River damming is threatening global migratory fish populations

It has long been believed that river damming poses a serious threat to migratory fish populations within them. However little evidence had been reported until now. To prove this theory, scientists at the China Institute of Water Resources and Hydropower Research studied China’s Yangtze River and now understand why Chinese sturgeon population is dwindling and why the sturgeon population has been so difficult to observe in recent decades.

Damming of the Yangtze began in 1981. Before dam construction, Chinese sturgeon would fast and migrate upriver every summer. They would then spawn in the fall and return to sea. This activity could be clearly tracked before 1981. But in recent years, scientists had trouble following the sturgeon’s migration.

In the study, published in Current Biology on November 1st, the Institute’s Zhenli Huang explained, “We have found that the loss of effective breeding and environmental capacity are two crucial factors resulting in an ongoing decline in adult abundances of Chinese sturgeon in the Yangtze River.”

Huang and co-author Luhai Wang looked back at the historical data mapping out the Yangtze’s damming and sturgeon activity. They found that the Gezhouba Dam reduced the sturgeon’s migration path by 1,175 kilometers (about 730 miles). Over time, this caused the sturgeon to reach sexual maturity about a month later than normal, therefore lessening the population size due to the fact there aren’t as many sturgeon ready to breed.

What’s more is that Huang and Wang found that environmental capacity of the lessened breeding ground has been reduced, and water temperatures have risen with the building of new dams within the past ten years.

The team estimates that the number of adult sturgeon in the Yangtze has dropped from about 32,000 before 1981, to 6,000 in 2010, and about 2,500 in 2015. They predict that if the numbers continue on this track, the natural Chinese sturgeon population will go extinct within the next decade.

“The protection of the wild Chinese sturgeon requires effective measures taken immediately,” Huang and Wang note. “Artificial restocking, which China has been doing without maintaining breeding activity, is inadequate and unsustainable.”

Although the future looks bleak for the Chinese sturgeon in the Yangtze, the researchers want their new findings to alert other nations that migrant fish populations are at risk of extinction at the hands of damming. In knowing this, those put in charge of damming can take extra measures to ensure fish populations are cared for properly.

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By Olivia Harvey, Earth.com Staff Writer