Modern sonar technology includes 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 sonar emits an omnidirectional ping and then rapidly scans a steered receiving beam to provide directional, as well as range, information. More advanced sonars transmit multiple preformed beams, listening to echoes from several directions simultaneously and providing efficient detection of both direction and range.

The tactical military sonars to be deployed during testing and training in the HRC are designed to detect submarines in tactical training scenarios. This task requires the use of the sonar mid frequency range (1 kilohertz [kHz] to 10 kHz) predominantly, as well as one source in the high frequency range (above 10 kHz) that operates at a level high enough to be considered in the modeling. The high frequency source will contribute a comparatively very small amount to the total amount of active sonar that marine mammals will be exposed to during the Navy's proposed activities, however, for this document we will refer to the collective high and midfrequency sonar sources as MFAS/HFAS. A narrative description of the types of acoustic sources used in ASW training exercises is included below. Table 1 (below) summarizes the nominal characteristics of the acoustic sources used in the modeling to predict take of marine mammals.
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Surface Ship SonarsA variety of surface ships participate in testing and training events. Some ships (e.g., aircraft carriers, amphibious assault ships) do not have any onboard active sonar systems, other than fathometers. Others, like guided missile cruisers, are equipped with active as well as passive tactical sonars for mine avoidance and submarine detection and tracking. Within Navy ASW exercises in the HRC, two types of hullmounted sonar sources account for the majority of the estimated impacts to marine mammals. The AN/ SQS53 hullmounted sonar, which has a nominal source level of 235 decibels (dB) re 1 [mu]Pa and transmits at center frequencies of 2.6 kHz and 3.3 kHz, is the Navy's most powerful sonar source used in ASW exercises in the HRC. The AN/SQS56 hullmounted sonar has a nominal source level of 225 dB re 1 [mu]Pa and transmits at a center frequency of 7.5 kHz. Sonar ping transmission durations were modeled as lasting 1 second per ping and omnidirectional, which is a conservative assumption that may overestimate potential effects. Actual ping durations will be less than 1 second. Details concerning the tactical use of specific frequencies and the repetition rate for the sonar pings is classified but was modeled based on the required tactical training setting. The AN/SQS53 and the AN/SQS56 were modeled using the number of hours of predicted use (typically at two pings per minute; meaning an hour of sonar operation results in approximately 120 onesecond pings). Based on modeling results, the Navy anticipates that the operation of these two sources will likely result in take of marine mammals (see Estimated Take of Marine Mammals Section).

Hullmounted sonars occasionally operate in a mode called ``Kingfisher,'' which is designed to better detect smaller objects. The Kingfisher mode uses the same source level and frequency as normal search modes, however, it uses a different waveform (designed for small objects), a shorter pulse length (< 1 sec), a higher pulse repetition rate (due to the short ranges), and the ping is not omnidirectional, but directed forward. All Kingfisher use in the HRC (approximately 27 hours/year) was modeled as AN/SQS53, though the less powerful AN/SQS 56 likely accounts for part of the total Kingfisher use as well.

Submarine SonarsSubmarine sonars (AN/BQQ10, AN/BQQ5, or AN/BSY 1) are used to detect and target enemy submarines and surface ships. Because they are trying to avoid being detected, a submarine's use of MFAS is generally rare, very brief, using minimal power, and may be narrowly focused. Modeling for the AN/BQQ10 (all three submarine types were modeled as AN/BQQ10, the most powerful submarine sonar source) assumes sonar use of two pings an hour (which is higher than typical), for one second each, at 235 dB re 1 [mu]Pa, and using an omni directional transmission. The AN/BQQ10 was modeled using the number of hours of predicted use (at two pings per hour). Based on modeling results, the Navy anticipates that the operation of this source may result in some take of marine mammals (see Estimated Take of Marine Mammals Section).

