# 75 FR 64508: Taking and Importing Marine Mammals; Military Training Activities Conducted Within the Gulf of Alaska (GoA) Temporary Maritime Activities Area (TMAA)

> Federal · Regulations · In force

URL: https://www.frixlaw.com/law-library/statutes/FR_PRORULE_2010-25230

## Section

- **Citation:** 75 FR 64508
- **Heading:** Taking and Importing Marine Mammals; Military Training Activities Conducted Within the Gulf of Alaska (GoA) Temporary Maritime Activities Area (TMAA)
- **Jurisdiction:** Federal
- **Kind:** Regulations
- **Status:** In force
- **Text as of:** August 14, 2026
- **Source:** Compiled text
- **Location:** Federal Register / Vol. 75 / 75 FR 64508

## Text

DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration 50 CFR Part 218 [Docket No. 100817363-0365-02] RIN 0648-BA14 Taking and Importing Marine Mammals; Military Training Activities Conducted Within the Gulf of Alaska (GoA) Temporary Maritime Activities Area (TMAA) 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 training activities conducted in the Gulf of Alaska (GoA) Temporary Maritime Activities Area (TMAA) for the period December 2010 through December 2015. Pursuant to the Marine Mammal Protection Act (MMPA), NMFS proposes regulations to govern that take and requests information, suggestions, and comments on these proposed regulations. Specifically, we encourage the public to recommend effective, regionally specific methods for augmenting existing marine mammal density, distribution, and abundance information in the GoA TMAA and to prioritize the specific density and distribution data needs in the area (species, time of year, etc.). This information will ensure the design of the most effective Monitoring Plan with the resources available.

DATES:
Comments and information must be received no later than November 18, 2010.

ADDRESSES:
You may submit comments, identified by 0648-BA14, by any one of the following methods:
• Electronic Submissions: Submit all electronic public comments via the Federal eRulemaking Portal http://www.regulations.gov.
• Hand delivery or mailing of paper, disk, or CD-ROM comments should be addressed to Michael Payne, Chief, Permits, Conservation and Education Division, Office of Protected Resources, National Marine Fisheries Service, 1315 East-West Highway, Silver Spring, MD 20910-3225
• Electronic Submissions: Submit all electronic public comments via the Federal eRulemaking Portal http://www.regulations.gov.
• Hand delivery or mailing of paper, disk, or CD-ROM comments should be addressed to Michael Payne, Chief, Permits, Conservation and Education Division, Office of Protected Resources, National Marine Fisheries Service, 1315 East-West Highway, Silver Spring, MD 20910-3225.
Instructions: All comments received are a part of the public record and will generally be posted to http://www.regulations.gov without change. All Personal Identifying Information (for example, name, address, etc.) voluntarily submitted by the commenter may be publicly accessible. Do not submit Confidential Business Information or otherwise sensitive or protected information.
NMFS will accept anonymous comments (enter N/A in the required fields if you wish to remain anonymous). Attachments to electronic comments will be accepted in Microsoft Word, Excel, WordPerfect, or Adobe PDF file formats only.
FOR FURTHER INFORMATION CONTACT:
Jolie Harrison, Brian D. Hopper, or Michelle Magliocca, Office of Protected Resources, NMFS, (301) 713-2289.

SUPPLEMENTARY INFORMATION:
Availability
A copy of the Navy's application, as well as the draft Monitoring Plan and the draft Stranding Response Plan for GoA TMAA, may be obtained by writing to the address specified above (See ADDRESSES ), telephoning the contact listed above (see FOR FURTHER INFORMATION CONTACT ), or visiting the internet at: http://www.nmfs.noaa.gov/pr/permits/incidental.htm#applications. The Navy's Draft Environmental Impact Statement (DEIS) for GoA TMAA was published on December 11, 2009 and may be viewed at http://www.nmfs.noaa.gov/pr/permits/incidental.htm#applications. NMFS participates in the development of the Navy's EIS as a cooperating agency under NEPA.
Background
Sections 101(a)(5)(A) and (D) of the MMPA (16 U.S.C. 1361 et seq
/pr/permits/incidental.htm#applications. The Navy's Draft Environmental Impact Statement (DEIS) for GoA TMAA was published on December 11, 2009 and may be viewed at http://www.nmfs.noaa.gov/pr/permits/incidental.htm#applications. NMFS participates in the development of the Navy's EIS as a cooperating agency under NEPA.
Background
Sections 101(a)(5)(A) and (D) of the MMPA (16 U.S.C. 1361 et seq. ) direct the Secretary of Commerce (Secretary) to allow, upon request, the incidental, but not intentional taking of marine mammals by U.S. citizens who engage in a specified activity (other than commercial fishing) during periods of not more than five consecutive years each if certain findings are made and regulations are issued or, if the taking is limited to harassment, notice of a proposed authorization is provided to the public for review.
Authorization shall be granted if NMFS finds that the taking will have a negligible impact on the species or stock(s), will not have an unmitigable adverse impact on the availability of the species or stock(s) for subsistence uses, and if the permissible methods of taking and requirements pertaining to the mitigation, monitoring and reporting of such taking are set forth. NMFS has defined “negligible impact” in 50 CFR 216.103 as an impact resulting from the specified activity that cannot be reasonably expected to, and is not reasonably likely to, adversely affect the species or stock through effects on annual rates of recruitment or survival.
The National Defense Authorization Act of 2004 (NDAA) (Pub. L
tion, monitoring and reporting of such taking are set forth. NMFS has defined “negligible impact” in 50 CFR 216.103 as an impact resulting from the specified activity that cannot be reasonably expected to, and is not reasonably likely to, adversely affect the species or stock through effects on annual rates of recruitment or survival.
The National Defense Authorization Act of 2004 (NDAA) (Pub. L. 108-136) modified the MMPA by removing the “small numbers” and “specified geographical region” limitations and amended the definition of “harassment” as it applies to a “military readiness activity” to read as follows (Section 3(18)(B) of the MMPA): any act that injures or has the significant potential to injure a marine mammal or marine mammal stock in the wild [Level A Harassment]; or any act that disturbs or is likely to disturb a marine mammal or marine mammal stock in the wild by causing disruption of natural behavioral patterns, including, but not limited to, migration, surfacing, nursing, breeding, feeding, or sheltering, to a point where such behavioral patterns are abandoned or significantly altered [Level B Harassment].
Summary of Request
In March 2009, NMFS received an application from the Navy requesting authorization to take individuals of 20 species of marine mammals (15 cetaceans and 5 pinnipeds) incidental to upcoming training activities to be conducted from December 2010 through December 2015 in the GoA TMAA, which is a 42,146 square nautical mile (nm 2 ) (145,482 km 2 ) polygon roughly the shape of a 300 nm (555.6 km) by 150 nm (277.8 km) rectangle oriented northwest to southeast in the long direction. NMFS subsequently requested additional information, which was provided in November 2009 in the form of a revised application. These training activities are classified as military readiness activities under the provisions of the NDAA of 2004
(nm 2 ) (145,482 km 2 ) polygon roughly the shape of a 300 nm (555.6 km) by 150 nm (277.8 km) rectangle oriented northwest to southeast in the long direction. NMFS subsequently requested additional information, which was provided in November 2009 in the form of a revised application. These training activities are classified as military readiness activities under the provisions of the NDAA of 2004. These military readiness activities may incidentally take marine mammals within the TMAA by exposing them to sound from mid-frequency or high-frequency active sonar (MFAS/HFAS) or underwater detonations. The Navy requests authorization to take individuals of 20 species of cetaceans and pinnipeds by Level B Harassment. Further, although it does not anticipate that it will occur, the Navy requests authorization to take, by injury or mortality, up to 15 individual beaked whales (of any of the following species: Baird's beaked whale, Cuvier's beaked whale, Stejneger's beaked whale) over the course of the 5-year regulations.
Description of Specified Activities
Purpose and Background
The Navy's mission is to maintain, train, and equip combat-ready naval forces capable of winning wars, deterring aggression, and maintaining freedom of the seas. Section 5062 of Title 10 of the United States Code directs the Chief of Naval Operations to train all military forces for combat. The Chief of Naval Operations meets that direction, in part, by conducting at-sea training exercises and ensuring naval forces have access to ranges, operating areas (OPAREAs) and airspace where they can develop and maintain skills for wartime missions and conduct research, development, testing, and evaluation (RDT&E) of naval systems.
The specified training activities addressed in this proposed rule are a subset of the Proposed Action described in the GoA TMAA DEIS, which would support and maintain Department of Defense training and assessments of current capabilities
nd airspace where they can develop and maintain skills for wartime missions and conduct research, development, testing, and evaluation (RDT&E) of naval systems.
The specified training activities addressed in this proposed rule are a subset of the Proposed Action described in the GoA TMAA DEIS, which would support and maintain Department of Defense training and assessments of current capabilities. Training does not include combat operations, operations in direct support of combat, or other activities conducted primarily for purposes other than training. The Department of Defense proposes to implement actions within the GoA TMAA to:
• Increase the number of training activities from current levels (up to 14 days) as necessary to support Fleet exercise requirements (that could last up to 21 days between April and October);
• Conduct training in the Primary Mission Areas (PMARs) including Anti-Air Warfare (AAW), Anti-Surface Warfare (ASUW), Anit-Submarine Warfare (ASW), Naval Special Warfare (NSW), Strike Warfare (STW), and Electronic Combat (EC). Conduct of training may include that necessary for newer systems, instrumentation, and platforms, including the EA-18G Growler aircraft, Guided Missile Submarines (SSGN), P-8 Poseidon Multimission Maritime Aircraft (MMA), Guided Missile Destroyer (DDG) 1000 (Zumwalt Class) destroyer, and several types of Unmanned Aerial Systems (UASs);
• Accommodate training enhancement instrumentation, to include the use of a Portable Undersea Tracking Range (PUTR);
• Conduct an additional Carrier Strike Group (CSG) exercise during the months of April through October, which could also last up to 21 days (first CSG exercise being part of the baseline No Action Alternative); and
• Conduct a Sinking Exercise (SINKEX) during each summertime exercise (maximum of two) in the TMAA
instrumentation, to include the use of a Portable Undersea Tracking Range (PUTR);
• Conduct an additional Carrier Strike Group (CSG) exercise during the months of April through October, which could also last up to 21 days (first CSG exercise being part of the baseline No Action Alternative); and
• Conduct a Sinking Exercise (SINKEX) during each summertime exercise (maximum of two) in the TMAA.
The proposed action would result in the following increases (above those conducted in previous years, i.e., the No Action Alternative in the Navy's DEIS) in activities associated with the annual take of marine mammals:
• Helicopter Anti-submarine Warfare (ASW) tracking exercise (TRACKEX) (includes use of MFAS and HFAS dipping sonar and sonobuoys)
• Surface ASW TRACKEX (includes use of hull-mounted MFAS)
• Submarine ASW (includes use of hull-mounted MFAS and HFAS)
• Fixed-wing Marine Patrol Aircraft (MPA) ASW TRACKEX (includes use of sonobuoys)
• Extended Echo Ranging ASW (includes explosive sonobuoys)
• Bombing Exercises (BOMBEX)
• Sinking Exercises (SINKEX)
• Gunnery Exercises (GUNEX)
Overview of the GoA TMAA
Since the 1990s, the Navy has participated in a major joint training exercise that involves the Departments of the Navy, Army, Air Force, and Coast Guard participants reporting to a unified or joint commander who coordinates the activities planned to demonstrate and evaluate the ability of the services to engage in a conflict and carry out plans in response to a threat to national security. Previous exercises in the TMAA have occurred in the summer (April-October) timeframe due to the extreme cold weather and sea state conditions in the TMAA during the winter months. The areas making up the Alaska Training Areas (ATAs) (see figure 1-1 in the Navy's application) consist of 3 components: (1) TMAA; (2) U.S. Air Force over-land Special Use Airspace (SUA) and air routes over the GoA and State of Alaska; and (3) U.S. Army training lands
the summer (April-October) timeframe due to the extreme cold weather and sea state conditions in the TMAA during the winter months. The areas making up the Alaska Training Areas (ATAs) (see figure 1-1 in the Navy's application) consist of 3 components: (1) TMAA; (2) U.S. Air Force over-land Special Use Airspace (SUA) and air routes over the GoA and State of Alaska; and (3) U.S. Army training lands.
