The selectivity of different mesh sized-codends of shrimp trawl to by-catch species
不同尺寸虾拖网网囊网目对副渔获物的选择性研究

In order to reveal the selectivity to by-catch species by shrimp trawls ,which is operated in the Yellow Sea, experiments of codends with mesh sizes, 30, 33, or 40 mm were conducted using the cover-net method. The escape rates of main by-catch species were measured, and the selectivity parameters of Chaeturichthys stigmatias were estimated by using the maximum likelihood method. The results indicated that the escape rates of main by-catch species increased as the mesh sizes were increased. For mesh sizes of 30, 33, and 40 mm the escape rates of C. stigmatias were 48.3%, 59.7%, and 62.6%, respectively; the escape rates of Parapenaeopsis tenella are 67.0%, 68.2% and 68.7%, respectively. The selectivity parameters of C. stigmatias also increased as mesh sizes were increased. For the mesh sizes of 30, 33, 40 mm, the L50 of C. stigmatias were 81.858, 86.715, and 88.028 mm, respectively; while the SR were 41.097, 45.007, and 50.423 mm, respectively. Based on the results, we concluded that the effect of releasing by-catch species were not very good only by enlarging mesh sizes.