Spatial Pattern for Larvae of the Major Carps in the Middle Reach of the Yangtze River: Impacts of the Three Gorges Dam

Distirbution and growth for larvae of the major carps (silver carp, bighead carp, grass carp and black carp) were compared at 4 sections in the middle Yangtze River, which, from near to far to the dam, were Jianli (335.62 km to the dam)，Honghu (525.9 km)，Tuanfeng (695.1 km) and Wuxue (823.8 km). Density of larval fish was lowest at Jianli, and increased downward. Density of larvae at Jianli was 20.0% of that at Honghu, 8.2-8.8% at Tuanfeng, and 4.9 – 6.5% at Wuxue. Growth during the larval stage for juveniles caught nearer to the dam was slower than those further from the dam, indicating a stronger negative impact on early growth for the fish born nearer to the dam. Significant proportions of larval fish at Jianli showed no clear increments deposited in their otoliths, while all the surviving juveniles had clear increments observed formed during the larval stage. It indicated that those larvae with no clear increment could not survive to the juvenile stage. The results suggested that impacts of the Three Gorges Dam on fish resources below the dam are not only reducing abundance, but also inducing lower growth and condition of the early individuals.