Takes of Marine Mammals Incidental to Specified Activities; Taking Marine Mammals Incidental to an Exploration Drilling Program in the Chukchi Sea, AK

DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

RIN 0648-XC494

Takes of Marine Mammals Incidental to Specified Activities; Taking Marine Mammals Incidental to an Exploration Drilling Program in the Chukchi Sea, AK

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 ConocoPhillips Company (COP) 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 COP 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 March 25, 2013.

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 25-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 COP'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 March 1, 2012, from COP for the taking, by harassment, of marine mammals incidental to offshore exploration drilling on OCS leases in the Chukchi Sea, Alaska. However, before NMFS had an opportunity to review and comment on the March 1, 2012, submission, COP notified NMFS that they were making changes to the request and submitted a new application on July 16, 2012. NMFS reviewed COP's application and identified a number of issues requiring further clarification. After addressing comments from NMFS, COP modified its application and submitted a final revised application on December 6, 2012. NMFS carefully evaluated COP's application, including their analyses, and determined that the application was complete. The December 6, 2012, submission (2nd application revision) is the one available for public comment (see

ADDRESSES

) and considered by NMFS for this proposed IHA.

COP plans to drill up to two exploration wells on OCS leases offshore in the Chukchi Sea, Alaska, at the Devils Paw prospect during the 2014 Arctic open-water season (July through October). Impacts to marine mammals may occur from noise produced by the drill rig and support vessels alongside the drill rig in dynamic positioning (DP) mode, vertical seismic profile (VSP) surveys, and supporting vessels (including icebreakers) and aircraft. COP has requested an authorization to take 12 marine mammal species by Level B harassment, and NMFS is proposing to authorize take incidental to COP's offshore exploration drilling in the Chukchi Sea of the following species: 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

COP plans to conduct an offshore exploration drilling program on U.S.

Department of the Interior (DOI), Bureau of Ocean Energy Management (BOEM) Alaska OCS leases located greater than 70 mi (113 km) from the Chukchi Sea coast during the 2014 open-water season. During the 2014 drilling program, COP plans to drill up to two exploration wells at the prospect known as Devils Paw. See Figure 1 in COP's application for the lease block and drill site locations (see

ADDRESSES

). The purpose of COP's program is to test whether oil deposits are present in a commercially viable quantity and quality. COP has stated that only if a significant accumulation of hydrocarbons is discovered will the company consider proceeding with development and production of the field.

Exploration Drilling

All of the possible Chukchi Sea offshore drill sites are located approximately 120 mi (193 km) west of Wainwright, the community proposed to be used for permanent infrastructure support for the project. Approximate distances from the exploration drilling project area to other communities along the Chukchi coast are 200 mi (322 km) from Barrow, 90 mi (145 km) from Point Lay, and 175 mi (282 km) from Point Hope. Water depths at the potential drill sites range from 132-138 ft (40.2-42 m). Table 2 in COP's application provides the coordinates for the potential drill sites (see

ADDRESSES

).

(1) Drill Rig Mobilization and Positioning

COP proposes to use a jack-up rig, instead of a drillship, to conduct the proposed program. Generally, jack-up rigs consist of a buoyant steel hull with three or more legs on which the hull can be “jacked” up or down. The jack-up drill rig has no self-propulsion capability and therefore needs to be transported by a heavy-lift vessel (HLV) from its original location to an area in the Bering Sea where it would then be placed in a floating mode under the control of three towing vessels. After delivering the jack-up rig, the HLV would depart immediately via the Bering Strait and would not return until completion of the project. When weather and ice conditions at the Devils Paw Prospect are favorable, the support vessels will tow the rig into position over the DP-5 drill site and initiate offloading.

Offloading procedures are estimated to take from 24 to 36 hrs, dependent on weather. Initial drill rig placement and orientation would be determined by logistics, current and forecasted weather events, ice extent, ice type, underwriter requirements, and safety considerations. Actual positioning of the rig would be determined by the well design, geology, shallow hazards, and seabed conditions. The rig would then be jacked up, manned with a crew, and provisioned for commencing drilling. The horizontal dimensions of the rig will be approximately 230 × 225 ft (70 × 68 m). When operating, the hull will be about 40 ft (12 m) above seawater surface. Maximum dimension of one leg spud can, which is the part on the seafloor, is about 60 ft (18 m).

If weather and ice conditions at the Devils Paw Prospect area are initially unfavorable, the HLV would transport the jack-up rig to the alternate staging area located about 20 mi (32 km) south of Kivalina and 6 mi (9.7 km) offshore (see Figure 1 in COP's application), offload the rig, and depart the Chukchi Sea via the Bering Strait. This alternative location has been chosen based on its proximity to infrastructure and likelihood to be ice free at the time of transfer. It may take up to 3 days to reach the prospect location from the alternate staging area (approximately 190 mi away [306 km]).

