of most species and situations, particularly when feeding 
whales are involved. Few mysticetes are expected to be encountered 
during the proposed survey in the ETPO (Table 2) and disturbance 
effects would be confined to shorter distances given the low-energy 
acoustic source to be used during this project. In addition, the 
estimated numbers presented in Table 2 are considered overestimates of 
actual numbers that may be harassed.
    Odontocete reactions to seismic pulses, or at least the reactions 
of dolphins, are expected to extend to lesser distances than are those 
of mysticetes. Odontocete low-frequency hearing is less sensitive than 
that of mysticetes, and dolphins are often seen from seismic vessels. 
In fact, there are documented instances of dolphins approaching active 
seismic vessels. However, dolphins as well as some other types of 
odontocetes sometimes show avoidance responses and/or other changes in 
behavior when near operating seismic vessels.
    Taking into account the small size and the relatively low sound 
output of the 3 GI-guns to be used, and the mitigation measures that 
are planned, effects on cetaceans are generally expected to be limited 
to avoidance of a small area around the seismic operation and short-
term changes in behavior, falling within the MMPA definition of Level B 
harassment. Furthermore, the estimated numbers of animals potentially 
exposed to sound levels sufficient to cause appreciable disturbance are 
very low percentages of the affected populations.
    Based on the 160-dB criterion, the best estimates of the numbers of 
individual cetaceans that may be exposed to sounds [gteqt] 160 dB re 1 
microPa (rms) represent 0 to approximately 0.4 percent (except for 
approximately 2.4 percent for dwarf sperm whales) of the regional ETPO 
species populations (Table 2). L-DEO also estimates that approximately 
0.1 percent of the estimated (corrected) regional ETPO population of 
approximately 26,053 sperm whales (Table 2) would be exposed to sounds 
[gteqt] 160 dB re 1 microPa (rms). In the case of endangered 
balaenopterids, it is most likely that no humpback, sei, or fin whales 
will be exposed to seismic sounds [gteqt] 160 dB re 1 microPa (rms), 
based on the reported (corrected) densities of those species in the 
survey region. However, L-DEO has requested an authorization to expose 
up to 2 individuals of each of those species to seismic sounds of 
[gteqt] 160 dB during the proposed survey given the possibility of 
encountering one or more groups. Best estimates of blue whales are 3 
individuals that might be potentially exposed to seismic pulses with 
received levels [gteqt] 160 dB re 1 microPa (rms), representing 
approximately 0.2 percent of the estimated regional ETP population of 
approximately 1400 blue whales (Table 2).
    Larger numbers of delphinids may be affected by the proposed 
seismic surveys, but the population sizes of species likely to occur in 
the survey area are large, and the numbers potentially affected are 
small relative to population sizes (Table 2). The best estimates of the 
numbers of individual delphinids that will potentially be exposed to 
sounds [gteqt] 160 dB re 1 microPa (rms) represent less than 0.1 
percent of the approximately 10,000,000 dolphins estimated to occur in 
the ETPO, and less than 0.3 percent of the bottlenose dolphin 
population occurring there (Table 2).
    Mitigation measures such as controlled speed, course alteration, 
observers, use of the PAM system, non-pursuit, ramp ups, and power 
downs or shut downs when marine mammals are seen within defined ranges 
should further reduce short-term reactions, and minimize any effects on 
hearing. In all cases, the effects are expected to be short-term, with 
no lasting biological consequence. In light of the type of take 
expected and the small percentages of affected stocks of cetaceans, the 
action is expected to have no more than a negligible impact on the 
affected species or stocks of cetaceans.

