# Takes of Marine Mammals Incidental to Specified Activities; Taking Marine Mammals Incidental to the Port of Alaska's North Extension Stabilization Step 1 (NES1) Project in Anchorage, Alaska > Briefs, arguments, decisions, and more. URL: https://www.frixlaw.com/law-library/documents/fr%3A2023-24238 ## Record - **Collection:** Federal Register - **Document type:** Notice - **Published:** November 6, 2023 - **Citation:** 88 FR 76576 ## Text DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration [RTID 0648-XD366] Takes of Marine Mammals Incidental to Specified Activities; Taking Marine Mammals Incidental to the Port of Alaska's North Extension Stabilization Step 1 (NES1) Project in Anchorage, Alaska AGENCY: National Marine Fisheries Service (NMFS), National Oceanic and Atmospheric Administration (NOAA), Commerce. ACTION: Notice; proposed incidental harassment authorization; request for comments on proposed authorization and possible renewal. SUMMARY: NMFS has received a request from the Port of Alaska (POA) for authorization to take marine mammals incidental to the NES1 project at the existing port facility in Anchorage, Alaska. Pursuant to the Marine Mammal Protection Act (MMPA), NMFS is requesting comments on its proposal to issue an incidental harassment authorization (IHA) to incidentally take marine mammals during the specified activities. NMFS is also requesting comments on a possible one-time, 1-year renewal that could be issued under certain circumstances and if all requirements are met, as described in the Request for Public Comments section at the end of this notice. 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 December 5, 2023. ADDRESSES: Comments should be addressed to Jolie Harrison, Chief, Permits and Conservation Division, Office of Protected Resources, National Marine Fisheries Service and should be submitted via email to ITP.tyson.moore@noaa.gov. 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-construction-activities. In case of problems accessing these documents, please call the contact listed above. Instructions: NMFS is not responsible for comments sent by any other method, to any other address or individual, or received after the end of the comment period. Comments, including all attachments, must not exceed a 25-megabyte file size. All comments received are a part of the public record and will generally be posted online at https://www.fisheries.noaa.gov/national/marine-mammal-protection/incidental-take-authorizations-construction-activities without change. All personal identifying information ( e.g., name, address) voluntarily submitted by the commenter may be publicly accessible. Do not submit confidential business information or otherwise sensitive or protected information. FOR FURTHER INFORMATION CONTACT: Reny Tyson Moore, Office of Protected Resources, NMFS, (301) 427-8401. SUPPLEMENTARY INFORMATION: 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 proposed or, if the taking is limited to harassment, a notice of a proposed IHA is provided to the public for review. Authorization for incidental takings shall be granted if NMFS finds that the taking will have a negligible impact on the species or stock(s) 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 the 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 the takings are set forth. The definitions of all applicable MMPA statutory terms cited above are included in the relevant sections below. 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 IHA) with respect to potential impacts on the human environment. Accordingly, NMFS has prepared an Environmental Assessment (EA) to consider the environmental impacts associated with the issuance of the proposed IHA. NMFS' EA is available at https://www.fisheries.noaa.gov/national/marine-mammal-protection/incidental-take-authorizations-construction-activities. We will review all comments submitted in response to this notice prior to concluding our NEPA process or making a final decision on the IHA request. Summary of Request On July 19, 2022, NMFS received a request from the POA for an IHA to take marine mammals incidental to construction activities related to the NES1 project in Anchorage, Alaska. Following NMFS' review of the application, the POA submitted revised versions on December 27, 2022, July 28, 2023, and August 31, 2023. The application was deemed adequate and complete on September 7, 2023. The POA submitted a final version addressing additional minor corrections on September 21, 2023. The POA's request is for take of seven species of marine mammals by Level B harassment and, for a subset of these species ( i.e., harbor seal ( Phoca vitulina ) and harbor porpoise ( Phocoena phocoena )), Level A harassment. Neither the POA nor NMFS expect serious injury or mortality to result from this activity and, therefore, an IHA is appropriate. NMFS previously issued IHAs to the POA for similar work (85 FR 19294, April 6, 2020; 86 FR 50057, September 7, 2021). The POA complied with all the requirements ( e.g., mitigation, monitoring, and reporting) of the previous IHAs, and information regarding their monitoring results may be found in the Effects of the Specified Activity on Marine Mammals and their Habitat and Estimated Take section of this notice and online at https://www.fisheries.noaa.gov/national/marine-mammal-protection/incidental-take-authorizations-construction-activities. This proposed IHA would cover 1 year of the ongoing Port of Alaska Modernization Program (PAMP) for which the POA obtained prior IHAs and intends to request additional take authorization for subsequent facets of the program. The PAMP involves construction activities related to the modernization of the POAs marine terminals. Description of Proposed Activity Overview The POA, located on Knik Arm in upper Cook Inlet, provides critical infrastructure for the citizens of Anchorage and a majority of the citizens of Alaska. The North Extension at the POA is a failed bulkhead structure that was constructed between 2005 and 2011. Parts of the North Extension bulkhead structure and the surrounding upland area are unstable and collapsing, and some of the sheet piles are visibly twisted and buckled. The structure presents safety hazards and logistical impediments to ongoing Port operations, and much of the upland area is currently unusable. The NES project would result in removal of the failed sheet pile structure and reconfiguration and realignment of the shoreline within the North Extension, including the conversion of approximately 0.05 square kilometers (km 2 ; 13 acres) of developed land back to intertidal and subtidal habitat within Knik Arm. The NES project would be completed in two distinct steps, NES1 and NES2, separated by multiple years and separate permitting efforts. This notice is applicable to a proposed IHA for the incidental take of marine mammals during in-water construction associated with NES1. The NES1 project would involve the removal of portions of the failed sheet pile structure to stabilize the North Extension. The POA anticipates this project would begin on April 1, 2024 and extend through November 2024. They estimate that work would occur over approximately 250 hours on 110 nonconsecutive days. The NES1 project would remove approximately half of the North Extension structure extending approximately 274 meters (m) north from the southern end of the North Extension. This project would also stabilize the remaining portion of the North Extension by creating an end-state embankment. In-water construction associated with this project includes vibratory installation and removal of 81 24-inch (61-centimeter (cm)) or 36-inch (91-cm) temporary steel pipe stability template piles and vibratory removal, pile splitting and pile cutting (and possible impact removal) of approximately 4,216 sheet piles from the structure tailwalls, cell faces (bulkhead), and closure walls. Sound produced by these construction activities may result in the take of marine mammals, by harassment only. Dates and Duration The POA anticipates that NES1 in-water construction activities would begin on April 1, 2024 and extend through November 2024. In-water pile installation and removal associated with the NES1 project is anticipated to take place over approximately 246.5 hours on 110 nonconsecutive days between these dates (see table 1 for estimated production rates and durations). While the exact sequence of demolition and construction is uncertain, an estimated schedule of sheet pile removal and temporary stability template pile installation and removal is shown in Table 2. Table 1—Pile Installation and Removal Methods and Estimated Durations Pile type Pile size Structural feature Total estimated number of piles Estimated number of piles in the water Average vibratory and/or splitter duration Maximum impact strikes per day Total duration of removal and installation in water (hours) Average production rate, piles per day (range) Estimated number of days PS 27.5 and PS 31 Sheets 19.69 inches (50 cm) Tailwalls 3,536 2,267 2 hours/day 150 157 50 (10 to 100) 46 PS 27.5 and PS 31 Sheets 19.69 inches (50 cm) Cell Faces (Bulkhead) 568 568 2 hours/day 150 41 30 (10 to 60) 19 PZC26 Sheets 27.88 inches (70 cm) Closure Walls 110 110 2 hours/day 150 8 50 (10 to 100) 3 Steel Pipe 24- or 36-inch (61- or 91-cm) install Temporary Stability Templates 81 81 15 min/pile 0 20.25 4 (2 to 10) 21 Steel Pipe 24- or 36-inch (61- or 91-cm) removal Temporary Stability Templates 81 81 15 min/pile 0 20.25 4 (2 to 10) 21 Total 246.5 110 Note: cm = centimeter(s). Table 2—Estimated Timing and Duration by Month of Pile Installation and Removal Activities Activity April May June July August September October November Total 36-inch (91-cm) or 24-inch (61-cm) stability template pile installation: Piles 27 14 14 10 10 3 3 0 81 Hours 6.75 3.50 3.50 2.5 2.5 0.75 0.75 0 20.25 36-inch (91-cm) or 24-inch (61.cm) stability template pile removal: Piles 0 27 13 13 13 10 4 1 81 Hours 0 6.75 3.25 3.25 3.25 2.5 1 0.25 20.25 Sheet pile vibratory hammer removal: Piles Hours 10 45 60 60 13 10 4 2 206 Total hours 16.75 55.25 66.75 65.75 18.75 15.25 5.75 2.25 246.50 The POA has presented this schedule using the best available information derived from what is known of the North Extension Site and the POA's experience with similar construction and demolition projects. The POA plans to conduct as much work as possible prior to August through October, when there is higher Cook Inlet beluga whale (CIBW; Delphinapterus leucas ) abundance. However, as described below, due to the instability of the North Extension site, it is important that the POA attempt to complete the NES1 in a single construction season, which may necessitate work in August through October. Potential consequences of pausing the construction season ( i.e., stopping work from August through October) include de-rating the structural capacity of existing POA docks, a shutdown of dock operations due to deteriorated conditions, or an actual collapse of one or more dock structures. The potential for collapse increases with schedule delays, due to both worsening deterioration and the higher probability of a significant seismic event. A typical construction season at the POA extends from approximately mid-April to mid-October (6 months) and may include November. Exact dates of ice-out in the spring and formation of new ice in the fall vary from year to year and cannot be predicted with accuracy. In-water pile installation and removal cannot occur during the winter months when ice is present because of the hazards associated with moving ice floes that change directions four times a day, preventing the use of tugs, barges, workboats, and other vessels. Ice movement also prevents accurate placement of piles. Due to the design of the existing sheet pile wall, demolition must occur in a sequential and uninterrupted manner to prevent structural failure of the wall as demolition progresses. This safety requirement limits the POA's ability to re-sequence in-water sheet pile extraction and temporary pile installation, as the already compromised bulkhead structure may become further destabilized. The POA therefore plans to complete all work between April and November 2024, and requests an IHA for the NES1 project for 1 year that is effective as of April 1, 2024. All pile-driving would occur during daylight hours. Specific Geographic Region The Municipality of Anchorage is located in the lower reaches of Knik Arm of upper Cook Inlet (see Figure 2-1 in the POA's application). The POA sits on the industrial waterfront of Anchorage, just south of Cairn Point and north of Ship Creek (lat. 61°15′ N, long. 149°52′ W; Seward Meridian). Knik Arm and Turnagain Arm are the two branches of upper Cook Inlet, and Anchorage is located where the two arms join. Cook Inlet is a large tidal estuary that exchanges waters at its mouth with the Gulf of Alaska. The inlet is roughly 20,000 km 2 in area, with approximately 1,350 linear kilometer (km) of coastline (Rugh et al., 2000) and an average depth of approximately 100 m. Cook Inlet is generally divided into upper and lower regions by the East and West Forelands. Freshwater input to Cook Inlet comes from snowmelt and rivers, many of which are glacially fed and carry high sediment loads. Currents throughout Cook Inlet are strong and tidally periodic, with average velocities ranging from 3 to 6 knots (Sharma and Burrell, 1970). Extensive tidal mudflats occur throughout Cook Inlet, especially in the upper reaches, and are exposed at low tides. Cook Inlet is a seismically active region susceptible to earthquakes and has some of the highest tides in North America (NOAA, 2015) that drive surface circulation. Cook Inlet contains substantial quantities of mineral resources, including coal, oil, and natural gas. During winter, sea, beach, and river ice are dominant physical forces within Cook Inlet. In upper Cook Inlet, sea ice generally forms in October to November, and continues to develop through February or March (Moore et al., 2000). Northern Cook Inlet bifurcates into Knik Arm to the north and Turnagain Arm to the east. Knik Arm is generally considered to begin at Point Woronzof, 7.4 km southwest of the POA. From Point Woronzof, Knik Arm extends about 48 km in a north-northeasterly