Wikipedia

Marine mammals and sonar

The interactions betweenmarine mammals and sonarhave been a subject of debate since the invention of the technology.

Ahumpback whale

Activesonar,the transmission equipment used on some ships to assist with submarine detection, is detrimental to the health and livelihood of somemarine animals.[1]Research has recently shown thatbeakedandblue whalesare sensitive to mid-frequency active sonar and move rapidly away from the source of the sonar, a response that disrupts their feeding and can cause mass strandings.[2]Some marine animals, such aswhalesanddolphins,useecholocationor "biosonar" systems to locatepredatorsand prey. It is conjectured that active sonartransmitterscould confuse these animals and interfere with basic biological functions such as feeding and mating. The study has shown whales experiencedecompression sickness,a disease that forces nitrogen into gas bubbles in the tissues and is caused by rapid and prolonged surfacing. Although whales were originally thought to be immune to this disease, sonar has been implicated in causing behavioral changes that can lead to decompression sickness.[3]

History

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TheSOFAR channel(short for "sound fi xing and ranging channel" ), ordeep sound channel(DSC),[4]is a horizontal layer of water in the ocean centered around the depth at which thespeed of soundis at a minimum. The SOFAR channel acts as awaveguidefor sound, and low frequencysound waveswithin the channel may travel thousands of miles before dissipating.[5]This phenomenon is an important factor insubmarine warfare.The deep sound channel was discovered and described independently by Dr.Maurice Ewing,andLeonid Brekhovskikhin the 1940s.[6]

Despite the use of theSOFAR channelin naval applications, the idea that animals might make use of this channel was not proposed until 1971.Roger Payneand Douglas Webb calculated that before ship traffic noise permeated the oceans, tones emitted byfin whalescould have traveled as far as four thousand miles and still be heard against the normal background noise of the sea. Payne and Webb further determined that, on a quiet day in the pre–ship-propeller oceans, fin whale tones would only have fallen to the level ofbackground noiseafter traveling thirteen thousand miles, that is, more than thediameterof the Earth.

Early confusion between fin whales and military sonar

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Before extensive research onwhale vocalizationswas completed, the low-frequency pulses emitted by some species of whales were often not correctly attributed to them. Dr Payne wrote: "Before it was shown that fin whales were the cause [of powerful sounds], 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."[7]This unknown sound was popularly known by navy acousticians as theJezebel Monster.[citation needed](Jezebelwas narrow-band passive long-range sonar.) Some researchers[who?]believed that these sounds could be attributed to geophysical vibrations or an unknownRussian militaryprogram, and it wasn't until biologistsWilliam SchevillandWilliam A. Watkinsproved that whales possessed the biological capacity to emit sounds that the unknown sounds were correctly attributed.[citation needed]

Low frequency sonar

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Theelectromagnetic spectrumhas rigid definitions for "super low frequency", "extremely low frequency", "low frequency" and "medium frequency".Acousticsdoes not have a similar standard. The terms "low" and "mid" have roughly-defined historical meanings in sonar, because not many frequencies have been used over the decades. However, as more experimental sonars have been introduced, the terms have become muddled.

American low frequency sonar was originally introduced to the general public in a June 1961Timemagazine article,New A.S.W.[Note 1]Project Artemis,the low-frequency sonar used at the time, could fill a whole ocean with searching sound and spot anything sizable that was moving in the water. Artemis grew out of a 1951 suggestion byHarvardphysicistFrederick V. Hunt(Artemisis theAncient Greekgoddess of the hunt), who convinced Navy anti-submarine experts that submarines could be detected at great distances only by unheard-of volumes of low-pitched sound.[8] At the time, an entire Artemis system was envisioned to form a sort of underwater DEW (Distant Early Warning) line to warn the U.S. of hostile submarines. Giant, unattendedtransducers,powered by cables from land, would be lowered to considerable depths where sound travels best. TheTimemagazine article was published during the maiden voyage of theSoviet submarineK-19,which was the firstSovietsubmarine equipped withballistic 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 sonarwas 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 whenScripps Institute of Oceanographyborrowed and modified a military sonar for theHeard IslandFeasibility Test conducted in January and February 1991.[9]The sonar modified for the test was an early version ofSURTASSdeployed in theMVCory Chouest.[10]As a result of this test a "Committee on Low-Frequency Sound and Marine Mammals" was organized by theNational Research Council.Their findings were published in 1994, inLow-Frequency Sound and Marine Mammals: Current Knowledge and Research Needs.[11]

