Small Takes of Marine Mammals Incidental to Specified Activities; Rim of the Pacific (RIMPAC) Antisubmarine Warfare (ASW) Exercise Training Events Within the Hawaiian Islands Operating Area (OpArea), 20986-21003 [06-3831]

Agencies

• DEPARTMENT OF COMMERCE
• National Oceanic and Atmospheric Administration

[Federal Register Volume 71, Number 78 (Monday, April 24, 2006)]
[Notices]
[Pages 20986-21003]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 06-3831]


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DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

[I.D. 011806L]


Small Takes of Marine Mammals Incidental to Specified Activities; 
Rim of the Pacific (RIMPAC) Antisubmarine Warfare (ASW) Exercise 
Training Events Within the Hawaiian Islands Operating Area (OpArea)

AGENCY: National Marine Fisheries Service (NMFS), National Oceanic and 
Atmospheric Administration (NOAA), Commerce.

ACTION: Notice; receipt of application and proposed incidental take 
authorization; request for comments.

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SUMMARY: NMFS has received an application from the U.S. Navy (Navy) for 
an Incidental Harassment Authorization (IHA) to take marine mammals, by 
harassment, incidental to conducting RIMPAC ASW training events, in 
which submarines, surface ships, and aircraft from the United States 
and multiple foreign nations participate in ASW training exercises, 
utilizing mid-frequency sonar (1 kilohertz (kHz) to 10 kHz), in the 
U.S. Navy's Hawaiian Operating Area (OpArea) in the summer of 2006. 
Pursuant to the Marine Mammal Protection Act (MMPA), NMFS is requesting 
comments on its proposal to issue an authorization to the Navy to 
incidentally harass several species of marine mammals during the 
training exercises.

DATES: Comments and information must be received no later than May 24, 
2006.

ADDRESSES: Comments on the application should be addressed to Steve 
Leathery, Chief, Permits, Conservation and Education Division, Office 
of Protected Resources, National Marine Fisheries Service, 1315 East-
West Highway, Silver Spring, MD 20910-3225. The mailbox address for 
providing email comments is PR1.011806L@noaa.gov. NMFS is not 
responsible for e-mail comments sent to addresses other than the one 
provided here. Comments sent via e-mail, including all attachments, 
must not exceed a 10-megabyte file size.
    A copy of the application containing a list of the references used 
in this document may be obtained by writing to the address specified 
above, telephoning the contact listed below (see FOR FURTHER 
INFORMATION CONTACT), or visiting the internet at: https://
www.nmfs.noaa.gov/pr/permits/incidental.htm.
    Documents cited in this notice may be viewed, by appointment, 
during regular business hours, at the aforementioned address.
    In March, 2006, the Navy prepared a revised 2006 Supplement on the 
2002 Programmatic Environmental Assessment on RIMPAC. That document 
will be posted on the Navy's website (https://www.smdcen.us/rimpac06/) 
concurrently with this notice and the Navy will be accepting public 
comments.
    The Navy has also prepared a Draft Environmental Impact Statement 
(DEIS) for its Undersea Warfare Training Range (USWTR), which contains 
detailed supporting information for some of the issues discussed in 
this document and may be viewed at: https://projects.earthtech.com.
    NMFS' Ocean Acoustics Program has made additional information and 
references relating to the effects of anthropogenic sound available on 
the NMFS website at: https://www.nmfs.noaa.gov/pr/acoustics/
bibliography.htm.

FOR FURTHER INFORMATION CONTACT: Jolie Harrison, Office of Protected 
Resources, NMFS, (301) 713-2289, ext 166.

SUPPLEMENTARY INFORMATION:

Background

    Sections 101(a)(5)(A) and (D) of the MMPA (16 U.S.C. 1361 et seq.) 
direct the Secretary of Commerce to allow, upon request, the 
incidental, but not intentional, taking of marine mammals

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by U.S. citizens who engage in a specified activity (other than 
commercial fishing) within a specified geographical region if certain 
findings are made and either regulations are issued or, if the taking 
is limited to harassment, a notice of a proposed 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 that the permissible methods of 
taking and requirements pertaining to the mitigation, monitoring and 
reporting of such takings are set forth. NMFS has defined ``negligible 
impact'' in 50 CFR 216.103 as ''...an impact resulting from the 
specified activity that cannot be reasonably expected to, and is not 
reasonably likely to, adversely affect the species or stock through 
effects on annual rates of recruitment or survival.''
    Section 101(a)(5)(D) of the MMPA established an expedited process 
by which citizens of the United States can apply for an authorization 
to incidentally take small numbers of marine mammals by harassment. The 
National Defense Authorization Act of 2004 (NDAA) (Public Law 108-136) 
removed the ``small numbers'' limitation and amended the definition of 
``harassment'' as it applies to a ``military readiness activity'' to 
read as follows:
    (i) 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 (ii) 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]
    Section 101(a)(5)(D) establishes a 45-day time limit for NMFS 
review of an application followed by a 30-day public notice and comment 
period on any proposed authorizations for the incidental harassment of 
marine mammals. Within 45 days of the close of the comment period, NMFS 
must either issue or deny issuance of the authorization.

Summary of Request

    NMFS received an application from the Navy for the taking, by 
harassment, of several species of marine mammals incidental to 
conducting RIMPAC ASW training events, in which submarines, surface 
ships, and aircraft from the United States and multiple foreign nations 
participate in ASW training exercises, in the OpArea, in the summer of 
2006. The RIMPAC ASW exercises are considered a military readiness 
activity. Based on discussions between the agencies regarding 
behavioral thresholds and mitigation and monitoring, the Navy submitted 
a modified application on March 16, 2006.

Description of the Activity

    RIMPAC 2006 ASW activities are scheduled to take place from June 
26, 2006, to about July 28, 2006, with ASW training events planned on 
21 days. The OpArea is approximately 210,000 square nautical miles 
(nm), however, nearly all RIMPAC ASW training would occur in the six 
areas delineated in Figure 2-1 in the Navy's application (approximate 
46,000 square nm). ASW events typically rotate between these six 
modeled areas. Sonar training exercises will occur within these areas 
for the most part; however, sonar may be operated briefly for battle 
preparation while forces are in transit from one of the modeled areas 
to another. These six areas were used for analysis as being 
representative of the marine mammal habitats and the bathymetric, 
seabed, wind speed, and sound velocity profile conditions within the 
entire OpArea. For purposes of this analysis, all likely RIMPAC ASW 
events were modeled as occurring in these six areas.
    As a combined force during the exercises, submarines, surface 
ships, and aircraft will conduct ASW against opposition submarine 
targets. Submarine targets include real submarines, target drones that 
simulate the operations of an actual submarine, 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 P-3 aircraft searching for one or more submarines. 
There will be approximately four SAGs for RIMPAC 2006. For the purposes 
of analysis, each event in which a SAG participates is counted as an 
ASW operation. There will be approximately 44 ASW operations during 
RIMPAC with an average event length of approximately 12 hours.
    One or more ASW events may occur simultaneously within the OpArea. 
Each event was identified and modeled separately. If a break of more 
than 1 hour in ASW operations occurred, then the subsequent event was 
modeled as a separate event. Training event durations ranged from 2 
hours to 24 hours. A total of 532 training hours were modeled for 
RIMPAC acoustic exposures. This total includes all potential ASW 
training that is expected to occur during RIMPAC.

