Are river protected areas sufficient for fish conservation? Implications from large-scale hydroacoustic surveys in the middle reach of the Yangtze River

BACKGROUND: The Yangtze River is the third largest river in the world and suffers from extensive anthropogenic impacts. The fishes in the Yangtze River are essential for the sustainable development of freshwater fisheries and the conservation of aquatic biodiversity in China. However, the fishery resources in the Yangtze River Basin have shown rapid decline due to various human activities. In recent years, nature reserves and germplasm resource reserves have become important means to protect fishes in the Yangtze River. However, nature reserves and germplasm resource reserves that regard freshwater fishes as the main object of protection are not common and have been rarely studied in China. In this paper, a hydroacoustic method and systematic conservation planning tool (Marxan) were combined to evaluate the effectiveness of reserves based on the spatial and temporal patterns of mature fishes in the middle reach of the Yangtze River (MRYR) from 2010 to 2017. RESULTS: The hydroacoustic survey results indicated that in the longitudinal direction, low densities of mature fish species were observed in the Jingzhou (S2) and Jianli (S4, S5, S6) sections, whereas high densities of fish were observed in other sections, such as the Yichang (S1), Chenglingji to Huangsangkou (S7–S12), and Hukou (S15) sections. Among the regions preferred by fish, S7, S10 and S12 were non-reserves. No significant difference in mature fish density was observed between the non-reserves and nature reserves, and a similar result was obtained between the non-reserves and germplasm resource reserves. In Marxan, the optimal conservation sites selected for habitat restoration, such as the Chenglingji, Dengjiakou, Zhuankou, Hankou, Yangluo, and Huangsangkou sections, which are located in non-reserves, were identified in the MRYR. CONCLUSIONS: The Chenglingji, Dengjiakou, Zhuankou, Hankou, Yangluo, and Huangsangkou sections, which are located in non-reserves, play equally important roles in the conservation of fish populations in the MRYR. Our results indicated that further optimization is urgently needed for the currently protected areas in this region. These areas should be designated as reserves, and classification protection mechanisms should be adopted to strengthen the effectiveness of fish conservation in the MRYR.