# Takes of Marine Mammals Incidental to Specified Activities; Taking Marine Mammals Incidental to a 3D Seismic Survey in Prudhoe Bay, Beaufort Sea, Alaska

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URL: https://www.frixlaw.com/law-library/documents/fr%3A2014-08352

## Record

- **Collection:** Federal Register
- **Document type:** Notice
- **Published:** April 15, 2014
- **Citation:** 79 FR 21354

## Text

DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
RIN 0648-XD210
Takes of Marine Mammals Incidental to Specified Activities; Taking Marine Mammals Incidental to a 3D Seismic Survey in Prudhoe Bay, Beaufort Sea, Alaska

AGENCY:

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

ACTION:

Notice; proposed incidental harassment authorization; request for comments.

SUMMARY:

NMFS has received an application from BP Exploration (Alaska) Inc. (BP) for an Incidental Harassment Authorization (IHA) to take marine mammals, by harassment, incidental to conducting an ocean-bottom sensor seismic survey in Prudhoe Bay, Beaufort Sea, Alaska, during the 2014 open water season. Pursuant to the Marine Mammal Protection Act (MMPA), NMFS is requesting comments on its proposal to issue an IHA to BP to incidentally take, by Level B harassment only, marine mammals during the specified activity.

DATES:

Comments and information must be received no later than May 15, 2014.

ADDRESSES:

Comments on the application should be addressed to Jolie Harrison, Supervisor, Incidental Take Program, Permits and Conservation Division, Office of Protected Resources, National Marine Fisheries Service, 1315 East-West Highway, Silver Spring, MD 20910. The mailbox address for providing email comments is
ITP.Nachman@noaa.gov
. NMFS is not responsible for email comments sent to addresses other than the one provided here. Comments sent via email, including all attachments, must not exceed a 25-megabyte file size.

Instructions: All comments received are a part of the public record and will generally be posted to
http://www.nmfs.noaa.gov/pr/permits/incidental.htm
without change. All Personal Identifying Information (e.g., name, address) voluntarily submitted by the commenter may be publicly accessible. Do not submit Confidential Business Information or otherwise sensitive or protected information.

An electronic copy of the application containing a list of the references used in this document may be obtained by writing to the address specified above, telephoning the contact listed below (see
FOR FURTHER INFORMATION CONTACT
), or visiting the Internet at:
http://www.nmfs.noaa.gov/pr/permits/incidental.htm
. Documents cited in this notice may also be viewed, by appointment, during regular business hours, at the aforementioned address.

FOR FURTHER INFORMATION CONTACT:

Candace Nachman, Office of Protected Resources, NMFS, (301) 427-8401.

SUPPLEMENTARY INFORMATION:

Background

Sections 101(a)(5)(A) and (D) of the MMPA (16 U.S.C. 1361
et seq.
) direct the Secretary of Commerce to allow, upon request, the incidental, but not intentional, taking of small numbers of marine mammals by U.S. citizens who engage in a specified activity (other than commercial fishing) within a specified geographical region if certain findings are made and either regulations are issued or, if the taking is limited to harassment, a notice of a proposed authorization is provided to the public for review.

Authorization for incidental takings shall be granted if NMFS finds that the taking will have a negligible impact on the species or stock(s), will not have an unmitigable adverse impact on the availability of the species or stock(s) for subsistence uses (where relevant), and if the permissible methods of taking, other means of effecting the least practicable impact on the species or stock and its habitat, and requirements pertaining to the mitigation, monitoring and reporting of such takings are set forth. NMFS has defined “negligible impact” in 50 CFR 216.103 as “. . . an impact resulting from the specified activity that cannot be reasonably expected to, and is not reasonably likely to, adversely affect the species or stock through effects on annual rates of recruitment or survival.”

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 December 30, 2013, NMFS received an application from BP for the taking of marine mammals incidental to conducting a 3D ocean-bottom sensor (OBS) seismic survey. NMFS determined that the application was adequate and complete on February 14, 2014.

BP proposes to conduct a 3D OBS seismic survey with a transition zone component on state and private lands and Federal and state waters in the Prudhoe Bay area of the Beaufort Sea during the open-water season of 2014. The proposed activity would occur between July 1 and September 30; however, airgun operations would cease on August 25. The following specific aspects of the proposed activity are likely to result in the take of marine mammals: airguns and pingers. Take, by Level B harassment only, of 9 marine mammal species is anticipated to result from the specified activity.

Description of the Specified Activity

Overview

BP's proposed OBS seismic survey would utilize sensors located on the ocean bottom or buried below ground nearshore (surf zone) and onshore. A total of two seismic source vessels will be used during the proposed survey, each carrying two airgun sub-arrays. The discharge volume of each airgun sub-array will not exceed 620 cubic inches (in
3
). To limit the duration of the total survey, the source vessels will be operating in a flip-flop mode (i.e., alternating shots); this means that one vessel discharges airguns when the other vessel is recharging. The program is proposed to be conducted during the 2014 open-water season.

The purpose of the proposed OBS seismic survey is to obtain current, high-resolution seismic data to image existing reservoirs. The data will increase BP's understanding of the reservoir, allowing for more effective reservoir management. Existing datasets of the proposed survey area include the 1985 Niakuk and 1990 Point McIntyre vibroseis on ice surveys. Data from these two surveys were merged for reprocessing in 2004. A complete set of OBS data has not previously been acquired in the proposed survey area.

Dates and Duration

The planned start date of receiver deployment is approximately July 1, 2014, with seismic data acquisition beginning when open water conditions allow. This has typically been around July 15. Seismic survey data acquisition may take approximately 45 days to complete, which includes downtime for weather and other circumstances. Seismic data acquisition will occur on a 24-hour per day schedule with staggered crew changes. Receiver retrieval and demobilization of

equipment and support crew will be completed by the end of September. To limit potential impacts to the bowhead whale fall migration and subsistence hunting, airgun operations will cease by midnight on August 25. Receiver and equipment retrieval and crew demobilization would continue after airgun operations end but would be completed by September 30. Therefore, the proposed dates for the IHA (if issued) are July 1 through September 30, 2014.

Specified Geographic Region

The proposed seismic survey would occur in Federal and state waters in the Prudhoe Bay area of the Beaufort Sea, Alaska. The seismic survey project area lies mainly within the Prudhoe Bay Unit and also includes portions of the Northstar, Dewline, and Duck Island Units, as well as non-unit areas. Figures 1 and 2 in BP's application outline the proposed seismic acquisition areas. The project area encompasses approximately 190 mi
2
, comprised of approximately 129 mi
2
in water depths of 3 ft and greater, 28 mi
2
in waters less than 3 ft deep, and 33 mi
2
on land. The approximate boundaries of the project area are between 70°16′ N. and 70°31′ N. and between 147°52′ W. and 148°47′ W. and include state and federal waters, as well as state and private lands. Activity outside the 190 mi
2
area may include source vessels turning from one line to the other while using mitigation guns, vessel transits, and project support and logistics.

Detailed Description of Activities

OBS seismic surveys are typically used to acquire 3D seismic data in water that is too shallow for towed streamer operations or too deep to have grounded ice in winter. Data acquired through this type of survey will allow for the generation of a 3D sub-surface image of the reservoir area. The generation of a 3D image requires the deployment of many parallel receiver lines spaced close together over the area of interest. The activities associated with the proposed OBS seismic survey include equipment and personnel mobilization and demobilization, housing and logistics, temporary support facilities, and seismic data acquisition.

1. Equipment and Personnel Mobilization and Demobilization

Mobilization, demobilization, and support activities are primarily planned to occur at West Dock, East Dock, and Endicott. Other existing pads within the Prudhoe Bay Unit area may be utilized for equipment staging or support as necessary. All vessels are expected to be transported to the North Slope by truck. Any mobilization by truck does not have the potential to take marine mammals. It is possible that one of the vessels will be mobilized by sea past Barrow when ice conditions allow. The vessels will be prepared at the seismic contractor's base in Deadhorse, West Dock, or East Dock. Vessel preparation will include assembly of navigation and source equipment, testing receiver deployment and retrieval systems, loading recording and safety equipment, and initial fueling. Once assembled, the systems (including airguns) will be tested within the project area. Equipment will be retrieved as part of the operations and during demobilization. Receiver retrieval and demobilization of equipment and support crew will be completed by the end of September.

2. Housing and Logistics

Approximately 220 people will be involved in the operation including seismic crew, management, mechanics, and Protected Species Observers (PSOs). Most of the crew will be accommodated at BP operated camps or Deadhorse. Some offshore crew will be housed on vessels.

Personnel transportation between camps, pads, and support facilities will take place by trucks and crew transport buses traveling on existing gravel roads. This type of crew transfer does not have the potential to take marine mammals. Shallow-water craft such as Zodiac-type vessels and ARKTOS
TM
(and Northstar hovercraft if needed and available) will be used to transport equipment and crews to shallow water and surf-zone areas of the survey area not accessible by road; ARKTOS
TM
will not be used in vegetated areas, including tundra. Helicopters will be used to transport equipment and personnel to onshore tundra areas, and crews on foot will deploy equipment onshore. Trucks may also be used on the existing road system to transfer survey equipment and crews to the onshore portions of the survey area accessible by road and pads. Helicopter operations will be supported in Deadhorse.

Up to 10,000 gallons of fuel (mostly ultra-low sulfur diesel and small quantities of gasoline) may be temporarily stored on existing pads to support survey activities. Fuel may be transported to locations to refuel equipment. The vehicle transporting fuel to locations off pads (helicopter, boat, tracked buggy, or truck) will supply the necessary quantity of fuel at the time of transfer. Fueling of equipment may occur in floodplains and near water to accommodate marine and surf zone operations. All fueling will occur in accordance with applicable regulations and BP spill prevention practices.

3. Support Facilities

West Dock, Endicott, and East Dock, as well as other existing Prudhoe Bay Unit infrastructure, will be utilized for seismic staging, crew transfers, resupply, and other support activities. Crew transfers and resupply may also occur at other nearby vessel accessible locations (e.g., by beaching) if needed. For protection from weather, vessels may anchor near West Dock, near the barrier islands, or other nearshore area locations.

Receivers (i.e., nodes placed into cache bags) to be transported by helicopter via sling-load to the onsite project area for on-foot deployment may be temporarily staged on tundra adjacent to pads. These staging areas are not expected to exceed 200 ft by 200 ft and will be rotated as practicable to minimize tundra disturbance.

Helicopter support for equipment and personnel transport is scheduled to take place during one shift per 24-hour day. The helicopter will be based at the Deadhorse airport. A few staging areas may be strategically located at existing pads or gravel locations in the Prudhoe Bay Unit to minimize flight time and weather exposure.

