Small Takes of Marine Mammals Incidental to Specified Activities; Marine Geophysical Survey off Central America, February-April 2008, 71625-71644 [E7-24508]

Agencies

• DEPARTMENT OF COMMERCE
• National Oceanic and Atmospheric Administration

[Federal Register Volume 72, Number 242 (Tuesday, December 18, 2007)]
[Notices]
[Pages 71625-71644]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: E7-24508]


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

DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

[RIN 0648-XE34]


Small Takes of Marine Mammals Incidental to Specified Activities; 
Marine Geophysical Survey off Central America, February-April 2008

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

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

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

SUMMARY: NMFS has received an application from Lamont-Doherty Earth 
Observatory (L-DEO), a part of Columbia University, for an Incidental 
Harassment Authorization (IHA) to take marine mammals incidental to 
conducting a marine seismic survey off Central America during February-
April 2008. Pursuant to the Marine Mammal Protection Act (MMPA), NMFS 
is requesting comments on its proposal to issue an IHA to L-DEO to 
incidentally take, by Level B harassment only, small numbers of several 
species of marine mammals during the aforementioned activity.

[[Page 71626]]


DATES: Comments and information must be received no later than January 
17, 2008.

ADDRESSES: Comments on the application should be addressed to P. 
Michael Payne, Chief, Permits, Conservation and Education Division, 
Office of Protected Resources, National Marine Fisheries Service, 1315 
East-West Highway, Silver Spring, MD 20910-3225. The mailbox address 
for providing e-mail comments is PR1.0648XE34@noaa.gov. Comments sent 
via e-mail, including all attachments, must not exceed a 10-megabyte 
file size.
    A copy of the application containing a list of the references used 
in this document may be obtained by writing to the address specified 
above, telephoning the contact listed below (see FOR FURTHER 
INFORMATION CONTACT), or visiting the internet at: https://
www.nmfs.noaa.gov/pr/permits/incidental.htm#applications.
    Documents cited in this notice may be viewed, by appointment, 
during regular business hours, at the aforementioned address.

FOR FURTHER INFORMATION CONTACT: Candace Nachman, Office of Protected 
Resources, NMFS, (301) 713-2289.

SUPPLEMENTARY INFORMATION: 

Background

    Sections 101(a)(5)(A) and (D) of the MMPA (16 U.S.C. 1361 et seq.) 
direct the Secretary of Commerce to allow, upon request, the 
incidental, but not intentional, taking of marine mammals by U.S. 
citizens who engage in a specified activity (other than commercial 
fishing) within a specified geographical region if certain findings are 
made and either regulations are issued or, if the taking is limited to 
harassment, a notice of a proposed authorization is provided to the 
public for review.
    Authorization shall be granted if NMFS finds that the taking will 
have a negligible impact on the species or stock(s), will not have an 
unmitigable adverse impact on the availability of the species or 
stock(s) for subsistence uses (where relevant), and if the permissible 
methods of taking and requirements pertaining to the mitigation, 
monitoring and reporting of such takings are set forth. NMFS has 
defined ``negligible impact'' in 50 CFR 216.103 as `` * * * an impact 
resulting from the specified activity that cannot be reasonably 
expected to, and is not reasonably likely to, adversely affect the 
species or stock through effects on annual rates of recruitment or 
survival.''
    Section 101(a)(5)(D) of the MMPA established an expedited process 
by which citizens of the United States can apply for an authorization 
to incidentally take small numbers of marine mammals by harassment. 
Except with respect to certain activities not pertinent here, the MMPA 
defines ``harassment'' as:

any act of pursuit, torment, or annoyance which (i) has the 
potential to injure a marine mammal or marine mammal stock in the 
wild [Level A harassment]; or (ii) has the potential to disturb a 
marine mammal or marine mammal stock in the wild by causing 
disruption of behavioral patterns, including, but not limited to, 
migration, breathing, nursing, breeding, feeding, or sheltering 
[Level B harassment].

    Section 101(a)(5)(D) establishes a 45-day time limit for NMFS 
review of an application followed by a 30-day public notice and comment 
period on any proposed authorizations for the incidental harassment of 
marine mammals. Within 45 days of the close of the comment period, NMFS 
must either approve or deny the authorization.

Summary of Request

    On August 24, 2007, NMFS received an application from L-DEO for the 
taking, by Level B harassment only, of small numbers of 26 species of 
marine mammals incidental to conducting, under a cooperative agreement 
with the National Science Foundation (NSF), a seismic survey in the 
Pacific Ocean and Caribbean Sea off Central America as part of the 
Subduction Factory (SubFac) initiative of NSF's MARGINS program from 
January-March, 2008. (The dates of the cruise were subsequently moved 
to the February-April 2008 timeframe.) The MARGINS program was 
developed to facilitate the study of continental margins. The SubFac 
initiative will determine the inputs, outputs, and controlling 
processes of subduction zone systems by obtaining seismic measurements 
of magma flux, arc composition, and lower-plate serpentinization at the 
Central American Focus Site.

Description of the Activity

    The seismic survey will involve one source vessel, the R/V Marcus 
G. Langseth (Langseth), which will operate in two regions during the 
proposed survey: the Caribbean Sea and the Pacific Ocean. The Langseth 
will deploy an array of 36 airguns (6,600 in\3\ ) as an energy source 
and, at times, a receiving system consisting of a 6-km (3.7-mi) towed 
hydrophone streamer. The streamer will be towed at a depth of 5-8 m 
(16-26 ft). As the airgun array is towed along the survey lines, the 
hydrophone streamer will receive the returning acoustic signals and 
transfer the data to the on-board processing system. In the Caribbean 
region, the Langseth will also deploy Ocean Bottom Seismometers (OBSs) 
to receive the returning acoustic signals. In the Pacific Ocean, a 
second vessel, the R/V New Horizon, will deploy and retrieve the OBSs.
    For the first part of the cruise, the Langseth is expected to 
depart Puerto Limon, Costa Rica, on approximately February 3, 2008 for 
the study area in the Caribbean Sea (see Figure 1 in the application). 
The seismic survey will commence following the transit and deployment 
of the streamer and airgun array. Following approximately 25 days of 
surveying in the Caribbean Sea, all equipment will be recovered, and 
the vessel will return to Puerto Limon on approximately March 5, 2008. 
The vessel will then transit through the Panama Canal, likely taking on 
fuel in Panama. The second part of the survey will commence in the 
Pacific Ocean on approximately March 11, 2008 from Puerto Caldera, 
Costa Rica. The Pacific survey is estimated to last approximately 25 
days. Currently, the vessel is scheduled to arrive at an unspecified 
port (likely in Panama) on April 6, 2008. The order of the two surveys 
may be reversed due to logistics, if necessary. The exact dates of the 
activities depend upon logistics, as well as weather conditions and/or 
the need to repeat some lines if data quality is substandard.
    The Central American SubFac survey will encompass the area from 
9.6[deg]-14[deg] N., 82[deg]-83.8[deg] W. in the Caribbean Sea and the 
area 8[deg]-11.5[deg] N., 83.6[deg]-88[deg] W. in the Pacific Ocean 
(see Figure 1 in the application). Water depths in the survey area 
range from less than 100 m (328 ft) to greater than 2,500 m (8,202 ft). 
The seismic survey will take place in the Exclusive Economic Zones 
(EEZ) of Costa Rica and Nicaragua.
    The marine seismic survey will consist of approximately 2,149 km 
(1,335 mi) of unique survey lines: 753 km (468 mi) in the Caribbean and 
1,396 km (867 mi) in the Pacific (see Table 1 in the application). With 
the exception of two lines (D and E) located in shallow to 
intermediate-depth water, all lines will be shot twice, once at 
approximately a 50 m (164 ft; 20-s) shot spacing for multichannel 
seismic data and once at approximately a 200 m (656 ft; 80-s) shot 
spacing for OBS refraction data, for a total of approximately 3,980 km 
(2,473 mi) of survey lines (see Table 1 in the application). The 
approximate numbers of line kilometers expected to