Long-range transmission does not require high power. All frequencies of sound lose an average of 65dBin the first few seconds before thesound wavesstrike the ocean bottom[citation needed].After that the acoustic energy in mid or high-frequency sound is converted into heat, primarily by theepsom saltdissolved in sea water.[12]Very little of low frequency acoustic energy is converted into heat, so the signal can be detected for long ranges. Fewer than five of the transducers from thelow frequency active arraywere 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 50hertz,which is lower than their normal operating frequency.

A year after theHeard Island Feasibility Testa new low-frequency active sonar was installed in theCory Chouestwith 18 transducers instead of 10. Anenvironmental impact statementwas prepared for that system.[13]

Mid-frequency sonar

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The termmid-frequencysonar is usually used to refer to sonars that project sound in the 3 to 4kilohertz(kHz) range. Ever since the launch of theUSSNautilus(SSN-571)on 17 January 1955[14]the US Navy knew it was only a matter of time until the other naval powers had their ownnuclear submarines.The mid-frequency sonar was developed foranti-submarine warfareagainst these future boats. The standard post-WWIIactive 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 1961Timemagazine article by the quote "the latest shipboard sonar weighs 30 tons and consumes 1,600 times as much power as the standard postwar sonar".[8]A modern system produced byLockheed Martinsince the early 1980s is theAN/SQQ-89.[15]On June 13, 2001, Lockheed Martin announced that it had delivered its 100th AN/SQQ-89undersea warfare systemto theU.S. Navy.

There wasanecdotal evidencethat 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:

Another innovation by the whalers was the use of sonar to track whales they were pursuing underwater. But there was a problem; as the boat gained on the whale, the whale started exhaling while still submerged. This produced a cloud of bubbles in the water that reflected sound better than the whale did and made a false target (akin to what a pilot does when releasing metal chaff to create a false radar echo). I suspect that this behavior by whales was simply fortuitous since exhaling while still submerged is simply a means by which a whale can reduce the time it has to remain at the surface, where surface drag will slow it down.

Whalers quickly discovered that a frequency of three thousand hertz seemed to panic the whales, causing them to surface much more often for air, This was a "better" use for sonar because it afforded the whalers more chances to shoot the whales. So they equipped their catcher boats with sonar at that frequency. Of course the sonar also allows the whalers to follow the whale underwater, but that is its secondary use. Its primary use is for scaring whales so that they start "panting" at the surface.[16]

In 1996 twelveCuvier's beaked whalesbeached themselves alive along the coast ofGreecewhileNATO(North Atlantic Treaty Organisation) was testing an active sonar with combined low and mid-range frequency transducers, according to a paper published in the journalNaturein 1998. The author established for the first time the link between atypical massstrandingsof whales and the use of military sonar by concluding thatalthough pure coincidence cannot be excludedthere was better than a 99.3% likelihood that sonar testing caused that stranding.[17][18]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 on board 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(decibels)at 3 kHz which is low compared to an operational sonar) would have made the damage mechanism even more puzzling.[19]
  • The experimental sonar used in the test, Towed Vertically Directive Source (TVDS) which had the dual 600 Hz and 3 kHz 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".[20]

Since the source level of this experimental sonar was only 226 dB at 3 kHz re 1 uPa m, 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 55-65 dB less (about a million times lower intensity) than the threshold for hearing damage specified at 215 dB by a panel of marine mammal experts.[21]

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 did not even mention strandings.[22]

In 2013, research showedbeaked whaleswere highly sensitive to mid-frequency active sonar.[2][23]Blue whaleshave also been shown to flee from the source of mid-frequency sonar,[24]while naval use of mid- and high- frequency side-scan sonar was deemed "the most probable cause" of amass strandingof around 50short-beaked common dolphin(Delphinus delphis) on 9 June 2008 inFalmouthBay,Cornwall,UK.[25]

