Abstract:

In order to investigate the spatial and temporal distribution of fish, the hydroacoustic survey was undertaken in the near downstream of Gezhouba Dam (from the dam to downstream reach of Zhenjiangge) using two methods including sonar sailing by ship and sonar fixedpoint monitoring, during April and June 2013. The fish density and the activities in water column were obtained after denoised in the observation data. The results show that there is significant spatial difference in the fish density distribution in the near downstream of Gezhouba Dam. The fish density in the water body of Dajiang is significant higher than that in Sanjiang. Moreover, the fish density in the reach of near the dam is higher than that in the downstream. The highest value is 6924 ind./1 000 m3, and lies on the downstream reach which is 1 km away the Dajiang project, while, the minimum value is 153 ind./1 000 m3, and is located in the downstream reach closing to Yihua building. The distribution of fish resources has difference for April and June. In details, the dielmovements of fish are more active in June, and the fish moves to the surface water at daytime, with less activity from nightfall to dawn. Further analysis displays that the complex operation of the ship lock, the available food, and the different fish population with special life habitat will have important impact on the spatial and temporal distribution of fish. In addition, the study was conducted during the closed fishing season. The closed fishing leads to plenty of fish in the water body, which has vital effect on the fish resource protection for the near downstream of Gezhouba Dam in spring and summer. DualFrequency Identification Sonar applied to the water area where terrain hardly changes. It is necessary to adjust the speed of ship at 7km/h or below for a better image effects. This research of the implementation by DualFrequency Identification Sonar SMC300 in water area near Gezhouba Dam proves that the method was effective. It is meaningful to attempt to this approach in other fish surveys of inland river. Using the acoustic surveys we conduct an unbiased survey of all species in the study area. Based on this research, DIDSON also has a blind spot, which is concerned that instability in precision of monitoring