A temporary flexi-float dock may be located at West Dock to provide support for vessel supply operations, personnel transfers, and refueling. The dock size will be a maximum of 170 × 30 ft and will be comprised of sections that will be fastened on location and secured with spuds to the seafloor. If needed, a smaller temporary dock (up to 100 × 15 ft) may be used at Endicott for additional support during some operations in the eastern project area. Minimal and temporary disturbance to marine sediments is expected when docks are placed and removed.

4. Seismic Data Acquisition

The proposed seismic survey will use sensors located on the ocean bottom or buried below ground nearshore (surf zone) and onshore and is described in more detail below. Sensors will be placed along north-south oriented receiver lines, with a minimum line spacing of 1,320 ft. The sound source will be submerged compressed airgun arrays towed behind source vessels. Source lines will be oriented perpendicular to receiver lines with typical minimum line spacing of 550 ft. In certain situations, such as when lines have been modified to avoid cultural sites, mitigate impacts to wildlife, or

due to bathymetry or geographic features, additional infill source and receiver lines may be added to improve data imaging.

Equipment and Vessels:
Equipment will include geophones/receivers, airguns, nodes and batteries, helicopters, tracked drills, and vessels. Table 1 here and in BP's application lists the number and type of vessels and other vehicles anticipated to be used for the data acquisition. In the event that a specific vehicle or vessel is not available, a vehicle or vessel with similar parameters will be used.

EN15AP14.000

Navigation and Data Management:
Surveyors will deploy up to three navigation positioning base stations (survey control) onshore or on an island and may mark receiver locations in advance of the lay-out crews. Scouting of the project area and collecting bathymetry information necessary to identify site-specific conditions, such as water depth in near-shore areas will be performed prior to receiver deployment. A Differential Global Positioning System will be used for navigation. This navigation system connects to the onshore base stations and remotely links the operating systems on the vessels. The navigation system will display known obstructions, islands, identified areas of sensitivity, and pre-plotted source and receiver line positions; this information will be updated as necessary. The asset monitor will update the positions of each vessel in the survey area every few seconds providing the crew a quick display as to each vessel's position. Tide gauges will also be temporarily installed in the operation area. Tide gauges will be used to provide real-time water depth to ensure operations occur in the prescribed water depths. The tide gauge information will be input into the navigation system to provide real-time assessment.

Receiver Deployment and Retrieval:
The survey area has been separated into three different zones based upon the different types of receivers that will be used and the method of receiver deployment and retrieval for that zone. Deployment and retrieval methods have been designed to facilitate complete equipment retrieval at the end of the survey. The three zones are: Offshore zone; surf zone; and onshore zone. Details on operations in each zone are provided next.

The
offshore zone
is defined as waters of 3 ft or deeper. Receiver boats will be used for the deployment and retrieval of receivers (marine nodes) that will be placed in lines onto the ocean bottom at about 110 ft spacing. Receivers will not be placed east of the Endicott Main Production Island, and will therefore not be placed in mapped concentrations of the Boulder Patch. Acoustic pingers will be deployed on every second node to determine exact positions of the receivers. The pingers transmit at frequencies ranging from about 19-36 kHz and have an estimated source level of 188-193 dB re μPa at 1m.

The
surf zone
includes waters up to 6 ft deep along the coastline, non-vegetated tidelands, and lands within the river delta areas that are intermittently submerged with tidal, precipitation, and storm surge events. ARKTOS
TM
and utility type vehicles equipped with a bit of approximately 4-

inch diameter will be used to either drill or flush the receivers to approximately 6 ft. Small vessels will then attach autonomous nodes to the receivers. The nodes will be protected from the water either through placement on specially designed floats anchored to the bottom or on support poles. Support poles will primarily be used in water less than 18 inches deep and in tidal surge areas to ensure that the nodes stay above surface waters and prevent them from becoming inundated as a result of fluctuating water levels. Receivers that are installed in the seabed may require warm water flushing to facilitate removal.

The
onshore zone
is the vegetated area from the coastline inland. Autonomous node receivers with geophones will be used in this area. Helicopters will be the main method to transport land crews and equipment. Equipment will be bagged, with each bag holding several nodes. Multiple bags will be transported via sling load from the staging area to the receiver lines and temporarily cached. Bag drop zones will be 500 to 1,000 ft apart and will be cleared for the presence of nesting birds prior to use. Crews on foot will walk from bag to bag and lay out the equipment at the surveyed location. Vessels may also be used to transport personnel and equipment to a staging area on the beach, and vehicles may be used to transport personnel and equipment along the road system. Zodiac-type boats may be used in large lakes to deploy marine nodes. Boats, nodes, and crews will be transported via helicopter to and from the lakes.

Nodes will be located on the ground surface, and the geophone(s) will be inserted approximately 3 ft below ground surface. Geophone installation will be either by hand using a planting pole or will be inserted into 1.5 inch diameter holes made with a hand-held drill. Support poles may be placed in lake margins and marshy areas of tundra as needed to ensure the nodes stay above surface waters and prevent them from becoming inundated as a result of fluctuating water levels. If conditions allow, geophones may be installed in the Sagavanirktok River Delta in early April until tundra closure using two tracked utility vehicle and a support vehicle. Upon completion of data acquisition and recording operations in a particular area, land crews will retrieve the nodes. Activities that occur onshore are not considered in the take assessment analysis in this proposed IHA.

Source Vessel Operations:
A total of two seismic source vessels will be used during the proposed survey. The source vessels will carry an airgun array that consists of two sub-arrays, however, it is possible that one of the source vessels will tow only one sub-array. The discharge volume of the sub-array will not exceed 620 in
3
. Each sub-array consists of eight airguns (2 × 110, 2 × 90, 2 × 70, and 2 × 40 in
3
) totaling 16 guns for the two sub-arrays with a total discharge volume of 2 × 620 in
3
, or 1240 in
3
. The 620 in
3
sub-array has an estimated source level of ~218 decibels referenced to 1 microPascal root mean squared (dB re 1 μPa rms) at 1 meter from the source. The estimated source level of the two sub-arrays combined is ~224 dB re 1 μPa rms. In the shallowest areas, only one sub-array may be used for a given source vessel. Table 2 here and in BP's application summarizes the acoustic properties of the proposed airgun array. The smallest gun in the array (40 in
3
) or a separate 10 in
3
airgun will be used for mitigation purposes.

The airgun sub-arrays will be towed at a distance of approximately 50 ft from the source vessel's stern at depths ranging from approximately 3 to 6 ft, depending on water depth and sea conditions. The source vessels will travel along pre-determined lines with a speed varying from 1 to 5 knots, mainly depending on the water depth.

To limit the duration of the total survey, the source vessels will be operating in flip-flop mode (i.e., alternating shots); this means that one vessel discharges airguns when the other vessel is recharging. In some instances, only one source vessel will be operating, while the second source vessel will be engaged in refueling, maintenance, or other activities that do not require the operation of airguns. The expected shot interval for each source will be 10 to 12 seconds, resulting in a shot every 5 to 6 seconds due to the flip-flop mode of operation. The exact shot intervals will depend on the compressor capacity, which determines the time needed for the airguns to be recharged. Data will record autonomously on the nodes placed offshore, in the surf zone, and onshore and may be periodically checked for quality control.

Table 2—Proposed Airgun Array Configuration and Sound Source Signatures as Predicted by the Gundalf Airgun Array Model for 2 m Depth

Array specifics

620 in
3
array

1240 in
3
array

Number of guns

Eight 2000 psi sleeve airguns (2 × 110, 2 × 90, 2 × 70, and 2 × 40 in
3
) in one array

Sixteen 2000 psi sleeve airguns (4 × 110, 4 × 90, 4 × 70, and 4 × 40 in
3
), equally divided over two sub-arrays of eight guns each.

Zero to peak
6.96 bar-m (~237 dB re μPa @1 m)
13.8 bar-m (~249 dB re 1 μPa @1 m).

Peak to peak
14.9 bar-m (~243 dB re μPa @1 m)
29.8 bar-m (~243 dB re 1 μPa @1 m).

RMS pressure
0.82 bar-m (~218 dB re μPa @1 m)
1.65 bar-m (~224 dB re 1 μPa @1 m).

Dominant frequencies
Typically less than 1 kHz
Typically less than 1 kHz.

Description of Marine Mammals in the Area of the Specified Activity

The Beaufort Sea supports a diverse assemblage of marine mammals. Table 3 lists the 12 marine mammal species under NMFS jurisdiction with confirmed or possible occurrence in the proposed project area.

Table 3—Marine Mammal Species With Confirmed or Possible Occurrence in the Proposed Seismic Survey Area

Common name
Scientific name
Status
Occurrence
Seasonality
Range
Abundance

Odontocetes:

Beluga whale (Beaufort Sea stock)

Delphinapterus leucas

Common
Mostly spring and fall with some in summer
Russia to Canada
39,258

Killer whale

Orcinus orca

Occasional/Extralimital
Mostly summer and early fall
California to Alaska
552

Harbor porpoise

Phocoena phocoena

Occasional/Extralimital
Mostly summer and early fall
California to Alaska
48,215

Narwhal

Monodon monoceros

45,358

Mysticetes:

Bowhead whale

Balaena mysticetus

Endangered; Depleted
Common
Mostly spring and fall with some in summer
Russia to Canada
16,892

Gray whale

Eschrichtius robustus

Somewhat common
Mostly summer
Mexico to the U.S. Arctic Ocean
19,126

Minke whale

Balaenoptera acutorostrata

810-1,003

Humpback whale (Central North Pacific stock)

Megaptera novaeangliae

Endangered; Depleted

21,063

Pinnipeds:

Bearded seal (Beringia distinct population segment)

Erigathus barbatus

Threatened; Depleted
Common
Spring and summer
Bering, Chukchi, and Beaufort Seas
155,000

Ringed seal (Arctic stock)

Phoca hispida

Threatened; Depleted
Common
Year round
Bering, Chukchi, and Beaufort Seas
300,000

Spotted seal

Phoca largha

Common
Summer
Japan to U.S. Arctic Ocean
141,479

Ribbon seal

Histriophoca fasciata

Species of concern
Occasional
Summer
Russia to U.S. Arctic Ocean
49,000

Endangered, threatened, or species of concern under the Endangered Species Act (ESA); Depleted under the MMPA.

