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WUHAN, Sept. 23 (Xinhua) -- Millions of sturgeon that escaped in central China during this year's floods are not only a loss for the aquiculturalists who bred them, but are a serious threat to the local environment.
According to the National Aquatic Wildlife Conservation Association, about two million sturgeon with a total biomass over 12,000 tonnes escaped from the Qing River, a tributary of the Yangtze, and one of the biggest sturgeon-raising bases in China.
The clean river in the southwestern part of Hubei Province is the source of large quantities of sturgeon meat and caviar exported to the Middle East and Europe.
The Qing flooded from July 18 to 20, forcing authorities to open spillways to release water downstream. The increased flow damaged the net cages in fish farms along the river, allowing the fish to swim away.
The losses to fish farmers in Hubei were huge. Almost 600 of them lost a total of around 750 million yuan (115 million U.S. dollars).
Liao Fenglei is one of the fish farmers to have suffered. Around 100,000 kilograms of his fish, worth more than three million yuan made a break for freedom. "My father and I spent more than a decade building this business and now it's all gone," he said.
Beyond the human, financial cost, the escaped fish are a very severe environmental concern.
Downstream, and completely unprepared for such an alien invasion, lives the critically endangered Chinese sturgeon, a species which enjoys the highest level of national protection. Rapid economic development along the river, pollution and illegal fishing have driven these native sturgeon to the verge of extinction.
Their numbers in the Yangtze are estimated at around 100 adults, down from thousands in the 1980s, mainly due to human activity and pollution. China has been working to breed and preserve this endangered species, and now all that good work may have been in vain.
Ichthyologist Wei Qiwei, a sturgeon expert with the Yangtze River Fisheries Research Institute (YRFRI), said that the runaway sturgeon include many different varieties, and could be a severe threat, not just to the native population, but to many other vulnerable species in the Yangtze.
"An escape on such a big scale is quite rare," Wei said. "Of the escapees, about 200,000 are at least six years old, with each weighing about 40 kg. These sturgeon have very strong reproductive capacity and could certainly threaten the already endangered local Chinese sturgeon, which has a very slow breeding cycle."
Du Hao, a YRFRI researcher, described many of the escaped sturgeon as "ferocious" and "competitive." If they survive and form shoals, they could rob food from local species, and eventually replace them, causing "irreversible damage to the ecological chain."
According to the YRFRI, the renegade sturgeon have been found swimming in large groups in the lower reaches of the Yangtze.
In the preservation area of the Chinese sturgeon, local fishermen recently captured more than 100 kg of the fugitive fish in just one day. Such is the amount caught since the big breakout that "all the refrigerators of restaurants along the Yangtze are stuffed," according to one fisherman.
Pressure is mounting on authorities to take action.
Wei Qiwei said that while it is necessary to assess the damage done to the ecosystem so far, "various departments should be working together to capture the escaped fish."
"We can mitigate the damage by catching the fish where they are found in large groups," he added.
