# Taking and Importing Marine Mammals; Taking Marine Mammals Incidental to U.S. Navy Construction at Portsmouth Naval Shipyard, Kittery, Maine > Briefs, arguments, decisions, and more. URL: https://www.frixlaw.com/law-library/documents/fr%3A2023-00332 ## Record - **Collection:** Federal Register - **Document type:** Proposed Rule - **Published:** January 18, 2023 - **Citation:** 88 FR 3146 ## Text DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration 50 CFR Part 217 [Docket No. 230104-0003] RIN 0648-BL78 Taking and Importing Marine Mammals; Taking Marine Mammals Incidental to U.S. Navy Construction at Portsmouth Naval Shipyard, Kittery, Maine AGENCY: National Marine Fisheries Service (NMFS), National Oceanic and Atmospheric Administration (NOAA), Commerce. ACTION: Proposed rule; request for comments. SUMMARY: NMFS has received a request from the U.S. Navy (Navy) for authorization to take marine mammals incidental to construction at the Portsmouth Naval Shipyard in Kittery, Maine, over the course of five years (2023-2028). Pursuant to the Marine Mammal Protection Act (MMPA), NMFS is proposing regulations to govern that take and requests comments on the proposed regulations. NMFS responses to comments will be included in the notice of the final decision. DATES: Comments and information must be received no later than February 17, 2023. ADDRESSES: A copy of the Navy's application and any supporting documents, as well as a list of the references cited in this document, may be obtained online at: https://www.fisheries.noaa.gov/action/incidental-take-authorization-us-navy-construction-portsmouth-naval-shipyard-kittery-maine-0. In case of problems accessing these documents, please call the contact listed below. Submit all electronic public comments via the Federal e-Rulemaking Portal. Go to www.regulations.gov and enter NOAA-NMFS-2022-0133 in the Search box. Click on the “Comment” icon, complete the required fields, and enter or attach your comments. Instructions: Comments sent by any other method, to any other address or individual, or received after the end of the comment period, may not be considered by NMFS. All comments received are a part of the public record and will generally be posted for public viewing on www.regulations.gov without change. All personal identifying information ( e.g., name, address), confidential business information, or otherwise sensitive information submitted voluntarily by the sender will be publicly accessible. NMFS will accept anonymous comments (enter “N/A” in the required fields if you wish to remain anonymous). Attachments to electronic comments will be accepted in Microsoft Word, Excel, or Adobe PDF file formats only. FOR FURTHER INFORMATION CONTACT: Reny Tyson Moore, Office of Protected Resources, NMFS, ITP.tyson.moore@noaa.gov, (301) 427-8401. SUPPLEMENTARY INFORMATION: Purpose and Need for Regulatory Action We received an application from the Navy requesting 5-year regulations and authorization to take multiple species of marine mammals. This proposed rule would establish a framework under the authority of the MMPA (16 U.S.C. 1361 et seq. ) to allow for the authorization of take by Level A and Level B harassment of marine mammals incidental to the Navy's construction activities related to the multifunctional expansion and modification of Dry Dock 1 at the Portsmouth Naval Shipyard in Kittery, Maine. Please see “Background” below for definitions of harassment. Legal Authority for the Proposed Action Section 101(a)(5)(A) of the MMPA (16 U.S.C. 1371(a)(5)(A)) directs the Secretary of Commerce to allow, upon request, the incidental, but not intentional, taking of small numbers of marine mammals by U.S. citizens who engage in a specified activity (other than commercial fishing) within a specified geographical region for up to 5 years if, after notice and public comment, the agency makes certain findings and issues regulations that set forth permissible methods of taking pursuant to that activity and other means of effecting the “least practicable adverse impact” on the affected species or stocks and their habitat (see the discussion below in the Proposed Mitigation section), as well as monitoring and reporting requirements. Section 101(a)(5)(A) of the MMPA and the implementing regulations at 50 CFR part 216, subpart I provide the legal basis for issuing this proposed rule containing 5-year regulations, and for any subsequent Letters of Authorization (LOAs). As directed by this legal authority, this proposed rule contains mitigation, monitoring, and reporting requirements. Summary of Major Provisions Within the Proposed Rule Following is a summary of the major provisions of this proposed rule regarding the Navy's construction activities. These measures include: • Required monitoring of the in-water construction areas to detect the presence of marine mammals before beginning in-water construction activities; • Shutdown of in-water construction activities under certain circumstances to avoid injury of marine mammals; • Soft start for impact pile driving to allow marine mammals the opportunity to leave the area prior to beginning impact pile driving at full power; and • Implementation of a bubble curtain during rock hammering and down-the-hole (DTH) cluster drilling to reduce underwater noise impacts. 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 incidental take authorization is provided to the public for review. Authorization for incidental takings shall be granted if NMFS finds that the taking will have a negligible impact on the species or stock(s) 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 the proposed action ( i.e., the promulgation of regulations and subsequent issuance of LOAs) with respect to potential impacts on the human environment. This action is consistent with categories of activities identified in Categorical Exclusion B4 (incidental take authorizations with no anticipated serious injury or mortality) of the Companion Manual for NOAA Administrative Order 216-6A, which do not individually or cumulatively have the potential for significant impacts on the quality of the human environment and for which we have not identified any extraordinary circumstances that would preclude this categorical exclusion. Accordingly, NMFS has preliminarily determined that the proposed action qualifies to be categorically excluded from further review under NEPA. Information in the Navy's application and this document collectively provide the environmental information related to the proposed issuance of these regulations and subsequent incidental take authorization for public review and comment. We will review all comments submitted in response to this document prior to concluding our review process under NEPA and making a final decision on the request for an incidental take authorization. Summary of Request On May 9, 2022, NMFS received a request from the Navy for authorization to take marine mammals incidental to construction activities related to the multifunctional expansion and modification of Dry Dock 1 at Portsmouth Naval Shipyard in Kittery, Maine. We provided comments on the application, and the Navy submitted revised versions and responses to our comments on July 5, 2022, August 15, 2022, August 19, 2022, and August 25, 2022, with the latter version deemed adequate and complete. On September 1, 2022, we published a notice of receipt of the Navy's application in the Federal Register (87 FR 53731), requesting comments and information related to the request. During the 30-day comment period, we received two supportive letters from private citizens. On October 19 and 25, 2022, NMFS was notified by the Navy of project modifications and shifting Fleet submarine schedules that required the resequencing of certain activities associated with the construction at Dry Dock 1 in order to accommodate the modifications and meet the new vessel docking demands. On October 31, 2022, the Navy submitted an addendum to its application describing these changes. The requested regulations would be valid for 5 years, from April 1, 2023 through March 31, 2028. The Navy's request is to be authorized to take five species by Level A and Level B harassment. Neither the Navy nor NMFS expect serious injury or mortality to result from this activity. NMFS previously issued five IHAs to the Navy for waterfront improvement work at the Portsmouth Naval Shipyard: in 2016 (81 FR 85525; November 28, 2016), 2018 (83 FR 3318; January 24, 2018), 2019 (84 FR 24476; May 28, 2019), a renewal of the 2019 IHA (86 FR 14598; March 17, 2021), and in 2022 (87 FR 19886; April 6, 2022). The most recent IHA (87 FR 19886) provided authorization to take marine mammals during the first year of the construction project described in this notice. As required, the applicant provided monitoring reports (available at: https://www.fisheries.noaa.gov/national/marine-mammal-protection/incidental-take-authorizations-construction-activities ) which confirm that the applicant has implemented the required mitigation and monitoring, and which also shows that no impacts of a scale or nature not previously analyzed or authorized have occurred as a result of the activities conducted. Description of Proposed Activity Overview Multifunctional Expansion of Dry Dock 1 (P-381) is one of three projects that support the overall expansion and modification of Dry Dock 1, located in the western extent of the Portsmouth Naval Shipyard. The two additional projects, construction of a super flood basin (P-310) and extension of portal crane rail and utilities (P-1074), are currently under construction. In-water work associated with these projects was completed under the aforementioned separate IHAs issued by NMFS. The projects have been phased to support Navy mission schedules. P-381 will be constructed within the same footprint of the super flood basin over an approximate 7-year period, during which 5 years of in-water work would occur. An IHA was issued by NMFS for the first year of P-381 construction activities between April 1, 2022 and March 31, 2023 (87 FR 19866; April 6, 2022). This request is associated with the remaining 4 years of P-381 in-water construction activities planned to occur from April 1, 2023 through March 31, 2028, as well as for additional in-water construction activities associated with the removal of emergency repair components of the super flood basin that will occur during the proposed period of effectiveness for the proposed regulations. Although the in-water construction described in this proposed rule is anticipated to be completed by December 2026, unanticipated schedule delays could result in the Navy conducting construction activity over the full 5 years. The purpose of the proposed project (P-381) is to modify the super flood basin to create two additional dry docking positions (Dry Dock 1 North and Dry Dock 1 West) in front of the existing Dry Dock 1 East. The Navy's specified activity also includes emergency repairs of the P-310 super flood basin. Construction activities will include the excavation and/or installation of 1,118 holes, 198 shafts, and 580 sheet piles via impact and vibratory pile driving, hydraulic rock hammering, rotary drilling, and mono and cluster DTH. The construction activities are expected to require approximately 2,498 days if the activities are considered independently over the 5-year period. However, the actual construction duration is expected to be within four years as many of the construction activities will occur concurrently. Harbor porpoises ( Phocoena phocoena ), harbor seals ( Phoca vitulina ), gray seals ( Halichoerus grypus ), and harp seals ( Pagophilus groenlandicus ) have been observed in the proposed action area. In addition, hooded seals ( Cystophora cristata ) could occur in the proposed action area. Dates and Duration The in-water construction activities associated with this proposed rule are anticipated to begin in April 2023 and proceed to December 2026 (4 years); however, the request for incidental take authorization is for 5 years in the event of unexpected scheduled delays. In-water construction activities would occur consecutively over a 4-year period. The Navy plans to conduct all in-water work activities with expected potential for incidental harassment of marine mammals during daylight hours. Table 1 provides the estimated schedule and production rates for P-381 construction activities. Many of the activities included in Table 1 would span across multiple construction years and/or would occur concurrently. Because of mission requirements and operational schedules at the dry docking positions and berths, this schedule is subject to change. In-water construction activities for P-381 would occur consecutively over a 4-year period. Note, for the purposes of this analysis, the proposed construction years are identified as years 2 through 5; Year 1 of the Navy's construction activities is currently ongoing in association with a previously issued IHA (87 FR 19886; April 6, 2022). Vibratory pile driving and extraction is assumed to occur for 141 days. Impact pile driving would occur for 34 days. DTH excavation (mono-hammer and cluster drill) would occur for 1,446 days. Rotary drilling would occur for 238 days (assuming that casings and sockets for cluster drills would be set, excavated, and removed in a single day). Rock hammering would occur for 277 days. Note that pile driving days are not necessarily consecutive, and certain activities may occur at the same time, decreasing the total number of actual in-water construction days. The contractor could be working in more than one area of the berths at a time. Table 1—In-Water Construction Activities Activity ID Activity Total amount and estimated dates (construction years *) Activity component Method Daily production rate Total production days A1 1 Center Wall—Install Foundation Support Piles Drill 18 shafts Apr 23 3 to Aug 23 (2) Install 102-inch diameter outer casing Rotary drill 1 shaft/day,1 hour/day 4 18 A2 1 Pre-drill 