Effects of net height of crab entangling nets on the capture of targeted economically important portunid species and non-target species

The aim of this study was to determine the effects of net height on the capture performance of crab entangling nets. Fishing trials were conducted using nets at varying net heights (1) 12 meshes down (MD), (2) 24 MD and (3) 50 MD. A total of 1290 individuals comprising 87 species belonging to 53 families were caught. One-way analysis of variance showed that net height significantly affected the various catch parameters, including catch per unit effort (CPUE) of the total and target catch, amount of non-target catch, size of catch and species richness. The use of appropriate net height is a potential technical measure for a selective but still efficient crab entangling net fishery. Lower net height significantly reduced non-target catch by up to 70%. Lower net height also decreased the CPUE of target catch such as Portunus pelagicus and Charybdis feriatus by up to 65% at 12 MD, but catch at 24 MD was not significantly different than that at 50 MD. The use of a net height of 24 MD also resulted in the capture of larger-sized P. pelagicus. The richness of the catch species decreased by up to 58% in lower nets. These results are useful to fishery managers and government institutions when developing and/or improving existing regulations towards a sustainable crab fishery, particularly blue swimming crabs.