Published in the Proceedings, Beacon Conference, 2002.
SUNY/WESTCHESTER Community College
Valhalla, New York 10595-1698 USA
New York Whale and Dolphin Action League
PO Box 273
Yonkers, NY 10707 USA
This report is not intended to be a comprehensive study of marine acoustics or the proliferation of mid or low frequency sound in water. Its focus is on the problems and known effects of tactical military sonars (especially low frequency active) on the biomass of the area of intended use comprising 80% of the world's oceans.
A powerful sonar system known as Surveillance Towed Array System Low Frequency Active (SURTASS LFA) may soon be deployed in up to 80% of the world's oceans. The Navy asserts that its need to detect quieter submarines at long range can only be met with the new low frequency active sonar (Johnson, 2001). But many scientists are concerned that propagating low frequency sound at levels up to 240 decibels (dB) into the oceans threatens the survival of marine life.
Intensity levels of LFA Sonar are far greater than those known to harm cetaceans (whales and dolphins). National and international regulations aimed at protecting marine life (Appendix A) such as endangered whales and turtles have been cast aside or altered to allow for the new technology. Marine acousticians, environmental groups and private citizens have called for a review of the powerful acoustic device and the pursuit of new passive sonars. Three coastal states have enacted pre-deployment prohibitions which severely restrict operation (Appendix B). This follows a series of mass strandings of whales and dolphins that coincided with documented naval exercises. The Navy has not sufficiently addressed the problem of the known potential of lethality in marine life caused by the use of these high intensity acoustic devices.
By far the most well known and significant of the multi-species mass strandings that occurred during naval exercises took place in the Bahamas in March of 2000. The incident is often called the "smoking gun" as it presented ample opportunity for necropsy and investigation lacking in previous military-associated strandings.
Over a 36-hour period on March 15th and 16th, 2000, 14 beaked whales, 2 minke whales and 1 spotted dolphin stranded on the Abaco, Grand Bahama and Eleuthera islands in the Bahamas. Scientists Ken Balcomb and Diane Claridge from the Center for Whale Research in Friday Harbor, Washington, were on hand at the research facility at Sandy Point, Abaco, studying a rare resident pod of 35 Cuvier's beaked whales (Ziphius cavirostris). On March 15th, one of the whales being studied beached itself in shallow water in front of the research station.
The whale was guided back into deep waters where it swam in a large left circle and restranded. After beaching itself several times, the whale reached deeper water and did not return. Coincidently, the research station received calls for assistance with live-stranded cetaceans from points north and south throughout the islands. By 7:30 p.m., 4 more whales and a dolphin were reported live-stranded. Later that evening, the station learned that seven more whales had stranded on Grand Bahama while two minke whales beached near Royal Island, North Eleuthera.
The following two days, Balcomb and Claridge conducted vessel and aerial surveys of the south, east and southwest Abaco coastline. Three more stranded or decomposing whales were spotted, along with several naval warships. In all, the stranding event involved 18 cetaceans of 4 different species covering a 240 km (149 mile) arc. Five Cuvier's beaked whales, one Blainville's dense-beaked whale (Mesoplodon densirostris) and one spotted dolphin (Stenella frontalis) died within hours of stranding. Post mortem examinations were performed on these six, and heads and tissues were collected and fresh frozen. Due to the badly decomposed condition of an additional Gervais' beaked whale (Mesoplodon europaeus) a post mortem examination was not possible.
Because of the remoteness of the numerous sandbars and the vast expanse of water covered, Balcomb believes there were many more strandings that weren't reported (Balcomb, 2001b). In all, ten of the animals were helped back into deeper water, but they have not restranded or been re-sighted to date. The whales that were not assisted died within a few hours of their stranding. It was determined that the stranding incidents occurred initially at the southern end of the arc and moved northwesterly over the next 36 hours (NOAA, JIR, 2001; Appendix C).
Balcomb's post-mortem examination noted tissue tearing in the inner ears, lungs and areas around the brain as well as bands of hemorrhage in the lungs. Strictly following National Marine Fisheries Service (NMFS) protocol, the preserved and frozen specimens were flown to Harvard Medical School for ultra-high resolution (UHR-CT) analysis of the ears and crania with dissection at Woods Hole Oceanographic Institution.