102-inch diameter socket Rotary drill 1 shaft/day, 9 hours/day 4 18 A3 1 Remove 102-inch outer casing Rotary drill 1 casing/day,15 minutes/casing 4 18 A4 1 Drill 78-inch diameter shaft Cluster drill DTH 6.5 days/shaft, 10 hours/day 4 117 R 1 Dry Dock 1 North Entrance—Install Temporary Cofferdam Install 48 sheet piles Apr 23 3 to May 23 (2) 28-inch wide Z-shaped sheets Impact with initial vibratory set 8 sheets/day, 5 minutes and 300 blows/pile 4 6 1 Berth 11—Remove Shutter Panels Remove 112 panels Apr 23 3 to May 23 (2) Concrete shutter panels Hydraulic rock hammering 5 hours/day 4 56 2 Berth 1— Remove Sheet Piles Remove 168 sheet piles Apr 23 3 to Jun 24 (2, 3) 25-inch-wide Z- shaped Vibratory extraction 4 piles/day 4 42 3 Berth 1—Remove Granite Block Quay Wall 2,800 cubic yards (cy) Apr 23 3 to Jun 24 (2, 3) Removal of granite blocks Hydraulic rock hammering 2.5 hours/day 4 47 4 Berth 1—Top of Wall Removal for Waler Installation 320 linear feet (lf) Apr 23 3 to Jun 24 (2, 3) Mechanical concrete removal Hydraulic rock hammering 10 hours/day 4 74 5 Berth 1—Install southeast corner Support of Excavation (SOE) Install 28 sheet piles Apr 23 to Jul 23 (2) 28-inch-wide Z-shaped Impact with initial vibratory set 4 piles/day, 5 minutes/pile and 300 blows/pile 4 8 6 Berth 11—Mechanical Rock Removal at Basin Floor 700 cy Apr 23 3 to Aug 23 (2) Excavate Bedrock Hydraulic rock hammering 12 hours/day 34 60 7 Berth 11 Face—Mechanical Rock Removal at Basin Floor Drill 924 relief holes Apr 23 3 to Aug 23 (2) 4-6 inch diameter holes DTH mono-hammer 27 holes/day, 22 min/hole 4 35 8 Install Temporary Cofferdam Extension Install 14 sheet piles Apr 23 to Jun 23 (2) 28-inch-wide Z-shaped Impact with initial vibratory set 4 piles/day, 5 minutes/pile and 300 blows/pile 4 9a Gantry Crane Support Piles at Berth 1 West Drill 16 shafts Apr 23 to Aug 23 (2) Set 102-inch diameter casing Rotary drill 1 shaft/day, 1 hours/day 16 9b Pre-drill 102-inch rock socket Rotary drill 1 shaft/day, 9 hours/day 16 9c Remove 102- inch casing Rotary drill 1 casing/day 15, minutes/casing 16 9d 72-inch diameter shafts Cluster drill DTH 5 days/shaft, 10 hours/day 80 10 2 Berth 1—Mechanical Rock Removal at Basin Floor 300 cy Apr 23 3 to Sep 23 (2) Excavate Bedrock Hydraulic rock hammering 13 cy/day 12 hours/day 5 25 11 Dry Dock 1 North Entrance—Drill Tremie Tie Downs Drill 50 rock anchors Apr 23 3 to Oct 23 (2) 9-inch diameter holes DTH mono-hammer 2 holes/day, 5 hours/hole 4 25 12 Center Wall—Install Tie-In to Existing West Closure Wall Install 15 sheet piles Apr 23 to Dec 23 (2) 28-inch wide Z- shaped Impact with initial vibratory set 4 piles/day 5 minutes/pile and 300 blows/pile 4 13a Dry Dock 1 North—Temporary Work Trestle Piles Drill 20 shafts May 23 to Nov 24 (2, 3) Set 102-inch diameter casing Rotary drill 1 shaft/day, 1 hours/day 20 13b Pre-drill 102- inch rock socket Rotary drill 1 shaft/day, 9 hours/day 20 13c Remove 102- inch casing Rotary drill 1 casing/day, 15 minutes/casing 20 13d 84-inch diameter shafts Cluster drill DTH 3.5 days/shaft, 10 hours/day 70 14 Dry Dock 1 North—Remove Temporary Work Trestle Piles Remove 20 piles May 23 to Nov 24 (2, 3) 84-inch diameter drill piles Rotary drill 1 day/pile, 15 minutes/pile 20 15a Dry Dock 1 North—Install Leveling Piles (Diving Board Shafts) Drill 18 shafts May 23 to Nov 24 (2, 3) Set 84-inch casing Rotary drill 1 shaft/day, 1 hours/day 18 15b Pre-drill 84-inch rock socket Rotary drill 1 shaft/day, 9 hours/day 18 15c Remove 84-inch casing Rotary drill 1 casing/day, 15 minutes/casing 18 15d 78-inch diameter shaft Cluster drill DTH 7.5 days/shaft, 10 hours/day 135 16a Wall Support Shafts for Dry Dock 1 North (Berth 11 Face and Head Wall) Drill 20 shafts Jun 23 to Nov 24 (2, 3) Set 102-inch diameter casing Rotary drill 1 shaft/day, 1 hours/day 20 16b Pre-drill 102-inch rock socket Rotary drill 1 shaft/day, 9 hours/day 20 16c Remove 102-inch casing Rotary drill 1 casing/day, 15 minutes/casing 20 16d Drill 78-inch diameter shaft Cluster drill DTH 7.5 days/shaft, 10 hours/day 150 17a Foundation (Floor) Shafts for Dry Dock 1 North (Foundation Support Piles) Drill 23 shafts Jun 23 to Nov 24 (Const. years 2, 3) Set 126-inch diameter Casing Rotary drill 1 shaft/day, 1 hours/day 23 17b Pre-drill 126-inch rock socket Rotary drill 1 shaft/day, 9 hours/day 23 17c Remove 126-inch casing Rotary drill 1 casing/day, 60 minutes/casing 23 17d Drill 108-inch diameter shafts Cluster drill DTH 8.5 days/shaft, 10 hours/day 196 18 Berth 11 End Wall—Remove Temporary Guide Wall Remove 60 sheet piles Jul 23 to Aug 23 (2, 3) 28-inch wide Z- shaped Vibratory extraction 8 piles/day, 5 minutes/pile 5 10 19 Remove Berth 1 southeast corner SOE Remove 28 sheet piles Jul 23 to Sep 23 (2) 28-inch-wide Z-shaped Vibratory extraction 8 piles/day, 5 minutes/pile 4 5 20 2 Removal of Berth 1 Emergency Repair Sheet Piles Remove 108 sheet piles Apr 23 3 to Jul 23 (2) 28-inch-wide Z-shaped Vibratory extraction 6 piles/day, 5 minutes/pile 18 21 2 Removal of Berth 1 Emergency Repair Tremie Concrete 500 cy Apr 23 3 to Aug 23 (2) Mechanical concrete removal Hydraulic rock hammering 4 hours/day 15 22 Center Wall Foundation—Drill in Monolith Tie Downs Install 72 rock anchors Aug 23 to May 24 (2, 3) 9-inch diameter holes DTH mono- hammer 2 holes/day, 5 hours/hole 36 23 Center Wall—Remove Tie-In to Existing West Closure Wall (Dry Dock 1 North) 4 Remove 16 sheet piles 6 Aug 23 to Aug 24 (2, 3) 28-inch-wide Z- shaped Vibratory extraction 8 piles/day, 5 minutes/pile 5 3 24 Center Wall East—Sheet Pile Tie-In to Existing Wall Install 23 sheet piles Aug 23 to Oct 24 (2, 3) 28-inch wide Z-shaped Impact with initial vibratory set 2 piles/day, 5 minutes/pile and 300 blows/pile 12 25 Remove Tie-In to West Closure Wall (Dry Dock 1 West) Remove 15 sheet pile Dec 23 to Dec 24 (2, 3) 28-inch wide Z- shaped Vibratory extraction 8 piles/day, 5 minutes/pile 5 3 26 Remove Center Wall East—Sheet Pile Tie-In to Existing Wall (Dry Dock 1 West) Remove 23 sheet piles Dec 23 to Dec 24 (2, 3) 28-inch wide Z-shaped Vibratory extraction 8 piles/day, 5 minutes/pile 5 12 27 Dry Dock 1 North Entrance—Remove Temporary Cofferdam Remove 96 sheet piles Jan 24 to Sep 24 (Const. years 2, 3) 28-inch wide Z-shaped Vibratory extraction 8 piles/day, 5 minutes/pile 12 28 Remove Temporary Cofferdam Extension Remove 14 sheet piles Jan 24 to Sep 24 (2, 3) 28-inch wide Z-shaped Vibratory extraction 8 piles/day, 5 minutes/pile 2 29a Dry Dock 1 West—Install Temporary Work Trestle Piles Drill 20 shafts Apr 24 to Feb 26 (3, 4) Set 102-inch diameter casing Rotary drill 1 shaft/day, 1 hours/day 20 29b Pre-drill 102-inch rock socket Rotary drill 1 shaft/day, 9 hours/day 20 29c Remove 102-inch casing Rotary drill 1 casing/day, 15 minutes/casing 20 29d 84-inch diameter shafts Cluster drill DTH 3.5 days/shaft, 10 hours/day 70 30 Dry Dock 1 West—Remove Temporary Work Trestle Piles Remove 20 piles Apr 24 to Feb 26 (3, 4) 84-inch diameter piles Rotary drill 1 day/pile, 15 minutes/pile 20 31a Wall Support Shafts for Dry Dock 1 West (Berth 1 Face) Drill 22 shafts Jun 24 to Feb 26 (3, 4) Set 102-inch diameter casing Rotary drill 1 shaft/day, 1 hours/day 22 31b Pre-drill 102-inch rock socket Rotary drill 1 shaft/day, 9 hours/day 22 31c Remove 102-inch casing Rotary drill 1 casing/day, 15 minutes/casing 22 31d 78-inch diameter shaft Cluster drill DTH 7.5 days/shaft, 10 hours/day 165 32a Foundation (Floor) Shafts for Dry Dock 1 West (Foundation Support Piles) Drill 23 shafts Jun 24 to Feb 26 (3, 4) Set 126-inch casing Rotary drill 1 shaft/day, 1 hours/day 23 32b Pre-drill 126- inch rock socket Rotary drill 1 shaft/day, 9 hours/day 23 32c Remove 126- inch casing Rotary drill 1 casing/day, 15 minutes/casing 23 32d Drill 108-inch diameter shaft Cluster drill DTH 8.5 days/shaft, 10 hours/day 196 33a Dry Dock 1 West—Install Leveling Piles (Diving Board Shafts) Drill 18 shafts Jun 24 to Feb 26 (3, 4) Set 84-inch casing Rotary Drill 1 shaft/day, 1 hours/day 18 33b Pre-drill 84-inch rock socket Rotary drill 1 shaft/day, 9 hours/day 18 33c Remove 84-inch casing Rotary drill 1 casing/day, 15 minutes/casing 18 33d Drill 78-inch diameter shaft Cluster drill DTH 7.5 days/shaft, 10 hours/day 135 34 Dry Dock 1 North—Tie Downs Install 36 rock anchors Jul 24 to Jul 25 (3, 4) 9-inch diameter holes DTH mono-hammer 2 holes/day, 5 hours/hole 18 35 Dry Dock 1 West—Install Tie Downs Install 36 rock anchors Dec 25 to Dec 26 (4, 5) 9-inch diameter hole DTH mono-hammer 2 holes/day, 5 hours/hole 18 Total excavated holes/drilled shafts/sheet piles 1,118/198/580 2,498 * Note, for the purposes of this analysis, the proposed construction years are identified as years 2 through 5; potential marine mammal takes incidental to Year 1 of the Navy's construction activities were authorized under a previously issued IHA (87 FR 19886; April 6, 2022). 1 These activities were not included in the original application made available for public review during the Notice of Receipt comment period (NOR; 87 FR 53731), but have been added due to changes needed in the proposed construction schedule. 2 These activities were included in the original application, but the amount of activity proposed has been modified due to changes needed in the proposed construction schedule. 3 These activities began in construction year 1. 4 These activities began in year 1. Only the number of production days occurring in construction years 2 through 6 are presented. 5 Additional production days are included to account for equipment repositioning. 6 Sheet piles were installed in construction year 1. Specific Geographic Region The shipyard is located in the Piscataqua River in Kittery, Maine. The Piscataqua River originates at the boundary of Dover, New Hampshire, and Eliot, Maine (Figure 1). The river flows in a southeasterly direction for 2,093 meters (m) (13 miles (mi)) before entering Portsmouth Harbor and emptying into the Atlantic Ocean. The lower Piscataqua River is part of the Great Bay Estuary system and varies in width and depth. Many large and small islands break up the straight-line flow of the river as it continues toward the Atlantic Ocean. Seavey Island, the location of the proposed activities, is located in the lower Piscataqua River approximately 500 m, 1640 feet (ft) from its southwest bank, 200 m (656 ft) from its north bank, and approximately 4 kilometers (km) (2.5 mi) from the mouth of the river. Water depths in the proposed project area range from 6.4 m (21 ft) to 11.9 m (39 ft) at Berths 11, 12, and 13. Water depths in the lower Piscataqua River near the proposed project area range from 4.6 m (15 ft) in the shallowest areas to 21 m (69 ft) in the deepest areas. The river is approximately 914 m (3,300 ft) wide near the proposed project area, measured from the Kittery shoreline north of Wattlebury Island to the Portsmouth shoreline west of Peirce Island. The furthest direct line of sight from the proposed project area would be 1,287 m (0.8 mi) to the southeast and 418 m (0.26 mi) to the northwest. The nearshore environment of the Shipyard is characterized by a mix of hard bottom, gravel, soft sediments, rock outcrops, and rocky shoreline associated with fast tidal currents near the installation. The nearshore areas surrounding Seavey Island are predominately hard bottom (65 percent of benthic habitat) and gravel (26 percent) habitat, with only 9 percent soft bottom sediments within the surveyed area around Seavey Island (Tetra Tech, 2016). Much of the shoreline in the proposed project area is composed of hard shores (rocky intertidal). In general, rocky intertidal areas consist of bedrock that alternates between marine and terrestrial habitats, depending on the tide. Rocky intertidal areas consist of “bedrock, stones, or boulders that singly or in combination cover 75 percent or more of an area that is covered less than 30 percent by vegetation” (Federal Geographic Data Committee, 2013). The lower Piscataqua River is home to Portsmouth Harbor and is used by commercial, recreational, and military vessels. Between 150 and 250 commercial shipping vessels transit the lower Piscataqua River each year (Magnusson et al., 2012). Commercial fishing vessels are also very common in the river year-round, as are recreational vessels, which are more common in the warmer summer months. The shipyard is a dynamic industrial facility situated on an island with a narrow separation of waterways between the installation and the communities of Kittery and Portsmouth (Figure 2). The predominant noise sources from Shipyard industrial operations consist of dry dock cranes; passing vessels; and industrial equipment ( e.g., forklifts, loaders, rigs, vacuums, fans, dust collectors, blower belts, heating, air conditioning, and ventilation (HVAC) units, water pumps, and exhaust tubes and lids). Other components such as construction, vessel ground support equipment for maintenance purposes, vessel traffic across the Piscataqua River, and vehicle traffic on the shipyard's bridges and on local roads in Kittery and Portsmouth produce noise, but such noise generally represents a transitory contribution to the average noise level environment (Blue Ridge Research and Consulting (BRRC), 2015; ESS Group, 2015). Ambient sound levels recorded at the shipyard are considered typical of a large outdoor industrial facility and vary widely in space and time (ESS Group, 2015). BILLING CODE 3510-22-P EP18JA23.000 EP18JA23.001 BILLING CODE 3510-22-C Detailed Description of the Specified Activity The Navy's proposed P-381 project would modify the super flood basin to create two additional dry docking positions (Dry Dock 1 North and Dry Dock 1 West) in front of the existing Dry Dock 1 East. The super flood basin provides the starting point for the P-381 work. Several steps are required to convert the super flood basin to a dry dock with two positions fully capable of supporting the maintenance of submarines while maintaining access to the existing interior dry dock (Dry Dock 1 East). The dry dock positions (including