Takes of Marine Mammals Incidental to Specified Activities; Taking Marine Mammals Incidental to an Exploration Drilling Program in the Chukchi Sea, Alaska
Federal RegisterNov 9, 2011
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DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
RIN 0648-XA811
Takes of Marine Mammals Incidental to Specified Activities; Taking Marine Mammals Incidental to an Exploration Drilling Program in the Chukchi Sea, Alaska
AGENCY:
National Marine Fisheries Service (NMFS), National Oceanic and Atmospheric Administration (NOAA), Commerce.
ACTION:
Notice; proposed incidental harassment authorization; request for comments.
SUMMARY:
NMFS received an application from Shell Offshore Inc. (Shell) for an Incidental Harassment Authorization (IHA) to take marine mammals, by harassment, incidental to offshore exploration drilling on Outer Continental Shelf (OCS) leases in the Chukchi Sea, Alaska. Pursuant to the Marine Mammal Protection Act (MMPA), NMFS is requesting comments on its proposal to issue an IHA to Shell to take, by Level B harassment only, 12 species of marine mammals during the specified activity.
DATES:
Comments and information must be received no later than December 9, 2011.
ADDRESSES:
Comments on the application should be addressed to Michael Payne, Chief, Permits and Conservation Division, Office of Protected Resources, National Marine Fisheries Service, 1315 East-West Highway, Silver Spring, MD 20910. The mailbox address for providing email comments is
ITP.Nachman@noaa.gov.
NMFS is not responsible for email comments sent to addresses other than the one provided here. Comments sent via email, including all attachments, must not exceed a 10-megabyte file size.
Instructions:
All comments received are a part of the public record and will generally be posted to
http://www.nmfs.noaa.gov/pr/permits/incidental.htm
without change. All Personal Identifying Information (for example, name, address,
etc.
) voluntarily submitted by the commenter may be publicly accessible. Do not submit Confidential Business Information or otherwise sensitive or protected information.
A copy of the application, which contains several attachments, including Shell's marine mammal mitigation and monitoring plan and Plan of Cooperation, 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:
http://www.nmfs.noaa.gov/pr/permits/incidental.htm.
Documents cited in this notice may also be viewed, by appointment, during regular business hours, at the aforementioned address.
FOR FURTHER INFORMATION CONTACT:
Candace Nachman, Office of Protected Resources, NMFS, (301) 427-8401.
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 small numbers 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 for incidental takings shall be granted if NMFS finds that the taking will have a negligible impact on the species or stock(s), will not have an unmitigable adverse impact on the availability of the species or stock(s) for subsistence uses (where relevant), and if the permissible methods of taking and requirements pertaining to the mitigation, monitoring and reporting of such takings are set forth. NMFS has defined “negligible impact” in 50 CFR 216.103 as “* * * an impact resulting from the specified activity that cannot be reasonably expected to, and is not reasonably likely to, adversely affect the species or stock through effects on annual rates of recruitment or survival.”
Section 101(a)(5)(D) of the MMPA established an expedited process by which citizens of the U.S. can apply for an authorization to incidentally take small numbers of marine mammals by 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 the authorization.
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”].
Summary of Request
NMFS received an application on June 30, 2011, from Shell for the taking, by harassment, of marine mammals incidental to offshore exploration drilling on OCS leases in the Chukchi Sea, Alaska. NMFS reviewed Shell's application and identified a number of issues requiring further clarification. After addressing comments from NMFS, Shell modified its application and submitted a revised application on September 12, 2011. NMFS carefully evaluated Shell's application, including their analyses, and determined that the application is complete. The September 12, 2011, application is the one available for public comment (see
ADDRESSES
) and considered by NMFS for this proposed IHA.
Shell plans to drill up to three exploration wells at three possible drill sites and potentially a partial well at a fourth drill site on OCS leases offshore in the Chukchi Sea, Alaska, during the 2012 Arctic open-water season (July through October). Impacts to marine mammals may occur from noise produced by the drillship, zero-offset vertical seismic profile (ZVSP) surveys, and supporting vessels (including icebreakers) and aircraft. Shell has requested an authorization to take 13 marine mammal species by Level B harassment. However, the narwhal (
Monodon monoceros
) is not expected to be found in the activity area. Therefore, NMFS is proposing to authorize take of 12 marine mammal species, by Level B harassment, incidental to Shell's offshore exploration drilling in the Chukchi Sea. These species include: Beluga whale (
Delphinapterus leucas
); bowhead whale (
Balaena mysticetus
); gray whale (
Eschrichtius robustus
); killer whale (
Orcinus orca
); minke whale (
Balaenoptera acutorostrata
); fin whale (
Balaenoptera physalus
); humpback whale (
Megaptera novaeangliae
); harbor porpoise (
Phocoena phocoena
); bearded seal (
Erignathus barbatus
); ringed seal (
Phoca hispida
); spotted seal (
P. largha
); and ribbon seal (
Histriophoca fasciata
).
Description of the Specified Activity and Specified Geographic Region
Shell plans to conduct an offshore exploration drilling program on U.S. Department of the Interior, Bureau of Ocean Energy Management (BOEM, formerly the Minerals Management
Service) Alaska OCS leases located greater than 64 mi (103 km) from the Chukchi Sea coast during the 2012 open-water season. The leases were acquired during the Chukchi Sea Oil and Gas Lease Sale 193 held in February 2008. During the 2012 drilling program, Shell plans to drill up to three exploration wells at three drill sites and potentially a partial well at a fourth drill site at the prospect known as Burger. See Figure 1-1 in Shell's application for the lease block and drill site locations (see
ADDRESSES
). All drilling is planned to be vertical.
Exploration Drilling
All of the possible Chukchi Sea offshore drill sites are located between 65 and 78 mi (105 and 125.5 km) from the Chukchi coast in water depths between 143 and 150 ft (43.7 and 45.8 m). Table 2-1 in Shell's application provides the coordinates for the drill sites (see
ADDRESSES
). All of the proposed wells would be at Shell's Burger prospect. Shell has identified a total of six lease blocks on this prospect where drilling could occur.
(1) Drilling Vessel
Shell proposes to use the ice strengthened drillship
Discoverer
to drill the wells. The
Discoverer
is a true drillship and is a largely self-contained drillship that offers full accommodations for a crew of up to 140 persons. The
Discoverer
is 514 ft (156.7 m) long with a maximum height (above keel) of 274 ft (83.7 m). It is an anchored drillship with an 8-point anchored mooring system and would likely have a maximum anchor radius of 2,969-2,986 ft (905-910 m) at either the Sivulliq or Torpedo drill sites. While on location at the drill sites, the
Discoverer
will be affixed to the seafloor using eight 7,000 kg (7.7 ton) Stevpris anchors arranged in a radial array. The underwater fairleads prevent ice fouling of the anchor lines. Turret mooring allows orientation of the vessel's bow into the prevailing ice drift direction to present minimum hull exposure to drifting ice. The vessel is rotated around the turret by hydraulic jacks. Rotation can be augmented by the use of the fitted bow and stern thrusters. The hull has been reinforced for ice resistance. Ice-strengthened sponsons have been retrofitted to the ship's hull. Additional details about the drillship can be found in Attachment A of Shell's IHA application (see
ADDRESSES
).
(2) Support Vessels
During the 2012 drilling season, the
Discoverer
will be attended by eight vessels that will be used for ice management, anchor handling, oil spill response (OSR), refueling, resupply, and servicing of the exploration drilling operations. The ice-management vessels will consist of an icebreaker and an anchor handler. The OSR vessels supporting the exploration drilling program include a dedicated OSR barge and an OSR vessel, both of which have associated smaller workboats, an oil spill tanker, and a containment barge. Tables 1-2a and 1-2b in Shell's application provide a list of the support and OSR vessels that will be used during the drilling program.
Shell's base plan is for the ice management vessel and the anchor handler, or similar vessels, the oil spill vessels (OSVs), and potentially some of the OSR vessels to accompany the
Discoverer
traveling north from Dutch Harbor through the Bering Strait, on or about July 1, 2012, then into the Chukchi Sea, before arriving on location approximately July 4. Exploration drilling is expected to be complete by October 31, 2012. At the completion of the drilling season, one or two ice-management vessels, along with various support vessels, such as the OSR fleet, will accompany the
Discoverer
as it travels south out of the Chukchi Sea and through the Bering Strait to Dutch Harbor. Subject to ice conditions, alternate exit routes may be considered.
The
M/V Fennica
(
Fennica
), or a similar vessel, will serve as the primary ice management vessel, and the
M/V Tor Viking
(
Tor Viking
), or a similar vessel, will serve as the primary anchor handling vessel in support of the
Discoverer.
The
Fennica
and
Tor Viking
will remain at a location approximately 25 mi (40 km) upwind and upcurrent of the drillship when not in use. Any ice management would be expected to occur within 0.6-6 mi (1-9.6 km) upwind from the
Discoverer.
When managing ice, the vessels will generally be confined to a 40° arc up to 3.1 mi (4.9 km) upwind originating at the drilling vessel (see Figure 1-3 in Shell's application). It is anticipated that the ice management vessels will be managing ice for up to 38% of the time when within 25 mi (40 km) of the
Discoverer.
Active ice management involves using the ice management vessel to steer larger floes so that their path does not intersect with the drill site. Around-the-clock ice forecasting using real-time satellite coverage (available through Shell Ice and Weather Advisory Center [SIWAC]) will support the ice management duties. The proposed exploration drilling operations will require two OSVs to resupply the
Discoverer
with exploration drilling materials and supplies from facilities in Dutch Harbor and fuel.
(3) Aircraft
Offshore operations will be serviced by helicopters operated out of onshore support base locations. A Sikorsky S-92 or Eurocopter EC225 capable of transporting 10 to 12 persons will be used to transport crews between the onshore support base and the drillship. The helicopters will also be used to haul small amounts of food, materials, equipment, and waste between vessels and the shorebase. The helicopter will be housed at facilities at the Barrow airport. Shell will have a second helicopter for Search and Rescue (SAR). The SAR helicopter is expected to be a Sikorsky S-61, S-92, Eurocopter EC225, or similar model. This aircraft will stay grounded at the Barrow shorebase location except during training drills, emergencies, and other non-routine events.
A fixed wing propeller or turboprop aircraft, such as a Saab 340-B 30-seat, Beechcraft 1900, or deHavilland Dash8 will be used to routinely transport crews, materials, and equipment between the shorebase and hub airports such as Barrow or Fairbanks. A fixed wing aircraft, deHavilland Twin Otter (DHC-6) will be used for marine mammal monitoring flights. Table 1-2c in Shell's application presents the aircraft planned to support the exploration drilling program.
Zero-Offset Vertical Seismic Profile
At the end of each drill hole, Shell may conduct a geophysical survey referred to as ZVSP at each drill site where a well is drilled in 2012. During ZVSP surveys, an airgun array is deployed at a location near or adjacent to the drilling vessel, while receivers are placed (temporarily anchored) in the wellbore. The sound source (airgun array) is fired repeatedly, and the reflected sonic waves are recorded by receivers (geophones) located in the wellbore. The geophones, typically in a string, are then raised up to the next interval in the wellbore, and the process is repeated until the entire wellbore has been surveyed. The purpose of the ZVSP is to gather geophysical information at various depths, which can then be used to tie-in or ground-truth geophysical information from the previous seismic surveys with geological data collected within the wellbore.
Shell intends to conduct a particular form of vertical seismic profile known as a ZVSP, in which the sound source is maintained at a constant location near the wellbore (see Figure 1-2 in Shell's
application). A typical sound source that would be used by Shell in 2012 is the ITAGA eight-airgun array, which consists of four 150 in
3
airguns and four 40 in
3
airguns. These airguns can be activated in any combination, and Shell intends to utilize the minimum airgun volume required to obtain an acceptable signal. Current specifications of the array are provided in Table 1-3 of Shell's application. The airgun array is depicted within its frame or sled, which is approximately 6 ft x 5 ft x 10 ft (1.8 m x 1.5 m x 3 m) (see photograph in Shell's application). Typical receivers would consist of a Schlumberger wireline four level Vertical Seismic Imager (VSI) tool, which has four receivers 50-ft (15-m) apart.
A ZVSP survey is normally conducted at each well after total depth is reached but may be conducted at a shallower depth. For each survey, Shell plans to deploy the airgun array over the side of the
Discoverer
with a crane (sound source will be 50-200 ft [15-61 m] from the wellhead depending on crane location) to a depth of approximately 10-23 ft (3-7 m) below the water surface. The VSI, with its four receivers, will be temporarily anchored in the wellbore at depth. The sound source will be pressured up to 2,000 pounds per square inch (psi) and activated 5-7 times at approximately 20-second intervals. The VSI will then be moved to the next interval of the wellbore and reanchored, after which the airgun array will again be activated 5-7 times. This process will be repeated until the entire well bore is surveyed in this manner. The interval between anchor points for the VSI usually is between 200 and 300 ft (61 and 91 m). A normal ZVSP survey is conducted over a period of about 10-14 hours, depending on the depth of the well and the number of anchoring points. Therefore, considering a few different scenarios, the airgun array could be fired between 117 and 245 times during the 10-14 hour period. For example, a 7,000-ft (2,133.6-m) well with 200-ft (61-m) spacing and seven activations per station would result in the airgun array being fired 245 times to survey the entire well. That same 7,000-ft (2,133.6-m) well with 300-ft (91-m) spacing and five activations would result in the airgun array being fired 117 times to survey the entire well. The remainder of the time during those 10-14 hours when the airgun is not firing is used to move and anchor the geophone array.
Ice Management and Forecasting
Shell recognizes that the drilling program is located in an area that is characterized by active sea ice movement, ice scouring, and storm surges. In anticipation of potential ice hazards that may be encountered, Shell has developed and will implement an Ice Management Plan (IMP; see Attachment B in Shell's IHA application) to ensure real-time ice and weather forecasting is conducted in order to identify conditions that might put operations at risk and will modify its activities accordingly. The IMP also contains ice threat classification levels depending on the time available to suspend drilling operations, secure the well, and escape from advancing hazardous ice. Real-time ice and weather forecasting will be available to operations personnel for planning purposes and to alert the fleet of impending hazardous ice and weather conditions. Ice and weather forecasting is provided by SIWAC. The center is continuously manned by experienced personnel, who rely on a number of data sources for ice forecasting and tracking, including:
• Radarsat and Envisat data—satellites with Synthetic Aperture Radar, providing all-weather imagery of ice conditions with very high resolution;
• Moderate Resolution Imaging Spectroradiometer—a satellite providing lower resolution visual and near infrared imagery;
• Aerial reconnaissance—provided by specially deployed fixed wing or rotary wing aircraft for confirmation of ice conditions and position;
• Reports from ice specialists on the ice management and anchor handling vessels and from the ice observer on the drillship;
• Incidental ice data provided by commercial ships transiting the area; and
• Information from NOAA ice centers and the University of Colorado.
Drift ice will be actively managed by ice management vessels, consisting of an ice management vessel and an anchor handling vessel. Ice management for safe operation of Shell's planned exploration drilling program will occur far out in the OCS, remote from the vicinities of any routine marine vessel traffic in the Chukchi Sea causing no threat to public safety or services that occur near to shore. Shell vessels will also communicate movements and activities through the 2012 North Slope Communications Centers. Management of ice by ice management vessels will occur during a drilling season predominated by open water and thus is not expected to contribute to ice hazards, such as ridging, override, or pileup in an offshore or nearshore environment.
The ice-management/anchor handling vessels would manage the ice by deflecting any ice floes that could affect the
Discoverer
when it is drilling and would also handle the
Discoverer's
anchors during connection to and separation from the seafloor. When managing ice, the ice management and anchor handling vessels will generally be operating at a 40° arc up to 3.1 mi (4.9 km) upwind originating at the
Discoverer
(see Figure 1-3 in Shell's application).
