For 20 million years, the white-fin dolphin, or baiji, swam China's longest river, the Yangtze. But a few years of breakneck development, overfishing and a massive increase in shipping have reduced sightings of this shy, graceful creature to zero.
A recent expedition failed to spot a single Lipotes vexillifer, and now conservationists fear the almost-blind, long-beaked animal is gone for good, the first big aquatic mammal to become extinct due to human activity.
"We have to accept the fact that the baiji is extinct. It is a tragedy, a loss not only for China, but for the entire world," said the joint leader of the expedition, August Pfluger, an economist who runs the Swiss-based baiji.org, an environmental group dedicated to saving the dolphins.
Scientists say the search for the dolphin will continue, even though the 30-strong team which has plied the length of the Yangtze for the past six weeks failed to sight the cetacean.
Measuring up to 8ft 2in (2.5 metres) in length, the baiji is a relative of other freshwater dolphins in the Mekong, Indus, Ganges and Amazon rivers.
It used to be worshipped as a goddess by the Chinese. According to legend, the baiji is the reincarnation of a princess who refused to marry a man she did not love and was drowned by her father for shaming the family.
When it was listed as one of the most endangered species in the world in 1986, there were still 400 white-fin dolphins alive, but the population dropped alarmingly to fewer than 150 over the past decade. A survey in 1997 listed just 13 sightings, with the last confirmed sighting in 2004. The final baiji in captivity, Qi Qi, died in 2002.
Keen to repeat the success at breeding endangered species that it had with pandas, the Chinese government set up a reserve in a lake in central Hubei province to look after captured baiji, but could not find any of the dolphins to start an artificial propagation programme.
The expedition surveyed the 1,700km river using acoustic equipment to detect the sound of dolphins. There is some slight hope, as some of the sounds gathered have yet to be identified. But as Mr Pfluger says, even if one or two dolphins are left, they are ultimately doomed.
If the dolphin is indeed extinct, it will be the first big aquatic mammal to disappear since hunters killed off the Caribbean monk seal in the 1950s.
Wang Ding, a scientist from the Chinese Academy of Sciences, who led the team of 25 scientists from China, the US, Britain, Japan, Germany and Switzerland, said the search would go on as there might still be some left. "We will try every effort to save them as long as it is not announced to be extinct," he said, adding that the monitoring of hot spots and small-scale searches would continue.
"The expedition only covered the main section of the Yangtze River and the scientists only searched for the dolphins eight hours a day, which means some dolphins might have been missed," he said. By definition, an animal is declared extinct only if it has not been seen in the wild for 50 years, he pointed out.
The white-fin dolphin is top of food chain in the Yangtze and has no natural enemies, except for man. The Yangtze is also China's busiest waterway, and the baiji shared the river with huge ships, tugboats and fishing boats.
Experts describe the white-fin dolphin, which is native to China, as a living fossil as it has not changed in appearance since it first entered the Yangtze from the sea.
China's dolphins are in trouble, facing threats from pollution and economic expansion. The expedition also highlighted the threats to other species. They spotted about 300 members of another endangered species of freshwater mammal, the Yangtze finless porpoise, far fewer than expected.
Scientists said illegal fishing on the river, sometimes using explosives, had wreaked havoc on the dolphin population.
Baiji are also prone to crashing into ship's propellers. Because they have poor eyesight, the dolphins use sound to orient themselves, but their sonar systems are easily disrupted.
The United Nations environment programme has declared the Yangtze a dead zone, saying its water lacks sufficient oxygen to support fish.
"If the Yangtze river can not support the white-fin dolphin at present, maybe it can not support human beings in the future," said Dr Wang. "We must learn a lesson from it."Reuse content