Tuesday, February 24, 2009

Mother Nature Does It

STRUNG out along a sand spit, a herd of dead sperm whales lies as stark evidence to scientists that forces of nature off the Tasmanian coast appear to be conspiring against cetaceans.

A Southern Ocean wind pattern has been linked to a recent cluster of strandings in the area, luring deep-sea whales into prey-rich waters near a coast riddled with death traps for them.

On top of that, ferocious gales blew through Bass Strait shortly before the sperm whales became stranded. The winds churned the waters into a maelstrom where just one of the highly social mammals needed to get into trouble for others to follow.

Of the 48 ocean giants stranded on Perkins Island in Tasmania's north-west late on Thursday, only five remained alive late yesterday.

A Tasmanian Parks and Wildlife Service whale rescue spokesman, Warwick Brennan, said the task of saving such large animals, some of them more than 10 metres long, was complicated by the inability to get machinery into such a difficult spot.

"The best chance to move the surviving animals, which are jumbled up with the dead ones, may be at high tide in the morning," Mr Brennan said.

The sperm whales lay only a few kilometres from Anthony's Beach at Stanley, where 64 pilot whales became stranded on November 22. About 80 kilometres away on Tasmania's west coast, more than 150 pilot whales died at Sandy Cape on November 29.

Both species are regarded as deep-ocean dwellers, using sonar navigation to hunt prey in waters such as long canyons that run up to the continental shelf off Tasmania's north-west.

CSIRO scientist Karen Evans and the University of Tasmania's Mark Hindell have found that in these waters, a 10-year cycle of zonal westerly winds appears to coincide with a peak in whale strandings.

Dr Evans said the strong winds generated an upwelling of nutrients that linked up the food chain to bring whales' prey — such as squid — to the area and eventually the whales themselves.

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