# Takes of Marine Mammals Incidental to Specified Activities; Taking Marine Mammals Incidental to Oil and Gas Activities in Cook Inlet, Alaska > Briefs, arguments, decisions, and more. URL: https://www.frixlaw.com/law-library/documents/fr%3A2019-05781 ## Record - **Collection:** Federal Register - **Document type:** Proposed Rule - **Published:** April 1, 2019 - **Citation:** 84 FR 12330 ## Text DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration 50 CFR Part 217 [Docket No. 190214112-9112-01] RIN 0648-BI62 Takes of Marine Mammals Incidental to Specified Activities; Taking Marine Mammals Incidental to Oil and Gas Activities in Cook Inlet, Alaska AGENCY: National Marine Fisheries Service (NMFS), National Oceanic and Atmospheric Administration (NOAA), Commerce. ACTION: Proposed rule; request for comments. SUMMARY: NMFS has received a request from Hilcorp Alaska LLC (Hilcorp) for authorization to take marine mammals incidental to oil and gas activities in Cook Inlet, Alaska, over the course of five years (2019-2024). As required by the Marine Mammal Protection Act (MMPA), NMFS is proposing regulations to govern that take, and requests comments on the proposed regulations. 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 May 1, 2019. ADDRESSES: You may submit comments, identified by NOAA-NMFS-2019-0026, by any of the following methods: • Electronic submissions: Submit all electronic public comments via the Federal eRulemaking Portal, Go to www.regulations.gov/#!docketDetail;D=NOAA-NMFS-2019-0026, click the “Comment Now!” icon, complete the required fields, and enter or attach your comments. • Mail: Submit comments to Jolie Harrison, Chief, Permits and Conservation Division, Office of Protected Resources, National Marine Fisheries Service, 1315 East-West Highway, Silver Spring, MD 20910-3225. Instructions: Comments sent by any other method, to any other address or individual, or received after the end of the comment period, may not be considered by NMFS. All comments received are a part of the public record and will generally be posted for public viewing on www.regulations.gov without change. All personal identifying information ( e.g., name, address, etc.), confidential business information, or otherwise sensitive information submitted voluntarily by the sender may be publicly accessible. Do not submit Confidential Business Information or otherwise sensitive or protected information. NMFS will accept anonymous comments (enter “N/A” in the required fields if you wish to remain anonymous). Attachments to electronic comments will be accepted in Microsoft Word, Excel, or Adobe PDF file formats only. FOR FURTHER INFORMATION CONTACT: Sara Young, 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: https://www.fisheries.noaa.gov/national/marine-mammal-protection/incidental-take-authorizations-oil-and-gas . In case of problems accessing these documents, please call the contact listed above. SUPPLEMENTARY INFORMATION: Purpose and Need for Regulatory Action This proposed rule would establish a framework under the authority of the MMPA (16 U.S.C. 1361 et seq. ) to allow for the authorization of take of marine mammals incidental to Hilcorp's oil and gas activities in Cook Inlet, Alaska. We received an application from Hilcorp requesting five-year regulations and authorization to take multiple species of marine mammals. Take would occur by Level A and Level B harassment incidental to a variety of sources including: 2D and 3D seismic surveys, geohazard surveys, vibratory sheet pile driving, and drilling of exploratory wells. Please see “Background” below for definitions of harassment. Legal Authority for the Proposed Action Section 101(a)(5)(A) of the MMPA (16 U.S.C. 1371(a)(5)(A)) directs the Secretary of Commerce to allow, upon request, the incidental, but not intentional taking of small numbers of marine mammals by U.S. citizens who engage in a specified activity (other than commercial fishing) within a specified geographical region for up to five years if, after notice and public comment, the agency makes certain findings and issues regulations that set forth permissible methods of taking pursuant to that activity and other means of effecting the least practicable adverse impact on the affected species or stocks and their habitat (see the discussion below in the “Proposed Mitigation” section), as well as monitoring and reporting requirements. Section 101(a)(5)(A) of the MMPA and the implementing regulations at 50 CFR part 216, subpart I provide the legal basis for issuing this proposed rule containing five-year regulations, and for any subsequent letters of authorization (LOAs). As directed by this legal authority, this proposed rule contains mitigation, monitoring, and reporting requirements. Summary of Major Provisions Within the Proposed Rule Following is a summary of the major provisions of this proposed rule regarding Hilcorp's activities. These measures include: • Required monitoring of the ensonified areas to detect the presence of marine mammals before beginning activities; • Shutdown of activities under certain circumstances to minimize injury of marine mammals; • Ramp up at the beginning of seismic surveying to allow marine mammals the opportunity to leave the area prior to beginning the survey at full power, as well as power downs, and vessel strike avoidance; • Ramp up of impact hammering of the drive pipe for the conductor pipe driven from the drill rig; and • Ceasing noise producing activities within 10 miles (16 km) of the mean higher high water (MHHW) line of the Susitna Delta (Beluga River to the Little Susitna River) between April 15 and October 15. Background The MMPA prohibits the “take” of marine mammals, with certain exceptions. 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 incidental take authorization may be provided to the public for review. Authorization for incidental takings shall be granted if NMFS finds that the taking will have a negligible impact on the species or stock(s) and will not have an unmitigable adverse impact on the availability of the species or stock(s) for taking for subsistence uses (where relevant). Further, NMFS must prescribe the permissible methods of taking and other means of effecting the least practicable adverse impact on the affected species or stocks and their habitat, paying particular attention to rookeries, mating grounds, and areas of similar significance, and on the availability of such species or stocks for taking for certain subsistence uses (referred to in shorthand as “mitigation”); 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 rule. NMFS' EA will be made available at https://www.fisheries.noaa.gov/national/marine-mammal-protection/incidental-take-authorizations-oil-and-gas on the date of publication of the proposed rule. We will review all comments submitted in response to this notice prior to concluding our NEPA process or making a final decision on the rulemaking request. Summary of Request On April 17, 2018, NMFS received an application from Hilcorp requesting authorization to incidentally take marine mammals, by Level A and Level B harassment, incidental to noise exposure resulting from oil and gas activities in Cook Inlet, Alaska, from May 2019 to April 2024. These regulations would be valid for a period of five years. On October 8, 2018, NMFS deemed the application adequate and complete. The use of sound sources such as those described in the application ( e.g., seismic airguns) may result in the take of marine mammals through disruption of behavioral patterns or may cause auditory injury of marine mammals. Therefore, incidental take authorization under the MMPA is warranted. Description of Proposed Activity Overview The scope of Hilcorp's Petition includes four stages of activity, including exploration, development, production, and decommissioning activities within the Applicant's area of operations in and adjacent to Cook Inlet within the Petition's geographic area (Figures 3 and 8 in the application). Table 1 summarizes the planned activities within the geographic scope of this Petition, and the following text describes these activities in more detail. This section is organized into two primary areas within Cook Inlet: lower Cook Inlet (south of the Forelands to Homer) and middle Cook Inlet (north of the Forelands to Susitna/Point Possession). Table 1—Summary of Planned Activities Included in Incidental Take Regulations (ITR) Petition Project name Cook Inlet region Year(s) planned Seasonal timing Anticipated duration Anticipated noise sources Anchor Point 2D seismic survey Lower Cook Inlet, Anchor Point to Kasilof 2021 or 2022 April-October 30 days Marine: 1 source vessel with airgun, 1 node vessel Onshore/Intertidal: Shot holes, tracked vehicles, helicopters. Outer Continental Shelf (OCS) 3D seismic survey Lower Cook Inlet OCS 2019 April-June 45-60 days 1 source vessel with airguns, 2 support vessels, 1 mitigation vessel potentially. OCS geohazard survey Lower Cook Inlet OCS 2019 or 2020 Fall 2019 or spring 20202 30 days 1 vessel with chosounders and/or sub-bottom profilers. OCS exploratory wells Lower Cook Inlet OCS 2020-2022 April-October 40-60 days per well, 2-4 wells per year 1 jack-up rig, drive pipe installation, vertical seismic profiling, 2-3 tugs for towing rig, support vessels, helicopters. Iniskin Peninsula exploration and development Lower Cook Inlet, west side 2019-2020 April-October 180 days Construction of causeway, vibratory sheet pile driving, dredging, vessels. Platform & pipeline maintenance Middle Cook Inlet 2019-2024 April-October 180 days Vessels, water jets, hydraulic grinders, pingers, helicopters, and/or sub-bottom profilers. North Cook Inlet Unit subseawell geohazard survey Middle Cook Inlet 2020 May 14 days 1 vessel with echosounders and/or sub-bottom profilers. North Cook Inlet Unit well abandonment activity Middle Cook Inlet 2020 May-July 90 days 1 jack-up rig, tugs towing rig, support vessel, helicopters. Trading Bay area geohazard survey Middle Cook Inlet 2020 May 30 days 1 vessel with echosounders and/or sub-bottom profilers. Trading Bay area exploratory wells Middle Cook Inlet 2020 May-October 120-150 days 1 jack-up rig, drive pipe installation, vertical seismic profiling, tugs towing rig, support vessel, helicopters. Drift River terminal decommissioning Lower Cook Inlet, west side 2023 April-October 120 days Vessels. Dates and Duration The scope of the Petition includes exploration, development, production, and decommissioning activities within the Applicant's area of operations in and adjacent to Cook Inlet within the Petition's geographic area (Figures 3 and 8 in the application) for the period of five years beginning May 1, 2019, extending through April 30, 2024. Specific Geographic Region The geographic area of activity covers a total of approximately 2.7 million acres (10,926 km 2 ) in Cook Inlet. It includes land and adjacent waters in Cook Inlet including both State of Alaska and Federal OCS waters (Figure 3 and 8 in the application). The area extends from the north at the Susitna Delta on the west side (61°10′ 48 N, 151°0′ 55 W) and Point Possession on the east side (61°2′ 11 N, 150°23′ 30 W) to the south at Ursus Cove on the west side (59°26′ 20 N, 153°45′ 5 W) and Nanwalek on the east side (59°24′ 5 N, 151°56′ 30 W). The area is depicted in Figures 3 amd 8 of the application. Detailed Description of Specific Activity Activities in Lower Cook Inlet Based on potential future lease sales in both State and Federal waters, operators collect two-dimensional (2D) seismic data to determine the location of possible oil and gas prospects. Generally, 2D survey lines are spaced farther apart than three-dimensional (3D) surveys and are conducted in a regional pattern that provides less detailed geological information. 