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Rescuers help stranded whales return to sea, but many questions remain

March 24, 2009 |  7:06 pm


Pilot whales -- a species whose members have beached themselves on Australia's coastline in numbers totaling hundreds in the last few months -- are incredibly social animals.  They're known to follow each other into danger, which may, in some respects, explain why they're so prone to mass stranding.  In the most recent case, more than 80 long-finned pilot whales and dolphins became stranded in Hamelin Bay south of Perth, where they were discovered Monday.  Most had already died when rescuers arrived. 

Today, 11 surviving whales were guided back out to sea at nearby Flinders Bay.  West Australian reports that most have disappeared, raising rescuers' hopes that they won't beach themselves again.  But they're not taking any chances -- some rescuers and volunteers with canoes, jet skis and boats worked today to keep the whales from coming too close to shore, and there are plans to monitor them by airplane Wednesday. 

See more photosOne of the whales had noticeable trouble breathing after her return to sea; rescuers brought her back to shore rather than risking the possibility of her leading the other whales back to the beach.  By late afternoon, she was barely breathing and the decision was made to put her down.  The remaining 10 are believed to be swimming in deep waters.

"Certain species of whales are more prone to mass strandings because the social bonds between them are incredibly strong," conservationist Mike Bossley told the Associated Press about pilot whales and sperm whales, another species prone to beaching. "If one animal is in trouble, the others won't leave him." 

But what makes the first whale strand, causing the others to follow?  That's still unclear.  From the Associated Press:

Scientists have offered some theories: The whales may be chased by predators such as killer whales, or they could be following prey themselves. The sonar they use to navigate the dark seas could be hindered by natural geomagnetic factors such as iron ore deposits. They may swim into an area where sandbars or peninsulas block their exit. Or they may follow one ill or injured pod member and refuse to leave it.

Human activity such as undersea exploration for petroleum or the sonar of submarines also can interfere with whale and dolphin navigation.

More than 500 pilot whales and sperm whales have become beached in Australia since November; more than 400 have died.  One scientist pointed out a trend in the number of strandings during an interview with the AP:

Marine researcher Karen Evans said the timing is right for an increase in beachings. In 2004 she co-authored a study concluding that beachings peak in a 10-year cycle linked to climate changes in the oceans.

"We're in a peak period now," said Evans, of Australia's Commonwealth Scientific and Industrial Research Organization. "What happens in that period is the climate factors increase the prey field near the shore, forcing whales closer to shore and thereby increasing the probability that they will strand."

Evans acknowledged that her research doesn't explain the cause of the beachings, but said that the cycle it shows -- which dates back to the 1920s -- could help governments prepare for future peak periods.

-- Lindsay Barnett

Photo: Tony Ashby / AFP

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