Incidental Takes of Marine Mammals During Specified Activities; Seismic Testing and Calibration in the Northern Gulf of Mexico, Fall 2006, 58790-58804 [E6-16412]
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Federal Register / Vol. 71, No. 193 / Thursday, October 5, 2006 / Notices
nominee’s qualifications and interest in
serving on the Committee. Selfnominations are acceptable. The
following contact information should
accompany each nominee’s submission:
name, address, phone number, fax
number, and e-mail address (if
available).
Nominations should be sent to (see
ADDRESSES) and must be received by
(see DATES). The full text of the
Committee Charter and its current
membership can be viewed at the
NMFS’s web page at
www.nmfs.noaa.gov/mafac.htm.
Dated: October 2, 2006.
William T. Hogarth,
Assistant Administrator for Fisheries,
National Marine Fisheries Service.
[FR Doc. E6–16486 Filed 10–4–06; 8:45 am]
BILLING CODE 3510–22–S
DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric
Administration
[I.D. 090706B]
Incidental Takes of Marine Mammals
During Specified Activities; Seismic
Testing and Calibration in the Northern
Gulf of Mexico, Fall 2006
National Marine Fisheries
Service (NMFS), National Oceanic and
Atmospheric Administration (NOAA),
Commerce.
ACTION: Notice; proposed incidental take
authorization; request for comments.
mstockstill on PROD1PC61 with NOTICES
AGENCY:
SUMMARY: NMFS has received an
application from the Lamont-Doherty
Earth Observatory (L-DEO) for an
Incidental Harassment Authorization
(IHA) to take small numbers of marine
mammals, by harassment, incidental to
conducting an acoustic calibration and
seismic testing program in the northern
Gulf of Mexico in Fall, 2006. Under the
Marine Mammal Protection Act
(MMPA), NMFS is requesting comments
on its proposed IHA for these activities.
DATES: Comments and information must
be received no later than November 6,
2006.
ADDRESSES: Comments on the
application should be addressed to
Michael Payne, Chief, Permits,
Conservation and Education Division,
Office of Protected Resources, National
Marine Fisheries Service, 1315 EastWest Highway, Silver Spring, MD
20910–3225. The mailbox address for
providing email comments is
PR1.090706B@noaa.gov. NMFS is not
responsible for e-mail comments sent to
addresses other than the one provided
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here. Comments sent via e-mail,
including all attachments, must not
exceed a 10–megabyte file size.
A copy of the application containing
a list of the references used in this
document may be obtained by writing to
the address specified above, telephoning
the contact listed below (see FOR
FURTHER INFORMATION CONTACT), or
visiting the internet at: https://
www.nmfs.noaa.gov/pr/permits/
incidental.htm.
Documents cited in this notice may be
viewed, by appointment, during regular
business hours, at the aforementioned
address.
FOR FURTHER INFORMATION CONTACT: Jolie
Harrison, Office of Protected Resources,
NMFS, (301) 713–2289, ext 166.
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,
and that 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,
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but not limited to, migration, breathing,
nursing, breeding, feeding, or sheltering
[Level B harassment].
Section 101(a)(5)(D) establishes a 45–
day time limit for NMFS review of an
application followed by a 30–day public
notice and comment period on any
proposed authorizations for the
incidental harassment of marine
mammals. Within 45 days of the close
of the comment period, NMFS must
either issue or deny issuance of the
authorization.
Summary of Request
On June 2, 2006, NMFS received an
application from L-DEO for the taking,
by Level B harassment, of several
species of marine mammals incidental
to conducting, with research funding
from the National Science Foundation
(NSF), an acoustic calibration and
seismic testing program in the northern
Gulf of Mexico in Fall, 2006. This
project will be conducted with L-DEO’s
new seismic vessel, the R/V Marcus G.
Langseth (Langseth), which will deploy
different configurations of airguns and a
different bottom-mapping sonar than
used previously by L-DEO. L-DEO
requests that it be issued an IHA
allowing Level B Harassment takes of
marine mammals incidental to the
planned seismic surveys in the Gulf of
Mexico.
The primary purpose of the
calibration program is to obtain
measurement data to better understand
the sound fields around various
configurations of the 36–airgun array
and the GI guns, during seismic
operations in different water depths.
The data will be used to verify and
refine model-based estimates of ‘‘safety
radii’’ for different configurations of the
36–airgun array and the GI guns that
will be used during future seismic
surveys to be conducted by L-DEO.
Such data are important to better define
the distances within which mitigation
may be necessary in order to avoid
exposing marine mammals to received
sound levels above those believed to
have adverse effects, as well as to
develop a better general understanding
of the impact of man-made acoustic
sources on marine mammals.
Description of the Specified Activity
The Langseth is expected to depart
Mobile, AL in late October 2006 (at the
earliest) and will transit to the survey
area in the northern Gulf of Mexico. The
survey will encompass an area between
24oN. and 31oN. and between 83°W.
and 96°W., which is within the
Exclusive Economic Zone (EEZ) of the
U.S.A. The proposed study will consist
of three phases: (1) an initial testing/
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shakedown phase, (2) measurements of
the sounds produced by various airgun
arrays to be used by the Langseth
(calibration), and (3) a threedimensional (3D) seismic testing phase.
The entire survey, calibration and
testing included, will take
approximately 25 days and include
approximately 1420 km (174 hours) of
airgun operation. Measurements will be
made during seismic operations in three
categories of water depth: shallow (<100
m or <328 ft), intermediate/slope (100–
1000 m or 328–3281 ft), and deep
(>1000 m or >3281 ft). The vessel will
transit to Miami after the study is
completed. The exact dates of the
activities will depend on logistics and
weather conditions.
Vessel Specifications
The Langseth is owned by NSF and
operated by L-DEO. The Langseth will
tow the airgun array and, at times, up
to four 6–km (3.7–mi) streamers
containing hydrophones along
predetermined lines. The Langseth will
also deploy a floating spar buoy and a
bottom-moored hydrophone array.
The Langseth has a length of 71.5 m
(235 ft), a beam of 17.0 m (56 ft), and
a maximum draft of 5.9 m (19 ft). The
gross tonnage is 2925 and the Langseth
can accommodate 55 people. The ship
is powered by two Bergen BRG–6
engines each producing 3550 hp; 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 (13,500 nm).
Given the presence of the airgun array
(and at times streamer(s)) behind the
vessel, the turning rate of the ship while
the gear is deployed is limited to five
degrees per minute. Thus, the
maneuverability of the vessel is limited
during operations.
Acoustic Source Specifications
Airguns
The full airgun array on the Langseth
consists of 36 airguns, with a total
discharge volume of 6600 in3. The array
is made up of four identical linear
arrays or strings, with 10 airguns on
each string. For each operating string,
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nine airguns 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
calibration phase will use the full 36–
airgun array and subsets thereof. The
subsets will consist of either 1 string (9
airguns, 1650 in3) or 2 strings (18
airguns, 3300 in3). In addition, sounds
from a single 45 in3 GI gun and 2 GI
guns (210 in3) will be measured. During
the seismic testing phase, the 2–string
array will be used at most times,
although the full 36–airgun array may
also be used.
The 36–airgun array will consist of a
mixture of Bolt 1500LL and 1900LLX
airguns, ranging in size from 40 to 360
in3. The airguns will fire for a brief (0.1
s) pulse every 30 s and will be silent
during the intervening periods. The
airgun array will be towed
approximately 50–100 m (164–328 ft)
behind the seismic vessel at a depth of
6–12 m (20–39 ft). The dominant
frequency component is 0–188 Hz.
The specifications of each source
planned for use are described in Table
1.
1 GI Gun
2 GI Guns
1 Single Airgun
9-Airgun Array
(1 String)
18-Airgun Array
(2 Strings)
36-Airgun Array
(4 Strings)
One 45 in3 GI
Airgun
Two 105 in3 GI
Airguns
One 2000 psi
Bolt Airgun
Nine 2000 psi
Bolt Airguns of
40-360 in3
Eighteen 2000
psi Bolt Airguns
of 40-360 in3
Thirty-six 2000
psi Bolt Airguns
of 40-360 in3
Air Discharge Volume (in3)
45 in3
210 in3
40 in3
1650 in3
3300 in3
6600 in3
Towing Depth of Source
2.5m
3m
6m
6m
6m
6m or 12m
225.3 (230.7)
237 (243)
246 (253)
252 (259)
259 (265)
10km
10km
34km
34km
34km
34km
34km≤
34km
45km
45km
45km
Airgun Specifications
Energy Source
Source Output (dB re 1 miPa
m) 0-pk (pk.pk)*
Proposed Approximate Airgun Use
Calibration Phase
Shallow Site (30-60m)
Intermediate/Slope Site
(475m)
Deep Site (1500m)
10km
10km
Testing Phase
89km
24km
175km
58km
Intermediate/Slope (1001000 m)
89km
24km
175km
58km
Deep (>1000 m)
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Shallow Site (<100m)
89km
24km
175km
58km
Table 1. L-DEO airgun configurations and proposed approximate use for each configuration by depth and phase.
* The root mean square values (typically discussed in biological literature) for these sources will generally be about 10-15 dB lower than those
reflected here
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Federal Register / Vol. 71, No. 193 / Thursday, October 5, 2006 / Notices
Multibeam Sonar
The ocean floor will be mapped with
the 12–kHz Simrad EM120 MBB sonar.
This sonar will be operated from the
Langseth simultaneous with the airgun
array during the seismic testing
program, but will likely be operated on
its own during the acoustic calibration
study. The Simrad EM120 operates at
11.25–12.6 kHz and will be hullmounted on the Langseth. The
beamwidth is 1° fore-aft and 150°
athwartship. The maximum source level
is 242 dB re 1 µPa. The pressure level
is expected to drop to 180 dB at a
distance of 1 km or 0.5 nm (this distance
is the maximum estimate for on-axis
and with no defocusing); pressure level
does not vary with water depth. Each
‘‘ping’’ consists of nine successive fanshaped transmissions, each ensonifying
a sector that extends 1° fore-aft and 16°
in the cross-track direction. The
transmission length varies with water
depth; each of the nine transmissions is
approximately 2 ms in shallow water, 5
ms at intermediate water depths, and 15
ms in deep water. The nine successive
transmissions span an overall crosstrack angular extent of about 150°, with
16 ms gaps between the pulses for
successive sectors. A receiver in the
overlap area between two sectors would
receive two pulses separated by a 16–ms
gap. The ‘‘ping’’ interval varies with
water depth and ranges from 0.2 s in
really shallow water, to approximately 5
s at 1000 m (3281 ft) and 20 s at 4000
m (13,124 ft).
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Airgun Operations
Acoustic Calibration Study
Location of Sites – L-DEO will work
together with Texas A&M University to
choose the exact study sites at the three
depths, however, the approximate
locations are indicated in Figure 1 of LDEO’s application. Site locations will
depend on currents, surface ducts, and
concentrations of marine mammals.
Sites will be chosen to avoid high
currents with large vertical shear, as
were encountered during the 2003
study. Conductivity/Temperature/Depth
(CTDs) and Expendable
Bathythermograph (XBTs)
measurements will be taken at each site
to confirm local water column
properties. Near-surface ducts may play
a significant role in the propagation of
sound, so a deep site with and without
a surface duct will be surveyed if
practical. Areas with concentrations of
marine mammals will be avoided.
L-DEO proposes to start with the
shallow site, where the instrument
redundancy will allow some flexibility
in gain settings to ensure that signals
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will not be clipped. This information
will be used to optimize gain settings at
the slope and deep sites. The water
depths at the three different depth sites
are expected to be 30–60 m (98–197 ft)
at the shallow site, approximately 475 m
(1,558 ft) at the intermediate/slope site,
and approximately1500 m (4922 ft) at
the deep site. This phase of the study
will take approximately 14 days.
Acoustic Measurements – The 2006
program is designed to document the
received levels of the airgun sounds,
relative to distance, during operation of
the Langseth’s 36–airgun 4–string array
and subsets thereof, and up to 2 GI guns.
During the calibration study, three
configurations (1, 2, and 4 strings in
equal amounts) of the 36–airgun array
will be measured in three different
water depths (deep, intermediate/slope,
and shallow). A single and two GI guns
will be measured in deep and shallow
water only. Measurements will be made
at varying distances from the guns using
suitable electronics installed in the spar
buoy and a bottom-moored hydrophone
array. In addition, one 6–km (3.7–mi)
long hydrophone streamer will be used
at times for calibrations of shallowwater safety radii. The hydrophones
will be deployed and retrieved by the
Langseth.
At each of the three sites, the
Langseth, towing various configurations
of the 36–airgun array at a depth of 6 m
(20 ft), will travel toward the spar buoy
and/or moored hydrophone array from a
distance of approximately10–15 km
(5.4–8.1 nm) away and will pass over
the receiving system. The Langseth will
then continue out to a distance of
approximately 10–15 km beyond the
hydrophones. The approximate 15 km
distance will be used at the shallow and
slope sites (total line length of 30 km or
16 nm), and the approximate 10 km
distance will be used at the deep-water
site (total line length of 20 km or 11
nm). Longer lines are planned at the
shallow and slope sites than at the deep
site because in 2003, received sound
levels diminished below 160 dB re 1
µPa (rms) well within 10 km at the deep
site, but not at the shallow site (Tolstoy
et al., 2004a,b). After completing the
straight line, the airgun array will then
be towed in a spiral fashion towards the
hydrophones in order to measure
received levels as a function of distance
when the receiving hydrophones are to
the side of the trackline. The spirals are
designed such that the radius will
decrease linearly with time.
At each site, the Langseth will make
one straight line pass over the receiving
hydrophones with the 36–airgun array,
followed by the spiral pattern towards
the hydrophones. At the deep site, two
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additional 20–km (11–nm) straight lines
will be shot, for a total of three 20–km
straight lines at that site: (a) with the
airgun array at 6 m (20 ft) tow depth, (b)
with the array at a tow depth of 12 m
(39 ft), and (c) in waters with/without a
surface duct [whichever was not the
case in (a) and (b)]. In addition, two 10–
km (5.4–nm) straight line passes will be
made at the deep as well as the shallowwater sites; one pass at each site will be
made with a single GI gun, and one pass
will be made using 2 GI guns.