Active Acoustic Sources

    Tactical military sonars are designed to search for, detect, 
localize, classify, and track submarines. There are two types of 
sonars, passive and active. Passive sonars only listen to incoming 
sounds and, since they do not emit sound energy in the water, lack the 
potential to acoustically affect the environment. Active sonars 
generate and emit acoustic energy specifically for the purpose of 
obtaining information concerning a distant object from the sound energy 
reflected back from that object.
    Modern sonar technology has developed a multitude of sonar sensor 
and processing systems. In concept, the simplest active sonars emit 
omnidirectional 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 in RIMPAC are designed 
to detect submarines in tactical operational scenarios. This task 
requires the use of the sonar mid-frequency (MF) range (1 kilohertz 
[kHz] to 10 kHz) predominantly.
    The types of tactical acoustic sources that would be used in 
training events during RIMPAC are discussed in the following 
paragraphs. For more information regarding how the Navy's determined 
which sources should not be included in their analysis, see the 
Estimates of Take Section later in this document.
    Surface Ship Sonars - A variety of surface ships participate in 
RIMPAC, including guided missile cruisers, destroyers, guided missile 
destroyers, and frigates. Some ships (e.g., aircraft carriers) do not 
have any onboard active sonar systems, other than fathometers. Others, 
like guided missile cruisers, are equipped with active as well as 
passive sonars for submarine detection and tracking. For purposes of 
the analysis, all surface ship sonars were modeled as equivalent to 
SQS-53 having the nominal source level of 235 decibels (dB) re 1mPa2-s 
(SEL). Since the SQS-

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53 hull mounted sonar is the U.S. Navy's most powerful surface ship 
hull mounted sonar, modeling this source is a conservative assumption 
tending towards an overestimation of potential effects (although, the 
conservativeness is offset some by the fact that the Navy did not model 
for any of the times (though brief and infrequent) that they may use a 
source level higher than 235 dB). Sonar ping transmission durations 
were modeled as lasting 1 second per ping and omnidirectional, which is 
a conservative assumption that overestimates potential exposures, since 
actual ping durations will be less than 1 second. The SQS-53 hull 
mounted sonar transmits at center frequencies of 2.6 kHz and 3.3 kHz.
    Submarine Sonars - Submarine sonars can be used to detect and 
target enemy submarines and surface ships. However, submarine active 
sonar use is very rare in the planned RIMPAC exercises, and, when used, 
very brief. Therefore, use of active sonar by submarines is unlikely to 
have any effect on marine mammals, and it was not modeled for RIMPAC 
2006.
    Aircraft Sonar Systems - Aircraft sonar systems that would operate 
during RIMPAC include sonobuoys and dipping sonar. Sonobuoys may be 
deployed by P-3 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 generate active acoustic signals as 
well. Dipping sonar is an active or passive sonar device lowered on 
cable by helicopters to detect or maintain contact with underwater 
targets. During RIMPAC, these systems active modes are only used 
briefly for localization of contacts and are not used in primary search 
capacity. Because active mode dipping sonar use is very brief, it is 
extremely unlikely its use would have any effect on marine mammals. The 
AN/AQS 13 (dipping sonar) used by carrier based helicopters was 
determined in the Environmental Assessment/Overseas Environmental 
Assessment of the SH-60R Helicopter/ALFS Test Program, October 1999, 
not to be problematic due to its limited use and very short pulse 
length. Therefore, the aircraft sonar systems were not modeled for 
RIMPAC 2006.
    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. All torpedoes used for ASW 
during RIMPAC would be located in the range area managed by Pacific 
Missile Range Facility (PMRF) and would be non-explosive and recovered 
after use.
    Acoustic Device Countermeasures (ADC) - ADCs are, in effect, 
submarine simulators that make noise to act as decoys to avert 
localization and/or torpedo attacks. Previous classified analysis has 
shown that, based on the operational characteristics (source output 
level and/or frequency) of these acoustic sources, the potential to 
affect marine mammals was unlikely, and therefore they were not modeled 
for RIMPAC 2006.
    Training Targets - ASW training targets are used to simulate target 
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. Based on the operational characteristics (source 
output level and/or frequency) of these acoustic sources, the potential 
to affect marine mammals is unlikely, and therefore they were not 
modeled for RIMPAC 2006.
    Range Sources - Range pingers are active acoustic devices that 
allow each of the in-water platforms on the range (e.g., ships, 
submarines, target simulators, and exercise torpedoes) to be tracked by 
the range transducer nodes. In addition to passively tracking the 
pinger signal from each range participant, the range transducer nodes 
also are capable of transmitting acoustic signals for a limited set of 
functions. These functions include submarine warning signals, acoustic 
commands to submarine target simulators (acoustic command link), and 
occasional voice or data communications (received by participating 
ships and submarines on range). Based on the operational 
characteristics (source output level and/or frequency) of these 
acoustic sources, the potential to affect marine mammals is unlikely, 
and therefore they were not modeled for RIMPAC 2006.
    For detailed information regarding the proposed activity, please 
see the Navy's application and the associated Environmental Assessment 
(EA) (see ADDRESSES).

