Three-Gorges Dam: risk to ancient fish.

THE HUGE THREE-GORGES DAM (TGD) OF THE Yangtze River is going to demonstrate the mighty power of humanity to change and fragment an area of about 58,000 km2 with the formation of a huge reservoir of 1080 km2. It is expected to exert disastrous influences on many terrestrial plants and animals, as discussed by J. Wu et al. in their Policy Forum “Three-Gorges Dam— experiment in habitat fragmentation?” (23 May, p. 1239). However, loss of biodiversity will take place not only terrestrially but also aquatically. More attention should be given to ancient endemic fish species that are extremely vulnerable. The Yangtze River basin is one of the richest areas in freshwater fish species diversity, with 361 fish species belonging to 29 families and 131 genera, accounting for 36% of all freshwater fish species in China (1). There are as many as 177 endemic fish species in this area, of which 25 already have endangered status, accounting for 27% of all endangered freshwater fish species in China (2). The construction of the Gezhou Dam (38 km downstream from the TGD) in 1981 led to sharp declines in the populations of three endemic ancient fish species, Chinese sturgeon (Acipenser sinensis), River sturgeon (A. dabryanus), and Chinese paddlefish (Psephurus gladius) (3). These three species are listed as Grade I endangered species in China Red Data Book of Endangered Animals (2). The Chinese sturgeon originally migrated from brackish water or the sea into their breeding ground in Jinsha River, the upper branch of the Yangtze River, swimming over 3000 km. However, the construction of the Gezhou Dam has completely prevented their upstream spawning migration, and although a new spawning site formed below the dam, their breeding ground shrank from 600 km to only 7 km. The TGD will reduce 41% of the water flow below the dam, which will most likely destroy the only breeding ground. The spawning of Chinese paddlefish was also severely impaired by the completion of the Gezhou Dam, and since 1988, only 3 to 10 adults have been found below the dam annually. Some spawning takes place above the dam, but TGD will further damage the paddlefish population when it is completed. The middle and lower basins of the Yangtze River are the most densely populated part of China. This region was originally a huge flood plain characteristic of a network of water systems, including the river and its tributaries, and many interconnected shallow lakes (4). Mainly to increase farmland, the Chinese have constructed numerous floodcontrol projects along the river and separated thousands (almost all) of the lakes from the river, which caused serious fragmentation of the water system and lamentably promoted, in turn, the construction of the world’s largest dam, which has decreasing flooding as one of its major roles (5). Many ancient fish coevolved with the flood plain, and the local monsoon climate has been threatened by these environmental modifications to such a rate and extent that the TGD will deepen fragmentation of the river and will undoubtedly bring more problems to migratory fish such as Chinese sturgeon. Additionally, consequential salinization of the estuary might potentially contribute to the extinction of related fish species. Although the dam will start storing water and generating electric power in late 2003, these concerns could possibly change the way the dam is operated in the future, increasing public awareness and promoting urgent adoption of a conservation agenda and substantial international collaborations in research and protection activities for endangered fish in the Yangtze River, where the Chinese government is still planning to construct more than 10 dams in the future. PING XIE Donghu Experimental Station of Lake Ecosystems, State Key Laboratory for Freshwater Ecology and Biotechnology of China, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, People’s Republic of China. E-mail: [email protected]