[Federal Register Volume 68, Number 70 (Friday, April 11, 2003)]
[Notices]
[Pages 17773-17783]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 03-8935]


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DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

[I.D. 031703A]


Small Takes of Marine Mammals Incidental to Specified Activities; 
Marine Seismic Testing in the Northern Gulf of Mexico

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

ACTION: Notice of receipt of application and proposed authorization for 
a small take exemption; request for comments.

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SUMMARY: NMFS has received an application from the Lamont-Doherty Earth 
Observatory (LDEO) for an Incidental Harassment Authorization (IHA) to 
take small numbers of marine mammals, by harassment, incidental to 
conducting calibration measurements of its seismic array in the 
northern Gulf of Mexico (GOM). Under the Marine Mammal Protection Act 
(MMPA), NMFS is requesting comments on its proposal to issue a small 
take authorization to LDEO to incidentally take, by harassment, small 
numbers of several species of cetaceans for a short period of time 
within the next 12 months.

DATES: Comments and information must be received no later than My 12, 
2003.

ADDRESSES: Comments on the application should be addressed to the 
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. A copy of the application, and/or the Environmental Assessment 
(EA), which contain the list of references used in this document, may 
be obtained by writing to this address or by telephoning the contact 
listed here. Comments cannot be accepted if submitted via e-mail or the 
Internet.

FOR FURTHER INFORMATION CONTACT: Kenneth R. Hollingshead, Office of 
Protected Resources, NMFS, (301) 713-2055, ext 128.

SUPPLEMENTARY INFORMATION:

Background

    Sections 101(a)(5)(A) and (D) of the MMPA ((16 U.S.C. 1361 et seq.) 
directs 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.''
    Subsection 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 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; 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.
    (B) The term ``Level A harassment'' means harassment described 
in subparagraph (A)(i).
    (C) The term ``Level B harassment'' means harassment described 
in subparagraph (A)(ii).
    Subsection 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 
small numbers 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 February 24, 2003, NMFS received an application from LDEO for 
the taking, by harassment, of several species of marine mammals 
incidental to conducting calibration measurements of its seismic array 
in the northern GOM. The LDEO plans to measure sound levels from each 
of the airgun arrays that will be used during their seismic survey 
programs during future studies. These measurements will be made in 
shallow, shelf slope, and deep waters in the GOM during late May and/or 
June 2003, but may be rescheduled. The purpose of these measurements is 
to verify estimates of sound fields around the airgun arrays that have 
been made using LDEO acoustical models. Verification of the output from 
these models is needed to confirm the distances from the airguns 
(safety radii) within which mitigation may be necessary to avoid 
exposing marine mammals to airgun sounds at received levels exceeding 
established limits, e.g. the 180 and 190 dB re 1 [mu]Pa (rms) limits 
set for cetaceans and pinnipeds, respectively. The measurements will 
also verify the distances at which the sounds diminish below other 
lower levels that may be assumed to characterize the zone where 
disturbance is possible or likely.
    The data to be collected during this project can be used to develop 
a better understanding of the impact of man-made acoustic sources on 
marine mammals. There is a paucity of calibrated data on levels of man-
made sounds in relation to the differing responses of marine mammals to 
these sources. The planned project will obtain the first calibrated 
measurements of the R/V Maurice Ewing's (Ewing) acoustic sources across 
a broad range of frequencies from 1 Hz to 25 kHz, and for various 
configurations of the Ewing's airgun array. Calibration experiments 
will be conducted in the shallow, shelf slope, and deep water of the 
GOM to quantify the differences in sound attenuation in relation to 
water depth. Once calibration measurements have been made, they will be 
used to model the full propagation field of the Ewing in varying 
geographical settings. This modeling will provide data needed to help 
minimize any potential risk to marine mammals during future seismic 
surveys.

Description of Activity

    The proposed seismic sound measurements will involve one vessel, 
the Ewing. It will deploy and retrieve a spar buoy that will record 
received airgun sounds, and it will tow the airgun arrays whose sounds 
will be measured at various distances from the buoy. The Ewing will 
deploy two different airgun arrays in each of the three water depths 
where measurement will be made. One array will be a 20-

[[Page 17774]]

gun array and the other will be a 20-gun array (with varying numbers of 
those 20 guns active at any one time). While towing each of the arrays 
and firing the guns at 20-sec intervals, the Ewing will approach the 
spar buoy from 10 km (5.4 nm) away, pass the spar buoy about 100 m (54 
nm) to the side of it, and continue until it is 10 km (5.4 nm) past the 
spar buoy. Sounds will be recorded at the spar buoy and telemetered to 
the Ewing. The Ewing will be self-contained, and the crew of the vessel 
will live aboard
    During the GOM cruise, water depths in the study area will range 
from <100 to 2000 m (<330 6500 ft). Airgun 
operations will be conducted along a total of about 132 km (71.3 nm) of 
trackline. This includes 66 km (35.6 nm) of trackline for each of the 
2-Generator-Injector (GI) guns and the 20-gun array. About one third of 
the survey effort will be in water <100 m (328.1 ft), one third will be 
in water 100-2,000 m (328.1-6,561.7 ft), and one third will be in water 
2,000 m (6,561.7 ft). These linear figures 
represent the planned surveys. There may be additional operations 
associated with equipment testing and repeat coverage of any 
calibration run where initial data quality is sub-standard. To allow 
for these possible additional operations, the estimates of marine 
mammals that may be taken includes an allowance for an additional 44 km 
(23.7 nm) of airgun operations or 110 km (59.4 nm) for each of the 2-GI 
and 20-gun configurations (220 km (118.8 nm) of total trackline).
    About one-half of the airgun operations in each water depth 
category will be conducted with the 2-gun array and the other half will 
be with varying proportions of the 20-airgun array. During operations 
with the larger array, the number of airguns active will vary from 6 to 
20. The five configurations to be tested (2, 6, 10, 12 and 20 airguns) 
will include all of the airgun configurations that are anticipated to 
be used during LDEO's subsequent 2003 cruises.
    The procedures to be used during the airgun calibration surveys 
will be similar to those used during previous seismic surveys by LDEO, 
e.g., in the equatorial Pacific Ocean (Carbotte et al., 1998, 2000). 
The proposed program will use conventional seismic methodology with a 
towed airgun array as the energy source and a LDEO spar buoy as the 
receiver system. At one of the locations, a moored US Navy/University 
of New Orleans EARS (Environmental Acoustic Recording System) buoy will 
also record received sound levels as an independent calibration of the 
data that are received by the LDEO spar buoy.
    The energy for the airgun array is compressed air supplied by 
compressors on board the source vessel. The specific configuration of 
the airgun array will be varied to represent all of the different 
arrays that will be used during 2003 and the most common arrays that 
will be used in future years. In addition, a multi-beam bathymetric 
sonar will be operated from the source vessel for part of the 
calibration survey. A lower-energy sub-bottom profiler will also be 
operated for part of this cruise. Detailed specifications on the 
acoustic instrumentation planned for this calibration study can be 
found in LDEO's application.

