# Takes of Marine Mammals Incidental To Specified Activities; Taking Marine Mammals Incidental to a Geophysical Survey in the Central Pacific Ocean

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URL: https://www.frixlaw.com/law-library/documents/fr%3A2017-15455

## Record

- **Collection:** Federal Register
- **Document type:** Notice
- **Published:** July 24, 2017
- **Citation:** 82 FR 34352

## Text

DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
RIN 0648-XF330
Takes of Marine Mammals Incidental To Specified Activities; Taking Marine Mammals Incidental to a Geophysical Survey in the Central Pacific Ocean

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 a request from the University of Hawaii (UH) for authorization to take marine mammals incidental to a marine geophysical survey in the Central Pacific Ocean. Pursuant to the Marine Mammal Protection Act (MMPA), NMFS is requesting comments on its proposal to issue an incidental harassment authorization (IHA) to incidentally take marine mammals during the specified activities. NMFS will consider public comments prior to making any final decision on the issuance of the requested MMPA authorization and agency responses will be summarized in the final notice of our decision.

DATES:

Comments and information must be received no later than August 23, 2017.

ADDRESSES:

Comments should be addressed to Jolie Harrison, Chief, Permits and Conservation Division, Office of Protected Resources, National Marine Fisheries Service. Physical comments should be sent to 1315 East-West Highway, Silver Spring, MD 20910 and electronic comments should be sent to
ITP.Carduner@noaa.gov.

Instructions:
NMFS is not responsible for comments sent by any other method, to any other address or individual, or received after the end of the comment period. Comments received electronically, including all attachments, must not exceed a 25-megabyte file size. Attachments to electronic comments will be accepted in Microsoft Word or Excel or Adobe PDF file formats only. All comments received are a part of the public record and will generally be posted online at
www.nmfs.noaa.gov/pr/permits/incidental/research.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.

FOR FURTHER INFORMATION CONTACT:

Jordan Carduner, Office of Protected Resources, NMFS, (301) 427-8401. Electronic copies of the application and supporting documents, as well as a list of the references cited in this document, may be obtained online at:
www.nmfs.noaa.gov/pr/permits/incidental/research.htm.
In case of problems accessing these documents, please call the contact listed above.

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 (as delegated to NMFS) 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.

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

NMFS has defined “negligible impact” in 50 CFR 216.103 as an impact resulting from the specified activity that cannot be reasonably expected to, and is not reasonably likely to, adversely affect the species or stock through effects on annual rates of recruitment or survival.

The MMPA states that the term “take” means to harass, hunt, capture, kill or attempt to harass, hunt, capture, or kill any marine mammal.

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).

National Environmental Policy Act

To comply with the National Environmental Policy Act of 1969 (NEPA; 42 U.S.C. 4321
et seq.
) and NOAA Administrative Order (NAO) 216-6A, NMFS must review our proposed action (
i.e.,
the issuance of an incidental harassment authorization) with respect to potential impacts on the human environment. Accordingly, NMFS is preparing an Environmental Assessment (EA) to consider the environmental impacts associated with the issuance of the proposed IHA. NMFS' EA is available at
www.nmfs.noaa.gov/pr/permits/incidental/research.htm.
We will review all comments submitted in response to this notice prior to concluding our NEPA process or making a final decision on the IHA request.

Summary of Request

On March 15, 2016, NMFS received a request from the UH for an IHA to take marine mammals incidental to conducting a marine geophysical survey in the Central Pacific Ocean. On May 16, 2017, we deemed UH's application for authorization to be adequate and complete. UH's request is for take of a small number of 24 species of marine mammals by Level B harassment and Level A harassment. Neither UH nor NMFS expects mortality to result from this activity, and, therefore, an IHA is appropriate. The planned activity is not expected to exceed one year, hence, we do not expect subsequent MMPA incidental harassment authorizations would be issued for this particular activity.

Description of Proposed Activity

Overview

UH, in collaboration with the Japan Agency for Marine-Earth Science and Technology (JAMSTEC), proposes to conduct a marine seismic survey north of Hawaii in the Central Pacific Ocean over the course of five and a half days in September 2017. The proposed survey would occur north of the Hawaiian Islands, in the approximate area 22.6-25.0° N. and 153.5-157.4° W. (See Figure 1 in IHA application). The project area is partly within the exclusive economic zone (EEZ) of the United States and partly in adjacent international waters. Water depths in the area range from 4000 to 5000 m. The survey would involve one source vessel, the Japan-flagged R/V (research vessel)
Kairei.
The
Kairei
would deploy a 32-airgun array with a total volume of ~7800 cubic inches (in
3
) as an energy source.

Dates and Duration

The seismic survey would be carried out for approximately five and a half days, including three and half days within the Hawaiian Islands EEZ and two days in international waters. The survey would start on approximately September 15, 2017. Exact dates of the activities are not known as they are dependent on logistics and weather conditions. Seismic activities would occur 24 hours per day during the proposed survey.

Specific Geographic Region

The survey would encompass the approximate area 22.6-25.0° N. and 153.5-157.4° W. in the central Pacific Ocean north of Hawaii, partly within the Hawaiian Islands EEZ and partly in international waters. Water depth in the survey area ranges from approximately 4000 to 5000 m. Representative survey track lines are shown in Figure 1 in the IHA application. However, some deviation in actual track lines could be necessary for reasons such as poor data quality, inclement weather, or mechanical issues with the research vessel and/or equipment. The
Kairei
would likely depart from Honolulu, Hawaii and return to Honolulu.

Detailed Description of Specific Activity

Conventional seismic methodology would be used to image a typical/stable oceanic crust, mantle, and the boundary between the Earth's crust and the mantle (called the Mohorovičić discontinuity (Moho)). The data obtained from the survey would be used to help better inform and further refine planning efforts for a proposed “Project Mohole” under consideration for scheduling by the International Ocean Discovery Program (IODP). The total survey effort would consist of ~1083 kilometers (km) of transect lines (Figure 1 in IHA application).

The R/V
Kairei
has a length of 106.0 meters (m), a beam of 16.0 m, and a maximum draft of 4.7 m. Its propulsion system consists of two diesel engines, each producing 2206 kW, which drive the two propellers at 600 revolutions per minute (rpm). The operation speed during seismic acquisition would be ~8.3 km/hour (~4.5 knots (kn)). When not towing seismic survey gear, the
Kairei
typically cruises at 30 km/hour (~16.2 kn) and has a range of ~18,000 km.

During the survey, the
Kairei
would deploy an airgun array (
i.e.,
a certain number of airguns of varying sizes in a certain arrangement) as an energy source (Table 1). An airgun is a device used to emit acoustic energy pulses into the seafloor and generally consists of a steel cylinder that is charged with high-pressure air. Release of the compressed air into the water column generates a signal that reflects (or refracts) off the seafloor and/or subsurface layers having acoustic impedance contrast. When fired, a brief (~0.1 second) pulse of sound is emitted by all airguns nearly simultaneously. The airguns are silent during the intervening periods with the array typically fired on a fixed distance (or shot point) interval. The return signal is recorded by a listening device and later analyzed with computer interpretation and mapping systems used to depict the subsurface.

The airgun array to be used would consist of 32 Bolt Annular Port airguns, with a total volume of ~7800 in
3
. The airguns would be configured as four identical linear arrays or “strings” (See Figure 2 in the IHA application for a visual representation of the strings). Each string would have 8 airguns; the first and last airguns in the strings would be spaced 10 m apart. All 8 airguns in each string would be fired simultaneously. The 4 airgun strings would be towed behind the
Kairei
and would be distributed across an area ~40 m × 10 m. The shot interval would be ~22 seconds. The firing pressure of the array would be ~2000 psi. During firing, a brief (~0.1 s) pulse of sound would be emitted. The airguns would be silent during the intervening periods. The array would be towed at a depth of 10 m. It is expected that the aigun array would be active 24 hours per day during seismic activities. Specifications of the
Kairei'
s airgun array are shown in Table 1. Source levels of the
Kairei'
s airgun array are shown in Table 6.

Table 1—Specifications of the R/V Kairei Airgun Array

Number of airguns
32.

Tow depth of energy source
10 meters (m).

Dominant frequency components
2-120 Hz.

Total volume

~7800 in.
3

Pulse duration
~0.1 second.

Shot interval
~22 seconds.

The receiving system would consist of one 6 km long hydrophone streamer and ocean bottom seismometers (OBSs). As the airgun array is towed along the survey lines, the hydrophone streamer would receive the returning acoustic signals and transfer the data to the on-board processing system. The OBSs would record the returning acoustic signals internally for later analysis. Upon arrival at the survey area, two OBSs would be deployed. The streamer and airgun array would then be deployed, and seismic operations would commence. After completion of seismic operations, the OBSs would be recovered by UH via a separate vessel; the recovery cruise would be funded by the National Science Foundation.

Survey protocols generally involve a predetermined set of survey, or track, lines. The seismic acquisition vessel (source vessel) travels down a linear track for some distance until a line of data is acquired, then turn and acquire data on a different track. In the case of the proposed survey, the two shorter north-south lines would each be surveyed once, while the longer west-east line would be surveyed twice (see Figure 1 in the IHA application).

In addition to the operations of the airgun array, a SeaBeam 3012 multibeam echosounder (MBES) would also be operated from the
Kairei
continuously throughout the survey. The MBES would operate at 12 kilohertz (kHz) and would be hull-mounted on the
Kairei.
The transmitting beamwidth of the MBES would be 2° fore-aft and 150° (max.) athwartship, or 120° (in water up to 4500 m deep), and 100° (in water up to 8000 m).

Proposed mitigation, monitoring, and reporting measures are described in detail later in this document (please see “Proposed Mitigation” and “Proposed Monitoring and Reporting”).

Description of Marine Mammals in the Area of Specified Activities

Section 4 of the application summarizes available information regarding status and trends, distribution and habitat preferences, and behavior and life history, of the potentially affected species. Additional information regarding population trends and threats may be found in NMFS' Stock Assessment Reports (SAR;
www.nmfs.noaa.gov/pr/sars/
), and more general information about these species (
e.g.,
physical and behavioral descriptions) may be found on NMFS' Web site (
www.nmfs.noaa.gov/pr/species/mammals/
).

Table 2 lists all species with expected potential for occurrence in the central Pacific Ocean and summarizes information related to the population or stock, including regulatory status under the MMPA and ESA and potential biological removal (PBR), where known. For taxonomy, we follow Committee on Taxonomy (2016). PBR is defined by the MMPA as the maximum number of animals, not including natural mortalities, that may be removed from a marine mammal stock while allowing that stock to reach or maintain its optimum sustainable population (as

described in NMFS' SARs). While no mortality is anticipated or authorized here, PBR and annual serious injury and mortality from anthropogenic sources are included here as gross indicators of the status of the species and other threats.

Marine mammal abundance estimates presented in this document represent the total number of individuals that make up a given stock or the total number estimated within a particular study or survey area. NMFS' stock abundance estimates for most species represent the total estimate of individuals within the geographic area, if known, that comprises that stock. For some species, this geographic area may extend beyond U.S. waters. All managed stocks in this region are assessed in NMFS' U.S. Pacific SARs (
e.g.,
Carretta
et al.
2017). All values presented in Table 2 are the most recent available at the time of publication and are available in the 2016 SARs (Carretta
et al.
2017), available online at:
www.nmfs.noaa.gov/pr/sars,
except where noted otherwise.

Table 2—Marine Mammals that Could Occur in the Project Area

Species
Stock

ESA/MMPA
status;
strategic

(Y/N)
1

Stock abundance
2
(CV, Nmin, most
recent abundance

survey)
3

PBR
4

Relative
occurrence in
project area

Order Cetartiodactyla—Cetacea—Superfamily Mysticeti (baleen whales)

Family: Balaenopteridae

Humpback whale (
Megaptera novaeangliae
)
5

Central North Pacific
-/-; N
10,103 (0.300; 7,890; 2006)
83
Seasonal; throughout known breeding grounds during winter and spring (most common November through April).

Blue whale (
Balaenoptera musculus
)

Central North Pacific
E/D; Y
81 (1.14; 38; 2010)
0.1
Seasonal; infrequent winter migrant; few sightings, mainly fall and winter; considered rare.

Fin whale (
Balaenoptera physalus
)

Hawaii
E/D; Y
58 (1.12; 27; 2010)
0.1
Seasonal, mainly fall and winter; considered rare.

Sei whale (
Balaenoptera borealis
)

Hawaii
E/D; Y
178 (0.90; 93; 2010)
0.2
Rare; limited sightings of seasonal migrants that feed at higher latitudes.