Effects on Pinnipeds

    It is unlikely that any pinnipeds will be encountered during the 
proposed survey. However, to ensure that the L-DEO project remains in 
compliance with the MMPA in the event that a few pinnipeds are 
encountered, L-DEO has requested an authorization to expose up to 10 
individuals of each of four pinniped species to seismic sounds with rms 
levels [gteqt] 160 dB re 1 microPa. If pinnipeds are encountered, they 
will be stray individuals outside of their normal range. The proposed 
survey would have, at most, a short-term effect on their behavior and 
no long-term impacts on individual pinnipeds or their populations. 
Responses of pinnipeds to acoustic disturbance are variable, but 
usually quite limited. Effects are expected to be limited to short-term 
and localized behavioral changes falling within the MMPA definition of 
Level B harassment. As is the case for cetaceans, the short-term 
exposures to sounds from the three GI-guns are not expected to result 
in any long-term consequences for the individuals or their populations 
and the activity is expected to have no more than a negligible impact 
on the affected species or stocks of pinnipeds.

Potential Effects on Habitat

    The proposed seismic survey will not result in any permanent impact 
on habitats used by marine mammals, or to the food sources they 
utilize. The main impact issue associated with the proposed activity 
will be temporarily elevated noise levels and the associated direct 
effects on marine mammals.
    One of the reasons for the adoption of airguns as the standard 
energy source for marine seismic surveys was that they (unlike the 
explosives used in the distant past) do not result in any appreciable 
fish kill. Various experimental studies showed that airgun discharges 
cause little or no fish kill, and that any injurious effects were 
generally limited to the water within a meter or so of an airgun. 
However, it has recently been found that injurious effects on captive 
fish, especially on fish hearing, may occur at somewhat greater 
distances than previously thought (McCauley et al., 2000a,b, 2002; 
2003). Even so, any injurious effects on fish would be limited to short 
distances from the source. Also, many of the fish that might otherwise 
be within the injury-zone are likely to be displaced from this region 
prior to the approach of the airguns through avoidance reactions to the 
passing seismic vessel or to the airgun sounds as received at distances 
beyond the injury radius.
    Fish often react to sounds, especially strong and/or intermittent 
sounds of low frequency. Sound pulses at received levels of 160 dB re 1 
microPa (peak) may cause subtle changes in behavior. Pulses at levels 
of 180 dB (peak) may cause noticeable changes in behavior (Chapman and 
Hawkins, 1969; Pearson et al., 1992; Skalski et al., 1992). It also 
appears that fish often habituate to repeated strong sounds rather 
rapidly, on time scales of minutes to an hour. However, the habituation 
does not endure, and resumption of the disturbing activity may again 
elicit disturbance responses from the same fish.
    Fish near the airguns are likely to dive or exhibit some other kind 
of behavioral response. This might have short-term

[[Page 58409]]

impacts on the ability of cetaceans to feed near the survey area. 
However, only a small fraction of the available habitat would be 
ensonified at any given time, and fish species would return to their 
pre-disturbance behavior once the seismic activity ceased. Thus, the 
proposed surveys would have little impact on the abilities of marine 
mammals to feed in the area where seismic work is planned. Some of the 
fish that do not avoid the approaching airguns (probably a small 
number) may be subject to auditory or other injuries.
    Zooplankton that are very close to the source may react to the 
airgun's shock wave. These animals have an exoskeleton and no air sacs; 
therefore, little or no mortality is expected. Many crustaceans can 
make sounds and some crustacea and other invertebrates have some type 
of sound receptor. However, the reactions of zooplankton to sound are 
not known. Some mysticetes feed on concentrations of zooplankton. A 
reaction by zooplankton to a seismic impulse would only be relevant to 
whales if it caused a concentration of zooplankton to scatter. Pressure 
changes of sufficient magnitude to cause this type of reaction would 
probably occur only very close to the source, so few zooplankton 
concentrations would be affected. Impacts on zooplankton behavior are 
predicted to be negligible, and this would translate into negligible 
impacts on feeding mysticetes.

Potential Effects on Subsistence Use of Marine Mammals

    There is no legal subsistence hunting for marine mammals in the 
ETPO off Central America, so the proposed L-DEO activities will not 
have any impact on the availability of these species or stocks for 
subsistence users.