[[Page 71627]]

be surveyed in the Pacific and Caribbean in three different water depth 
categories are shown in Table 2 of the application. There will be 
additional operations associated with equipment testing, startup, line 
changes, and repeat coverage of any areas where initial data quality is 
substandard. There may also be an additional 77 km (48 mi) of survey 
effort in the Pacific Ocean around Culebra off Nicoya Peninsula not 
reflected in Table 1 of L-DEO's application. These additional six 
transect lines will occur in water greater than 100 m (328 ft) deep and 
are not expected to increase the number of takes by harassment (see 
below).
    The New Horizon will be the dedicated OBS vessel during the Pacific 
part of the survey and will deploy and retrieve the OBSs. A combination 
of 85 OBSs (150 total deployments) will be used during the project. A 
total of 60 OBS deployments will take place in the Caribbean (from the 
Langseth), and 90 deployments will take place in the Pacific from the 
New Horizon.
    In addition to the operations of the airgun array, a 12-kHz Simrad 
EM120 multibeam echosounder (MBES) will be operated from the Langseth 
continuously throughout the cruise. Also, a 3.5-kHz sub-bottom profiler 
(SBP) will be operated by the Langseth during most of the survey and 
during normal operations by the New Horizon.

Vessel Specifications

    The Langseth has a length of 71.5 m (234.6 ft), a beam of 17 m 
(55.8 ft), and a maximum draft of 5.9 m (19.4 ft). The ship was 
designed as a seismic research vessel, with a propulsion system 
designed to be as quiet as possible to avoid interference with the 
seismic signals. The ship is powered by two Bergen BRG-6 diesel 
engines, each producing 3,550 hp, that drive the two propellers 
directly. Each propeller has four blades, and the shaft typically 
rotates at 750 rpm. The vessel also has an 800-hp bowthruster. The 
operation speed during seismic acquisition is typically 7.4-9.3 km/h 
(4-5 kt). When not towing seismic survey gear, the Langseth can cruise 
at 20-24 km/h (11-13 kt). The Langseth has a range of 25,000 km (15,534 
mi).
    The New Horizon will be the dedicated OBS vessel during the Pacific 
part of the survey and will deploy and retrieve the OBSs. The ship has 
a length of 51.8 m (170 ft), a beam of 11 m (36 ft), and a maximum 
draft of 3.7 m (12 ft). The ship is powered by two 850 hp D398 
Caterpillar engines. The typical cruising speed is 18.5 km/h (10 kt) 
with a maximum speed of 22.8 km/h (12.3 kt). The New Horizon has a 
range of 18,000 km (11,185 mi).

Acoustic Source Specifications

Seismic Airguns

    During the survey, the airgun array to be used will consist of 36 
airguns, with a total volume of approximately 6,600 in3. The 
airguns will comprise a mixture of Bolt 1500LL and 1900LL airguns. The 
array will consist of four identical linear arrays or ``strings'' (see 
Figure 2 in L-DEO's application). Each string will have ten airguns; 
the first and last airguns in each string are spaced 16 m (52.5 ft) 
apart. Nine airguns in each string will be fired simultaneously, while 
the tenth is kept in reserve as a spare, to be turned on in case of 
failure of another airgun. The four airgun strings will be distributed 
across an approximate area of 24 x 16 m (78.7 x 52.5 ft) behind the 
Langseth and will be towed approximately 50-100 m (164-328 ft) behind 
the vessel. The firing pressure of the array is 2,000 psi. The airgun 
array will fire in two modes: every 50 m (164 ft; 20 s) or every 200 m 
(656 ft; 80 s). During firing, a brief (approximately 0.1 s) pulse of 
sound is emitted. The airguns will be silent during the intervening 
periods. The airguns will be towed at a depth of 9 or 12 m (29.5 or 39 
ft). The dominant frequency components are 0-188 Hz.
    Received sound levels have been predicted by L-DEO for the 36-
airgun array operating in deep water and for a single 1900LL 40 
in3 airgun to be used during power-downs (see below). The 
predicted received levels depend upon distance and direction from the 
airguns. This source, which is directed downward, was found to have an 
output (0-peak) of 258 dB re 1 [mu]Pa m. The maximum relevant depth 
(2,000 m; 6,562 ft) represents the maximum anticipated dive depth of 
marine mammals and is relevant for predicting safety or exclusion zones 
(EZs; see below). A detailed description of L-DEO's modeling effort is 
provided in Appendix A of the application.
    The rms (root mean square) received levels that are used as impact 
criteria for marine mammals are not directly comparable to the peak or 
peak-to-peak values normally used to characterize source levels of 
airgun arrays. The measurement units used to describe airgun sources, 
peak or peak-to-peak decibels, are always higher than the rms decibels 
referred to in biological literature. A measured received level of 160 
dB rms in the far field would typically correspond to a peak 
measurement of approximately 170 to 172 dB, and to a peak-to-peak 
measurement of approximately 176 to 178 dB, as measured for the same 
pulse received at the same location (Greene, 1997; McCauley et al., 
1998, 2000a). The precise difference between rms and peak or peak-to-
peak values depends on the frequency content and duration of the pulse, 
among other factors. However, the rms level is always lower than the 
peak or peak-to-peak level for an airgun-type source.

Multibeam Echosounder

    The Simrad EM120 operates at 11.25-12.6 kHz and is hull-mounted on 
the Langseth. The beamwidth is 1[deg] fore-aft and 150[deg] 
athwartship. The maximum source level is 242 dB re 1 [mu]Pa (rms; 
Hammerstad, 2005). For deep-water operation, each ``ping'' consists of 
nine successive fan-shaped transmissions, each 15 ms in duration and 
each ensonifying a section that extends 1[deg] fore-aft. The nine 
successive transmissions span an overall cross-track angular extent of 
about 150[deg], with 16 ms gaps between the pulses for successive 
sectors. A receiver in the overlap area between the two sectors would 
receive two 15-ms pulses separated by a 16-ms gap. In shallower water, 
the pulse duration is reduced to 5 or 2 ms, and the number of transmit 
beams is also reduced. The ping interval varies with water depth, from 
approximately 5 s at 1,000 m (3,280 ft) to 20 s at 4,000 m (13,123 ft; 
Kongsberg Maritime, 2005).

Sub-Bottom Profiler

    The SBP is normally operated to provide information about the 
sedimentary features and the bottom topography that is simultaneously 
being mapped by the MBES. The energy from the SBP is directed downward 
by a 3.5 kHz transducer in the hull of the Langseth. The output varies 
with water depth from 50 watts in shallow water to 800 watts in deep 
water. The pulse interval is 1 s, but a common mode of operation is to 
broadcast five pulses at 1-s intervals followed by a 5-s pause.

