Taking and Importing Marine Mammals; Taking Marine Mammals Incidental to Operation of Offshore Oil and Gas Facilities in the U.S. Beaufort Sea

DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

50 CFR Part 217

[Docket No. 100217096-1312-01]

RIN 0648-AY63

Taking and Importing Marine Mammals; Taking Marine Mammals Incidental to Operation of Offshore Oil and Gas Facilities in the U.S. Beaufort Sea

AGENCY:

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

ACTION:

Proposed rule; request for comments.

SUMMARY:

NMFS has received a request from BP Exploration (Alaska) Inc. (BP) for authorization for the take of marine mammals incidental to operation of offshore oil and gas facilities in the U.S. Beaufort Sea, Alaska, for the period 2011-2016. Pursuant to the Marine Mammal Protection Act (MMPA), NMFS is proposing to issue regulations to govern that take and requesting information, suggestions, and comments on these proposed regulations. These regulations, if issued, would include required mitigation measures to ensure the least practicable adverse impact on the affected marine mammal species and stocks.

DATES:

Comments and information must be received no later than August 5, 2011.

ADDRESSES:

You may submit comments, identified by 0648-AY63, by any one of the following methods:

• Electronic Submissions: Submit all electronic public comments via the Federal eRulemaking Portal

http://www.regulations.gov.

• Hand delivery or mailing of paper, disk, or CD-ROM comments should be addressed to Michael Payne, Chief, Permits, Conservation and Education Division, Office of Protected Resources, National Marine Fisheries Service, 1315 East-West Highway, Silver Spring, MD 20910.

Comments regarding any aspect of the collection of information requirement contained in this proposed rule should be sent to NMFS via one of the means stated here and to the Office of Information and Regulatory Affairs, NEOB-10202, Office of Management and Budget (OMB), Attn: Desk Office, Washington, DC 20503,

OIRA@omb.eop.gov.

Instructions:

All comments received are a part of the public record and will generally be posted to

http://www.regulations.gov

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.

NMFS will accept anonymous comments (enter N/A in the required fields if you wish to remain anonymous). Attachments to electronic comments will be accepted in Microsoft Word, Excel, WordPerfect, or Adobe PDF file formats only.

FOR FURTHER INFORMATION CONTACT:

Candace Nachman, Office of Protected Resources, NMFS, (301) 713-2289, ext. 156, or Brad Smith, Alaska Region, NMFS, (907) 271-3023.

SUPPLEMENTARY INFORMATION:

Availability

A copy of BP's application may be obtained by writing to the address specified above (see

ADDRESSES

), calling the contact listed above (see

FOR FURTHER INFORMATION CONTACT

), or visiting the Internet at:

http://www.nmfs.noaa.gov/pr/permits/incidental.htm.

To help NMFS process and review comments more efficiently, please use only one method to submit comments.

Background

Sections 101(a)(5)(A) and (D) of the MMPA (16 U.S.C. 1361

et seq.

) direct the Secretary of Commerce (Secretary) to allow, upon request, the incidental, but not intentional taking of marine mammals by U.S. citizens who engage in a specified activity (other than commercial fishing) during periods of not more than five consecutive years each if certain findings are made and regulations are issued or, if the taking is limited to harassment, notice of a proposed authorization is provided to the public for review.

Authorization shall be granted if NMFS finds that the taking will have a negligible impact on the species or stock(s), will not have an unmitigable adverse impact on the availability of the species or stock(s) for subsistence uses, and if the permissible methods of taking and requirements pertaining to the mitigation, monitoring and reporting of such taking 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.

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

On November 6, 2009, NMFS received an application from BP requesting authorization for the take of six marine mammal species incidental to operation of the Northstar development in the Beaufort Sea, Alaska, over the course of 5 years, which would necessitate the promulgation of new five-year regulations. Construction of Northstar was completed in 2001. The proposed activities for 2011-2016 include a continuation of drilling, production, and emergency training operations but no construction or activities of similar intensity to those conducted between 1999 and 2001. The likely or possible impacts of the planned continuing operations at Northstar on marine mammals involve both non-acoustic and acoustic effects. Potential non-acoustic effects could result from the physical presence of personnel, structures and equipment, construction or maintenance activities, and the occurrence of oil spills. Petroleum development and associated activities in marine waters introduce sound into the environment, produced by island construction, maintenance, and drilling, as well as vehicles operating on the ice, vessels, aircraft, generators, production machinery, gas flaring, and camp operations. BP requests authorization to take individuals of three cetacean and three pinniped species by Level B Harassment. They are: Bowhead, gray, and beluga whales and ringed, bearded, and spotted seals. Further, BP requests authorization to take five individual ringed seals by injury or mortality annually over the course of the 5-year rule.

Description of the Specified Activity

Background on the Northstar Development Facility

BP is currently producing oil from an offshore development in the Northstar Unit (see Figure 1 in BP's application). This development is the first in the Beaufort Sea that makes use of a subsea pipeline to transport oil to shore and

then into the Trans-Alaska Pipeline System. The Northstar facility was built in State of Alaska waters on the remnants of Seal Island approximately 6 mi (9.5 km) offshore from Point Storkersen, northwest of the Prudhoe Bay industrial complex, and 3 mi (5 km) seaward of the closest barrier island. It is located approximately 54 mi (87 km) northeast of Nuiqsut, an Inupiat community.

The main facilities associated with Northstar include a gravel island work surface for drilling and oil production facilities and two pipelines connecting the island to the existing infrastructure at Prudhoe Bay. One pipeline transports crude oil to shore, and the second imports gas from Prudhoe Bay for gas injection at Northstar. Permanent living quarters and supporting oil production facilities are also located on the island.

The construction of Northstar began in early 2000 and continued through 2001. BP states that activities with similar intensity to those that occurred during the construction phase between 2000 and 2001 are not planned or expected for any date within the 5-year period that would be governed by the proposed regulations (

i.e.,

2011-2016). Well drilling began on December 14, 2000, and oil production commenced on October 31, 2001. Construction and maintenance activities occurred annually on the protection barrier around Northstar due to ice and storm impacts. In August 2003, two barges made a total of 52 round-trips to haul 30,000 cubic yards of gravel from West Dock for berm construction. Depending on the actual damage, repair and maintenance in the following years consisted of activities such as creating a moat for diver access, removing concrete blocks in areas that had sustained erosion and/or block damage, and installing a new layer of filter fabric. In 2008, BP installed large boulders at the NE corner of the barrier instead of replacing the lower concrete blocks that were removed during a storm.

The planned well-drilling program for Northstar was completed in May 2004. Drilling activities to drill new wells, conduct well maintenance, and drill well side-tracks continued in 2006 (six wells), 2007 (two wells), and 2008 (two wells). The drill rig was demobilized and removed from the island by barge during the 2010 open water period. Although future drilling is not specifically planned, drilling of additional wells or well work-over may be required at some time in the future. A more detailed description of past construction, drilling, and production activities at Northstar can be found in BP's application (see

ADDRESSES

).

Expected Activities in 2011-2016

During the 5-year period from 2011-2016, BP intends to continue production and emergency training operations. As mentioned previously, drilling is not specifically planned for the 2011-2016 time period but may be required at some point in the future. The activities described next could occur at any time during the 5-year period. Table 2 in BP's application (see

ADDRESSES

) summarizes the vehicles and machinery used during BP's Northstar activities since the development of Northstar Island. Although all these activities are not planned to take place during the 2011-2016 operational phase, some of the equipment may be required to repair or replace existing structures or infrastructure on Northstar in the future.

(1) Transportation of Personnel, Equipment, and Supplies

Transportation needs for the Northstar project include the ability to safely transport personnel, supplies, and equipment to and from the site during repairs or maintenance, drilling, and operations in an offshore environment. During proposed island renewal construction that may take place during the requested time period, quantities of pipes, vertical support members (

i.e.,

posts that hold up terrestrial pipelines), gravel, and a heavy module will be transported to the site. Drilling operations require movement of pipe materials, chemicals, and other supplies to the island. During ongoing field operations, equipment and supplies will need to be transported to the site. All phases of construction, drilling, and operation require movement of personnel to and from the Northstar area.

During the operations phase from 2002-2009, fewer ice roads were required compared to the construction phase (2000-2001). The future scope of ice road construction activities during ongoing production is expected to be similar to the post-construction period of 2002-2009. The locations, dimensions, and construction techniques of these ice roads are described in the multi-year final comprehensive report (Richardson [ed.], 2008). The presence of ice roads allows the use of standard vehicles such as pick-ups, SUVs, buses and trucks for transport of personnel and equipment to and from Northstar during the ice-covered period. Ice roads are planned to be constructed and used as a means of winter transportation for the duration of Northstar operations. The orientation of future ice roads is undetermined, but will not exceed the number of ice roads created during the winter of 2000/2001.

Barges and Alaska Clean Seas (ACS) vessels are used to transport personnel and equipment from the Prudhoe Bay area to Northstar during the open-water season, which extends from approximately mid- to late-July through early to mid-October. Seagoing barges are used to transport large modules and other supplies and equipment during the construction period.

Helicopter access to Northstar Island continues to be an important transportation option during break-up and freeze-up of the sea ice when wind, ice conditions, or other operational considerations prevent or limit hovercraft travel. Helicopters will be used for movement of personnel and supplies in the fall after freeze-up begins and vessel traffic is not possible but before ice roads have been constructed. Helicopters will also be used in the spring after ice roads are no longer safe for all-terrain vehicles (ATVs) but before enough open water is available for vessel traffic. Helicopters are also available for use at other times of year in emergency situations. Helicopters fly at an altitude of at least 1,000 ft (305 m), except for take-off, landing, and as dictated for safe aircraft operations. Designated flight paths are assigned to minimize potential disturbance to wildlife and subsistence users.

The hovercraft is used to transport personnel and supplies during break-up and freeze-up periods to reduce helicopter use. BP intends to continue the use of the hovercraft in future years. Specifications of the hovercraft and sound characteristics are described in Richardson ([ed.] 2008) and Blackwell and Greene (2005).

(2) Production Operations

The process facilities for the Northstar project are primarily prefabricated sealift modules that were shipped to the island and installed in 2001. The operational aspects of the Northstar production facility include the following: Two diesel generators (designated emergency generators); three turbine generators for the power plant, operating at 50 percent duty cycle (

i.e.,

only two will be operating at any one time); two high pressure turbine compressors; one low pressure flare; and one high pressure flare. Both flares are located on the 215 ft (66 m) flare tower. Modules for the facility include permanent living quarters (

i.e.,

housing, kitchen/dining, lavatories, medical, recreation, office, and laundry space), utility module (

i.e.,

desalinization plant,

emergency power, and wastewater treatment plant), warehouse/shop module, communications module, diesel and potable water storage, and chemical storage. Operations have been continuing since oil production began on October 31, 2001 and are expected to continue beyond 2016.

(3) Drilling Operations

The drilling rig and associated equipment was moved by barge to Northstar Island from Prudhoe Bay during the open-water season in 2000. Drilling began in December 2000 using power supplied by the installed gas line. The first well drilled was the Underground Injection Control well, which was commissioned for disposal of permitted muds and cuttings on January 26, 2001. After Northstar facilities were commissioned, drilling above reservoir depth resumed, while drilling below that depth is allowed only during the ice covered period. Although future drilling is not specifically planned during the requested time period for this proposed rule, drilling of additional wells or well work-over may be required at some time during 2011-2016.

(4) Pipeline Design, Inspection, and Maintenance

The Northstar pipelines have been designed, installed, and monitored to assure safety and leak prevention. Pipeline monitoring and surveillance activities have been conducted since oil production began, and BP will conduct long-term monitoring of the pipeline system to assure design integrity and to detect any potential problems through the life of the Northstar development. The program will include visual inspections/aerial surveillance and pig (a gauging/cleaning device) inspections.

The Northstar pipelines include the following measures to assure safety and leak prevention:

• Under the pipeline design specifications, the tops of the pipes are 6-8 ft (1.8-2.4 m) below the original seabed (this is 2 times the deepest measured ice gouge);

• The oil pipeline uses higher yield steel than required by design codes as applied to internal pressure (by a factor of over 2.5 times). This adds weight and makes the pipe stronger. The 10-in (25.4-cm) diameter Northstar oil pipeline has thicker walls than the 48-in (122-cm) diameter Trans-Alaska Pipeline;

• The pipelines are designed to bend without leaking in the event of ice keel impingement or the maximum predicted subsidence from permafrost thaw;

• The pipelines are coated on the outside and protected with anodes to prevent corrosion; and

• The shore transition is buried to protect against storms, ice pile-up, and coastal erosion. The shore transition valve pad is elevated and set back from the shoreline.

A best-available-technology leak detection system is being used during operations to monitor for any potential leaks. The Northstar pipeline incorporates two independent, computational leak detection systems: (1) The Pressure Point Analysis (PPA) system, which detects a sudden loss of pressure in the pipeline; and (2) the mass balance leak detection system, which supplements the PPA. Furthermore, an independent hydrocarbon sensor, the LEOS leak detection system, located between the two pipelines, can detect hydrocarbon vapors and further supplements the other systems.

• Intelligent inspection pigs are used during operations to monitor pipe conditions and measure any changes.

• The line is constructed with no flanges, valves, or fittings in the subsea section to reduce the likelihood of equipment failure.

