For some whales, sonar may provoke suicidal behaviour

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Scientists have long known that some beaked whales beach themselves and die in agony after exposure to naval sonar, and now they know why: the giant sea mammals suffer decompression sickness, just like scuba divers. At first blush, the explanation laid out Wednesday by 21 experts in the Royal Society journal Proceedings B seems implausible.

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Millions of years of evolution have turned whales into perfectly calibrated diving machines that plunge kilometres (miles) below the surface for hours at a stretch, foraging for food in the inky depths. The heart rate slows, blood flow is restricted, oxygen is conserved. So how could the ocean's most accomplished deep-sea diver wind up with nitrogen bubbles poisoning its veins, like a scuba novice rising too quickly to the surface? Short answer: beaked whales -- especially one species known as Cuvier's -- get really, really scared.

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"In the presence of sonar they are stressed and swim vigorously away from the sound source, changing their diving pattern," lead author Yara Bernaldo de Quiros, a researcher at the Institute of Animal Health at the University of Las Palmas de Gran Canaria, Spain, told AFP. "The stress response, in other words, overrides the diving response, which makes the animals accumulate nitrogen," she added. "It's like an adrenalin shot."

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