Within the northeastern GoA, the TMAA is comprised of the 42,146 square nautical miles (nm 2 ) (145,482 square kilometer (km 2 ) of surface and subsurface area and 88,731 nm 2 (305,267 km 2 )) of special use airspace (SUA) (not including the portion of Warning Area 612 [W-612] that falls outside of the TMAA). The TMAA is roughly rectangular and oriented from northwest to southeast, approximately 300 nautical miles (nm) (556 kilometer (km)) long by 150 nm (278 km) wide, situated south of Prince William Sound and east of Kodiak Island. With the exception of Cape Cleare on Montague Island located over 12 nm (22 km) from the northern point of the TMAA, the nearest shoreline (Kenai Peninsula) is located approximately 24 nm (44 km) north of the TMAA's northern boundary. The approximate middle of the TMAA is located 140 nm (259 km) offshore.
The abyssal plain in the GoA gradually shoals from a 16,400 feet (ft) (5,000 meter (m)) depth in the southwestern GoA to less than 9,843 ft (3,000 m) in the northeastern expanses of the Gulf. Maximal depths exceed 22,965 ft (7,000 m) near the central Aleutian Trench along the continental slope south of the Aleutian Islands. Numerous seamounts, remnants of submarine volcanoes, are scattered across the central basin. Several of the seamounts rise to within a few hundred meters of the sea surface.
Ocean circulation in the GoA is defined by the cyclonic motion of the Pacific subpolar gyre (also referred to as the Alaska Gyre), which is composed of the North Pacific Current, the Alaska Current, and the Alaskan Stream
s. Numerous seamounts, remnants of submarine volcanoes, are scattered across the central basin. Several of the seamounts rise to within a few hundred meters of the sea surface.
Ocean circulation in the GoA is defined by the cyclonic motion of the Pacific subpolar gyre (also referred to as the Alaska Gyre), which is composed of the North Pacific Current, the Alaska Current, and the Alaskan Stream. Circulation patterns along the shelf divide the region into the inner shelf (or Alaska Coastal Current domain), the mid-shelf, and the outer shelf including the shelf break (DoN, 2006). The center of the gyre is located at approximately 52 to 53 °N and 145 to 155 °W. Nearshore flow is dominated by the Alaskan Coastal Current and is less organized than the flow found along the shelf break and slope. The northwestern GoA also includes several prominent geological features that influence the regional oceanography. For example, Kayak Island extends 50 km across the continental shelf to the east of the Copper River. This island can deflect shelf waters farther offshore delivering high concentrations of suspended sediment to the outer shelf (DoN, 2006).
During winter months, intense circulation over the GoA produces easterly coastal winds and downwelling, both of which result in a well-mixed water column. During the summer, stratification develops due to decreased winds, increased freshwater discharge, and increased solar radiation. Under summer and fall conditions, the shelf waters are stratified with the upper water column temperatures at their maximum and salinities at their minimum. On longer time scales, there is evidence of interannual variation in the circulation patterns within the GoA. These variations result from the climatic variability of the El Niño Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO) (DoN, 2006).
Generally, two surface temperature regimes characterize the northern expanses of the GoA throughout the year
alinities at their minimum. On longer time scales, there is evidence of interannual variation in the circulation patterns within the GoA. These variations result from the climatic variability of the El Niño Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO) (DoN, 2006).
Generally, two surface temperature regimes characterize the northern expanses of the GoA throughout the year. Relatively warm surface water occurs over the continental shelf, while colder water is found farther offshore
Specified Activities
As mentioned above, the Navy has requested MMPA authorization to take marine mammals incidental to training in the GoA TMAA that would result in the generation of sound or pressure waves in the water at or above levels that NMFS has determined will likely result in take (see Acoustic Take Criteria Section), either through the use of MFAS/HFAS or the detonation of explosives in the water. These activities are discussed in the subsections below. In addition to use of active sonar sources and explosives, these activities include the operation and movement of vessels that are necessary to conduct the training, and the effects of this part of the activities are also analyzed in this document.
The Navy's application also briefly summarizes Air Combat Maneuvers (ACM), Visit Board Search and Seizure/Vessels of Interest (VBSS/VOI), Maritime Interdiction (MI), Chaff Exercises, Sea Surface Control (SSC), and Naval Special Warfare Insertion/Extraction exercises; however, these activities are primarily air or land based and do not utilize sound sources or explosives in the water. No take of marine mammals is anticipated to result from these activities and, therefore, they are not discussed further.
Activities Utilizing Active Sonar Sources
For the GoA TMAA, the training activities that utilize active tactical sonar sources fall primarily into the category of Anti-submarine Warfare (ASW)
rily air or land based and do not utilize sound sources or explosives in the water. No take of marine mammals is anticipated to result from these activities and, therefore, they are not discussed further.
Activities Utilizing Active Sonar Sources
For the GoA TMAA, the training activities that utilize active tactical sonar sources fall primarily into the category of Anti-submarine Warfare (ASW). This section includes a description of ASW, the active acoustic devices used in ASW exercises, and the exercise types in which these acoustic sources are used.
ASW Training and Active Sonar
ASW training involves helicopter and sea control aircraft, ships, and submarines, operating alone or in combination, to locate, track, and neutralize submarines. Various types of active and passive sonar are used by the Navy to determine water depth, locate mines, and identify, track, and target submarines. Passive sonar “listens” for sound waves by using underwater microphones, called hydrophones, which receive, amplify, and process underwater sounds. No sound is introduced into the water when using passive sonar. Passive sonar can indicate the presence, character, and movement of submarines. However, passive sonar only provides information about the bearing (direction) to a sound-emitting source; it does not provide an accurate range (distance) to the source. Also, passive sonar relies on the underwater target itself to provide sufficient sound to be detected by hydrophones. Active sonar is needed to locate objects that emit little or no noise (such as mines or diesel-electric submarines operating in electric mode) and to establish both bearing and range to the detected contact.
Active sonar transmits pulses of sound that travel through the water, reflect off objects, and return to a receiver. By knowing the speed of sound in water and the time taken for the sound wave to travel to the object and back, active sonar systems can quickly calculate direction and distance from the sonar platform to the underwater object
tablish both bearing and range to the detected contact.
Active sonar transmits pulses of sound that travel through the water, reflect off objects, and return to a receiver. By knowing the speed of sound in water and the time taken for the sound wave to travel to the object and back, active sonar systems can quickly calculate direction and distance from the sonar platform to the underwater object. There are three frequency range classifications for active sonar: Low-frequency (LF), mid-frequency (MF), and high-frequency (HF).
MFAS, as defined in the Navy's GoA TMAA LOA application, operates between 1 and 10 kHz, with detection ranges up to 10 nm (19 km). Because of this detection ranging capability, MFAS is the Navy's primary tool for conducting ASW. Many ASW experiments and exercises have demonstrated that the improved capability (of MFAS over other sources) for mid-range detection of adversary submarines before they are able to conduct an attack is essential to U.S. ship survivability. Today, ASW is the Navy's number one war-fighting priority. Navies across the world utilize modern, quiet, diesel-electric submarines that pose the primary threat to the U.S. Navy's ability to perform a number of critical missions. Extensive ASW training is necessary for sailors on ships and in strike groups to gain proficiency using MFAS. Moreover, if a strike group does not demonstrate MFAS proficiency, it cannot be certified as combat ready.
HFAS, as defined in the Navy's GoA TMAA LOA application, operates at frequencies greater than 10 kilohertz (kHz). At higher acoustic frequencies, sound rapidly dissipates in the ocean environment, resulting in short detection ranges, typically less than five nm (9 km). High-frequency sonar is used primarily for determining water depth, hunting mines, and guiding torpedoes, which are all short range applications. Training exercises in the GoA TMAA will include the use of HFAS.
Low-frequency sources operate below 1 kHz
acoustic frequencies, sound rapidly dissipates in the ocean environment, resulting in short detection ranges, typically less than five nm (9 km). High-frequency sonar is used primarily for determining water depth, hunting mines, and guiding torpedoes, which are all short range applications. Training exercises in the GoA TMAA will include the use of HFAS.
Low-frequency sources operate below 1 kHz. Sonar in this frequency range is designed to detect extremely quiet diesel-electric submarines at ranges far beyond the capabilities of MFA sonars. Currently, there are only two ships in use by the Navy equipped with low-frequency sonar; both are ocean surveillance vessels operated by Military Sealift Command. While Surveillance Towed Array Sensor System (SURTASS) low-frequency active sonar was analyzed in a separate EIS/OEIS, use of low-frequency active sonar is not part of the planned training activities considered for the GoA TMAA.
Acoustic Sources Used for ASW Exercises in the GoA TMAA
Modern sonar technology has developed a multitude of sonar sensor and processing systems. In concept, the simplest active sonars emit omni-directional pulses (“pings”) and time the arrival of the reflected echoes from the target object to determine range. More sophisticated active sonars emit an omni-directional ping and then rapidly scan a steered receiving beam to provide directional, as well as range, information. More advanced active sonars transmit multiple preformed beams, listening to echoes from several directions simultaneously and providing efficient detection of both direction and range. The types of active sonar and other sound sources employed during training exercises in the GoA TMAA are identified in Table 1.
BILLING CODE 3510-22-P EP19OC10.005
BILLING CODE 3510-22-C ASW sonar systems are deployed from certain classes of surface ships, submarines, helicopters, and fixed-wing maritime patrol aircraft (MPA)
ously and providing efficient detection of both direction and range. The types of active sonar and other sound sources employed during training exercises in the GoA TMAA are identified in Table 1.
BILLING CODE 3510-22-P EP19OC10.005
BILLING CODE 3510-22-C ASW sonar systems are deployed from certain classes of surface ships, submarines, helicopters, and fixed-wing maritime patrol aircraft (MPA).
Surface Ship Sonar —A variety of surface ships participate in training events, including the Fast Frigate (FFG), the Guided Missile Destroyer (DDG), and the Guided Missile Cruiser (CG). These three classes of ships are equipped with active as well as passive tactical sonar for mine avoidance and submarine detection and tracking. DDG and CG class ships are equipped with the AN/SQS-53 sonar system (the most powerful system), with a nominal source level of 235 decibels (dB) re 1 μPa @ 1 m. The FFG class ship uses the SQS-56 sonar system, with a nominal source level of 225 decibels (dB) re 1 μPa @ 1 m. Sonar ping transmission durations were modeled as lasting 1 second per ping and omni-directional, which is a conservative assumption that will overestimate potential effects because actual ping durations will be less than 1 second. The AN/SQS-53 hull-mounted sonar transmits at a center frequency of 3.5 kHz. The SQS-56 transmits at a center frequency of 7.5 kHz. Details concerning the tactical use of specific frequencies and the repetition rate for the sonar pings are classified but were modeled based on the required tactical training setting.
Submarine Sonars —Submarines use sonar ( e.g., AN/BQQ-10) to detect and target enemy submarines and surface ships. Because submarine active sonar use is very rare and in those rare instances, very brief, it is extremely unlikely that use of active sonar by submarines would have any measurable effect on marine mammals
re classified but were modeled based on the required tactical training setting.
Submarine Sonars —Submarines use sonar ( e.g., AN/BQQ-10) to detect and target enemy submarines and surface ships. Because submarine active sonar use is very rare and in those rare instances, very brief, it is extremely unlikely that use of active sonar by submarines would have any measurable effect on marine mammals. In addition, submarines use high-frequency sonar (AN/BQS-15 or BQQ-24) for navigation safety, mine avoidance, and a fathometer that is not unlike a standard fathometer in source level or output. There is, at present, no mine training range in the GoA TMAA. Therefore, given their limited use and rapid attenuation as high frequency sources, the AN/BQS-15 and BQQ-24 are not expected to result in the take of marine mammals.
Aircraft Sonar Systems —Aircraft sonar systems that would operate in the GoA TMAA include sonobuoys from fixed and rotary-wing aircraft and dipping sonar from helicopters. Sonobuoys may be deployed by maritime patrol aircraft or helicopters; dipping sonars are used by carrier-based helicopters. A sonobuoy is an expendable device used by aircraft for the detection of underwater acoustic energy and for conducting vertical water column temperature measurements. Most sonobuoys are passive, but some can also generate active acoustic signals. Dipping sonar is an active or passive sonar device lowered by cable from helicopters to detect or maintain contact with underwater targets. During ASW training, these systems' active modes are only used briefly for localization of contacts and are not used in primary search capacity. Helicopters and MPA (P-3 or P-8 in approximately 2013) may deploy sonobuoys in the GoA TMAA during ASW training exercises.
Extended Echo Ranging/Improved Extended Echo Ranging (EER/IEER) Systems —EER/IEER are airborne ASW systems used to conduct “large area” searches for submarines
stems' active modes are only used briefly for localization of contacts and are not used in primary search capacity. Helicopters and MPA (P-3 or P-8 in approximately 2013) may deploy sonobuoys in the GoA TMAA during ASW training exercises.