The ice-management/anchor handling vessels would manage any ice floes upwind of the
Discoverer
by deflecting those that could affect the
Discoverer
when it is on location conducting exploration drilling operations. The ice-management/anchor handling vessels would also manage the
Discoverer'
s anchors during connection to and separation from the seafloor. The ice floe frequency and intensity are unpredictable and could range from no ice to ice sufficiently dense that the fleet has insufficient capacity to continue operating, and the
Discoverer
would need to disconnect from its anchors and move off site. If ice is present, ice management activities may be necessary in early July and towards the end of operations in late October, but it is not expected to be needed throughout the proposed drilling season. Shell has indicated that when ice is present at the drill site, ice disturbance will be limited to the minimum needed to allow drilling to continue. First-year ice (
i.e.,
ice that formed in the most recent autumn-winter period) will be the type most likely to be encountered. The ice management vessels will be tasked with managing the ice so that it will flow easily around and past the
Discoverer
without building up in front of or around it. This type of ice is managed by the ice management vessel continually moving back and forth across the drift line, directly up-drift of the
Discoverer
and making turns at both ends. During ice management, the vessel's propeller is rotating at approximately 15-20 percent of the vessel's propeller rotation capacity. Ice management occurs with slow movements of the vessel using lower power and therefore slower propeller rotation speed (
i.e.,
lower cavitation), allowing for fewer repositions of the vessel, thereby reducing cavitation effects in the water. Occasionally, there may be multi-year ice (
i.e.,
ice that has survived at least one summer melt season) ridges that would be managed at a much slower speed than that used to manage first-year ice.
During Chukchi Sea exploration drilling operations, Shell has indicated
that they do not intend to conduct any icebreaking activities; rather, Shell would deploy its support vessels to manage ice as described here. As detailed in Shell's IMP (see Attachment B of Shell's IHA application), actual breaking of ice would occur only in the unlikely event that ice conditions in the immediate vicinity of operations create a safety hazard for the drilling vessel. In such a circumstance, operations personnel will follow the guidelines established in the IMP to evaluate ice conditions and make the formal designation of a hazardous, ice alert condition, which would trigger the procedures that govern any actual icebreaking operations. Historical data relative to ice conditions in the Chukchi Sea in the vicinity of Shell's planned operations, and during the timeframe for those operations, establish that there is a very low probability (
e.g.,
minimal) for the type of hazardous ice conditions that might necessitate icebreaking (
e.g.,
records of the National Naval Ice Center archives). This probability could be greater at the shoulders of the drilling season (early July or late October); therefore, for purposes of evaluating possible impacts of the planned activities, Shell has assumed limited icebreaking activities for a very limited period of time, and estimated incidental takes of marine mammals from such activities.
Timeframe of Activities
Shell proposes to mobilize the drillship and its fleet of vessels from Dutch Harbor and to travel through the Bering Strait on or about July 1, 2012. The vessels would then travel into the Chukchi Sea, arriving on location at the Burger prospect in the Chukchi Sea on approximately July 4, 2012. Shell proposes to conduct the exploration drilling program through October 31, 2012. At the end of the exploration drilling season, the
Discoverer
and its support vessels would travel south out of the Chukchi Sea through the Bering Strait to Dutch Harbor. Subject to ice conditions, alternate exit routes may be considered.
Shell anticipates that the exploration drilling program will require approximately 32 days per well, including mudline cellar construction. Therefore, if Shell is able to drill three exploration wells during the 2012 open-water season, it would require a total of 96 days. If Shell is able to drill part of a fourth well, it would add an additional 1-32 days to the season but would not extend beyond October 31, 2012. These estimates do not include any downtime for weather or other operational delays. Time to conduct the ZVSP surveys for each well is included in the 32 drilling days for each well. Shell also assumes approximately 10 additional days will be needed for transit, drillship mobilization and mooring, drillship moves between locations, and drillship demobilization.
Activities associated with the 2012 Chukchi Sea exploration drilling program include operation of the
Discoverer,
associated support vessels, crew change support, and resupply, ZVSP surveys, and icebreaking. The
Discoverer
will remain at the location of the designated exploration drill sites except when mobilizing and demobilizing to and from the Chukchi Sea, transiting between drill sites, and temporarily moving off location if it is determined ice conditions require such a move to ensure the safety of personnel and/or the environment in accordance with Shell's IMP. The anchor handler and OSR vessels will remain in close proximity to the drillship during drilling operations.
Exploratory Drilling Program Sound Characteristics
Potential impacts to marine mammals could occur from the noise produced by the drillship and its support vessels (including the icebreakers), aircraft, and the airgun array during ZVSP surveys. The drillship produces continuous noise into the marine environment. NMFS currently uses a threshold of 120 dB re 1 μPa (rms) for the onset of Level B harassment from continuous sound sources. This 120 dB threshold is also applicable for the icebreakers when actively managing or breaking ice. The drilling vessel to be used will be the
Discoverer.
The airgun array proposed to be used by Shell for the ZVSP surveys produces pulsed noise into the marine environment. NMFS currently uses a threshold of 160 dB re 1 μPa (rms) for the onset of Level B harassment from pulsed sound sources.
(1) Drilling Sounds
Exploratory drilling will be conducted from the
Discoverer,
a vessel specifically designed for such operations in the Arctic. Underwater sound propagation results from the use of generators, drilling machinery, and the rig itself. Received sound levels during vessel-based operations may fluctuate depending on the specific type of activity at a given time and aspect from the vessel. Underwater sound levels may also depend on the specific equipment in operation. Lower sound levels have been reported during well logging than during drilling operations (Greene, 1987b), and underwater sound levels appeared to be lower at the bow and stern aspects than at the beam (Greene, 1987a).
Most drilling sounds generated from vessel-based operations occur at relatively low frequencies below 600 Hz although tones up to 1,850 Hz were recorded by Greene (1987a) during drilling operations in the Beaufort Sea. At a range of 558 ft (170 m) the 20-1000 Hz band level was 122-125 dB for the drillship
Explorer I.
Underwater sound levels were slightly higher (134 dB) during drilling activity from the
Northern Explorer II
at a range of 656 ft (200 m), although tones were only recorded below 600 Hz. Underwater sound measurements from the
Kulluk
at 0.62 mi (1 km) were higher (143 dB) than from the other two vessels.
Sound measurements from the
Discoverer
have not previously been conducted in the Arctic. However, measurements of sounds produced by the
Discoverer
were made in the South China Sea in 2009 (Austin and Warner, 2010). The results of those measurements were used to model the sound propagation from the
Discoverer
(including a nearby support vessel) at planned exploration drilling locations in the Chukchi Sea (Warner and Hannay, 2011). Broadband source levels of sounds produced by the
Discoverer
varied by activity and direction from the ship but were generally between 177 and 185 dB re 1 µPa at 1 m (rms) (Austin and Warner, 2010). Once on location at the drill sites in Chukchi Sea, Shell plans to take measurements of the drillship to quantify the absolute sound levels produced by drilling and to monitor their variations with time, distance, and direction from the drilling vessel.
(2) Vessel Sounds
In addition to the drillship, various types of vessels will be used in support of the operations, including ice management vessels, anchor handlers, offshore supply vessels, barges and tugs, and OSR vessels. Sounds from boats and vessels have been reported extensively (Greene and Moore, 1995; Blackwell and Greene, 2002, 2005, 2006). Numerous measurements of underwater vessel sound have been performed in support of recent industry activity in the Chukchi and Beaufort Seas. Results of these measurements were reported in various 90-day and comprehensive reports since 2007 (
e.g.,
Aerts
et al.,
2008; Hauser
et al.,
2008; Brueggeman, 2009; Ireland
et al.,
2009). For example, Garner and Hannay (2009) estimated sound pressure levels of 100 dB at distances ranging from approximately 1.5 to 2.3 mi (2.4 to 3.7 km) from various types of barges. MacDonald
et
al.
(2008) estimated higher underwater sound pressure levels (SPLs) from the seismic vessel
Gilavar
of 120 dB at approximately 13 mi (21 km) from the source, although the sound level was only 150 dB at 85 ft (26 m) from the vessel. Like other industry-generated sound, underwater sound from vessels is generally at relatively low frequencies.
The primary sources of sounds from all vessel classes are propeller cavitation, propeller singing, and propulsion or other machinery. Propeller cavitation is usually the dominant noise source for vessels (Ross, 1976). Propeller cavitation and singing are produced outside the hull, whereas propulsion or other machinery noise originates inside the hull. There are additional sounds produced by vessel activity, such as pumps, generators, flow noise from water passing over the hull, and bubbles breaking in the wake. Icebreakers contribute greater sound levels during icebreaking activities than ships of similar size during normal operation in open water (Richardson
et al.,
1995a). This higher sound production results from the greater amount of power and propeller cavitation required when operating in thick ice.
Measurements of the icebreaking supply ship
Robert Lemeur
pushing and breaking ice during exploration drilling operations in the Beaufort Sea in 1986 resulted in an estimated broadband source level of 193 dB re 1 µPa at 1 m (Greene, 1987a; Richardson
et al.,
1995a).
Sound levels during ice management activities would not be as intense as during icebreaking, and the resulting effects to marine species would be less significant in comparison. During ice management, the vessel's propeller is rotating at approximately 15-20 percent of the vessel's propeller rotation capacity. Instead of actually breaking ice, during ice management, the vessel redirects and repositions the ice by pushing it away from the direction of the drillship at slow speeds so that the ice floe does not slip past the vessel bow. Basically, ice management occurs at slower speed, lower power, and slower propeller rotation speed (
i.e.,
lower cavitation), allowing for fewer repositions of the vessel, thereby reducing cavitation effects in the water than would occur during icebreaking. Once on location at the drill sites in the Chukchi Sea, Shell plans to measure the sound levels produced by vessels operating in support of drilling operations. These vessels will include crew change vessels, tugs, ice management vessels, and OSR vessels.
(3) Aircraft Sound
Helicopters may be used for personnel and equipment transport to and from the drillship. Under calm conditions, rotor and engine sounds are coupled into the water within a 26° cone beneath the aircraft. Some of the sound will transmit beyond the immediate area, and some sound will enter the water outside the 26° area when the sea surface is rough. However, scattering and absorption will limit lateral propagation in the shallow water.
Dominant tones in noise spectra from helicopters are generally below 500 Hz (Greene and Moore, 1995). Harmonics of the main rotor and tail rotor usually dominate the sound from helicopters; however, many additional tones associated with the engines and other rotating parts are sometimes present.
Because of doppler shift effects, the frequencies of tones received at a stationary site diminish when an aircraft passes overhead. The apparent frequency is increased while the aircraft approaches and is reduced while it moves away.
Aircraft flyovers are not heard underwater for very long, especially when compared to how long they are heard in air as the aircraft approaches an observer. Helicopters flying to and from the drillship will generally maintain straight-line routes at altitudes of at least 1,500 ft (457 m) above sea level, thereby limiting the received levels at and below the surface. Aircraft travel would be controlled by Federal Aviation Administration approved flight paths.
(4) Vertical Seismic Profile Sound
A typical eight airgun array (4 × 40 in
3
airguns and 4 × 150 in
3
airguns, for a total discharge volume of 760 in
3
) would be used to perform ZVSP surveys, if conducted after the completion of each exploratory well. Typically, a single ZVSP survey will be performed when the well has reached proposed total depth or final depth; although, in some instances, a prior ZVSP will have been performed at a shallower depth. A typical survey will last 10-14 hours, depending on the depth of the well and the number of anchoring points, and include firings of the full array, plus additional firing of a single 40-in
3
airgun to be used as a “mitigation airgun” while the geophones are relocated within the wellbore. The source level for the airgun array proposed for use by Shell will differ based on source depth. At a depth of 9.8 ft (3 m), the SPL is 238 dB re 1 μPa at 1 m, and at a depth of 16.4 ft (5 m), the SPL is 241 dB re 1 μPa at 1 m, with most energy between 20 and 140 Hz.
Airguns function by venting high-pressure air into the water. The pressure signature of an individual airgun consists of a sharp rise and then fall in pressure, followed by several positive and negative pressure excursions caused by oscillation of the resulting air bubble. The sizes, arrangement, and firing times of the individual airguns in an array are designed and synchronized to suppress the pressure oscillations subsequent to the first cycle. Typical high-energy airgun arrays emit most energy at 10-120 Hz. However, the pulses contain significant energy up to 500-1,000 Hz and some energy at higher frequencies (Goold and Fish, 1998; Potter
et al.,
2007).
Although there will be several support vessels in the drilling operations area, NMFS considers the possibility of collisions with marine mammals highly unlikely. Once on location, the majority of the support vessels will remain in the area of the drillship throughout the 2012 drilling season and will not be making trips between the shorebase and the offshore vessels. When not needed for ice management/icebreaking operations, the icebreaker and anchor handler will remain approximately 25 mi (40 km) upwind and upcurrent of the drillship. Any ice management/icebreaking activity would be expected to occur at a distance of 0.6-12 mi (1-19 km) upwind and upcurrent of the drillship. As the crew change/resupply activities are considered part of normal vessel traffic and are not anticipated to impact marine mammals in a manner that would rise to the level of taking, those activities are not considered further in this document.
Description of Marine Mammals in the Area of the Specified Activity
The Chukchi Sea supports a diverse assemblage of marine mammals, including: bowhead, gray, beluga, killer, minke, humpback, and fin whales; harbor porpoise; ringed, ribbon, spotted, and bearded seals; narwhals; polar bears (
Ursus maritimus
); and walruses (
Odobenus rosmarus divergens;
see Table 4-1 in Shell's application). The bowhead, humpback, and fin whales are listed as “endangered” under the Endangered Species Act (ESA) and as depleted under the MMPA. Certain stocks or populations of gray, beluga, and killer whales and spotted seals are listed as endangered or are proposed for listing under the ESA; however, none of those stocks or populations occur in the proposed activity area. On December 10, 2010, NMFS published a notice of
proposed threatened status for subspecies of the ringed seal (75 FR 77476) and a notice of proposed threatened and not warranted status for subspecies and distinct population segments of the bearded seal (75 FR 77496) in the
Federal Register.
Neither of these two ice seal species is considered depleted under the MMPA. Additionally, the ribbon seal is considered a “species of concern” under the ESA. Both the walrus and the polar bear are managed by the U.S. Fish and Wildlife Service (USFWS) and are not considered further in this proposed IHA notice.
Of these species, 12 are expected to occur in the area of Shell's proposed operations. These species include: The bowhead, gray, humpback, minke, fin, killer, and beluga whales; harbor porpoise; and the ringed, spotted, bearded, and ribbon seals. Beluga, bowhead, and gray whales, harbor porpoise, and ringed, bearded, and spotted seals are anticipated to be encountered more than the other marine mammal species mentioned here. The marine mammal species that is likely to be encountered most widely (in space and time) throughout the period of the proposed drilling program is the ringed seal. Encounters with bowhead and gray whales are expected to be limited to particular seasons, as discussed later in this document. Where available, Shell used density estimates from peer-reviewed literature in the application. In cases where density estimates were not readily available in the peer-reviewed literature, Shell used other methods to derive the estimates. NMFS reviewed the density estimate descriptions and articles from which estimates were derived and requested additional information to better explain the density estimates presented by Shell in its application. This additional information was included in the revised IHA application. The explanation for those derivations and the actual density estimates are described later in this document (see the “Estimated Take by Incidental Harassment” section).
The narwhal occurs in Canadian waters and occasionally in the Alaskan Beaufort Sea and the Chukchi Sea, but it is considered extralimital in U.S. waters and is not expected to be encountered. There are scattered records of narwhal in Alaskan waters, including reports by subsistence hunters, where the species is considered extralimital (Reeves
et al.,
2002). Due to the rarity of this species in the proposed project area and the remote chance it would be affected by Shell's proposed Chukchi Sea drilling activities, this species is not discussed further in this proposed IHA notice.