direction to the mouths of the Matanuska and Knik rivers. At Cairn Point, just northeast of the POA, Knik Arm narrows to about 2.4 km before widening to as much as 8 km at the tidal flats northwest of Eagle Bay at the mouth of Eagle River. Knik Arm comprises narrow channels flanked by large tidal flats composed of sand, mud, or gravel, depending upon location. Approximately 60 percent of Knik Arm is exposed at Mean Lower Low Water (MLLW). The intertidal (tidally influenced) areas of Knik Arm are mudflats, both vegetated and unvegetated, which consist primarily of fine, silt-sized glacial flour. Freshwater sources often are glacially born waters, which carry high suspended sediment loads, as well as a variety of metals such as zinc, barium, mercury, and cadmium. Surface waters in Cook Inlet typically carry high silt and sediment loads, particularly during summer, making Knik Arm an extremely silty, turbid waterbody with low visibility through the water column. The Matanuska and Knik Rivers contribute the majority of fresh water and suspended sediment into Knik Arm during summer. Smaller rivers and creeks also enter along the sides of Knik Arm (U.S. Department of Transportation and Port of Anchorage, 2008). Tides in Cook Inlet are semidiurnal, with two unequal high and low tides per tidal day (tidal day = 24 hours, 50 minutes). Due to Knik Arm's predominantly shallow depths and narrow widths, tides near Anchorage are greater than those in the main body of Cook Inlet. The tides at the POA have a mean range of about 8 m, and the maximum water level has been measured at more than 12.5 m at the Anchorage station (NMFS, 2015). Maximum current speeds in Knik Arm, observed during spring ebb tide, exceed 7 knots. These tides result in strong currents in alternating directions through Knik Arm and a well-mixed water column. The navigation harbor at the POA is a dredged basin in the natural tidal flat. Sediment loads in upper Cook Inlet can be high; spring thaws occur, and accompanying river discharges introduce considerable amounts of sediment into the system (Ebersole and Raad, 2004). Natural sedimentation processes act to continuously infill the dredged basin each spring and summer. The POA's boundaries currently occupy an area of approximately 0.52 km 2 . Other commercial and industrial activities related to secured maritime operations are located near the POA on Alaska Railroad Corporation property immediately south of the POA, on approximately 0.45 km 2 at a similar elevation. The POA is located north of Ship Creek, an area that experiences concentrated marine mammal activity during seasonal runs of several salmon species. Ship Creek serves as an important recreational fishing resource and is stocked twice each summer. Ship Creek flows into Knik Arm through the Municipality of Anchorage industrial area. Joint Base Elmendorf-Richardson (JBER) is located east of the POA, approximately 30.5 m higher in elevation. The U.S. Army Defense Fuel Support Point-Anchorage site is located east of the POA, south of JBER, and north of Alaska Railroad Corporation property. The perpendicular distance to the west bank directly across Knik Arm from the POA is approximately 4.2 km. The distance from the POA (east side) to nearby Port MacKenzie (west side) is approximately 4.9 km. Detailed Description of the Specified Activity The POA, located on Knik Arm in upper Cook Inlet (Figure 1), provides critical infrastructure for the citizens of Anchorage and a majority of the citizens of Alaska. Marine-side infrastructure and facilities at the POA were constructed largely in the 1960s and are in need of replacement because they are substantially past their design life and in poor and deteriorating structural condition. Those facilities include three general cargo terminals, two petroleum terminals, a dry barge landing, and an upland sheet-pile-supported storage and work area. To address deficiencies, the POA is modernizing its marine terminals through the PAMP to enable safe, reliable, and cost-effective Port operations. The PAMP will support infrastructure resilience in the event of a catastrophic natural disaster over a 75-year design life. EN06NO23.054 The PAMP is critical to maintaining food and fuel security for the state. At the completion of the PAMP, the POA will have modern, safe, resilient, and efficient facilities through which more than 90 percent of Alaskans will continue to obtain food, supplies, tools, vehicles, and fuel. The PAMP is divided into five separate phases; these phases are designed to include projects that have independent utility yet streamline agency permitting. The projects associated with the PAMP include: • Phase 1: Petroleum and Cement Terminal (PCT Phase 1 and 2) and South Floating Dock (SFD) replacement; • Phase 2A: NES1; • Phase 2B: General Cargo Terminals Replacement (construction planned to begin in 2025); • Phase 3: Petroleum, Oil and Lubricants Terminal 2 Replacement; • Phase 4: NES2; and • Phase 5: Demolition of Terminal 3. Phase 1 of the PAMP was completed in 2022. IHAs were issued by NMFS for both the PCT (Phase 1 and Phase 2; 85 FR 19294, April 6, 2020) and SFD projects associated with this Phase (86 FR 50057, September 7, 2021). The NES Project would be completed in two distinct steps, NES1 and NES2, separated by multiple years and separate permitting efforts. The project discussed herein, NES1, is Phase 2A of the PAMP. Ground improvements work in preparation for NES1 began in 2023, and on-shore and in-water work for NES1 is planned to commence in April 2024. The North Extension (the area north of the existing general cargo docks) was constructed in 2005-2011 under the Port Intermodal Expansion Project (PIEP), the predecessor effort to the PAMP. The POA considers the North Extension a failed structure. Parts of the North Extension bulkhead structure and the surrounding upland area are unstable and collapsing, and some of the sheet piles are visibly twisted and buckled. The structure presents safety hazards and logistical impediments to ongoing Port operations, and much of the upland area is currently unusable. The currently proposed NES Project overall would result in removal of the failed sheet pile structure and reconfiguration and realignment of the shoreline within the North Extension. NES1 would include the conversion of approximately 0.05 km 2 (13 acres) of developed land back to intertidal and subtidal habitat within Knik Arm. While the majority of the Project will be demolition work, the term “construction” as used herein refers to both construction and demolition work. The purpose of the NES Project is to stabilize the previously failed North Extension bulkhead structure and create a new shoreline that is structurally and seismically stable and balances the preservation of uplands created in the past while addressing the formation of unwanted sedimentation within the U.S. Army Corps of Engineers (USACE) Anchorage Harbor. The NES Project will also improve safety for maneuvering vessels at the northern berths. Previous establishment of the North Extension changed the hydrodynamics of the area and resulted in more rapid accumulation of sediments at the existing cargo dock faces, as well as a smaller turning area for vessels. The Municipality of Anchorage and the POA have identified the NES Project as a priority for the PAMP, due to the impact of the existing structure's geometry upon the USACE Anchorage Harbor Project, mariners' concerns regarding impacts to safe ship-berthing operations, and engineering concerns regarding structural and geotechnical stability of the system. The existing structure poses significant risk for continued deterioration and could result in significant release of impounded fill material into the Port's vessel operating and mooring areas, and into the USACE Anchorage Harbor Project. Accordingly, a significant portion of the NES work has been designated for inclusion in NES1 as Phase 2A PAMP efforts, specifically those portions of the existing structure that are closest to the north end of the existing cargo terminals. Creation of a safe and stable uplands area will support POA operations while also addressing concerns of adverse impacts upon the Federal Navigation Channel and Dredging Program. Existing North Extension Structure The existing North Extension bulkhead structure is an OPEN CELL SHEET PILE (OCSP) design. Demolition of the existing OCSP structure will include removal and disposal of the southerly OCSP bulkhead walls and associated backlands. The OCSP bulkhead is a retaining structure filled with soil that is composed of 29 interconnected open cells, each approximately 8 m wide, with 30 tailwalls that are up to 61 m long (see Figure 1-3 in the POA's application). Each cell is about 20 sheets wide across the face, which is along the water. Each tailwall consists of approximately 118 sheet piles that extend landward into the filled area, orthogonal to the sheet piles along the face (table 1). The sheet piles interlock through a series of thumb-finger joints or interlocks (where two sheet piles are connected along their length; see Figure 1-5 in the POA's application) along the cell faces and tailwalls. Wye joints occur where three sheet piles are connected at the interface between two neighboring sheet pile cell faces and the adjoining tailwall (see Figure 1-6 in the POA's application). Two z-pile closure walls close the gaps between structures, one on each end of the bulkhead (see Figure 1-4 in the POA's application). The total number of sheet piles in the existing structure that would be removed is approximately 4,216, although the exact number of sheet piles in the existing structure is not known with certainty. Demolition of the failed sheet pile structure would be accomplished through excavation and dredging of impounded soils (fill material), and cutting and removal of the existing sheet piles, most likely through use of a splitter and vibratory hammer. Demolition of the OCSP cell components would not commence until ground improvements necessary to protect the horizontal to vertical ratio (H:V) of 2H:1V embankment slope have been completed. Ground improvements were scheduled for 2023 and are underway. The sequencing of in-water events, including how construction would proceed while maintaining stability among the structure's cells, is unknown. It is anticipated that the actual methods, including types of equipment and numbers of hours and days of each activity, would be determined based on the engineering specifications for the NES1 project as determined by the Construction Contractor and the Design Build Team designer of record (DOR). The NES1 DOR and Construction Contractor have been selected by the POA, but their Construction Work Plan has not yet been completed and some actual construction techniques are likely to be refined adaptively as construction advances due to the stability risk of the existing impounded materials. The following project description is based on the best available information at this time considering the POA's knowledge of the condition of the North Extension and their experience with similar marine construction and demolition projects, which NMFS has determined sufficient for the purposes of the IHA application. NES1 Project Activities The NES1 Project would result in a reconfiguration and realignment of the shoreline through removal of portions of the failed sheet pile structure to stabilize the North Extension. Before NES1 commences, the upland area would be prepared with ground improvements to stabilize the existing fill. Ground improvements will take place in the dry, landward of the existing failed sheet pile structure and underneath the area where filter rock and armor rock would later be placed to stabilize the new shoreline. Ground improvement work began in 2023. Construction of NES1 will include completion of the following tasks: • Dredging and offshore disposal of approximately 1.35 million cubic yards (CY) of material down to −12 m MLLW; • Excavation of 115,000 CY of material; • Demolition and removal of the failed existing sheet pile structure; and • Shoreline stabilization including placement of granular fill, filter rock, and armor rock along the new face of the shoreline. NES1 would remove approximately half of the North Extension structure extending approximately 274 m north from the southern end of the North Extension. NES1 would also stabilize the remaining portion of the North Extension by creating an end-state embankment with a top elevation of +12 m MLLW, sloping to a toe elevation of approximately −12 m MLLW. The lower portion of the embankment slope from −12 m MLLW to approximately 0 m MLLW would be constructed with a 6H:1V slope and would be unarmored. A grade-break would occur above these elevations as the slope will transition to a 2H:1V slope armored rock revetment. At the cell faces, the depth of the face wall sections varies, with most extending from a tip elevation of approximately −60 MLLW to a cutoff elevation of approximately +9 m MLLW (27 m long). The mudline at the face sheets varies but is thought to be at approximately −11 m MLLW. This translates into a requirement to demolish sheet piles approximately 25 m high from the −14-m MLLW elevation to the top of the containment. Demolition of the failed sheet pile structure would be accomplished through excavation and dredging of impounded soils (fill material), and cutting and removal of the existing sheet piles. Approximately 1,465,000 CY of material would be removed. The material removed from excavation (115,000 CY) would be stockpiled in the North Extension area for future use, while the dredged material (1,350,000 CY) would be disposed of offshore into the Anchorage Harbor Open Water Disposal Site, which is the authorized USACE offshore disposal area used by the POA under USACE permit POA-2003-00503-M20. The NES1 Project in-water work would begin with landside excavation and in-water dredging along the south shoreline and south half of the failed sheet pile structure. Any methodology considered for cutting and removing the steel sheet piles would account for worker safety, constructability, and minimization of potential acoustic impacts that the operation may have on marine mammals. The first attempt would be to extract the sheet piles with direct vertical pulling or with a vibratory hammer; however, there may be complications with the sheet pile interlocks, which could become seized, and other means of pile removal may be required ( i.e. shearing or torching). Demolition activities would begin with the south half of the existing structure, followed by the north half of NES1 (see Figure 1-8 in the POA's application). The majority of the demolition work would occur from the water side to eliminate safety hazards from unexpected movements of fill material or the sheet piles themselves. The demolition plan also includes stabilization of the face sheets through installation of temporary piles and dredging back into the cell to relieve pressure on the sheet piles and to eliminate any release of material into Cook Inlet beyond natural tidal forces. Safety is a top priority regarding planning and executing the work. There are several risks at the project site to consider when planning demolition activities, such as strong currents and large tidal swings. Existing sheet piles and their interlocks are in poor condition. Many of the sheets may be damaged and bound up, making removal difficult. There are stability concerns with the failed OCSP structure, where the POA would have to closely manage allowable fill differentials between adjacent cells and loading on the face sheets. In-water NES1 activities and quantities are summarized in Table 3 (NES1 activities to be completed on land are summarized in table 1-2 in the POA's application). Table 3—Summary of In-Water NES1 Project Stages, Activities, and Approximate Quantities Type of activity Size and type Total anticipated amount or number Dredging of fill material Granular fill 1,350,000 CY. At-sea transit and disposal of dredged fill Granular fill 1,350,000 CY. Cutting piles with sheet splitter (vertical) 19.69-inch (50 cm) sheet piles, cut into vertical Unknown. 