Prediction of square mesh panel and codend size selectivity of blue whiting based on fish morphology

Abstract

Square mesh panels (SMPs) are selective devices used extensively to supplement codend size selectivity in trawl fisheries. Therefore, predictions of the effect of mesh size in both SMPs and codends on size selectivity are valuable. Here, we established a framework to predict the size selection of blue whiting through different SMPs and diamond mesh codends based on the morphological characteristics of this species. We hypothesized that size selection for an SMP is determined by different fish contact angles, whereas different mesh opening angles determine size selection for the codend. Based on these hypotheses, we first developed a model that enabled us to predict which sizes of blue whiting are able to pass through meshes of different sizes and shapes. We then tested whether the selectivity for blue whiting of the SMP, the codend, and the combination of both could be explained by the models. Finally, we predicted the size selectivity of multiple combinations of SMPs and diamond mesh codends. The method presented here can potentially be applied to make predictions for species other than blue whiting.