DOLPHINS ‘DECOMPRESS LIKE HUMANS’
ARMENPRESS
10:06, 15 October, 2011
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.
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.