A man-made ecological disaster is unfolding on the Yangtze River in China which could drive a critically endangered species of fish closer to extinction in the wild, according to a news website report.
The increased threat to the Chinese sturgeon, which has existed for about 140 million years, comes after dams were opened to cope with flooding on higher reaches of the river this year.
Huge numbers of several similar, commercially farmed species were then washed into its habitat of the wild fish on the Yangtze, Thepaper.cn reported.
Experts feared that the other species of sturgeon will compete with the endangered native breed and wipe it out, the report said. Only 57 are thought to survive in the wild because of factors that include water pollution and dams keeping the fish from getting to their spawning grounds.
The article also quoted an expert as saying that the influx of non-native species could have a catastrophic impact on other types of fish and on the ecological environment of the river.
Nearly 10,000 of tonnes of non-native sturgeon were swept into stretches of the river after dams in central Hubei province had to release huge amounts of water in July, the report said
The rush of floodwater destroyed pens at fish farms containing species including Amur, Kaluga and Siberian sturgeon, according to the article.
“The commercially bred sturgeon have reached the tributaries of the lower reaches of the Yangtze,” an unidentified official in charge of fisheries on the river was quoted as saying.
“They are everywhere in Dongting Lake and Poyang Lake. The affected areas are large and might have a catastrophic impact on the aquatic organisms and ecologic environment in the Yangtze.”
The government is conducting an assessment on the incident’s ecological impact, according to the report.
Wei Qiwei, an official at the Chinese Academy of Fishery Sciences and a member of the investigation team, told the news website that the escaped commercially bred sturgeon not only outnumbered the wild Chinese variety, but also the total numbers of some fish species in tributaries on the lower reaches of the Yangtze.
“Once these foreign sturgeons form a population they will squeeze the ecological niche of native fish such as the Chinese sturgeon and even replace them.”
Wei was also concerned the non-native species might breed with Chinese sturgeons, putting a further strain on its chances of survival in the wild, the report said.
Zhang Jie, a researcher with the Institute of Zoology at the Chinese Academy of Sciences, said the situation could have further degraded the ecological system in the Yangtze, but that it was too early to assess the damage.
It takes Chinese sturgeons seven to eight years to mature and it is only after they do so that any genetic contamination can be detected. “The priority is to draft plans on how to assess the impact and amend the damage, and the latter will be very difficult,” Zhang said.
The Chinese sturgeon is on the International Union for Conservation of Nature’s “red list” of endangered species.
Scientists said in 2014 they had found no evidence of Chinese sturgeon breeding over the previous year for the first time since records began in 1982 after the Gezhou Dam was built on the river.
The dam has been blamed for cutting off the spawning grounds of the fish, which usually swim from the sea to the upper reaches of the Yangtze to lay their eggs.
The threat to the Chinese sturgeon comes after the Yangtze river dolphin was formally declared extinct in 2007.
Three hydropower dams are stationed along the Qing River, a tributary of the Yangtze River in Hubei province, and one of the three, the Geheyan Dam discharged floodwaters for the first time in 18 years on the night of July 19 after huge downpours.
Floodwaters of 10,000 square metres per second washed away huge numbers of fish cages where commercially bred sturgeon were kept, according to the news website report.
About 9,800 tonnes of commercially bred sturgeon died or escaped, the article said.