Abstract:

From October 2004 to May 2006, hydroacoustic survey on fishes was carried out in the 30 km reach from Gezhouba Dam to Gulaobei in the Nature Reserve for Acipenser sinensis Gray in the Yangtze River with Bisonics DTX Scientific Echosounder (200 kHz). Fishes were distributed not homogeneously, being assembled in deep pools but rarely in saults. Mean densities of fishes in the reach from Gezhouba Dam to Aijia River were obviously greater than those in the reach from Aijia River to Gulaobei. In spawning period of Acipenser sinensis Gray, fishes congregated in the reach from Gezhou Dam to Miaozui, with mean densities being 62.62 ± 24.77 ind./1 000 m3 in 2004 and 70.58 ± 37.45 ind./1 000 m3 in 2005. The proportion of fishes with the body length ranging among 60 mm and 106 mm was higher than other length groups along the reach, accounting for approximately over 7.0% of the total fishes. Moreover, the ratio of fishes with body length less than 53 mm and longer than 750 mm were lower than other length groups in the reach, accounting for less than 2.0%. During the survey period, spawners of Acipenser sinensis Gray were found, with 1 453 estimated in 2004 and 789 in 2005, at 95% confidence limits of 1 370~1 537, 775~803 respectively.

Key words: hydro acoustics, fish stock assessment, fish distribution, natural reserve, Acipenser sinensis Gray