The unique Yangtze dolphin, only found in China’s largest river, has now been declared officially extinct, after six weeks intensive search showed no sign of its existence.

Already on UN’s list of 12 most endangered species of animals, the Yangtze dolphin’s disappearance is the result of the intense pollution caused by China booming industry and by heavy fishing.

After a six weeks search, conservationists and ecologists failed to come up with any conclusive evidence that the dolphin, also known in the local dialect as “baiji” or "goddess of the Yangtze", might still be alive. Researchers said that even if they had missed the few specimens assumed to be swimming in the river’s waters, those specimens would be too weak and their number too small to ensure the healthy reproduction of the species.

The white-flag dolphin is now officially the first cetacean on record to be driven to extinction by human activity like water pollution, as the dolphin has no natural enemy.

The Baiji (Lipotes vexillifer) was the sole freshwater dolphin to live in Yangtze River’s waters, in central China. Fossil records indicate that the dolphins may have migrated from the Pacific Ocean to the Yangtze River 20 million years ago. It was one of four species of dolphins known to have made fresh water their exclusive habitat.

"Our inability to detect any baiji in the main channel of the river despite this intensive search effort has the sad consequence that the prospect of finding and translocating any surviving dolphins to an ex situ reserve-their only conservation hope- has all but vanished," said zoologist Samuel Turvey of the Zoological Society of London.

Despite researchers’ efforts, no specific whistle (that is usually carried by the water) could be recorded on the team’s microphones during the expedition. More then 1,500 kilometers have been carefully examined by scientists from the Zoological Society of London, who have now declared the dolphin as “functionally” extinct

Baiji populations have steadily declined since China declared the species endangered in 1979. In 1986 official estimates placed the Baiji population around 300 but an extensive survey in 1998 found only 7 individuals. The last confirmed sighting was in 2004 and the last captive baiji, Qi Qi, died in 2002 at the Institute of Hydrobiology in Wuhan. The Chinese government had set up a reserve in a lake in Hubei province to protect any captured baiji, but the attempt came too late to save the species. 

Last year, in December, another team of researchers, this time from Switzerland and focused exclusively on the study of the baiji, also came empty handed from an expedition that covered the main section of the Yangtze River (3,400 km). Although the team admitted that 8 h of daylight search could have caused them to miss a few specimens, the professionalism of its members stands proof that those misses are less than 1 percent.

Turvey added: "We witnessed massive amounts of fishing daily along the river, both legal fishing (gill nets) but also large amounts of illegal rolling-hook long-lining and electrofishing, which have long been banned. … In fact, before we even set off on the survey, fishermen were fishing with long lines right next to our survey boats at the dock in Wuhan." 

Technically, the Baiji can't be classified as extinct until 50 years after the last sighting according to the standards of the International Union for the Conservation of Nature / World Conservation Union (IUCN).

There are currently 3,071 "critically endangered" species in the world, according to the same organization.