This paper describes a method of comparing mesh selectivity curves of square-mesh and diamond-mesh codends by AIC (Akaike's Information Criterion) 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 codends; and a two-curve model in which the two mesh codends have different curves. The parameters of Richard equations are estimated as the selectivity curve by the maximum likelihood method, and then the AIC values 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, Argyrosomus argentatus, Loligo japonica) were estimated from the data of a small otter-trawl fishing experiment using two inner mesh lengths of 21.2 and 25.0mm carried out in the eastern area of the Seto Inland Sea. The single-curve model was appropriate for 21.2mm mesh size for Argyrosomus argentatus. It revealed that the single-curve model was enough to express selectivity for Argyrosomus argentatus of both mesh codends. From the available data of cover-net fishing experiments, this method is useful and easy to evaluate the difference in mesh selectivity curve between the square-mesh codend and diamond-mesh one.