the center wall) will be constructed using large precast segments (referred to as monoliths) that require both sidewall and base support. The monoliths will be manufactured offsite and transported to the construction site. Segments will be floated and/or lifted into place to create the center wall, followed by Dry Dock 1 North, and finally Dry Dock 1 West. Once the monoliths are set and grouted in place, the respective dry docks can be dewatered allowing the remaining interior construction to be performed in dry conditions. P-381 years 2 through 5 ( i.e., the time period of the Navy's specified activity for this proposed rule) construction activities will complete bedrock removal and the preparation of the walls and floors of the super flood basin to support the placement of the monoliths and the construction of the two dry dock positions. Most of the in-water construction will occur behind the existing super flood basin walls that would act as a barrier to sound and would contain underwater noise to within a small portion of the Piscataqua River. However, the west closure wall will be removed in order to install the Dry Dock 1 North entrance structure and caisson. In addition, the caissons may not always be in place throughout in-water construction. As such, the analyses presented herein conservatively assume the west closure wall, as well as the future caissons, would not be present throughout in-water construction activities. The Navy's request also considers emergency repairs of the P-310 super flood basin. During P-310 super flood testing in January 2022, excessive exfiltration ( i.e., transport of material outside of the basin) was observed along Berths 1 and 2 and between the west closure wall and super flood basin entrance structure. Emergency structural repairs were required to reduce excessive transport of material through the berths and west closure wall/entrance structure and prevent further damage. As a result, 216 28-inch Z-shaped sheet piles were installed along the Berth 1 face. After installation, these sheet piles were cut off approximately 10 ft above the mudline and concrete was tremie placed behind them to plug any gaps in the existing structure that contributed to the exfiltration. The removal of these 216 Berth 1 emergency repair piles and excess tremie concrete (approximately 382 cubic meters, 500 cubic yards (cy)) will be completed during this LOA period and are accounted for in the Navy's request. Similarly, 10 28-inch wide, Z-shaped sheet piles were installed between the super flood basin entrance structure and the west closure wall, cut off approximately 3 m (10 ft) above the mudline, and had concrete tremie placed behind them. These 10 sheet piles will be removed during the P-381 year 1 IHA period (covered under the IHA issued by NMFS for the first year of P-381 construction activities; 87 FR 19866; April 6, 2022). Several additional preparatory activities ( e.g., torch cutting, dredging, etc) will not create noise expected to result in harassment of marine mammals. Noise created during dredging of sediment and demolition debris ( e.g., bedrock, granite blocks, concrete) is unlikely to exceed that generated by other normal shipyard activities and is not expected to result in incidental take of marine mammals. Activities such as grouting ( i.e., pouring of concrete) and torch cutting are not noisy by design and would not result in incidental take of marine mammals. These activities are not addressed in the analyses of noise producing actions in the Navy's request, and are not considered by NMFS in our analysis, but are included in the work descriptions to clarify the construction progression. P-381 In-Water Construction Activities The proposed work remaining for P-381 can be generally grouped into five categories for ease of explanation: temporary structures, mechanical bedrock removal, continued demolition of super flood basin wall components, center wall tie-downs, and dry dock foundation and gantry crane support. Each category involves one or more activities expected to generate noise that could result in injury or harassment of marine mammals. Some of these activities are a continuation of work started in year 1, which were covered under a separate IHA issued by NMFS on April 6, 2022 (87 FR 19886). Temporary Structures —Several temporary structures would be installed and removed to facilitate the construction of the dry docks. The conversion of the existing west closure wall to the Dry Dock 1 North entrance requires reinforcement of the section of the west closure wall that will become the new dry dock entrance. The existing west closure wall structure will be surrounded by a temporary cofferdam. The cofferdam will be constructed with 48 28-inch wide, Z-shaped sheet piles. The sheet piles will be installed using an initial vibratory set followed by driving with impact hammers to refusal. The temporary guide wall along the Berth 11 end wall installed during year 1 (60 28-inch wide, Z-shaped sheet piles) would be removed with a vibratory hammer. An extension to the temporary cofferdam around the Dry Dock 1 entrance structure installed during P-381 year 1 would also be constructed. The extension would consist of 14 28-inch wide, Z-shaped sheet piles. The extension and the cofferdam (96 28-inch wide, Z-shaped sheet piles) would be removed in 2024 using a vibratory hammer. A temporary work trestle would be constructed to support the excavation of large shafts within the individual dry docking positions. The trestle would be installed in Dry Dock 1 North first and then relocated to Dry Dock 1 West. The trestle system would be supported by 4 84-inch steel pipe piles and would be relocated five times within each dry dock. As a result, the piles would be installed and removed 20 times in Dry Dock 1 North and 20 times in Dry Dock 1 West. The piles would be installed with a cluster drill consisting of multiple DTH hammers and removed with a rotary drill. Before the cluster drill would be deployed, a 102-inch casing would be set into bedrock and a 5-ft (1.5-m) deep rock socket would be excavated with a rotary drill (see Figure 1-4 in the Navy's application). The socket would be filled with concrete and a second, 84-inch casing would be installed inside the larger casing and set in the concrete. No drilling would be required to install the second casing. The outer casing would then be removed with a rotary drill. The 84-inch diameter cluster drill would operate independently inside the second casing to excavate the shaft. Once the shaft is drilled the inner casing would be removed by torch cutting. A temporary tie-in consisting of 15 28-inch wide, Z-shaped sheet piles would be installed between the center wall foundation and the west closure wall at Dry Dock 1 West. Twenty-three 28-inch wide, Z-shaped sheet piles would also be installed on the easterly end of Dry Dock 1 west to provide a similar temporary tie-in to the center wall foundation near the entrance to Dry Dock 1 east. The sheet piles would be installed using an initial vibratory set followed by driving with impact hammers. These tie-ins would be removed using a vibratory hammer along with the Dry Dock 1 North tie-in to the west closure wall (16 28-inch wide, Z-shaped sheet piles) that was installed under the P-381 year 1 IHA (87 FR 19886). To support excavation activities along Berth 1, 28 28-inch wide, Z-shaped sheet piles would be installed at the southeast corner of the berth using a combination of vibratory and impact hammers. These piles would be removed using a vibratory hammer. Mechanical Bedrock Removal —Mechanical removal of bedrock would be completed by the end of 2023 using various methods appropriate for the removal location and as needed to avoid damage to adjacent structures. Bedrock removal would occur along the Berth 11 face and abutment and along Berth 1. Bedrock would be removed by breaking it up with a hydraulic hammer ( i.e., hoe ram or breaker). To protect adjacent structures during mechanical bedrock removal, 924 4-6-inch diameter relief holes would be drilled using a DTH mono-hammer. A total of approximately 918 cubic meters (1,200 cy) of bedrock are anticipated to be removed. Demolition of Super Flood Basin Wall Components —Demolition of existing wall components would include the removal of shutter panels, granite quay walls, sheet piles, and concrete making up the super flood basin. Demolition of existing wall structures would be conducted using a rock hammer. Specifically, the remaining sections of the existing concrete shutter panels making up the face of Berth 11 (112 panels), portions of the granite block quay wall (2,141 cm, 2,800 cy) at Berth 1, and the remaining existing sheet pile wall at Berth 1 (168 25-inch wide, Z-shaped sheet piles) would be removed. The installation of a structural support waler (steel beam) at Berth 1 would also be completed. To complete the installation of the waler, about 98 m (320 linear ft) of concrete wall would be demolished using a hydraulic rock hammer. Center Wall Tie-downs —Additional work in the center wall area would involve the installation of support tie downs for future tremie concrete work. The tie downs require the placement of a total of 194 rock anchors requiring 9-inch diameter holes. The rock anchors would be installed using a DTH mono-hammer. Dry Dock and Gantry Crane Support —The location of the future center wall requires reinforcement to allow placement of the large pre-cast monolith structures forming the separation between the two new dry docking positions. Specifically, the floor of the existing basin must be able to provide an adequate foundation for the pre-cast monoliths that will make up the dry dock interiors and center wall. The basin floor will be reinforced by excavating 18 78-inch diameter shafts throughout the footprint of the center wall that will be filled with concrete to create the structural support piles for the center wall. The shafts will be excavated using a cluster drill consisting of multiple DTH mono-hammers. Before the cluster drill is deployed, a 102-inch diameter casing would be set into bedrock and a 5 foot deep rock socket would be excavated using a 102-inch diameter rotary drill (see Figure 1-4 of the Navy's application). The rock socket would be filled with concrete and a second, 78-inch diameter casing would be installed inside the 102-inch casing and set in the concrete. No drilling is required to install the second casing. The 102-inch diameter outer casing would then be removed with a rotary drill. The future Dry Dock 1 North and Dry Dock 1 West require significant structural reinforcement to provide an adequate foundation for the installation of the large pre-cast monolith structures forming the dry dock interior. Reinforcement of the individual dry dock foundations and walls would begin first at Dry Dock 1 North and, once completed, continue at Dry Dock 1 West. Twenty 78-inch diameter shafts would be excavated along the Berth 11 face and head wall to support the walls of Dry Dock 1 North. Along the floor of Dry Dock 1 North, 23 108-inch diameter shafts would be excavated for the installation of the foundation support piles and 18 78-inch diameter shafts would be excavated for the installation of leveling piles ( i.e., diving board shafts). The dry dock foundation and wall support pile and leveling pile shafts would be filled with concrete to create the support piles for the dry dock walls and floors. The shafts would be excavated using a cluster drill consisting of multiple DTH hammers in the same manner as previously described for the temporary work trestle piles. Once the wall and foundation support piles and leveling piles for Dry Dock 1 North have been installed, foundation and wall support piles and leveling piles would be installed for Dry Dock 1 West. Twenty-two 78-inch diameter shafts would be excavated along the Berth 1 face to support the walls of Dry Dock 1 West. Twenty-three 108-inch diameter shafts would be excavated along the floor of Dry Dock 1 West for the installation of foundation support piles and 18 78-inch shafts would be excavated for the installation of leveling piles ( i.e., diving board shafts). The casing sizes and rotary drill sizes proposed for each shaft are specified in Table 1. The large concrete monolithic sections used to create the dry docks and the center wall separation would be placed using a gantry crane. The gantry crane system would be structurally supported by the installation of 16 72-inch diameter shafts installed along the western extent of the Berth 1 face. The shafts would be installed using a DTH cluster drill as described for the temporary work trestle piles. The casing sizes and rotary drill sizes proposed for the gantry crane support shafts are specified in Table 1. P-310 Emergency Repairs Testing of the super flood basin on January 5, 2022 resulted in excess exfiltration through Berths 1 and 2, prompting the need for emergency repairs along Berth 1 as well as between the super flood basin entrance structure and the west closure wall. Emergency repairs consisted of the installation of sheet piles and the tremie pouring of concrete to fill in gaps along the structure walls and floor. Installation of emergency repairs at Berth 1 and the installation and removal of emergency repairs at the west closure wall and entrance structure occurred before the period described in the Navy's LOA application. Only the removal of Berth 1 emergency repair components would occur during the requested LOA period. The removal of the 216 28-inch wide, Z-shaped sheet piles along the Berth 1 face would be completed through direct pulling via barge-mounted crane or by vibratory hammer. Specific methods will be determined by the contractor based on resistance to extraction from the seabed. Direct pulling via crane is not anticipated to generate harmful levels of underwater sound. If required, the use of the vibratory hammer to extract the installed sheet piles would be limited to an initial