[Federal Register Volume 69, Number 109 (Monday, June 7, 2004)]
[Notices]
[Pages 31792-31806]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 04-12810]


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DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

[I.D. 031104B]


Small Takes of Marine Mammals Incidental to Specified Activities; 
Marine Seismic Survey on the Blanco Fracture Zone in the Northeastern 
Pacific Ocean

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 
on the Blanco Fracture Zone in the Northeastern Pacific Ocean. 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 July 7, 
2004.

[[Page 31793]]


ADDRESSES: Comments on the application should be addressed to P. 
Michael Payne, Chief, Marine Mammal Conservation 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: 031104B. Comments sent via email, 
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. 
Under section 3(18)(A), 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 March 8, 2004, NMFS received an application from L-DEO for the 
taking, by harassment, of several species of marine mammals incidental 
to conducting a seismic survey program. L-DEO plans to conduct a marine 
seismic survey in the Northeastern Pacific Ocean (NPO), off Oregon, 
during August, 2004. Up to two seismic surveys are scheduled to take 
place in the NPO. The main survey is planned to occur near the 
intersection of the Blanco Transform with the Juan de Fuca Ridge. Time 
permitting, a second survey may be conducted at Gorda Ridge. The main 
seismic survey will take place between 44[deg] 20' and 44[deg] 42' N. 
and between 129[deg] 50' and 130[deg] 30' W. or at least 450 km (243 
nm) offshore and outside the Exclusive Economic Zone (EEZ) of any 
nation. The Gorda Ridge survey is located between 42[deg] 20' and 
43[deg] N. and between 126[deg] 30' and 127-157 km, at least 84 nm 
(155.6 km) offshore, but within the EEZ of the United States.
    The purpose of the seismic survey is to obtain information on the 
structure of the oceanic crust created at the Juan de Fuca Ridge. More 
specifically, the survey will obtain information on the geologic nature 
of boundaries of the earth's crust created at the intermediate-
spreading Juan de Fuca Ridge. Past studies have mapped those boundaries 
using manned submersibles, but they have not provided a link between 
geologic and seismic structure. This study will provide the seismic 
data to assess the geologic nature of the previously mapped areas.

Description of the Activity

    The proposed seismic survey will involve one vessel, the R/V 
Maurice Ewing (Ewing). The Ewing will deploy a 10- or 12-airgun array 
as an energy source, with discharge volumes of 3050 in3 and 3705 in\3\, 
respectively. The Ewing will also deploy and retrieve 12 Ocean Bottom 
Seismometers (OBSs), plus tow a 6-km (3.2 nm) streamer containing 
hydrophones, to receive the returning acoustic signals. As the airguns 
are towed along the survey lines, these two systems will receive the 
returning acoustic signals.
    A total of approximately 150 kilometers (km) (81 nautical miles 
(nm)) of OBS surveys using a 12-gun array (24 hours of operation) and 
approximately 1017 km (549 nm) of Multi-Channel Seismic (MCS) profiles 
using a 10-gun array (6.5 days of operation) are planned to be 
conducted during the main survey. These line-kilometer figures include 
operations associated with start up, line changes of 10 km (5 nm) for 
the 12-gun array and 90 km (49 nm) for the 10-gun array), equipment 
testing, contingency profiles, and repeat coverage of any areas where 
initial data quality is sub-standard. In the unlikely event that there 
are no weather or equipment delays, additional MCS profiles may be 
acquired at the northern end of the Gorda Ridge where it intersects the 
Blanco Transform. The contingency survey would consist of 220 km (119 
nm) of survey lines, plus 63 km (34 nm) for turns and connecting lines, 
for a total of 283 km (153 nm). Water depths within the seismic survey 
areas are 1600-5000 m (5250-16,405 ft).
    During the airgun operations, the vessel will travel at 7.4-9.3 km/
hr (4-5 knots), and seismic pulses will be emitted at intervals of 60-
90 sec (OBS lines) and approximately 20 sec for the Multi-Channel 
Seismic profiles (MCS lines). The 20-sec spacing corresponds to a shot 
interval of about 50 m (164 ft), while the 60-90 sec spacing 
corresponds to a distance of 150 m (492 ft) to 220 m (722 ft), 
respectively. The 60-90 sec spacing along OBS lines is to minimize 
reverberation from previous shot noise during OBS data acquisition, and 
the exact spacing will depend on water depth.
    For the 10- and 12-airgun arrays, the sound pressure fields have 
been modeled by L-DEO in relation to distance and direction from the 
airguns, and in relation to depth. Predicted sound levels are depicted 
in Figures 6 and 7 in L-DEO's application. Empirical data concerning 
those sound levels have been acquired 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. L-DEO's analysis of the acoustic 
data from that study (Tolstoy et al.,