Shell's application contains information on the status, distribution, seasonal distribution, abundance, and life history of each of the species under NMFS jurisdiction mentioned in this document. When reviewing the application, NMFS determined that the species descriptions provided by Shell correctly characterized the status, distribution, seasonal distribution, and abundance of each species. Please refer to the application for that information (see
ADDRESSES
). Additional information can also be found in the NMFS Stock Assessment Reports (SAR). The Alaska 2010 SAR is available at:
http://www.nmfs.noaa.gov/pr/pdfs/sars/ak2010.pdf.
Brief Background on Marine Mammal Hearing
When considering the influence of various kinds of sound on the marine environment, it is necessary to understand that different kinds of marine life are sensitive to different frequencies of sound. Based on available behavioral data, audiograms have been derived using auditory evoked potentials, anatomical modeling, and other data, Southall
et al.
(2007) designate “functional hearing groups” for marine mammals and estimate the lower and upper frequencies of functional hearing of the groups. The functional groups and the associated frequencies are indicated below (though animals are less sensitive to sounds at the outer edge of their functional range and most sensitive to sounds of frequencies within a smaller range somewhere in the middle of their functional hearing range):
• Low frequency cetaceans (13 species of mysticetes): functional hearing is estimated to occur between approximately 7 Hz and 22 kHz (however, a study by Au
et al.
(2006) of humpback whale songs indicate that the range may extend to at least 24 kHz);
• Mid-frequency cetaceans (32 species of dolphins, six species of larger toothed whales, and 19 species of beaked and bottlenose whales): functional hearing is estimated to occur between approximately 150 Hz and 160 kHz;
• High frequency cetaceans (eight species of true porpoises, six species of river dolphins, Kogia, the franciscana, and four species of cephalorhynchids): functional hearing is estimated to occur between approximately 200 Hz and 180 kHz; and
• Pinnipeds in Water: functional hearing is estimated to occur between approximately 75 Hz and 75 kHz, with the greatest sensitivity between approximately 700 Hz and 20 kHz.
As mentioned previously in this document, 12 marine mammal species (four pinniped and eight cetacean species) are likely to occur in the proposed drilling area. Of the eight cetacean species likely to occur in Shell's project area, five are classified as low frequency cetaceans (
i.e.,
bowhead, gray, humpback, minke, and fin whales), two are classified as mid-frequency cetaceans (
i.e.,
beluga and killer whales), and one is classified as a high-frequency cetacean (
i.e.,
harbor porpoise) (Southall
et al.,
2007).
Underwater audiograms have been obtained using behavioral methods for four species of phocinid seals: the ringed, harbor, harp, and northern elephant seals (reviewed in Richardson
et al.,
1995a; Kastak and Schusterman, 1998). Below 30-50 kHz, the hearing threshold of phocinids is essentially flat down to at least 1 kHz and ranges between 60 and 85 dB re 1 μPa. There are few published data on in-water hearing sensitivity of phocid seals below 1 kHz. However, measurements for one harbor seal indicated that, below 1 kHz, its thresholds deteriorated gradually to 96 dB re 1 μPa at 100 Hz from 80 dB re 1 μPa at 800 Hz and from 67 dB re 1 μPa at 1,600 Hz (Kastak and Schusterman, 1998). More recent data suggest that harbor seal hearing at low frequencies may be more sensitive than that and that earlier data were confounded by excessive background noise (Kastelein
et al.,
2009a,b). If so, harbor seals have considerably better underwater hearing sensitivity at low frequencies than do small odontocetes like belugas (for which the threshold at 100 Hz is about 125 dB).
Pinniped call characteristics are relevant when assessing potential masking effects of man-made sounds. In addition, for those species whose hearing has not been tested, call characteristics are useful in assessing the frequency range within which hearing is likely to be most sensitive. The four species of seals present in the study area, all of which are in the phocid seal group, are all most vocal during the spring mating season and much less so during late summer. In each species, the calls are at frequencies from several hundred to several thousand hertz—above the frequency range of the dominant noise components from most of the proposed oil exploration activities.
Cetacean hearing has been studied in relatively few species and individuals. The auditory sensitivity of bowhead, gray, and other baleen whales has not been measured, but relevant anatomical
and behavioral evidence is available. These whales appear to be specialized for low frequency hearing, with some directional hearing ability (reviewed in Richardson
et al.,
1995a; Ketten, 2000). Their optimum hearing overlaps broadly with the low frequency range where exploration drilling activities, airguns, and associated vessel traffic emit most of their energy.
The beluga whale is one of the better-studied species in terms of its hearing ability. As mentioned earlier, the auditory bandwidth in mid-frequency odontocetes is believed to range from 150 Hz to 160 kHz (Southall
et al.,
2007); however, belugas are most sensitive above 10 kHz. They have relatively poor sensitivity at the low frequencies (reviewed in Richardson
et al.,
1995a) that dominate the sound from industrial activities and associated vessels. Nonetheless, the noise from strong low frequency sources is detectable by belugas many kilometers away (Richardson and Wursig, 1997). Also, beluga hearing at low frequencies in open-water conditions is apparently somewhat better than in the captive situations where most hearing studies were conducted (Ridgway and Carder, 1995; Au, 1997). If so, low frequency sounds emanating from drilling activities may be detectable somewhat farther away than previously estimated.
Call characteristics of cetaceans provide some limited information on their hearing abilities, although the auditory range often extends beyond the range of frequencies contained in the calls. Also, understanding the frequencies at which different marine mammal species communicate is relevant for the assessment of potential impacts from manmade sounds. A summary of the call characteristics for bowhead, gray, and beluga whales is provided next.
Most bowhead calls are tonal, frequency-modulated sounds at frequencies of 50-400 Hz. These calls overlap broadly in frequency with the underwater sounds emitted by many of the activities to be performed during Shell's proposed exploration drilling program (Richardson
et al.,
1995a). Source levels are quite variable, with the stronger calls having source levels up to about 180 dB re 1 μPa at 1 m. Gray whales make a wide variety of calls at frequencies from < 100-2,000 Hz (Moore and Ljungblad, 1984; Dalheim, 1987).
Beluga calls include trills, whistles, clicks, bangs, chirps and other sounds (Schevill and Lawrence, 1949; Ouellet, 1979; Sjare and Smith, 1986a). Beluga whistles have dominant frequencies in the 2-6 kHz range (Sjare and Smith, 1986a). This is above the frequency range of most of the sound energy produced by the proposed exploratory drilling activities and associated vessels. Other beluga call types reported by Sjare and Smith (1986a,b) included sounds at mean frequencies ranging upward from 1 kHz.
The beluga also has a very well developed high frequency echolocation system, as reviewed by Au (1993). Echolocation signals have peak frequencies from 40-120 kHz and broadband source levels of up to 219 dB re 1 μPa-m (zero-peak). Echolocation calls are far above the frequency range of the sounds produced by the devices proposed for use during Shell's Chukchi Sea exploratory drilling program. Therefore, those industrial sounds are not expected to interfere with echolocation.
Potential Effects of the Specified Activity on Marine Mammals
The likely or possible impacts of the proposed exploratory drilling program in the Chukchi Sea on marine mammals could involve both non-acoustic and acoustic effects. Potential non-acoustic effects could result from the physical presence of the equipment and personnel. Petroleum development and associated activities introduce sound into the marine environment. Impacts to marine mammals are expected to primarily be acoustic in nature. Potential acoustic effects on marine mammals relate to sound produced by drilling activity, vessels, and aircraft, as well as the ZVSP airgun array. The potential effects of sound from the proposed exploratory drilling program might include one or more of the following: tolerance; masking of natural sounds; behavioral disturbance; non-auditory physical effects; and, at least in theory, temporary or permanent hearing impairment (Richardson
et al.,
1995a). However, for reasons discussed later in this document, it is unlikely that there would be any cases of temporary, or especially permanent, hearing impairment resulting from these activities. As outlined in previous NMFS documents, the effects of noise on marine mammals are highly variable, and can be categorized as follows (based on Richardson
et al.,
1995a):
(1) The noise may be too weak to be heard at the location of the animal (
i.e.,
lower than the prevailing ambient noise level, the hearing threshold of the animal at relevant frequencies, or both);
(2) The noise may be audible but not strong enough to elicit any overt behavioral response;
(3) The noise may elicit reactions of variable conspicuousness and variable relevance to the well being of the marine mammal; these can range from temporary alert responses to active avoidance reactions such as vacating an area at least until the noise event ceases but potentially for longer periods of time;
(4) Upon repeated exposure, a marine mammal may exhibit diminishing responsiveness (habituation), or disturbance effects may persist; the latter is most likely with sounds that are highly variable in characteristics, infrequent, and unpredictable in occurrence, and associated with situations that a marine mammal perceives as a threat;
(5) Any anthropogenic noise that is strong enough to be heard has the potential to reduce (mask) the ability of a marine mammal to hear natural sounds at similar frequencies, including calls from conspecifics, and underwater environmental sounds such as surf noise;
(6) If mammals remain in an area because it is important for feeding, breeding, or some other biologically important purpose even though there is chronic exposure to noise, it is possible that there could be noise-induced physiological stress; this might in turn have negative effects on the well-being or reproduction of the animals involved; and
(7) Very strong sounds have the potential to cause a temporary or permanent reduction in hearing sensitivity. In terrestrial mammals, and presumably marine mammals, received sound levels must far exceed the animal's hearing threshold for there to be any temporary threshold shift (TTS) in its hearing ability. For transient sounds, the sound level necessary to cause TTS is inversely related to the duration of the sound. Received sound levels must be even higher for there to be risk of permanent hearing impairment. In addition, intense acoustic or explosive events may cause trauma to tissues associated with organs vital for hearing, sound production, respiration and other functions. This trauma may include minor to severe hemorrhage.
Potential Acoustic Effects From Exploratory Drilling Activities
(1) Tolerance
Numerous studies have shown that underwater sounds from industry activities are often readily detectable by marine mammals in the water at distances of many kilometers. Numerous studies have also shown that marine mammals at distances more than a few kilometers away often show no apparent response to industry activities
of various types (Miller
et al.,
2005; Bain and Williams, 2006). This is often true even in cases when the 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) pinnipeds have been shown to react behaviorally to underwater sound such as airgun pulses or vessels under some conditions, at other times mammals of all three types have shown no overt reactions (
e.g.,
Malme
et al.,
1986; Richardson
et al.,
1995; Madsen and Mohl, 2000; Croll
et al.,
2001; Jacobs and Terhune, 2002; Madsen
et al.,
2002; Miller
et al.,
2005). In general, pinnipeds and small odontocetes seem to be more tolerant of exposure to some types of underwater sound than are baleen whales. Richardson
et al.
(1995a) found that vessel noise does not seem to strongly affect pinnipeds that are already in the water. Richardson
et al.
(1995a) went on to explain that seals on haul-outs sometimes respond strongly to the presence of vessels and at other times appear to show considerable tolerance of vessels, and Brueggeman
et al.
(1992, cited in Richardson
et al.,
1995a) observed ringed seals hauled out on ice pans displaying short-term escape reactions when a ship approached within 0.25-0.5 mi (0.4-0.8 km).
(2) Masking
Masking is the obscuring of sounds of interest by other sounds, often at similar frequencies. Marine mammals are highly dependent on sound, and their ability to recognize sound signals amid other noise is important in communication, predator and prey detection, and, in the case of toothed whales, echolocation. Even in the absence of manmade sounds, the sea is usually noisy. Background ambient noise often interferes with or masks the ability of an animal to detect a sound signal even when that signal is above its absolute hearing threshold. Natural ambient noise includes contributions from wind, waves, precipitation, other animals, and (at frequencies above 30 kHz) thermal noise resulting from molecular agitation (Richardson
et al.,
1995a). Background noise also can include sounds from human activities. Masking of natural sounds can result when human activities produce high levels of background noise. Conversely, if the background level of underwater noise is high (
e.g.,
on a day with strong wind and high waves), an anthropogenic noise source will not be detectable as far away as would be possible under quieter conditions and will itself be masked.
Although some degree of masking is inevitable when high levels of manmade broadband sounds are introduced into the sea, marine mammals have evolved systems and behavior that function to reduce the impacts of masking. Structured signals, such as the echolocation click sequences of small toothed whales, may be readily detected even in the presence of strong background noise because their frequency content and temporal features usually differ strongly from those of the background noise (Au and Moore, 1988, 1990). The components of background noise that are similar in frequency to the sound signal in question primarily determine the degree of masking of that signal.
Redundancy and context can also facilitate detection of weak signals. These phenomena may help marine mammals detect weak sounds in the presence of natural or manmade noise. Most masking studies in marine mammals present the test signal and the masking noise from the same direction. The sound localization abilities of marine mammals suggest that, if signal and noise come from different directions, masking would not be as severe as the usual types of masking studies might suggest (Richardson
et al.,
1995a). The dominant background noise may be highly directional if it comes from a particular anthropogenic source such as a ship or industrial site. Directional hearing may significantly reduce the masking effects of these noises by improving the effective signal-to-noise ratio. In the cases of high-frequency hearing by the bottlenose dolphin, beluga whale, and killer whale, empirical evidence confirms that masking depends strongly on the relative directions of arrival of sound signals and the masking noise (Penner
et al.,
1986; Dubrovskiy, 1990; Bain
et al.,
1993; Bain and Dahlheim, 1994). Toothed whales, and probably other marine mammals as well, have additional capabilities besides directional hearing that can facilitate detection of sounds in the presence of background noise. There is evidence that some toothed whales can shift the dominant frequencies of their echolocation signals from a frequency range with a lot of ambient noise toward frequencies with less noise (Au
et al.,
1974, 1985; Moore and Pawloski, 1990; Thomas and Turl, 1990; Romanenko and Kitain, 1992; Lesage
et al.,
1999). A few marine mammal species are known to increase the source levels or alter the frequency of their calls in the presence of elevated sound levels (Dahlheim, 1987; Au, 1993; Lesage
et al.,
1993, 1999; Terhune, 1999; Foote
et al.,
2004; Parks
et al.,
2007, 2009; Di Iorio and Clark, 2009; Holt
et al.,
2009).
These data demonstrating adaptations for reduced masking pertain mainly to the very high frequency echolocation signals of toothed whales. There is less information about the existence of corresponding mechanisms at moderate or low frequencies or in other types of marine mammals. For example, Zaitseva
et al.
(1980) found that, for the bottlenose dolphin, the angular separation between a sound source and a masking noise source had little effect on the degree of masking when the sound frequency was 18 kHz, in contrast to the pronounced effect at higher frequencies. Directional hearing has been demonstrated at frequencies as low as 0.5-2 kHz in several marine mammals, including killer whales (Richardson
et al.,
1995a). This ability may be useful in reducing masking at these frequencies. In summary, high levels of noise generated by anthropogenic activities may act to mask the detection of weaker biologically important sounds by some marine mammals. This masking may be more prominent for lower frequencies. For higher frequencies, such as that used in echolocation by toothed whales, several mechanisms are available that may allow them to reduce the effects of such masking.
Masking effects of underwater sounds from Shell's proposed activities on marine mammal calls and other natural sounds are expected to be limited. For example, beluga whales primarily use high-frequency sounds to communicate and locate prey; therefore, masking by low-frequency sounds associated with drilling activities is not expected to occur (Gales, 1982, as cited in Shell, 2009). If the distance between communicating whales does not exceed their distance from the drilling activity, the likelihood of potential impacts from masking would be low (Gales, 1982, as cited in Shell, 2009). At distances greater than 660-1,300 ft (200-400 m), recorded sounds from drilling activities did not affect behavior of beluga whales, even though the sound energy level and frequency were such that it could be heard several kilometers away (Richardson
et al.,
1995b). This exposure resulted in whales being deflected from the sound energy and changing behavior. These minor changes are not expected to affect the beluga whale population (Richardson
et al.,
1991; Richard
et al.,
1998). Brewer
et al.
(1993) observed belugas within 2.3 mi (3.7 km) of the drilling unit
Kulluk
during drilling; however, the authors do
not describe any behaviors that may have been exhibited by those animals. Please refer to the Arctic Multiple-Sale Draft Environmental Impact Statement (USDOI MMS, 2008), available on the Internet at:
http://www.mms.gov/alaska/ref/EIS%20EA/ArcticMultiSale_209/_DEIS.htm,
for more detailed information.