Description of Marine Mammals Potentially Affected by the Activity

    There are 27 marine mammal species with possible or confirmed 
occurrence in the Navy's OpArea (Table 1): 25 cetacean species (whales, 
dolphins, and porpoises) and 2 pinnipeds (seals). In addition, five 
species of sea turtles are known to occur in the OpArea.
    The most abundant marine mammals are rough-toothed dolphins, dwarf 
sperm whales, and Fraser's dolphins. The most abundant large whales are 
sperm whales. There are three seasonally migrating baleen whale species 
that winter in Hawaiian waters: minke, fin, and humpback whales. 
Humpback whales utilize Hawaiian waters as a major breeding ground 
during winter and spring (November through April), but should not be 
present during the RIMPAC exercise, which takes place in July. Because 
definitive information on the other two migrating species is lacking, 
their possible presence during the July timeframe is assumed, although 
it is considered unlikely. Seven marine mammal species listed as 
federally endangered under the Endangered Species Act (ESA) occur in 
the area: the humpback whale, North Pacific right whale, sei whale, fin 
whale, blue whale, sperm whale, and Hawaiian monk seal.
    The Navy has used data compiled from available sighting records, 
literature, satellite tracking, and stranding and bycatch data to 
identify the species of marine mammals present in the OpArea. A 
combination of inshore survey data (within 25 nm; Mobley et al., 2000) 
and offshore data (from 25 nm offshore out to the U.S. EEZ, Barlow 
2003) was used to estimate the density and abundance of marine mammals 
within the OpArea (Table 1). Additional information regarding the 
status and distribution of the 27 marine mammal species that occur in 
the OpArea may be found in the Navy's application and the associated EA 
(See ADDRESSES) and in NMFS' Stock Assessment Reports, which are 
available at: https://www.nmfs.noaa.gov/pr/PR2/Stock_Assessment_
Program/individual_sars.html.
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Potential Effects on Marine Mammals

    The Navy has requested an IHA for the take, by harassment, of 
marine mammals incidental to RIMPAC ASW exercises in the OpArea. 
Section 101(a)(5)(D) of the MMPA, the section pursuant to which IHAs 
are issued, may not be used to authorize mortality or serious injury 
leading to mortality. The Navy's analysis of the RIMPAC ASW exercises 
concluded that no mortality or serious injury leading to mortality 
would result from the proposed activities. However, NMFS believes, 
based on our interpretation of the limited available data bearing on 
this point, that some marine mammals may react to mid-frequency sonar, 
at received levels lower than those thought to cause direct physical 
harm, with behaviors that may, in some circumstances, lead to 
physiological harm, stranding, or, potentially, death. Therefore, NMFS 
is proposing to require additional mitigation and monitoring measures 
that were not originally proposed in the Navy's application to ensure 
(in addition to the standard statutory requirement to effect the 
``least practicable adverse impact upon the affected species or stoc'') 
that mortality or serious injury leading to mortality does not result 
from the proposed activities. Below, NMFS describes the potential 
effects on marine mammals of exposure to tactical sonar. However, due 
to the mitigation and monitoring required by this IHA, NMFS does not 
expect marine mammals to be exposed to sound of the strength or 
duration necessary to potentially induce the more severe of the effects 
discussed below.

Metrics Used in Acoustic Effect Discussions

    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 (mPa), where 1 Pa is the pressure resulting 
from a force of one newton exerted over an area of one square meter.
    The sound levels to which most mammals are sensitive extend over 
many orders of magnitude and, for this reason, it is convenient to use 
a logarithmic scale (the decibel (dB) scale) when measuring sound. 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 mPa, and the units for SPLs are dB re: 1 mPa.
    SPL (in dB) = 20 log (pressure / reference pressure)
    SPL is an instantaneous measurement and can be expressed as the 
peak, the peak-peak, 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. SPL does not take the duration of a 
sound into account.
SEL
    In this proposed authorization, effect thresholds are expressed in 
terms of sound exposure level 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 mPa2-s.
    SEL = SPL + 10log(duration)
    As applied to tactical sonar, the SEL includes both the ping SPL 
and the duration. Longer-duration pings and/or higher-SPL pings 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. Since mammalian 
threshold shift (TS) data show less effect from intermittent exposures 
compared to continuous exposures with the same energy (Ward, 1997), 
basing the effect thresholds on the total received SEL may be a 
conservative approach for treating multiple pings; as some recovery may 
occur between pings and lessen the effect of a particular exposure.
    The total SEL depends on the SPL, duration, and number of pings 
received. The acoustic effects on hearing that result in temporary 
threshold shift (TTS) and permanent threshold shift (PTS), do not imply 
any specific SPL, duration, or number of pings. The SPL and duration of 
each received ping are used to calculate the total SEL and determine 
whether the received SEL meets or exceeds the effect thresholds. For 
example, the sub-TTS behavioral effects threshold of 173 dB SEL would 
be reached through any of the following exposures:
    A single ping with SPL = 173 dB re 1 mPa and duration = 1 second.
    A single ping with SPL = 170 dB re 1 mPa and duration = 2 seconds.
    Two pings with SPL = 170 dB re 1 mPa and duration = 1 second.
    Two pings with SPL = 167 dB re 1 mPa and duration = 2 seconds.

Potential Physiological Effects

    Physiological function is any of a collection of processes ranging 
from biochemical reactions to mechanical interaction and operation of 
organs and tissues within an animal. A physiological effect may range 
from the most significant of impacts (i.e., mortality and serious 
injury) to lesser effects that would define the lower end of the 
physiological impact range, such as non-injurious short-term impacts to 
auditory tissues.
    Exposure to some types of noise may cause a variety of 
physiological effects in mammals. For example, exposure to very high 
sound levels may affect the function of the visual system, vestibular 
system, and internal organs (Ward, 1997). Exposure to high-intensity 
sounds of sufficient duration may cause injury to the lungs and 
intestines (e.g., Dalecki et al., 2002). Sudden, intense sounds may 
elicit a ``startle'' response and may be followed by an orienting 
reflex (Ward, 1997; Jansen, 1998). The primary physiological effects of 
sound, however, are on the auditory system (Ward, 1997).
Hearing Threshold Shift
    In mammals, high-intensity sound may rupture the eardrum, damage 
the small bones in the middle ear, or over-stimulate the 
electromechanical hair cells that convert the fluid motions caused by 
sound into neural impulses that are sent to the brain. Lower level 
exposures may cause hearing loss, which is called a threshold shift 
(TS) (Miller, 1974). Incidence of TS may be either permanent, in which 
case it is called a permanent threshold shift (PTS), or temporary, in 
which case it is called a temporary threshold shift (TTS). PTS consists 
of non-recoverable physical damage to the sound receptors in the ear, 
which can include total or partial deafness, or an impaired ability to 
hear sounds in specific frequency ranges. TTS is recoverable and is 
considered to result from temporary, non-injurious impacts to hearing-
related tissues. Hearing loss may affect an animal's ability to react 
normally to the sounds around it.
    The amplitude, duration, frequency, and temporal pattern of sound 
exposure all affect the amount of associated TS. As amplitude and 
duration of sound exposure increase, so, generally, does the amount of 
TS. For continuous sounds, exposures of equal energy will lead to 
approximately equal effects (Ward, 1997). 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). Additionally, though TTS is temporary, very prolonged 
exposure to sound strong enough to elicit TTS, or