Bryde's whale (
Balaenoptera brydei/edeni
)

Hawaii
-/-; N
798 (0.28; 633; 2010)
6.3
Uncommon; distributed throughout the Hawaiian Exclusive Economic Zone.

Minke Whale (
Balaenoptera acutorostrata
)

Hawaii
-/-; N
n/a (n/a; n/a; 2010)
Undet.
Seasonal, mainly fall and winter; considered rare.

Order Cetartiodactyla—Cetacea—Superfamily Odontoceti (toothed whales, dolphins, and porpoises
)

Family: Physeteridae

Sperm whale (
Physeter macrocephalus
)

Hawaii
E/D; Y
3,354 (0.34; 2,539; 2010)
10.2
Widely distributed year round.

Order Cetartiodactyla—Cetacea—Superfamily Odontoceti (toothed whales, dolphins, and porpoises)

Family: Kogiidae

Pygmy sperm whale
6
(
Kogia breviceps
)

Hawaii
-/-; N
7,139 (2.91; n/a; 2006)
Undet.
Widely distributed year round.

Dwarf sperm whale
6
(
Kogia sima
)

Hawaii
-/-; N
17,519 (7.14; n/a; 2006)
Undet.
Widely distributed year round.

Order Cetartiodactyla—Cetacea—Superfamily Odontoceti (toothed whales, dolphins, and porpoises
)

Family: Delphinidae

Killer whale (
Orcinus orca
)

Hawaii
-/-; N
101 (1.00; 50; 2010)
1
Uncommon; infrequent sightings.

False killer whale (
Pseudorca crassidens
)

Hawaii Pelagic
-/-; N
1,540 (0.66; 928; 2010)
9.3
Regular.

Pygmy killer whale (
Feresa attenuata
)

Hawaii
-/-; N
3,433 (0.52; 2,274; 2010)
23
Year-round resident.

Short-finned pilot whale (
Globicephala macrorhynchus
)

Hawaii
-/-; N
12,422 (0.43; 8,872; 2010)
70
Commonly observed around Main Hawaiian Islands and Northwestern Hawaiian Islands.

Melon headed whale (
Peponocephala electra
)

Hawaiian Islands
-/-; N
5,794 (0.20; 4,904; 2010)
4
Regular.

Bottlenose dolphin (
Tursiops truncatus
)

Hawaii pelagic
-/-; N
5,950 (0.59; 3,755; 2010)
38
Common in deep offshore waters.

Pantropical spotted dolphin (
Stenella attenuata
)

Hawaii pelagic
-/-; N
15,917 (0.40; 11,508; 2010)
115
Common; primary occurrence between 100 and 4,000 m depth.

Striped dolphin (
Stenella coeruleoala
)

Hawaii
-/-; N
20,650 (0.36; 15,391; 2010)
154
Occurs regularly year round but infrequent sighting during survey.

Spinner dolphin
6
(
Stenella longirostris
)

Hawaii pelagic
-/-; N
3,351 (0.74; n/a; 2006)
Undet.
Common year-round in offshore waters.

Rough-toothed dolphin (
Steno bredanensis
)

Hawaii
-/-; N
6,288 (0.39; 4,581; 2010)
46
Common throughout the Main Hawaiian Islands and Hawaiian Islands EEZ.

Fraser's dolphin (
Lagenodelphis hosei
)

Hawaii
-/-; N
16,992 (0.66; 10,241; 2010)
102
Tropical species only recently documented within Hawaiian Islands EEZ (2002 survey).

Risso's dolphin (
Grampus griseus
)

Hawaii
-/-; N
7,256 (0.41; 5,207; 2010)
42
Previously considered rare but multiple sightings in Hawaiian Islands EEZ during various surveys conducted from 2002-2012.

Order Cetartiodactyla—Cetacea—Superfamily Odontoceti (toothed whales, dolphins, and porpoises)

Family: Ziphiidae

Cuvier's beaked whale (
Ziphius cavirostris
)

Hawaii
-/-; N
1,941 (n/a; 1,142; 2010)
11.4
Year-round occurrence but difficult to detect due to diving behavior.

Blainville's beaked whale (
Mesoplodon densirostris
)

Hawaii
-/-; N
2,338 (1.13; 1,088; 2010)
11
Year-round occurrence but difficult to detect due to diving behavior.

Longman's beaked whale (
Indopacetus pacificus
)

Hawaii
-/-; N
4,571 (0.65; 2,773; 2010)
28
Considered rare; however, multiple sightings during 2010 survey.

1
Endangered Species Act (ESA) status: Endangered (E), Threatened (T)/MMPA status: Depleted (D). A dash (−) indicates that the species is not listed under the ESA or designated as depleted under the MMPA. Under the MMPA, a strategic stock is one for which the level of direct human-caused mortality exceeds PBR (see footnote 3) or which is determined to be declining and likely to be listed under the ESA within the foreseeable future. Any species or stock listed under the ESA is automatically designated under the MMPA as depleted and as a strategic stock.

2
Abundance estimates from Carretta
et al.
(2017) unless otherwise noted.

3
CV is coefficient of variation; N
min
is the minimum estimate of stock abundance. In some cases, CV is not applicable. For certain stocks, abundance estimates are actual counts of animals and there is no associated CV. The most recent abundance survey that is reflected in the abundance estimate is presented; there may be more recent surveys that have not yet been incorporated into the estimate.

4
Potential biological removal (PBR), defined by the MMPA as the maximum number of animals, not including natural mortalities, that may be removed from a marine mammal stock while allowing that stock to reach or maintain its optimum sustainable population size (OSP).

5
Values for humpback whale are from the 2015 Alaska SAR (Muto
et al.
2015).

6
Values for spinner dolphin, dwarf and pygmy sperm whale are from Barlow
et al.
(2006).

All species that could potentially occur in the proposed survey area are included in Table 2. We have reviewed UH's species descriptions, including life history information, distribution, regional distribution, diving behavior, and acoustics and hearing, for accuracy and completeness. We refer the reader to Section 4 of UH's IHA application, rather than reprinting the information here. Below, for the 24 species that are likely to be taken by the activities described, we offer a brief introduction to the species and relevant stock as well as available information regarding population trends and threats, and describe any information regarding local occurrence.

Humpback Whale

Humpback whales are found worldwide in all ocean basins. In winter, most humpback whales occur in the subtropical and tropical waters of the Northern and Southern Hemispheres (Muto
et al.,
2015). These wintering grounds are used for mating, giving birth, and nursing new calves. Humpback whales migrate nearly 3,000 mi (4,830 km) from their winter breeding grounds to their summer foraging grounds in Alaska.

There are five stocks of humpback whales, one of which occurs in Hawaii: The Central North Pacific Stock, which consists of winter/spring populations in the Hawaiian Islands, which migrate primarily to northern British Columbia/Southeast Alaska, the Gulf of Alaska, and the Bering Sea/Aleutian Islands (Muto
et al.,
2015). Humpback whales occur seasonally in Hawaii, with peak sightings between December and May each year; however, sightings have occurred in other months in very low numbers. Most humpback whales congregate off the island of Maui in the shallow protected waters but can be seen off all of the islands including the Northwestern Hawaiian Islands (Baird 2016).

Humpback whales were listed as endangered under the Endangered Species Conservation Act (ESCA) in June 1970. In 1973, the ESA replaced the ESCA, and humpbacks continued to be listed as endangered. NMFS recently evaluated the status of the species, and on September 8, 2016, NMFS divided the species into 14 distinct population segments (DPS), removed the current species-level listing, and in its place listed four DPSs as endangered and one DPS as threatened (81 FR 62259; September 8, 2016). The remaining nine DPSs were not listed. The Hawaii DPS is the only DPS that occurs in the survey area and is not listed under the ESA (81 FR 62259; September 8, 2016). The Central North Pacific stock is still considered a depleted and strategic stock under the MMPA.

Blue Whale

The blue whale has a cosmopolitan distribution and tends to be pelagic, only coming nearshore to feed and possibly to breed (Jefferson
et al.
2008). Blue whale migration is less well defined than for some other rorquals, and their movements tend to be more closely linked to areas of high primary productivity, and hence prey, to meet their high energetic demands (Branch
et al.
2007). Generally, blue whales are seasonal migrants between high latitudes in the summer, where they feed, and low latitudes in the winter, where they mate and give birth (Lockyer and Brown 1981). Some individuals may stay in low or high latitudes throughout the year (Reilly and Thayer 1990; Watkins
et al.
2000). Blue whales belonging to the central Pacific stock appear to feed in summer southwest of Kamchatka, south of the Aleutians, and in the Gulf of Alaska (Stafford 2003; Watkins
et al.
2000), and in winter migrate to lower latitudes in the western and central Pacific, including Hawaii (Stafford
et al.
2001).

From ship line-transect surveys, Wade and Gerrodette (1993) estimated 1,400 blue whales for the eastern tropical Pacific. A 2010 shipboard line-transect survey of the entire Hawaiian Islands EEZ resulted in a summer/fall abundance estimate of 81 (CV = 1.14) blue whales (Bradford
et al.
2013). This is currently the best available abundance estimate for this stock within the Hawaii EEZ, though the majority of blue whales would be expected to be at higher latitudes feeding grounds at this time of year. Blue whales are listed as endangered under the ESA, and the Central North Pacific Stock of blue whales is considered a depleted and strategic stock under the MMPA.

Fin Whale

Fin whales are found throughout all oceans from tropical to polar latitudes. They have been considered rare in Hawaiian waters and are absent to rare in eastern tropical Pacific waters (Hamilton
et al.
2009). The fin whale most commonly occurs offshore but can also be found in coastal areas (Aguilar 2009). Most populations migrate seasonally between temperate waters where mating and calving occur in winter, and polar waters where feeding occurs in summer (Aguilar 2009). However, recent evidence suggests that some animals may remain at high latitudes in winter or low latitudes in summer (Edwards
et al.
2015).

During spring and summer, fin whale occurrence in Hawaii is considered rare (DoN 2005). There were 5 sightings of fin whales during summer-fall surveys in 2002, most to the northwest of the Main Hawaiian Islands (Barlow
et al.
2004) and two sightings in the Hawaiian Islands EEZ during summer-fall 2010 (Bradford
et al.
2013); there were no sightings in or near the proposed survey area (Carretta
et al.
2015). Two additional sightings in the EEZ were made by observers on Hawaii-based longline fishing vessels, including one near the proposed survey area (Carretta
et al.
2015). Fin whales are listed as endangered under the ESA, and the Hawaii stock of fin whales is considered depleted under the MMPA.

Sei Whale

The sei whale occurs in all ocean basins (Horwood 2009) but appears to prefer mid-latitude temperate waters (Jefferson
et al.
2008). It undertakes seasonal migrations to feed in subpolar latitudes during summer and returns to lower latitudes during winter to calve (Horwood 2009). The sei whale is pelagic and generally not found in coastal waters (Harwood and Wilson 2001). It occurs in deeper waters characteristic of the continental shelf edge region (Hain
et al.
1985) and in other regions of steep bathymetric relief such as seamounts and canyons (Kenney and Winn 1987; Gregr and Trites 2001).

Sei whales occur seasonally in Hawaii in the winter and spring months and feed in higher latitude feeding grounds in the summer and fall (Carretta
et al.,
2016). Sightings of this species are rare in Hawaii. The species stays offshore of the islands in deeper waters (Baird 2016). Sei whales are listed as endangered under the ESA, and the Hawaii stock of sei whales is considered a depleted and strategic stock under the MMPA.

Bryde's Whale

The Bryde's whale occurs in all tropical and warm temperate waters in the Pacific, Atlantic, and Indian oceans, between 40° N. and 40° S. (Kato and Perrin 2009). Although there is a pattern of movement toward the Equator in the winter and the poles during the summer, Bryde's whale does not undergo long seasonal migrations, remaining in warm (>16 °C) water year-round (Kato and Perrin 2009).

Bryde's whales are known to occur in both shallow coastal and deeper offshore waters (Jefferson
et al.
2008). In Hawaii, Bryde's whales are typically seen offshore (
e.g.,
Barlow
et al.
2004; Barlow 2006), but Hopkins
et al.
(2009) reported a Bryde's whale within 70 km of the Main Hawaiian Islands. During summer-fall surveys of the Hawaiian Islands EEZ, 13 sightings were made in 2002 (Barlow 2006) and 32 sightings were made during 2010 (Bradford
et al.
2013). Bryde's whales were primarily sighted in the western half of the Hawaiian Islands EEZ, with the majority of sightings associated with the Northwestern Hawaiian Islands; none was made in or near the proposed survey area (Barlow
et al.
2004; Barlow 2006; Bradford
et al.
2013; Carretta
et al.
2015). The Bryde's whale is not listed under the ESA, and the Hawaii stock is not listed as depleted or strategic under the MMPA.

