Acoustical Estimate of Fish Distribution in the Three Gorges Reservoir, China

The Three Gorges Reservoir is the most important habitat for many rare, unique and economic fishes, but the fish density and distribution in the reach lack extensive and continuous investigation. In order to find out the fish quantity and their changing tendency, also to figure out their spatial and temporal distribution, two kinds of echo-sounder equipments (HTI Model 241 and SIMRAD EY60) were used to detect fish density and fish spatio-temporal distribution in the Three Gorges Reservoir and 8 investigations had been conducted from 2006 to 2010. The results showed a tendency that the average fish density in the Three Gorges Reservoir was increasing year by year from 15.5 ind./1000m³ to 123 ind./1000m³ and it was apparently correlated with the corresponding water level. In horizontal direction, fish density increased from lower reaches to upper reaches, and fishes preferred to inhabit around Zhongxian section in winter and Chongqing section in spring. In vertical direction, fish density in the Three Gorges Reservoir was largest in lower layer, then in middle layer and last in upper layer. And the difference of fish density in different water layers in spring is not that evident as in winter. The increasing tendency of fish density and the spatio-temporal distribution of fish species were closely related with the impounding of the Three Gorges Reservoir. Other influencing factors included water flow, water depth, reservoir shape, fish’s living habit and protection policy.