Conservationists say many of the world's turtle species, which have survived for millions of years, are now at risk of imminent extinction.

Scientists who attended a conference in Nevada say the situation is critical.

Dr Russell Mittermeier, the president of Conservation International, said: "We are on the brink of losing a group of animals that has managed to survive the upheavals of the last 200 million years, including the great extinction episode that eliminated the dinosaurs".

The conference identified human consumption of turtles, both as food and for traditional medicine, as the main cause of the crisis.

This contrasts with the equally serious plight facing many amphibian species, which are suffering stress apparently caused by changes in the environment.

Demand rises

Turtles are eaten as a luxury by rich people, especially in south east Asia, while the poor, in countries like Madagascar and Mexico, use them as subsistence food.

The Chinese bighead turtle: Demand is soaring (Photo: Turtle and Tortoise Preservation Group)

The Asian trade is driven by growing demand from China, with its ancient traditions of using turtles both for food and as medicine.

Some species can fetch $1,000, and the demand is being fuelled by the recent convertibility of the Chinese currency.

Dr Mittermeier said what was being done in the name of tradition now threatened the survival of a globally important group of animals, and the use of turtles should be stopped.

Scientists frequently see turtles rarely spotted in the wild on sale in markets and restaurants. They think several Chinese species discovered within the last two decades may already be extinct.

US export trade

China imports large numbers of turtles from Vietnam, Bangladesh and Indonesia.

And the USA, where many species have little or no protection, exports more than seven million turtles annually, as pets or for food.

The pressure is especially acute for freshwater turtles, according to Dr Peter Pritchard, director of the Chelonian Research Institute.

"While many people are aware that sea turtles are endangered, few realise that many freshwater turtles and tortoises, several with very restricted geographic ranges, face an even more critical situation."

Some tortoise species are at risk as well (Photo: TTPG)

Only one freshwater species is known to have become extinct this century, a small mud turtle from Mexico, though human exploitation has consigned to history many giant tortoises on oceanic islands.

Large, slow-growing river turtles are of particular concern, with large females at special risk.

Co-operation the key

One possible way forward was spelt out by Dr Whit Gibbons, of the Savannah River Ecology Laboratory.

"We have done a good job of educating the public about the plight of amphibians, but, like them, reptiles need protection too.

"Partners in Amphibian and Reptile Conservation has begun to address this whole class of threatened animals. If turtles are to be saved, it will have to be through co-operative efforts like this."

The conference called for enforcement of wildlife laws and monitoring of the turtle trade. It also urged discussions between scientists and the Chinese authorities.