[[Page 20991]]

shorter-term exposure to sound levels well above the TTS threshold, can 
cause PTS, at least in terrestrial mammals (Kryter, 1985).
    Additional detailed information regarding threshold shifts may be 
viewed in the Navy's RIMPAC application and in the USWTR DEIS.
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 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 sonar 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. Yet another 
hypothesis 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). 
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). To date, Energy Levels (ELs) predicted to 
cause in vivo bubble formation within diving cetaceans have not been 
evaluated (NOAA, 2002b). Further, 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. Because evidence supporting 
the potential for acoustically mediated bubble growth is debatable, 
this proposed IHA does not give it any special treatment. Additionally, 
the required mitigation measures, which are designed to avoid 
behavioral disruptions that could result in abnormal vertical movement 
by whales through the water column, should also reduce the potential 
for creating circumstances that theoretically contribute to harmful 
bubble growth.
    Additional information on the physiological effects of sound on 
marine mammals may be found in the Navy's IHA application and 
associated Environmental Assessment, the USWTR DEIS, and on the Ocean 
Acoustic Program section of the NMFS website (see ADDRESSES).
Stress Responses
    In addition to PTS and TTS, exposure to mid-frequency sonar is 
likely to result in other physiological changes that have other 
consequences for the health and ecological fitness of marine mammals. 
There is mounting evidence that wild animals respond to human 
disturbance in the same way that they respond to predators (Beale and 
Monaghan, 2004; Frid, 2003; Frid and Dill, 2002; Gill et al., 2000; 
Gill and Sutherland, 2001; Harrington and Veitch, 1992; Lima, 1998; 
Romero, 2004). These responses manifest themselves as interruptions of 
essential behavioral or physiological events, alteration of an animal's 
time or energy budget, or stress responses in which an animal perceives 
human activity as a potential threat and undergoes physiological 
changes to prepare for a flight or fight response or more serious 
physiological changes with chronic exposure to stressors (Frid and 
Dill, 2002; Romero, 2004; Sapolsky et al., 2000; Walker et al., 2005).
    Classic stress responses begin when an animal's central nervous 
system perceives a potential threat to its homeostasis. That perception 
triggers stress responses regardless of whether a stimulus actually 
threatens the animal; the mere perception of a threat is sufficient to 
trigger a stress response (Sapolsky et al., 2005; Seyle, 1950). Once an 
animal's central nervous system perceives a threat, it develops a 
biological response or defense that consists of a combination of the 
four general biological defense responses: behavioral responses, 
autonomic nervous system responses, neuroendocrine responses, or immune 
response.
    The physiological mechanisms behind stress responses involving the 
hypothalamus-pituitary-adrenal glands have been well-established 
through controlled experiment in the laboratory and natural settings 
(Korte et al. 2005; McEwen and Seeman, 2000; Moberg, 1985; 2000; 
Sapolsky et al., 2005). Relationships between these physiological 
processes, animal behavior, neuroendocrine responses, immune responses, 
inhibition of reproduction (by suppression of pre-ovulatory luteinizing 
hormones), and the costs of stress responses have also been documented 
through controlled experiment in both laboratory and free-living 
animals (for examples see, Holberton et al., 1996; Hood et al., 1998; 
Jessop et al., 2003; Krausman et al., 2004; Lankford et al., 2005; 
Reneerkens et al., 2002; Thompson and Hamer, 2000; Tilbrook et al., 
2000).
    The available evidence suggests that: with the exception of 
unrelieved pain or extreme environmental conditions, in most animals 
(including humans) chronic stress results from exposure to a series of 
acute stressors whose cumulative biotic costs produce a pathological or 
pre-pathological state in an animal. The biotic costs can result from 
exposure to an acute stressor or from the accumulation of a series of 
different stressors acting in concert before the animal has a chance to 
recover.
    Although these responses have not been explicitly identified in 
marine mammals, they have been identified in other vertebrate animals 
and every vertebrate mammal that has been studied, including humans. 
Because of the physiological similarities between marine mammals and 
other mammal species, NMFS believes that acoustic energy sufficient to 
trigger onset PTS or TTS is likely to initiate physiological stress 
responses. More importantly, NMFS believes that marine mammals might 
experience stress responses at received levels lower than those 
necessary to trigger onset TTS.

Potential Behavioral Effects

    For a military readiness activity, Level B Harassment is defined as 
``any act that disturbs or is likely to disturb a marine mammal or 
marine mammal stock in the wild by causing disruption of natural

[[Page 20992]]