[[Page 31794]]

2004) provides limited measurements in deep water, such as found at 
Blanco Fracture and Gorda Ridge. Those data indicate that, for deep 
water, L-DEO's model tends to overestimate the received sound levels at 
a given distance. NMFS and L-DEO, therefore, propose that the 180-dB 
and 190-dB (re 1 microPascal (root-mean-squared (rms)) sound pressure 
fields that will correspond to the proposed safety radii (see 
Mitigation) will be the values predicted by L-DEO's model during airgun 
operations in deep water, including these planned survey operations.
    In addition to the operations of the airgun array, the ocean floor 
will be mapped continuously throughout the entire cruise with an Atlas 
Hydrosweep DS-2 Multibeam 15.5-kHz bathymetric sonar, and a 3.5-kHz 
sub-bottom profiler. Both of these sound sources are commonly operated 
simultaneously with the airgun array, but may, on occasion, be utilized 
independent of the seismic array.
    The Atlas Hydrosweep 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 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 (<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 1/5th of these values 
or 2/5th 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.
    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 30o 
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.
    Sound levels have not been measured directly for the sub-bottom 
profiler used by the Ewing, but Burgess and Lawson (2000) measured 
sounds propagating more or less horizontally from a similar unit with 
similar source output (205 dB re 1 microPa m). The 160 and 180 dB re 1 
microPa rms radii in the horizontal direction were estimated to be, 
respectively, near 20 m (66 ft) and 8 m (26 ft) from the source, as 
measured in 13 m or 43 ft water depth. The corresponding distances for 
an animal in the beam below the transducer would be greater, on the 
order of 180 m (591 ft) and 18 m (59 ft), assuming spherical spreading.
    The sub-bottom profiler on the Ewing has a stated maximum source 
level of 204 dB re 1 microPa. Thus the received level would be expected 
to decrease to 160 and 180 dB about 160 m (525 ft) and 16 m (52 ft) 
below the transducer, respectively, assuming spherical spreading. 
Corresponding distances in the horizontal plane would be lower, given 
the directionality of this source (30[deg] beamwidth) and the 
measurements of Burgess and Lawson (2000).

Characteristics of Airgun Pulses

    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. The peak-to-peak (P-P) source 
levels of the 10-gun array and 12-gun arrays that will be used for the 
Blanco Fracture project are 255 dB re 1 microPa (55 bar-m) and 257 dB 
dB re 1 microPa (68 bar-m), respectively. These are the nominal source 
levels applicable to downward propagation. The effective source level 
for horizontal propagation is lower.
    Several important mitigating 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 P-P levels, in bar-meters or dB re 1 microPa-m. The peak (zero-
to-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 P-P 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

[[Page 31795]]

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 duration as 
received at long horizontal distances can be much greater.
    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. For the 
Blanco Fracture survey using 10-gun and 12-gun arrays, the distances at 
which seismic pulses are expected to diminish to received levels of 190 
dB, 180 dB, 170 dB and 160 dB re 1 microPa rms are as follows:

 Table 1. Distances to which sound levels might be received from the airgun arrays planned for use in the Blanco
                                                 Fracture Zone.
----------------------------------------------------------------------------------------------------------------
                                                                                RMS Radii (m/ft)
                         Airgun Array                          -------------------------------------------------
                                                                  190 dB      180 dB       170 dB       160 dB
----------------------------------------------------------------------------------------------------------------
1 airgun......................................................      13/43       36/118      110/361     350/1148
10 airguns....................................................    200/656     550/1805    2000/6562   6500/21325
12 airguns....................................................    200/656     600/1968    2200/1718   7250/23786
----------------------------------------------------------------------------------------------------------------

    Additional information is contained in the L-DEO application, 
especially in Appendix A.