Extended Echo Ranging/Improved Extended Echo Ranging (EER/IEER) Systems —EER/IEER are airborne ASW systems used to conduct “large area” searches for submarines. These systems are made up of airborne avionics ASW acoustic processing and sonobuoy types that are deployed in pairs. The EER/IEER system's active sonobuoy has two components: An AN/SSQ-110A Sonobuoy, which generates an explosive sound impulse; and a passive receiver sonobuoy (SSQ-77), which “listens” for the return echo that has been bounced off the surface of a submarine. These sonobuoys are designed to provide underwater acoustic data necessary for naval aircrews to quickly and accurately detect submerged submarines. The sonobuoy pairs are dropped from a maritime patrol aircraft into the ocean in a predetermined pattern with a few buoys covering a very large area. The AN/SSQ-110A Sonobuoy Series is an expendable and commandable sonobuoy. In other words, the equipment is not retrieved after deployment and, once deployed, it can be remotely controlled. For example, upon command from the aircraft, the explosive charge would detonate, creating the sound impulse. Within the sonobuoy pattern, only one detonation is commanded at a time. Sixteen to twenty SSQ-110A source sonobuoys may be used in a typical exercise. Both charges of each sonobuoy would be detonated independently during the course of the training. The first detonation would be for tactical reasons—to locate the submarine; and the second occurs when the sonobuoy is commanded to scuttle at the conclusion of the exercise. The AN/SSQ-110A is listed in Table 1 because it functions like a sonar ping; however, the source creates an explosive detonation and its effects are considered in the underwater explosive section
g the course of the training. The first detonation would be for tactical reasons—to locate the submarine; and the second occurs when the sonobuoy is commanded to scuttle at the conclusion of the exercise. The AN/SSQ-110A is listed in Table 1 because it functions like a sonar ping; however, the source creates an explosive detonation and its effects are considered in the underwater explosive section.
Multistatic Active Coherent (MAC) system -Formerly referred to as the Advanced Extended Echo Ranging (AEER) system, the proposed SSQ-125 MAC sonobuoy system is operationally similar to the existing EER/IEER system. The MAC system will use the same Air Deployed Active Receiver (ADAR) sonobuoy (SSQ-101A) as the acoustic receiver and will be used for a large area ASW search capability in both shallow and deep water. However, instead of using an explosive AN/SSQ-110A as an impulsive source for the active acoustic wave, the MAC system will use a battery powered (electronic) source for the AN/SSQ 125 sonobuoy. The output and operational parameters for the AN/SSQ-125 sonobuoy (source levels, frequency, wave forms, etc.) are classified. However, this sonobuoy is intended to replace the EER/IEER's use of explosives and is scheduled to enter the fleet in 2011. For purposes of analysis, replacement of the EER/IEER system by the MAC system will be assumed to occur at 25 percent per year as follows: 2011—25 percent replacement; 2012—50 percent replacement; 2013—75 percent replacement; 2014—100 percent replacement with no further use of the EER/IEER system beginning in 2015 and beyond.
Torpedoes —Torpedoes are the primary ASW weapon used by surface ships, aircraft, and submarines. The guidance systems of these weapons can be autonomous or electronically controlled from the launching platform through an attached wire. The autonomous guidance systems are acoustically based
ment; 2014—100 percent replacement with no further use of the EER/IEER system beginning in 2015 and beyond.
Torpedoes —Torpedoes are the primary ASW weapon used by surface ships, aircraft, and submarines. The guidance systems of these weapons can be autonomous or electronically controlled from the launching platform through an attached wire. The autonomous guidance systems are acoustically based. They operate either passively, exploiting the emitted sound energy by the target, or actively, ensonifying the target and using the received echoes for guidance. With the exception of SINKEX, torpedoes will not be used in the GoA TMAA during the proposed training activities.
Portable Undersea Tracking Range (PUTR) —The PUTR is a self-contained, portable, undersea tracking capability that employs modern technologies to support coordinated undersea warfare training in numerous locations. The system tracks submarines, surface ships, 2 (46.3-185.2 km 2 ) or smaller and provide high-fidelity feedback and scoring of crew performance during ASW training activities. No on-shore construction would take place. Seven electronics packages, each approximately 3 ft (0.9 m) long by 2 ft (0.6 m) in diameter, would be temporarily installed on the seafloor by a range boat. The anchors used to keep the electronics packages on the seafloor consist of either concrete or sand bags, each of which are approximately 1.5 ft-by-1.5 ft (0.45 m-by-0.45 m) and 300 pounds (136 kilograms). PUTR equipment can be recovered for maintenance or when training is completed. Two separate sound sources are associated with the operation of the PUTR:
Range tracking pingers—Range tracking pingers would be used on ships, submarines, and ASW targets when training is conducted on the PUTR. A typical MK 84 range tracking pinger generates a 12.93 kHz sine wave in pulses with a maximum duty cycle of 30 milliseconds and has a design power of 194 dB re 1 micro-Pascal at 1 meter. Ping rate is selectable and typically one pulse every two seconds
PUTR:
Range tracking pingers—Range tracking pingers would be used on ships, submarines, and ASW targets when training is conducted on the PUTR. A typical MK 84 range tracking pinger generates a 12.93 kHz sine wave in pulses with a maximum duty cycle of 30 milliseconds and has a design power of 194 dB re 1 micro-Pascal at 1 meter. Ping rate is selectable and typically one pulse every two seconds. Under the proposed action, up to four range pingers would operate simultaneously for 4 hours each of the 20 PUTR operating days per year. Total time operated would be 80 hours annually.
Transponders—Each transponder package consists of a hydrophone that receives pinger signals, and a transducer that sends an acoustic “uplink” of locating data to the range boat. The uplink signal is transmitted at 8.8 kHz, 17 kHz, or 40 kHz, at a source level of 190 dB at 40 kHz, and 186 dB at 8.8 kHz. The uplink frequency is selectable and typically uses the 40 kHz signal, however the lower frequency may be used when PUTR is deployed in deep waters where conditions may not permit the 40 kHz signal to establish and maintain the uplink. The PUTR system also incorporates an emergency underwater voice capability that transmits at 8-11 kHz and a source level of 190 dB. Under the proposed action, the uplink transmitters would operate 20 days per year, for 4 hours each day of use. Total time operated would be 80 hours annually.
Training Targets —ASW training targets are used to simulate opposition submarines. They are equipped with one or a combination of the following devices: (1) Acoustic projectors emanating sounds to simulate submarine acoustic signatures; (2) echo repeaters to simulate the characteristics of the echo of a particular sonar signal reflected from a specific type of submarine; and (3) magnetic sources to trigger magnetic detectors. Two ASW training target types may be used in the TMAA: The MK-30, which is recovered after each use and the MK-39 Expendable Mobile ASW Training Target (EMATT), which is not recovered
ne acoustic signatures; (2) echo repeaters to simulate the characteristics of the echo of a particular sonar signal reflected from a specific type of submarine; and (3) magnetic sources to trigger magnetic detectors. Two ASW training target types may be used in the TMAA: The MK-30, which is recovered after each use and the MK-39 Expendable Mobile ASW Training Target (EMATT), which is not recovered. Under the proposed action, approximately 12 EMATTs may be expended annually during training in the TMAA. A small percentage of these EMATTS may be replaced by the more costly yet recoverable MK-30.
As described above, ASW training exercises are the primary type of exercises that utilize MFAS and HFAS sources in the GoA TMAA. Unit level tracking and torpedo ASW exercises may occur over the course of several days during the proposed training period in the GoA TMAA. Under the Navy's preferred alternative, in a single year the GoA TMAA may have two exercises lasting up to 21 days, both of which may involve one ASW unit (aircraft, ship, or submarine) versus one target (usually a MK-39 EMATT or live submarine). ASW exercise descriptions are included below and summarized (along with the exercises utilizing explosives) in Table 2.
ASW Tracking Exercise (TRACKEX) —Generally, TRACKEXs train aircraft, ship, and submarine crews in tactics, techniques, and procedures for search, detection, localization, and tracking of submarines with the goal of determining a firing solution that could be used to launch a torpedo and destroy the submarine. Use of torpedoes is not a proposed activity in the TMAA, with the exception of SINKEX. ASW Tracking Exercises occur during both day and night. A typical unit-level exercise involves one (1) ASW unit (aircraft, ship, or submarine) versus one (1) target—either a MK-39 (EMATT), or a live submarine. The target may be non-evading while operating on a specified track or fully evasive
troy the submarine. Use of torpedoes is not a proposed activity in the TMAA, with the exception of SINKEX. ASW Tracking Exercises occur during both day and night. A typical unit-level exercise involves one (1) ASW unit (aircraft, ship, or submarine) versus one (1) target—either a MK-39 (EMATT), or a live submarine. The target may be non-evading while operating on a specified track or fully evasive. Participating units use active and passive sensors, including hull-mounted sonar, towed arrays, dipping sonar, variable-depth sonar, and sonobuoys for tracking.
ASW training activities will take place during the summer months, in the form of one or two major exercises or focused activity periods. These exercises or activity periods would each last up to 21 days and consist of multiple component training activities. Unlike Navy Training activities in other areas, the GOA TMAA is not a Range Complex and as such, there are no other or ongoing small scale Navy Training activities conducted outside these activity periods. Descriptions of each ASW tracking exercise type are provided below.
Helicopter ASW TRACKEX
A helicopter ASW TRACKEX typically involves one or two MH-60R helicopters using both passive and active sonar for tracking submarine targets. For passive tracking, the MH-60R may deploy patterns of passive sonobuoys to receive underwater acoustic signals, providing the helicopter crew with locating information on the target. Active sonobuoys may also be used. An active sonobuoy, as in any active sonar system, emits an acoustic pulse that travels through the water, returning echoes if any objects, such as a submarine, are within the range of acoustic detection. For active sonar tracking, the MH-60R crew will rely primarily on its AQS-22 Dipping Sonar. The sonar is lowered into the ocean while the helicopter hovers within 50 ft (15m) of the surface. Similar to the active sonobuoy, the dipping sonar emits acoustic energy and receives any returning echoes, indicating the presence of an underwater object
submarine, are within the range of acoustic detection. For active sonar tracking, the MH-60R crew will rely primarily on its AQS-22 Dipping Sonar. The sonar is lowered into the ocean while the helicopter hovers within 50 ft (15m) of the surface. Similar to the active sonobuoy, the dipping sonar emits acoustic energy and receives any returning echoes, indicating the presence of an underwater object. Use of dipping sonar has the potential to disturb a marine mammal or marine mammal stock resulting in MMPA Level B harassment as defined for military readiness activities.
The target for this exercise is either an EMATT or live submarine which may be either nonevading and assigned to a specified track or fully evasive depending on the state of training of the helicopter crew. A Helicopter TRACKEX usually takes 2 to 4 hours. No torpedoes are fired during this exercise. A total of 192 AQS-22 “dips” annually were analyzed for potential acoustic impacts under the proposed training activities.
MPA 1 ASW TRACKEX
During these exercises, a typical scenario involves a single MPA dropping sonobuoys, from an altitude below 3,000 ft (914 m), into specific patterns designed for both the anticipated threat submarine and the specific water conditions. These patterns vary in size and coverage area based on anticipated threat and water
1 MPA currently refers to the P-3C Orion aircraft. The P-8 Multi-Mission Maritime Aircraft is scheduled to replace the P-3C as the Navy's MPA.
The MPA will typically operate below 3,000 ft (914 m) to drop sonobuoys, will sometimes be as low as 400 ft (122 m), then may climb to several thousand feet after the buoy pattern is deployed. The higher altitude allows monitoring of the buoys over a much larger search pattern area. The target for this exercise is either an EMATT or live submarine, which may be either non-evading and assigned to a specified track or fully evasive depending on the state of training of the MPA. An MPA TRACKEX usually takes 2 to 4 hours
may climb to several thousand feet after the buoy pattern is deployed. The higher altitude allows monitoring of the buoys over a much larger search pattern area. The target for this exercise is either an EMATT or live submarine, which may be either non-evading and assigned to a specified track or fully evasive depending on the state of training of the MPA. An MPA TRACKEX usually takes 2 to 4 hours. The annual use of a total of 266 DICASS sonobuoys was analyzed for potential acoustic impacts under the proposed training activities.
EER/IEER ASW Training Exercises
This is an at-sea flying exercise designed to train MPA crews in the deployment and use of the EER/IEER sonobuoy systems. This system uses the SSQ-110A as the signal source and the SSQ-77 as the receiver buoy. This activity differs from the MPA ASW TRACKEX in that the SSQ-110A sonobuoy uses two explosive charges per buoy for the acoustic source. Other active sonobuoys use an electrically generated “ping.” Use of explosive sonobuoys has the potential to disturb a marine mammal or marine mammal stock resulting in MMPA Level B harassment as defined for military readiness activities.