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.''
    As discussed above, TTS consists of temporary, short-term impacts 
to auditory tissue that alter physiological function, but that are 
fully recoverable without the requirement for tissue replacement or 
regeneration. An animal that experiences a temporary reduction in 
hearing sensitivity suffers no permanent injury to its auditory system, 
but, for an initial time post-exposure, may not perceive some sounds 
due to the reduction in sensitivity. As a result, the animal may not 
respond to sounds that would normally produce a behavioral reaction 
(such as a predator or the social calls of conspecifics, which play 
important roles in mother-calf relations, reproduction, foraging, and 
warning of danger). This lack of response qualifies as a temporary 
disruption of normal behavioral patterns - the animal is impeded from 
responding in a normal manner to an acoustic stimulus.
    NMFS also considers disruption of the behavior of marine mammals 
that can result from sound levels lower than those considered necessary 
for TTS to occur (often referred to as sub-TTS behavioral disruption). 
Though few studies have specifically documented the effects of tactical 
mid-frequency sonar on the behavior of marine mammals in the wild, many 
studies have reported the effects of a wide range of intense 
anthropogenic acoustic stimuli on specific facets of marine mammal 
behavior, including migration (Malme et al., 1984; Ljungblad et al., 
1988; Richardson et al., 1999), feeding (Malme et al., 1988), and 
surfacing (Nowachek et al., 2004). Below, NMFS summarizes the results 
of two studies and one after-the-fact investigation wherein the natural 
behavior patterns of marine mammals exposed to levels of tactical mid-
frequency sonar, or sounds similar to mid-frequency sonar, lower than 
those thought to induce TTS were disrupted to the point where it was 
abandoned or significantly altered:
    (1) Finneran and Schlundt (2004) analyzed behavioral observations 
from related TTS studies (Schlundt et al., 2000; Finneran et al., 2001; 
2003) to calculate cetacean behavioral reactions as a function of known 
noise exposure. During the TTS experiments, 4 dolphins and 2 white 
whales were exposed during a total of 224 sessions to 1-s pulses 
between 160 and 204 dB re 1 microPa (root-mean-square sound pressure 
level (SPL)), at 0.4, 3, 10, 20, and 75 kHz. Finneran and Schlundt 
(2004) evaluated the behavioral observations in each session and 
determined whether a ``behavioral alteration'' (ranging from 
modifications of response behavior during hearing sessions to attacking 
the experimental equipment) occurred. For each frequency, the 
percentage of sessions in which behavioral alterations occurred was 
calculated as a function of received noise SPL. By pooling data across 
individuals and test frequencies, respective SPL levels coincident with 
responses by 25, 50, and 75 percent behavioral alteration were 
documented. 190 dB re 1 microPa (SPL) is the point at which 50 percent 
of the animals exposed to 3, 10, and 20 kHz tones were deemed to 
respond with some behavioral alteration, and the threshold that the 
Navy originally proposed for sub-TTS behavioral disturbance.
    (2) Nowacek et al. (2004) conducted controlled exposure experiments 
on North Atlantic right whales using ship noise, social sounds of con-
specifics, and an alerting stimulus (frequency modulated tonal signals 
between 500 Hz and 4.5 kHz). Animals were tagged with acoustic sensors 
(D-tags) that simultaneously measured movement in three dimensions. 
Whales reacted strongly to alert signals at received levels of 133-148 
dB SPL, mildly to conspecific signals, and not at all to ship sounds or 
actual vessels. The alert stimulus caused whales to immediately cease 
foraging behavior and swim rapidly to the surface. Although SEL values 
were not directly reported, based on received exposure durations, 
approximate received values were on the order of 160 dB re: 1 
microPa\2\-s.
    (3) NMFS (2005) evaluated the acoustic exposures and coincident 
behavioral reactions of killer whales in the presence of tactical mid-
frequency sonar. In this case, none of the animals were directly fitted 
with acoustic dosimeters. However, based on a Naval Research Laboratory 
(NRL) analysis that took advantage of the fact that calibrated 
measurements of the sonar signals were made in situ and using advanced 
modeling to bound likely received exposures, estimates of received 
sonar signals by the killer whales were possible. Received SPL values 
ranged from 121 to 175 dB re: 1 microPa. The most probable SEL values 
were 169.1 to 187.4 dB re: 1 microPa\2\-s; worst-case estimates ranged 
from 177.7 to 195.8 dB re: 1 microPa\2\-s. Researchers observing the 
animals during the course of sonar exposure reported unusual 
alterations in swimming, breathing, and diving behavior.
    For more detailed information regarding how marine mammals may 
respond to sound, see the Navy's IHA application, the Navy's associated 
EA, Richardson's Marine Mammals and Noise (1995), or the references 
cited on NMFS' Ocean Acoustic Program website (see ADDRESSES)

Proposed Harassment Thresholds

    For the purposes of the proposed IHA for this activity, NMFS 
recognizes three levels of take; Level A Harassment (Injury), Level B 
Harasssment (Behavioral Disruption), and mortality (or serious injury 
that may lead to mortality) (Table 2). Mortality, or serious injury 
leading to mortality, may not be authorized with an IHA.
    NMFS has determined that for acoustic effects, acoustic thresholds 
are the most effective way to consistently both apply measures to avoid 
or minimize the impacts of an action and to quantitatively estimate the 
effects of an action. Thresholds are commonly used in two ways: (1) To 
establish a shut-down or power down zone, i.e., if an animal enters an 
area calculated to be ensonified above the level of an established 
threshold, a sound source is powered down or shut down; and (2) to 
calculate take, for example, if the Level A Harassment threshold is 215 
dB, a model may be used to calculate the area around the sound source 
that will be ensonified to that level or above, then, based on the 
estimated density of animals and the distance that the sound source 
moves, NMFS can estimate the number of marine mammals exposed to 215 
dB. The rationale behind the acoustic thresholds proposed for this 
authorization are discussed below.

[[Page 20993]]



----------------------------------------------------------------------------------------------------------------
        Levels of Take Pursuant to the MMPA              Basis of Threshold             Proposed Threshold
----------------------------------------------------------------------------------------------------------------
            Level A harassment (Injury)               Permanent Threshold Shift                      215 dB (SEL)
                                                                          (PTS)
      Level B Harassment (Behavioral Effects)         Temporary Threshold Shift                          195 dB
                                                                          (PTS)
                                                     Sub-TTS Behavioral Effects                      173 dB (SEL)
   Mortality, or Serious Injury That May Lead to     Not enough information for   May not be authorized with an
               Mortality (Stranding)                     quantitative threshold                             IHA
----------------------------------------------------------------------------------------------------------------
Table 2. The three levels of take addressed in the MMPA, how NMFS measures them in regard to acoustic effects,
  and the propsed thresholds for this authorization.

