Characteristics of spatial distributions of fish community in upper and lower approach channels of the Three Gorges ship lock, Yangtze River

Abstract:

In order to assess the spatial distributions of fish community in upper and lower approach channels of the Three Gorges shiplock, the hydroacoustic surveys were carried out in January, May, October in 2018 and May 2019, respectively. Survey areas were set as:area Ⅰ (Jingjiang River), area Ⅱ (upper approach channel), area Ⅲ (lower approach channel) and area Ⅳ (Sandouping section). Fish body length was estimated based on target strength and the estimates showed that fish body length in area Ⅰ, area Ⅱ and area Ⅳ ranged from 2.5 to 5.0 cm, while that in area Ⅲ ranged from 7.0 to 20.0 cm. Average fish densities in area Ⅰ, area Ⅱ, area Ⅲ and area Ⅳ were (99.53±47.78) ind./1 000 m³, (57.37±33.45) ind./1 000 m³, (61.51±1.72) ind./1 000 m³ and (30.61±15.75) ind./1 000 m³, respectively. The fish densities of low water levels in area Ⅰ and area Ⅱ were significantly higher than those of high water levels, while fish densities of lower water levels in area Ⅲ were significantly lower than those of high water levels. Fishes in area Ⅰ and area Ⅱ were mainly distributed in middle-lower water layer at different periods, however fishes in area Ⅲ tended to move to shallow water layer (less than 6 m) at high water levels, but deep water layer (more than 8 m) at low water levels. Spatial distributions of fishes in the upper and lower approach channels were greatly influenced by the water level of the Three Gorges reservoir and ships passing the lock.