The highlighted (grayed out) species in Table 3 are so rarely sighted in the central Alaskan Beaufort Sea that their presence in the proposed project area, and therefore take, is unlikely. Minke whales are relatively common in the Bering and southern Chukchi seas and have recently also been sighted in the northeastern Chukchi Sea (Aerts
et al.,
2013; Clarke
et al.,
2013). Minke whales are rare in the Beaufort Sea. They have not been reported in the Beaufort Sea during the Bowhead Whale Aerial Survey Project/Aerial Surveys of Arctic Marine Mammals (BWASP/ASAMM) surveys (Clarke
et al.,
2011, 2012; 2013; Monnet and Treacy, 2005), and there was only one observation in 2007 during vessel-based surveys in the region (Funk
et al.,
2010). Humpback whales have not generally been found in the Arctic Ocean. However, subsistence hunters have spotted humpback whales in low numbers around Barrow, and there have been several confirmed sightings of humpback whales in the northeastern Chukchi Sea in recent years (Aerts
et al.,
2013; Clarke
et al.,
2013). The first confirmed sighting of a humpback whale in the Beaufort Sea was recorded in August 2007 (Hashagen
et al.,
2009) when a cow and calf were observed 54 mi east of Point Barrow. No additional sightings have been documented in the Beaufort Sea. Narwhal are common in the waters of northern Canada, west Greenland, and in the European Arctic, but rarely occur in the Beaufort Sea (COSEWIC, 2004). Only a handful of sightings have occurred in Alaskan waters (Allen and Angliss, 2013). These three species are not considered further in this proposed IHA notice. Both the walrus and the polar bear could occur in the U.S. Beaufort Sea; however, these species are managed by the U.S. Fish and Wildlife Service (USFWS) and are not considered further in this Notice of Proposed IHA.

The Beaufort Sea is a main corridor of the bowhead whale migration route. The main migration periods occur in spring from April to June and in fall from late August/early September through October to early November. During the fall migration, several locations in the U.S. Beaufort Sea serve as feeding grounds for bowhead whales. Small numbers of bowhead whales that remain in the U.S. Arctic Ocean during summer also feed in these areas. The U.S. Beaufort Sea is not a main feeding or calving area for any other cetacean species. Ringed seals breed and pup in the Beaufort Sea; however, this does not occur during the summer or early fall. Further information on the biology and local distribution of these species can be found in BP's application (see
ADDRESSES
) and the NMFS Marine Mammal Stock Assessment Reports, which are available online at:
http://www.nmfs.noaa.gov/pr/species/
.

Potential Effects of the Specified Activity on Marine Mammals

This section includes a summary and discussion of the ways that the types of stressors associated with the specified activity (e.g., seismic airgun and pinger operation, vessel movement) have been observed to or are thought to impact marine mammals. This section may include a discussion of known effects that do not rise to the level of an MMPA take (for example, with acoustics, we may include a discussion of studies that showed animals not reacting at all to sound or exhibiting barely measurable avoidance). The discussion may also include reactions that we consider to rise to the level of a take and those that we do not consider to rise to the level of a take. This section is intended as a background of potential effects and does not consider either the specific manner in which this activity will be carried out or the mitigation that will be implemented or how either of those will shape the anticipated impacts from this specific activity. The “Estimated Take by Incidental Harassment” section later in this document will include a quantitative analysis of the number of individuals that are expected to be taken by this activity. The “Negligible Impact Analysis” section will include the analysis of how this specific activity will impact marine mammals and will consider the content of this section, the “Estimated Take by Incidental Harassment” section, the “Mitigation” section, and the “Anticipated Effects on

Marine Mammal Habitat” section to draw conclusions regarding the likely impacts of this activity on the reproductive success or survivorship of individuals and from that on the affected marine mammal populations or stocks.

Background on Sound

Sound is a physical phenomenon consisting of minute vibrations that travel through a medium, such as air or water, and is generally characterized by several variables. Frequency describes the sound's pitch and is measured in hertz (Hz) or kilohertz (kHz), while sound level describes the sound's intensity and is measured in decibels (dB). Sound level increases or decreases exponentially with each dB of change. The logarithmic nature of the scale means that each 10-dB increase is a 10-fold increase in acoustic power (and a 20-dB increase is then a 100-fold increase in power). A 10-fold increase in acoustic power does not mean that the sound is perceived as being 10 times louder, however. Sound levels are compared to a reference sound pressure (micro-Pascal) to identify the medium. For air and water, these reference pressures are “re: 20 μPa” and “re: 1 μPa,” respectively. Root mean square (RMS) is the quadratic mean sound pressure over the duration of an impulse. RMS is calculated by squaring all of the sound amplitudes, averaging the squares, and then taking the square root of the average (Urick, 1975). RMS accounts for both positive and negative values; squaring the pressures makes all values positive so that they may be accounted for in the summation of pressure levels (Hastings and Popper, 2005). This measurement is often used in the context of discussing behavioral effects, in part, because behavioral effects, which often result from auditory cues, may be better expressed through averaged units rather than by peak pressures.

Acoustic Impacts

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) to 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 30 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;

• Phocid pinnipeds in Water: functional hearing is estimated to occur between approximately 75 Hz and 100 kHz; and

• Otariid pinnipeds in Water: functional hearing is estimated to occur between approximately 100 Hz and 40 kHz.

As mentioned previously in this document, nine marine mammal species (five cetaceans and four phocid pinnipeds) may occur in the proposed seismic survey area. Of the five cetacean species likely to occur in the proposed project area and for which take is requested, two are classified as low-frequency cetaceans (i.e., bowhead and gray whales), two are classified as mid-frequency cetaceans (i.e., beluga and killer whales), and one is classified as a high-frequency cetacean (i.e., harbor porpoise) (Southall
et al.,
2007). A species functional hearing group is a consideration when we analyze the effects of exposure to sound on marine mammals.

1. Tolerance

Numerous studies have shown that underwater sounds from industry activities are often readily detectable by marine mammals in the water at distances of many kilometers. Numerous studies have also shown that marine mammals at distances more than a few kilometers away often show no apparent response to industry activities of various types (Miller
et al.,
2005; Bain and Williams, 2006). This is often true even in cases when the sounds must be readily audible to the animals based on measured received levels and the hearing sensitivity of that mammal group. Although various baleen whales, toothed whales, and (less frequently) pinnipeds have been shown to react behaviorally to underwater sound such as airgun pulses or vessels under some conditions, at other times mammals of all three types have shown no overt reactions (e.g., Malme
et al.,
1986; Richardson
et al.,
1995; Madsen and Mohl, 2000; Croll
et al.,
2001; Jacobs and Terhune, 2002; Madsen
et al.,
2002; Miller
et al.,
2005). Weir (2008) observed marine mammal responses to seismic pulses from a 24 airgun array firing a total volume of either 5,085 in
3
or 3,147 in
3
in Angolan waters between August 2004 and May 2005. Weir recorded a total of 207 sightings of humpback whales (n = 66), sperm whales (n = 124), and Atlantic spotted dolphins (n = 17) and reported that there were no significant differences in encounter rates (sightings/hr) for humpback and sperm whales according to the airgun array's operational status (i.e., active versus silent). The airgun arrays used in the Weir (2008) study were much larger than the array proposed for use during this seismic survey (total discharge volumes of 620 to 1,240 in
3
). In general, pinnipeds and small odontocetes seem to be more tolerant of exposure to some types of underwater sound than are baleen whales. Richardson
et al.
(1995) found that vessel noise does not seem to strongly affect pinnipeds that are already in the water. Richardson
et al.
(1995) went on to explain that seals on haul-outs sometimes respond strongly to the presence of vessels and at other times appear to show considerable tolerance of vessels.

2. Masking

Masking is the obscuring of sounds of interest by other sounds, often at similar frequencies. Marine mammals use acoustic signals for a variety of purposes, which differ among species, but include communication between individuals, navigation, foraging, reproduction, avoiding predators, and learning about their environment (Erbe and Farmer, 2000; Tyack, 2000). Masking, or auditory interference, generally occurs when sounds in the environment are louder than, and of a similar frequency as, auditory signals an animal is trying to receive. Masking is a phenomenon that affects animals that are trying to receive acoustic information about their environment, including sounds from other members of their species, predators, prey, and sounds that allow them to orient in their environment. Masking these acoustic signals can disturb the behavior of individual animals, groups of animals, or entire populations.

Masking occurs when anthropogenic sounds and signals (that the animal utilizes) overlap at both spectral and temporal scales. For the airgun sound generated from the proposed seismic survey, sound will consist of low frequency (under 500 Hz) pulses with extremely short durations (less than one second). Lower frequency man-made sounds are more likely to affect detection of communication calls and other potentially important natural sounds such as surf and prey noise. There is little concern regarding masking near the sound source due to the brief duration of these pulses and relatively longer silence between airgun shots (approximately 5-6 seconds). However, at long distances (over tens of kilometers away), due to multipath propagation and reverberation, the durations of airgun pulses can be “stretched” to seconds with long decays (Madsen
et al.,
2006), although the intensity of the sound is greatly reduced.

This could affect communication signals used by low frequency mysticetes when they occur near the noise band and thus reduce the communication space of animals (e.g., Clark
et al.,
2009) and cause increased stress levels (e.g., Foote
et al.,
2004; Holt
et al.,
2009). Marine mammals are thought to be able to compensate for masking by adjusting their acoustic behavior by shifting call frequencies, and/or increasing call volume and vocalization rates. For example, blue whales are found to increase call rates when exposed to seismic survey noise in the St. Lawrence Estuary (Di Iorio and Clark, 2010). The North Atlantic right whales exposed to high shipping noise increase call frequency (Parks
et al.,
2007), while some humpback whales respond to low-frequency active sonar playbacks by increasing song length (Miller
el al.,
2000). Bowhead whale calls are frequently detected in the presence of seismic pulses, although the number of calls detected may sometimes be reduced (Richardson
et al.,
1986; Greene
et al.,
1999), possibly because animals moved away from the sound source or ceased calling (Blackwell
et al.,
2013). Additionally, beluga whales have been known to change their vocalizations in the presence of high background noise possibly to avoid masking calls (Au
et al.,
1985; Lesage
et al.,
1999; Scheifele
et al.,
2005). 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.,
1995). 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 sounds by improving the effective signal-to-noise ratio. In the cases of higher 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.,
1995). This ability may be useful in reducing masking at these frequencies. In summary, high levels of sound 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.

3. Behavioral Disturbance

Marine mammals may behaviorally react when exposed to anthropogenic sound. These behavioral reactions are often shown as: changing durations of surfacing and dives, number of blows per surfacing, or moving direction and/or speed; reduced/increased vocal activities; changing/cessation of certain behavioral activities (such as socializing or feeding); visible startle response or aggressive behavior (such as tail/fluke slapping or jaw clapping); avoidance of areas where sound sources are located; and/or flight responses (e.g., pinnipeds flushing into water from haulouts or rookeries).

