Effects of annual flow characteristics on the freshwater life history of Chinese sturgeon: concern inferred from the number of seaward migrating juveniles

Since 2003, the flow characteristics of the Yangtze River, currently the only river where the protected Chinese sturgeon, Acipenser sinensis, spawns and where the young grows to the 6 to 8 month juvenile stage, has been regulated by the operation of the Three Gorges Project. The number of seaward migrating juveniles captured (NSMJC) in the Yangtze estuary from 2002 to 2010 was significantly positively related (Pearson correlation, P (two tailed) <0.01; Lg (NSMJC) = 0.870 + 3.930 × AASC, R = 0.940, P = 0.000) to the annual sediment load and annual average sediment concentration (AASC) of the previous year, when adults entered the river and migrated upstream, used refuge areas, and spawned, and when early life stages were reared. This suggests that silt content may have a major effect on adult spawning success and rearing of early life stages. Based on the correlation between numbers of juveniles captured and numbers of adults in the spawning areas in the previous year (Pearson correlation, R = 0.965, P (two tailed) = 0.008), we speculated that the sediment characteristics affected the migration and gonad development of mature individuals and, indirectly, the number of juveniles reaching the Yangtze estuary during the following year. Decreased silt levels in the Yangtze River following installation of the Three Gorges Project may be having a deleterious effect on Chinese sturgeon reproduction and needs further research.