FISH SEPARATING EFFICIENCY OF SORTING GRID RIGGED IN BEAM TRAWLS
桁拖网渔具刚性栅栏对鱼类的分隔效率研究

Poor selection of the beam trawl fishing in the East China Sea has exerted negative influences on conservation of fish resources and management of fisheries. To solve the issue, sorting grid was developed to separate catch effectively by species retained in non-selective codends in trawl fisheries. In this paper, the separating efficiency of sorting grid of different bar spacings (15, 20, and 25mm) for three-lined tongue sole Cynoglossus abbreviatus, little yellow croaker Pseudosciaena polyactis, and spinyhead croaker Collichthys lucida was analyzed in sea trials carried out in Lvsi Fishing Ground in the SELECT model. The results show that the separating ratio of catch weight of fishes decreases with the increase in bar spacing. The 50% retention length of different grids increases with the bar spacing. For three-lined tongue sole, the probability of contacting grid of shrimps is indicated by a parameter, which means the contact probability is independent of individual size. The maximum likelihood estimates of contact probability for sorting grids of different bar spacings are between 0.2 and 0.4 and increase insignificantly (P>0.05) with the bar spacings. For little yellow croaker and spinyhead croaker, all individuals entering codends would encounter the sorting grids. The difference in contact probability for different fishes indicates distinct swimming behavior patterns in trawl.