The biological significance of many of these behavioral disturbances is difficult to predict, especially if the detected disturbances appear minor. However, the consequences of behavioral modification have the potential to be biologically significant if the change affects growth, survival, or reproduction. Examples of significant behavioral modifications include:

• Drastic change in diving/surfacing patterns (such as those thought to be causing beaked whale stranding due to exposure to military mid-frequency tactical sonar);

• Habitat abandonment due to loss of desirable acoustic environment; and

• Cessation of feeding or social interaction.

The onset of behavioral disturbance from anthropogenic noise depends on both external factors (characteristics of

noise sources and their paths) and the receiving animals (hearing, motivation, experience, demography, current activity, reproductive state) and is also difficult to predict (Gordon
et al.,
2004; Southall
et al.,
2007; Ellison
et al.,
2011).

Mysticetes:
Baleen whales generally tend to avoid operating airguns, but avoidance radii are quite variable. Whales are often reported to show no overt reactions to pulses from large arrays of airguns at distances beyond a few kilometers, even though the airgun pulses remain well above ambient noise levels out to much greater distances (Miller
et al.,
2005). However, baleen whales exposed to strong noise pulses often react by deviating from their normal migration route (Richardson
et al.,
1999). Migrating gray and bowhead whales were observed avoiding the sound source by displacing their migration route to varying degrees but within the natural boundaries of the migration corridors (Schick and Urban, 2000; Richardson
et al.,
1999; Malme
et al.,
1983). Baleen whale responses to pulsed sound however may depend on the type of activity in which the whales are engaged. Some evidence suggests that feeding bowhead whales may be more tolerant of underwater sound than migrating bowheads (Miller
et al.,
2005; Lyons
et al.,
2009; Christie
et al.,
2010).

Results of studies of gray, bowhead, and humpback whales have determined that received levels of pulses in the 160-170 dB re 1 μPa rms range seem to cause obvious avoidance behavior in a substantial fraction of the animals exposed. In many areas, seismic pulses from large arrays of airguns diminish to those levels at distances ranging from 2.8-9 mi (4.5-14.5 km) from the source. For the much smaller airgun array used during BP's proposed survey (total discharge volume of 640 in
3
), distances to received levels in the 160 dB re 1 μPa rms range are estimated to be 0.5-3 mi (0.8-5 km). Baleen whales within those distances may show avoidance or other strong disturbance reactions to the airgun array. Subtle behavioral changes sometimes become evident at somewhat lower received levels, and recent studies have shown that some species of baleen whales, notably bowhead and humpback whales, at times show strong avoidance at received levels lower than 160-170 dB re 1 μPa rms. Bowhead whales migrating west across the Alaskan Beaufort Sea in autumn, in particular, are unusually responsive, with avoidance occurring out to distances of 12.4-18.6 mi (20-30 km) from a medium-sized airgun source (Miller
et al.,
1999; Richardson
et al.,
1999). However, more recent research on bowhead whales (Miller
et al.,
2005) corroborates earlier evidence that, during the summer feeding season, bowheads are not as sensitive to seismic sources. In summer, bowheads typically begin to show avoidance reactions at a received level of about 160-170 dB re 1 μPa rms (Richardson et al., 1986; Ljungblad
et al.,
1988; Miller
et al.,
2005).

Malme
et al.
(1986, 1988) studied the responses of feeding eastern gray whales to pulses from a single 100 in
3
airgun off St. Lawrence Island in the northern Bering Sea. They estimated, based on small sample sizes, that 50% of feeding gray whales ceased feeding at an average received pressure level of 173 dB re 1 μPa on an (approximate) rms basis, and that 10% of feeding whales interrupted feeding at received levels of 163 dB. Those findings were generally consistent with the results of experiments conducted on larger numbers of gray whales that were migrating along the California coast and on observations of the distribution of feeding Western Pacific gray whales off Sakhalin Island, Russia, during a seismic survey (Yazvenko
et al.,
2007).

Data on short-term reactions (or lack of reactions) of cetaceans to impulsive noises do not necessarily provide information about long-term effects. While it is not certain whether impulsive noises affect reproductive rate or distribution and habitat use in subsequent days or years, certain species have continued to use areas ensonified by airguns and have continued to increase in number despite successive years of anthropogenic activity in the area. Gray whales continued to migrate annually along the west coast of North America despite intermittent seismic exploration and much ship traffic in that area for decades (Appendix A in Malme
et al.,
1984). Bowhead whales continued to travel to the eastern Beaufort Sea each summer despite seismic exploration in their summer and autumn range for many years (Richardson
et al.,
1987). Populations of both gray whales and bowhead whales grew substantially during this time. In any event, the proposed survey will occur in summer (July through late August) when most bowhead whales are commonly feeding in the Mackenzie River Delta, Canada.

Patenaude
et al.
(2002) reported fewer behavioral responses to aircraft overflights by bowhead compared to beluga whales. Behaviors classified as reactions consisted of short surfacings, immediate dives or turns, changes in behavior state, vigorous swimming, and breaching. Most bowhead reaction resulted from exposure to helicopter activity and little response to fixed-wing aircraft was observed. Most reactions occurred when the helicopter was at altitudes ≤492 ft (150 m) and lateral distances ≤820 ft (250 m; Nowacek
et al.,
2007).

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

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

Odontocetes:
Few systematic data are available describing reactions of toothed whales to noise pulses. However, systematic work on sperm whales is underway (Tyack
et al.,
2003), and there is an increasing amount of information about responses of various odontocetes to seismic surveys based on monitoring studies (e.g., Stone, 2003; Smultea
et al.,
2004; Moulton and Miller, 2005). Miller
et al.
(2009) conducted at-sea experiments where reactions of sperm whales were monitored through the use of controlled sound exposure experiments from large airgun arrays consisting of 20-guns and 31-guns. Of 8 sperm whales observed, none changed their behavior when exposed to either a ramp-up at 4-8 mi (7-13 km) or full array exposures at 0.6-8 mi (1-13 km).

Seismic operators and marine mammal observers sometimes see dolphins and other small toothed whales near operating airgun arrays, but, in general, there seems to be a tendency for most delphinids to show some limited avoidance of seismic vessels operating large airgun systems. However, some dolphins seem to be attracted to the seismic vessel and floats, and some ride the bow wave of the seismic vessel even when large arrays of airguns are firing. Nonetheless, there have been indications that small toothed whales sometimes move away or maintain a somewhat greater distance from the vessel when a large array of airguns is operating than when it is silent (e.g., Goold, 1996a,b,c; Calambokidis and Osmek, 1998; Stone, 2003). The beluga may be a species that (at least in certain geographic areas) shows long-distance avoidance of seismic vessels. Aerial surveys during seismic operations in the southeastern Beaufort Sea recorded much lower sighting rates of beluga whales within 10-20 km (6.2-12.4 mi) of an active seismic vessel. These results were consistent with the low number of beluga sightings reported by observers aboard the seismic vessel, suggesting that some belugas might have been avoiding the seismic operations at distances of 10-20 km (6.2-12.4 mi) (Miller
et al.,
2005).

Captive bottlenose dolphins and (of more relevance in this project) beluga whales exhibit changes in behavior when exposed to strong pulsed sounds similar in duration to those typically used in seismic surveys (Finneran
et al.,
2002, 2005). However, the animals tolerated high received levels of sound (pk-pk level >200 dB re 1 μPa) before exhibiting aversive behaviors.

Observers stationed on seismic vessels operating off the United Kingdom from 1997-2000 have provided data on the occurrence and behavior of various toothed whales exposed to seismic pulses (Stone, 2003; Gordon
et al.,
2004). Killer whales were found to be significantly farther from large airgun arrays during periods of shooting compared with periods of no shooting. The displacement of the median distance from the array was approximately 0.5 km (0.3 mi) or more. Killer whales also appear to be more tolerant of seismic shooting in deeper water.

Reactions of toothed whales to large arrays of airguns are variable and, at least for delphinids, seem to be confined to a smaller radius than has been observed for mysticetes. However, based on the limited existing evidence, belugas should not be grouped with delphinids in the “less responsive” category.

Patenaude
et al.
(2002) reported that beluga whales appeared to be more responsive to aircraft overflights than bowhead whales. Changes were observed in diving and respiration behavior, and some whales veered away when a helicopter passed at ≤820 ft (250 m) lateral distance at altitudes up to 492 ft (150 m). However, some belugas showed no reaction to the helicopter. Belugas appeared to show less response to fixed-wing aircraft than to helicopter overflights.

Pinnipeds:
Pinnipeds are not likely to show a strong avoidance reaction to the airgun sources proposed for use. Visual monitoring from seismic vessels has shown only slight (if any) avoidance of airguns by pinnipeds and only slight (if any) changes in behavior. Monitoring work in the Alaskan Beaufort Sea during 1996-2001 provided considerable information regarding the behavior of Arctic ice seals exposed to seismic pulses (Harris
et al.,
2001; Moulton and Lawson, 2002). These seismic projects usually involved arrays of 6 to 16 airguns with total volumes of 560 to 1,500 in
3
. The combined results suggest that some seals avoid the immediate area around seismic vessels. In most survey years, ringed seal sightings tended to be farther away from the seismic vessel when the airguns were operating than when they were not (Moulton and Lawson, 2002). However, these avoidance movements were relatively small, on the order of 100 m (328 ft) to a few hundreds of meters, and many seals remained within 100-200 m (328-656 ft) 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.,
1995). However, initial telemetry work suggests that avoidance and other behavioral reactions by two other species of seals to small airgun sources may at times be stronger than evident to date from visual studies of pinniped reactions to airguns (Thompson
et al.,
1998). Even if reactions of the species occurring in the present study area are as strong as those evident in the telemetry study, reactions are expected to be confined to relatively small distances and durations, with no long-term effects on pinniped individuals or populations.

Blackwell
et al.
(2004) 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.
(2004) 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.,
1995; Born
et al.,
1999).

4. Threshold Shift (Noise-induced Loss of Hearing)

When animals exhibit reduced hearing sensitivity (i.e., sounds must be louder for an animal to detect them) following exposure to an intense sound or sound for long duration, it is referred to as a noise-induced threshold shift (TS). An animal can experience temporary threshold shift (TTS) or permanent threshold shift (PTS). TTS can last from minutes or hours to days (i.e., there is complete recovery), can occur in specific frequency ranges (i.e., an animal might only have a temporary loss of hearing sensitivity between the frequencies of 1 and 10 kHz), and can be of varying amounts (for example, an animal's hearing sensitivity might be reduced initially by only 6 dB or reduced by 30 dB). PTS is permanent, but some recovery is possible. PTS can also occur in a specific frequency range and amount as mentioned above for TTS.