During operations, BP conducts aerial forward looking infrared (FLIR) surveillance of the offshore and onshore pipeline corridors at least once per week (when conditions allow), to detect pipeline leaks. Pipeline isolation valves are inspected on a regular basis. In addition to FLIR observations/inspections, BP conducts a regular oil pipeline pig inspection program to assess continuing pipeline integrity. The LEOS Leak Detection System is used continuously to detect under-ice releases during the ice covered period.

The pipelines are also monitored annually to determine any potential sources of damage along the pipeline route. The monitoring work has been conducted in two phases: (1) A helicopter-based reconnaissance of strudel drainage features in early June; and (2) a vessel-based survey program in late July and early August. During the vessel-based surveys, multi-beam, single-beam, and side scan sonar are used. These determine the locations and characteristics of ice gouges and strudel scour depressions in the sea bottom along the pipeline route and at additional selected sites where strudel drainage features have been observed. If strudel scour depressions are identified, additional gravel fill is placed in the open water season to maintain the sea bottom to original pipeline construction depth.

(5) Routine Repair and Maintenance

Various routine repair and maintenance activities have occurred since the construction of Northstar. Examples of some of these activities include completion and repair of the island slope protection berm and well cellar retrofit repairs. Activities associated with these repairs or modifications are reported in the 1999-2004 final comprehensive report (Rodrigues and Williams, 2006) and since 2005 in the various Annual Reports (Rodrigues

et al.,

2006; Rodrigues and Richardson, 2007; Aerts and Rodrigues, 2008; Aerts, 2009). Some of these activities, such as repair of the island slope protection berm, were major repairs that involved the use of barges and heavy equipment, while others were smaller-scale repairs involving small pieces of equipment and hand operated tools. The berm surrounding the island is designed to break waves and ice movement before they contact the island work surface and is subjected to regular eroding action from these forces. The berm and sheet pile walls will require regular surveying and maintenance in the future. Potential repair and maintenance activities that are expected to occur at Northstar during the period 2011-2016 include pile driving, traffic, gravel transport, dock construction and maintenance, diving and other activities similar to those that have occurred in the past.

(6) Emergency and Oil Spill Response Training

Emergency and oil spill response training activities are conducted at various times throughout the year at Northstar. Oil spill drill exercises are conducted by ACS during both the ice-covered and open-water periods. During the ice-covered periods, exercises are conducted for containment of oil in water and for detection of oil under ice. These spill drills have been conducted on mostly bottom-fast ice in an area 200 ft × 200 ft (61 m × 61 m) located just west of the island, using snow machines and ATVs. The spill drill includes the use of various types of equipment to cut ice slots or drill holes through the floating sea ice. Typically, the snow is cleared from the ice surface with a Bobcat loader and snow blower to allow access to the ice. Two portable generators are used to power light plants at the drill site. The locations and frequency of future spill drills or exercises will vary depending on the condition of the sea ice and training needs.

ACS conducts spill response training activities during the open-water season

during late July through early October. Vessels used as part of the training typically include Zodiacs, Kiwi Noreens, and Bay-class boats that range in length from 12-45 ft (3.7-13.7 m). Future exercises could include other vessels and equipment.

ARKTOS amphibious emergency escape vehicles are stationed on Northstar Island. Each ARKTOS is capable of carrying 52 people. Training exercises with the ARKTOS are conducted monthly during the ice-covered period. ARKTOS training exercises are not conducted during the summer. Equipment and techniques used during oil spill response exercises are continually updated, and some variations relative to the activities described here are to be expected.

(7) Northstar Abandonment

Detailed plans for the decommissioning of Northstar will be prepared near the end of field life, which will not occur during the period requested for these proposed regulations. For additional information on abandonment and decommissioning of the Northstar facility, refer to BP's application (see

ADDRESSES

).

Northstar Sound Characteristics

During continuing production activities at Northstar, sounds and non-acoustic stimuli will be generated by vehicle traffic, vessel operations, helicopter operations, drilling, and general operations of oil and gas facilities (

e.g.,

generator sounds and gas flaring). The sounds generated from transportation activities will be detectable underwater and/or in air some distance away from the area of activity. The distance will depend on the nature of the sound source, ambient noise conditions, and the sensitivity of the receptor. Take of marine mammals by Level B harassment incidental to the activities mentioned in this document could occur for the duration of these proposed regulations. The type and significance of the harassment is likely to depend on the species and activity of the animal at the time of reception of the stimulus, as well as the distance from the sound source and the level of the sound relative to ambient conditions.

(1) Construction Sounds

Sounds associated with construction of Seal Island in 1982 were studied and described by Greene (1983a) and summarized in the previous petition for regulations submitted by BP (BPXA, 1999). Underwater and in-air sounds and iceborne vibrations of various activities associated with the final construction phases of Northstar were recorded in the winter of 2000-2002 (Greene

et al.,

2008). The main purpose of these measurements was to characterize the properties of island construction sounds and to use this information in assessing their possible impacts on wildlife. Activities recorded included ice augering, pumping sea water to flood the ice and build an ice road, a bulldozer plowing snow, a Ditchwitch cutting ice, trucks hauling gravel over an ice road to the island site, a backhoe trenching the sea bottom for a pipeline, and both vibratory and impact sheet pile driving (Greene

et al.,

2008). Table 5 in BP's application presents a summary of the levels of construction sounds and vibrations measured around the Northstar prospect.

Ice road construction is difficult to separate into its individual components, as one or more bulldozers and several rolligons normally work concurrently. Of the construction activities reported, those related to ice road construction (bulldozers, augering and pumping) produced the least amount of sound, in all three media. The distance to median background for the strongest one-third octave bands for bulldozers, augering, and pumping was less than 1.24 mi (2 km) for underwater sounds, less than 0.62 mi (1 km) for in-air sounds, and less than 2.5 mi (4 km) for iceborne vibrations (see Table 5 in BP's application). Vibratory sheet pile driving produced the strongest sounds, with broadband underwater levels of 143 dB re 1 µPa at 328 ft (100 m). Most of the sound energy was in a tone close to 25 Hz. Distances to background levels of underwater sounds (approximately 1.86 mi [3 km]) were somewhat smaller than expected. Shepard

et al.

(2001) recorded sound near Northstar in April 2001 during construction and reported that the noisiest conditions occurred during sheet pile installation with a vibrating hammer. BP's estimates were 8-10 dB higher at 492 ft (150 m) and 5-8 dB lower at 1.24 mi (2 km) than the measurements by Shepard

et al.

(2001). Greene

et al.

(2008) describes sound levels during impact sheet pile driving. However, satisfactory recordings for this activity were only obtained at one station 2,395 ft (730 m) from the sheet pile driven into the island. The maximum peak pressure recorded on the hydrophone was 136.1 dB re 1 µPa and 141.1 dB re 1 µPa on the geophone (Greene

et al.,

2008).

(2) Operational Sounds

Drilling operations started in December 2000 and were the first sound-producing activities associated with the operational phase at Northstar. The four principal operations that occur during drilling are drilling itself, tripping (extracting and lowering the drillstring), cleaning, and well-logging (lowering instruments on a cable down the hole). Drilling activities can be categorized as non-continuous sounds,

i.e.,

they contribute to Northstar sounds intermittently. Other non-continuous sounds are those from heavy equipment operation for snow removal, berm maintenance, and island surface maintenance. Sounds from occasional movements of a “pig” through the pipeline may also propagate into the marine or nearshore environment.

Sounds from generators, process operations (

e.g.,

flaring, seawater treatment, oil processing, gas injection), and island lighting are more continuous and contribute to the operational sounds from Northstar. Drilling and operational sounds underwater, in air, and of ice-borne vibrations were obtained at Northstar Island and are summarized here and in a bit more detail in BP's application (Blackwell

et al.,

2004b; Blackwell and Greene, 2006).

Drilling

—During the ice covered seasons from 1999 to 2002, drilling sounds were measured and readily identifiable underwater, with a marked increase in received levels at 60-250 Hz and 700-1400 Hz relative to no-drilling times. The higher-frequency peak, which was distinct enough to be used as a drilling “signature”, was clearly detectible 3.1 mi (5 km) from the drill rig, but had fallen to background values by 5.8 mi (9.4 km). Distances at which background levels were reached were defined as the distance beyond which broadband levels remained constant with increasing distance from the source. Sound pressure levels of island production with and without drilling activities measured at approximately 1,640 ft (500 m) from Northstar are similar, with most of the sound energy below 100 Hz. The broadband (10-10,000 Hz) level was approximately 2 dB higher during drilling than without, but relatively low in both cases (99 vs. 97 dB re 1 µPa; Blackwell and Greene, 2006).

In air, drilling sounds were not distinguishable from overall island sounds based on spectral characteristics or on broadband levels (Blackwell

et al.,

2004b). A similar result was found for recordings from geophones: broadband levels of iceborne vibrations with or without drilling were indistinguishable (Blackwell

et al.,

2004b). Thus, airborne sounds and iceborne vibrations were not strong enough during drilling to have much influence on overall Northstar sound, in contrast to underwater

sounds, which were higher during drilling (Blackwell and Greene, 2006).

Richardson

et al.

(1995b) summarized then-available data by stating that sounds associated with drilling activities vary considerably, depending on the nature of the ongoing operations and the type of drilling platform (island, ship, etc.). Underwater sound associated with drilling from natural barrier islands or an artificial island built mainly of gravel is generally weak and is inaudible at ranges beyond several kilometers. The results from the Northstar monitoring work in more recent years are generally consistent with the earlier evidence.

Other Operational Sounds: Ice-covered Season

—Both with and without drilling, underwater broadband levels recorded north of the island during the ice-covered season were similar with and without production (Blackwell

et al.,

2004b). Although the broadband underwater levels did not seem to be affected appreciably by production activities, a peak at 125-160 Hz could be related to production. This peak was no longer detectable 3.1 mi (5 km) from the island, either with or without simultaneous drilling (Blackwell

et al.,

2004b).

Other Operational Sounds: Open-water Season

—Underwater and in-air production sounds from Northstar Island were recorded and characterized during nine open-water seasons from 2000 to 2008 (Blackwell and Greene, 2006; Blackwell

et al.,

2009). Island activity sounds recorded during 2000-2003 included construction of the island, installation of facilities, a large sealift transported by several barges and associated Ocean, River, and Point Class tugs, conversion of power generation from diesel-powered generators to Solar gas turbines, drilling, production, and reconstruction of an underwater berm for protection against ice. From 2003-2008 island activities mainly consisted of production related sounds and maintenance activities of the protection barrier. During the open water season, vessels were the main contributors to the underwater sound field at Northstar (Blackwell and Greene, 2006). Vessel noise is discussed in the next subsection.

During both the construction phase in 2000 and the drilling and production phase, island sounds underwater reached background values at distances of 1.2-2.5 mi (2-4 km; Blackwell and Greene, 2006). For each year, percentile levels of broadband sound (maximum, 95th, 50th, and 5th percentile, and minimum) were computed over the entire field season. The range of broadband levels recorded over 2001-2008 for all percentiles is 80.8-141 dB re 1 µPa. The maximum levels are mainly determined by the presence of vessels and can be governed by one specific event. The 95th percentile represents the sound level generated at Northstar during 95% of the time. From 2004 to 2008 these levels ranged from 110 to 119.5 dB re 1 µPa at approximately 0.3 mi (450 m) from Northstar. Much of the variation in received levels was dependent on sea state, which is correlated with wind speed. The lowest sound levels in the time series are indicative of the quietest times in the water near the island and generally correspond to times with low wind speeds. Conversely, times of high wind speed usually correspond to increased broadband levels in the directional seafloor acoustic recorder (DASAR) record (Blackwell

et al.,

2009). The short-term variability in broadband sound levels in 2008 was higher than in previous years. This was attributed to the presence of a new type of impulsive sound on the records of the near-island DASARs, referred to as “pops”. Bearings pointed to the northeastern part of Northstar Island, but to date the source is not known. Pops were broadband in nature, of short duration (approximately 0.05 s), and with received sound pressure levels at the near-island DASAR ranging from 107 to 144 dB re 1 μPa. This sound was also present on the 2009 records, but the source remains unknown.

Airborne sounds were recorded concurrently with the boat-based recordings in 2000-2003 (Blackwell and Greene, 2006). The strongest broadband airborne sounds were recorded approximately 985 ft (300 m) from Northstar Island in the presence of vessels, and reached 61-62 dBA re 20 μPa. These values are expressed as A-weighted levels on the scale normally used for in-air sounds. In-air sounds generally reached a minimum 0.6-2.5 mi (1-4 km) from the island, with or without the presence of boats.

(3) Transportation Sounds

Sounds related to winter construction activities of Seal Island in 1982 were reported by Greene (1983a) and information on this topic can be found in BP's 1999 application (BPXA, 1999). During the construction and operation of Northstar Island from 2000 to 2002, underwater sound from vehicles constructing and traveling along the ice road diminished to background levels at distances ranging from 2.9 to 5.9 mi (4.6 to 9.5 km). In-air sound levels of these activities reached background levels at distances ranging from 328-1,969 ft (100-600 m; see Table 5 in BP's application).

