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Active sonar may harm marine animals, although the precise mechanisms for this are not well understood. Some marine animals, such as whales and dolphins, use echolocation systems, sometimes called biosonar to locate predators and prey. It is conjectured that active sonar transmitters could confuse these animals and interfere with basic biological functions such as feeding and mating.

History

The SOFAR channel (short for Sound Fixing and Ranging channel), or deep sound channel (DSC), is a horizontal layer of water in the ocean centered around the depth at which the speed of sound is minimum. The SOFAR channel acts as a waveguide for sound, and low frequency sound waves within the channel may travel thousands of miles before dissipating. This phenomenon is an important factor in submarine warfare. The deep sound channel was discovered and described independently by Dr. Maurice Ewing, and Leonid Brekhovskikh in the 1940s.

Despite the use in naval applications, the idea that animals may make use of this channel was not proposed until 1971. Roger Payne and Douglas Webb calculated that before ship traffic noise permeated the oceans, tones emitted by fin whales could have traveled as far as four thousand miles and still be heard against the normal background noise of the sea, and that on a quiet day in the pre-ship-propeller oceans they would only have fallen to the level of background noise after traveling thirteen thousand miles.

Early Confusion Between Fin Whales and Military Sonar

Fin Whales produce nearly pure tones centered at about twenty cycles per second. Each tone lasts for about a second and is repeated at very regular intervals several times each minute. Sometimes it is hours before the whale either stops or modifies its pattern. Before it was shown that fin whales were the cause, no one could take seriously the idea that such regular, loud, low, and relatively pure frequency tones were coming from within the ocean, let alone from whales. The sounds were first thought to be a simple malfunction in the amplifier—something causing its volume control to oscillate. But when it became obvious that there was nothing wrong with the amplifiers, it was postulated that the sounds were artifacts from geophysical sources located outside the ocean. It was suggested that sources like geomagnetic anomalies, airborne sounds, or seismic signal from inside the earth were responsible. Accordingly, recorders were set up to monitor the same frequency band in these media. But even with the hydrophone recorders overloading on the twenty-hertz acoustic signal, the other monitors showed no signals above the background noise, forcing the conclusion that the sound originated from within the sea and were not—in the words of one of the engineers at the time—“from deep within the earth not from the action of breaking surf on continental shorelines.” Even so, there was still great reluctance to believe that such loud and regular sounds could be coming from whales.

Then someone suggested that the sounds might be a scheme by the Russians to fill the ocean with very low frequency sounds that would establish standing wave patterns in the sea—the idea being that when a U.S. submarines moved it would interrupt the pattern and sub’s position could be determined—a kind of grand expansion of the same technique behind those sonic burglar alarms that insonify a room with a high-frequency sound so that when an intruder moves through it the standing wave pattern is interrupted (or in later versions a Doppler shift created) and an alarm bell activated. With the Russians as possible cause of blips, there was suddenly lots of money available to study the mysterious twenty-hertz noises, But biologists William Schevill and William Watkins soon showed that the sounds were coming from fin whales, and as soon as it was obvious whales were responsible, the party was over and funds dried up. Every now and then paranoia pays a small dividend.

The sound was popularly known by navy acousticians as the Jezebel Monster. Jezebel was an early code name for the research and development program that was listening to undersea sound. Eventually the code name was changed to SOSUS.

Low Frequency Sonar

The electromagnetic spectrum has very rigid definitions for super low frequency, extremely low frequency, low frequency, medium frequency, etc. Acoustics does not have a similar standard. The terms low and mid have roughly defined historical meanings in Sonar, because not that many frequencies have been used over the decades. However, as more experimental Sonars have been introduced the terms can become muddled.

