In a six-week survey of the 1,669-kilometre stretch of the Yangtze from the Three Gorges Dam to Shanghai, not a single river dolphin was found. The report of the researchers, who scoured the river four times in two boats, was published on Wednesday in the British journal Biology Letters.
"The loss of such a unique and charismatic species is a shocking tragedy," according to Sam Turvey, a conservation biologist who worked on the survey with Chinese government scientists. He added: "This extinction represents the disappearance of a complete branch of the evolutionary tree of life."
A freshwater marine mammal, the baiji is the first large vertebrate forced to extinction by human activity in 50 years. Its extinction marks only the fourth time since 1500 that an entire evolutionary line of mammals has vanished from the earth.