Sounds and vibrations from vehicles traveling along an ice road constructed across the grounded sea ice and along Flaxman Island (a barrier Island east of Prudhoe Bay) were recorded in air and within artificially constructed polar bear dens in March 2002 (MacGillivray

et al.,

2003). Underwater recordings were not made. Sounds from vehicles traveling along the ice road were attenuated strongly by the snow cover of the artificial dens; broadband vehicle traffic noise was reduced by 30-42 dB. Sound also diminished with increasing distance from the station. Most vehicle noise was indistinguishable from background (ambient) noise at 1,640 ft (500 m), although some vehicles were detectable to more than 1.2 mi (2,000 m). Ground vibrations (measured as velocity) were undetectable for most vehicles at a distance of 328 ft (100 m) but were detectable to 656 ft (200 m) for a Hägglunds tracked vehicle (MacGillivray

et al.,

2003).

Helicopters were used for personnel and equipment transport to and from Northstar during the unstable ice periods in spring and fall. Helicopters flying to and from Northstar generally maintain straight-line routes at altitudes of 1,000 ft (300 m) ASL, thereby limiting the received levels at and below the surface. Helicopter sounds contain 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), which is the minimum allowed altitude for the Northstar helicopter under normal operating conditions, varied between 106 and 111 dB re 1 μPa at 30 and 59 ft (9 and 18 m) water depth (Greene, 1982, 1985). 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 (Patenaude

et al.,

2002).

Under calm conditions, rotor and engine sounds are coupled into the water within a 26° cone beneath the aircraft. Some of the sound transmits beyond the immediate area, and some sound enters the water outside the 26° cone when the sea surface is rough. However, scattering and absorption limit lateral propagation in shallow water. For these reasons, helicopter and fixed-wing aircraft flyovers are not heard underwater for very long, especially when compared to how long they are heard in air as the aircraft approaches, passes and moves away

from an observer. Tones from helicopter traffic were detected underwater at a horizontal distance approximately 1,476 ft (450 m) from Northstar, but only during helicopter departures from Northstar (Blackwell

et al.,

2009). The duration of the detectable tones, when present, was short (20-50 s), and the received sound levels were weak, sometimes barely detectable. The lack of detectable tones during 65% of the investigated helicopter departures and arrivals supports the importance of the aircraft's path in determining whether tones will be detectable underwater. Helicopter tones were not detectable underwater at the most southern DASAR location approximately 4 mi (6.5 km) north of Northstar.

Principally the crew boat, tugs, and self-propelled barges were the main contributors to the underwater sound field at Northstar during the construction and production periods (Blackwell and Greene, 2006). Vessel sounds are a concern due to the potential disturbance to marine mammals (Richardson

et al.,

1995b). Characteristics of underwater sounds from boats and vessels have been reported extensively, including specific measurements near Northstar (Greene and Moore, 1995; Blackwell and Greene, 2006). Broadband source levels for most small ships (lengths about 180-279 ft [55-85 m]) are approximately 160-180 dB re 1 μPa. Both the crew boat and the tugs produced substantial broadband sound in the 50-2,000 Hz range, which could at least in part be accounted for by propeller cavitation (Ross, 1976). Several tones were also apparent in the vessel sounds, including one at 17.5 Hz, corresponding to the propeller blade rate of Ocean Class tugs. Two tones were identified for the crew boat: one at 52-55 Hz, which corresponds to the blade rate, and one at 22-26 Hz, which corresponds to a harmonic of the shaft rate.

The presence of boats considerably expanded the distances to which Northstar-related sound was detectable. On days with average levels of background sounds, sounds from tug boats were detectable on offshore DASAR recordings to at least 13.4 mi (21.5 km) from Northstar (Blackwell

et al.,

2009). On other occasions, vessel sounds from crew boat, tugs, and self-propelled barges were often detectable underwater as much as approximately 18.6 mi (30 km) offshore (Blackwell and Greene, 2006). BP therefore looked into options to reduce vessel use. During the summer of 2003, a small, diesel-powered hovercraft (Griffon 2000TD) was tested to transport crew and supplies between the mainland and Northstar Island. Acoustic measurements showed that the hovercraft was considerably quieter underwater than similar-sized conventional vessels (Blackwell and Greene, 2005). Received underwater broadband sound levels at 21.3 ft (6.5 m) from the hovercraft reached 133 and 131 dB re 1 μPa for hydrophone depths 3 ft and 23 ft (1 m and 7 m), respectively. In-air unweighted and A-weighted broadband (10-10,000 Hz) levels reached 104 and 97 dB re 20 μPa, respectively. Use of the hovercraft for Northstar transport resulted in a decreased number of periods of elevated vessel noise in the acoustic records of the near-island DASARs (Blackwell

et al.,

2009).

Description of Marine Mammals in the Area of the Specified Activity

The Beaufort Sea supports a diverse assemblage of marine mammals, including: Bowhead, gray, beluga, killer, minke, and humpback whales; harbor porpoises; ringed, ribbon, spotted, and bearded seals; narwhals; polar bears; and walruses. The bowhead and humpback whales and polar bear are listed as “endangered” under the Endangered Species Act (ESA) and as depleted under the MMPA. Certain stocks or populations of gray, beluga, and killer whales and spotted seals are listed as endangered or are proposed for listing under the ESA; however, none of those stocks or populations occur in the proposed activity area. On December 10, 2010, NMFS published a notice of proposed threatened status for subspecies of the ringed seal (75 FR 77476) and a notice of proposed threatened and not warranted status for subspecies and distinct population segments of the bearded seal (75 FR 77496) in the

Federal Register

. Neither of these two ice seal species is considered depleted under the MMPA. Additionally, the ribbon seal is considered a “species of concern” under the ESA. Both the walrus and the polar bear are managed by the U.S. Fish and Wildlife Service (USFWS) and are not considered further in this proposed rulemaking.

Of the species mentioned here, the ones that are most likely to occur near the Northstar facility include: bowhead, gray, and beluga whales and ringed, bearded, and spotted seals. Ringed seals are year-round residents in the Beaufort Sea and are anticipated to be the most frequently encountered species in the proposed project area. Bowhead whales are anticipated to be the most frequently encountered cetacean species in the proposed project area; however, their occurrence is not anticipated to be year-round. The most common time for bowheads to occur near Northstar is during the fall migration westward through the Beaufort Sea, which typically occurs from late August through October each year.

Other marine mammal species that have been observed in the Beaufort Sea but are uncommon or rarely identified in the project area include harbor porpoise, narwhal, killer, minke, and humpback whales, and ribbon seals. These species could occur in the project area, but each of these species is uncommon or rare in the area and relatively few encounters with these species are expected during BP's activities. The narwhal occurs in Canadian waters and occasionally in the Beaufort Sea, but it is rare there 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). Point Barrow, Alaska, is the approximate northeastern extent of the harbor porpoise's regular range (Suydam and George, 1992), though there are extralimital records east to the mouth of the Mackenzie River in the Northwest Territories, Canada, and recent sightings in the Beaufort Sea in the vicinity of Prudhoe Bay during surveys in 2007 and 2008 (Christie

et al.,

2009). Monnett and Treacy (2005) did not report any harbor porpoise sightings during aerial surveys in the Beaufort Sea from 2002 through 2004. Humpback and minke whales have recently been sighted in the Chukchi Sea but very rarely in the Beaufort Sea. Greene

et al.

(2007) reported and photographed a humpback whale cow/calf pair east of Barrow near Smith Bay in 2007, which is the first known occurrence of humpbacks in the Beaufort Sea. Savarese

et al.

(2009) reported one minke whale sighting in the Beaufort Sea in 2007 and 2008. Ribbon seals do not normally occur in the Beaufort Sea; however, two ribbon seal sightings were reported during vessel-based activities near Prudhoe Bay in 2008 (Savarese

et al.,

2009). Due to the rarity of these species in the proposed project area and the remote chance they would be affected by BP's proposed activities at Northstar, these species are not discussed further in these proposed regulations.

BP's application contains information on the status, distribution, seasonal distribution, and abundance of each of the six species under NMFS jurisdiction likely to be impacted by the proposed activities. When reviewing the application, NMFS determined that the species descriptions provided by BP 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 2010 Alaska Marine Mammal SAR is available on the Internet at:

http://www.nmfs.noaa.gov/pr/pdfs/sars/ak2010.pdf.

Brief Background on Marine Mammal Hearing

When considering the influence of various kinds of sound on the marine environment, it is necessary to understand that different kinds of marine life are sensitive to different frequencies of sound. Based on available behavioral data, audiograms have been derived using auditory evoked potentials, anatomical modeling, and other data, Southall

et al.

(2007) designate “functional hearing groups” for marine mammals and estimate the lower and upper frequencies of functional hearing of the groups. The functional groups and the associated frequencies are indicated below (though animals are less sensitive to sounds at the outer edge of their functional range and most sensitive to sounds of frequencies within a smaller range somewhere in the middle of their functional hearing range):

• Low frequency cetaceans (13 species of mysticetes): functional hearing is estimated to occur between approximately 7 Hz and 22 kHz (however, a study by Au

et al.

(2006) of humpback whale songs indicate that the range may extend to at least 24 kHz);

• Mid-frequency cetaceans (32 species of dolphins, six species of larger toothed whales, and 19 species of beaked and bottlenose whales): functional hearing is estimated to occur between approximately 150 Hz and 160 kHz;

• High frequency cetaceans (eight species of true porpoises, six species of river dolphins, Kogia, the franciscana, and four species of cephalorhynchids): functional hearing is estimated to occur between approximately 200 Hz and 180 kHz;

• 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; and

• Pinnipeds in Air: functional hearing is estimated to occur between approximately 75 Hz and 30 kHz.

As mentioned previously in this document, six marine mammal species (three cetacean and three pinniped species) are likely to occur in the Northstar facility area. Of the three cetacean species likely to occur in BP's project area, two are classified as low frequency cetaceans (

i.e.,

bowhead and gray whales) and one is classified as a mid-frequency cetacean (

i.e.,

beluga whales) (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.,

1995b; 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). In air, the upper frequency limit of phocid seals is lower (about 20 kHz).

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 three 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 production and operational 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.,

1995b; Ketten, 2000). Their optimum hearing overlaps broadly with the low frequency range where BP's production activities 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.,

1995b) 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 production 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. More information is available in BP's application (see

ADDRESSES

).

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 construction and operational activities (Richardson

et al.,

1995b). 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 planned Northstar production 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 from the planned Northstar activities. 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 planned offshore oil developments at Northstar on marine mammals involve both non-acoustic and acoustic effects. Potential non-acoustic effects could result from the physical presence of personnel, structures and equipment, construction or maintenance activities, and the occurrence of oil spills. In winter, during ice road construction, and in spring, flooding on the sea ice may displace some ringed seals along the ice road corridor. There is a small chance that a seal pup might be injured or killed by on-ice construction or transportation activities. A major oil spill is unlikely and, if it occurred, its effects are difficult to predict. Potential impacts from an oil spill are discussed in more detail later in this section.

Petroleum development and associated activities in marine waters introduce sound into the environment, produced by island construction, maintenance, and drilling, as well as vehicles operating on the ice, vessels, aircraft, generators, production machinery, gas flaring, and camp operations. The potential effects of sound from the proposed activities might include one or more of the following: masking of natural sounds; behavioral disturbance and associated habituation effects; and, at least in theory, temporary or permanent hearing impairment. 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 well being of the marine mammal; these can range from temporary alert responses to active avoidance reactions such as vacating an area at least until the noise event ceases but potentially for longer periods of time;

(4) Upon repeated exposure, a marine mammal may exhibit diminishing responsiveness (habituation), or disturbance effects may persist; the latter is most likely with sounds that are highly variable in characteristics, infrequent, and unpredictable in occurrence, and associated with situations that a marine mammal perceives as a threat;

(5) Any anthropogenic noise that is strong enough to be heard has the potential to reduce (mask) the ability of a marine mammal to hear natural sounds at similar frequencies, including calls from conspecifics, and underwater environmental sounds such as surf noise;

(6) If mammals remain in an area because it is important for feeding, breeding, or some other biologically important purpose even though there is chronic exposure to noise, it is possible that there could be noise-induced physiological stress; this might in turn have negative effects on the well-being or reproduction of the animals involved; and

(7) Very strong sounds have the potential to cause a temporary or permanent reduction in hearing sensitivity. In terrestrial mammals, and presumably marine mammals, received sound levels must far exceed the animal's hearing threshold for there to be any temporary threshold shift (TTS) in its hearing ability. For transient sounds, the sound level necessary to cause TTS is inversely related to the duration of the sound. Received sound levels must be even higher for there to be risk of permanent hearing impairment. In addition, intense acoustic or explosive events may cause trauma to tissues associated with organs vital for hearing, sound production, respiration and other functions. This trauma may include minor to severe hemorrhage.

The characteristics of the various sound sources at Northstar were summarized earlier in this document (see the “Description of the Specified Activity” section). Additionally, BP's application contains more details on the Northstar sound characteristics, underwater and in-air sound propagation in and around Northstar, and ambient noise levels in the waters near Prudhoe Bay, Alaska. Please refer to that document for more information (see

ADDRESSES

).

Potential Effects of Sound on Cetaceans

(1) 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.