TTS
    Because it is non-injurious, NMFS considers TTS as Level B 
harassment (behavioral disruption) that is mediated by physiological 
effects on the auditory system. The smallest measurable amount of TTS 
(onset-TTS) is taken as the best indicator for slight temporary sensory 
impairment. However, as mentioned earlier, NMFS believes that 
behavioral disruptions may result from received levels of tactical 
sonar lower than those thought to induce TTS and, therefore, NMFS does 
not consider on-set TTS to be the lowest level at which Level B 
Harassment may occur. NMFS considers the threshold for Level B 
Harasment as the received levels from which sub-TTS behavioral 
disruptions are likely to result (discussed in Sub-TTS sub-section). 
However, the threshold for Level A Harassment (PTS) is derived from the 
threshold for TTS and, therefore, it is necessary to describe how the 
TTS threshold was developed.
    The proposed TTS threshold is primarily based on the cetacean TTS 
data from Schlundt et al. (2000). These tests used short-duration tones 
similar to sonar pings, and they are the most directly relevant data 
for the establishing TTS criteria. The mean exposure EL required to 
produce onset-TTS in these tests was 195 dB re 1 microPa\2\-s. This 
result is corroborated by the short-duration tone data of Finneran et 
al. (2000, 2003) and the long-duration noise data from Nachtigall et 
al. (2003a,b). Together, these data demonstrate that TTS in cetaceans 
is correlated with the received EL and that onset-TTS exposures are fit 
well by an equal-energy line passing through 195 dB re 1 microPa\2\-s.
    The justification for establishing the 195 dB acoustic criteria for 
TTS is described in detail in both the Navy's RIMPAC IHA application 
and the USWTR DEIS (see ADDRESSES).
PTS
    PTS consists of non-recoverable physical damage to the sound 
receptors in the ear and is, therefore, classified as Level A 
harassment under the MMPA. For acoustic effects, because the tissues of 
the ear appear to be the most susceptible to the physiological effects 
of sound, and because threshold shifts (TSs) tend to occur at lower 
exposures than other more serious auditory effects, NMFS has determined 
that permanent threshold shift (PTS) is the best indicator for the 
smallest degree of injury that can be measured. Therefore, the acoustic 
exposure associated with onset-PTS is used to define the lower limit of 
the Level A harassment.
    PTS data do not currently exist for marine mammals and are unlikely 
to be obtained due to ethical concerns. However, PTS levels for these 
animals may be estimated using TTS data and relationships between TTS 
and PTS. NMFS proposes the use of 215 dB re 1 mPa\2\-s as the acoustic 
threshold for PTS. This threshold is based on a 20 dB increase in 
exposure EL over that required for onset-TTS (195 dB). Extrapolations 
from terrestrial mammal data indicate that PTS occurs at 40 dB or more 
of TS, and that TS growth occurs at a rate of approximately 1.6 dB TS 
per dB increase in EL. There is a 34 dB TS difference between onset-TTS 
(6 dB) and onset-PTS (40 dB). Therefore, an animal would require 
approximately 20dB of additional exposure (34 dB divided by 1.6 dB) 
above onset-TTS to reach PTS.
    The justification for establishing the 215 dB acoustic criteria for 
PTS is described in detail in both the Navy's RIMPAC IHA application 
and the Undersea Warfare Training Range USWTR DEIS (see ADDRESSES).
Sub-TTS Behavioral Disruption
    NMFS believes that behavioral disruption of marine mammals may 
result from received levels of mid-frequency sonar lower than those 
believed necessary to induce TTS, and further, that the lower limit of 
Level B Harassment may be defined by the received sound levels 
associated with these sub-TTS behavioral disruptions. As of yet, no 
controlled exposure experiments have been conducted wherein wild 
cetaceans are deliberately exposed to tactical mid-frequency sonar and 
their reactions carefully observed. However, NMFS believes that in the 
absence of controlled exposure experiments, the following 
investigations and reports (described previously in the Behavioral 
Effects section) constitute the best available scientific information 
for establishing an appropriate acoustic threshold for sub-TTS 
behavioral disruption: (1) Finneran and Schlundt (2004), in which 
behavioral observations from TTS studies of captive bottlenose dophins 
and beluga whales are analyzed as a function of known noise exposure; 
(2) Nowachek et al. (2004), in which controlled exposure experiments 
were conducted on North Atlantic right whales using ship noise, social 
sounds of con-specifics, and an alerting stimulus; and (3) NMFS (2005), 
in which the behavioral reactions of killer whales in the presence of 
tactical mid-frequency sonar were observed, and analyzed after the 
fact. Based on these three studies, NMFS has set the sub-TTS behavioral 
disruption threshold at 173 dB re 1 mPa\2\-s (SEL).
    The Finneran and Schlundt (2004) analysis is an important piece in 
the development of an appropriate acoustic threshold for sub-TTS 
behavioral disruption because: (1) researchers had superior control 
over and ability to quantify noise exposure conditions; (2) behavioral 
patterns of exposed marine mammals were readily observable and 
definable; and, (3) fatiguing noise consisted of tonal noise exposures 
with frequencies contained in the tactical mid-frequency sonar 
bandwidth. In Finneran and Schlundt (2004) 190 dB re 1 mPa (SPL) is the 
point at which 50 percent of the animals exposed to 3, 10, and 20 kHz 
tones were deemed to respond with some behavioral alteration. This 50 
percent behavior alteration level (190 dB SPL) may be converted to an 
SEL criterion of 190 dB re 1 mPa\2\-s (the numerical values are 
identical because exposure durations were 1-s), which provides 
consistency with the Level A (PTS) effects threshold, which are also 
expressed in SEL. The Navy proposed 190 dB (SEL) as the acoustic 
threshold for sub-TTS

[[Page 20994]]

behavioral disruption in the first IHA application they submitted to 
NMFS.
    NMFS acknowledges the advantages arising from the use of behavioral 
observations in controlled laboratory conditions; however, there is 
considerable uncertainty regarding the validity of applying data 
collected from trained captives conditioned to not respond to noise 
exposure in establishing thresholds for behavioral reactions of naive 
wild individuals to a sound source that apparently evokes strong 
reactions in some marine mammals. Although wide-ranging in terms of 
sound sources, context, and type/extent of observations reported, the 
large and growing body of literature regarding behavioral reactions of 
wild, naive marine mammals to anthropogenic exposure generally suggests 
that wild animals are behaviorally affected at significantly lower 
levels than those determined for captive animals by Finneran and 
Schlundt (2004). For instance, some cetaceans exposed to human noise 
sound sources, such as seismic airgun sounds and low frequency sonar 
signals, have been shown to exhibit avoidance behavior when the animals 
are exposed to noise levels of 140-160 dB re: 1 mPa under certain 
conditions (Malme et al., 1983; 1984; 1988; Ljungblad et al., 1988; 
Tyack and Clark, 1998). Richardson et al. (1995) reviewed the 
behavioral response data for many marine mammal species and a wide 
range of human sound sources.
    Two specific situations for which exposure conditions and 
behavioral reactions of free-ranging marine mammals exposed to sounds 
very similar to those proposed for use in RIMPAC are considered by 
Nowacek et al. (2004) and NMFS (2005) (described previously in 
Behavioral Effects subsection). In the Nowacek et al. (2004) study, 
North Atlantic right whales reacted strongly to alert signals at 
received levels of 133-148 dB SPL, which, based on received exposure 
durations, is approximately equivalent to 160 dB re: 1 mPa2-s (SEL). In 
the NMFS (2005) report, unusual alterations in swimming, breathing, and 
diving behaviors of killer whales observed by researchers in Haro 
Strait were correlated, after the fact, with the presence of estimated 
received sound levels between 169.1and 187.4 dB re: 1 mPa\2\-s (SEL).
    While acknowledging the limitations of all three of these studies 
and noting that they may not necessarily be predictive of how wild 
cetaceans might react to mid-frequency sonar signals in the OpArea, 
NMFS believes that these three studies are the best available science 
to support the selection of an acoustic sub-TTS behavioral disturbance 
threshold at this time. Taking into account all three studies, NMFS has 
established 173 dB re: 1 mPa\2\ (SEL) as the threshold for sub-TTS 
behavioral disturbance.