Aircraft Sonar SystemsAircraft sonar systems that would operate in the HRC include sonobuoys (SSQ62) and dipping sonar (AN/AQS22). A sonobuoy is an expendable device, which may be deployed by maritime patrol aircraft or helicopters, used for the detection of underwater acoustic energy and for conducting vertical water column temperature measurements. Most sonobuoys are passive, but some, like the SSQ62, can also generate active acoustic signals. The SSQ62 has a nominal source level of 201 dB re 1 [mu]Pa and transmits at a center frequency of 8 kHz. Dipping sonar is an active or passive sonar device lowered on cable 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. The AN/AQS22 has a nominal source level of 217 dB re 1 [mu]Pa and transmits at a center frequency of 4.1 kHz. Based on modeling results, the Navy anticipates that the operation of these two sources may result in some take of marine mammals (see Estimated Take of Marine Mammals Section).

TorpedoesTorpedoes are the primary ASW weapon used by surface ships, aircraft, and submarines. The guidance systems of these weapons can be autonomous (acoustically based) or electronically controlled from the launching platform through an attached wire. They operate either passively, exploiting the emitted sound energy by the target, or actively, ensonifying the target and using the received echoes for guidance. We know that the MK48 operates in the high frequency range (>10 kHZ), however, the nominal source level and the center frequency are classified. Based on modeling results, the Navy anticipates that the operation of this source may result in some take of marine mammals (see Estimated Take of Marine Mammals Section). In addition to the HFA sonar source used to guide the torpedo, the MK48 is discussed in the ``Activities Utilizing Underwater Detonations'' Section.

Other Acoustic SourcesThe Navy uses other acoustic sources in ASW exercises. However, based on operational characteristics (such as frequency and source level), the Navy determined that use of the following acoustic sources would not likely result in the take of marine mammals:

Types of ASW Exercises in the HRC

ASW training conducted within the HRC involves the use of surface ships, submarines, aircraft, nonexplosive and explosive exercise weapons, and other trainingrelated devices. ASW training involves the use of active and passive acoustic devices with training activities occurring in both offshore (<12 nm (22 km) from shore) and open ocean (>12 nm (22 km) from shore) areas. A description of the different exercise types is provided below. Table 2 lists the types of ASW exercises and indicates the areas they are conducted in, the average duration of an exercise, the average number of exercises/per year, and the time of year they are conducted. Table 3, at the end of this section, indicates the total number of hours for each source type anticipated for each year for each exercise type.

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AntiSubmarine Warfare Tracking Exercise (ASW TRACKEX)An ASW TRACKEX trains aircraft, ship, and submarine crews in tactics, techniques, and procedures for search, detection, and tracking of submarines. No torpedoes are fired during a TRACKEX. ASW TRACKEX includes ships, fixed wing aircraft, helicopters, torpedo targets, submarines, and weapons recovery boats and/or helicopters. As a unit level exercise, an aircraft, ship, or submarine is typically used versus one target submarine or simulated target. TRACKEXs can include the use of hullmounted sonar, submarines, or sonobuoys. No explosive ordnance is used in TRACKEX exercises.

The target may be nonevading while operating on a specified track or it may be fully evasive, depending on the state of training of the ASW unit. Duration of a TRACKEX is highly dependent on the tracking platform and its available onstation time. A maritime patrol aircraft can remain on station for eight hours, and typically conducts tracking exercises that last three to six hours. An ASW helicopter has a much shorter onstation time, and conducts a typical TRACKEX in one to two hours. Surface ships and submarines, which measure their onstation time in days, conduct tracking exercises exceeding eight hours and averaging up to 18 hours. For modeling purposes, TRACKEX and TORPEX (explained in next section) sonar hours are averaged, resulting in a sonar time of 13.5 hours.

ASW TRACKEX events are conducted on ranges within PMRF Warning Area W188, the Hawaii Offshore Areas and/or the open ocean. Whenever aircraft use the ranges for ASW training, range clearance procedures include a detailed visual range search for marine mammals and unauthorized boats and planes by the aircraft releasing the inert torpedoes, range safety boats/aircraft, and range controllers. TRACKEXs can include the use of hullmounted sonar, submarines, or sonobuoys, which can result in the take of marine mammals.