effort to break the sheets loose, allowing them to be directly pulled out. As a conservative measure, vibratory extraction of these sheet piles is assumed for all analyses. The removal of 765 cubic meters (1,000 cy) of tremie concrete is anticipated to require use of a hydraulic rock hammer to break up material into smaller pieces. Smaller pieces would then be retrieved via excavator bucket for offsite disposal. The Navy estimates daily active use of the rock hammer for the removal of concrete from emergency repairs to be 4 hours per day. Means and Methods for Noise Producing Activities Only 28-inch wide, Z-shaped sheet piles would be installed or removed with pile-driving equipment during P-381 construction. The installation of 28-inch wide, Z-shaped steel sheet piles would be installed initially using vibratory means and then finished with impact hammers, if necessary. Impact hammers would also be used to push obstructions out of the way and where sediment conditions do not permit the efficient use of vibratory hammers. Pile removal activities would use cranes and vibratory hammers exclusively. The removal of bedrock and concrete and the demolition of concrete shutter panels at Berth 11 and granite blocks and sheet piles at Berth 1 during P-381 construction would be by mechanical means. These features would be demolished using a hydraulic rock hammer ( i.e., hoe ram). The type/size of rock hammers used would be determined by the contractor selected to perform the work. Two methods of rock excavation would be used during P-381 construction; DTH excavation and rotary drilling. During P-381 construction, rotary drilling would be used to set the casings and pre-drill rock sockets for DTH cluster drills. DTH excavation using mono-hammers would be used to create shafts for rock anchors and tie downs and for the excavation of relief holes during mechanical bedrock removal. For the largest shafts (greater than 42-inches in diameter), DTH excavation would use a cluster drill. A cluster drill uses multiple mono-hammers within a single bit to efficiently break up bedrock and create large diameter holes (see Figure 1-5 in the Navy's application). Concurrent Activities In order to maintain project schedules, it is likely that multiple pieces of equipment would operate at the same time within the basin. No ancillary activities are anticipated during the construction period that would require unimpeded access to the super flood basin. Therefore, it is anticipated that there would be space available within the project area for additional construction equipment. A maximum of 13 pieces of equipment could potentially operate in the project area at a single time. While this is an unlikely scenario, it could occur for a very brief period. Construction equipment would be staged along the perimeter of the super flood basin (Berth 11, Berth 1 and head wall) as well on multiple barges within the super flood basin. Table 2 provides a summary of possible equipment combinations that could be used simultaneously over the course of the proposed construction period. Table 2—Summary of Multiple Equipment Scenarios Year Quantity Equipment 2023 5 Rock Hammer (2), Vibratory Hammer (2), Impact Hammer (1). 5 Rock Hammer (2), Vibratory Hammer (1), Impact Hammer (1), DTH Mono-hammer (1). 5 Rock Hammer (1), Vibratory Hammer (1), Impact Hammer (1), DTH Mono-hammer (1), Rotary Drill (1). 5 Rock Hammer (1), Vibratory Hammer (1), DTH Mono-hammer (1), Cluster Drill (2). 5 Cluster Drill (2), Vibratory Hammer (1), Mono-hammer DTH (1), Rotary Drill (1). 5 Rock Hammer (1), Impact Hammer (1), DTH Mono-hammer (1), Cluster Drill (2). 6 Rock Hammer (2), DTH Mono-hammer (2), Cluster Drill (1), Rotary Drill (1). 6 Rock Hammer (2), Vibratory Hammer (1), DTH Mono-hammer (1), Rotary Drill (2). 8 Rock Hammer (2), Vibratory Hammer (2), DTH Mono-hammer (2), Cluster Drill (2). 10 Rock Hammer (3), Vibratory Hammer (2), Impact hammer (1), DTH Mono-hammer (2), Cluster Drill (2). 13 Rock Hammer (5), Cluster Drill (2), Vibratory Hammer (2), Impact Hammer (1), Mono-hammer DTH (3). 2024 8 Rock Hammer (2), Vibratory Hammer (2), DTH Mono-hammer (2), Cluster Drill (2). 5 Cluster Drill (2), DTH mono-hammer (1), Vibratory hammer (1), Impact Hammer (1). 3 Cluster Drill (2), DTH mono-hammer (1). 3 Cluster Drill (1), Rotary Drill (1), DTH mono-hammer (1). 3 Rotary Drill (2), DTH mono-hammer (1). 2025 3 Cluster Drill (2), DTH mono-hammer (1). 3 Cluster Drill (1), Rotary Drill (1), DTH mono-hammer (1). 3 Rotary Drill (2), DTH mono-hammer (1). 2 Rotary Drill (2). 2 Cluster Drill (2). Source: 381 Constructors, 2022. 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 Sections 3 and 4 of the application summarize available information regarding status and trends, distribution and habitat preferences, and behavior and life history of the potentially affected species. NMFS fully considered all of this information, and we refer the reader to these descriptions, incorporated in this preamble by reference, instead of reprinting the information. Additional information regarding population trends and threats may be found in NMFS' Stock Assessment Reports (SARs; 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 ). Table 3 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 expected to occur, 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 stocks managed under the MMPA in this region are assessed in NMFS' U.S. Atlantic and Gulf of Mexico SARs. All values presented in Table 3 are the most recent available at the time of publication (including from the 2021 SARs) and are available online at: www.fisheries.noaa.gov/national/marine-mammal-protection/marine-mammal-stock-assessments ). Table 3—Species Likely Impacted by the Specified Activities Common name Scientific name MMPA stock ESA/MMPA status; strategic (Y/N) 1 Stock abundance Nbest, (CV, N min , most recent abundance survey) 2 PBR Annual M/SI 3 Order Cetartiodactyla—Superfamily Odontoceti (toothed whales, dolphins, and porpoises) Family Phocoenidae (porpoises): Harbor Porpoise Phocoena phocoena Gulf of Maine/Bay of Fundy -; N 95,543 (0.31; 74,034; 2016) 851 164 Order Carnivora—Superfamily Pinnipedia Family Phocidae (earless seals): Harbor seal Phoca vitulina Western North Atlantic -; N 61,336 (0.08, 57,637; 2018) 1,729 339 Gray seal Halichoerus grypus Western North Atlantic -; N 27,300 4 (0.22; 22,785; 2016) 1,389 4,453 Harp seal Pagophilus groenlandicus Western North Atlantic -; N 7,600,000 (unk,7,100.000, 2019) 426,000 178,573 Hooded seal Cystophora cristata Western North Atlantic -; N 593,500 Unknown 1,680 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; N min 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 This abundance value and the associated PBR value reflect the US population only. Estimated abundance for the entire Western North Atlantic stock, including animals in Canada, is 451,600. The annual M/SI estimate is for the entire stock. As indicated above, all five species (with five managed stocks) in Table 3 temporally and spatially co-occur with the activity to the degree that take is reasonably likely to occur. Harbor Porpoise Harbor porpoises occur from the coastline to deep waters (>1,800 m, 5906 ft); Westgate et al., 1998), although the majority of the population is found over the continental shelf (Hayes et al., 2022). Based on genetic analysis, it is assumed that harbor porpoises in U.S. and Canadian waters are divided into four populations, as follows: (1) Gulf of St. Lawrence; (2) Newfoundland; (3) Greenland; and (4) Gulf of Maine/Bay of Fundy (Hayes et al., 2022). For management purposes in U.S. waters, harbor porpoises have been divided into ten stocks along both the East and West Coasts. In the project area, only the Gulf of Maine/Bay of Fundy stock of harbor porpoise may be present. This stock is found in U.S. and Canadian Atlantic waters and is concentrated in the northern Gulf of Maine and southern Bay of Fundy region, generally in waters less than 150 m (492 ft) deep (Hayes et al., 2022). The Navy has been collecting data on marine mammals in the Piscataqua River since 2017 through construction monitoring and non-construction related monthly surveys (2017-2018). Three harbor porpoises were observed travelling quickly through the river channel during marine mammal monitoring conducted between April and December 2017 in support of the Berth 11 Waterfront Improvements Project (Cianbro, 2018). Two harbor porpoises were observed during construction monitoring that occurred between January 2018 and January 2019 (Cianbro, 2018; Navy, 2019). One harbor porpoise was observed in March 2017 during non-construction related surveys conducted on 12 days (one per month) in 2017, and two harbor porpoises (one in August and one in November) were observed in monthly surveys conducted in 2018 (Naval Facilities Engineering Systems Command (NAVFAC) Mid-Atlantic 2018, 2019b). There was one sighting of a harbor porpoise during P-310 year 1 monitoring events (May through December 2020) (NAVFAC, 2021). No harbor porpoise were sighted in 2021 (NAVFAC, 2022). Harbor Seal Harbor seals are found in all nearshore waters of the North Atlantic and North Pacific Oceans and adjoining seas above about 30° N (Burns, 2009). They can be found year-round in coastal waters of eastern Canada and Maine and occur seasonally (September through late May) along the coasts of southern New England to Virginia (Ampela et al., 2018; Hayes et al., 2022; Jones and Rees, 2020). Overall, there are five recognized subspecies of harbor seal, two of which occur in the Atlantic Ocean. The western Atlantic harbor seal is the subspecies likely to occur in the proposed project area. There is some uncertainty about the overall population stock structure of harbor seals in the western North Atlantic Ocean. However, it is theorized that harbor seals along the eastern U.S. and Canada are all from a single population (Temte et al., 1991). Haulout and pupping sites are located off Manomet, MA and the Isles of Shoals, ME (Hayes et al., 2022). Harbor seals are the most abundant pinniped in the Piscataqua River. The majority of harbor seals occur along the Maine coast with a large portion of them hauling out at the Isles of Shoals (see Figure 4-1 of the Navy's application), which is located approximately 14.5 km (9 mi) from the project area. There are no major rookeries near the Navy's proposed project area. The closest haul-out site is at Hicks Rocks, located approximately 2.4 km (1.5 mi) from the proposed project area, but it is on the opposite side of Seavey Island and not within the project area. Pupping season for harbor seals is May to June. No harbor seal pups were observed during recent monitoring events conducted in the area (Cianbro, 2018) as pupping sites are north of the Maine-New Hampshire border (Hayes et al., 2022). During construction monitoring between the months of April and December 2017, there were 199 observations of harbor seals (Cianbro, 2018) in the project area. A total of 249 harbor seals were observed during construction monitoring between the months of January 2018 and January 2019 for the same project (Navy, 2019). The primary behaviors observed during monitoring were milling that occurred almost 60 percent of the time followed by swimming and traveling by the proposed project area at 29 percent and 12 percent, respectively (Cianbro, 2018). A total of 17 and 83 harbor seals were observed during the one-day monthly surveys conducted in 2017 and 2018, respectively (NAVFAC Mid-Atlantic, 2018; 2019b). Construction monitoring conducted between May and December of 2020 and January through December 2021 as part of P-310 recorded 721 harbor seals and 451 harbor seals, respectively (NAVFAC, 2021; 2022). Gray Seal There are three major populations of gray seals found in the world; eastern Canada (western North Atlantic stock), northwestern Europe and the Baltic Sea. Gray seals in the project area belong to the western North Atlantic stock. The range for this stock is from New Jersey to Labrador. Current population trends show that gray seal abundance is likely increasing in the U.S. Atlantic Exclusive Economic Zone (EEZ) (Hayes et al., 2022). Although the rate of increase is unknown, surveys conducted since their arrival in the 1980s indicate a steady increase in abundance in both Maine and Massachusetts (Hayes et al., 2022). It is believed that recolonization by Canadian gray seals is the source of the U.S. population (Hayes et al., 2022). In U.S. waters, gray seals have been observed using an historic pupping site on Muskeget Island in Massachusetts since 1988 and on Seal and Green Islands in Maine since approximately the mid-1990s. All of these sites are more than 180 km (112 mi) from the Shipyard. In general, this species can be found year-round in the coastal waters of the Gulf of Maine (Hayes et al., 2022). During construction monitoring for the waterfront improvements project, there were 24 observations of gray seals within the proposed project area between the months of April and December 2017 (Cianbro, 2018) and a total of 12 observed between January 2018 and January 2019 (Navy, 2019). Ten of the 12 observations occurred during the winter months (Navy, 2019). The primary behavior observed during surveys was milling at just over 60 percent of the time followed by swimming within and traveling through the proposed project area. Gray seals were observed foraging approximately 5 percent of the time (Cianbro, 2018). The one-day monthly marine mammal surveys during 2017 and 2018 recorded six and three sightings, respectively, of gray seal (NAVFAC Mid-Atlantic, 2018, 2019b). A total of 47 gray seals were observed during P-310 year 1 monitoring events from May through December 2020 (NAVFAC, 2021). In 2021, 21 gray seals were sighted during monitoring (NAVFAC, 2022). No gray seal pups were observed during the surveys (Cianbro, 2018; Navy, 2019) as pupping sites for gray seals (like harbor seals) are known to occur north of Maine-New Hampshire