The Yangtze river dolphin, until recently one of the most endangered species on the planet, has been declared officially extinct following an intensive survey of its natural habitat.
The freshwater marine mammal, which could grow to 2.4m long and weigh up to one-fourth of a tonne, is the first large vertebrate forced to extinction by human activity in 50 years, and only the fourth time an entire evolutionary line of mammals has vanished from the face of the Earth since the year 1500.
Conservationists described the extinction as a "shocking tragedy" on Tuesday, caused not by active persecution but accidentally and carelessly through a combination of factors including unsustainable fishing and mass shipping.
In the 1950s, the Yangtze river and neighboring watercourses had a population of thousands of freshwater dolphins, but their numbers declined dramatically after China industrialized and transformed the Yangtze into an artery of mass shipping, fishing and power generation. A survey in 1999 estimated the population of river dolphins was close to just 13 animals.
Sam Turvey, a conservation biologist at London Zoo, worked with Chinese government scientists to survey the entire 1,669km stretch of the Yangtze river downstream of the giant Three Gorges Dam to Shanghai.
The team scoured the river four times in two boats during the six-week survey, using high-powered binoculars to spot the dolphins. Sensitive hydrophones were towed behind to listen for their calls.
The researchers hoped that if any dolphins were spotted, they could be taken to a reserve in an oxbow lake which was once part of the Yangtze.
Around half of all river dolphins were killed as a result of indiscriminate fishing practices.
"The Yangtze river dolphin was a remarkable mammal that separated from all other species over 20 million years ago. This extinction represents the disappearance of a complete branch of the evolutionary tree of life," Turvey said.