If the rig is offloaded at the alternate staging area, it would be placed into standby mode, which means it would be temporarily jacked up and manned by a limited crew to wait for conditions to improve at the prospect. In addition, support helicopters would be mobilized to Red Dog Mine near Kotzebue as necessary. Once ice conditions and weather at the Devils Paw Prospect area turn favorable, the anchor handling supply tug (AHST) and other vessels standing by in the immediate vicinity of the rig would move the rig to the prospect area. The rig would then be jacked up, manned with a crew, and supplied to commence drilling. (2) Support Vessel and Aircraft Movements

Various vessels will be involved in the drilling project, as summarized in Table 1 of COP's application (see

ADDRESSES

). The vessels involved in supporting the drilling operations will remain at about 5.5 mi (9 km) distance from the drill rig when they are not actively supporting the drilling operations. Several vessels will also be available for oil spill response purposes (see Table 1 in COP's application). Most of these vessels are relatively small and will be located aboard a mother vessel, either the oil spill response barge or the landing craft. These vessels will not be deployed in the water, unless needed to respond to a spill or to conduct oil spill response exercises as directed by DOI's Bureau of Safety and Environmental Enforcement (BSEE). The oil spill response vessel (OSRV) will also be on standby at 5.5 mi (9 km) from the drill rig. In addition to the vessels required for the actual drilling operations, a science vessel will be conducting monitoring activities. Figure 3 in COP's application provides an overview of the approximate locations of the vessels relative to the rig. The vessels will be located upwind from the rig, and, as such, they could be moved to any quadrant (A, B, C, or D) denoted in the figure, depending on the prevailing wind and currents.

COP also intends to have two helicopters and one fixed-wing airplane available as part of the operations. Helicopters would be used for personnel and equipment transport between shore and the drill rig consistently during operations. The airplane would be used for personnel and equipment transport between onshore locations. Wainwright would be the principal port from which crew transfers would take place; however, it is possible that under certain circumstances these activities might need to be conducted through Barrow or another location.

(3) Drill Rig Resupply

Transport of supplies to and from the drill rig will primarily be done with the ware vessel and offshore supply vessels (OSVs), although any other project vessel with the capability of DP could be used. The supplies would be loaded in Wainwright onto the large landing craft from where they would be transferred to the supply vessels. This transfer of supplies will take place somewhere between 5.5 mi (9 km) of the drill rig and 5 mi (8 km) offshore of Wainwright. When not engaged in transfers of supplies, the ware vessel and OSVs will be located about 5.5 mi (9 km) from the drill rig. The large landing craft will be located somewhere between 5.5 mi (9 km) of the drill site and 5 mi (8 km) offshore of Wainwright.

The duration of each supply trip by the ware vessel and OSV is estimated to be up to 7 hrs, assuming the vessels depart from their standby location at about 5.5 mi (9 km) of the rig. It would take approximately 0.5 hr to travel one-way to the drill rig (cruising mode). The supply vessel would be dynamically positioned next to the rig for about 6 hrs for each transfer of fuel and less than 6 hrs for each transfer of other supplies. The transit time between the large landing craft and the supply vessels is about 3 hrs one-way.

The ware vessel is estimated to make about two to three trips per week to the rig but could make an average of almost four resupply trips per week over 14 weeks. Based on an estimated 53 trips per season and a maximum of 6 hrs for

supply transfer, the ware vessel would be in DP mode up to a total of 318 hrs over the drilling season. The OSVs are estimated to make four and a half resupply trips per week over 14 weeks. Based on an estimated total of 63 trips, unloading supplies from the OSV to the rig would take up to a total of 378 hrs (in DP mode) over the course of the drilling season. Assuming that at any time only one supply vessel will be in DP alongside the drill rig, the total duration of DP is 696 hrs.

(4) Personnel Transfer and Refueling

About 300 persons are estimated to be involved in the proposed exploration drilling overall. The jack-up drill rig, support and oil spill response vessels will be self-contained, and the crew will live aboard the rig and vessels. Air support will be necessary to meet personnel and supply needs once the rig is operational. The helicopter will fly a direct route between Wainwright and the drill rig, eight to ten times per week.

Three refueling events per well are expected to be required for the drill rig, depending on the circumstances. The duration of a rig-fueling event will be approximately 6 hrs. All refueling operations will follow procedures approved by the U.S. Coast Guard.

Vertical Seismic Profile Test

COP intends to conduct two or three VSP data acquisition runs inside the wellbore to obtain high-resolution seismic images with detailed time-depth relationships and velocity profiles of the various geological layers. The VSP data can be used to help reprocess existing 2D or 3D seismic data prior to drilling a potential future appraisal well in case oil or gas is discovered during the proposed exploration drilling.

