Abstract:

Dam construction is a major threat of human activities to freshwater fish species. River damming often leads to habitat segregation, degradation and loss, and ultimately extirpates some aboriginal fish species. Four large cascade dams (Wudongde, Baihetan, Xiluodu and Xiangjiaba) are being built or will be built in the future in the lower reach of the Jinsha River. Many fish species in the Lower Jinsha River are likely to be threatened by the impoundment because of the tremendous change of their habitats. Moreover, among these fishes, some endemic fishes of the Upper Yangtze River need the rapidly flowing tributaries of the Lower Jinsha River as substitute habitats to spawn and survive. In order to optimize the utilization of limited habitat resources to conserve the fish species threatened by the cascade dams, the present study assessed the fish habitats of 12 tributaries of the Lower Jinsha River and set their conservation priorities based on habitat evaluation and other related concerns. The habitat evaluation was realized based on a new method combining spatial data analysis and field surveys. Firstly, at the reach (approximately10 km) level, 168 reaches of the 12 tributaries were classified into 9 groups on the basis of seven criteria: gradient, altitude, width, reach order, sinuosity, riparian vegetation index and dam construction status. Spatial data of these criteria was derived from Spot Maps in the Google Earth and digital elevation map and land cover map in the Geographical Information System. Secondly, several reach samples of each identified reach group were surveyed in the field at the microhabitat level using an adjusted qualitative habitat evaluation index derived from the original version of the Environmental Protection Agency of the United States. Thirdly, each reach group was scored using a weightedmean method, and subsequently each tributary was evaluated with the same approach. On the other hand, twice recent fish samplings were conducted in some reaches of several tributaries. The surveyed and historical fish sampling data was then used to determine the richness of endemic fish species in each tributary. Finally, the habitat evaluation results, the richness of endemic fish species, the annual runoff and the total number of dams were used to set the conservation priority of each tributary with a hierarchical ranking method. The all 12 tributaries were ranked by their priorities as follows: Niulan > Xixi > Heishui > Pudu > Longchuan > Canyu > Xining > Meigu > Yili > Pulong > Mengguo > Xiaojiang. In order to conserve at least one to two tributaries in each of the four future reservoirs, seven tributaries were chosen according to the ranking list. These tributaries were: Longchuan and Canyu in the Wudongde Reservoir, Heishui and Pude in the Baihetan Reservoir, Niulan and Xixi in the Xiluodu Reservoir, and Xining in the Xiangjiaba Reservoir. To conserve fishes in these tributaries, reaches with high habitat qualities should also be first protected. Specific conservation policies and projects on these priority tributaries should be designed in the not too distant future