Minke Whale

The minke whale has a cosmopolitan distribution ranging from the tropics and subtropics to the ice edge in both hemispheres (Jefferson
et al.
2008) and is thought to occur seasonally in Hawaii, from November through March (Rankin and Barlow 2005), though their migration routes or destinations are unknown. While they are generally believed to be uncommon in Hawaiian waters, several studies using acoustic detections suggest that minke whales may be more common than previously thought (Rankin
et al.
2007; Oswald
et al.
2011; Martin
et al.
2012). Acoustic detections have been recorded around the Hawaiian Islands during fall-spring surveys in 1997 and 2000-2006 (Rankin and Barlow 2005; Barlow
et al.
2008; Rankin
et al.
2008), and from seafloor hydrophones positioned ~50 km from the coast of Kauai during February-April 2006 (Martin
et al.
2012). Passive acoustic detections of minke whales have been recorded at ALOHA station (22.75° N., 158° W.) from October to May for decades (Oswald
et al.
2011). A lack of sightings is likely related to misidentification or low detection capability in poor sighting conditions (Rankin
et al.
2007). The minke whale is not listed under the ESA, and the Hawaii stock is not listed as depleted under the MMPA.

Sperm Whale

Sperm whales are widely distributed across the entire North Pacific and into the southern Bering Sea in summer, but the majority are thought to be south of 40° N. in winter (Rice 1974, 1989; Gosho
et al.
1984; Miyashita
et al.
1995). The Hawaii stock includes animals found both within the Hawaiian Islands EEZ and in adjacent high seas waters; however, because data on abundance, distribution, and human-caused impacts are largely lacking for high seas waters, the status of the Hawaii stock is evaluated based on data from U.S. EEZ waters of the Hawaiian Islands (NMFS 2005).

Sperm whales are widely distributed in Hawaiian waters throughout the year (Mobley
et al.
2000). During summer-fall surveys of the Hawaiian Islands EEZ, 43 sightings were made in 2002 (Barlow 2006) and 41 were made in 2010 (Bradford
et al.
2013). Sightings were widely distributed across the EEZ during both surveys; numerous sightings occurred in and adjacent to the proposed survey area (Barlow
et al.
2004; Barlow 2006; Bradford
et al.
2013). Sperm whales are listed as endangered under the ESA, and the Hawaii stock is considered depleted and strategic under the MMPA.

Pygmy Sperm Whale

Pygmy sperm whales are found in tropical and warm-temperate waters throughout the world (Ross and Leatherwood 1994) and prefer deeper waters with observations of this species in greater than 4,000 m depth (Baird
et al.,
2013). Sightings are rare of this species. They are difficult to sight at sea, because of their dive behavior and perhaps because of their avoidance reactions to ships and behavior changes in relation to survey aircraft (Würsig
et al.
1998). Both pygmy and dwarf sperm whales are sighted primarily along the continental shelf edge and slope and over deeper waters off the shelf (Hansen
et al.
1994; Davis
et al.
1998; Jefferson
et al.
2008). There is a single stock of Pygmy sperm whales in Hawaii. Current abundance estimates for this stock are unknown. Pygmy sperm whales are not listed as endangered or threatened under the ESA, and the Hawaii stock is not considered strategic or designated as depleted under the MMPA.

Dwarf Sperm Whale

Dwarf sperm whales are found throughout the world in tropical to

warm-temperate waters (Carretta
et al.,
2014). They are usually found in waters deeper than 500 m, most often sighted in depths between 500 and 1,000 m, but they have been documented in depths as shallow as 106 m and as deep as 4,700 m (Baird 2016). This species is often alone or in small groups of up to two to four individuals (Baird 2016). When there are more than two animals together, they are often loosely associated, with up to several hundred meters between pairs of individuals (Baird 2016). There is one stock of dwarf sperm whales in Hawaii. Sighting data suggests a small resident population off Hawaii Island (Baird 2016). It has been suggested that this species is probably one of the more abundant species of cetaceans in Hawaiian waters (Baird 2016), though there are no current abundance estimates for this stock. Dwarf sperm whales are not listed as endangered or threatened under the ESA, and the Hawaii stock is not designated as depleted or strategic under the MMPA.

Killer Whale

Killer whales have been observed in all oceans and seas of the world (Leatherwood and Dahlheim 1978). Although reported from tropical and offshore waters (Heyning and Dahlheim 1988), killer whales prefer the colder waters of both hemispheres, with greatest abundances found within 800 km of major continents (Mitchell 1975). High densities of the species occur in high latitudes, especially in areas where prey is abundant.

Killer whales are considered rare in Hawaiian waters (Carretta
et al.
2017). Twenty one sighting records were reported in Hawaiian waters between 1994 and 2004 (Baird
et al.
2006). During summer-fall surveys of the Hawaiian Islands EEZ, two sightings were made in 2002 (Barlow
et al.
2004; Barlow 2006) and one was made in 2010 (Bradford
et al.
2013), none near the proposed survey area (Barlow et al. 2004; Bradford
et al.
2013; Carretta
et al.
2017). Numerous additional sightings in and north of the EEZ have been made by observers on longliners, some in and near the proposed survey area (Carretta
et al.
2017). Killer whales are not listed as endangered or threatened under the ESA (with the exception of the endangered Southern Resident DPS which does not occur in the survey area), and the Hawaii stock is not designated as depleted or strategic under the MMPA.

False Killer Whale

False killer whales are found worldwide in tropical and warm-temperate waters (Stacey et al. 1994). In the North Pacific, this species is well known from southern Japan, Hawaii, and the eastern tropical Pacific. The species generally inhabits deep, offshore waters, but sometimes is found over the continental shelf and occasionally moves into very shallow water (Jefferson
et al.
2008; Baird 2009).

Telemetry, photo-identification, and genetic studies have identified three independent populations of false killer whales in Hawaiian waters: Main (insular) Hawaiian Islands, Northwestern Hawaiian Islands, and surrounding pelagic stock (Chivers
et al.
2010; Baird
et al.
2010, 2013; Bradford
et al.
2014). Based on the ranges of these stocks, only the Hawaii pelagic stock is expected to occur in the survey area (Carretta
et al.
2017). False killer whales are not listed as endangered or threatened under the ESA (with the exception of the endangered Main Hawaiian Islands insular DPS which does not occur in the survey area), and the Hawaii pelagic stock is not designated as depleted or strategic under the MMPA.

Pygmy Killer Whale

The pygmy killer whale has a worldwide distribution in tropical and subtropical waters (Donahue and Perryman 2009), generally not ranging south of 35° S. (Jefferson
et al.
2008). In warmer water, it is usually seen close to the coast (Wade and Gerrodette 1993), but it is also found in deep waters. In Hawaiian waters, the pygmy killer whale is found in nearshore waters but rarely offshore (Carretta
et al.
2015). During small-boat surveys around the Hawaiian Islands in 2000-2012, sightings were made in water up to 3,000 m deep (Baird
et al.
2013).

Though a small resident population occurs in the main Hawaiian Islands, pygmy killer whales are relatively rare in Hawaiian waters (McSweeney
et al.
2009). Satellite telemetry data from four tagged pygmy killer whales suggest the resident group remains within 20 km of shore (Baird
et al.
2011) so would be unlikely in the proposed survey area. Movements have been documented between Hawaii Island and Oahu and between Oahu and Lanai (Baird
et al.
2011a). Pygmy killer whales are not listed under the ESA, and the Hawaii stock is not listed as is not considered a depleted or strategic stock under the MMPA.

Short-Finned Pilot Whale

Short-finned pilot whales are found in all oceans, primarily in tropical and warm-temperate waters (Carretta
et al.,
2016). The species prefers deeper waters, ranging from 324 m to 4,400 m, with most sightings between 500 m and 3,000 m (Baird 2016). This stock forms stable social groups, with average group size of 18 individuals but may form large aggregations of close to 200 individuals (Baird 2016). Other research suggests a larger average group size of 40.9 individuals (Bradford
et al.,
2017), but most of these sightings were farther offshore in pelagic waters.

Short-finned pilot whales are commonly observed around the main Hawaiian Islands and are also present around the Northwestern Hawaiian Islands (Shallenberger 1981, Baird
et al.
2013). Photo-identification and telemetry studies suggest there may be inshore and pelagic populations of short finned pilot whales in Hawaiian waters. Resighting and social network analyses of individuals photographed off Hawaii Island suggest the occurrence of one large and several smaller social clusters that use those waters, with some individuals within the smaller social clusters commonly resighted off Hawaii Island (Mahaffy 2012). Short-finned pilot whales are not listed as endangered or threatened under the ESA, and the Hawaii stock is not considered a depleted or strategic stock under the MMPA.

Melon-Headed Whale

Melon-headed whales are found in tropical and warm-temperate waters throughout the world (Carretta
et al.,
2016). The distribution of reported sightings suggests that the oceanic habitat of this species is primarily equatorial waters (Perryman
et al.
1994). The species forms large groups, with average group size of almost 250 individuals, with the largest group documented at close to 800 individuals (Baird 2016).

There are two demographically-independent populations in Hawaiian waters, the Hawaiian Islands stock and the Kohala resident stock (Carretta
et al.,
2016). The Kohala resident stock have a small range restricted to the shallow waters around Hawaii Island, whereas the Hawaiian Islands stock are found throughout the islands and offshore in pelagic areas (Carretta
et al.,
2016). As such, only the Hawaiian Islands stock may be affected by the proposed activities. This stock prefers waters deeper than 1,000 m (Baird 2016). Satellite telemetry data revealed distant pelagic movements, associated with feeding, nearly to the edge of the Hawaiian Islands EEZ; the most distal telemetry locations were near the proposed survey area at ~22.3° N., 154.0° W. (Oleson
et al.
2013). Melon-headed whales are not listed as

endangered or threatened under the ESA and the Hawaiian Islands stock is not considered a depleted or strategic stock under the MMPA.

Bottlenose Dolphin

Bottlenose dolphins are widely distributed throughout the world in tropical and warm-temperate waters (Perrin
et al.
2009). Generally, there are two distinct bottlenose dolphin ecotypes: One mainly found in coastal waters and one mainly found in oceanic waters (Duffield
et al.
1983; Hoelzel
et al.
1998; Walker
et al.
1999). As well as inhabiting different areas, these ecotypes differ in their diving abilities (Klatsky 2004) and prey types (Mead and Potter 1995).

There are four resident insular stocks of bottlenose dolphins around the Main Hawaiian Islands and one pelagic stock (Carretta
et al.,
2016). Photo-identification studies have suggested that the 1,000-m isobath serves as the boundary between resident insular stocks of the Main Hawaiian Islands and the Hawaii pelagic stock (Martien
et al.
2012). Only the pelagic stock may be affected by the proposed activity. Bottlenose dolphins are not listed as endangered or threatened under the ESA, and the Hawaii pelagic stock is not considered a depleted or strategic stock under the MMPA.

Pantropical Spotted Dolphin

Pantropical spotted dolphins are primarily found in tropical and subtropical waters worldwide (Perrin
et al.
2009). There are two forms of pantropical spotted dolphin: Coastal and offshore. Pantropical spotted dolphins prefer deeper waters between 1,500 m and 3,000 m and forms large groups with average group size of 60 individuals, with the largest group estimated at 400 individuals (Baird 2016).

Pantropical spotted dolphins are common and abundant throughout the Hawaiian archipelago (Baird
et al.
2013). It is expected that it would be one of the most abundant cetaceans in the proposed survey area. There are four resident coastal stocks in Hawaii in addition to the Hawaii pelagic stock. Due to their ranges, only the pelagic stock is likely to be encountered in the project area (Carretta
et al.,
2016). Pantropical spotted dolphins are not listed as endangered or threatened under the ESA, and the Hawaii pelagic stock is not considered a depleted or strategic stock under the MMPA.

Striped Dolphin

Striped dolphins are found in tropical to warm-temperate waters throughout the world (Carretta
et al.,
2016). This is a deep water species, preferring depths greater than 3,500 m (Baird 2016). Striped dolphins occur primarily in pelagic waters, but have been observed approaching shore where there is deep water close to the coast (Jefferson
et al.
2008). This species forms large groups, with an average group size of 28 individuals, and a maximum group size of 100 individuals (Baird 2016).