Necropsies of the whale carcasses revealed similar cranial CT findings. There were no fractures or cutaneous/subcutaneous hemorrhages or other evidence of blunt trauma or primary blast injury from explosive shockwaves. But the evidence for acoustic trauma was strong:
The most significant findings consisted of bilateral intra-cochlear and unilateral temporal region subarachnoid hemorrhage with blood clots bilaterally in the lateral ventricles in the Blainville's beaked whale and intra-cochlear hemorrhages in the Cuvier's beaked whale... Similar ear injuries were seen grossly in the two moderately decomposed Cuvier's beaked whales as well as intracranial staining. In simpler terms, there were deposits of blood within some of the inner ear chambers, and in at least one animal the blood train can be traced to a hemorrhage in a discrete region of a fluid space surrounding the temporal regions and within a ventricle of the brain. Some type of auditory structural damage findings is present in all four beaked whales examined (all showed bloody effusions or hemorrhage near and around the ears).... The presence of blood in only restricted intracranial spaces and the intact inner ear membranes in the best preserved ear are not consistent with simple post-mortem pooling.... The pattern of injury in the two freshest animals, therefore, suggests the ears were structurally intact and the animals were alive at the time of injury. In summary, this pattern of damage is most consistent with acoustic trauma (NOAA, JIR, 2001).
The lack of evidence of chronic debilitating disease or blunt force injury contributed to the medical finding that an in vivo (in the live animal) acoustic or pressure related trauma affected these animals found over a broad geographical area.
National Oceanic and Atmospheric Administration (NOAA) acoustic monitoring stations in the Bahamas confirmed the passage of 7 naval warships and 3 submarines through the Northeast and Northwest Providence channels from midnight on March 14th through 4 p.m., March 15th. Four of the ships (Appendix C) were projecting tactical mid-frequency AN/SQS-53C and AN/SQS-56 sonars. AN/SQS-53C operated at mid-frequencies of 2.6 and 3.3 kHz at a nominal source level of 235 dB, and for four hours at levels greater than 235 dB (at classified levels). (Operation typically involves three half-second "pings" at a two second interval, followed by a 24 second silent, receiving period.) The "nominal" source level (SL) is calculated through the complex array output and convergence/magnification levels into a simplified expression of a single point source (NOAA, JIR, 2001).
Research has shown that biological scatterers can reduce sound propagation by absorbing energy in gas-filled spaces. The swim bladders of fish and marine invertebrates, the carapaces of zooplankton, and air cavities in marine mammals are capable of contributing to the attenuation of sound (NOAA, JIR, 2001). When sound pressure waves pass through these air or gas-filled spaces a resonance effect occurs. The intense compression of gas and the rapidity of resonance vibration may cause rapid tear down destruction of tissues and severe bleeding. This has been compared to explosions within the ears, cranium and lungs. The bands of hemorrhage on the lungs of the Bahamas whales could reflect violent banging of the lungs against the rib cage. Bleeding from the ears and around the brain attest to the rupture of delicate tissues from the force of the acoustic event (Balcomb, pers. comm. August, 2001).
Like the Richter scale, the deciBel (dB) scale is measured logarithmically, so that a tenfold increase in energy occurs with every 10 dB increase in sound output. For example, an increase from 90 dB to 100 dB results in ten times the energy output, but a 60 dB increase will result in sound energy levels a million times greater! Typical fire alarms are at 105 dB; these interfere with normal speech and may cause pain after just a few minutes. Humans sustain permanent hearing damage after about 7 minutes at 120 dB. Death may occur with exposure to 140 dB for a short time. The SuperSonic Transport (SST) at take off is 150 dB. LFA Sonar emits sound originating at 215 dB from 18 bathtub-sized projectors lowered to a depth of 400 feet. The sound waves typically magnify through convergence to a nominal level of 240 dB (NOAA, JIR, 2001). These are literally some of the loudest sounds ever heard on earth.
Frequency refers to the number of cycles per second that a sound produces. Low frequency sonar generally ranges from 100 to 500 Hz. Using concert pitch (A=440), the A above middle C on the piano and notes below would compare to LFA Sonar frequency levels. Mid-frequency extends to about 10,000 Hz, around the highest notes of the piano. As frequency is increased, the pitch of the sound rises. The lower the frequency the lower the pitch, and in water, the farther the sound will travel. Compared to air, the density of water produces low attenuation (weakening) rates. Factors such as salinity and temperature also contribute to the distance the sounds will travel. With computer modeling, Navy documents show that 300 nautical miles from the source, given the right conditions, LFA Sonar (100-500 Hz) will have attenuated to only 140 dB. A distance of 300 nautical miles from the source in all directions would thus cover an astonishingly large area of over 374,000 square miles of ocean within which sound levels received would range anywhere from 140 dB to 240 dB (Reynolds, 2001).