Safety Radii

    NMFS has determined that for acoustic effects, using acoustic 
thresholds in combination with corresponding safety radii is the most 
effective way to consistently apply measures to avoid or minimize the 
impacts of an action, and to quantitatively estimate the effects of an 
action. Thresholds are used in two ways: (1) To establish a mitigation 
shut-down or power down zone, i.e., if an animal enters an area 
calculated to be ensonified above the level of an established 
threshold, a sound source is

[[Page 71628]]

powered down or shut down; and (2) to calculate take, in that a model 
may be used to calculate the area around the sound source that will be 
ensonified to that level or above, then, based on the estimated density 
of animals and the distance that the sound source moves, NMFS can 
estimate the number of marine mammals that may be ``taken''. NMFS 
believes that to avoid permanent physiological damage (Level A 
Harassment), cetaceans and pinnipeds should not be exposed to pulsed 
underwater noise at received levels exceeding, respectively, 180 and 
190 dB re 1 [mu]Pa (rms). NMFS also assumes that cetaceans or pinnipeds 
exposed to levels exceeding 160 dB re 1[mu]Pa (rms) may experience 
Level B Harassment.
    The depth at which the source is towed impacts the maximum near-
field output and the shape of the frequency spectrum. If the source is 
towed at a relatively deep depth (e.g., approximately 12 m; 39 ft), the 
effective source level for sound propagating in near-horizontal 
directions is substantially greater than if the array is towed at 
shallower depths (e.g., approximately 9 m; 29.5 ft; see Figure 4 vs. 
Figure 3 in the application).
    Empirical data concerning 180 and 160 dB re 1 [mu]Pa distances in 
deep and/or shallow water were acquired for various airgun 
configurations during the acoustic calibration study of the R/V Maurice 
Ewing's (Ewing) 20-airgun 8,600 in3 array in 2003 (Tolstoy 
et al., 2004a, b). The results showed that radii around the airguns 
where the received level was 160 dB re 1 [mu]Pa varied with water 
depth. Similar depth-related variation is likely for the 180-dB re 1 
[mu]Pa safety criterion applicable to cetaceans and the 190-dB re 1 
[mu]Pa radius applicable to pinnipeds, although these were not 
measured. The L-DEO model does not allow for bottom interactions, and 
thus is most directly applicable to deep water and to relatively short 
ranges.
    The empirical data indicated that, for deep water (>1,000 m; 3,280 
ft), the L-DEO model overestimates the received sound levels at a given 
distance (Tolstoy et al., 2004a,b). However, to be conservative, the 
distances predicted by L-DEO's model will be applied to deep-water 
areas during the proposed study (see Table 3 in the application and 
Table 1 here). As very few, if any, mammals are expected to occur below 
2,000 m (6,562 ft), this depth was used as the maximum relevant depth.
    Empirical measurements indicated that in shallow water (<100 m; 328 
ft), the L-DEO model underestimates actual levels. In previous L-DEO 
projects done since the calibration results were obtained by Tolstoy et 
al. (2004a,b), the EZs in shallow water were typically adjusted upward 
from the values predicted by L-DEO's model by factors of 1.3x to 15x 
depending on the size of the airgun array and the sound level measured 
(Tolstoy et al., 2004b). During the proposed cruise, similar factors 
will be applied to the shallow-water radii (see Table 3 in the 
application and Table 1 here).
    Empirical measurements were not conducted for intermediate depths 
(100-1,000 m; 328-3,280 ft). On the expectation that results would be 
intermediate between those from shallow and deep water, a correction 
factor of 1.5x was applied during former L-DEO cruises to the estimates 
provided by the model for deep-water situations to obtain estimates for 
intermediate-depth sites. The correction factor was used during 
previous L-DEO surveys and will be used during the proposed study for 
intermediate depths (see Table 3 in the application and Table 1 here).
    Table 3 in the application and Table 1 here outline the distances 
to which sound levels of the various EZs might be received, considering 
both the 36-airgun array and a single airgun in three different water 
depths. In deep water, the maximum depth considered is 2,000 m (6,562 
ft). If marine mammals are detected within or about to enter the 
appropriate EZ, the airguns will be powered down (or shutdown if 
necessary) immediately.

   Table 1.--Predicted Distances to Which Sound Levels >=190, 180, and 160 dB re 1 [mu]Pa Might Be Received in
 Shallow (<100 m; 328 ft), Intermediate (100-1,000 m; 328-3,280 ft), and Deep (>1,000 m; 3,280 ft) Water During
                                       the Central American SubFac Survey
----------------------------------------------------------------------------------------------------------------
                                                                                Predicted RMS distances (m)
          Source and volume            Tow depth         Water depth      --------------------------------------
                                          (m)                                 190 dB       180 dB       160 dB
----------------------------------------------------------------------------------------------------------------
Single Bolt airgun 40 in3...........            9  Deep..................           12           40          385
                                      ...........  Intermediate..........           18           60          578
                                      ...........  Shallow...............          150          296         1050
4 strings 36 airguns 6600 in3.......            9  Deep..................          300          950         6000
                                      ...........  Intermediate..........          450         1425         6667
                                      ...........  Shallow...............         2182         3694         8000
4 strings 36 airguns 6600 in3.......           12  Deep..................          340         1120         7400
                                      ...........  Intermediate..........          510         1680         8222
                                      ...........  Shallow...............         2473         4356         9867
----------------------------------------------------------------------------------------------------------------

    Because the predictions in Table 3 in the application and Table 1 
here are based in part on empirical correction factors derived from 
acoustic calibration of different airgun configurations than those to 
be used on the Langseth (cf. Tolstoy et al., 2004a,b), L-DEO is 
planning an acoustic calibration study of the Langseth's 36-airgun 
(6,600 in3) array, which is scheduled to go out in the Gulf 
of Mexico in January 2008. Distances where sound levels (e.g., 190, 
180, and 160 dB re 1 [mu]Pa) are received in deep, intermediate, and 
shallow water will be determined for various airgun configurations. The 
empirical data from the calibration study will be used to refine the 
EZs used during the Central American SubFac survey, if the data are 
appropriate and available at the time of the survey.

Description of Marine Mammals in the Activity Area

    A total of 34 marine mammal species are known to or may occur in 
the study area off Central America, including 25 odontocete (dolphins 
and small and large toothed whales) species, six mysticete (baleen 
whales) species, two pinniped species, and the West Indian manatee. Six 
of the species that may occur in the project area are listed under the 
U.S. Endangered Species Act (ESA) as Endangered: The sperm, humpback, 
sei, fin, and blue whale and the manatee. The West Indian manatee is 
under the jurisdiction of the U.S. Fish and Wildlife Service and 
therefore is not considered further in this analysis.