A typical EER/IEER exercise lasts approximately 6 hours. The aircrew will first deploy 16 to 20 SSQ-110A sonobuoys and 16 to 20 passive sonobuoys in 1 hour. For the next 5 hours, the sonobuoy charges will be detonated, while the EER/IEER system analyzes the returns for evidence of a submarine. This exercise may or may not include a practice target. For potential acoustic impacts, the annual deployments of 40 SSQ-110 (two explosions per buoy) sonobuoys were analyzed under the proposed training activities.
In the future, the SSQ-125 MAC sonobuoy will be deployed in the GoA TMAA as a replacement for the SSQ-110 in EER/IEER exercises.
ASW TRACKEX (Surface Ship)
Surface ships operating in the GoA TMAA would use hull-mounted active sonar to conduct ASW Tracking exercises
, the annual deployments of 40 SSQ-110 (two explosions per buoy) sonobuoys were analyzed under the proposed training activities.
In the future, the SSQ-125 MAC sonobuoy will be deployed in the GoA TMAA as a replacement for the SSQ-110 in EER/IEER exercises.
ASW TRACKEX (Surface Ship)
Surface ships operating in the GoA TMAA would use hull-mounted active sonar to conduct ASW Tracking exercises. Typically, this exercise would involve the coordinated use of other ASW assets, to include MPA, helicopters, and other ships. A total of 578 hours of SQS-53 and 52 hours of SQS-56 sonar annually were analyzed for potential acoustic impacts under the proposed training activities. Acoustic cumulative and synergistic effects are incorporated into the modeling as detailed in Appendix B of the Navy's LOA application (see Supplementary Information section for information on obtaining copies of supporting documents). Use of active sonar by surface ships for ASW has the potential to disturb a marine mammal or marine mammal stock resulting in MMPA Level B harassment as defined for military readiness activities.
ASW or Anti-Surface Warfare (ASUW) (Submarine)
During these exercises, submarines use passive sonar sensors to search, detect, classify, localize, and track the threat submarine with the goal of developing a firing solution that could be used to launch a torpedo and destroy the threat submarine. However, no torpedoes are fired during this exercise. Submarines also use their high-frequency sonar for object avoidance and navigation safety. Sonar use by submarines has the potential to disturb a marine mammal or marine mammal stock resulting in MMPA Level B harassment as defined for military readiness activities.
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Underwater detonation activities can occur at various depths. They may include activities with detonations at or just below the surface (such as SINKEX or gunnery exercises (GUNEX))
mal or marine mammal stock resulting in MMPA Level B harassment as defined for military readiness activities.
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Underwater detonation activities can occur at various depths. They may include activities with detonations at or just below the surface (such as SINKEX or gunnery exercises (GUNEX)). When the weapons hit the target, there is no explosion in the water, and so a “hit” is not modeled ( i.e., the energy (either acoustic or pressure) from the hit is not expected to reach levels that would result in take of marine mammals). When a live weapon misses, it is modeled to explode below the water surface at 1 ft (5-inch naval gunfire, 76-mm rounds), 2 meters (Maverick, Harpoon, MK-82, MK-83, MK-84), or 50 ft (MK-48 torpedo) as shown in Appendix A of the Navy's application (the depth is chosen to represent the worst case of the possible scenarios as related to potential marine mammals impacts). Exercises may utilize either live or inert ordnance of the types listed in Table 2. Additionally, successful hit rates are known to the Navy and are utilized in the effects modeling. Training events that involve explosives and underwater detonations are described below and summarized in Table 3.
Table 3—Sources of At-Sea Explosives Used in GoA TMAA for Which Take of Marine Mammals Is Anticipated Ordnance/explosive Net explosive weight (in lbs.) Sub-TTS 177dB TTS 182 SEL/23psi Injury 50% TM rupture, 205db or 23 psi-ms Mortality Onset massive lung injury or 31 psi-ms Exclusion zone Used (m) 5″ Naval gunfire 9.54 413 227/269 43 23 549 76 mm Rounds 1.6 168 95/150 19 13 549 MK-82 238 2720 1584/809 302 153 914 MK-83 574 4056 2374/1102 468 195 914 MK-84 945 5196 3050/1327 611 226 914 SSQ-110 IEER 5 NA 325/271 155 76 914 MK-48 851 NA 2588/1198 762 442 1852 Table Also Indicates Range to Indicated Threshold and Size of Navy Exclusion Zone Used in Mitigation. Units Are Meters
on zone Used (m) 5″ Naval gunfire 9.54 413 227/269 43 23 549 76 mm Rounds 1.6 168 95/150 19 13 549 MK-82 238 2720 1584/809 302 153 914 MK-83 574 4056 2374/1102 468 195 914 MK-84 945 5196 3050/1327 611 226 914 SSQ-110 IEER 5 NA 325/271 155 76 914 MK-48 851 NA 2588/1198 762 442 1852 Table Also Indicates Range to Indicated Threshold and Size of Navy Exclusion Zone Used in Mitigation. Units Are Meters. Sinking Exercise (SINKEX)—In a SINKEX, a specially prepared, deactivated vessel is deliberately sunk using multiple weapons systems. The exercise provides training to ship and aircraft crews in delivering both live and inert ordnance on a real target. These target vessels are empty, cleaned, and environmentally-remediated ship hulks. A SINKEX target is towed to sea and set adrift at the SINKEX location. The duration of a SINKEX is unpredictable since it ends when the target sinks, sometimes immediately after the first weapon impact and sometimes only after multiple impacts by a variety of weapons. Typically, the exercise lasts for 4 to 8 hours over 1 to 2 days. The Navy proposes to conduct one SINKEX during each summertime exercise in the GoA TMAA (maximum of two). Potential harassment would be from underwater detonation. SINKEX events have been conducted in the Pacific at Navy training range complexes off Southern California, the Pacific Northwest, Hawaii, and the Mariana Islands, in compliance with 40 CFR 229.2.
The Environmental Protection Agency (EPA) grants the Navy a general permit through the Marine Protection, Research, and Sanctuaries Act to transport vessels “for the purpose of sinking such vessels in ocean waters * * *” (40 CFR 229.2). Subparagraph (a)(3) of this regulation states “All such vessel sinkings shall be conducted in water at least 1,000 fathoms (6,000 feet) deep and at least 50 nautical miles from land.”
SINKEX events typically include at least one surface combatant (frigate, destroyer, or cruiser); one submarine; and numerous fixed-wing and rotary-wing aircraft
g such vessels in ocean waters * * *” (40 CFR 229.2). Subparagraph (a)(3) of this regulation states “All such vessel sinkings shall be conducted in water at least 1,000 fathoms (6,000 feet) deep and at least 50 nautical miles from land.”
SINKEX events typically include at least one surface combatant (frigate, destroyer, or cruiser); one submarine; and numerous fixed-wing and rotary-wing aircraft. One surface ship will serve as a surveillance platform to ensure the hulk does not pose a hazard to navigation prior to and during the SINKEX. The weapons actually expended during a SINKEX can vary greatly. Table 1-7 in the Navy's application indicates the typical ordnance that may be used in a SINKEX, which may include missiles, bombs, 5” gunfire, and a single MK-48 torpedo. This table reflects the planning for weapons, which may be expended during one SINKEX in the GoA TMAA. This level of ordnance is expected for each of the two possible SINKEX events in the GoA TMAA. With the exception of the single torpedo, which is designed to explode below the target hulk in the water column, the weapons deployed during a SINKEX are intended to strike the target hulk, and thus not explode within the water column.
Surface-to-Surface Gunnery Exercise (S-S GUNEX) —These exercises train surface ship crews in high-speed surface engagement procedures against mobile (towed or self-propelled) seaborne targets. Both live and inert training rounds are used against the targets. The training consists of the pre-attack phase, including locating, identifying, and tracking the threat vessel, and the attack phase in which the missile is launched and flies to the target. In a live-fire event, aircraft conduct a surveillance flight to ensure that the range is clear of nonparticipating ships. These activities may occur within the GoA TMAA and have the potential to disturb a marine mammal or marine mammal stock resulting in MMPA Level B harassment as defined for military readiness activities
d the attack phase in which the missile is launched and flies to the target. In a live-fire event, aircraft conduct a surveillance flight to ensure that the range is clear of nonparticipating ships. These activities may occur within the GoA TMAA and have the potential to disturb a marine mammal or marine mammal stock resulting in MMPA Level B harassment as defined for military readiness activities.
For S-S GUNEX from a Navy ship, gun crews engage surface targets at sea with their main battery 5-inch and 76mm guns as well as smaller surface targets with 25mm, 0.50-caliber (cal), or 7.62mm machine guns, with the goal of disabling or destroying the threat target. For a surface-to-surface GUNEX from a Navy small boat, the weapon used is typically a 0.50 cal, 7.62-mm, or 40-mm machine gun.
The number of rounds fired depends on the weapon used for S-S GUNEX. For 0.50-cal, 7.62-mm, or 40-mm ordnance, the number of rounds is approximately 200, 800, and 10 rounds, respectively. For the ship main battery guns, the gun crews typically fire approximately 60 rounds of 5-inch or 76-mm ordnance during one exercise. These activities may occur within the GoA TMAA.
Air-to-Surface Gunnery Exercise (A-S GUNEX) —Strike fighter aircraft and helicopter crews, including embarked
For fixed-wing A-S GUNEX, a flight of two F/A-18 aircraft will begin a descent to the target from an altitude of about 3,000 ft (914 m) while still several miles away. Within a distance of 4,000 ft (1,219 m) from the target, each aircraft will fire a burst of about 30 rounds before reaching an altitude of 1,000 ft (305 m), then break off and reposition for another strafing run until each aircraft expends its exercise ordnance allowance of about 250 rounds from its 20mm cannon.
For rotary-wing A-S GUNEX, a single helicopter will carry several air crewmen needing gunnery training and fly at an altitude between 50 and 100 ft (15 to 30 m) in a 300-ft (91-m) racetrack pattern around an at-sea target
f 1,000 ft (305 m), then break off and reposition for another strafing run until each aircraft expends its exercise ordnance allowance of about 250 rounds from its 20mm cannon.
For rotary-wing A-S GUNEX, a single helicopter will carry several air crewmen needing gunnery training and fly at an altitude between 50 and 100 ft (15 to 30 m) in a 300-ft (91-m) racetrack pattern around an at-sea target. Each gunner will expend about 200 rounds of 0.50 cal and 800 rounds of 7.62-mm ordnance in each exercise. The target is normally a noninstrumented floating object such as an expendable smoke float, steel drum, or cardboard box, but may be a remote-controlled speed boat or jet ski type target. The exercise lasts about 1 hour and occurs within the GoA TMAA.
Air-to-Surface Missile Exercise (A-S MISSILEX )—An air-to-surface MISSILEX involves fixed-winged aircraft and helicopter crews launching missiles at surface maritime targets, day and night, with the goal of training to destroy or disable enemy ships or boats. These activities may occur within the TMAA; however, all missile launches would be simulated; therefore, MISSILEX activities are not likely to disturb a marine mammal or marine mammal stock resulting in MMPA Level B harassment as defined for military readiness activities.
For helicopter A-S MISSILEX, one or two MH-60R/S helicopters approach and acquire an at-sea surface target, which is then designated with a laser to guide an AGM-114 Hellfire missile to the target. The laser designator may be onboard the helicopter firing the hellfire, another helicopter, or another source. The helicopter simulates launching a missile from an altitude of about 300 ft (91 m) against a specially prepared target with an expendable target area on a nonexpendable platform
sea surface target, which is then designated with a laser to guide an AGM-114 Hellfire missile to the target. The laser designator may be onboard the helicopter firing the hellfire, another helicopter, or another source. The helicopter simulates launching a missile from an altitude of about 300 ft (91 m) against a specially prepared target with an expendable target area on a nonexpendable platform. The platform fitted with the expendable target could be a stationary barge, a remote-controlled speed boat, or a jet ski towing a trimaran whose infrared signature has been augmented with a heat source (charcoal or propane) to better represent a typical threat vessel. All missile firings would be simulated.
For an air-to-surface MISSILEX fired from fixed-wing aircraft, the simulated missile used is typically an AGM-84 Standoff Land Attack Missile-Expanded Response (SLAM-ER), an AGM-84 Harpoon, or an AGM-65 Maverick. A flight of one or two aircraft approach an at-sea surface target from an altitude between 40,000 ft (12,192 m) and 25,000 ft (7,620 m) for SLAM-ER or Harpoon, and between 25,000 ft (7,620 m) and 5,000 ft (1,524 m) for Maverick, complete the internal targeting process, and simulate launching the weapon at the target from beyond 150 nm (278 km) for SLAM-ER and from beyond 12 nm (22 km) for Maverick. The majority of unit level exercises involve the use of captive carry (inert, no release) training missiles; the aircraft perform all detection, tracking, and targeting requirements without actually releasing a missile. These activities may occur within the GoA TMAA and all missile launches would be simulated.