Description of Habitat and Marine Mammals Affected by the Activity

    A detailed description of the NPO in the Blanco Fracture/Gorda 
Ridge 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. The main Blanco Transform survey 
site, and the Gorda Ridge contingency survey site, are located 
approximately 450 and 150 km (243 and 81 nm) offshore from Oregon, 
respectively, over water depths of 1600 to 5000 m (5250 to 16405 ft). 
Based on their preference for offshore (>2000 m (6560 ft) depth) and/or 
slope (200-2000 m or 656-6560 ft) waters, 19 of the 39 marine mammal 
species known for Oregon and Washington waters are considered likely to 
occur near the survey areas. An additional 14 species could occur, but 
are unlikely to do so in the project area because they are rare or 
uncommon in slope and offshore waters or they generally do not occur 
off Oregon or Washington. While these 14 species are addressed in the 
L-DEO application it is unlikely that they will occur in the survey 
area. An additional six species are not expected in the project area 
because their occurrence off Oregon is limited to coastal/shallow 
waters (gray whale (Eschrichtius robustus) and sea otter (Enhydra 
lutris)) or they are considered extralimital (beluga whale 
(Delphinapterus leucas), ringed seals (Phoca hispida), ribbon seal 
(Phoca fasciata), and hooded seal (Cystophora cristata)). As it is 
unlikely that these rare, vagrant mammals would occur during the short 
time period of this seismic survey, these latter six species are not 
addressed further as they are unlikely to be impacted by seismic 
signals from this research operation.
    The six species of marine mammals expected to be most common in the 
deep pelagic or slope waters of the project area include the Pacific 
white-sided dolphin (Lagenorhynchus obliquidens), northern right whale 
dolphin(Lissodelphis borealis), Risso's dolphin (Grampus griseus), 
short-beaked common dolphin (Delphinus delphis), Dall's porpoise 
(Phocoenoides dalli), and northern fur seal (Callorhinus ursinus)(Green 
et al., 1992, 1993; Buchanan et al., 2001; Carretta et al., 2002; 
Barlow, 2003). The sperm whale (Physeter macrocephalus), pygmy sperm 
whale (Kogia breviceps), mesoplodont species (Blainville's beaked whale 
(Mesoplondon densirostris), Stejneger's beaked whale (M. stejnegeri), 
and Hubb's beaked whale (M. carlhubbsi)), Baird's beaked whale 
(Berardius bairdii), Cuvier's beaked whale (Ziphius cavirostris), and 
northern elephant seals (Mirounga angustirostris) are considered 
pelagic species but are generally uncommon in the waters near the 
survey area.
    Of the five species of pinnipeds known to occur regularly in waters 
off Oregon, Washington, or northern California, only the northern fur 
seal and northern elephant seal are likely to be present in the pelagic 
waters of the proposed project area, located approximately 150-450 km 
(243-481 nm) offshore. The Steller sea lion (Eumetopias jubatus) may 
also occur there in small numbers. The California sea lion (Zalophus 
californianus)and harbor seal (Phoca vitulina) occur in shallow coastal 
or shelf waters off Oregon and Washington (Bonnell et al., 1992, Green 
et al., 1993, Buchanan et al., 2001), and are not expected to be seen 
in the proposed study area. Sea otters were translocated to shallow 
coastal waters off the Olympic Peninsula of Washington, but are not 
found in the pelagic waters of the project area off Oregon. More 
detailed information on these species is contained in the L-DEO 
application and additional information is contained in Caretta et al., 
(2002) which are available at: http://www.nmfs.noaa.gov/prot_res/PR2/Small_Take/smalltake_info.htm#applications, and http://
www.nmfs.noaa.gov/prot--res/

[[Page 31796]]

PR2/Stock--Assessment--Program/sars.html, respectively.

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). 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) masking, (2) disturbance, and (3) potential hearing impairment and 
other physical effects. Additional discussion on species specific 
effects can be found in the L-DEO application for taking marine mammals 
incidental to this activity.

Masking

    Masking effects of pulsed sounds on marine mammal calls and other 
natural sounds are expected to be limited, although there are very few 
specific data on this. Seismic sounds are short pulses occurring for 
less than 1 sec every 20 or 60-90 sec in this project. 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\th\ or at most 2/5\th\ 
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). 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 that 
sounds important to these species 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 frequencies are 
mainly used by mysticetes, but 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 
cetacean signal. If little or no overlap occurs between the industrial 
noise and the frequencies used, as in the case of many marine mammals 
vs. 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 and 
preadaptation to tolerate some masking by natural sounds (Richardson et 
al., 1995), would all reduce the importance of masking.

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 disruption of a 
behavioral pattern. However, if a sound source would displace marine 
mammals from an important feeding or breeding area for a prolonged 
period, such a disturbance would constitute Level B harassment. 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. This 
likely overestimates the numbers of marine mammals that are affected in 
some biologically important manner. The sound criteria used to estimate 
how many marine mammals might be harassed behaviorally by the seismic

[[Page 31797]]

survey are based on behavioral observations during studies of several 
species. However, information is lacking for many species.