Description of Habitat and Marine Mammals Affected by the Activity

    A total of 28 cetacean species and one species of sirenian (West 
Indian manatee) are known to occur in the GOM. These species are the 
sperm whale (Physeter macrocephalus), pygmy sperm whale (Kogia 
breviceps), dwarf sperm whale (Kogia sima), Cuvier's beaked whale 
(Ziphius cavirostris), Sowerby's beaked whale (Mesoplodon bidens), 
Gervais' beaked whale (Mesoplodon europaeus), Blainville's beaked whale 
(Mesoplodon densirostris), rough-toothed dolphin (Steno bredanensis), 
bottlenose dolphin (Tursiops truncatus), pantropical spotted dolphin 
(Stenella attenuata), Atlantic spotted dolphin (Stenella frontalis), 
spinner dolphin (Stenella longirostris), Clymene dolphin (Stenella 
clymene), striped dolphin (Stenella coeruleoalba), 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), 
short-finned pilot whale (Globicephala macrorhynchus), North Atlantic 
right whale (Eubalaena glacialis), humpback whale (Megaptera 
novaeangliae), minke whale (Balaenoptera acutorostrata), Bryde's whale 
(Balaenoptera edeni), sei whale (Balaenoptera borealis), fin whale 
(Balaenoptera physalus), and the blue whale (Balaenoptera musculus). 
Another 3 species (long-beaked common dolphin (Delphinus capensis), 
short-beaked common dolphin (Delphinus delphis), and long-finned pilot 
whale (Globicephala melas)) could potentially occur in the GOM.
    In the northern GOM, cetaceans are concentrated along the 
continental slope near cyclonic eddy and confluence areas of cyclonic-
anticyclonic eddy pairs, due to nutrient-rich water which is thought to 
increase zooplankton stocks and thus prey abundance in those areas 
(Davis et al., 2002). The narrow continental shelf south of the 
Mississippi River delta appears to be an important habitat for some 
cetacean species (Baumgartner et al., 2001; Davis et al., 2002). Low 
salinity, nutrient-rich waters may occur over the continental slope 
near the mouth of the Mississippi River or be entrained within the 
confluence areas and transported beyond the continental slope, creating 
a deep-water environment with increased productivity (Davis et al., 
2002). The rate of primary productivity and the standing stocks of 
chlorophyll and plankton are higher in this area as compared with other 
regions in the oceanic Gulf (Dagg et al., 1988; Ortner et al., 1989; 
Muller-Karger et al., 1991). This increased productivity may explain 
the presence of a breeding population of endangered sperm whales within 
100 km (54 nm) of the Mississippi River delta (Davis et al., 2002). The 
southwestern Florida continental shelf may be another region of high 
productivity, and an important habitat for several cetacean species 
(Baumgartner et al., 2001).
    Several species of cetaceans are also widespread outside the 
previously described areas, on the continental shelf and/or along the 
shelf break. These include bottlenose dolphins, Atlantic spotted 
dolphins, and Bryde's whales (Davis et al., 2002). Thus, cetaceans in 
the GOM seem to be partitioned by their habitat preferences, which are 
likely based on prey distribution (Baumgartner et al., 2001).
    Detailed descriptions of the marine mammal species are provided in 
the LDEO application and EA (both documents are available upon request 
(see ADDRESSES)). Please refer to those documents for additional 
information. Additional information on these species can also be found 
in Waring et al. (2001, 2002). These latter reports are available at 
the following location: http://www.nmfs.noaa.gov/prot_res/PR2/Stock_Assessment_Program/sars.html

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

[[Page 17775]]

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 (as are 
vehicle launches), 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.