The procedure of one VSP data acquisition run can be summarized as follows (Figure 2 in COP's application provides a schematic of the layout):

• The source of energy for the VSP data acquisition, typically consisting of one or more airguns, will be lowered from the drilling platform or a vessel to a depth of approximately 10 ft (3 m) to 30 ft (10 m) below the water surface (depending on sea state). The total volume of the airgun(s) is not expected to exceed 760 in

3

.

• A minimum of two geophones positioned 50 ft (15.2 m) apart will be placed at the end of a wireline cable, which will be lowered into the wellbore to total depth. Once total depth has been reached, the wireline cable will be pulled up and stopped at predefined depths (geophone stations). Data will be acquired by producing a series of sound pulses from the airgun(s) over a period of approximately 1 min. The sound waves generated by the source and reflected from various geological layers will be recorded by the two geophones.

• After each 1-minute airgun activity, the wireline cable with the geophones will be pulled up to a shallower position in the well after which the airgun(s) will again produce a series of sound pulses over a period of approximately 1 min. This process will be repeated until data have been acquired at all pre-identified geophone stations.

Two or three VSP data acquisition runs will be conducted; the first run will take place upon reaching the bottom of the 17.5-in (44.5 cm) borehole at approximately 5,220 ft (1,590 m) below sea level (bsl), the second run upon reaching the bottom of the 13.5 and 8.5 in (34.2 and 21.5 cm) borehole at approximately 9,580 ft (2,920 m) bsl, and a possible third run upon reaching the bottom of the 6.5 in (16.5 cm) borehole at approximately 11,020 ft (33,590 m) bsl. If the integrity of the 8.5 in borehole allows drilling to 11,020 ft without the need for an extra casing a third VSP run might not be needed. The number of geophone stations for each of the three VSP data acquisition runs varies depending on the length of the wellbore to be surveyed. The time required to finish a VSP data acquisition run depends on the depth of the wellbore (resulting in longer time to lower and pull up the wire cable with geophones) and the number of stations (resulting in longer data acquisition time). The period between VSP data acquisition runs is about 7-10 days, depending on the drilling progress. The total amount of time that airguns are operating for the three runs combined that might be performed in a well is about 2 hrs, not including ramp up. In case a second well is drilled, two or three additional VSP data acquisition runs might be conducted, meaning an additional 2 hrs of airgun operations over the course of the entire open-water drilling season.

Ice Management

Understanding ice systems and monitoring their movement are important aspects of COP's Chukchi Sea operations. COP has monitored Chukchi Sea ice since 2008 and would continue that monitoring through the proposed drilling season. Initial monitoring would incorporate satellite imagery to observe the early stages of sea ice retreat. Upon arrival in the project area, the ice management vessel, possibly with one other project vessel, would operate at the edge of the ice pack and monitor ice activity, updating all interested parties on ice pack coordinates to help determine scheduling for mobilization of the rig. COP has submitted an Ice Alerts Plan to BOEM for approval in connection with the Exploration Plan. The Ice Alerts Plan summarizes historic ice monitoring results which has assisted COP in estimating the timing and placement of the rig and support vessels. Under the COP Ice Alerts Plan, an ice monitoring and management center based out of Anchorage will monitor and interpret information collected from project vessels and satellite imagery during the entire drilling operation. A summary of the major components of COP's Ice Alerts Plan is provided below.

The ice edge position will be tracked in near real time using observations from satellite images, from the ice management vessel or other project vessels. The ice management and project vessels used for ice observations will remain on standby within about 5.5 mi (9 km) of the drill rig, unless deployed to investigate migrating ice-floes. When investigating ice, the vessels will likely stay within about 75 mi (121 km) of the rig. The Ice Alerts Plan includes a process for determining how close hazardous ice can approach before the well needs to be secured and the jack-up rig moved. This critical distance is a function of rig operations at that time, the speed and direction of the ice, the weather forecast, and the method of ice management.

Based on available historical and more recent ice data, there is low probability of ice entering the drilling area during the open water season. However, if hazardous ice is on a trajectory to approach the rig, the ice management vessel will be available to respond. One option for responding is to use the vessels fire monitor (water cannon) to modify the trajectory of the floe. Another option is to redirect the ice by applying pressure with the bow of the ice management vessel, slowly pushing the ice away from the direction of the drill rig. At these slow speeds, the vessel would use low power and slow propeller rotation speed, thereby reducing noise generation from propeller rotation effects in the water. Icebreaking is not planned as a way to manage ice that may be on a trajectory toward the drilling rig. In case the jack-up rig needs to be moved due to approaching ice, the support vessels will tow the rig to a secure location.

