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Marine mammals could suffer bends, say scientists

Seal in Canada
Image caption Scientists say deep dives and rapid ascents could be dangerous for marine mammals

Whales and seals could be prone to the same decompression sickness as human divers, according to a new study.

The work by scientists at St Andrews University found evidence of bubble formation in the bodies of cetaceans.

The researchers said this indicated that the marine mammals could be prone to the condition known as "the bends".

They have also suggested the animals diving behaviour could be affected by excessive human noise, such as exposure to military sonar.

Dr Sascha Hooker of St Andrews University, who led the research, said: "Decompression sickness, commonly known as 'the bends' is a serious problem for human divers, but the jury has been out as to whether marine mammals could get the bends or if it would be as serious for them.

"Unfortunately the technology doesn't yet exist to measure what is going on physiologically inside a free-living whale during its descent to depths of over 1000 metres.

"However, our review of recent work on marine mammal diving physiology leads us to the conclusion that they could suffer from the bends in the same way that humans do."

Pressure-induced increases in nitrogen levels in the blood and body tissues can be followed by depressurisation, which causes the nitrogen to come out as bubbles.

The St Andrews research involved experts from diverse fields including human diving medics, veterinary pathologists and experts in comparative animal anatomy, physiology, ecology and behaviour.

They studied cases including bubbles in the major organs of beaked whales that had beached following exposure to sonar; bubbles in the kidney and liver region of mass stranded dolphins, and bubbles in the tissues of dolphins and seals caught accidentally, for instance by becoming snagged in fishing nets.

The researchers concluded that marine mammals are not all free from the dangers associated with deep dives and rapid ascents.

They suggested that environmental changes could push some species beyond the limits of their coping mechanisms.

Dr Hooker added: "One concern is that these naturally evolving mechanisms may be stretched by human pressures.

"An apparent threat to these animals, such as sudden high-levels of noise, could cause them to react; altering their dive trajectory or eliciting a fight-or-flight response - that causes them to exceed their normal coping mechanisms for the prevention of the bends.

"While the bends is rare under normal circumstances, excessive human noise or disturbance may cause a marine mammal to change its diving behaviour in ways that result in serious illness or injury."

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