Characteristics of Airgun Pulses

    Airguns were first developed by the offshore seismic industry as a 
replacement to the use of explosives to obtain necessary acoustic 
signals (Richardson et al., 1995). 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 sizes, arrangement and firing times of 
the individual airguns in an array are designed and synchronized to 
suppress the pressure oscillations subsequent to the first cycle. 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 2-20-gun arrays to be 
studied in the planned project range from 236 to 262 dB re 1 [mu]Pascal 
at 1 m. These are the nominal source levels applicable to downward 
propagation. The effective source level for horizontal propagation is 
lower than the nominal source level, at least for the 6- to 20-gun 
arrays.
    Several factors may reduce the effects of sounds on marine mammals. 
First, 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. Second, 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. Finally 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 [mu]Pa-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, 2000a). A fourth 
measure that is sometimes used is the energy level, in dB re 1 
[mu]Pa\2\. Because the pulses are <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. In the past, NMFS has commonly referenced 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. (However, sound travel in the bottom may travel faster than that 
in the water and, thus, may arrive earlier than the direct arrival 
despite traveling a greater distance.) 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. For example, for one airgun array operating in the 
Beaufort Sea, pulse duration was about 300 ms at a distance of 8 km 
(4.3 nm), 500 ms at 20 km (10.8 nm), and 850 ms at 73 km (39.4 nm) 
(Greene and Richardson, 1988).
    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 marine 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

[[Page 17776]]

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, 
even during operations in nearshore waters (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 mPa). 
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.
    The distances at which seismic pulses from the Ewing's airguns are 
expected to diminish to various received levels of 190, 180, 170 dB and 
160 dB re 1 mPa, on an rms basis) are as follows:

----------------------------------------------------------------------------------------------------------------
                                                                                 RMS Radii (m/ft)
                          Airgun Array                           -----------------------------------------------
                                                                    190 dB     180 dB      170 dB       160 dB
----------------------------------------------------------------------------------------------------------------
2 GI airguns*                                                         15/49     50/164      155/508     520/1706
6 airguns**                                                          50/164    220/722     700/2296    2700/8858
10 airguns**                                                        250/820   830/2723    2330/7644   6500/21325
12 airguns**                                                        300/984   880/2887    2680/8793   7250/23786
20 airguns**                                                       400/1312   950/3117   3420/11220  9000/29527
----------------------------------------------------------------------------------------------------------------
* Airgun depth 6 m (20 ft)
**airgun depth 7.5 m (24.6 ft)

    The primary objective of LDEO's planned study is to verify or 
improve these estimated distances. Additional details concerning the 
expected levels at various distances and angles relative to each of 
these airgun arrays can be found in the LDEO application.

Effects of Seismic Surveys on Marine Mammals

    The LDEO application provides the following information on what is 
known about the effects on marine mammals of the types of seismic 
operations planned by LDEO. 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 LDEO application.

Masking

    Masking effects on marine mammal calls and other natural sounds are 
expected to be limited. Seismic sounds are short pulses occurring for 
less than 1 sec every 20 or 60-90 sec in this project. Sounds from the 
multi-beam 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 multi-beam sonar as received 
at any one location would actually be only 1/5th or at most 2/5th 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 (e.g., Richardson et al., 
1986; McDonald et al., 1995; Greene et al., 1999). Although there has 
been one report that sperm whales cease calling when exposed to pulses 
from a very distant seismic ship (Bowles et al., 1994), a recent study 
reports that sperm whales 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 plus the 
fact that sounds important to them 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; 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. Disturbance is the primary concern for this project. 
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 be significant to the individual let alone the stock or 
the species as a whole. However, if a sound source displaces marine 
mammals from an important feeding or breeding area for a prolonged 
period, impacts on the animals could be significant. 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 were 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 disturbed to some biologically important degree by a seismic program 
are based on behavioral observations during studies of several species

[[Page 17777]]

(humpback, gray and bowhead whales; ringed seals). However, information 
is lacking for many other species. These potential impacts are 
discussed further in the LDEO application.

Hearing Impairment and Other Physical Effects

    Temporary or permanent hearing impairment is a possibility when 
marine mammals are exposed to very strong sounds. 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 temporary threshold shift (TTS). The level associated 
with the onset of TTS is considered to be a level below which there is 
no danger of damage and current NMFS policy regarding exposure of 
marine mammals to high-level sounds is that cetaceans and pinnipeds 
should not be exposed to impulsive sounds exceeding 180 and 190 dB re 1 
micro Pa (rms), respectively.
    Several aspects of the planned monitoring and mitigation measures 
for this project are designed to detect marine mammals occurring near 
the airgun array (and multi-beam 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 might (in theory) occur 
include stress, neurological effects, bubble formation, resonance 
effects, and other types of organ or tissue damage. It is possible that 
some marine mammal species (i.e., beaked whales) may be especially 
susceptible to injury and/or stranding when exposed to strong pulsed 
sounds.

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. The magnitude of TTS depends on the level and duration of 
noise exposure, among other considerations (Richardson et al., 1995). 
For sound exposures at or somewhat above the TTS threshold, hearing 
sensitivity recovers rapidly after exposure to the noise ends. Only a 
few data on sound levels and durations necessary to elicit mild TTS 
have been obtained for marine mammals.
    The predicted 180- and 190-dB distances for the airgun arrays 
operated by LDEO during this activity were summarized previously in 
this document. These sound levels are not considered to be the levels 
at or above which TTS would occur. Rather, they are the received levels 
above which, in the view of a panel of bioacoustics specialists 
convened by NMFS, one cannot be certain that there will be no injurious 
effects, auditory or otherwise, to marine mammals. It has 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. 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, ramping 
up airgun arrays, which has become standard operational protocol for 
many seismic operators, including LDEO, 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, and 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 do not cause permanent 
auditory damage in terrestrial mammals, and presumably do not do so in 
marine 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). In terrestrial mammals, the received sound level from a single 
sound exposure must be far above the TTS threshold for any risk of 
permanent hearing damage (Kryter, 1994; Richardson et al., 1995). 
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.
    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 [mu]Pa (P-P) in odontocetes, then the PTS 
threshold might be about 240 dB re 1 [mu]Pa (P-P). 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 and pinnipeds are not 
found in the GOM. Therefore, 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.