[[Page 71629]]

    The distribution and occurrence of marine mammal species are 
different on the Pacific and Caribbean coasts of Central America; 
therefore, these two areas are discussed separately here and in greater 
detail in L-DEO's application. Thirty-two species of marine mammals 
have been documented to occur in Costa Rican waters, most of which are 
cetaceans (Rodr[iacute]guez-Herrera et al., 2002). At least 10 of the 
32 species are known to occur on the Caribbean side, including the 
manatee (Rodr[iacute]guez-Fonseca, 2001 and pers. comm.; 
Rodr[iacute]guez-Herrera et al., 2002). Twenty-seven species are known 
to occur on the Pacific side of Costa Rica, including the California 
and Gal[aacute]pagos sea lions (see Wade and Gerrodette, 1993; Ferguson 
and Barlow, 2001; Rodr[iacute]guez-Fonseca, 2001; Rodr[iacute]guez-
Herrera et al., 2002; Rasmussen et al., 2004; Holst et al., 2005a; May-
Collado et al., 2005). In addition there are two other species that 
could potentially occur in the Pacific study area: the ginkgo-toothed 
(e.g., Rodr[iacute]guez-Fonseca, 2001) and Longman's beaked whales 
(e.g., Pitman et al., 1999; Ferguson and Barlow, 2001). Information on 
the occurrence, distribution, population size, and conservation status 
for each of the 34 marine mammal species that may occur in the proposed 
project area is presented in Table 5 of L-DEO's application.

Caribbean

    Studies of marine mammals inhabiting the Caribbean have been scarce 
(Jefferson and Lynn, 1994; Rodr[iacute]guez-Fonseca, 2001), and 
abundance in this area is mostly unknown (Roden and Mullin, 2000). At 
least one systematic ship-based study employing visual and passive-
acoustic survey methods has been undertaken in the eastern Caribbean 
(Swartz and Burks, 2000; Swartz et al., 2001, 2003). In addition, an 
extensive visual and acoustic survey was conducted in the SE Caribbean 
Sea off northern Venezuela from the Ewing and the R/V Seward Johnson II 
as part of a marine mammal monitoring program during an L-DEO marine 
seismic cruise in April-June 2004 (Smultea et al., 2004). Data on the 
western Caribbean is even more limited.
    One mysticete, eight odontocetes, and one sirenian are known to 
occur in the Caribbean study area (Rodr[iacute]guez-Fonseca, 2001 and 
pers. comm.; Rodr[iacute]guez-Herrera et al., 2002). These include the 
fin, sperm, short-finned pilot, and killer whale; the bottlenose, 
Atlantic spotted, and clymene dolphin; tucuxi, Gervais' beaked whale, 
and West Indian manatee. The last four of these species only occur in 
the Caribbean part of the study area (see Table 5 of the application). 
Based on other available information (Swartz and Burks, 2000; Romero et 
al., 2001; Swartz et al., 2001, 2003; Smultea et al., 2004), an 
additional five species may potentially occur in the study area: two 
mysticetes (humpback and Bryde's whale) and three delphinids 
(pantropical spotted, striped, and rough-toothed dolphin). Pinnipeds 
are unlikely to be seen in the Caribbean part of the study area. 
Vagrant hooded seals have been seen in the Caribbean (Rice, 1998; 
Mignucci-Giannoni and Odell, 2001; Reeves et al., 2002), but are not 
considered further here. The Caribbean monk seal (Monachus tropicalis) 
is considered extinct (Debrot, 2000; Mignucci-Giannoni and Odell, 
2001).

Pacific

    Of the 36 marine mammal species known to occur in the eastern 
tropical Pacific (ETP), 29 may occur in the proposed survey area off 
the west coast of Costa Rica and Nicaragua (see Table 5 of the 
application). Seven species that are present in the wider ETP but not 
in the proposed survey area are excluded from Table 5. They include: 
Pacific white-sided dolphin (Lagenorhynchus obliquidens) and Baird's 
beaked whale (Berardius bairdii), which are seen very occasionally (6 
and 2 sightings, respectively, in several years of surveys) in the 
northernmost portions of the ETP (Ferguson and Barlow, 2001); Long-
beaked common dolphin (Delphinus capensis), which is known to occur in 
the northernmost areas of the ETP off Baja California, Mexico, and off 
the coast of Peru (Heyning and Perrin, 1994); Dusky dolphin 
(Lagenorhynchus obscurus), southern right whale dolphin (Lissodelphis 
peronii), Burmeister's porpoise (Phocoena spinipinnis), and long-finned 
pilot whale (Globicephala melas) occur near the Peruvian coast but are 
unlikely to occur in the present study area (Leatherwood et al., 1991; 
Van Waerebeek et al., 1991; Brownell and Clapham, 1999; Olson and 
Reilly, 2002).
    Although unlikely, two of the six species of pinnipeds known to 
occur in the ETP could potentially occur in the proposed project area 
on rare occasions. These include the California and Gal[aacute]pagos 
sea lions, which have been documented off western Costa Rica (Acevedo-
Gutierrez, 1994; Cubero-Parado and Rodr[iacute]guez, 1999; 
Rodr[iacute]guez-Herrera et al., 2002; May-Collado, 2006, in press). 
The remaining four pinniped species known from the ETP, the Guadalupe 
fur seal (Arctocephalus townsendi), South American fur seal (A. 
australis), southern sea lion (Otaria flavescens), and Gal[aacute]pagos 
fur seal, are not expected to occur in the survey area because their 
known ranges are substantially farther north or south of the proposed 
seismic survey area (Reeves et al., 2002).
    Most cetacean research off the west coast of Central America has 
involved three of the most common, coastal resident species: The 
bottlenose and coastal pantropical spotted dolphin and humpback whale 
(May-Collado et al., 2005). The remaining marine mammal populations in 
the region have not been studied in much detail. The most extensive 
regional distribution and abundance data that encompass the entire 
study area come primarily from multi-year vessel surveys conducted in 
the wider ETP by the NMFS Southwest Fisheries Science Center.
    Table 5 of L-DEO's application summarizes the abundance, habitat, 
and conservation status of all marine mammal species considered likely 
to occur in the proposed survey area in the Pacific. Based on a 
compilation of data from 1979 to 2001, many cetaceans within the 
Pacific EEZ of Costa Rica occur in both oceanic and coastal waters. 
However, beaked, sperm, dwarf/pygmy sperm, and baleen whales (except 
for the humpback) occur predominantly in oceanic waters (May-Collado et 
al., 2005). Bottlenose and pantropical spotted dolphins, as well as the 
humpback whale, tend to be coastal.
    The proposed survey area in the Pacific is part of the ``Central 
American Bight'', which extends from Guatemala to Ecuador. Costa Rican 
waters in particular are one of the most biologically productive 
regions of the world (Philbrick et al., 2001; Rodr[iacute]guez-Herrera 
et al., 2002; May-Collado et al., 2005; Ferguson et al., 2006a). The 
characteristics that likely make this region so productive are linked 
to the thermal structure of the water column, including a shallow 
thermocline (see Fielder and Talley, 2006). Two regions within the ETP 
that are considered to be important to certain species of cetaceans 
include the Costa Rica Dome (CRD) and the countercurrent thermocline 
ridge at approximately 10[deg] N. (see Au and Perryman, 1985; Reilly, 
1990; Reilly and Thayer, 1990; Fielder, 2002; Ballance et al., 2006).
    At least five marine areas are considered ecologically important 
for different marine mammals off western Costa Rica, including areas 
near the proposed transect lines (Acevedo and Burkhart, 1998; 
Rodr[iacute]guez-Fonseca, 2001; May-Collado et al., 2005; Ferguson et 
al., 2006a). From north to south, the five areas are as follows: Gulf 
of Papagayo; Punta Guiones to Cabo

[[Page 71630]]

Blanco, southern Nicoya Peninsula; CRD; Quepos-Manuel Antonio National 
Park region; and Isla del Ca[ntilde]o, Golfo Dulce, and Osa Peninsula. 
Marine mammal species inhabiting these five areas, as well as their 
seasonal use of the habitats, are described in the species accounts in 
L-DEO's application.
    Table 2 below outlines the species, their habitat and abundance in 
the proposed project area, and the requested take levels. Additional 
information regarding the distribution of these species expected to be 
found in the project area and how the estimated densities were 
calculated may be found in L-DEO's application.