The striped dolphin is expected to be one of the most abundant cetaceans in the proposed survey area. It has been sighted near the proposed survey area during summer-fall shipboard surveys of the Hawaii Islands EEZ (Carretta
et al.
2017). Striped dolphins are not listed as endangered or threatened under the ESA, and the Hawaii stock of striped dolphins is not considered a depleted or strategic stock under the MMPA.

Spinner Dolphin

Spinner dolphins are found in tropical and warm-temperate waters worldwide (Carretta
et al.,
2016). They are pantropical in distribution, including oceanic tropical and sub-tropical waters between 40° N. and 40° S. (Jefferson
et al.,
2008). Generally considered a pelagic species (Perrin 2009b), spinner dolphins can also be found in coastal waters and around oceanic islands (Rice 1998). There are six separate stocks managed within the Hawaiian Islands EEZ (Carretta
et al.
2017); only individuals of the Hawaii pelagic stock are expected to overlap with the proposed survey area. Spinner dolphins have been sighted near the proposed survey area during summer-fall surveys of the Hawaiian Islands EEZ (Carretta
et al.
2017). The spinner dolphin is not listed as endangered or threatened under the ESA, and the Hawaii pelagic stock is not considered a depleted or strategic stock under the MMPA.

Rough-Toothed Dolphin

Rough-toothed dolphins are found in tropical and warm-temperate waters (Carretta
et al.,
2016). While there is evidence for two island-associated stocks and one pelagic stock in Hawaii, there is only one stock designated for Hawaii (Carretta
et al.,
2016). Most sightings of this species off Kauai are in water depths of less than 1,000 m; however, it is the most often sighted species in depths greater than 3,000 m (Baird 2016). This species forms stable associations as part of larger groups, with average group sizes of 11 animals and maximum group sizes, observed off Kauai, of 140 individuals (Baird 2016).

The rough-toothed dolphin is expected to be one of the most abundant cetaceans in the proposed survey area (Barlow
et al.
2004; Barlow 2006; Bradford
et al.
2013). During summer-fall surveys of the Hawaiian Islands EEZ in 2002 and 2010, rough-toothed dolphins were observed throughout the EEZ and near the proposed survey area. The rough-toothed dolphin is not listed as endangered or threatened under the ESA, and the Hawaii stock is not considered a depleted or strategic stock under the MMPA.

Fraser's Dolphin

Fraser's dolphin are found in tropical waters (Carretta
et al.,
2011). This is a deep water species occurring offshore of the Hawaiian islands, with sightings occurring in water depths between 1,515 m and 4,600 m (Baird 2016). The species forms large groups with average group sizes between 75 and 110 individuals (Baird 2016). Fraser's dolphin is one of the most abundant cetaceans in the Hawaiian Islands EEZ (Barlow 2006; Bradford
et al.
2013). Fraser's dolphin is not listed as endangered or threatened under the ESA, and the Hawaii stock is not considered a depleted or strategic stock under the MMPA.

Risso's Dolphin

Risso's dolphins are found in tropical to warm-temperate waters (Carretta
et al.,
2016). The species occurs from coastal to deep water but is most often found in depths greater than 3,000 m with the highest sighting rate in depths greater than 4,500 m (Baird 2016). It occurs between 60° N. and 60° S. where surface water temperatures are at least 10º C (Kruse
et al.
1999). The species forms small groups with an average group size of 4 individuals, and a maximum group size of 25 individuals off the coast of Hawaii (Baird 2016). Risso's dolphins are not listed as endangered or threatened under the ESA, and the Hawaii stock is not considered a depleted or strategic stock under the MMPA.

Longman's Beaked Whale

The Longman's beaked whale, also known as Indo-Pacific beaked whale, is considered one of the least known cetacean species (Carretta
et al.,
2016). Longman's beaked whales are found in tropical waters from the eastern Pacific westward through the Indian Ocean to the eastern coast of Africa (Carretta
et al.,
2016). The species occurs is most often sighted in waters with temperatures ≥26° C and depth >2,000 m, and sightings have also been reported along the continental slope (Anderson
et al.
2006; Pitman 2009). Group sizes range from 18 to 110

individuals (Baird 2016). The Longman's beaked whale is not listed as endangered or threatened under the ESA, and the Hawaii stock is not considered a depleted or strategic stock under the MMPA.

Cuvier's Beaked Whale

Cuvier's beaked whale is the most widespread of the beaked whales occurring in almost all temperate, subtropical, and tropical waters and even some sub-polar and polar waters (MacLeod
et al.
2006). It is found in deep water over and near the continental slope (Jefferson
et al.
2008). In the eastern tropical Pacific, the mean water depth for sighted Cuvier's beaked whales was ~3.4 km (Ferguson
et al.
2006). During small-boat surveys around the Hawaiian Islands in 2000-2012, sightings were made in water depths of 500-4000 m (Baird
et al.
2013). Summer/fall shipboard surveys of the waters within the U.S. EEZ of the Hawaiian Islands resulted in 4 sightings in 2002 and 22 in 2010, including markedly higher sighting rates during nearshore surveys in the Northwestern Hawaiian Islands. (Barlow 2006, Bradford
et al.
2013). Resighting and movement data of individual Cuvier's beaked whales suggest the existence of insular and offshore populations of this species in Hawaiian waters. A 21-yr study off Hawaii Island suggests long-term site fidelity and year-round occurrence (McSweeney
et al.
2007). The Cuvier's beaked whale is not listed as endangered or threatened under the ESA, and the Hawaii stock is not considered a depleted or strategic stock under the MMPA.

Blainville's Beaked Whale

Blainville's beaked whale is found in tropical and warm temperate waters of all oceans; it has the widest distribution throughout the world of all mesoplodont species and appears to be common (Pitman 2009b). Recent analysis of Blainville's beaked whale resightings and movements near the main Hawaiian Islands suggest the existence of insular and pelagic populations of this species in Hawaiian waters (McSweeney
et al.
2007, Schorr
et al.
2009, Baird
et al.
2013). Photo-identification of individual Blainville's beaked whales from Hawaii Island since 1986 reveal repeated use of this area by individuals for over 17 years (Baird
et al.
2011) and 75% of individuals seen off Hawaii Island link by association into a single social network (Baird
et al.
2013). Those individuals seen farthest from shore and in deep water (>2100m) have not been resighted, suggesting they may be part of an offshore, pelagic population (Baird
et al.
2011). The Hawaii stock of Blainville's beaked whales includes animals found both within the Hawaiian Islands EEZ and in adjacent high seas waters. The Blainville's beaked whale is not listed as endangered or threatened under the ESA, and the Hawaii stock is not considered a depleted or strategic stock under the MMPA.

Potential Effects of Specified Activities on Marine Mammals and Their Habitat

This section includes a summary and discussion of the ways that components of the specified activity may impact marine mammals and their habitat. The “Estimated Take by Incidental Harassment” section later in this document includes a quantitative analysis of the number of individuals that are expected to be taken by this activity. The “Negligible Impact Analysis and Determination” section considers the content of this section, the “Estimated Take by Incidental Harassment” section, and the “Proposed Mitigation” section, to draw conclusions regarding the likely impacts of these activities on the reproductive success or survivorship of individuals and how those impacts on individuals are likely to impact marine mammal species or stocks.

Description of Active Acoustic Sound Sources

This section contains a brief technical background on sound, the characteristics of certain sound types, and on metrics used in this proposal inasmuch as the information is relevant to the specified activity and to a discussion of the potential effects of the specified activity on marine mammals found later in this document.

Sound travels in waves, the basic components of which are frequency, wavelength, velocity, and amplitude. Frequency is the number of pressure waves that pass by a reference point per unit of time and is measured in hertz (Hz) or cycles per second. Wavelength is the distance between two peaks or corresponding points of a sound wave (length of one cycle). Higher frequency sounds have shorter wavelengths than lower frequency sounds, and typically attenuate (decrease) more rapidly, except in certain cases in shallower water. Amplitude is the height of the sound pressure wave or the “loudness” of a sound and is typically described using the relative unit of the decibel (dB). A sound pressure level (SPL) in dB is described as the ratio between a measured pressure and a reference pressure (for underwater sound, this is 1 microPascal (μPa)) and is a logarithmic unit that accounts for large variations in amplitude; therefore, a relatively small change in dB corresponds to large changes in sound pressure. The source level (SL) represents the SPL referenced at a distance of 1 m from the source (referenced to 1 μPa) while the received level is the SPL at the listener's position (referenced to 1 μPa).

Root mean square (rms) is the quadratic mean sound pressure over the duration of an impulse. Root mean square is calculated by squaring all of the sound amplitudes, averaging the squares, and then taking the square root of the average (Urick, 1983). Root mean square 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 than by peak pressures.

Sound exposure level (SEL; represented as dB re 1 μPa
2
-s) represents the total energy contained within a puls and considers both intensity and duration of exposure. Peak sound pressure (also referred to as zero-to-peak sound pressure or 0-p) is the maximum instantaneous sound pressure measurable in the water at a specified distance from the source and is represented in the same units as the rms sound pressure. Another common metric is peak-to-peak sound pressure (pk-pk), which is the algebraic difference between the peak positive and peak negative sound pressures. Peak-to-peak pressure is typically approximately 6 dB higher than peak pressure (Southall
et al.,
2007).

When underwater objects vibrate or activity occurs, sound-pressure waves are created. These waves alternately compress and decompress the water as the sound wave travels. Underwater sound waves radiate in a manner similar to ripples on the surface of a pond and may be either directed in a beam or beams or may radiate in all directions (omnidirectional sources), as is the case for pulses produced by the airgun arrays considered here. The compressions and decompressions associated with sound waves are detected as changes in pressure by aquatic life and man-made sound receptors such as hydrophones.

Even in the absence of sound from the specified activity, the underwater environment is typically loud due to ambient sound. Ambient sound is defined as environmental background sound levels lacking a single source or

point (Richardson
et al.,
1995), and the sound level of a region is defined by the total acoustical energy being generated by known and unknown sources. These sources may include physical (
e.g.,
wind and waves, earthquakes, ice, atmospheric sound), biological (
e.g.,
sounds produced by marine mammals, fish, and invertebrates), and anthropogenic (
e.g.,
vessels, dredging, construction) sound. A number of sources contribute to ambient sound, including the following (Richardson
et al.,
1995):

• Wind and waves: The complex interactions between wind and water surface, including processes such as breaking waves and wave-induced bubble oscillations and cavitation, are a main source of naturally occurring ambient sound for frequencies between 200 Hz and 50 kHz (Mitson, 1995). In general, ambient sound levels tend to increase with increasing wind speed and wave height. Surf sound becomes important near shore, with measurements collected at a distance of 8.5 km from shore showing an increase of 10 dB in the 100 to 700 Hz band during heavy surf conditions.

• Precipitation: Sound from rain and hail impacting the water surface can become an important component of total sound at frequencies above 500 Hz, and possibly down to 100 Hz during quiet times.

• Biological: Marine mammals can contribute significantly to ambient sound levels, as can some fish and snapping shrimp. The frequency band for biological contributions is from approximately 12 Hz to over 100 kHz.

•
Anthropogenic:
Sources of ambient sound related to human activity include transportation (surface vessels), dredging and construction, oil and gas drilling and production, seismic surveys, sonar, explosions, and ocean acoustic studies. Vessel noise typically dominates the total ambient sound for frequencies between 20 and 300 Hz. In general, the frequencies of anthropogenic sounds are below 1 kHz and, if higher frequency sound levels are created, they attenuate rapidly. Sound from identifiable anthropogenic sources other than the activity of interest (
e.g.,
a passing vessel) is sometimes termed background sound, as opposed to ambient sound.

The sum of the various natural and anthropogenic sound sources at any given location and time—which comprise “ambient” or “background” sound—depends not only on the source levels (as determined by current weather conditions and levels of biological and human activity) but also on the ability of sound to propagate through the environment. In turn, sound propagation is dependent on the spatially and temporally varying properties of the water column and sea floor, and is frequency-dependent. As a result of the dependence on a large number of varying factors, ambient sound levels can be expected to vary widely over both coarse and fine spatial and temporal scales. Sound levels at a given frequency and location can vary by 10-20 dB from day to day (Richardson
et al.,
1995). The result is that, depending on the source type and its intensity, sound from a given activity may be a negligible addition to the local environment or could form a distinctive signal that may affect marine mammals. Details of source types are described in the following text.