There is an ongoing debate between Navy and non-Navy marine acousticians concerning the differences in sound energy levels of air and water. All agree to the conventional 26 dB figure which accounts for the difference of 20 micro-Pascals (20 uPa), the standard reference pressure for atmospheric sounds, and 1 micro-Pascal (1 uPa), the standard for water-borne sounds. This translates to the reduction of 26 dB from the levels projected in water. However, the Navy chooses to combine an additional 35.5 dB to account for pressure differences, which non-Navy marine acousticians would argue is inaccurate and misleading (Jasny, 1999). By raising the difference from 26 dB to 62 dB it becomes easier to accept a nominal level of 240 dB for the low frequency sonar, as the RL (received level) will actually be no greater than 178 dB. The Navy is trying to persuade NMFS to raise the allowable limits of Level B Harassment (see below, in More Legal Problems) of marine mammals from 120 dB to 180 dB. It will then be possible to legally project high powered sonars at nominal levels of 240 dB without threat of legal action by environmental organizations or citizen enforcers.
Prior to 1963, when the use of high powered sonars began, mass strandings of beaked whales were rare. Explanations of other species' stranding include loss of navigational skills (making a wrong turn into a shallow area), the beaching of an isolated cetacean that might draw others to their closely related pod member, creating a mass stranding, and a phenomenon known as red tide, where a sudden over-production of dinoflagellates creates a toxic environment and depleted oxygen levels. Over the years, damage to auditory organs had rarely been considered a precursor for strandings. Necropsies omitted information about hearing loss on stranded animals. However, as early as 1987, a scientist with the U.S. Geological Service, Dr. J. Geraci, reported dolphins exposed to sonar at 235 dB stranded with explosive ruptures to tissues and lungs. When the report surfaced in the late 1990's, future requests to perform analysis of hearing loss in mass stranded whales were ignored and necropsy reports not made public (Sandoz, 2001). As of this writing, the author has had no response to 3 separate Freedom Of Information Act requests for necropsy reports on strandings from NMFS.
In 1991, the science journal Nature published an article that linked Navy exercises with three separate mass stranding events in the Canary Islands in 1985, 1988 and 1989 (Appendix D). Whales had never before stranded on these islands. In 1998 Nature published a discussion by Dr. A. Frantzis on the 1996 LFA Sonar trials of a NATO vessel near Greece that coincided with a mass cetacean stranding. Scientists in the Caribbean, in October, 1999, heard loud underwater sonar "pings" and observed another mass stranding (Sandoz, 2001).
Facing growing concerns expressed in scientific reports on the effects of high intensity sound, the Marine Mammal Commission voiced its fears over the fate of marine life, and especially whales. The MMC's 1997 annual report to Congress states:
If the LFA system were made available for worldwide use as proposed, all species and populations of marine mammals including those listed as endangered and threatened under the Endangered Species Act could be affected (MMC, 1997, in Green, 2001).
Included in the list of possible effects were loss of hearing, disruption of feeding, calving and communication activities, abandonment of breeding grounds, loss of prey species, stress, a general decrease in survival rates and death.
The Navy has apparently long been aware that high intensity sounds like those produced by the new sonars could cause injury exceeding those for Level B Harassment, as indicated by this 2001 report:
1998 NATO and the US Naval Undersea Warfare Center had calculated that resonance frequency of airspaces in Cuvier beaked whales (Ziphius cavirostris) to be about 290 Hz at 500 meters depth (page H2, SACLANTCEN M-133), which is almost precisely the middle frequency of LFA (100-500 Hz) described in your OEIS/EIS! That information is quite important, with reference to Technical Report 3 of your DOEIS/EIS, wherein there are several citations of Navy sponsored studies that clearly demonstrated vestibular dysfunction (eg. Dizziness, vertigo) and lung hemorrhage, etc. in laboratory animals exposed to LFA at their lung resonance frequency (Balcomb, 2001a).