There is evidence of other marine mammal species continuing to call in the presence of industrial activity. Annual acoustical monitoring near BP's Northstar production facility during the fall bowhead migration westward through the Beaufort Sea has recorded thousands of calls each year (for examples, see Richardson
et al.,
2007; Aerts and Richardson, 2008). Construction, maintenance, and operational activities have been occurring from this facility for over 10 years. To compensate and reduce masking, some mysticetes may alter the frequencies of their communication sounds (Richardson
et al.,
1995a; Parks
et al.,
2007). Masking processes in baleen whales are not amenable to laboratory study, and no direct measurements on hearing sensitivity are available for these species. It is not currently possible to determine with precision the potential consequences of temporary or local background noise levels. However, Parks
et al.
(2007) found that right whales (a species closely related to the bowhead whale) altered their vocalizations, possibly in response to background noise levels. For species that can hear over a relatively broad frequency range, as is presumed to be the case for mysticetes, a narrow band source may only cause partial masking. Richardson
et al.
(1995a) note that a bowhead whale 12.4 mi (20 km) from a human sound source, such as that produced during oil and gas industry activities, might hear strong calls from other whales within approximately 12.4 mi (20 km), and a whale 3.1 mi (5 km) from the source might hear strong calls from whales within approximately 3.1 mi (5 km). Additionally, masking is more likely to occur closer to a sound source, and distant anthropogenic sound is less likely to mask short-distance acoustic communication (Richardson
et al.,
1995a).
Although some masking by marine mammal species in the area may occur, the extent of the masking interference will depend on the spatial relationship of the animal and Shell's activity. Almost all energy in the sounds emitted by drilling and other operational activities is at low frequencies, predominantly below 250 Hz with another peak centered around 1,000 Hz. Most energy in the sounds from the vessels and aircraft to be used during this project is below 1 kHz (Moore
et al.,
1984; Greene and Moore, 1995; Blackwell
et al.,
2004b; Blackwell and Greene, 2006). These frequencies are mainly used by mysticetes but not by odontocetes. Therefore, masking effects would potentially be more pronounced in the bowhead and gray whales that might occur in the proposed project area. If, as described later in this document, certain species avoid the proposed drilling locations, impacts from masking are anticipated to be low.
(3) Behavioral Disturbance Reactions
Behavioral responses to sound are highly variable and context-specific. Many different variables can influence an animal's perception of and response to (in both nature and magnitude) an acoustic event. An animal's prior experience with a sound or sound source affects whether it is less likely (habituation) or more likely (sensitization) to respond to certain sounds in the future (animals can also be innately pre-disposed to respond to certain sounds in certain ways; Southall
et al.,
2007). Related to the sound itself, the perceived nearness of the sound, bearing of the sound (approaching vs. retreating), similarity of a sound to biologically relevant sounds in the animal's environment (
i.e.,
calls of predators, prey, or conspecifics), and familiarity of the sound may affect the way an animal responds to the sound (Southall
et al.,
2007). Individuals (of different age, gender, reproductive status,
etc.
) among most populations will have variable hearing capabilities and differing behavioral sensitivities to sounds that will be affected by prior conditioning, experience, and current activities of those individuals. Often, specific acoustic features of the sound and contextual variables (
i.e.,
proximity, duration, or recurrence of the sound or the current behavior that the marine mammal is engaged in or its prior experience), as well as entirely separate factors such as the physical presence of a nearby vessel, may be more relevant to the animal's response than the received level alone.
Exposure of marine mammals to sound sources can result in (but is not limited to) no response or any of the following observable responses: Increased alertness; orientation or attraction to a sound source; vocal modifications; cessation of feeding; cessation of social interaction; alteration of movement or diving behavior; avoidance; habitat abandonment (temporary or permanent); and, in severe cases, panic, flight, stampede, or stranding, potentially resulting in death (Southall
et al.,
2007). On a related note, many animals perform vital functions, such as feeding, resting, traveling, and socializing, on a diel cycle (24-hr cycle). Behavioral reactions to noise exposure (such as disruption of critical life functions, displacement, or avoidance of important habitat) are more likely to be significant if they last more than one diel cycle or recur on subsequent days (Southall
et al.,
2007). Consequently, a behavioral response lasting less than one day and not recurring on subsequent days is not considered particularly severe unless it could directly affect reproduction or survival (Southall
et al.,
2007).
Detailed studies regarding responses to anthropogenic sound have been conducted on humpback, gray, and bowhead whales and ringed seals. Less detailed data are available for some other species of baleen whales, sperm whales, small toothed whales, and sea otters. The following sub-sections provide examples of behavioral responses that provide an idea of the variability in behavioral responses that would be expected given the different sensitivities of marine mammal species to sound.
Baleen Whales
—Richardson
et al.
(1995b) reported changes in surfacing and respiration behavior and the occurrence of turns during surfacing in bowhead whales exposed to playback of underwater sound from drilling activities. These behavioral effects were localized and occurred at distances up to 1.2-2.5 mi (2-4 km).
Some bowheads appeared to divert from their migratory path after exposure to projected icebreaker sounds. Other bowheads however, tolerated projected icebreaker sound at levels 20 dB and more above ambient sound levels. The source level of the projected sound however, was much less than that of an actual icebreaker, and reaction distances to actual icebreaking may be much greater than those reported here for projected sounds.
Brewer
et al.
(1993) and Hall
et al.
(1994) reported numerous sightings of marine mammals including bowhead whales in the vicinity of offshore drilling operations in the Beaufort Sea. One bowhead whale sighting was reported within approximately 1,312 ft (400 m) of a drilling vessel although most other bowhead sightings were at much greater distances. Few bowheads were recorded near industrial activities by aerial observers. After controlling for spatial autocorrelation in aerial survey data from Hall
et al.
(1994) using a Mantel test, Schick and Urban (2000) found that the variable describing
straight line distance between the rig and bowhead whale sightings was not significant but that a variable describing threshold distances between sightings and the rig was significant. Thus, although the aerial survey results suggested substantial avoidance of the operations by bowhead whales, observations by vessel-based observers indicate that at least some bowheads may have been closer to industrial activities than was suggested by results of aerial observations.
Richardson
et al.
(2008) reported a slight change in the distribution of bowhead whale calls in response to operational sounds on BP's Northstar Island. The southern edge of the call distribution ranged from 0.47 to 1.46 mi (0.76 to 2.35 km) farther offshore, apparently in response to industrial sound levels. This result however, was only achieved after intensive statistical analyses, and it is not clear that this represented a biologically significant effect.
Patenaude
et al.
(2002) reported fewer behavioral responses to aircraft overflights by bowhead compared to beluga whales. Behaviors classified as reactions consisted of short surfacings, immediate dives or turns, changes in behavior state, vigorous swimming, and breaching. Most bowhead reaction resulted from exposure to helicopter activity and little response to fixed-wing aircraft was observed. Most reactions occurred when the helicopter was at altitudes ≤492 ft (150 m) and lateral distances ≤820 ft (250 m; Nowacek
et al.,
2007).
During their study, Patenaude
et al.
(2002) observed one bowhead whale cow-calf pair during four passes totaling 2.8 hours of the helicopter and two pairs during Twin Otter overflights. All of the helicopter passes were at altitudes of 49-98 ft (15-30 m). The mother dove both times she was at the surface, and the calf dove once out of the four times it was at the surface. For the cow-calf pair sightings during Twin Otter overflights, the authors did not note any behaviors specific to those pairs. Rather, the reactions of the cow-calf pairs were lumped with the reactions of other groups that did not consist of calves.
Richardson
et al.
(1995b) and Moore and Clarke (2002) reviewed a few studies that observed responses of gray whales to aircraft. Cow-calf pairs were quite sensitive to a turboprop survey flown at 1,000 ft (305 m) altitude on the Alaskan summering grounds. In that survey, adults were seen swimming over the calf, or the calf swam under the adult (Ljungblad
et al.,
1983, cited in Richardson
et al.,
1995b and Moore and Clarke, 2002). However, when the same aircraft circled for more than 10 minutes at 1,050 ft (320 m) altitude over a group of mating gray whales, no reactions were observed (Ljungblad
et al.,
1987, cited in Moore and Clarke, 2002). Malme
et al.
(1984, cited in Richardson
et al.,
1995b and Moore and Clarke, 2002) conducted playback experiments on migrating gray whales. They exposed the animals to underwater noise recorded from a Bell 212 helicopter (estimated altitude = 328 ft [100 m]), at an average of three simulated passes per minute. The authors observed that whales changed their swimming course and sometimes slowed down in response to the playback sound but proceeded to migrate past the transducer. Migrating gray whales did not react overtly to a Bell 212 helicopter at greater than 1,394 ft (425 m) altitude, occasionally reacted when the helicopter was at 1,000-1,198 ft (305-365 m), and usually reacted when it was below 825 ft (250 m; Southwest Research Associates, 1988, cited in Richardson
et al.,
1995b and Moore and Clarke, 2002). Reactions noted in that study included abrupt turns or dives or both. Green
et al.
(1992, cited in Richardson
et al.,
1995b) observed that migrating gray whales rarely exhibited noticeable reactions to a straight-line overflight by a Twin Otter at 197 ft (60 m) altitude. Restrictions on aircraft altitude will be part of the proposed mitigation measures (described in the “Proposed Mitigation” section later in this document) during the proposed drilling activities, and overflights are likely to have little or no disturbance effects on baleen whales. Any disturbance that may occur would likely be temporary and localized.
Southall
et al.
(2007, Appendix C) reviewed a number of papers describing the responses of marine mammals to non-pulsed sound, such as that produced during exploratory drilling operations. In general, little or no response was observed in animals exposed at received levels from 90-120 dB re 1 µPa (rms). Probability of avoidance and other behavioral effects increased when received levels were from 120-160 dB re 1 µPa (rms). Some of the relevant reviews contained in Southall
et al.
(2007) are summarized next.
Baker
et al.
(1982) reported some avoidance by humpback whales to vessel noise when received levels were 110-120 dB (rms) and clear avoidance at 120-140 dB (sound measurements were not provided by Baker but were based on measurements of identical vessels by Miles and Malme, 1983).
Malme
et al.
(1983, 1984) used playbacks of sounds from helicopter overflight and drilling rigs and platforms to study behavioral effects on migrating gray whales. Received levels exceeding 120 dB induced avoidance reactions. Malme
et al.
(1984) calculated 10%, 50%, and 90% probabilities of gray whale avoidance reactions at received levels of 110, 120, and 130 dB, respectively. Malme
et al.
(1986) observed the behavior of feeding gray whales during four experimental playbacks of drilling sounds (50 to 315 Hz; 21- min overall duration and 10% duty cycle; source levels of 156-162 dB). In two cases for received levels of 100-110 dB, no behavioral reaction was observed. However, avoidance behavior was observed in two cases where received levels were 110-120 dB.
Richardson
et al.
(1990) performed 12 playback experiments in which bowhead whales in the Alaskan Arctic were exposed to drilling sounds. Whales generally did not respond to exposures in the 100 to 130 dB range, although there was some indication of minor behavioral changes in several instances.
McCauley
et al.
(1996) reported several cases of humpback whales responding to vessels in Hervey Bay, Australia. Results indicated clear avoidance at received levels between 118 to 124 dB in three cases for which response and received levels were observed/measured.
Palka and Hammond (2001) analyzed line transect census data in which the orientation and distance off transect line were reported for large numbers of minke whales. The authors developed a method to account for effects of animal movement in response to sighting platforms. Minor changes in locomotion speed, direction, and/or diving profile were reported at ranges from 1,847 to 2,352 ft (563 to 717 m) at received levels of 110 to 120 dB.
Biassoni
et al.
(2000) and Miller
et al.
(2000) reported behavioral observations for humpback whales exposed to a low-frequency sonar stimulus (160- to 330-Hz frequency band; 42-s tonal signal repeated every 6 min; source levels 170 to 200 dB) during playback experiments. Exposure to measured received levels ranging from 120 to 150 dB resulted in variability in humpback singing behavior. Croll
et al.
(2001) investigated responses of foraging fin and blue whales to the same low frequency active sonar stimulus off southern California. Playbacks and control intervals with no transmission were used to investigate behavior and distribution on time scales of several weeks and spatial scales of tens of kilometers. The general conclusion was that whales remained feeding within a region for which 12 to
30 percent of exposures exceeded 140 dB.
Frankel and Clark (1998) conducted playback experiments with wintering humpback whales using a single speaker producing a low-frequency “M-sequence” (sine wave with multiple-phase reversals) signal in the 60 to 90 Hz band with output of 172 dB at 1 m. For 11 playbacks, exposures were between 120 and 130 dB re 1 µPa (rms) and included sufficient information regarding individual responses. During eight of the trials, there were no measurable differences in tracks or bearings relative to control conditions, whereas on three occasions, whales either moved slightly away from (n = 1) or towards (n = 2) the playback speaker during exposure. The presence of the source vessel itself had a greater effect than did the M-sequence playback.
Finally, Nowacek
et al.
(2004) used controlled exposures to demonstrate behavioral reactions of northern right whales to various non-pulse sounds. Playback stimuli included ship noise, social sounds of conspecifics, and a complex, 18-min “alert” sound consisting of repetitions of three different artificial signals. Ten whales were tagged with calibrated instruments that measured received sound characteristics and concurrent animal movements in three dimensions. Five out of six exposed whales reacted strongly to alert signals at measured received levels between 130 and 150 dB (
i.e.,
ceased foraging and swam rapidly to the surface). Two of these individuals were not exposed to ship noise, and the other four were exposed to both stimuli. These whales reacted mildly to conspecific signals. Seven whales, including the four exposed to the alert stimulus, had no measurable response to either ship sounds or actual vessel noise.
Toothed Whales
—Most toothed whales have the greatest hearing sensitivity at frequencies much higher than that of baleen whales and may be less responsive to low-frequency sound commonly associated with oil and gas industry exploratory drilling activities. Richardson
et al.
(1995b) reported that beluga whales did not show any apparent reaction to playback of underwater drilling sounds at distances greater than 656-1,312 ft (200-400 m). Reactions included slowing down, milling, or reversal of course after which the whales continued past the projector, sometimes within 164-328 ft (50-100 m). The authors concluded (based on a small sample size) that the playback of drilling sounds had no biologically significant effects on migration routes of beluga whales migrating through pack ice and along the seaward side of the nearshore lead east of Point Barrow in spring.
At least six of 17 groups of beluga whales appeared to alter their migration path in response to underwater playbacks of icebreaker sound (Richardson
et al.,
1995b). Received levels from the icebreaker playback were estimated at 78-84 dB in the 1/3-octave band centered at 5,000 Hz, or 8-14 dB above ambient. If beluga whales reacted to an actual icebreaker at received levels of 80 dB, reactions would be expected to occur at distances on the order of 6.2 mi (10 km). Finley
et al.
(1990) also reported beluga avoidance of icebreaker activities in the Canadian High Arctic at distances of 22-31 mi (35-50 km). In addition to avoidance, changes in dive behavior and pod integrity were also noted.
Patenaude
et al.
(2002) reported that beluga whales appeared to be more responsive to aircraft overflights than bowhead whales. Changes were observed in diving and respiration behavior, and some whales veered away when a helicopter passed at ≤820 ft (250 m) lateral distance at altitudes up to 492 ft (150 m). However, some belugas showed no reaction to the helicopter. Belugas appeared to show less response to fixed-wing aircraft than to helicopter overflights.
In reviewing responses of cetaceans with best hearing in mid-frequency ranges, which includes toothed whales, Southall
et al.