Mitigation

    For the proposed seismic survey in the ETPO off Central America, L-
DEO will deploy 3 GI-airguns as an energy source, with a total 
discharge volume of 315 in\3\. The energy from the airguns will be 
directed mostly downward. The directional nature of the airguns to be 
used in this project is an important mitigating factor. This 
directionality will result in reduced sound levels at any given 
horizontal distance as compared with the levels expected at that 
distance if the source were omnidirectional with the stated nominal 
source level. Also, the small size of these airguns is an inherent and 
important mitigation measure that will reduce the potential for effects 
relative to those that might occur with large airgun arrays. This 
measure is in conformance with NMFS encouraging seismic operators to 
use the lowest intensity airguns practical to accomplish research 
objectives.
    The following mitigation measures, as well as marine mammal visual 
monitoring (discussed later in this document), will be implemented for 
the subject seismic surveys: (1) Speed and course alteration (provided 
that they do not compromise operational safety requirements); (2) 
power-down and shut-down procedures; (3) ramp-up procedures, and (4) 
use of passive acoustics to detect vocalizing marine mammals.

Speed and Course Alteration

    If a marine mammal is detected outside its respective safety zone 
(180 dB for cetaceans, 190 dB for pinnipeds) and, based on its position 
and the relative motion, is likely to enter the safety zone, the 
vessel's speed and/or direct course may, when practical and safe, be 
changed in a manner that also minimizes the effect to the planned 
science objectives. The marine mammal activities and movements relative 
to the seismic vessel will be closely monitored to ensure that the 
marine mammal does not approach within the safety zone. If the mammal 
appears likely to enter the safety zone, further mitigative actions 
will be taken (i.e., either further course alterations or shut down of 
the airguns).

Power-down and Shut-down Procedures

    A power down involves decreasing the number of airguns in use such 
that the radius of the 180-dB (or 190-dB) zone is decreased to the 
extent that marine mammals are not in the safety zone. During a power 
down, one GI-airgun will continue to be operated. The continued 
operation of one airgun is intended to alert marine mammals to the 
presence of the seismic vessel in the area. In contrast, a shut down 
occurs when all airgun activity is suspended.
    If a marine mammal is detected outside the safety radius but is 
likely to enter the safety radius, and if the vessel's speed and/or 
course cannot be changed to avoid having the mammal enter the safety 
radius, the GI-guns will be powered down before the mammal is within 
the safety radius. Likewise, if a mammal is already within the safety 
zone when first detected, the airguns will be powered down immediately. 
During a power down, one GI-airgun (i.e., 105 in\3\) will be operated. 
If a marine mammal is detected within or near the smaller safety radius 
around that single GI-gun (Table 1), all guns will be shut down.
    Following a power down, airgun activity will not resume until the 
marine mammal has cleared the safety zone. The animal will be 
considered to have cleared the safety zone if it (1) is visually 
observed to have left the safety zone, or (2) has not been seen within 
the zone for 15 min in the case of small odontocetes and pinnipeds, or 
(3) has not been seen within the zone for 30 min in the case of 
mysticetes and large odontocetes, including sperm, pygmy sperm, dwarf 
sperm, and beaked whales.
    During airgun operations following a power-down whose duration has 
exceeded these specified limits, the airgun array will be ramped-up 
gradually. Ramp-up is described later in this document.
    During a power down, the operating GI-airgun will be shut down if a 
marine mammal approaches and is about to enter the modeled safety 
radius for the operating single GI gun. For a 105 in\3\ GI gun, the 
predicted 180-dB distances applicable to cetaceans are 27-189 m (89-620 
ft), depending on water depth, and the corresponding 190-dB radii 
applicable to pinnipeds are 10-150 m (33-492 ft), depending on depth 
(Table 1). Airgun activity will not resume until the marine mammal has 
cleared the safety radius, as described for power-down situations.