Table 2.--The Habitat, Abundance, and Requested Take Levels of Marine Mammals That May Be Encountered During the
                      Proposed Central American SubFac Seismic Survey Off Central America.
----------------------------------------------------------------------------------------------------------------
                                                   Abun. in NW                     Rqstd take in   Rqstd take in
           Species                  Habitat       Atlantic \1\   Abun. in ETP\2\    Carib. Sea          ETP
----------------------------------------------------------------------------------------------------------------
Odontocetes:
    Sperm whale (C,P)          Pelagic.........       \a\13,190  26,053 \b\.....               5             239
     (Physeter macrocephalus).                            4,804
    Pygmy sperm whale (C*,P)   Deeper water off         \c\ 395  N.A............               0               0
     (Kogia breviceps).         shelf.
    Dwarf sperm whale (C*,P)   Deeper waters            \c\ 395  11,200 \d\.....               0             856
     (Kogia sima).              off shelf.
    Cuvier's beaked whale      Pelagic.........       \e\ 3,513  20,000.........               0             302
     (C*,P) (Ziphius                                             90,725 \bb\....
     cavirostris).
    Longman's beaked whale     Pelagic.........            N.A.  291 \bb\.......               0               9
     (P?) (Indopacetus
     pacificus).
    Pygmy beaked whale (P)     Pelagic.........            N.A.  25,300 \f\.....               0               0
     (Mesoplodon peruvianus).                                    32,678\cc\.....
    Gingko-toothed beaked      Pelagic.........            N.A.  25,300 \f\.....               0               0
     whale (P?) (Mesoplodon                                      32,678\cc\.....
     ginkgodens).
    Gervais' beaked whale      Pelagic.........            N.A.  N.A............               4               0
     (C?) (Mesoplodon
     europaeus).
    Blainville's beaked whale  Pelagic.........            N.A.  25,300 \f\.....               0              29
     (C*,P) (Mesoplodon                                          32,678\cc\.....
     densirostris).
    Rough-toothed dolphin      Mainly pelagic..       \g\ 2,223  145,900........               9             954
     (C?,P) (Steno
     bredanensis).
    Tucuxi (C) (Sotalia        Freshwater and            \h\ 49  N.A............               0               0
     fluviatilis).              coastal waters.          \i\705
    Bottlenose dolphin (C,P)   Coastal, shelf         \j\43,951  243,500........             389           2,380
     (Tursiops truncatus).      and pelagic.         \k\ 81,588
    Pantropical spotted        Coastal and                4,439  2,059,100......              37           7,560
     dolphin (C?,P) (Stenella   pelagic.
     attenuata).
    Atlantic spotted dolphin   Coastal and               50,978  N.A............             440               0
     (C) (Stenella frontalis).  shelf.
    Spinner dolphin (C*,P)     Coastal and            \g\11,971  1,651,100......               0           7,856
     (Stenella longirostris).   pelagic.
    Costa Rican spinner        Coastal.........            N.A.  N.A............               0           3,358
     dolphin (P) (Stenella l.
     centroamericana).
    Clymene dolphin (C?)       Pelagic.........           6,086  N.A............              29               0
     (Stenella clymene).
    Striped dolphin (C*,P)     Coastal and               94,462  1,918,000......              31           8,110
     (Stenella coeruleoalba).   pelagic.
    Short-beaked common        Shelf and                   N.A.  3,093,300......               0          14,045
     dolphin (P) (Delphinus     pelagic.
     delphis).
    Fraser's dolphin (C*,P)    Pelagic.........         \g\ 726  289,300........               0             144
     (Lagenodelphis hosei).
    Risso's dolphin (C*,P)     Shelf and                 20,479  175,800........               0             651
     (Grampus griseus).         pelagic.
    Melon-headed whale (C*,P)  Pelagic.........       \g\ 3,451  45,400.........               0           1,315
     (Peponocephala electra).
    Pygmy killer whale (C*,P)  Pelagic.........           \l\ 6  38,900.........               0             231
     (Feresa attenuata).                                \g\ 408
    False killer whale (C*,P)  Pelagic.........       \g\ 1,038  39,800.........               0             479
     (Pseudorca crassidens).
    Killer whale (C,P)         Coastal.........         \g\ 133  8,500..........              10              17
     (Orcinus orca).                                   \m\6,600
    Short-finned pilot whale   Pelagic.........      \n\ 31,139  160,200 \n\....              36           3,717
     (C,P) (Globicephala
     macrorhynchus).
Mysticetes:
    Humpback whale (C?,P)      Mainly nearshore      \o\ 10,400  NE Pacific                    3             101
     (Megaptera novaeangliae).  waters and            \p\11,570   1,391\q\;.
                                banks.                           SE Pacific
                                                                  2,900\r\.
    Minke whale (C*,P)         Coastal.........       \s\ 3,618  N.A............               0               0
     (Balaenoptera                                   \t\174,000
     acutorostrata).
    Bryde's whale (C?,P)       Coastal and               \g\ 35  13,000 \u\.....               3              68
     (Balaenoptera edeni).      pelagic.
    Sei whale (C*,P)           Pelagic.........             12-  N.A............               0               0
     (Balaenoptera borealis).                        \v\ 13,000

[[Page 71631]]