Timeframe of Activities

COP's anticipated start and end dates of the mobilization, drilling operations, and demobilization are on or about June 15, 2014, and November 16, 2014,

respectively, with actual activities in the lease sale area taking place roughly from July through October. Vessels would not arrive at the prospect prior to July 1. The HLV with the jack-up drill rig is expected to originate from Southeast Asia or the North Sea. The HLV will depart the area as soon as it has offloaded the rig. The AHST, OSVs, and ware vessel will mobilize from the Gulf of Mexico in early June and will be traveling north in close proximity to the HLV and jack-up rig. The ice management vessel will be the first to mobilize to the drill site to provide information on ice conditions to the HLV and other vessels.

COP anticipates the drilling of one well will take approximately 40 days. After the first Devils Paw well is drilled, it will be plugged and abandoned. If there is enough time, as estimated by the ice monitoring system, COP intends to drill a second well, which could take another 40 days. Relocation of the rig from the first to the second well would take approximately 24-48 hrs. If a second well is drilled, it would also be plugged and abandoned.

When drilling is completed, the jack-up rig will be demobilized and excess material transferred from the rig to supply vessels. The rig will then be jacked down and taken under tow by the AHST and OSVs to the load-out site, anticipated to be located south of the Devils Paw prospect area. The rig will remain in tow by the AHST until the HLV arrives. In case the drilling season ends earlier than anticipated, the rig may be towed to the alternate staging area and jacked up until the HLV arrives. In that situation, helicopters will be mobilized to Nome or the Red Dog Mine to support the rig as necessary. Once the AHST has the jack-up rig under tow, all other support vessels would be dismissed. The AHST and OSVs would accompany the rig until it is loaded onto the HLV. Once the rig has been loaded onto the HLV, the AHST, supply vessels, and air support will be demobilized.

Exploratory Drilling Program Sound Characteristics

Potential impacts to marine mammals could occur from the noise produced by the jack-up rig and its support vessels (including the ice management vessels and during DP), aircraft, and the airgun array during VSP tests. The drill rig 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 support vessels during DP. The airgun array proposed to be used by COP for the VSP tests 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) Drill Rig Sounds

The main contributors to the underwater sound levels from jack-up rig drilling activities are the use of generators and drilling machinery. Few underwater noise measurements exist from operations using a drill rig. Here we summarize the results from the drilling rig

Ocean General

and its two support vessels in the Timor Sea, Northern Australia (McCauley, 1998) and the jack-up rig

Spartan 151

in Cook Inlet, Alaska (MAI, 2011). For comparison, COP also included information on drilling sound measurements from a concrete drilling island and drillship. However, the sound propagation of a jack-up rig is substantially less than that of a drillship because the components that generate sound from a jack-up rig sit above the surface of the water instead of in the water.

McCauley (1998) conducted measurements under three different conditions: (a) Drilling rig sounds without drilling; (b) actively drilling, with the support vessel on anchor; and (c) drilling with the support vessel loading the rig (McCauley, 1998). The primary noise sources from the drill rig itself were from mechanical plants, fluid discharges, pumping systems and miscellaneous banging of gear on the rig. The overall noise level was low (117 dB re 1μPa at 410 ft [125 m]) mainly because the deck of the rig was well above the waterline (which is also the case for jack-up rigs). When the rig was actively drilling, the drill rig noise dominated the drilling sounds to a distance of about 1,312 ft (400 m). Beyond that distance, the energy from the drill string tones (in the 31 and 62 Hz

1/3

octaves) became apparent and resulted in an increase in the overall received noise level. With the rig drilling, the highest noise levels encountered were on the order of 117 dB re 1μPa at 410 ft (125 m) and 115 dB re1μPa at 1,228 ft (405 m). The noise source that far exceeded the previous two was from the support vessel standing alongside the rig for loading purposes. The thrusters and main propellers were engaged to keep the vessel in position and produced high levels of cavitation sound. The sound was broadband in nature, with highest levels of 137 dB 1μPa at 1,328 ft (405 m) and levels of 120 dB re 1μPa at 1.8-2.4 mi (3-4 km) from the well head.

Acoustic measurements of the drilling rig

Spartan 151

were conducted to report on underwater sound characteristics as a function of range using two different systems (moored hydrophone and real time system). Both systems provided consistent results. Primary sources of rig-based underwater sounds were from the diesel engines, mud pump, ventilation fans (and associated exhaust), and electrical generators. The loudest source levels (from the diesel engines) were estimated at 137 dB re 1 μPa at 1 m (rms) in the 141-178 Hz

1/3

octave band. Based on this estimate, the 120 dB (rms) re 1 μPa sound pressure level would be at about 154 ft (50 m) away from where the energy enters the water (jack-up leg or drill riser).