American low frequency sonar was originally introduced to the general public in a 1961 article in Time Magazine entitled New A.S.W. (Anti-Submarine Warfare). The low frequency SONAR used at the time was called Artemis, that could fill a whole ocean with searching sound and spot anything sizable that is moving in the water. Artemis grew out of a 1951 suggestion by Harvard Physicist Frederick V. Hunt (Artemis is the god of the hunt), who convinced Navy A.S.W. experts that submarines could be detected at great distances only by unheard-of volumes of low-pitched sound. At the time, an entire Artemis system was envisioned to form a sort of underwater Defense Early Warning line to warn the U.S. of hostile submarines. Giant, unattended transducers, powered by cables from land, will be lowered to considerable depths where sound travels best. The Time magazine article was published during the maiden voyage of the Soviet submarine K-19, which was the first Soviet submarine equipped with ballistic missiles. Four days later the submarine would have the accident that gave it its nickname. The impact on marine mammals by this system was certainly not a consideration. Artemis never became an operational system.

Low Frequency SONAR was revived in the early 1980s for military and research applications. The idea that the sound could interfere with whale biologics became widely discussed outside of research circles when Scripps Institute of Oceanography borrowed and modified a military SONAR for the Heard Island Feasability Test conducted in January and February 1991. The SONAR modified for the test was an early version of SURTASS/LFA deployed on the Cory Chouest. As a result of this test a Committee on Low-Frequency Sound and Marine Mammals was organized by the National Research Council. Their findings were published in 1994, in Low-Frequency Sound and Marine Mammals: Current Knowledge and Research Needs.

Long range transmission is not synonymous with high power. The acoustic energy in low frequency sound is not converted into heat by the epsom salt in the ocean and can be detected for long ranges. Less than five of the transducers from the LFA array were used in the Heard Island Feasibility Test, and the sound was detected on the opposite side of the earth. The transducers were temporarily altered for this test to transmit sound at 50 Hertz.

A year after the Heard Island Feasability Test a new LFA SONAR was installed on the Cory Chouest which had 18 transducers instead of 10. An environmental Impact Statement was prepared for that system.

Mid Frequency Sonar

The term Mid Frequency Sonar is usually used to refer to Sonars that project sound in the 3 to 4 kilohertz range. Ever since the launch of the USS Nautilus on 17 January 1955 the US Navy knew it was only a matter of time until the other naval powers had their own nuclear submarines. The mid-frequency Sonar was developed for Anti-Submarine Warfare against these future boats. The standard post WWII active sonars (which were usually above 7 kHz) had an insufficient range against this new threat. Active sonar went from a piece of equipment attached to a ship, to a piece of equipment that was central to the design of a ship. They are described in the same 1961 Time magazine article by the quote the latest shipboard sonar weighs 30 tons and consumes 1,600 times as much power as the standard postwar sonar. A modern system produced by Lockheed Martin since the early 1980s is the AN/SQQ-89.. On June 13, 2001 Lockheed Martin announced that it has delivered its 100th AN/SQQ-89 undersea warfare system to the U.S. Navy.

There was anecdotal evidence that mid-frequency sonar could have adverse effects on whales dating back to the days of whaling. The following story is recounted in a book published in 1995.

In 1996 twelve Cuvier's beaked whales beached themselves alive along the coast of Greece while NATO was testing an active sonar with combined low and mid-range frequency transducers, according to a paper published in the journal Nature in 1998. The author established for the first time the link between atypical mass strandings of whales and the use of military sonar by concluding that although pure coincidence cannot be excluded there was better than a 99.3% likelihood that sonar testing caused that stranding. He noted that the whales were spread along 38.2 kilometres of coast and were separated by a mean distance of 3.5 km (sd=2.8, n=11). This spread in time and location was atypical , as usually whales mass strand at the same place and at the same time.

At the time that Dr. Frantzis wrote the article he was unaware of several important factors.

