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.
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.
Read full story: BBC