Hall and Francine (1991) measured drilling sounds from an offshore concrete island drilling structure. Source sound pressure level was 131 dB re 1μPa at 1 m for the drilling structure at idle (no drilling), and a transmission loss rate of 2.6 dB per doubling of distance, slightly less than theoretical cylindrical spreading. At a distance of 912 ft (278 m) from the drilling island the broadband sound pressure level was 109 dB re 1μPa. Strong tonal components at 1.375-1.5 Hz were detected in the acoustic records during drilling activities. These were likely associated with the rotary turntable, which was rotating between 75 and 110 rpm (which corresponds to 1.25-1.83 Hz). The received broadband sound pressure level at 849 ft (259 m) was 124 dB re 1μPa. The sounds measured from the concrete drilling island were almost entirely (>95%) composed of energy below 20 Hz.

Sound pressure levels of drilling activities from the concrete drilling island were substantially less than those reported for drill ships (Greene, 1987a). At a range of 557 ft (170 m) the 20-1000 Hz band level was 122-125 dB for the drillship

Explorer I,

with most energy below 600 Hz (although tones up to 1850 Hz were recorded). Drilling activity from the

Explorer

was measured as 134 dB at a range of 656 ft (200 m), with all energy below 600 Hz. Underwater sound measurements from the drillship

Kulluk

at 3,215 ft (980 m) were substantially higher (143 dB re 1μPa). Underwater sound levels recorded from the drillship

Stena Forth

in Disko Bay, Greenland, corresponded to measurements from other drillships and were higher than sound levels reported for semi-submersibles and drill rigs (Kyhn et al., 2011). The broadband source levels were similar to a fast

moving merchant vessel with source levels up to 184-190 dB re 1 μPa during drilling and maintenance work, respectively. At a range of 1,640 ft (500 m) from the drillship the 10-1000 Hz band level during drilling at 295 ft (90 m) ranged from approximately 100-128 dB re1 μPa, with the highest sound level at 100 and 400 Hz. Sound levels were ≤110 dB re1 μPa at 1.2 mi (2 km) distance.

Expected sound pressure levels for the proposed drilling activities have been modeled by JASCO Applied Research, Inc. for drilling sounds only and for drilling sounds in combination with the proximity of a support vessel using DP. The acoustic modeling results show that the maximum radii to received sound levels of 120 and 160 dB re 1 μPa from drilling operations alone are 689 ft (210 m) and <33 ft (10 m), respectively (O'Neill et al., 2012). More detailed results are included in Attachment A of COP's IHA application.

(2) Vessel Sounds

In addition to the drill rig, various types of vessels will be used in support of the operations including ice management vessels, anchor handlers, supply vessels and oil-spill response vessels. Like other industry-generated sound, underwater sound from vessels is generally most apparent at relatively low frequencies (20-500 Hz). The sound characteristic of each vessel is unique depending upon propulsion unit, machinery, hull size and shape. These characteristics change with load, vessel speed and weather conditions. For example, increase in vessel size, power and speed produces increasing broadband and tonal noise. The sound produced by vessels is generated by engine machinery and propeller cavitation. When a vessel increases speed, broadband sound from propeller cavitation and hull vibration becomes dominant over machinery sound. It has been estimated that propeller cavitation produces at least 90% of all ship generated ambient noise (Ross, 2005). Sound from large vessels is generally higher at low frequencies. Small high-powered (>100 horse power [HP]) propeller driven boats often exceed large vessel sound at frequencies above 1 kHz.

Ice management vessels operating in thick ice require a greater amount of power and propeller cavitation and hence produce higher sound levels than ships of similar size during normal operation in open water (Richardson et al., 1995b). Roth and Schmidt (2010) examined ice management vessel sound pressure levels during different sea ice conditions and modes of propulsion. Comparison of source spectra in open-water and while breaking moderate ice showed increases as much as 15 dB between 20 Hz and 2 kHz. For low frequencies, a sound pressure level of about 193 dB re 1μPa at 1 m was estimated to be a reasonable peak value.