A review of evidence on the mass strandings of beaked whale linked to naval exercises where sonar was used was published in 2019. It concluded that the effects of mid-frequency active sonar are strongest on Cuvier's beaked whales but vary among individuals or populations, which may depend on whether the individuals had prior exposure to sonar, and that symptoms of decompression sickness have been found in stranded whales that may be due to their response to sonar. It noted that no more mass strandings had occurred in the Canary Islands once naval exercises where sonar was used were banned there, and recommended that the ban be extended to other areas where mass strandings continue to occur.[26][27]

Acoustically induced bubble formation

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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 ofdecompression sickness.In general trauma caused by rapid changes of pressure is known asbarotrauma.The idea of acoustically enhanced bubble formation was first raised by a paper published inThe Journal of the Acoustical Society of Americain 1996[28]and againNaturein 2003. It reported acute gas-bubble lesions (indicative of decompression sickness) in whales that beached shortly after the start of a military exercise off theCanary Islandsin September 2002.[29]

In theBahamasin 2000, a sonar trial by theUnited States Navyof transmitters in the frequency range 3–8kHzat a source level of 223–235decibelsre 1 μPa m was associated with the beaching of seventeen whales, seven of which were found dead. Environmental groups claimed that some of the beached whales were bleeding from the eyes and ears, which they considered an indication of acoustically-induced trauma.[30]The groups allege that the resulting disorientation may have led to the stranding.[31]

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Worldwide, use of active sonar has been linked to about 50 marine mammal strandings between 1996 and 2006. In all of these occurrences, there were other contributing factors, such as unusual (steep and complex) underwater geography, limited egress routes, and a specific species of marine mammal — beaked whales — that are suspected to be more sensitive to sound than other marine mammals.

— Rear Admiral Lawrence Rice (11 April 2008)[32]
Date Location Species and Number Naval Activity Reference
1963-05 Gulf of Genoa,Italy Cuvier's beaked whale (15) stranded Naval maneuvers [33]
1988-11 Canary Islands Cuvier's beaked whale (12+) Gervais' beaked whale (1) stranded FLOTA 88 exercise [34]
1989-10 Canary Islands Cuvier's beaked whale (15+), Gervais' beaked whale (3), Blainville's beaked whale (2) stranded CANAREX 89 exercise [35]
1991-12 Canary Islands Cuvier's beaked whale (2) stranded SINKEX 91 exercise [34]
1996-05-12 Gulf of Kyparissia,Greece Cuvier's beaked whale (12) stranded NATO Shallow Water Acoustic Classification exercise [36]
1998-07 Kauai,Hawaii beaked whale (1), sperm whale (1) stranded RIMPAC98 exercise [37]
1999-10 U.S. Virgin IslandsandPuerto Rico Cuvier's beaked whale (4) stranded COMPTUEXexercise [34][37]
2000-03-15 Bahamas Cuvier's beaked whale (9), Blainville's beaked whale (3), beaked whale spp (2), Minke whale (2), Atlantic spotted dolphin (1) stranded Naval MFA [31][38]
2000-05-10 Madeira Cuvier's beaked whale (3) stranded NATO Linked Seas 2000 and MFA [39]
2002-09 Canary Islands Cuvier's beaked whale (9), Gervais' beaked whale (1), Blainville's beaked whale (1), beaked whale spp. (3) stranded Neo Tapon 2002 exercise and MFA [40]
2003-05 Haro Strait,Washington Harbor porpoise (14), Dall's porpoise (1) Orca avoidance "stampede" U.S.S. Shouptransiting while using MFA (AN/SQS-53C) [34]
2004-07 Kauai,Hawaii Melon-headed whale (~200) avoidance "stampede" RIMPAC04 exercise with MFA [41]
2004-07-22 Canary Islands Cuvier's beaked whale (4) stranded Majestic Eagle 04 exercise [34]
2005-10-25 Marion Bay, Tasmania Long-finned pilot whales (145) stranded Two minesweepers using active sonar [42]
2006-01-26 Almería Coast,Spain Cuvier's beaked whale (4) stranded HMS Kentusing active MF sonar [43][44]
2008-06-09 Cornwall,UK Short-beaked common dolphin(Delphinus delphis) (c50, at least 26 died) Naval exercise but no ship sonar in use except HF hydrographic sonar onHMSEnterprise [45][46]