• The time correlation was much tighter than he knew. He knew about the test from a notice to mariners which only published that the test would occur over a five day period within a large area of the ocean. In fact the first time the sonar was turned on was the morning of 12 May 1996, and six whales stranded that afternoon. The next day the sonar was turned on again and another six whales stranded that afternoon. Without knowing the coordinates of the ships he would not have realized that the ship was only about 10–15 miles offshore.
• The sonar being used in the test was an experimental research and development sonar, which was considerably smaller and less powerful than an operational sonar onboard a deployed naval vessel. Dr Frantzis believed that wide distribution of the stranded whales indicated that the cause has a large synchronous spatial extent and a sudden onset. Knowing that the sound source level was fairly low (it was only 226 dB @ 3 kHz which is low compared to an operational sonar) would have made the damage mechanism even more puzzling.
• The experimental sonar used in the test, Towed Vertically Directive Source (TVDS) which had the dual 600Hz and 3kHz transducers, had been used for the first time in the Mediterranean Sea south of Sicily the year before in June 1995. Previous activated towed array sonar research using different sources on board the same ship included participation in NATO exercises "Dragon Hammer '92" and "Resolute Response '94".

Since the source level of this experimental sonar was only 226 dB @ 3 kHz re. 1 meter, at only 100 meters the received level would drop by 40 dB (to 186 dB). A NATO panel investigated the above stranding and concluded the whales were exposed to 150-160 dB re 1 μPa of low and mid-range frequency sonar. This level is about 66 dB less (more than a million times lower intensity) than the threshold for hearing damage specified by a panel of marine mammal experts.

The idea that a relatively low power sonar could cause a mass stranding of such a large number of whales was very unexpected by the scientific community. Most research had been focused on the possibility of masking signals, interference with mating calls, and similar biological functions. Deep diving marine mammals were species of concern, but very little definitive information was known. In 1995 a comprehensive book on the relation between marine mammals and noise had been published, and it didn't even mention strandings.

Acoustically induced bubble formation

There was anecdotal evidence from whalers (see section above) that sonar could panic whales and cause them to surface more frequently making them vulnerable to harpooning. It has also been theorized that military sonar may induce whales to panic and surface too rapidly leading to a form of decompression sickness. In general trauma caused by rapid changes of pressure is known as barotrauma. The idea of acoustically enhanced bubble formation was first raised by a paper published in the The Journal of the Acoustical Society of America in 1996 and again Nature in 2003. It reported acute gas-bubble lesions (indicative of decompression sickness) in whales that beached shortly after the start of a military exercise off the Canary Islands in September 2002.

In the Bahamas in 2000, a sonar trial by the United States Navy of transmitters in the frequency range 3–8 kHz at a source level of 223–235 decibels re 1 μPa (scaled to a distance of 1 m) resulted in the beaching of seventeen whales, seven of which were found dead. The Navy accepted blame in a report, which found the dead whales to have experienced acoustically-induced hemorrhages and bleeding around the animals' ears and eyes. The resulting disorientation may have led to the stranding.

Naval Sonar Linked Incidents

Court Cases

Since mid-frequency sonar has been correlated with mass cetacean strandings throughout the world's oceans, it has been singled out by some environmentalists as a focus for activisim. A lawsuit filed by the Natural Resources Defense Council in Santa Monica, California on 20 October, 2005 contended that the U.S. Navy has conducted sonar exercises in violation of several environmental laws, including the National Environmental Policy Act, the Marine Mammal Protection Act, and the Endangered Species Act. Mid-frequency sonar is by far the most common type of active sonar in use by the world's navies, and has been widely deployed since the 1960s.

On November 13, 2007, a United States appeals court restored a ban on the U.S. Navy's use of submarine-hunting sonar in training missions off Southern California until it adopted better safeguards for whales, dolphins and other marine mammals. On 16 January, 2008, President George W. Bush exempted the US Navy from the law and argued that naval exercises are crucial to national security. On 4 February, 2008, a Federal judge ruled that despite President Bush's decision to exempt it, the Navy must follow environmental laws placing strict limits on mid-frequency sonar. In a 36-page decision, U.S. District Judge Florence-Marie Cooper wrote that the Navy is not "exempted from compliance with the National Environmental Policy Act" and the court injunction creating a 12 nautical-mile no-sonar zone off Southern California. On 29 February, 2008, a three-judge federal appeals court panel upheld the lower court order requiring the Navy to take precautions during sonar training to minimize harm to marine life. The U.S. Supreme Court overturned the ruling in a 5:4 decision on 12 November 2008.