1 Cutting piles with shears or torch (horizontal) 2 19.69-inch (50 cm) sheet piles Unknown. 1 Vibratory or direct pull removal of sheet piles 3 19.69-inch (50 cm) sheet piles, removed in vertical panels 4,216 sheet piles. Installation and removal of temporary steel pipe piles 81 24- or 36-inch (61- or 91-cm) piles 81 installations, 81 removals. Slope construction Bedding, filter rock, armor stone 60,500 CY. 1 The total number of sheet piles to be cut would be a subset of the estimated 4,216 sheet piles needed to be removed. 2 Deploying divers or underwater shear equipment would be the last resort for removing sheet piles. 3 Most of the waterside face and tailwall sheets would be cut in the dry to improve operational safety. Dredging and Disposal Dredging would be performed with a derrick barge using a clamshell bucket, and would likely take place for 24 hours per day for the duration of the project. One barge would perform the dredging associated with the sheet pile removal, working concurrently and in support of the crane barge removing the sheets. Another barge would perform dredging in the remaining proposed project area. This barge would start with removing the existing armor rock on the south slope and work its way north behind the OSCP bulkhead. Dredged material would be placed on a dump barge and taken by tug boat for disposal at the Anchorage Harbor Open Water Disposal Site. Dredging for NES1 will take place in an area that has been part of a working port for more than 50 years, where dredging activities are common. Take of marine mammals by dredging is not anticipated or proposed to be authorized due to the low intensity and stationary nature of the sounds produced by dredging and its perennial presence over many years in the same general location near the project site. Further, the sounds produced by dredging are not meaningfully different and are unlikely to exceed sounds produced by ongoing normal industrial activities at the port. Lastly, mitigation measures described in the Proposed Mitigation section would ensure that direct physical interaction with marine mammals during dredging activities would be avoided. Therefore, dredging will not be considered further in this notice. Excavation Landside excavation would occur with loaders and excavators to remove the top portion of fill material and open up work for initial sheet pile cutting and removal. This excavation would begin to relieve pressure along the sheet wall face and expose the tops of the sheet piles to mitigate the risk of damaging sheets while dredging with a clamshell bucket. The sheet piles could be more easily extracted if undamaged. The removal elevation would remain above +5 m MLLW in order for the land equipment to reach the excavation depth with the groundwater and tidal elevations and ensure that the removed material would be in good condition. The material removed would be stockpiled at the POA for future use. Excavation would occur out of water. Therefore, take of marine mammals related to excavation activities is not anticipated or proposed to be authorized, and it will not be considered further in this notice. Pile Installation and Removal The sheet pile removal process would begin with the installation of stability templates (steel pipe piles) along the face of the sheet pile structure, following excavation and initial dredging work. Once landside excavation has removed the top portion of fill along the face of the wall, the POA would follow behind and begin dredging the material within the cells while maintaining the allowable fill differential between adjacent cells to maintain structural integrity. Before dredging deeper than the allowable elevation determined by the engineer, a crane barge would install temporary stability templates along the face of the sheet pile structure. The addition of about 27 temporary stability templates would support about one-third of the bulkhead sheet pile wall during removal of the impounded material. These templates would reinforce the sheets as material is dredged and hold them upright to prohibit any sheet deformation and improve the efficiency and effectiveness of removal. The templates would also minimize the need to perform horizontal cuts at multiple elevations, including underwater. With strong currents and low visibility, performing horizontal cuts underwater poses significant challenges. After that area has been demolished, the temporary stability template piles would be removed and re-installed along the next third of the bulkhead. It is anticipated that three sets of 27 temporary piles would be required for a total of 81 installations and 81 removals (table 1). The POA anticipates that the temporary stability template piles would be 24-inch (61-cm) steel pipe piles. However, it is possible that 36-inch (91-cm) steel pipe piles would be used instead. Temporary piles would be installed and removed with a vibratory hammer. The POA would begin on the southern end of the sheet pile structure and work their way north along the sheet wall face, installing templates and dredging fill material while managing fill elevations from cell to cell (see Figure 1-10 in the POA's application for an example section for the proposed demolition work). Fill material would slide down into the dredge area and would continue to be removed until a cell has been dredged down to −12 m MLLW adjacent to the face sheets and all pressure of the fill material on the face has been relieved. At this point in time, the crane barge would begin removing the sheet piles, starting with the face sheets. Some sheet piles from the tailwalls would be removed in the dry, potentially during excavation, depending on construction sequencing and tide heights. To minimize potential impacts on marine mammals from in-water sheet pile removal with a vibratory hammer, removal in the dry would be maximized as feasible; however, until the Construction Contractor and DOR are under contract, the exact number of sheet piles that may be removed in the dry is unknown. It is estimated that approximately 20-30 percent of sheet piles would be removed in the dry. Additionally, it is possible that some sheet piles may be removed by direct pulling. Removal of sheet piles by direct pulling where and when possible would also be maximized as feasible. Once fill material and impounded soils have been excavated or dredged from both sides of the sheet piles, it may be adequate to dislodge the sheet piles out of interlock by lifting or direct pulling. Although some sheet piles and sheet pile sections would be removed by direct pulling and/or in the dry, it is anticipated that some sheet piles and sheet pile sections would need to be removed with a vibratory hammer in water. Sheet piles may not be extracted easily if soil adheres to the sheet piles along the embedded length. It is also possible that competent portions of the interlocks would resist movement, or that interlocks that are bent or damaged by shearing would be difficult to separate and require shaking with a vibratory hammer. During vibratory removal, a vibratory hammer would be suspended from a crane and connected to a powerpack. The extractor jaw would be hydraulically locked onto the web of the sheet pile. The pile would be vibrated as upward vertical force is applied to extract the pile. Ideally, the piles would slide within the interlock, separating from the adjacent piles. This may not always be the case, as the pile may bind, and multiple piles may be dislodged from the original installed position. Another potential outcome of a pile that binds up is that the pile web (the thin, flat part between the interlocks) may be compromised from corrosion or other damage, resulting in the web steel tearing and partially ripping the pile, necessitating the application of vertical force to a neighboring pile. Vertical cuts to split the sheet piles into panels may be made with a sheet splitter if the interlocks do not release (see Figure 1-10 in the POA's application). The specific tools that would be used for pile splitting are not known, but it is anticipated that a splitter would be used. A pile splitter is a stiffened steel H-beam with some of the webbing removed. The edges of the H-beam webbing are hardened and form a large wedge between the flanges. The wedge is set on top of the sheet pile webbing where a cut is required. The splitter is then driven with a hammer down the webbing of the sheet pile until the tip of the H-beam passes the tip of the sheets, cutting the sheet pile all the way through and separating it into two parts. Multiple cuts split the sheet pile wall into tall vertical panels that can be removed in smaller pieces. Cuts in the sheet piles may be spaced 4 to 6 sheets apart and multiple sheets or pieces would be removed together. Splitters can be used in the air, water, or in soils and can be driven with impact or vibratory hammers. The splitter would be used in conjunction with a vibratory hammer and the POA assumed splitting would produce the same or similar sound levels to a vibratory hammer used without the splitter attachment. Therefore, the POA combined use of a vibratory hammer to remove sheet piles and use of a splitter into a single category ( i.e., vibratory hammer removal) and treated them the same for time ( i.e., table 1) and take estimation (see the Estimated Take section). The POA estimates that an average of approximately 5 minutes of vibratory hammer application would be required to remove sheet pile sections. It is unknown how many sheet piles may be included in a section; the POA anticipates that this number will vary widely. If sheet piles remain seized in the sediments and cannot be loosened or broken free with a vibratory hammer, they may be dislodged with an impact hammer. Use of an impact hammer to dislodge is expected to be uncommon, with up to 150 strikes (an estimated 50 strikes per pile for up to three piles) on any individual day or approximately 5 percent of active hammer duration for each sheet pile. The POA would not use two vibratory hammers with or without splitters simultaneously. Alternative means of pile removal include dredging or excavation to reduce further pile embedment, and cutting sheet piles using hydraulic shears or underwater ultrathermic cutting. When feasible, sheet piles would be removed in one piece, without cutting. Similarly, use of cutting methods to cut piles into sections that could be more easily removed would take place out of water when feasible. The POA anticipates that hydraulic shears may be used to cut sheet piles both in and out of water. The POA anticipates that sounds produced by hydraulic shears would be brief, low level, and intermittent, imparting minimal sound energy into the water column. A single closure of the shears on sheet pile is anticipated to successfully sever one or multiple sheets depending on the model and jaw depth. The POA anticipates that a single cut may require up to 2 minutes for the shears to close, although the duration of a single cut is likely to be less than 2 minutes. Therefore, take of marine mammals associated with hydraulic shearing is not anticipated or proposed to be authorized. Underwater ultrathermic cutting is performed by commercial divers using hand-held equipment to cut or melt through ferrous and non-ferrous metals, and could be used to cut the zinc-coated OCSP structure. These systems operate through a torch-like process, initiated by applying a melting amperage to a steel tube packed with alloy steel rods, sometimes mixed with aluminum rods to increase the heat output. In the hands of skilled commercial divers, underwater ultrathermic cutting is reputed to be relatively fast and efficient, cutting through approximately 2 to 4 inches (5 to 10 cm) per minute, depending upon the number of divers deployed. This efficacy may be constrained by the requirement to secure the severed piles from falling into the inlet to prevent an extreme hazard to the diver cutting the piles. Tidally driven currents in Cook Inlet may limit dive times to approximately 2 to 3 hours per high- and low-tide event, depending upon the tide cycle and the ability of divers to efficiently perform the cutting task while holding position during high current periods. Take of marine mammals associated with underwater ultrathermic cutting is not anticipated or proposed to be authorized as this activity