Fish entrainment model for decision support in ecosystem management: A case study from China's Maling Reservoir

Fish entrainment from reservoirs to downstream rivers by various water release structures may result in serious consequences for reservoir ecosystems. This study proposed an integrated modeling approach for determining fish entrainment risk zones and suitable reservoir regulations. The modeling approach combines hydrodynamic and fish risk assessment modeling with using fuzzy rules set defined by expert knowledge in fish ecology. We applied this modeling approach in the Maling Reservoir in China, where fish entrainment in the reservoir has been observed in the turbine, spillway, and irrigation system. Percocypris pingi (Tchang, 1930) and Onychostoma simum (Sauvage & Dabry de Thiersant, 1874), representing the main and protected fish species, were selected as target fish species. Five reservoir operation schemes were investigated under normal and designed water levels. The modeling results suggest that the fish entrainment risk for protected fish species (Onychostoma simum) is higher than that for the main fish species (Percocypris pingi). The results indicate a ranking of the fish entrainment risk from high to low in the following scenarios: with all spillways in operations, with one spillway in operation, with intakes in operation, with an irrigation system in operation, and with intakes and the irrigation system in combined operations. In addition, under normal and designed water levels, dead fish entrainment zone areas and percentages were extremely low compared to the entire forebay of the reservoir. These results indicate that the operation of the Maling Reservoir does not affect the ecological status of fish. These findings are generally applicable to any fish species in reservoirs that balance reservoir operations and ecological protection of fish, and could assist reservoir managers in making informed decisions on how to mitigate and compensate for fish entrainment.