The total number of kilometers and
hours of airgun shooting during the
calibration phase of the project are
indicated in Table 1. However,
operations at each site will require
approximately 36 hours, allowing for
the time needed to deploy and recover
the hydrophones as well as the time to
shoot the survey. Although the lines
will be longer for the slope and shallow
sites, the deep site is likely to take the
longest, because of the increased drop
and surfacing time for the instruments
plus the plans to shoot three 20 km (11
nm) lines.
Airguns will fire every 30 s, and
operations are proposed to occur 24
hours per day to maximize effective and
economic use of the limited ship time
and to maximize the amount of
calibration data collected. Operating
airguns over 24–hour periods will also
reduce the overall duration of airgun
operations at each site, thus reducing
the span of time when marine mammals
in those areas will be exposed to airgun
sounds.
Systematic Testing Phase
The exact site of the seismic testing
phase has not yet been chosen, but is
planned to range from shallow
(approximately 30 m or 98 ft) to deep
(>1000 m or 3281 ft) water and will fall
within the general area described
earlier. During the testing phase, the
Langseth will deploy the 2–string 18–
airgun array (and at times the 36–airgun
array) as an energy source; a single 40
in3 airgun will be fired during turns.
The Langseth will also deploy a
receiving system consisting of up to four
6–km (3.7–mi) towed hydrophone
streamers. There will be 200 m (656 ft)
separation between adjacent pairs of the
four streamers. As the airgun array is
towed along the survey lines, the
receiving system will receive the
returning acoustic signals and transfer
the data to the on-board processing
system. The airgun array will be towed
at a depth of 9 m (30 ft).
The testing phase will consist of a
series of tracklines in a racetrack-type
configuration. This racetrack will
consist of 17 loops, with a total of 35
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Federal Register / Vol. 71, No. 193 / Thursday, October 5, 2006 / Notices
tracklines. Each trackline will be
approximately 20 km (10.8 nm) long, for
a total of approximately 700 km (378
nm) of shooting along tracklines. The
spacing between adjacent tracklines will
be 400 m (1312 ft). An additional 10 km
(5.4 nm) of seismic will be shot during
each turn between lines and during the
ensuing run-in (the distance from the
end of the turn to the start of the line
during which the airgun array will be
ramped up). In total, this will account
for an additional 340 km (183 nm). Of
this 340 km, approximately 73 km (39.4
nm) will consist of ramp ups, and 267
km (144.2 nm) will be shot with a 40 in3
airgun during turns. These numbers are
also presented in Table 1.
In total, 1040 km (562 nm) of seismic
will be shot. The seismic testing
program will take approximately 4 to 7
days.
Characteristics of Airgun Pulses
Discussion of the characteristics of
airgun pulses has been provided in
Appendix B of L-DEO’s application and
in previous Federal Register notices
(see 69 FR 31792 (June 7, 2004) or 69
FR 34996 (June 23, 2004)). Reviewers
are referred to those documents for
additional information.
Safety Radii
To aid in determining at what point
during exposure to seismic airguns (and
other acoustic sources) marine
mammals are harassed, pursuant to the
MMPA, and in developing effective
mitigation measures, NMFS applies
certain acoustic thresholds. The
distance from the sound source at which
an animal would be exposed to these
different received sound levels may be
estimated and is typically referred to as
a safety radii. These safety radii are
specifically used to help NMFS estimate
the number of marine mammals likely
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to be harassed by the proposed activity
and in deciding how close a marine
mammal may approach an operating
sound source before the applicant will
be required to power-down or shut
down the sound source.
L-DEO has estimated the safety radii
around their proposed operations using
a model, but also by adjusting the model
results based on empirical data gathered
in the Gulf of Mexico in 2003.
Additional information regarding how
the safety radii were calculated and how
the empirical measurements were used
to correct the modeled numbers may be
found in Section I and Appendix A of
L-DEO’s application. Using the modeled
distances and various correction factors,
Table 2 shows the distances at which
three rms sound levels (190 dB, 180 dB,
and 160 dB) are expected to be received
from the various airgun configurations
in shallow, intermediate, and deep
water depths.
Predicted RMS Radii (m)
Source and Volume
Tow Depth (m)
Water Depth
190 dB
25
236
Intermediate/Slope
13.5
38
354
Shallow
113
185
645
20
69
670
Intermediate/Slope
30
104
1005
Shallow
294
511
1970
Deep
12
36
360
Intermediate/Slope
18
54
540
Shallow
150
267
983
Deep
200
650
6200
Intermediate/Slope
300
975
7880
Shallow
1450
2360
8590
Deep
250
820
6700
Intermediate/Slope
375
1230
7370
Shallow
1820
3190
8930
Deep
410
1320
8000
Intermediate/Slope
615
1980
8800
Shallow
2980
5130
10670
Deep
620
1980
12000
Intermediate/Slope
930
2970
13200
Shallow
4500
7700
16000
in3
2 GI guns
3
in3
210
Single Bolt
40
9
Deep
45
2.5
160 dB
Deep
Single GI gun
180 dB
6
in3
1 string
9 airguns
1650
6
in3
2 strings/ENT≤
18 airguns
3300
6
in3
4 strings
36 airguns
6600
6
in3
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4 strings
36 airguns
6600
12
in3
Table 2. Modeled distances towhich sound levels 190,180, and 160 dB re 1uPa (rms) might be received in shallow (>100 m), intermediate/
slope (100-1000 m), and deep (<1000 m) water from the various sources planned for use during the Gulf of Mexico study, fall 2006.
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Federal Register / Vol. 71, No. 193 / Thursday, October 5, 2006 / Notices
Description of Marine Mammals in the
Activity Area
In the Gulf of Mexico, 28 cetacean
species and one species of manatee are
known to occur (Jefferson and Schiro,
1997; Wursig et al., 2000; Table 3). In
the U.S., manatees are managed by the
U.S. Fish & Wildlife Service (USFWS),
are unlikely to be encountered in or
near the open waters of the Gulf of
Mexico where seismic operations will
occur, and are, therefore, not addressed
further in this document. Most of these
species of cetaceans occur in oceanic
waters (>200 m or 656 ft deep) of the
Gulf, whereas the continental shelf
waters (<200 m) are primarily inhabited
by bottlenose dolphins and Atlantic
spotted dolphins (Mullin and Fulling
2004).
BEST
MAXIMUM
Habitat
Occurrence
in GOM
Abundance in
GOM and/or
North Atlantic
Estimated
Exposures
Approx. %
of Population
Est. Exposures Prop.
IHA**
Approx. %
of Population
Usually pelagic and
deep seas
Common
1349/13190 (add)
22
0.2
27
0.2
Pygmy sperm whale
Deeper waters off the
shelf
Common
742/695 (add)
56
3.9
Dwarf sperm whale
Deeper waters off the
shelf
Common
Cuvier’s beaked whale
Pelagic
Rare
159/3196 (add)
10
0.3
21
0.7
Sowerby’s beaked whale
Pelagic
Extralimital
5
0.8
8
1.2
Gervais’ beaked whale
Pelagic
Uncommon
5
0.8
8
1.2
Blainville’s beaked whale
Pelagic
Rare
5
0.8
8
1.2
Mostly pelagic
Common
2223/274 (add)
58
2.3
92
3.7
Cont. shelf, coastal and
offshore
Common
25,320/2239/
29774 (add)
773
1.3
1713
5.0
Pantropical spotted dolphin
Mainly pelagic
Common
91,321/13117
(add)
1282
1.2
1587
1.5
Atlantic spotted dolphin
Mainly coastal waters
Common
30,947/52279
(add)
876
1.1
1755
0.2
Spinner dolphin
Pelagic in Gulf of Mexico
Common
11,971
168
1.4
921
7.7
Clymene dolphin
Pelagic
Common
17,355/6086
(add)
244
1.0
311
1.3
Stripped dolphin
Off the continental
shelf
Common
6505/61546 (add)
91
0.1
134
0.2
Short-beaked common
dolphin
Cont. shelf and pelagic
waters
Possible
30,768
0
0.0
0(5)**
<0.1
Long-beaked common
dolphin
Coastal
Possible
N.A.
0
0.0
0(5)**
0.0
Praser’s dolphin
Water>l000m
Common
726
10
1.4
60
8.3
Risso’s dolphin
Waters 400-1000 m
Common
2169/29110 (add)
54
0.2
81
0.3
Mellon-headed whale
Oceanic
Common
3451
49
1.4
142
4.1
Pygmy killer whale
Oceanic
Uncommon
408
10
2.6
21
5.1
False killer whale
Pelagic
Uncommon
1038
14
1.4
28
2.7
Widely distributed
Uncommon
133/6600 (add)
3
<0.1
5
0.1
Short-finned pilot whale
Mostly pelagic
Common
2388/780000/
14524
34
<0.1
98
<0.1
Long-finned pilot whale
Mostly pelagic
Possible
N.A.
0
Species
Odontocetes
Sperm whale
Rough-toothed dolphin
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Bottlenose dolphin
Killer whale
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BEST
MAXIMUM
Habitat
Occurrence
in GOM
Abundance in
GOM and/or
North Atlantic
Estimated
Exposures
North Atlantic right
whale*
Coastal and shelf waters
Extralimital
291
0
0
Humpback whale*
Mainly near-shore waters/banks
Rare
11,570/10400
0
0
Minke whale
Coastal waters
Rare
149,000
0
0
Bryde’s whale
Pelagic and coastal
Uncommon
40/90000
1
Sei whale*
Primarily offshore, pelagic
Rare
12-13,000
0
0
Fin whale*
Cont. slope, mostly pelagic
Rare
2814/47300
0
0
Blue whale*
Coastal, shelf, and
oceanic waters
Extralimital
308
0
0
Coastal
Vagrant
400,000z
0
0(2)**
3770
7096
Species
Approx. %
of Population
Est. Exposures Prop.
IHA**
Approx. %
of Population
Mysticetes
2.5
2
5.0
Pinnipeds
Hooded seal
Total
<0.1
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Table 3. Abundance, preferred habitat, and commonness of the marine mammal species found in the survey area. The far right columns indicate the estimated number each species that will be exposed to 160 dB based on best and maximum density estimates. NMFS believes that,
when mitigation measures are taken into consideration, the activity is likely to result in take of numbers of animals less than those indicated by
the best column, however, L-DEO has asked for authorization of the maximum.
*Federally listed endangered,
** Parenthetical number indicates take authorization, though exposure estimate is 0
Seven species that may occur in the
Gulf of Mexico are listed as endangered
under provisions of the U.S. Endangered
Species Act (ESA), including the sperm,
North Atlantic right, humpback, sei, fin,
and blue whale, as well as the West
Indian manatee. However, of those
species, only sperm whales are likely to
be encountered. In addition to the 28
species known to occur in the Gulf of
Mexico, another three species of
cetaceans could potentially occur there:
the long-finned pilot whale, the longbeaked common dolphin, and the shortbeaked common dolphin (Table 3).
Though any pinnipeds sighted in the
study area would be extralimital,
hooded seals have been reported in
Florida and L-DEO has requested
authorization for the take of 2 animals.
During the 2003 acoustical calibration
study in the Gulf of Mexico from 28
May to 2 June, a total of seven visual
sightings of marine mammals were
documented from the Maurice Ewing;
these included a total of approximately
38–40 individuals (LGL Ltd. 2003). In
addition, three sea turtles were sighted.
These totals include times when airguns
were not operating as well as times
when airguns were firing. Visual
monitoring effort consisted of 60.9
hours of observations (all in daylight)
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along 891.5 km of vessel trackline on
seven days, and passive acoustic
monitoring (PAM) occurred for
approximately 32 hours. Most of the
monitoring effort (visual as well as
acoustic) occurred when airguns were
not operating, since airgun operations
were limited during the 2003 study. No
marine mammals were detected during
acoustic monitoring. Marine mammal
and sea turtle sightings and locations
during the 2003 calibration study are
summarized in Appendix C of L-DEOs
application.
Detailed information regarding the
status and distribution of these marine
mammals may be found in sections III
and IV of L-DEOs application.
Potential Effects of the Proposed
Activity on Marine Mammals
Summary of Potential Effects of Airgun
Sounds on Marine Mammals
The effects of sounds from airguns
might include one or more of the
following: tolerance, masking of natural
sounds, behavioral disturbance, and at
least in theory, temporary or permanent
hearing impairment, or non-auditory
physical or physiological effects
(Richardson et al., 1995). These effects
are discussed below, but also in further
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detail in Appendix B of L-DEO’s
application.
The potential effects of airguns
discussed below are presented without
consideration of the mitigation
measures that L-DEO has presented and
that will be required by NMFS. When
these measures are taken into account,
it is unlikely that this project would
result in temporary, or especially,
permanent hearing impairment or any
significant non-auditory physical or
physiological effects.
Tolerance
Numerous studies have shown that
pulsed sounds from airguns are often
readily detectable in the water at
distances of many kilometers. A
summary of the characteristics of airgun
pulses is provided in Appendix B of LDEO’s application. Studies have also
shown that marine mammals at
distances more than a few kilometers
from operating seismic vessels often
show no apparent response (tolerance)
(Appendix B (e)). That is often true even
in cases when the pulsed sounds must
be readily audible to the animals based
on measured received levels and the
hearing sensitivity of that mammal
group. Although various baleen whales,
toothed whales, and (less frequently)
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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, small odontocetes, and sea
otters seem to be more tolerant of
exposure to airgun pulses than are
baleen whales. Pinnipeds and sea otters
are not found in the Gulf of Mexico;
small odontocetes of numerous species
are the predominant marine mammals
in the area.
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Masking
Masking effects of pulsed sounds
(even from large arrays of airguns) on
marine mammal calls and other natural
sounds are expected to be limited,
although there are very few specific data
of relevance. Some whales are known to
continue calling in the presence of
seismic pulses. Their calls can be heard
between the seismic pulses (e.g.,
Richardson et al., 1986; McDonald et al.,
1995; Greene et al., 1999; Nieukirk et
al., 2004). Although there has been one
report that sperm whales 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 (Tyack et al.,
2003). 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. Also, the sounds important to
small odontocetes are predominantly at
much higher frequencies than are airgun
sounds. Masking effects, in general, are
discussed further in Appendix B (d).
Disturbance Reactions
Disturbance includes a variety of
effects, including subtle changes in
behavior, more conspicuous changes in
activities, and displacement. Simple
exposure to sound, or brief reactions
that do not disrupt behavioral patterns
in a potentially significant manner, do
not constitute harassment or ‘‘taking’’.
By potentially significant, we mean ‘‘in
a manner that might have deleterious
effects to the well-being of individual
marine mammals or their populations’’.