[[Page 17778]]

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 there 
is no evidence that they can cause serious injury, death, or stranding. 
However, the association of mass strandings of beaked whales with naval 
exercises and, in a recent case, an LDEO 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 Channel 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 [mu] 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.
    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 recent 
(September, 2002) stranding of two Cuvier's beaked whales in the Gulf 
of California (Mexico) when a seismic survey by the National Science 
Foundation (NSF)/LDEO vessel 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, as discussed later in this 
document, 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

    As mentioned previously, possible types of non-auditory 
physiological effects or injuries that might occur in marine mammals 
exposed to strong underwater sound might, in theory, include stress, 
neurological effects, bubble formation, resonance effects, and other 
types of organ or tissue damage. There is no proof that any of these 
effects occur in marine mammals exposed to sound from airgun arrays. 
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 of 
the type planned by LDEO, where the tracklines are generally not as 
closely spaced as in many 3-dimensional industry surveys, or the brief 
acoustic measurement program planned for the northern GOM.
    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. Diving marine 
mammals are not subject to the bends or air embolism because, unlike a 
human SCUBA diver, they only breath air at sea level pressure and have 
protective adaptations against getting the bends. There may be a 
possibility that high sound levels could cause bubble formation in the 
blood of diving mammals that in turn could cause an air embolism, 
tissue separation, and high, localized pressure in nervous tissue 
(Gisner (ed.), 1999; Houser et al., 2001).
    A recent workshop (Gentry (ed.), 2002) was held 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

[[Page 17779]]

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 auditory impairment or other physical effects in marine 
mammals. Available data suggest that such effects, if they occur at 
all, would be limited to situations where the marine mammal is located 
at a short distance 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) 
will be operated from the source vessel at some time during the 
calibration study. Sounds from the multi-beam sonar are very short 
pulses, occurring for 1-10 msec once every 1 to 15 sec, depending on 
water depth. Most of the energy in the sound pulses emitted by this 
multi-beam sonar is at high frequencies, centered at 15.5 kHz. The beam 
is narrow (2.67[deg]) in fore-aft extent, and wide (140[deg]) in the 
cross-track extent. Each ping consists of five successive transmissions 
(segments) at different cross-track angles. Any given mammal at depth 
near the trackline would be in the main beam for only one or two of the 
five segments, i.e. for 1/5\th\ or at most 2/5\th\ of the 1-10 msec.
    Navy sonars that have been linked to avoidance reactions and 
stranding of cetaceans (1) generally 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). Marine mammals that 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.

Masking by Mid-Frequency Sonar Signals

    There is little chance that marine mammal communications will be 
masked appreciably by the multi-beam sonar signals given the low duty 
cycle of the sonar 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

    Marine mammal behavioral reactions to military and other sonars 
appear to vary by species and circumstance. Sperm whales reacted to 
military sonar, apparently from a submarine, by dispersing from social 
aggregations, moving away from the sound source, remaining relatively 
silent and becoming difficult to approach (Watkins et al., 1985). Other 
early and generally limited observations were summarized in Richardson 
et al. (1995). More recently, Rendell and Gordon (1999) recorded vocal 
behavior of pilot whales during periods of active naval sonar 
transmission. The sonar signal was made up of several components each 
lasting 0.17 sec and sweeping up from 4 to 5 kHz. The pilot whales were 
significantly more vocal while the pulse trios were being emitted than 
during the intervening quiet periods, but did not leave the area even 
after several hours of exposure to the sonar.
    Reactions of beaked whales near the Bahamas to mid-frequency naval 
sonars were summarized earlier. Following extended exposure to pulses 
from a variety of ships, some individuals beached themselves, and 
others may have abandoned the area (Balcomb and Claridge, 2001; NOAA 
and USN, 2001). Pulse durations from these sonars were much longer than 
those of the LDEO multi-beam sonar, and a given mammal would probably 
receive many pulses. All of these observations are of limited relevance 
to the present situation because exposures to multi-beam pulses are 
expected to be brief as the vessel passes by, and the individual pulses 
will be very short.
    Captive bottlenose dolphins and a beluga 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 LDEO 
(Ridgway et al., 1997; Schlundt et al., 2000), and to shorter broadband 
pulsed signals (Finneran et al., 2000, 2002). Behavioral changes 
typically involved what appeared to be deliberate attempts to avoid the 
sound exposure or to avoid the location of the exposure site during 
subsequent tests (Schlundt et al., 2000; Finneran et al., 2002). 
Dolphins exposed to 1-sec intense tones exhibited short-term changes in 
behavior above received sound levels of 178 to 193 dB re 1 [mu]Pa rms 
and belugas did so at received levels of 180 to 196 dB and above. 
Received levels necessary to elicit such reactions to shorter pulses 
were higher (Finneran et al., 2000, 2002). Test animals sometimes 
vocalized after exposure to pulsed, mid-frequency sound from a watergun 
(Finneran et al., 2002). In some instances, animals exhibited 
aggressive behavior toward the test apparatus (Ridgway et al., 1997; 
Schlundt et al., 2000). The relevance of these data to free-ranging 
odontocetes is uncertain. In the wild, cetaceans sometimes avoid sound 
sources well before they are exposed to the levels listed above, and 
reactions in the wild may be more subtle than those described by 
Ridgway et al. (1997) and Schlundt et al.(2000).
    In summary, cetacean behavioral reactions to military and other 
sonars appear to vary by species and circumstance. While there may be a 
link between naval sonar use and changes in cetacean vocalization rates 
and movements, it is unclear what impact these behavioral changes 
(which are likely to be short-term) might have on the animals. 
Therefore, as mentioned previously, because simple momentary behavioral 
reactions that are within normal behavioral patterns for that species 
are not considered to be a taking, the very brief exposure of cetaceans 
to signals from the Hydrosweep is unlikely to result in a ``take'' by 
harassment.