The National Environmental Policy Act (NEPA) requires submission of an Environmental Impact Statement (EIS) assessing the consequences of any activity that will cause potential irrevocable or severe harm to the environment, yet the Navy defiantly tested and deployed the high powered sonars from 1980 until 1995 without regard for the necessary environmental assessments. In fact, it wasn't until the Natural Resources Defense Council (NRDC) threatened the Navy with legal action that it agreed to comply. It was then that the Navy set out to prove that the high intensity low frequency sound was not detrimental to cetaceans or the environment.
Experiments in the Navy's 1998 Scientific Research Program (SRP) in Hawaii were aimed at establishing that cetaceans would not be harmed from RL's at 180 dB. Four species of whales were exposed to low frequency sounds for one month; scientists reported no significant behavioral changes. However, the protocol for the research limited sound to 150 dB, levels it was assumed would not damage the whales. The scientists who performed the tests warned that typical sonar RL's are 5000 times greater than the SRP testing levels, and that at these levels cetacean injury would be unavoidable. Furthermore, in 80% of the world's oceans, LFA Sonar will affect over 70 species of cetaceans. One can not extrapolate from these 4 species what the effects might be in the others (Green, 2001). There were no follow up reports made on the animals exposed to 150 dB. The Navy did not address harmful effects on prey species, fish, marine invertebrates, zooplankton or spawning areas. In the FOEIS, the Navy based its conclusions on the safety of the LFA Sonar on the SRP (Johnson, 2001), but because of the lack of comprehensive testing at levels comparable to the Navy's planned operation, the publication of the draft EIS provoked calls for its immediate withdrawal as inadequate and unscientific (Sinkin, 2000).
It is a violation of the Marine Mammal Protection Act (MMPA) to interfere with the normal behavior or cause the death of marine mammals. In terms of the MMPA, Level B Harassment refers to activities that would result in a deviation from habitual migration paths, cessation of vocalization (which may impact mating, communication and perhaps hunting) or in any sublethal physical injury. Noise that would cause whales to bleed internally or beach themselves would be considered harassment, even though the beaching is a nearly inevitable death sentence. Level B Harassment levels for noise have been based on studies from the 1980's by Richardson (Richardson et al, 1985) and later by Malme (Malme, et al, 1989) that showed avoidance behavior in cetaceans to sounds at 115 dB and even lower. Since regulators assume that harm would occur to marine mammals if those levels are exceeded, those responsible for the activities, including active sonar, must go through a process to obtain a "Small Take Permit" or "Incidental Harassment Authorization." This allows the proponent of that activity to take (harass, injure or even kill) marine mammals, provided that the "take" is restricted to a specific geographical area, that a small number of animals will be taken, and there is negligible impact on the species or stock.
The Navy's application for a Small Take Permit from NMFS requests permission to kill from 5 to 10% of whale populations in a given area, a large amount by any standards. Remembering the moratorium on take for cetaceans, this is in direct violation of the MMPA for marine mammals and the ESA for any threatened or endangered species.
Difficulty in scientific assessment of populations in the water leaves marine mammals in a precarious position. The interpretation of "negligible amount" might allow for the decimation of entire populations of specific species of whales, as was the case with the rare Cuvier's beaked whale population in the Bahamas (Balcomb, 2001a, 2001b). The effect on the entire global population of Cuvier's beaked whales might arguably be negligible, but typically geographically diverse populations of the same species do not interbreed. The extinction of one subspecies after another may only hasten the overall demise from a worldwide assault on the waters. The intended plan is to patrol 80% of the world's oceans with this low frequency active sonar.
Since the advent of cold war military sonar use in the 1980's, NMFS has been under pressure to raise the allowable standards for acoustic-based harassment. There are numerous sources of intense sound in the oceans, including shipping, oil and gas exploration, ATOC, recreational vehicles, and military explosions in "ship shock trials." Levels of sound produced are frequently high enough to place the marine environment at risk. Yet more often than not small or incidental take permits are not obtained, and the costs of enforcement to NMFS are prohibitive.