AntiSubmarine Warfare Torpedo Exercises (ASW TORPEX)Anti Submarine Warfare Torpedo Exercises (ASW TORPEX) train crews in tracking and attack of submerged targets, firing one or more Recoverable Exercise Torpedoes. TORPEX targets used in the Offshore Areas include submarines, MK30 ASW training targets, and MK39 Expendable Mobile ASW Training Targets. The target may be nonevading while operating on a specified track, or it may be fully evasive, depending on the training requirements. Submarines periodically conduct torpedo firing training exercises within the Hawaii Offshore OPAREA. Typical duration of a submarine TORPEX event is 22.7 hours, while air and surface ASW platform TORPEX events are considerably shorter. For modeling purposes, TRACKEX and TORPEX sonar hours are averaged resulting in a sonar time of 13.5 hours. TORPEXs can
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include the use of hullmounted sonar, submarines, sonobuoys, or MK48 torpedoes (inert), which can result in the take of marine mammals.

Rim of the Pacific (RIMPAC)RIMPAC is a multithreat maritime exercise where submarines, surface ships, and aircraft from the U.S. and other countries conduct many different exercise events, including ASW against opposition submarine targets to improve coordination and interoperability of combined, bilateral and joint forces of participating nations. RIMPAC occurs during the summer over a 1month period every other year (currently in even numbered years). Submarine targets include real submarines, targets that simulate the operations of an actual submarine including those described previously under TORPEX, and virtual submarines interjected into the training events by exercise controllers. ASW training events are complex and highly variable. For RIMPAC, the primary event involves a Surface Action Group (SAG), consisting of one to five surface ships equipped with sonar, with one or more helicopters, and a P3 aircraft searching for one or more submarines. There will be approximately four to eight SAGs for a typical RIMPAC. For the purposes of analysis, each SAG event is counted as an ASW training activity. One or more ASW events may occur simultaneously within the HRC. There will be approximately 44 ASW training events during a typical RIMPAC, with an average event length of approximately 12 hours (ranging from 224 hours).

In addition to including potential training with of all of the acoustic sources mentioned previously, RIMPAC includes training events that involve underwater detonations (described in the next section: Activities Utilizing Underwater Detonations), including Sinking Exercise, AirtoSurface Gunnery Exercise, SurfacetoSurface Gunnery Exercise, Naval Surface Fire Support, AirtoSurface Missile Exercise, SurfacetoSurface Missile Exercise, Bombing Exercise, Mine
Neutralization Exercise, and IEER/EER Exercise. Both the use of the acoustic sources as well as the underwater detonations could result in the take of marine mammals. These exercises involving underwater detonations do not overlap in space and time with sonar exercises. Explosives from RIMPAC have been included in the training events described in the next Section.

Undersea Warfare Exercise (USWEX)Carrier Strike Groups (CSGs) and Expeditionary Strike Groups (ESGs) that deploy from the west coast of the United States will experience realistic submarine combat conditions and assess submarine warfare training capabilities postures in the HRC prior to their deployment to real world operations elsewhere. As a combined force, submarines, surface ships, and aircraft will conduct ASW against opposition submarine targets, which include real submarines, targets that simulate the operations of an actual submarine, and virtual submarines interjected into the training events by exercise controllers. USWEX training events are complex and highly variable. The primary event involves from one to five surface ships equipped with sonar, with one or more helicopters, and a P3 aircraft searching for one or more submarines. A total of five exercises using MFAS/HFAS, lasting three to four days each, could occur throughout the year for USWEX.