There would be no masking effects on cetaceans from BP's proposed activities during the ice-covered season because cetaceans will not occur near Northstar at that time. The sounds from oil production and any drilling activities are not expected to be detectable beyond several kilometers from the source (Greene, 1983; Blackwell

et al.,

2004b; Blackwell and Greene, 2005, 2006). Sounds from vessel activity, however, were detectable to distances as far as approximately 18.6 mi (30 km) from Northstar (Blackwell and Greene, 2006). Vessels under power to maintain position can be a source of continuous noise in the marine environment (Blackwell

et al.,

2004b; Blackwell and Greene, 2006) and therefore have the potential to cause some degree of masking.

Small numbers of bowheads, belugas and (rarely) gray whales could be present near Northstar during the open-water season. 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.

Because of the relatively low effective source levels and rapid attenuation of drilling and production sounds from artificial islands in shallow water, masking effects are unlikely even for mysticetes that are within several kilometers of Northstar Island. Vessels that are docking or under power to maintain position could cause some degree of masking. However, the adaptation of some cetaceans to alter the source level or frequency of their calls, along with directional hearing, pre-adaptation to tolerate some masking by natural sounds, and the brief periods when most individual whales occur near Northstar, would all reduce the potential impacts of masking from BP's proposed activities. Therefore, impacts from masking on cetaceans are anticipated to be minor.

(2) Behavioral Disturbance

Disturbance can induce a variety of effects, such as subtle changes in behavior, more conspicuous dramatic changes in activities, and displacement. A main concern about the impacts of manmade noise on marine mammals is the potential for disturbance. Behavioral reactions of marine mammals to sound are difficult to predict because they are dependent on numerous factors, including species, state of maturity, experience, current activity, reproductive state, time of day, and weather.

When the received level of noise exceeds some behavioral reaction threshold, it is possible that some cetaceans could exhibit disturbance reactions. The levels, frequencies and types of noise that elicit a response vary among and within species, individuals, locations, and seasons. Behavioral changes may be subtle alterations in surface-respiration-dive cycles, changes in activity or aerial displays, movement away from the sound source, or complete avoidance of the area. The reaction threshold and degree of response are related to the activity of the animal at the time of the disturbance. Whales engaged in active behaviors such as feeding, socializing, or mating are less likely than resting animals to show overt behavioral reactions. However, they may do so if the received noise level is high or the source of disturbance is directly threatening.

Some researchers have noted that behavioral reactions do not occur throughout the entire zone ensonified by industrial activity. In most cases that have been studied, including work on bowhead, gray, and beluga whales, the actual radius of effect is smaller than the radius of detectability (reviewed in Richardson and Malme, 1993; Richardson

et al.,

1995b; Nowacek

et al.,

2007; Southall

et al.,

2007).

Effects of Construction, Drilling, and Production Activity

—Spring migration of bowheads and belugas through the western and central Beaufort Sea occurs from April to June. Their spring migration corridors are far north of the barrier islands and of the Northstar project area. Whales, including bowhead, beluga, and gray, will not be within the Northstar project area during winter or spring. In addition, industrial sounds from Northstar are unlikely to be detectable far enough offshore to be heard by spring-migrating whales. In rare cases where these sounds might be audible to cetaceans in spring, the received levels would be weak and unlikely to elicit behavioral reactions. Consequently, noise from construction and operational activities at Northstar during the ice-covered season would have minimal, if any, effect on whales.

During the open-water season, sound propagation from sources on the island

is reduced because of poor coupling of sound through the gravel island into the shallow waters. In the absence of boats, underwater sounds from Northstar Island during construction, drilling, and production reached background values 1.2-2.5 mi (2-4 km) away in quiet conditions (Blackwell and Greene, 2006). However, when Northstar-related vessels were present, levels were higher and faint vessel sound was often still evident 12.4-18.6 mi (20-30 km) away.

Information about the reactions of cetaceans to construction or heavy equipment activity on artificial (or natural) islands is limited (Richardson

et al.,

1995b). During the construction of artificial islands and other oil-industry facilities in the Canadian Beaufort Sea during late summers of 1980-1984, bowheads were at times observed as close as 0.5 mi (0.8 km) from the construction sites (Richardson

et al.,

1985, 1990). Richardson

et al.

(1990) showed that, at least in summer, bowheads generally tolerated playbacks of low-frequency construction and dredging noise at received broadband levels up to about 115 dB re 1 μPa. At received levels higher than about 115 dB, some avoidance reactions were observed. Bowheads apparently reacted in only a limited and localized way (if at all) to construction of Seal Island, the precursor of Northstar (Hickie and Davis, 1983).

There are no specific data on reactions of bowhead or gray whales to noise from drilling on an artificial island. However, playback studies have shown that both species begin to display overt behavioral responses to various low-frequency industrial sounds when received levels exceed 110-120 dB re 1 μPa (Malme

et al.,

1984; Richardson

et al.,

1990, 1995a, 1995b). The overall received level of drilling sound from Northstar Island generally diminished to 115 dB within 0.62 mi (1 km; Blackwell

et al.,

2004b). Therefore, any reactions by bowhead or gray whales to drilling at Northstar were expected to be highly localized, involving few whales.

Prior to construction of Northstar, it was expected (based on early data mentioned earlier) that some bowheads would avoid areas where noise levels exceeded 115 dB re 1 μPa (Richardson

et al.,

1990). On their summer range in the Beaufort Sea, bowhead whales were observed reacting to drillship noises within 2.5-5 mi (4-8 km) of the drillship at received levels 20 dB above ambient (Richardson

et al.,

1990). It was expected that, during most autumn migration seasons, few bowheads would come close enough to shore to receive sound levels that high from Northstar. Thus disturbance effects from continuous construction and operational noise were expected to be limited to the closest whales and the times with highest sound emissions.

In 2000-2004, bowhead whales were monitored acoustically to determine the number of whales that might have been exposed to Northstar-related sounds. Data from 2001-2004 were useable for this purpose. The results showed that, during late summer and early autumn of 2001, a small number of bowhead whales in the southern part of the migration corridor (closest to Northstar) were apparently affected by vessel or Northstar operations. At these times, most “Northstar sound” was from maneuvering vessels, not the island itself. The distribution of calling whales was analyzed, and the results indicated that the apparent southern (proximal) edge of the call distribution was significantly associated with the level of industrial sound output each year, with the southern edge of the call distribution varying by 0.47 mi to 1.46 mi (0.76 km to 2.35 km; depending on year) farther offshore when underwater sound levels from Northstar and associated vessels were above average (Richardson

et al.,

2008a). It is possible that the apparent deflection effect was, at least in part, attributable to a change in calling behavior rather than actual deflection. In either case, there was a change in the behavior of some bowhead whales.

Nowacek

et al.

(2004) used controlled exposures to demonstrate behavioral reactions of North Atlantic right whales (a species closely related to the bowhead whale) 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.

There are no data on the reactions of gray whales to production activities similar to those in operation at Northstar. Oil production platforms of a very different type have been in place off California for many years. Gray whales regularly migrate through that area (Brownell, 1971), but no detailed data on distances of closest approach or possible noise disturbance have been published. Oil industry personnel have reported seeing whales near platforms, and that the animals approach more closely during low-noise periods (Gales, 1982; McCarty, 1982). Playbacks of recorded production platform noise indicate that gray whales react if received levels exceed approximately 123 dB re 1 μPa—similar to the levels of drilling noise that elicit avoidance (Malme

et al.,

1984).

A typical migrating gray whale tolerates steady, low-frequency industrial sounds at received levels up to about 120 dB re 1 μPa (Malme

et al.,

1984). Gray whales may tolerate higher-level sounds if the sound source is offset to the side of the migration path (Tyack and Clark, 1998). Also, gray whales generally tolerate repeated low-frequency seismic pulses at received levels up to about 163-170 dB re 1 μPa measured on an (approximate) rms basis. Above those levels, avoidance is common. Because the reaction thresholds to both steady and pulsed sounds are slightly higher than corresponding values for bowheads, reaction distances for gray whales would be slightly less than those for bowheads.

In the Canadian Beaufort Sea, beluga whales were seen within several feet of an artificial island. During the island's construction, belugas were displaced from the immediate vicinity of the island but not from the general area (Fraker, 1977a). Belugas in the Mackenzie River estuary showed less response to a stationary dredge than to moving tug/barge traffic. They approached as close as 1,312 ft (400 m) from stationary dredges. Underwater sounds from Northstar Island are weaker than those from the dredge. In addition, belugas occur only infrequently in nearshore waters in the Prudhoe Bay region. They also have relatively poor hearing sensitivity at the low frequencies of most construction noises. Therefore, effects of construction and related sounds on belugas would be expected to be minimal.

Responses of beluga whales to drilling operations are described in Richardson

et al.

(1995a) and summarized here. In the Mackenzie Estuary during summer, belugas have been seen regularly within 328 to 492 ft (100 to 150 m) of artificial islands (Fraker 1977a,b; Fraker and Fraker, 1979). However, in the Northstar area, belugas are present only during late summer and autumn, and almost all of them are migrating through offshore

waters far seaward of Northstar. Only a very small proportion of the population enters nearshore waters. In spring, migrating belugas showed no overt reactions to recorded drilling noise (<350 Hz) until within 656 to 1,312 ft (200 to 400 m) of the source, even though the sounds were measurable up to 3.1 mi away (5 km; Richardson

et al.,

1991). During another drilling noise playback study, overt reactions by belugas within 164 to 984 ft (50 to 300 m) involved increased swimming speed or reversal of direction of travel (Stewart

et al.,

1983). The short reaction distances are probably partly a consequence of the poor hearing sensitivity of belugas at low frequencies (Richardson

et al.,

1995b). In general, very few belugas are expected to approach Northstar Island, and any such occurrences would be restricted to the late summer/autumn period.

There are no specific data on the reactions of beluga whales to production operations similar to those at Northstar. Personnel from production platforms in Cook Inlet, Alaska, report that belugas are seen within 30 ft (9 m) of some rigs, and that steady noise is non-disturbing to belugas (Gales, 1982; McCarty, 1982). Beluga whales are regularly observed near the Port of Anchorage and the extensive dredging/maintenance activities that operate there (NMFS, 2003). Pilot whales, killer whales, and unidentified dolphins were also reported near Cook Inlet platforms. In that area, flare booms might attract belugas, possibly because the flares attract salmon in that area. Attraction of belugas to prey concentrations is not likely to occur at Northstar because belugas are predominantly migrating rather than feeding when in that area and because only a very small proportion of the beluga population occurs in nearshore waters. Overall, effects of routine production activities on belugas are expected to be minimal.

Effects of Aircraft Activity

—Helicopters are the only aircraft associated with Northstar drilling and oil production operations for crew transfer and supply and support. Helicopter traffic occurs during late spring/summer and fall/early winter when travel by ice roads, hovercraft, or vessels is not possible. Twin Otters are used for routine pipeline inspections.

Potential effects to cetaceans from aircraft activity could involve both acoustic and non-acoustic effects. It is uncertain if the animals react to the sound of the aircraft or to its physical presence flying overhead. Low passes by aircraft over a cetacean, including a bowhead, gray, or beluga whale, can result in short-term responses or no discernible reaction. Responses can include sudden dives, breaching, churning the water with the flippers and/or flukes, or rapidly swimming away from the aircraft track (reviewed in Richardson

et al.,

1995b; updated review in Luksenburg and Parsons, 2009). These studies have found that various factors affect cetacean responses to aircraft noise. Some of these factors include species, behavioral state at the time of the exposure, and altitude and lateral distance of the aircraft to the animal. For example, Wursig

et al.

(1998) found that resting individuals appeared to be more sensitive to the disturbance.

Patenaude

et al.

(2002) recorded reactions of bowhead and beluga whales to a Bell 212 helicopter and Twin Otter fixed-wing aircraft during four spring seasons (1989-1991 and 1994) in the western Beaufort Sea. Responses were more common to the helicopter than to the fixed-wing aircraft. The authors noted responses by 38% of belugas (n = 40) and 14% of bowheads (n = 63) to the helicopter, whereas only 3.2% of belugas (n = 760) and 2.2% of bowheads (n = 507) reacted to the Twin Otter. Common responses to the helicopter included immediate dives, changes in heading, changes in behavioral state, and apparent displacement for belugas and abrupt dives and breaching for bowheads (Patenaude

et al.,

2002). Similar reactions were observed by the authors from the fixed-wing aircraft: Immediate dives with a tail thrash, turns or changes in heading, and twists to look upwards for belugas and unusually short surfacing for bowheads. For both species, the authors noted that responses were seen more often when the helicopter was below 492 ft (150 m) altitude and at a lateral distance of less than 820 ft (250 m) and when the Twin Otter was below 597 ft (182 m) altitude and at a lateral distance of less than 820 ft (250 m).

During their study, Patenaude

et al.

(2002) observed one bowhead whale cow-calf pair during four passes totaling 2.8 hours of the helicopter and two pairs during Twin Otter overflights. All of the helicopter passes were at altitudes of 49-98 ft (15-30 m). The mother dove both times she was at the surface, and the calf dove once out of the four times it was at the surface. For the cow-calf pair sightings during Twin Otter overflights, the authors did not note any behaviors specific to those pairs. Rather, the reactions of the cow-calf pairs were lumped with the reactions of other groups that did not consist of calves.

Richardson

et al.

