Can water level management, stock enhancement, and fishery restriction offset negative effects of hydrological changes on the four major Chinese carps in China's largest freshwater lake?

Habitat degradation and fragmentation have been the leading cause of reduced fishery yields in many freshwater ecosystems around the world. In Poyang Lake, the largest freshwater lake in China, recent hydrological changes driven by the operation of Three Gorges Dam (TGD) and drought have caused a drastic loss of fishery resources. In response, managers have planned to build a sluice at Poyang Lake's outlet to manage the lake's water level and, as the sluice will unavoidably limit the river-lake migration of many fishery species, managers have also proposed implementing stock enhancement programs and restricting fisheries to sustain fisheries in the lake. In this study, we built and implemented a Poyang Lake Ecopath with Ecosim model to evaluate effects of water level management, stock enhancement, and fishery restriction on biomass of the four major Chinese carps: grass carp (Ctenopharyngodon idella), silver carp (Hypophthalmichthys molitrix), bighead carp (H. nobilis), and black carp (Mylopharyngodon piceus), of which all are river-lake migratory and important to fisheries. Results showed that the total biomass of the four major Chinese carps could increase with increases in water level, increases in stocking biomass, and decreases in fishing pressure. However, even in the best management effort scenario (i.e., highest water level, highest stocking biomass, and no fishing), simulated total biomass of the four major Chinese carps was still 16% lower than the biomass estimate in 2000, three years before the operation of TGD. These results suggest that a combination of managing water level, stocking, and restricting fisheries can substantially offset negative effects of hydrological changes on the four major Chinese carps, but may not be enough to restore the biomass of the four major Chinese carps to high levels that had occurred before the operation of TGD, because of the blockage of river-lake connectivity by the Poyang Lake sluice.