is not considered to produce sound. Once the face sheets have been removed, the crane barge would remove the stability templates for use on other cells. At this point, the tailwalls would become independent walls with only fill material between them. The crane barge would work to extract as many tailwall sheets as possible until additional relief dredging is required to allow for vibratory removal. At this point, the crane barge would continue ahead to the north while the dredge rig falls back to continue dredging between the sheets. The POA would continue to remove the face wall and tailwall sheets from south to north until the OCSP structure has been removed. A key consideration of the NES1 project is to avoid rapid release of the impounded soils into the inlet. This is an important safety issue presenting a risk to construction personnel working in or near the cells in the immediate area of such an event. It is also an important operational issue to the POA, as releasing large quantities of materials into the inlet could quickly foul the adjoining cargo terminal berths (see Figure 1-7 in the POA's application). To avoid rapid release of the impounded soils, the demolition would need to be managed to account for the soil pressure of the adjacent adjoining cells. Failure to properly manage this process would likely result in the earth pressure generated by adjacent adjoining cells exerting lateral forces that would cause catastrophic tailwall failures. Also, the sheets joined in interlock are susceptible to bending in the weak axis, which could result in rotational forces that may overcome the vertical interlocks, causing the interlocks to unzip, again resulting in catastrophic tailwall failures and or face wall failures. Qualified professional engineers on the Design Build Team would develop the Construction Work Plan with the technical details to ameliorate these risks. The sheet pile interlocks would not prevent the flow of seawater into soils impounded within the OCSP cells. The water infiltration would be most prevalent at the face sheets; however, dynamic wave forces, the variable sea level height of the inlet, and variations in the impounded soils and associated permeability would make the interface elevation between unsaturated and saturated soils dynamic. Because saturated soils cannot resist shear, land-based excavation could be safely accomplished at a height above the saturated soil depth to be determined by the DOR, lest the equipment weight exceed the soil-bearing capacity. Shoreline Stabilization After the existing sheet pile structure has been removed, the sloped shoreline would be secured with armor stone placed on a layer of filter rock and granular fill. Placement of armor rock requires good visibility of the shore as each rock would be placed carefully to interlock with surrounding armor rock. The POA therefore anticipates that placement of armor rock would occur in the dry at low tide levels when feasible; however, some placement of armor rock, filter rock, and granular fill would occur in water. No impacts on marine mammals from placement of armor rock, filter rock, and granular fill in the dry are anticipated and therefore this activity will not be discussed 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 There are seven species of marine mammals that may be found in upper Cook Inlet during the proposed construction and demolition activities. Sections 3 and 4 of the IHA application summarize available information regarding status and trends, distribution and habitat preferences, and behavior and life history of the potentially affected species. NMFS fully considered all of this information, and we refer the reader to these descriptions, instead of reprinting the information. Additional information regarding population trends and threats may be found in NMFS' Stock Assessment Reports (SARs; https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessments ) and more general information about these species ( e.g., physical and behavioral descriptions) may be found on NMFS' website ( https://www.fisheries.noaa.gov/find-species ). Additional information on CIBWs may be found in NMFS' 2016 Recovery Plan for the CIBW, available online at https://www.fisheries.noaa.gov/resource/document/recovery-plan-cook-inlet-beluga-whale-delphinapterus-leucas, and NMFS' 2023 report on the abundance and trend of CIBWs in Cook Inlet in June 2021 and June 2022, available online at https://www.fisheries.noaa.gov/resource/document/abundance-and-trend-belugas-delphinapterus-leucas-cook-inlet-alaska-june-2021-and. Table 4 lists all species or stocks for which take is expected and proposed to be authorized for this activity, and summarizes information related to the population or stock, including regulatory status under the MMPA and Endangered Species Act (ESA) and potential biological removal (PBR), where known. 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 serious injury or mortality is anticipated or proposed to be authorized here, PBR and annual serious injury and mortality from anthropogenic sources are included here as gross indicators of the status of the species or stocks and other threats. Marine mammal abundance estimates presented in this document represent the total number of individuals that make up a given stock or the total number estimated within a particular study or survey area. NMFS' stock abundance estimates for most species represent the total estimate of individuals within the geographic area, if known, that comprises that stock. For some species, this geographic area may extend beyond U.S. waters. All managed stocks in this region are assessed in NMFS' U.S. Alaska and Pacific SARs ( e.g., Carretta, et al., 2023; Young et al., 2023). Values presented in Table 4 are the most recent available at the time of publication and are available online at: https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessments. The most recent abundance estimate for CIBWs, however, is available from Goetz et al. (2023) and available online at https://www.fisheries.noaa.gov/feature-story/new-abundance-estimate-endangered-cook-inlet-beluga-whales. Table 4—Species Likely Impacted by the Specified Activities Common name Scientific name MMPA stock ESA/MMPA status; strategic (Y/N) 1 Stock abundance N best , (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 N Pacific -/-; N 26,960 (0.05, 25,849, 2016) 801 131 Family Balaenopteridae (rorquals): Humpback whale Megaptera novaeangliae Hawaii -, -, N 11,278 (0.56, 7,265, 2020) 127 27.09 Mexico-North Pacific T, D, Y N/A (N/A, N/A, 2006) 6 UND 0.57 Order Cetartiodactyla—Superfamily Odontoceti (toothed whales, dolphins, and porpoises) Family Delphinidae: Beluga whale Delphinapterus leucas Cook Inlet E/D; Y 5 331 (0.076, 290, 2022) 0.53 0 Killer whale Orcinus orca Eastern North Pacific Alaska Resident -/-; N 1,920 (N/A, 1,920, 2019) 19 1.3 Eastern North Pacific Gulf of Alaska, Aleutian Islands and Bering Sea Transient -/-; N 587 (N/A, 587, 2012) 5.9 0.8 Family Phocoenidae (porpoises): Harbor porpoise Phocoena phocoena Gulf of Alaska -/-; Y 31,046 (0.214, N/A, 1998) 6 UND 72 Order Carnivora—Superfamily Pinnipedia Family Otariidae (eared seals and sea lions): Steller sea lion Eumetopias jubatus Western E/D; Y 52,932 (N/A, 52,932 2019) 318 255 Family Phocidae (earless seals): Harbor seal Phoca vitulina Cook Inlet/Shelikof Strait -/-; N 28,411 (N/A, 26,907, 2018) 807 107 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: https://www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessments. CV is coefficient of variation; Nmin is the minimum estimate of stock abundance. In some cases, CV is not applicable (N.A.). 3 These values, found in NMFS's 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. 4 UNK means unknown. 5 This abundance estimate is from Goetz et al. (2023). 6 UND means undetermined. On June 15, 2023, NMFS released an updated abundance estimate for endangered CIBWs in Alaska (Goetz et al., 2023) that incorporates aerial survey data from June 2021 and 2022, but which is not included in the most recent SAR (Young et al., 2023). Data collected during NMFS recent aerial survey effort suggest that the whale population is stable or may be increasing slightly. Goetz et al. (2023) estimated that the population size is currently between 290 and 386, with a median best estimate of 331. In accordance with the MMPA, this population estimate will be incorporated into the next draft CIBW SAR, which will be reviewed by an independent panel of experts, the Alaska Scientific Review Group. After this review, the SAR will be made available as a draft for public review before being finalized. We have determined that it is appropriate to consider the CIBW estimate of abundance reported by Goetz et al. (2023) in our analysis rather than the older estimate currently available from the Alaska SAR (Young et al., 2023) because it is based on the most recent and best available science. As indicated above, all seven species (with nine managed stocks) in Table 4 temporally and spatially co-occur with the activity to the degree that take is reasonably likely to occur. Minke whales ( Balaenoptera acutorostrata ) and Dall's porpoises ( Phocoenoides dalli ) also occur in Cook Inlet; however, the spatial occurrence of these species is such that take is not expected to occur, and they are not discussed further beyond the explanation provided here. Data from the Alaska Marine Mammal Stranding Network database (NMFS, unpublished data) provide additional support for these determinations. From 2011 to 2020, only one minke whale and one Dall's porpoise were documented as stranded in the portion of Cook Inlet north of Point Possession. Both were dead upon discovery; it is unknown if they were alive upon their entry into upper Cook Inlet or drifted into the area with the tides. With very few exceptions, minke whales and Dall's porpoises do not occur in upper Cook Inlet, and therefore take of these species is considered unlikely. In addition, sea otters ( Enhydra lutris ) may be found in Cook Inlet. However, sea otters are managed by the U.S. Fish and Wildlife Service (USFWS) and are not considered further in this document. Gray Whale The stock structure for gray whales in the Pacific has been studied for a number of years and remains uncertain as of the most recent (2022) Pacific SARs (Carretta et al., 2023). Gray whale population structure is not determined by simple geography and may be in flux due to evolving migratory dynamics (Carretta et al., 2023). Currently, the SARs delineate a western North Pacific (WNP) gray whale stock and an eastern North Pacific (ENP) stock based on genetic differentiation (Carretta et al., 2023). WNP gray whales are not known to feed in or travel to upper Cook Inlet (Conant and Lohe, 2023; Weller et al., 2023). Therefore, we assume that gray whales near the project area are members of the ENP stock. An Unusual Mortality Event (UME) along the West Coast and in Alaska was declared for gray whales in January 2019 (NMFS, 2022a). Since 2019, 143 gray whales have stranded off the coast of Alaska. Preliminary findings for several of the whales indicate evidence of emaciation, but the UME is still under investigation, and the cause of the mortalities remains unknown (NMFS, 2022a; see https://www.fisheries.noaa.gov/national/marine-life-distress/2019-2023-gray-whale-unusual-mortality-event-along-west-coast-and for more information). Gray whales are infrequent visitors to Cook Inlet, but can be seasonally present during spring and fall in the lower inlet (Bureau of Ocean Energy Management (BOEM), 2021). Migrating gray whales pass through the lower inlet during their spring and fall migrations to and from their primary summer feeding areas in the Bering, Chukchi, and Beaufort seas (Swartz, 2018; Silber et al., 2021; BOEM, 2021). Gray whales are rarely documented in upper Cook Inlet and in the project area. Gray whales were not documented during POA construction or scientific monitoring from 2005 to 2011 or during 2016 (Prevel-Ramos et al., 2006; Markowitz and McGuire, 2007; Cornick and Saxon-Kendall, 2008, 2009; Cornick et al., 2010, 2011; Integrated Concepts and Research Corporation (ICRC), 2009, 2010, 2011, 2012; Cornick and Pinney, 2011; Cornick and Seagars, 2016); however, one gray whale was observed near Port MacKenzie during 2020 PCT construction (61 North (61N) Environmental, 2021) and a second whale was observed off of Ship Creek during 2021 PCT construction monitoring (61N Environmental, 2022a, Easley-Appleyard and Leonard, 2022). The whale observed in 2020 is believed to be the same whale that later stranded in the Twentymile River, at the eastern end of Turnagain Arm, approximately 80 km southeast of Knik Arm. There was no indication that work at the PCT had any effect on the animal (see https://www.fisheries.noaa.gov/feature-story/alaska-gray-whale-ume-update-twentymile-river-whale-likely-one-twelve-dead-gray-whales for more information). No gray whales were observed during POA's transitional dredging or SFD construction monitoring from May to August, 2022 (61N Environmental, 2022b, 2022c). Humpback Whale On September 8, 2016, NMFS divided the humpback whales into 14 distinct population segments (DPS) under the ESA, removed the species-level listing as endangered, and, in its place, listed four DPSs as endangered and one DPS as threatened (81 FR 62259, September 8, 2016). The remaining nine DPSs were not listed. There are four DPSs in the North Pacific, including Western North Pacific and Central America, which are listed as endangered, Mexico, which is listed as threatened, and Hawaii, which is not listed. The 2022 Alaska and Pacific SARs described a revised stock structure for humpback whales which modifies the previous stocks designated under the MMPA to align more closely with the ESA-designated DPSs (Carretta et al., 2023; Young et al., 2023). Specifically, the three previous North Pacific humpback whale stocks (Central and Western North Pacific stocks and a CA/OR/WA stock) were replaced by five stocks, largely corresponding with the ESA-designated DPSs. These include Western North Pacific and Hawaii stocks and a Central America/Southern Mexico-CA/OR/WA stock (which corresponds with the Central America DPS). The remaining two