Beijing (AFP) - The wild Chinese sturgeon is at risk of extinction, state media reported, after none of the rare fish were detected reproducing naturally in the polluted and crowded Yangtze river last year.

One of the world's oldest living species, the wild Chinese sturgeon are thought to have existed for more than 140 million years but have seen their numbers crash as China's economic boom brings with it pollution, dams and boat traffic along the world's third-longest river.

For the first time since researchers began keeping records 32 years ago, there was no natural reproduction of wild Chinese sturgeon in 2013, according to a report published by the Chinese Academy of Fishery Sciences.

No eggs were found to have been laid by wild sturgeons in an area in central China's Hubei province, and no young sturgeons were found swimming along the Yangtze toward the sea in August, the month when they typically do so.

"No natural reproduction means that the sturgeons would not expand its population and without protection, they might risk extinction," Wei Qiwei, an investigator with the academy, told China's official Xinhua news agency on Saturday.

The fish is classed as "critically endangered" on the International Union for the Conservation of Nature's "Red List" of threatened species, just one level ahead of "extinct in the wild".

Only around 100 of the sturgeon remain, Wei said, compared with several thousand in the 1980s.

Chinese authorities have built dozens of dams -- including the world's largest, the Three Gorges -- along the Yangtze river, which campaigners say have led to environmental degradation and disrupted the habitats of a range of endangered species.

Many sturgeon have also been killed, injured by ship propellers or after becoming tangled in fishermen's nets.

Animal populations in many of China's ecosystems have plummeted during the country's decades of development and urbanisation, the World Wildlife Fund (WWF) said in a 2012 study.

According to findings compiled by WWF from various sources, the Yangtze river dolphin population crashed by 99.4 percent from 1980 to 2006, while that of the Chinese alligator fell by 97 percent from 1955 to 2010.