Influence of Manwan Reservoir on fish habitat in the middle reach of the Lancang River

The Lancang–Mekong River is the most important international river in Southeast Asia. Where the river flows through China, it is called the Lancang River. The Lancang River basin has become the most abundant species resource and the most bio-diverse region of China and has significant potential as a source of hydropower. The construction of cascade hydropower dams on the main river has brought great economic benefit, but has also changed the river as a physical habitat. Many fishes, especially endemic species and those with economic value in this area, have been affected by these changes. An ESHIPPO-PPm model was established to evaluate the extinction risk of fish species in this area. Four endemic fish were evaluated, two of which (Tor sinensis, and Cosmochilus cardinalis) are classified as critical extinction risk. The habitat quality of T. sinensis, an endemic and economically important fish, was simulated using a habitat suitability index model. The habitat suitability index (HSI) model was developed by coupling a one-dimensional (1-D) hydraulic model with habitat suitability curves. Considering the spawning characteristics of the fish, habitat suitability curves were established for key factors influencing adult fish and spawning behavior of T. sinensis. A hydraulic model was developed to simulate and predict parameter of the physical habitat. Based on the simulated result of the HSI model, Weighted Usable Areas for adult (WUAd) and spawning (WUAs) were obtained. A Mann–Kendall test was used to analyze the variation trend of WUAs and WUAd before and after the construction of the Manwan dam. Abrupt change in WUAd and WUAs occurred during the dam construction and operation period, respectively. According to the simulation and analysis, habitat suitability has been changed during the construction and operation of Manwan Reservoir. For the spawning of T. sinensis (WUAs), the dam has a visible influence on the minimal and medium level habitat, but little influence on the optimal habitat. For the adults habitat, the dam reduced the medium and optimal WUAd. Optimal discharge for spawning is much greater than for adult. Different discharges for maintaining different degrees of habitat quality are suggested.