2D surveys are used to cover wider areas to map geologic structures on a regional scale. Airgun array sizes used during 2D surveys are similar to those used during 3D surveys. Activities in Middle Cook Inlet 2D Seismic Survey During the timeframe of this Petition, the region of interest for the 2D survey is the marine, intertidal, and onshore area on the eastern side of Cook Inlet from Anchor Point to Kasilof. The area of interest is approximately 8 km (5 miles) offshore of the coastline. The anticipated timing of the planned 2D survey is in the open water season (April through October) in either 2020 or 2021. The actual survey duration is approximately 30 days in either year. The 2D seismic data are acquired using airguns in the marine zone, airguns in the intertidal zone when the tide is high and drilled shot holes in the intertidal zone when the tide is low and drilled shot holes in the land zone. The data are recorded using an autonomous nodal system ( i.e., no cables) that are deployed in the marine, intertidal, and land zones. The planned source lines (airgun and shot holes) are approximately 16 km (10 mi) in length running perpendicular to the coastline (see Figure 1 in application). The source lines are spaced every 8 km (5 mi) in between Anchor Point and Kasilof, with approximately 9-10 lines over the area of interest. In the marine and high tide intertidal zones, data will be acquired using a shallow water airgun towed behind one source vessel. Although the precise volume of the airgun array is unknown at this time, Hilcorp will use an airgun array similar to what has been used for surveys in Cook Inlet by Apache (2011-2013) and SAExploration (2015): Either a 2,400 cubic inch (cui) or 1,760 cui array. A 2,400 cui airgun was assumed for analysis in this proposed rule to be conservative in take estimation. In addition, the source vessel will be equipped with a 440 cui shallow water source which it can deploy at high tide in the intertidal area in less than 1.8 meter (6 feet) of water. Source lines are oriented along the node line. A single vessel is capable of acquiring a source line in approximately 1-2 hours (hrs). In general, only one source line will be collected in one day to allow for all the node deployments and retrievals, and intertidal and land zone shot holes drilling. There are up to 10 source lines, so if all operations run smoothly, there will only be 2 hr per day over 10 days of airgun activity. Hilcorp anticipates the entire operation to take approximately 30 days to complete to account for weather and equipment contingencies. The recording system that will be employed is an autonomous system “nodal” ( i.e., no cables), which is expected to be made up of at least two types of nodes; one for the land and one for the intertidal and marine environment. For the intertidal and marine zone, this will be a submersible multi-component system made up of three velocity sensors and a hydrophone. These systems have the ability to record continuous data. Inline receiver intervals for the node systems are approximately 50 m (165 ft). For 2D seismic surveys, the nodes are deployed along the same line as the seismic source. The deployment length is restricted by battery duration and data storage capacity. The marine nodes will be placed using one node vessel. The vessels required for the 2D seismic survey include just a source vessel and a node vessel that is conducting only passive recording. In the marine environment, once the nodes are placed on the seafloor, the exact position of each node is required. In very shallow water, the node positions are either surveyed by a land surveyor when the tide is low, or the position is accepted based on the position at which the navigator has laid the unit. In deeper water, a hull or pole mounted pinger to send a signal to the transponder which is attached to each node will be used. The transponders are coded and the crew knows which transponder goes with which node prior to the layout. The transponders response (once pinged) is added together with several other responses to create a suite of range and bearing between the pinger boat and the node. Those data are then calculated to precisely position the node. In good conditions, the nodes can be interrogated as they are laid out. It is also common for the nodes to be pinged after they have been laid out. Onshore and intertidal locating of source and receivers will be accomplished with Differential Global Positioning System/roving units (DGPS/RTK) equipped with telemetry radios which will be linked to a base station established on the source vessel. Survey crews will have both helicopter and light tracked vehicle support. Offshore source and receivers will be positioned with an integrated navigation system (INS) utilizing DGPS/RTK link to the land base stations. The integrated navigation system will be capable of many features that are critical to efficient safe operations. The system will include a hazard display system that can be loaded with known obstructions, or exclusion zones. Apache conducted a sound source verification (SSV) for the 440 cui and 2,400 cui arrays in 2012 (Austin and Warner 2012; 81 FR 47239). The location of the SSV was in Beshta Bay on the western side of Cook Inlet (between Granite Point and North Forelands). Water depths ranged from 30-70 m (98-229 ft). For the 440 cui array, the measured levels for the broadside direction were 217 decibel (dB) re: 1microPa (μPa) peak, 190 dB sound exposure level (SEL), and 201 dB root mean square (rms) at a distance of 50 m. The estimated distance to the 160 dB rms (90th percentile) threshold assuming the empirically measured transmission loss of 20.4 log R (Austin and Warner, 2012) was 2,500 m. Sound level near the source were highest between 30 and 300 hertz (Hz) in the endfire direction and between 20 Hz and 300 Hz in the broadside direction. For the 2,400 cui array, the measured levels for the endfire direction were 217 dB peak, 185 dB SEL, and 197 dB rms at a distance of 100 m. The estimate distance to the 160 dB rms (90th percentile) thresholds assuming the empirically measured transmission loss of 16.9 log R was 7,770 m. Sound levels near the source were highest between 30 and 150 Hz in the endfire direction and between 50 and 200 Hz in the broadside direction. These measured levels were used to evaluate potential Level A (217 dB peak and 185 dB SEL at 100 m assuming 15 log transmission loss) and Level B (7,330 m distance to 160 dB threshold) harassment isopleths from these sound sources (see Estimated Take section). 3D Seismic Survey During the timeframe of this Petition, Hilcorp plans to collect 3D seismic data for approximately 45-60 days starting May 1, 2019 over 8 of the 14 OCS lease blocks in lower Cook Inlet. The 3D seismic survey is comprised of an area of approximately 790 km 2 (305 mi 2 ) through 8 lease blocks (6357, 6405, 6406, 6407, 6455, 6456, 6457, 6458). Hilcorp submitted an application for an Incidental Harassment Authorization (IHA) in late 2017 for a planned survey in 2018 but withdrew the application and now plan for the survey to take place in 2019 and cover several years of surveying and development. The survey program is anticipated to begin May 1, 2019, and last for approximately 45-60 days through June 2019 in compliance with identified Bureau of Ocean Energy Management (BOEM) lease stipulations. The length of the survey will depend on weather, equipment, and marine mammal delays (contingencies of 20 percent weather, 10 percent equipment, 10 percent marine mammal were assumed in this analysis, or a 40 percent increase in expected duration to account for the aforementioned delays). Polarcus is the intended seismic contractor, and the general seismic survey design is provided below. The 3D seismic data will be acquired using a specially designed marine seismic vessel towing between 8 and 12 ~2,400-m (1.5 mi) recording cables with a dual air gun array. The survey will involve one source vessel, one support vessel, one chase vessel, and potentially one mitigation vessel. The anticipated seismic source to be deployed from the source vessel is a 14-airgun array with a total volume of 1,945 cui. Crew changes are expected to occur every four to six weeks using a helicopter or support vessel from shore bases in lower Cook Inlet. The proposed seismic survey will be active 24 hrs per day. The array will be towed at a speed of approximately 7.41 km/hr (4 knots), with seismic data collected continuously. Data acquisition will occur for approximately 5 hrs, followed by a 1.5-hr period to turn and reposition the vessel for another pass. The turn radius on the seismic vessel is approximately 3,200 m (2 mi). The data will be shot parallel to the Cook Inlet shorelines in a north/south direction. This operational direction will keep recording equipment/streamers in line with Cook Inlet currents and tides and keep the equipment away from shallow waters on the east and west sides. The program may be modified if the survey cannot be conducted as a result of noise conditions onsite ( i.e., ambient noise). The airguns will typically be turned off during the turns. However, depending on the daylight hours and length of the turn, Hilcorp may use the smallest gun in the array (45 cui) as a mitigation airgun where needed for no longer than 3 hours. The vessel will turn into the tides to ensure the recording cables/streamers remain in line behind the vessel. Hilcorp plans to use an array that provides for the lowest possible sound source to collect the target data. The proposed array is a Bolt 1900 LLXT dual gun array. The airguns will be configured as two linear arrays or “strings;” each string will have 7 airguns shooting in a “flip-flop” configuration for a total of 14 airguns. The airguns will range in volume from 45 to 290 cui for a total of 1,945 cui. The first and last are spaced approximately 14 m (45.9 ft) apart and the strings are separated by approximately 10 m (32.8 ft). The two airgun strings will be distributed across an approximate area of 30 x 14 m (98.4 x 45.9 ft) behind the source vessel and will be towed 300-400 m (984-1,312 ft) behind the vessel at a depth of 5 m (16.4 ft). The firing pressure of the array is 2,000 pounds per square inch (psi). The airgun will fire every 4.5 to 6 seconds, depending on the exact speed of the vessel. When fired, a brief (25 milliseconds [ms] to 140 ms) pulse of sound is emitted by all airguns nearly simultaneously. Hilcorp proposes to use a single 45 cui airgun, the smallest airgun in the array, for mitigation purposes. Hilcorp intends to use 8 Sercel-type solid streamers or functionally similar for recording the seismic data (Figure 5 in the application). Each streamer will be approximately 2,400 m (150 mi) in length and will be towed approximately 8-15 m (26.2-49.2 ft) or deeper below the surface of the water. The streamers will be placed approximately 50 m (165 ft) apart to provide a total streamer spread of 400 m (1,148 ft). Hilcorp recognizes solid streamers as best in class for marine data acquisition because of unmatched reliability, signal to noise ratio, low frequency content, and noise immunity. The survey will involve one source vessel, one support vessel, one or two chase vessels, and potentially one mitigation vessel. The source vessel tows the airgun array and the streamers. The support vessel provides general support for the source vessel, including supplies, crew changes, etc. The chase vessel monitors the in-water equipment and maintains a security perimeter around the streamers. The mitigation vessel provides a viewing platform to augment the marine mammal monitoring program. The planned volume of the airgun array is 1,945 cui. Hilcorp and their partners will be conducting detailed modeling of the array output, but a detailed SSV has not been conducted for this array in Cook Inlet. Therefore, for the purposes of estimating acoustic harassment, results from previous seismic surveys in Cook Inlet by Apache and SAExploration, particularly the 2,400 cui array, were used. Apache conducted an SSV for the 440 cui and 2,400 cui arrays in 2012 (Austin and Warner 2012; 81 FR 47239). The location of the SSV was in Beshta Bay on the western side of Cook Inlet (between Granite Point and North Forelands). Water depths ranged from 30-70 m (98-229 ft). For the 2,400 cui array, the measured levels for the endfire direction were 217 dB peak, 185 dB SEL, and 197 dB rms at a distance of 100 m. The estimate distance to the 160 dB rms (90th percentile) thresholds assuming the empirically measured transmission loss of 16.9 log R was 7,770 m. Sound levels near the source were highest between 30 and 150 Hz in the endfire direction and between 50 and 200 Hz in the broadside direction. These measured levels were used to evaluate potential Level A (217 dB peak and 185 dB