Need to shift in river-lake connection scheme under the “ten-year fishing ban” in the Yangtze River, China

The ecological degradation of freshwater river and lake system has developed into a global crisis. From January 2020, a “ten-year fishing ban” has been conducted in the Yangtze River and its affiliated lakes in China, which is an unprecedented and one of the most stringent biodiversity conservation plans in the World. However, there are still uncertainties about its restorative effect, because the river-lake isolation has not been properly addressed. To provide more references for the management of widespread sluice-controlled lakes, we constructed Ecopath models for three oxbow lakes under different management modes, compared the outputs, and manipulated through Ecosim simulations. The model comparison showed that, the lakes with longer protection, which only connected to the river in flood phase, were more developed but not more complex in ecological structure. Whereas year-round connected lake had also been simplified after the fishing ban: a 10 cm mesh net allowed small fish flowing in but restricted large fish wintering out, thus caused its biomass accumulation. According to the trophodynamic simulations, the maturity and complexity could be improved simultaneously when large individuals of river-lake migratory fish were removed from the system. Our results indicated a possible widespread food web simplification in sluice-controlled lakes of the middle and lower Yangtze floodplain during the “ten-year fishing ban”, and we suggested that future seasonal connecting scheme should be aiming at driving large river-lake migratory species back to the river, including enlarging net mesh and increasing water discharge in autumn and winter. Our findings make new complements to seasonal connecting methods and may benefit the conservation of floodplain lakes worldwide.