Reactions to sound, if any, depend on
species, state of maturity, experience,
current activity, reproductive state, time
of day, and many other factors. If a
marine mammal does react briefly to an
underwater sound by minorly changing
its behavior or moving a small distance,
the impacts of the change are unlikely
to be significant to the individual, let
alone the stock or the species as a
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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.
There are many uncertainties in
predicting the quantity and types of
impacts of noise on marine mammals.
As mentioned earlier in this document,
NMFS applies acoustic criteria
developed to help estimate the number
of animals likely to be harassed by a
particular sound source in a given area
and for use in the development of
shutdown zones for mitigation. The
sound criteria used to estimate how
many marine mammals might be
disturbed to some biologicallyimportant 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 on 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. There is no specific
information about reactions of Bryde’s
whales-the baleen whales most likely to
be encountered in the Gulf of Mexicoto seismic pulses. 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, baleen
whales exposed to strong noise pulses
from airguns often react by deviating
from their normal migration route and/
or interrupting their feeding and moving
away. 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 µPa 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 to 14.5 km (2.4–7.8 nm) from the
source. A substantial proportion of the
baleen whales within those distances
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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
have shown that some species of baleen
whales, notably bowhead and
humpback whales, at times show strong
avoidance at received levels lower than
160–170 dB re 1 µPa rms. Bowhead
whales migrating west across the
Alaskan Beaufort Sea in autumn, in
particular, are unusually responsive.
Substantial avoidance occurred out to
distances of 20–30 km (11–16 nm) from
a medium-sized airgun source, where
received sound levels were on the order
of 130 dB re 1 µPa rms (Miller et al.,
1999; Richardson et al., 1999; see
Appendix B (e)). More recent research
on bowhead whales (Miller et al., 2005),
however, suggests that during the
summer feeding season, bowheads are
not nearly as sensitive to seismic
sources, with onset of avoidance at the
more typical level of 160–170 dB re 1
µPa rms.
Malme et al., (1986, 1988) studied the
responses of feeding eastern gray whales
to pulses from a single 100 in3 airgun
off St. Lawrence Island in the northern
Bering Sea. They 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 µPa 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.
Blue, sei, fin, and minke whales have
occasionally been reported in areas
ensonified by airgun pulses. Sightings
by observers on seismic vessels off the
U.K. 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).
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
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traffic in that area for decades
(Appendix A in Malme et al., 1984).
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).
Populations of both gray and bowhead
whales grew substantially during this
time. In any event, the 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 and in Appendix B have been
reported for toothed whales. However,
systematic work on sperm whales is
underway (Tyack et al., 2003), and there
is an increasing amount of information
about responses of various odontocetes
to seismic surveys based on monitoring
studies (e.g., Stone, 2003; Haley and
Koski, 2004; Smultea et al., 2004; Holst
et al., 2005a,b; MacLean and Koski,
2005).
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
arrays of airguns are firing. Nonetheless,
there have been indications that small
toothed whales sometimes move away,
or maintain a somewhat greater distance
from the vessel, when a large array of
airguns is operating than when it is
silent (e.g., Goold, 1996a,b,c;
Calambokidis and Osmek, 1998; Stone,
2003). In most cases the avoidance radii
for delphinids appear to be small, on the
order of 1 km (0.5 nm) or less. However,
aerial surveys during seismic operations
in the southeastern Beaufort Sea
recorded much lower sighting rates of
beluga whales within 10–20 km (5–11
nm) 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 (Miller et al.,
2005).
Captive bottlenose dolphins and
beluga whales exhibit changes in
behavior when exposed to strong pulsed
sounds similar in duration to those
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typically used in seismic surveys
(Finneran et al., 2000, 2002; Finneran
and Schlundt 2004). The animals
tolerated high received levels of sound
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 µPa2 .
s, respectively (Finneran and Schlundt,
2004).
Pinnipeds
No pinnipeds are expected to be
encountered in the Gulf of Mexico, and
thus it is most likely that none will be
affected by the proposed activity. At
most, up to two extralimital hooded
seals might be encountered and
potentially be behaviorally disturbed or
have a low-level physiological response
to the seismic exposure.
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 exposed to impulsive
sounds of 180 and 190 dB re 1 µPa (rms)
or above, respectively, are considered to
have been incidentally taken by Level A
Harassment. These levels are
precautionary.
Several aspects of the planned
monitoring and mitigation measures for
this project are designed to detect
marine mammals occurring near the
airguns, and to avoid exposing them to
sound pulses that could potentially
cause hearing impairment. In addition,
many cetaceans are likely to show some
avoidance of the area with high received
levels of airgun sound. In those cases,
the avoidance responses of the animals
themselves will reduce or (most likely)
avoid any possibility of hearing
impairment.
Non-auditory physical effects might
also occur in marine mammals exposed
to strong underwater pulsed sound.
Possible types of non-auditory
physiological effects or injuries that
theoretically might occur in mammals
close to a strong sound source include
stress, neurological effects, bubble
formation, and other types of organ or
tissue damage. It is possible that some
marine mammal species (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
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58797
evidence that any of these effects occur
even for marine mammals in close
proximity to large arrays of airguns. It is
unlikely that any effects of these types
would occur during the 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, permanent
threshold shift (PTS), and non-auditory
physical effects.
Temporary Threshold Shift (TTS)
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.
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
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).
Sound exposure level (SEL), which
takes into account the duration of the
sound, is the metric used to measure
energy and uses the units dB re 1 µPa2
. s, as opposed to sound pressure level
(SPL), which is the pressure metric used
in the rest of this document (units - dB
re 1 µPa). Given the available data, the
received energy level of a single seismic
pulse might need to be approximately
186 dB re 1 µPa2 . 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 at 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 distances from the
Langseth’s airguns at which the received
energy level would be expected to be
175 dB SEL are the distances shown in
the 190 dB rms column in Table 2
(given that the rms level is
approximately 15 dB higher than the
SEL value for the same pulse). In deep
water, where L DEO’s model is directly
applicable, seismic pulses with received
energy levels 175 dB SEL (190 dB rms)
are expected to be restricted to radii no
more than 200–620 m (656–2034 ft)
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around the airguns. The specific radius
would depend on number of operating
airguns (9–36) and their operating depth
(6 vs. 12 m). The depth associated with
the above radii ranges from about 125 m
(410 ft) for a 9–airgun array to =500 m
(=1640 ft) for the 36–airgun array. For
an odontocete closer to the surface, the
maximum radius with 175 dB SEL or
190 dB rms would be smaller. In
intermediate-depth and shallow water,
the 175 dB SEL or 190 dB rms radius
would be larger.
For baleen whales, there are no data,
direct or indirect, on levels or properties
of sound that are required to induce
TTS. However, no cases of TTS are
expected given two considerations: (1)
the low abundance of baleen whales in
the planned study area, and (2) the
strong likelihood that baleen whales
would avoid the approaching airguns
(or vessel) before being exposed to
levels high enough for there to be any
possibility of TTS.
In pinnipeds, TTS thresholds
associated with exposure to brief pulses
(single or multiple) of underwater sound
have not been measured. Initial
evidence from prolonged exposures
suggested that some pinnipeds may
incur TTS at somewhat lower received
levels than do small odontocetes
exposed for similar durations (Kastak et
al., 1999; Ketten et al., 2001; cf. Au et
al., 2000). However, pinnipeds are not
expected to occur in or near the planned
study area.
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, whereas in other cases,
the animal has an impaired ability to
hear sounds in specific frequency
ranges.
There is no specific evidence that
exposure to pulses of airgun sound can
cause PTS in any marine mammal, even
with large arrays of airguns. However,
given the possibility that mammals
close to an airgun array might incur
TTS, there has been further speculation
about the possibility that some
individuals occurring very close to
airguns might incur PTS. Single or
occasional occurrences of mild TTS are
not indicative of permanent auditory
damage in terrestrial mammals.
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. PTS might occur at
a received sound level at least several
decibels above that inducing mild TTS
if the animal were exposed to strong
sound pulses with rapid rise.
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Given the higher level of sound
necessary to cause PTS as compared
with TTS, it is even less likely that PTS
could occur. In fact, even the levels
immediately adjacent to the airguns may
not be sufficient to induce PTS,
especially because a mammal would not
be exposed to more than one strong
pulse unless it swam immediately
alongside the airgun for a period longer
than the inter-pulse interval. Baleen
whales generally avoid the immediate
area around operating seismic vessels.
The planned monitoring and mitigation
measures, including visual monitoring,
PAM, power-downs, and shut downs of
the airguns when mammals are seen
within the ‘‘safety radii’’, will minimize
the probability of exposure of marine
mammals to sounds strong enough to
induce PTS.
Non-auditory Physiological Effects
Non-auditory physiological effects or
injuries that theoretically might occur in
marine mammals exposed to strong
underwater sound include stress,
neurological effects, bubble formation,
and other types of organ or tissue
damage. However, studies examining
such effects are very limited. If any such
effects do occur, they probably would be
limited to unusual situations when
animals might be exposed at close range
for unusually long periods. It is doubtful
that any single marine mammal would
be exposed to strong seismic sounds for
sufficiently long that significant
physiological stress would develop.
Until recently, it was assumed that
diving marine mammals are not subject
to the bends or air embolism. This
possibility was first explored at a
workshop (Gentry [ed.] 2002) held to
discuss whether the stranding of beaked
whales in the Bahamas in 2000
(Balcomb and Claridge 2001; NOAA and
USN 2001) might have been related to
bubble formation in tissues caused by
exposure to noise from naval sonar.
However, the opinions were
inconclusive. Jepson et al. (2003) first
suggested a possible link between midfrequency sonar activity and acute and
chronic tissue damage that results from
the formation in vivo of gas bubbles,
based on the beaked whale stranding in
the Canary Islands in 2002 during naval
exercises. Fernandez et al. (2005a)
showed those beaked whales did indeed
have gas bubble-associated lesions as
well as fat embolisms. Fernandez et al.
(2005b) also found evidence of fat
embolism in three beaked whales that
stranded 100 km (54 nm) north of the
Canaries in 2004 during naval exercises.
Examinations of several other stranded
species have also revealed evidence of
gas and fat embolisms (e.g., Arbelo et
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al., 2005; Jepson et al., 2005a; Mendez
et al., 2005). Most of the afflicted
species were deep divers. There is
speculation that gas and fat embolisms
may occur if cetaceans ascend
unusually quickly when exposed to
aversive sounds, or if sound in the
environment causes the destabilization
of existing bubble nuclei (Potter, 2004;
Arbelo et al., 2005; Fernandez et al.,
2005a; Jepson et al., 2005b). Even if gas
and fat embolisms can occur during
exposure to mid-frequency sonar, there
is no evidence that that type of effect
occurs in response to airgun sounds.
In general, 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
short distances and probably to projects
involving large arrays of airguns.
However, the available data do not
allow for meaningful quantitative
predictions of the numbers (if any) of
marine mammals that might be affected
in those ways. Marine mammals that
show behavioral avoidance of seismic
vessels, including most baleen whales
and some odontocetes, are especially
unlikely to incur auditory impairment
or other physical effects. Also, the
planned monitoring and mitigation
measures include shut downs of the
airguns, which will reduce any such
effects that might otherwise occur.
Strandings and Mortality
Marine mammals close to underwater
detonations of high explosive can be
killed or severely injured, and the
auditory organs are especially
susceptible to injury (Ketten et al., 1993;
Ketten, 1995). Airgun pulses are less
energetic and have slower rise times,
and there is no proof that they can cause
serious injury, death, or stranding even
in the case of large airgun arrays.
However, the association of mass
strandings of beaked whales with naval
exercises and, in one case, an L-DEO
seismic survey, has raised the
possibility that beaked whales exposed
to strong pulsed sounds may be
especially susceptible to injury and/or
behavioral reactions that can lead to
stranding.
Seismic pulses and mid-frequency
sonar pulses are quite different. Sounds
produced by airgun arrays are
broadband with most of the energy
below 1 kHz. Typical military midfrequency sonars operate at frequencies
of 2–10 kHz, generally with a relatively
narrow bandwidth at any one time.
Thus, it is not appropriate to assume
that there is a direct connection between
the effects of military sonar and seismic
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surveys on marine mammals. However,
evidence that sonar pulses can, in
special circumstances, lead to physical
damage and mortality (NOAA and USN
2001; Jepson et al., 2003; Fernandez et
al., 2005a), even if only indirectly,
suggests that caution is warranted when
dealing with exposure of marine
mammals to any high-intensity pulsed
sound.
In May 1996, 12 Cuvier’s beaked
whales stranded along the coasts of
Kyparissiakos Gulf in the Mediterranean
Sea. That stranding was subsequently
linked to the use of low- and mediumfrequency active sonar by a North
Atlantic Treaty Organization (NATO)
research vessel in the region (Frantzis
1998). In March 2000, a population of
Cuvier’s beaked whales being studied in
the Bahamas disappeared after a U.S.
Navy task force using mid-frequency
tactical sonars passed through the area;
some beaked whales stranded (Balcomb
and Claridge, 2001; NOAA and USN
2001). In September 2002, a total of 14
beaked whales of various species
stranded coincident with naval
exercises in the Canary Islands (Martel
n.d.; Jepson et al., 2003; Fernandez et
al., 2004). Some additional related
incidents have also been reported, e.g.,
Southall et al. (2006).
Also in Sept. 2002, there was a
stranding of two Cuvier’s beaked whales
in the Gulf of California, Mexico, when
the L-DEO vessel Maurice Ewing was
operating a 20 airgun, 8490 in3 airgun
array in the general area. The link
between the stranding and the seismic
surveys was inconclusive and not based
on any physical evidence (Hogarth,
2002; Yoder, 2002). Nonetheless, that
plus the incidents involving beaked
whale strandings near naval exercises
suggests a need for caution in
conducting seismic surveys in areas
occupied by beaked whales. No injuries
of beaked whales are anticipated during
the proposed study, due to the proposed
monitoring and mitigation measures.
Possible Effects of Multibeam
Bathymetric (MBB) Sonar Signals
The Simrad EM120 12–kHz sonar will
be operated from the source vessel at
some times during the planned study.