stocks, corresponding with the Mexico DPS, are the Mainland Mexico-CA/OR/WA and Mexico-North Pacific stocks (Carretta et al., 2023; Young et al., 2023). The former stock is expected to occur along the west coast from California to southern British Columbia, while the latter stock may occur across the Pacific, from northern British Columbia through the Gulf of Alaska and Aleutian Islands/Bering Sea region to Russia. The Hawaii stock consists of one demographically independent population (DIP) (Hawaii—Southeast Alaska/Northern British Columbia DIP) and the Hawaii—North Pacific unit, which may or may not be composed of multiple DIPs (Wade et al., 2021). The DIP and unit are managed as a single stock at this time, due to the lack of data available to separately assess them and lack of compelling conservation benefit to managing them separately (NMFS, 2019, 2022b, 2023). The DIP is delineated based on two strong lines of evidence: genetics and movement data (Wade et al., 2021). Whales in the Hawaii—Southeast Alaska/Northern British Columbia DIP winter off Hawaii and largely summer in Southeast Alaska and Northern British Columbia (Wade et al., 2021). The group of whales that migrate from Russia, western Alaska (Bering Sea and Aleutian Islands), and central Alaska (Gulf of Alaska excluding Southeast Alaska) to Hawaii have been delineated as the Hawaii-North Pacific unit (Wade et al., 2021). There are a small number of whales that migrate between Hawaii and southern British Columbia/Washington, but current data and analyses do not provide a clear understanding of which unit these whales belong to (Wade et al., 2021; Carretta et al., 2023; Young et al., 2023). The Mexico-North Pacific stock is likely composed of multiple DIPs, based on movement data (Martien et al., 2021; Wade, 2021; Wade et al., 2021). However, because currently available data and analyses are not sufficient to delineate or assess DIPs within the unit, it was designated as a single stock (NMFS, 2019, 2022c, 2023). Whales in this stock winter off Mexico and the Revillagigedo Archipelago and summer primarily in Alaska waters (Martien et al., 2021; Carretta et al., 2023; Young et al., 2023). The most comprehensive photo-identification data available suggest that approximately 89 percent of all humpback whales in the Gulf of Alaska are members of the Hawaii stock, 11 percent are from the Mexico stock, and less than 1 percent are from the Western North Pacific stock (Wade, 2021). Members of different stocks are known to intermix in feeding grounds. On October 9, 2019, NMFS proposed to designate critical habitat for the Western North Pacific, Mexico, and Central America DPSs of humpback whales (84 FR 54354). NMFS issued a final rule on April 21, 2021 to designate critical habitat for ESA-listed humpback whales pursuant to Section 4 of the ESA (86 FR 21082). There is no designated critical habitat for humpback whales in or near the Project area (86 FR 21082, April 21, 2021). Humpback whales are encountered regularly in lower Cook Inlet and occasionally in mid-Cook Inlet; however, sightings are rare in upper Cook Inlet ( e.g., Witteveen et al., 2011). During aerial surveys conducted in summers between 2005 and 2012, Shelden et al. (2013) reported dozens of sightings in lower Cook Inlet, a handful of sightings in the vicinity of Anchor Point and in lower Cook Inlet, and no sightings north of 60° N latitude. NMFS changed to a biennial survey schedule starting in 2014 after analysis showed there would be little reduction in the ability to detect a trend given the current growth rate of the population (Hobbs, 2013). No survey took place in 2020. Instead, consecutive surveys took place in 2021 and 2022 (Shelden et al., 2022). During the 2014-2022 aerial surveys, sightings of humpback whales were recorded in lower Cook Inlet and mid-Cook Inlet, but none were observed in upper Cook Inlet (Shelden et al., 2015b, 2017, 2019, 2022). Vessel-based observers participating in the Apache Corporation's 2014 survey operations recorded three humpback whale sightings near Moose Point in upper Cook Inlet and two sightings near Anchor Point, while aerial and land-based observers recorded no humpback whale sightings, including in the upper inlet (Lomac-MacNair et al., 2014). Observers monitoring waters between Point Campbell and Fire Island during summer and fall 2011 and spring and summer 2012 recorded no humpback whale sightings (Brueggeman et al., 2013). Monitoring of Turnagain Arm during ice-free months between 2006 and 2014 yielded one humpback whale sighting (McGuire, unpublished data, cited in LGL Alaska Research Associates, Inc., and DOWL, 2015). There have been few sightings of humpback whales in the vicinity of the proposed project area. Humpback whales were not documented during POA construction or scientific monitoring from 2005 to 2011, in 2016, or during 2020 (Prevel-Ramos et al., 2006; Markowitz and McGuire, 2007; Cornick and Saxon-Kendall, 2008, 2009; Cornick et al., 2010, 2011; ICRC, 2009, 2010, 2011, 2012; Cornick and Pinney, 2011; Cornick and Seagars, 2016; 61N Environmental, 2021). Observers monitoring the Ship Creek Small Boat Launch from August 23 to September 11, 2017 recorded two sightings, each of a single humpback whale, which was presumed to be the same individual (POA, 2017). One other humpback whale sighting has been recorded for the immediate vicinity of the project area. This event involved a stranded whale that was sighted near a number of locations in upper Cook Inlet before washing ashore at Kincaid Park in 2017; it is unclear as to whether the humpback whale was alive or deceased upon entering Cook Inlet waters. Another juvenile humpback stranded in Turnagain Arm in April 2019 near mile 86 of the Seward Highway. One additional humpback whale was observed in July during 2022 transitional dredging monitoring (61N Environmental, 2022c). No humpback whales were observed during the 2020 to 2021 PCT construction monitoring, the NMFS marine mammal monitoring, or the 2022 SFD construction monitoring from April to June (61N Environmental, 2021, 2022a, 2022b, 2022c; Easley-Appleyard and Leonard, 2022). Beluga Whale Five stocks of beluga whales are recognized in Alaska: the Beaufort Sea stock, eastern Chukchi Sea stock, eastern Bering Sea stock, Bristol Bay stock, and Cook Inlet stock (Young et al., 2023). The Cook Inlet stock is geographically and genetically isolated from the other stocks (O'Corry-Crowe et al., 1997; Laidre et al., 2000) and resides year-round in Cook Inlet (Laidre et al., 2000; Castellote et al., 2020). Only the Cook Inlet stock (CIBWs) inhabits the proposed project area. CIBWs were designated as a DPS and listed as endangered under the ESA in October 2008 (73 FR 62919, October 10, 2008). Shelden and Wade (2019) analyzed time-series CIBW abundance data from 2008 to 2018 and reported that the CIBW population was declining at an annual rate of 2.3 percent during this time. Goetz et al., (2023) suggest that this decline could have been part of a natural oscillation in the population or possibly due to impacts of the unprecedented heatwave in the Gulf of Alaska during the same time period. The CIBW time-series abundance data were analyzed using a Bayesian statistical method to estimate group size for calculating CIBW abundance. This method produced an abundance estimate of 279 CIBWs, with a 95 percent probability range of 250 to 317 whales (Shelden and Wade, 2019). In June 2023, NMFS released an updated abundance estimate for CIBWs in Alaska that incorporates aerial survey data from June 2021 and 2022 and accounted for visibility bias ( i.e., availability bias due to diving behavior; proximity bias due to individuals concealed by another individual in the video data; perception bias due to individuals not detected because of small image size in the video data; and individual observer bias in visual observer data) (Goetz et al., 2023). This report estimated that CIBW abundance is between 290 and 386, with a median best estimate of 331. Goetz et al. (2023) also present an analysis of population trends for the most recent 10-year period (2012-2022). The addition of data from the 2021 and 2022 survey years in the analysis resulted in a 65.1 percent probability that the CIBW population is now increasing at 0.9 percent per year (95 percent prediction interval of −3 to 5.7 percent). This increase drops slightly to 0.2 percent per year (95 percent prediction interval of −1.8 to 2.6 percent) with a 60 percent probability that the CIBW population is increasing more than 1 percent per year when data from 2021, which had limited survey coverage due to poor weather, are excluded from the analysis. Median group size estimates in 2021 and 2022 were 34 and 15, respectively (Goetz et al., 2023). For management purposes, NMFS has determined that the carrying capacity of Cook Inlet is 1,300 CIBWs (65 FR 34590, May 31, 2000) based on historical CIBW abundance estimated by Calkins (1989). Live stranding events of CIBWs have been regularly observed in upper Cook Inlet. This can occur when an individual or group of individuals strands as the tide recedes. Most live strandings have occurred in Knik Arm and Turnagain Arm, which are shallow and have large tidal ranges, strong currents, and extensive mudflats. Most whales involved in a live stranding event survive, although some associated deaths may not be observed if the whales die later from live-stranding- related injuries (Vos and Shelden, 2005; Burek-Huntington et al., 2015). Between 2014 and 2018, there were reports of approximately 79 CIBWs involved in three known live stranding events, plus one suspected live stranding event with two associated deaths reported (NMFS, 2016b; NMFS, unpublished data; Muto et al., 2020). In 2014, necropsy results from two whales found in Turnagain Arm suggested that a live stranding event contributed to their deaths as both had aspirated mud and water. No live stranding events were reported prior to the discovery of these dead whales, suggesting that not all live stranding events are observed. Another source of CIBW mortality in Cook Inlet is predation by transient-type (mammal-eating) killer whales (NMFS, 2016b; Shelden et al., 2003). No human-caused mortality or serious injury of CIBWs through interactions with commercial, recreational, and subsistence fisheries, takes by subsistence hunters, and or human-caused events ( e.g., entanglement in marine debris, ship strikes) has been recently documented and harvesting of CIBWs has not occurred since 2008 (NMFS, 2008b). Recovery Plan. In 2010, a Recovery Team, consisting of a Science Panel and Stakeholder Panel, began meeting to develop a Recovery Plan for the CIBW. The Final Recovery Plan was published in the Federal Register on January 5, 2017 (82 FR 1325). In September 2022, NMFS completed the ESA 5-year review for the CIBW DPS and determined that the CIBW DPS should remain listed as endangered (NMFS, 2022d). In its Recovery Plan (82 FR 1325, January 5, 2017), NMFS identified several potential threats to CIBWs, including: (1) high concern: catastrophic events ( e.g., natural disasters, spills, mass strandings), cumulative effects of multiple stressors, and noise; (2) medium concern: disease agents ( e.g., pathogens, parasites, and harmful algal blooms), habitat loss or degradation, reduction in prey, and unauthorized take; and (3) low concern: pollution, predation, and subsistence harvest. The recovery plan did not treat climate change as a distinct threat but rather as a consideration in the threats of high and medium concern. Other potential threats most likely to result in direct human-caused mortality or serious injury of this stock include vessel strikes. Critical Habitat. On April 11, 2011, NMFS designated two areas of critical habitat for CIBW (76 FR 20179). The designation includes 7,800 km 2 of marine and estuarine habitat within Cook Inlet, encompassing approximately 1,909 km 2 in Area 1 and 5,891 km 2 in Area 2 (see Figure 1 in 76 FR 20179). Area 1 of the CIBW critical habitat encompasses all marine waters of Cook Inlet north of a line connecting Point Possession (lat. 61.04° N, long. 150.37° W) and the mouth of Three Mile Creek (lat. 61.08.55° N, long. 151.04.40° W), including waters of the Susitna, Little Susitna, and Chickaloon Rivers below mean higher high water. From spring through fall, Area 1 critical habitat has the highest concentration of CIBWs due to its important foraging and calving habitat. Area 2 critical habitat has a lower concentration of CIBWs in spring and summer but is used by CIBWs in fall and winter. Critical habitat does not include two areas of military usage: the Eagle River Flats Range on Fort Richardson and military lands of JBER between Mean Higher High Water and MHW. Additionally, the POA, adjacent navigation channel, and turning basin were excluded from critical habitat designation due to national security reasons (76 FR 20180, April 11, 2011). The POA exclusion area is within Area 1, however, marine mammal monitoring results from the POA suggest that this exclusion area is not a particularly important feeding or calving area. CIBWs have been occasionally documented to forage around Ship Creek (south of the POA) but are typically transiting through the area to other, potentially richer, foraging areas to the north ( e.g., Six Mile Creek, Eagle River, Eklutna River) ( e.g., 61N Environmental, 2021, 2022a, 2022b, 2022c, Easley-Appleyard and Leonard, 2022). These locations contain predictable salmon runs, an important food source for CIBWs, and the timing of these runs has been correlated with CIBW movements into the upper reaches of Knik Arm (Ezer et al., 2013). More information on CIBW critical habitat can be found at https://www.fisheries.noaa.gov/action/critical-habitat-cook-inlet-beluga-whale. The designation identified the following Primary Constituent Elements, essential features important to the conservation of the CIBW: (1) Intertidal and subtidal waters of Cook Inlet with depths of less than 9 m (MLLW) and within 8 km of high- and medium-flow anadromous fish streams; (2) Primary prey species, including four of the five species of Pacific salmon (chum ( Oncorhynchus keta ), sockeye ( Oncorhynchus nerka ), Chinook ( Oncorhynchus tshawytscha ), and coho ( Oncorhynchus