(1995b) and Moore and Clarke (2002) reviewed a few studies that observed responses of gray whales to aircraft. Cow-calf pairs were quite sensitive to a turboprop survey flown at 1,000 ft (305 m) altitude on the Alaskan summering grounds. In that survey, adults were seen swimming over the calf, or the calf swam under the adult (Ljungblad

et al.,

1983, cited in Richardson

et al.,

1995b and Moore and Clarke, 2002). However, when the same aircraft circled for more than 10 minutes at 1,050 ft (320 m) altitude over a group of mating gray whales, no reactions were observed (Ljungblad

et al.,

1987, cited in Moore and Clarke, 2002). Malme

et al.

(1984, cited in Richardson

et al.,

1995b and Moore and Clarke, 2002) conducted playback experiments on migrating gray whales. They exposed the animals to underwater noise recorded from a Bell 212 helicopter (estimated altitude = 328 ft [100 m]), at an average of three simulated passes per minute. The authors observed that whales changed their swimming course and sometimes slowed down in response to the playback sound but proceeded to migrate past the transducer. Migrating gray whales did not react overtly to a Bell 212 helicopter at greater than 1,394 ft (425 m) altitude, occasionally reacted when the helicopter was at 1,000-1,198 ft (305-365 m), and usually reacted when it was below 825 ft (250 m; Southwest Research Associates, 1988, cited in Richardson

et al.,

1995b and Moore and Clarke, 2002). Reactions noted in that study included abrupt turns or dives or both. Green

et al.

(1992, cited in Richardson

et al.,

1995b) observed that migrating gray whales rarely exhibited noticeable reactions to a straight-line overflight by a Twin Otter at 197 ft (60 m) altitude.

There is little likelihood of project-related helicopter and aircraft traffic over bowheads during their westward fall migration through the Beaufort Sea. Helicopter and aircraft traffic is between the shore and Northstar Island. Most bowhead whales migrate west in waters farther north than the island. Helicopters maintain an altitude of 1,000 ft (305 m) above sea level while traveling over water to and from Northstar whenever weather conditions allow. It is unlikely that there will be any need for helicopters or aircraft to circle or hover over the open water other than when landing or taking off. Gray whales are uncommon in the area, and there is little likelihood that any will be overflown by a helicopter or aircraft. The planned flight altitude will minimize any disturbance that might occur if a gray whale is encountered. Likewise, there is little likelihood of helicopter disturbance to belugas.

Because of the predominantly offshore migration route of belugas, very few (if any) will be overflown during flights over nearshore waters. Any overflights are most likely to be at an altitude of 1,000 ft (305 m) or more, weather permitting. This is greater than the altitude at which belugas and bowheads typically react to aircraft (Patenaude

et al.,

2002). Therefore, few belugas or bowheads are expected to react to aircraft overflights near the Northstar facility. Additionally, reactions are expected to be brief.

Effects of Vessel Activity

—Reactions of cetaceans to vessels often include changes in general activity (

e.g.,

from resting or feeding to active avoidance), changes in surfacing-respiration-dive cycles, and changes in speed and direction of movement. As with aircraft, responses to vessel approaches tend to be reduced if the animals are actively involved in a specific activity such as feeding or socializing (reviewed in Richardson

et al.,

1995b). Past experiences of the animals with vessels are important in determining the degree and type of response elicited from a whale-vessel encounter.

Whales react most noticeably to erratically moving vessels with varying engine speeds and gear changes and to vessels in active pursuit. Avoidance reactions by bowheads sometimes begin as subtle alterations in whale activity, speed and heading as far as 2.5 mi (4 km) from the vessel. Consequently, the closest point of approach is farther from the vessel than if the cetacean had not altered course. Bowheads sometimes begin to swim actively away from approaching vessels when they come within 1.2-2.5 mi (2-4 km). If the vessel approaches to within several hundred meters, the response becomes more noticeable, and whales sometimes change direction to swim perpendicularly away from the vessel path (Richardson

et al.,

1985, 1995b; Richardson and Malme, 1993).

North Atlantic right whales (a species closely related to the bowhead whale) also display variable responses to boats. There may be an initial orientation away from a boat, followed by a lack of observable reaction (Atkins and Swartz, 1989). A slowly moving boat can approach a right whale, but an abrupt change in course or engine speed usually elicits a reaction (Goodyear, 1989; Mayo and Marx, 1990; Gaskin, 1991). When approached by a boat, right whale mothers will interpose themselves between the vessel and calf and will maintain a low profile (Richardson

et al.,

1995b). In a long-term study of baleen whale reactions to boats, while other baleen whale species appeared to habituate to boat presence over the 25-year period, right whales continued to show either uninterested or negative reactions to boats with no change over time (Watkins, 1986).

Beluga whales are generally quite responsive to vessels. Belugas in Lancaster Sound in the Canadian Arctic showed dramatic reactions in response to icebreaking ships, with received levels of sound ranging from 101 dB to 136 dB re 1 μPa in the 20 to 1,000-Hz band at a depth of 66 ft (20 m; Finley

et al.,

1990). Responses included emitting distinctive pulsive calls that were suggestive of excitement or alarm and rapid movement in what seemed to be a flight response. Reactions occurred out to 50 mi (80 km) from the ship. Another study found belugas use higher-frequency calls, a greater redundancy in their calls (more calls emitted in a series), and a lower calling rate in the presence of vessels (Lesage

et al.,

1999). The level of response of belugas to vessels is thought to be partly a function of habituation.

During the drilling and oil production phase of the Northstar development, most vessel traffic involves slow-moving tugs and barges and smaller faster-moving vessels providing local transport of equipment, supplies, and personnel. Much of this traffic will occur during August and early September before many whales are in the area. Some vessel traffic during the broken ice periods in the spring and fall may also occur. Alternatively, small hovercraft may be used during the spring and fall when the ice is too thin to allow safe passage by large vehicles over the ice road.

Whale reactions to slow-moving vessels are less dramatic than their reactions to faster and/or erratic vessel movements. Bowhead, gray, and beluga whales often tolerate the approach of slow-moving vessels within several hundred meters. This is especially so when the vessel is not directed toward the whale and when there are no sudden changes in direction or engine speed (Wartzok

et al.,

1989; Richardson

et al.,

1995b; Heide-Jorgensen

et al.,

2003).

Most vessel traffic associated with Northstar will be inshore of the bowhead and beluga migration corridor and/or prior to the migration season of bowhead and beluga whales. Underwater sounds from hovercraft are generally lower than for standard vessels since the sound is generated in air, rather than underwater. If vessels or hovercraft do approach whales, a small number of individuals may show short-term avoidance reactions.

The highest levels of underwater sound produced by routine Northstar operations are generally associated with Northstar-related vessel operations. These vessel operations around Northstar sometimes result in sound levels high enough that a small number of the bowheads in the southern part of the migration corridor appear to be deflected slightly offshore. To the extent that offshore deflection occurs as a result of Northstar, it is mainly attributable to Northstar-related vessel operations. As previously described, this deflection is expected to involve few whales and generally small deflections.

(3) 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 sounds, particularly at higher frequencies. There are no beaked whale species found in the proposed project area. Cetaceans are not anticipated to experience non-auditory physiological effects as a result of operation of the Northstar facility, as none of the activities associated with the facility will generate sounds loud enough to cause such effects.

Temporary Threshold Shift (TTS)

—TTS is the mildest form of hearing impairment that can occur during exposure to a strong sound (Kryter, 1985). While experiencing TTS, the hearing threshold rises, and a sound must be stronger in order to be heard. At least in terrestrial mammals, TTS can last from minutes or hours to (in cases of strong TTS) days. For sound exposures at or somewhat above the TTS threshold, hearing sensitivity in both terrestrial and marine mammals recovers rapidly after exposure to the noise ends. Few data on sound levels and durations necessary to elicit mild TTS have been obtained for marine mammals, and none of the published data concern TTS elicited by exposure to multiple pulses of sound.

Human non-impulsive noise exposure guidelines are based on exposures of equal energy (the same sound exposure

level [SEL]) producing equal amounts of hearing impairment regardless of how the sound energy is distributed in time (NIOSH, 1998). Until recently, previous marine mammal TTS studies have also generally supported this equal energy relationship (Southall

et al.,

2007). Three newer studies, two by Mooney

et al.

(2009a, b) on a single bottlenose dolphin either exposed to playbacks of U.S. Navy mid-frequency active sonar or octave-band noise (4-8 kHz) and one by Kastak

et al.

(2007) on a single California sea lion exposed to airborne octave-band noise (centered at 2.5 kHz), concluded that for all noise exposure situations, the equal energy relationship may not be the best indicator to predict TTS onset levels. Generally, with sound exposures of equal energy, those that were quieter (lower sound pressure level [SPL]) with longer duration were found to induce TTS onset more than those of louder (higher SPL) and shorter duration. Given the available data, the received level of a single seismic pulse (with no frequency weighting) might need to be approximately 186 dB re 1 μPa · 2. s (

i.e.,

186 dB SEL) in order to produce brief, mild TTS. NMFS considers TTS to be a form of Level B harassment, which temporarily causes a shift in an animal's hearing, and the animal is able to recover. Data on TTS from continuous sound (such as that produced by many of BP's Northstar activities) are limited, so available data from seismic activities are used as a proxy. Exposure to several strong seismic pulses that each have received levels near 175-180 dB SEL might result in slight TTS in a small odontocete, assuming the TTS threshold is (to a first approximation) a function of the total received pulse energy. Given that the SPL is approximately 10-15 dB higher than the SEL value for the same pulse, an odontocete would need to be exposed to a sound level of 190 dB re 1 μPa (rms) in order to incur TTS.

TTS was measured in a single, captive bottlenose dolphin after exposure to a continuous tone with maximum SPLs at frequencies ranging from 4 to 11 kHz that were gradually increased in intensity to 179 dB re 1 μPa and in duration to 55 minutes (Nachtigall

et al.,

2003). No threshold shifts were measured at SPLs of 165 or 171 dB re 1 μPa. However, at 179 dB re 1 μPa, TTSs greater than 10 dB were measured during different trials with exposures ranging from 47 to 54 minutes. Hearing sensitivity apparently recovered within 45 minutes after noise exposure.

Schlundt

et al.

(2000) measure masked TTS (

i.e.,

band-limited white noise, masking noise, was introduced into the testing environment to keep thresholds consistent despite variations in ambient noise levels) in five bottlenose dolphins and two beluga whales during eight experiments conducted over 2.3 years. The test subjects were exposed to 1-s pure tones at frequencies of 0.4, 3, 10, 20, and 75 kHz. Over the course of the eight experiments, Schlundt

et al.

(2000) conducted a total of 195 masked TTS sessions, and 11 of those sessions produced masked TTSs. The authors found that the levels needed to induce a 6 dB or larger masked TTS were generally between 192 and 201 dB re 1 μPa. No subjects exhibited shifts at levels up to 193 dB re 1 μPa for tones played at 0.4 kHz (Schlundt

et al.,

2000). The authors found that at the conclusion of each experiment, all thresholds were within 3 dB of baseline values. Additionally, they did not note any permanent shifts in hearing thresholds (Schlundt

et al.,

2000).

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 lower than those to which odontocetes are most sensitive, and natural background noise levels at those low frequencies tend to be higher. Marine mammals can hear sounds at varying frequency levels. However, sounds that are produced in the frequency range at which an animal hears the best do not need to be as loud as sounds in less functional frequencies to be detected by the animal. 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). Therefore, for a sound to be audible, 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. Based on this information, it is suspected that received levels causing TTS onset may also be higher in baleen whales. 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.

NMFS (1995, 2000) concluded that cetaceans should not be exposed to pulsed underwater noise at received levels exceeding 180 dB re 1 μPa (rms). The established 180-dB re 1 μPa (rms) criterion is not considered to be the level above which TTS might occur in cetaceans. Rather, it is the received level above which, in the view of a panel of bioacoustics specialists convened by NMFS before TTS measurements for marine mammals started to become available, one could not be certain that there would be no injurious effects, auditory or otherwise, to cetaceans. Levels of underwater sound from production and drilling activities that occur continuously over extended periods at Northstar are not very high (Blackwell and Greene, 2006). For example, received levels of prolonged drilling sounds are expected to diminish below 140 dB re 1 μPa at a distance of about 131 ft (40 m) from the center of activity. Sound levels during production activities other than drilling usually would diminish below 140 dB re 1 μPa at a closer distance. The 140 dB re 1 μPa radius for drilling noise is within the island and drilling sounds are attenuated to levels below 140 dB re 1 μPa in the water near Northstar. Additionally, cetaceans are not commonly found in the area during the ice-covered season. Based on this information and the available data, TTS of cetaceans is not expected from the operations at Northstar.

Permanent Threshold Shift (PTS)

—When PTS occurs, there is physical damage to the sound receptors in the ear. In some cases, there can be total or partial deafness, whereas in other cases, the animal has an impaired ability to hear sounds in specific frequency ranges.

There is no specific evidence that exposure to underwater industrial sounds can cause PTS in any marine mammal (see Southall

et al.,

2007). However, given the possibility that marine mammals might incur TTS, there has been further speculation about the possibility that some individuals occurring very close to industrial activities might incur PTS. Richardson

et al.