Sounds from the MBB sonar are very
short pulses, occurring for 15 ms once
every 5 to 20 s, depending on water
depth. Most of the energy in the sound
pulses emitted by this MBB sonar is at
frequencies centered at 12 kHz. The
beam is narrow (1°) in fore-aft extent
and wide (150°) in the cross-track
extent. Each ping consists of nine
successive fan-shaped transmissions
(segments) at different cross-track
angles. Any given mammal at depth
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near the trackline would be in the main
beam for only one or two of the nine
segments. Also, marine mammals that
encounter the Simrad EM120 are
unlikely to be subjected to repeated
pulses because of the narrow fore-aft
width of the beam and will receive only
limited amounts of pulse energy
because of the short pulses. Animals
close to the ship (where the beam is
narrowest) are especially unlikely to be
ensonified for more than one 15 ms
pulse (or two pulses if in the overlap
area). Similarly, Kremser et al. (2005)
noted that the probability of a cetacean
swimming through the area of exposure
when an MBB sonar emits a pulse is
small. The animal would have to pass
the transducer at close range and be
swimming at speeds similar to the
vessel in order to be subjected to sound
levels that could cause TTS.
Navy sonars that have been linked to
avoidance reactions and stranding of
cetaceans (1) generally have a longer
pulse duration than the Simrad EM120,
and (2) are often directed close to
horizontally vs. downward for the
Simrad EM120. The area of possible
influence of the Simrad EM120 is much
smaller-a narrow band below the source
vessel. The duration of exposure for a
given marine mammal can be much
longer for a Navy sonar.
Because of the unlikelihood of an
animal being exposed to more than one
or two pulses and the low energy the
animal would most likely be exposed to
due to the short pulses, NMFS does not
expect the operation of the MBB sonar
to result in the harassment of any
marine mammals.
Proposed Monitoring and Mitigation
Measures
Monitoring
L-DEO proposes to sponsor marine
mammal monitoring of its seismic
program, in order to implement the
planned mitigation measures and to
satisfy the requirements of the IHA. The
monitoring work described here has
been planned as a self-contained project
independent of any other related
monitoring projects that may be
occurring simultaneously in the same
regions. L-DEO is prepared to discuss
coordination of its monitoring program
with any related work that might be
done by other groups insofar as this is
practical and desirable.
Vessel Based Monitoring
Vessel-based marine mammal
observers (MMOs) will watch for marine
mammals and turtles near the seismic
source vessel during all daytime airgun
operations and during any start ups of
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the airguns at night. Airgun operations
will be suspended when marine
mammals or turtles are observed within,
or about to enter, designated safety radii
where there is concern about effects on
hearing or other physical effects. MMOs
also will watch for marine mammals
and turtles near the seismic vessel for at
least 30 min prior to the planned start
of airgun operations after an extended
shut down of the airguns. When
feasible, observations will also be made
during daytime periods without seismic
operations (e.g., during transits).
During seismic operations in the Gulf
of Mexico, five observers will be based
aboard the vessel. MMOs will be
appointed by L-DEO with NMFS
concurrence. At least one MMO, and
when practical two MMOs, will watch
for marine mammals and turtles near
the seismic vessel during ongoing
daytime operations and nighttime start
ups of the airguns. Use of two
simultaneous observers will increase the
proportion of the animals present near
the source vessel that are detected.
MMO(s) will be on duty in shifts of
duration no longer than 4 h. The crew
will also be instructed to assist in
detecting marine mammals and turtles
and implementing mitigation
requirements (if practical). Before the
start of the seismic survey the crew will
be given additional instruction in how
to do so.
The Langseth is a suitable platform for
marine mammal and turtle observations.
When stationed on the observation
platform, the eye level will be
approximately 17.8 m (58.4 ft) above sea
level, and the observer will have a good
view around the entire vessel. However,
neither the actual bow of the vessel nor
the stern will be visible from the
observation platform, although it will be
possible to see the airguns. To monitor
the areas immediately at the bow and
stern of the vessel, two video cameras
will be installed at the bow (one on the
starboard and one on the port side), and
a wide-angle camera will be installed at
the stern. Real-time footage from these
cameras will be played on the
observation platform, so that the
MMO(s) are able to monitor those areas.
In addition a high-power video camera
will be mounted on the observation
platform to assist with species
identification.
During daytime, the MMO(s) will scan
the area around the vessel
systematically with reticle binoculars
(e.g., 7 50 Fujinon), Big-eye binoculars
(25 150), and with the naked eye. At
night, Night Vision Devices (NVDs) will
be available (ITT F500 Series Generation
3 binocular-image intensifier or
equivalent), when required. Laser
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rangefinding binoculars (Leica LRF 1200
laser rangefinder or equivalent) will be
available to assist with distance
estimation. Those are useful in training
observers to estimate distances visually,
but are generally not useful in
measuring distances to animals directly.
MMOs will not be on duty during
ongoing seismic operations at night. At
night, bridge personnel will watch for
marine mammals and turtles (insofar as
practical at night) and will call for the
airguns to be shut down if marine
mammals or turtles are observed in or
about to enter the safety radii. If the
airguns are started up at night, two
MMOs will watch for marine mammals
and turtles near the source vessel for 30
min prior to start up of the airguns using
NVDs, if the proper conditions for
nighttime start up exist (see Mitigation
below).
The vessel-based monitoring will
provide data to estimate the numbers of
marine mammals exposed to various
received sound levels, to document any
apparent disturbance reactions or lack
thereof, and thus to estimate the
numbers of mammals potentially
‘‘taken’’ by harassment. It will also
provide the information needed in order
to power down or shut down the
airguns at times when mammals and
turtles are present in or near the safety
radii. When a 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 the
airguns or vessel (e.g., none, avoidance,
approach, paralleling, etc.), and
behavioral pace.
2. Time, location, heading, speed,
activity of the vessel, sea state,
visibility, 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 observations and power-downs or
shut downs will be recorded in a
standardized format. Data will be
entered into a custom database using a
notebook computer. The accuracy of the
data entry will be verified by
computerized validity data checks as
the data are entered and by subsequent
manual checking of the database. These
procedures will allow initial summaries
of data to be prepared during and
shortly after the field program, and will
facilitate transfer of the data to
statistical, graphical, or other programs
for further processing and archiving.
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Results from the vessel-based
observations will provide:
1. The basis for real-time mitigation
(airgun power-down or shut down).
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 and turtles in the area where
the seismic study is conducted.
4. Information to compare the
distance and distribution of marine
mammals and turtles relative to the
source vessel at times with and without
seismic activity.
5. Data on the behavior and
movement patterns of marine mammals
and turtles seen at times with and
without seismic activity.
Passive Acoustic Monitoring
Passive acoustic monitoring will take
place to complement the visual
monitoring program. Visual monitoring
typically is less effective during periods
of bad weather or at night, and even
with good visibility, is unable to detect
marine mammals when they are below
the surface or beyond visual range.
Acoustical monitoring can be used in
addition to visual observations to
improve detection, identification,
localization, and tracking of cetaceans.
The acoustic monitoring will serve to
alert visual observers when vocalizing
cetaceans are detected. It will be
monitored in real time so that the visual
observers can be advised when
cetaceans are detected.
SEAMAP (Houston, TX) will be used
as the primary acoustic monitoring
system. This system was also used
during previous L-DEO seismic cruises
(e.g., Smultea et al., 2004, 2005; Holst et
al., 2004a,b). The PAM system consists
of hardware (i.e., the hydrophone) and
software. The ‘‘wet end’’ of the
SEAMAP system consists of a lownoise, towed hydrophone array that is
connected to the vessel by a ‘‘hairy’’
faired cable. The array will be deployed
from a winch located on the back deck.
A deck cable will connect from the
winch to the main computer lab where
the acoustic station and signal
conditioning and processing system will
be located. The lead-in from the
hydrophone array is approximately 400
m (1312 ft) long, and the active part of
the hydrophone array is approximately
56 m (184 ft) long. The hydrophone
array is typically towed at depths of less
than 20 m or 66 ft.
The acoustical array will be
monitored 24 hour per day while at the
seismic survey area during airgun
operations and during most periods
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when airguns are not operating. One
MMO will monitor the acoustic
detection system at any one time, by
listening to the signals from two
channels via headphones and/or
speakers and watching the real-time
spectrographic display for frequency
ranges produced by cetaceans. MMOs
monitoring the acoustical data will be
on shift from 1–6 h. All MMOs are
expected to rotate through the PAM
position, although the most experienced
with acoustics will be on PAM duty
more frequently.
When a vocalization is detected, the
acoustic MMO will contact the visual
MMO immediately (so a power-down or
shut down can be initiated, if required),
and the information regarding the call
will be entered into a database. The data
to be entered include an acoustic
encounter identification number,
whether it was linked with a visual
sighting, GMT date, GMT time when
first and last heard and whenever any
additional information was recorded,
GPS position and water depth when
first detected, species or species group
(e.g., unidentified dolphin, sperm
whale), types and nature of sounds
heard (e.g., clicks, continuous, sporadic,
whistles, creaks, burst pulses, strength
of signal, etc.), and any other notable
information. The acoustic detection can
also be recorded onto the hard-drive for
further analysis.
Mitigation
For the proposed study in the
northern Gulf of Mexico, L-DEO will
deploy an energy source of up to 36
airguns (6600 in3). The airguns
comprising the array will be spread out
horizontally, so that the energy will be
directed mostly downward. The
directional nature of the array to be used
in this project 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.
Localized and temporally-variable
areas of concentrated feeding or of
special significance for marine
mammals may occur within or near the
planned area of operations during the
season of operations. However, L-DEO
will avoid conducting the proposed
activities near important concentrations
of marine mammals insofar as these can
be identified in advance from other
sources of information, or during the
cruise.
Safety Radii
As noted earlier (Table 2), received
sound levels were modeled by L-DEO
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for various configurations of the 36–
airgun array in relation to distance and
direction from the airguns, and for a
single and 2 GI guns. Correction factors
based on empirical measurements were
applied to estimate safety radii in
shallow and intermediate-depth water.
The distances from the airguns where
sound levels of 190, 180, and 160 dB re
1 µPa (rms) are estimated to be received
are shown Table 2. Also, the safety radii
for a single (40 in3) airgun are given, as
that source will be in operation when
the 36–airgun array is powered down.
Airguns will be powered down (or shut
down if necessary) immediately when
marine mammals or turtles are detected
within or about to enter the appropriate
radius: 180 dB (rms) for cetaceans and
turtles, and 190 dB (rms) for pinnipeds,
in the very unlikely event that
pinnipeds are encountered.
Mitigation During Operations
Mitigation measures that will be
required will include (1) speed or
course alteration, provided that doing so
will not compromise operational safety
requirements, (2) power-down
procedures, (3) shut-down procedures,
(4) special shut-down procedures for
any endangered baleen whales, (5)
ramp-up procedures, (6) avoidance of
areas with concentrations of marine
mammal, and (7) shut down and
notification of NMFS if an injured or
dead marine mammal is found and is
judged likely to have resulted from the
operation of the airguns.
Speed or Course Alteration - If a
marine mammal or sea turtle is detected
outside the safety radius and, based on
its position and the relative motion, is
likely to enter the safety radius, the
vessel’s speed and/or direct course may
be changed. This would be done if
practicable while minimizing the effect
to the planned science objectives. The
activities and movements of the marine
mammal or sea turtle (relative to the
seismic vessel) will be closely
monitored to determine whether the
animal is approaching the applicable
safety radius. If the animal appears
likely to enter the safety radius, further
mitigative actions will be taken, i.e.,
either further course alterations or a
power-down or shut down of the
airguns.
Power-down Procedures - A powerdown involves decreasing the number of
airguns in use such that the radius of
the 180–dB (or 190–dB) zone is
decreased to the extent that marine
mammals or turtles are no longer in or
about to enter the safety zone. A powerdown may also occur when the vessel
is moving from one seismic line to
another (i.e., during a turn). During a
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power-down, one airgun will be
operated. The continued operation of
one airgun is intended to alert marine
mammals and turtles to the presence of
the seismic vessel in the area. In
contrast, a shut down occurs when all
airgun activity is suspended.
If a marine mammal or turtle is
detected outside the safety zone but is
likely to enter the safety radius, and if
the vessel’s speed and/or course cannot
be changed to avoid having the animal
enter the safety radius, the airguns will
be powered down before the animal is
within the safety radius. Likewise, if a
mammal or turtle is already within the
safety zone when first detected, the
airguns will be powered down
immediately. During a power-down of
the airgun array, at least one airgun (e.g.,
40 in3) will be operated. If a marine
mammal or turtle is detected within or
near the smaller safety radius around
that single airgun (Table 2), all airguns
will be shut down (see next subsection).
Following a power-down, airgun
activity will not resume until the marine
mammal or turtle has cleared the safety
zone. The animal will be considered to
have cleared the safety zone if it: (1) is
visually observed to have left the safety
zone; or, (2) has not been seen within
the zone for 15 min in the case of small
odontocetes and pinnipeds; or, (3) has
not been seen within the zone for 30
min in the case of mysticetes and large
odontocetes, including sperm, pygmy
sperm, dwarf sperm, and beaked
whales; or, (4) the vessel has moved
outside the safety zone for turtles.
During airgun operations following a
power-down whose duration has
exceeded specified limits, the airgun
array will be ramped up gradually.
Ramp-up procedures are described
below.
Shut-down Procedures - During a
power-down, the operating airgun will
be shut down if a marine mammal or
turtle approaches within the modeled
safety radius for the then-operating
source, typically a single 40 in3 gun or
a GI gun (Table 2). If a marine mammal
or turtle is detected within or about to
enter the appropriate safety radius
around the small source in use during
a power-down, airgun operations will be
entirely shut down.
Airgun activity will not resume until
the animal has cleared the safety zone,
or until the MMO is confident that the
marine mammal or turtle has left the
vicinity of the vessel. Criteria for
judging that the animal has cleared the
safety zone will be as described in the
preceding subsection.
Special Shut-down Provision for
Highly Endangered Mysticetes - The
airguns will be shut down (not just
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58801
powered down) if an endangered
mysticete is sighted anywhere near the
vessel, even if the whale is located
outside the safety radius. In this cruise,
this provision would apply in the
unlikely event of sighting any of the
following whales: the North Atlantic
right whale; the humpback whale; the
sei whale; the fin whale; or the blue
whale. This measure is planned because
of the assumed greater effects of seismic
surveys on mysticetes in general (as
compared with other marine mammals).