In addition to the use of hullmounted sonar (AN/SQS53 and AN/SQS 56), submarine sonar, helicopter dipping sonar, and sonobuoys, USWEX includes training events that involve underwater detonations as described in the next section (Activities Utilizing Underwater Detonations), including AirtoSurface Gunnery Exercise, AirtoSurface Missile Exercise, and Bombing Exercise. Both the use of the acoustic sources as well as the underwater detonations could result in the take of marine mammals. These exercises utilizing underwater detonations do not overlap in space and time with sonar exercises. Explosives from USWEX have been included in the training events described in the next section.

Multiple Strike Group ExerciseA Multiple Strike Group Exercise consists of events that involve Navy assets engaging in a schedule of events battle scenario, with U.S. forces (blue forces) pitted against a notional opposition force (red force). Participants use and build upon previously gained training skill sets to maintain and improve the proficiency needed for a missioncapable, deploymentready unit. The exercise would occur over a 5day to 10day period at any time during the year. As described above for USWEX, as a combined force, submarines, surface ships, and aircraft will conduct ASW against opposition submarine targets.

In addition to the use of hullmounted sonar (AN/SQS53 and AN/SQS 56), submarine sonar, helicopter dipping sonar, and sonobuoys , the Multiple Strike Group Exercise includes training events that involve underwater detonations as described in the next Section (Activities Utilizing Underwater Detonations), including Sinking Exercise, Airto Surface Missile Exercise, Mine Neutralization Exercise, and EER/IEER Exercise. Both the use of the acoustic sources as well as the underwater detonations could result in the take of marine mammals. These exercises utilizing underwater detonations do not overlap in space and time with sonar exercises. Explosives from the Multiple Strike Group Exercise have been included in the events described in the next Section.
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Activities Utilizing Underwater Detonations

Underwater detonation activities can occur at various depths depending on the activity (sinking exercise [SINKEX] and mine neutralization), but may also include activities which may have detonations at or just below the surface (SINKEX, gunnery exercise [GUNEX], or missile exercise [MISSILEX]). When the weapons hit the target except for live torpedo shot, 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 as exploding below the water surface at 1 ft (5inch naval gunfire, 76mm rounds), 2 meters (Maverick, Harpoon, MK82, MK83, MK 84), or 50ft (MK48 torpedo) as shown in Appendix A of the Navy's application, Table A7 (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 4. Additionally, successful hit rates are known to the Navy and are utilized in the effects modeling. Training events that involve explosives and underwater detonations occur throughout the year and are described below and summarized in Table 5 at the end of this section.

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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 submarine and aircraft crews in delivering both live and inert ordnance on a real target. These target vessels are remediated to standards set by the Environmental Protection Agency. 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 four to eight hours over one to two days. SINKEXs typically occur only once or twice a year in the HRC.
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Underwater detonation of several different explosive types could result in the take of marine mammals. Some or all of the following weapons may be employed in a SINKEX: Three HARPOON surfacetosurface and airto surface missiles; two to eight airtosurface Maverick missiles; two to four MK82 General Purpose Bombs; two Hellfire airtosurface missiles; one SLAMER airtosurface missile; twohundred and fifty rounds for a 5inch gun; and one MK48 heavyweight submarinelaunched torpedo.

SurfacetoSurface Gunnery Exercise (SS GUNEX)Surface gunnery exercises (GUNEX) take place in the open ocean to provide gunnery practice for Navy and Coast Guard ship crews. GUNEX training events conducted in the Offshore OPAREA involve stationary targets such as a MK42 FAST or a MK58 marker (smoke) buoy. The gun systems employed against surface targets include the 5inch, 76 millimeter (mm), 25mm chain gun, 20mm Closein Weapon System (CIWS), and .50 caliber machine gun. Typical ordnance expenditure for a single GUNEX is a minimum of 21 rounds of 5inch or 76mm ammunition, and approximately 150 rounds of 25mm or .50caliber ammunition. Both live and inert training rounds are used. After impacting the water, the rounds and fragments sink to the bottom of the ocean. A SS GUNEX lasts approximately two to four hours, depending on target services and weather conditions. Detonation of the live 5inch and 76mm rounds could result in the take of marine mammals.

