"Henrik Manley" <m@nley.dk> wrote in message
news:HQYyUnQpFHA.2088@gud.bends.dk...
> >Hvorfor for hvaler ikke dykkersyge ligesom os andre ?
>
> Som andre har skrevet så ånder de ikke under dykket og så tager de heller
> ikke kvælstof med ned da de ånder ud før de dykker. Ilten de har brug for
> under dykket er i deres blod.
Ok, men er der ikke også kvælstof opmagasineret i deres blod, på samme måde
som hos mennesker?
Fandt i øvrigt:
http://news.bbc.co.uk/2/hi/science/nature/4122119.stm
(På linket er et billede af hvad der måske er hvalknogler udsat for
dykkersyge)
Whales 'suffer from the bends'
By Julianna Kettlewell
BBC News science reporter
A swift ascent from deep water may be just as dangerous for whales as
it is for humans, Science magazine reports.
Damage consistent with the bends - every diver's nightmare - has been
found in the bones of sperm whales.
An acute form of the illness was also suspected in beaked 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.
These findings will come as a surprise to many people, because it has
long been assumed that marine mammals are immune to the illness.
Pits and lesions
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.
Michael Moore and his team, of Woods Hole Oceanographic Institution,
US, have been inspecting bones from a collection of sperm whales.
They noticed that many of the bones contained lesions and pits,
indicating the whales may have suffered mild, but chronic, decompression
sickness over the course of their lives.
"I see it as the cost of living in a pressure gradient environment,"
said Michael Moore.
Professor Moore examined bones from whales of a range of ages and
found that older individuals exhibited greater damage.
"It is a bit like the ageing process," said Professor Moore. "Old
whales show the stresses that they face in their daily lives."
It seems that chronic decompression sickness is not a recent
phenomenon in whales - the oldest bones Professor Moore examined were over
100 years old.
He believes the whales avoid a more acute form of the illness by
making sure they ascend gradually, pausing frequently.
"Natural selection has in the large part solved the problem by
developing dive behaviours that allow the animals to manage the problem," he
said.
"Previous research does show that the animals display mid-water stops.
At the time it wasn't apparent to anybody why they were stopping - but it
fits with this hypothesis."
Beaked whales
Apparently acute forms of the bends have been observed in beaked
whales, which beached themselves in the Canary Islands in 2002, following a
military sonar exercise.
Paul Jepson, of the Zoological Society of London, studied the dead
whales. He found 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.
"There is a very good correlation between naval sonar and the mass
strandings of beaked whales, going back to the 1960s," said Dr Jepson. "The
question is how is it making the animals strand?"
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.
Michael Moore said: "One of the quietest zones in the ocean is right
up at the surface - they might be trying to get away from the noise."
Before scientists can be sure, more research needs to be done.
"We don't fully understand how they behave in response to sound," said
Dr Jepson. "If we know the mechanism we can try to mitigate it and prevent
it being potentially damaging to the animals."
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