Hearing Impairment and Other Physical Effects

    Given recent stranding events that have been associated with the 
operation of naval sonar, there is much concern that sonar noise can 
cause serious impacts to marine mammals (for discussion see Effects of 
Seismic Surveys on Marine Mammals). It is worth noting that the multi-
beam sonar

[[Page 17780]]

proposed for use by LDEO 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.

Possible Effects of the Sub-bottom Profiler Signals

    A sub-bottom profiler will be operated from the source vessel at 
some times during the planned study. Sounds from the sub-bottom 
profiler are very short pulses, occurring for 1, 2 or 4 msec once every 
second. Most of the energy in the sound pulses emitted by this multi-
beam sonar is at mid frequencies, centered at 3.5 kHz. The beamwidth is 
approximately 300 and is directed downward.
    Sound levels have not been measured for the sub-bottom profiler 
used by the Ewing, but Burgess and Lawson (2000) measured the sounds 
propagating more or less horizontally from a similar unit with similar 
source output (205 dB re 1 [mu]Pa-m source level). The 160 and 180 dB 
re 1 [mu]Pa (rms) radii, in the horizontal direction, were estimated to 
be near 20 m (65.6 ft) and 8 m (26.2 ft) from the source, as measured 
in 13 m (42.6 ft) water depth. The corresponding distances for an 
animal in the beam below the transducer would be greater, on the order 
of 180 m (590.5 ft) and 18 m (59 ft) (assuming spherical spreading).
    The sub-bottom profiler on the Ewing has a maximum source level of 
204 dB re 1 [mu]Pa-m. Thus the received level should be expected to 
decrease to 160 and 180 dB about 160 and 16 m (525 and 52.5 ft) below 
the transducer, respectively (again assuming spherical spreading). 
Corresponding distances in the horizontal plane would be lower, given 
the directionality of this source (30[deg] beamwidth) and the 
measurements of Burgess and Lawson (2000).

Masking by Sub-bottom Profiler Signals

    There is little chance that marine mammal communications will be 
masked appreciably by the sub-bottom profiler signals given its 
relatively low power output, the low duty cycle 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 by Sub-bottom Profiler Signals

    Marine mammal behavioral reactions to pulsed sound sources are 
discussed above and responses to the sub-bottom profiler are likely to 
be similar to those of other pulsed sources at the same received 
levels. However, the pulsed signals from the sub-bottom profiler are 
much weaker than those from the airgun array and the multi-beam, so 
behavioral responses are not expected unless marine mammals were very 
close to the source, e.g. with about 160 m (525 ft) below the vessel, 
or a lesser distance to the side. Thus, the very brief exposure of 
cetaceans to small numbers of signals from the sub-bottom profiler 
would not result in Level B harassment.

Hearing Impairment and Other Physical Effects

    Source levels of the sub-bottom profiler are much lower than 
airguns and the multi-beam. Sound levels from a sub-bottom profiler 
similar to the one on the Ewing were estimated to decrease to 180 dB re 
1 [mu]Pa (rms) at 8 m (26.2 ft) horizontally from the source (Burgess 
and Lawson, 2000), and about 18 m (59 ft) downward from the source. 
Thus few, if any, marine mammals are likely to approach close enough to 
the sub-bottom profiler to be exposed to pulse levels that might cause 
hearing impairment or other physical injuries.
    Furthermore, 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 before the mammals would be close enough to be affected by the 
less intense sounds from the sub-bottom profiler. In the event that 
mammals 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

    As described previously in this document and in the LDEO 
application, animals subjected to sound levels greater than 160 dB may 
alter their behavior or distribution, and, therefore, might be 
considered to be taken by harassment. However, the 160-dB criterion, 
used by NMFS as an indicator of where Level B harassment may result 
from impulse sounds, is based on studies of baleen whales. Odontocete 
hearing at low frequencies is relatively insensitive, and the dolphins 
generally appear to be more tolerant of strong sounds than are most 
baleen whales. For that reason, it has been suggested that for purposes 
of estimating incidental harassment of odontocetes, a 170-dB criterion 
might be appropriate.
    All anticipated takes would be Level B harassment takes involving 
temporary changes in behavior. The mitigation measures to be applied by 
LDEO will minimize the possibility of injurious takes during the 
planned acoustic calibration project in the northern GOM. The estimate 
of the number of marine mammals that might be taken by harassment is 
based on a consideration of the number of marine mammals that might be 
disturbed by operations with the specific airgun arrays planned for 
each of the calibration runs past the spar buoy. LDEO's initial 
estimates of the numbers that might be disturbed assume that, on 
average, cetaceans exposed to airgun sounds with received levels 
160 dB re 1 [mu]Pa (rms) might be sufficiently disturbed to 
be ``taken by harassment.'' The best estimate also includes an 
allowance for four extra source-vessel transits past the spar buoy in 
order to obtain the required calibration data and, therefore, is an 
overestimate if the calibrations measurements require only six 
transits. The best estimates take account of data on marine mammal 
abundance from previous surveys in that area.
    The anticipated radii of influence of the multi-beam sonar and the 
sub-bottom profiler are much less than that for the airgun array (see 
previous discussion). It is assumed that any marine mammal close enough 
to be affected by the multi-beam sonar or the sub-bottom profiler would 
already be affected by the airguns. Therefore, no additional takings by 
harassment would occur for animals that might be affected by the multi-
beam sonar or the sub-bottom profiler.