Ramp-up Procedure

    When airgun operations commence after a specified period without 
airgun operations, the number of guns firing will be increased 
gradually, or ``ramped up'' (also described as a ``soft start''). The 
specified period of time for the GI-airguns varies depending on the 
speed of the source vessel. Under normal operational conditions (vessel 
speed 4.9 knots or 9 km/h), the Ewing would travel 574 m (1476 ft) in 
about 4 minutes. The 574-m distance is the calculated 180-dB safety 
radius for the three GI-gun array operating in shallow water. Thus, a 
ramp up would be required after a power down or shut down period 
lasting about 4 minutes or longer if the Ewing was traveling at 4.9 
knots and was towing the three GI-airgun array. Ramp up will begin with 
one of the 105-in\3\ GI guns. The other two GI-guns will be added at 5 
min intervals. During ramp up, the safety radius for the full gun array 
will be maintained.
    During the day, ramp-up cannot begin from a shut-down unless the 
entire 180-dB safety radius has been visible for at least 30 minutes 
prior to the ramp up (i.e., no ramp-up can begin in heavy fog or high 
sea states). However, ramp up may occur from a power down in heavy fog 
or high sea states, as long as at least one GI gun has been maintained 
during the interruption of seismic activity.

[[Page 58410]]

    During nighttime operations, if the entire safety radius is visible 
using vessel lights and night-vision devices (NVDs) (as may be the case 
in deep and intermediate waters), then start up of the airguns from a 
shut down may occur. However, lights and NVDs will probably not be very 
effective as a basis for monitoring the larger safety radii around the 
three GI-guns operating in shallow water. It is proposed that, in 
shallow water, nighttime start ups of the airguns will not be 
authorized. However, ramp-up may occur from a power-down at night, as 
long as at least one GI-gun has been maintained during the interruption 
of the seismic signal. Also, if the airgun array has been operational 
before nightfall, it can remain operational throughout the night, even 
though the entire safety radius may not be visible.
    Comments on past IHAs raised the issue of prohibiting nighttime 
operations as a practical mitigation measure. However, this is not 
practicable due to cost considerations and ship time schedules. The 
daily cost to the federal government to operate vessels such as Ewing 
is approximately $33,000-$35,000 /day (Ljunngren, pers. comm. May 28, 
2003). If the vessels were prohibited from operating during nighttime, 
each trip could require an additional three to five days to complete, 
or up to $175,000 more, depending on average daylight at the time of 
work.
    If a seismic survey vessel is limited to daylight seismic 
operations, efficiency would also be much reduced. Without commenting 
specifically on how that would affect the present project, for seismic 
operators in general, a daylight-only requirement would be expected to 
result in one or more of the following outcomes: cancellation of 
potentially valuable seismic surveys; reduction in the total number of 
seismic cruises annually due to longer cruise durations; a need for 
additional vessels to conduct the seismic operations; or work conducted 
by non-U.S. operators or non-U.S. vessels when in waters not subject to 
U.S. law.