(2007) reported that combined field and laboratory data for mid-frequency cetaceans exposed to non-pulse sounds did not lead to a clear conclusion about received levels coincident with various behavioral responses. In some settings, individuals in the field showed profound (significant) behavioral responses to exposures from 90-120 dB, while others failed to exhibit such responses for exposure to received levels from 120-150 dB. Contextual variables other than exposure received level, and probable species differences, are the likely reasons for this variability. Context, including the fact that captive subjects were often directly reinforced with food for tolerating noise exposure, may also explain why there was great disparity in results from field and laboratory conditions—exposures in captive settings generally exceeded 170 dB before inducing behavioral responses. A summary of some of the relevant material reviewed by Southall
et al.
(2007) is next.
LGL and Greeneridge (1986) and Finley
et al.
(1990) documented belugas and narwhals congregated near ice edges reacting to the approach and passage of icebreaking ships. Beluga whales responded to oncoming vessels by (1) fleeing at speeds of up to 12.4 mi/hr (20 km/hr) from distances of 12.4-50 mi (20-80 km), (2) abandoning normal pod structure, and (3) modifying vocal behavior and/or emitting alarm calls. Narwhals, in contrast, generally demonstrated a “freeze” response, lying motionless or swimming slowly away (as far as 23 mi [37 km] down the ice edge), huddling in groups, and ceasing sound production. There was some evidence of habituation and reduced avoidance 2 to 3 days after onset.
The 1982 season observations by LGL and Greeneridge (1986) involved a single passage of an icebreaker with both ice-based and aerial measurements on June 28, 1982. Four groups of narwhals (n = 9 to 10, 7, 7, and 6) responded when the ship was 4 mi (6.4 km) away (received levels of approximately 100 dB in the 150- to 1,150-Hz band). At a later point, observers sighted belugas moving away from the source at more than 12.4 mi (20 km; received levels of approximately 90 dB in the 150- to 1,150-Hz band). The total number of animals observed fleeing was about 300, suggesting approximately 100 independent groups (of three individuals each). No whales were sighted the following day, but some were sighted on June 30, with ship noise audible at spectrum levels of approximately 55 dB/Hz (up to 4 kHz).
Observations during 1983 (LGL and Greeneridge, 1986) involved two icebreaking ships with aerial survey and ice-based observations during seven sampling periods. Narwhals and belugas generally reacted at received levels ranging from 101 to 121 dB in the 20- to 1,000-Hz band and at a distance of up to 40.4 mi (65 km). Large numbers (100s) of beluga whales moved out of the area at higher received levels. As noise levels from icebreaking operations diminished, a total of 45 narwhals returned to the area and engaged in diving and foraging behavior. During the final sampling period, following an 8-h quiet interval, no reactions were seen from 28 narwhals and 17 belugas (at received levels ranging up to 115 dB).
The final season (1984) reported in LGL and Greeneridge (1986) involved aerial surveys before, during, and after the passage of two icebreaking ships. During operations, no belugas and few narwhals were observed in an area approximately 16.8 mi (27 km) ahead of the vessels, and all whales sighted over 12.4-50 mi (20-80 km) from the ships were swimming strongly away. Additional observations confirmed the spatial extent of avoidance reactions to this sound source in this context.
Buckstaff (2004) reported elevated dolphin whistle rates with received levels from oncoming vessels in the 110 to 120 dB range in Sarasota Bay, Florida. These hearing thresholds were apparently lower than those reported by a researcher listening with towed hydrophones. Morisaka
et al.
(2005) compared whistles from three populations of Indo-Pacific bottlenose dolphins. One population was exposed to vessel noise with spectrum levels of approximately 85 dB/Hz in the 1- to 22-kHz band (broadband received levels approximately 128 dB) as opposed to approximately 65 dB/Hz in the same band (broadband received levels approximately 108 dB) for the other two sites. Dolphin whistles in the noisier environment had lower fundamental frequencies and less frequency modulation, suggesting a shift in sound parameters as a result of increased ambient noise.
Morton and Symonds (2002) used census data on killer whales in British Columbia to evaluate avoidance of non-pulse acoustic harassment devices (AHDs). Avoidance ranges were about 2.5 mi (4 km). Also, there was a dramatic reduction in the number of days “resident” killer whales were sighted during AHD-active periods compared to pre- and post-exposure periods and a nearby control site.
Monteiro-Neto
et al.
(2004) studied avoidance responses of tucuxi (
Sotalia fluviatilis
) to Dukane® Netmark acoustic deterrent devices. In a total of 30 exposure trials, approximately five groups each demonstrated significant avoidance compared to 20 pinger off and 55 no-pinger control trials over two quadrats of about 0.19 mi
2
(0.5 km
2
). Estimated exposure received levels were approximately 115 dB.
Awbrey and Stewart (1983) played back semi-submersible drillship sounds (source level: 163 dB) to belugas in Alaska. They reported avoidance reactions at 984 and 4,921 ft (300 and 1,500 m) and approach by groups at a distance of 2.2 mi (3.5 km; received levels were approximately 110 to 145 dB over these ranges assuming a 15 log R transmission loss). Similarly, Richardson
et al.
(1990) played back drilling platform sounds (source level: 163 dB) to belugas in Alaska. They conducted aerial observations of eight individuals among approximately 100 spread over an area several hundred meters to several kilometers from the sound source and found no obvious reactions. Moderate changes in movement were noted for three groups swimming within 656 ft (200 m) of the sound projector.
Two studies deal with issues related to changes in marine mammal vocal behavior as a function of variable background noise levels. Foote
et al.
(2004) found increases in the duration of killer whale calls over the period 1977 to 2003, during which time vessel traffic in Puget Sound, and particularly whale-watching boats around the animals, increased dramatically. Scheifele
et al.
(2005) demonstrated that belugas in the St. Lawrence River increased the levels of their vocalizations as a function of the background noise level (the “Lombard Effect”).
Several researchers conducting laboratory experiments on hearing and the effects of non-pulse sounds on hearing in mid-frequency cetaceans have reported concurrent behavioral responses. Nachtigall
et al.
(2003) reported that noise exposures up to 179 dB and 55-min duration affected the trained behaviors of a bottlenose dolphin participating in a TTS experiment. Finneran and Schlundt (2004) provided a detailed, comprehensive analysis of the behavioral responses of belugas and bottlenose dolphins to 1-s tones (received levels 160 to 202 dB) in the context of TTS experiments. Romano
et al.
(2004) investigated the physiological responses of a bottlenose dolphin and a beluga exposed to these tonal exposures and demonstrated a decrease in blood cortisol levels during a series of exposures between 130 and 201 dB. Collectively, the laboratory observations suggested the onset of a behavioral response at higher received levels than did field studies. The differences were likely related to the very different conditions and contextual variables between untrained, free-ranging individuals vs. laboratory subjects that were rewarded with food for tolerating noise exposure.
Pinnipeds
—Pinnipeds generally seem to be less responsive to exposure to industrial sound than most cetaceans. Pinniped responses to underwater sound from some types of industrial activities such as seismic exploration appear to be temporary and localized (Harris
et al.,
2001; Reiser
et al.,
2009).
Blackwell
et al.
(2004) reported little or no reaction of ringed seals in response to pile-driving activities during construction of a man-made island in the Beaufort Sea. Ringed seals were observed swimming as close as 151 ft (46 m) from the island and may have been habituated to the sounds which were likely audible at distances <9,842 ft (3,000 m) underwater and 0.3 mi (0.5 km) in air. Moulton
et al.
(2003) reported that ringed seal densities on ice in the vicinity of a man-made island in the Beaufort Sea did not change significantly before and after construction and drilling activities.
Southall
et al.
(2007) reviewed literature describing responses of pinnipeds to non-pulsed sound and reported that the limited data suggest exposures between approximately 90 and 140 dB generally do not appear to induce strong behavioral responses in pinnipeds exposed to non-pulse sounds in water; no data exist regarding exposures at higher levels. It is important to note that among these studies, there are some apparent differences in responses between field and laboratory conditions. In contrast to the mid-frequency odontocetes, captive pinnipeds responded more strongly at lower levels than did animals in the field. Again, contextual issues are the likely cause of this difference.
Jacobs and Terhune (2002) observed harbor seal reactions to AHDs (source level in this study was 172 dB) deployed around aquaculture sites. Seals were generally unresponsive to sounds from the AHDs. During two specific events, individuals came within 141 and 144 ft (43 and 44 m) of active AHDs and failed to demonstrate any measurable behavioral response; estimated received levels based on the measures given were approximately 120 to 130 dB.
Costa
et al.
(2003) measured received noise levels from an Acoustic Thermometry of Ocean Climate (ATOC) program sound source off northern California using acoustic data loggers placed on translocated elephant seals. Subjects were captured on land, transported to sea, instrumented with archival acoustic tags, and released such that their transit would lead them near an active ATOC source (at 939-m depth; 75-Hz signal with 37.5- Hz bandwidth; 195 dB maximum source level, ramped up from 165 dB over 20 min) on their return to a haul-out site. Received exposure levels of the ATOC source for experimental subjects averaged 128 dB (range 118 to 137) in the 60- to 90-Hz band. None of the instrumented animals terminated dives or radically altered behavior upon exposure, but some statistically significant changes in diving parameters were documented in nine individuals. Translocated northern elephant seals exposed to this particular non-pulse source began to demonstrate subtle behavioral changes at exposure to received levels of approximately 120 to 140 dB.
Kastelein
et al.
(2006) exposed nine captive harbor seals in an approximately 82 × 98 ft (25 × 30 m) enclosure to non-pulse sounds used in underwater data
communication systems (similar to acoustic modems). Test signals were frequency modulated tones, sweeps, and bands of noise with fundamental frequencies between 8 and 16 kHz; 128 to 130 [± 3] dB source levels; 1- to 2-s duration [60-80 percent duty cycle]; or 100 percent duty cycle. They recorded seal positions and the mean number of individual surfacing behaviors during control periods (no exposure), before exposure, and in 15-min experimental sessions (n = 7 exposures for each sound type). Seals generally swam away from each source at received levels of approximately 107 dB, avoiding it by approximately 16 ft (5 m), although they did not haul out of the water or change surfacing behavior. Seal reactions did not appear to wane over repeated exposure (
i.e.,
there was no obvious habituation), and the colony of seals generally returned to baseline conditions following exposure. The seals were not reinforced with food for remaining in the sound field.
Potential effects to pinnipeds from aircraft activity could involve both acoustic and non-acoustic effects. It is uncertain if the seals react to the sound of the helicopter or to its physical presence flying overhead. Typical reactions of hauled out pinnipeds to aircraft that have been observed include looking up at the aircraft, moving on the ice or land, entering a breathing hole or crack in the ice, or entering the water. Ice seals hauled out on the ice have been observed diving into the water when approached by a low-flying aircraft or helicopter (Burns and Harbo, 1972, cited in Richardson
et al.,
1995a; Burns and Frost, 1979, cited in Richardson
et al.,
1995a). Richardson
et al.
(1995a) note that responses can vary based on differences in aircraft type, altitude, and flight pattern. Additionally, a study conducted by Born
et al.
(1999) found that wind chill was also a factor in level of response of ringed seals hauled out on ice, as well as time of day and relative wind direction.
Blackwell
et al.
(2004a) observed 12 ringed seals during low-altitude overflights of a Bell 212 helicopter at Northstar in June and July 2000 (9 observations took place concurrent with pipe-driving activities). One seal showed no reaction to the aircraft while the remaining 11 (92%) reacted, either by looking at the helicopter (n = 10) or by departing from their basking site (n = 1). Blackwell
et al.
(2004a) concluded that none of the reactions to helicopters were strong or long lasting, and that seals near Northstar in June and July 2000 probably had habituated to industrial sounds and visible activities that had occurred often during the preceding winter and spring. There have been few systematic studies of pinniped reactions to aircraft overflights, and most of the available data concern pinnipeds hauled out on land or ice rather than pinnipeds in the water (Richardson
et al.,
1995a; Born
et al.,
1999).
Born
et al.
(1999) determined that 49 percent of ringed seals escaped (
i.e.,
left the ice) as a response to a helicopter flying at 492 ft (150 m) altitude. Seals entered the water when the helicopter was 4,101 ft (1,250 m) away if the seal was in front of the helicopter and at 1,640 ft (500 m) away if the seal was to the side of the helicopter. The authors noted that more seals reacted to helicopters than to fixed-wing aircraft. The study concluded that the risk of scaring ringed seals by small-type helicopters could be substantially reduced if they do not approach closer than 4,921 ft (1,500 m).
Spotted seals hauled out on land in summer are unusually sensitive to aircraft overflights compared to other species. They often rush into the water when an aircraft flies by at altitudes up to 984-2,461 ft (300-750 m). They occasionally react to aircraft flying as high as 4,495 ft (1,370 m) and at lateral distances as far as 1.2 mi (2 km) or more (Frost and Lowry, 1990; Rugh
et al.,
1997).
(4) Hearing Impairment and Other Physiological Effects
Temporary or permanent hearing impairment is a possibility when marine mammals are exposed to very strong sounds. Non-auditory physiological effects might also occur in marine mammals exposed to strong underwater 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 later in this document, there is no definitive evidence that any of these effects occur even for marine mammals in close proximity to industrial sound sources, and beaked whales do not occur in the proposed activity area. Additional information regarding the possibilities of TTS, permanent threshold shift (PTS), and non-auditory physiological effects, such as stress, is discussed for both exploratory drilling activities and ZVSP surveys in the following section (“
Potential Effects from ZVSP Activities
”).
Potential Effects from ZVSP Activities
(1) Tolerance
Numerous studies have shown that pulsed sounds from airguns are often readily detectable in the water at distances of many kilometers. Weir (2008) observed marine mammal responses to seismic pulses from a 24 airgun array firing a total volume of either 5,085 in
3
or 3,147 in
3
in Angolan waters between August 2004 and May 2005. Weir recorded a total of 207 sightings of humpback whales (n = 66), sperm whales (n = 124), and Atlantic spotted dolphins (n = 17) and reported that there were no significant differences in encounter rates (sightings/hr) for humpback and sperm whales according to the airgun array's operational status (
i.e.,
active versus silent). For additional information on tolerance of marine mammals to anthropogenic sound, see the previous subsection in this document (“
Potential Effects from Exploratory Drilling Activities
”).
(2) Masking
As stated earlier in this document, masking is the obscuring of sounds of interest by other sounds, often at similar frequencies. For full details about masking, see the previous subsection in this document (“
Potential Effects from Exploratory Drilling Activities
”). Some additional information regarding pulsed sounds is provided here.
There is evidence of some marine mammal species continuing to call in the presence of industrial activity. McDonald
et al.
(1995) heard blue and fin whale calls between seismic pulses in the Pacific. 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 reported that sperm whales off northern Norway continued calling in the presence of seismic pulses (Madsen
et al.,
2002). Similar results were also reported during work in the Gulf of Mexico (Tyack
et al.,
2003). Bowhead whale calls are frequently detected in the presence of seismic pulses, although the numbers of calls detected may sometimes be reduced (Richardson
et al.,
1986; Greene
et al.,
1999; Blackwell
et al.,
2009a). Bowhead whales in the Beaufort Sea may decrease their call rates in response to seismic operations, although movement out of the area might also have contributed to the lower call detection rate (Blackwell
et al.,
2009a,b). Additionally, there is
increasing evidence that, at times, there is enough reverberation between airgun pulses such that detection range of calls may be significantly reduced. In contrast, Di Iorio and Clark (2009) found evidence of increased calling by blue whales during operations by a lower-energy seismic source, a sparker.
There is little concern regarding masking due to the brief duration of these pulses and relatively longer silence between airgun shots (9-12 seconds) near the sound source. However, at long distances (over tens of kilometers away) in deep water, due to multipath propagation and reverberation, the durations of airgun pulses can be “stretched” to seconds with long decays (Madsen
et al.,
2006; Clark and Gagnon, 2006). Therefore it could affect communication signals used by low frequency mysticetes when they occur near the noise band and thus reduce the communication space of animals (
e.g.,
Clark
et al.,
2009a,b) and cause increased stress levels (
e.g.,
Foote
et al.,
2004; Holt
et al.,
2009). Nevertheless, the intensity of the noise is also greatly reduced at long distances. Therefore, masking effects are anticipated to be limited, especially in the case of odontocetes, given that they typically communicate at frequencies higher than those of the airguns.