Hearing Impairment and Other Physical Effects

    Temporary or permanent hearing impairment is a possibility when 
marine mammals are exposed to very strong sounds, but there has been no 
specific documentation of this for marine mammals exposed to airgun 
pulses. Current NMFS policy regarding exposure of marine mammals to 
high-level sounds is that cetaceans and pinnipeds should not be exposed 
to impulsive sounds [gteqt]180 and 190 dB re 1 microPa (rms), 
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.
    Several aspects of the planned monitoring and mitigation measures 
for this project are designed to detect marine mammals occurring near 
the airgun array (and multibeam sonar), and to avoid exposing them to 
sound pulses that might cause hearing impairment. In addition, many 
cetaceans are likely to show some avoidance of the area with ongoing 
seismic operations. In these cases, the avoidance responses of the 
animals themselves will reduce or avoid the possibility of hearing 
impairment.
    Non-auditory physical effects may also occur in marine mammals 
exposed to strong underwater pulsed sound. Possible types of non-
auditory physiological effects or injuries that theoretically might 
occur in mammals close to a strong sound source include stress, 
neurological effects, bubble formation, resonance effects, and other 
types of organ or tissue damage. It is possible that some marine mammal 
species (i.e., beaked whales) may be especially susceptible to injury 
and/or stranding when exposed to strong pulsed sounds. 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) notes 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 (Fineran 
et al., 2002). Seismic pulses with received levels of 200 205 dB or 
more are usually restricted to a radius of no more than 100 m (328 ft) 
around a seismic vessel.
    There are no data, direct or indirect, on levels or properties of 
sound that are required to induce TTS in any baleen whale. 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 (Fineran 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 radius of <=100 m (<= 328 ft) around a 
typical 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. 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 
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. If some 
cetaceans did incur TTS through exposure to airgun sounds, this would 
very likely be a temporary and reversible phenomenon.
    Currently, NMFS believes that, whenever possible 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 elsewhere 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 that 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.

[[Page 31798]]

 Therefore, there is little potential for whales being close enough to 
an array to experience TTS. In addition ramping up airgun arrays, 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 
airgun array.

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. Physical damage to a mammal's hearing 
apparatus can occur if it is exposed to sound impulses that have very 
high peak pressures, especially if they have very short rise times 
(time required for sound pulse to reach peak pressure from the baseline 
pressure). Such damage can result in a permanent decrease in functional 
sensitivity of the hearing system at some or all frequencies.
    Single or occasional occurrences of mild TTS are not indicative of 
permanent auditory damage in terrestrial mammals. However, very 
prolonged exposure to sound strong enough to elicit TTS, or shorter-
term exposure to sound levels well above the TTS threshold, can cause 
PTS, at least in terrestrial mammals (Kryter 1985). Relationships 
between TTS and PTS thresholds have not been studied in marine mammals 
but are assumed to be similar to those in humans and other terrestrial 
mammals. The low-to-moderate levels of TTS that have been induced in 
captive odontocetes and pinnipeds during recent controlled studies of 
TTS have been confirmed to be temporary, with no measurable residual 
PTS (Kastak et al., 1999; Schlundt et al., 2000, Finneran et al., 2002; 
Nachtigall et al., 2003). In terrestrial mammals, the received sound 
level from a single non-impulsive sound exposure must be far above the 
TTS threshold for any risk of permanent hearing damage (Kryter, 1994; 
Richardson et al., 1995). For impulse sounds with very rapid rise times 
(e.g., those associated with explosions or gunfire), a received level 
not greatly in excess of the TTS threshold may start to elicit PTS. 
Rise times for airgun pulses are rapid, but less rapid than for 
explosions.
    Some factors that contribute to onset of PTS are as follows: (1) 
exposure to single very intense noises, (2) repetitive exposure to 
intense sounds that individually cause TTS but not PTS, and (3) 
recurrent ear infections or (in captive animals) exposure to certain 
drugs.
    Cavanagh (2000) has reviewed the thresholds used to define TTS and 
PTS. Based on his review and SACLANT (1998), it is reasonable to assume 
that PTS might occur at a received sound level 20 dB or more above that 
which induces mild TTS. However, for PTS to occur at a received level 
only 20 dB above the TTS threshold, it is probable that the animal 
would have to be exposed to the strong sound for an extended period.
    Sound impulse duration, peak amplitude, rise time, and number of 
pulses are the main factors thought to determine the onset and extent 
of PTS. Based on existing data, Ketten (1994) has noted that the 
criteria for differentiating the sound pressure levels that result in 
PTS (or TTS) are location and species-specific. PTS effects may also be 
influenced strongly by the health of the receiver's ear.
    Given that marine mammals are unlikely to be exposed to received 
levels of seismic pulses that could cause TTS, it is highly unlikely 
that they would sustain permanent hearing impairment. If we assume that 
the TTS threshold for exposure to a series of seismic pulses may be on 
the order of 220 dB re 1 microPa (pk-pk) in odontocetes, 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). 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. 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. However, pinnipeds are 
expected to be (at most) uncommon in the Blanco Fracture survey area. 
However, although it is unlikely that the planned seismic surveys could 
cause PTS in any marine mammals, caution is warranted given the limited 
knowledge about noise-induced hearing damage in marine mammals, 
particularly baleen whales.

