Changes of Fish Resources in the Hanjiang River and the Danjiangkou Reservoir of the Main Branch of the Yangtze River, China

The Hanjiang River is the biggest branch of the Yangtze River and the Danjingkou Dam was built in 1958 in the middle and upper reach of this branch. During the past over 50 years, fish resources changed significantly in the middle and lower Hanjiang River and the Danjiangkou Reservoir. Some fish spawning grounds disappeared below or up the dam. Spawning time of important commercial fishes was delayed and their growth rate decreased. Fish landings of commercial fisheries decreased below the dam, but increased up the dam. The spawning scale of main carps has shown the trend of decrease both below and up the dam. Changes of fish resources in the Hangjiang River and the reservoir area are related with narrower range of year-round water temperature below the dam, decrease of seasonal water flow fluctuation range below the dam and changes of food organisms below and up the dam. In order to implement the water diversion policy from South China to North China, the dam was increased 10 meters in 2012 and the new impoundment will begin in 2014. Further change of fish resources could be expected.