Development of a Method to Calcualte Gillnet Selectivity

摘要

A method to estimate size selectivity of gillnets has been developed at Kagoshima University on the basis of an hypothesized capture process where a fish is caught if; direct1a certain anterior section of a fish passs a mesh, and direct2 the amximum body section is blocked by the mesh. According to the theory, selectivity curves are calcuated simply on statistics of measured lengths and girths at the anterior, net-mark and the maximum body sections of fish. Tank experiments for carp, rainbow trout and tilapia and recalculation of at-sea experimental data for whiting were concluded as the method;direct1 gives reliable selectivity for species and size ranges mainly caught by the wedge function of gill-net. direct2 may give under-estimated selectivity over the lengths and species where capture by entangling is prevailing and direct3is not directey applicable for the species diagonally wedged. The method is also effective for trammelnets to calculte partial selectivity for small individuals.