Mitigation methods

Environmental impacts of the operation of active sonar are required to be carried out by US law. Procedures for minimising the impact of sonar are developed in each case where there is significant impact.

The impact of underwater sound can be reduced by limiting the sound exposure received by an animal. The maximum sound exposure level recommended by Southall et al. for cetaceans is 183 dB re 1 μPa s for behavioural effects and 198 dB re 1 μPa s for hearing damage.

A great deal of the legal and media conflict on this issue has to do with questions of who determines what type of mitigation is sufficient. Coastal commissions, for example, were originally thought to only have legal responsibility for beachfront property, and state waters (three miles into sea). Because active sonar is instrumental to ship defense, mitigation measures that may seem sensible to a civilian agency without any military or scientific background can have disastrous effects on training and readiness. Navies therefore often define their own mitigation requirements.

Examples of mitigation measures include (1) not operating at nighttime, (2) not operating at specific areas of the ocean that are considered sensitive, (3) slow ramp-up of intensity of signal to give whales a warning, (4) air cover to search for mammals, (5) not operating when a mammal is known to be within a certain range, (6) onboard observers from civilian groups, (6) using fish-finders to look for whales in the vicinity, (7)large margins of safety for exposure levels, (8) not operating when dolphins are bow-riding, (9) operations at less than full power, and (10) paid teams of veterans to investigate strandings after sonar operation. Besides the expense of some of the mitigation measures some of them might interfere with operations. For this reason, mitigation requirements for wartime use of naval sonars can differ from either civilian mitigation requirements or from military requirements during exercises or peacetime operations. Prohibition on night time operations may be a huge waste of expensive assets. Ramping up a signal in intensity may have no impact on geophysical operations, but Sonar does not work very well if you give the target submarine a warning so that he can do countermeasures. On board civilian observers are used in tuna-boat operations, and in dredging exercises, which are radically different from military operations.

