Abstract:

Four hydroacoustic surveys were conducted in June and November 2009 by using the SIMRAD EY60 echo sounder with a 200 kHz splitbeam transducer in the upstream and downstream of the Gezhouba Dam in the Yangtze River in order to understand the temporal and spatial distribution of fishes. The result indicated that the average individual density (total fish number in a given water area) ranged from 2.8 to 122.7 ind./ 1 000 m3 and 8.8 to 888.8 ind./1 000 m3 in the upper and lower reaches of the Gezhouba Dam, respectively. Fishes unevenly distributed in the investigated area and mainly concentrated in three sections, which were the mouth of Xiling Gorge, tailwater of Dajiang power plant and Sanjiang section. Fishes always concentrated in the middle and bottom layers of the lotic reach below Dajiang power plant. In the sections of the slowflow and lentic sections, fishes preferred to middle and surface layers in June but bottom layer in November. Fish body length was not correlated (〖WTBX〗P〖WTBZ〗>005) or negatively correlated (〖WTBX〗P〖WTBZ〗<005) with water depth in June. However, there were positive correlations (〖WTBX〗P〖WTBZ〗<005) between them in November. It is suggested that the fishes which were suitable for the different ecological groups were regionally distributed in horizontal direction due to the different hydrological regimes of the upper and lower reaches of Gezhouba Dam. In the sections of the slowflow and lentic sections, there was variation of the vertical distribution between seasons. The seasonal variation also influenced significantly the relationship between fish body length and distributing water depth in the upper and lower reaches of Gezhouba Dam.