Marine Mammal Monitoring

    L-DEO must have at least three visual observers on board the Ewing, 
and at least two must be an experienced marine mammal observer that 
NMFS has approved in advance of the start of the ETPO cruise. These 
observers will be on duty in shifts of no longer than 4 hours.
    The visual observers will monitor marine mammals and sea turtles 
near the seismic source vessel during all daytime airgun operations, 
during any nighttime start-ups of the airguns and at night, whenever 
daytime monitoring resulted in one or more shut-down situations due to 
marine mammal presence. During daylight, vessel-based observers will 
watch for marine mammals and sea turtles near the seismic vessel during 
periods with shooting (including ramp-ups), and for 30 minutes prior to 
the planned start of airgun operations after a shut-down.
    Use of multiple observers will increase the likelihood that marine 
mammals near the source vessel are detected. L-DEO bridge personnel 
will also assist in detecting marine mammals and implementing 
mitigation requirements whenever possible (they will be given 
instruction on how to do so), especially during ongoing operations at 
night when the designated observers are on stand-by and not required to 
be on watch at all times.
    The observer(s) will watch for marine mammals from the highest 
practical vantage point on the vessel, which is either the bridge or 
the flying bridge. On the bridge of the Ewing, the observer's eye level 
will be 11 m (36 ft) above sea level, allowing for good visibility 
within a 210 arc. If observers are stationed on the flying bridge, the 
eye level will be 14.4 m (47.2 ft) above sea level. The observer(s) 
will systematically scan the area around the vessel with Big Eyes 
binoculars, reticle binoculars (e.g., 7 X 50 Fujinon) and with the 
naked eye during the daytime. Laser range-finding binoculars (Leica 
L.F. 1200 laser rangefinder or equivalent) will be available to assist 
with distance estimation. The observers will be used to determine when 
a marine mammal or sea turtle is in or near the safety radii so that 
the required mitigation measures, such as course alteration and power-
down or shut-down, can be implemented. If the GI-airguns are powered-
down or shut down, observers will maintain watch to determine when the 
animal is outside the safety radius.
    Observers will not be on duty during ongoing seismic operations at 
night; bridge personnel will watch for marine mammals during this time 
and will call for the airguns to be powered-down or shut-down if marine 
mammals are observed in or about to enter the safety radii. However, a 
biological observer must be on standby at night and available to assist 
the bridge watch if marine mammals are detected. If the airguns are 
ramped-up at night (see previous section), two marine mammal observers 
will monitor for marine mammals for 30 minutes prior to ramp-up and 
during the ramp-up using either deck lighting or NVDs that will be 
available (ITT F500 Series Generation 3 binocular image intensifier or 
equivalent).

Post-Survey Monitoring

    In addition, the biological observers will be able to conduct 
monitoring of most recently-run transect lines as the Ewing returns 
along a parallel transect track. A final post-survey transect will be 
conducted by the Ewing as it retrieves the hydrophone array. This will 
provide the biological observers with opportunities to look for injured 
or dead marine mammals (although no injuries or mortalities are 
expected during this research cruise).

Passive Acoustic Monitoring (PAM)

    L-DEO has agreed to use the PAM system whenever the Ewing is 
operating in waters deep enough for the PAM hydrophone array to be 
towed. Passive acoustic equipment was first used on the Ewing during 
the 2003 Sperm Whale Seismic Study conducted in the Gulf of Mexico and 
subsequently was evaluated by L-DEO to determine whether it was 
practical to incorporate it into future seismic research cruises. The 
SEAMAP system has been used successfully in L-DEO's SE Caribbean study 
(69 FR 24571, May 4, 2004). The SEAMAP PAM system has four hydrophones, 
which allow the SEAMAP system to derive the bearing toward the a 
vocalizing marine mammal. In order to operate the SEAMAP system, the 
marine mammal monitoring contingent onboard the Ewing will be increased 
by 2 additional biologists/acousticians who will monitor the SEAMAP 
system. Verification of acoustic contacts will then be attempted 
through visual observation by the marine mammal observers. However, the 
PAM system by itself usually does not determine the distance that the 
vocalizing mammal might be from the seismic vessel. It can be used as a 
cue by the visual observers as to the presence of an animal and to its 
approximate bearing (with some ambiguity). At this time, however, it is 
doubtful if PAM can be used as a trigger to initiate power-down of the 
array. NMFS encourages L-DEO to continue to study the relationship 
between a signal on a passive acoustic array and distance from the 
array can be determined with sufficient accuracy to be used for this 
purpose without complementary visual observations.
    Taking into consideration the additional costs of prohibiting 
nighttime operations and the likely impact of the activity (including 
all mitigation and monitoring), NMFS has preliminarily determined that 
the proposed mitigation and monitoring ensures that the activity will 
have the least practicable impact on

[[Page 58411]]

the affected species or stocks. Marine mammals will have sufficient 
notice of a vessel approaching with operating seismic airguns, thereby 
giving them an opportunity to avoid the approaching array; if ramp-up 
is required, two marine mammal observers will be required to monitor 
the safety radii using shipboard lighting or NVDs for at least 30 
minutes before ramp-up begins and verify that no marine mammals are in 
or approaching the safety radii; ramp-up may not begin unless the 
entire safety radii are visible. Therefore as mentioned earlier, it is 
likely that the 3 GI-airgun array will not be ramped-up from a shut-
down at night when in waters shallower than 100 m (328 ft).