Numerous measurements of underwater vessel sound have been performed since 2000 (for review see Wyatt, 2008) mostly in support of industry activity. Results of underwater vessel sounds that have been measured in the Chukchi and Beaufort Seas were reported in various 90-day and comprehensive reports since 2007 (e.g., Aerts

et al.,

2008; Hauser

et al.,

2008; Brueggeman

et al.,

2009a; Ireland

et al.,

2009). Due to the highly variable conditions under which these measurements were conducted, including equipment and methodology used, it is difficult to compare source levels (i.e., back calculated sound levels at a theoretical 1 m from the source) or even received levels between vessels. For example, source sound pressure levels of the same tug with barge varied from 173 dB to 182 dB re 1μPa at 1 m, depending on the speed and load at the time of measurement (Zykov and Hannay, 2006). Sound pressure levels of a drill rig support vessel traveling at a speed of about 11 knots (20 kph) was measured to be 136 dB re 1μPa at 1,312 ft (400 m) (McCauley, 1998). Acoustic measurements of an anchor handling support tug of similar size and horsepower traveling at 4.3 knots (8 kph) resulted in sound pressure levels of approximately 137 dB re 1μPa at 1,312 ft (400 m) and 120 dB re 1μPa at 4,855 ft (1,480 m) (Funk

et al.,

2008).

(3) Aircraft Sounds

Helicopters are proposed to be used for personnel and equipment transport to and from the drill rig. Over calm water away from shore, the maximum transmission of rotor and engine sounds from helicopters into the water can generally be visualized as a 26° cone under the aircraft. The size of the water surface area where transmission of sound can take place is therefore generally larger with a higher flight altitude, though the sound levels will be much lower due to the larger distance from the water. In practice, the width of the area where aircraft sounds will be received is usually wider than the 26° cone and varies with sea state because waves provide suitable angles for additional transmission of the sound. In shallow water, scattering and absorption will limit lateral propagation. 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.

Underwater sounds were measured for a Bell 212 helicopter (Greene 1982, 1985; Richardson

et al.,

1990). These measurements show that there are numerous prominent tones at frequencies up to about 350 Hz, with the strongest measured tone at 20-22 Hz. Received peak sound levels of a Bell 212 passing over a hydrophone at an altitude of approximately 1,000 ft (300 m), varied between 106-111 dB re 1μPa at 29 and 59 ft (9 and 18 m) water depth. Two Class 1 or Group A type helicopters will fly to and from the jack-up rig for transportation of manpower and supplies. Helicopters will be operated by a flight crew of two and capable of carrying 12 to 13 passengers.

(4) Vertical Seismic Profile Airgun Sounds

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. Most energy emitted from airguns is at relatively low frequencies. Typical high-energy airgun arrays emit most energy at 10-120 Hz. However, the pulses contain significant energy up to 500-1000 Hz and some energy at higher frequencies (Goold and Fish, 1998; Potter

et al.,

2007). Studies in the Gulf of Mexico have shown that the horizontally-propagating sound can contain significant energy above the frequencies that airgun arrays are designed to emit (DeRuiter

et al.,

2006; Madsen

et al.,

2006; Tyack

et al.,

2006). Energy at frequencies up to 150 kHz was found in tests of single 60-in

3

and 250-in

3

airguns (Goold and Coates, 2006). Nonetheless, the predominant energy is at low frequencies.

The strengths of airgun pulses can be measured in different ways, and it is important to know which method is being used when interpreting quoted source or received levels. Geophysicists usually quote peak-to-peak (p-p) levels, in bar-meters or (less often) dB re 1 μPa.

Peak level (zero-to-peak [0-p]) for the same pulse is typically approximately 6 dB less. In the biological literature, levels of received airgun pulses are often described based on the average or rms level, where the average is calculated over the duration of the pulse. The rms value for a given airgun pulse is typically approximately 10 dB lower than the peak level and 16 dB lower than the p-p value (Greene, 1997; McCauley

et al.,

1998, 2000). A fourth measure that is increasingly used is the Sound Exposure Level (SEL), in dB re 1 μPa2s. Because the pulses, even when stretched by propagation effects (see below), are usually <1 s in duration, the numerical value of the energy is usually lower than the rms pressure level. However, the units are different.

Because the level of a given pulse will differ substantially depending on which of these measures is being applied, it is important to be aware which measure is in use when interpreting any quoted pulse level. NMFS refers to rms levels when discussing levels of pulsed sounds that may harass marine mammals; these are the units used in this IHA notice. Specifics about the VSP airgun(s) and expected radii of various received rms sound levels are included in the acoustic modeling report of JASCO Applied Sciences (Attachment A of COP's application). The airgun array proposed for use will not exceed 760 in

3

. The VSP airgun operations differ from normal marine seismic surveys in that the airguns are fixed to one location (the drill rig), and a limited number of shots will be fired (a total of about 2 hrs of airgun activity per well, not including time required for ramp ups).

