Dolphins 'decompress like humans'

Common dolphin (Credit: IFAW) Stranded dolphins are common along the coast of Cape Cod in winter months

Related Stories

Scientists have found tiny bubbles beneath the blubber of dolphins that have beached themselves.

The bubbles were discovered by taking ultrasound scans of the animals within minutes of stranding off Cape Cod, US.

The team's findings help confirm what many researchers have long suspected: dolphins avoid the bends by taking long, shallow decompression dives after feeding at depth.

The study is reported in Proceedings of the Royal Society B.

Many biologists believe that marine mammals do not struggle, as human divers do, with decompression sickness - "the bends" - when ascending from great depths.

In humans, breathing air at the comparatively high pressures delivered by scuba equipment causes more nitrogen to be absorbed into the blood and the body's tissues, and this nitrogen comes back out as divers ascend.

If divers ascend too quickly, the dissolved nitrogen forms bubbles in the body, causing decompression sickness.

But marine mammals such as whales, dolphins, and seals are highly adept at dealing with the pressures of the deep.

They 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 that happens at depth.

'The bends'

  • As a diver descends, nitrogen, which makes up about 80% of the air, is absorbed into the body's tissues
  • If a diver ascends slowly, the nitrogen slowly seeps out of the body's tissues and is exhaled in a process called off-gassing
  • If a diver ascends too quickly without ample time to off-gas, nitrogen forms tiny bubbles in the blood, which if left untreated can be fatal
  • Joint pain is a common symptoms of having nitrogen bubbles in the blood, and causes sufferers to bend and contort - giving the decompression sickness its colloquial name "the bends".

However, veterinary scientist Michael Moore from Woods Hole Oceanographic Institute in the US, thinks that it is "naive" to think that diving mammals do not also struggle with these laws of chemistry.

Even marine mammals ascending from the deep must rid themselves of the gas that has built up in their tissues, or risk developing the bends.

If dolphins, he explained, come up too quickly then there is evidence that they "grab another gulp of air and go back down again," in much the same way a human diver would "re-tank and re-ascend" to try to prevent the bends.

"But there's one place you can't do that [if you are a dolphin] and that's sitting on the beach," Dr Moore told BBC News.

And so when he and his team scanned eight Atlantic white-sided dolphins and 14 short-beaked common stranded dolphins using ultrasound, they were not surprised to find tiny bubbles below the blubber of the animals.

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.

Bends over

Sascha Hooker, a marine mammal ecologist with the Sea Mammal Research Unit in St Andrews, UK, commented: "This study is much less about why animals strand, and much more about using stranded animals to give us a bit more insight [into] what is going on inside live marine mammals.

"[What's] particularly interesting from this is that the animals that were released... survived.

"So it looks like these animals are able to deal with some bubbles."

She explained that studying the behaviour and physiology of diving animals is incredibly difficult because researchers cannot follow them down to the deep.

Stranded animals, therefore, offer researchers rare access to these expert divers to measure what changes they undergo to avoid the bends.

More on This Story

Related Stories

The BBC is not responsible for the content of external Internet sites

More Science & Environment stories

RSS

Features

  • Alana Saarinen at pianoMum, Dad and Mum

    The girl with three biological parents


  • Polish and British flags alongside British roadsideWar debt

    Does the UK still feel a sense of obligation towards Poles?


  • Islamic State fighters parade in Raqqa, Syria (30 June 2014)Who backs IS?

    Where Islamic State finds support to become a formidable force


  • Bride and groom-to-be photographed underwaterWetted bliss

    Chinese couples told to smile, but please hold your breath


  • A ship is dismantled for scrap in the port city of Chittagong, BangladeshDangerous work

    Bangladesh's ship breakers face economic challenge


BBC © 2014 The BBC is not responsible for the content of external sites. Read more.

This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.