Scientists believe Chinese sturgeon may have failed to breed in the wild over the past year, putting the critically endangered species of fish at risk of extinction. Wei Qiwei, an official at the Chinese Academy of Fishery Sciences, told Xinhua that researchers had found no sturgeon eggs in a spawning ground downstream from the Gezhou Dam on the Yangtze River in the final two months of last year. Scientists also found no trace of young sturgeon swimming in the river to the sea in a month-long survey held during the fish's usual migration period in August last year. "It is the first time we have found no natural reproduction of endangered sturgeons since records began 32 years ago when the dam was built," Wei was quoted as saying. "No natural reproduction means that the sturgeon will not expand its population and without protection they might be at risk of extinction." Chinese sturgeon is on the Swiss-based International Union for Conservation of Nature's "red list" of endangered species. Wei was quoted by Xinhua as saying that its population may have dwindled to about 100 because of "human activities" and water pollution. The international conservation union says the stretch of river near the Gezhou Dam is the species' only remaining spawning ground on the Yangtze and that overfishing over decades has also massively depleted stocks. Sturgeon have existed for more than 140 million years when dinosaurs still walked the earth. The fish usually swam from the sea up the Yangtze to lay eggs around mid to late November after they became mature, but the dam had cut off of some spawning grounds and disrupted their patten of reproduction, said Xie Yan, a researcher at the Institute of Zoology at the Chinese Academy of Sciences. "Wild animals must have a complete living environment and the dam has affected their living conditions. Their extinction was forecast when the dam was built," Xie said. The Gezhou Dam on the Yangtze was the mainland's largest hydroelectric dam when it was completed in the 1980s.