Reporting

    L-DEO will submit a report to NMFS within 90 days after the end of 
the cruise, which is currently predicted to occur during November and 
December, 2004. The report will describe the operations that were 
conducted and the marine mammals that were detected. The report must 
provide full documentation of methods, results, and interpretation 
pertaining to all monitoring tasks. The report will summarize the dates 
and locations of seismic operations, marine mammal sightings (dates, 
times, locations, activities, associated seismic survey activities), 
and estimates of the amount and nature of potential take of marine 
mammals by harassment or in other ways.

Endangered Species Act (ESA)

    Under section 7 of the ESA, the National Science Foundation (NSF), 
the agency funding L-DEO, has begun consultation on the proposed 
seismic survey. NMFS will also consult on the issuance of an IHA under 
section 101(a)(5)(D) of the MMPA for this activity. Consultation will 
be concluded prior to a determination on the issuance of an IHA.

National Environmental Policy Act (NEPA)

    The NSF has prepared an EA for the ETPO oceanographic surveys. NMFS 
is reviewing this EA and will either adopt it or prepare its own NEPA 
document before making a determination on the issuance of an IHA. A 
copy of the NSF EA for this activity is available upon request (see 
ADDRESSES).

Preliminary Conclusions

    NMFS has preliminarily determined that the impact of conducting the 
seismic survey in the ETPO off Central America may result, at worst, in 
a temporary modification in behavior by certain species of marine 
mammals. This activity is expected to result in no more than a 
negligible impact on the affected species or stocks.
    For reasons stated previously in this document, this preliminary 
determination is supported by (1) the likelihood that, given sufficient 
notice through slow ship speed and ramp-up, marine mammals are expected 
to move away from a noise source that it is annoying prior to its 
becoming potentially injurious; (2) recent research that indicates that 
TTS is unlikely (at least in delphinids) until levels closer to 200-205 
dB re 1 microPa are reached rather than 180 dB re 1 microPa; (3) the 
fact that 200-205 dB isopleths would be well within 100 m (328 ft) of 
the vessel even in shallow water; and (4) the likelihood that marine 
mammal detection ability by trained observers is close to 100 percent 
during daytime and remains high at night to that distance from the 
seismic vessel. As a result, no take by injury or death is anticipated, 
and the potential for temporary or permanent hearing impairment is very 
low and will be avoided through the incorporation of the proposed 
mitigation measures mentioned in this document.
    While the number of potential incidental harassment takes will 
depend on the distribution and abundance of marine mammals in the 
vicinity of the survey activity, the number of potential harassment 
takings is estimated to be small. In addition, the proposed seismic 
program will not interfere with any legal subsistence hunts, since 
seismic operations will not take place in subsistence whaling and 
sealing areas and will not affect marine mammals used for subsistence 
purposes.

Proposed Authorization

    NMFS proposes to issue an IHA to L-DEO for conducting a 
oceanographic seismic survey in the ETPO off Central America, provided 
the previously mentioned mitigation, monitoring, and reporting 
requirements are incorporated. NMFS has preliminarily determined that 
the proposed activity would result in the harassment of small numbers 
of marine mammals; would have no more than a negligible impact on the 
affected marine mammal stocks; and would not have an unmitigable 
adverse impact on the availability of species or stocks for subsistence 
uses.

Information Solicited

    NMFS requests interested persons to submit comments and information 
concerning this request (see ADDRESSES).

    Dated: September 24, 2004.
Laurie K. Allen,
Director, Office of Protected Resources, National Marine Fisheries 
Service.
[FR Doc. 04-21973 Filed 9-29-04; 8:45 am]
BILLING CODE 3510-22-S`