Estimates of Take by Harassment for the GOM

    Extensive aircraft- and ship-based surveys have been conducted for 
marine mammals in the GOM, including the area where the calibration 
study will be conducted (Davis et al., 2000, 2002; Wursig et al., 2000; 
Baumgartner et al., 2001). However, oceanographic and other conditions 
strongly influence the distribution and numbers of marine mammals 
present in an area (Davis et al., 2002). Thus, for some species the 
densities derived from recent surveys may not be representative of the 
densities that will be encountered

[[Page 17781]]

during the proposed acoustical calibration study. Table 3 in the LGEO 
application gives the densities for each species or species group of 
marine mammals in LDEO's proposed study area based on the 1996/97 
GulfCet II surveys (Davis et al., 2000). The densities from the GulfCet 
studies had been corrected by the original authors for detectability 
bias but not for availability bias. Therefore, in Table 3, LDEO has 
adjusted the originally reported densities and population estimates to 
account for availability bias. Based on those densities, the numbers of 
each species that might be taken by harassment and the requested level 
of take by harassment are shown in that table.
    Dolphins account for 94 percent of the ``best estimate'' (i.e., 486 
of 520 animals). There is no general agreement regarding any 
alternative ``take'' criterion for dolphins exposed to airgun pulses. 
However, if only those dolphins exposed to [gteqt]170 dB re 1 [mu]Pa 
(rms) were affected sufficiently to be considered ``taken by 
harassment'', then the best estimate for dolphins would be 183 rather 
than 486. This is based on the predicted 170 dB radii around the 2 GI 
gun and 20-airgun arrays (155 m (508 ft) and 3,420 m (11, 220 ft), 
respectively). This number of 183 animals is considered by LDEO to be a 
more realistic ``best estimate'' of the number of dolphins that may be 
disturbed (i.e., Level B harassment). This number is about 0.1 percent 
of the estimated GOM population of dolphins (approx. 165,715). 
Therefore, the total number of dolphins likely to react behaviorally is 
considerably lower than the estimated 486 animals.
    Of the 520 marine mammals that might be exposed to airgun sounds 
with received levels 160 dB re 1 [mu]Pa (rms), an estimated 
two would be sperm whales. Two sperm whales represent 0.4 percent of 
the estimated GOM population of about 530 sperm whales.

Mitigation

    The directional nature of the alternative airgun arrays to be used 
in this project (especially the larger arrays) is an important 
mitigating factor. This directionality will result in reduced sound 
levels at any given horizontal distance than would be expected at that 
distance if the source were omnidirectional with the stated nominal 
source level.
    For the proposed airgun calibration work in the GOM in 2003, LDEO 
at times will use 2 GI-guns with total volume 210 in\3\, and at other 
times will use a 20-gun array with 6-20 active guns and total volume 
1350-8600 in\3\. Individual airguns will range in size from 80 to 850 
in\3\. The airguns comprising these arrays will be spread out 
horizontally, so that the energy from the array will be directed mostly 
downward.
    The sound pressure fields have been modeled in relation to distance 
and direction from each of the five array configurations and are shown 
in Figs. 7-11 in LDEO's application. The radii around the arrays where 
the received level would be 180 dB re 1 [mu]Pa (rms), the shutdown 
criterion applicable to cetaceans, were estimated as 50 m (164 ft), 220 
m (722 ft), 830 m (2,723 ft), 880 m (2,887 ft) and 950 m (3,117 ft) for 
the 2-, 6-, 10-, 12-, and 20-gun arrays, respectively.
    Vessel-based observers will watch for marine mammals in the 
vicinity of the arrays. Until such time as the sound pressure fields 
estimated by the model have been confirmed by measurements of actual 
sound pressure levels, LDEO proposes to use 1.5 times the 180 dB 
isopleth. One of the main purposes of the measurements that will be 
made during the GOM project is to verify or refine these safety radii. 
The current plan is to measure sounds produced by the 6-, 10-, 12- and 
20-gun arrays during the same transit past the spar buoy, operating 
these four combinations of airguns in a repeating sequence. The safety 
radius for the 20-gun array (x1.5) will be used whenever the sequence 
including (at times) 20 active guns is in progress. Sounds from the 2 
GI guns will be measured during separate transits past the spar buoy. 
During the GOM cruise, the proposed safety radii for cetaceans are 75 m 
(246 ft) and 1,425 m (4,675 ft), respectively, for the 2 GI-guns and 
20-gun array. LDEO proposes to shut down the airguns if marine mammals 
are detected within the proposed safety radii.
    Also, LDEO proposes to use a ramp-up (soft-start) procedure when 
commencing operations. Ramp-up will begin with the smallest gun in the 
array that is being used (80 in3 for all subsets of the 20-gun array). 
Guns will be added in a sequence such that the source level of the 
array will increase at a rate no greater than 6 dB per 5-minutes.

Marine Mammal Mitigation Monitoring

    Vessel-based observers will monitor marine mammals near the source 
vessel starting 30 minutes before all airgun operations. Airguns will 
be operated only during daylight; they will not be operated or started 
up during nighttime. Airgun operations will be suspended when marine 
mammals are observed within, or about to enter, designated safety zones 
where there is a possibility of significant effects on hearing or other 
physical effects. Vessel-based observers will watch for marine mammals 
near the seismic vessel during daylight periods with shooting, and for 
at least 30 minutes prior to the planned start of airgun operations.
    Two observers will monitor marine mammals near the Ewing during all 
airgun operations in the GOM. The Ewing is a suitable platform for 
marine mammal observations. The observer's eye level will be 
approximately 11 m (36 ft) above sea level when stationed on the 
bridge, allowing for good visibility within a 21[deg] arc for each 
observer. In addition to visual observations, a towed hydrophone array 
will be used to detect and locate marine mammals. This will increase 
the likelihood of detecting and identifying any marine mammals that are 
present during airgun operations. The proposed monitoring plan is 
summarized later in this document.