SEL at 100 m assuming 15 log transmission loss) and B (7,330 m distance to 160 dB threshold) acoustic harassment of marine mammals in this Petition. Geohazard and Geotechnical Surveys Upon completion of the 3D seismic survey over the lower Cook Inlet OCS leases, Hilcorp plans to conduct a geohazard survey on site-specific regions within the area of interest prior to conducting exploratory drilling. The precise location is not known, as it depends on the results of the 3D seismic survey, but the location will be within the lease blocks. The anticipated timing of the activity is in either the fall of 2019 or the spring of 2020. The actual survey duration will take approximately 30 days. The suite of equipment used during a typical geohazards survey consists of single beam and multi-beam echosounders, which provide water depths and seafloor morphology; a side scan sonar that provides acoustic images of the seafloor; a sub-bottom profiler which provides 20 to 200 m (66 to 656 ft) sub-seafloor penetration with a 6- to 20-centimeter (cm, 2.4-7.9-inch [in]) resolution. Magnetometers, to detect ferrous items, may also be used. Geotechnical surveys are conducted to collect bottom samples to obtain physical and chemical data on surface and near sub-surface sediments. Sediment samples typically are collected using a gravity/piston corer or grab sampler. The surveys are conducted from a single support vessel. The echosounders and sub-bottom profilers are generally hull-mounted or towed behind a single vessel. The ship travels at 3-4.5 knots (5.6-8.3 km/hr). Surveys are site specific and can cover less than one lease block in a day, but the survey extent is determined by the number of potential drill sites in an area. BOEM guidelines at NTL-A01 require data to be gathered on a 150 by 300 m (492 by 984 ft) grid within 600 m (1,969 ft) of the surface location of the drill site, a 300 by 600 m (984 by 1,969 ft) grid along the wellbore path out to 1,200 m (3,937 ft) beyond the surface projection of the conductor casing, and extending an additional 1,200 m beyond that limit with a 1,200 by 1,200 m grid out to 2,400 m (7,874 ft) from the well site. The multibeam echosounder, single beam echosounder, and side scan sonar operate at frequencies of greater than 200 kHz. Based on the frequency ranges of these pieces of equipment and the hearing ranges of the marine mammals that have the potential to occur in the action area, the noise produced by the echosounders and side scan sonar are not likely to result in take of marine mammals and are not considered further in this document. The geophysical surveys include use of a low resolution and high resolution sub-bottom profiler. The proposed high-resolution sub-bottom profiler operates at source level of 210 dB re 1 μPa RMS at 1 m. The proposed system emits energy in the frequency bands of 2 to 24 kHz. The beam width is 15 to 24 degrees. Typical pulse rate is between 3 and 10 Hz. The secondary low-resolution sub-bottom profiler will be utilized as necessary to increase sub-bottom profile penetration. The proposed system emits energy in the frequency bands of 1 to 4 kHz. Exploratory Drilling Operators will drill exploratory wells based on mapping of subsurface structures using 2D and 3D seismic data and historical well information. Hilcorp plans to conduct the exploratory drilling program April to October between 2020 and 2022. The exact start date is currently unknown and is dependent on the results of the seismic survey, geohazard survey, and scheduling availability of the drill rig. It is expected that each well will take approximately 40-60 days to drill and test. Beginning in spring 2020, Hilcorp Alaska plans to possibly drill two and as many as four exploratory wells, pending results of the 3D seismic survey in the lower Cook Inlet OCS leases. After testing, the wells may be plugged and abandoned. Hilcorp Alaska proposes to conduct its exploratory drilling using a rig similar to the Spartan 151 drill rig. The Spartan 151 is a 150 H class independent leg, cantilevered jack-up drill rig with a drilling depth capability of 7,620 m (25,000 ft) that can operate in maximum water depths up to 46 m (150 ft). Depending on the rig selection and location, the drilling rig will be towed on site using up to three ocean- going tugs licensed to operate in Cook Inlet. Rig moves will be conducted in a manner to minimize any potential risk regarding safety as well as cultural or environmental impact. While under tow to the well sites, rig operations will be monitored by Hilcorp and the drilling contractor management. Very High Frequency (VHF) radio, satellite, and cellular phone communication systems will be used while the rig is under tow. Helicopter transport will also be available. Similarly to transiting vessels, although some marine mammals could receive sound levels in exceedance of the general acoustic threshold of 120 dB from the tugs towing the drill rig during this project, take is unlikely to occur, primarily because of the predictable movement of vessels and tugs. Marine mammal population density in the project area is low (see Estimated Take section below), and those that are present are likely habituated to the existing baseline of commercial ship traffic. Further, there are no activity-, location-, or species-specific circumstances or other contextual factors that would increase concern and the likelihood of take from towing of the drill rig. The drilling program for the well will be described in detail in an Exploration Plan to BOEM. The Exploration Plan will present information on the drilling mud program; casing design, formation evaluation program; cementing programs; and other engineering information. After rig up/rig acceptance by Hilcorp Alaska, the wells will be spudded and drilled to bottom-hole depths of approximately 2,100 to 4,900 m (7,000 to 16,000 ft) depending on the well. It is expected that each well will take about 40-60 days to drill and up to 10-21 days of well testing. If two wells are drilled, it will take approximately 80-120 days to complete the full program; if four wells are drilled, it will take approximately 160-240 days to complete the full program. Primary sources of rig-based acoustic energy were identified as coming from the D399/D398 diesel engines, the PZ-10 mud pump, ventilation fans (and associated exhaust), and electrical generators. The source level of one of the strongest acoustic sources, the diesel engines, was estimated to be 137 dB re 1 µPa rms at 1 m in the 141-178 Hz bandwidth. Based on this measured level, the 120 dB rms acoustic received level isopleth would be 50 m (154 ft) away from where the energy enters the water (jack-up leg or drill riser). Drilling and well construction sounds are similar to vessel sounds in that they are relatively low-level and low-frequency. Since the rig is stationary in a location with low marine mammal density, the impact of drilling and well construction sounds produced from the jack up rig is expected to be lower than a typical large vessel. There is open water in all directions from the drilling location. Any marine mammal approaching the rig would be fully aware of its presence long before approaching or entering the zone of influence for behavioral harassment, and we are unaware of any specifically important habitat features ( e.g., concentrations of prey or refuge from predators) within the rig's zone of influence that would encourage marine mammal use and exposure to higher levels of noise closer to the source. Given the absence of any activity-, location-, or species-specific circumstances or other contextual factors that would increase concern, we do not expect routine drilling noise to result in the take of marine mammals. When planned and permitted operations are completed, the well will be suspended according to Bureau of Safety and Environmental Enforcement (BSEE) regulations. The well casings will be landed in a mudline hanger after each hole section is drilled. When the well is abandoned, the production casing is sealed with mechanical plugging devices and cement to prevent the movement of any reservoir fluids between various strata. Each casing string will be cutoff below the surface and sealed with a cement plug. A final shallow cement plug will be set to approximately 3.05 m (10 ft) below the mudline. At this point, the surface casing, conductor, and drive pipe will be cutoff and the three cutoff casings and the mudline hanger are pulled to the deck of the jack-up rig for final disposal. The plugging and abandonment procedures are part of the Well Plan which is reviewed by BSEE prior to being issued an approved Permit to Drill. A drive pipe is a relatively short, large-diameter pipe driven into the sediment prior to the drilling of oil wells. The drive pipe serves to support the initial sedimentary part of the well, preventing the looser surface layer from collapsing and obstructing the wellbore. Drive pipes are installed using pile driving techniques. Hilcorp proposed to drive approximately 60 m of 76.2-cm pipe at each well site prior to drilling using a Delmar D62-22 impact hammer (or similar). This hammer has an impact weight of 6,200 kg (13,640 lbs). The drive pipe driving event is expected to last one to three days at each well site, although actual pounding of the pipe will only occur intermittently during this period. Conductors are slightly smaller diameter pipes than the drive pipes used to transport or “conduct” drill cuttings to the surface. For these wells, a 50.8-cm [20-in] conductor pipe may be drilled, not hammered, inside the drive pipe, dependent on the integrity of surface formations. Illingworth & Rodkin (2014) measured the hammer noise for hammering the drive pipe operating from the rig Endeavour for Buccaneer in 2013 and report the source level at 190 dB at 55 m, with underwater levels exceeding 160 dB rms threshold at 1.63 km (1 mi). The measured sound levels for the pipe driving were used to evaluate potential Level A (source level of 221dB @1m and assuming 15 logR transmission loss) and Level B (1,630 m distance to the 160 dB threshold) acoustic harassment of marine mammals. Conductors are slightly smaller diameter pipes than the drive pipes used to transport or “conduct” drill cuttings to the surface. For these wells, a 50.8-cm (20-in) conductor pipe may be drilled, not hammered, inside the drive pipe, dependent on the integrity of surface formations. There are no noise concerns associated with the conductor pipe drilling. Once the well is drilled, accurate follow-up seismic data may be collected by placing a receiver at known depths in the borehole and shooting a seismic airgun at the surface near the borehole, called vertical seismic profiling (VSP). These data provide high-resolution images of the geological layers penetrated by the borehole and can be used to accurately correlate original surface seismic data. The actual size of the airgun array is not determined until the final well depth is known, but typical airgun array volumes are between 600 and 880 cui. VSP typically takes less than two full days at each well site. Illingworth & Rodkin (2014) measured a 720 cui array for Buccaneer in 2013 and report the source level at 227 dB at 1 m, with underwater levels exceeding 160 dB rms threshold at 2.47 km (1.54 mi). The measured sound levels for the VSP were used to evaluate potential Level A (227 dB rms at 1 m assuming 15 logR transmission loss) and Level B (2,470 m distance to the 160 dB threshold) harassment isopleths. Iniskin Peninsula Exploration Hilcorp Alaska initiated baseline exploratory data collection in 2013 for a proposed land-based oil and gas exploration and development project on the Iniskin Peninsula of Alaska, near Chinitna Bay. The proposed project is approximately 97 km (60 mi) west of Homer on the west side of Cook Inlet in the Fitz Creek drainage. New project infrastructure includes material sites, a 6.9 km (4.3 mi) long access road, prefabricated bridges to cross four streams, an air strip, barge landing/staging areas, fuel storage facilities, water wells and extraction sites, an intertidal causeway, a camp/staging area, and a drill pad. Construction is anticipated to start in 2020. An intertidal rock causeway is proposed to be constructed adjacent to the Fitz Creek staging area to improve