Sounds are often considered to fall into one of two general types: Pulsed and non-pulsed (defined in the following). The distinction between these two sound types is important because they have differing potential to cause physical effects, particularly with regard to hearing (
e.g.,
Ward, 1997 in Southall
et al.,
2007). Please see Southall
et al.
(2007) for an in-depth discussion of these concepts.

Pulsed sound sources (
e.g.,
airguns, explosions, gunshots, sonic booms, impact pile driving) produce signals that are brief (typically considered to be less than one second), broadband, atonal transients (ANSI, 1986, 2005; Harris, 1998; NIOSH, 1998; ISO, 2003) and occur either as isolated events or repeated in some succession. Pulsed sounds are all characterized by a relatively rapid rise from ambient pressure to a maximal pressure value followed by a rapid decay period that may include a period of diminishing, oscillating maximal and minimal pressures, and generally have an increased capacity to induce physical injury as compared with sounds that lack these features.

Non-pulsed sounds can be tonal, narrowband, or broadband, brief or prolonged, and may be either continuous or non-continuous (ANSI, 1995; NIOSH, 1998). Some of these non-pulsed sounds can be transient signals of short duration but without the essential properties of pulses (
e.g.,
rapid rise time). Examples of non-pulsed sounds include those produced by vessels, aircraft, machinery operations such as drilling or dredging, vibratory pile driving, and active sonar systems (such as those used by the U.S. Navy). The duration of such sounds, as received at a distance, can be greatly extended in a highly reverberant environment.

Airgun arrays produce pulsed signals with energy in a frequency range from about 10-2,000 Hz, with most energy radiated at frequencies below 200 Hz. The amplitude of the acoustic wave emitted from the source is equal in all directions (
i.e.,
omnidirectional), but airgun arrays do possess some directionality due to different phase delays between guns in different directions. Airgun arrays are typically tuned to maximize functionality for data acquisition purposes, meaning that sound transmitted in horizontal directions and at higher frequencies is minimized to the extent possible.

As described above, a SeaBeam 3012 MBES would also be operated from the
Kairei
continuously throughout the survey. Due to the lower source level of the MBES relative to the
Kairei's
airgun array (241 dB re 1 μPa · m for the MBES versus 259 dB re 1 μPa · m (rms) for the airgun array), the sounds from the MBES are expected to be effectively subsumed by the sounds from the airgun array. In addition, given the movement and speed of the vessel, the intermittent and narrow downward-directed nature of the sounds emitted by the MBES would result in no more than one or two brief ping exposures of any individual marine mammal, if any exposure were to occur. For these reasons, any marine mammal that was exposed to sounds from the MBES would already have been exposed to sounds from the airgun array, which are expected to propagate further in the water. As such, the MBES is not expected to result in the take of any marine mammal that has not already been taken by the sounds from the airgun array, and therefore we do not consider noise from the MBES further in this analysis.

Acoustic Effects

Here, we first provide background information on marine mammal hearing before discussing the potential effects of the use of active acoustic sources on marine mammals.

Marine Mammal Hearing
—Hearing is the most important sensory modality for marine mammals underwater, and exposure to anthropogenic sound can have deleterious effects. To appropriately assess the potential effects of exposure to sound, it is necessary to understand the frequency ranges marine mammals are able to hear. Current data indicate that not all marine mammal species have equal hearing capabilities (
e.g.,
Richardson
et al.,
1995; Wartzok and Ketten, 1999; Au and Hastings, 2008). To reflect this, Southall
et al.
(2007) recommended that marine mammals be divided into functional

hearing groups based on directly measured or estimated hearing ranges on the basis of available behavioral response data, audiograms derived using auditory evoked potential techniques, anatomical modeling, and other data. Note that no direct measurements of hearing ability have been successfully completed for mysticetes (
i.e.,
low-frequency cetaceans). Subsequently, NMFS (2016) described generalized hearing ranges for these marine mammal hearing groups. Generalized hearing ranges were chosen based on the approximately 65 dB threshold from the normalized composite audiograms, with the exception for lower limits for low-frequency cetaceans where the lower bound was deemed to be biologically implausible and the lower bound from Southall
et al.
(2007) retained. Pinniped functional hearing is not discussed here, as no pinnipeds are expected to be affected by the specified activity. The functional groups and the associated frequencies are indicated below (note that these frequency ranges correspond to the range for the composite group, with the entire range not necessarily reflecting the capabilities of every species within that group):

•
Low-frequency cetaceans (mysticetes):
Generalized hearing is estimated to occur between approximately 7 Hz and 35 kHz, with best hearing estimated to be from 100 Hz to 8 kHz;

•
Mid-frequency cetaceans (larger toothed whales, beaked whales, and most delphinids):
Generalized hearing is estimated to occur between approximately 150 Hz and 160 kHz, with best hearing from 10 to less than 100 kHz;

•
High-frequency cetaceans (porpoises, river dolphins, and members of the genera Kogia and Cephalorhynchus; including two members of the genus Lagenorhynchus, on the basis of recent echolocation data and genetic data):
Generalized hearing is estimated to occur between approximately 275 Hz and 160 kHz.

Table 3—Marine Functional Mammal Hearing Groups and Their Generalized Hearing Ranges

Hearing group
Generalized hearing range *

Low frequency (LF) cetaceans (baleen whales)
7 Hz to 35 kHz.

Mid-frequency (MF) cetaceans (dolphins, toothed whales, beaked whales, bottlenose whales)
150 Hz to 160 kHz.

High-frequency (HF) cetaceans (true porpoises, Kogia, river dolphins, cephalorhynchid,
Lagenorhynchus cruciger
and
L. australis
)

275 Hz to 160 kHz.

Phocid pinnipeds (PW) (underwater) (true seals)
50 Hz to 86 kHz.

Otariid pinnipeds (OW) (underwater) (sea lions and fur seals)
60 Hz to 39 kHz.

* Represents the generalized hearing range for the entire group as a composite (
i.e.,
all species within the group), where individual species' hearing ranges are typically not as broad. Generalized hearing range chosen based on ~65 dB threshold from normalized composite audiogram, with the exception for lower limits for LF cetaceans (Southall
et al.,
2007) and PW pinniped (approximation).

For more detail concerning these groups and associated frequency ranges, please see NMFS (2016) for a review of available information. Twenty four marine mammal species (all cetaceans) have the reasonable potential to co-occur with the proposed survey activities. Please refer to Table 2. Of the cetacean species that may be present, six are classified as low-frequency cetaceans (
i.e.,
all mysticete species), 16 are classified as mid-frequency cetaceans (
i.e.,
all delphinid and ziphiid species and the sperm whale), and two are classified as high-frequency cetaceans (
i.e.,
Kogia spp.).

Potential Effects of Underwater Sound
—Please refer to the information given previously (“Description of Active Acoustic Sources”) regarding sound, characteristics of sound types, and metrics used in this document. Note that, in the following discussion, we refer in many cases to a recent review article concerning studies of noise-induced hearing loss conducted from 1996-2015 (
i.e.,
Finneran, 2015). For study-specific citations, please see that work. Anthropogenic sounds cover a broad range of frequencies and sound levels and can have a range of highly variable impacts on marine life, from none or minor to potentially severe responses, depending on received levels, duration of exposure, behavioral context, and various other factors. The potential effects of underwater sound from active acoustic sources can potentially result in one or more of the following: Temporary or permanent hearing impairment, non-auditory physical or physiological effects, behavioral disturbance, stress, and masking (Richardson
et al.,
1995; Gordon
et al.,
2004; Nowacek
et al.,
2007; Southall
et al.,
2007; Götz
et al.,
2009). The degree of effect is intrinsically related to the signal characteristics, received level, distance from the source, and duration of the sound exposure. In general, sudden, high level sounds can cause hearing loss, as can longer exposures to lower level sounds. Temporary or permanent loss of hearing will occur almost exclusively for noise within an animal's hearing range. We first describe specific manifestations of acoustic effects before providing discussion specific to the use of airgun arrays.

Richardson
et al.
(1995) described zones of increasing intensity of effect that might be expected to occur, in relation to distance from a source and assuming that the signal is within an animal's hearing range. First is the area within which the acoustic signal would be audible (potentially perceived) to the animal, but not strong enough to elicit any overt behavioral or physiological response. The next zone corresponds with the area where the signal is audible to the animal and of sufficient intensity to elicit behavioral or physiological responsiveness. Third is a zone within which, for signals of high intensity, the received level is sufficient to potentially cause discomfort or tissue damage to auditory or other systems. Overlaying these zones to a certain extent is the area within which masking (
i.e.,
when a sound interferes with or masks the ability of an animal to detect a signal of interest that is above the absolute hearing threshold) may occur; the masking zone may be highly variable in size.

We describe the more severe effects certain non-auditory physical or physiological effects only briefly as we do not expect that use of airgun arrays are reasonably likely to result in such effects (see below for further discussion). Potential effects from impulsive sound sources can range in severity from effects such as behavioral disturbance or tactile perception to physical discomfort, slight injury of the internal organs and the auditory system, or mortality (Yelverton
et al.,
1973). Non-auditory physiological effects or injuries that theoretically might occur in

marine mammals exposed to high level underwater sound or as a secondary effect of extreme behavioral reactions (
e.g.,
change in dive profile as a result of an avoidance reaction) caused by exposure to sound include neurological effects, bubble formation, resonance effects, and other types of organ or tissue damage (Cox
et al.,
2006; Southall
et al.,
2007; Zimmer and Tyack, 2007; Tal
et al.,
2015). The survey activities considered here do not involve the use of devices such as explosives or mid-frequency tactical sonar that are associated with these types of effects.

1.
Threshold Shift
—Marine mammals exposed to high-intensity sound, or to lower-intensity sound for prolonged periods, can experience hearing threshold shift (TS), which is the loss of hearing sensitivity at certain frequency ranges (Finneran, 2015). TS can be permanent (PTS), in which case the loss of hearing sensitivity is not fully recoverable, or temporary (TTS), in which case the animal's hearing threshold would recover over time (Southall
et al.,
2007). Repeated sound exposure that leads to TTS could cause PTS. In severe cases of PTS, there can be total or partial deafness, while in most cases the animal has an impaired ability to hear sounds in specific frequency ranges (Kryter, 1985).

When PTS occurs, there is physical damage to the sound receptors in the ear (
i.e.,
tissue damage), whereas TTS represents primarily tissue fatigue and is reversible (Southall
et al.,
2007). In addition, other investigators have suggested that TTS is within the normal bounds of physiological variability and tolerance and does not represent physical injury (
e.g.,
Ward, 1997). Therefore, NMFS does not consider TTS to constitute auditory injury.

Relationships between TTS and PTS thresholds have not been studied in marine mammals, and there is no PTS data for cetaceans but such relationships are assumed to be similar to those in humans and other terrestrial mammals. PTS typically occurs at exposure levels at least several decibels above (a 40-dB threshold shift approximates PTS onset;
e.g.,
Kryter
et al.,
1966; Miller, 1974) that inducing mild TTS (a 6-dB threshold shift approximates TTS onset;
e.g.,
Southall
et al.
2007). Based on data from terrestrial mammals, a precautionary assumption is that the PTS thresholds for impulse sounds (such as airgun pulses as received close to the source) are at least 6 dB higher than the TTS threshold on a peak-pressure basis and PTS cumulative sound exposure level thresholds are 15 to 20 dB higher than TTS cumulative sound exposure level thresholds (Southall
et al.,
2007). Given the higher level of sound or longer exposure duration necessary to cause PTS as compared with TTS, it is considerably less likely that PTS could occur.

For mid-frequency cetaceans in particular, potential protective mechanisms may help limit onset of TTS or prevent onset of PTS. Such mechanisms include dampening of hearing, auditory adaptation, or behavioral amelioration (
e.g.,
Nachtigall and Supin, 2013; Miller
et al.,
2012; Finneran
et al.,
2015; Popov
et al.,
2016).

TTS is the mildest form of hearing impairment that can occur during exposure to sound (Kryter, 1985). While experiencing TTS, the hearing threshold rises, and a sound must be at a higher level in order to be heard. In terrestrial and marine mammals, TTS can last from minutes or hours to days (in cases of strong TTS). In many cases, hearing sensitivity recovers rapidly after exposure to the sound ends. Few data on sound levels and durations necessary to elicit mild TTS have been obtained for marine mammals.

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. 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.

