Three Gorges Reservoir (TGR), the largest reservoir worldwide, has a short history and expanded water bodies in the upper reach of the Yangtze River, China. It provides multiple ecosystem and social services including water supply and fisheries, while receiving multiple stresses such as habitat changes, eutrophication, and overfishing. Meanwhile, there is a great need in such large reservoir to shift the traditional fisheries management to the ecosystem-based fisheries management (EBFM) for comprehensive benefits and ecosystem sustainability. In this study, we sampled seasonally across the TGR to investigate the spatio-temporal dynamics of environment, fish community and fishery forage resources. We used these basic data and the ECOPATH approach to explore the ecosystem structure and functioning for a better understanding of trophic processes and fishery management. The main biological components of the TGR ecosystem were divided into 23 functional groups, according to their biological and ecological characteristics, with the basic inputs of biomass, production, consumption, harvests and diet composition. Trophic flows and ecosystem properties were analyzed quantitatively through the balanced food web models.
Results/Conclusions
The result indicated that forage fish were less used with low ecological efficiency (EE <0.35), while predatory fish were over-exploited (EE>0.90). Phytoplankton and predatory fish Culter spp. were identified as keystone species, which have great importance in maintaining ecosystem functions. The contribution of detritus as energy source was nearly 30% of the contribution of phytoplankton. Trophic transfer efficiencies along the trophic levels varied between 9.0~15.6%. The index of PPR/Catch (Primary Production Required per Catch) for commercial fish ranged between 13 and 204. These results implied that it is advisable to strengthen the piscivorous roles in controlling the less-exploited small planktivorous fishes and intensifying the cascading reduction effects on phytoplankton biomass. The detritus is an important pool for decayed phytoplankton and allochthonous materials from the land. Thus, it is necessary to increase the trophic roles of zoobenthos and especially shrimps in utilizing the detritus resources by selective harvesting on omnivorous fishes and small carnivorous fishes, whose diets comprise large proportions of zoobenthos. Overall, the present model provides us knowledges for the approach to ecosystem-based fishery management in the TGR, which manages fisheries in the context of direct and indirect trophic interactions for ensuring ecosystem sustainability and healthy.