the accessibility of the barge landing during construction and drilling operations. The causeway will extend seaward from the high tide line approximately 366 m (1,200 ft) to a landing area 46 m (150 ft) wide. A dock face will be constructed around the rock causeway so that barges will be able to dock along the causeway. Rock placement for the causeway is not known to generate sound at levels expected to disturb marine mammals. The causeway is also not proposed at a known pinniped haulout or other biologically significant location for local marine mammals. Therefore, rock laying for the causeway is not considered further in this document. The causeway will need to be 75 percent built before the construction of the dock face will start. The dock face will be constructed with 18-m (60-ft) tall Z-sheet piles, all installed using a vibratory hammer. It will take approximately 14-25 days, depending on the length of the work shift, assuming approximately 25 percent of the day actual pile driving. The timing of pile driving will be in late summer or early winter, after the causeway has been partially constructed. Illingworth & Rodkin (2007) compiled measured near-source (10 m [32.8 ft]) SPL data from vibratory pile driving for different pile sizes ranging in diameter from 30.5 to 243.8 cm (12 to 96 in). For this petition, the source level of the 61.0-cm (24-in) AZ steel sheet pile from Illingworth & Rodkin (2007) was used for the sheet pile. The measured sound levels of 160 dB rms at 10 m assuming 15 logR transmission loss for the vibratory sheet pile driving was used to evaluate potential Level A and B harassment isopleths. Activities in Middle Cook Inlet Offshore Production Platforms Of the 17 production platforms in central Cook Inlet, 15 are owned by Hilcorp. Hilcorp performs routine construction on their platforms, depending on needs of the operations. Construction activities may take place up to 24 hrs a day. In-water activities include support vessels bringing supplies five days a week up to two trips per day between offshore systems at Kenai (OSK) and the platform. Depending on the needs, there may also be barges towed by tugs with equipment and helicopters for crew and supply changes. Routine supply-related transits from vessels and helicopters are not substantially different from routine vessel and air traffic already occurring in Cook Inlet, and take is not expected to occur from these activities. Offshore Production Drilling Hilcorp routinely conducts development drilling activities at offshore platforms on a regular basis to meet the asset's production needs. Development drilling activities occurs from existing platforms within the Cook Inlet through either open well slots or existing wellbores in existing platform legs. Drilling activities from platforms within Cook Inlet are accomplished by using conventional drilling equipment from a variety of rig configurations. Some other platforms in Cook inlet have permanent drilling rigs installed that operate under power provided by the platform power generation systems, while others do not have drill rigs, and the use of a mobile drill rig is required. Mobile offshore drill rigs may be powered by the platform power generation (if compatible with the platform power system) or self-generate power with the use of diesel fired generators. For the reasons outlined above for the Lower Inlet, noise from routine drilling is not considered further in this document. Helicopter logistics for development drilling programs operations will include transportation for personnel and supplies. The helicopter support will be managed through existing offshore services based at the OSK Heliport to support rig crew changes and cargo handling. Helicopter flights to and from the platform while drilling is occurring is anticipated to increase (on average) by two flights per day from normal platform operations. Major supplies will be staged on-shore at the OSK Dock in Nikiski. Required supplies and equipment will be moved from the staging area to the platform in which drilling occurring by existing supply vessels that are currently in use supporting offshore operations within Cook Inlet. Vessel trips to and from the platform while drilling is occurring is anticipated to increase (on average) by two trips per day from normal platform operations. During mobile drill rig mobilization and demobilization, one support vessel is used continuously for approximately 30 days to facilitate moving rig equipment and materials. Oil and Gas Pipeline Maintenance Each year, Hilcorp Alaska must verify the structural integrity of their platforms and pipelines located within Cook Inlet. Routine maintenance activities include: subsea pipeline inspections, stabilizations, and repairs; platform leg inspections and repairs; and anode sled installations and/or replacement. In general, pipeline stabilization and pipeline repair are anticipated to occur in succession for a total of 6-10 weeks. However, if a pipeline stabilization location also requires repair, the divers will repair the pipeline at the same time they are stabilizing it. Pipeline repair activities are only to be conducted on an as-needed basis whereas pipeline stabilization activities will occur annually. During underwater inspections, if the divers identify an area of the pipeline that requires stabilization, they will place Sea-Crete bags at that time rather than waiting until the major pipeline stabilization effort that occurs later in the season. Natural gas and oil pipelines located on the seafloor of the Cook Inlet are inspected on an annual basis using ultrasonic testing (UT), cathodic protection surveys, multi-beam sonar surveys, and sub-bottom profilers. Deficiencies identified are corrected using pipeline stabilization methods or USDOT-approved pipeline repair techniques. The Applicant employs dive teams to conduct physical inspections and evaluate cathodic protection status and thickness of subsea pipelines on an annual basis. If required for accurate measurements, divers may use a water jet to provide visual access to the pipeline. For stabilization, inspection dive teams may place Sea-Crete bags beneath the pipeline to replace any materials removed by the water jet. Results of the inspections are recorded and significant deficiencies are noted for repair. Multi-beam sonar and sub-bottom profilers may also be used to obtain images of the seabed along and immediately adjacent to all subsea pipelines. Elements of pipeline inspections that could produce underwater noise include: the dive support vessel, water jet, multi-beam sonar/sub-bottom profiler and accompanying vessel. A water jet is a zero-thrust water compressor that is used for underwater removal of marine growth or rock debris underneath the pipeline. The system operates through a mobile pump which draws water from the location of the work. Water jets likely to be used in Cook Inlet include, but are not limited to, the CaviDyne CaviBlaster® and the Gardner Denver Liqua-Blaster. Noise generated during the use of the water jets would be very short in duration (30 minutes or less at any given time) and intermittent. Hilcorp Alaska conducted underwater measurements during 13 minutes of CaviBlaster® use in Cook Inlet in April 2017 (Austin 2017). Received sound levels were measured up to 143 dB re 1 µPa rms at 170 m and up to 127 dB re 1 µPa rms at 1,100 m. Sounds from the Caviblaster® were clearly detectable out to the maximum measurement range of 1.1 km. Using the measured transmission loss of 19.5 log R (Austin 2017), the source level for the Caviblaster® was estimated as 176 dB re 1 μPa at 1 m. The sounds were broadband in nature, concentrated above 500 Hz with a dominant tone near 2 kHz. Specifications for the GR 29 Underwater Hydraulic Grinder state that the SPL at the operator's position would be 97 dB in air (Stanley 2014). There are no underwater measurements available for the grinder, so using a rough estimate of converting sound level in dB in air to water by adding 61.5 dB would result in an underwater level of approximately 159 dB2. The measured sound levels for the water jet and grinder were used to evaluate potential Level A and B acoustic harassment isopleths. If necessary, Hilcorp may use an underwater pipe cutter to replace existing pipeline segments in Cook Inlet. The following tools are likely to be used for pipeline cutting activities: • A diamond wire saw used for remote cutting underwater structures such as pipes and I-Beams. These saws use hydraulic power delivered by a dedicated power source. The saw usually uses a method that pushes the spinning wire through the pipe. • A hydraulically-powered Guillotine saw which uses an orbital cutting movement similar to traditional power saws. Generally, sound radiated from the diamond wire cutter is not easily discernible from the background noise during the cutting operation. The Navy measured underwater sound levels when the diamond saw was cutting caissons for replacing piles at an old fuel pier at Naval Base Point Loma (Naval Base Point Loma Naval Facilities Engineering Command Southwest 2017). They reported an average SPL for a single cutter at 136.1-141.4 dB rms at 10 m. Specifications for the Guillotine saw state that the SPL at the operator's position would be 86 dB in air (Wachs 2014). There are no underwater measurements available for the grinder, so using a rough estimate of converting sound level in dB in air to water by adding 61.5 dB would result in an underwater level of approximately 148 dB. Because the measured levels for use of underwater saws do not exceed the NMFS criteria, the noise from underwater saws was not considered further in this document. Scour spans beneath pipelines greater than 23 m (75 ft) have the potential to cause pipeline failures. To be conservative, scour spans of 15 m (50 ft) or greater identified using multi-beam sonar surveys are investigated using dive teams. Divers perform tactile inspections to confirm spans greater than 15 m (50 ft). The pipeline is stabilized along these spans with Sea-Crete concrete bags. While in the area, the divers will also inspect the external coating of the pipeline and take cathodic protection readings if corrosion wrap is found to be absent. Elements of pipeline stabilization that could produce underwater noise include: Dive support vessel and water jet. Significant pipeline deficiencies identified during pipeline inspections are repaired as soon as practicable using methods including, but not limited to, USDOT-approved clamps and/or fiber glass wraps, bolt/flange replacements, and manifold replacements. In some cases, a water jet may be required to remove sand and gravel from under or around the pipeline to allow access for assessment and repair. The pipeline surface may also require cleaning using a hydraulic grinder to ensure adequate repair. If pipeline replacement is required, an underwater pipe cutter such as a diamond wire saw or hydraulically-powered Guillotine saw may be used. Elements of pipeline repair that could produce underwater noise include: Dive support vessel, water jet, hydraulic grinder, and underwater pipe cutter. Platform Leg Inspection and Repair Hilcorp's platforms in Cook Inlet are inspected on a routine basis. Divers and certified rope access technicians visually inspect subsea platform legs. These teams also identify and correct significant structural deficiencies. Platform leg integrity and pipeline-to-platform connections beneath the water surface are evaluated by divers on a routine basis. Platform legs, braces, and pipeline-to-platform connections are evaluated for cathodic protection status, structure thickness, excessive marine growth, damage, and scour. If required, divers may use a water jet to clean or provide access to the structure. If necessary, remedial grinding using a hydraulic under water grinder may be required to determine extent damage and/or to prevent further crack propagation. All inspection results are recorded and significant deficiencies are noted for repair. Elements of subsea platform leg inspection and repair that could produce underwater noise include: Dive support vessel, hydraulic grinder, water jet. Platform leg integrity along the tidal zone is inspected on a routine basis. Difficult-to-reach areas may be accessed using either