Finneran
et al.
(2015) measured hearing thresholds in three captive bottlenose dolphins before and after exposure to ten pulses produced by a seismic airgun in order to study TTS induced after exposure to multiple pulses. Exposures began at relatively low levels and gradually increased over a period of several months, with the highest exposures at peak SPLs from 196 to 210 dB and cumulative (unweighted) SELs from 193-195 dB. No substantial TTS was observed. In addition, behavioral reactions were observed that indicated that animals can learn behaviors that effectively mitigate noise exposures (although exposure patterns must be learned, which is less likely in wild animals than for the captive animals considered in this study). The authors note that the failure to induce more significant auditory effects likely due to the intermittent nature of exposure, the relatively low peak pressure produced by the acoustic source, and the low-frequency energy in airgun pulses as compared with the frequency range of best sensitivity for dolphins and other mid-frequency cetaceans.

Currently, TTS data only exist for four species of cetaceans (bottlenose dolphin, beluga whale, harbor porpoise, and Yangtze finless porpoise) exposed to a limited number of sound sources (
i.e.,
mostly tones and octave-band noise) in laboratory settings (Finneran, 2015). In general, harbor porpoises have a lower TTS onset than other measured cetacean species (Finneran, 2015). Additionally, the existing marine mammal TTS data come from a limited number of individuals within these species. There are no data available on noise-induced hearing loss for mysticetes.

Critical questions remain regarding the rate of TTS growth and recovery after exposure to intermittent noise and the effects of single and multiple pulses. Data at present are also insufficient to construct generalized models for recovery and determine the time necessary to treat subsequent exposures as independent events. More information is needed on the relationship between auditory evoked potential and behavioral measures of TTS for various stimuli. For summaries of data on TTS in marine mammals or for further discussion of TTS onset thresholds, please see Southall
et al.
(2007), Finneran and Jenkins (2012), Finneran (2015), and NMFS (2016).

2.
Behavioral Effects
—Behavioral disturbance may include a variety of effects, including subtle changes in behavior (
e.g.,
minor or brief avoidance of an area or changes in vocalizations), more conspicuous changes in similar behavioral activities, and more sustained and/or potentially severe reactions, such as displacement from or abandonment of high-quality habitat. Behavioral responses to sound are highly variable and context-specific and any reactions depend on numerous intrinsic and extrinsic factors (
e.g.,
species, state of maturity, experience, current activity, reproductive state, auditory sensitivity, time of day), as well as the interplay between factors (
e.g.,
Richardson
et al.,
1995; Wartzok
et al.,
2003; Southall
et al.,
2007; Weilgart, 2007; Archer
et al.,
2010). Behavioral reactions can vary not only among

individuals but also within an individual, depending on previous experience with a sound source, context, and numerous other factors (Ellison
et al.,
2012), and can vary depending on characteristics associated with the sound source (
e.g.,
whether it is moving or stationary, number of sources, distance from the source). Please see Appendices B-C of Southall
et al.
(2007) for a review of studies involving marine mammal behavioral responses to sound.

Habituation can occur when an animal's response to a stimulus wanes with repeated exposure, usually in the absence of unpleasant associated events (Wartzok
et al.,
2003). Animals are most likely to habituate to sounds that are predictable and unvarying. It is important to note that habituation is appropriately considered as a “progressive reduction in response to stimuli that are perceived as neither aversive nor beneficial,” rather than as, more generally, moderation in response to human disturbance (Bejder
et al.,
2009). The opposite process is sensitization, when an unpleasant experience leads to subsequent responses, often in the form of avoidance, at a lower level of exposure. As noted, behavioral state may affect the type of response. For example, animals that are resting may show greater behavioral change in response to disturbing sound levels than animals that are highly motivated to remain in an area for feeding (Richardson
et al.,
1995; NRC, 2003; Wartzok
et al.,
2003). Controlled experiments with captive marine mammals have showed pronounced behavioral reactions, including avoidance of loud sound sources (Ridgway
et al.,
1997). Observed responses of wild marine mammals to loud pulsed sound sources (typically seismic airguns or acoustic harassment devices) have been varied but often consist of avoidance behavior or other behavioral changes suggesting discomfort (Morton and Symonds, 2002; see also Richardson
et al.,
1995; Nowacek
et al.,
2007). However, many delphinids approach acoustic source vessels with no apparent discomfort or obvious behavioral change (
e.g.,
Barkaszi
et al.,
2012).

Available studies show wide variation in response to underwater sound; therefore, it is difficult to predict specifically how any given sound in a particular instance might affect marine mammals perceiving the signal. If a marine mammal does react briefly to an underwater sound by changing its behavior or moving a small distance, the impacts of the change are unlikely to be significant to the individual, let alone the stock or population. However, if a sound source displaces marine mammals from an important feeding or breeding area for a prolonged period, impacts on individuals and populations could be significant (
e.g.,
Lusseau and Bejder, 2007; Weilgart, 2007; NRC, 2005). However, there are broad categories of potential response, which we describe in greater detail here, that include alteration of dive behavior, alteration of foraging behavior, effects to breathing, interference with or alteration of vocalization, avoidance, and flight.

Changes in dive behavior can vary widely, and may consist of increased or decreased dive times and surface intervals as well as changes in the rates of ascent and descent during a dive (
e.g.,
Frankel and Clark, 2000; Ng and Leung, 2003; Nowacek
et al.;
2004; Goldbogen
et al.,
2013a, b). Variations in dive behavior may reflect interruptions in biologically significant activities (
e.g.,
foraging) or they may be of little biological significance. The impact of an alteration to dive behavior resulting from an acoustic exposure depends on what the animal is doing at the time of the exposure and the type and magnitude of the response.

Disruption of feeding behavior can be difficult to correlate with anthropogenic sound exposure, so it is usually inferred by observed displacement from known foraging areas, the appearance of secondary indicators (
e.g.,
bubble nets or sediment plumes), or changes in dive behavior. As for other types of behavioral response, the frequency, duration, and temporal pattern of signal presentation, as well as differences in species sensitivity, are likely contributing factors to differences in response in any given circumstance (
e.g.,
Croll
et al.,
2001; Nowacek
et al.;
2004; Madsen
et al.,
2006; Yazvenko
et al.,
2007). A determination of whether foraging disruptions incur fitness consequences would require information on or estimates of the energetic requirements of the affected individuals and the relationship between prey availability, foraging effort and success, and the life history stage of the animal.

Visual tracking, passive acoustic monitoring, and movement recording tags were used to quantify sperm whale behavior prior to, during, and following exposure to airgun arrays at received levels in the range 140-160 dB at distances of 7-13 km, following a phase-in of sound intensity and full array exposures at 1-13 km (Madsen
et al.,
2006; Miller
et al.,
2009). Sperm whales did not exhibit horizontal avoidance behavior at the surface. However, foraging behavior may have been affected. The sperm whales exhibited 19 percent less vocal (buzz) rate during full exposure relative to post exposure, and the whale that was approached most closely had an extended resting period and did not resume foraging until the airguns had ceased firing. The remaining whales continued to execute foraging dives throughout exposure; however, swimming movements during foraging dives were 6 percent lower during exposure than control periods (Miller
et al.,
2009). These data raise concerns that seismic surveys may impact foraging behavior in sperm whales, although more data are required to understand whether the differences were due to exposure or natural variation in sperm whale behavior (Miller
et al.,
2009).

Variations in respiration naturally vary with different behaviors and alterations to breathing rate as a function of acoustic exposure can be expected to co-occur with other behavioral reactions, such as a flight response or an alteration in diving. However, respiration rates in and of themselves may be representative of annoyance or an acute stress response. Various studies have shown that respiration rates may either be unaffected or could increase, depending on the species and signal characteristics, again highlighting the importance in understanding species differences in the tolerance of underwater noise when determining the potential for impacts resulting from anthropogenic sound exposure (
e.g.,
Kastelein
et al.,
2001, 2005, 2006; Gailey
et al.,
2007; Gailey
et al.,
2016).

Marine mammals vocalize for different purposes and across multiple modes, such as whistling, echolocation click production, calling, and singing. Changes in vocalization behavior in response to anthropogenic noise can occur for any of these modes and may result from a need to compete with an increase in background noise or may reflect increased vigilance or a startle response. For example, in the presence of potentially masking signals, humpback whales and killer whales have been observed to increase the length of their songs (Miller
et al.,
2000; Fristrup
et al.,
2003; Foote
et al.,
2004), while right whales have been observed to shift the frequency content of their calls upward while reducing the rate of calling in areas of increased anthropogenic noise (Parks
et al.,
2007). In some cases, animals may cease sound production during production of aversive signals (Bowles
et al.,
1994).

Cerchio
et al.
(2014) used passive acoustic monitoring to document the presence of singing humpback whales

off the coast of northern Angola and to opportunistically test for the effect of seismic survey activity on the number of singing whales. Two recording units were deployed between March and December 2008 in the offshore environment; numbers of singers were counted every hour. Generalized Additive Mixed Models were used to assess the effect of survey day (seasonality), hour (diel variation), moon phase, and received levels of noise (measured from a single pulse during each ten minute sampled period) on singer number. The number of singers significantly decreased with increasing received level of noise, suggesting that humpback whale breeding activity was disrupted to some extent by the survey activity.

Castellote
et al.
(2012) reported acoustic and behavioral changes by fin whales in response to shipping and airgun noise. Acoustic features of fin whale song notes recorded in the Mediterranean Sea and northeast Atlantic Ocean were compared for areas with different shipping noise levels and traffic intensities and during a seismic airgun survey. During the first 72 h of the survey, a steady decrease in song received levels and bearings to singers indicated that whales moved away from the acoustic source and out of the study area. This displacement persisted for a time period well beyond the 10-day duration of seismic airgun activity, providing evidence that fin whales may avoid an area for an extended period in the presence of increased noise. The authors hypothesize that fin whale acoustic communication is modified to compensate for increased background noise and that a sensitization process may play a role in the observed temporary displacement.

Seismic pulses at average received levels of 131 dB re 1 µPa
2
-s caused blue whales to increase call production (Di Iorio and Clark, 2010). In contrast, McDonald
et al.
(1995) tracked a blue whale with seafloor seismometers and reported that it stopped vocalizing and changed its travel direction at a range of 10 km from the acoustic source vessel (estimated received level 143 dB pk-pk). Blackwell
et al.
(2013) found that bowhead whale call rates dropped significantly at onset of airgun use at sites with a median distance of 41-45 km from the survey. Blackwell
et al.
(2015) expanded this analysis to show that whales actually increased calling rates as soon as airgun signals were detectable before ultimately decreasing calling rates at higher received levels (
i.e.,
10-minute SEL
cum
of ~127 dB). Overall, these results suggest that bowhead whales may adjust their vocal output in an effort to compensate for noise before ceasing vocalization effort and ultimately deflecting from the acoustic source (Blackwell
et al.,
2013, 2015). These studies demonstrate that even low levels of noise received far from the source can induce changes in vocalization and/or behavior for mysticetes.

Avoidance is the displacement of an individual from an area or migration path as a result of the presence of a sound or other stressors, and is one of the most obvious manifestations of disturbance in marine mammals (Richardson
et al.,
1995). For example, gray whales are known to change direction—deflecting from customary migratory paths—in order to avoid noise from seismic surveys (Malme
et al.,
1984). Humpback whales showed avoidance behavior in the presence of an active seismic array during observational studies and controlled exposure experiments in western Australia (McCauley
et al.,
2000). Avoidance may be short-term, with animals returning to the area once the noise has ceased (
e.g.,
Bowles
et al.,
1994; Goold, 1996; Stone
et al.,
2000; Morton and Symonds, 2002; Gailey
et al.,
2007). Longer-term displacement is possible, however, which may lead to changes in abundance or distribution patterns of the affected species in the affected region if habituation to the presence of the sound does not occur (
e.g.,
Bejder
et al.,
2006; Teilmann
et al.,
2006).

A flight response is a dramatic change in normal movement to a directed and rapid movement away from the perceived location of a sound source. The flight response differs from other avoidance responses in the intensity of the response (
e.g.,
directed movement, rate of travel). Relatively little information on flight responses of marine mammals to anthropogenic signals exist, although observations of flight responses to the presence of predators have occurred (Connor and Heithaus, 1996). The result of a flight response could range from brief, temporary exertion and displacement from the area where the signal provokes flight to, in extreme cases, marine mammal strandings (Evans and England, 2001). However, it should be noted that response to a perceived predator does not necessarily invoke flight (Ford and Reeves, 2008), and whether individuals are solitary or in groups may influence the response.