The following physiological mechanisms are thought to play a role

in inducing auditory TS: effects to sensory hair cells in the inner ear that reduce their sensitivity, modification of the chemical environment within the sensory cells, residual muscular activity in the middle ear, displacement of certain inner ear membranes, increased blood flow, and post-stimulatory reduction in both efferent and sensory neural output (Southall
et al.,
2007). The amplitude, duration, frequency, temporal pattern, and energy distribution of sound exposure all can affect the amount of associated TS and the frequency range in which it occurs. As amplitude and duration of sound exposure increase, so, generally, does the amount of TS, along with the recovery time. For intermittent sounds, less TS could occur than compared to a continuous exposure with the same energy (some recovery could occur between intermittent exposures depending on the duty cycle between sounds) (Kryter
et al.,
1966; Ward, 1997). For example, one short but loud (higher SPL) sound exposure may induce the same impairment as one longer but softer sound, which in turn may cause more impairment than a series of several intermittent softer sounds with the same total energy (Ward, 1997). Additionally, though TTS is temporary, prolonged exposure to sounds strong enough to elicit TTS, or shorter-term exposure to sound levels well above the TTS threshold, can cause PTS, at least in terrestrial mammals (Kryter, 1985). Although in the case of the proposed seismic survey, animals are not expected to be exposed to sound levels high for a long enough period to result in PTS.

PTS is considered auditory injury (Southall
et al.,
2007). Irreparable damage to the inner or outer cochlear hair cells may cause PTS; however, other mechanisms are also involved, such as exceeding the elastic limits of certain tissues and membranes in the middle and inner ears and resultant changes in the chemical composition of the inner ear fluids (Southall
et al.,
2007).

Although the published body of scientific literature contains numerous theoretical studies and discussion papers on hearing impairments that can occur with exposure to a loud sound, only a few studies provide empirical information on the levels at which noise-induced loss in hearing sensitivity occurs in nonhuman animals. For marine mammals, published data are limited to the captive bottlenose dolphin, beluga, harbor porpoise, and Yangtze finless porpoise (Finneran
et al.,
2000, 2002b, 2003, 2005a, 2007, 2010a, 2010b; Finneran and Schlundt, 2010; Lucke
et al.,
2009; Mooney
et al.,
2009a, 2009b; Popov
et al.,
2011a, 2011b; Kastelein
et al.,
2012a; Schlundt
et al.,
2000; Nachtigall
et al.,
2003, 2004). For pinnipeds in water, data are limited to measurements of TTS in harbor seals, an elephant seal, and California sea lions (Kastak
et al.,
1999, 2005; Kastelein
et al.,
2012b).

Marine mammal hearing plays a critical role in communication with conspecifics, and interpretation of environmental cues for purposes such as predator avoidance and prey capture. Depending on the degree (elevation of threshold in dB), duration (i.e., recovery time), and frequency range of TTS, and the context in which it is experienced, TTS can have effects on marine mammals ranging from discountable to serious (similar to those discussed in auditory masking, below). For example, a marine mammal may be able to readily compensate for a brief, relatively small amount of TTS in a non-critical frequency range that occurs during a time where ambient noise is lower and there are not as many competing sounds present. Alternatively, a larger amount and longer duration of TTS sustained during time when communication is critical for successful mother/calf interactions could have more serious impacts. Also, depending on the degree and frequency range, the effects of PTS on an animal could range in severity, although it is considered generally more serious because it is a permanent condition. Of note, reduced hearing sensitivity as a simple function of aging has been observed in marine mammals, as well as humans and other taxa (Southall
et al.,
2007), so we can infer that strategies exist for coping with this condition to some degree, though likely not without cost.

Marine mammals are unlikely to be exposed to received levels of seismic pulses strong enough to cause more than slight TTS, and, given the higher level of sound necessary to cause PTS, it is even less likely that PTS could occur as a result of the proposed seismic survey.

5. Non-Auditory Physical Effects

Non-auditory physical effects might 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. Some marine mammal species (i.e., beaked whales) may be especially susceptible to injury and/or stranding when exposed to strong pulsed sounds.

Classic stress responses begin when an animal's central nervous system perceives a potential threat to its homeostasis. That perception triggers stress responses regardless of whether a stimulus actually threatens the animal; the mere perception of a threat is sufficient to trigger a stress response (Moberg, 2000; Sapolsky
et al.,
2005; Seyle, 1950). Once an animal's central nervous system perceives a threat, it mounts a biological response or defense that consists of a combination of the four general biological defense responses: Behavioral responses; autonomic nervous system responses; neuroendocrine responses; or immune responses.

In the case of many stressors, an animal's first and most economical (in terms of biotic costs) response is behavioral avoidance of the potential stressor or avoidance of continued exposure to a stressor. An animal's second line of defense to stressors involves the sympathetic part of the autonomic nervous system and the classical “fight or flight” response, which includes the cardiovascular system, the gastrointestinal system, the exocrine glands, and the adrenal medulla to produce changes in heart rate, blood pressure, and gastrointestinal activity that humans commonly associate with “stress.” These responses have a relatively short duration and may or may not have significant long-term effects on an animal's welfare.

An animal's third line of defense to stressors involves its neuroendocrine or sympathetic nervous systems; the system that has received the most study has been the hypothalmus-pituitary-adrenal system (also known as the HPA axis in mammals or the hypothalamus-pituitary-interrenal axis in fish and some reptiles). Unlike stress responses associated with the autonomic nervous system, virtually all neuroendocrine functions that are affected by stress—including immune competence, reproduction, metabolism, and behavior—are regulated by pituitary hormones. Stress-induced changes in the secretion of pituitary hormones have been implicated in failed reproduction (Moberg, 1987; Rivier, 1995), altered metabolism (Elasser
et al.,
2000), reduced immune competence (Blecha, 2000), and behavioral disturbance. Increases in the circulation of glucocorticosteroids (cortisol, corticosterone, and aldosterone in marine mammals; see Romano
et al.,
2004) have been equated with stress for many years.

The primary distinction between stress (which is adaptive and does not normally place an animal at risk) and

distress is the biotic cost of the response. During a stress response, an animal uses glycogen stores that can be quickly replenished once the stress is alleviated. In such circumstances, the cost of the stress response would not pose a risk to the animal's welfare. However, when an animal does not have sufficient energy reserves to satisfy the energetic costs of a stress response, energy resources must be diverted from other biotic functions, which impair those functions that experience the diversion. For example, when mounting a stress response diverts energy away from growth in young animals, those animals may experience stunted growth. When mounting a stress response diverts energy from a fetus, an animal's reproductive success and fitness will suffer. In these cases, the animals will have entered a pre-pathological or pathological state which is called “distress” (sensu Seyle, 1950) or “allostatic loading” (sensu McEwen and Wingfield, 2003). This pathological state will last until the animal replenishes its biotic reserves sufficient to restore normal function. Note that these examples involved a long-term (days or weeks) stress response exposure to stimuli.

Relationships between these physiological mechanisms, animal behavior, and the costs of stress responses have also been documented fairly well through controlled experiment; because this physiology exists in every vertebrate that has been studied, it is not surprising that stress responses and their costs have been documented in both laboratory and free-living animals (for examples see, Holberton
et al.,
1996; Hood
et al.,
1998; Jessop
et al.,
2003; Krausman
et al.,
2004; Lankford
et al.,
2005; Reneerkens
et al.,
2002; Thompson and Hamer, 2000). Although no information has been collected on the physiological responses of marine mammals to anthropogenic sound exposure, studies of other marine animals and terrestrial animals would lead us to expect some marine mammals to experience physiological stress responses and, perhaps, physiological responses that would be classified as “distress” upon exposure to anthropogenic sounds.

For example, Jansen (1998) reported on the relationship between acoustic exposures and physiological responses that are indicative of stress responses in humans (e.g., elevated respiration and increased heart rates). Jones (1998) reported on reductions in human performance when faced with acute, repetitive exposures to acoustic disturbance. Trimper
et al.
(1998) reported on the physiological stress responses of osprey to low-level aircraft noise while Krausman
et al.
(2004) reported on the auditory and physiology stress responses of endangered Sonoran pronghorn to military overflights. Smith
et al.
(2004a, 2004b) identified noise-induced physiological transient stress responses in hearing-specialist fish (i.e., goldfish) that accompanied short- and long-term hearing losses. Welch and Welch (1970) reported physiological and behavioral stress responses that accompanied damage to the inner ears of fish and several mammals.

Hearing is one of the primary senses marine mammals use to gather information about their environment and communicate with conspecifics. Although empirical information on the relationship between sensory impairment (TTS, PTS, and acoustic masking) on marine mammals remains limited, we assume that reducing a marine mammal's ability to gather information about its environment and communicate with other members of its species would induce stress, based on data that terrestrial animals exhibit those responses under similar conditions (NRC, 2003) and because marine mammals use hearing as their primary sensory mechanism. Therefore, we assume that acoustic exposures sufficient to trigger onset PTS or TTS would be accompanied by physiological stress responses. More importantly, marine mammals might experience stress responses at received levels lower than those necessary to trigger onset TTS. Based on empirical studies of the time required to recover from stress responses (Moberg, 2000), NMFS also assumes that stress responses could persist beyond the time interval required for animals to recover from TTS and might result in pathological and pre-pathological states that would be as significant as behavioral responses to TTS.

Resonance effects (Gentry, 2002) and direct noise-induced bubble formations (Crum
et al.,
2005) are implausible in the case of exposure to an impulsive broadband source like an airgun array. If seismic surveys disrupt diving patterns of deep-diving species, this might result in bubble formation and a form of the bends, as speculated to occur in beaked whales exposed to sonar. However, there is no specific evidence of this upon exposure to airgun pulses. Additionally, no beaked whale species occur in the proposed project area.

In general, very little is known about the potential for strong, anthropogenic underwater sounds to cause non-auditory physical effects in marine mammals. Such effects, if they occur at all, would presumably be limited to short distances and to activities that extend over a prolonged period. The available data do not allow identification of a specific exposure level above which non-auditory effects can be expected (Southall
et al.,
2007) or any meaningful quantitative predictions of the numbers (if any) of marine mammals that might be affected in those ways. There is no definitive evidence that any of these effects occur even for marine mammals in close proximity to large arrays of airguns, which are not proposed for use during this program. In addition, marine mammals that show behavioral avoidance of industry activities, including bowheads, belugas, and some pinnipeds, are especially unlikely to incur non-auditory impairment or other physical effects.