border. Hooded Seal Hooded seals are generally found in deeper waters or on drifting pack ice. The world population of hooded seals has been divided into three stocks, which coincide with specific breeding areas, as follows: (1) Northwest Atlantic, (2) Greenland Sea, and (3) White Sea (Hayes et al., 2022). The hooded seal is a highly migratory species, and its range can extend from the Canadian arctic to Puerto Rico. In U.S. waters, the species has an increasing presence in the coastal waters between Maine and Florida (Hayes et al., 2022). In the U.S., they are considered members of the western North Atlantic stock and generally occur in New England waters from January through May and further south in the summer and fall seasons (Hayes et al., 2022). Hooded seals are known to occur in the Piscataqua River; however, they are not as abundant as the more commonly observed harbor seal. Anecdotal sighting information indicates that two hooded seals were observed from the Shipyard in August 2009, but no other observations have been recorded (Trefry November 20, 2015). Hooded seals were not observed during marine mammal monitoring or survey events that took place in 2017, 2018, 2020, or 2021 (Cianbro, 2018; NAVFAC Mid-Atlantic 2018, 2019b; Navy 2019; NAVFAC 2021, 2022). Harp Seal The harp seal is a highly migratory species, its range extending throughout the Arctic and North Atlantic Oceans. The world's harp seal population is separated into three stocks, based on associations with specific locations of pagophilic breeding activities: (1) off eastern Canada, (2) on the West Ice off eastern Greenland, and (3) in the White Sea off the coast of Russia. The largest stock, which includes two herds that breed either off the coast of Newfoundland/Labrador or near the Magdelan Islands in the Gulf of St. Lawrence, is equivalent to the western North Atlantic stock. Harp seals that occur in the United States are considered members of the western North Atlantic stock and generally occur in New England waters from January through May (Hayes et al., 2022). Harp seals are known to occur in the Piscataqua River; however, they are not as abundant as the more commonly observed harbor seal and were last documented in the river in May of 2020. Two harp seals were sighted on two separate occasions (on May 12 and May 14, 2020) during construction monitoring for P-310 (Stantec, 2020). No pile-driving was occurring at the time of the sighting. Previous to that, the last harp seal sighting was in 2016 (NAVFAC Mid-Atlantic, 2016; NMFS, 2016). Harp seals were not observed during marine mammal monitoring or survey events that took place in 2017 and 2018 (Cianbro, 2018; NAVFAC Mid-Atlantic, 2018, 2019b; Navy, 2019). No harp seals were sighted in 2021 (NAVFAC, 2021, 2022). Unusual Mortality Events (UMEs) Between July 2018 and March 2020 elevated numbers of harbor seal and gray seal mortalities occurred across Maine, New Hampshire and Massachusetts. This event was declared an Unusual Mortality Event (UME). Seals showing clinical signs were observed stranding as far south as Virginia, although not in elevated numbers. Therefore the UME investigation encompassed all seal strandings from Maine to Virginia. Lastly, ice seals (harp and hooded seals) also started stranding with clinical signs, again not in elevated numbers, and those two seal species were added to this UME investigation. Information on this UME is available online at: https://www.fisheries.noaa.gov/new-england-mid-atlantic/marine-life-distress/2018-2020-pinniped-unusual-mortality-event-along. Since July 2022, a second UME of harbor seals and gray seals in this region has been declared after elevated numbers of sick and dead individuals were documented along the southern and central coast of Maine from Biddeford to Boothbay (including Cumberland, Lincoln, Knox, Sagadahoc and York Counties). Information on this UME is available online at: https://www.fisheries.noaa.gov/2022-pinniped-unusual-mortality-event-along-maine-coast. 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 (2018a) 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 4. Table 4—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). For more detail concerning these groups and associated frequency ranges, please see NMFS (2018a) 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 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 can occur from impact and vibratory pile installation and removal, rotary drilling, DTH, and rock hammering. The effects of underwater noise from the Navy's proposed activities have the potential to result in Level A and Level B harassment of marine mammals in the action area. Description of Sound Sources This section contains a brief technical background on sound, on the characteristics of certain sound types, and on metrics used in this proposal inasmuch as the information is relevant to the specified activity and to a discussion of the potential effects of the specified activity on marine mammals found later in this document. For general information on sound and its interaction with the marine environment, please see, e.g., Au and Hastings (2008); Richardson et al. (1995); Urick (1983). Sound travels in waves, the basic components of which are frequency, wavelength, velocity, and amplitude. Frequency is the number of pressure waves that pass by a reference point per unit of time and is measured in hertz (Hz) or cycles per second. Wavelength is the distance between two peaks or corresponding points of a sound wave (length of one cycle). Higher frequency sounds have shorter wavelengths than lower frequency sounds, and typically attenuate (decrease) more rapidly, except in certain cases in shallower water. Amplitude is the height of the sound pressure wave or the “loudness” of a sound and is typically described using the relative unit of the dB. A sound pressure level (SPL) in dB is described as the ratio between a measured pressure and a reference pressure (for underwater sound, this is 1 microPascal (μPa)), and is a logarithmic unit that accounts for large variations in amplitude; therefore, a relatively small change in dB corresponds to large changes in sound pressure. The source level represents the SPL referenced at a distance of 1 m from the source (referenced to 1 μPa), while the received level is the SPL at the listener's position (referenced to 1 μPa). The received level is the sound level at the listener's position. Note that all underwater sound levels in this document are referenced to a pressure of 1 µPa and all airborne sound levels in this document are referenced to a pressure of 20 µPa. Root mean square (RMS) is the quadratic mean sound pressure over the duration of an impulse. RMS is calculated by squaring all of the sound amplitudes, averaging the squares, and then taking the square root of the average (Urick, 1983). RMS accounts for both positive and negative values; squaring the pressures makes all values positive so that they may be accounted for in the summation of pressure levels (Hastings and Popper, 2005). This measurement is often used in the context of discussing behavioral effects, in part because behavioral effects, which often result from auditory cues, may be better expressed through averaged units than by peak pressures. Sound exposure level (SEL; represented as dB referenced to 1 micropascal squared per second (re 1 μPa2-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 is calculated over the time window containing the entire pulse ( i.e., 100 percent of the acoustic energy). SEL is a cumulative metric; it can be accumulated over a single pulse, or calculated over periods containing multiple pulses. Cumulative SEL (SELcum) represents the total energy accumulated by a receiver over a defined time window or during an event. Peak sound pressure (also referred to as zero-to-peak sound pressure or 0-pk) is the maximum instantaneous sound pressure measurable in the water at a specified distance from the source, and is represented in the same units as the RMS sound pressure. When underwater objects vibrate or activity occurs, sound-pressure waves are created. These waves alternately compress and decompress the water as the sound wave travels. Underwater sound waves radiate in a manner similar to ripples on the surface of a pond and may be either directed in a beam or beams or may radiate in all directions (omnidirectional sources), as is the case for sound produced by the construction activities considered here. The compressions and decompressions associated with sound waves are detected as changes in pressure by aquatic life and man-made sound receptors such as hydrophones. Even in the absence of sound from the specified activity, the underwater environment is typically loud due to ambient sound, which is defined as the all-encompassing sound in a given place and is usually a composite of sound from many sources both near and far (American National Standards Institute standards (ANSI), 1995). The sound level of a region is defined by the total acoustical energy being generated by known and unknown sources. These sources may include physical ( e.g., wind and waves, earthquakes, ice, atmospheric sound), biological ( e.g., sounds produced by marine mammals, fish, and invertebrates), and anthropogenic ( e.g., vessels, dredging, construction) sound. A number of sources contribute to ambient sound, including wind and waves, which are a main source of naturally occurring ambient sound for frequencies between 200 Hz and 50 kilohertz (kHz) (Mitson, 1995). In general, ambient sound levels tend to increase with increasing wind speed and wave height. Precipitation can become an important component of total sound at frequencies above 500 Hz, and possibly down to 100 Hz during quiet times. Marine mammals can contribute significantly to ambient sound levels, as can some fish and snapping shrimp. The frequency band for biological contributions is from approximately 12 Hz to over 100 kHz. Sources of ambient sound related to human activity include transportation (surface vessels), dredging and construction, oil and gas drilling and production, geophysical surveys, sonar, and explosions. Vessel noise typically dominates the total ambient sound for frequencies between 20 and 300 Hz. In general, the frequencies of anthropogenic sounds are below 1 kHz and, if higher frequency sound levels are created, they attenuate rapidly. The Shipyard is a dynamic industrial facility situated on an island with a narrow separation of waterways between the installation and the communities of Kittery and Portsmouth. The predominant noise sources from Shipyard industrial operations consist of dry dock cranes; passing vessels; and industrial equipment ( e.g., forklifts, loaders, rigs, vacuums, fans, dust collectors, blower belts, heating, air conditioning, and ventilation units, water pumps, and exhaust tubes and lids). Other components such as construction, vessel ground support equipment for maintenance purposes, vessel traffic across the Piscataqua River, and vehicle traffic on the Shipyard's bridges and on local roads in Kittery and Portsmouth produce noise, but such noise generally represents a transitory contribution to the average noise level environment (Blue Ridge Research and Consulting, 2015; ESS Group, 2015). Ambient sound levels recorded at the Shipyard are considered typical of a large outdoor industrial facility and vary widely in space and time (ESS Group, 2015). Thirteen underwater acoustic recordings were logged in 2017 with sensors placed in depths of 4.5 m (15 ft) within the security fencing area of the Shipyard Berth 11. Recordings ranged from 140 dB to 161.3 dB peak SPL and from 128.2 dB to 133.8 dB RMS SPL. Conditions at which the recordings were made were with little wind and near peak tidal flow. A mean SPL of 131 dB RMS was evenly distributed within the security fencing area and is consistent with observations made at other locations near the Shipyard and documented background sound levels in estuarine or tidal locations (Hydrosonic LLC, 2017). Due to the close proximity to the Shipyard that measurements were recorded, ambient underwater noise levels further into the navigation channel are likely to be lower. The sum of the various natural and anthropogenic sound sources at any given location and time—which comprise “ambient” or “background” sound—depends not only on the source levels (as determined by current weather conditions and levels of biological and shipping activity) but also on the ability of sound to propagate through the environment. In turn, sound propagation is dependent on the spatially and temporally varying properties of the water column and sea floor, and is frequency-dependent. As a result of the dependence on a large number of varying factors, ambient sound levels can be expected to vary widely over both coarse and fine spatial and temporal scales. Sound levels at a given frequency and location can vary by 10-20 dB from day to day (Richardson et al., 1995). The result is that, depending on the source type and its intensity, sound from the specified activity may be a negligible addition to the local environment or could form a distinctive signal that may affect marine mammals. In-water construction activities associated with the project would include impact and vibratory pile installation and removal, rotary drilling, DTH, and rock hammering. The sounds produced by these activities fall into one of two general sound types: impulsive and non-impulsive (defined below). The distinction between these two sound types is important because they have differing potential to cause physical effects, particularly with regard to hearing ( e.g., Ward, 1997 in Southall et al., 2007). Please see Southall et al. (2007) for an in-depth discussion of these concepts. Impulsive sound sources ( e.g., explosions, gunshots, sonic booms, impact pile driving) produce signals that are brief (typically considered to be less than one second), broadband, atonal transients (ANSI, 