The Effects of Dam Removal on Fish Assemblage Structure and Spatial Distributions in a Tributary of the Upper Mekong River, China

The Mekong River is the second richest river in the world for its fish diversity. At the moment, the mega-dams along the Mekong mainstream constitute a major threat to freshwater species diversity and abundance. In order to protect those fishes, a low-head dam built on the Jidu River, a tributary of the upper Mekong River, China, was removed in the fall 2012. We evaluated fish assemblage structure and spatial distributions in the Jidu River, to compare sites before and after the removal of this dam. After dam removal, in downstream from the dam, the number of fish species increased from 3 (2 native) sampled in 2011 to 17 (10 native) in 2013. 10 of the 14 recolonized species were only sampled during summer and fall, suggesting that these fishes recolonized seasonally, perhaps for spawning or feeding. Some species, such as Schizothorax lissolabiatus, were reproducing successfully in downstream areas of this river within the first year after removal. However, only 4 species (2 native) were collected in 2013 at the upstream from the dam, indicating that this dam did not act as a barrier to the upstream migration of fish; however, the dam did cause great effect on fish in downstream areas.