Ramp-up Procedures - A ramp-up
procedure will be followed when the
airgun array begins operating after a
specified-duration without airgun
operations. It is proposed that, for the
present cruise, this period would be
approximately 10 min. This duration is
based on provisions during previous LDEO surveys and on the approximately
180–dB radius for the 4–string array in
deep water in relation to the planned
speed of the Langseth while shooting.
Ramp up will begin with the smallest
gun in the array. Airguns will be added
in a sequence such that the source level
of the array will increase in steps not
exceeding approximately 6 dB per 5–
min period over a total duration of 20–
30 min. During ramp up, the safety zone
for the full airgun array to be used will
be maintained.
If the complete safety radius has not
been visible for at least 30 min prior to
the start of operations in either daylight
or nighttime, ramp up will not
commence unless at least one airgun has
been operating during the interruption
of seismic survey operations. That
airgun will have a source level of more
than 180 dB re 1 µPa . m (rms). It is
likely that the airgun array will not be
ramped up from a complete shut down
at night or in thick fog (the array will
definitely not be ramped up from a
complete shut down at night in shallow
water), because the outer part of the
safety zone for the array will not be
visible during those conditions. If one
airgun has operated during a powerdown period, ramp up to full power will
be permissible at night or in poor
visibility, on the assumption that
marine mammals will be alerted to the
approaching seismic vessel by the
sounds from the single airgun and could
move away if they choose. Ramp up of
the airguns will not be initiated if a sea
turtle or marine mammal is sighted
within or near the applicable safety
radii during the day or close to the
vessel at night.
Avoidance of Areas with
Concentrations of Marine Mammals Beaked whales may be highly sensitive
to sounds produced by airguns, based
mainly on what is known about their
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responses to other sound sources.
Beaked whales tend to concentrate in
continental slope areas, and especially
in areas where there are submarine
canyons on the slope. Therefore, L DEO
will, if possible, avoid airgun operations
over or near submarine canyons within
the present study area. Also, if
concentrations of beaked whales are
observed at the slope site just prior to
or during the airgun operations there,
those operations will be moved to
another location along the slope based
on recommendations by the lead MMO
aboard the Langseth. Furthermore, any
areas where concentrations of sperm
whales are known to be present will be
avoided if possible.
Shutdown if Injured or Dead Whale is
Found - In the unanticipated event that
any cases of marine mammal injury or
mortality are found and are judged
likely to have resulted from these
activities, L-DEO will cease operating
seismic airguns and report the incident
to the Office of Protected Resources,
NMFS immediately.
mstockstill on PROD1PC61 with NOTICES
Reporting
L-DEO will provide brief field reports
on the progress of the project on a
weekly basis.
A report will be submitted to NMFS
within 90 days after the end of the
cruise. The report will describe the
operations that were conducted and the
marine mammals and turtles that were
detected near the operations. The report
will be submitted to NMFS, providing
full documentation of methods, results,
and interpretation pertaining to all
monitoring. The 90–day report will
summarize the dates and locations of
seismic operations, and all marine
mammal and turtle sightings (dates,
times, locations, activities, associated
seismic survey activities). The report
will also include estimates of the
amount and nature of potential ‘‘take’’
of marine mammals by harassment or in
other ways.
Estimated Take by Incidental
Harassment
Because of the mitigation measures
that will be required and the likelihood
that some cetaceans will avoid the area
around the operating airguns of their
own accord, NMFS does not expect any
marine mammals to approach the sound
source close enough to be injured (Level
A harassment). All anticipated takes
would be ‘‘takes by Level B
harassment’’, as described previously,
involving temporary behavioral
modifications or low level physiological
effects.
Estimates of the numbers of marine
mammals that might be affected during
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the proposed seismic program in the
northern Gulf of Mexico are based on
consideration of the number of marine
mammals that might be disturbed
appreciably by approximately 1420 km
(767 nm) of seismic surveys during the
Gulf of Mexico program. The numbers
of animals estimated below do not take
into consideration the implementation
of mitigation measures and, therefore,
probably overestimate the take to some
degree. These estimates are calculated
using density estimates of marine
mammals and the total area around the
source vessel that is ensonified to 160
dB or more (based on the calculated
safety radii, discussed previously), the
received sound level at which NMFS
estimates marine mammals are
behaviorally disturbed to an extent that
rises to Level B Harassment. The basis
for estimating the densities of marine
mammals in the proposed study area is
discussed in section VII of L-DEO’s
application and the estimates are listed
in Table 3, in the same section.
The potential number of different
individuals that might be exposed to
received levels 160 dB re 1 µPa (rms)
was calculated for each of the three
water depth categories (<100 m or <328
ft, 100–1000 m or 328–3281 ft, and
>1000 m or >3281 ft) by multiplying the
expected species density, either ‘‘mean’’
(i.e., best estimate) or ‘‘maximum’’, for
a particular water depth, times the
anticipated minimum area to be
ensonified during operations with each
airgun array to be used in each water
depth category.
The area expected to be ensonified
was determined by entering the planned
survey lines (including turns) into a
MapInfo Geographic Information
System (GIS), using the GIS to identify
the relevant areas by ‘‘drawing’’ the
applicable 160 dB buffer around each
seismic line (depending on the water
depth and array to be used), and then
calculating the total area within the
buffers. Areas where overlap occurred
(due to closely spaced survey lines or
repeat passes) were included only once
to determine the minimum area
expected to be ensonified.
Due to the spiral pattern of the
calibration survey, and the fact that
shots from each of the three subsets (1–
string, 2–string, and 4–string) of the 36–
airgun array will be fired in sequence 30
s apart, the 4–string array was used for
area calculations during the calibration
phase; the GI guns were considered
separately. For the seismic testing
survey, the three different airgun
configurations that will operate (single
40 in3 airgun; 2–string and 4–string
array) were used to determine the area
ensonified. The area for both of those
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phases was then summed, and a
contingency factor of 15 percent was
added, because of the initial seismic
testing/shakedown phase, for which
line-km effort is unknown at this time.
For the maximum estimates for
oceanic species, the reported maximum
densities were assumed to occur in
intermediate and deep waters, and a
density of zero was assumed for shallow
waters. For species occurring in shallow
water (as shown in Table 3), the
maximum reported densities were used
for intermediate and deep waters,
whereas 2x the mean density was used
for shallow water.
Applying the approach described
above, approximately 9045 km2 would
be within the 160 dB isopleth on one or
more occasions. However, this approach
does not allow for turnover in the
mammal populations in the study area
during the course of the study. This
might somewhat underestimate actual
numbers of individuals exposed,
although the conservative distances
used to calculate the area may offset
this. In addition, the approach assumes
that no cetaceans move away or toward
in response to increasing sound levels
prior to the time the levels reach 160
dB. Another way of interpreting the
estimates that follow is that they
represent the number of individuals that
are expected (in the absence of a seismic
program) to occur in the waters that will
be exposed to 160 dB re 1 µPa (rms).
To determine the mean number of
times an individual might be exposed
during the survey, the maximum area
ensonified by sounds 160 dB during the
survey was used. This area was
determined by GIS, as described above,
but instead of including all overlapping
areas only once, the overlapping
segments and areas with repeat coverage
were added together. This maximum
area was then multiplied by the
appropriate species densities to
determine the total number of exposures
during the survey. The total number of
exposures to sound levels 160 dB was
then divided by the total number of
individuals for each species. The mean
number of times an individual may be
exposed to levels 160 dB during the
survey range from 3x (for two shallowwater species) to 4x.
The ‘‘best estimate’’ of the number of
individual marine mammals that might
be exposed, absent any mitigation
measures, to seismic sounds with
received levels 160 dB re 1 µPa (rms) is
3770 (Table 3). That total includes 22
endangered sperm whales, 25 beaked
whales, and one Bryde’s whale (Table
3). Pantropical spotted dolphins,
Atlantic spotted dolphins, and
bottlenose dolphins are expected to be
E:\FR\FM\05OCN1.SGM
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Federal Register / Vol. 71, No. 193 / Thursday, October 5, 2006 / Notices
the most common species in the study
area; the best estimates for those
species, absent any mitigation, are 1282,
876, and 773, respectively (Table 3).
Estimates for other species are lower.
The ‘‘Maximum Estimate’’ column in
Table 3 shows estimates totaling 7082
individual marine mammals based on
maximum densities, and taking into
account an adjustment for small
numbers of other species that might be
encountered in the survey area, even
though there were not recorded during
previous surveys. These are the
numbers for which ‘‘take authorization’’
is requested. NMFS does not expect the
total number of marine mammal takes to
be this high, however, it is appropriate
to err on the cautious side to ensure that
L-DEO is covered in the event that an
unexpectedly large number of any
particular species were exposed to >160
dB during the survey and, further, to
ensure that this exposure would result
in a negligible impact to the species or
stock.
Based on numbers of animals
encountered during L-DEO’s 2003 cruise
in the Gulf of Mexico, the likelihood of
the successful implementation of the
required mitigation measure, and the
likelihood that some animals will avoid
the area around the operating airguns,
NMFS believes that L-DEOs airgun
calibration and seismic testing program
may result in the Level B harassment of
some lower number of individual
marine mammals than is indicated by
the ‘‘best estimates’’ in Table 3. These
best estimates compose no more than
3.9 percent of any given species
population in the northern Gulf of
Mexico, and NMFS has preliminarily
determined that these numbers are
small relative to the population sizes in
the specified geographic area (Table 3).
L-DEO has asked for authorization for
take of their ‘‘maximum estimate’’ of
numbers for each species, which
includes the take of two hooded seals.
Though NMFS believes that take of the
maximum numbers is unlikely, we still
find these numbers small (up to 8.3
percent of the Fraser’s dolphin
population and 7.7 percent of the
spinner dolphin population, but less
than 5 percent the others) relative to the
population sizes.
mstockstill on PROD1PC61 with NOTICES
Potential Effects on Habitat
The proposed airgun operations will
not result in any permanent impact on
habitats used by marine mammals or to
the food sources they utilize. The main
impact issue associated with the
proposed activity will be temporarily
elevated noise levels and the associated
direct effects on marine mammals.
VerDate Aug<31>2005
15:42 Oct 04, 2006
Jkt 211001
The actual area contacted temporarily
by the bottom-moored hydrophone array
will be an insignificant and very small
fraction of the marine mammal habitat
and the habitat of their food species in
the area. The use of this equipment
would result in no more than a
negligible and highly localized shortterm disturbance to sediments and
benthic organisms. The area that might
be disturbed is a very small fraction of
the overall area.
One of the reasons for the adoption of
airguns as the standard energy source
for marine seismic surveys was that,
unlike explosives, they do not result in
any appreciable fish kill. However, the
existing body of information relating to
the impacts of seismic on marine fish
and invertebrate species is very limited.
The potential effects of exposure to
seismic on fish and invertebrates can be
considered in three categories: (1)
Pathological, (2) physiological, and (3)
behavioral. Pathological effects include
lethal and sub-lethal damage to the
animals, physiological effects include
temporary primary and secondary stress
responses, and behavioral effects refer to
changes in exhibited behavior of the fish
and invertebrates. The three categories
are interrelated in complex ways. For
example, it is possible that certain
physiological and behavioral changes
could potentially lead to the ultimate
pathological effect on individual
animals (i.e., mortality).
The available information on the
impacts of seismic surveys on marine
fish and invertebrates provides limited
insight on the effects only at the
individual level. Ultimately, the most
important knowledge in this area relates
to how significantly seismic affects
animal populations. However, the few
available data suggest that there may be
physical impacts on eggs and on larval,
juvenile, and adult stages at very close
range. Considering typical source levels
associated with airgun arrays, close
proximity to the source would result in
exposure to high energy levels. Whereas
egg and larval stages are not able to
escape such exposures, juveniles and
adults most likely would avoid them. In
the cases of eggs and larvae, it is likely
that the numbers adversely affected by
such exposure would be small in
relation to natural mortality. The
limited data regarding physiological
impacts on fish and invertebrates
indicate that these impacts are shortterm and are most apparent after
exposure at close range.
Exposure to seismic surveys may else
cause changes in the distribution,
migration patterns, and catchability of
fish. There have been well-documented
observations of fish and invertebrates
PO 00000
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Fmt 4703
Sfmt 4703
58803
exhibiting behaviors that appeared to be
responses to exposure to seismic energy
(i.e., startle response, change in
swimming direction and speed, and
change in vertical distribution), but the
ultimate importance of those behaviors
is unclear. Some studies indicate that
such behavioral changes are very
temporary, whereas others imply that
fish might not resume pre-seismic
behaviors or distributions for a number
of days. There appears to be a great deal
of inter- and intra-specific variability. In
the case of finfish, three general types of
behavioral responses have been
identified: startle, alarm, and avoidance.
The type of behavioral reaction appears
to depend on many factors, including
the type of behavior being exhibited
before exposure, and proximity and
energy level of the sound source. There
is a need for more information on
exactly what effects seismic sounds
might have on the detailed behavior
patterns of fish and invertebrates at
different ranges.
During the proposed study, only a
small fraction of the available habitat
would be ensonified at any given time,
and fish and invertebrate species would
be expected to return to their predisturbance behavior once the seismic
activity ceased. The proposed seismic
survey is predicted to have negligible to
low physical and behavioral effects on
the various life stages of fish and
invertebrates, because of its short
duration and 1420 km (767 nm) extent.
More detailed information on studies of
potential impacts of sounds on fish and
invertebrates is provided in Appendix D
of L-DEO’s application.
The effects of the planned activity on
marine mammal habitats and food
resources are expected to be negligible,
as described above. A small minority of
the marine mammals that are present
near the proposed activity may be
temporarily displaced as much as a few
kilometers by the planned activity.
Areas with concentrations of marine
mammals will be avoided when specific
study sites are selected immediately
before the start of acoustic measurement
activities in deep, intermediate, and
shallow regions. In this manner, any
major feeding area that might occur in
the general vicinity of the project will be
avoided. Therefore, the proposed
activity is not expected to have any
habitat-related effects that could cause
significant or long-term consequences
for individual marine mammals or their
populations.
Negligible Impact Determination
NMFS has preliminarily determined,
provided that the aforementioned
mitigation and monitoring measures are
E:\FR\FM\05OCN1.SGM
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58804
Federal Register / Vol. 71, No. 193 / Thursday, October 5, 2006 / Notices
National Environmental Policy Act
(NEPA)
In 2003, NSF prepared an
Environmental Assessment (EA) for a
marine seismic survey by the R/V
Maurice Ewing in the Northern Gulf of
Mexico. This EA addressed the potential
effects of a different combination of
airgun arrays, but with a higher total
output (20 airguns, total volume 8580
in3) being operated in the same part of
the ocean as is proposed for the
Langseth in this application. NMFS will
either adopt NSF’s EA or prepare its
own supplemental NEPA document
before making a determination on the
issuance of an IHA. NSF’s EA has been
posted on NMFS’ website.