Behavioral disturbance can also impact marine mammals in more subtle ways. Increased vigilance may result in costs related to diversion of focus and attention (
i.e.,
when a response consists of increased vigilance, it may come at the cost of decreased attention to other critical behaviors such as foraging or resting). These effects have generally not been demonstrated for marine mammals, but studies involving fish and terrestrial animals have shown that increased vigilance may substantially reduce feeding rates (
e.g.,
Beauchamp and Livoreil, 1997; Fritz
et al.,
2002; Purser and Radford, 2011). In addition, chronic disturbance can cause population declines through reduction of fitness (
e.g.,
decline in body condition) and subsequent reduction in reproductive success, survival, or both (
e.g.,
Harrington and Veitch, 1992; Daan
et al.,
1996; Bradshaw
et al.,
1998). However, Ridgway
et al.
(2006) reported that increased vigilance in bottlenose dolphins exposed to sound over a five-day period did not cause any sleep deprivation or stress effects.

Many animals perform vital functions, such as feeding, resting, traveling, and socializing, on a diel cycle (24-hour cycle). Disruption of such functions resulting from reactions to stressors such as sound exposure are more likely to be significant if they last more than one diel cycle or recur on subsequent days (Southall
et al.,
2007). Consequently, a behavioral response lasting less than one day and not recurring on subsequent days is not considered particularly severe unless it could directly affect reproduction or survival (Southall
et al.,
2007). Note that there is a difference between multi-day substantive behavioral reactions and multi-day anthropogenic activities. For example, just because an activity lasts for multiple days does not necessarily mean that individual animals are either exposed to activity-related stressors for multiple days or, further, exposed in a manner resulting in sustained multi-day substantive behavioral responses.

Stone (2015) reported data from at-sea observations during 1,196 seismic surveys from 1994 to 2010. When large arrays of airguns (considered to be 500 in
3
or more) were firing, lateral displacement, more localized avoidance, or other changes in behavior were evident for most odontocetes. However, significant responses to large arrays were found only for the minke whale and fin whale. Behavioral responses observed included changes in swimming or surfacing behavior, with indications that cetaceans remained near the water surface at these times. Cetaceans were recorded as feeding less often when large arrays were active. Behavioral observations of gray whales during a seismic survey monitored whale movements and respirations pre-, during and post-seismic survey

(Gailey
et al.,
2016). Behavioral state and water depth were the best ‘natural’ predictors of whale movements and respiration and, after considering natural variation, none of the response variables were significantly associated with seismic survey or vessel sounds.

3.
Stress Responses
—An animal's perception of a threat may be sufficient to trigger stress responses consisting of some combination of behavioral responses, autonomic nervous system responses, neuroendocrine responses, or immune responses (
e.g.,
Seyle, 1950; Moberg, 2000). In many cases, an animal's first and sometimes most economical (in terms of energetic costs) response is behavioral avoidance of the potential stressor. Autonomic nervous system responses to stress typically involve changes in heart rate, blood pressure, and gastrointestinal activity. These responses have a relatively short duration and may or may not have a significant long-term effect on an animal's fitness.

Neuroendocrine stress responses often involve the hypothalamus-pituitary-adrenal 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, altered metabolism, reduced immune competence, and behavioral disturbance (
e.g.,
Moberg, 1987; Blecha, 2000). Increases in the circulation of glucocorticoids are also equated with stress (Romano
et al.,
2004).

The primary distinction between stress (which is adaptive and does not normally place an animal at risk) and “distress” is the 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 serious fitness consequences. 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 functions. This state of distress will last until the animal replenishes its energetic reserves sufficiently to restore normal function.

Relationships between these physiological mechanisms, animal behavior, and the costs of stress responses are well-studied through controlled experiments and for both laboratory and free-ranging animals (
e.g.,
Holberton
et al.,
1996; Hood
et al.,
1998; Jessop
et al.,
2003; Krausman
et al.,
2004; Lankford
et al.,
2005). Stress responses due to exposure to anthropogenic sounds or other stressors and their effects on marine mammals have also been reviewed (Fair and Becker, 2000; Romano
et al.,
2002b) and, more rarely, studied in wild populations (
e.g.,
Romano
et al.,
2002a). For example, Rolland
et al.
(2012) found that noise reduction from reduced ship traffic in the Bay of Fundy was associated with decreased stress in North Atlantic right whales. These and other studies lead to a reasonable expectation that some marine mammals will experience physiological stress responses upon exposure to acoustic stressors and that it is possible that some of these would be classified as “distress.” In addition, any animal experiencing TTS would likely also experience stress responses (NRC, 2003).

4.
Auditory Masking
—Sound can disrupt behavior through masking, or interfering with, an animal's ability to detect, recognize, or discriminate between acoustic signals of interest (
e.g.,
those used for intraspecific communication and social interactions, prey detection, predator avoidance, navigation) (Richardson
et al.,
1995; Erbe
et al.,
2016). Masking occurs when the receipt of a sound is interfered with by another coincident sound at similar frequencies and at similar or higher intensity, and may occur whether the sound is natural (
e.g.,
snapping shrimp, wind, waves, precipitation) or anthropogenic (
e.g.,
shipping, sonar, seismic exploration) in origin. The ability of a noise source to mask biologically important sounds depends on the characteristics of both the noise source and the signal of interest (
e.g.,
signal-to-noise ratio, temporal variability, direction), in relation to each other and to an animal's hearing abilities (
e.g.,
sensitivity, frequency range, critical ratios, frequency discrimination, directional discrimination, age or TTS hearing loss), and existing ambient noise and propagation conditions.

Under certain circumstances, marine mammals experiencing significant masking could also be impaired from maximizing their performance fitness in survival and reproduction. Therefore, when the coincident (masking) sound is man-made, it may be considered harassment when disrupting or altering critical behaviors. It is important to distinguish TTS and PTS, which persist after the sound exposure, from masking, which occurs during the sound exposure. Because masking (without resulting in TS) is not associated with abnormal physiological function, it is not considered a physiological effect, but rather a potential behavioral effect.

The frequency range of the potentially masking sound is important in determining any potential behavioral impacts. For example, low-frequency signals may have less effect on high-frequency echolocation sounds produced by odontocetes but are more likely to affect detection of mysticete communication calls and other potentially important natural sounds such as those produced by surf and some prey species. The masking of communication signals by anthropogenic noise may be considered as a reduction in the communication space of animals (
e.g.,
Clark
et al.,
2009) and may result in energetic or other costs as animals change their vocalization behavior (
e.g.,
Miller
et al.,
2000; Foote
et al.,
2004; Parks
et al.,
2007; Di Iorio and Clark, 2009; Holt
et al.,
2009). Masking can be reduced in situations where the signal and noise come from different directions (Richardson
et al.,
1995), through amplitude modulation of the signal, or through other compensatory behaviors (Houser and Moore, 2014). Masking can be tested directly in captive species (
e.g.,
Erbe, 2008), but in wild populations it must be either modeled or inferred from evidence of masking compensation. There are few studies addressing real-world masking sounds likely to be experienced by marine mammals in the wild (
e.g.,
Branstetter
et al.,
2013).

Masking affects both senders and receivers of acoustic signals and can potentially have long-term chronic effects on marine mammals at the population level as well as at the individual level. Low-frequency ambient sound levels have increased by as much as 20 dB (more than three times in terms of SPL) in the world's ocean from pre-industrial periods, with most of the increase from distant commercial shipping (Hildebrand, 2009). All anthropogenic sound sources, but especially chronic and lower-frequency signals (
e.g.,
from vessel traffic), contribute to elevated ambient sound levels, thus intensifying masking.

Ship Strike

Vessel collisions with marine mammals, or ship strikes, can result in death or serious injury of the animal. Wounds resulting from ship strike may include massive trauma, hemorrhaging, broken bones, or propeller lacerations (Knowlton and Kraus, 2001). An animal at the surface may be struck directly by a vessel, a surfacing animal may hit the bottom of a vessel, or an animal just below the surface may be cut by a

vessel's propeller. Superficial strikes may not kill or result in the death of the animal. These interactions are typically associated with large whales (
e.g.,
fin whales), which are occasionally found draped across the bulbous bow of large commercial ships upon arrival in port. Although smaller cetaceans are more maneuverable in relation to large vessels than are large whales, they may also be susceptible to strike. The severity of injuries typically depends on the size and speed of the vessel, with the probability of death or serious injury increasing as vessel speed increases (Knowlton and Kraus, 2001; Laist
et al.,
2001; Vanderlaan and Taggart, 2007; Conn and Silber, 2013). Impact forces increase with speed, as does the probability of a strike at a given distance (Silber
et al.,
2010; Gende
et al.,
2011).

Pace and Silber (2005) also found that the probability of death or serious injury increased rapidly with increasing vessel speed. Specifically, the predicted probability of serious injury or death increased from 45 to 75 percent as vessel speed increased from 10 to 14 kn, and exceeded 90 percent at 17 kn. Higher speeds during collisions result in greater force of impact, but higher speeds also appear to increase the chance of severe injuries or death through increased likelihood of collision by pulling whales toward the vessel (Clyne, 1999; Knowlton
et al.,
1995). In a separate study, Vanderlaan and Taggart (2007) analyzed the probability of lethal mortality of large whales at a given speed, showing that the greatest rate of change in the probability of a lethal injury to a large whale as a function of vessel speed occurs between 8.6 and 15 kn. The chances of a lethal injury decline from approximately 80 percent at 15 kn to approximately 20 percent at 8.6 kn. At speeds below 11.8 kn, the chances of lethal injury drop below 50 percent, while the probability asymptotically increases toward one hundred percent above 15 kn.

The
Kairei
travels at a speed of ~8.3 km/hour while towing seismic survey gear (LGL 2017). At this speed, both the possibility of striking a marine mammal and the possibility of a strike resulting in serious injury or mortality are discountable. At average transit speed, the probability of serious injury or mortality resulting from a strike is less than 50 percent. However, the likelihood of a strike actually happening is again discountable. Ship strikes, as analyzed in the studies cited above, generally involve commercial shipping, which is much more common in both space and time than is geophysical survey activity. Jensen and Silber (2004) summarized ship strikes of large whales worldwide from 1975-2003 and found that most collisions occurred in the open ocean and involved large vessels (
e.g.,
commercial shipping). Commercial fishing vessels were responsible for three percent of recorded collisions, while no such incidents were reported for geophysical survey vessels during that time period.

It is possible for ship strikes to occur while traveling at slow speeds. For example, a hydrographic survey vessel traveling at low speed (5.5 kn) while conducting mapping surveys off the central California coast struck and killed a blue whale in 2009. The State of California determined that the whale had suddenly and unexpectedly surfaced beneath the hull, with the result that the propeller severed the whale's vertebrae, and that this was an unavoidable event. This strike represents the only such incident in approximately 540,000 hours of similar coastal mapping activity (
p
= 1.9 × 10
−6
; 95% CI = 0 −5.5 × 10
−6
; NMFS, 2013b). In addition, a research vessel reported a fatal strike in 2011 of a dolphin in the Atlantic, demonstrating that it is possible for strikes involving smaller cetaceans to occur. In that case, the incident report indicated that an animal apparently was struck by the vessel's propeller as it was intentionally swimming near the vessel. While indicative of the type of unusual events that cannot be ruled out, neither of these instances represents a circumstance that would be considered reasonably foreseeable or that would be considered preventable.

Although the likelihood of the vessel striking a marine mammal is low, we require a robust ship strike avoidance protocol (see “Proposed Mitigation”), which we believe eliminates any foreseeable risk of ship strike. We anticipate that vessel collisions involving a seismic data acquisition vessel towing gear, while not impossible, represent unlikely, unpredictable events for which there are no preventive measures. Given the required mitigation measures, the relatively slow speed of the vessel towing gear, the presence of bridge crew watching for obstacles at all times (including marine mammals), the presence of marine mammal observers, and the short duration of the survey (5.5 days), we believe that the possibility of ship strike is discountable and, further, that were a strike of a large whale to occur, it would be unlikely to result in serious injury or mortality. No incidental take resulting from ship strike is anticipated, and this potential effect of the specified activity will not be discussed further in the following analysis.

Stranding
—When a living or dead marine mammal swims or floats onto shore and becomes “beached” or incapable of returning to sea, the event is a “stranding” (Geraci
et al.,
1999; Perrin and Geraci, 2002; Geraci and Lounsbury, 2005; NMFS, 2007). The legal definition for a stranding under the MMPA is that “(A) a marine mammal is dead and is (i) on a beach or shore of the United States; or (ii) in waters under the jurisdiction of the United States (including any navigable waters); or (B) a marine mammal is alive and is (i) on a beach or shore of the United States and is unable to return to the water; (ii) on a beach or shore of the United States and, although able to return to the water, is in need of apparent medical attention; or (iii) in the waters under the jurisdiction of the United States (including any navigable waters), but is unable to return to its natural habitat under its own power or without assistance.”

