ESTIMATION ON ABUNDANCE OF BENTHONIC FISHES PREYING ON EGGS OF CHINESE STURGEON IN REACH BELOW THE GEZHOUBA DAM IN THE YANGTZE RIVER

From 1997 to 2001, assessment on the annual abundance of benthonic fishes which prey on eggs of Chinese sturgeon were undertaken through commercial fisheries surveys in the reach below the Gezhouba Dam where the spawning ground of Chinese sturgeon located in the Yangtze River. Eleven species of benthonic fishes were confirmed to be egg predators through the examination of gut contents. The dominant species of egg predatory fishes were Coreius guichenoti, C. heterodon and Pelteobagrus vachelli. First of all, by applying Jones Length based cohort analysis, annual abundance of C. heterodon was estimated with fishing data collected in springs and autumns. Then, abundance of the rest egg predatory fishes were counted according to the quantitative ratios of them to C. heterodon in catches. Summarily, annual abundance of egg predatory fishes fluctuated from 197487 to 744487 with an average of 444822 individuals within the research period. Due to assemblage for preying on eggs, abundances of egg predatory fishes were obviously higher in course of egg deposition of Chinese sturgeon, and numbered from 335005 to 2064607 with an average of 486750 individuals annually. It was estimated also that approximately 2565172 eggs, corresponding to the fecundity of 4 females, were eaten by egg predatory fishes daily in the egg deposition periods of Chinese sturgeon.