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, and, 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, more recently, an L-DEO seismic 
survey has 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

[[Page 31799]]

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 in some 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 the bends or air embolism.
    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 Cuviers 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 this 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 broad-scale seismic surveys 
where the tracklines are generally not as closely spaced as in many 
industry seismic surveys.
    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 th 
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.
    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.

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 
during much of 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, (2) have a longer pulse duration, and (3) are directed 
close to horizontally (vs. downward for the Hydrosweep). The area of 
possible influence of the Hydrosweep is much 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

[[Page 31800]]

mammals that do encounter the Hydrosweep 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 Hydrosweep signals 
(approximately 10 ms) such sounds 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 be not 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 do not overlap with the 
predominant frequencies in the calls, which would avoid significant 
masking.

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 
beachings 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. Finally, the pulsed 
signals from the sub-bottom profiler are much weaker than those from 
the airgun array and the multibeam sonar. Therefore, 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). It is worth noting that the multi-beam sonar proposed 
for use by L-DEO is quite different than sonars used for navy 
operations. Pulse duration of the multi-beam sonar 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 beamwidth. (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 the 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 Blanco Fracture Zone Survey
    Although information contained in this document indicates that 
injury to marine mammals from seismic sounds potentially occurs at 
sound pressure levels 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 typically about 10 dB less than its 
peak 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. L-DEO has calculated the ``best estimates'' for the numbers 
of animals that could be taken by level B harassment during the 
proposed Blanco Fracture 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 (Table 1).
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    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 10- and 12-gun array planned to be used for this project. The 
anticipated radius of influence of the multi-beam sonar is less than 
that for the airgun array, 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.

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. Furthermore, if they are 
encountered, the numbers of mysticetes estimated to occur within the 
160-dB isopleth at the Blanco Fracture and Gorda Ridge survey sites are 
expected to be low. In addition, the estimated numbers presented in 
Table 2 are considered overestimates of actual numbers for two primary 
reasons. First, the number of line kilometers used to estimate the 
number of exposures and individuals exposed assumes that both the main 
and contingency surveys will be completed; this is highly unlikely 
given the likelihood that some inclement weather, equipment 
malfunction, and/or implementation of mitigative shut downs or power 
downs will occur. Secondly, the estimated 160-dB radii used here are 
probably overestimates of the actual 160-dB radii at deep water sites 
such as the Blanco Fracture and Gorda Ridge sites (Tolstoy et al., 
2004).
    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 mitigation measures that are planned, 
effects on cetaceans are generally expected to be limited to avoidance 
of the 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 population sizes in the NPO generally.
    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 0.7 percent of the populations of each 
species in the NPO. For species listed as endangered under the 
Endangered Species Act (ESA), this includes no North Pacific right 
whales or sei whales; less than 0.02 percent of the NPO populations of 
sperm, humpback and blue whales; and 0.1 percent of the fin whale 
population (Table 2). In the cases of mysticetes, beaked whales, and 
sperm whales, these potential reactions are expected to involve no more 
than very small numbers (0 to 7) of individual cetaceans. Sperm and fin 
whales are the endangered species that are most likely to be exposed, 
and their NPO populations are approximately 26,053 and 8520, 
respectively (Ohsumi and Wada 1974, Carretta et al. 2002).
    It is highly unlikely that any right whales will be exposed to 
seismic sounds [gteqt]160 dB re 1 microPa (rms). This conclusion is 
based on the rarity of this species off Oregon/Washington and in the 
NPO generally (less than 100, Carretta et al. 2002), and that the 
remnant population of this species apparently migrates to more 
northerly areas during the summer. However, L-DEO has requested an 
authorization to expose up to two North Pacific right whales to 160 dB, 
given the possibility (however unlikely) of encountering one or more of 
this endangered species. If a right whale is sighted by the vessel-
based observers, the airguns will be shut down (not just powered down) 
regardless of the distance of the whale from the airgun array.
    Larger numbers of delphinids may be affected by the proposed main 
and contingency seismic studies, but the population sizes of species 
likely to occur in the operating area are large, and the numbers 
potentially affected are small relative to the population sizes. As 
indicated in Table 2, the best estimate of number of individual 
delphinids that might be exposed to sounds less than or equal to 160 dB 
re 1 microPa (rms) represents a small percentage of the populations of 
each species occurring there.
    Varying estimates of the numbers of marine mammals that might be 
exposed to airgun sounds during the August 2004 seismic surveys off 
Oregon have been presented, depending on the specific exposure 
criteria, calculation procedures (exposures vs. individuals), and 
density criteria used (best vs. maximum). The requested ``take 
authorization'' for each species is based on the estimated maximum 
number of exposures to [gteqt]160 dB re 1 microPa (rms). That figure 
likely overestimates (in most cases by a large margin) the actual 
number of animals that will be exposed to these sounds; the reasons for 
this are outlined above. Even so, the