6. Stranding and Mortality

Marine mammals close to underwater detonations of high explosive can be killed or severely injured, and the auditory organs are especially susceptible to injury (Ketten
et al.,
1993; Ketten, 1995). Airgun pulses are less energetic and their peak amplitudes have slower rise times. To date, there is no evidence that serious injury, death, or stranding by marine mammals can occur from exposure to airgun pulses, even in the case of large airgun arrays. Additionally, BP's project will use medium sized airgun arrays in shallow water. NMFS does not expect any marine mammals will incur serious injury or mortality in the shallow waters of Prudhoe Bay or strand as a result of the proposed seismic survey.

7. Potential Effects From Pingers on Marine Mammals

Active acoustic sources other than the airguns have been proposed for BP's 2014 seismic survey in Prudhoe Bay, Beaufort Sea, Alaska. The specifications for the pingers (source levels and frequency ranges) were provided earlier in this document. In general, the potential effects of this equipment on marine mammals are similar to those from the airguns, except the magnitude of the impacts is expected to be much less due to the lower intensity of the source.

Vessel Impacts

Vessel activity and noise associated with vessel activity will temporarily increase in the action area during BP's seismic survey as a result of the operation of 8-10 vessels. To minimize the effects of vessels and noise associated with vessel activity, BP will alter speed if a marine mammal gets too

close to a vessel. In addition, source vessels will be operating at slow speed (1-5 knots) when conducting surveys. Marine mammal monitoring observers will alert vessel captains as animals are detected to ensure safe and effective measures are applied to avoid coming into direct contact with marine mammals. Therefore, NMFS neither anticipates nor authorizes takes of marine mammals from ship strikes.

McCauley
et al.
(1996) reported several cases of humpback whales responding to vessels in Hervey Bay, Australia. Results indicated clear avoidance at received levels between 118 to 124 dB in three cases for which response and received levels were observed/measured.

Palka and Hammond (2001) analyzed line transect census data in which the orientation and distance off transect line were reported for large numbers of minke whales. The authors developed a method to account for effects of animal movement in response to sighting platforms. Minor changes in locomotion speed, direction, and/or diving profile were reported at ranges from 1,847 to 2,352 ft (563 to 717 m) at received levels of 110 to 120 dB.

Odontocetes, such as beluga whales, killer whales, and harbor porpoises, often show tolerance to vessel activity; however, they may react at long distances if they are confined by ice, shallow water, or were previously harassed by vessels (Richardson
et al.,
1995). Beluga whale response to vessel noise varies greatly from tolerance to extreme sensitivity depending on the activity of the whale and previous experience with vessels (Richardson
et al.,
1995). Reactions to vessels depends on whale activities and experience, habitat, boat type, and boat behavior (Richardson
et al.,
1995) and may include behavioral responses, such as altered headings or avoidance (Blane and Jaakson, 1994; Erbe and Farmer, 2000); fast swimming; changes in vocalizations (Lesage
et al.,
1999; Scheifele
et al.,
2005); and changes in dive, surfacing, and respiration patterns.

There are few data published on pinniped responses to vessel activity, and most of the information is anecdotal (Richardson
et al.,
1995). Generally, sea lions in water show tolerance to close and frequently approaching vessels and sometimes show interest in fishing vessels. They are less tolerant when hauled out on land; however, they rarely react unless the vessel approaches within 100-200 m (330-660 ft; reviewed in Richardson
et al.,
1995).

The addition of 8-10 vessels and noise due to vessel operations associated with the seismic survey is not expected to have effects that could cause significant or long-term consequences for individual marine mammals or their populations.

Anticipated Effects on Marine Mammal Habitat

The primary potential impacts to marine mammal habitat and other marine species are associated with elevated sound levels produced by airguns and other active acoustic sources. However, other potential impacts to the surrounding habitat from physical disturbance are also possible. This section describes the potential impacts to marine mammal habitat from the specified activity. Because the marine mammals in the area feed on fish and/or invertebrates there is also information on the species typically preyed upon by the marine mammals in the area.

Common Marine Mammal Prey in the Project Area

All 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. Ribbon seals feed primarily on pelagic fish and invertebrates, such as shrimp, crabs, squid, octopus, cod, sculpin, pollack, and capelin. Juveniles feed mostly on krill and shrimp.

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). 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 120 mi east of BP's proposed seismic area) 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).

Recent articles and reports have noted bowhead whales feeding in several areas of the U.S. Beaufort Sea. The Barrow area is commonly used as a feeding area during spring and fall, with a higher proportion of photographed individuals displaying evidence of feeding in fall rather than spring (Mocklin, 2009). A bowhead whale feeding “hotspot” (Okkonen
et al.,
2011) commonly forms on the western Beaufort Sea shelf off Point Barrow in late summer and fall. Favorable conditions concentrate euphausiids and copepods, and bowhead whales congregate to exploit the dense prey (Ashjian
et al.,
2010, Moore
et al.,
2010; Okkonen
et al.,
2011). Surveys have also noted bowhead whales feeding in the Camden Bay area during the fall (Koski and Miller, 2009; Quakenbush
et al.,
2010).

The 2006-2008 BWASP Final Report (Clarke
et al.,
2011a) and the 2009 BWASP Final Report (Clarke
et al.,
2011b) note sightings of feeding bowhead whales in the Beaufort Sea during the fall season. During that 4 year period, the largest groups of feeding whales were sighted between Smith Bay and Point Barrow (hundreds of miles to the west of Prudhoe Bay), and none were sighted feeding in Camden Bay (Clarke
et al.,
2011a,b). Clarke and Ferguson (undated) examined the raw BWASP data from the years 2000-2009. They noted that feeding behavior was noted more often in September than October and that while bowheads were observed feeding throughout the study area (which includes the entire U.S. Beaufort Sea), sightings were less frequent in the central Alaskan Beaufort than they were east of Kaktovik and west of Smith Bay. Additionally, Clarke and Ferguson (undated) and Clarke
et al.
(2011b) refer to information from Ashjian
et al.
(2010), which describes the importance of wind-driven currents that produce favorable feeding conditions for bowhead whales in the area between Smith Bay and Point Barrow. Increased winds in that area may be increasing the incidence of upwelling, which in turn may be the reason for increased sightings of feeding bowheads in the area. Clarke and Ferguson (undated) also note that the incidence of feeding bowheads in the eastern Alaskan Beaufort Sea has decreased since the early 1980s.

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

offshore. Like several of the other species in the area, harbor porpoise feed on demersal and benthic species, mainly schooling fish and cephalopods. Depending on the type of killer whale (transient or resident), they feed on fish and/or marine mammals. However, harbor porpoises and killer whales are not commonly found in Prudhoe Bay.

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). However, the central Beaufort Sea is not known to be a primary feeding ground for gray whales.

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 1.5-2.5 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.

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 Beaufort Sea lagoons 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

With regard to fish as a prey source for odontocetes and seals, 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 commonly used in the production of fish audiograms (Yan, 2004). Generally, most fish have their best hearing in the low-frequency range (i.e., less than 1 kHz). Even though some fish are able to detect sounds in the ultrasonic frequency

range, the thresholds at these higher frequencies tend to be considerably higher than those at the lower end of the auditory frequency range.

Literature relating to the impacts of sound on marine fish species can be divided into the following categories: (1) Pathological effects; (2) physiological effects; and (3) behavioral effects. Pathological effects include lethal and sub-lethal physical damage to fish; physiological effects include primary and secondary stress responses; and behavioral effects include changes in exhibited behaviors of fish. Behavioral changes might be a direct reaction to a detected sound or a result of the anthropogenic sound masking natural sounds that the fish normally detect and to which they respond. The three types of effects are often interrelated in complex ways. For example, some physiological and behavioral effects could potentially lead to the ultimate pathological effect of mortality. Hastings and Popper (2005) reviewed what is known about the effects of sound on fishes and identified studies needed to address areas of uncertainty relative to measurement of sound and the responses of fishes. Popper
et al.
(2003/2004) also published a paper that reviews the effects of anthropogenic sound on the behavior and physiology of fishes.

Potential effects of exposure to sound on marine fish include TTS, physical damage to the ear region, physiological stress responses, and behavioral responses such as startle response, alarm response, avoidance, and perhaps lack of response due to masking of acoustic cues. Most of these effects appear to be either temporary or intermittent and therefore probably do not significantly impact the fish at a population level. The studies that resulted in physical damage to the fish ears used noise exposure levels and durations that were far more extreme than would be encountered under conditions similar to those expected during BP's proposed survey.

The level of sound at which a fish will react or alter its behavior is usually well above the detection level. Fish have been found to react to sounds when the sound level increased to about 20 dB above the detection level of 120 dB (Ona, 1988); however, the response threshold can depend on the time of year and the fish's physiological condition (Engas
et al.,
1993). In general, fish react more strongly to pulses of sound rather than a continuous signal (Blaxter
et al.,
1981), such as the type of sound that will be produced by the drillship, and a quicker alarm response is elicited when the sound signal intensity rises rapidly compared to sound rising more slowly to the same level.

Investigations of fish behavior in relation to vessel noise (Olsen
et al.,
1983; Ona, 1988; Ona and Godo, 1990) have shown that fish react when the sound from the engines and propeller exceeds a certain level. Avoidance reactions have been observed in fish such as cod and herring when vessels approached close enough that received sound levels are 110 dB to 130 dB (Nakken, 1992; Olsen, 1979; Ona and Godo, 1990; Ona and Toresen, 1988). However, other researchers have found that fish such as polar cod, herring, and capeline are often attracted to vessels (apparently by the noise) and swim toward the vessel (Rostad
et al.,
2006). Typical sound source levels of vessel noise in the audible range for fish are 150 dB to 170 dB (Richardson
et al.,
1995a). In calm weather, ambient noise levels in audible parts of the spectrum lie between 60 dB to 100 dB.

Short, sharp sounds can cause overt or subtle changes in fish behavior. Chapman and Hawkins (1969) tested the reactions of whiting (hake) in the field to an airgun. When the airgun was fired, the fish dove from 82 to 180 ft (25 to 55 m) depth and formed a compact layer. The whiting dove when received sound levels were higher than 178 dB re 1 μPa (Pearson
et al.,
1992).

Pearson
et al.
(1992) conducted a controlled experiment to determine effects of strong noise pulses on several species of rockfish off the California coast. They used an airgun with a source level of 223 dB re 1 μPa. They noted:

• Startle responses at received levels of 200-205 dB re 1 μPa and above for two sensitive species, but not for two other species exposed to levels up to 207 dB;

• Alarm responses at 177-180 dB for the two sensitive species, and at 186 to 199 dB for other species;

• An overall threshold for the above behavioral response at about 180 dB;

• An extrapolated threshold of about 161 dB for subtle changes in the behavior of rockfish; and

• A return to pre-exposure behaviors within the 20-60 minute exposure period.

