Science News

Hanging out at the shark café

Sun, 8th Nov 2009

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Scientists have come a step closer to understanding the mysterious lives of some of the oceans biggest predators – the Great White Sharks – in a 10-year study that tracked nearly 200 sharks as they swim around the eastern Pacific Ocean.

A great white shark at Isla Guadalupe, Mexico. Published by the Royal Society in their Series B journal, the study by a big team of researchers led by Salvador Jorgensen from Stanford University in the US unpicked some great white secrets, including pinpointing their favourite mid-ocean hang out: a spot of sea between Hawaii and the Californian coast nicknamed the shark ‘Café’.

The team used a combination of cutting edge satellite tagging technology, acoustic tags that are detected by sensors placed around the Pacific Ocean and DNA analysis of samples taken from wild sharks

Jorgensen and the team discovered that every winter the sharks regularly migrate away from coastal waters off California and head out 4000 km to the warm waters of Hawaii, before heading east again the following summer.

The big question is, why do great white sharks bother swimming so far every year, backwards and forwards, using up so much energy?

And the answer – unfortunately – is that we don’t really know. But, researchers think the sharks are probably visiting Hawaii every year to feed since the tags showed the sharks regularly diving down deep probably hunting for prey.

And as for the mid-ocean shark café? It’s likely that the great white sharks are feeding and also mating there too. The tagging studies showed males and females mingling in the shark café, at around the right time ahead of females giving birth in likely nursery grounds in coastal waters further east. Great white females gestate foetuses for 12 or possibly even 18 months before they give birth.

The study also revealed that sharks keep on returning to the same area of coastal habitat off the American coast. It’s possible that sharks hunt more successfully when they know the area well.

The study also showed that great white sharks in the northeast Pacific are a distinct population from other sharks in Australia and South Africa. This is vital information for conservationists, because even if many people are still scared of these toothy predators they are, sadly, facing an uncertain future because of overfishing. Their large fins are highly prized for the trade in sharks fin soup.

Studies like these are revealing vital details about the lives of great whites, highlighting that they are not simply mindless killing machines milling around aimlessly, but they undergo complex migration that we are only just beginning to understand.

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