Traps are known to be selective with respect to species and size of catch, which is related to passive behaviours and the attraction of appropriate bait. The ICW50% of the catch in collapsible vertical traps and collapsible box traps (Table 1) was higher than the size at 50% maturity reported by Nitiratsuwan et al. [9]. The ICW50% from fixed box traps, on the other hand, was smaller than the maturity size. The variation of ICW50% among trap types was also due to the differences among fishing grounds, which were clearly separated because of movements of blue swimming crabs between near-shore and off-shore areas