Size Selectivity of Hair Crab Pots

Abstract

In the fishery management of hair crabs in Hokkaido, restriction of the catch size forms one of the main features. In order to develop and improve the selective fishing methods that correspond to the regulations for catch size restriction, mesh selectivity experiments, and escape vent experiments were conducted. By applying the SELECT model and master curve method, selection curves for mesh size and escape vent size of hair crab pots were estimated. A mesh size and an escape vent size, to which the rostral length of 50% retention corresponds to the minimum legal size of 80 mm rostral length for males, were estimated to be 112 and 51 mm, respectively. The selectivity range of the mesh size (112 mm) and the escape vent size (51 mm) were estimated to be 5.2 and 5.1 mm, respectively. This indicates that both the mesh selection and escape vent selection of hair crab pots are sharp. The results of the model selection showed that the assumption of equal relative fishing efficiencies of hair crab pots with various mesh sizes or escape vents are not always applicable. In estimates of the mesh selectivity master curve, the assumption that a proportional relationship exists between rostral length and mesh sizes that show the same retention probability was not accepted.