Endangered Species Act
mstockstill on PROD1PC61 with NOTICES
implemented, that the impact of
conducting an acoustic calibration and
seismic testing program in the Gulf of
Mexico may result, at worst, in a
temporary modification in behavior
and/or low-level physiological effects
(Level B Harassment) of small numbers
of certain species of marine mammals.
While behavioral and avoidance
reactions may be made by these species
in response to the resultant noise from
the airguns, these behavioral changes
are expected to have a negligible impact
on the affected species and stocks of
marine mammals.
While the number of potential
incidental harassment takes will depend
on the distribution and abundance of
marine mammals in the area of seismic
operations, the number of potential
harassment takings is estimated to be
relatively small in light of the
population size (see Table 3). NMFS
anticipates the actual take of individuals
to be lower than the numbers depicted
in the table, because those numbers do
not reflect either the implementation of
the mitigation numbers or the fact that
some animals will avoid the sound at
levels lower than those expected to
result in harassment. Additionally,
mitigation measures requires that the
Langseth avoid any areas where marine
mammals are concentrated.
In addition, no take by death and/or
serious injury is anticipated, and the
potential for temporary or permanent
hearing impairment will be avoided
through the incorporation of the
required mitigation measures described
in this document. This determination is
supported by (1) the likelihood that,
given sufficient notice through slow
ship speed and ramp-up of the seismic
array, marine mammals are expected to
move away from a noise source that it
is annoying prior to its becoming
potentially injurious; (2) TTS is unlikely
to occur, especially in odontocetes, until
levels above 180 dB re 1 µPa are
reached; (3) the fact that injurious levels
of sound are only likely very close to the
vessel; and (4) the likelihood that
marine mammal detection ability by
trained observers is close to 100 percent
during daytime (in good weather) and
remains high at night close to the vessel.
AGENCY:
Under section 7 of the ESA, the
National Science Foundation (NSF) has
begun consultation on this proposed
seismic survey. NMFS will also consult
on the issuance of an IHA under section
101(a)(5)(D) of the MMPA for this
activity. Consultation will be concluded
prior to a determination on the issuance
of an IHA.
VerDate Aug<31>2005
15:42 Oct 04, 2006
Jkt 211001
Preliminary Conclusions
Based on the preceding information,
and provided that the proposed
mitigation and monitoring are
incorporated, NMFS has preliminarily
concluded that the proposed activity
will incidentally take, by Level B
harassment only, small numbers of
marine mammals. NMFS has further
preliminarily determined that the
proposed activity will have a negligible
impact on the affected species or stocks
of marine mammals.
Proposed Authorization
NMFS proposes to issue an IHA to LDEO for an acoustic calibration and
seismic testing program in the northern
Gulf of Mexico in Fall, 2006 provided
the previously mentioned mitigation,
monitoring, and reporting requirements
are incorporated.
Dated: September 27, 2006.
James H. Lecky,
Director, Office of Protected Resources,
National Marine Fisheries Service.
[FR Doc. E6–16412 Filed 10–4–06; 8:45 am]
BILLING CODE 3510–22–S
DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric
Administration
Publication of North American Datum
of 1983 State Plane Coordinates in
Feet in Idaho
National Geodetic Survey
(NGS), National Ocean Service (NOS),
National Oceanic and Atmospheric
Administration, Department of
Commerce
ACTION: Notice.
SUMMARY: The National Geodetic Survey
(NGS) will publish North American
Datum of 1983 (NAD 83) State Plane
Coordinate (SPC) grid values in both
PO 00000
Frm 00021
Fmt 4703
Sfmt 4703
meters and U.S. Survey Feet (1 ft =
1200/3937 m) in Idaho, for all welldefined geodetic survey control
monuments maintained by NGS in the
National Spatial Reference System
(NSRS) and computed from various
geodetic positioning utilities. The
adoption of this standard is
implemented in accordance with NGS
policy and a request from the Idaho
Transportation Department, the Idaho
Society of Professional Land Surveyors,
and the Idaho Department of
Administration GIS Coordinator.
DATES: Individuals or organizations
wishing to submit comments on the
Publication of North American Datum of
1983 State Plan Coordinates in feet in
Idaho, should do by November 6, 2006.
ADDRESSES: Written comments should
be sent to the attention of David Doyle,
Chief Geodetic Surveyor, Office of the
National Geodetic Survey, National
Ocean Service (N/NGS2), 1315 EastWest Highway, Silver Spring, MD,
20910; fax 301–7313–4324, or via e-mail
Dave.Doyle@noaa.gov.
FOR FURTHER INFORMATION CONTACT:
Requests for additional information
should be directed to David Doyle, Chief
Geodetic Surveyor, National Geodetic
Survey (N/NGS2), 1315 East-West
Highway, Silver Spring, MD, 20910;
Phone: (301) 713–3178.
SUPPLEMENTARY INFORMATION:
Abstract
In 1991, NGS adopted a policy that
defines the conditions under which
NAD 83 State Plane Coordinates (SPCs)
would be published in feet in addition
to meters. As outlined in that policy,
each State or territory must adopt NAD
83 legislation (typically referenced as
Codes, Laws or Statutes), which
specifically defines a conversion to
either U.S. Survey or International Feet
as defined by the U.S. Bureau of
Standards in Federal Register notice 59–
5442. To date, 48 States have adopted
the NAD 83 legislation however, for
various reasons, only 33 included a
specific definition of the relationship
between meters and feet. This lack of
uniformity has led to confusion and
misuse of SPCs as provided in various
NGS products, services and tools, and
created errors in mapping, charting and
surveying programs in numerous States
due to inconsistent coordinate
conversions.
Dated: September 29, 2006.
David B. Zilkoski,
Director, Office of National Geodetic Survey,
National Ocean Service, National Oceanic
and Atmospheric Administration.
[FR Doc. 06–8512 Filed 10–4–06; 8:45 am]
BILLING CODE 3510–JE–M
E:\FR\FM\05OCN1.SGM
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]]>Agencies
[Federal Register Volume 71, Number 193 (Thursday, October 5, 2006)]
[Notices]
[Pages 58790-58804]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: E6-16412]
-----------------------------------------------------------------------
DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
[I.D. 090706B]
Incidental Takes of Marine Mammals During Specified Activities;
Seismic Testing and Calibration in the Northern Gulf of Mexico, Fall
2006
AGENCY: National Marine Fisheries Service (NMFS), National Oceanic and
Atmospheric Administration (NOAA), Commerce.
ACTION: Notice; proposed incidental take authorization; request for
comments.
-----------------------------------------------------------------------
SUMMARY: NMFS has received an application from the Lamont-Doherty Earth
Observatory (L-DEO) for an Incidental Harassment Authorization (IHA) to
take small numbers of marine mammals, by harassment, incidental to
conducting an acoustic calibration and seismic testing program in the
northern Gulf of Mexico in Fall, 2006. Under the Marine Mammal
Protection Act (MMPA), NMFS is requesting comments on its proposed IHA
for these activities.
DATES: Comments and information must be received no later than November
6, 2006.
ADDRESSES: Comments on the application should be addressed to 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 email comments is PR1.090706B@noaa.gov. NMFS is not
responsible for e-mail comments sent to addresses other than the one
provided here. Comments sent via e-mail, including all attachments,
must not exceed a 10-megabyte file size.
A copy of the application containing a list of the references used
in this document may be obtained by writing to the address specified
above, telephoning the contact listed below (see FOR FURTHER
INFORMATION CONTACT), or visiting the internet at: https://
www.nmfs.noaa.gov/pr/permits/incidental.htm.
Documents cited in this notice may be viewed, by appointment,
during regular business hours, at the aforementioned address.
FOR FURTHER INFORMATION CONTACT: Jolie Harrison, Office of Protected
Resources, NMFS, (301) 713-2289, ext 166.
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, and that the permissible methods of
taking and requirements pertaining to the mitigation, monitoring and
reporting of such takings are set forth. NMFS has defined ``negligible
impact'' in 50 CFR 216.103 as ''...an impact resulting from the
specified activity that cannot be reasonably expected to, and is not
reasonably likely to, adversely affect the species or stock through
effects on annual rates of recruitment or survival.''
Section 101(a)(5)(D) of the MMPA established an expedited process
by which citizens of the United States can apply for an authorization
to incidentally take small numbers of marine mammals by harassment.
Except with respect to certain activities not pertinent here, the MMPA
defines ``harassment'' as:
any act of pursuit, torment, or annoyance which (i) has the
potential to injure a marine mammal or marine mammal stock in the
wild [Level A harassment]; or (ii) has the potential to disturb a
marine mammal or marine mammal stock in the wild by causing
disruption of behavioral patterns, including, but not limited to,
migration, breathing, nursing, breeding, feeding, or sheltering
[Level B harassment].
Section 101(a)(5)(D) establishes a 45-day time limit for NMFS
review of an application followed by a 30-day public notice and comment
period on any proposed authorizations for the incidental harassment of
marine mammals. Within 45 days of the close of the comment period, NMFS
must either issue or deny issuance of the authorization.
Summary of Request
On June 2, 2006, NMFS received an application from L-DEO for the
taking, by Level B harassment, of several species of marine mammals
incidental to conducting, with research funding from the National
Science Foundation (NSF), an acoustic calibration and seismic testing
program in the northern Gulf of Mexico in Fall, 2006. This project will
be conducted with L-DEO's new seismic vessel, the R/V Marcus G.
Langseth (Langseth), which will deploy different configurations of
airguns and a different bottom-mapping sonar than used previously by L-
DEO. L-DEO requests that it be issued an IHA allowing Level B
Harassment takes of marine mammals incidental to the planned seismic
surveys in the Gulf of Mexico.
The primary purpose of the calibration program is to obtain
measurement data to better understand the sound fields around various
configurations of the 36-airgun array and the GI guns, during seismic
operations in different water depths. The data will be used to verify
and refine model-based estimates of ``safety radii'' for different
configurations of the 36-airgun array and the GI guns that will be used
during future seismic surveys to be conducted by L-DEO. Such data are
important to better define the distances within which mitigation may be
necessary in order to avoid exposing marine mammals to received sound
levels above those believed to have adverse effects, as well as to
develop a better general understanding of the impact of man-made
acoustic sources on marine mammals.
Description of the Specified Activity
The Langseth is expected to depart Mobile, AL in late October 2006
(at the earliest) and will transit to the survey area in the northern
Gulf of Mexico. The survey will encompass an area between 24oN. and
31oN. and between 83[deg]W. and 96[deg]W., which is within the
Exclusive Economic Zone (EEZ) of the U.S.A. The proposed study will
consist of three phases: (1) an initial testing/
[[Page 58791]]
shakedown phase, (2) measurements of the sounds produced by various
airgun arrays to be used by the Langseth (calibration), and (3) a
three-dimensional (3D) seismic testing phase. The entire survey,
calibration and testing included, will take approximately 25 days and
include approximately 1420 km (174 hours) of airgun operation.
Measurements will be made during seismic operations in three categories
of water depth: shallow (<100 m or <328 ft), intermediate/slope (100-
1000 m or 328-3281 ft), and deep (>1000 m or >3281 ft). The vessel will
transit to Miami after the study is completed. The exact dates of the
activities will depend on logistics and weather conditions.
Vessel Specifications
The Langseth is owned by NSF and operated by L-DEO. The Langseth
will tow the airgun array and, at times, up to four 6-km (3.7-mi)
streamers containing hydrophones along predetermined lines. The
Langseth will also deploy a floating spar buoy and a bottom-moored
hydrophone array.
The Langseth has a length of 71.5 m (235 ft), a beam of 17.0 m (56
ft), and a maximum draft of 5.9 m (19 ft). The gross tonnage is 2925
and the Langseth can accommodate 55 people. The ship is powered by two
Bergen BRG-6 engines each producing 3550 hp; 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 (13,500 nm).
Given the presence of the airgun array (and at times streamer(s))
behind the vessel, the turning rate of the ship while the gear is
deployed is limited to five degrees per minute. Thus, the
maneuverability of the vessel is limited during operations.
Acoustic Source Specifications
Airguns
The full airgun array on the Langseth consists of 36 airguns, with
a total discharge volume of 6600 in\3\. The array is made up of four
identical linear arrays or strings, with 10 airguns on each string. For
each operating string, nine airguns 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 calibration phase will use the full 36-
airgun array and subsets thereof. The subsets will consist of either 1
string (9 airguns, 1650 in\3\) or 2 strings (18 airguns, 3300 in\3\).
In addition, sounds from a single 45 in\3\ GI gun and 2 GI guns (210
in\3\) will be measured. During the seismic testing phase, the 2-string
array will be used at most times, although the full 36-airgun array may
also be used.
The 36-airgun array will consist of a mixture of Bolt 1500LL and
1900LLX airguns, ranging in size from 40 to 360 in\3\. The airguns will
fire for a brief (0.1 s) pulse every 30 s and will be silent during the
intervening periods. The airgun array will be towed approximately 50-
100 m (164-328 ft) behind the seismic vessel at a depth of 6-12 m (20-
39 ft). The dominant frequency component is 0-188 Hz.
The specifications of each source planned for use are described in
Table 1.
----------------------------------------------------------------------------------------------------------------
9-Airgun 18-Airgun 36-Airgun
1 GI Gun 2 GI Guns 1 Single Array (1 Array (2 Array (4
Airgun String) Strings) Strings)
----------------------------------------------------------------------------------------------------------------
Airgun Specifications ............ ............ ........... ........... ........... ...........
----------------------------------------------------------------------------------------------------------------
Energy Source One 45 in\3\ Two 105 One 2000 Nine 2000 Eighteen Thirty-six
GI Airgun in\3\ GI psi Bolt psi Bolt 2000 psi 2000 psi
Airguns Airgun Airguns of Bolt Bolt
40-360 Airguns of Airguns of
in\3\ 40-360 40-360
in\3\ in\3\
----------------------------------------------------------------------------------------------------------------
Air Discharge Volume (in\3\) 45 in3 210 in\3\ 40 in\3\ 1650 in\3\ 3300 in\3\ 6600 in\3\
----------------------------------------------------------------------------------------------------------------
Towing Depth of Source 2.5m 3m 6 m 6m 6m 6m or 12m
----------------------------------------------------------------------------------------------------------------
Source Output (dB re 1 miPa m) 225.3 237 (243) ........... 246 (253) 252 (259) 259 (265)
0-pk (pk.pk)* (230.7)
----------------------------------------------------------------------------------------------------------------
Proposed Approximate Airgun Use
-------------- ------------- ------------
Calibration Phase ............ ............ ........... ........... ........... ...........
