due to low production, as measured in terms of the quantity of fishing gear. Moreover, the size of the blue swimming crabs was also smaller than in the previous years [6-7]. Traps are a major type of gear for catching blue swimming crab apart from bottom gillnets. Since traps were introduced from Japan in 1981, there has been intensive fishing by small-scale fishers, who set 100-300 traps per boat [8]. In Trang province, southern Thailand, there are three types of traps, namely fixed box trap, collapsible vertical trap and collapsible box trap. Boutson et al. [8] reported that 32-42% of blue swimming crabs in Thailand are immature based on onboard monitoring. Nitiratsuwan et al. [9], and Jindalikit [10] reported that 64.2% of the total landings on the Trang coast are small-sized