(1995b) hypothesized that PTS caused by prolonged exposure to continuous anthropogenic sound is unlikely to occur in marine mammals, at least for sounds with source levels up to approximately 200 dB re 1 μPa at 1 m (rms). Single or occasional occurrences of mild TTS are not indicative of permanent auditory damage in terrestrial mammals. Relationships between TTS and PTS thresholds have not been studied in marine mammals but are assumed to be similar to those in humans and other terrestrial mammals. PTS might occur at a received sound level at least several decibels above that inducing mild TTS.

It is highly unlikely that cetaceans could receive sounds strong enough (and over a sufficient duration) to cause PTS (or even TTS) during the proposed operation of the Northstar facility. Source levels for much of the equipment

used at Northstar do not reach the threshold of 180 dB (rms) currently used for cetaceans. Based on this conclusion, it is highly unlikely that any type of hearing impairment, temporary or permanent, would occur as a result of BP's proposed 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-dB re 1 μPa (rms) in-water threshold currently used by NMFS. Table 1 in this document summarizes the SPL and SEL levels thought to cause auditory injury to cetaceans. For more information, please refer to Southall

et al.

(2007).

Table 1—Proposed Injury Criteria for Low- and Mid-Frequency Cetaceans Exposed to “Discrete” Noise Events (Either Single Pulses, Multiple Pulses, or Non-Pulses Within a 24-Hr Period; Southall et al., 2007)

Single pulses

Multiple pulses

Non pulses

Low-frequency cetaceans

Sound pressure level

230 dB re 1 μPa (peak) (flat)

230 dB re 1 μPa (peak) (flat)

230 dB re 1 μPa (peak) (flat)

Sound exposure level

198 dB re 1 μPa

2

-s (M

lf

)

198 dB re 1 μPa

2

-s (M

lf

)

215 dB re 1 μPa

2

-s (M

lf

)

Mid-frequency cetaceans

Sound pressure level

230 dB re 1 μPa (peak) (flat)

230 dB re 1 μPa (peak) (flat)

230 dB re 1 μPa (peak) (flat)

Sound exposure level

198 dB re 1 μPa

2

-s (M

lf

)

198 dB re 1 μPa

2

-s (M

lf

)

215 dB re 1 μPa

2

-s (M

lf

)

Potential Effects of Sound on Pinnipeds

(1) Masking

As stated previously in this document, masking is the obscuring of sounds of interest by other sounds, often at similar frequencies. There are fewer data available regarding the potential impacts of masking on pinnipeds than on cetaceans. Cummings

et al.

(1984) subjected breeding ringed seals to recordings of industrial sounds. The authors did not document any impacts to ringed seal vocalizations as a result of exposure to the recordings.

During the ice-covered season, only ringed seals and small numbers of bearded seals are found near Northstar. Therefore, there would be no masking effects on spotted seals, as they do not occur in the area during that time. All three pinniped species can be found in and around Northstar during the summer open-water season. As stated previously in this document, sounds from oil production and any drilling activities are not expected to be detectable beyond several kilometers from the source; however, sounds from vessels were detectable to distances as far as approximately 18.6 mi (30 km) from Northstar. There is the potential for vessels to cause some degree of masking.

It is expected that masking of calls or other natural sounds would not extend beyond the maximum distance where the construction or operational sounds are detectable, and, at that distance, only the weakest sounds would be masked. The maximum distances for masking will vary greatly depending on ambient noise and sound propagation conditions but will typically be about 1.2-3.1 mi (2-5 km) in air and 1.9-6.2 mi (3-10 km) underwater. Also, some types of Northstar sounds (especially the stronger ones) vary over time, and, at quieter times, masking would be absent or limited to closer distances. While some masking is possible, it is usually more prominent for lower frequencies. Although the functional hearing range for pinnipeds is estimated to occur between approximately 75 Hz and 75 kHz, the range with the greatest sensitivity is estimated to occur between approximately 700 Hz and 20 kHz. Therefore, BP's proposed activities are expected to have minor masking effects on pinnipeds.

(2) Behavioral Disturbance

As stated earlier in this document, disturbance can induce a variety of effects, such as subtle changes in behavior, more conspicuous dramatic changes in activities, and displacement. When the received level of noise exceeds some behavioral reaction threshold, it is possible that some pinnipeds could exhibit disturbance reactions. The levels, frequencies and types of noise that elicit a response vary among and within species, individuals, locations, and seasons. Behavioral changes may be an upright posture for hauled out seals, movement away from the sound source, or complete avoidance of the area. The reaction threshold and degree of response are related to the activity of the animal at the time of the disturbance. Some researchers have noted that behavioral reactions do not occur throughout the entire zone ensonified by industrial activity. In most cases that have been studied, including recent work on ringed seals, the actual radius of effect is smaller than the radius of detectability (reviewed in Richardson

et al.,

1995b; Moulton

et al.,

2003a, 2005; Blackwell

et al.,

2004a).

Effects of Construction, Drilling, and Production Activity

—Systematic aerial surveys to assess ringed seal responses to the construction of Seal Island were done both for Shell Oil (Green and Johnson, 1983) and for the Minerals Management Service, now the Bureau of Ocean Energy Management, Regulation and Enforcement (Frost and Burns, 1989; Kelly

et al.,

1988). Green and Johnson (1983) found that some seals within several kilometers of Seal Island were apparently displaced by construction of the island during the winter of 1981-82. Similarly, Frost and Lowry (1988) found lower densities of seals within 2.3 mi (3.7 km) of artificial islands than in a zone 2.3-4.6 mi (3.7-7.4 km) away when exploration activity was high. During years with construction or drilling activities, there was a 38-40% reduction in seal densities near the islands (Frost and Lowry, 1988). However, these early analyses did not account for non-industrial factors known to influence basking activity of seals (Moulton

et al.,

2002, 2005). Also, the numbers of sightings were small relative to the variation in the data.

Kelly

et al.

(1988) used trained dogs to study the use by seals of breathing holes and lairs in relation to exposure to industrial activities. They reported that the proportion of structures abandoned within 5 mi (8 km) of Seal Island was similar to that within 492 ft (150 m) of on-ice seismic lines. There were no differences in abandonment rate within or beyond 492 ft (150 m) from Seal Island. Kelly

et al.

(1988) indicated that the data were not adequate to evaluate at what distances

from the island abandonment of structures began to decrease. In a final analysis of those data, Frost and Burns (1989) reported that the proportion of abandoned structures was significantly higher within 1.2 mi (2 km) of Seal Island than 1.2-6.2 mi (2-10 km) away. Complicating the interpretation is that dog-based searches were conducted where structures were expected to be found, rather than over the entire study area, and multiple searches over a given area were not conducted. Hammill and Smith (1990) found that dogs missed as many as 73% of the structures during the first search of an area. Frost and Burns (1989) also noted that the analyses of disturbance and abandonment as a result of Seal Island construction were complicated by other noise sources that were active at the same time. These included on-ice seismic exploration, excavation of structures by their investigations, and snow machine traffic. Frost and Burns (1989) suspected that, overall, there was no area-wide increase in abandonment of structures. Finally, it is unknown whether there are differences in detection rates by dogs for open versus abandoned structures or for areas of different structure density. This detection bias potentially confounds interpretation of the data.

Utilizing radio telemetry to examine the short-term behavioral responses of ringed seals to human activities, Kelly

et al.

(1988) found that some ringed seals temporarily departed from lairs when various sources of noise were within 97-3,000 m (0.06-1.9 mi) of an occupied structure. Radio-tagged ringed seals did return to re-occupy those lairs. However, the authors did not note the amount of time it took the ringed seals to re-occupy the lairs. The durations of haul-out bouts during periods with and without disturbance were not significantly different. Also, the time ringed seals spent in the water after disturbance did not differ significantly from that during periods of no disturbance (Kelly

et al.,

1988). Kelly

et al.

(1988) observed that rates of ringed seal abandonment of lairs were three times higher in areas with noise disturbance than in areas without noise disturbance. However, the abandonment rates in areas with noise disturbance were similar to rates of disturbance in areas of frequent predator activity (

e.g.,

polar bears trying to break into lairs).

Moulton

et al.

(2003a, 2005) conducted intensive and replicated aerial surveys during the springs of 1997-1999 (prior to the construction of Northstar) and 2000-2002 (with Northstar activities) to study the distribution and abundance of ringed seals within an approximately 1,598 mi

2

(4,140 km

2

) area around the Northstar Development. The main objective was to determine whether, and to what extent, oil development affected the local distribution and abundance of ringed seals. The 1997-1999 surveys were conducted coincidentally with aerial surveys over a larger area of the central Beaufort Sea (Frost

et al.,

2004). Moulton

et al.

(2003a, 2005) determined that the raw density of ringed seals over their study area ranged from 0.39 to 0.83 seals/km

2

, while Frost

et al.

(2004) obtained raw densities of 0.64 to 0.87 seals/km

2

in a similar area at about the same times. There was no evidence that construction, drilling, and production activities at Northstar in 2000-2002 significantly affected local ringed seal distribution and abundance relative to the baseline years (1997-1999). Additionally, after natural variables that affect haul-out behavior were considered (Moulton

et al.,

2003a, 2005), there was no significant evidence of reduced seal densities close to Northstar as compared with farther away during the springs of 2000, 2001, and 2002. The survey methods and associated analyses were shown to have high statistical power to detect such changes if they occurred. Environmental factors such as date, water depth, degree of ice deformation, presence of meltwater, and percent cloud cover had more conspicuous and statistically-significant effects on seal sighting rates than did any human-related factors (Moulton

et al.,

2003a, 2005).

To complement the aerial survey program on a finer scale, specially-trained dogs were used to find seal structures and to monitor the fate of structures in relation to distance from industrial activities (Williams

et al.,

2006c). In late 2000, surveys began before construction of ice roads but concurrent with drilling and other island activities. In the winter of 2000-2001, a total of 181 structures were located, of which 118 (65%) were actively used by late May 2001. However, there was no relationship between structure survival or the proportion of structures abandoned and distance to Northstar-related activities. The most important factors predicting structure survival were time of year when found and ice deformation. The covariate distance to the ice road improved the fit of the model, but the relationship indicated that structure survival was lower farther away from the ice road, contrary to expectation. However, new structures found after the ice road was constructed were, on average, farther from the ice road than were structures found before construction (though this was marginally statistically significant). This may have been related to the active flooding of the ice road, which effectively removed some of the ice as potential ringed seal habitat.

Blackwell

et al.

(2004a) investigated the effects of noise from pipe-driving and other construction activities on Northstar to ringed seals in June and July 2000, during and just after break-up of the landfast ice. None of the ringed seals seen during monitoring showed any strong reactions to the pipe-driving or other construction activities on Northstar. Eleven of the seals (48%) appeared either indifferent or curious when exposed to construction or pipe-driving sounds. One seal approached within 9.8 ft (3 m) of the island's edge during pipe-driving and others swam in the 9.8-49.2 ft (3-15 m) moat around the island. Seals in the moat may have been exposed to sound levels up to 153-160 dB re 1 µPa (rms) when they dove close to the bottom.

Consistent with Blackwell

et al.

(2004a), seals are often very tolerant of exposure to other types of pulsed sounds. For example, seals tolerate high received levels of sounds from airgun arrays (Arnold, 1996; Harris

et al.,

2001; Moulton and Lawson, 2002). 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

(0.01 to 0.03 m

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.,

1995b). Therefore, the short distance for avoidance reactions to impulsive pile driving sounds from the pile driving operations on Northstar is consistent with these other data.

Effects of Aircraft Activity

—Helicopters are the only aircraft associated with Northstar oil production activities. Helicopter traffic occurs primarily during late spring and autumn when travel by ice road, hovercraft, or vessel is not possible.

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.,

1995b; Burns and Frost, 1979, cited in Richardson

et al.,

1995b). Richardson

et al.

(1995b) 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.,

1995b; Born

et al.,

1999).

Born

et al.

(1999) determined that 49% 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). However, no spotted seal haul-outs are located near Northstar.

Effects of Vessel Activity

—Few authors have specifically described the responses of pinnipeds to boats, and most of the available information on reactions to boats concerns pinnipeds hauled out on land or ice. Ringed seals hauled out on ice pans often showed short-term escape reactions when a ship approached the animal within 0.16 to 0.31 mi (0.25 to 0.5 km; Brueggeman

et al.,

1992). Jansen

et al.

(2006) reported that harbor seals approached by vessels within 328 ft (100 m) were 25 times more likely to enter the water than were seals approached at 1,640 ft (500 m). However, during the open water season in the Beaufort Sea, ringed and bearded seals are commonly observed close to vessels (Harris

et al.,

2001; Moulton and Lawson, 2002).

In places where boat traffic is heavy, there have been cases where seals have habituated to vessel disturbance. In England, harbor and gray seals at specific haul-outs appear to have habituated to close approaches by tour boats (Bonner, 1982). Jansen

et al.

(2006) found that harbor seals in Disenchantment Bay, Alaska, increased in abundance during the summer as ship traffic also increased. In Maine, Lelli and Harris (2001) found that boat traffic was the best predictor of variability in harbor seal haulout behavior, followed by wave height and percent sunshine, utilizing multiple regressions. Lelli and Harris (2001) reported that increasing boat traffic reduced the number of seals counted on the haul-out. Suryan and Harvey (1999) reported that Pacific harbor seals commonly left the shore when powerboat operators approached to observe the seals. Those seals detected a powerboat at a mean distance of 866 ft (264 m), and seals left the haul-out site when boats approached to within 472 ft (144 m). Southall

et al.