Stranding and Mortality

    Over the past 10 years, there have been four stranding events 
coincident with military mid-frequency sonar use that are believed to 
most likely have been caused by exposure to the sonar. These occurred 
in Greece (1996), the Bahamas (2000), Madeira (2000) and Canary Islands 
(2002). A number of other stranding events coincident to the operation 
of mid-frequency sonar and resulting in the death of beaked whales or 
other species (minke whales, dwarf sperm whales, pilot whales) have 
been reported, though the majority have not been investigated to the 
level of the Bahamas stranding and, therefore, other causes cannot be 
ruled out. One of these strandings occurred in Hanalei Bay during the 
last RIMPAC exercise in 2004.
Greece, Madeira, and Canary Islands
    Twelve Cuvier's beaked whales stranded along the western coast of 
Greece in 1996. The test of a low- and mid-frequency active sonar 
system conducted by NATO was correlated with the strandings by an 
analysis published in Nature. A subsequent NATO investigation found the 
strandings to be closely related, in time, to the movements of the 
sonar vessel, and ruled out other physical factors as a cause.
    In 2000, four beaked whales stranded in Madeira while several NATO 
ships were conducting an exercise near shore. Scientists investigating 
the stranding found that the injuries, which included blood in and 
around the eyes, kidney lesions, and pleural hemorrhage, as well as the 
pattern of the stranding suggested that a similar pressure event 
precipitated or contributed to strandings in both Madeira and Bahamas 
(see Bahamas sub-section).
    In 2002, at least 14 beaked whales of three different species 
stranded in the Canary Islands while a naval exercise including Spanish 
vessels, U.S. vessels, and at least one vessel equipped with mid-
frequency sonar was conducted in the vicinity. Four more beaked whales 
stranded over the next several days. The subsequent investigation, 
which was reported in both Nature and Veterinary Pathology, revealed a 
variety of traumas, including emboli and lesions suggestive of 
decompression sickness.
Bahamas
    NMFS and the Navy prepared a joint report addressing the multi-
species stranding in the Bahamas in 2000, which took place within 24 
hours of U.S. Navy ships using active mid-frequency sonar as they 
passed through the Northeast and Northwest Providence Channels. Of the 
17 cetaceans that stranded (Cuvier's beaked whales, Blainsville's 
beaked whales, Minke whales, and a spotted dolphin), seven animals died 
on the beach (5 Cuvier's beaked whales, 1 Blainsville's beaked whale, 
and the spotted dolphin) and the other 10 were returned to the water 
alive (though their fate is unknown). A comprehensive investigation was 
conducted and all possible causes of the stranding event were 
considered, whether they seemed likely at the outset or not. The only 
possible contributory cause to the strandings and cause of the lesions 
that could not be ruled out was intense acoustic signals (the dolphin 
necropsy revealed a disease and the death is considered unrelated to 
the others).
    Based on the way in which the strandings coincided with ongoing 
naval activity involving tactical mid-frequency sonar use, in terms of 
both time and geography, the nature of the physiological effects 
experienced by the dead animals, and the absence of any other acoustic 
sources, the investigation team concluded that mid-frequency sonars 
aboard U.S. Navy ships that were in use during the sonar exercise in 
question were the most plausible source of this acoustic or impulse 
trauma. This sound source was active in a complex environment that 
included the presence of a surface duct, unusual and steep bathymentry, 
a constricted channel with limited egress, intensive use of multiple, 
active sonar units over an extended period of time, and the presence of 
beaked whales that appear to be sensitive to the frequencies produced 
by these sonars. The investigation team concluded that the cause of 
this stranding event was the confluence of the Navy mid-frequency sonar 
and these contributory factors working together, and further 
recommended that the Navy avoid operating mid-frequency sonar in 
situations where these five factors would be likely to occur. This 
report does not conclude that all five of these factors must be present 
for a stranding to occur, nor that beaked whales are the only species 
that could potentially be affected by the confluence of the other 
factors. Based on this, NMFS believes that the presence of surface 
ducts, steep bathymetry, and/or constricted channels added to the 
operation of mid-frequency

[[Page 20995]]

sonar in the presence of cetaceans (especially beaked whales and, 
potentially, deep divers) may increase the likelihood of producing a 
sound field with the potential to cause cetaceans to strand, and 
therefore, necessitates caution.
Hanalei Bay
    Approximately 150-200 melon-headed whales (Peponocephala electra - 
a deep water species) live stranded (i.e. the animals entered and 
remained in unusual habitat) in Hanalei Bay on the morning of July 3, 
2004 at approximately 7 a.m. RIMPAC exercises involving mid-frequency 
sonar were conducted on July 3, but the official exercise did not 
commence until approximately 8 a.m. and, thus, could not have been the 
original triggering event. However, as six naval surface vessels 
traveled to the operational area the previous day, each intermittently 
transmitted active sonar during ``coordinated submarine training 
exercises'' as they approached Kauai from the south. NMFS conducted a 
detailed sound propagation analysis of the sonar transmissions of 
Japanese and U.S. naval vessels transiting from Pearl Harbor to Kauai 
on the afternoon and evening of 2 July 2004. Predicted sound fields 
were calculated for five positions along the known tracks. For each 
ship position where active sonar was used, transit speeds from areas to 
the south and east of Kauai necessary to reach Hanalei Bay by 7a.m. 
were determined. These transit rates were then compared with the ship 
locations and predicted sound fields. Results indicate that animals 
exposed to military sonar signals near the vessels could have reached 
the Bay while swimming at rates believed sustainable over relatively 
long periods for this species.
    The analysis is by no means conclusive evidence that exposure to 
tactical sonar on 2 July resulted in the pod of whales stranding in 
Hanalei Bay on July 3. However, based on these results, NMFS concludes 
that it was possible that sonar transmissions caused behavioral 
responses in the animals that led to their swimming away from the sound 
source, into the sound shadow of the island of Kauai, and entering 
Hanalei Bay (a shallower environment than they usually inhabit). 
Further, it is possible that sonar transmissions during the official 
RIMPAC exercise on July 3 could have prevented some of whales from 
leaving the Bay (witnesses observed whales attempting several times to 
depart the Bay, only to return rapidly once just outside it). The Navy 
modeled the sound transmissions during the event and calculated that 
the received level at Hanalei Bay from the sonar operated at the PMRF 
range on July 3 would have been approximately 147.5 dB re 1 mPa.

