Growing human pressure means the survival of two-thirds of the world's tortoises and freshwater turtles is under threat, conservationists say.
By Alex Kirby
BBC News Online environment correspondent
They are launching a $5m campaign to try to save the 25 most endangered species.
The greatest threat is the use of the reptiles for food and Far Eastern traditional medicine.
Scientists say some species could be driven to extinction within 20 years.
The campaign is the work of the Turtle Conservation Fund (TCF), set up by the Center for Applied Biodiversity Science (Cabs), based at Conservation International, and two partners of IUCN-The World Conservation Union.
They are the Turtle Survival Alliance, and the Tortoise and Freshwater Turtle Specialist Group.
It does not include the eight marine turtle species. Dr Kurt Buhlmann, TCF executive director, told BBC News Online: "Substantial resources and study have been expended for the marine turtles, but not for the smaller but no less charismatic freshwater turtles."
The fund's list of the 25 species at highest risk includes:
the Roti snake-necked turtle of Indonesia, driven to commercial extinction by the pet trade
the Chinese three-striped box turtle, hunted with dogs for use in making supposedly cancer-curing soup and jelly
the Burmese star tortoise, now protected by Buddhist monks
the southern speckled padloper tortoise of South Africa, which grows to a maximum length of four inches (10 cm)
the yellow-blotched map turtle of Mississippi, shot for fun by US sportsmen.
The fund says 200 of the world's 300 surviving tortoises and freshwater turtles are threatened and need protection, with human exploitation and development-related pressures a growing danger.
It says: "Of particular concern is the unrelenting demand from the Asian food and traditional medicine market, with more than half of the continent's 90 species endangered or critically endangered.
Chinese three-striped box turtle (Image: Kurt Buhlmann)
"Tonnes of live turtles are imported each day to southern China... The non-sustainable harvest has decimated natural populations near the consumer source... and is now even beginning to impact turtles in North America, Africa, Europe and elsewhere."
Hundreds of thousands of adult and hatchling snapping and softshell turtles have been exported from the US to China for food in the last decade.
Frank Momberg is the Vietnam country programme director for Fauna & Flora International, based in Cambridge, UK.
Ignorance is total
He told BBC News Online: "Borneo is already empty of turtles, the trade is going into Myanmar, the whole of Asia is being emptied out for China.
"That's where the volume trade is, but there's also local consumption in Vietnam.
I've been invited to turtle feasts by forest department officials.
"I've seen macho youths slitting the throats of softshelled turtles and letting the blood drip into glasses of rice wine. There's no awareness whatsoever."
Yellow-blotched map turtle (Image: David E Collins)
Other threats include habitat loss, the pet trade, alien species, pollution, and introduced pathogens.
Twenty-one of the 25 listed species live in 11 of the world's 25 "biodiversity hotspots", areas which house the greatest number of species and yet face the severest threats.
The fund hopes to raise $5.6m to implement its five-year action plan, which will include captive breeding, turtle farming, research and monitoring, and sustainable harvest programmes.
Nine turtle and tortoise species have been driven to extinction in the modern era, including seven giant tortoises from Africa and Latin America.
An eighth, the Abingdon Island giant tortoise of the Galapagos, is represented by one survivor named Lonesome George, who may survive another century in solitary state.
Roti snake-necked turtle image courtesy and copyright of R Andrew Odum, Toledo Zoologica