 
    Fin whale (C,P)            Pelagic.........           2,814  1,851\q\.......               2               0
     (Balaenoptera physalus).                        \t\ 30,000
    Blue whale (C*,P)          Coastal, shelf,          \w\ 320  1,400..........               0              15
     (Balaenoptera musculus).   and pelagic.
Sirenian:
    West Indian manatee (C)    Freshwater and            \x\ 86  N.A............               0               0
     (Trichechus manatus        coastal waters.         \y\ 340
     manatus).
Pinnipeds:
    California sea lion (P)    Coastal.........            N.A.  237,000-.......               0               0
     (Zalophus californianus).                                   244,000 \z\....
    Gal[aacute]pagos sea lion  Coastal.........            N.A.  30,000 \aa\....               0              0
     (P?) (Zalophus
     wollebaeki).
----------------------------------------------------------------------------------------------------------------
Note: Abun. = abundance, NWA = Northwest Alantic Ocean, P = may occur off Pacific coast of proposed project
  area, C = may occur off Caribbean coast of proposed project area, * = very unlikely to occur in proposed
  project area, ? = potentially possible but somewhat unlikely to occur in proposed project area, N.A. = Not
  available or not applicable.
\1\ For cetaceans, abundance estimates are given for U.S. Western North Atlantic stocks (Waring et al. 2006)
  unless otherwise noted.
\2\ Abundance estimates for the ETP from Wade and Gerrodette (1993) unless otherwise indicated.
\a\ g(o) corrected total estimate for the Northeast Atlantic, Faroes-Iceland, and the U.S. east coast (Whitehead
  2002).
\b\ Whitehead 2002.
\c\ This estimate is for Kogia sp.
\d\ This abundance estimate is mostly for K. sima but may also include some K. breviceps.
\e\ This estimate is for Mesoplodon and Ziphius spp.
\f\ This estimate includes all species of the genus Mesoplodon from Wade and Gerrodette (1993).
\g\ This estimate is for the northern Gulf of Mexico.
\h\ Estimate from a portion of Cayos Miskito Reserve, Nicaragua (Edwards and Schnell 2001).
\i\ Estimate from the Canan[eacute]ia estuarine region of Brazil (Geise et al. 1999).
\j\ Estimate for the Western North Atlantic coastal stocks (North Carolina (summer), South Carolina, Georgia,
  Northern Florida, and Central Florida).
\k\ Estimate for the for the Western North Atlantic offshore stock.
\l\ Based on a single sighting.
\m\ Estimate for Icelandic and Faroese waters (Reyes 1991).
\n\ This estimate is for G. macrorhynchus and G. melas.
\o\ Estimate for the entire North Atlantic (Smith et al. 1999).
\p\ This estimate is for the entire North Atlantic (Stevick et al. 2001, 2003).
\q\ Carretta et al. 2007.
\r\ Felix et al. 2005.
\s\ This estimate is for the Canadian East Coast stock.
\t\ Estimate is for the North Atlantic (IWC 2007a).
\u\ This estimate is mainly for Balaenoptera edeni but may include some B. borealis.
\v\ Abundance estimate for the North Atlantic (Cattanach et al. 1993).
\w\ Minimum abundance estimate (Sears et al. 1990).
\x\ Antillean Stock in Puerto Rico only.
\y\ Antillean Stock in Belize (Reeves et al. 2002).
\z\ Estimate for the U.S. stock (Carretta et al. 2007).
\aa\ Reeves et al. 2002.
\bb\ Ferguson and Barlow 2001 in Barlow et al. 2006.
\cc\ This estimate includes all species of the genus Mesoplodon (Ferguson and Barlow 2001 in Barlow et al.
  2006).

Potential Effects on Marine Mammals

Potential Effects of Airguns

    The effects of sounds from airguns might include one or more of the 
following: tolerance, masking of natural sounds, behavioral 
disturbances, and at least in theory, temporary or permanent hearing 
impairment, or non-auditory physical or physiological effects 
(Richardson et al., 1995; Gordon et al., 2004; Nowacek et al., 2007). 
However, it is unlikely that there would be any cases of temporary or 
especially permanent hearing impairment or any significant non-auditory 
physical or physiological effects. Also, behavioral disturbance is 
expected to be limited to relatively short distances.

Tolerance

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

Masking

    Obscuring of sounds of interest by interfering sounds, generally at 
similar frequencies, is known as masking. Masking effects of pulsed 
sounds (even from large arrays of airguns) on marine mammal calls and 
other natural sounds are expected to be limited, although there are few 
specific data of relevance. Some whales are known to continue calling 
in the presence of seismic pulses. The airgun sounds are pulsed, with 
quiet periods between the pulses,

[[Page 71632]]

and whale calls often can be heard between the seismic pulses 
(Richardson et al., 1986; McDonald et al., 1995; Greene et al., 1999; 
Nieukirk et al., 2004; Smultea et al., 2004). 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 more recent study 
reports that sperm whales off northern Norway continued calling in the 
presence of seismic pulses (Madsen et al., 2002). That has also been 
shown during recent work in the Gulf of Mexico and Caribbean Sea 
(Smultea et al., 2004; Tyack et al., 2006). Masking effects of seismic 
pulses are expected to be negligible in the case of the small 
odontocetes given the intermittent nature of seismic pulses. Dolphins 
and porpoises commonly are heard calling while airguns are operating 
(Gordon et al., 2004; Smultea et al., 2004; Holst et al., 2005a,b). 
Also, the sounds important to small odontocetes are predominantly at 
much higher frequencies than the airgun sounds. Masking effects, in 
general, are discussed further in Appendix C (d) of L-DEO's 
application.

Disturbance Reactions

    Disturbance includes a variety of effects, including subtle changes 
in behavior, more conspicuous changes in activities, and displacement. 
Reactions to sound, if any, depend on species, state of maturity, 
experience, current activity, reproductive state, time of day, and many 
other factors. If a marine mammal responds to an underwater sound by 
changing its behavior or moving a small distance, the response may or 
may not rise to the level of harassment, let alone affect the stock or 
the species as a whole. Alternatively, if a sound source displaces 
marine mammals from an important feeding or breeding area, effects on 
the stock or species could potentially be more than negligible. Given 
the many uncertainties in predicting the quantity and types of impacts 
of noise on marine mammals, it is common practice to estimate how many 
mammals are likely to be present within a particular distance of 
industrial activities, or exposed to a particular level of industrial 
sound. This practice potentially 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. 
However, information is lacking for many species. Detailed studies have 
been done on humpback, gray, and bowhead whales and ringed seals. Less 
detailed data are available for some other species of baleen whales, 
sperm whales, small toothed whales, and sea otters.
    Baleen Whales--Baleen whales generally tend to avoid operating 
airguns, but avoidance radii are quite variable. Whales are often 
reported to show no overt reactions to pulses from large arrays of 
airguns at distances beyond a few kilometers, even though the airgun 
pulses remain well above ambient noise levels out to much longer 
distances. However, as reviewed in Appendix C (e) of L-DEO's 
application, baleen whales exposed to strong noise pulses from airguns 
often react by deviating from their normal migration route and/or 
interrupting their feeding activities and moving away from the sound 
source. In the case of the migrating gray and bowhead whales, the 
observed changes in behavior appeared to be of little or no biological 
consequence to the animals. They simply avoided the sound source by 
displacing their migration route to varying degrees, but within the 
natural boundaries of the migration corridors.
    Studies of gray, bowhead, and humpback whales have determined that 
received levels of pulses in the 160-170 dB re 1 [mu]Pa rms range seem 
to cause obvious avoidance behavior in a substantial fraction of the 
animals exposed. In many areas, seismic pulses from large arrays of 
airguns diminish to those levels at distances ranging from 4.5-14.5 km 
(2.8-9 mi) from the source. A substantial proportion of the baleen 
whales within those distances may show avoidance or other strong 
disturbance reactions to the airgun array. Subtle behavioral changes 
sometimes become evident at somewhat lower received levels, and recent 
studies, reviewed in Appendix C (e) of L-DEO's application, have shown 
that some species of baleen whales, notably bowheads and humpbacks, at 
times show strong avoidance at received levels lower than 160-170 dB re 
1 [mu]Pa rms.
    Responses of humpback whales to seismic surveys have been studied 
during migration and on the summer feeding grounds, and there has also 
been discussion of effects on the Brazilian wintering grounds. McCauley 
et al. (1998, 2000) studied the responses of humpback whales off 
Western Australia to a full-scale seismic survey with a 16-airgun, 
2,678-in\3\ array, and to a single 20-in\3\ airgun with a source level 
of 227 dB re 1 [mu]Pa m. McCauley et al. (1998) documented that 
avoidance reactions began at 5-8 km (3.1-5 mi) from the array, and that 
those reactions kept most pods approximately 3-4 km (1.9-2.5 mi) from 
the operating seismic boat. McCauley et al. (2000) noted localized 
displacement during migration of 4-5 km (2.5-3.1 mi) by traveling pods 
and 7-12 km (4.3-7.5 mi) by cow-calf pairs. Avoidance distances with 
respect to the single airgun were smaller but consistent with the 
results from the full array in terms of received sound levels. Mean 
avoidance distance from the airgun corresponded to a received sound 
level of 140 dB re 1 [mu]Pa (rms); that was the level at which 
humpbacks started to show avoidance reactions to an approaching airgun. 
The standoff range, i.e., the closest point of approach of the whales 
to the airgun, corresponded to a received level of 143 dB re 1 [mu]Pa 
(rms). The initial avoidance response generally occurred at distances 
of 5-8 km (3.1-5 mi) from the airgun array and 2 km (1.2 mi) from the 
single airgun. However, some individual humpback whales, especially 
males, approached within distances of 100-400 m (328-1,312 ft), where 
the maximum received level was 179 dB re 1 [mu]Pa (rms).
    Humpback whales summering in southeast Alaska did not exhibit 
persistent avoidance when exposed to seismic pulses from a 1.64-L (100 
in\3\) airgun (Malme et al., 1985). Some humpbacks seemed ``startled'' 
at received levels of 150-169 dB re 1 [mu]Pa on an approximate rms 
basis. Malme et al. (1985) concluded that there was no clear evidence 
of avoidance, despite the possibility of subtle effects, at received 
levels up to 172 re 1 [mu]Pa (approximately rms).
    Results from bowhead whales show that responsiveness of baleen 
whales to seismic surveys can be quite variable depending on the 
activity (migrating vs. feeding) of the whales. Bowhead whales 
migrating west across the Alaskan Beaufort Sea in autumn, in 
particular, are unusually responsive, with substantial avoidance 
occurring out to distances of 20-30 km (12.4-18.6 mi) from a medium-
sized airgun source, where received sound levels were on the order of 
130 dB re 1 [mu]Pa (rms) (Miller et al., 1999; Richardson et al., 
1999). However, more recent research on bowhead whales (Miller et al., 
2005a) corroborates earlier evidence that, during the summer feeding 
season, bowheads are not as sensitive to seismic sources. In summer, 
bowheads typically begin to show avoidance reactions at a received 
level of about 160-170 dB re 1 [mu]Pa (rms) (Richardson et al., 1986; 
Ljungblad et al., 1988; Miller et al., 1999). There are not data on 
reactions of wintering bowhead whales to seismic surveys. See Appendix 
C (e) of L-DEO's