[[Page 31803]]

combined estimates for the main and contingency surveys are quite low 
percentages of the population sizes. Also, these relatively short-term 
exposures are unlikely to result in any long-term negative consequences 
for the individuals or their populations.
    The many cases of apparent tolerance by cetaceans of seismic 
exploration, vessel traffic, and some other human activities show that 
co-existence is possible. Mitigation measures such as controlled speed, 
course alternation, look outs, 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 sensitivity. 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, the action is expected to have no more than a 
negligible impact on the affected species or stocks of marine mammals. 
In addition, mitigation measures such as controlled vessel speed, 
course alteration, look-outs, ramp-ups, and power-downs when marine 
mammals are seen within defined ranges (see Mitigation) should further 
reduce short-term reactions to disturbance, and minimize any effects on 
hearing sensitivity.

Conclusions--Effects on Pinnipeds

    Two pinniped species, the northern fur seal and the northern 
elephant seal, are likely to be encountered at the survey sites, as 
they are associated with pelagic slope and offshore waters off Oregon. 
In addition, it is possible (although unlikely) that a small number of 
Steller sea lions, California sea lions, and/or harbor seals may also 
be encountered, most likely at the Gorda Ridge survey area located 
closer to shore in continental slope water; these three species tend to 
inhabit primarily coastal and shelf waters. An estimated 79 individual 
fur seals and 15 individual elephant seals may be exposed to airgun 
sounds with received levels [gteqt]160 dB re 1 microPa (rms). It is 
most likely that no California sea lions, Steller sea lions, or harbor 
seals will be exposed to such sounds. Similar to cetaceans, the 
estimated numbers of pinnipeds that may be exposed to received levels 
[gteqt]160 dB are probably overestimates of the actual numbers that 
will be significantly affected. This action would therefore have no 
more than a negligible impact on the affected species or stocks of 
pinnipeds.

Mitigation

    For the proposed Blanco Fracture seismic survey, L-DEO will deploy 
a 10- or 12-airgun array as an energy source, with discharge volumes of 
3050 in3 and 3705 in3, respectively. The airguns in the arrays will be 
spread out horizontally so the energy from the array will be directed 
mostly downward. The directional nature of the arrays 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. Because the 
actual seismic source is a distributed sound source (10-12 airguns) 
rather than a single point source, the highest sound levels measurable 
at any location in the water will be less than the nominal source 
level. Also, the size of the airgun arrays (which are smaller than the 
20-gun array used for some other surveys) is another important 
mitigation measure that will reduce the potential for effects relative 
to those that might occur with a larger array of airguns. This is in 
conformance with NMFS' encouraging seismic operators to use the lowest 
intensity airguns practical to accomplish research objectives. Also, 
that this project is proposed to occur in deep water is also important 
as sound levels tend to be lower in deep than in shallow waters at 
various distances from the airguns.