kisutch )), Pacific eulachon ( Thaleichthys pacificus ), Pacific cod ( Gadus macrocephalus ), walleye Pollock ( Gadus chalcogrammus ), saffron cod ( Eleginus gracilis ), and yellowfin sole ( Limanda aspera ) ; (3) The absence of toxins or other agents of a type or amount harmful to CIBWs; (4) Unrestricted passage within or between the critical habitat areas; and (5) The absence of in-water noise at levels resulting in the abandonment of habitat by CIBWs. Biologically Important Areas. Wild et al. (2023) delineated portions of Cook Inlet, including near the proposed project area, as a Biologically Important Area (BIA) for the small and resident population of CIBWs based on scoring methods outlined by Harrison et al. (2023) (see https://oceannoise.noaa.gov/biologically-important-areas for more information). The BIA is used year-round by CIBWs for feeding and breeding, and there are limits on food supply such as salmon runs and seasonal movement of other fish species (Wild et al., 2023). The boundary of the CIBW BIA is consistent with NMFS' critical habitat designation, and does not include the aforementioned exclusion areas ( e.g., the POA and surrounding waters) (Wild et al., 2023). Foraging Ecology. CIBWs feed on a wide variety of prey species, particularly those that are seasonally abundant. From late spring through summer, most CIBW stomachs sampled contained salmon, which corresponded to the timing of fish runs in the area. Anadromous smolt and adult fish aggregate at river mouths and adjacent intertidal mudflats (Calkins, 1989). All five Pacific salmon species ( i.e., Chinook, pink ( Oncorhynchus gorbuscha ), coho, sockeye, and chum) spawn in rivers throughout Cook Inlet (Moulton, 1997; Moore et al., 2000). Overall, Pacific salmon represent the highest percent frequency of occurrence of prey species in CIBW stomachs. This suggests that their spring feeding in upper Cook Inlet, principally on fat-rich fish such as salmon and eulachon, is important to the energetics of these animals (NMFS, 2016b). The nutritional quality of Chinook salmon in particular is unparalleled, with an energy content four times greater than that of a Coho salmon. It is suggested the decline of the Chinook salmon population has left a nutritional void in the diet of the CIBWs that no other prey species can fill in terms of quality or quantity (Norman et al., 2020, 2022). In fall, as anadromous fish runs begin to decline, CIBWs return to consume fish species (cod and bottom fish) found in nearshore bays and estuaries. Stomach samples from CIBWs are not available for winter (December through March), although dive data from CIBWs tagged with satellite transmitters suggest that they feed in deeper waters during winter (Hobbs et al., 2005), possibly on such prey species as flatfish, cod, sculpin, and pollock. Distribution in Cook Inlet. The CIBW stock remains within Cook Inlet throughout the year, showing only small seasonal shifts in distribution (Goetz et al., 2012a; Lammers et al., 2013; Castallotte et al., 2015; Shelden et al., 2015a, 2018; Lowery et al., 2019). During spring and summer, CIBWs generally aggregate near the warmer waters of river mouths where prey availability is high and predator occurrence is low (Moore et al., 2000; Shelden and Wade, 2019; McGuire et al., 2020). In particular, CIBW groups are seen in the Susitna River Delta, the Beluga River and along the shore to the Little Susitna River, Knik Arm, and along the shores of Chickaloon Bay. Small groups were recorded farther south in Kachemak Bay, Redoubt Bay (Big River), and Trading Bay (McArthur River) prior to 1996, but rarely thereafter. Since the mid-1990s, most CIBWs (96 to 100 percent) aggregate in shallow areas near river mouths in upper Cook Inlet, and they are only occasionally sighted in the central or southern portions of Cook Inlet during summer (Hobbs et al., 2008). Almost the entire population can be found in northern Cook Inlet from late spring through the summer and into the fall (Muto et al., 2020). Data from tagged whales (14 tags deployed July 2000 through March 2003) show that CIBWs use upper Cook Inlet intensively between summer and late autumn (Hobbs et al., 2005). CIBWs tagged with satellite transmitters continue to use Knik Arm, Turnagain Arm, and Chickaloon Bay as late as October, but some range into lower Cook Inlet to Chinitna Bay, Tuxedni Bay, and Trading Bay (McArthur River) in fall (Hobbs et al., 2005, 2012). From September through November, CIBWs move between Knik Arm, Turnagain Arm, and Chickaloon Bay (Hobbs et al., 2005; Goetz et al., 2012b). By December, CIBWs are distributed throughout the upper to mid-inlet. From January into March, they move as far south as Kalgin Island and slightly beyond in central offshore waters. CIBWs make occasional excursions into Knik Arm and Turnagain Arm in February and March in spite of ice cover (Hobbs et al., 2005). Although tagged CIBWs move widely around Cook Inlet throughout the year, there is no indication of seasonal migration in and out of Cook Inlet (Hobbs et al., 2005). Data from NMFS aerial surveys, opportunistic sighting reports, and corrected satellite-tagged CIBWs confirm that they are more widely dispersed throughout Cook Inlet during winter (November-April), with animals found between Kalgin Island and Point Possession. Generally fewer observations of CIBWs are reported from the Anchorage and Knik Arm area from November through April (76 FR 20179, April 11, 2011; Rugh et al., 2000, 2004). The NMFS Marine Mammal Lab has conducted long-term passive acoustic monitoring demonstrating seasonal shifts in CIBW concentrations throughout Cook Inlet. Castellote et al. (2015) conducted long-term acoustic monitoring at 13 locations throughout Cook Inlet between 2008 and 2015: North Eagle Bay, Eagle River Mouth, South Eagle Bay, Six Mile, Point MacKenzie, Cairn Point, Fire Island, Little Susitna, Beluga River, Trading Bay, Kenai River, Tuxedni Bay, and Homer Spit; the former six stations being located within Knik Arm. In general, the observed seasonal distribution is in accordance with descriptions based on aerial surveys and satellite telemetry: CIBW detections are higher in the upper inlet during summer, peaking at Little Susitna, Beluga River, and Eagle Bay, followed by fewer detections at those locations during winter. Higher detections in winter at Trading Bay, Kenai River, and Tuxedni Bay suggest a broader CIBW distribution in the lower inlet during winter. Goetz et al. (2012b) modeled habitat preferences using NMFS' 1994-2008 June abundance survey data. In large areas, such as the Susitna Delta (Beluga to Little Susitna Rivers) and Knik Arm, there was a high probability that CIBWs were in larger groups. CIBW presence and acoustic foraging behavior also increased closer to rivers with Chinook salmon runs, such as the Susitna River ( e.g., Castellote et al., 2021). Movement has been 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 results from passive acoustic monitoring across the entire inlet (Castellote et al., 2015) also support seasonal patterns observed with other methods. Based on long-term passive acoustic monitoring, seasonally, foraging behavior was more prevalent during summer, particularly at upper inlet rivers, than during winter. Foraging index was highest at Little Susitna, with a peak in July‐August and a secondary peak in May, followed by Beluga River and then Eagle Bay; monthly variation in the foraging index indicates CIBWs shift their foraging behavior among these three locations from April through September. CIBWs are believed to mostly calve in the summer, and concurrently breed between late spring and early summer (NMFS, 2016b), primarily in upper Cook Inlet. The only known observed occurrence of calving occurred on July 20, 2015, in the Susitna Delta area (T. McGuire, personal communication, March 27, 2017). The first neonates encountered during each field season from 2005 through 2015 were always seen in the Susitna River Delta in July. The photographic identification team's documentation of the dates of the first neonate of each year indicate that calving begins in mid-late July/early August, generally coinciding with the observed timing of annual maximum group size. Probable mating behavior of CIBWs was observed in April and May of 2014, in Trading Bay. Young CIBWs are nursed for 2 years and may continue to associate with their mothers for a considerable time thereafter (Colbeck et al., 2013). Important calving grounds are thought to be located near the river mouths of upper Cook Inlet. Presence in Project Area. Knik Arm is one of three areas in upper Cook Inlet where CIBWs are concentrated during spring, summer, and early fall. Most CIBWs observed in or near the POA are transiting between upper Knik Arm and other portions of Cook Inlet, and the POA itself is not considered high-quality foraging habitat. CIBWs tend to follow their anadromous prey and travel in and out of Knik Arm with the tides. The predictive habitat model derived by Goetz et al. (2012a) indicated that CIBW density ranges from 0 to 1.12 whales per km 2 in Cook Inlet. The highest predicted densities of CIBWs are in Knik Arm, near the mouth of the Susitna River, and in Chickaloon Bay. The model suggests that the density of CIBWs at the mouth of Knik Arm, near the POA, ranges between approximately 0.013 and 0.062 whales per km 2 . The distribution presented by Goetz et al. (2012a) is generally consistent with CIBW distribution documented in upper Cook Inlet throughout ice-free months (NMFS, 2016b). Several marine mammal monitoring programs and studies have been conducted at or near the POA during the last 17 years. These studies offer some of the best available information on the presence of CIBWs in the proposed project area. Studies that occurred prior to 2020 are summarized in Section 4.5.5 of the POA's application. More recent programs, which most accurately portray current information regarding CIBW presence in the proposed project area, are summarized here. PCT Construction Monitoring (2020-2021). A marine mammal monitoring program was implemented during construction of the PCT in 2020 (Phase 1) and 2021 (Phase 2), as required by the NMFS IHAs (85 FR 19294, April 6, 2020). PCT Phase 1 construction included impact installation of 48-inch (122-cm) attenuated piles; impact installation of 36-inch (91-cm) and 48-inch (122-cm) unattenuated piles; vibratory installation of 24-inch (61-cm), 36-inch (91-cm), and 48-inch (122 cm) attenuated and unattenuated piles; and vibratory installation of an unattenuated 72-inch (183-cm) bubble curtain across 95 days. PCT Phase 2 construction included vibratory installation of 36-inch (91-cm) attenuated piles and impact and vibratory installation of 144-inch (366-cm) attenuated breasting and mooring dolphins across 38 days. Marine mammal monitoring in 2020 occurred during 128 non-consecutive days, with a total of 1,238.7 hours of monitoring from April 27 to November 24, 2020 (61N Environmental, 2021). Marine mammal monitoring in 2021 occurred during 74 non-consecutive days, with a total of 734.9 hours of monitoring from April 26 to June 24 and September 7 to 29, 2021 (61N Environmental, 2022a). A total of 1,504 individual CIBWs across 377 groups were sighted during PCT construction monitoring. Sixty-five and sixty-seven percent of CIBW observations occurred on non-pile driving days or before pile driving occurred on a given day during PCT Phase 1 and PCT Phase 2 construction, respectively. The monitoring effort and data collection were conducted before, during, and after pile driving activities from four locations as stipulated by the PCT IHAs (85 FR 19294, April 6, 2020): (1) the Anchorage Public Boat Dock by Ship Creek, (2) the Anchorage Downtown Viewpoint near Point Woronzof, (3) the PCT construction site, and (4) the North End (North Extension) at the north end of the POA, near Cairn Point. Marine mammal sighting data from April to September both before, during, and after pile driving indicate that CIBWs swam near the POA and lingered there for periods of time ranging from a few minutes to a few hours. CIBWs were most often seen traveling at a slow or moderate pace, either from the north near Cairn Point or from the south or milling at the mouth of Ship Creek. Groups of CIBWs were also observed swimming north and south in front of the PCT construction, and did not appear to exhibit avoidance behaviors either before, during, or after pile driving activities (61N Environmental, 2021, 2022a). CIBW sightings in June were concentrated on the west side of Knik Arm from the Little Susitna River Delta to Port MacKenzie. From July through September, CIBWs were most often seen milling and traveling on the east side of Knik Arm from Point Woronzof to Cairn Point (61N Environmental, 2021, 2022a). SFD Construction Monitoring and Transitional Dredging (2022). In 2022, a marine mammal monitoring program almost identical to that used during PCT construction was implemented during construction of the SFD, as required by the NMFS IHA (86 FR 50057, September 7, 2021). SFD construction included the vibratory installation of ten 36-inch (91-cm) attenuated plumb piles and two unattenuated battered piles (61N Environmental, 2022b). Marine mammal monitoring was conducted during 13 non-consecutive days, with a total of 108.2 hours of monitoring observation from May 20 through June 11, 2022 (61N Environmental, 2022b). Forty-one individual CIBWs across 9 groups were sighted (61N Environmental, 2022b). One group was observed on a day with no pile-driving, three groups were seen on days before pile driving activities started, and five groups were seen during vibratory pile driving activities (61N Environmental, 2022b). During SFD construction, the position of the Ship Creek monitoring station was adjusted to allow monitoring of a portion of the shoreline north of Cairn Point that could not be seen by the station at the northern end of the POA (61N Environmental, 2022b). Eleven protected species observers (PSOs) worked from four monitoring stations located along a 9-km (6-mi) stretch of coastline surrounding the POA. The monitoring effort and data collection were conducted at the following four locations: (1) Point Woronzof approximately 6.5 km (4 mi) southwest of the