Whale sharks prove egg lovers

Encounter in the deep: Two researchers, one whale shark

By Alex Kirby BBC News Online environment correspondent

Whale sharks will wait for hours on end for fish to spawn so they can eat their eggs.

UK scientists studying the sharks in the Caribbean also found they can tolerate very cold water on their deep dives.

They are investigating whether whale shark tourism could be a substitute for commercial fishing in the area.

The sharks, the world's biggest fish, can grow to 20m in maturity.

The research project leaders are Dr Callum Roberts and Rachel Graham, of the University of York, UK.

Their work, along the Barrier Reef off Belize, is funded by the UK Government's Darwin Initiative, which works with poor countries to conserve their biodiversity.

Different image

The researchers are studying the impact on the whale sharks of both tourism and the commercial fishing of the sharks' food sources.

Snappers beware: Sharks ahead

Satellite tagging shows that the sharks are swimming hundreds of miles in search of food, as far as Mexico and the north of Honduras.

The researchers found that the sharks dive to depths of more than 1,000 metres (3,300 feet), withstanding temperatures of less than 4.5C and pressures of more than 1,500 pounds per square inch (105.5 kg/cm2).

Rachel Graham said the team used pressure sensors on the satellite tags to record the sharks' diving patterns.

She said: "This project has really raised the profile of whale sharks in Belize and helped to introduce many local people to this ambassador of sharks.

Good timekeepers

"Because it is a large, gentle animal, it has dispelled many fears people have about sharks."

The Darwin Initiative helps vultures

She and her colleagues also found that the sharks will wait in a small area for up to 14 hours for snappers to spawn on the reef, so they can eat the eggs.

However far the sharks roam, they always arrive at the spawning grounds exactly on time.

They normally eat plankton, and will travel long distances in search of food. One whale shark was tracked over 13,000 km (8,000 miles) across the Pacific.

Spending boosted

They give birth to live young, and can produce litters of up to 300 pups, though pup mortality is thought to be very high.

Whale sharks are vulnerable to fishing pressures, because they do not reach sexual maturity until they are 25 years old and an estimated 9m long.

Funding for the Darwin Initiative, at present £3m ($4.65m) a year, will reach £7m ($10.85m) by 2005.

Other projects it supports include a penguin-monitoring scheme off South Africa, a snail survey in Sri Lanka, and, in India, the conservation of critically endangered vultures.