Proposed Safety Radii

    Received sound levels have been modeled for the 2-, 6-, 10-, 12-, 
and 20-airgun arrays and are depicted in Figures 7-11 of the LDEO 
application. Based on the modeling, estimates of the 190-, 180-, 170-, 
and 160-dB re 1 [mu]Pa (rms) distances (safety radii) for these arrays 
are shown in Table 1 in the application and previously in this 
document. Acoustic measurements in shallow (<100 m/328 ft), mid-depths 
(100-2000 m/328-6,562 ft), but probably about 1000 m (3,281 ft)), and 
deep (2000 m) water will be taken during the proposed 
cruise, in order to check the modeled received sound levels during 
operation of these airgun arrays in a wide variety of water depths. 
Because the safety radii will not be confirmed before the cruise, 
conservative safety radii will be used during the proposed GOM surveys. 
Conservative radii will be established at 1.5 times the distances 
calculated for the 2 GI-guns and the 20 airgun array. Thus, during the 
GOM cruise the proposed conservative safety radii for cetaceans are 75 
m (246 ft) and 1,425 m (4,675 ft) for the 2 GI guns and 20-gun arrays, 
respectively.
    Airgun operations will be suspended immediately when cetaceans are 
detected within or about to enter the appropriate 180-dB (rms) radius. 
This 180 dB criterion is consistent with guidelines listed for 
cetaceans by NMFS (2000) and other guidance by NMFS.

Mitigation During Operations

    The following mitigation measures, as well as marine mammal 
monitoring, will be adopted during the GOM

[[Page 17782]]

acoustic verification program, provided that doing so will not 
compromise operational safety requirements:

Course alteration

    If a marine mammal is detected outside the safety radius and, based 
on its position and the relative motion, is likely to enter the safety 
radius, alternative ship tracks will be plotted against anticipated 
mammal locations. If practical, the vessel's course and/or speed will 
be changed in a manner that avoids approaching within the safety radius 
while also minimizing 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 radius. If the mammal appears likely to 
enter the safey radius, further mitigative actions will be taken (i.e., 
either further course alterations or shutdown of the airguns).

Shutdown procedures

    Vessel-based observers using visual aids and acoutical arrays will 
monitor marine mammals near the seismic vessel for 30 minutes prior to 
start up and during all airgun operations. No airguns will be operated 
during periods of darkness. Airgun operations will be suspended 
immediately when marine mammals are observed or otherwise detected 
within, or about to enter, designated safety zones where there is a 
possibility of physical effects, including effects on hearing (based on 
the 180 dB criterion specified by NMFS). The shutdown procedure should 
be accomplished within several seconds (or a ``one shot'' period) of 
the determination that a marine mammal is within or about to enter the 
safety zone. Airgun operations will not resume until the marine mammal 
is outside the safety radius. Once the safety zone is clear of marine 
mammals, the observers will advise that seismic surveys can re-
commence. The ``ramp-up'' procedure will then be followed.

Ramp-up procedure

    A ``ramp-up'' procedure will be followed when the airgun arrays 
begin operating after a specified-duration period without airgun 
operations. Under normal operational conditions (vessel speed 4-5 
knots), a ramp-up would be required after a ``no shooting'' period 
lasting 2 minutes or longer. At 4 knots, the source vessel would travel 
247 m (810 ft) during a 2-minute period. If the towing speed is reduced 
to 3 knots or less, as sometimes required when maneuvering in shallow 
water, it is proposed that a ramp-up would be required after a ``no 
shooting'' period lasting 3 minutes or longer. At towing speeds not 
exceeding 3 knots, the source vessel would travel no more than 277 m 
(909 ft) in 3 minutes. These guidelines would require modification if 
the normal shot interval were more than 2 or 3 min, respectively, but 
that is not expected to occur during the GOM project.
    Ramp-up will begin with the smallest gun in the array that is being 
used (80 in3). Guns will be added in a sequence such that the source 
level of the array will increase in steps not exceeding 6 dB per 5-
minute period over a total duration of approximately 18-20 min (10-12 
gun arrays).

Avoidance of Cetacean Concentrations

    The Ewing will be involved in separately-permitted studies of sperm 
whales during the late May and June period when the proposed acoustical 
measurements will be obtained. Thus the scientists in charge of this 
program will have first-hand knowledge of the locations of 
concentrations of sperm whales and other cetaceans. The proposed 
acoustical measurements therefore will be able to avoid operating near 
known concentrations of marine mammals.