(2007) report that pinnipeds exposed to sounds at approximately 110 to 120 dB re 20 μPa in-air tended to respond by leaving their haul-outs and seeking refuge in the water, while animals exposed to in-air sounds of approximately 60 to 70 dB re 20 μPa often did not respond at all.

(3) Hearing Impairment and Other Physiological Effects

Pinnipeds are able to hear both in-water and in-air sounds. However, they have significantly different hearing capabilities in the two media. 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. Pinnipeds are not anticipated to experience non-auditory physiological effects as a result of operation of the Northstar facility, as none of the activities associated with the facility will generate sounds loud enough to cause such effects.

TTS

—As stated earlier in this document, TTS is the mildest form of hearing impairment that can occur during exposure to a strong sound (Kryter, 1985). For additional background about TTS, please refer to the discussion on impacts to cetaceans from sound found earlier in this section of the document.

As stated earlier in this document, the functional hearing range for pinnipeds in-air is 75 Hz to 30 kHz (Southall

et al.,

2007). Richardson

et al.

(1995b) note that dominant tones in noise spectra from both helicopters and fixed-wing aircraft are generally below 500 Hz. Kastak and Schustermann (1995) state that the in-air hearing sensitivity is less than the in-water hearing sensitivity for pinnipeds. In-air hearing sensitivity deteriorates as frequency decreases below 2 kHz, and generally pinnipeds appear to be considerably less sensitive to airborne sounds below 10 kHz than humans. There is a dearth of information on the acoustic effects of helicopter overflights on pinniped hearing and communication (Richardson

et al.,

1995b), and, to NMFS' knowledge, there has been no specific documentation of TTS in free-ranging pinnipeds exposed to helicopter operations during realistic field conditions.

In free-ranging 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). Kastak

et al.

(1999) reported TTS of approximately 4-5 dB in three species of pinnipeds (harbor seal, California sea lion, and northern elephant seal) after underwater exposure for approximately 20 minutes to noise with frequencies ranging from 100-2,000 Hz at received levels 60-75 dB above hearing threshold. This approach allowed similar effective exposure conditions to each of the subjects, but resulted in variable absolute exposure values depending on subject and test frequency. Recovery to near baseline levels was reported within 24 hours of noise exposure (Kastak

et al.,

1999). Kastak

et al.

(2005) followed up on their previous work using higher sensitivity levels and longer exposure times (up to 50 min) and corroborated their previous findings. The sound exposures necessary to cause slight threshold shifts were also determined for two California sea lions and a juvenile elephant seal exposed to underwater sound for a similar duration. 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 (1995, 2000) concluded that pinnipeds should not be exposed to pulsed underwater noise at received levels exceeding 190 dB re 1 μPa (rms). The established 190-dB re 1 μPa (rms) criterion is not considered to be the level above which TTS might occur in pinnipeds. Rather, it is the received level above which, in the view of a panel of bioacoustics specialists convened by NMFS before TTS measurements for marine mammals started to become available, one could not be certain that there would be no injurious effects, auditory or otherwise, to pinnipeds. Levels of underwater sound from production and drilling activities that occur continuously over extended periods at Northstar are not very high (Blackwell and Greene, 2006). For example, received levels of prolonged drilling sounds are expected to diminish below 140 dB re 1 μPa at a distance of about 131 ft (40 m) from the center of activity. Sound levels during other production activities aside from drilling usually would diminish below 140 dB re 1 μPa at a closer distance. The 140 dB re 1 μPa radius for drilling noise is within the island and drilling sounds are attenuated to levels below 140 dB re 1 μPa in the water near Northstar. Therefore, TTS is not expected from the operations at Northstar.

PTS

—As stated earlier in this document, when PTS occurs, there is physical damage to the sound receptors in the ear. For additional background about PTS, please refer to the discussion with respect to impacts from sound on cetaceans found earlier in this section of the document.

It is highly unlikely that pinnipeds could receive sounds strong enough (and over a sufficient duration) to cause PTS (or even TTS) during the proposed operation of the Northstar facility. Source levels for much of the equipment used at Northstar do not reach the threshold of 190 dB currently used for pinnipeds. Based on this conclusion, it is highly unlikely that any type of hearing impairment, temporary or permanent, would occur as a result of BP's proposed 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 190-dB re 1 μPa (rms) in-water threshold currently used by NMFS. Table 2 in this document summarizes the SPL and SEL levels thought to cause auditory injury to pinnipeds both in-water and in-air. For more information, please refer to Southall

et al.

(2007).

Table 2—Proposed Injury Criteria for Pinnipeds Exposed to “Discrete” Noise Events (Either Single Pulses, Multiple Pulses, or Non-Pulses Within a 24-Hr Period; Southall et al., 2007)

Single pulses

Multiple pulses

Non pulses

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

)

Pinnipeds (in air)

Sound pressure level

149 dB re 20 µPa (peak) (flat)

149 dB re 20 µPa (peak) (flat)

149 dB re 20 µPa (peak) (flat)

Sound exposure level

144 dB re (20 µPa)

2

-s (M

pa

)

144 dB re (20 µPa)

2

-s (M

pa

)

144.5 dB re (20 µPa)

2

-s (M

pa

)

Potential Effects of Oil on Cetaceans

The specific effects an oil spill would have on bowhead, gray, or beluga whales are not well known. While direct 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 whales that might be contacted by a spill would depend on the size, timing, and duration of the spill. 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 concrete 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 Exxon Valdez spill (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 h (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 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 whales in open water are likely to be minimal, but there could be effects on whales 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. However, given the probable alongshore trajectory of oil spilled from Northstar in relation to the whale migration route through offshore waters, interactions between oil slicks and whales are unlikely in spring, as any spilled oil would likely remain closer to shore.

In fall, the migration route of bowheads can be close to shore (Blackwell

et al.,

2009). 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 past the Northstar area extends over several weeks, and many of the whales travel along routes well north of Northstar. Thus, only a small portion of the whales are likely to approach patches of spilled oil. Additionally, vessel activity associated with spill cleanup efforts may deflect the small number of whales traveling nearshore farther offshore, thereby reducing the likelihood of contact with spilled oil. Also, during years when movements of oil and whales might be partially confined by ice, the bowhead migration corridor tends to be farther offshore (Treacy, 1997; LGL and Greeneridge, 1996a; Moore, 2000).

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.,

1995b). Therefore, a spill in winter or summer would not be expected to have major impacts on these species. Additionally, while gray whales have commonly been sighted near Point Barrow, they are much less frequently found in the Prudhoe Bay area. Therefore, an oil spill is not expected to have major impacts to gray whales.

(6) Effects of Oil-Spill Cleanup Activities

Oil spill cleanup activities could increase disturbance effects on either whales or seals, causing temporary disruption and possible displacement (MMS, 1996). The Northstar Oil Discharge Prevention and Contingency Plan (ODPCP; BPXA, 1998a, b) includes a scenario of a production well blowout to the open-water in August. In this scenario, approximately 177,900 barrels of North Slope crude oil will reach the open-water. It is estimated that response activities would require 186 staff (93 per shift) using 33 vessels (see Table 1.6.1-3 in BPXA, 1998b) for about 15 days to recover oil in open-water. Shoreline cleanup would occur for approximately 45 days employing low pressure, cold water deluge on the soiled shorelines. In a similar scenario during solid ice conditions, it is estimated that 97 pieces of equipment along with 246 staff (123 per shift) would be required for response activities (BPXA, 1998a).

The potential effects on cetaceans are expected to be less than those on seals (described later in this section of the document). Cetaceans tend to occur well offshore where cleanup activities (in the open-water season) are unlikely to be as concentrated. Also, cetaceans are transient and, during the majority of the year, absent from the area. However, if intensive cleanup activities were necessary during the autumn whale hunt, this could affect subsistence hunting. Impacts to subsistence uses of marine mammals are discussed later in this document (see the “Impact on Availability of Affected Species or Stock for Taking for Subsistence Uses” section).

Potential Effects of Oil on Pinnipeds

Ringed, bearded, and spotted seals are present in open-water areas during summer and early autumn, and ringed seals remain in the area through the ice-covered season. During the spring periods in 1997-2002, the observed densities of ringed seals on the fast-ice in areas greater than 9.8 ft (3 m) deep ranged from 0.35 to 0.72 seals/km

2

. After allowance for seals not seen by aerial surveyors, actual densities may have been about 2.84 times higher (Moulton

et al.,

2003a). Therefore, an oil spill from the Northstar development or its pipeline could affect seals. Any oil spilled under the ice also has the potential to directly contact seals.

Externally oiled phocid seals often survive and become clean, but heavily oiled seal pups and adults may die, depending on the extent of oiling and characteristics of the oil. Prolonged exposure could occur if fuel or crude oil was spilled in or reached nearshore waters, was spilled in a lead used by seals, or was spilled under the ice when seals have limited mobility (NMFS, 2000). Adult seals may suffer some temporary adverse effects, such as eye and skin irritation, with possible infection (MMS, 1996). Such effects may increase stress, which could contribute to the death of some individuals. Ringed seals may ingest oil-contaminated foods, but there is little evidence that oiled seals will ingest enough oil to cause lethal internal effects. There is a likelihood that newborn seal pups, if contacted by oil, would die from oiling through loss of insulation and resulting hypothermia. These potential effects are addressed in more detail in subsequent paragraphs.

Reports of the effects of oil spills have shown that some mortality of seals may have occurred as a result of oil fouling; however, large scale mortality had not been observed prior to the EVOS (St. Aubin, 1990). Effects of oil on marine mammals were not well studied at most spills because of lack of baseline data and/or the brevity of the post-spill surveys. The largest documented impact of a spill, prior to EVOS, was on young seals in January in the Gulf of St. Lawrence (St. Aubin, 1990). Brownell and Le Boeuf (1971) found no marked effects of oil from the Santa Barbara oil spill on California sea lions or on the mortality rates of newborn pups.

Intensive and long-term studies were conducted after the EVOS in Alaska. There may have been a long-term decline of 36% in numbers of molting harbor seals at oiled haul-out sites in Prince William Sound following EVOS (Frost

et al.,

1994a). However, in a reanalysis of those data and additional years of surveys, along with an examination of assumptions and biases associated with the original data, Hoover-Miller

et al.

(2001) concluded that the EVOS effect had been overestimated. The decline in attendance at some oiled sites was more likely a continuation of the general decline in harbor seal abundance in Prince William Sound documented since 1984 (Frost

et al.,

1999) than a

result of EVOS. The results from Hoover-Miller

et al.

(2001) indicate that the effects of EVOS were largely indistinguishable from natural decline by 1992. However, while Frost

et al.

(2004) concluded that there was no evidence that seals were displaced from oiled sites, they did find that aerial counts indicated 26% less pups were produced at oiled locations in 1989 than would have been expected without the oil spill. Harbor seal pup mortality at oiled beaches was 23% to 26%, which may have been higher than natural mortality, although no baseline data for pup mortality existed prior to EVOS (Frost

et al.,

1994a). There was no conclusive evidence of spill effects on Steller sea lions (Calkins

et al.,

1994). Oil did not persist on sea lions themselves (as it did on harbor seals), nor did it persist on sea lion haul-out sites and rookeries (Calkins

et al.,

1994). Sea lion rookeries and haul out sites, unlike those used by harbor seals, have steep sides and are subject to high wave energy (Calkins

et al.,

1994).

(1) Oiling of External Surfaces

Adult seals rely on a layer of blubber for insulation, and oiling of the external surface does not appear to have adverse thermoregulatory effects (Kooyman

et al.,

1976, 1977; St. Aubin, 1990). Contact with oil on the external surfaces can potentially cause increased stress and irritation of the eyes of ringed seals (Geraci and Smith, 1976; St. Aubin, 1990). These effects seemed to be temporary and reversible, but continued exposure of eyes to oil could cause permanent damage (St. Aubin, 1990). Corneal ulcers and abrasions, conjunctivitis, and swollen nictitating membranes were observed in captive ringed seals placed in crude oil-covered water (Geraci and Smith, 1976), and in seals in the Antarctic after an oil spill (Lillie, 1954).

Newborn seal pups rely on their fur for insulation. Newborn ringed seal pups in lairs on the ice could be contaminated through contact with oiled mothers. There is the potential that newborn ringed seal pups that were contaminated with oil could die from hypothermia.

(2) Ingestion

Marine mammals can ingest oil if their food is contaminated. Oil can also be absorbed through the respiratory tract (Geraci and Smith, 1976; Engelhardt

et al.,

1977). Some of the ingested oil is voided in vomit or feces but some is absorbed and could cause toxic effects (Engelhardt, 1981). When returned to clean water, contaminated animals can depurate this internal oil (Engelhardt, 1978, 1982, 1985). In addition, seals exposed to an oil spill are unlikely to ingest enough oil to cause serious internal damage (Geraci and St. Aubin, 1980, 1982).