Naval Surface Fire Support ExerciseNavy surface combatants conduct fire support exercise (FIREX) training events at PMRF on a virtual range against ``Fake Island'', located on Barking Sands Tactical Underwater Range (BARSTUR). Fake Island is unique in that it is a virtual landmass simulated in three dimensions. Ships conducting FIREX training against targets on the island are given the coordinates and elevation of targets. PMRF is capable of tracking fired rounds to an accuracy of 30 feet (9.1 m). Detonation of the live 5inch and 76mm rounds fired into ocean during this exercise could result in the take of marine mammals.

AirtoSurface Missile Exercise (AS MISSILEX)The AS MISSILEX consists of the attacking platform releasing a forwardfired, guided weapon at the designated towed target. The exercise involves locating the target, then designating the target, usually with a laser.

AS MISSILEX training can take place without the release of a live weapon if the attacking platform is carrying a captive air training missile (CATM) simulating the weapon involved in the training. The CATM MISSILEX is identical to a livefire exercise in every aspect except that a weapon is not released, nor does it contain any explosives or propellant. The event requires a lasersafe range as the target is designated just as in a livefire exercise.

From 1 to 16 aircraft, carrying live, inert, or CATMs, or flying without ordnance (dry runs) are used during the exercise. At sea, seaborne powered targets (SEPTARs), Improved Surface Towed Targets (ISTTs), and decommissioned hulks are used as targets. AS MISSILEX assets include helicopters and/or one to 16 fixed wing aircraft with airtosurface missiles and antiradiation missiles (electromagnetic radiation source seeking missiles). When a highspeed antiradiation missile (HARM) is used, the exercise is called a HARMEX. Targets include SEPTARs, ISTTs, and decommissioned ship hulks. Detonation of live ordnance could result in the take of marine mammals.

SurfacetoSurface Missile Exercise (SS MISSILEX)Surfaceto surface missile exercise (SS MISSILEX) involves the attack of surface targets at sea by use of cruise missiles or other missile systems, usually by a single ship conducting training in the detection, classification, tracking and engagement of a surface target. Engagement is usually with Harpoon missiles or Standard missiles in the surface tosurface mode. Targets could include virtual targets or the SEPTAR or ship deployed surface target. SS MISSILEX training is routinely conducted on individual ships with embedded training devices. A SS MISSILEX could include four to 20 surfacetosurface missiles, SEPTARs, a weapons recovery boat, and a helicopter for environmental and photo evaluation. All missiles are equipped with instrumentation packages or a warhead. Surfacetoair missiles can also be used in a surfaceto surface mode. SS MISSILEX activities are conducted within PMRF Warning area W188. Each exercise typically lasts five hours, though future SS MISSILEXs could range from four to 35 hours. Missile detonation could result in the take of marine mammals.

Bombing Exercise (BOMBEX)Fixedwing aircraft conduct BOMBEX events against stationary targets (MK42 FAST or MK58 smoke buoy) at sea. An aircraft will clear the area, deploy a smoke buoy or other floating target, and then set up a racetrack pattern, dropping on the target with each pass. At PMRF, a range boat might be used to deploy the target for an aircraft to attack. A BOMBEX may involve either live or inert ordnance. Underwater detonation of live ordnance could result in the take of marine mammals.

Mine NeutralizationMine Neutralization events involve the detection, identification, evaluation, rendering safe, and disposal of mines and unexploded ordnance (UXO) that constitutes a threat to ships or personnel. Mine neutralization training can be conducted by a variety of air, surface and subsurface assets. Tactics for neutralization of ground or bottom mines involve a diver placing a specific amount of explosives, which when detonated underwater at a specific distance from a mine results in neutralization of the mine. Floating, or moored, mines involve the diver placing a specific amount of explosives directly on the mine. Floating mines encountered by Fleet ships in open ocean areas will be detonated at the surface. Inert dummy mines are used in the exercises. The total net explosive weight used against each mine ranges from less than one pound to 20 pounds (0.5 to 9.1 kg). Mine neutralization training takes place offshore in Puuloa Underwater Range, Lima Landing, Naval Inactive Ship Maintenance Facility, MCBH, MCTAB, Barters Point Range, Ewa Training Minefield; and in openocean areas. Detonation of live ordnance could result in the take of marine mammals.