SFD, (2) the promontory near the boat launch at Ship Creek, (3) the SFD project site, and (4) the northern end of the POA (61N Environmental, 2022b). Ninety groups comprised of 529 CIBWs were also sighted during the transitional dredging monitoring that occurred from May 3 to 15, 2022 and June 27 to August 24, 2022 (61N Environmental, 2022b). Of the nine groups of CIBWs sighted during SFD construction, traveling was recorded as the primary behavior for each group (61N Environmental, 2022b). CIBWs traveled and milled between the SFD construction area, Ship Creek, and areas to the south of the POA for more than an hour at a time, delaying some construction activities. Killer Whale Along the west coast of North America, seasonal and year-round occurrence of killer whales has been noted along the entire Alaska coast (Braham and Dahlheim, 1982), in British Columbia and Washington inland waterways (Bigg et al., 1990), and along the outer coasts of Washington, Oregon, and California (Green et al., 1992; Barlow 1995, 1997; Forney et al., 1995). Killer whales from these areas have been labeled as “resident,” “transient,” and “offshore” type killer whales (Bigg et al., 1990; Ford et al., 2000; Dahlheim et al., 2008) based on aspects of morphology, ecology, genetics, and behavior (Ford and Fisher, 1982; Baird and Stacey, 1988; Baird et al., 1992; Hoelzel et al., 1998, 2002; Barrett Lennard, 2000; Dahlheim et al., 2008). Based on data regarding association patterns, acoustics, movements, and genetic differences, eight killer whale stocks are now recognized within the U.S. Pacific, two of which have the potential to be found in the proposed project area: the Eastern North Pacific Alaska Resident stock and the Gulf of Alaska, Aleutian Islands, and the Bering Sea Transient stock. Both stocks overlap the same geographic area; however, they maintain social and reproductive isolation and feed on different prey species. Resident killer whales are primarily fish-eaters, while transients primarily hunt and consume marine mammals, such as harbor seals, Dall's porpoises, harbor porpoises, beluga whales and sea lions. Killer whales are not harvested for subsistence in Alaska. Potential threats most likely to result in direct human-caused mortality or serious injury of killer whales in this region include oil spills, vessel strikes, and interactions with fisheries. Killer whales are rare in Cook Inlet, and most individuals are observed in lower Cook Inlet (Shelden et al., 2013). The infrequent sightings of killer whales that are reported in upper Cook Inlet tend to occur when their primary prey (anadromous fish for resident killer whales and beluga whales for transient killer whales) are also in the area (Shelden et al., 2003). During CIBW aerial surveys between 1993 and 2012, killer whales were sighted in lower Cook Inlet 17 times, with a total of 70 animals (Shelden et al., 2013); no killer whales were observed in upper Cook Inlet during this time. Surveys over 20 years by Shelden et al. (2003) documented an increase in CIBW sightings and strandings in upper Cook Inlet beginning in the early 1990s. Several of these sightings and strandings reported evidence of killer whale predation on CIBWs. The pod sizes of killer whales preying on CIBWs ranged from one to six individuals (Shelden et al., 2003). Passive acoustic monitoring efforts throughout Cook Inlet documented killer whales at the Beluga River, Kenai River, and Homer Spit, although they were not encountered within Knik Arm (Castellote et al., 2016). These detections were likely resident killer whales. Transient killer whales likely have not been acoustically detected due to their propensity to move quietly through waters to track prey (Small, 2010; Lammers et al., 2013). Few killer whales, if any, are expected to approach or be in the vicinity of the proposed project area. No killer whales were spotted in the vicinity of the POA during surveys by Funk et al. (2005), Ireland et al. (2005), or Brueggeman et al. (2007, 2008a, 2008b). Killer whales have also not been documented during any POA construction or scientific monitoring from 2005 to 2011, in 2016, or in 2020 (Prevel-Ramos et al., 2006; Markowitz and McGuire, 2007; Cornick and Saxon-Kendall, 2008; ICRC, 2009, 2010, 2011, 2012; Cornick et al., 2010, 2011; Cornick and Pinney, 2011; Cornick and Seagars, 2016; 61N Environmental, 2021). Two killer whales, one male and one juvenile of unknown sex, were sighted offshore of Point Woronzof in September 2021 during PCT Phase 2 construction monitoring (61N Environmental, 2022a). The pair of killer whales moved up Knik Arm, reversed direction near Cairn Point, and moved southwest out of Knik Arm toward the open water of Upper Cook Inlet. No killer whales were sighted during the 2021 NMFS marine mammal monitoring or the 2022 transitional dredging and SFD construction monitoring that occurred between May and June 2022 (61N Environmental, 2022b, 2022c; Easley-Appleyard and Leonard, 2022). Harbor Porpoise In the eastern North Pacific Ocean, harbor porpoise range from Point Barrow, along the Alaska coast, and down the west coast of North America to Point Conception, California. The 2022 Alaska SARs describe a revised stock structure for harbor porpoises (Young et al., 2023). Previously, NMFS had designated three stocks of harbor porpoises: the Bering Sea stock, the Gulf of Alaska stock, and the Southeast Alaska stock (Muto et al., 2022; Zerbini et al., 2022). The 2022 Alaska SARs splits the Southeast Alaska stock into three separate stocks, resulting in five separate stocks in Alaskan waters for this species. This update better aligns harbor porpoise stock structure with genetics, trends in abundance, and information regarding discontinuous distribution trends (Young et al., 2023). Harbor porpoises found in Cook Inlet are assumed to be members of the Gulf of Alaska stock (Young et al., 2023). Harbor porpoises occur most frequently in waters less than 100 m deep (Hobbs and Waite, 2010). They can be opportunistic foragers but consume primarily schooling forage fish (Bowen and Siniff, 1999). Given their shallow water distribution, harbor porpoise are vulnerable to physical modifications of nearshore habitats resulting from urban and industrial development (including waste management and nonpoint source runoff) and activities such as construction of docks and other over-water structures, filling of shallow areas, dredging, and noise (Linnenschmidt et al., 2013). Subsistence users have not reported any harvest from the Gulf of Alaska harbor porpoise stock since the early 1900s (Shelden et al., 2014). Calving occurs from May to August; however, this can vary by region. Harbor porpoises are often found traveling alone, or in small groups of less than 10 individuals (Schmale, 2008). Harbor porpoises occur throughout Cook Inlet, with passive acoustic detections being more prevalent in lower Cook Inlet. Although harbor porpoises 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). 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 CIBWs, as CIBWs move into upper inlet waters to forage on Pacific salmon during the summer months (Shelden et al., 2014). An increase in harbor porpoise sightings in upper Cook Inlet was observed over recent decades ( e.g., 61N Environmental, 2021, 2022a; Shelden et al., 2014). Small numbers of harbor porpoises have been consistently reported in upper Cook Inlet between April and October (Prevel-Ramos et al., 2008). The overall increase in the number of harbor porpoise sightings in upper Cook Inlet is unknown, although it may be an artifact from increased studies and marine mammal monitoring programs in upper Cook Inlet. It is also possible that the contraction in the CIBW's range has opened up previously occupied CIBW range to harbor porpoises (Shelden et al., 2014). Harbor porpoises have been observed within Knik Arm during monitoring efforts from 2005 to 2016. Between April 27 and November 24, 2020, 18 harbor porpoises were observed near the POA during the PCT Phase 1 construction monitoring (61N Environmental, 2021). Twenty-seven harbor porpoises were observed near the POA during the PCT Phase 2 construction monitoring conducted between April 26 and September 29, 2021 (61N Environmental, 2022a). During NMFS marine mammal monitoring conducted in 2021, one harbor porpoise was observed in August and six harbor porpoises were observed in October (Easley-Appleyard and Leonard, 2022). During 2022, five harbor porpoises were sighted during transitional dredging monitoring (61N Environmental, 2022c). No harbor porpoises were sighted at the POA during the 2022 SFD construction monitoring that occurred between May and June 2022 (61N Environmental, 2022b). Steller Sea Lion Two Distinct Population Segments (DPSs) of Steller sea lion occur in Alaska: the western DPS and the eastern DPS. The western DPS includes animals that occur west of Cape Suckling, Alaska, and therefore includes individuals within the Project area. The western DPS was listed under the ESA as threatened in 1990 (55 FR 49204, November 26, 1990), and its continued population decline resulted in a change in listing status to endangered in 1997 (62 FR 24345, May 5, 1997). Since 2000, studies indicate that the population east of Samalga Pass ( i.e., east of the Aleutian Islands) has increased and is potentially stable (Young et al., 2023). There is uncertainty regarding threats currently impeding the recovery of Steller sea lions, particularly in the Aleutian Islands. Many factors have been suggested as causes of the steep decline in abundance of western Steller sea lions observed in the 1980s, including competitive effects of fishing, environmental change, disease, contaminants, killer whale predation, incidental take, and illegal and legal shooting (Atkinson et al., 2008; NMFS, 2008a). A number of management actions have been implemented since 1990 to promote the recovery of the Western U.S. stock of Steller sea lions, including 5.6-km (3-nautical mile) no-entry zones around rookeries, prohibition of shooting at or near sea lions, and regulation of fisheries for sea lion prey species ( e.g., walleye pollock, Pacific cod, and Atka mackerel ( Pleurogrammus monopterygius )) (Sinclair et al., 2013; Tollit et al., 2017). Additionally, potentially deleterious events, such as harmful algal blooms (Lefebvre et al., 2016) and disease transmission across the Arctic (VanWormer et al., 2019) that have been associated with warming waters, could lead to potentially negative population-level impacts on Steller sea lions. NMFS designated critical habitat for Steller sea lions on August 27, 1993 (58 FR 45269). The critical habitat designation for the Western DPS of was determined to include a 37-km (20-nautical mile) buffer around all major haul-outs and rookeries, and associated terrestrial, atmospheric, and aquatic zones, plus three large offshore foraging areas, none of which occurs in the project area. Steller sea lions are opportunistic predators, feeding primarily on a wide variety of seasonally abundant fishes and cephalopods, including Pacific herring ( Clupea pallasi ), walleye pollock, capelin ( Mallotus villosus ), Pacific sand lance ( Ammodytes hexapterus ), Pacific cod, salmon ( Oncorhynchus spp. ), and squid ( Teuthida spp. ); (Jefferson et al., 2008; Wynne et al., 2011). Steller sea lions do not generally eat every day, but tend to forage every 1-2 days and return to haulouts to rest between foraging trips (Merrick and Loughlin, 1997; Rehberg et al., 2009). 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). Within Cook Inlet, Steller sea lions primarily inhabit lower Cook Inlet. However, they occasionally venture to upper Cook Inlet and Knik Arm and may be attracted to salmon runs in the region. Steller sea lions have not been documented in upper Cook Inlet during CIBW aerial surveys conducted annually in June from 1994 through 2012 and in 2014 (Shelden et al., 2013, 2015b, 2017; Shelden and Wade, 2019); however, there has been an increase in individual Steller sea lion sightings near the POA in recent years. Steller sea lions were observed near the POA in 2009, 2016, and 2019 through 2022 (ICRC, 2009; Cornick and Seagars, 2016; POA, 2019; 61N Environmental, 2021, 2022a, 2022b, 2022c). In 2009, there were three Steller sea lion sightings that were believed to be the same individual (ICRC, 2009). In 2016, Steller sea lions were observed on 2 separate days. On May 2, 2016, one individual was sighted, while on May 25, 2016, there were five Steller Sea lion sightings within a 50-minute period, and these sightings occurred in areas relatively close to one another (Cornick and Seagars, 2016). Given the proximity in time and space, it is believed these five sightings were of the same individual sea lion. In 2019, one Steller sea lion was observed in June at the POA during transitional dredging (POA, 2019). There were six sightings of individual Steller sea lions near the POA during PCT Phase 1 construction monitoring (61N Environmental, 2021). At least two of these sightings may have been re-sights on the same individual. An additional seven unidentified pinnipeds were observed that could have been Steller sea lions or harbor seals (61N Environmental, 2021). In 2021, there were a total of eight sightings of individual Steller sea lions observed near the POA during PCT Phase 2 construction monitoring (61N Environmental, 2022a). During NMFS marine mammal monitoring, one Steller sea lion was observed in August 2021 in the middle of the inlet (Easley-Appleyard and Leonard, 2022). In 2022, there were three Steller sea lion sightings during the transitional dredging monitoring and three during SFD construction monitoring (61N Environmental, 2022b, 2022c). All sightings occurred during summer, when the sea lions were likely attracted to ongoing salmon runs. Sea lion observations near the POA may be increasing due to more consistent observation effort or due to increased presence; observations continue to be occasional. Harbor Seal Harbor seals inhabit waters all along the western coast of the United States, British Columbia, and north through Alaska waters to the Pribilof Islands and Cape Newenham. NMFS currently identifies 12 stocks of harbor seals in Alaska based largely on genetic structure (Young et