Long-term changes in fish assemblage following the impoundments of the Three Gorges Reservoir in Hejiang, a protected reach of the upper Yangtze River

The construction of the Three Gorges Reservoir (TGR) has seriously affected the fish assemblage in the impounded reaches. However, fish assemblage changes in the riverine zone remain poorly documented. In order to explore how upstream fish assemblage has responded to the successive impoundments of the TGR, fish investigations were conducted biannually in Hejiang, a protected reach of the upper Yangtze River, during the period from 1997 to 2011. Multivariate analysis revealed significant temporal differences in fish assemblage following the impoundments of the TGR. Prior to the impoundments, the fish assemblage appeared to be very diversified and very even. Immediately after the first and the second impoundment, the lotic species, such as Coreius guichenoti, Rhinogobio ventralis, Rhinogobio cylindricus and Coreius heterodon, became evidently dominant, due to their upstream migrations from the reservoir. However, two years after the third impoundment, the lotic species decreased dramatically, while lentic Hypophthalmichthys molitrix and Pelteobagrus vachelli became the new dominant species. Based on this and other studies, we can see the habitats of the riverine fish in the upper Yangtze River have been shrunk seriously because of the impoundments of the TGR. The cascade hydropower development in the lower Jinsha River will pose an accumulative effect on the aquatic environment in the mainstream of the upper Yangtze River. Free-flowing tributaries, such as the Chishui River, will play more important roles in fish conservation.