Whales 'Suffer From the Bends'
A swift ascent from deep water may be just as dangerous for whales as it is for humansn acute form of the illness was also suspected in beak whales, which were beached after a naval sonar exercise.
This has led researchers to speculate that sonar may distress whales into rising too quickly, resulting in potentially lethal cases of the bends.
It has long been assumed that marine mammals are immune to the illness. Since whales have evolved in the sea for millions of years, it is reasonable to suspect that natural selection would have "found" a physiological solution to decompression sickness.
But there is accumulating evidence to suggest this is not the case.
A collection of sperm whales have been inspected and it has been noticed many of the bones contained lesions and pits, indicating the whales may have suffered mild decompression sickness over the course of their lives, the result of living in a pressure gradient environment. It has also been found that older whales exhibited greater damage and it seems that chronic decompression sickness is not a recent phenomenon in whales - the oldest bones examined were over 100 years old.
It is believed the whales avoid a more acute form of the illness by making sure they ascend gradually, pausing frequently.
Previous research shows that whales display mid-water stops. At the time it wasn't apparent to anybody why they were stopping - but it fits with this hypothesis.
Acute forms of the bends have been observed in beak whales, which beached themselves in the Canary Islands in 2002, following a military sonar exercise.
It was found that they had bubbles in their tissues, which were consistent with severe decompression sickness.
It is not certain how they got into this state, but it seems likely sonar was to blame. One theory suggests that the noxious boom of sonar causes the terrified animals to flee to the surface, triggering an acute form of the bends.
Before scientists can be sure, more research needs to be carried out.