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 drill rig throughout the 2014 drilling season and will not be making trips between the shorebase and the offshore vessels (with the exception of the resupply transits). As noted earlier in this document and in Figure 3 of COP's application, the majority of the vessels will sit on standby mode approximately 5.5 mi (9 km) upwind of the drill rig. 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 (

Monodon monoceros

); polar bears (

Ursus maritimus

); and walruses (

Odobenus rosmarus divergens;

see Table 3 in COP's application). The bowhead, humpback, and fin whales are listed as “endangered” under the Endangered Species Act (ESA) and as depleted under the MMPA. The ringed and bearded seals are listed as “threatened” under the ESA. 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. 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 COP'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, gray, and killer whales, harbor porpoise, and ringed, bearded, and spotted seals are anticipated to be encountered more than the other four 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. Where available, COP used density estimates from peer-reviewed literature in the application. In cases where density estimates were not readily available in the peer-reviewed literature, COP used other methods to derive the estimates. NMFS reviewed the density estimate descriptions and documents and determined that they were acceptable for these purposes. 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 COP's proposed Chukchi Sea drilling activities, this species is not discussed further in this proposed IHA notice.

COP'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 COP 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 2011 SAR is available at:

http://www.nmfs.noaa.gov/pr/pdfs/sars/ak2011.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 COP'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 COP'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 COP'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, supply and support vessels on DP, and aircraft, as well as the VSP 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.,

1995b):

(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 wellbeing 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.

(1995b) found that vessel noise does not seem to strongly affect pinnipeds that are already in the water. Richardson

et al.

(1995b) 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.,

1995b) 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.,

1995b). 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.,

1995b). 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.,

1995b). 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 COP'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.

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 since the late 1990s. To compensate and reduce masking, some mysticetes may alter the frequencies of their communication sounds (Richardson

et al.,

1995b; 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.

(1995b) 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.,

1995b).

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 COP'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. Moreover, the very small radius of the 120 dB isopleth of the drill rig (670 ft [210 m]) will reduce the possibility of masking even further. The larger 120 dB isopleth of the drill rig while a support vessel is in DP mode beside it (5 mi [8 km]) and over the VSP airguns (3 mi [5 km]) are also not anticipated to result in substantial or long-term masking effects as these activities will only occur for a short time during the entire open-water season (696 hrs and 2-4 hrs total, respectively).

(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.

(1995a) 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. However, icebreaking is not a component of COP's proposed operations.

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.

(1995a) 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.

(1995a) 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.,

1995a). 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 VSP surveys in the following section (“

Potential Effects from VSP Activities”

).

Potential Effects from VSP 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. Moreover, because of the extremely short time period over which airguns will be used during operations (a total of 2 hrs per well), masking is not anticipated to occur.

(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 VSP 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 1.44-3 mi (2.31-5 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, 2012). In any event, the brief exposures to sound pulses from the proposed airgun source (the airguns will only be fired for a period of 2 hrs for each of the two 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 (p-p 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 very short time during the entire exploration drilling program (approximately 2 hrs for each well, for a total of 4 hrs over the entire open-water season, which lasts for approximately 4 months, if both wells are drilled).

(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, COP 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 an 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 source level of the drill rig will be below the 180 dB threshold (O'Neill

et al.,

2012), 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 0.6 mi (920 m) and 525 ft (160 m), respectively, from the source. Because of the short duration that the airguns will be used (no more than 4 hrs 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. Modeled source levels for a jack-up drill rig suggest that marine mammals located immediately adjacent to the rig 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 thresholds of 190 dB currently used for pinnipeds and 180 dB 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 sound pressure levels (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—Injury Criteria for Cetaceans and Pinnipeds Exposed to “Discrete” Noise Events (Either Single Pulses, Multiple Pulses, or Non-Pulses Within a 24-Hr Period; Cited in Southall et al., 2007). This Table Reflects Thresholds Based on Studies Reviewed in Southall et al. (2007) But Do Not Influence the Estimation of Take in This Proposed IHA Notice as No Injury Is Anticipated To Occur

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 level of the drill rig is not loud enough to induce PTS or 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 drill rigs. Sounds produced by airgun arrays are broadband impulses with most of the energy below 1 kHz, and the low-energy continuous sounds produced by drill rigs have most of the energy between 20 and 1,000 Hz. Additionally, the non-impulsive, continuous sounds produced by the jack-up rig proposed to be used by COP does 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.

Oil Spill Response Preparedness and Potential Impacts of an 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. The likelihood of a large or very large oil spill occurring during COP's proposed exploratory drilling program is remote. 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). BOEM's Supplemental Environmental Impact Statement for the Chukchi Sea Oil and Gas Lease Sale 193 (BOEM, 2011) provides a discussion of the extremely low likelihood of an oil spill occurring (available on the Internet at:

http://www.boem.gov/About-BOEM/BOEM-Regions/Alaska-Region/Environment/Environmental-Analysis/OCS-EIS/EA-BOEMRE-2011-041.aspx

). For more recent updates on occurrence rates for offshore oil spills from drilling platforms, including spills greater than or equal to 1,000 barrels (bbls) and greater than or equal to 10,000 bbls, we refer to the BOEM-funded study of McMahon-Anders

et al.