[[Page 71633]]

application for more information regarding bowhead whale reactions to 
airguns.
    Malme et al. (1986, 1988) studied the responses of feeding Eastern 
Pacific gray whales to pulses from a single 100 in\3\ airgun off St. 
Lawrence Island in the northern Bering Sea. Malme et al. (1986, 1988) 
estimated, based on small sample sizes, that 50 percent of feeding gray 
whales ceased feeding at an average received pressure level of 173 dB 
re 1 [mu]Pa on an (approximate) rms basis, and that 10 percent of 
feeding whales interrupted feeding at received levels of 163 dB. Those 
findings were generally consistent with the results of experiments 
conducted on larger numbers of gray whales that were migrating along 
the California coast and on observations of Western Pacific gray whales 
feeding off Sakhalin Island, Russia (Johnson, 2002).
    We are not aware of any information on reactions of Bryde's whales 
to seismic surveys. However, other species of Balaenoptera (blue, sei, 
fin, and minke whales) have occasionally been reported in areas 
ensonified by airgun pulses. Sightings by observers on seismic vessels 
off the United Kingdom from 1997 to 2000 suggest that, at times of good 
sightability, numbers of rorquals seen are similar when airguns are 
shooting and not shooting (Stone, 2003). Although individual species 
did not show any significant displacement in relation to seismic 
activity, all baleen whales combined were found to remain significantly 
further from the airguns during shooting compared with periods without 
shooting (Stone, 2003; Stone and Tasker, 2006). In a study off Nova 
Scotia, Moulton and Miller (in press) found only a little or no 
difference in sighting rates and initial sighting distances of 
balaenopterid whales when airguns were operating vs. silent. However, 
there were indications that these whales were more likely to be moving 
away when seen during airgun operations.
    Data on short-term reactions (or lack of reactions) of cetaceans to 
impulsive noises do not necessarily provide information about long-term 
effects. It is not known whether impulsive noises affect reproductive 
rate or distribution and habitat use in subsequent days or years. 
However, gray whales continued to migrate annually along the west coast 
of North America despite intermittent seismic exploration and much ship 
traffic in that area for decades (see Appendix A in Malme et al., 
1984). The western Pacific gray whale population did not seem affected 
by a seismic survey in its feeding ground during a prior year (Johnson 
et al., 2007). Bowhead whales continued to travel to the eastern 
Beaufort Sea each summer despite seismic exploration in their summer 
and autumn range for many years (Richardson et al., 1987). In any 
event, brief exposures to sound pulses from the proposed airgun source 
are highly unlikely to result in prolonged effects.
    Toothed Whales--Little systematic information is available about 
reactions of toothed whales to noise pulses. Few studies similar to the 
more extensive baleen whale/seismic pulse work summarized above have 
been reported for toothed whales. Controlled exposure experiments on 
sperm whales took place in the Gulf of Mexico in 2002 and 2003 (see 
Miller et al., 2006; Tyack et al., 2006), and there is an increasing 
amount of information about responses of various odontocetes to seismic 
surveys based on monitoring studies (Stone, 2003; Smultea et al., 2004; 
Bain and Williams, 2006; Holst et al., 2006; Moulton and Miller, in 
press).
    Seismic operators sometimes see dolphins and other small toothed 
whales near operating airgun arrays, but in general there seems to be a 
tendency for most delphinids to show some limited avoidance of seismic 
vessels operating large airgun systems. However, some dolphins seem to 
be attracted to the seismic vessel and floats, and some ride the bow 
wave of the seismic vessel even when large airgun arrays are firing. 
Nonetheless, there have been indications that small toothed whales 
sometimes tend to head away or to maintain a somewhat greater distance 
from the vessel, when a large array of airguns is operating than when 
it is silent (Goold, 1996a,b,c; Calambokidis and Osmek, 1998; Stone, 
2003; Stone and Tasker, 2003). In most cases, the avoidance radii for 
delphinids appear to be small, on the order of 1 km (0.62 mi) or less. 
The beluga may be a species that (at least at times) shows long-
distance avoidance of seismic vessels. Aerial surveys during seismic 
operations in the southeastern Beaufort Sea recorded much lower 
sighting rates of beluga whales within 10-20 km (6.2-12.4 mi) of an 
active seismic vessel. These results were consistent with the low 
number of beluga sightings reported by observers aboard the seismic 
vessel, suggesting that some belugas might be avoiding the seismic 
operations at distances of 10-20 km (6.2-12.4 mi) (Miller et al., 
2005a). No other odontocete is known to show avoidance at such 
distances.
    Captive bottlenose dolphins and beluga whales exhibit changes in 
behavior when exposed to strong pulsed sounds similar in duration to 
those typically used in seismic surveys (Finneran et al., 2000, 2002, 
2005; Finneran and Schlundt, 2004). The animals tolerated high received 
levels of sound (pk-pk level >200 dB re 1 [mu]Pa) before exhibiting 
aversive behaviors. For pooled data at 3, 10, and 20 kHz, sound 
exposure levels during sessions with 25, 50, and 75 percent altered 
behavior were 180, 190, and 199 dB re 1 [mu]Pa\2\, respectively 
(Finneran and Schlundt, 2004).
    Results for porpoises depend on species. Dall's porpoises seem 
relatively tolerant of airgun operations (MacLean and Koski, 2005; Bain 
and Williams, 2006), whereas the limited available data suggest that 
harbor porpoises show stronger avoidance (Stone, 2003; Bain and 
Williams, 2006). This apparent difference in responsiveness of these 
two porpoise species is consistent with their relative responsiveness 
to boat traffic in general (Richardson et al., 1995).
    Sperm whales show considerable tolerance of airgun pulses. In most 
cases, the whales do not show strong avoidance and continue to call 
(see Appendix C of L-DEO's application). However, controlled exposure 
experiments in the Gulf of Mexico indicate that foraging effort is 
somewhat reduced upon exposure to airgun pulses from a seismic vessel 
operating in the area, and there may be a delay in diving to foraging 
depth (Miller et al. 2006; Tyack et al., 2006).
    There are no specific data on the behavioral reactions of beaked 
whales to seismic surveys. Most beaked whales tend to avoid approaching 
vessels of other types (W[uuml]rsig et al., 1998). They may also dive 
for an extended period when approached by a vessel (Kasuya, 1986). It 
is likely that these beaked whales would normally show strong avoidance 
of an approaching seismic vessel, but this has not been documented 
explicitly.
    Odontocete reactions to large arrays of airguns are variable and, 
at least for delphinids and some porpoises, seem to be confined to a 
smaller radius than has been observed for mysticetes (Appendix C of L-
DEO's application).
    Pinnipeds--Pinnipeds are not likely to show a strong avoidance 
reaction to the airgun sources that will be used. Visual monitoring 
from seismic vessels, usually employing larger sources, has shown only 
slight (if any) avoidance of airguns by pinnipeds, and only slight (if 
any) changes in behavior (see Appendix C (e) of L-DEO's application). 
Ringed seals frequently do not avoid the area within a few hundred 
meters of operating airgun arrays (Harris et al., 2001; Moulton and 
Lawson, 2002;