Monitoring and Reporting

Vessel-based Visual Monitoring

    As mentioned under Mitigation, two observers dedicated to marine 
mammal observations will be stationed aboard LDEO's seismic survey 
vessel during the acoustical measurement program in the GOM. It is 
proposed that two marine mammal observers aboard the seismic vessel 
will search for and observe marine mammals whenever airgun operations 
are in progress. Airgun operations will be restricted to periods with 
good visibility during daylight hours. Two observers will be on duty 
for at least 30 minutes prior to the start of airgun operations and 
during ramp-up procedures. The observers will watch for marine mammals 
from the highest practical vantage point on the vessel, which is the 
bridge. The observer(s) will systematically scan the area around the 
vessel with 7X50 Fujinon reticle binoculars or with the naked eye. 
``Bigeye'' (25 X 150) binoculars will be available during this cruise 
to assist with species identification of marine mammals that are 
sighted. Laser rangefinding binoculars (Bushnell Lytespeed 800 laser 
rangefinder with 4X optics or equivalent) will be available to assist 
with distance estimation. If a marine mammal is detected well outside 
the safety radius, the vessel may be maneuvered to avoid having the 
mammal come within the safety radius. When mammals are detected within 
or about to enter the designated safety radii, the airguns will be shut 
down immediately. The observer(s) will continue to maintain watch to 
determine when the animal is outside the safety radius. Airgun 
operations will not resume until the animal is outside the safety 
radius.
    The vessel-based monitoring will provide data required to estimate 
the numbers of marine mammals exposed to various received sound levels, 
to document any apparent disturbance reactions, and thus to estimate 
the numbers of mammals potentially taken by harassment. It will also 
provide the information needed in order to shut down the airguns at 
times when mammals are present in or near the safety zone. When a 
mammal sighting is made, the following information about the sighting 
will be recorded: (1) Species, group size, age/size/sex categories (if 
determinable), behavior when first sighted and after initial sighting, 
heading (if consistent), bearing and distance from seismic vessel, 
sighting cue, apparent reaction to seismic vessel (e.g., none, 
avoidance, approach, paralleling, etc.), and behavioral pace; (2) Time, 
location, heading, speed, activity of the vessel (shooting or not), sea 
state, visibility, cloud cover, and sun glare (The data listed under 
(2) will also be recorded at the start and end of each observation 
watch and during a watch, whenever there is a change in one or more of 
the variables.) All mammal observations and airgun shutdowns will be 
recorded in a standardized format.
    At least two experienced marine mammal observers (with at least one 
previous year of marine mammal observation experience) will be on duty 
aboard the seismic vessel.
    Prior to the start of the project, the primary observers will 
participate in a 1-day meeting and training or refresher course on the 
specific marine mammal monitoring procedures required for this project.
    Two observers will be on duty in shifts of duration no longer than 
4 hours. Use of two simultaneous observers will increase the proportion 
of the marine mammals present near the source vessel that are detected. 
Bridge personnel additional to the dedicated marine mammal observers 
will also assist in detecting marine mammals and implementing 
mitigation requirements, and before the start of the seismic survey 
will be given instruction in how to do so. The results from the vessel-
based observations will provide (1) the

[[Page 17783]]

basis for real-time mitigation (airgun shutdown); (2) information 
needed to estimate the number of marine mammals potentially taken by 
harassment, which must be reported to NMFS; (3) data on the occurrence, 
distribution, and activities of marine mammals in the area where the 
seismic study is conducted; (4) information to compare the distance and 
distribution of marine mammals relative to the source vessel at times 
with and without seismic activity; and (5) data on the behavior and 
movement patterns of marine mammals seen at times with and without 
seismic activity.

Vessel-based Passive Acoustic Monitoring

    A towed hydrophone array will be deployed during the airgun 
measurements in the GOM. The acoustical array will be monitored during 
airgun operations to detect, locate and identify marine mammals near 
the Ewing, insofar as this is possible via passive acoustic methods. 
The acoustical array will provide additional ability to detect, locate 
and identify marine mammals over and above that provided by visual 
observations. The acoustical data will be integrated, in real time, 
with the visual observations to ensure that marine mammals do not enter 
the 180-dB safety radius.

Acoustical Measurements of Airgun Sounds

    The acoustic measurement program is designed to document the 
received levels of the airgun sounds, relative to distance, during 
operation of each standard configuration of airgun array deployed from 
the Ewing. In particular, these data will be used to verify or refine 
present estimates of the safety radii. Those radii are used to 
determine when the airguns need to be shut down to prevent exposure of 
cetaceans to received levels [gteqt]180 dB. Sound measurements will be 
made and reported as discussed previously in this document. LDEO will 
use the standard methods that have been used and reported during other 
recent studies of seismic and marine mammals (Greene et al., 1997; 
McCauley et al., 1998, 2000a,b).

Reporting

    A report will be submitted to NMFS within 90 days after the end of 
the acoustic measurement program in the GOM. The report will describe 
the operations that were conducted, the marine mammals that were 
detected near the operations, and at least some of the results of the 
acoustical measurements to verify the safety radii. (Data from the LDEO 
spar buoy are expected to be available quickly, but it is uncertain how 
quickly the EARS data will be available given the nature of the EARS 
buoys.) The report will be submitted to NMFS, providing full 
documentation of methods, results, and interpretation pertaining to all 
monitoring tasks with the possible exception of the backup EARS data. 
The 90-day report will summarize the dates and locations of seismic 
operations, sound measurement data, 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, NMFS has begun consultation on the 
proposed issuance of an IHA under section 101(a)(5)(D) of the MMPA for 
this activity. Consultation will be concluded prior to the issuance of 
an IHA.

National Environmental Policy Act (NEPA)

    The NSF has prepared an EA for the GOM calibration study. 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 short-term impact of 
conducting a short-term calibration study of the seismic airgun array 
onboard the Ewing in the northern GOM in 2003, will result, at worst, 
in a temporary modification in behavior by certain species of marine 
mammals. While behavioral modifications may be made by these species as 
a result of seismic survey activities, this behavioral change is 
expected to result in no more than a negligible impact on the affected 
species.
    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, no take by injury and/or 
death is anticipated, and the potential for temporary or permanent 
hearing impairment is low and will be avoided through the incorporation 
of the mitigation measures mentioned in this document.

Proposed Authorization

    NMFS proposes to issue an IHA to LDEO for conducting a calibration 
study of the seismic airgun arrays onboard the Ewing in the northern 
GOM 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 
only 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 stocks for 
subsistence uses.

Information Solicited

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

    Dated: April 7, 2003.
Laurie K. Allen,
Acting Director, Office of Protected Resources, National Marine 
Fisheries Service.
[FR Doc. 03-8935 Filed 4-10-03; 8:45 am]
BILLING CODE 3510-22-S