Scientists have said the long-threatened Yangtze River dolphin in China may be extinct due to human activity.
If they are correct, it would be the first extinction of a large vertebrate for more than 50 years and the first whale or dolphin to be wiped out due to human activity.
The white long-beaked fresh water dolphin, or baiji, was last spotted several years ago and an intensive six-week search in late 2006 failed to find any evidence of the species.
Dr Samuel Turvey, a conservation biologist at the Zoological Society of London, said the dolphin's demise resulted from over-fishing, pollution and lack of intervention.
He added that news of the probable extinction should spur governments and scientists to act to save other species verging on extinction.
The team, which published its findings in the Journal of the Royal Society Biology Letters today, included researchers from the US, Britain, Japan and China. The Chinese government also authorised the survey.
The last confirmed baiji sighting was in 2002, although there have been a handful of unconfirmed sightings since then. Dr Turvey added that the last baiji in captivity died in 2002.
During the six-week search, the team carried out both visual and acoustic surveys and used two boats to twice cover the dolphin's 1,669km 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 Dr Turvey said fishing, pollution and boat traffic in the busy river, home to about 10% of the world's population, has likely meant the baiji's end.
The dolphins will now be classified as critically endangered and possibly extinct but Dr Turvey said there is little chance any remaining baiji are alive.
He added that 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.
