Dolphins get the bends

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Although it may not be something you would normally associate with dolphins, scientists have shown that they have the potential to suffer from a very human diving complaint - 'the bends'.

In fact they believe that this may well be the cause of a number of dolphin strandings after scanning a number of stranded dolphins and finding bubbles of gas beneath their blubber.

Before this study, many biologists believed that cetaceans did not suffer from decompression sickness - where dissolved nitrogen forms bubbles in the body- as they take long, shallow decompression dives after feeding at depth. In addition they also slow their hearts, collapse the tiny air-filled chambers in their lungs, and channel blood to essential organs – like the brain – to conserve oxygen and limit the build-up of nitrogen bubbles in the blood.

By taking a gulp of air and then diving again after deep dives, the dolphins avoid the nitrogen building up in their tissues. However it is impossible for the dolphins to do this if they are too close to the shore.

Veterinary scientist Michael Moore from Woods Hole Oceanographic Institute together with a team from the International Fund for Animal Welfare (IFAW), and the Chicago Zoological Society scanned the liver, kidneys, eyes, and blubber-muscle interface of eight Atlantic white-sided dolphins and 14 Short-beaked common stranded dolphins using ultrasound. The found nitrogen bubbles in the kidneys of all but one of the dolphins.

Because three of the dolphins were scanned within minutes of their stranding, the team ruled out the possibility that the air pockets were a result of beaching, and instead think that they formed while the animals were still in the water.

The paper says: "In contrast to marine mammals repeatedly diving in the wild, stranded animals are unable to recompress by diving, and thus may form bubbles. Since the majority of beached dolphins released did not re-strand, it also suggests that minor bubble formation is tolerated and will not lead to clinically significant decompression sickness."

Like most humans it appears that whilst many dolphins might get the bubbles, very few actually suffer from decompression sickness.

The study which was partially funded by the U.S. Office of Naval Research also found that ‘acoustic stressors’ such as sonar can affect the way that cetaceans deal with the gas bubbles. Showing just one of the possible effects of how human or environmentally induced changes to ocean conditions might affect the health and behaviour of dolphins.

For more information see the paper.

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