Scientific attention

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Since the 1990s, scientific research has been carried out on the effects of sonar on marine life. This scientific research is reported in peer reviewed journals and at international conferences such as The Effects of Sound on Marine Mammals[47]andThe Effects of Noise on Aquatic Life.[48]

A study on the effects of certain sonar frequencies onblue whaleswas published in 2013. Mid-frequency (1–10 kHz) military sonars have been associated with lethalmass strandingsof deep-divingtoothed whales,but the effects on endangeredbaleen whalespecies were virtually unknown. Controlled exposure experiments, using simulated military sonar and other mid-frequency sounds, measured behavioral responses of tagged blue whales in feeding areas within theSouthern California Bight.Despite using source levels orders of magnitude below some operational military systems, the results demonstrated that mid-frequency sound can significantly affect blue whale behavior, especially during deep feeding modes. When a response occurred, behavioral changes varied widely from cessation of deep feeding to increased swimming speed and directed travel away from the sound source. The variability of these behavioral responses was largely influenced by a complex interaction of behavioral state, the type of mid-frequency sound and received sound level. Sonar-induced disruption of feeding and displacement from high-quality prey patches could have significant and previously undocumented impacts on baleen whale foraging ecology, individualfitnessand population health.[49]

Court cases

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Since mid-frequency sonar has been correlated with masscetacean strandingsthroughout the world's oceans, it has been singled out by some environmentalists as a focus for activism.[50]A lawsuit filed by theNatural Resources Defense Council(NRDC) inSanta Monica, Californiaon 20 October 2005 contended that the U.S. Navy has conducted sonar exercises in violation of several environmental laws, including theNational Environmental Policy Act,theMarine Mammal Protection Act,and theEndangered Species Act.[51]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 (22 km) no-sonar zone off Southern California.[52][53]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.[30]InWinter v. Natural Resources Defense Council.the U.S. Supreme Court overturned the circuit court ruling in a 5:4 decision on 12 November 2008.

Mitigation methods

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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 thesound exposurereceived by an animal. The maximum sound exposure level recommended by Southall et al.[54]forcetaceansis 215 dB re 1 μPa2s for hearing damage. Maximumsound pressure levelfor behavioural effects is dependent on context (Southall et al.[54]).

In the US, 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 defence, mitigation measures that may seem sensible to a civilian agency without any military or scientific background can have disastrous effects on training and readiness. The US Navy therefore often define their own mitigation requirements.[55]

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 cetaceans a warning
  4. air cover to search for cetaceans
  5. not operating when cetaceans are known to be within a certain range
  6. onboard observers from civilian groups
  7. using fish-finders to look for cetaceans in the vicinity
  8. large margins of safety for exposure levels
  9. not operating when dolphins are bow-riding
  10. operations at less than full power
  11. paid teams of veterans to investigate strandings after sonar operation.

See also

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Further reading

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  • Joshua Horwitz (2014).War of the Whales: A True Story.Simon & Schuster.ISBN978-1-4516-4501-9.

Notes

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  1. ^ASW is an acronym for "anti-submarine warfare"

References

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  50. ^"LFAS / Active Sonar In the News".Act Now for Ocean Natives.Retrieved2007-06-23.
  51. ^"Natural Resources Defense Council v. United States Navy"(PDF).2005-10-19.Retrieved2007-06-23.
  52. ^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.
  53. ^Judge to Navy: Limit sonar training - Judge overrules Bush on Navy sonar trainingArchived2008-12-18 at theWayback Machine
  54. ^abSouthall et al., Marine Mammal Noise Exposure Criteria: Initial Scientific Recommendations, Aquatic Mammals 2007, 33(4), 411-521Archived2011-07-24 at theWayback Machine
  55. ^"Navy letter to CCC"(PDF).
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