Abstract:

Aimed to provide background information of the effects of the Three Gorges Project on endemic fish resources of the upper reach of the Yangtze River,the assessment on the annual abundance of Rhinogobio ventralis in Yibin Reach of the Yangtze River was undertaken.The research reach was from the edge of Yibin County and Shuifu County to Erersi Bridge of Yibin with the length of 17 km.From 1998 to 2002,the information of fishing effort in Yibin reach of the Yangtze River was collected,and the data of commercial fisheries in this reach were sampled.Initially the total annual harvest yield (Y) was estimated by the parameters which obtained through commercial fisheries surveys,such as annual fishing efforts and CPUE.Then,the annual yield of R.ventralis was counted according to its quantitative ratio in sampling.The parameter of L∞ and k was from relative references;the parameter of M was calculated by the Pauly's method.The exploit rate (Et) of maximum length group was set at 0.8. Finally,by applying Jones lengthbased cohort analysis,the annual abundance of R.ventralis  was calculated.The results were showed as follows:from 1998 to 2002,the total annual yield (Y ) was 315 718,732 873,591 337,569 402 and 611 858 individuals respectively;accordingly,the annual yield of  R.ventralis was 39 219,22 528,24 458,39 743 and 13 845 individuals,respectively.From 1998 to 2002,it was estimated that the annual abundance of R.ventralis was 75 162,22 594,49 951,43 308 and 21 996 individuals respectively with an average of 42 602 individuals.The 95% confidence interval of annual abundance of  R.ventralis  ranged from 23 300 to 61 903 individuals.
 

Key words: Rhinogobio ventralis/abundance/lengthbased cohort analysis/Yibin Reach of the Yangtze River