Gillnet selectivity and its relationship with body shape for eight freshwater fish species

Abstract

Knowledge of the size-selectivity of fishing gear types is crucial to fisheries management and ecology. The gillnet selectivity of most freshwater fish is poorly known. We caught 694 individuals of eight widely-distributed freshwater fish species (seven cyprinids and the pikeperch, Sander lucioperca) with multi-mesh gillnets in Spanish reservoirs. The SELECT method was applied to fit four different gillnet selectivity models (normal location, normal scale, lognormal, and gamma). The normal scale model (spread proportional to mesh size) had the best fit in four of the eight fish species. Predicted modal lengths for the best fit models are given to describe gillnet selectivity for the eight fish species. Significant variation in the selectivity parameters was explained by simple shape descriptors such as percent girth or percent depth, suggesting that these shape descriptors might be used as a preliminary tool to describe gillnet selectivity for other fish species.