Air-to-Surface Bombing Exercise (BOMBEX) —During an air-to-surface BOMBEX, maritime patrol aircraft (MPA) or F/A-18 deliver free-fall bombs against surface maritime targets, with the goal of destroying or disabling enemy ships or boats
king, and targeting requirements without actually releasing a missile. These activities may occur within the GoA TMAA and all missile launches would be simulated.
Air-to-Surface Bombing Exercise (BOMBEX) —During an air-to-surface BOMBEX, maritime patrol aircraft (MPA) or F/A-18 deliver free-fall bombs against surface maritime targets, with the goal of destroying or disabling enemy ships or boats.
A flight of one or two aircraft will approach the target from an altitude of 15,000 ft (4,570 m) to less than 3,000 ft (914 m) while adhering to designated ingress and egress routes. Typical bomb release altitude is below 3,000 ft (914 m) and within a range of 1,000 yards (yd) (914 m) for unguided munitions, and above 15,000 ft (4,572 m) and in excess of 10 nm (18 km) for precision-guided munitions. Exercises at night will normally be done with captive carry (no drop) weapons because of safety considerations. Laser designators from aircraft releasing ordnance or a support aircraft are used to illuminate certified targets for use with lasers when using laser guided weapons. Bombs used could include BDU-45 (inert) or MK-82/83/84 (live and inert). These activities may occur within the GoA TMAA and have the potential to disturb a marine mammal or marine mammal stock resulting in MMPA Level B harassment as defined for military readiness activities. In the near future, the Navy will be transitioning all carrier based MK-80 series bombs to BLU 110, 111, and 117 live and inert bombs. The difference is that the BLU-series bombs contain insensitive (less likely to accidently explode) high explosives, which make them safer for carrier-based operations. All other attributes would remain the same.
EER-IEER AN/SSQ-110A —The Extended Echo Ranging and Improved Extended Echo Ranging (EER/IEER) systems are airborne ASW systems used in conducting “large area” searches for submarines. These systems are made up of airborne avionics ASW acoustic processing and sonobuoy types that are deployed in pairs
, which make them safer for carrier-based operations. All other attributes would remain the same.
EER-IEER AN/SSQ-110A —The Extended Echo Ranging and Improved Extended Echo Ranging (EER/IEER) systems are airborne ASW systems used in conducting “large area” searches for submarines. These systems are made up of airborne avionics ASW acoustic processing and sonobuoy types that are deployed in pairs. The IEER system's active sonobuoy has two components: An AN/SSQ-110A Sonobuoy, which generates a sound similar to a “sonar ping” using a small explosive; and a passive AN/SSQ-77 Sonobuoy, which “listens” for the return echo of the “sonar ping” that has been bounced off the surface of a submarine. These sonobuoys are designed to provide underwater acoustic data necessary for naval aircrews to quickly and accurately detect submerged submarines. The sonobuoy pairs are dropped from a fixed-wing aircraft into the ocean in a predetermined pattern with a few buoys covering a very large area. The AN/SSQ-110A Sonobuoy Series is an expendable and commandable sonobuoy. Upon command from the aircraft, the bottom payload is released to sink to a designated operating depth. A second command is required from the aircraft to cause the second payload to release and detonate the explosive to generate a “ping.” There is only one detonation in the pattern of buoys at a time. Potential harassment would be from underwater detonations.
The MAC system (described in the sonar source section) will eventually replace the EER/IEER system and was analyzed for this proposed rule.
Vessel Movement
Many of the proposed activities within the GoA TMAA involve maneuvers by various types of surface ships, boats, and submarines (collectively referred to as vessels). According to the Navy's application, up to seven Navy vessels (six surface ships and one submarine) may be operating within the GoA TMAA
entually replace the EER/IEER system and was analyzed for this proposed rule.
Vessel Movement
Many of the proposed activities within the GoA TMAA involve maneuvers by various types of surface ships, boats, and submarines (collectively referred to as vessels). According to the Navy's application, up to seven Navy vessels (six surface ships and one submarine) may be operating within the GoA TMAA. In addition, the Navy's DEIS stated that under the preferred alternative (Alternative 2) 19 contracted support vessels may also be operating within the GoA TMAA. Within the maximum two summer exercises, the length of the exercise, the number of vessels, and the allotted at-sea time within the GoA TMAA during an exercise will be variable between years. These variations cannot be predicted given unknowns including the availability of participants for the e.g., tactical deployments, disaster relief, humanitarian assistance, etc.), planned and unplanned deployments, vessel availability due to funding and maintenance cycles, and logistic concerns with conducting an exercise in the GoA.
Vessel movements have the potential to affect marine mammals by directly striking or disturbing individual animals. The probability of vessel and marine mammal interactions occurring in the GoA TMAA is dependent on several factors including numbers, types, and speeds of vessels; the regularity, duration, and spatial extent of activities; the presence/absence and density of marine mammals; and protective measures implemented by the Navy. During training activities, speeds vary and depend on the specific training activity. In general, Navy vessels move in a coordinated manner, but can be separated by many miles in distance. These activities are widely dispersed throughout the GoA TMAA, which is a vast area encompassing 42,146 nm 2 (145,458 km 2 ). Consequently, the density of Navy vessels within the GoA TMAA at any given time is extremely low
ning activities, speeds vary and depend on the specific training activity. In general, Navy vessels move in a coordinated manner, but can be separated by many miles in distance. These activities are widely dispersed throughout the GoA TMAA, which is a vast area encompassing 42,146 nm 2 (145,458 km 2 ). Consequently, the density of Navy vessels within the GoA TMAA at any given time is extremely low.
Additional information on the Navy's proposed activities may be found in the LOA Application and the Navy's GoA TMAA DEIS.
Description of Marine Mammals in the Area of the Specified Activities
Twenty-six marine mammal species or populations/stocks have confirmed or possible occurrence within or adjacent to the GoA, including seven species of baleen whales (mysticetes), 13 species of toothed whales (odontocetes), five species of seals (pinnipeds), and the sea otter (mustelid). Nine of these species are ESA-listed and considered depleted under the MMPA: Blue whale, fin whale, humpback whale, sei whale, sperm whale, North Pacific right whale, Cook Inlet beluga whale, Steller sea lion, and sea otter. Table 4 summarizes their abundance, Endangered Species Act (ESA) status, occurrence, density, and likely occurrence in the TMAA during the April to October timeframe. The sea otter is managed by the U.S. Fish and Wildlife Service and will not be addressed further here.
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Cook Inlet Beluga Whale —The likelihood of a Cook Inlet beluga whale ( Delphinapterus leucas ) occurring in the TMAA is extremely low. Only 28 sightings of beluga whales in the GoA have been reported from 1936 to 2000 (Laidre et al., 2000). The nearest beluga whales to the TMAA are in Cook Inlet with a 2008 abundance estimate of 375 whales in the Cook Inlet stock (NMFS 2008). In October 2008, the Cook Inlet beluga whale distinct population segment was listed as endangered under the ESA (73 FR 62919, October 22, 2008)
tremely low. Only 28 sightings of beluga whales in the GoA have been reported from 1936 to 2000 (Laidre et al., 2000). The nearest beluga whales to the TMAA are in Cook Inlet with a 2008 abundance estimate of 375 whales in the Cook Inlet stock (NMFS 2008). In October 2008, the Cook Inlet beluga whale distinct population segment was listed as endangered under the ESA (73 FR 62919, October 22, 2008). Prior to listing, the population had been designated as depleted under the MMPA (NMFS, 2008). Cook Inlet is approximately 70 nm (129.6 km) from the nearest edge of the TMAA and the Cook Inlet beluga whales do not leave the waters of Cook Inlet (NMFS, 2007, 2008). Based on this information, it is highly unlikely for a Cook Inlet beluga whale to be present in the action area. Consequently, this distinct population segment will not be considered in the remainder of this analysis.
False Killer Whale —The likelihood of a false killer whale ( Pseudorca crassidens ) being present in the TMAA is extremely low. False killer whales are found in tropical and temperate waters, generally between 50° S and 50° N latitude (Baird et al., 1989; Odell and McClune, 1999). The southernmost point boundary of the TMAA is well north of 55° N latitude. There have been records of false killer whale sightings as far north as the Aleutian Islands and Prince William Sound in the past (Leatherwood et al., 1988). In addition, a false killer whale was sighted in May 2003 near Juneau, but this was considered to be far north of its normal range (DoN, 2006). There are no abundance estimates available for this
Northern Right Whale Dolphin —The likelihood of a northern right whale dolphin ( Lissodelphis borealis ) occurring in the TMAA is extremely low. This species occurs in North Pacific oceanic waters and along the outer continental shelf and slope in cool temperate waters colder than 20° C. This species is distributed approximately from 30° N to 55° N and 145° W to 118° E (both south and east of the TMAA)
ern Right Whale Dolphin —The likelihood of a northern right whale dolphin ( Lissodelphis borealis ) occurring in the TMAA is extremely low. This species occurs in North Pacific oceanic waters and along the outer continental shelf and slope in cool temperate waters colder than 20° C. This species is distributed approximately from 30° N to 55° N and 145° W to 118° E (both south and east of the TMAA). There are two records of northern right whale dolphins in the GoA (one just south of Kodiak Island), but these are considered extremely rare (DoN, 2006). There are no abundance estimates for this species in the NMFS stock assessment report for this area of the Pacific. Given the extremely low likelihood of this species occurrence in the action area, the northern right whale dolphin will not be considered further in this analysis.
Risso's Dolphin —The likelihood of Risso's dolphin ( Grampus griseus ) occurring in the action area is extremely low. The Risso's dolphin is distributed worldwide in tropical to warm-temperate waters, roughly between 60° N and 60° S, where surface water temperature is usually greater than 10° C (Kruse et al., 1999). The average sea surface temperature for the GoA is reported to be approximately 9.6° C and has undergone a warming trend since 1957 (Aquarone and Adams, 2008). The average summer temperature within the upper 328 ft (100 m) of the TMAA is approximately 11° C based on data as presented in the modeling analysis undertaken by the Navy. In the eastern Pacific, Risso's dolphins range from the GoA to Chile (Leatherwood et al., 1980; Reimchen, 1980; Braham, 1983; Olavarria et al., 2001). Water temperature appears to be a factor that affects the distribution of Risso's dolphins in the Pacific (Leatherwood et al., 1980; Kruse et al., 1999). Risso's dolphins are expected to be extralimital in the TMAA. They prefer tropical to warm temperate waters and have seldom been sighted in the cold waters of the GoA
eatherwood et al., 1980; Reimchen, 1980; Braham, 1983; Olavarria et al., 2001). Water temperature appears to be a factor that affects the distribution of Risso's dolphins in the Pacific (Leatherwood et al., 1980; Kruse et al., 1999). Risso's dolphins are expected to be extralimital in the TMAA. They prefer tropical to warm temperate waters and have seldom been sighted in the cold waters of the GoA. Records of Risso's dolphins near the TMAA include sightings near Chirikof Island (southwest of Kodiak Island) and offshore in the GoA, just south of the TMAA boundary (Consiglieri et al., 1980; Braham, 1983). Given the extremely low likelihood of this species occurrence in the action area, the Risso's dolphin will not be considered further in this analysis.
Short-Finned Pilot Whale —Short-finned pilot whales ( Globicephala macrohynchus ) are not expected to occur in the GoA TMAA. This species is found in tropical to warm temperate seas, generally in deep offshore areas, and they do not usually range north of 50° N (DoN, 2006). There are two records of this species in Alaskan waters. In 1937, a short-finned pilot whale was taken near Katanak on the Alaska Peninsula and a group of five short-finned pilot whales were sighted just southeast of Kodiak Island in May 1977 (DoN, 2006). There are no abundance estimates available for this species in the NMFS stock assessment report for this area of the Pacific. Given the extremely low likelihood of this species' occurrence in the action area, the short-finned pilot whale will not be considered further in this analysis.
The Navy has compiled information on the abundance, behavior, status and distribution, and vocalizations of marine mammal species in the GoA TMAA waters from the Navy Marine Resource Assessment and has supplemented this information with additional citations derived from new survey efforts and scientific publications
a, the short-finned pilot whale will not be considered further in this analysis.
The Navy has compiled information on the abundance, behavior, status and distribution, and vocalizations of marine mammal species in the GoA TMAA waters from the Navy Marine Resource Assessment and has supplemented this information with additional citations derived from new survey efforts and scientific publications. NMFS has designated stocks of marine mammals in the waters surrounding the GoA TMAA and, therefore, compiles stock assessment reports for this area. This information may be viewed in the Navy's LOA application and/or the Navy's DEIS for the GoA TMAA (see Availability), and is incorporated by reference herein.
