A Yangtze River dolphin, also known as a baiji, is seen in this undated handout...
LONDON (Reuters) - The long-threatened Yangtze River dolphin in China is probably extinct, according to an international team of researchers who said this would mark the first whale or dolphin to be wiped out due to human activity.
The freshwater dolphin, or baiji, was last spotted several years ago and an intensive six-week search in late 2006 failed to find any evidence that one of the rarest species on earth survives, said Samuel Turvey, a conservation biologist, at the Zoological Society of London, who took part in the search.
He said the dolphin's demise -- which resulted from overfishing, pollution and lack of intervention -- might serve as a cautionary tale and should spur governments and scientists to act to save other species verging on extinction.
"Ours is the first scientific study which didn't find any," he said in a telephone interview. "Even if there are a few left we can't find them and we can't do anything to stop their extinction."
The team, which published its findings in the Journal of the Royal Society Biology Letters on Wednesday, included researchers from the United States, Britain, Japan and China. The survey was also authorized by the Chinese government, Turvey said.
The last confirmed baiji sighting was 2002, although there have been a handful of unconfirmed sightings since then. The last baiji in captivity died in 2002, Turvey said.
During the six-week search, the team carried out both visual and acoustic surveys and used two boats to twice cover the dolphin's 1,669 kilometer range stretching from the city of Yichang just downstream from the Three Gorges dam to Shanghai.
The last such survey conducted from 1997 to 1999 turned up 13 of the mammals, but Turvey said fishing, pollution and boat traffic in the busy river, home to about 10 percent of the world's population, has likely meant the baiji's end.
"We covered the whole range of the dolphin twice," Turvey said. "It is difficult to see how we could miss any animals."
The dolphins will now be classified as critically endangered and possibly extinct but Turvey said there is little chance any remaining baiji are alive.
Researchers have known for years about the dolphin's precarious situation but indecision about how best to save the species meant little was actually done, he added.
This underscores the need to act quickly to prevent the extinction of other similar shallow-water aquatic mammals like the vaquita found in the Sea of Cortez and the Yangtze finless porpoise, Turvey said.
"One really needs to learn from this to make sure future conservation efforts are more dynamic," he said. "There has always been so much focus on 'save the whale' and 'prevent whaling' that it has led to these range-restricted shallow cetaceans slipping through the crack."
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