(3) Avoidance and Behavioral Effects

Although seals may have the capability to detect and avoid oil, they apparently do so only to a limited extent (St. Aubin, 1990). Seals may abandon the area of an oil spill because of human disturbance associated with cleanup efforts, but they are most likely to remain in the area of the spill. One notable behavioral reaction to oiling is that oiled seals are reluctant to enter the water, even when intense cleanup activities are conducted nearby (St. Aubin, 1990; Frost

et al.,

1994b, 2004).

(4) Factors Affecting the Severity of Effects

Seals that are under natural stress, such as lack of food or a heavy infestation by parasites, could potentially die because of the additional stress of oiling (Geraci and Smith, 1976; St. Aubin, 1990; Spraker

et al.,

1994). Female seals that are nursing young would be under natural stress, as would molting seals. In both cases, the seals would have reduced food stores and may be less resistant to effects of oil than seals that are not under some type of natural stress. Seals that are not under natural stress (

e.g.,

fasting, molting) would be more likely to survive oiling. In general, seals do not exhibit large behavioral or physiological reactions to limited surface oiling or incidental exposure to contaminated food or vapors (St. Aubin, 1990; Williams

et al.,

1994). Effects could be severe if seals surface in heavy oil slicks in leads or if oil accumulates near haul-out sites (St. Aubin, 1990). An oil spill in open-water is less likely to impact seals.

Seals exposed to heavy doses of oil for prolonged periods could die. This type of 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 in winter when seals have limited mobility. Seals residing in these habitats may not be able to avoid prolonged contamination and some could die. Impacts on regional populations of seals would be expected to be minor.

Since ringed seals are found year-round in the U.S. Beaufort Sea and more specifically in the project area, an oil spill at any time of year could potentially have effects on ringed seals. However, they are more widely dispersed during the open-water season. Spotted seals are unlikely to be found in the project area during late winter and spring. Therefore, they are more likely to be affected by a spill in the summer or fall seasons. Bearded seals typically overwinter south of the Beaufort Sea. However, some have been reported around Northstar during early spring (Moulton

et al.,

2003b). Oil spills during the open-water period and fall are the most likely to impact bearded seals.

(5) Effects of Oil-Spill Cleanup Activities

Oil spill cleanup activities could increase disturbance effects on either whales or seals, causing temporary disruption and possible displacement (MMS, 1996). General issues related to oil spill cleanup activities are discussed earlier in this section for cetaceans. In the event of a large spill contacting and extensively oiling coastal habitats, the presence of response staff, equipment, and the many aircraft involved in the cleanup could (depending on the time of the spill and the cleanup) potentially displace seals. If extensive cleanup operations occur in the spring, they could cause increased stress and reduced pup survival of ringed seals. Oil spill cleanup activity could exacerbate and increase disturbance effects on subsistence species, cause localized displacement of subsistence species, and alter or reduce access to those species by hunters. On the other hand, the displacement of marine mammals away from oil-contaminated areas by cleanup activities would reduce the likelihood of direct contact with oil. Impacts to subsistence uses of marine mammals are discussed later in this document (see the “Impact on Availability of Affected Species or Stock for Taking for Subsistence Uses” section).

Summary of Potential Effects on Marine Mammals

The likely or possible impacts of the planned offshore oil developments at Northstar on marine mammals involve both non-acoustic and acoustic effects. Potential non-acoustic effects are most likely to impact pinnipeds in the area through temporary displacement from haul-out areas near the Northstar facility. There is a small chance that a seal pup might be injured or killed by on-ice construction or transportation activities. A major oil spill is unlikely and, if it occurred, its effects are difficult to predict. A major oil spill might cause serious injury or mortality to small numbers of marine mammals by impacting the animals' ability to eat or find uncontaminated prey or by causing respiratory distress from

inhalation of hydrocarbon vapors. Oiled newborn seal pups could also die from hypothermia. However, BP has an oil spill contingency and prevention plan (discussed later in this document) in place that will help avoid the occurrence of a spill and the impacts to the environment (including marine mammals) should one occur.

BP's activities at Northstar will also introduce sound into the environment. The potential effects of sound from the proposed activities might include one or more of the following: Masking of natural sounds; behavioral disturbance and associated habituation effects; and, at least in theory, temporary or permanent hearing impairment. Because of the low source levels for the majority of equipment used at Northstar, no hearing impairment is expected in any pinnipeds or cetaceans. Other types of effects are expected to be less for cetaceans, as the higher sound levels are found close to shore, usually further inshore than the migration paths of cetaceans. Additionally, cetaceans are not found in the Northstar area during the ice-covered season; therefore, they would only be potentially impacted during certain times of the year. As discussed earlier in the document, cetaceans often avoid sound sources, which would further reduce impacts from sound. Pinnipeds may exhibit some behavioral disturbance reactions, but they are anticipated to be minor. In summary, impacts to marine mammals that may occur in the Northstar area are expected to be minor, as source levels are low and many of the species are found farther out to sea.

Moreover, the potential effects to marine mammals described in this section of the document do not take into consideration the proposed monitoring and mitigation measures described later in this document (see the “Proposed Mitigation” and “Proposed Monitoring and Reporting” sections).

Anticipated Effects on Habitat

Potential impacts to marine mammals and their habitat as a result of operation of the Northstar facility are mainly associated with elevated sound levels. However, potential impacts are also possible from ice road construction and an oil spill (should one occur).

Common Marine Mammal Prey in the Project Area

All six of the marine mammal species that may occur in the proposed project area prey on either marine fish or invertebrates. The ringed seal feeds on fish and a variety of benthic species, including crabs and shrimp. Bearded seals feed mainly on benthic organisms, primarily crabs, shrimp, and clams. Spotted seals feed on pelagic and demersal fish, as well as shrimp and cephalopods. They are known to feed on a variety of fish including herring, capelin, sand lance, Arctic cod, saffron cod, and sculpins.

Bowhead whales feed in the eastern Beaufort Sea during summer and early autumn, but continue feeding to varying degrees while on their migration through the central and western Beaufort Sea in the late summer and fall (Richardson and Thomson [eds.], 2002). Aerial surveys in recent years have sighted bowhead whales feeding in Camden Bay on their westward migration through the Beaufort Sea. [Camden Bay is more than 62 mi (100 km) east of Northstar.] When feeding in relatively shallow areas, bowheads feed throughout the water column. However, feeding is concentrated at depths where zooplankton is concentrated (Wursig

et al.,

1984, 1989; Richardson [ed.], 1987; Griffiths

et al.,

2002). Lowry and Sheffield (2002) found that copepods and euphausiids were the most common prey found in stomach samples from bowhead whales harvested in the Kaktovik area from 1979 to 2000. Areas to the east of Barter Island (which is approximately 110 mi [177 km] east of Northstar) appear to be used regularly for feeding as bowhead whales migrate slowly westward across the Beaufort Sea (Thomson and Richardson, 1987; Richardson and Thomson [eds.], 2002). However, in some years, sizable groups of bowhead whales have been seen feeding as far west as the waters just east of Point Barrow (which is more than 155 mi [250 km] west of Northstar) near the Plover Islands (Braham

et al.,

1984; Ljungblad

et al.,

1985; Landino

et al.,

1994). The situation in September-October 1997 was unusual in that bowheads fed widely across the Alaskan Beaufort Sea, including higher numbers in the area east of Barrow than reported in any previous year (S. Treacy and D. Hansen, MMS, pers. comm.).

Beluga whales feed on a variety of fish, shrimp, squid and octopus (Burns and Seaman, 1985). Very few beluga whales occur near Northstar; their main migration route is much further offshore.

Gray whales are primarily bottom feeders, and benthic amphipods and isopods form the majority of their summer diet, at least in the main summering areas west of Alaska (Oliver

et al.,

1983; Oliver and Slattery, 1985). Farther south, gray whales have also been observed feeding around kelp beds, presumably on mysid crustaceans, and on pelagic prey such as small schooling fish and crab larvae (Hatler and Darling, 1974).

Two kinds of fish inhabit marine waters in the study area: (1) True marine fish that spend all of their lives in salt water, and (2) anadromous species that reproduce in fresh water and spend parts of their life cycles in salt water.

Most arctic marine fish species are small, benthic forms that do not feed high in the water column. The majority of these species are circumpolar and are found in habitats ranging from deep offshore water to water as shallow as 16.4-33 ft (5-10 m; Fechhelm

et al.,

1995). The most important pelagic species, and the only abundant pelagic species, is the Arctic cod. The Arctic cod is a major vector for the transfer of energy from lower to higher trophic levels (Bradstreet

et al.,

1986). In summer, Arctic cod can form very large schools in both nearshore and offshore waters (Craig

et al.,

1982; Bradstreet

et al.,

1986). Locations and areas frequented by large schools of Arctic cod cannot be predicted, but can be almost anywhere. The Arctic cod is a major food source for beluga whales, ringed seals, and numerous species of seabirds (Frost and Lowry, 1984; Bradstreet

et al.,

1986).

Anadromous Dolly Varden char and some species of whitefish winter in rivers and lakes, migrate to the sea in spring and summer, and return to fresh water in autumn. Anadromous fish form the basis of subsistence, commercial, and small regional sport fisheries. Dolly Varden char migrate to the sea from May through mid-June (Johnson, 1980) and spend about 1.5 to 2.5 months there (Craig, 1989). They return to rivers beginning in late July or early August with the peak return migration occurring between mid-August and early September (Johnson, 1980). At sea, most anadromous corregonids (whitefish) remain in nearshore waters within several kilometers of shore (Craig, 1984, 1989). They are often termed “amphidromous” fish in that they make repeated annual migrations into marine waters to feed, returning each fall to overwinter in fresh water.

Benthic organisms are defined as bottom dwelling creatures. Infaunal organisms are benthic organisms that live within the substrate and are often sedentary or sessile (bivalves, polychaetes). Epibenthic organisms live on or near the bottom surface sediments and are mobile (amphipods, isopods, mysids, and some polychaetes). Epifauna, which live attached to hard substrates, are rare in the Beaufort Sea because hard substrates are scarce there. A small community of epifauna, the

Boulder Patch, occurs in Stefansson Sound.

The benthic environment near Northstar appears similar to that reported in various other parts of the Arctic (Ellis, 1960, 1962, 1966; Dunbar, 1968; Wacasey, 1975). Many of the nearshore benthic marine invertebrates of the Arctic are circumpolar and are found over a wide range of water depths (Carey

et al.,

1975). Species identified include polychaetes (

Spio filicornis, Chaetozone setosa,

Eteone longa

), bivalves (

Cryrtodaria kurriana, Nucula tenuis,

Liocyma fluctuosa

), an isopod (

Saduria entomon

), and amphipods (

Pontoporeia femorata, P. affinis

).

Nearshore benthic fauna have been studied in lagoons west of Northstar and near the mouth of the Colville River (Kinney

et al.,

1971, 1972; Crane and Cooney, 1975). The waters of Simpson Lagoon, Harrison Bay, and the nearshore region support a number of infaunal species including crustaceans, mollusks, and polychaetes. In areas influenced by river discharge, seasonal changes in salinity can greatly influence the distribution and abundance of benthic organisms. Large fluctuations in salinity and temperature that occur over a very short time period, or on a seasonal basis, allow only very adaptable, opportunistic species to survive (Alexander

et al.,

1974). Since shorefast ice is present for many months, the distribution and abundance of most species depends on annual (or more frequent) recolonization from deeper offshore waters (Woodward Clyde Consultants, 1995). Due to ice scouring, particularly in water depths of less than 8 ft (2.4 m), infaunal communities tend to be patchily distributed. Diversity increases with water depth until the shear zone is reached at 49-82 ft (15-25 m; Carey, 1978). Biodiversity then declines due to ice gouging between the landfast ice and the polar pack ice (Woodward Clyde Consultants, 1995).

Potential Impacts From Sound Generation

Fish are known to hear and react to sounds and to use sound to communicate (Tavolga

et al.,

1981) and possibly avoid predators (Wilson and Dill, 2002). Experiments have shown that fish can sense both the strength and direction of sound (Hawkins, 1981). Primary factors determining whether a fish can sense a sound signal, and potentially react to it, are the frequency of the signal and the strength of the signal in relation to the natural background noise level.

Fishes produce sounds that are associated with behaviors that include territoriality, mate search, courtship, and aggression. It has also been speculated that sound production may provide the means for long distance communication and communication under poor underwater visibility conditions (Zelick

et al.,

1999), although the fact that fish communicate at low-frequency sound levels where the masking effects of ambient noise are naturally highest suggests that very long distance communication would rarely be possible. Fishes have evolved a diversity of sound generating organs and acoustic signals of various temporal and spectral contents. Fish sounds vary in structure, depending on the mechanism used to produce them (Hawkins, 1993). Generally, fish sounds are predominantly composed of low frequencies (less than 3 kHz).

Since objects in the water scatter sound, fish are able to detect these objects through monitoring the ambient noise. Therefore, fish are probably able to detect prey, predators, conspecifics, and physical features by listening to environmental sounds (Hawkins, 1981). There are two sensory systems that enable fish to monitor the vibration-based information of their surroundings. The two sensory systems, the inner ear and the lateral line, constitute the acoustico-lateralis system.

Although the hearing sensitivities of very few fish species have been studied to date, it is becoming obvious that the intra- and inter-specific variability is considerable (Coombs, 1981). Nedwell

et al.

(2004) compiled and published available fish audiogram information. A noninvasive electrophysiological recording method known as auditory brainstem response is now comm

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