In summary, fish often react to sounds, especially strong and/or intermittent sounds of low frequency. Sound pulses at received levels of 160 dB re 1 μPa may cause subtle changes in behavior. Pulses at levels of 180 dB may cause noticeable changes in behavior (Chapman and Hawkins, 1969; Pearson
et al.,
1992; Skalski
et al.,
1992). It also appears that fish often habituate to repeated strong sounds rather rapidly, on time scales of minutes to an hour. However, the habituation does not endure, and resumption of the strong sound source may again elicit disturbance responses from the same fish.

Some of the fish species found in the Arctic are prey sources for odontocetes and pinnipeds. A reaction by fish to sounds produced by BP's proposed survey would only be relevant to marine mammals if it caused concentrations of fish to vacate the area. Pressure changes of sufficient magnitude to cause that type of reaction would probably occur only very close to the sound source, if any would occur at all. Impacts on fish behavior are predicted to be inconsequential. Thus, feeding odontocetes and pinnipeds would not be adversely affected by this minimal loss or scattering, if any, of reduced prey abundance.

Some mysticetes, including bowhead whales, feed on concentrations of zooplankton. Some feeding bowhead whales may occur in the Alaskan Beaufort Sea in July and August, but feeding bowheads are more likely to occur in the area after the cessation of airgun operations. Reactions of zooplankton to sound are, for the most part, not known. Their ability to move significant distances is limited or nil, depending on the type of zooplankton. Behavior of zooplankters is not expected to be affected by the survey. These animals have exoskeletons and no air bladders. Many crustaceans can make sounds, and some crustacea and other invertebrates have some type of sound receptor. A reaction by zooplankton to sounds produced by the seismic survey would only be relevant to whales if it caused concentrations of zooplankton to scatter. Pressure changes of sufficient magnitude to cause that type of reaction would probably occur only very close to the sound source, if any would occur at all. Impacts on zooplankton behavior are predicted to be inconsequential. Thus, feeding mysticetes would not be adversely affected by this minimal loss or scattering, if any, of reduced zooplankton abundance.

Based on the preceding discussion, the proposed activity is not expected to have any habitat-related effects that could cause significant or long-term consequences for individual marine mammals or their populations.

Proposed Mitigation

In order to issue an incidental take authorization (ITA) under section 101(a)(5)(D) of the MMPA, NMFS must set forth the permissible methods of taking pursuant to such activity, and

other means of effecting the least practicable impact on such species or stock and its habitat, paying particular attention to rookeries, mating grounds, and areas of similar significance, and on the availability of such species or stock for taking for certain subsistence uses (where relevant). Later in this document in the “Proposed Incidental Harassment Authorization” section, NMFS lays out the proposed conditions for review, as they would appear in the final IHA (if issued).

Mitigation Measures Proposed by BP

For the proposed mitigation measures, BP proposed general mitigation measures that apply to all vessels involved in the survey and specific mitigation measures that apply to the source vessels operating airguns. The proposed protocols are discussed next and can also be found in Section 11 of BP's application (see
ADDRESSES
).

1. General Mitigation Measures

These general mitigation measures are proposed to apply to all vessels that are part of the Prudhoe Bay seismic survey, including crew transfer vessels. The two source vessels would also operate under an additional set of specific mitigation measures during airgun operations (described a bit later in this document).

The general mitigation measures include: (1) adjusting speed to avoid collisions with whales and during periods of low visibility; (2) checking the waters immediately adjacent to vessels with propellers to ensure that no marine mammals will be injured; (3) avoiding concentrations of groups of whales and not operating vessels in a way that separates members of a group; (4) reducing vessel speeds to less than 10 knots in the presence of feeding whales; (5) reducing speed and steering around groups of whales if circumstances allow (but never cutting off a whale's travel path) and avoiding multiple changes in direction and speed when within 900 ft of whales; (6) maintaining an altitude of at least 1,000 ft when flying helicopters, except in emergency situations or during take-offs and landings; and (7) not hovering or circling with helicopters above or within 0.3 mi of groups of whales.

2. Seismic Airgun Mitigation Measures

BP proposes to establish and monitor Level A harassment exclusion zones for all marine mammal species. These zones will be monitored by PSOs (more detail later). Should marine mammals enter these exclusion zones, the PSOs will call for and implement the suite of mitigation measures described next.

Ramp-up Procedure:
Ramp-up procedures of an airgun array involve a step-wise increase in the number of operating airguns until the required discharge volume is achieved. The purpose of a ramp-up (sometimes referred to as “soft-start”) is to provide marine mammals in the vicinity of the activity the opportunity to leave the area and to avoid the potential for injury or impairment of their hearing abilities.

During ramp-up, BP proposes to implement the common procedure of doubling the number of operating airguns at 5-minute intervals, starting with the smallest gun in the array. For the 620 in
3
sub-array this is estimated to take approximately 15 minutes and for the 1,240 in
3
airgun array approximately 20 minutes. During ramp-up, the exclusion zone for the full airgun array will be observed. The ramp-up procedures will be applied as follows:

1. A ramp-up, following a cold start, can be applied if the exclusion zone has been free of marine mammals for a consecutive 30-minute period. The entire exclusion zone must have been visible during these 30 minutes. If the entire exclusion zone is not visible, then ramp-up from a cold start cannot begin.

2. Ramp-up procedures from a cold start will be delayed if a marine mammal is sighted within the exclusion zone during the 30-minute period prior to the ramp-up. The delay will last until the marine mammal(s) has been observed to leave the exclusion zone or until the animal(s) is not sighted for at least 15 minutes (seals) or 30 minutes (cetaceans).

3. A ramp-up, following a shutdown, can be applied if the marine mammal(s) for which the shutdown occurred has been observed to leave the exclusion zone or until the animal(s) has not been sighted for at least 15 minutes (seals) or 30 minutes (cetaceans). This assumes there was a continuous observation effort prior to the shutdown and the entire exclusion zone is visible.

4. If, for any reason, power to the airgun array has been discontinued for a period of 10 minutes or more, ramp-up procedures need to be implemented. Only if the PSO watch has been suspended, a 30-minute clearance of the exclusion zone is required prior to commencing ramp-up. Discontinuation of airgun activity for less than 10 minutes does not require a ramp-up.

5. The seismic operator and PSOs will maintain records of the times when ramp-ups start and when the airgun arrays reach full power.

Power Down Procedure:
A power down is the immediate reduction in the number of operating airguns such that the radii of the 190 dB and 180 dB (rms) zones are decreased to the extent that an observed marine mammal is not in the applicable exclusion zone of the full array. During a power down, one airgun (or some other number of airguns less than the full airgun array) continues firing. The continued operation of one airgun is intended to (a) alert marine mammals to the presence of airgun activity, and (b) retain the option of initiating a ramp up to full operations under poor visibility conditions.

1. The array will be immediately powered down whenever a marine mammal is sighted approaching close to or within the applicable exclusion zone of the full array, but is outside the applicable exclusion zone of the single mitigation airgun;

2. Likewise, if a mammal is already within the exclusion zone when first detected, the airguns will be powered down immediately;

3. If a marine mammal is sighted within or about to enter the applicable exclusion zone of the single mitigation airgun, it too will be shut down; and

4. Following a power down, ramp-up to the full airgun array will not resume until the marine mammal has cleared the applicable exclusion zone. The animal will be considered to have cleared the exclusion zone if it has been visually observed leaving the exclusion zone of the full array, or has not been seen within the zone for 15 minutes (seals) or 30 minutes (cetaceans).

Shut-down Procedures:
The operating airgun(s) will be shut down completely if a marine mammal approaches or enters the 190 or 180 dB (rms) exclusion radius of the smallest airgun. Airgun activity will not resume until the marine mammal has cleared the applicable exclusion radius of the full array. The animal will be considered to have cleared the exclusion radius as described above under ramp-up procedures.

Poor Visibility Conditions:
BP plans to conduct 24-hr operations. PSOs will not be on duty during ongoing seismic operations during darkness, given the very limited effectiveness of visual observation at night (there will be no periods of darkness in the survey area until mid-August). The proposed provisions associated with operations at night or in periods of poor visibility include the following:

• If during foggy conditions, heavy snow or rain, or darkness (which may be encountered starting in late August), the full 180 dB exclusion zone is not visible, the airguns cannot commence a ramp-up procedure from a full shut-down; and

• If one or more airguns have been operational before nightfall or before the

onset of poor visibility conditions, they can remain operational throughout the night or poor visibility conditions. In this case ramp-up procedures can be initiated, even though the exclusion zone may not be visible, on the assumption that marine mammals will be alerted by the sounds from the single airgun and have moved away.

BP is aware that available techniques to effectively detect marine mammals during limited visibility conditions (darkness, fog, snow, and rain) are in need of development and has in recent years supported research and field trials intended to improve methods of detecting marine mammals under these conditions. BP intends to continue research and field trials to improve methods of detecting marine mammals during periods of low visibility.

Additional Mitigation Measures Proposed by NMFS

The mitigation airgun will be operated at approximately one shot per minute and will not be operated for longer than three hours in duration during daylight hours and good visibility. In cases when the next start-up after the turn is expected to be during lowlight or low visibility, use of the mitigation airgun may be initiated 30 minutes before darkness or low visibility conditions occur and may be operated until the start of the next seismic acquisition line. The mitigation gun must still be operated at approximately one shot per minute.

Mitigation Conclusions

NMFS has carefully evaluated BP's proposed mitigation measures and considered a range of other measures in the context of ensuring that NMFS prescribes the means of effecting the least practicable impact on the affected marine mammal species and stocks and their habitat. Our evaluation of potential measures included consideration of the following factors in relation to one another:

• The manner in which, and the degree to which, the successful implementation of the measures are expected to minimize adverse impacts to marine mammals;

• The proven or likely efficacy of the specific measure to minimize adverse impacts as planned; and

• The practicability of the measure for applicant implementation.

Any mitigation measure(s) prescribed by NMFS should be able to accomplish, have a reasonable likelihood of accomplishing (based on current science), or contribute to the accomplishment of one or more of the general goals listed below:

1. Avoidance or minimization of injury or death of marine mammals wherever possible (goals 2, 3, and 4 may contribute to this goal).

2. A reduction in the numbers of marine mammals (total number or number at biologically important time or location) exposed to received levels of seismic airguns, or other activities expected to result in the take of marine mammals (this goal may contribute to 1, above, or to reducing harassment takes only).

3. A reduction in the number of times (total number or number at biologically important time or location) individuals would be exposed to received levels of seismic airguns or other activities expected to result in the take of marine mammals (this goal may contribute to 1, above, or to reducing harassment takes only).

