The Response of the Spawning of the Four Major Chinese Carps to the Flow Re-Operation of the Three Gorges Reservoir in the Yangtze River, China

The flow regime is a critical factor in the sustained ecological integrity of flowing water systems. The Yangtze River is the most important river in China. The Three Gorges Reservoir greatly changed the flow regime of the Yangtze River, resulting in effects on fish populations, particularly those of the four major Chinese carp (FMCC): black carp, grass carp, silver carp, and bighead carp. Spawning has dramatically decreased since the Three Gorges Reservoir was established in 2003.. Flow re-operation which raising duration time over 3 days and daily discharge change over 1000 m3/s/d were executed in 2012 for 2 times, This study investigated the impacts of flow regulation and re-operation on fish spawning, particularly for the FMCC, and validated the environmental factors that promote spawning of the FMCC. A significant difference in FMCC egg density was observed among five floods, and the FMCC mean egg density after the re-operation was nearly four times that of the regulation flood. A difference in community composition was observed between re-operation and regulation, indicating that the re-operation schedule was sufficient to change the egg community composition. The egg community was significantly correlated with water transparency, change in daily water discharge, and change in daily water level. The better regulation schedule we suggest was the mean daily discharge increase was approximately great than 2000 m3·s-1·d-1 but less than 3050 m3·s-1·d-1, and daily water level increase greater than 0.46 m·d-1.