Shark's deep sea dive hits new level

Shack the Great White Shark

A New Zealand great white shark is believed to have set a world record for deep-sea diving, plunging to 1.2km below the surface on his way to Brisbane.

Shack the shark - the biggest tagged in five years of research - has been unofficially crowned the deepest diver after scientists took his records to an international conference.

And although the Aussies may try to claim him, Shack's original home appears to the waters off Stewart Island.

A principal scientist with the National Institute of Water and Atmospheric Research (Niwa), Malcolm Francis, said no one at a great white conference in Hawaii last month had heard of a deeper dive.

The next-deepest recorded by his team was about 1000m.

Shack was tagged by researchers near a seal colony off Stewart Island a year ago and followed for more than three months before his tracking device popped to the surface and transmitted his movements to a computer.

"This one shark has really broken all the records by doing quite a few dives below 1000m and hitting 1200m in one of them - that is a world record as far as we are aware," said Dr Francis.

At 4.8m, Shack is big for a male, suggesting he may be up to 30 or 40 years old. Females grow bigger, with the largest reaching at least 6m long.

Dr Francis said there were several theories about why sharks dived, but the most likely explanation was they were hunting deep-sea prey such as squid. They could also be listening for humpback whales, he said.

Despite their fearsome reputation, great whites seldom attack humans and are considered endangered. Researchers hope they can help to prevent them being accidentally caught by fishers.

The research - a joint effort between Department of Conservation and Niwa with help from the Foundation for Research, Science and Technology - began in 2005 and has revealed some surprising details about sharks' lives.

Great whites were once thought to be predominantly cold-water creatures. But Dr Francis said it appeared that almost all sharks tagged in waters off Stewart Island and the Chatham Islands took regular winter "holidays" to warmer waters such as those around New Caledonia and Norfolk Island.

Of the 31 sharks tagged so far, three had returned from holiday to the exact spot where they were tagged, and another two lost their tags on the way back to New Zealand, he said.

Shack headed from Stewart Island to the coast of Brisbane, where he lost his tag, deep-sea diving along the way.

Once or twice a year researchers travel to favoured shark hang-outs and lure great whites with minced tuna.

They wait until the muscle below the shark's dorsal fin is exposed and jab it with a pole, at the end of which is a barbed tracking device programmed to float to the surface after between nine months and a year.

Some devices detach early and transmit a summary of the shark's movements via satellite to scientists.