(3) Behavioral Disturbance Reactions
As was described in more detail in the previous sub-section (“
Potential Effects of Exploratory Drilling Activities”
), behavioral responses to sound are highly variable and context-specific. Summaries of observed reactions and studies are provided next.
Baleen Whales
—Baleen whale responses to pulsed sound (
e.g.,
seismic airguns) have been studied more thoroughly than responses to continuous sound (
e.g.,
drillships). Baleen whales generally tend to avoid operating airguns, but avoidance radii are quite variable. Whales are often reported to show no overt reactions to pulses from large arrays of airguns at distances beyond a few kilometers, even though the airgun pulses remain well above ambient noise levels out to much greater distances (Miller
et al.,
2005). However, baleen whales exposed to strong noise pulses often react by deviating from their normal migration route (Richardson
et al.,
1999). Migrating gray and bowhead whales were observed avoiding the sound source by displacing their migration route to varying degrees but within the natural boundaries of the migration corridors (Schick and Urban, 2000; Richardson
et al.,
1999; Malme
et al.,
1983). Baleen whale responses to pulsed sound however may depend on the type of activity in which the whales are engaged. Some evidence suggests that feeding bowhead whales may be more tolerant of underwater sound than migrating bowheads (Miller
et al.,
2005; Lyons
et al.,
2009; Christie
et al.,
2010).
Results of 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 2.8-9 mi (4.5-14.5 km) from the source. For the much smaller airgun array used during the ZVSP survey (total discharge volume of 760 in
3
), distances to received levels in the 170-160 dB re 1 µPa rms range are estimated to be 1.44-2.28 mi (2.31-3.67 km). 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 μPa rms. Bowhead whales migrating west across the Alaskan Beaufort Sea in autumn, in particular, are unusually responsive, with avoidance occurring out to distances of 12.4-18.6 mi (20-30 km) from a medium-sized airgun source (Miller
et al.,
1999; Richardson
et al.,
1999). However, more recent research on bowhead whales (Miller
et al.,
2005) corroborates earlier evidence that, during the summer feeding season, bowheads are not as sensitive to seismic sources. In summer, bowheads typically begin to show avoidance reactions at a received level of about 160-170 dB re 1 µPa rms (Richardson
et al.,
1986; Ljungblad
et al.,
1988; Miller
et al.,
2005).
Malme
et al.
(1986, 1988) studied the responses of feeding eastern gray whales to pulses from a single 100 in
3
airgun off St. Lawrence Island in the northern Bering Sea. They estimated, based on small sample sizes, that 50% 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% of feeding whales interrupted feeding at received levels of 163 dB. Those findings were generally consistent with the results of experiments conducted on larger numbers of gray whales that were migrating along the California coast and on observations of the distribution of feeding Western Pacific gray whales off Sakhalin Island, Russia, during a seismic survey (Yazvenko
et al.,
2007).
Data on short-term reactions (or lack of reactions) of cetaceans to impulsive noises do not necessarily provide information about long-term effects. While it is not certain whether impulsive noises affect reproductive rate or distribution and habitat use in subsequent days or years, certain species have continued to use areas ensonified by airguns and have continued to increase in number despite successive years of anthropogenic activity in the area. Gray whales continued to migrate annually along the west coast of North America despite intermittent seismic exploration and much ship traffic in that area for decades (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 whales and bowhead whales grew substantially during this time. Bowhead whales have increased by approximately 3.4% per year for the last 10 years in the Beaufort Sea (Allen and Angliss, 2011). In any event, the brief exposures to sound pulses from the proposed airgun source (the airguns will only be fired for a period of 10-14 hours for each of the three, possibly four, wells) are highly unlikely to result in prolonged effects.
Toothed Whales
—Few systematic data are available describing reactions of toothed whales to noise pulses. Few studies similar to the more extensive baleen whale/seismic pulse work summarized earlier in this document 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; Smultea
et al.,
2004; Moulton and Miller, 2005).
Seismic operators and marine mammal observers 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). The beluga may be a species that (at least at times) shows long-distance avoidance of seismic vessels. Aerial surveys during seismic operations in the southeastern Beaufort Sea recorded much lower sighting rates of beluga whales within 6.2-12.4 mi (10-20 km) 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 6.2-12.4 mi (10-20 km) (Miller
et al.,
2005).
Captive bottlenose dolphins and (of more relevance in this project) 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.,
2002, 2005). However, the animals tolerated high received levels of sound (pk-pk level >200 dB re 1 μPa) before exhibiting aversive behaviors.
Reactions of toothed whales to large arrays of airguns are variable and, at least for delphinids, seem to be confined to a smaller radius than has been observed for mysticetes. However, based on the limited existing evidence, belugas should not be grouped with delphinids in the “less responsive” category.
Pinnipeds
—Pinnipeds are not likely to show a strong avoidance reaction to the airgun sources proposed for use. Visual monitoring from seismic vessels has shown only slight (if any) avoidance of airguns by pinnipeds and only slight (if any) changes in behavior. Ringed seals frequently do not avoid the area within a few hundred meters of operating airgun arrays (Harris
et al.,
2001; Moulton and Lawson, 2002; Miller
et al.,
2005). Monitoring work in the Alaskan Beaufort Sea during 1996-2001 provided considerable information regarding the behavior of seals exposed to seismic pulses (Harris
et al.,
2001; Moulton and Lawson, 2002). These seismic projects usually involved arrays of 6 to 16 airguns with total volumes of 560 to 1,500 in
3
. The combined results suggest that some seals avoid the immediate area around seismic vessels. In most survey years, ringed seal sightings tended to be farther away from the seismic vessel when the airguns were operating than when they were not (Moulton and Lawson, 2002). However, these avoidance movements were relatively small, on the order of 328 ft (100 m) to a few hundreds of meters, and many seals remained within 328-656 ft (100-200 m) of the trackline as the operating airgun array passed by. Seal sighting rates at the water surface were lower during airgun array operations than during no-airgun periods in each survey year except 1997. Similarly, seals are often very tolerant of pulsed sounds from seal-scaring devices (Mate and Harvey, 1987; Jefferson and Curry, 1994; Richardson
et al.,
1995a). However, initial telemetry work suggests that avoidance and other behavioral reactions by two other species of seals to small airgun sources may at times be stronger than evident to date from visual studies of pinniped reactions to airguns (Thompson
et al.,
1998). Even if reactions of the species occurring in the present study area are as strong as those evident in the telemetry study, reactions are expected to be confined to relatively small distances and durations, with no long-term effects on pinniped individuals or populations. Additionally, the airguns are only proposed to be used for a short time during the exploration drilling program (approximately 10-14 hours for each well, for a total of 40-56 hours, and more likely to be 30-42 hours if the fourth well is not completed, over the entire open-water season, which lasts for approximately 4 months).
(4) Hearing Impairment and Other Physiological Effects
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. At least in terrestrial mammals, TTS can last from minutes or hours to (in cases of strong TTS) days, can be limited to a particular frequency range, and can be in varying degrees (
i.e.,
a loss of a certain number of dBs of sensitivity). For sound exposures at or somewhat above the TTS threshold, hearing sensitivity in both terrestrial and marine mammals recovers rapidly after exposure to the noise ends. Few data on sound levels and durations necessary to elicit mild TTS have been obtained for marine mammals, and none of the published data concern TTS elicited by exposure to multiple pulses of sound.
Marine mammal hearing plays a critical role in communication with conspecifics and in interpretation of environmental cues for purposes such as predator avoidance and prey capture. Depending on the degree (elevation of threshold in dB), duration (
i.e.,
recovery time), and frequency range of TTS and the context in which it is experienced, TTS can have effects on marine mammals ranging from discountable to serious. For example, a marine mammal may be able to readily compensate for a brief, relatively small amount of TTS in a non-critical frequency range that takes place during a time when the animal is traveling through the open ocean, where ambient noise is lower and there are not as many competing sounds present. Alternatively, a larger amount and longer duration of TTS sustained during a time when communication is critical for successful mother/calf interactions could have more serious impacts if it were in the same frequency band as the necessary vocalizations and of a severity that it impeded communication. The fact that animals exposed to levels and durations of sound that would be expected to result in this physiological response would also be expected to have behavioral responses of a comparatively more severe or sustained nature is also notable and potentially of more importance than the simple existence of a TTS.
Researchers have derived TTS information for odontocetes from studies on the bottlenose dolphin and beluga. For the one harbor porpoise tested, the received level of airgun sound that elicited onset of TTS was lower (Lucke
et al.,
2009). If these results from a single animal are representative, it is inappropriate to assume that onset of TTS occurs at similar received levels in all odontocetes (
cf.
Southall
et al.,
2007). Some cetaceans apparently can incur TTS at considerably lower sound exposures than are necessary to elicit TTS in the beluga or bottlenose dolphin.
For baleen whales, there are no data, direct or indirect, on levels or properties of sound that are required to induce TTS. The frequencies to which baleen whales are most sensitive are assumed to be lower than those to which odontocetes are most sensitive, and natural background noise levels at those low frequencies tend to be higher. As a result, auditory thresholds of baleen whales within their frequency band of best hearing are believed to be higher (less sensitive) than are those of odontocetes at their best frequencies (Clark and Ellison, 2004), meaning that baleen whales require sounds to be louder (
i.e.,
higher dB levels) than odontocetes in the frequency ranges at which each group hears the best. From this, it is suspected that received levels causing TTS onset may also be higher in baleen whales (Southall
et al.,
2007). Since current NMFS practice assumes the same thresholds for the onset of hearing impairment in both odontocetes and mysticetes, NMFS' onset of TTS threshold is likely conservative for mysticetes. For this proposed activity,
Shell expects no cases of TTS given the strong likelihood that baleen whales would avoid the airguns before being exposed to levels high enough for TTS to occur. The source levels of the drillship are far lower than those of the airguns.
In pinnipeds, TTS thresholds associated with exposure to brief pulses (single or multiple) of underwater sound have not been measured. However, systematic TTS studies on captive pinnipeds have been conducted (Bowles
et al.,
1999; Kastak
et al.,
1999, 2005, 2007; Schusterman
et al.,
2000; Finneran
et al.,
2003; Southall
et al.,
2007). Initial evidence from more prolonged (non-pulse) exposures suggested that some pinnipeds (harbor seals in particular) incur TTS at somewhat lower received levels than do small odontocetes exposed for similar durations (Kastak
et al.,
1999, 2005; Ketten
et al.,
2001; cf. Au
et al.,
2000). The TTS threshold for pulsed sounds has been indirectly estimated as being a sound exposure level (SEL) of approximately 171 dB re 1 μPa
2
·s (Southall
et al.,
2007) which would be equivalent to a single pulse with a received level of approximately 181 to 186 dB re 1 μPa (rms), or a series of pulses for which the highest rms values are a few dB lower. Corresponding values for California sea lions and northern elephant seals are likely to be higher (Kastak
et al.,
2005). For harbor seal, which is closely related to the ringed seal, TTS onset apparently occurs at somewhat lower received energy levels than for odonotocetes. The sound level necessary to cause TTS in pinnipeds depends on exposure duration, as in other mammals; with longer exposure, the level necessary to elicit TTS is reduced (Schusterman
et al.,
2000; Kastak
et al.,
2005, 2007). For very short exposures (
e.g.,
to a single sound pulse), the level necessary to cause TTS is very high (Finneran
et al.,
2003). For pinnipeds exposed to in-air sounds, auditory fatigue has been measured in response to single pulses and to non-pulse noise (Southall
et al.,
2007), although high exposure levels were required to induce TTS-onset (SEL: 129 dB re: 20 μPa
2.
s; Bowles
et al.,
unpub. data).
NMFS has established acoustic thresholds that identify the received sound levels above which hearing impairment or other injury could potentially occur, which are 180 and 190 dB re 1 μPa (rms) for cetaceans and pinnipeds, respectively (NMFS 1995, 2000). The established 180- and 190-dB re 1 μPa (rms) criteria are the received levels above which, in the view of a panel of bioacoustics specialists convened by NMFS before additional TTS measurements for marine mammals became available, one could not be certain that there would be no injurious effects, auditory or otherwise, to marine mammals. TTS is considered by NMFS to be a type of Level B (non-injurious) harassment. The 180- and 190-dB levels are shutdown criteria applicable to cetaceans and pinnipeds, respectively, as specified by NMFS (2000) and are used to establish exclusion zones (EZs), as appropriate. Additionally, based on the summary provided here and the fact that modeling indicates the back-propagated source level for the
Discoverer
to be between 177 and 185 dB re 1 μPa at 1 m (Austin and Warner, 2010), TTS is not expected to occur in any marine mammal species that may occur in the proposed drilling area since the source level will not reach levels thought to induce even mild TTS. While the source level of the airgun is higher than the 190-dB threshold level, an animal would have to be in very close proximity to be exposed to such levels. Additionally, the 180- and 190-dB radii for the airgun are 0.8 mi (1.24 km) and 0.3 mi (524 m), respectively, from the source. Because of the short duration that the airguns will be used (no more than 30-56 hours throughout the entire open-water season) and mitigation and monitoring measures described later in this document, hearing impairment is not anticipated.
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 (Kryter, 1985).
There is no specific evidence that exposure to underwater industrial sound associated with oil exploration can cause PTS in any marine mammal (see Southall
et al.,
2007). However, given the possibility that mammals might incur TTS, there has been further speculation about the possibility that some individuals occurring very close to such activities might incur PTS (
e.g.,
Richardson
et al.,
1995, p. 372
ff;
Gedamke
et al.,
2008). 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 (Southall
et al.,
2007; Le Prell, in press). PTS might occur at a received sound level at least several decibels above that inducing mild TTS. Based on data from terrestrial mammals, a precautionary assumption is that the PTS threshold for impulse sounds (such as airgun pulses as received close to the source) is at least 6 dB higher than the TTS threshold on a peak-pressure basis and probably greater than 6 dB (Southall
et al.,
2007).
It is highly unlikely that marine mammals could receive sounds strong enough (and over a sufficient duration) to cause PTS during the proposed exploratory drilling program. As mentioned previously in this document, the source levels of the drillship are not considered strong enough to cause even slight TTS. Given the higher level of sound necessary to cause PTS, it is even less likely that PTS could occur. In fact, based on the modeled source levels for the drillship, the levels immediately adjacent to the drillship may not be sufficient to induce PTS, even if the animals remain in the immediate vicinity of the activity. The modeled source level from the
Discoverer
suggests that marine mammals located immediately adjacent to a drillship would likely not be exposed to received sound levels of a magnitude strong enough to induce PTS, even if the animals remain in the immediate vicinity of the proposed activity location for a prolonged period of time. Because the source levels do not reach the threshold of 190 dB currently used for pinnipeds and is at the 180 dB threshold currently used for cetaceans, it is highly unlikely that any type of hearing impairment, temporary or permanent, would occur as a result of the exploration drilling activities. Additionally, Southall
et al.
(2007) proposed that the thresholds for injury of marine mammals exposed to “discrete” noise events (either single or multiple exposures over a 24-hr period) are higher than the 180- and 190-dB re 1 μPa (rms) in-water threshold currently used by NMFS. Table 1 in this document summarizes the SPL and SEL levels thought to cause auditory injury to cetaceans and pinnipeds in-water. For more information, please refer to Southall
et al.
(2007).
Table 1—Proposed Injury Criteria for Cetaceans and Pinnipeds Exposed to “Discrete” Noise Events (Either Single Pulses, Multiple Pulses, or Non-Pulses Within a 24-Hr Period; Southall
et al.,
2007)
Single pulses
Multiple pulses
Non pulses
Low-frequency cetaceans
Sound pressure level
230 dB re 1 μPa (peak) (flat)
230 dB re 1 μPa (peak) (flat)
230 dB re 1 μPa (peak) (flat).