As discussed earlier, raising the standard for Level B Harassment by acoustic trauma from 120 dB to 180 dB would remove the permitting requirement for the Navy's high intensity sonar based on the calculations they have sought to impose into the scientific literature. If NMFS allows a difference of 62 dB to stand (as opposed to the non-Navy acousticians 26 dB conversion figure), projecting nominal levels of 240 dB would not violate the standard. The results of these calculations could be grave. No study has proven 180 dB exposure levels are noninjurious. For NMFS, raising the levels to 180 dB translates to fewer enforcement activities and a lot less paperwork.
The Navy has actually been trying to eliminate Level B Harassment as a component of the MMPA, noting that normal behavior is poorly understood in most marine species and behavior changes are therefore difficult to study. This would restrict questions of compliance to actual tissue damaging events.
Perhaps most disturbing of all is the Navy's request to Congress early in 2001 for exemption from environmental laws, citing the Marine Mammal Protection Act, the Endangered Species Act and the need for national security.
The Navy is a repeat offender of the 120 dB standard (Appendix F). After ship shock trials (where explosions were set off to test vessel durability) the Natural Resources Defense Council (NRDC) sued the Navy for violating harassment levels, and won. Since then, NMFS has allowed 160 dB for different ship shock trials. In practice, if an application is made for a small take permit at 180 dB one can be certain RL's will be 180 dB (Jasny, pers. comm.).
The Navy has stated that prior to deployment of LFA Sonar mitigation efforts designed to limit exposure to cetaceans would be implemented. These include visually scanning the area for whales, standard high frequency fish-finding sonar searches and aerial surveys. However, one can hardly see beyond one kilometer of open ocean. A complete scan would require a 360 degree scope of the vessel and involve several personnel. Low frequency active sonar can travel hundreds of miles without attenuation, far beyond the reach of normal high frequency fish finding sonars. Can one assume the Navy would add the expense of launching aircraft to patrol for whales before a naval maneuver? Additionally, if the sonar is hull-mounted or towed from a submarine, the Navy would have a hard time performing a visual scan, and aircraft can't take off from underwater vessels. Cetacean experts are concerned about the effectiveness of these mitigation efforts:
Clearly, the impact of high-powered rapid-rise acoustic energy (such as sonar), particularly at airspace resonance frequency, on these animals is occurring at significant distances well beyond the current mitigation distance (1-2.2 km) used by the Navy. These impact distances can be easily calculated, and they are more like 20 to 100 kilometers, and more well over the horizon of shipboard observers (Balcomb, 2001a).
Public response has been encouraging. After an application for a small take permit is received, NMFS' position in the matter and the rules under which the activity is allowed to take place are published by federal register. The public is given a period (usually 45-90 days) to submit comments to NMFS about the proposed rule. During the comment period for the Navy's small take permit for SURTASS LFA, 30,000 people responded with petitions calling for a denial of the Letter Of Authorization (LOA) to take marine mammals incidental to the LFA Sonar project. Over 1,000 of these were published in the second volume of the FOEIS. NMFS has stated it will respond to every comment.
Since the Bahamas event brought worldwide attention to the issue of military sonars by the strong correlation between acoustic trauma and mass strandings, several organizations have devoted funding and personnel to important bioacoustics research (Appendix E). Public outcry has been so great that plans to test LFA Sonar off the coast of New Jersey in the summer of 2000 (and elsewhere) were withdrawn. In the meantime, environmental activists and cetacean advocates have flooded NMFS and Secretary of Commerce Don Evans requesting a rejection of any permit applications to test or deploy these inevitably deadly sonars. Members of Congress and the Senate were inundated with requests to deny funding for military sonar, and to publicly voice opposition to the LFA Sonar project. Legislators spoke for their constituents before the Subcommittee on Fisheries Conservation, Wildlife and Oceans of the House Committee on Resources on the Marine Mammal Protection Act and Surveillance Towed Array System Low Frequency Active Sonar on October 11, 2001:
Rep. Patsy Mink, a Hawaii Democrat, testified on Thursday that the low-frequency sound waves may cause tissue damage to whale's lungs, heart and nervous systems, and make it more difficult for them to breed. "Never in my 23 years in Congress has there been so many responses on one issue," said Mink, who said she has received nearly 3,000 comments on the effects of sonar on whales from her constituents. (Mink, in Doering, 2001).
