Direct and indirect effects of a fishing ban on lacustrine fish community do not result in a full recovery.
Abstract
Protected areas are increasingly being promoted as an important means of protecting freshwater biological diversity and ecological processes. A robust assessment of ecological changes in protected areas is fundamental to optimize conservation policies and adaptive management. China's efforts to establish aquatic reserves have attracted worldwide attention, especially the "10-year fishing ban" implemented in the Yangtze River basin. We focused on Liangzi Lake, a freshwater protected area in the Yangtze River basin, to understand the effect of a fishing ban occurring after a short period of overfishing. In this aim, the time series of fish community taxonomic and functional structure encompassing the overfishing period and a post-ban period have been analysed. Fish community metrics with direct, indirect and no responses to fishing bans were identified. The results indicate that in the early period of the fishing ban, the trophic level and body size structure of the fish community were in the way of recovery. However, species that prefer benthic habitats did not recover after fishing-induced habitat degradation. Functional traits were more sensitive than taxonomic indices and revealed subtle community changes, such as the recovery of some ecological functions, despite a non-recovering species richness. Synthesis and applications: This study provides a rare case of a freshwater protected area in which the effects of conservation measures are studied with a temporal survey. The effectiveness of the functional trait approach in the application of protected area assessment was demonstrated by revealing the recovery of trophic level and body size structure of fish communities after the implementation of fishing ban, and the inadequacy of habitat restoration efforts. We suggest that in freshwater protected areas, insistence on fishing ban is necessary but not sufficient for full biodiversity recovery, and other measures are needed, such as habitat restoration and species-focused stocking.