Sound exposure level
198 dB re 1 μPa
2
-s (M
lf
)
198 dB re 1 μPa
2
-s (M
lf
)
215 dB re 1 μPa
2
-s (M
lf
).
Mid-frequency cetaceans
Sound pressure level
230 dB re 1 μPa (peak) (flat)
230 dB re 1 μPa (peak) (flat)
230 dB re 1 μPa (peak) (flat).
Sound exposure level
198 dB re 1 μPa
2
-s (M
lf
)
198 dB re 1 μPa
2
-s (M
lf
)
215 dB re 1 μPa
2
-s (M
lf
).
High-frequency cetaceans
Sound pressure level
230 dB re 1 μPa (peak) (flat)
230 dB re 1 μPa (peak) (flat)
230 dB re 1 μPa (peak) (flat).
Sound exposure level
198 dB re 1 μPa
2
-s (M
lf
)
198 dB re 1 μPa
2
-s (M
lf
)
215 dB re 1 μPa
2
-s (M
lf
).
Pinnipeds (in water)
Sound pressure level
218 dB re 1 μPa (peak) (flat)
218 dB re 1 μPa (peak) (flat)
218 dB re 1 μPa (peak) (flat).
Sound exposure level
186 dB re 1 μPa
2
-s (M
pw
)
186 dB re 1 μPa
2
-s (M
pw
)
203 dB re 1 μPa
2
-s (M
pw
).
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 (Cox
et al.,
2006; Southall
et al.,
2007). Studies examining any such effects are 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 sounds for sufficiently long that significant physiological stress would develop.
Classic stress responses begin when an animal's central nervous system perceives a potential threat to its homeostasis. That perception triggers stress responses regardless of whether a stimulus actually threatens the animal; the mere perception of a threat is sufficient to trigger a stress response (Moberg, 2000; Sapolsky
et al.,
2005; Seyle, 1950). Once an animal's central nervous system perceives a threat, it mounts a biological response or defense that consists of a combination of the four general biological defense responses: behavioral responses; autonomic nervous system responses; neuroendocrine responses; or immune responses.
In the case of many stressors, an animal's first and most economical (in terms of biotic costs) response is behavioral avoidance of the potential stressor or avoidance of continued exposure to a stressor. An animal's second line of defense to stressors involves the sympathetic part of the autonomic nervous system and the classical “fight or flight” response, which includes the cardiovascular system, the gastrointestinal system, the exocrine glands, and the adrenal medulla to produce changes in heart rate, blood pressure, and gastrointestinal activity that humans commonly associate with “stress.” These responses have a relatively short duration and may or may not have significant long-term effects on an animal's welfare.
An animal's third line of defense to stressors involves its neuroendocrine or sympathetic nervous systems; the system that has received the most study has been the hypothalmus-pituitary-adrenal system (also known as the HPA axis in mammals or the hypothalamus-pituitary-interrenal axis in fish and some reptiles). Unlike stress responses associated with the autonomic nervous system, virtually all neuroendocrine functions that are affected by stress—including immune competence, reproduction, metabolism, and behavior—are regulated by pituitary hormones. Stress-induced changes in the secretion of pituitary hormones have been implicated in failed reproduction (Moberg, 1987; Rivier, 1995), altered metabolism (Elasser
et al.,
2000), reduced immune competence (Blecha, 2000), and behavioral disturbance. Increases in the circulation of glucocorticosteroids (cortisol, corticosterone, and aldosterone in marine mammals; see Romano
et al.,
2004) have been equated with stress for many years.
The primary distinction between stress (which is adaptive and does not normally place an animal at risk) and distress is the biotic cost of the response. During a stress response, an animal uses glycogen stores that can be quickly replenished once the stress is alleviated. In such circumstances, the cost of the stress response would not pose a risk to the animal's welfare. However, when an animal does not have sufficient energy reserves to satisfy the energetic costs of a stress response, energy resources must be diverted from other biotic functions, which impair those functions that experience the diversion. For example, when mounting a stress response diverts energy away from growth in young animals, those animals may experience stunted growth. When mounting a stress response diverts energy from a fetus, an animal's reproductive success and fitness will suffer. In these cases, the animals will have entered a pre-pathological or pathological state which is called “distress” (sensu Seyle, 1950) or “allostatic loading” (sensu McEwen and Wingfield, 2003). This pathological state will last until the animal replenishes its biotic reserves sufficient to restore normal function. Note that these examples involved a long-term (days or weeks) stress response exposure to stimuli.
Relationships between these physiological mechanisms, animal behavior, and the costs of stress responses have also been documented fairly well through controlled experiment; because this physiology exists in every vertebrate that has been studied, it is not surprising that stress responses and their costs have been documented in both laboratory and free-living animals (for examples see, Holberton
et al.,
1996; Hood
et al.,
1998; Jessop
et al.,
2003; Krausman
et al.,
2004; Lankford
et al.,
2005; Reneerkens
et al.,
2002; Thompson and Hamer, 2000). Although no information has been collected on the physiological responses of marine mammals to anthropogenic sound exposure, studies of other marine animals and terrestrial animals would lead us to expect some marine mammals to experience physiological stress responses and, perhaps, physiological responses that would be classified as “distress” upon exposure to anthropogenic sounds.
For example, Jansen (1998) reported on the relationship between acoustic exposures and physiological responses that are indicative of stress responses in humans (
e.g.,
elevated respiration and increased heart rates). Jones (1998) reported on reductions in human performance when faced with acute, repetitive exposures to acoustic disturbance. Trimper
et al.
(1998) reported on the physiological stress responses of osprey to low-level aircraft noise while Krausman
et al.
(2004) reported on the auditory and physiology stress responses of endangered Sonoran pronghorn to military overflights. Smith
et al.
(2004a, 2004b) identified noise-induced physiological transient stress responses in hearing-specialist fish (
i.e.,
goldfish) that accompanied short- and long-term hearing losses. Welch and Welch (1970) reported physiological and behavioral stress responses that accompanied damage to the inner ears of fish and several mammals.
Hearing is one of the primary senses marine mammals use to gather information about their environment and communicate with conspecifics. Although empirical information on the relationship between sensory impairment (TTS, PTS, and acoustic masking) on marine mammals remains limited, it seems reasonable to assume that reducing an animal's ability to gather information about its environment and to communicate with other members of its species would be stressful for animals that use hearing as their primary sensory mechanism. Therefore, we assume that acoustic exposures sufficient to trigger onset PTS or TTS would be accompanied by physiological stress responses because terrestrial animals exhibit those responses under similar conditions (NRC, 2003). More importantly, marine mammals might experience stress responses at received levels lower than those necessary to trigger onset TTS. Based on empirical studies of the time required to recover from stress responses (Moberg, 2000), NMFS also assumes that stress responses could persist beyond the time interval required for animals to recover from TTS and might result in pathological and pre-pathological states that would be as significant as behavioral responses to TTS. However, as stated previously in this document, the source levels of the drillships are not loud enough to induce PTS or likely even TTS.
Resonance effects (Gentry, 2002) and direct noise-induced bubble formations (Crum
et al.,
2005) are implausible in the case of exposure to an impulsive broadband source like an airgun array. If seismic surveys disrupt diving patterns of deep-diving species, this might result in bubble formation and a form of the bends, as speculated to occur in beaked whales exposed to sonar. However, there is no specific evidence of this upon exposure to airgun pulses. Additionally, no beaked whale species occur in the proposed exploration drilling area.
In general, very little is known about the potential for strong, anthropogenic underwater sounds to cause non-auditory physical effects in marine mammals. Such effects, if they occur at all, would presumably be limited to short distances and to activities that extend over a prolonged period. The available data do not allow identification of a specific exposure level above which non-auditory effects can be expected (Southall
et al.,
2007) or any meaningful quantitative predictions of the numbers (if any) of marine mammals that might be affected in those ways. The low levels of continuous sound that will be produced by the drillship are not expected to cause such effects. Additionally, marine mammals that show behavioral avoidance of the proposed activities, including most baleen whales, some odontocetes (including belugas), and some pinnipeds, are especially unlikely to incur auditory impairment or other physical effects.
Stranding and Mortality
Marine mammals close to underwater detonations of high explosives can be killed or severely injured, and the auditory organs are especially susceptible to injury (Ketten
et al.,
1993; Ketten, 1995). However, explosives are no longer used for marine waters for commercial seismic surveys; they have been replaced entirely by airguns or related non-explosive pulse generators. Underwater sound from drilling, support activities, and airgun arrays is less energetic and has 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 involving mid-frequency active sonar, and, in one case, a Lamont-Doherty Earth Observatory (L-DEO) seismic survey (Malakoff, 2002; Cox
et al.,
2006), 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 (
e.g.,
Hildebrand, 2005; Southall
et al.,
2007).
Specific sound-related processes that lead to strandings and mortality are not well documented, but may include:
(1) Swimming in avoidance of a sound into shallow water;
(2) A change in behavior (such as a change in diving behavior) that might contribute to tissue damage, gas bubble formation, hypoxia, cardiac arrhythmia, hypertensive hemorrhage or other forms of trauma;
(3) A physiological change, such as a vestibular response leading to a behavioral change or stress-induced hemorrhagic diathesis, leading in turn to tissue damage; and
(4) Tissue damage directly from sound exposure, such as through acoustically-mediated bubble formation and growth or acoustic resonance of tissues.
Some of these mechanisms are unlikely to apply in the case of impulse sounds. However, there are indications that gas-bubble disease (analogous to “the bends”), induced in supersaturated tissue by a behavioral response to acoustic exposure, could be a pathologic mechanism for the strandings and mortality of some deep-diving cetaceans exposed to sonar. However, the evidence for this remains circumstantial and is associated with exposure to naval mid-frequency sonar, not seismic surveys or exploratory drilling programs (Cox
et al.,
2006; Southall
et al.,
2007).
Both seismic pulses and continuous drillship sounds are quite different from mid-frequency sonar signals, and some mechanisms by which sonar sounds have been hypothesized to affect beaked whales are unlikely to apply to airgun pulses or drillships. Sounds produced by airgun arrays are broadband impulses with most of the energy below 1 kHz, and the low-energy continuous sounds produced by drillships have most of the energy between 20 and 1,000 Hz. Additionally, the non-impulsive, continuous sounds produced by the drillship proposed to be used by Shell do not have rapid rise times. Rise time is the fluctuation in sound levels of the source. The type of sound that would be produced during the proposed drilling program will be constant and will not exhibit any sudden fluctuations or changes. Typical military mid-frequency sonar emits non-impulse sounds at frequencies of 2-10 kHz, generally with a relatively narrow bandwidth at any
one time. A further difference between them is that naval exercises can involve sound sources on more than one vessel. Thus, it is not appropriate to assume that there is a direct connection between the effects of military sonar and oil and gas industry operations on marine mammals. However, evidence that sonar signals can, in special circumstances, lead (at least indirectly) to physical damage and mortality (
e.g.,
Balcomb and Claridge, 2001; NOAA and USN, 2001; Jepson
et al.,
2003; Fernández
et al.,
2004, 2005; Hildebrand, 2005; Cox
et al.,
2006) suggests that caution is warranted when dealing with exposure of marine mammals to any high-intensity “pulsed” sound.
There is no conclusive evidence of cetacean strandings or deaths at sea as a result of exposure to seismic surveys, but a few cases of strandings in the general area where a seismic survey was ongoing have led to speculation concerning a possible link between seismic surveys and strandings. Suggestions that there was a link between seismic surveys and strandings of humpback whales in Brazil (Engel
et al.,
2004) were not well founded (IAGC, 2004; IWC, 2007). In September 2002, there was a stranding of two Cuvier's beaked whales in the Gulf of California, Mexico, when the L-DEO vessel R/V
Maurice Ewing
was operating a 20 airgun (8,490 in
3
) 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, the Gulf of California incident, plus the beaked whale strandings near naval exercises involving use of mid-frequency sonar, suggests a need for caution in conducting seismic surveys in areas occupied by beaked whales until more is known about effects of seismic surveys on those species (Hildebrand, 2005). No injuries of beaked whales are anticipated during the proposed exploratory drilling program because none occur in the proposed area.
Exploratory Drilling Program and Potential for Oil Spill
As noted above, the specified activity involves the drilling of exploratory wells and associated activities in the Chukchi Sea during the 2012 open-water season. The impacts to marine mammals that are reasonably expected to occur will be acoustic in nature. In response to previous IHA applications submitted by Shell, various entities have asserted that NMFS cannot authorize the take of marine mammals incidental to exploratory drilling under an IHA. Instead, they contend that incidental take can be allowed only with a letter of authorization (LOA) issued under five-year regulations because of the potential that an oil spill will cause serious injury or mortality.
There are two avenues for authorizing incidental take of marine mammals under the MMPA. NMFS may, depending on the nature of the anticipated take, authorize the take of marine mammals incidental to a specified activity through regulations and LOAs or annual IHAs.
See
16 U.S.C. 1371(a)(5)(A) and (D). In general, regulations (accompanied by LOAs) may be issued for any type of take (
e.g.,
Level B harassment (behavioral disturbance), Level A harassment (injury), serious injury, or mortality), whereas IHAs are limited to activities that result only in harassment (
e.g.,
behavioral disturbance or injury). Following the 1994 MMPA Amendments, NMFS promulgated implementing regulations governing the issuance of IHAs in Arctic waters. See 60 FR 28379 (May 31, 1995) and 61 FR 15884 (April 10, 1996). NMFS stated in the preamble of the proposed rulemaking that the scope of IHAs would be limited to “* * * those authorizations for harassment involving incidental harassment that may involve
non-serious injury
.” See 60 FR 28380 (May 31, 1995; emphasis added); 50 CFR 216.107(a). (“[e]xcept for activities that have the potential to result in serious injury or mortality, which must be authorized under 216.105, incidental harassment authorizations may be issued, * * * to allowed activities that may result in only the incidental harassment of a small number of marine mammals.”) NMFS explained further that applications would be reviewed to determine whether the activity would result in more than harassment, and, if so, the agency would either (1) attempt to negate the potential for serious injury through mitigation requirements, or (2) deny the incidental harassment authorization and require the applicant to apply for incidental take regulations. See
id.
at 28380-81.
NMFS' determination of whether the type of incidental take authorization requested is appropriate occurs shortly after the applicant submits an application for an incidental take authorization. The agency evaluates the proposed action and all information contained in the application to determine whether it is adequate and complete and whether the type of taking requested is appropriate. See 50 CFR 216.104; see also 60 FR 28380 (May 31, 1995). Among other things, NMFS considers the specific activity or class of activities that can reasonably be
expected
to result in incidental take; the
type
of incidental take authorization that is being requested; and the
anticipated
impact of the activity upon the species or stock and its habitat. See
id.
at 216.104(a) (emphasis added). Any application that is determined to be incomplete or inappropriate for the type of taking requested will be returned to the applicant with an explanation of why the application is being returned. See
id.
Finally, NMFS evaluates the best available science to determine whether a proposed activity is reasonably expected or likely to result in serious injury or mortality.
NMFS evaluated Shell's incidental take application for its proposed 2012 drilling activities in light of the foregoing criteria and has concluded that Shell's request for an IHA is warranted. Shell submitted information with its IHA Application indicating that an oil spill is a highly unlikely event that is not reasonably expected to occur during the course of exploration drilling or ZVSP surveys.
See
Chukchi Sea IHA Application, p. 3 and Attachment E—Analysis of the Probability of an “Unspecified Activity” and Its Impacts: Oil Spill. In addition, Shell's 2012 Exploration Plan indicates there is a “very low likelihood of a large oil spill event.”
See
Shell Offshore, Inc.'s Revised Outer Continental Shelf Lease Exploration Plan, Chukchi Sea, Alaska (May 2011), at p. 8-1;
see also,
Appendix F to Shell's Revised Outer Continental Shelf Lease Exploration Plan, at p. 4-174.