commercially-piloted unmanned aerial systems (UAS). Commercially-piloted UASs may be deployed from the top-side of the platform to obtain images of the legs. Generally, the UAS is in the air for 15-20 minutes at a time due to battery capacity, which allows for two legs and part of the underside of the platform to be inspected. The total time to inspect a platform is approximately 1.5 hrs of flight time. The UAS is operated at a distance of up to 30.5 m (100 ft) from the platform at an altitude of 9-15 m (30-50 ft) above sea level. To reduce potential harassment of marine mammals, the area around the platform would be inspected prior to launch of the UAS to ensure there are no flights directly above marine mammals. As no flights will be conducted directly over marine mammals, the effects of drone use for routine maintenance are not considered further in this application. Anode Sled Installation and Replacement Galvanic and impressed current anode sleds are used to provide cathodic protection for the pipelines and platforms in Cook Inlet. Galvanic anode sleds do not require a power source and may be installed along the length of the pipelines on the seafloor. Impressed current anode sleds are located on the seafloor at each of the corners of each platform and are powered by rectifiers located on the platform. Anodes are placed at the seafloor using dive vessels and hand tools. If necessary, a water jet may be used to provide access for proper installation. Anodes and/or cables may be stabilized using Sea-Crete bags. Pingers Several types of moorings are deployed in support of Hilcorp operations; all of which require an acoustic pinger for location or release. The pinger is deployed over the side of a vessel and a short signal is emitted to the mooring device. The mooring device responds with a short signal to indicate that the device is working, to indicate range and bearing data, or to illicit a release of the unit from the anchor. These are used for very short periods of time when needed. The types of moorings requiring the use of pingers anticipated to be used in the Petition period include acoustic moorings during the 3D seismic survey (assumed 2-4 moorings), node placement for the 2D survey (used with each node deployment), and potential current profilers deployed each season (assumed 2-4 moorings). The total amount of time per mooring device is less than 10 minutes during deployment and retrieval. To avoid disturbance, the pinger would not be deployed if marine mammals have been observed within 135 m (443 ft) of the vessel. The short duration of the pinger deployment as well as Hilcorp's mitigation suggests take of marine mammals from pinger use is unlikely to occur and pingers are not considered further in this analysis. North Cook Inlet Unit Subsea Well Plugging and Abandonment The discovery well in the North Cook Inlet Unit was drilled over 50 years ago and is planned to be abandoned, so Hilcorp Alaska plans to conduct a geohazard survey to locate the well and conduct plugging and abandonment (P&A) activities for a previously drilled subsea exploration well in 2020. The geohazard survey location is approximately 402-804 m ( 1/4 - 1/2 mi) south of the Tyonek platform and will take place over approximately seven days with a grid spacing of approximately 250 m (820 ft). The suite of equipment used during a typical geohazards survey consists of single beam and multi-beam echosounders, which provide water depths and seafloor morphology; a side scan sonar that provides acoustic images of the seafloor; a sub-bottom profiler which provides 20 to 200 m (66 to 656 ft) sub-seafloor penetration with a 6- to 20-cm (2.4-7.9-in) resolution. The echosounders and sub-bottom profilers are generally hull-mounted or towed behind a single vessel. The vessel travels at 3-4.5 knots (5.6-8.3 km/hr). After the well has been located, Hilcorp plans to conduct plugging and abandonment activities over a 60-90 day time period in May through July in 2020. The jack-up rig will be similar to what is described above (the Spartan 151 drill rig, or similar). The rig will be towed onsite using up to three ocean-going tugs. Once the jack-up rig is on location, divers working off a boat will assist in preparing the subsea wellhead and mudline hanger for the riser to tie the well to the jack-up. Once the riser is placed, the BOP equipment is made up to the riser. At this point, the well will be entered and well casings will be plugged with mechanical devices and cement and then cutoff and pulled. A shallow cement plug will be set in the surface casing to 3.05 m (10 ft) below the mudline hanger. The remaining well casings will be cutoff and the mudline hanger will be recovered to the deck of the jack-up rig for disposal. The well abandonment will be performed in accordance to Alaska Oil and Gas Conservation Commission (AOGCC) regulations. Trading Bay Exploratory Drilling Hilcorp plans to conduct exploratory drilling activities in the Trading Bay area. The specific sites of interest have not yet been identified, but the general area is shown in Figure 3 in the application. Hilcorp will conduct geohazard surveys over the areas of interest to locate potential hazards prior to drilling with the same suite of equipment as described above for exploratory drilling in the lower Inlet. The survey is expected to take place over 30-60 days in 2019 from a single vessel. The exploratory drilling and well completion activities will take place in site-specific areas based on the geohazard survey. Hilcorp plans to drill 1-2 exploratory wells in this area in the open water season of 2020 with the same equipment and methods as described above for lower Inlet exploratory drilling. The noise of routine drilling is not considered further as explained in the description of activities in the Lower Inlet. However, drive pipe installation and vertical seismic profiling will be considered further. 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 Eleven species of marine mammal have the potential to occur in the action area during the five year period of activities proposed by Hilcorp. These species are described in further detail below. Fin Whales For management purposes, three stocks of fin whales are currently recognized in U.S. Pacific waters: Alaska (Northeast Pacific), California/Washington/Oregon, and Hawaii. Recent analyses provide evidence that the population structure should be reviewed and possibly updated. However, substantially new data on the stock structure is lacking (Muto et al. 2017). Fin whales, including the Northeastern Pacific stock, are listed as endangered under the ESA. Mizroch et al. (2009) provided a comprehensive summary of fin whale sightings data, including whaling catch data and determined there could be at least six populations of fin whales. Evidence suggests two populations are migratory (eastern and western North Pacific) and two to four more are year-round residents in peripheral seas such as the Gulf of California, East China Sea, Sanriku-Hokkaido, and possibly the Sea of Japan. The two migratory stocks are likely mingling in the Bering Sea in July and August. Moore et al. (1998, 2006), Watkins et al. (2000), and Stafford et al. (2007) documented high rates of calling along the Alaska coast beginning in August/September and lasting through February. Fin whales are regularly observed in the Gulf of Alaska during the summer months, even though calls are seldom detected during this period (Stafford et al. 2007). Instruments moored in the southeast Bering Sea detected calls over the course of a year and found peaks from September to November as well as in February and March (Stafford et al. 2010). Delarue et al. (2013) detected calls in the northeastern Chukchi Sea from instruments moored from July through October from 2007 through 2010. Fin whales are found seasonally in the Gulf of Alaska, Bering Sea, and as far north as the northern Chukchi Sea (Muto et al. 2017). Surveys conducted in coastal waters of the Aleutians and the Alaska Peninsula found that fin whales occurred primarily from the Kenai Peninsula to the Shumagin Islands and were abundant near the Semidi Islands and Kodiak Island (Zerbini et al. 2006). An opportunistic survey conducted on the shelf of the Gulf of Alaska found fin whales concentrated west of Kodiak Island in Shelikof Strait, and in the southern Cook Inlet region. Smaller numbers were also observed over the shelf east of Kodiak to Prince William Sound (AFSC, 2003). In the northeastern Chukchi Sea, visual sightings and acoustic detections have been increasing, which suggests the stock may be re-occupying habitat used prior to large-scale commercial whaling (Muto et al. 2017). Most of these areas are feeding habitat for fin whales. Fin whales are rarely observed in Cook Inlet, and most sightings occur near the entrance of the inlet. During the NMFS aerial surveys in Cook Inlet from 2000-2016, 10 sightings of 26 estimated individual fin whales in lower Cook Inlet were observed (Shelden et al. 2013, 2015, 2016). Humpback Whales Currently, three populations of humpback whales are recognized in the North Pacific, migrating between their respective summer/fall feeding areas and winter/spring calving and mating areas as follows (Baker et al. 1998; Calambokidis et al. 1997). Although there is considerable distributional overlap in the humpback whale stocks that use Alaska, the whales seasonally found in lower Cook Inlet are probably of the Central North Pacific stock (Muto et al. 2017). Listed as endangered under the ESA, this stock has recently been estimated at 7,890 animals (Muto et al. 2017). The Central North Pacific stock winters in Hawaii and summers from British Columbia to the Aleutian Islands (Calambokidis et al. 1997), including Cook Inlet. Humpback whales in the high latitudes of the North Pacific Ocean are seasonal migrants that feed on euphausiids and small schooling fishes (Muto et al. 2017). During the spring, these animals migrate north and spend the summer feeding in the prey-rich sub-polar waters of southern Alaska, British Columbia, and the southern Chukchi Sea. Individuals from the Western North Pacific (endangered), Hawaii (not listed under the ESA), and the Mexico (threatened) DPSs migrate to areas near and potentially in the Petition region. However, most of the individuals that migrate to the Cook Inlet area are likely from the Hawaii DPS and not the Western North Pacific or Mexico DPSs (NMFS 2017). In the summer, humpback whales are regularly present and feeding in the Cook Inlet region, including Shelikof Strait, Kodiak Island bays, and the Barren Islands, in addition to Gulf of Alaska regions adjacent to the southeast side of Kodiak Island (especially Albatross Banks), the Kenai and Alaska peninsulas, Elizabeth Island, as well as south of the Aleutian Islands. Humpbacks also may be present in some of these areas throughout autumn (Muto et al. 2017). Humpback whales have been observed during marine mammal surveys conducted in Cook Inlet. However, their presence is largely confined to lower Cook Inlet. Recent monitoring by Hilcorp in upper Cook Inlet has also included sightings of humpbacks near Tyonek. During SAExploration's 2015 seismic program, three humpback whales were observed in Cook Inlet; two near the Forelands and one in Kachemak Bay (Kendall et al. 2015). During NMFS' Cook Inlet beluga whale aerial surveys from 2000-2016, there were 88 sightings of 191 estimated individual humpback whales in lower Cook Inlet (Shelden et al. 2017). They have been regularly seen near Kachemak Bay during the summer months (Rugh et al. 2005). There are observations of humpback whales as far north as Anchor Point, with recent summer observations extending to Cape Starichkof (Owl Ridge 2014). Although several humpback whale sightings occurred mid-inlet between Iniskin Peninsula and Kachemak Bay, most sightings occurred outside of the Petition region near Augustine, Barren, and Elizabeth Islands (Shelden et al. 2013, 2015, 2017). Ferguson et al. (2015) has established Biologically Important Areas (BIAs) as part of the NOAA Cetacean Density and Distribution Mapping Working Group (CetMap) efforts. This information supplements the quantitative information on cetacean density, distribution, and occurrence by: (1) Identifying areas where cetacean species or