All demolition activities are conducted in accordance with current Navy directives and approved standard operating procedures. Before any explosive is detonated, divers are transported a safe distance away from the explosive. Standard practices for tethered mines in Hawaiian waters require ground mine explosive charges to be suspended 10 feet (3.0 m) below the surface of the water.

EER/IEER AN/SSQ110AThe Extended Echo Ranging and Improved Extended Echo Ranging (EER/IEER) Systems are airlaunched 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 component, the AN/SSQ110A Sonobuoy, would generate a ``ping'' (small detonation) and the passive AN/SSQ101 ADAR Sonobuoy would ``listen'' 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 [[Page 35517]]
and accurately detect submerged submarines. The expendable and commandable sonobuoy pairs are dropped from a fixedwing aircraft into the ocean in a predetermined pattern (array) with a few buoys covering a very large area. 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 generating a ``ping''. There is only one detonation in the pattern of buoys at a time. Detonation of the buoys could result in the take of marine mammals.

AirtoSurface Gunnery Exercise (AS GUNEX)AirtoSurface GUNEX events are conducted by rotarywing aircraft against stationary targets (Floating atsea Target [FAST] and smoke buoy). Rotarywing aircraft involved in this training activity would include a single SH60 using either 7.62mm or .50caliber doormounted machine guns. A typical AS GUNEX will last approximately one hour and involve the expenditure of approximately 400 rounds of 50caliber or 7.62mm ammunition. Due to the use of small, inert rounds, AS GUNEXs are not expected to result in the take of marine mammals.

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Additional information on the Navy's proposed activities may be found in the LOA Application and the FEIS (Section 2 and Appendices D, E, and J).
Description of Marine Mammals in the Area of the Specified Activities

There are 27 marine mammal species with possible or confirmed occurrence in the HRC. As indicated in Table 6, there are 25 cetacean species (7 mysticetes and 18 odontocetes) and two pinnipeds. Table 6 also includes the estimated abundance, estimated group size, and estimated probability of detection (based on Barlow 2006) of the species that occur in the HRC. Seven marine mammal species listed as federally endangered under the Endangered Species Act (ESA) occur in the HRC: the humpback whale, North Pacific right whale, sei whale, fin whale, blue whale, sperm whale, and Hawaiian monk seal. The most abundant marine mammals appear to be dwarf sperm whales, striped dolphins, and Fraser's dolphins. The most abundant large whales are sperm whales.
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The Navy has compiled information on the abundance, behavior, status and distribution, and vocalizations of marine mammal species in the Hawaiian waters from peer reviewed literature, the Navy Marine Resource Assessment, NMFS Stock Assessment Reports, and marine mammal surveys using acoustics or visual observations from aircraft or ships. This information may be viewed in the Navy's LOA application and/or the Navy's FEIS for the HRC (see Availability). Additional information is available in NMFS Stock Assessment Reports, which may be viewed at: http://www.nmfs.noaa.gov/pr/sars/species.htm.

Based on their rare occurrence in the HRC, the Navy and NMFS do not anticipate any effects to Blue whales, North Pacific right whales, or Northern elephant seals and, therefore, they are not addressed further in this document.

