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Whale and dolphin strandings fit predictions
Emma Young, Sydney  

New Scientist

1st December 2004

Three whale and dolphin strandings have left more than 170 animals dead on the beaches of Australia and New Zealand in the past few days.  The precise causes are unclear, but the beachings tally with predictions made by Tasmanian scientists in New Scientist in July 2004.

“We identified that 2004 would be a year for lots of strandings - and this is exactly what we are seeing,” says Mark Hindell of the Antarctic Wildlife Research Unit at the University of Tasmania, Hobart, Australia.

On Sunday, 66 pilot whales and 28 bottlenose dolphins died after beaching themselves on King Island, in the Bass Strait, off the north-west coast of Tasmania.  On the same day, about 60 pilot whales died on Opoutere Beach in New Zealand.  Then on Monday, 42 pilot whales beached themselves on Maria Island, off east Tasmania, and only 23 were successfully refloated.

Possible causes for cetacean beaching are thought to include seismic testing for oil and gas.  But this is not clearly implicated in these new cases.  And whales can also swim into trouble if they follow prey too close into shore.

Westerly winds
Hindell and his colleagues’ analysis of more than 80 years of stranding data

in south-east Australia suggested that every 10 to 12 years, shifts in a climate phenomenon - called the zonal westerly winds - cause colder, nutrient-rich waters to move closer to the shore.  Whales and dolphins follow this cold water towards the coast, and so their risk of beaching increases.  During the last peak, in 1992, there were 29 stranding events.

“We still can’t say precisely why individual pods go ashore.  But since the number of strandings seems to have been high overall this year, it does match our predictions closely,” Hindell says.

The total number of reported strandings has increased dramatically over the last five years, points out Rosemary Gales, senior marine biologist with the Tasmanian National Parks and Wildlife Service: “This follows our concerted efforts to increase public reporting - and it is difficult to disentangle any real increase in strandings with increased notifications.”  But she adds that the 10 to 12-year pattern still seems to hold.