Combined effects of fish cage culture and increased fishing pressure on wild fish assemblages in a large reservoir, Yangtze River basin, China

Local fishers often claim that cage culture practices in reservoirs result in high fish catches as fish cages attract a diverse variety of wild fish, which mainly aggregate to forage on waste from the practices. Previous studies have focused on fish aggregation effects brought about by fish cages. In the present study, we explored the responses of wild fish assemblages to fish cages and increased fishing pressure in the vicinity of cage farms in the Geheyan reservoir (110.80°-111.22° E, 30.35°-30.48° N) which located on the middle reaches of the Qingjiang River of the Yangtze River basin. Seasonal hydroacoustic surveys were conducted between April 2016 and January 2017 using a Simrad EY60 echosounder to determine the changes of fish assemblages along the density gradient of fish cages in the reservoir. Significant negative correlations between wild fish density and the density of fish cages were observed in April 2016 and January 2017. In other two seasons, we also found analogous trends. In general, the abundance of wild fish assemblages around fish cages declined resulting from increased fishing pressure in the reservoir. This study suggests that the commercial capture of indigenous fish around cage farms should be limited to protect the indigenous fish resources in reservoirs.