Proposed Safety Radii

    Received sound levels have been modeled by L-DEO in relation to 
distance and direction from the two arrays. The radii around the 10-
airgun array where the received levels would be 180 dB and 190 dB re 1 
microPa (rms) were estimated as 550 m (1805 ft) and 200 m (656 ft), 
respectively. For the 12-airgun array, the radii around the array where 
the received levels would be 180 dB and 190 dB re 1 microPa (rms) were 
estimated as 600 m (1969 ft) and 200 m (656 ft), respectively. The 180 
and 190 dB shutdown criteria, applicable to cetaceans and pinnipeds, 
respectively, are specified by NMFS (2000) and, as mentioned previously 
in this document, are considered conservative for protecting marine 
mammals from potential injury.
    Empirical data concerning these safety radii have been acquired 
based on measurements during the acoustic verification study conducted 
by L-DEO in the northern Gulf of Mexico from 27 May to 3 June 2003 (see 
68 FR 32460, May 30, 2003). L-DEO's analysis of the acoustic data from 
that study (Tolstoy et al. 2004) provides limited measurements in deep 
water, the situation relevant here. Those data indicate that, for deep 
water, the model tends to overestimate the received sound levels at a 
given distance. Until additional data become available, it is proposed 
that safety radii during airgun operations in deep water, including the 
planned operations off Oregon, will be the values predicted by L-DEO's 
model. Previously, more conservative (larger) safety radii that are 1.5 
times the modeled radii have been used for these surveys. However, 
given that these modeled radii are already conservative (i.e., 
overestimates) for deep water situations, even without the X 1.5 
factor, these larger radii are not being proposed to be used during 
this seismic survey.

Additional Mitigation Measures

    The following mitigation measures, as well as marine mammal visual 
monitoring (discussed later in this document), are proposed for the 
subject seismic surveys, provided that they do not compromise 
operational safety requirements: (1) Speed and course alteration; (2) 
power-down and shut-down procedures; (3) ramp-up procedures and (4) use 
of passive acoustics to detect vocalizing marine mammals. In addition, 
special mitigation measures will be implemented for the North Pacific 
right whale.

Speed and Course Alteration

    If a marine mammal is detected outside the appropriate safety 
radius and, based on its position and the relative motion, is likely to 
enter the safety radius, the vessel's speed and/or direct course will 
be changed if this is practical while minimizing the effects on planned 
science objectives. Given the presence of the streamer and airgun array 
behind the vessel, the turning rate of the vessel with trailing 
streamer and array is no more than five degrees per minute, limiting 
the maneuverability of the vessel during operations. 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 radius. If the mammal appears likely to enter the safety radius, 
further mitigative actions will be taken, (i.e., either further course 
alterations or shutdown 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

[[Page 31804]]

marine mammals are not in the safety zone. A power down may also occur 
when the vessel is moving from one seismic line to another, unless the 
full airgun array is scheduled to be operated during line changes. 
During a power down, one 80 in3 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 vessels speed and/or 
course cannot be changed to avoid having the mammal enter the safety 
radius, the airguns 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, at least one airgun (e.g., 80 in\3\) will be 
operated. If a marine mammal is detected within or near the smaller 
safety radius around that single airgun (Table 1), all airguns 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 a power down, the operating airgun will be shut down if a 
marine mammal approaches within the modeled safety radius for the then-
operating source, typically a single gun of 80 in3. Because no 
calibration measurements have been done to confirm the modeled safety 
radii for the single gun, conservative radii may be used (1.5 times the 
modeled safety radius). For an 80 in3 airgun, the predicted 180-dB 
distance applicable to cetaceans is 36 m (118 ft) and the x1.5 
conservative radius is 54 m (177 ft). The corresponding 190-dB radius 
applicable to pinnipeds is 13 m (43 ft), with the x1.5 conservative 
radius being 20 m (66 ft). If a marine mammal is detected within or 
about to enter the appropriate safety radius around the small source in 
use during a power down, airgun operations will be entirely shut down. 
In addition, the airguns will be shut down if a North Pacific right 
whale is sighted anywhere near the vessel, even if it is located 
outside the safety radius, because of the rarity and sensitive status 
of this species. Resumption of airgun activity will follow procedures 
described for power-down operations.