[[Page 71634]]

Miller et al., 2005a). However, initial telemetry work suggests that 
avoidance and other behavioral reactions by two other species of seals 
to small airgun sources may at times be stronger than evident to date 
from visual studies of pinniped reactions to airguns (Thompson et al., 
1998). Even if reactions of any pinnipeds that might be encountered in 
the present study area are as strong as those evident in the telemetry 
study, reactions are expected to be confined to relatively small 
distances and durations, with no long-term effects on pinniped 
individuals or populations. It should be noted that pinnipeds are not 
likely to be encountered often, if at all, during the present study.
    Additional details on the behavioral reactions (or the lack 
thereof) by all types of marine mammals to seismic vessels can be found 
in Appendix C (e) of L-DEO's application.

Hearing Impairment and Other Physical Effects

    Temporary or permanent hearing impairment is a possibility when 
marine mammals are exposed to very strong sounds, but there has been no 
specific documentation of this for marine mammals exposed to sequences 
of 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 of 180 and 190 dB re 1 [mu]Pa (rms), 
respectively. Those criteria have been used in defining the safety 
(shut-down) radii planned for the proposed seismic survey. The 
precautionary nature of these criteria is discussed in Appendix C (f) 
of L-DEO's application, including the fact that 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) and the level 
associated with the onset of TTS is often considered to be a level 
below which there is no danger of permanent damage. NMFS is presently 
developing new noise exposure criteria for marine mammals that take 
account of the now-available scientific data on TTS, the expected 
offset between the TTS and permanent threshold shift (PTS) thresholds, 
differences in the acoustic frequencies to which different marine 
mammal groups are sensitive, and other relevant factors.
    Several aspects of the planned monitoring and mitigation measures 
for this project (see below) are designed to detect marine mammals 
occurring near the airguns to avoid exposing them to sound pulses that 
might, at least in theory, cause hearing impairment. In addition, many 
cetaceans are likely to show some avoidance of the area with high 
received levels of airgun sound (see above). In those cases, the 
avoidance responses of the animals themselves will reduce or (most 
likely) avoid any possibility of hearing impairment.
    Non-auditory physical effects may also occur in marine mammals 
exposed to strong underwater pulsed sound. Possible types of non-
auditory physiological effects or injuries that theoretically might 
occur in mammals close to a strong sound source include stress, 
neurological effects, bubble formation, resonance effects, and other 
types of organ or tissue damage. It is possible that some marine mammal 
species (i.e., beaked whales) may be especially susceptible to injury 
and/or stranding when exposed to strong pulsed sounds. However, as 
discussed below, there is no definitive evidence that any of these 
effects occur even for marine mammals in close proximity to large 
arrays of airguns. It is especially unlikely that any effects of these 
types would occur during the present project given the brief duration 
of exposure of any given mammal and the planned monitoring and 
mitigation measures (see below). The following subsections discuss in 
somewhat more detail the possibilities of TTS, PTS, and non-auditory 
physical effects.
    Temporary Threshold Shift--TTS is the mildest form of hearing 
impairment that can occur during exposure to a strong sound (Kryter, 
1985). While experiencing TTS, the hearing threshold rises and a sound 
must be stronger in order to be heard. At least in terrestrial mammals, 
TTS can last from minutes or hours to (in cases of strong TTS) days. 
For sound exposures at or somewhat above the TTS threshold, hearing 
sensitivity in both terrestrial and marine mammals recovers rapidly 
after exposure to the noise ends. Few data on sound levels and 
durations necessary to elicit mild TTS have been obtained for marine 
mammals, and none of the published data concern TTS elicited by 
exposure to multiple pulses of sound.
    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, 2005). Given the 
available data, the received level of a single seismic pulse (with no 
frequency weighting) might need to be approximately 186 dB re 1 
[mu]Pa\2\[middot]s (i.e., 186 dB SEL or approximately 221-226 dB pk-pk) 
in order to produce brief, mild TTS. Exposure to several strong seismic 
pulses that each have received levels near 175-180 dB SEL 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. 
The distance from the Langseth's airguns at which the received energy 
level (per pulse) would be expected to be >=175-180 dB SEL are the 
distances shown in the 190 dB re 1 [mu]Pa (rms) column in Table 3 of L-
DEO's application and Table 1 above (given that the rms level is 
approximately 10-15 dB higher than the SEL value for the same pulse). 
Seismic pulses with received energy levels >=175-180 dB SEL (190 dB re 
1 [mu]Pa (rms)) are expected to be restricted to radii no more than 
140-200 m (459-656 ft) around the airguns. The specific radius depends 
on the number of airguns, the depth of the water, and the tow depth of 
the airgun array. For an odontocete closer to the surface, the maximum 
radius with >=175-180 dB SEL or >=190 dB re 1 [mu]Pa (rms) would be 
smaller.
    For baleen whales, direct or indirect data do not exist on levels 
or properties of sound that are required to induce TTS. The frequencies 
to which baleen whales are most sensiti