1986; Harris, 1998; National Institute for Occupational Safety and Health (NIOSH), 1998; International Organization for Standardization (ISO) 2003; ANSI 2005) and occur either as isolated events or repeated in some succession. Impulsive sounds are all characterized by a relatively rapid rise from ambient pressure to a maximal pressure value followed by a rapid decay period that may include a period of diminishing, oscillating maximal and minimal pressures, and generally have an increased capacity to induce physical injury as compared with sounds that lack these features. Non-impulsive sounds can be tonal, narrowband, or broadband, brief or prolonged, and may be either continuous or non-continuous (ANSI, 1995; NIOSH, 1998). Some of these non-impulsive sounds can be transient signals of short duration but without the essential properties of impulses ( e.g., rapid rise time). Examples of non-impulsive sounds include those produced by vessels, aircraft, machinery operations such as drilling or dredging, vibratory pile driving, and active sonar systems. The duration of such sounds, as received at a distance, can be greatly extended in a highly reverberant environment. Impact and vibratory hammers would be used on this project. Impact hammers operate by repeatedly dropping and/or pushing a heavy piston onto a pile to drive the pile into the substrate. Sound generated by impact hammers is characterized by rapid rise times and high peak levels, a potentially injurious combination (Hastings and Popper, 2005). Vibratory hammers install piles by vibrating them and allowing the weight of the hammer to push them into the sediment. Vibratory hammers produce significantly less sound than impact hammers. Peak SPLs may be 180 dB or greater, but are generally 10 to 20 dB lower than SPLs generated during impact pile driving of the same-sized pile (Oestman et al., 2009). Rise time is slower, reducing the probability and severity of injury, and sound energy is distributed over a greater amount of time (Nedwell and Edwards, 2002; Carlson et al., 2005). Vibratory pile drivers will be used to the greatest extent possible during the Navy's proposed construction activities to minimize high SPLs associated with impact pile driving. Hydraulic rock hammers ( i.e., hoe rams) will be used for removal and demolition purposes. These tools are impact devices designed to break rock or concrete. A rock hammer operates by using a chisel-like hammer to rapidly strike an exposed surface to break it up into smaller pieces that will be removed by a clamshell dredge or bucket excavator, as appropriate. Few data exist regarding the underwater sounds produced by rock hammers. Data reported by Escude (2012), however, suggest that the sounds produced by hoe rams are comparable to impact hammers. Therefore, for the purposes of this analysis, it is assumed that hydraulic rock hammers act as an impulsive source characterized by rapid rise times and high peak levels. DTH systems, involving both mono-hammers and cluster-hammers, and rotary drills will also be used during the proposed construction. In rotary drilling, the drill bit rotates on the rock while the drill rig applies pressure. The bit rotates and grinds continuously to fracture the rock and create a hole. Rotary drilling is considered a non-impulsive noise source, similar to vibratory pile driving. A DTH hammer is essentially a drill bit that drills through the bedrock using a rotating function like a normal drill, in concert with a hammering mechanism operated by a pneumatic (or sometimes hydraulic) component integrated into to the DTH hammer to increase speed of progress through the substrate ( i.e., it is similar to a “hammer drill” hand tool). Rock socketing involves using DTH equipment to create a hole in the bedrock inside which the pile is placed to give it lateral and longitudinal strength. The sounds produced by the DTH methods contain both a continuous non-impulsive component from the drilling action and an impulsive component from the hammering effect. Therefore, we treat DTH systems as both impulsive and continuous, non-impulsive sound source types simultaneously. The likely or possible impacts of the Navy's proposed activities on marine mammals could involve both non-acoustic and acoustic stressors. Potential non-acoustic stressors could result from the physical presence of the equipment and personnel; however, given there are no known pinniped haul-out sites in the vicinity of the Shipyard, visual and other non-acoustic stressors would be limited, and any impacts to marine mammals are expected to primarily be acoustic in nature. Acoustic Impacts The introduction of anthropogenic noise into the aquatic environment from pile driving or drilling is the primary means by which marine mammals may be harassed from the Navy's specified activity. In general, animals exposed to natural or anthropogenic sound may experience physical and psychological effects, ranging in magnitude from none to severe (Southall et al., 2007, 2019). In general, exposure to pile driving or drilling noise has the potential to result in auditory threshold shifts and behavioral reactions ( e.g., avoidance, temporary cessation of foraging and vocalizing, changes in dive behavior). Exposure to anthropogenic noise can also lead to non-observable physiological responses such an increase in stress hormones. Additional noise in a marine mammal's habitat can mask acoustic cues used by marine mammals to carry out daily functions such as communication and predator and prey detection. The effects of pile driving or drilling noise on marine mammals are dependent on several factors, including, but not limited to, sound type ( e.g., impulsive vs. non-impulsive), the species, age and sex class ( e.g., adult male vs. mom with calf), duration of exposure, the distance between the pile and the animal, received levels, behavior at time of exposure, and previous history with exposure (Wartzok et al., 2004; Southall et al., 2007). Here we discuss physical auditory effects (threshold shifts) followed by behavioral effects and potential impacts on habitat. NMFS defines a noise-induced threshold shift (TS) as a change, usually an increase, in the threshold of audibility at a specified frequency or portion of an individual's hearing range above a previously established reference level (NMFS, 2018a). The amount of threshold shift is customarily expressed in dB. A TS can be permanent or temporary. As described in NMFS (2018a), there are numerous factors to consider when examining the consequence of TS, including, but not limited to, the signal temporal pattern ( e.g., impulsive or non-impulsive), likelihood an individual would be exposed for a long enough duration or to a high enough level to induce a TS, the magnitude of the TS, time to recovery (seconds to minutes or hours to days), the frequency range of the exposure ( i.e., spectral content), the hearing and vocalization frequency range of the exposed species relative to the signal's frequency spectrum ( i.e., how animal uses sound within the frequency band of the signal; e.g., Kastelein et al., 2014), and the overlap between the animal and the source ( e.g., spatial, temporal, and spectral). When analyzing the auditory effects of noise exposure, it is often helpful to broadly categorize sound as either impulsive or non-impulsive. When considering auditory effects, vibratory pile driving and rotary drilling are considered non-impulsive sources while impact pile driving and rock hammering are treated as an impulsive source. DTH is considered to have both non-impulsive and impulsive components. Permanent Threshold Shift (PTS) —NMFS defines PTS as a permanent, irreversible increase in the threshold of audibility at a specified frequency or portion of an individual's hearing range above a previously established reference level (NMFS, 2018). Available data from humans and other terrestrial mammals indicate that a 40 dB threshold shift approximates PTS onset (see Ward et al., 1958, 1959; Ward, 1960; Kryter et al., 1966; Miller, 1974; Ahroon et al., 1996; Henderson et al., 2008). PTS levels for marine mammals are estimates, as with the exception of a single study unintentionally inducing PTS in a harbor seal (Kastak et al., 2008), there are no empirical data measuring PTS in marine mammals largely due to the fact that, for various ethical reasons, experiments involving anthropogenic noise exposure at levels inducing PTS are not typically pursued or authorized (NMFS, 2018). Temporary Threshold Shift (TTS) —A temporary, reversible increase in the threshold of audibility at a specified frequency or portion of an individual's hearing range above a previously established reference level (NMFS, 2018). Based on data from cetacean TTS measurements (see Southall et al. 2007), a TTS of 6 dB is considered the minimum threshold shift clearly larger than any day-to-day or session-to-session variation in a subject's normal hearing ability (Schlundt et al., 2000; Finneran et al., 2000, 2002). As described in Finneran (2015), marine mammal studies have shown the amount of TTS increases with SELcum in an accelerating fashion: at low exposures with lower SELcum, the amount of TTS is typically small and the growth curves have shallow slopes. At exposures with higher SELcum, the growth curves become steeper and approach linear relationships with the noise SEL. Depending on the degree (elevation of threshold in dB), duration ( i.e., recovery time), and frequency range of TTS, and the context in which it is experienced, TTS can have effects on marine mammals ranging from discountable to serious (similar to those discussed in auditory masking, below). For example, a marine mammal may be able to readily compensate for a brief, relatively small amount of TTS in a non-critical frequency range that takes place during a time when the animal is traveling through the open ocean, where ambient noise is lower and there are not as many competing sounds present. Alternatively, a larger amount and longer duration of TTS sustained during time when communication is critical for successful mother/calf interactions could have more serious impacts. We note that reduced hearing sensitivity as a simple function of aging has been observed in marine mammals, as well as humans and other taxa (Southall et al., 2007), so we can infer that strategies exist for coping with this condition to some degree, though likely not without cost. Relationships between TTS and PTS thresholds have not been studied in marine mammals, and there is no PTS data for cetaceans, but such relationships are assumed to be similar to those in humans and other terrestrial mammals. PTS typically occurs at exposure levels at least several decibels above (a 40-dB threshold shift approximates PTS onset; e.g., Kryter et al., 1966; Miller, 1974) that inducing mild TTS (a 6-dB threshold shift approximates TTS onset; e.g., Southall et al., 2007). Based on data from terrestrial mammals, a precautionary assumption is that the PTS thresholds for impulsive sounds (such as impact pile driving pulses as received close to the source) are at least 6 dB higher than the TTS threshold on a peak-pressure basis and PTS cumulative sound exposure level thresholds are 15 to 20 dB higher than TTS cumulative sound exposure level thresholds (Southall et al., 2007). Given the higher level of sound or longer exposure duration necessary to cause PTS as compared with TTS, it is considerably less likely that PTS could occur. TTS is the mildest form of hearing impairment that can occur during exposure to sound (Kryter, 1985). While experiencing TTS, the hearing threshold rises, and a sound must be at a higher level in order to be heard. In terrestrial and marine mammals, TTS can last from minutes or hours to days (in cases of strong TTS). In many cases, hearing sensitivity recovers rapidly after exposure to the sound ends. Currently, TTS data only exist for four species of cetaceans (bottlenose dolphin), beluga whale ( Delphinapterus leucas ), harbor porpoise, and Yangtze finless porpoise ( Neophocoena asiaeorientalis )) and five species of pinnipeds exposed to a limited number of sound sources ( i.e., mostly tones and octave-band noise) in laboratory settings (Finneran, 2015). TTS was not observed in trained spotted ( Phoca largha ) and ringed ( Pusa hispida ) seals exposed to impulsive noise at levels matching previous predictions of TTS onset (Reichmuth et al., 2016). In general, harbor seals and harbor porpoises have a lower TTS onset than other measured pinniped or cetacean species (Finneran, 2015). Additionally, the existing marine mammal TTS data come from a limited number of individuals within these species. No data are available on noise-induced hearing loss for mysticetes. For summaries of data on TTS in marine mammals or for further discussion of TTS onset thresholds, please see Southall et al. (2007), Finneran and Jenkins (2012), Finneran (2015), and Table 5 in NMFS (2018). Behavioral Harassment —Exposure to noise from pile driving and drilling also has the potential to behaviorally disturb marine mammals. Behavioral disturbance may include a variety of effects, including subtle changes in behavior ( e.g., minor or brief avoidance of an area or changes in vocalizations), more conspicuous changes in similar behavioral activities, and more sustained and/or potentially severe reactions, such as displacement from or abandonment of high-quality habitat. Disturbance may result in changing durations of surfacing and dives, changing direction and/or speed; reducing/increasing vocal activities; changing/cessation of certain behavioral activities (such as socializing or feeding); eliciting a visible startle response or aggressive behavior (such as tail/fin slapping or jaw clapping); avoidance of areas where sound sources are located. Pinnipeds may increase their haul out time, possibly to avoid in-water disturbance (Thorson and Reyff, 2006). Behavioral responses to sound are highly variable and context-specific