Multivariate analysis performed to identify the temporal responses of fish assemblages to abiotic changes downstream of the Gezhouba Dam on the Yangtze River

Impoundment of the Three Gorges Reservoir (TGR) and overharvesting are anthropogenic factors that have had a dramatic effect on Yangtze fish. This study used the multivariate analysis to quantify the relationship between abiotic alterations (seven variables from the TGR impoundment and fishing activities) and fish response, revealing the processes through which abiotic changes affect fish assemblages over a 14-year period (1999-2012). Fish assemblages temporally clustered into three groups that were strongly associated with the TGR impoundment. Eleven species that accounted for 98.44% of dissimilarities contributed to these three clustered groups. Variation in fish assemblages primarily resulted from a decline in three lotic species without spawning grounds downstream, fluctuations in four lotic species with spawning grounds downstream, and increases in three eurytopic species. Abiotic changes resulted from the TGR impoundment (TGR water levels, sediment, and water temperature), together with fish activities (fishing intensity), significantly affected the temporal patterns of the fish assemblages. Results suggest that the decline in lotic species can be attributed to the blocking and declines in the downstream movement of lotic species caused by increased water levels in the TGR. Increases in eurytopic species and declines in other species were caused by habitat fragmentation via a decline in sediment discharge and changes in water temperature. Fishing activities affected fish assemblages throughout the entire period of observation, particularly during the initial impoundment period from 2003 to 2005. These findings highlight the degree to which those anthropogenic factors affected the fish assemblages in temporal processing