Changes in Fisheries Resources in the Hanjiang River and Danjiangkou Reservoir, China

The Hanjiang River is the largest tributary of the Yangtze River and contains Danjiangkou Dam, which forms Danjiangkou Reservoir in the middle and upper reaches of the river. During the past 50 years, fisheries resources have changed significantly in the middle and lower Hanjiang River and in Danjiangkou Reservoir. Spawning grounds for major carps and other commercially important fishes have disappeared. Downstream of Danjiangkou Dam, total egg quantity spawned by major carps and other commercially important fishes have decreased while similar measures from small-bodied fishes have increased. Important commercial fishes have experienced delayed spawning times and decreased growth. Overall catches of commercial fishes have decreased downstream of the dam, though increased upstream. Some exotic fishes captured in the Danjiangkou Reservoir were likely escapees from cage culture fish farms in the reservoir or from land-based fish farms around the reservoir. Changes in fisheries resources were presumed related to reservoir management strategies, which produced a narrower range of year-round water temperatures and caused decreases in seasonal water flow variation downstream, overfishing, and eutrophication in the reservoir. To implement a national water diversion policy in central China, the height of the Danjiangkou Dam was increased 15 m in 2012, which significantly increased the impoundment area of the Danjiangkou Reservoir at the end of 2014. Further changes in fisheries resources can be expected in the future. At the present time, management and conservation strategies for fisheries resources need to be developed to ensure future fisheries sustainability for both the Hanjiang River and the Danjiangkou Reservoir.