COMPARISON OF SELECTIVITY CURVE BETWEEN SQUARE-MESH AND DIAMOND-MESH CODENDS BY AIC

This paper describes a method of comparing mesh selectivity curves of square-mesh and diamond-mesh codends by AIC (Akaike's Information Crit erion) from the data of cover-net fishing experiments. Two models are assumed for comparison: a single-curve model where a single curve can be fitted for both selectivity values of square and diamond mesh coden ds; and a two-curve model in which the two mesh codends have different curves. The parameters of Richard equations are estimated as the sele ctivity curve by the maximum likelihood method, and then the AIC value s of each model are also obtained to determine which is the better of the two models. The better-fit model is that with the smaller AIC. The AIC values of three species (Apogon lineatus, Argyrosmus argentatus, Loligo japonica) were estimated from the data of a small otter-trawl f ishing experiment using two inner mesh lengths of 21.2 and 25.0 mm car ried out in the eastern area of the Seto Inland Sea. The single-curve model was appropriate for 21.2 mm mesh size for Argyrosomus argentatus . It revealed that the single-curve model was enough to express select ivity for Argyrosomus argentatus of both mesh codends. From the availa ble data of cover-net fishing experiments, this method is useful and e asy to evaluate the difference in mesh selectivity curve between the s quare-mesh codend and diamond-mesh one.