References

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2. "The Heard Island Feasibility Test". Acoustical Society of America. 1994.
3. "CITATION FOR LEONID BREKHOVSKIKH".
4. Among Whales By Dr. Roger Payne, Copyright 1995.
5. "SOFAR channel history".
6. ^ "New A.S.W." June 30, 1961.
7. "The Heard Island Feasability Test".
8. "Photo of the Cory Chouest in Heard Island Feasability Test".
9. "National Academy Press online book".
10. "SURTASS/LFA EIS homepage".
11. "USS Nautilus history".
12. "AN/SSQ-89A Sensor Suite".
13. Payne, Roger (1995). Among Whales. Scribner. ISBN 0684802104.
14. A. Frantzis (5 March 1998). "Does acoustic testing strand whales?". Nature. 392 (392): 29. doi:10.1038/32068. {{cite journal}}: More than one of |pages= and |page= specified (help)
15. "Pelagos Institute (President Alexandros Frantzis) has a copy of the Nature article" (PDF).
16. "Navy Sonars and Whales". November 3, 2004.
17. "SACLANTCEN goes active".
18. Southall et al., Marine mammal noise exposure criteria: Initial scientific recommendations, Aquatic Mammals 33(4), 411-521 (2007).
19. "Marine Mammals and Noise".
20. Crum L A and Mao Y (9 October 1996). "Acoustically enhanced bubble growth at low frequencies and its implications for human diver and marine mammal safety". The Journal of the Acoustical Society of America (99): 2898-907.
21. P. D. Jepson; et al. (9 October 2003). "Gas-bubble lesions in stranded cetaceans". Nature. 425 (425): 575. doi:10.1038/425575a. {{cite journal}}: Explicit use of et al. in: |author= (help); More than one of |pages= and |page= specified (help)
22. ^ Appeals court rejects sonar waiver for Navy
23. ^ "Joint Interim Report Bahamas Marine Mammal Stranding Event of 15-16 March 2000" (PDF). NOAA and United States Navy. 2001. Retrieved 2007-11-22. {{cite web}}: Unknown parameter |month= ignored (help)
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25. "International Whaling Commission, Scientific Committee (IWC-SC) Report - Annex K: Report of the Standing Working Group on Environmental Concerns". 2004-05. {{cite web}}: Check date values in: |date= (help)
26. ^ Jasny, Michael (2005-11). Sounding the Depths II: The Rising Toll of Sonar, Shipping and Industrial Ocean Noise on Marine Life (PDF) (Report). Natural Resources Defense Council. {{cite report}}: Check date values in: |date= (help)
27. Simmonds, M. P. (1991-06-06). "Whales and the military". Nature (351): 448. doi:10.1038/351448a0. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
28. Frantzis, Alexandros (2004), "The First Mass Stranding That Was Associated with the Use of Active Sonar (Kyparissiakos Gulf, Greece, 1996)", in Evans, Peter G.H.; Miller, Lee A. (eds.), Proceedings of the Workshop on Active Sonar and Cetaceans, European Cetacean Society, pp. 14–20
29. ^ Green, Marsha L., PhD. "The US Navy's Low Frequency Active Sonar: Cause for Concern". Ocean Mammal Institute.{{cite web}}: CS1 maint: multiple names: authors list (link)
30. Balcomb, K.C. "Mass Stranding of Cetaceans in the Bahamas Caused by Navy Sonar". Bahamas Journal of Science. 8(2001:2): 2–12. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
31. Freitas, L. (2004), Evans, Peter G.H.; Miller, Lee A. (eds.), Proceedings of the Workshop on Active Sonar and Cetaceans, European Cetacean Society, pp. 28–32
32. Martin, V. (2004), "Mass Strandings of Beaked Whales in the Canary Islands", in Evans, Peter G.H.; Miller, Lee A. (eds.), Proceedings of the Workshop on Active Sonar and Cetaceans, European Cetacean Society, pp. 33–36 {{citation}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
33. U.S. Navy (2004-07-29). "Update on Melon-Headed Whales Stranded in Hawaii, presentation at the Third Plenary Meeting of the Marine Mammal Commission Advisory Committee on Acoustic Impacts on Marine Mammals".
34. Kaufman, Marc (2005-01-28). "Whale Stranding in N.C. Followed Navy Sonar Use - Military Says Connection to Death of 37 Animals Is 'Unlikely'". Washington Post. pp. A03.
35. "Navy Sonar Deleted From Report on Whales". L.A. Times. 2006-01-20. pp. A23.
36. "Marion Bay Whale Stranding - Incident Review Findings". Australian Government Department of the Environment and Heritage. 2005-12-01.
37. Fernández, Antonio (2006-03-17). Beaked whale mass stranding on Almería´s coasts in Southern Spain (26th-27th January, 2006) (Report). University of Las Palmas de Gran Canaria.
38. "European Whale Deaths Linked to British Navy". Animal Welfare Institute.
39. Weiss, Kenneth R. (2008-02-22). "Dolphin dies near sonar site". Los Angeles Times.
40. "MoD admits sonar activity ahead of dolphin stranding". The Times. 2008-06-11.
41. Ko, Nalea J. (2008-07-30). "HPU opening up whale - Researchers will examine the creature that stranded itself". Honolulu Star Bulletin.
42. Mogato, Manny (2009-02-12). "Hundreds Of Dolphins Stranded At Philippine Bay". Planet Ark.
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44. "Natural Resources Defense Council v. United States Navy" (PDF). 2005-10-19. Retrieved 2007-06-23. {{cite web}}: Check date values in: |date= (help)
45. Navy not exempt from California sonar curbs: judge - President George W. Bush should not have exempted the Navy from obeying laws intended to protect endangered whales and other marine mammals by curbing the use of sonar off the California coast, a federal judge ruled on Monday.
46. Judge to Navy: Limit sonar training - Judge overrules Bush on Navy sonar training
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48. "Navy letter to CCC" (PDF).

Links

• Research by Antonella Servidio in a German TV Documentary by Volker Barth

• Sonar