Ramp-up Procedure

    When airgun operations commence after a certain period without 
airgun operations, the number of guns firing will be increased 
gradually, or ``ramped up'' (also described as a ``soft start''). 
Operations will begin with the smallest gun in the array (80 in3). Guns 
will be added in sequence such that the source level of the array will 
increase in steps not exceeding 6 dB per 5-min period over a total 
duration of approximately 18-20 minutes. Throughout the ramp-up 
procedure, the safety zone for the full 10- or 12-gun array will be 
maintained.
    The ``ramp-up'' procedure will be required under the following 
circumstances. Under normal operational conditions (vessel speed 4 
knots (7.4 km/hr)), a ramp-up would be required after a power-down or 
shut-down period lasting more than 4 minutes if the Ewing was towing 
the 10- or 12-gun array. At 4 knots, the Ewing would travel 600 m (1969 
ft) during a 5-minute period. The 600-m (1969 ft) distance is the 
calculated 180-dB safety radius.
    If the towing speed is reduced to 3 knots (5.6 km/hr) or less, as 
sometimes required when maneuvering in shallow water (not a factor 
here), it is proposed that a ramp-up would be required after a ``no 
shooting'' period lasting greater than 7 minutes. At towing speeds not 
exceeding 3 knots (5.6 km/hr), the source vessel would travel no more 
than 600 m (1969 ft) in about 7 minutes. Based on the same calculation, 
a ramp-up procedure would be required after a 4-minute period if the 
speed of the source vessel was 5 knots (9.3 km/hr).
    Ramp-up will not occur if the safety radius has not been visible 
for at least 30 minutes prior to the start of ramp-up operations in 
either daylight or nighttime. If the safety radius has not been visible 
for that 30-minute period (e.g., during darkness or fog), ramp-up will 
not commence unless at least one airgun has been firing continuously 
during the interruption of seismic activity. That airgun will have a 
source level of at least 180 dB re 1 microPa m (rms). It is likely that 
the airgun arrays will not be ramped up from a complete shut down at 
night or in thick fog, because the outer part of the safety zone for 
those arrays will not be visible during those conditions. If one airgun 
has operated during a power down period, ramp up to full power will be 
permissible at night or in poor visibility, on the assumption that 
marine mammals will be alerted to the approaching seismic vessel by the 
sounds from the single airgun and could move away if they choose. Ramp 
up of the airguns will not be initiated if a marine mammal is sighted 
within or near the applicable safety radii during the day or close to 
the vessel at night.
    Comments on past proposed IHAs raised the issue of prohibiting 
night-time operations as mitigation. However, this is not practicable 
due to cost considerations. The daily cost to the Federal Government to 
operate vessels such as Ewing is approximately $33,000 to $35,000/day 
(Ljunngren, pers. comm. May 28, 2003). If the vessels were prohibited 
from operating during nighttime, it is possible that each trip would 
require an additional three to five days, or up to $175,000 more, 
depending on average daylight at the time of work.
    Taking into consideration the additional costs of prohibiting 
night-time 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 the affected species or stocks. 
Marine mammals will have sufficient notice of a vessel approaching with 
operating seismic airguns (at least 1 hour in advance), thereby giving 
them an opportunity to avoid the approaching array; if ramp-up is 
required after an extended power-down, two marine mammal observers will 
be required to monitor the safety radii using night vision devices for 
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; and ramp-up may occur at night only if 
one airgun with a sound pressure level of at least 180 dB has been 
maintained during interruption of seismic activity. Therefore it is 
likely that the 10-12-airgun array will not be ramped-up from a shut-
down at night.

Marine Mammal Monitoring

    L-DEO must have at least three visual observers and two passive 
acoustic system biological monitors on board the vessels, and at least 
two must be an experienced marine mammal observer that NMFS approves. 
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

[[Page 31805]]

nighttime start-ups of the airguns and at night, whenever daytime 
monitoring resulted in one or more power-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 an extended power-down or 
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 Maurice 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 airguns are powered 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 if marine mammals are 
observed in or about to enter the safety radii. However, an 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 from 
a power-down situation, two marine mammal observers will monitor for 
marine mammals for 30 minutes prior to ramp-up and during the ramp-up 
using night vision equipment that will be available (ITT F500 Series 
Generation 3 binocular image intensifier or equivalent). All observer 
activity will be assisted by the passive acoustic monitoring (PAM) 
system where its use is feasible.

Passive (Acoustic) Monitoring

    L-DEO will use the PAM system whenever the vessel 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 to 3 
additional biologists 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. 
Perhaps with continued studies 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.

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 August, 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.

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 Blanco Fracture Zone 
oceanographic seismic 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 on the Blanco Fracture Zone in the NPO. will 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 finds annoying prior to its 
becoming potentially injurious; (2) recent research that indicates that 
TTS is unlikely (at least in delphinids) at 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 within 100 m (328 ft) of 
the vessel; 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 and/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 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

[[Page 31806]]

harassment takings is estimated to be small. In addition, the proposed 
seismic program is not expected to interfere with any 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 surveys on the Blanco Fracture Zone in the NPO, 
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: May 25, 2004.
Laurie K. Allen,
Director, Office of Protected Resources, National Marine Fisheries 
Service.
[FR Doc. 04-12810 Filed 6-4-04; 8:45 am]
BILLING CODE 3510-22-S