Marine mammals and sonar
Active sonar, the transmission equipment used on some ships to assist with submarine detection, is detrimental to the health and livelihood of some marine animals.
The study has shown whales experience decompression sickness, a disease that forces nitrogen into gas bubbles in the tissues and is caused by rapid and prolonged surfacing.
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 of background noise after traveling thirteen thousand miles, that is, more than the diameter of the Earth.
[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.
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 Feasibility Test conducted in January and February 1991.
After that the acoustic energy in mid or high-frequency sound is converted into heat, primarily by the epsom salt dissolved in sea water.
Fewer than five of the transducers from the low frequency active array were used in the Heard Island Feasibility Test, and the sound was detected on the opposite side of the Earth.
[16] In 1996 twelve Cuvier's beaked whales beached themselves alive along the coast of Greece while NATO (North Atlantic Treaty Organisation) was testing an active sonar with combined low and mid-range frequency transducers, according to a paper published in the journal Nature in 1998.
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.
[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.
[26][27] 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 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.
[29] 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 m was associated with the beaching of seventeen whales, seven of which were found dead.
Controlled exposure experiments, using simulated military sonar and other mid-frequency sounds, measured behavioral responses of tagged blue whales in feeding areas within the Southern 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.
Sonar-induced disruption of feeding and displacement from high-quality prey patches could have significant and previously undocumented impacts on baleen whale foraging ecology, individual fitness and population health.
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.
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.