There are no designated marine mammal critical habitats or known foraging areas within the GoA TMAA; however, critical habitats for two ESA-listed species have been designated in the vicinity of the GoA TMAA. On April 8, 2008, NMFS designated two areas as North Pacific right whale critical habitat—one in the GoA and one in the Bering Sea (73 FR 19000). The GoA critical habitat is located approximately 16 nm (30 km) west of the southwest corner of the TMAA. NMFS designated critical habitat for Steller sea lions on August 27, 1993 (58 FR 45269). For the western Distinct Population Segment (DPS), “aquatic zone” critical habitat surrounding haulouts and rookeries extends 20 nm (37 km) seaward in state and federally managed waters, portions of which are adjacent to the TMAA.
Much is unknown about the feeding habits of the dolphin and porpoise species in the GoA TMAA, but they are thought to feed opportunistically throughout their range (like better studied species and stocks are known to do) and possibly throughout the year. Even less is known about the feeding habits of beaked whales. Baleen whales and sperm whales are thought to forage seasonally in areas within and around the GoA TMAA. For example, Moore et al
central nervous system. Acoustic energy causes the basilar membrane in the cochlea to vibrate. Sensory cells at different positions along the basilar membrane are excited by different frequencies of sound (Pickles, 1998). Baleen whales have inner ears that appear to be specialized for low-frequency hearing. Conversely, dolphins and porpoises have ears that are specialized to hear high frequencies.
Marine mammal vocalizations often extend both above and below the range of human hearing; vocalizations with frequencies lower than 18 Hz are labeled as infrasonic and those higher than 20 kHz as ultrasonic (National Research Council (NRC), 2003; Figure 4-1). Measured data on the hearing abilities of cetaceans are sparse, particularly for the larger cetaceans such as the baleen whales. The auditory thresholds of some of the smaller odontocetes have been determined in captivity. It is generally believed that cetaceans should at least be sensitive to the frequencies of their own vocalizations. Comparisons of the anatomy of cetacean inner ears and models of the structural properties and the response to vibrations of the ear's components in different species provide an indication of likely sensitivity to
Baleen whale vocalizations are composed primarily of frequencies below 1 kHz, and some contain fundamental frequencies as low as 16 Hz (Watkins et al., 1987; Richardson et al., 1995; Rivers, 1997; Moore et al., 1998; Stafford et al., 1999; Wartzok and Ketten, 1999) but can be as high as 24 kHz (humpback whale; Au et al., 2006). Clark and Ellison (2004) suggested that baleen whales use low-frequency sounds not only for long-range communication, but also as a simple form of echo ranging, using echoes to navigate and orient relative to physical features of the ocean. Information on auditory function in mysticetes is extremely lacking
; Wartzok and Ketten, 1999) but can be as high as 24 kHz (humpback whale; Au et al., 2006). Clark and Ellison (2004) suggested that baleen whales use low-frequency sounds not only for long-range communication, but also as a simple form of echo ranging, using echoes to navigate and orient relative to physical features of the ocean. Information on auditory function in mysticetes is extremely lacking. Sensitivity to low-frequency sound by baleen whales has been inferred from observed vocalization frequencies, observed reactions to playback of sounds, and anatomical analyses of the auditory system. Although there is apparently much variation, the source levels of most baleen whale vocalizations lie in the range of 150-190 dB re 1 μPa at 1 m. Low-frequency vocalizations made by baleen whales and their corresponding auditory anatomy suggest that they have good low-frequency hearing (Ketten, 2000), although specific data on sensitivity, frequency or intensity discrimination, or localization abilities are lacking. Marine mammals, like all mammals, have typical U-shaped audiograms that begin with relatively low sensitivity (high threshold) at some specified low frequency with increased sensitivity (low threshold) to a species specific optimum followed by a generally steep rise at higher frequencies (high threshold) (Fay, 1988).
The toothed whales produce a wide variety of sounds, which include species-specific broadband “clicks” with peak energy between 10 and 200 kHz, individually variable “burst pulse” click trains, and constant frequency or frequency-modulated (FM) whistles ranging from 4 to 16 kHz (Wartzok and Ketten, 1999). The general consensus is that the tonal vocalizations (whistles) produced by toothed whales play an important role in maintaining contact between dispersed individuals, while broadband clicks are used during echolocation (Wartzok and Ketten, 1999)
ly variable “burst pulse” click trains, and constant frequency or frequency-modulated (FM) whistles ranging from 4 to 16 kHz (Wartzok and Ketten, 1999). The general consensus is that the tonal vocalizations (whistles) produced by toothed whales play an important role in maintaining contact between dispersed individuals, while broadband clicks are used during echolocation (Wartzok and Ketten, 1999). Burst pulses have also been strongly implicated in communication, with some scientists suggesting that they play an important role in agonistic encounters (McCowan and Reiss, 1995), while others have proposed that they represent “emotive” signals in a broader sense, possibly representing graded communication signals (Herzing, 1996). Sperm whales, however, are known to produce only clicks, which are used for both communication and echolocation (Whitehead, 2003). Most of the energy of toothed whale social vocalizations is concentrated near 10 kHz, with source levels for whistles as high as 100 to 180 dB re 1 µPa at 1 m (Richardson et al., 1995). No odontocete has been shown audiometrically to have acute hearing (<80 dB re 1 µPa) below 500 Hz (DoN, 2001). Sperm whales produce clicks, which may be used to echolocate (Mullins et al., 1988), with a frequency range from less than 100 Hz to 30 kHz and source levels up to 230 dB re 1 µPa 1 m or greater (Mohl et al., 2000).
Table 5a and Table 5b list the species found in the GoA TMAA and include a summary of their vocalizations, if available. The “Brief Background on Sound” section below contains a description of the functional hearing groups designated by Southall et al. (2007), which includes the functional hearing range of various marine mammal groups ( i.e., what frequencies that can actually hear)
al., 2000).
Table 5a and Table 5b list the species found in the GoA TMAA and include a summary of their vocalizations, if available. The “Brief Background on Sound” section below contains a description of the functional hearing groups designated by Southall et al. (2007), which includes the functional hearing range of various marine mammal groups ( i.e., what frequencies that can actually hear).
BILLING CODE 3510-22-P EP19OC10.008
EP19OC10.009
BILLING CODE 35-22-C Marine Mammal Density Estimates
Understanding the distribution and abundance of a particular marine mammal species or stock is necessary to analyze the potential impacts of an action on that species or stock. Furthermore, it is necessary to know the density of the animals in the affected area in order to quantitatively assess the likely acoustic impacts of a potential action on individuals and estimate take (discussed further in the Estimated Take section).
Density is nearly always reported for an area ( e.g., animals per km 2 ). Analyses of survey results using distance sampling techniques include correction factors for animals at the surface but not seen as well as animals below the surface and not seen. Therefore, although the area ( e.g., km 2 ) appears to represent only the surface of the water (two-dimensional), density actually implicitly includes animals anywhere within the water column under that surface area. In addition, density assumes that animals are uniformly distributed within the prescribed area, even though this is likely a rare occurrence. Marine mammals are usually concentrated in areas of greater importance, such as areas of high productivity, low predation, safe calving, etc. Density can occasionally be calculated for smaller areas that are regularly used by marine mammals, but more often than not, there are insufficient data to calculate density for small areas. Therefore, assuming an even distribution within the prescribed area remains the norm
e usually concentrated in areas of greater importance, such as areas of high productivity, low predation, safe calving, etc. Density can occasionally be calculated for smaller areas that are regularly used by marine mammals, but more often than not, there are insufficient data to calculate density for small areas. Therefore, assuming an even distribution within the prescribed area remains the norm.
Recent survey data for marine mammals in the GoA is limited and most survey efforts were localized and extremely nearshore. In addition to the visual surveys, there is evidence of several species based on acoustic studies, but these do not provide measurements of abundance ( e.g., Stafford, 2009).
In April 2009, the Navy funded and NMFS conducted the Gulf of Alaska Line-Transect Survey (GOALS) to address the data needs for this analysis (Rone et al., 2009). Line-transect survey visual data to support distance sampling statistics and acoustic data were collected over a 10-day period both within and outside the TMAA. This survey resulted in sightings of several species and allowed for the derivation of densities for fin and humpback whale (Rone et al., 2009). In addition to this latest survey, two previous vessel surveys conducted in the nearshore region of the TMAA were also used to derive the majority of the density data used in acoustic modeling for this analysis. The methods used to derive density estimates for all remaining species in the TMAA are detailed in Appendix B of the LOA application and summarized below.
Zerbini et al. (2006) conducted dedicated vessel surveys for large whales in summer 2001-2003 from Resurrection Bay on the Kenai Peninsula to Amchitka Island in the Aleutian Islands. Survey effort near the TMAA was nearshore (within approximately 46 nm (85 km) of shore), and is delineated as “Block 1” in the original paper. Densities for this region were published for fin and humpback whales
ow.
Zerbini et al. (2006) conducted dedicated vessel surveys for large whales in summer 2001-2003 from Resurrection Bay on the Kenai Peninsula to Amchitka Island in the Aleutian Islands. Survey effort near the TMAA was nearshore (within approximately 46 nm (85 km) of shore), and is delineated as “Block 1” in the original paper. Densities for this region were published for fin and humpback whales.
Waite (2003) conducted vessel surveys for cetaceans near Kenai Peninsula, within Prince William Sound and around Kodiak Island, during acoustic-trawl surveys for pollock in summer 2003. Surveys extended offshore to the 1,000 m isobaths and therefore overlapped with some of the TMAA. Waite (2003) did not calculate densities, but did provide some of the elements necessary for calculating density (please see Appendix B of the LOA application for more information).
Mysticetes occurring in the GoA include blue, fin, gray, humpback, minke, North Pacific right, and sei whales (Angliss and Allen, 2008; Rone et al., 2009). Blue, North Pacific right, and sei whales are considered rare, and are included here only for discussion purposes due to their designations as “depleted” under the MMPA and “endangered” under the ESA.
Gray whale density was calculated from data obtained during nearshore feeding studies in the GoA. Gray whales are found almost exclusively in near shore areas; therefore, they would not be expected to be found in the majority of the TMAA (>50 nm (93 km) offshore and >5,997 ft (1,828 m) depth) (DoN, 2006). The recent 2009 survey encountered one group of two gray whales on the shelf within the western edge of the TMAA and two groups well outside the TMAA near shore at Kodiak Island (Rone et al., 2009).
Odontocetes occurring regularly include sperm whale, Cuvier's, Baird's, and Stejneger's beaked whales, killer whale, Pacific white-sided dolphin, and Dall's porpoise (Angliss and Allen, 2008; Rone et al., 2009)
2009 survey encountered one group of two gray whales on the shelf within the western edge of the TMAA and two groups well outside the TMAA near shore at Kodiak Island (Rone et al., 2009).
Odontocetes occurring regularly include sperm whale, Cuvier's, Baird's, and Stejneger's beaked whales, killer whale, Pacific white-sided dolphin, and Dall's porpoise (Angliss and Allen, 2008; Rone et al., 2009). In Alaska waters, harbor porpoise inhabit coastal waters where depths are less than 328 ft (100 m) in depth (DoN, 2006; Angliss and Allen, 2008). The majority of the TMAA is well offshore of the normal habitat range for harbor porpoise. There is no density data available for this species in the nearshore portion of the TMAA that overlaps the harbor porpoise range. An estimated quantification of impacts for harbor porpoise was, however, undertaken as described in the Potential Effects of Specified Activities on Marine Mammals section.
Pinnipeds occurring regularly include Steller sea lion, northern fur seal, and northern elephant seal. The range of California sea lions extends as far north as the Pribolof Islands in the Bering Sea. Tagging data indicate that most northern fur seal foraging and migration takes place to the west of the TMAA (Ream et al., 2005), although the derived density for this species assumed the population would be present in the area for modeling purposes. Harbor seals are primarily a coastal species and are rarely found more than 12 mi (20 km) from shore (DoN, 2006). Harbor seals should be very rare in the TMAA and there was no attempt to model for this species.
Pinniped at-sea density is not often available because pinniped abundance is obtained via shore counts of animals at known rookeries and haulouts. Lacking any other available means of quantification, densities of pinnipeds were derived using shore counts
ore than 12 mi (20 km) from shore (DoN, 2006). Harbor seals should be very rare in the TMAA and there was no attempt to model for this species.
Pinniped at-sea density is not often available because pinniped abundance is obtained via shore counts of animals at known rookeries and haulouts. Lacking any other available means of quantification, densities of pinnipeds were derived using shore counts. Several parameters were identified for pinnipeds from the literature, including area of stock occurrence, number of animals (which may vary seasonally) and season, and those parameters were then used to calculate density. Once density per “pinniped season” was determined, those values were prorated to fit the warm water (June through October) and cold water (November through May) seasons. Determining density in this manner is risky because the parameters used usually contain error ( e.g., geographic range is not exactly known and needs to be estimated and abundance estimates usually have large variances). As is true of all density estimates, they assume that the animals are always distributed evenly within an area which is likely never true.
