Trophic level changes of fishery catches in Lake Chaohu, Anhui Province, China: Trends and causes

Fishing activity has been suggested to affect food web structure and functioning of aquatic ecosystems. Based on changes of the mean trophic level index of fishery catch, the present study demonstrates long-term ecosystem impacts of fisheries in Lake Chaohu, a freshwater lake in Anhui Province, China. The decline of mean trophic level (MTL) in the last five decades, coupled with a dramatic increasing of the fishery catches from the lake, can be interpreted as a result of a decrease in the abundance of high trophic level, large piscivorous benthic fishes relative to low-trophic level, small planktivorous pelagic fishes. The mean trophic level of the total fishery catches declined as fishing effort (number of fishing boats and fishermen) increased, which suggests that an expansion of fishing capacity can lead to changes in the food web structures of a lake. Various direct and indirect relationships between MTL, nutrient concentrations and air temperatures were observed, suggesting that environmental changes, jointly with fishing, may have caused cascading effects which make the system less resistant to disturbance. In such context, our results, which complement traditional fisheries assessment, add to the understanding of the interactions among different trophic level of the ecosystem and their alterations due to fisheries and environmental changes.

► We report on long-term ecosystem impacts of fisheries in a lake in China.
► The mean trophic level (MTL) of fishery catches declined steadily in recent decades.
► The decline of MTL may be an indicator of changes in fish community function.
► Eutrophication and climate change had synergetic and cascading effect on the lake ecosystem.