Navy sonars blamed for beached whales
9th October 2003
Powerful naval sonars are most likely to blame for a series of mass whale beachings in recent years, according to scientists.
Mass beachings of marine mammals have been linked to several naval exercises in the past two decades. In most cases the mammals began to be washed up after sonars, which use sound waves to detect submarines, were switched on.
Last year 14 beaked whales were stranded during an international naval exercise off the Canary Islands. They appeared on beaches four hours after the sonars were turned on.
To investigate the mass beachings Antonio Fernandez of the University of Las Palmas in Gran Canaria examined tissues and organs from 10 of the whales beached in the Canaries. Writing in the journal Nature today, he reports how tissues from all of the whales were riddled with holes.
The damage suggests the whales had suffered decompression sickness, or "the bends", shortly before becoming beached. The condition affects divers who surface too quickly from the depths. Nitrogen dissolved in their tissues and blood turns into bubbles with potentially fatal consequences.
"We think the sound of the sonar is making the whales panic, making them surface quickly to try and get away from the noise," says team member Paul Jepson of the Institute of Zoology in London.
The most commonly beached whales after naval exercises are beak whales. Among the deepest of divers, they can swim to depths of more than 1,000m (3,281ft).
Their ability as divers makes them more susceptible to decompression sickness. "This would explain why in these mass strandings it's usually beak whales that are stranded even though there may be other whales and dolphins in the area."
The scientists called on governments to take the findings into account when planning naval exercises.
"This should be enough to stop people in their tracks and think about when they really need to use these sonars," said Mark Simmonds, director of science at the Whale and Dolphin Conservation Society. "Governments need to take this into account. They need to ask themselves what is the right balance between national security interests and the health of marine wildlife?"
Many governments, including Britain, are developing low-frequency sonars which could be even more problematic.
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