(2012). However, this study did not focus solely on the Alaskan OCS. Another BOEM-directed study discusses most recent oil spill occurrence estimators and their variability for the Beaufort and Chukchi Seas for various sizes of spills as small as 50 bbls (Bercha, 2011). Bercha (2011) notes that because of the difference in oil spill indicators between non-Arctic OCS areas and the Beaufort and Chukchi Seas OCS areas, the non-Arctic areas are likely to result in a somewhat higher oil spill occurrence probability than comparable developments in the Chukchi or Beaufort Seas.

COP will have various measures and protocols in place that will be implemented to prevent oil releases from the wellbore, such as:

• Using information from previous wells in addition to recent data collected from 3D seismic and shallow hazard surveys, where applicable, to increase knowledge of the subsurface environment;

• Using skilled personnel and providing them with project-specific training. Implementing frequent drills to keep personnel alert;

• Implementation of visual and automated procedures for the early detection of a spill:

○ The drilling operation will be monitored continuously by Pit-Volume Totalizer equipment and visual monitoring of the mud circulating system.

○ Alarms will be sounded if there is a significant volume increase of drilling mud in the pits due to an influx into the wellbore.

○ Multiple walk-through inspections of the rig are performed every day by each crew to inspect and verify all control systems are functioning properly.

○ Mobile Offshore Drilling Unit's (MODU) Central Control & Radio Room monitors all safety aspects of the rig and is manned 24 hrs per day by qualified rig personnel.

○ Established emergency shutdown philosophies will be documented in the Contractor's Operations manuals and the crews will be trained accordingly. An emergency shutdown can be initiated manually by operators at the instrument/control panels or automatically under certain conditions.

• Maintaining a minimum of two barriers; the jack-up rig has the capability of utilizing advanced well control barriers:

○ Surface blow out preventer (BOP) located on the rig in a place that is easily accessible. This BOP can close in well on drill pipe or open hole.

○ Thick walled high strength riser designed to contain full well pressure.

○ Pre-Positioned Capping Device (PCD) will be installed above the wellhead on the sea floor. The PCD can keep the well isolated with pressure containment, even if the rig is moved off location. The PCD can be triggered remotely from the drill rig or from support vessels.

Mechanical containment and recovery is COP's primary form of response. Actual spill response decisions depend on safety considerations, weather, and other environmental conditions. It is the discretion of the Incident Commander and Unified Command to select any sequence, response measure, or take as much time as necessary, to employ an effective response. COP's spill response fleet is mobile and capable of responding to incidents affecting open-water, nearshore, and shoreline environments. Offshore spill response would be provided by the following vessels:

• Oil Spill Response Vessel (OSRV), the primary offshore oil spill response platform, located within about 5.5 mi (9 km) of the drilling rig;

• Offshore Supply Vessel (OSV), a vessel of opportunity response platform, located within about 5.5 mi (9 km) of the drilling rig;

• Four workboats, two are located on the OSRV and two on the OSV; and

• One Oil Spill Tanker (OST), with a storage capacity of at least 520,000 barrels, also located within about 5.5 mi (9 km) from the drilling rig.

Alaska Clean Seas personnel will be stationed on OSRV, OSV, and the drill rig. OSRV is the primary spill response vessel; it will also be used to support refueling of the jack-up rig. In the event of an emergency, OSV will provide oil spill response and fast response craft capability near the ware vessel. During non-emergency operations, OSV will provide operational drill rig support, including standby support during vessel refueling operations. From the standby locations, it will take about 30 min for the vessels to arrive at the rig.

Spill response support for nearshore operations will be located about 5.5 mi (9 km) from the drill rig location and approximately 5 mi (8 km) offshore of Wainwright. Nearshore spill response operations are provided by the following vessels:

• One Oil Spill Response Barge (OSRB) and tug with a storage capacity of 40,000 bbls;

• Four workboats, located on the OSRB;

• One large landing craft, located adjacent to the OSRB; and

• Four 32-foot shallow draft landing craft located on the large landing craft.

The OSRB and large landing craft are designed to carry and deploy a majority of the nearshore and onshore spill response assets. In the event of a spill, additional responders would be mobilized to man the OSRB, large landing craft, and other support vessels. From 5 mi (8 km) offshore of Wainwright it will take about 24 hrs for the OSRB to arrive at the rig, assuming a travel speed of 5 knots and including notification time. However, because this barge is equipped primarily for nearshore response, it is unlikely to be needed offshore near the rig.

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 COP's specified activity for which NMFS is proposing to authorize take, 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 COP 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 Devils Paw 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-sp

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