Elephant Seals Dive Deepest
HOBART, April 6 AAP - The world mammal diving champions have been
discovered - the giant elephant seals of Australia's sub-Antarctic Macquarie
Island.
They can dive more than a kilometre deep and stay underwater for two
hours. The trick is in their ability to slow their heart rate.
The remarkable exploits of the world's biggest seal have been discovered
by a research team from the University of Tasmania.
Team leader Mark Hindell, a lecturer in Antarctic biology, said today
that during the three-year project satellite transmitters were attached to
the seals to see how far they ranged and how deep they dived.
They were also fitted with data loggers, or mini computers, which
recorded swimming speed and heart rate.
Dr Hindell said the seals dived much longer than would have been expected
from what was known about their oxygen reserves.
"The only way they could do this, which is very strange for a mammal, is
by slowing their metabolism," he said.
"All diving animals do this to some degree, but our results suggest that
it is quite dramatic in these seals."
Their heart rate, which was 100 to 110 a minute at the surface, fell as
low as ten during a dive.
"As far as we know this is unique," he said. "They are the best divers."
The team, using satellite tracking technology, also discovered the
remarkable precocity of young elephant seals.
Dr Hindell said mothers stayed with their young for only six weeks, then
left them to fend for themselves.
"In tracking the juveniles, we expected them to spread randomly looking
for food, with some being more successful in foraging than others," he said.
"But to the contrary, with virtually no guidance from the adults, they
managed to find their way to the same area of ocean, about 1,000 kilometres
south-east of Macquarie Island, in search of squid.
"We're now keen to pursue this to determine how the juveniles know just
where to forage for this food."
Dr Hindell said most of their work was done on female adults, which grew
to 500 kilograms. Males could be 2,500 kilograms.
He said elephant seals were found around all sub-Antarctic islands. There
were 80,000 to 90,000 around Macquarie Island, with the population having
declined over the past 30 years.
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