----------------------------------------------------------------------------------------------------------------
Shallow Site (30-60m) 10km 10km ........... 34km 34km 34km
----------------------------------------------------------------------------------------------------------------
Intermediate/Slope Site ............ ............ ........... 34km 34km> 34km
(475m)
----------------------------------------------------------------------------------------------------------------
Deep Site (1500m) 10km 10km ........... 45km 45km 45km
----------------------------------------------------------------------------------------------------------------
Testing Phase ............ ............ ........... ........... ........... ...........
----------------------------------------------------------------------------------------------------------------
Shallow Site (<100m) ............ ............ 89km 24km 175km 58km
----------------------------------------------------------------------------------------------------------------
Intermediate/Slope (100-1000 ............ ............ 89km 24km 175km 58km
m)
----------------------------------------------------------------------------------------------------------------
Deep (>1000 m) ............ ............ 89km 24km 175km 58km
----------------------------------------------------------------------------------------------------------------
Table 1. L-DEO airgun configurations and proposed approximate use for each configuration by depth and phase.
* The root mean square values (typically discussed in biological literature) for these sources will generally be
about 10-15 dB lower than those reflected here
[[Page 58792]]
Multibeam Sonar
The ocean floor will be mapped with the 12-kHz Simrad EM120 MBB
sonar. This sonar will be operated from the Langseth simultaneous with
the airgun array during the seismic testing program, but will likely be
operated on its own during the acoustic calibration study. The Simrad
EM120 operates at 11.25-12.6 kHz and will be 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 microPa. The pressure level is
expected to drop to 180 dB at a distance of 1 km or 0.5 nm (this
distance is the maximum estimate for on-axis and with no defocusing);
pressure level does not vary with water depth. Each ``ping'' consists
of nine successive fan-shaped transmissions, each ensonifying a sector
that extends 1[deg] fore-aft and 16[deg] in the cross-track direction.
The transmission length varies with water depth; each of the nine
transmissions is approximately 2 ms in shallow water, 5 ms at
intermediate water depths, and 15 ms in deep water. The nine successive
transmissions span an overall cross-track angular extent of about
150[deg], with 16 ms gaps between the pulses for successive sectors. A
receiver in the overlap area between two sectors would receive two
pulses separated by a 16-ms gap. The ``ping'' interval varies with
water depth and ranges from 0.2 s in really shallow water, to
approximately 5 s at 1000 m (3281 ft) and 20 s at 4000 m (13,124 ft).
Airgun Operations
Acoustic Calibration Study
Location of Sites - L-DEO will work together with Texas A&M
University to choose the exact study sites at the three depths,
however, the approximate locations are indicated in Figure 1 of L-DEO's
application. Site locations will depend on currents, surface ducts, and
concentrations of marine mammals. Sites will be chosen to avoid high
currents with large vertical shear, as were encountered during the 2003
study. Conductivity/Temperature/Depth (CTDs) and Expendable
Bathythermograph (XBTs) measurements will be taken at each site to
confirm local water column properties. Near-surface ducts may play a
significant role in the propagation of sound, so a deep site with and
without a surface duct will be surveyed if practical. Areas with
concentrations of marine mammals will be avoided.
L-DEO proposes to start with the shallow site, where the instrument
redundancy will allow some flexibility in gain settings to ensure that
signals will not be clipped. This information will be used to optimize
gain settings at the slope and deep sites. The water depths at the
three different depth sites are expected to be 30-60 m (98-197 ft) at
the shallow site, approximately 475 m (1,558 ft) at the intermediate/
slope site, and approximately1500 m (4922 ft) at the deep site. This
phase of the study will take approximately 14 days.
Acoustic Measurements - The 2006 program is designed to document
the received levels of the airgun sounds, relative to distance, during
operation of the Langseth's 36-airgun 4-string array and subsets
thereof, and up to 2 GI guns. During the calibration study, three
configurations (1, 2, and 4 strings in equal amounts) of the 36-airgun
array will be measured in three different water depths (deep,
intermediate/slope, and shallow). A single and two GI guns will be
measured in deep and shallow water only. Measurements will be made at
varying distances from the guns using suitable electronics installed in
the spar buoy and a bottom-moored hydrophone array. In addition, one 6-
km (3.7-mi) long hydrophone streamer will be used at times for
calibrations of shallow-water safety radii. The hydrophones will be
deployed and retrieved by the Langseth.
At each of the three sites, the Langseth, towing various
configurations of the 36-airgun array at a depth of 6 m (20 ft), will
travel toward the spar buoy and/or moored hydrophone array from a
distance of approximately10-15 km (5.4-8.1 nm) away and will pass over
the receiving system. The Langseth will then continue out to a distance
of approximately 10-15 km beyond the hydrophones. The approximate 15 km
distance will be used at the shallow and slope sites (total line length
of 30 km or 16 nm), and the approximate 10 km distance will be used at
the deep-water site (total line length of 20 km or 11 nm). Longer lines
are planned at the shallow and slope sites than at the deep site
because in 2003, received sound levels diminished below 160 dB re 1
microPa (rms) well within 10 km at the deep site, but not at the
shallow site (Tolstoy et al., 2004a,b). After completing the straight
line, the airgun array will then be towed in a spiral fashion towards
the hydrophones in order to measure received levels as a function of
distance when the receiving hydrophones are to the side of the
trackline. The spirals are designed such that the radius will decrease
linearly with time.
At each site, the Langseth will make one straight line pass over
the receiving hydrophones with the 36-airgun array, followed by the
spiral pattern towards the hydrophones. At the deep site, two
additional 20-km (11-nm) straight lines will be shot, for a total of
three 20-km straight lines at that site: (a) with the airgun array at 6
m (20 ft) tow depth, (b) with the array at a tow depth of 12 m (39 ft),
and (c) in waters with/without a surface duct [whichever was not the
case in (a) and (b)]. In addition, two 10-km (5.4-nm) straight line
passes will be made at the deep as well as the shallow-water sites; one
pass at each site will be made with a single GI gun, and one pass will
be made using 2 GI guns.
The total number of kilometers and hours of airgun shooting during
the calibration phase of the project are indicated in Table 1. However,
operations at each site will require approximately 36 hours, allowing
for the time needed to deploy and recover the hydrophones as well as
the time to shoot the survey. Although the lines will be longer for the
slope and shallow sites, the deep site is likely to take the longest,
because of the increased drop and surfacing time for the instruments
plus the plans to shoot three 20 km (11 nm) lines.
Airguns will fire every 30 s, and operations are proposed to occur
24 hours per day to maximize effective and economic use of the limited
ship time and to maximize the amount of calibration data collected.
Operating airguns over 24-hour periods will also reduce the overall
duration of airgun operations at each site, thus reducing the span of
time when marine mammals in those areas will be exposed to airgun
sounds.
Systematic Testing Phase
The exact site of the seismic testing phase has not yet been
chosen, but is planned to range from shallow (approximately 30 m or 98
ft) to deep (>1000 m or 3281 ft) water and will fall within the general
area described earlier. During the testing phase, the Langseth will
deploy the 2-string 18-airgun array (and at times the 36-airgun array)
as an energy source; a single 40 in3 airgun will be fired during turns.
The Langseth will also deploy a receiving system consisting of up to
four 6-km (3.7-mi) towed hydrophone streamers. There will be 200 m (656
ft) separation between adjacent pairs of the four streamers. As the
airgun array is towed along the survey lines, the receiving system will
receive the returning acoustic signals and transfer the data to the on-
board processing system. The airgun array will be towed at a depth of 9
m (30 ft).
The testing phase will consist of a series of tracklines in a
racetrack-type configuration. This racetrack will consist of 17 loops,
with a total of 35
[[Page 58793]]
tracklines. Each trackline will be approximately 20 km (10.8 nm) long,
for a total of approximately 700 km (378 nm) of shooting along
tracklines. The spacing between adjacent tracklines will be 400 m (1312
ft). An additional 10 km (5.4 nm) of seismic will be shot during each
turn between lines and during the ensuing run-in (the distance from the
end of the turn to the start of the line during which the airgun array
will be ramped up). In total, this will account for an additional 340
km (183 nm). Of this 340 km, approximately 73 km (39.4 nm) will consist
of ramp ups, and 267 km (144.2 nm) will be shot with a 40 in\3\ airgun
during turns. These numbers are also presented in Table 1.
In total, 1040 km (562 nm) of seismic will be shot. The seismic
testing program will take approximately 4 to 7 days.
Characteristics of Airgun Pulses
Discussion of the characteristics of airgun pulses has been
provided in Appendix B of L-DEO's application and in previous Federal
Register notices (see 69 FR 31792 (June 7, 2004) or 69 FR 34996 (June
23, 2004)). Reviewers are referred to those documents for additional
information.
Safety Radii
To aid in determining at what point during exposure to seismic
airguns (and other acoustic sources) marine mammals are harassed,
pursuant to the MMPA, and in developing effective mitigation measures,
NMFS applies certain acoustic thresholds. The distance from the sound
source at which an animal would be exposed to these different received
sound levels may be estimated and is typically referred to as a safety
radii. These safety radii are specifically used to help NMFS estimate
the number of marine mammals likely to be harassed by the proposed
activity and in deciding how close a marine mammal may approach an
operating sound source before the applicant will be required to power-
down or shut down the sound source.
L-DEO has estimated the safety radii around their proposed
operations using a model, but also by adjusting the model results based
on empirical data gathered in the Gulf of Mexico in 2003. Additional
information regarding how the safety radii were calculated and how the
empirical measurements were used to correct the modeled numbers may be
found in Section I and Appendix A of L-DEO's application. Using the
modeled distances and various correction factors, Table 2 shows the
distances at which three rms sound levels (190 dB, 180 dB, and 160 dB)
are expected to be received from the various airgun configurations in
shallow, intermediate, and deep water depths.
----------------------------------------------------------------------------------------------------------------
Predicted RMS Radii (m)
Source and Volume Tow Depth (m) Water Depth ---------------------------------------------
190 dB 180 dB 160 dB
----------------------------------------------------------------------------------------------------------------
.............. Deep 9 25 236
Single GI gun 2.5 Intermediate/ 13.5 38 354
Slope
45 in\3\ .............. Shallow 113 185 645
----------------------------------------------------------------------------------------------------------------
.............. Deep 20 69 670
2 GI guns 3 Intermediate/ 30 104 1005
Slope
210 in\3\ .............. Shallow 294 511 1970
----------------------------------------------------------------------------------------------------------------
.............. Deep 12 36 360
Single Bolt 6 Intermediate/ 18 54 540
Slope
40 in\3\ .............. Shallow 150 267 983
----------------------------------------------------------------------------------------------------------------
1 string .............. Deep 200 650 6200
9 airguns 6 Intermediate/ 300 975 7880
Slope
1650 in\3\ .............. Shallow 1450 2360 8590
----------------------------------------------------------------------------------------------------------------
2 strings/ENT> .............. Deep 250 820 6700
18 airguns 6 Intermediate/ 375 1230 7370
Slope
3300 in\3\ .............. Shallow 1820 3190 8930
----------------------------------------------------------------------------------------------------------------
4 strings .............. Deep 410 1320 8000
36 airguns 6 Intermediate/ 615 1980 8800
Slope
6600 in\3\ .............. Shallow 2980 5130 10670
----------------------------------------------------------------------------------------------------------------
4 strings .............. Deep 620 1980 12000
36 airguns 12 Intermediate/ 930 2970 13200
Slope
6600 in\3\ .............. Shallow 4500 7700 16000
----------------------------------------------------------------------------------------------------------------
Table 2. Modeled distances towhich sound levels 190,180, and 160 dB re 1uPa (rms) might be received in shallow
(>100 m), intermediate/slope (100-1000 m), and deep (<1000 m) water from the various sources planned for use
during the Gulf of Mexico study, fall 2006.
[[Page 58794]]
Description of Marine Mammals in the Activity Area
In the Gulf of Mexico, 28 cetacean species and one species of
manatee are known to occur (Jefferson and Schiro, 1997; Wursig et al.,
2000; Table 3). In the U.S., manatees are managed by the U.S. Fish &
Wildlife Service (USFWS), are unlikely to be encountered in or near the
open waters of the Gulf of Mexico where seismic operations will occur,
and are, therefore, not addressed further in this document. Most of
these species of cetaceans occur in oceanic waters (>200 m or 656 ft
deep) of the Gulf, whereas the continental shelf waters (<200 m) are
primarily inhabited by bottlenose dolphins and Atlantic spotted
dolphins (Mullin and Fulling 2004).
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
BEST MAXIMUM
Abundance in GOM and/or ------------------------------------------------------------------------------
Species Habitat Occurrence in GOM North Atlantic Estimated Approx. % of Est. Exposures Approx. % of
Exposures Population Prop. IHA** Population
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Odontocetes
---------------------------------- -------------------- -------------------- --------------------------------------
Sperm whale Usually pelagic and deep seas Common 1349/13190 (add) 22 0.2 27 0.2
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Pygmy sperm whale Deeper waters off the shelf Common 742/695 (add) 56 3.9 .................. 4.1
---------------------------------------------------------------------------------------
Dwarf sperm whale Deeper waters off the shelf Common ......................... .................. .................. .................. .................