Important Reproductive Areas

Because the consideration of areas where marine mammals are known to selectively breed or calve are important to both the negligible impact finding necessary for the issuance of an MMPA authorization and the need for NMFS to put forth the means of effecting the least practicable adverse impact paying particular attention to rookeries, mating grounds, and other areas of similar significance, we are emphasizing important reproductive areas within this section. Little is known about the breeding and calving behaviors of many of the marine mammals that occur in the HRC. Some delphinid species have calving peaks once or twice a year, but give birth throughout their ranges. The mysticete species that may occur in the HRC are generally thought to migrate from higher to lower latitudes to breed and calve in the winter. With one notable exception, no breeding or calving areas have been identified in the HRC for the species that occur there. However, the main Hawaiian Islands constitute one of the world's most important habitats for the endangered humpback whale. Nearly twothirds of the entire North Pacific population of humpback whales migrates to Hawaii each winter to engage in breeding, calving and nursing activities important for the survival of their species. The available sighting information and the known preferred breeding habitat (shallow water) indicates that humpback whale densities are much higher (up to almost four whales/square mile) in certain areas and that humpback mothers and calves are concentrated within the 200m isobath. The Hawaiian Humpback Whale National Marine Sanctuary worked with Dr. Joe Mobley to compile a figure that generally illustrates humpback whale survey data collected between 1993 and 2003 and indicates areas of high and low density (Mobley 2004, Figure 1).
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A 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 sonar 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 through a unit area in a specified direction and is expressed in watts per square meter (W/m\2\). Acoustic intensity is rarely measured directly, it is derived from ratios of pressures; the standard reference pressure for underwater sound is 1 microPascal ([mu]Pa); for airborne sound, the standard reference pressure is 20 [mu]Pa (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 [mu]Pa or, for airborne sound, 20 [mu]Pa). The logarithmic nature of the scale means that each 10 dB increase is a tenfold increase in power (e.g., 20 dB is a 100fold increase, 30 dB is a 1,000fold increase). Humans perceive a 10dB increase in noise as a doubling of sound level, or a 10 dB decrease in noise as a halving of sound level. 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: 1 [mu]Pa) 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. To estimate a comparison between sound in air and underwater, because of the different densities of air and water and the different decibel standards (i.e., reference pressures) in water and air, 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 is 160 dB loud underwater would have the same approximate effective intensity as a sound that is 97 dB loud in air.

Sound frequency is measured in cycles per second, or Hertz (abbreviated Hz), and is analogous to musical pitch; highpitched sounds contain high frequencies and lowpitched 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 and ultrasonic 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''; airguns are an example of a broadband sound source and 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, anatomical modeling, and other data, Southall et al. (2007) designate ``functional hearing groups'' 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 Mweighting functions developed for each group. More specific data is available for certain species (Table 17). The functional groups and the associated frequencies are indicated below:

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 away from its source, its loudness decreases as the distance traveled (propagates) 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 three kilometers 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. As a result, it is important not to confuse source levels and received levels when discussing the loudness of sound in the ocean.

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 sonar 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 ([mu]Pa), where 1 Pa is the pressure resulting from a force of one newton exerted over an area of one
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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 [mu]Pa, and the units for SPLs are dB re: 1 [mu]Pa.

SPL (in dB) = 20 log (pressure/reference pressure)

SPL is an instantaneous measurement and can be expressed as the peak, the peakpeak, or the root mean square (rms). Root mean square, which is the square root of the arithmetic average of the squared instantaneous pressure values, is typically used in discussions of the effects of sounds on vertebrates and all references to SPL in this document refer to the root mean square. SPL does not take the duration of a sound into account. SPL is the applicable metric used in the risk continuum, which is used to estimate behavioral harassment takes (see Level B Harassment Risk Function (Behavioral Harassment) Section). 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 [mu]Pa\2\s.

SEL = SPL + 10log(duration in seconds)

As applied to tactical sonar, 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.
Potential Effects of Specified Activities on Marine Mammals Exposure to MFAS/HFAS

The Navy has requested authorization for the take of marine mammals that may occur incidental to training activities in the HRC utilizing MFAS/HFAS or underwater explosives. The Navy has analyzed other Navy activities in the HRC, both ongoing and proposed, and in consultation with NMFS as a cooperating agency for the HRC EIS, has determined that take of marine mammals incidental to other Navy activities is unlikely and, therefore, has not requested authorization for take of marine mammals that might occur incidental to any other activities. Therefore, NMFS will analyze the potential effects on marine mammals from MFAS/ HFAS and underwater detonations, but not from other activities.