The likelihood of a large or very large (
i.e.,
≥1,000 barrels or ≥150,000 barrels, respectively) oil spill occurring during Shell's proposed program has been estimated to be low. A total of 35 exploration wells have been drilled between 1982 and 2003 in the Chukchi and Beaufort seas, and there have been no blowouts. In addition, no blowouts have occurred from the approximately 98 exploration wells drilled within the Alaskan OCS (MMS, 2007a). Attachment E in Shell's IHA Application contains information regarding the probability of an oil spill occurring during the proposed program and the potential impacts should one occur. Based on modeling conducted by Bercha (2008), the predicted frequency of an exploration well oil spill in waters similar to those in the Chukchi Sea, Alaska, is 0.000612 per well for a blowout sized between 10,000 barrels (bbl) to 149,000 bbl and 0.000354 per well for a blowout greater than 150,000 bbl. Please refer to Shell's application for additional information on the model and predicted frequencies (see
ADDRESSES
).
Shell has implemented several design standards and practices to reduce the already low probability of an oil spill occurring as part of its operations. The wells proposed to be drilled in the Arctic are exploratory and will not be converted to production wells; thus, production casing will not be installed, and the well will be permanently plugged and abandoned once exploration drilling is complete. Shell has also developed and will implement the following plans and protocols: Shell's Critical Operations Curtailment Plan; IMP; Well Control Plan; and Fuel Transfer Plan. Many of these safety measures are required by the Department of the Interior's interim final rule implementing certain measures to improve the safety of oil and gas exploration and development on the Outer Continental Shelf in light of the Deepwater Horizon event (
see
75 FR 63346, October 14, 2010). Operationally, Shell has committed to the following to help prevent an oil spill from occurring in the Chukchi Sea:
• Shell's Blow Out Preventer (BOP) was inspected and tested by an independent third party specialist;
• Further inspection and testing of the BOP have been performed to ensure the reliability of the BOP and that all functions will be performed as necessary, including shearing the drill pipe;
• Subsea BOP hydrostatic tests will be increased from once every 14 days to once every 7 days;
• A second set of blind/shear rams will be installed in the BOP stack;
• Full string casings will typically not be installed through high pressure zones;
• Liners will be installed and cemented, which allows for installation of a liner top packer;
• Testing of liners prior to installing a tieback string of casing back to the wellhead;
• Utilizing a two-barrier policy; and
• Testing of all casing hangers to ensure that they have two independent, validated barriers at all times.
NMFS has considered Shell's proposed action and has concluded that there is no reasonable likelihood of serious injury or mortality from the 2012 Chukchi Sea exploration drilling program. NMFS has consistently interpreted the term “potential,” as used in 50 CFR 216.107(a), to only include impacts that have more than a discountable probability of occurring, that is, impacts must be reasonably expected to occur. Hence, NMFS has regularly issued IHAs in cases where it found that the potential for serious injury or mortality was “highly unlikely” (
See
73 FR 40512, 40514, July 15, 2008; 73 FR 45969, 45971, August 7, 2008; 73 FR 46774, 46778, August 11, 2008; 73 FR 66106, 66109, November 6, 2008; 74 FR 55368, 55371, October 27, 2009).
Interpreting “potential” to include impacts with any probability of occurring (
i.e.,
speculative or extremely low probability events) would nearly preclude the issuance of IHAs in every instance. For example, NMFS would be unable to issue an IHA whenever vessels were involved in the marine activity since there is always some, albeit remote, possibility that a vessel could strike and seriously injure or kill a marine mammal. This would also be inconsistent with the dual-permitting scheme Congress created and undesirable from a policy perspective, as limited agency resources would be used to issue regulations that provide no additional benefit to marine mammals beyond what is proposed in this IHA.
Despite concluding that the risk of serious injury or mortality from an oil spill in this case is extremely remote, NMFS has nonetheless evaluated the potential effects of an oil spill on marine mammals. While an oil spill is not a component of Shell's specified activity, potential impacts on marine mammals from an oil spill are discussed in more detail below and will be addressed further in the Environmental Assessment.
Potential Effects of Oil on Cetaceans
The specific effects an oil spill would have on cetaceans are not well known. While mortality is unlikely, exposure to spilled oil could lead to skin irritation, baleen fouling (which might reduce feeding efficiency), respiratory distress from inhalation of hydrocarbon vapors, consumption of some contaminated prey items, and temporary displacement from contaminated feeding areas. Geraci and St. Aubin (1990) summarize effects of oil on marine mammals, and Bratton
et al.
(1993) provides a synthesis of knowledge of oil effects on bowhead whales. The number of cetaceans that might be contacted by a spill would depend on the size, timing, and duration of the spill and where the oil is in relation to the animals. Whales may not avoid oil spills, and some have been observed feeding within oil slicks (Goodale
et al.,
1981). These topics are discussed in more detail next.
In the case of an oil spill occurring during migration periods, disturbance of the migrating cetaceans from cleanup activities may have more of an impact than the oil itself. Human activity associated with cleanup efforts could deflect whales away from the path of the oil. However, noise created from cleanup activities likely will be short term and localized. In fact, whale avoidance of clean-up activities may benefit whales by displacing them from the oil spill area.
There is no direct evidence that oil spills, including the much studied Santa Barbara Channel and Exxon Valdez spills, have caused any deaths of cetaceans (Geraci, 1990; Brownell, 1971; Harvey and Dahlheim, 1994). It is suspected that some individually identified killer whales that disappeared from Prince William Sound during the time of the Exxon Valdez spill were casualties of that spill. However, no clear cause and effect relationship between the spill and the disappearance could be established (Dahlheim and Matkin, 1994). The AT-1 pod of transient killer whales that sometimes inhabits Prince William Sound has continued to decline after the Exxon Valdez oil spill (EVOS). Matkin
et al.
(2008) tracked the AB resident pod and the AT-1 transient group of killer whales from 1984 to 2005. The results of their photographic surveillance indicate a much higher than usual mortality rate for both populations the year following the spill (33% for AB Pod and 41% for AT-1 Group) and lower than average rates of increase in the 16 years after the spill (annual increase of about 1.6% for AB Pod compared to an annual increase of about 3.2% for other Alaska killer whale pods). In killer whale pods, mortality rates are usually higher for non-reproductive animals and very low for reproductive animals and adolescents (Olesiuk
et al.,
1990, 2005; Matkin
et al.,
2005). No effects on humpback whales in Prince William Sound were evident after the EVOS (von Ziegesar
et al.,
1994). There was some temporary displacement of humpback whales out of Prince William Sound, but this could have been caused by oil contamination, boat and aircraft disturbance, displacement of food sources, or other causes.
Migrating gray whales were apparently not greatly affected by the Santa Barbara spill of 1969. There appeared to be no relationship between the spill and mortality of marine mammals. The higher than usual counts of dead marine mammals recorded after the spill represented increased survey effort and therefore cannot be conclusively linked to the spill itself (Brownell, 1971; Geraci, 1990). The conclusion was that whales were either able to detect the oil and avoid it or were unaffected by it (Geraci, 1990).
(1) Oiling of External Surfaces
Whales rely on a layer of blubber for insulation, so oil would have little if any effect on thermoregulation by whales. Effects of oiling on cetacean skin appear to be minor and of little significance to the animal's health (Geraci, 1990). Histological data and ultrastructural studies by Geraci and St. Aubin (1990) showed that exposures of skin to crude oil for up to 45 minutes in four species of toothed whales had no effect. They switched to gasoline and applied the sponge up to 75 minutes. This produced transient damage to epidermal cells in whales. Subtle changes were evident only at the cell level. In each case, the skin damage healed within a week. They concluded that a cetacean's skin is an effective barrier to the noxious substances in petroleum. These substances normally damage skin by getting between cells and dissolving protective lipids. In cetacean skin, however, tight intercellular bridges, vital surface cells, and the extraordinary thickness of the epidermis impeded the damage. The authors could not detect a change in lipid concentration between and within cells after exposing skin from a white-sided dolphin to gasoline for 16 hours in vitro.
Bratton
et al.
(1993) synthesized studies on the potential effects of contaminants on bowhead whales. They concluded that no published data proved oil fouling of the skin of any free-living whales, and conclude that bowhead whales contacting fresh or weathered petroleum are unlikely to suffer harm. Although oil is unlikely to adhere to smooth skin, it may stick to rough areas on the surface (Henk and Mullan, 1997). Haldiman
et al.
(1985) found the epidermal layer to be as much as seven to eight times thicker than that found on most whales. They also found that little or no crude oil adhered to preserved bowhead skin that was dipped into oil up to three times, as long as a water film stayed on the skin's surface. Oil adhered in small patches to the surface and vibrissae (stiff, hairlike structures), once it made enough contact with the skin. The amount of oil sticking to the surrounding skin and epidermal depression appeared to be in proportion to the number of exposures and the roughness of the skin's surface. It can be assumed that if oil contacted the eyes, effects would be similar to those observed in ringed seals; continued exposure of the eyes to oil could cause permanent damage (St. Aubin, 1990).
(2) Ingestion
Whales could ingest oil if their food is contaminated, or oil could also be absorbed through the respiratory tract. Some of the ingested oil is voided in vomit or feces but some is absorbed and could cause toxic effects (Geraci, 1990). When returned to clean water, contaminated animals can depurate this internal oil (Engelhardt, 1978, 1982). Oil ingestion can decrease food assimilation of prey eaten (St. Aubin, 1988). Cetaceans may swallow some oil-contaminated prey, but it likely would be only a small part of their food. It is not known if whales would leave a feeding area where prey was abundant following a spill. Some zooplankton eaten by bowheads and gray whales consume oil particles and bioaccumulation can result. Tissue studies by Geraci and St. Aubin (1990) revealed low levels of naphthalene in the livers and blubber of baleen whales. This result suggests that prey have low concentrations in their tissues, or that baleen whales may be able to metabolize and excrete certain petroleum hydrocarbons. Whales exposed to an oil spill are unlikely to ingest enough oil to cause serious internal damage (Geraci and St. Aubin, 1980, 1982) and this kind of damage has not been reported (Geraci, 1990).
(3) Fouling of Baleen
Baleen itself is not damaged by exposure to oil and is resistant to effects of oil (St. Aubin
et al.,
1984). Crude oil could coat the baleen and reduce filtration efficiency; however, effects may be temporary (Braithwaite, 1983; St. Aubin
et al.,
1984). If baleen is coated in oil for long periods, it could cause the animal to be unable to feed, which could lead to malnutrition or even death. Most of the oil that would coat the baleen is removed after 30 min, and less than 5% would remain after 24 hr (Bratton
et al.,
1993). Effects of oiling of the baleen on feeding efficiency appear to be minor (Geraci, 1990). However, a study conducted by Lambertsen
et al.
(2005) concluded that their results highlight the uncertainty about how rapidly oil would depurate at the near zero temperatures in arctic waters and whether baleen function would be restored after oiling.
(4) Avoidance
Some cetaceans can detect oil and sometimes avoid it, but others enter and swim through slicks without apparent effects (Geraci, 1990; Harvey and Dahlheim, 1994). Bottlenose dolphins in the Gulf of Mexico apparently could detect and avoid slicks and mousse but did not avoid light sheens on the surface (Smultea and Wursig, 1995). After the Regal Sword spill in 1979, various species of baleen and toothed whales were observed swimming and feeding in areas containing spilled oil southeast of Cape Cod, MA (Goodale
et al.,
1981). For months following EVOS, there were numerous observations of gray whales, harbor porpoises, Dall's porpoises, and killer whales swimming through light-to-heavy crude-oil sheens (Harvey and Dalheim, 1994, cited in Matkin
et al.,
2008). However, if some of the animals avoid the area because of the oil, then the effects of the oiling would be less severe on those individuals.
(5) Factors Affecting the Severity of Effects
Effects of oil on cetaceans in open water are likely to be minimal, but there could be effects on cetaceans where both the oil and the whales are at least partly confined in leads or at ice edges (Geraci, 1990). In spring, bowhead and beluga whales migrate through leads in the ice. At this time, the migration can be concentrated in narrow corridors defined by the leads, thereby creating a greater risk to animals caught in the spring lead system should oil enter the leads. This situation would only occur if there were an oil spill late in the season and Shell could not complete cleanup efforts prior to ice covering the area. The oil would likely then be trapped in the ice until it began to thaw in the spring.
In fall, the migration route of bowheads can be close to shore (Blackwell
et al.,
2009c). If fall migrants were moving through leads in the pack ice or were concentrated in nearshore waters, some bowhead whales might not be able to avoid oil slicks and could be subject to prolonged contamination. However, the autumn migration through the Chukchi Sea extends over several weeks, and some of the whales travel along routes north or inland of the area, thereby reducing the number of whales that could approach patches of spilled oil. Additionally, vessel activity associated with spill cleanup efforts may deflect whales traveling near the Burger prospect in the Chukchi Sea, thereby reducing the likelihood of contact with spilled oil.
Bowhead and beluga whales overwinter in the Bering Sea (mainly from November to March). In the summer, the majority of the bowhead whales are found in the Canadian Beaufort Sea, although some have recently been observed in the U.S. Beaufort and Chukchi Seas during the summer months (June to August). Data from the Barrow-based boat surveys in
2009 (George and Sheffield, 2009) showed that bowheads were observed almost continuously in the waters near Barrow, including feeding groups in the Chukchi Sea at the beginning of July. The majority of belugas in the Beaufort stock migrate into the Beaufort Sea in April or May, although some whales may pass Point Barrow as early as late March and as late as July (Braham
et al.,
1984; Ljungblad
et al.,
1984; Richardson
et al.,
1995a). Therefore, a spill in summer would not be expected to have major impacts on these species. Additionally, humpback and fin whales are only sighted in the Chukchi Sea in small numbers in the summer, as this is thought to be the extreme northern edge of their range. Therefore, impacts to these species from an oil spill would be extremely limited.
Potential Effects of Oil on Pinnipeds
Ice seals are present in open-water areas during summer and early autumn. Externally oiled phocid seals often survive and become clean, but heavily oiled seal pups and adults may die, depending on the extent of oiling and characteristics of the oil. Prolonged exposure could occur if fuel or crude oil was spilled in or reached nearshore waters, was spilled in a lead used by seals, or was spilled under the ice when seals have limited mobility (NMFS, 2000). Adult seals may suffer some temporary adverse effects, such as eye and skin irritation, with possible infection (MMS, 1996). Such effects may increase stress, which could contribute to the death of some individuals. Ringed seals may ingest oil-contaminated foods, but there is little evidence that oiled seals will ingest enough oil to cause lethal internal effects. There is a likelihood that newborn seal pups, if contacted by oil, would die from oiling through loss of insulation and resulting hypothermia. These potential effects are addressed in more detail in subsequent paragraphs.
Reports of the effects of oil spills have shown that some mortality of seals may have occurred as a result of oil fouling; however, large scale mortality had not been observed prior to the EVOS (St. Aubin, 1990). Effects of oil on marine mammals were not well studied at most spills because of lack of baseline data and/or the brevity of the post-spill surveys. The largest documented impact of a spill, prior to EVOS, was on young seals in January in the Gulf of St. Lawrence (St. Aubin, 1990). Brownell and Le Boeuf (1971) found no marked effects of oil from the Santa Barbara oil spill on California sea lions or on the mortality rates of newborn pups.
Intensive and long-term studies were conducted after the EVOS in Alaska. There may have been a long-term decline of 36% in numbers of molting harbor seals at oiled haul-out sites in Prince William Sound following EVOS (Frost
et al.,
1994a). However, in a reanalysis of those data and additional years of surveys, along with an examination of assumptions and biases associated with the original data, Hoover-Miller
et al.
(2001) concluded that the EVOS effect had been overestimated. The decline in attendance at some oiled sites was more likely a continuation of the general decline in harbor seal abundance in Prince William Sound documented since 1984 (Frost
et al.,
1999) rather than a result of EVOS. The results from Hoover-Miller
et al.
(2001) indicate that the effects of EVOS were largely indistinguishable from natu
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