October 6, 2005

Great white shark crosses Indian ocean — and back

JOHANNESBURG (Reuters) - A great white shark has astounded scientists by swimming from South Africa to Australia and back in a journey that sheds new light on the murky world of the ocean's most feared predator.

The epic voyage of the tagged female shark -- named Nicole after Australian actress Nicole Kidman -- will be described in the Thursday edition of the U.S. journal "Science."

In the first transoceanic and longest ever recorded trip by a shark, Nicole swam an astonishing 12,400 miles -- and experts reckon she did it for love.

"We suspect that she went for reproductive reasons," Dr Ramon Bonfil of the Bronx Zoo-based Wildlife Conservation Society (WCS) told Reuters by telephone.

"There's plenty of food around South Africa and she would be using too much energy to just go to Australia to feed. Of course we can't prove this at this stage, it is just a hunch," said Bonfil, lead author of the study.

Nicole's tag recorded data on time, temperature, water depth and light levels -- but not whether she mated.

Bonfil said her path was remarkably straight -- after veering a few hundred kilometres south of South Africa's coastline toward Antarctica, she arced east and northeast to Australia.

Along with California, South Africa and Australia are the great white shark capitals of the world.


Nicole's long swim suggests the South African and Australian populations have far more interaction than previously thought and may not be entirely separate groups.

She also did it in just under 9 months -- which the WCS described as "the fastest return migration of any swimming marine organism known."

"We actually know very little about these things," said Bonfil.

Bonfil attached a satellite tag to Nicole's dorsal fin on November 7, 2003. She spent some time in South African waters before embarking on her journey.

On a pre-recorded date, it detaches and floats to the surface, where its data are transmitted via satellite.

"Although Nicole took frequent plunges to depths as great as 3,215 feet -- a record for white sharks -- while crossing the Indian Ocean, she spent most of her time, 61 percent, swimming along the surface," WCS said.

Scientists therefore suspect that great white sharks may use celestial cues for transoceanic navigation.

Over 30 great whites were tagged for the study, with many swimming up and down the eastern side of South Africa. But Nicole headed out for the vast Indian Ocean basin.

Her tag detached after 99 days when she was swimming a mile from shore just south of the Exmouth Gulf in Western Australia.

She popped up again on August 20, 2004, in Gansbaai, South Africa, where she had been tagged the previous November. Researchers recognised her from photographs of her distinctly notched dorsal fin.

Demonised by the hit 1975 movie "Jaws," great whites are fearsome predators but scientists say they are rarely man-eaters. Most attacks are believed to occur when they mistake humans for common prey such as seals or sea turtles.