Beaked Whales

    Recent beaked whale strandings have prompted inquiry into the 
relationship between mid-frequency active sonar and the cause of those 
strandings. Although Navy mid-frequency active tactical sonar has been 
identified as the most plausible contributory source to the 2000 
Bahamas stranding event, the specific mechanisms that led to that 
stranding are not understood, and there is uncertainty regarding the 
ordering of effects that led to the stranding. It is uncertain whether 
beaked whales were directly injured by sound (a physiological effect) 
prior to stranding or whether a behavioral response to sound occurred 
that ultimately caused the beaked whales to strand and be injured.
    Several potential physiological outcomes caused by behavioral 
responses to high-intensity sounds have been suggested by Cox et al. 
(in press). These include: gas bubble formation caused by excessively 
fast surfacing; remaining at the surface too long when tissues are 
supersaturated with nitrogen; or diving prematurely when extended time 
at the surface is necessary to eliminate excess nitrogen. Baird et al. 
(2005) found that slow ascent rates from deep dives and long periods of 
time spent within 50 m of the surface were typical for both Cuvier's 
and Blainsville's beaked whales, the two species involved in mass 
strandings related to naval sonar. These two behavioral mechanisms may 
be necessary to purge excessive dissolved nitrogen concentrated in 
their tissues during their frequent long dives (Baird et al., 2005). 
Baird et al. (2005) further suggests that abnormally rapid ascents or 
premature dives in response to high-intensity sonar could indirectly 
result in physical harm to the beaked whales, through the mechanisms 
described above (gas bubble formation or non-elimination of excess 
nitrogen).
    During the RIMPAC exercise there will be use of multiple sonar 
units in an area where three beaked whale species may be present. A 
surface duct may be present in a limited area for a limited period of 
time. Although most of the ASW training events will take place in the 
deep ocean, some will occur in areas of high bathymetric relief. 
However, none of the training events will take place in a location 
having a constricted channel with limited egress similar to the 
Bahamas. Consequently, not all five of the environmental factors 
believed to contribute to the Bahamas stranding (mid-frequency sonar, 
beaked whale presence, surface ducts, steep bathymetry, and constricted 
channels with limited egress) will be present during RIMPAC ASW 
exercises. However, as mentioned previously, NMFS believes caution 
should be used anytime either steep bathymetry, surface ducting 
conditions, or a constricted channel is present in addition to the 
operation of mid-frequency tactical sonar and the presence of cetaceans 
(especially beaked whales).
    In order to avoid the potential for mortality or serious injury 
leading to mortality (in the form of strandings), NMFS is requiring 
additional mitigation and monitoring beyond that proposed in the Navy's 
application. However, given the information regarding beaked whale 
strandings and the uncertainty regarding the mechanisms for the 
strandings, NMFS will treat all predicted behavioral disturbance of 
beaked whales as potential non-lethal injury. All predicted Level B 
harassment of beaked whales is therefore given consideration as non-
lethal Level A harassment.

Estimated Take by Incidental Harassment

    In order to estimate acoustic exposures from the RIMPAC ASW 
operations, acoustic sources to be used were examined with regard to 
their operational characteristics. Systems with acoustic source levels 
below 205 dB re 1 mPa were not included in the analysis given that at 
this source level (205 dB re 1 mPa) or below, a 1-second ping would 
attenuate below the behavioral disturbance threshold of 173 dB at a 
distance of about 100 meters. As additional verification that they did 
not need to be considered further, sources at this level were modeled, 
using spreadsheet calculations, to determine the marine mammal 
exposures estimated to result from their operation. For example, a 
sonobuoy's typical use yielded an exposure area that produced 0 marine 
mammal exposures based on the maximum animal density. Such a source was 
called non-problematic and was not modeled in the sense of running its 
parameters through the environmental model Comprehensive Acoustic 
System Simulation (CASS), generating an acoustic footprint, etc. The 
proposed counter measures source level was less than 205 dB but its 
operational modes were such that a simple ``look'' was not applicable, 
and a separate study was conducted to ensure it did not need to be 
considered further.
    In addition, systems with an operating frequency greater than 100 
kHz were not

[[Page 20996]]

analyzed in the detailed modeling as these signals attenuate rapidly, 
resulting in very short propagation distances. Acoustic countermeasures 
were previously examined and found not to be problematic. The AN/AQS 13 
(dipping sonar) used by carrier based helicopters was determined in the 
Environmental Assessment/Overseas Environmental Assessment of the SH-
60R Helicopter/ALFS Test Program, October 1999, not to be problematic 
due to its limited use and very short pulse length (2 to 5 pulses of 
3.5 to 700 msec). Since 1999, during the time of the test program, 
there have been over 500 hours of operation, with no environmental 
effects observed. The Directional Command Activated Sonobuoy System 
(DICASS) sonobuoy was determined not to be problematic having a source 
level of 201dB re 1 mPa. These acoustic sources, therefore, did not 
require further examination in this analysis.
    Based on the information above, only hull mounted mid-frequency 
active tactical sonar was determined to have the potential to affect 
marine mammals protected under the MMPA and ESA during RIMPAC ASW 
training events.

Model

    An analysis was conducted for RIMPAC 2006, modeling the potential 
interaction of hull mounted mid-frequency active tactical sonar with 
marine mammals in the OpArea. The model incorporates site-specific 
bathymetric data, time-of-year-specific sound speed information, the 
sound source's frequency and vertical beam pattern, and multipath 
pressure information as a function of range, depth and bearing. Results 
were calculated based on the typical ASW activities planned for RIMPAC 
2006. Acoustic propagation and mammal population and density data were 
analyzed for the July timeframe since RIMPAC occurs in July. The 
modeling occurred in five broad steps, listed below.
    Step 1. Perform a propagation analysis for the area ensonified 
using spherical spreading loss and the Navy's CASS/GRAB program, 
respectively.
    Step 2. Convert the propagation data into a two-dimensional 
acoustic footprint for the acoustic sources engaged in each training 
event as they move through the six acoustic exposure model areas.
    Step 3. Calculate the total energy flux density level for each 
ensonified area summing the accumulated energy of all received pings.
    Step 4. Compare the total energy flux density to the thresholds and 
determine the area at or above the threshold to arrive at a predicted 
marine mammal exposure area.
    Step 5. Multiply the exposure areas by the corresponding mammal 
population density estimates. Sum the products to produce