and any reactions depend on numerous intrinsic and extrinsic factors ( e.g., species, state of maturity, experience, current activity, reproductive state, auditory sensitivity, time of day), as well as the interplay between factors ( e.g., Richardson et al., 1995; Wartzok et al., 2003; Southall et al., 2007; Weilgart, 2007; Archer et al., 2010). Behavioral reactions can vary not only among individuals but also within an individual, depending on previous experience with a sound source, context, and numerous other factors (Ellison et al., 2012), and can vary depending on characteristics associated with the sound source ( e.g., whether it is moving or stationary, number of sources, distance from the source). In general, pinnipeds seem more tolerant of, or at least habituate more quickly to, potentially disturbing underwater sound than do cetaceans, and generally seem to be less responsive to exposure to industrial sound than most cetaceans. Please see Appendices B and C of Southall et al. (2007) and Gomez et al. (2016) for reviews of studies involving marine mammal behavioral responses to sound. Habituation can occur when an animal's response to a stimulus wanes with repeated exposure, usually in the absence of unpleasant associated events (Wartzok et al., 2003). Animals are most likely to habituate to sounds that are predictable and unvarying. It is important to note that habituation is appropriately considered as a “progressive reduction in response to stimuli that are perceived as neither aversive nor beneficial,” rather than as, more generally, moderation in response to human disturbance (Bejder et al., 2009). The opposite process is sensitization, when an unpleasant experience leads to subsequent responses, often in the form of avoidance, at a lower level of exposure. As noted above, behavioral state may affect the type of response. For example, animals that are resting may show greater behavioral change in response to disturbing sound levels than animals that are highly motivated to remain in an area for feeding (Richardson et al., 1995; National Research Council (NRC), 2003; Wartzok et al., 2003). Controlled experiments with captive marine mammals have showed pronounced behavioral reactions, including avoidance of loud sound sources (Ridgway et al., 1997; Finneran et al., 2003). Observed responses of wild marine mammals to loud pulsed sound sources (typically seismic airguns or acoustic harassment devices) have been varied but often consist of avoidance behavior or other behavioral changes suggesting discomfort (Morton and Symonds, 2002; see also Richardson et al., 1995; Nowacek et al., 2007). Available studies show wide variation in response to underwater sound; therefore, it is difficult to predict specifically how any given sound in a particular instance might affect marine mammals perceiving the signal. If a marine mammal does react briefly to an underwater sound by changing its behavior or moving a small distance, the impacts of the change are unlikely to be significant to the individual, let alone the stock or population. However, if a sound source displaces marine mammals from an important feeding or breeding area for a prolonged period, impacts on individuals and populations could be significant ( e.g., Lusseau and Bejder, 2007; Weilgart, 2007; NRC, 2005). However, there are broad categories of potential response, which we describe in greater detail here, that include alteration of dive behavior, alteration of foraging behavior, effects to breathing, interference with or alteration of vocalization, avoidance, and flight. Changes in dive behavior can vary widely and may consist of increased or decreased dive times and surface intervals as well as changes in the rates of ascent and descent during a dive ( e.g., Frankel and Clark, 2000; Costa et al., 2003; Ng and Leung, 2003; Nowacek et al., 2004; Goldbogen et al., 2013a,b). Variations in dive behavior may reflect interruptions in biologically significant activities ( e.g., foraging) or they may be of little biological significance. The impact of an alteration to dive behavior resulting from an acoustic exposure depends on what the animal is doing at the time of the exposure and the type and magnitude of the response. Disruption of feeding behavior can be difficult to correlate with anthropogenic sound exposure, so it is usually inferred by observed displacement from known foraging areas, the appearance of secondary indicators ( e.g., bubble nets or sediment plumes), or changes in dive behavior. As for other types of behavioral response, the frequency, duration, and temporal pattern of signal presentation, as well as differences in species sensitivity, are likely contributing factors to differences in response in any given circumstance ( e.g., Croll et al., 2001; Nowacek et al., 2004; Madsen et al., 2006; Yazvenko et al., 2007). A determination of whether foraging disruptions incur fitness consequences would require information on or estimates of the energetic requirements of the affected individuals and the relationship between prey availability, foraging effort and success, and the life history stage of the animal. Variations in respiration naturally vary with different behaviors and alterations to breathing rate as a function of acoustic exposure can be expected to co-occur with other behavioral reactions, such as a flight response or an alteration in diving. However, respiration rates in and of themselves may be representative of annoyance or an acute stress response. Various studies have shown that respiration rates may either be unaffected or could increase, depending on the species and signal characteristics, again highlighting the importance in understanding species differences in the tolerance of underwater noise when determining the potential for impacts resulting from anthropogenic sound exposure ( e.g., Kastelein et al., 2001, 2005, 2006; Gailey et al., 2007). Marine mammals vocalize for different purposes and across multiple modes, such as whistling, echolocation click production, calling, and singing. Changes in vocalization behavior in response to anthropogenic noise can occur for any of these modes and may result from a need to compete with an increase in background noise or may reflect increased vigilance or a startle response. For example, in the presence of potentially masking signals, humpback whales and killer whales have been observed to increase the length of their songs (Miller et al., 2000; Fristrup et al., 2003; Foote et al., 2004), while right whales ( Eubalaena glacialis ) have been observed to shift the frequency content of their calls upward while reducing the rate of calling in areas of increased anthropogenic noise (Parks et al., 2007). In some cases, animals may cease sound production during production of aversive signals (Bowles et al., 1994). Avoidance is the displacement of an individual from an area or migration path as a result of the presence of a sound or other stressors, and is one of the most obvious manifestations of disturbance in marine mammals (Richardson et al., 1995). For example, gray whales are known to change direction—deflecting from customary migratory paths—in order to avoid noise from seismic surveys (Malme et al., 1984). Avoidance may be short-term, with animals returning to the area once the noise has ceased ( e.g., Bowles et al., 1994; Goold, 1996; Stone et al., 2000; Morton and Symonds, 2002; Gailey et al., 2007). Longer-term displacement is possible, however, which may lead to changes in abundance or distribution patterns of the affected species in the affected region if habituation to the presence of the sound does not occur ( e.g., Blackwell et al., 2004; Bejder et al., 2006; Teilmann et al., 2006). A flight response is a dramatic change in normal movement to a directed and rapid movement away from the perceived location of a sound source. The flight response differs from other avoidance responses in the intensity of the response ( e.g., directed movement, rate of travel). Relatively little information on flight responses of marine mammals to anthropogenic signals exist, although observations of flight responses to the presence of predators have occurred (Connor and Heithaus, 1996, Bowers et al., 2018). The result of a flight response could range from brief, temporary exertion and displacement from the area where the signal provokes flight to, in extreme cases, marine mammal strandings (Evans and England, 2001). However, it should be noted that response to a perceived predator does not necessarily invoke flight (Ford and Reeves, 2008), and whether individuals are solitary or in groups may influence the response. Behavioral disturbance can also impact marine mammals in more subtle ways. Increased vigilance may result in costs related to diversion of focus and attention ( i.e., when a response consists of increased vigilance, it may come at the cost of decreased attention to other critical behaviors such as foraging or resting). These effects have generally not been demonstrated for marine mammals, but studies involving fish and terrestrial animals have shown that increased vigilance may substantially reduce feeding rates ( e.g., Beauchamp and Livoreil, 1997; Fritz et al., 2002; Purser and Radford, 2011). In addition, chronic disturbance can cause population declines through reduction of fitness ( e.g., decline in body condition) and subsequent reduction in reproductive success, survival, or both ( e.g., Harrington and Veitch, 1992; Daan et al., 1996; Bradshaw et al., 1998). However, Ridgway et al. (2006) reported that increased vigilance in bottlenose dolphins exposed to sound over a 5-day period did not cause any sleep deprivation or stress effects. Many animals perform vital functions, such as feeding, resting, traveling, and socializing, on a diel cycle (24-hour cycle). Disruption of such functions resulting from reactions to stressors such as sound exposure are more likely to be significant if they last more than one diel cycle or recur on subsequent days (Southall et al., 2007). Consequently, a behavioral response lasting less than one day and not recurring on subsequent days is not considered particularly severe unless it could directly affect reproduction or survival (Southall et al., 2007). Note that there is a difference between multi-day substantive behavioral reactions and multi-day anthropogenic activities. For example, just because an activity lasts for multiple days does not necessarily mean that individual animals are either exposed to activity-related stressors for multiple days or, further, exposed in a manner resulting in sustained multi-day substantive behavioral responses. Stress responses —An animal's perception of a threat may be sufficient to trigger stress responses consisting of some combination of behavioral responses, autonomic nervous system responses, neuroendocrine responses, or immune responses ( e.g., Seyle, 1950; Moberg, 2000). In many cases, an animal's first and sometimes most economical (in terms of energetic costs) response is behavioral avoidance of the potential stressor. Autonomic nervous system responses to stress typically involve changes in heart rate, blood pressure, and gastrointestinal activity. These responses have a relatively short duration and may or may not have a significant long-term effect on an animal's fitness. Neuroendocrine stress responses often involve the hypothalamus-pituitary-adrenal system. Virtually all neuroendocrine functions that are affected by stress—including immune competence, reproduction, metabolism, and behavior—are regulated by pituitary hormones. Stress-induced changes in the secretion of pituitary hormones have been implicated in failed reproduction, altered metabolism, reduced immune competence, and behavioral disturbance ( e.g., Moberg, 1987; Blecha, 2000). Increases in the circulation of glucocorticoids are also equated with stress (Romano et al., 2004). The primary distinction between stress (which is adaptive and does not normally place an animal at risk) and “distress” is the cost of the response. During a stress response, an animal uses glycogen stores that can be quickly replenished once the stress is alleviated. In such circumstances, the cost of the stress response would not pose serious fitness consequences. However, when an animal does not have sufficient energy reserves to satisfy the energetic costs of a stress response, energy resources must be diverted from other functions. This state of distress will last until the animal replenishes its energetic reserves sufficient to restore normal function. Relationships between these physiological mechanisms, animal behavior, and the costs of stress responses are well-studied through controlled experiments and for both laboratory and free-ranging animals ( e.g., Holberton et al., 1996; Hood et al., 1998; Jessop et al., 2003; Krausman et al., 2004; Lankford et al., 2005). Stress responses due to exposure to anthropogenic sounds or other stressors and their effects on marine mammals have also been reviewed (Fair and Becker, 2000; Romano et al., 2002b) and, more rarely, studied in wild populations ( e.g., Romano et al., 2002a). For example, Rolland et al. (2012) found that noise reduction from reduced ship traffic in the Bay of Fundy was associated with decreased stress in North Atlantic right whales. These and other studies lead to a reasonable expectation that some marine mammals will experience physiological stress responses upon exposure to acoustic stressors and that it is possible that some of these would be classified as “distress.” In addition, any animal experiencing TTS would likely also experience stress responses (NRC, 2003), however distress is an unlikely result of this project based on observations of marine mammals during previous, similar construction projects. Auditory Masking —Since many marine mammals rely on sound to find prey, moderate social interactions, and facilitate mating (Tyack, 2008), noise from anthropogenic sound sources can