Brief Background on Sound
An understanding of the basic properties of underwater sound is necessary to comprehend many of the concepts and analyses presented in this document. A summary is included below.
Sound is a wave of pressure variations propagating through a medium (for the MFAS/HFAS considered in this proposed rule, the medium is marine water). Pressure variations are created by compressing and relaxing the medium. Sound measurements can be expressed in two forms: Intensity and pressure. Acoustic intensity is the average rate of energy transmitted 2 ). Acoustic intensity is rarely measured directly, but rather from ratios of pressures; the standard reference pressure for underwater sound is 1 microPascal (μPa); for airborne sound, the standard reference pressure is 20 μPa (Richardson et al., 1995)
he medium. Sound measurements can be expressed in two forms: Intensity and pressure. Acoustic intensity is the average rate of energy transmitted 2 ). Acoustic intensity is rarely measured directly, but rather from ratios of pressures; the standard reference pressure for underwater sound is 1 microPascal (μPa); for airborne sound, the standard reference pressure is 20 μPa (Richardson et al., 1995).
Acousticians have adopted a logarithmic scale for sound intensities, which is denoted in decibels (dB). Decibel measurements represent the ratio between a measured pressure value and a reference pressure value (in this case 1 μPa or, for airborne sound, 20 μPa). The logarithmic nature of the scale means that each 10 dB increase is a ten-fold increase in power ( e.g., 20 dB is a 100-fold increase over 10 dB, 30 dB is a 1,000-fold increase over 10 dB). Humans perceive a 10 dB increase in noise as a doubling of loudness, or a 10 dB decrease in noise as a halving of loudness. The term “sound pressure level” implies a decibel measure and a reference pressure that is used as the denominator of the ratio. Throughout this document, NMFS uses 1 microPascal (denoted re: 1μPa) as a standard reference pressure unless noted otherwise.
It is important to note that decibels underwater and decibels in air are not the same and cannot be directly compared. Because of the different densities of air and water and the different decibel standards ( i.e., reference pressures) in air and water, a sound with the same intensity ( i.e., power) in air and in water would be approximately 63 dB quieter in air. Thus, a sound that measures 160 dB underwater would have the same approximate effective intensity as a sound that is 97 dB in air.
Sound frequency is measured in cycles per second, or Hertz (abbreviated Hz), and is analogous to musical pitch; high-pitched sounds contain high frequencies and low-pitched sounds contain low frequencies
n air and in water would be approximately 63 dB quieter in air. Thus, a sound that measures 160 dB underwater would have the same approximate effective intensity as a sound that is 97 dB in air.
Sound frequency is measured in cycles per second, or Hertz (abbreviated Hz), and is analogous to musical pitch; high-pitched sounds contain high frequencies and low-pitched sounds contain low frequencies. Natural sounds in the ocean span a huge range of frequencies: from earthquake noise at 5 Hz to harbor porpoise clicks at 150,000 Hz (150 kHz). These sounds are so low or so high in pitch that humans cannot even hear them; acousticians call these infrasonic (typically below 20 Hz) and ultrasonic (typically above 20,000 Hz) sounds, respectively. A single sound may be made up of many different frequencies together. Sounds made up of only a small range of frequencies are called “narrowband”, and sounds with a broad range of frequencies are called “broadband”; explosives are an example of a broadband sound source and active tactical sonars are an example of a narrowband sound source.
When considering the influence of various kinds of sound on the marine environment, it is necessary to understand that different kinds of marine life are sensitive to different frequencies of sound. Based on available behavioral data, audiograms derived using auditory evoked potential (AEP) techniques, anatomical modeling, and other data, Southall et al. (2007) designate “functional hearing groups” for marine mammals and estimate the lower and upper frequencies of functional hearing of the groups. Further, the frequency range in which each group's hearing is estimated as being most sensitive is represented in the flat part of the M-weighting functions (which are derived from the audiograms described above; see Figure 1 in Southall et al., 2007) developed for each group
tional hearing groups” for marine mammals and estimate the lower and upper frequencies of functional hearing of the groups. Further, the frequency range in which each group's hearing is estimated as being most sensitive is represented in the flat part of the M-weighting functions (which are derived from the audiograms described above; see Figure 1 in Southall et al., 2007) developed for each group. The functional groups and the associated frequencies are indicated below (though, again, animals are less sensitive to sounds at the outer edge of their functional range and most sensitive to sounds of frequencies within a smaller range somewhere in the middle of their functional hearing range):
• Low-frequency cetaceans (13 species of mysticetes): functional hearing is estimated to occur between approximately 7 Hz and 22 kHz;
• Mid-frequency cetaceans (32 species of dolphins, six species of larger toothed whales, and 19 species of beaked and bottlenose whales): functional hearing is estimated to occur between approximately 150 Hz and 160 kHz;
• High-frequency cetaceans (eight species of true porpoises, six species of river dolphins, Kogia, the franciscana, and four species of cephalorhynchids): functional hearing is estimated to occur between approximately 200 Hz and 180 kHz;
• Pinnipeds in water: functional hearing is estimated to occur between approximately 75 Hz and 75 kHz, with the greatest sensitivity between approximately 700 Hz and 20 kHz.
Because ears adapted to function underwater are physiologically different from human ears, comparisons using decibel measurements in air would still not be adequate to describe the effects of a sound on a whale. When sound travels (propagates) away from its source, its loudness decreases as the distance traveled by the sound increases. Thus, the loudness of a sound at its source is higher than the loudness of that same sound a kilometer distant
physiologically different from human ears, comparisons using decibel measurements in air would still not be adequate to describe the effects of a sound on a whale. When sound travels (propagates) away from its source, its loudness decreases as the distance traveled by the sound increases. Thus, the loudness of a sound at its source is higher than the loudness of that same sound a kilometer distant. Acousticians often refer to the loudness of a sound at its source (typically measured one meter from the source) as the source level and the loudness of sound elsewhere as the received level. For example, a humpback whale 3 km from an airgun that has a source level of 230 dB may only be exposed to sound that is 160 dB loud, depending on how the sound propagates (in this example, it is spherical spreading). As a result, it is important not to confuse source levels and received levels when discussing the loudness of sound in the ocean or its impacts on the marine environment.
As sound travels from a source, its propagation in water is influenced by various physical characteristics, including water temperature, depth, salinity, and surface and bottom properties that cause refraction, reflection, absorption, and scattering of sound waves. Oceans are not homogeneous and the contribution of each of these individual factors is extremely complex and interrelated. The physical characteristics that determine the sound's speed through the water will change with depth, season, geographic location, and with time of day (as a result, in actual MFAS/HFAS operations, crews will measure oceanic conditions, such as sea water temperature and depth, to calibrate models that determine the path the sonar signal will take as it travels through the ocean and how strong the sound signal will be at a given range along a particular transmission path). As sound travels through the ocean, the intensity associated with the wavefront diminishes, or attenuates
FAS operations, crews will measure oceanic conditions, such as sea water temperature and depth, to calibrate models that determine the path the sonar signal will take as it travels through the ocean and how strong the sound signal will be at a given range along a particular transmission path). As sound travels through the ocean, the intensity associated with the wavefront diminishes, or attenuates. This decrease in intensity is referred to as propagation loss, also commonly called transmission loss.
Metrics Used in This Document
This section includes a brief explanation of the two sound measurements (sound pressure level (SPL) and sound exposure level (SEL)) frequently used in the discussions of acoustic effects in this document.
SPL
Sound pressure is the sound force per unit area, and is usually measured in micropascals (μPa), where 1 Pa is the pressure resulting from a force of one newton exerted over an area of one square meter. SPL is expressed as the ratio of a measured sound pressure and a reference level. The commonly used reference pressure level in underwater acoustics is 1 μPa, and the units for SPLs are dB re: 1 μPa.
SPL (in dB) = 20 log (pressure/reference pressure) SPL is an instantaneous measurement and can be expressed as the peak, the
SEL
SEL is an energy metric that integrates the squared instantaneous sound pressure over a stated time interval. The units for SEL are dB re: 1 μPa 2 -s.
SEL = SPL + 10log(duration in seconds) As applied to MFAS/HFAS, the SEL includes both the SPL of a sonar ping and the total duration. Longer duration pings and/or pings with higher SPLs will have a higher SEL. If an animal is exposed to multiple pings, the SEL in each individual ping is summed to calculate the total SEL. The total SEL depends on the SPL, duration, and number of pings received. The thresholds that NMFS uses to indicate at what received level the onset of temporary threshold shift (TTS) and permanent threshold shift (PTS) in hearing are likely to occur are expressed in SEL
e a higher SEL. If an animal is exposed to multiple pings, the SEL in each individual ping is summed to calculate the total SEL. The total SEL depends on the SPL, duration, and number of pings received. The thresholds that NMFS uses to indicate at what received level the onset of temporary threshold shift (TTS) and permanent threshold shift (PTS) in hearing are likely to occur are expressed in SEL.
Potential Effects of Specified Activities on Marine Mammals
The Navy has requested authorization for the take of marine mammals that may occur incidental to training activities in the GoA TMAA utilizing MFAS/HFAS or underwater detonations. In addition to MFAS/HFAS and underwater detonations, the Navy has analyzed other potential impacts to marine mammals from training activities in the GoA TMAA DEIS, including ship strike, aerial overflights, ship noise and movement, and others, and, in consultation with NMFS as a cooperating agency for the GoA TMAA DEIS, has determined that take of marine mammals incidental to these non-acoustic components of the GoA TMAA is unlikely and, therefore, has not requested authorization for take of marine mammals that might occur incidental to these non-acoustic components. In this document, NMFS analyzes the potential effects on marine mammals from exposure to MFAS/HFAS and underwater detonations, but also includes some additional analysis of the potential impacts from vessel operations in the GoA TMAA.
For the purpose of MMPA authorizations, NMFS' effects assessments serve four primary purposes: (1) To help identify the permissible methods of taking, or the nature of the take ( e.g., resulting from anthropogenic noise vs. from ship strike, etc.); the regulatory level of take ( i.e., mortality vs
includes some additional analysis of the potential impacts from vessel operations in the GoA TMAA.
For the purpose of MMPA authorizations, NMFS' effects assessments serve four primary purposes: (1) To help identify the permissible methods of taking, or the nature of the take ( e.g., resulting from anthropogenic noise vs. from ship strike, etc.); the regulatory level of take ( i.e., mortality vs. Level A or Level B harassment); and the amount of take; (2) to inform the prescription of means of effecting the least practicable adverse impact on such species or stock and its habitat ( i.e., mitigation); (3) to support the determination of whether the specified activity will have a negligible impact on the affected species or stocks of marine mammals (based on the likelihood that the activity will adversely affect the species or stock through effects on annual rates of recruitment or survival); and (4) to determine whether the specified activity will have an unmitigable adverse impact on the availability of the species or stock(s) for subsistence uses.
More specifically, for activities involving sonar or underwater detonations, NMFS' analysis will identify the probability of lethal responses, physical trauma, sensory impairment (permanent and temporary threshold shifts and acoustic masking), physiological responses (particular stress responses), behavioral disturbance (that rises to the level of harassment), and social responses that would be classified as behavioral harassment or injury and/or would be likely to adversely affect the species or stock through effects on annual rates of recruitment or survival. In this section, we will focus qualitatively on the different ways that MFAS/HFAS and underwater explosive detonations may affect marine mammals (some of which NMFS would not classify as harassment)
social responses that would be classified as behavioral harassment or injury and/or would be likely to adversely affect the species or stock through effects on annual rates of recruitment or survival. In this section, we will focus qualitatively on the different ways that MFAS/HFAS and underwater explosive detonations may affect marine mammals (some of which NMFS would not classify as harassment). Then, in the Estimated Take of Marine Mammals Section, NMFS will relate the potential effects to marine mammals from MFAS/HFAS and underwater detonation of explosives to the MMPA regulatory definitions of Level A and Level B Harassment and attempt to quantify those effects.