Marine mammals strand for a variety of reasons, such as infectious agents, biotoxicosis, starvation, fishery interaction, ship strike, unusual oceanographic or weather events, sound exposure, or combinations of these stressors sustained concurrently or in series. However, the cause or causes of most strandings are unknown (Geraci
et al.,
1976; Eaton, 1979; Odell
et al.,
1980; Best, 1982). Numerous studies suggest that the physiology, behavior, habitat relationships, age, or condition of cetaceans may cause them to strand or might pre-dispose them to strand when exposed to another phenomenon. These suggestions are consistent with the conclusions of numerous other studies that have demonstrated that combinations of dissimilar stressors commonly combine to kill an animal or dramatically reduce its fitness, even though one exposure without the other does not produce the same result (Chroussos, 2000; Creel, 2005; DeVries
et al.,
2003; Fair and Becker, 2000; Foley
et al.,
2001; Moberg, 2000; Relyea, 2005a; 2005b, Romero, 2004; Sih
et al.,
2004).

Use of military tactical sonar has been implicated in a majority of investigated stranding events, although one stranding event was associated with the use of seismic airguns. This event occurred in the Gulf of California, coincident with seismic reflection profiling by the R/V
Maurice Ewing
operated by Columbia University's Lamont-Doherty Earth Observatory and involved two Cuvier's beaked whales (Hildebrand, 2004). The vessel had been firing an array of 20 airguns with a total

volume of 8,500 in
3
(Hildebrand, 2004; Taylor
et al.,
2004). Most known stranding events have involved beaked whales, though a small number have involved deep-diving delphinids or sperm whales (
e.g.,
Mazzariol
et al.,
2010; Southall
et al.,
2013). In general, long duration (~1 second) and high-intensity sounds (>235 dB SPL) have been implicated in stranding events (Hildebrand, 2004). With regard to beaked whales, mid-frequency sound is typically implicated (when causation can be determined) (Hildebrand, 2004). Although seismic airguns create predominantly low-frequency energy, the signal does include a mid-frequency component. We have considered the potential for the proposed survey to result in marine mammal stranding and have concluded that, based on the best available information, stranding is not expected to occur.

Other Potential Impacts
—Here, we briefly address the potential risks due to entanglement and contaminant spills. We are not aware of any records of marine mammal entanglement in towed arrays such as those considered here. The discharge of trash and debris is prohibited (33 CFR 151.51-77) unless it is passed through a machine that breaks up solids such that they can pass through a 25-mm mesh screen. All other trash and debris must be returned to shore for proper disposal with municipal and solid waste. Some personal items may be accidentally lost overboard. However, U.S. Coast Guard and Environmental Protection Act regulations require operators to become proactive in avoiding accidental loss of solid waste items by developing waste management plans, posting informational placards, manifesting trash sent to shore, and using special precautions such as covering outside trash bins to prevent accidental loss of solid waste. There are no meaningful entanglement risks posed by the described activity, and entanglement risks are not discussed further in this document.

Marine mammals could be affected by accidentally spilled diesel fuel from a vessel associated with proposed survey activities. Quantities of diesel fuel on the sea surface may affect marine mammals through various pathways: surface contact of the fuel with skin and other mucous membranes, inhalation of concentrated petroleum vapors, or ingestion of the fuel (direct ingestion or by the ingestion of oiled prey) (
e.g.,
Geraci and St. Aubin, 1980, 1985, 1990). However, the likelihood of a fuel spill during any particular geophysical survey is considered to be remote, and the potential for impacts to marine mammals would depend greatly on the size and location of a spill and meteorological conditions at the time of the spill. Spilled fuel would rapidly spread to a layer of varying thickness and break up into narrow bands or windrows parallel to the wind direction. The rate at which the fuel spreads would be determined by the prevailing conditions such as temperature, water currents, tidal streams, and wind speeds. Lighter, volatile components of the fuel would evaporate to the atmosphere almost completely in a few days. Evaporation rate may increase as the fuel spreads because of the increased surface area of the slick. Rougher seas, high wind speeds, and high temperatures also tend to increase the rate of evaporation and the proportion of fuel lost by this process (Scholz
et al.,
1999). We do not anticipate potentially meaningful effects to marine mammals as a result of any contaminant spill resulting from the proposed survey activities, and contaminant spills are not discussed further in this document.

Anticipated Effects on Marine Mammal Habitat

Effects to Prey
—Marine mammal prey varies by species, season, and location and, for some, is not well documented. Fish react to sounds which are especially strong and/or intermittent low-frequency sounds. Short duration, sharp sounds can cause overt or subtle changes in fish behavior and local distribution. Hastings and Popper (2005) identified several studies that suggest fish may relocate to avoid certain areas of sound energy. Additional studies have documented effects of pulsed sound on fish, although several are based on studies in support of construction projects (
e.g.,
Scholik and Yan, 2001, 2002; Popper and Hastings, 2009). Sound pulses at received levels of 160 dB may cause subtle changes in fish behavior. SPLs of 180 dB may cause noticeable changes in behavior (Pearson
et al.,
1992; Skalski
et al.,
1992). SPLs of sufficient strength have been known to cause injury to fish and fish mortality. The most likely impact to fish from survey activities at the project area would be temporary avoidance of the area. The duration of fish avoidance of a given area after survey effort stops is unknown, but a rapid return to normal recruitment, distribution and behavior is anticipated.

Information on seismic airgun impacts to zooplankton, which represent an important prey type for mysticetes, is limited. However, McCauley
et al.
(2017) reported that experimental exposure to a pulse from a 150 inch
3
airgun decreased zooplankton abundance when compared with controls, as measured by sonar and net tows, and caused a two- to threefold increase in dead adult and larval zooplankton. Although no adult krill were present, the study found that all larval krill were killed after air gun passage. Impacts were observed out to the maximum 1.2 km range sampled.

In general, impacts to marine mammal prey are expected to be limited due to the relatively small temporal and spatial overlap between the proposed survey and any areas used by marine mammal prey species. The proposed survey would occur over a relatively short time period (5.5 days) and would occur over a very small area relative to the area available as marine mammal habitat in the central Pacific Ocean. We do not have any information to suggest the proposed survey area represents a significant feeding area for any marine mammal, and we believe any impacts to marine mammals due to adverse affects to their prey would be insignificant due to the limited spatial and temporal impact of the proposed survey. However, adverse impacts may occur to a few species of fish and to zooplankton.

Acoustic Habitat
—Acoustic habitat is the soundscape—which encompasses all of the sound present in a particular location and time, as a whole—when considered from the perspective of the animals experiencing it. Animals produce sound for, or listen for sounds produced by, conspecifics (communication during feeding, mating, and other social activities), other animals (finding prey or avoiding predators), and the physical environment (finding suitable habitats, navigating). Together, sounds made by animals and the geophysical environment (
e.g.,
produced by earthquakes, lightning, wind, rain, waves) make up the natural contributions to the total acoustics of a place. These acoustic conditions, termed acoustic habitat, are one attribute of an animal's total habitat.

Soundscapes are also defined by, and acoustic habitat influenced by, the total contribution of anthropogenic sound. This may include incidental emissions from sources such as vessel traffic, or may be intentionally introduced to the marine environment for data acquisition purposes (as in the use of airgun arrays). Anthropogenic noise varies widely in its frequency content, duration, and loudness and these characteristics greatly influence the potential habitat-mediated effects to marine mammals (please see also the previous discussion on masking under “Acoustic Effects”), which may range from local effects for

brief periods of time to chronic effects over large areas and for long durations. Depending on the extent of effects to habitat, animals may alter their communications signals (thereby potentially expending additional energy) or miss acoustic cues (either conspecific or adventitious). For more detail on these concepts see,
e.g.,
Barber
et al.,
2010; Pijanowski
et al.,
2011; Francis and Barber, 2013; Lillis
et al.,
2014.

Problems arising from a failure to detect cues are more likely to occur when noise stimuli are chronic and overlap with biologically relevant cues used for communication, orientation, and predator/prey detection (Francis and Barber, 2013). Although the signals emitted by seismic airgun arrays are generally low frequency, they would also likely be of short duration and transient in any given area due to the nature of these surveys. As described previously, exploratory surveys such as these cover a large area but would be transient rather than focused in a given location over time and therefore would not be considered chronic in any given location.

In summary, activities associated with the proposed action are not likely to have a permanent, adverse effect on any fish habitat or populations of fish species or on the quality of acoustic habitat. Thus, any impacts to marine mammal habitat are not expected to cause significant or long-term consequences for individual marine mammals or their populations.

Estimated Take

This section provides an estimate of the number of incidental takes proposed for authorization through this IHA, which will inform both NMFS' consideration of whether the number of takes is “small” and the negligible impact determination.

Harassment is the only type of take expected to result from these activities. Except with respect to certain activities not pertinent here, section 3(18) of 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).

Authorized takes would primarily be by Level B harassment, as use of the seismic airguns have the potential to result in disruption of behavioral patterns for individual marine mammals. There is also some potential for auditory injury (Level A harassment) to result, primarily for mysticetes and high frequency cetaceans (
i.e.,
kogiidae spp.), due to larger predicted auditory injury zones for those functional hearing groups. Auditory injury is unlikely to occur for mid-frequency species given very small modeled zones of injury for those species. The proposed mitigation and monitoring measures are expected to minimize the severity of such taking to the extent practicable.

As described previously, no mortality is anticipated or proposed to be authorized for this activity. Below we describe how the take is estimated.

Described in the most basic way, we estimate take by considering: (1) Acoustic thresholds above which NMFS believes the best available science indicates marine mammals will be behaviorally harassed or incur some degree of permanent hearing impairment; (2) the area or volume of water that will be ensonified above these levels in a day; (3) the density or occurrence of marine mammals within these ensonified areas; and (4) and the number of days of activities. Below, we describe these components in more detail and present the exposure estimate and associated numbers of take proposed for authorization.

Acoustic Thresholds

Using the best available science, NMFS has developed acoustic thresholds that identify the received level of underwater sound above which exposed marine mammals would be reasonably expected to be behaviorally harassed (equated to Level B harassment) or to incur PTS of some degree (equated to Level A harassment).

Level B Harassment for non-explosive sources—
Though significantly driven by received level, the onset of behavioral disturbance from anthropogenic noise exposure is also informed to varying degrees by other factors related to the source (
e.g.,
frequency, predictability, duty cycle), the environment (
e.g.,
bathymetry), and the receiving animals (hearing, motivation, experience, demography, behavioral context) and can be difficult to predict (Southall
et al.,
2007, Ellison
et al.,
2011). Based on the best available science and the practical need to use a threshold based on a factor that is both predictable and measurable for most activities, NMFS uses a generalized acoustic threshold based on received level to estimate the onset of behavioral harassment. NMFS predicts that marine mammals are likely to be behaviorally harassed in a manner we consider to fall under Level B harassment when exposed to underwater anthropogenic noise above received levels of 120 dB re 1 μPa (rms) for continuous (
e.g.,
vibratory pile-driving, drilling) and above 160 dB re 1 μPa (rms) for non-explosive impulsive (
e.g.,
seismic airguns) or intermittent (
e.g.,
scientific sonar) sources. UH's proposed activity includes the use of impulsive seismic sources. Therefore, the 160 dB re 1 μPa (rms) criteria is applicable for analysis of level B harassment.

Level A harassment for non-explosive sources—
NMFS' Technical Guidance for Assessing the Effects of Anthropogenic Sound on Marine Mammal Hearing (NMFS, 2016) identifies dual criteria to assess auditory injury (Level A harassment) to five different marine mammal groups (based on hearing sensitivity) as a result of exposure to noise from two different types of sources (impulsive or non-impulsive). The Technical Guidance identifies the received levels, or thresholds, above which individual marine mammals are predicted to experience changes in their hearing sensitivity for all underwater anthropogenic sound sources, reflects the best available science, and better predicts the potential for auditory injury than does NMFS' historical criteria.

These thresholds were developed by compiling and synthesizing the best available science and soliciting input multiple times from both the public and peer reviewers to inform the final product, and are provided in Table 4 below. The references, analysis, and methodology used in the development of the thresholds are described in NMFS 2016 Technical Guidance, which may be accessed at:
http://www.nmfs.noaa.gov/pr/acoustics/guidelines.htm.
As described above, UH's propos

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Source: Frix Law Library, https://www.frixlaw.com/law-library/documents/fr%3A2017-15455. Public record. Not legal advice.