populations are known to concentrate for specific behaviors, or be range-limited, but for which there is not sufficient data for their importance to be reflected in the quantitative mapping effort; and (2) providing additional context within which to examine potential interactions between cetaceans and human activities. A “Feeding Area” BIA for humpback whales in the Gulf of Alaska region encompasses the waters east of Kodiak Island (the Albatross and Portlock Banks), a target for historical commercial whalers based out of Port Hobron, Alaska (Ferguson et al. 2015; Reeves et al. 1985; Witteveen et al. 2007). This BIA also includes waters along the southeastern side of Shelikof Strait and in the bays along the northwestern shore of Kodiak Island. The highest densities of humpback whales around the Kodiak Island BIA occur from July-August (Ferguson et al. 2015). Minke Whale Minke whales are most abundant in the Gulf of Alaska during summer and occupy localized feeding areas (Zerbini et al. 2006). Concentrations of minke whales have occurred along the north coast of Kodiak Island (and along the south coast of the Alaska Peninsula (Zerbini et al. 2006). The current estimate for minke whales between Kenai Fjords and the Aleutian Islands is 1,233 individuals (Zerbini et al. 2006). During shipboard surveys conducted in 2003, three minke whale sightings were made, all near the eastern extent of the survey from nearshore Prince William Sound to the shelf break (NMML 2003). Minke whales become scarce in the Gulf of Alaska in fall; most whales are thought to leave the region by October (Consiglieri et al. 1982). Minke whales are migratory in Alaska, but recently have been observed off Cape Starichkof and Anchor Point year-round (Muto et al. 2017). During Cook Inlet-wide aerial surveys conducted from 1993 to 2004, minke whales were encountered three times (1998, 1999, and 2006), both times off Anchor Point 16 miles northwest of Homer (Shelden et al. 2013, 2015, 2017). A minke whale was also reported off Cape Starichkof in 2011 (A. Holmes, pers. comm.) and 2013 (E. Fernandez and C. Hesselbach, pers. comm.), suggesting this location is regularly used by minke whales, including during the winter. Several minke whales were recorded off Cape Starichkof in early summer 2013 during exploratory drilling (Owl Ridge 2014), suggesting this location is regularly used by minke whales year-round. During Apache's 2014 survey, a total of 2 minke whale groups (3 individuals) were observed during this time period, one sighting to the southeast of Kalgin Island and another sighting near Homer (Lomac-MacNair et al. 2014). SAExploration noted one minke whale near Tuxedni Bay in 2015 (Kendall et al. 2015). This species is unlikely to be seen in upper Cook Inlet but may be encountered in the mid and lower Inlet. Killer Whales Two different stocks of killer whales inhabit the Cook Inlet region of Alaska: the Alaska Resident Stock and the Gulf of Alaska, Aleutian Islands, Bering Sea Transient Stock (Muto et al 2017). Seasonal and year-round occurrence has been noted for killer whales throughout Alaska (Braham and Dahlheim 1982), where whales have been labeled as “resident,” “transient,” and “offshore” type killer whales (Dahlheim et al. 2008; Ford et al. 2000). The killer whales using Cook Inlet are thought to be a mix of resident and transient individuals from two different stocks: the Alaska Resident Stock, and the Gulf of Alaska, Aleutian Islands, and Bering Sea Transient Stock (Allen and Angliss 2015). Although recent studies have documented movements of Alaska Resident killer whales from the Bering Sea into the Gulf of Alaska as far north as southern Kodiak Island, none of these whales have been photographed further north and east in the Gulf of Alaska where regular photo-identification studies have been conducted since 1984 (Muto et al. 2017). Killer whales are occasionally observed in lower Cook Inlet, especially near Homer and Port Graham (Shelden et al. 2003; Rugh et al. 2005). The few whales that have been photographically identified in lower Cook Inlet belong to resident groups more commonly found in nearby Kenai Fjords and Prince William Sound (Shelden et al. 2003). The availability of these prey species largely determines the likeliest times for killer whales to be in the area. During aerial surveys conducted between 1993 and 2004, killer whales were observed on only three flights, all in the Kachemak and English Bay area (Rugh et al. 2005). However, anecdotal reports of killer whales feeding on belugas in upper Cook Inlet began increasing in the 1990s, possibly in response to declines in sea lion and harbor seal prey elsewhere (Shelden et al. 2003). One killer whale group of two individuals was observed during the 2015 SAExploration seismic program near the North Foreland (Kendall et al. 2015). During NMFS aerial surveys, killer whales were observed in 1994 (Kamishak Bay), 1997 (Kachemak Bay), 2001 (Port Graham), 2005 (Iniskin Bay), 2010 (Elizabeth and Augustine Islands), and 2012 (Kachemak Bay; Shelden et al. 2013). Eleven killer whale strandings have been reported in Turnagain Arm, six in May 1991, and five in August 1993. This species is expected to be rarely seen in upper Cook Inlet but may be encountered in the mid and lower Inlet. Gray Whales Gray whales have been reported feeding near Kodiak Island, in southeastern Alaska, and south along the Pacific Northwest (Allen and Angliss 2013). Because most gray whales migrating through the Gulf of Alaska region are thought to take a coastal route, BIA boundaries for the migratory corridor in this region were defined by the extent of the continental shelf (Ferguson et al. 2015). Most gray whales calve and breed from late December to early February in protected waters along the western coast of Baja California, Mexico. In spring, the ENP stock of gray whales migrates approximately 8,000 km (5,000 mi) to feeding grounds in the Bering and Chukchi seas before returning to their wintering areas in the fall (Rice and Wolman 1971). Northward migration, primarily of individuals without calves, begins in February; some cow/calf pairs delay their departure from the calving area until well into April (Jones and Swartz 1984). Gray whales approach the proposed action area in late March, April, May, and June, and leave again in November and December (Consiglieri et al. 1982; Rice and Wolman 1971) but migrate past the mouth of Cook Inlet to and from northern feeding grounds. Some gray whales do not migrate completely from Baja to the Chukchi Sea but instead feed in select coastal areas in the Pacific Northwest, including lower Cook Inlet (Moore et al. 2007). Most of the population follows the outer coast of the Kodiak Archipelago from the Kenai Peninsula in spring or the Alaska Peninsula in fall (Consiglieri et al. 1982; Rice and Wolman 1971). Though most gray whales migrate past Cook Inlet, small numbers have been noted by fishers near Kachemak Bay, and north of Anchor Point (BOEM 2015). During the NMFS aerial surveys, gray whales were observed in the month of June in 1994, 2000, 2001, 2005 and 2009 on the east side of Cook Inlet near Port Graham and Elizabeth Island but also on the west side near Kamishak Bay (Shelden et al. 2013). One gray whale was sighted as far north at the Beluga River. Additionally, summering gray whales were seen offshore of Cape Starichkof by marine mammal observers monitoring Buccaneer's Cosmopolitan drilling program in 2013 (Owl Ridge 2014). During Apache's 2012 seismic program, nine gray whales were observed in June and July (Lomac-MacNair et al. 2013). During Apache's seismic program in 2014, one gray whale was observed (Lomac- MacNair et al. 2014). During SAExploration's seismic survey in 2015, no gray whales were observed (Kendall et al. 2015). This species is unlikely to be seen in upper Cook Inlet but may be encountered in the mid and lower Inlet. Cook Inlet Beluga Whales The Cook Inlet beluga whale DPS is a small geographically isolated population that is separated from other beluga populations by the Alaska Peninsula. The population is genetically distinct from other Alaska populations suggesting the peninsula is an effective barrier to genetic exchange (O'Corry-Crowe et al. 1997). The Cook Inlet beluga whale population is estimated to have declined from 1,300 animals in the 1970s (Calkins 1989) to about 340 animals in 2014 (Shelden et al. 2015). The precipitous decline documented in the mid-1990s was attributed to unsustainable subsistence practices by Alaska Native hunters (harvest of >50 whales per year) (Mahoney and Shelden 2000). In 2006, a moratorium to cease hunting was agreed upon to protect the species. In April 2011, NMFS designated critical habitat for the beluga under the ESA (76 FR 20180) as shown on Figure 13 of the application. NMFS finalized the Conservation Plan for the Cook Inlet beluga in 2008 (NMFS 2008a). NMFS finalized the Recovery Plan for Cook Inlet beluga whales in 2016 (NMFS 2016a). The Cook Inlet beluga stock remains within Cook Inlet throughout the year (Goetz et al. 2012a). Two areas, consisting of 7,809 km 2 (3,016 mi 2 ) of marine and estuarine environments considered essential for the species' survival and recovery were designated critical habitat. However, in recent years the range of the beluga whale has contracted to the upper reaches of Cook Inlet because of the decline in the population (Rugh et al. 2010). Area 1 of the Cook Inlet beluga whale critical habitat encompasses all marine waters of Cook Inlet north of a line connecting Point Possession (61.04° N, 150.37° W) and the mouth of Three Mile Creek (61.08.55° N, 151.04.40° W), including waters of the Susitna, Little Susitna, and Chickaloon Rivers below mean higher high water (MHHW). This area provides important habitat during ice-free months and is used intensively by Cook Inlet beluga between April and November (NMFS 2016a). Since 1993, NMFS has conducted annual aerial surveys in June, July or August to document the distribution and abundance of beluga whales in Cook Inlet. The collective survey results show that beluga whales have been consistently found near or in river mouths along the northern shores of upper Cook Inlet ( i.e., north of East and West Foreland). In particular, beluga whale groups are seen in the Susitna River Delta, Knik Arm, and along the shores of Chickaloon Bay. Small groups had also been recorded seen farther south in Kachemak Bay, Redoubt Bay (Big River), and Trading Bay (McArthur River) prior to 1996 but very rarely thereafter. Since the mid-1990s, most (96 to 100 percent) beluga whales in upper Cook Inlet have been concentrated in shallow areas near river mouths, no longer occurring in the central or southern portions of Cook Inlet (Hobbs et al. 2008). Based on these aerial surveys, the concentration of beluga whales in the northernmost portion of Cook Inlet appears to be consistent from June to October (Rugh et al. 2000, 2004a, 2005, 2006, 2007). Though Cook Inlet beluga whales can be found throughout the inlet at any time of year, they spend the ice-free months generally in the upper Cook Inlet, shifting into the middle and lower Inlet in winter (Hobbs et al. 2005). In 1999, one beluga whale was tagged with a satellite transmitter, and its movements were recorded from June through September of that year. Since 1999, 18 beluga whales in upper Cook Inlet have been captured and fitted with satellite tags to provide information on their movements during late summer, fall, winter, and spring. Using location data from satellite-tagged Cook Inlet belugas, Ezer et al. (2013) found most tagged whales were in the lower to middle inlet (70 to 100 percent of tagged whales) during January through March, near the Susitna River Delta from April to July (60 to 90 percent of tagged whales) and in the Knik and Turnagain Arms from August to December. During the spring and summer, beluga whales are generally concentrated near the warmer waters of river mouths where prey availability is high and predator occurrence is low (Moore et al. 2000). Beluga whales in Cook Inlet are believed to mostly calve between mid-May and mid-July, and concurrently breed between late spring and early summer (NMFS 2016a), primarily in upper Cook Inlet. Movement was correlated with the peak discharge of seven major rivers emptying into Cook