Dolphins are swimming not only in the sea, but also in the rivers. Or at least they used to. One of the three known species of freshwater dolphins, the Chinese one, is now "likely to be extinct"(the other two species inhabit Ganges and Indus and Amazon, respectively).

An American-British-Japanese-Chinese research team did not find any baiji (as the Chinese river dolphin is named) in its habitat, the Yangtze river, 1,000-mile (1,600 km) range stretching from the city of Yichang just downstream from the Three Gorges dam to Shanghai, during a six-week survey. The main cause for the extinction of this species could be unregulated fishing. This would be the first extinction of a large vertebrate in the last 50 years. The species was already classified as "critically endangered" by the World Conservation Union's Red List of Threaten Species.

"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 and emphasizes that we have yet to take full responsibility in our role as guardians of the planet." said co-author Dr. Sam Turvey of the Zoological Society of London (ZSL).

Baiji (Lipotes vexillifer) was the only member of the Lipotidae family, that split off from other cetaceans (whales, dolphins and porpoises) about 40-20 million years ago. This dolphin (like the other freshwater dolphins) had primitive traits, like a long, narrow beak, a mobile neck and low dorsal fins; baiji formed groups of three or four and fed on fish.

The six-week visual and acoustic survey (that took place in November and December 2006) used two research vessels. "While it is conceivable that a couple of surviving individuals were missed by the survey teams, our inability to detect any baiji despite this intensive search effort indicates that the prospect of finding and translocating them to a [reserve] has all but vanished.", wrote the team.

"Ours is the first scientific study which didn't find any. Even if there are a few left we can't find them and we can't do anything to stop their extinction." said Turvey.

Even if dam construction and boat collisions could have affected baiji, the main cause for their vanishing remains overfishing. "The primary factor was probably unsustainable by-catch in local fisheries, which used rolling hooks, nets and electrofishing," said the researchers.

"Unlike most historical-era extinctions of large bodied animals, the baiji was the victim not of active persecution but incidental mortality resulting from massive-scale human environmental impacts - primarily uncontrolled and unselective fishing," stated the scientists.

The researchers signal that Yangtze is home for about 10 % of the planet's population, with all the bleak consequences for baiji, from pollution and boat traffic in the busy river to overfishing, fact that doomed baiji's faith. "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.

"This underscores the need to act quickly to prevent the extinction of other similar shallow-water aquatic mammals like the vaquita found in Mexico's Sea of Cortez and the Yangtze finless porpoise. One really needs to learn from this to make sure future conservation efforts are more dynamic. 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.", Turvey explained.