interfere with these functions, but only if the noise spectrum overlaps with the hearing sensitivity of the marine mammal (Southall et al., 2007; Clark et al., 2009; Hatch et al., 2012). Chronic exposure to excessive, though not high-intensity, noise could cause masking at particular frequencies for marine mammals that utilize sound for vital biological functions (Clark et al., 2009). Acoustic masking is when other noises such as from human sources interfere with an animal's ability to detect, recognize, or discriminate between acoustic signals of interest ( e.g., those used for intraspecific communication and social interactions, prey detection, predator avoidance, navigation) (Richardson et al., 1995; Erbe et al., 2016). Therefore, under certain circumstances, marine mammals whose acoustical sensors or environment are being severely masked could also be impaired from maximizing their performance fitness in survival and reproduction. The ability of a noise source to mask biologically important sounds depends on the characteristics of both the noise source and the signal of interest ( e.g., signal-to-noise ratio, temporal variability, direction), in relation to each other and to an animal's hearing abilities ( e.g., sensitivity, frequency range, critical ratios, frequency discrimination, directional discrimination, age or TTS hearing loss), and existing ambient noise and propagation conditions. Under certain circumstances, marine mammals experiencing significant masking could also be impaired from maximizing their performance fitness in survival and reproduction. Therefore, when the coincident (masking) sound is man-made, it may be considered harassment when disrupting or altering critical behaviors. It is important to distinguish TTS and PTS, which persist after the sound exposure, from masking, which occurs during the sound exposure. Because masking (without resulting in TS) is not associated with abnormal physiological function, it is not considered a physiological effect, but rather a potential behavioral effect. The frequency range of the potentially masking sound is important in determining any potential behavioral impacts. For example, low-frequency signals may have less effect on high-frequency echolocation sounds produced by odontocetes but are more likely to affect detection of mysticete communication calls and other potentially important natural sounds such as those produced by surf and some prey species. The masking of communication signals by anthropogenic noise may be considered as a reduction in the communication space of animals ( e.g., Clark et al., 2009) and may result in energetic or other costs as animals change their vocalization behavior ( e.g., Miller et al., 2000; Foote et al., 2004; Parks et al., 2007; Di Iorio and Clark, 2009; Holt et al., 2009). Masking can be reduced in situations where the signal and noise come from different directions (Richardson et al., 1995), through amplitude modulation of the signal, or through other compensatory behaviors (Houser and Moore, 2014). Masking can be tested directly in captive species ( e.g., Erbe, 2008), but in wild populations it must be either modeled or inferred from evidence of masking compensation. There are few studies addressing real-world masking sounds likely to be experienced by marine mammals in the wild ( e.g., Branstetter et al., 2013). Marine mammals in the Piscataqua River are exposed to anthropogenic noise which may lead to some habituation, but is also a source of masking. Vocalization changes may result from a need to compete with an increase in background noise and include increasing the source level, modifying the frequency, increasing the call repetition rate of vocalizations, or ceasing to vocalize in the presence of increased noise (Hotchkin and Parks, 2013). Masking is more likely to occur in the presence of broadband, relatively continuous noise sources. Energy distribution of pile driving covers a broad frequency spectrum, and sound from pile driving would be within the audible range of pinnipeds and cetaceans present in the proposed action area. While some construction during the Navy's activities may mask some acoustic signals that are relevant to the daily behavior of marine mammals, the short-term duration and limited areas affected make it very unlikely that survival would be affected. Airborne Acoustic Effects —Pinnipeds that occur near the project site could be exposed to airborne sounds associated with construction activities that have the potential to cause behavioral harassment, depending on their distance from these activities. Airborne noise would primarily be an issue for pinnipeds that are swimming or hauled out near the project site within the range of noise levels elevated above airborne acoustic criteria. Although pinnipeds are known to haul-out regularly on man-made objects, we believe that incidents of take resulting solely from airborne sound are unlikely due to the sheltered proximity between the proposed project area and the haulout sites ( e.g., Hicks Rocks located on the opposite side of the island where activities are occurring). Cetaceans are not expected to be exposed to airborne sounds that would result in harassment as defined under the MMPA. We recognize that pinnipeds in the water could be exposed to airborne sound that may result in behavioral harassment when looking with their heads above water. Most likely, airborne sound would cause behavioral responses similar to those discussed above in relation to underwater sound. For instance, anthropogenic sound could cause hauled-out pinnipeds to exhibit changes in their normal behavior, such as reduction in vocalizations, or cause them to temporarily abandon the area and move further from the source. However, these animals would previously have been `taken' because of exposure to underwater sound above the behavioral harassment thresholds, which are in all cases larger than those associated with airborne sound. Thus, the behavioral harassment of these animals is already accounted for in these estimates of potential take. Therefore, we do not believe that authorization of incidental take resulting from airborne sound for pinnipeds is warranted, and airborne sound is not discussed further here. Potential Effects on Marine Mammal Habitat Water quality —Temporary and localized reduction in water quality will occur as a result of in-water construction activities. Most of this effect will occur during the installation and removal of piles and bedrock removal when bottom sediments are disturbed. The installation and removal of piles and bedrock removal and dredging will disturb bottom sediments and may cause a temporary increase in suspended sediment in the project area. Using available information collected from a project in the Hudson River, pile-driving activities are anticipated to produce total suspended sediment (TSS) concentrations of approximately 5.0 to 10.0 milligrams per liter (mg/L) above background levels within approximately 91 m (300 ft) of the pile being driven (Federal Highway Administration, 2012). During pile extraction, sediment attached to the pile moves vertically through the water column until gravitational forces cause it to slough off under its own weight. The small resulting sediment plume is expected to settle out of the water column within a few hours. Studies of the effects of turbid water on fish (marine mammal prey) suggest that concentrations of suspended sediment can reach thousands of milligrams per liter before an acute toxic reaction is expected (Burton, 1993). The TSS levels expected for pile-driving or removal (5.0 to 10.0 mg/L) are below those shown to have adverse effects on fish (580.0 mg/L for the most sensitive species, with 1,000.0 mg/L more typical) and benthic communities (390.0 mg/L; Environmental Protection Agency, 1986). Impacts to water quality from DTH mono-hammers are expected to be similar to those described for pile driving. Impacts to water quality would be localized and temporary and would have negligible impacts on marine mammal habitat. The cluster drill system and rotary drilling of shafts would have negligible impacts on water quality from sediment resuspension because the system would operate within a casing set into the bedrock. The cluster drill would collect excavated material inside of the apparatus where it would be lifted to the surface and placed onto a barge for subsequent disposal. TSS concentrations associated with mechanical clamshell bucket dredging operations have been shown to range from 105 mg/L in the middle of the water column to 445 mg/L near the bottom (210 mg/L, depth-averaged) (Army Corps of Engineers, 2001). Furthermore, a study by Burton (1993) measured TSS concentrations at distances of 152, 305, 610, and 1006 m (500, 1,000, 2,000, and 3,300 ft) from dredge sites in the Delaware River and were able to detect concentrations between 15 mg/L and 191 mg/L up to 610 m (2,000 ft) from the dredge site. In support of the New York/New Jersey Harbor Deepening Project, the U.S. Army Corps of Engineers conducted extensive monitoring of mechanical dredge plumes (Army Corps of Engineers, 2015). Independent of bucket type or size, plumes dissipated to background levels within 183 m (600 ft) of the source in the upper water column and 732 m (2,400 ft) in the lower water column. Based on these studies, elevated suspended sediment concentrations at several hundreds of mg/L above background may be present in the immediate vicinity of the bucket, but would settle rapidly within a 732 m (2,400 ft) radius of the dredge location. The TSS levels expected for mechanical dredging (up to 445.0 mg/L) are below those shown to have adverse effect on fish (typically up to 1,000.0 mg/L; see summary of scientific literature in Burton 1993, Wilber and Clarke 2001). Effects to turbidity and sedimentation are expected to be short-term, minor, and localized. Since the currents are so strong in the area, following the completion of sediment-disturbing activities, suspended sediments in the water column should dissipate and quickly return to background levels in all construction scenarios. Turbidity within the water column has the potential to reduce the level of oxygen in the water and irritate the gills of prey fish species in the proposed project area. However, turbidity plumes associated with the project would be temporary and localized, and fish in the proposed project area would be able to move away from and avoid the areas where plumes may occur. Therefore, it is expected that the impacts on prey fish species from turbidity, and therefore on marine mammals, would be minimal and temporary. In general, the area likely impacted by the proposed construction activities is relatively small compared to the available marine mammal habitat in Great Bay Estuary. Potential Effects on Prey —Sound may affect marine mammals through impacts on the abundance, behavior, or distribution of prey species ( e.g., crustaceans, cephalopods, fish, zooplankton). Marine mammal prey varies by species, season, and location and, for some, is not well documented. Studies regarding the effects of noise on known marine mammal prey are described here. Fish utilize the soundscape and components of sound in their environment to perform important functions such as foraging, predator avoidance, mating, and spawning ( e.g., Zelick and Mann, 1999; Fay, 2009). Depending on their hearing anatomy and peripheral sensory structures, which vary among species, fishes hear sounds using pressure and particle motion sensitivity capabilities and detect the motion of surrounding water (Fay et al., 2008). The potential effects of noise on fishes depends on the overlapping frequency range, distance from the sound source, water depth of exposure, and species-specific hearing sensitivity, anatomy, and physiology. Key impacts to fishes may include behavioral responses, hearing damage, barotrauma (pressure-related injuries), and mortality. Fish react to sounds that are especially strong and/or intermittent low-frequency sounds. Short duration, sharp sounds can cause overt or subtle changes in fish behavior and local distribution. The reaction of fish to noise depends on the physiological state of the fish, past exposures, motivation ( e.g., feeding, spawning, migration), and other environmental factors. Hastings and Popper (2005) identified several studies that suggest fish may relocate to avoid certain areas of sound energy. Additional studies have documented effects of pile driving on fish; several are based on studies in support of large, multiyear bridge construction projects ( e.g., Scholik and Yan, 2001, 2002; Popper and Hastings, 2009). Several studies have demonstrated that impulse sounds might affect the distribution and behavior of some fishes, potentially impacting foraging opportunities or increasing energetic costs ( e.g., Fewtrell and McCauley, 2012; Pearson et al., 1992; Skalski et al., 1992; Santulli et al., 1999; Paxton et al., 2017). However, some studies have shown no or slight reaction to impulse sounds ( e.g., Pena et al., 2013; Wardle et al., 2001; Jorgenson and Gyselman, 2009; Cott et al., 2012). More commonly, though, the impacts of noise on fish are temporary. SPLs of sufficient strength have been known to cause injury to fish and fish mortality (summarized in Popper et al., 2014). However, in most fish species, hair cells in the ear continuously regenerate and loss of auditory function likely is restored when damaged cells are replaced with new cells. Halvorsen et al. (2012a) showed that a TTS of 4-6 dB was recoverable within 24 hours for one species. Impacts would be most severe when the individual fish is close to the source and when the duration of exposure is long. Injury caused by barotrauma can range from slight to severe and can cause death, and is most likely for fish with swim bladders. Barotrauma injuries have been docume [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%3A2023-00332. Public record. Not legal advice.