Nicole the great white trawls ocean for mate

A great white shark called Nicole has made a remarkable return trip from South Africa to Australia, setting a new record in transoceanic travel.

Satellite tagging has revealed that the shark - named after shark-loving actress Nicole Kidman - travelled almost 20,000km in less than nine months and at one point dived to a record 980m.

Scientists said that they were amazed to discover that female sharks make such long-distance journeys, because until now females were thought to stay within the region of the ocean where they were born.

Dr Ramon Bonfil of the Wildlife Conservation Society in New York said that for 61 per cent of the journey, the shark swam within 5m of the sea surface, indicating that it may have used visual cues to navigate.

"I'm very excited about the possibility that she was using celestial cues such as the sun or the moon. She travelled along a very straight track, she knew where she was going. It just blew my mind when I saw it.

"Why else would a shark go to the surface of the sea in the middle of the ocean where there are no seals, penguins or other food? There is no reason unless she was trying to look at something."

In addition to using their excellent sense of vision, great white sharks may also be able to sense the direction of the Earth's magnetic field which they could be using as a compass for navigation, Bonfil added.

The shark was tagged with a transmitter off the coast of South Africa in November 2003 and four months later, when the instrument was automatically released to float to the surface, the shark was off the west coast of Australia.

Data transmitted from the instrument to a satellite revealed the precise movements of the animal, both in terms of the route it took and the depth it swam. The route is published in the journal Science.

Five months later, on August 20, 2004, the scientists spotted the same shark back off the coast of South Africa. They identified her by the unique notches on her dorsal fin.

Bonfil said that the shark, a sexually immature female, may have been making a dummy run to find a mate in Australia where there is a large breeding population of great white sharks.

"There is a possibility that she does this regularly, maybe to find a suitable mate off Australia and then return home to give birth in South Africa," Bonfil said.

The shark performed the fastest transoceanic return migration recorded by marine biologists, travelling for nine months at an average speed of about 5km/h, which is the fastest sustained speed known among sharks, putting Nicole's trip on a par with fast-swimming tuna.

Sharks in general, and great whites in particular, are threatened by over-fishing and loss of habitats and the findings that they travel so widely suggest that measures to protect them need to be global rather than local, Bonfil said.

"Our studies show that the protection by a handful of countries - just five in the world - is not enough if we want to protect this magnificent fish," he said.

- INDEPENDENT