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Cuvier's beaked whale Pelagic Rare 159/3196 (add) 10 0.3 21 0.7
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Sowerby's beaked whale Pelagic Extralimital ......................... 5 0.8 8 1.2
--------------------------------------------------------------------------------------- ------------------------------------------------------------------------------
Gervais' beaked whale Pelagic Uncommon 106/541 (add) 5 0.8 8 1.2
--------------------------------------------------------------------------------------- ------------------------------------------------------------------------------
Blainville's beaked whale Pelagic Rare ......................... 5 0.8 8 1.2
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Rough-toothed dolphin Mostly pelagic Common 2223/274 (add) 58 2.3 92 3.7
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Bottlenose dolphin Cont. shelf, coastal and Common 25,320/2239/29774 (add) 773 1.3 1713 5.0
offshore
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Pantropical spotted dolphin Mainly pelagic Common 91,321/13117 (add) 1282 1.2 1587 1.5
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Atlantic spotted dolphin Mainly coastal waters Common 30,947/52279 (add) 876 1.1 1755 0.2
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Spinner dolphin Pelagic in Gulf of Mexico Common 11,971 168 1.4 921 7.7
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Clymene dolphin Pelagic Common 17,355/6086 (add) 244 1.0 311 1.3
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Stripped dolphin Off the continental shelf Common 6505/61546 (add) 91 0.1 134 0.2
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Short-beaked common dolphin Cont. shelf and pelagic waters Possible 30,768 0 0.0 0(5)** <0.1
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Long-beaked common dolphin Coastal Possible N.A. 0 0.0 0(5)** 0.0
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Praser's dolphin Water>l000m Common 726 10 1.4 60 8.3
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Risso's dolphin Waters 400-1000 m Common 2169/29110 (add) 54 0.2 81 0.3
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Mellon-headed whale Oceanic Common 3451 49 1.4 142 4.1
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Pygmy killer whale Oceanic Uncommon 408 10 2.6 21 5.1
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
False killer whale Pelagic Uncommon 1038 14 1.4 28 2.7
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Killer whale Widely distributed Uncommon 133/6600 (add) 3 <0.1 5 0.1
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Short-finned pilot whale Mostly pelagic Common 2388/780000/14524 34 <0.1 98 <0.1
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Long-finned pilot whale Mostly pelagic Possible N.A. 0 .................. 0(5)** .................
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
[[Page 58795]]
Mysticetes
---------------------------------- -------------------- -------------------- --------------------------------------
North Atlantic right whale* Coastal and shelf waters Extralimital 291 0 .................. 0 .................
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Humpback whale* Mainly near-shore waters/banks Rare 11,570/10400 0 .................. 0 .................
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Minke whale Coastal waters Rare 149,000 0 .................. 0 .................
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Bryde's whale Pelagic and coastal Uncommon 40/90000 1 2.5 2 5.0
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Sei whale* Primarily offshore, pelagic Rare 12-13,000 0 .................. 0 .................
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Fin whale* Cont. slope, mostly pelagic Rare 2814/47300 0 .................. 0 .................
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Blue whale* Coastal, shelf, and oceanic Extralimital 308 0 .................. 0 .................
waters
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Pinnipeds
---------------------------------- -------------------- -------------------- --------------------------------------
Hooded seal Coastal Vagrant 400,000\z\ 0 .................. 0(2)** <0.1
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Total 3770 .................. 7096 .................
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Table 3. Abundance, preferred habitat, and commonness of the marine mammal species found in the survey area. The far right columns indicate the estimated number each species that will be
exposed to 160 dB based on best and maximum density estimates. NMFS believes that, when mitigation measures are taken into consideration, the activity is likely to result in take of numbers
of animals less than those indicated by the best column, however, L-DEO has asked for authorization of the maximum.
*Federally listed endangered,
** Parenthetical number indicates take authorization, though exposure estimate is 0
Seven species that may occur in the Gulf of Mexico are listed as
endangered under provisions of the U.S. Endangered Species Act (ESA),
including the sperm, North Atlantic right, humpback, sei, fin, and blue
whale, as well as the West Indian manatee. However, of those species,
only sperm whales are likely to be encountered. In addition to the 28
species known to occur in the Gulf of Mexico, another three species of
cetaceans could potentially occur there: the long-finned pilot whale,
the long-beaked common dolphin, and the short-beaked common dolphin
(Table 3). Though any pinnipeds sighted in the study area would be
extralimital, hooded seals have been reported in Florida and L-DEO has
requested authorization for the take of 2 animals.
During the 2003 acoustical calibration study in the Gulf of Mexico
from 28 May to 2 June, a total of seven visual sightings of marine
mammals were documented from the Maurice Ewing; these included a total
of approximately 38-40 individuals (LGL Ltd. 2003). In addition, three
sea turtles were sighted. These totals include times when airguns were
not operating as well as times when airguns were firing. Visual
monitoring effort consisted of 60.9 hours of observations (all in
daylight) along 891.5 km of vessel trackline on seven days, and passive
acoustic monitoring (PAM) occurred for approximately 32 hours. Most of
the monitoring effort (visual as well as acoustic) occurred when
airguns were not operating, since airgun operations were limited during
the 2003 study. No marine mammals were detected during acoustic
monitoring. Marine mammal and sea turtle sightings and locations during
the 2003 calibration study are summarized in Appendix C of L-DEOs
application.
Detailed information regarding the status and distribution of these
marine mammals may be found in sections III and IV of L-DEOs
application.
Potential Effects of the Proposed Activity on Marine Mammals
Summary of Potential Effects of Airgun Sounds on Marine Mammals
The effects of sounds from airguns might include one or more of the
following: tolerance, masking of natural sounds, behavioral
disturbance, and at least in theory, temporary or permanent hearing
impairment, or non-auditory physical or physiological effects
(Richardson et al., 1995). These effects are discussed below, but also
in further detail in Appendix B of L-DEO's application.
The potential effects of airguns discussed below are presented
without consideration of the mitigation measures that L-DEO has
presented and that will be required by NMFS. When these measures are
taken into account, it is unlikely that this project would result in
temporary, or especially, permanent hearing impairment or any
significant non-auditory physical or physiological effects.
Tolerance
Numerous studies have shown that pulsed sounds from airguns are
often readily detectable in the water at distances of many kilometers.
A summary of the characteristics of airgun pulses is provided in
Appendix B of L-DEO's application. Studies have also shown that marine
mammals at distances more than a few kilometers from operating seismic
vessels often show no apparent response (tolerance) (Appendix B (e)).
That is often true even in cases when the pulsed sounds must be readily
audible to the animals based on measured received levels and the
hearing sensitivity of that mammal group. Although various baleen
whales, toothed whales, and (less frequently)
[[Page 58796]]
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, small odontocetes, and sea
otters seem to be more tolerant of exposure to airgun pulses than are
baleen whales. Pinnipeds and sea otters are not found in the Gulf of
Mexico; small odontocetes of numerous species are the predominant
marine mammals in the area.
Masking
Masking effects of pulsed sounds (even from large arrays of
airguns) on marine mammal calls and other natural sounds are expected
to be limited, although there are very few specific data of relevance.
Some whales are known to continue calling in the presence of seismic
pulses. Their calls can be heard between the seismic pulses (e.g.,
Richardson et al., 1986; McDonald et al., 1995; Greene et al., 1999;
Nieukirk et al., 2004). Although there has been one report that sperm
whales 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 (Tyack et al., 2003). 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.
Also, the sounds important to small odontocetes are predominantly at
much higher frequencies than are airgun sounds. Masking effects, in
general, are discussed further in Appendix B (d).
Disturbance Reactions
Disturbance includes a variety of effects, including subtle changes
in behavior, more conspicuous changes in activities, and displacement.
Simple exposure to sound, or brief reactions that do not disrupt
behavioral patterns in a potentially significant manner, do not
constitute harassment or ``taking''. By potentially significant, we
mean ``in a manner that might have deleterious effects to the well-
being of individual marine mammals or their populations''. Reactions to
sound, if any, depend on species, state of maturity, experience,
current activity, reproductive state, time of day, and many other
factors. If a marine mammal does react briefly to an underwater sound
by minorly changing its behavior or moving a small distance, the
impacts of the change are unlikely to be significant to the individual,
let alone the stock or the species as a whole. However, if a sound
source displaces marine mammals from an important feeding or breeding
area for a prolonged period, impacts on the animals could be
significant.
There are many uncertainties in predicting the quantity and types
of impacts of noise on marine mammals. As mentioned earlier in this
document, NMFS applies acoustic criteria developed to help estimate the
number of animals likely to be harassed by a particular sound source in
a given area and for use in the development of shutdown zones for
mitigation. 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 on
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. There is no specific information
about reactions of Bryde's whales-the baleen whales most likely to be
encountered in the Gulf of Mexico-to seismic pulses. 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, baleen whales exposed to strong noise pulses from
airguns often react by deviating from their normal migration route and/
or interrupting their feeding and moving away. 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 microPa 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 to 14.5
km (2.4-7.8 nm) 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 have shown that some species of baleen whales, notably bowhead
and humpback whales, at times show strong avoidance at received levels
lower than 160-170 dB re 1 microPa rms. Bowhead whales migrating west
across the Alaskan Beaufort Sea in autumn, in particular, are unusually
responsive. Substantial avoidance occurred out to distances of 20-30 km
(11-16 nm) from a medium-sized airgun source, where received sound
levels were on the order of 130 dB re 1 microPa rms (Miller et al.,
1999; Richardson et al., 1999; see Appendix B (e)). More recent
research on bowhead whales (Miller et al., 2005), however, suggests
that during the summer feeding season, bowheads are not nearly as
sensitive to seismic sources, with onset of avoidance at the more
typical level of 160-170 dB re 1 microPa rms.
Malme et al., (1986, 1988) studied the responses of feeding eastern
gray whales to pulses from a single 100 in3 airgun off St. Lawrence
Island in the northern Bering Sea. They 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 microPa 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.
Blue, sei, fin, and minke whales have occasionally been reported in
areas ensonified by airgun pulses. Sightings by observers on seismic
vessels off the U.K. 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).
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
[[Page 58797]]
traffic in that area for decades (Appendix A in Malme et al., 1984).
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). Populations of both gray and
bowhead whales grew substantially during this time. In any event, the
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 and in
Appendix B have been reported for toothed whales. However, systematic
work on sperm whales is underway (Tyack et al., 2003), and there is an
increasing amount of information about responses of various odontocetes
to seismic surveys based on monitoring studies (e.g., Stone, 2003;
Haley and Koski, 2004; Smultea et al., 2004; Holst et al., 2005a,b;
MacLean and Koski, 2005).
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 arrays of airguns are
firing. Nonetheless, there have been indications that small toothed
whales sometimes move away, or maintain a somewhat greater distance
from the vessel, when a large array of airguns is operating than when
it is silent (e.g., Goold, 1996a,b,c; Calambokidis and Osmek, 1998;
Stone, 2003). In most cases the avoidance radii for delphinids appear
to be small, on the order of 1 km (0.5 nm) or less. However, aerial
surveys during seismic operations in the southeastern Beaufort Sea
recorded much lower sighting rates of beluga whales within 10-20 km (5-
11 nm) 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 (Miller et al., 2005).
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;
Finneran and Schlundt 2004). The animals tolerated high received levels
of sound 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 microPa\2\ .
s, respectively (Finneran and Schlundt, 2004).
Pinnipeds
No pinnipeds are expected to be encountered in the Gulf of Mexico,
and thus it is most likely that none will be affected by the proposed
activity. At most, up to two extralimital hooded seals might be
encountered and potentially be behaviorally disturbed or have a low-
level physiological response to the seismic exposure.
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 exposed to
impulsive sounds of 180 and 190 dB re 1 microPa (rms) or above,
respectively, are considered to have been incidentally taken by Level A
Harassment. These levels are precautionary.
Several aspects of the planned monitoring and mitigation measures
for this project are designed to detect marine mammals occurring near
the airguns, and to avoid exposing them to sound pulses that could
potentially cause hearing impairment. In addition, many cetaceans are
likely to show some avoidance of the area with high received levels of
airgun sound. In those cases, the avoidance responses of the animals
themselves will reduce or (most likely) avoid any possibility of
hearing impairment.
Non-auditory physical effects might also occur in marine mammals
exposed to strong underwater pulsed sound. Possible types of non-
auditory physiological effects or injuries that theoretically might
occur in mammals close to a strong sound source include stress,
neurological effects, bubble formation, and other types of organ or
tissue damage. It is possible that some marine mammal species (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
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, permanent threshold shift (PTS), and non-auditory physical
effects.
Temporary Threshold Shift (TTS)
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. 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 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). Sound
exposure level (SEL), which takes into account the duration of the
sound, is the metric used to measure energy and uses the units dB re 1
microPa2 . s, as opposed to sound pressure level (SPL), which is the
pressure metric used in the rest of this document (units - dB re 1
microPa). Given the available data, the received energy level of a
single seismic pulse might need to be approximately 186 dB re 1
microPa\2\ . 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 at 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
distances from the Langseth's airguns at which the received energy
level would be expected to be 175 dB SEL are the distances shown in the
190 dB rms column in Table 2 (given that the rms level is approximately
15 dB higher than the SEL value for the same pulse). In deep water,
where L DEO's model is directly applicable, seismic pulses with
received energy levels 175 dB SEL (190 dB rms) are expected to be
restricted to radii no more than 200-620 m (656-2034 ft)
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around the airguns. The specific radius would depend on number of
operating airguns (9-36) and their operating depth (6 vs. 12 m). The
depth associated with the above radii ranges from about 125 m (410 ft)
for a 9-airgun array to =500 m (=1640 ft) for the 36-airgun array. For
an odontocete closer to the surface, the maximum radius with 175 dB SEL
or 190 dB rms would be smaller. In intermediate-depth and shallow
water, the 175 dB SEL or 190 dB rms radius would be larger.
For baleen whales, there are no data, direct or indirect, on levels
or properties of sound that are required to induce TTS. However, no
cases of TTS are expected given two considerations: (1) the low
abundance of baleen whales in the planned study area, and (2) the
strong likelihood that baleen whales would avoid the approaching
airguns (or vessel) before being exposed to levels high enough for
there to be any possibility of TTS.
In pinnipeds, TTS thresholds associated with exposure to brief
pulses (single or multiple) of underwater sound have not been measured.
Initial evidence from prolonged exposures suggested that some pinnipeds
may incur TTS at somewhat lower received levels than do small
odontocetes exposed for similar durations (Kastak et al., 1999; Ketten
et al., 2001; cf. Au et al., 2000). However, pinnipeds are not expected
to occur in or near the planned study area.
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, whereas
in other cases, the animal has an impaired ability to hear sounds in
specific frequency ranges.
There is no specific evidence that exposure to pulses of airgun
sound can cause PTS in any marine mammal, even with large arrays of
airguns. However, given the possibility that mammals close to an airgun
array might incur TTS, there has been further speculation about the
possibility that some individuals occurring very close to airguns might
incur PTS. Single or occasional occurrences of mild TTS are not
indicative of permanent auditory damage in terrestrial mammals.
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. PTS might occur at a received sound level at
least several decib
