Military Sonar Blamed for Mass Dolphin Strandings
by Lewis Smith
Mass strandings of dolphins and whales could be caused because the animals are rendered temporarily deaf by military sonar, experiments have shown.
Tests on a captive dolphin have demonstrated that hearing can be lost for up to 40 minutes on exposure to sonar. Hearing is the most important sense for dolphins and other cetaeceans, and losing it is likely to cause them to become disorientated and alarmed.
The finding by the Hawaii Institute of Marine Biology may explain several strandings of dolphins and whales in the past decade. Most strandings are still thought to be natural events, but the tests strengthen fears that exercises by naval vessels equipped with sonar are responsible for at least some of them.
The study also suggested, however, that dolphins and whales would usually be able to swim away fast enough and far enough to escape any ill effects from sonar.
To induce deafness in the Atlantic bottlenose dolphin, Tursiops truncatus, the sonar device would have to be loud, close and would need to last for at least two minutes.
This should give the animals plenty of time to escape but in some circumstances noises can be caught in "underwater sound traps", Aran Mooney, of the University of Hawaii, said.
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http://www.commondreams.org/headline/2009/04/08-2