al., 2023). Harbor seals in the proposed project area are members of the Cook Inlet/Shelikof stock, which ranges from the southwest tip of Unimak Island east along the southern coast of the Alaska Peninsula to Elizabeth Island off the southwest tip of the Kenai Peninsula, including Cook Inlet, Knik Arm, and Turnagain Arm. Distribution of the Cook Inlet/Shelikof stock extends from Unimak Island, in the Aleutian Islands archipelago, north through all of upper and lower Cook Inlet (Young et al., 2023). Harbor seals forage in marine, estuarine, and occasionally freshwater habitat. They are opportunistic feeders that adjust their local distribution to take advantage of locally and seasonally abundant prey (Baird, 2001; Bjørge, 2002). In Cook Inlet, harbor seals have been documented in higher concentrations near steelhead ( Oncorhynchus mykiss ), Chinook, and salmon spawning streams during summer and may target more offshore prey species during winter (Boveng et al., 2012). Harbor seals haul out on rocks, reefs, beaches, and drifting glacial ice (Young et al., 2023). Their movements are influenced by tides, weather, season, food availability, and reproduction, as well as individual sex and age class (Lowry et al., 2001; Small et al., 2003; Boveng et al., 2012). The results of past and recent satellite tagging studies in Southeast Alaska, Prince William Sound, Kodiak Island, and Cook Inlet are also consistent with the conclusion that harbor seals are non-migratory (Lowry et al., 2001; Small et al., 2003; Boveng et al., 2012). However, some long-distance movements of tagged animals in Alaska have been recorded (Pitcher and McAllister, 1981; Lowry et al., 2001; Small et al., 2003; Womble, 2012; Womble and Gende, 2013). Strong fidelity of individuals for haul-out sites during the breeding season has been documented in several populations (Härkönen and Harding, 2001), including some regions in Alaska such as Kodiak Island, Prince William Sound, Glacier Bay/Icy Strait, and Cook Inlet (Pitcher and McAllister, 1981; Small et al., 2005; Boveng et al., 2012; Womble, 2012; Womble and Gende, 2013). Harbor seals usually give birth to a single pup between May and mid-July; birthing locations are dispersed over several haulout sites and not confined to major rookeries (Klinkhart et al., 2008). Harbor seals inhabit the coastal and estuarine waters of Cook Inlet and are observed in both upper and lower Cook Inlet throughout most of the year (Boveng et al., 2012; Shelden et al., 2013). Recent research on satellite-tagged harbor seals observed several movement patterns within Cook Inlet (Boveng et al., 2012), including a strong seasonal pattern of more coastal and restricted spatial use during the spring and summer (breeding, pupping, molting) and more wide-ranging movements within and outside of Cook Inlet during the winter months, with some seals ranging as far as Shumagin Islands. During summer months, movements and distribution were mostly confined to the west side of Cook Inlet and Kachemak Bay, and seals captured in lower Cook Inlet generally exhibited site fidelity by remaining south of the Forelands in lower Cook Inlet after release (Boveng et al., 2012). In the fall, a portion of the harbor seals appeared to move out of Cook Inlet and into Shelikof Strait, northern Kodiak Island, and coastal habitats of the Alaska Peninsula. The western coast of Cook Inlet had higher usage by harbor seals than eastern coast habitats, and seals captured in lower Cook Inlet generally exhibited site fidelity by remaining south of the Forelands in lower Cook Inlet after release (south of Nikiski; Boveng et al., 2012). The presence of harbor seals in upper Cook Inlet is seasonal. Harbor seals are commonly observed along the Susitna River and other tributaries within upper Cook Inlet during eulachon and salmon migrations (NMFS, 2003). The major haulout sites for harbor seals are in lower Cook Inlet; however, there are a few haulout sites in upper Cook Inlet, including near the Little and Big Susitna rivers, Beluga River, Theodore River, and Ivan River (Barbara Mahoney, personal communication, November 16, 2020; Montgomery et al., 2007). During CIBW aerial surveys of upper Cook Inlet from 1993 to 2012, harbor seals were observed 24 to 96 km south-southwest of Anchorage at the Chickaloon, Little Susitna, Susitna, Ivan, McArthur, and Beluga rivers (Shelden et al., 2013). Harbor seals have been observed in Knik Arm and in the vicinity of the POA (Shelden et al., 2013), but they are not known to haul out within the proposed project area. Harbor seals were observed during construction monitoring at the POA from 2005 through 2011 and in 2016 (Prevel-Ramos et al., 2006; Markowitz and McGuire, 2007; Cornick and Saxon-Kendall, 2008, 2009; Cornick et al., 2010, 2011). Harbor seals were observed in groups of one to seven individuals (Cornick et al., 2011; Cornick and Seagars, 2016). Harbor seals were also observed near the POA during construction monitoring for PCT Phase 1 in 2020 and PCT Phase 2 in 2021, NMFS marine mammal monitoring in 2021, and transitional dredging monitoring and SFD construction monitoring in 2022 (61N Environmental, 2021, 2022a, 2022b, 2022c, Easley-Appleyard and Leonard, 2022). During the 2020 PCT Phase 1 and 2021 PCT Phase 2 construction monitoring, harbor seals were regularly observed in the vicinity of the POA with frequent observations near the mouth of Ship Creek, located approximately 2,500 m southeast of the NES1 location. Harbor seals were observed almost daily during 2020 PCT Phase 1 construction, with 54 individuals documented in July, 66 documented in August, and 44 sighted in September (61N Environmental, 2021). During the 2021 PCT Phase 2 construction, harbor seals were observed with the highest numbers of sightings in June (87 individuals) and in September (124 individuals) (61 N Environmental, 2022a). Over the 13 days of SFD construction monitoring in May and June 2022, 27 harbor seals were observed (61N Environmental, 2022b). Seventy-two groups of 75 total harbor seals (3 groups of 2 individuals) were observed during transitional dredging monitoring in 2022 (61N Environmental, 2022c). Sighting rates of harbor seals have been highly variable and may have increased since 2005. It is unknown whether any potential increase was due to local population increases or habituation to ongoing construction activities. It is possible that increased sighting rates are correlated with more intensive monitoring efforts in 2020 and 2021, when the POA used 11 PSOs spread among four monitoring stations. 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. 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, 2019) recommended that marine mammals be divided into hearing groups based on directly measured (behavioral or auditory evoked potential techniques) or estimated hearing ranges (behavioral response data, anatomical modeling, etc. ). 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-decibel (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. Marine mammal hearing groups and their associated hearing ranges are provided in Table 5. Specific to this action, gray whales and humpback whales are considered low-frequency (LF) cetaceans, beluga whales and killer whales are considered mid-frequency (MF) cetaceans, harbor porpoises are considered high-frequency (HF) cetaceans, Steller sea lions are otariid pinnipeds, and harbor seals are phocid pinnipeds. Table 5—Marine Mammal Hearing Groups [NMFS, 2018] Hearing group Generalized hearing range * Low-frequency (LF) cetaceans (baleen whales) 7 Hz to 35 kHz. Mid-frequency (MF) cetaceans (dolphins, toothed whales, beaked whales, bottlenose whales) 150 Hz to 160 kHz. High-frequency (HF) cetaceans (true porpoises, Kogia, river dolphins, Cephalorhynchid, Lagenorhynchus cruciger & L. australis ) 275 Hz to 160 kHz. Phocid pinnipeds (PW) (underwater) (true seals) 50 Hz to 86 kHz. Otariid pinnipeds (OW) (underwater) (sea lions and fur seals) 60 Hz to 39 kHz. * Represents the generalized hearing range for the entire group as a composite ( i.e., all species within the group), where individual species' hearing ranges are typically not as broad. Generalized hearing range chosen based on ~65-dB threshold from normalized composite audiogram, with the exception for lower limits for LF cetaceans (Southall et al., 2007) and PW pinniped (approximation). 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). This division between phocid and otariid pinnipeds is now reflected in the updated hearing groups proposed in Southall et al. (2019). For more detail concerning these groups and associated frequency ranges, please see NMFS (2018) for a review of available information. Potential Effects of Specified Activities on Marine Mammals and Their Habitat This section provides a discussion of the ways in which components of the specified activity may impact marine mammals and their habitat. The Estimated Take of Marine Mammals 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 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 whether those impacts are reasonably expected to, or reasonably likely to, adversely affect the species or stock through effects on annual rates of recruitment or survival. Acoustic effects on marine mammals during the specified activity are expected to potentially occur from vibratory pile installation and removal, and impact pile removal. The effects of underwater noise from the POA's proposed activities have the potential to result in Level B harassment of marine mammals in the action area and, for some species as a result of certain activities, Level A harassment. Background on Sound This section contains a brief technical background on sound, on the characteristics of certain sound types, and on metrics used 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. For general information on sound and its interaction with the marine environment, please see: Erbe and Thomas (2022); Au and Hastings (2008); Richardson et al. (1995); Urick (1983); as well as the Discovery of Sound in the Sea website at https://dosits.org/. Sound is a vibration that travels as an acoustic wave through a medium such as a gas, liquid or solid. Sound waves alternately compress and decompress the medium as the wave travels. In water, sound waves radiate in a manner similar to ripples on the surface of a pond and may be either directed in a beam (narrow beam or directional sources) or sound may radiate in all directions (omnidirectional sources), as is the case for sound produced by the construction activities considered here. The compressions and decompressions associated with sound waves are detected as changes in pressure by marine mammals and human-made sound receptors such as hydrophones. Sound travels more efficiently in water than almost any other form of energy, making the use of sound as a primary sensory modality ideal for inhabitants of the aquatic environment. In seawater, sound travels at roughly 1,500 meters per second (m/s). In air, sound waves travel much more slowly at about 340 m/s. However, the speed of sound in water can vary by a small amount based on characteristics of the transmission medium such as temperature and salinity. The basic characteristics of a sound wave are frequency, wavelength, velocity, and amplitude. Frequency is the number of pressure waves that pass by a reference point per unit of time and is measured in hertz (Hz) or cycles per second. Wavelength is the distance between two peaks or corresponding points of a sound wave (length of one cycle). Higher frequency sounds have shorter wavelengths than lower frequency sounds, and typically attenuate (decrease) more rapidly with distance, except in certain cases in shallower water. The amplitude of a sound pressure wave is related to the subjective “loudness” of a sound and is typically expressed in decibels (dB), which are a relative unit of measurement that is used to express the ratio of one value of a power or pressure to another. A sound pressure level (SPL) in dB is described as the ratio between a measured pressure and a reference pressure, 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. For example, a 10-dB increase is a ten-fold increase in acoustic power. A 20-dB increase is then a 100-fold increase in power and a 30-dB increase is a 1000-fold increase in power. However, a ten-fold increase in acoustic power does not mean that the sound is perceived as being 10 times louder. The dB is a relative unit comparing two pressures; therefore, a reference pressure must always be indicated. For underwater sound, this is 1 microPascal (μPa). For in-air sound, the reference pressure is 20 microPascal (μPa). The amplitude of a sound can be presented in various ways; however, NMFS typically considers three metrics: sound exposure level (SEL), root-mean-square (RMS) SPL, and peak SPL (defined below). The source level represents the SPL referenced at a standard distance from the source, typically 1 m (Richardson et al., 1995; American National Standards Institute (ANSI, 2013), while the received level is the SPL at the receiver's position. For pile driving activities, the SPL is typically referenced at 10 m. SEL (represented as dB referenced to 1 micropascal squared second (re 1 μPa 2 -s)) represents the total energy in a stated frequency band over a stated time interval or event, and considers both intensity and duration of exposure. The per-pulse SEL ( e.g., single strike or single shot SEL) is calculated over the time window containing the entire pulse ( i.e., 100 percent of the acoustic energy). SEL can also be a cumulative metric; it can be accumulated over a single pulse (for pile driving this is the same as single-strike SEL, above; SEL ss ), or calculated over periods containing multiple pulses (SEL cum ). Cumulative SEL (SEL cum ) represents the total energy accumulated by a receiver over a defined time window or during an event. The SEL metric is useful because it allows sound exposures of different durations to be related to one another in terms of total acoustic energy. The duration of a sound event and the number of pulses, however, should be specified as there is no accepted standard duration o [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%3A2023-24238. Public record. Not legal advice.