Size selectivity of diamond and square mesh codends for hairfin anchovy Setipinna taty in Chinese stow net fisheries

Abstract

Selectivity experiments of diamond and square mesh codends with different mesh size (30, 35, 40 and 45 mm) for hairfin anchovy Setipinna taty were carried out using the covered codend method in Chinese stow net fisheries. In the present study, 5151 specimens were subsampled and asymmetric and symmetric selectivity curves (Richards and Logistic curves) were fitted to the catch data, using the maximum likelihood method according to the SELECT model. The results show that the Richards curve gives a better fit to the selectivity curve for diamond mesh codends with 30, 35 and 40-mm mesh sizes, whereas the logistic curve gives a better fit for the diamond mesh codend with 45 mm mesh size and square mesh codends with 30, 35, 40 and 45-mm mesh size. With the exception of 45-mm mesh size codends, the L 50 of diamond mesh codends were insignificantly larger than those of square mesh codends. However, the selectivity curves of square mesh codends were steeper than those of diamond mesh codends, except the 30-mm mesh size codends. As for diamond mesh codends, according to the linear relationship between the L 50 and mesh size, 36.5-mm mesh size codends could release 50% juvenile hairfin anchovy (below 1-year old). However, diamond mesh codends with such a mesh size are not selective for other species.