Inlet. Boat-based surveys from 2005 to the present (McGuire and Stephens 2017), and initial results from passive acoustic monitoring across the entire inlet (Castellote et al. 2016) also support seasonal patterns observed with other methods. Other surveys also confirm Cook Inlet belugas near the Kenai River during summer months (McGuire and Stephens 2017). During the summer and fall, beluga whales are concentrated near the Susitna River mouth, Knik Arm, Turnagain Arm, and Chickaloon Bay (Nemeth et al. 2007) where they feed on migrating eulachon (Thaleichthys pacificus) and salmon (Onchorhyncus spp.) (Moore et al. 2000). Data from tagged whales (14 tags between July and March 2000 through 2003) show beluga whales use upper Cook Inlet intensively between summer and late autumn (Hobbs et al. 2005). Critical Habitat Area 1 reflects this summer distribution. As late as October, beluga whales tagged with satellite transmitters continued to use Knik Arm and Turnagain Arm and Chickaloon Bay, but some ranged into lower Cook Inlet south to Chinitna Bay, Tuxedni Bay, and Trading Bay (McArthur River) in the fall (Hobbs et al. 2005). Data from NMFS aerial surveys, opportunistic sighting reports, and satellite-tagged beluga whales confirm they are more widely dispersed throughout Cook Inlet during the winter months (November-April), with animals found between Kalgin Island and Point Possession. In November, beluga whales moved between Knik Arm, Turnagain Arm, and Chickaloon Bay, similar to patterns observed in September (Hobbs et al. 2005). By December, beluga whales were distributed throughout the upper to mid-inlet. From January into March, they moved as far south as Kalgin Island and slightly beyond in central offshore waters. Beluga whales also made occasional excursions into Knik Arm and Turnagain Arm in February and March despite ice cover greater than 90 percent (Hobbs et al. 2005). During Apache's seismic test program in 2011 along the west coast of Redoubt Bay, lower Cook Inlet, a total of 33 beluga whales were sighted during the survey (Lomac-MacNair et al. 2013). During Apache's 2012 seismic program in mid-inlet, a total of 151 sightings of approximately 1,463 estimated individual beluga whales were observed (Lomac-MacNair et al. 2013). During SAExploration's 2015 seismic program, a total of eight sightings of approximately 33 estimated individual beluga whales were visually observed during this time period and there were two acoustic detections of beluga whales (Kendall et al. 2015). Hilcorp recently reported 143 sightings of beluga whales while conducting pipeline work near Ladd Landing in upper Cook Inlet, which is not near the area that seismic surveys are proposed but near some potential well sites. Ferguson et al. (2015) delineated one “Small” and “Resident” BIA for Cook Inlet beluga whales. Small and Resident BIAs are defined as “areas and time within which small and resident populations occupy a limited geographic extent” (Ferguson et al. 2015). The Cook Inlet beluga whale BIA was delineated using the habitat model results of Goetz et al. 2012 and the critical habitat boundaries (76 FR 20180). Harbor Porpoise In Alaskan waters, three stocks of harbor porpoises are currently recognized for management purposes: Southeast Alaska, Gulf of Alaska, and Bering Sea Stocks (Muto et al. 2017). Porpoises found in Cook Inlet belong to the Gulf of Alaska Stock which is distributed from Cape Suckling to Unimak Pass and most recently was estimated to number 31,046 individuals (Muto et al. 2017). They are one of the three marine mammals (the other two being belugas and harbor seals) regularly seen throughout Cook Inlet (Nemeth et al. 2007), especially during spring eulachon and summer salmon runs. Harbor porpoises primarily frequent the coastal waters of the Gulf of Alaska and Southeast Alaska (Dahlheim et al. 2000, 2008), typically occurring in waters less than 100 m deep (Hobbs and Waite 2010). The range of the Gulf of Alaska stock includes the entire Cook Inlet, Shelikof Strait, and the Gulf of Alaska. Harbor porpoises have been reported in lower Cook Inlet from Cape Douglas to the West Foreland, Kachemak Bay, and offshore (Rugh et al. 2005a). Although they have been frequently observed during aerial surveys in Cook Inlet (Shelden et al. 2014), most sightings are of single animals, and are concentrated at Chinitna and Tuxedni bays on the west side of lower Cook Inlet (Rugh et al. 2005) and in the upper inlet. The occurrence of larger numbers of porpoise in the lower Cook Inlet may be driven by greater availability of preferred prey and possibly less competition with beluga whales, as belugas move into upper inlet waters to forage on Pacific salmon during the summer months (Shelden et al. 2014). The harbor porpoise frequently has been observed during summer aerial surveys of Cook Inlet, with most sightings of individuals concentrated at Chinitna and Tuxedni Bays on the west side of lower Cook Inlet (Figure 14 of the application; Rugh et al. 2005). Mating probably occurs from June or July to October, with peak calving in May and June (as cited in Consiglieri et al. 1982). Small numbers of harbor porpoises have been consistently reported in the upper Cook Inlet between April and October, except for a recent survey that recorded higher numbers than typical. NMFS aerial surveys have identified many harbor porpoise sightings throughout Cook Inlet. During Apache's 2012 seismic program, 137 sightings (190 individuals) were observed between May and August (Lomac-MacNair et al. 2013). Lomac-MacNair et al. 2014 identified 77 groups of harbor porpoise totaling 13 individuals during Apache's 2014 seismic survey, both from vessels and aircraft, during the month of May. During SAExploration's 2015 seismic survey, 52 sightings (65 individuals) were observed north of the Forelands (Kendall et al. 2015). Recent passive acoustic research in Cook Inlet by Alaska Department of Fish and Game (ADF&G) and the Marine Mammal Laboratory (MML) have indicated that harbor porpoises occur more frequently than expected, particularly in the West Foreland area in the spring (Castellote et al. 2016), although overall numbers are still unknown at this time. Dall's Porpoise Dall's porpoises are widely distributed throughout the North Pacific Ocean including preferring deep offshore and shelf-slopes, and deep oceanic waters (Muto et al. 2017). The Dall's porpoise range in Alaska extends into the southern portion of the Petition region (Figure 14 of the application). Dall's porpoises are present year-round throughout their entire range in the northeast including the Gulf of Alaska, and occasionally the Cook Inlet area (Morejohn 1979). This porpoise also has been observed in lower Cook Inlet, around Kachemak Bay, and rarely near Anchor Point (Owl Ridge 2014; BOEM 2015). Throughout most of the eastern North Pacific they are present during all months of the year, although there may be seasonal onshore-offshore movements along the west coast of the continental United States and winter movements of populations out of areas with ice such as Prince William Sound (Muto et al. 2017). Dall's porpoises were observed (2 groups, 3 individuals) during Apache's 2014 seismic survey which occurred in the summer months (Lomac-MacNair et al. 2014). Dall's porpoises were observed during the month of June in 1997 (Iniskin Bay), 199 (Barren Island), and 2000 (Elizabeth Island, Kamishak Bay and Barren Island) (Shelden et al. 2013). Dall's porpoises have been observed in lower Cook Inlet, including Kachemak Bay and near Anchor Point (Owl Ridge 2014). One Dall's porpoise was observed in August north of Nikiski in the middle of the Inlet during SAExploration's 2015 seismic program (Kendall et al. 2015). Harbor Seal Harbor seals occupy a wide variety of habitats in freshwater and saltwater in protected and exposed coastlines and range from Baja California north along the west coasts of Washington, Oregon, and California, British Columbia, and Southeast Alaska; west through the Gulf of Alaska, Prince William Sound, and the Aleutian Islands; and north in the Bering Sea to Cape Newenham and the Pribilof Islands. Harbor seals are found throughout the entire lower Cook Inlet coastline, hauling out on beaches, islands, mudflats, and at the mouths of rivers where they whelp and feed (Muto et al. 2017). The major haul out sites for harbor seals are located in lower Cook Inlet. The presence of harbor seals in upper Cook Inlet is seasonal. In Cook Inlet, seal use of western habitats is greater than use of the eastern coastline (Boveng et al. 2012). NMFS has documented a strong seasonal pattern of more coastal and restricted spatial use during the spring and summer for breeding, pupping, and molting, and more wide- ranging seal movements within and outside of Cook Inlet during the winter months (Boveng et al. 2012). Large-scale patterns indicate a portion of harbor seals captured in Cook Inlet move out of the area in the fall, and into habitats within Shelikof Strait, Northern Kodiak Island, and coastal habitats of the Alaska Peninsula, and are most concentrated in Kachemak Bay, across Cook Inlet toward Iniskin and Iliamna Bays, and south through the Kamishak Bay, Cape Douglas and Shelikof Strait regions (Boveng et al. 2012). A portion of the Cook Inlet seals move into the Gulf of Alaska and Shelikof Strait during the winter months (London et al. 2012). Seals move back into Cook Inlet as the breeding season approaches and their spatial use is more concentrated around haul-out areas (Boveng et al. 2012; London et al. 2012). Some seals expand their use of the northern portion of Cook Inlet. However, in general, seals that were captured and tracked in the southern portion of Cook Inlet remained south of the Forelands (Boveng et al. 2012). Important harbor seal haul-out areas occur within Kamishak and Kachemak Bays and along the coast of the Kodiak Archipelago and the Alaska Peninsula. Chinitna Bay, Clearwater and Chinitna Creeks, Tuxedni Bay, Kamishak Bay, Oil Bay, Pomeroy and Iniskin Islands, and Augustine Island are also important spring- summer breeding and molting areas and known haul-outs sites (Figure 15 of the application). Small-scale patterns of movement within Cook Inlet also occur (Boveng et al. 2012). Montgomery et al. (2007) recorded over 200 haul out sites in lower Cook Inlet alone. However, only a few dozen to a couple hundred seals seasonally occur in upper Cook Inlet (Rugh et al. 2005), mostly at the mouth of the Susitna River where their numbers vary in concert with the spring eulachon and summer salmon runs (Nemeth et al. 2007; Boveng et al. 2012). The Cook Inlet/Shelikof Stock is distributed from Anchorage into lower Cook Inlet during summer and from lower Cook Inlet through Shelikof Strait to Unimak Pass during winter (Boveng et al. 2012). Large numbers concentrate at the river mouths and embayments of lower Cook Inlet, including the Fox River mouth in Kachemak Bay, and several haul outs have been identified on the southern end of Kalgin Island in lower Cook Inlet (Rugh et al. 2005; Boveng et al. 2012). Montgomery et al. (2007) recorded over 200 haul-out sites in lower Cook Inlet alone. During Apache's 2012 seismic program, harbor seals were observed in the project area from early May until the end of the seismic operations in late September (Lomac-MacNair et al. 2013). Also in 2012, up to 100 harbor seals were observed hauled out at the mouths of the Theodore and Lewis rivers during monitoring activity associated with Apache's 2012 Cook Inlet seismic program. During Apache's 2014 seismic program, 492 groups of harbor seals (613 individuals) were observed. This was the highest sighting rate of any marine mammal observed during the summer of 2014 (Lomac-MacNair et al. 2014). During SAExploration's 2015 seismic survey, 823 sightings (1,680 individuals) were observed north and between the Forelands (Kendall et al. 2015). Steller Sea Lions The western DPS (WDPS) stock of Steller sea lions most likely occurs in Cook Inlet (78 FR 66139). The center of abundance for the Western DPS is considered to extend from Kenai to Kiska Island (NMFS 2008b). The WDPS of the Steller sea lion is defined as all populations west of longitude 144° W to the western end of the Aleutian Islands. The range of the WDPS includes 38 rookeries and hundreds