Seasonal variability of fishery resources in Dahuofang Reservoirbased onacoustic survey method

With a split-beam scientific echosounder (Simrad, EY60, 70 kHz), we investigated the fishery resources in the Dahuofang Reservoir in Liaoning Provinceon July 19~21, September 14~16,2012 and May 12~14, 2013. The main hydrogeological parameters were surveyed in various stations distributed in the upper, middle and lower reaches. Moreover, the seasonal variation of fish density and distribution were analyzed to estimate the existing resource abundance in the reservoir, and the seasonal variability of vertically fish distribution was discussed with consideration to hydrological parameters. Results show that the fish mainly distributed at depth of 0~10 m in the spring, 5~15 m in summer, and 10~20 m in autumn, respectively. The horizontal fish distribution was uniform as small clusters in spring,assembled in upper and middle reaches as separating individuals in summer and moved to lower reaches in autumn. The seasonal changes in water temperature and dissolved oxygen were obvious, and the fish distribution, which was mainly in the layer above the thermocline, was influenced by water temperature. The hydrogeological parameterswere relative stable in autumn compared with the other seasons. There wasnt a thermocline in the reservoir and the fish echo was almostat single target echo state, which was suitable for acoustic survey and fishery resource assessment. The abundance of reservoir was estimated as 1 522 t in September.