Exposure to MFAS/HFAS
In the subsections below, the following types of impacts are discussed in more detail: Direct physiological impacts, stress responses, acoustic masking and impaired communication, behavioral disturbance, and strandings. An additional useful graphic tool for better understanding the layered nature of potential marine mammal responses to anthropogenic sound is presented in Figure 11 of NMFS' June 28, 2010, biological opinion for the Mariana Islands Range Complex (available at: http://www.nmfs.noaa.gov/pr/permits/incidental.htm#applications ). That document presents a conceptual model of the potential responses of endangered and threatened species upon being exposed to active sonar and the pathways by which those responses might affect the fitness of individual animals that have been exposed, and the resulting impact on the individual animal's ability to reproduce or survive. Literature supporting the framework, with examples drawn from many taxa (both aquatic and terrestrial) was included in the “Application of this Approach” and “Response Analyses” sections of that document
nd the pathways by which those responses might affect the fitness of individual animals that have been exposed, and the resulting impact on the individual animal's ability to reproduce or survive. Literature supporting the framework, with examples drawn from many taxa (both aquatic and terrestrial) was included in the “Application of this Approach” and “Response Analyses” sections of that document.
Direct Physiological Effects
Based on the literature, there are two basic ways that MFAS/HFAS might directly result in physical trauma or damage: Noise-induced loss of hearing sensitivity (more commonly called “threshold shift”) and acoustically mediated bubble growth. Separately, an animal's behavioral reaction to an acoustic exposure might lead to physiological effects that might ultimately lead to injury or death, which is discussed later in the Stranding section.
Threshold Shift (Noise-Induced Loss of Hearing)
When animals exhibit reduced hearing sensitivity ( i.e., sounds must be louder for an animal to recognize them) following exposure to a sufficiently intense sound, it is referred to as a noise-induced threshold shift (TS). An animal can experience temporary threshold shift (TTS) or permanent threshold shift (PTS). TTS can last from minutes or hours to days ( i.e., there is recovery), occurs in specific frequency ranges ( i.e., an animal might only have a temporary loss of hearing sensitivity between the frequencies of 1 and 10 kHz), and can be of varying amounts ( e.g., an animal's hearing sensitivity might be reduced by only 6 dB or reduced by 30 dB). PTS is permanent ( i.e., there is no recovery), but also occurs in a specific frequency range and amount as mentioned above for TTS
s in specific frequency ranges ( i.e., an animal might only have a temporary loss of hearing sensitivity between the frequencies of 1 and 10 kHz), and can be of varying amounts ( e.g., an animal's hearing sensitivity might be reduced by only 6 dB or reduced by 30 dB). PTS is permanent ( i.e., there is no recovery), but also occurs in a specific frequency range and amount as mentioned above for TTS.
The following physiological mechanisms are thought to play a role in inducing auditory TS: Effects to sensory hair cells in the inner ear that reduce their sensitivity, modification of the chemical environment within the sensory cells, residual muscular activity in the middle ear, displacement of certain inner ear membranes, increased et al., 2007). The amplitude, duration, frequency, temporal pattern, and energy distribution of sound exposure all affect the amount of associated TS and the frequency range in which it occurs. As amplitude and duration of sound exposure increase, so, generally, does the amount of TS, along with the recovery time. Human non-impulsive noise exposure guidelines are based on exposures of equal energy (the same SEL) producing equal amounts of hearing impairment regardless of how the sound energy is distributed in time (NIOSH, 1998). Until recently, previous marine mammal TTS studies have also generally supported this equal energy relationship (Southall et al., 2007). Three newer studies, two by Mooney et al. (2009a, 2009b) on a single bottlenose dolphin either exposed to playbacks of Navy MFAS or octave-band noise (4-8 kHz) and one by Kastak et al. (2007) on a single California sea lion exposed to airborne octave-band noise (centered at 2.5 kHz), concluded that for all noise exposure situations the equal energy relationship may not be the best indicator to predict TTS onset levels. All three of these studies highlight the inherent complexity of predicting TTS onset in marine mammals, as well as the importance of considering exposure duration when assessing potential impacts
lion exposed to airborne octave-band noise (centered at 2.5 kHz), concluded that for all noise exposure situations the equal energy relationship may not be the best indicator to predict TTS onset levels. All three of these studies highlight the inherent complexity of predicting TTS onset in marine mammals, as well as the importance of considering exposure duration when assessing potential impacts. Generally, with sound exposures of equal energy, those that were quieter (lower SPL) with longer duration were found to induce TTS onset more than those of louder (higher SPL) and shorter duration (more similar to MFAS). For intermittent sounds, less TS will occur than from a continuous exposure with the same energy (some recovery will occur between intermittent exposures) (Kryter et al., 1966; Ward, 1997). For example, one short but loud (higher SPL) sound exposure may induce the same impairment as one longer but softer sound, which in turn may cause more impairment than a series of several intermittent softer sounds with the same total energy (Ward, 1997). Additionally, though TTS is temporary, very prolonged exposure to sound strong enough to elicit TTS, or shorter-term exposure to sound levels well above the TTS threshold, can cause PTS, at least in terrestrial mammals (Kryter, 1985) (although in the case of MFAS/HFAS, animals are not expected to be exposed to levels high enough or durations long enough to result in PTS).
PTS is considered auditory injury (Southall et al., 2007). Irreparable damage to the inner or outer cochlear hair cells may cause PTS; however, other mechanisms are also involved, such as exceeding the elastic limits of certain tissues and membranes in the middle and inner ears and resultant changes in the chemical composition of the inner ear fluids (Southall et al., 2007)
gh to result in PTS).
PTS is considered auditory injury (Southall et al., 2007). Irreparable damage to the inner or outer cochlear hair cells may cause PTS; however, other mechanisms are also involved, such as exceeding the elastic limits of certain tissues and membranes in the middle and inner ears and resultant changes in the chemical composition of the inner ear fluids (Southall et al., 2007).
Although the published body of scientific literature contains numerous theoretical studies and discussion papers on hearing impairments that can occur with exposure to a loud sound, only a few studies provide empirical information on the levels at which noise-induced loss in hearing sensitivity occurs in nonhuman animals. For cetaceans, published data on the onset of TTS are limited to the captive bottlenose dolphin and beluga (Finneran et al., 2000, 2002b, 2005a; Schlundt et al., 2000; Nachtigall et al., 2003, 2004). For pinnipeds in water, data are limited to Kastak et al.' s measurement of TTS in one harbor seal, one elephant seal, and one California sea lion.
Marine mammal hearing plays a critical role in communication with conspecifics and in interpretation of environmental cues for purposes such as predator avoidance and prey capture. Depending on the degree (elevation of threshold in dB), duration ( i.e., recovery time), and frequency range of TTS, and the context in which it is experienced, TTS can have effects on marine mammals ranging from discountable to serious (similar to those discussed in auditory masking, below). For example, a marine mammal may be able to readily compensate for a brief, relatively small amount of TTS in a non-critical frequency range that 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
s 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 a time when communication is critical for successful mother/calf interactions could have more serious impacts if it were in the same frequency band as the necessary vocalizations and of a severity that it impeded communication. The fact that animals exposed to levels and durations of sound that would be expected to result in this physiological response would also be expected to have behavioral responses of a comparatively more severe or sustained nature is also notable and potentially of more importance than the simple existence of a TTS.
Also, depending on the degree and frequency range, the effects of PTS on an animal could range in severity, although it is considered generally more serious than TTS because it is a permanent condition. Of note, reduced hearing sensitivity as a simple function of development and 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. There is no empirical evidence that exposure to MFAS/HFAS can cause PTS in any marine mammals; instead, the probability of PTS has been inferred from studies of TTS (see Richardson et al., 1995).
Acoustically Mediated Bubble Growth
One theoretical cause of injury to marine mammals is rectified diffusion (Crum and Mao, 1996), the process of increasing the size of a bubble by exposing it to a sound field
no empirical evidence that exposure to MFAS/HFAS can cause PTS in any marine mammals; instead, the probability of PTS has been inferred from studies of TTS (see Richardson et al., 1995).
Acoustically Mediated Bubble Growth
One theoretical cause of injury to marine mammals is rectified diffusion (Crum and Mao, 1996), the process of increasing the size of a bubble by exposing it to a sound field. This process could be facilitated if the environment in which the ensonified bubbles exist is supersaturated with gas. Repetitive diving by marine mammals can cause the blood and some tissues to accumulate gas to a greater degree than is supported by the surrounding environmental pressure (Ridgway and Howard, 1979). The deeper and longer dives of some marine mammals ( e.g., beaked whales) are theoretically predicted to induce greater supersaturation (Houser et al., 2001b), although recent preliminary empirical data suggests that there is no increase in blood nitrogen levels or formation of bubbles in diving bottlenose dolphins (Houser, 2008). If rectified diffusion were possible in marine mammals exposed to high-level sound, conditions of tissue supersaturation could theoretically speed the rate and increase the size of bubble growth. Subsequent effects due to tissue trauma and emboli would presumably mirror those observed in humans suffering from decompression sickness.
It is unlikely that the short duration of MFAS pings would be long enough to drive bubble growth to any substantial size, if such a phenomenon occurs. However, an alternative but related hypothesis has also been suggested; stable bubbles could be destabilized by high-level sound exposures such that bubble growth then occurs through static diffusion of gas out of the tissues. In such a scenario the marine mammal would need to be in a gas-supersaturated state for a long enough period of time for bubbles to become of a problematic size
enon occurs. However, an alternative but related hypothesis has also been suggested; stable bubbles could be destabilized by high-level sound exposures such that bubble growth then occurs through static diffusion of gas out of the tissues. In such a scenario the marine mammal would need to be in a gas-supersaturated state for a long enough period of time for bubbles to become of a problematic size.
Yet another hypothesis (decompression sickness) speculates that rapid ascent to the surface following exposure to a startling sound et al., 2003; Fernandez et al., 2005). In this scenario, the rate of ascent would need to be sufficiently rapid to compromise behavioral or physiological protections against nitrogen bubble formation. Alternatively, Tyack et al. (2006) studied the deep diving behavior of beaked whales and concluded that: “Using current models of breath-hold diving, we infer that their natural diving behavior is inconsistent with known problems of acute nitrogen supersaturation and embolism.” Collectively, these hypotheses can be referred to as “hypotheses of acoustically mediated bubble growth.”
Although theoretical predictions suggest the possibility for acoustically mediated bubble growth, there is considerable disagreement among scientists as to its likelihood (Piantadosi and Thalmann, 2004; Evans and Miller, 2003; Cox et al., 2006; Rommel et al., 2006). Crum and Mao (1996) hypothesized that received levels would have to exceed 190 dB in order for there to be the possibility of significant bubble growth due to supersaturation of gases in the blood ( i.e., rectified diffusion). More recent work conducted by Crum et al. (2005) demonstrated the possibility of rectified diffusion for short duration signals, but at SELs and tissue saturation levels that are highly improbable to occur in diving marine mammals. To date, energy levels (ELs) predicted to cause in vivo bubble formation within diving cetaceans have not been evaluated (NOAA, 2002b)
ood ( i.e., rectified diffusion). More recent work conducted by Crum et al. (2005) demonstrated the possibility of rectified diffusion for short duration signals, but at SELs and tissue saturation levels that are highly improbable to occur in diving marine mammals. To date, energy levels (ELs) predicted to cause in vivo bubble formation within diving cetaceans have not been evaluated (NOAA, 2002b). Although it has been argued that traumas from some recent beaked whale strandings are consistent with gas emboli and bubble-induced tissue separations (Jepson et al., 2003), there is no conclusive evidence of this (Rommel et al., 2006). However, Jepson et al. (2003, 2005) and Fernandez et al. (2004, 2005) concluded that in vivo bubble formation, which may be exacerbated by deep, long-duration, repetitive dives, may explain why beaked whales appear to be particularly vulnerable to MFAS/HFAS exposures. Further investigation is needed to further assess the potential validity of these hypotheses. More information regarding hypotheses that attempt to explain how behavioral responses to MFAS/HFAS can lead to strandings is included in the Behaviorally Mediated Bubble Growth Section, after the summary of strandings.
Acoustic Masking
Marine mammals use acoustic signals for a variety of purposes, which differ among species, but include communication between individuals, navigation, foraging, reproduction, and learning about their environment (Erbe and Farmer, 2000; Tyack, 2000). Masking, or auditory interference, generally occurs when sounds in the environment are louder than, and of a similar frequency as, auditory signals an animal is trying to receive. Masking is a phenomenon that affects animals that are trying to receive acoustic information about their environment, including sounds from other members of their species, predators, prey, and sounds that allow them to orient in their environment. Masking these acoustic signals can disturb the behavior of individual animals, groups of animals, or entire populations
an animal is trying to receive. Masking is a phenomenon that affects animals that are trying to receive acoustic information about their environment, including sounds from other members of their species, predators, prey, and sounds that allow them to orient in their environment. Masking these acoustic signals can disturb the behavior of individual animals, groups of animals, or entire populations.
The extent of the masking interference depends on the spectral, temporal, and spatial relationships between the signals an animal is trying to receive and the masking noise, in addition to other factors. In humans, significant masking of tonal signals occurs as a result of exposure to noise in a narrow band of similar frequencies. As the sound level increases, the detection of frequenci

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