4. A reduction in the intensity of exposures (either total number or number at biologically important time or location) to received levels of seismic airguns or other activities expected to result in the take of marine mammals (this goal may contribute to 1, above, or to reducing the severity of harassment takes only).

5. Avoidance or minimization of adverse effects to marine mammal habitat, paying special attention to the food base, activities that block or limit passage to or from biologically important areas, permanent destruction of habitat, or temporary destruction/disturbance of habitat during a biologically important time.

6. For monitoring directly related to mitigation—an increase in the probability of detecting marine mammals, thus allowing for more effective implementation of the mitigation.

Based on our evaluation of the applicant's proposed measures, as well as other measures considered by NMFS, NMFS has preliminarily determined that the proposed mitigation measures provide the means of effecting the least practicable impact on marine mammals species or stocks and their habitat, paying particular attention to rookeries, mating grounds, and areas of similar significance. Proposed measures to ensure availability of such species or stock for taking for certain subsistence uses are discussed later in this document (see “Impact on Availability of Affected Species or Stock for Taking for Subsistence Uses” section).

Proposed Monitoring and Reporting

In order to issue an ITA for an activity, section 101(a)(5)(D) of the MMPA states that NMFS must set forth “requirements pertaining to the monitoring and reporting of such taking”. The MMPA implementing regulations at 50 CFR 216.104 (a)(13) indicate that requests for ITAs must include the suggested means of accomplishing the necessary monitoring and reporting that will result in increased knowledge of the species and of the level of taking or impacts on populations of marine mammals that are expected to be present in the proposed action area. BP submitted information regarding marine mammal monitoring to be conducted during seismic operations as part of the IHA application. That information can be found in Sections 11 and 13 of the application. The monitoring measures may be modified or supplemented based on comments or new information received from the public during the public comment period.

Monitoring measures proposed by the applicant or prescribed by NMFS should accomplish one or more of the following top-level goals:

1. An increase in our understanding of the likely occurrence of marine mammal species in the vicinity of the action, i.e., presence, abundance, distribution, and/or density of species.

2. An increase in our understanding of the nature, scope, or context of the likely exposure of marine mammal species to any of the potential stressor(s) associated with the action (e.g. sound or visual stimuli), through better understanding of one or more of the following: the action itself and its environment (e.g. sound source characterization, propagation, and ambient noise levels); the affected species (e.g. life history or dive pattern); the likely co-occurrence of marine mammal species with the action (in whole or part) associated with specific adverse effects; and/or the likely biological or behavioral context of exposure to the stressor for the marine mammal (e.g. age class of exposed animals or known pupping, calving or feeding areas).

3. An increase in our understanding of how individual marine mammals respond (behaviorally or physiologically) to the specific stressors associated with the action (in specific contexts, where possible, e.g., at what distance or received level).

4. An increase in our understanding of how anticipated individual responses, to individual stressors or anticipated combinations of stressors, may impact either: the long-term fitness and survival of an individual; or the population, species, or stock (e.g. through effects on annual rates of recruitment or survival).

5. An increase in our understanding of how the activity affects marine mammal habitat, such as through effects on prey sources or acoustic habitat (e.g., through characterization of longer-term contributions of multiple sound sources to rising ambient noise levels and assessment of the potential chronic effects on marine mammals).

6. An increase in understanding of the impacts of the activity on marine mammals in combination with the impacts of other anthropogenic activities or natural factors occurring in the region.

7. An increase in our understanding of the effectiveness of mitigation and monitoring measures.

8. An increase in the probability of detecting marine mammals (through improved technology or methodology), both specifically within the safety zone (thus allowing for more effective implementation of the mitigation) and in general, to better achieve the above goals.

Proposed Monitoring Measures

1. Visual Monitoring

Two observers referred to as PSOs will be present on each seismic source vessel. Of these two PSOs, one will be on watch at all times to monitor the 190 and 180 dB exclusion zones for the presence of marine mammals during airgun operations. The main objectives of the vessel-based marine mammal monitoring are as follows: (1) To implement mitigation measures during seismic operations (e.g. course alteration, airgun power down, shut-down and ramp-up); and (2) To record all marine mammal data needed to estimate the number of marine mammals potentially affected, which must be reported to NMFS within 90 days after the survey.

BP intends to work with experienced PSOs. At least one Alaska Native resident, who is knowledgeable about Arctic marine mammals and the subsistence hunt, is expected to be included as one of the team members aboard the vessels. Before the start of the seismic survey, the crew of the seismic source vessels will be briefed on the function of the PSOs, their monitoring protocol, and mitigation measures to be implemented.

On all source vessels, at least one observer will monitor for marine mammals at any time during daylight hours (there will be no periods of total darkness until mid-August). PSOs will be on duty in shifts of a maximum of 4 hours at a time, although the exact shift schedule will be established by the lead PSO in consultation with the other PSOs.

The source vessels will offer suitable platforms for marine mammal observations. Observations will be made from locations where PSOs have the best view around the vessel. During daytime, the PSO(s) will scan the area around the vessel systematically with reticle binoculars and with the naked eye. Because the main purpose of the PSO on board the vessel is detecting marine mammals for the implementation of mitigation measures according to specific guidelines, BP prefers to keep the information to be recorded as concise as possible, allowing the PSO to focus on detecting marine mammals. The following information will be collected by the PSOs:

• Environmental conditions—consisting of sea state (in Beaufort Wind force scale according to NOAA), visibility (in km, with 10 km indicating the horizon on a clear day), and sun glare (position and severity). These will be recorded at the start of each shift, whenever there is an obvious change in one or more of the environmental variables, and whenever the observer changes shifts;

• Project activity—consisting of airgun operations (on or off), number of active guns, line number. This will be recorded at the start of each shift, whenever there is an obvious change in project activity, and whenever the observer changes shifts; and

• Sighting information—consisting of the species (if determinable), group size, position and heading relative to the vessel, behavior, movement, and distance relative to the vessel (initial and closest approach). These will be recorded upon sighting a marine mammal or group of animals.

When marine mammals in the water are detected within or about to enter the designated exclusion zones, the airgun(s) power down or shut-down procedures will be implemented immediately. To assure prompt implementation of power downs and shut-downs, multiple channels of communication between the PSOs and the airgun technicians will be established. During the power down and shut-down, the PSO(s) will continue to maintain watch to determine when the animal(s) are outside the exclusion radius. Airgun operations can be resumed with a ramp-up procedure (depending on the extent of the power down) if the observers have visually confirmed that the animal(s) moved outside the exclusion zone, or if the animal(s) were not observed within the exclusion zone for 15 minutes (seals) or for 30 minutes (cetaceans). Direct communication with the airgun operator will be maintained throughout these procedures.

All marine mammal observations and any airgun power down, shut-down, and ramp-up will be recorded in a standardized format. Data will be entered into or transferred to a custom database. The accuracy of the data entry will be verified daily through QA/QC procedures. Recording procedures will allow initial summaries of data to be prepared during and shortly after the field program, and will facilitate transfer of the data to other programs for further processing and archiving.

2. Fish and Airgun Sound Monitoring

BP proposes to conduct research on fish species in relation to airgun operations, including prey species important to ice seals, during the proposed seismic survey. The North Prudhoe Bay OBS seismic survey offers a unique opportunity to assess the impacts of airgun sounds on fish, specifically on changes in fish abundance in fyke nets that have been sampled in the area for more than 30 years. The monitoring study would occur over a 2-month period during the open-water season. During this time, fish are counted and sized every day, unless sampling is prevented by weather, the presence of bears, or other events. Fish mortality is also noted.

The fish-sampling period coincides with the North Prudhoe seismic survey, resulting in a situation where each of the four fyke nets will be exposed to varying daily exposures to airgun sounds. That is, as source vessels move back and forth across the project area, fish caught in nets will be exposed to different sounds levels at different nets each day. To document relationships between fish catch in each fyke net and received sound levels, BP will attempt to instrument each fyke net location with a recording hydrophone. Recording hydrophones, to the extent possible, will have a dynamic range that extends low enough to record near ambient sounds and high enough to capture sound levels during relatively close approaches by the airgun array (i.e., likely levels as high as about 200 dB re 1 uPa). Bandwidth will extend from about 10 Hz to at least 500 Hz. In addition, because some fish (especially salmonids) are likely to be sensitive to particle velocity instead of or in addition to sound pressure level, BP will attempt to instrument each fyke net location with a recording particle velocity meter. Acoustic and environmental data will be used in statistical models to assess relationships

between acoustic and fish variables. Additional information on the details of the fish monitoring study can be found in Section 13.1 of BP's application (see
ADDRESSES
).

Monitoring Plan Peer Review

The MMPA requires that monitoring plans be independently peer reviewed “where the proposed activity may affect the availability of a species or stock for taking for subsistence uses” (16 U.S.C. 1371(a)(5)(D)(ii)(III)). Regarding this requirement, NMFS' implementing regulations state, “Upon receipt of a complete monitoring plan, and at its discretion, [NMFS] will either submit the plan to members of a peer review panel for review or within 60 days of receipt of the proposed monitoring plan, schedule a workshop to review the plan” (50 CFR 216.108(d)).

NMFS convened an independent peer review panel, comprised of experts in the fields of marine mammal ecology and underwater acoustics, to review BP's Prudhoe Bay OBS Seismic Survey Monitoring Plan. The panel met on January 8-9, 2013, and provided their final report to NMFS on February 25, 2013. The full panel report can be viewed on the Internet at:
http://www.nmfs.noaa.gov/pr/pdfs/permits/openwater/bp_panel2013.pdf
.

NMFS provided the panel with BP's monitoring plan and asked the panel to answer the following questions regarding the plan:

1. Will the applicant's stated objectives effectively further the understanding of the impacts of their activities on marine mammals and otherwise accomplish the goals stated above? If not, how should the objectives be modified to better accomplish the goals above?

2. Can the applicant achieve the stated objectives based on the methods described in the plan?

3. Are there technical modifications to the proposed monitoring techniques and methodologies proposed by the applicant that should be considered to better accomplish their stated objectives?

4. Are there techniques not proposed by the applicant (i.e., additional monitoring techniques or methodologies) that should be considered for inclusion in the applicant's monitoring program to better accomplish their stated objectives?

5. What is the best way for an applicant to present their data and results (formatting, metrics, graphics, etc.) in the required reports that are to be submitted to NMFS (i.e., 90-day report and comprehensive report)?

NMFS shared the panel's report with BP in March 2013. BP originally submitted this IHA application with a monitoring plan to conduct this program during the 2013 open-wa

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Source: Frix Law Library, https://www.frixlaw.com/law-library/documents/fr%3A2014-08352. Public record. Not legal advice.