of haul out sites. The Hilcorp action area only considers the WDPS stock. The most recent comprehensive aerial photographic and land-based surveys of WDPS Steller sea lions in Alaska were conducted during the 2014 and 2015 breeding seasons (Fritz et al. 2015). The WDPS of Steller sea lions is currently listed as endangered under the ESA (55 FR 49204) and designated as depleted under the MMPA. Critical habitat was designated on August 27, 1993 (58 FR 45269) south of the proposed project area in the Cook Inlet region (Figure 16 of the application). The critical habitat designation for the WDPS of Steller sea lions was determined to include a 37 km (20 nm) buffer around all major haul outs and rookeries, and associated terrestrial, atmospheric, and aquatic zones, plus three large offshore foraging areas (Figure 16 of the application). NMFS also designated no entry zones around rookeries (50 CFR 223.202). Designated critical habitat is located outside Cook Inlet at Gore Point, Elizabeth Island, Perl Island, and Chugach Island (NMFS 2008b). The geographic center of Steller sea lion distribution is the Aleutian Islands and the Gulf of Alaska, although as the WDPS has declined, rookeries in the west became progressively smaller (NMFS 2008b). Steller sea lion habitat includes terrestrial sites for breeding and pupping (rookeries), resting (haul outs), and marine foraging areas. Nearly all rookeries are at sites inaccessible to terrestrial predators on remote rocks, islands, and reefs. Steller sea lions inhabit lower Cook Inlet, especially near Shaw Island and Elizabeth Island (Nagahut Rocks) haul out sites (Rugh et al. 2005) but are rarely seen in upper Cook Inlet (Nemeth et al. 2007). Steller sea lions occur in Cook Inlet but south of Anchor Point around the offshore islands and along the west coast of the upper inlet in the bays (Chinitna Bay, Iniskin Bay, etc.) (Rugh et al. 2005). Portions of the southern reaches of the lower inlet are designated as critical habitat, including a 20-nm buffer around all major haulout sites and rookeries. Rookeries and haul out sites in lower Cook Inlet include those near the mouth of the inlet, which are far south of the project area. Steller sea lions feed largely on walleye pollock, salmon, and arrowtooth flounder during the summer, and walleye pollock and Pacific cod during the winter (Sinclair and Zeppelin 2002). Except for salmon, none of these are found in abundance in upper Cook Inlet (Nemeth et al. 2007). Steller sea lions can travel considerable distances (Baba et al. 2000). Steller sea lions are not known to migrate annually, but individuals may widely disperse outside of the breeding season (late May to early July; Jemison et al. 2013; Allen and Angliss 2014). Most adult Steller sea lions inhabit rookeries during the breeding season (late May to early July). Some juveniles and non-breeding adults occur at or near rookeries during the breeding season, but most are on haul outs. Adult males may disperse widely after the breeding season and, during fall and winter, many sea lions increase use of haul outs, especially terrestrial sites but also on sea ice in the Bering Sea (NMFS 2008b). Steller sea lions have been observed during marine mammal surveys conducted in Cook Inlet. In 2012, during Apache's 3D Seismic surveys, there were three sightings of approximately four individuals in upper Cook Inlet (Lomac-MacNair et al. 2013). Marine mammal observers associated with Buccaneer's drilling project off Cape Starichkof observed seven Steller sea lions during the summer of 2013 (Owl Ridge 2014). During SAExploration's 3D Seismic Program in 2015, four Steller sea lions were observed in Cook Inlet. One sighting occurred between the West and East Forelands, one near Nikiski and one northeast of the North Foreland in the center of Cook Inlet (Kendall et al. 2015). During NMFS Cook Inlet beluga whale aerial surveys from 2000-2016, there were 39 sightings of 769 estimated individual Steller sea lions in lower Cook Inlet (Shelden et al. 2017). Sightings of large congregations of Steller sea lions during NMFS aerial surveys occurred outside the Petition region, on land in the mouth of Cook Inlet ( e.g., Elizabeth and Shaw Islands). California Sea Lions There is limited information on the presence of California sea lions in Alaska. From 1973 to 2003, a total of 52 California sea lions were reported in Alaska, with sightings increasing in the later years. Most sightings occurred in the spring; however, they have been observed during all seasons. California sea lion presence in Alaska was correlated with increasing population numbers within their southern breeding range (Maniscalco et al. 2004). There have been relatively few California sea lions observed in Alaska, most are often alone or occasionally in small groups of two or more and usually associated with Steller sea lions at their haulouts and rookeries (Maniscalco et al. 2004). California sea lions are not typically observed farther north than southeast Alaska, and sightings are very rare in Cook Inlet. California sea lions have not been observed during the annual NMFS aerial surveys in Cook Inlet. However, a sighting of two California sea lions was documented during the Apache 2012 seismic survey (Lomac-MacNair et al. 2013). Additionally, NMFS' anecdotal sighting database has four sightings in Seward and Kachemak Bay. The California sea lion breeds from the southern Baja Peninsula north to Año Nuevo Island, California. Breeding season lasts from May to August, and most pups are born from May through July. Their nonbreeding range extends northward into British Columbia and occasionally farther north into Alaskan waters. California sea lions have been observed in Alaska during all four seasons; however, most of the sightings have occurred during the spring (Maniscalco et al. 2004). Sections 3 and 4 of the application summarize 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's Stock Assessment Reports (SAR; https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessment-reports-region ), and more general information about these species ( e.g., physical and behavioral descriptions) may be found on NMFS' website ( https://www.fisheries.noaa.gov/species-directory/ ). Table 2 lists all species with expected potential for occurrence in Cook Inlet 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' 2017 U.S. Alaska and Pacific SARs (Muto et al, 2017; 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 2017 SARs and draft 2018 SARs (available online at: https://www.fisheries.noaa.gov/action/2018-draft-marine-mammal-stock-assessment-reports-available ). Table 2—Species With the Potential To Occur in Cook Inlet, Alaska Common name Scientific name Stock ESA/ MMPA status; Strategic (Y/N) 1 Stock abundance (CV, N min , most recent abundance survey) 2 PBR Annual M/SI 3 Order Cetartiodactyla—Cetacea—Superfamily Mysticeti (baleen whales) Family Eschrichtiidae: Gray whale Eschrichtius robustus Eastern Pacific -/-; N 20,990 (0.05, 20,125, 2011) 624 4.25 Family Balaenopteridae (rorquals): Fin whale Balaenoptera physalus Northeastern Pacific E/D; Y 3,168 (0.26,2,554 2013) 5.1 0.4 Minke whale Balaenoptera acutorostrata Alaska -/-; N N/A N/A 0 Humpback whale Megaptera novaeangliae Western North Pacific E/D; Y 1,107 (0.3, 865, 2006) 3 3.2 Superfamily Odontoceti (toothed whales, dolphins, and porpoises) Family Delphinidae: Beluga whale Delphinapterus leucas Cook Inlet E/D; Y 312 (0.1, 287, 2014) 0.54 0.57 Killer whale Orcinus orca Alaska Resident -/-; N 2,347 (N/A, 2,347, 2012) 24 1 Alaska Transient -/-; N 587 (N/A, 587, 2012) 5.9 1 Family Phocoenidae (porpoises): Harbor porpoise Phocoena phocoena Gulf of Alaska -/-; Y 31,046 (0.214, N/A, 1998) Undet 72 Dall's porpoise Phocoenoides dalli Alaska -/-; N 83,400 (0.097, N/A, 1993) Undet 38 Order Carnivora—Superfamily Pinnipedia Family Otariidae (eared seals and sea lions): Steller sea lion Eumetopias jubatus Western E/D; Y 53,303 (N/A, 53,303, 2016) 320 241 California sea lion Zalophus californianus U.S. -/-; N 296,750 (153,337, N/A, 2011) 9,200 331 Family Phocidae (earless seals): Harbor seal Phoca vitulina Cook Inlet/Shelikof -/-; N 27,386 (25,651, N/A, 2011) 770 234 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 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 NMFS marine mammal stock assessment reports online at: www.nmfs.noaa.gov/pr/sars/ . CV is coefficient of variation; Nmin is the minimum estimate of stock abundance. In some cases, CV is not applicable [explain if this is the case] 3 These values, found in NMFS' SARs, represent annual levels of human-caused mortality plus serious injury from all sources combined ( e.g., commercial fisheries, ship strike). Annual M/SI often cannot be determined precisely and is in some cases presented as a minimum value or range. A CV associated with estimated mortality due to commercial fisheries is presented in some cases. Note: Italicized species are not expected to be taken or proposed for authorization. All species that could potentially occur in the proposed survey areas are included in Table 2. As described below, all 11 species (with 12 managed stocks) temporally and spatially co-occur with the activity to the degree that take is reasonably likely to occur, and we have proposed authorizing it. In addition, sea otters may be found in Cook Inlet. However, sea otters are managed by the U.S. Fish and Wildlife Service and are not considered further in this document. 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 (2018) 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. 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; • Mid-frequency cetaceans (larger toothed whales, beaked whales, and most delphinids): generalized hearing is estimated to occur between approximately 150 Hz and 160 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; • Pinnipeds in water; Phocidae (true seals): generalized hearing is estimated to occur between approximately 50 Hz to 86 kHz; and • Pinnipeds in water; Otariidae (eared seals): generalized hearing is estimated to occur between 60 Hz and 39 kHz. The pinniped functional hearing group was modified from Southall et al. (2007) on the basis of data indicating that phocid species have consistently demonstrated an extended frequency range of hearing compared to otariids, especially in the higher frequency range (Hemilä et al., 2006; Kastelein et al., 2009; Reichmuth and Holt, 2013). For more detail concerning these groups and associated frequency ranges, please see NMFS (2018) for a review of available information. Eleven marine mammal species (eight cetacean and three pinniped (two otariid and one phocid) species) 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, four are classified as low-frequency cetaceans ( i.e., all mysticete species), two 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., harbor porpoise and Kogia spp.). 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 in as much 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 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 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 μPa2-s) represents the total energy contained within a pulse 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 kilohertz (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; and • 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, two types of sub-bottom profiler would also be used by Hilcorp during the geotechnical and geohazard surveys: A low resolution unit (1-4 kHz) and a high resolution unit (2-24 kHz). Potential Effects of Underwater Sound —Please refer to the information given previously (“Description of Active Acoustic Sound 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 airguns. 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, sub-bottom profilers, drill rig construction, or sheet pile driving 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 suite of 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. 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) which would induce 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 (SELcum) thresholds are 1 [Text truncated at 120,000 characters. The full text is on the page linked above.] --- Source: Frix Law Library, https://www.frixlaw.com/law-library/documents/fr%3A2019-05781. Public record. Not legal advice.