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The Three Gorges Dam, the largest hydroelectric power station in the world and just one of four main dams situated along the Yangtze river. Credit: Reuters.

Science

The damming of the Yangtze river in 1981 has had a detrimental effect on migrating sturgeon fish, according to Zhenli Huang and Luhai Wang, scientists at the China Institute of Water Resources and Hydropower Research.

For many years it was unknown exactly how dam structures were causing declines in migrating fish populations, leading to underestimations of their far-reaching adverse effects. But this latest study published in the journal Current Biology, has finally begun to reveal the mechanism by which dams affect migrating fish such as the Chinese sturgeon.

"We have established a novel theoretical framework to study the relationship between dams and the fish and to reveal the mechanism by which dams impact anadromous fish," says Zhenli Huang. "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."

Since the dams were built, remedial measures of fish rescue for existing dams, including fish passage facilities and restocking, have been insufficient or inefficient.

"The protection of the wild Chinese sturgeon requires effective measures taken immediately," the researchers write. "Artificial restocking, which China has been doing without maintaining breeding activity, is inadequate and unsustainable."

To carry out their research, Huang and study co-author Luhai Wang combined field observations with theoretical analysis of historical data. They wanted to understand something that had already become clear: why the spawning activity of Chinese sturgeon had become more and more difficult to observe in recent years. Their results found that since 1981, the Gezhouba Dam has reduced the migration distance by 1,175 km, resulting in reproductive development being delayed by almost a month. This reduced the breeding population size by a quarter of the original size. Subsequently built dams, particularly the Three Gorges Dam and Xiluodu Dam, have since further reduced the effective breeding by elevating the water temperature to inhibit breeding activity during the breeding season.

Despite these results, the researcher's reserve hope that their findings will lead to improved measures that will help keep wild populations at a sustainable level because, without this, the Chinese sturgeon will undoubtedly become extinct in the future.

By Ellis Moloney

Huang, Z., & Wang, L. (2018). Yangtze Dams Increasingly Threaten the Survival of the Chinese Sturgeon. Current Biology. doi: 10.1016/j.cub.2018.09.032

This research was supported by the National Natural Science Foundation of China.