For the purposes of MMPA authorizations, NMFS's effects assessments have three primary purposes: (1) To put forth the permissible methods of taking within the context of MMPA Level B Harassment (behavioral harassment), Level A Harassment (injury), and mortality (i.e., identify the number and types of take that will occur); (2) to determine 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 (3) to determine whether the specified activity will have an unmitigable adverse impact on the availability of the species or stock(s) for subsistence uses (however, there are no subsistence communities that would be affected in the HRC, so this determination is inapplicable for the HRC).

More specifically, for activities involving active tactical sonar or underwater detonations, NMFS's 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). 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.

In its April 14, 2008, Biological Opinion of the U.S. Navy's proposal to conduct four training exercises in the Cherry Point, Virginia Capes, and Jacksonville, Range Complexes NMFS presented 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, which may then affect the reproduction and/or survival of those individuals. 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 (available at: http:// www.nmfs.noaa.gov/pr/permits/incidental.htm). This conceptual framework may also be used to describe the responses and pathways for non endangered and nonthreatened species and is included in this document for reference (Figure 2).
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Direct Physiological Effects

Based on the literature, there are two basic ways that MFAS/HFAS might directly result in physical trauma or damage: Noiseinduced loss of hearing sensitivity (more commonlycalled ``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 (NoiseInduced 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 noiseinduced 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 (for example, 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.

The following physiological mechanisms are thought to play a role in inducing auditory TSs: 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 blood flow, and poststimulatory reduction in both efferent and sensory neural output (Southall 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. For continuous sounds, exposures of equal energy (the same SEL) will lead to approximately equal effects. For intermittent sounds, less TS will occur than from a continuous exposure with the same energy (some recovery will occur between 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).

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 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 is 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 interpreting environmental cues for purposes such as predator avoidance and prey capture. Depending on the degree (dB), duration, and frequency range of TTS, and the context in which it is experienced, TTS can have effects on marine mammals ranging from discountable to serious (similar to those discussed in auditory masking, below). For example, a marine mammal may be able to readily compensate for a brief, relatively small amount of TTS in a non critical frequency range that takes place during a time when the animal is traveling through the open ocean, where ambient noise is lower and there are not as many competing sounds present. Alternatively, a larger amount and longer duration of TTS sustained during time when communication is critical for successful mother/calf interactions could have more serious impacts. 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 because it is a long term 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. 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 (for example, beaked whales) are theoretically predicted to induce greater supersaturation (Houser et al., 2001b). If rectified diffusion were possible in marine mammals exposed to highlevel 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 sonar pings would be long enough to drive bubble growth to any substantial size, if such a phenomenon occurs. Recent work conducted by Crum et al. (2005) demonstrated the possibility of rectified diffusion for short duration signals, but at sound exposure levels and tissue saturations levels that are improbable to occur in a diving marine mammal. However, an alternative but related hypothesis has also been suggested: Stable bubbles could be destabilized by highlevel 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 gassupersaturated state for a long enough period of time for bubbles to become of a problematic size. Yet
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another hypothesis (decompression sickness) has speculated that rapid ascent to the surface following exposure to a startling sound might produce tissue gas saturation sufficient for the evolution of nitrogen bubbles (Jepson 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. 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). 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). 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. However, Jepson et al. (2003, 2005) and Fernandez et al. (2004, 2005) concluded that in vivo bubble formation, which may be exacerbated by deep, longduration, repetitive dives may explain why beaked whales appear to be particularly vulnerable to sonar 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,

FOR FURTHER INFORMATION CONTACT Jolie Harrison, Office of Protected Resources, NMFS, (301) 7132289, ext. 166.