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A grim fish tale of the ones that got away
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IMPORTED species of farmed sturgeon that escaped during flooding in the upper reaches of the Yangtze River have recently been found to be spreading downstream. The rapid expansion of the feral species into the wild is alarming authorities.
“Dongting Lake, Poyang Lake ... The fish are everywhere,” said an official with the Yangtze River Fisheries Administration Office of the Agriculture Ministry, who declined to give his name. “It could be a disaster for the aquatic life and eco-system of the Yangtze.”
Aquatic biologists are now mobilizing teams to investigate and evaluate the situation. Certain species of sturgeon are perhaps best known to the general public as the source of caviar.
The crisis began in the reservoir region of the Qingjiang River, a tributary of the Yangtze in central China’s Hubei Province, which is one of the biggest breeding bases for imported species of sturgeon.
Due to heavy rain in late July, two dams on the Qingjiang River were forced to discharge water at a rate of up to 8,800 cubic meters a second.
Before fish farmers had the chance to take emergency precautions, hundreds of net-cages containing the fish were ripped open during the sudden water discharge. An estimated 9,800 tons of breeding sturgeon either died or escaped.
The escapees included foreign species like the Amur, Kaluga and Siberian sturgeon and crossbred varieties — none of which is native to the Yangtze River.
Some of the sturgeon were later caught and identified. More than 100 were snared in Hubei Province by August 2.
According to Wu Jinming of the Chinese Academy of Fishery Science, who has been monitoring the situation in the Honghu sector of the Yangtze River, more than 500 escaped feral sturgeon were found by September 21.
The monitoring data show that some of the sturgeon have entered Yangzhou in neighboring Jiangsu Province. Wu estimated that some of them may already have reached the estuary in Shanghai.
“The escaping sturgeon will not only spread in the middle and lower reaches of the river, but also swim against the current to the upper reaches,” said the official with the Yangtze River Fisheries Administration Office of the Agriculture Ministry. “It will be a disaster for the entire Yangtze River basin. It’s just impossible to recapture them all.”
The invasion of an alien fish species in the river’s eco-system will pose a direct threat to native fish, said Wei Qiwei, director of the Biodiversity Protection Lab on Freshwater Creatures at the Ministry of Agriculture.
According to Wei, the number of foreign and cross-bred sturgeon that escaped from the net-cages may already far surpass the number of wild Chinese sturgeon that are native in the Yangtze.
“The Kaluga sturgeon are carnivorous and eat other fish,” said Wei. “As long as feral sturgeon form a population here, they will rob native fish of food and habitat, posing a great threat to the natives and even replacing them eventually.”
Gene pollution is another big concern of the biologists. There are only three species of indigenous sturgeon in the Yangtze: white sturgeon, Dabry’s sturgeon and Chinese sturgeon. Both white sturgeon and Dabry’s sturgeon are functionally extinct now, with no trace of them detected in the past 10 years. Chinese sturgeon is on the verge of extinction.
“Foreign sturgeon in the Yangtze may cross-breed with native sturgeon, aggravating the decreasing number of the original native species,” said Wei. “We may lose all our pure Chinese sturgeon if this happens.”
The Chinese sturgeon is often called the “panda in water” because it is such a rare species and lives only in China.
It’s an old species, dating back an estimated 200 million years. The Chinese sturgeon migrates between ocean and fresh water at different phases of its life. It has the longest migration of any sturgeon in the world — more than 3,200 kilometers each time.
Chinese sturgeon spawn in the upper reaches of Yangtze River in November. The juvenile fish travel the length of the river from May to October, heading into the ocean. The fish then dwell along the eastern coast of China before returning to the estuary again after reaching sexual maturity — nine years for males and 14 years for females.
An adult fish measures up to four meters long and weighs over 450 kilograms, ranking among the largest sturgeon in the world.
In the 1970s, there were an estimated 2,000 spawning Chinese sturgeon in the Yangtze River, but that number has dwindled to several hundred due to habitat destruction. The channel for adult fish migrating upstream to spawning sites such as the Jinsha River was blocked by construction of the Gezhou Dam, a hydroelectric project, in the early 1980s.
“The number of Chinese sturgeons that we detect each year in the estuary of the Yangtze is decreasing, regardless of all the efforts at artificial breeding,” said Chen Jinhui, deputy director of the Department of Shanghai Yangtze Estuarine Nature Reserve for the Chinese Sturgeon.
About 5 million Chinese sturgeons were released in the middle Yangtze River in the past 30 years, and over 10,000 were released in Shanghai in the last 10 years. But only about 100 Chinese sturgeons were detected in the estuary in 2013.
Though no natural breeding of Chinese sturgeons was detected in 2013 and 2014, numbers of baby Chinese sturgeon were discovered in the estuary in Shanghai last year. However, their new spawning ground is still unknown.
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