In fact, the volume of response was so great against LFA Sonar, that three public hearings were granted and the comment period extended by NMFS to accommodate. During the first hearing, NRDC Senior Attorney Joel Reynolds noted that the organizations in attendance before NMFS represented 7 million constituents (Reynolds, 2001). Celebrities, educators, scientists and even the local Girl Scouts (a total of 256) were present while one Navy official voiced a solitary vote in favor of LFA Sonar. There was no sign of apathy toward this serious environmental issue among those attending.
The issues generated by the Bahamas incident have given rise to much debate and controversy among the scientific community and environmental groups. Even within the Navy there are many who oppose the use of these intense active sonars. Discussions of alternative passive sonar technologies have come to the forefront, as these have shown remarkable potential in detecting vessels at long range. One admiral remarked that a new Robust Passive System (RPS) is capable of detecting virtually anything in the ocean. The use of satellite detection technologies which can create bathymetric contours and chart the deepest ocean floor would further negate the need for such an environmentally injurious technology. Growing numbers within the Navy are bemoaning the litigation that these acoustic devices are generating while many grieve the unmistaken lethality to marine life. At least one defense contractor has advised the Navy to abandon use of active sonars because they illuminate the source vessel's position, making it an easy enemy target. In that case, the sonar's lethal effects might have a reverse effect on the proponents, and pose a costly and deadly threat to our own forces.
The latest finding of potential acoustically driven causes of strandings is the phenomenon of rectified diffusion, known in divers as "the bends":
Rectified diffusion causes gas bubble growth, which in an insonified animal may produce emboli, tissue separation and high, localized pressure in nervous tissue. Using the results of a dolphin dive study and a model of rectified diffusion for low-frequency exposure, we demonstrate that the diving behavior of cetaceans prior to an intense acoustic exposure may increase the chance of rectified diffusion. Specifically, deep diving and slow ascent/descent speed contributes to increased gas-tissue saturation, a condition that amplifies the likelihood of rectified diffusion (Houser et al, 2001).
Populations of cetaceans, fish, sea turtles, sharks, marine invertebrates and plankton could be decimated by ongoing acoustic assaults. The pod of 35 Cuvier's beaked whales and another pod of 120 pilot whales studied by Balcomb in the Bahamas have vanished from the area (Balcomb, pers. comm. 2001, 2001a, 2001b). The need for alternatives could not be more critical:
Cuvier's beaked whales were reasonably common in our field study area prior to the Bahamas incident; we had photo-identified about thirty-five of them, many repeatedly. We typically sighted small groups of these whales a dozen or more times per year in any month of the year. But since the Bahamas sonar incident we have seen this species only once in an entire year, and that was a sighting of two previously unidentified whales (i.e., new arrivals to our study area) about two months after the sonar exercise. None of the whales that were rescued have been seen again. In retrospect, it is probable that all Cuvier's beaked whales in the region when the naval exercise commenced were killed by the sonar, whether or not they were returned to sea by well-wishers pushing them off the shore.
Considering the observed damage to the whales that stranded and died, and the short time period between stranding and death, the NMFS statement that the whales died from stranding is patently absurd. The whales that we observed swimming toward shore and stranding were only temporary survivors of an acoustic holocaust that can be likened to fishing with dynamite (Balcomb, 2001).
The scientific community and environmental groups have often cited the reluctance of the Navy to heed the warnings of its own research. This places them at unwilling odds with the naval establishment, which appears to have placed a slant on interpretation of data to meet its agenda. In fact, the Navy has funded much of the current research on marine mammals and sound in the United States, possibly contributing to an air of intimidation and biased results (Appendix E). In 1995, the Society for Marine Mammalogy published a correspondence highlighting the uneasiness of marine mammal researchers to speak freely about the ship shock and ATOC (190 dB) projects, which involved large acoustic projections into the marine environment (Green, 2001).
All told, sound reason cries out against the use of intense acoustic energy in the marine environment. Continued disregard for the well being of marine life will taint our species and speak poorly of our judgment in these matters. The irrevocable harm that we inflict upon the biodiversity of our oceans will haunt us when we witness the emptiness we have created. Perhaps the challenge for our species is to respect the limitations of our resources and cope with our own presence without reckless disregard for the nurturing environment that sustains us.
Appendix A: Applicable Laws
Appendix B: Coastal States Restrictions
Appendix C: Maps of Bahamas Strandings
Appendix D: Mass Strandings
Appendix E: Research
Appendix F: U.S. Naval Exercises Using Low-Frequency Active Sonar
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