The crab pot fishery is one of the most important fisheries in the East China Sea Utilization of escape devices has resulted in improved the size selectivity of pots.We compared the catch frequencies of swimming crab Portunus trituberculatus among experimental crab pots rigged with rectangular escape gaps of 25 mm or 30 mm widths,,control pots,,and control stownets.We then estimated encounter selectivity and relative selectivity based on a catch equation and the selectanalysis model.The size of individuals captured in the stownet was smaller than in the control crab pots. The encounter selectivity of the experimental crab pots was analyzed using the catch frequency of the control pot. The 50% retention carapace width (l50) and fishing power increased whereas the selection range (SR) remained unchanged with an increase in the width of the escape gap. The relative selectivity (catchability) of the crab pots was estimated by comparison with the catch frequency of the stownet.Large crabs were more likely to contact and then enter the crab pots than small crabs and the 50% probability contact carapace width was 98.7 mm. There was little difference in l50 and SR between the relative and encounter selectivity measures for the 30 mm escape gap. The l50 and SR for relative selectivity were 118.4 mm and 10.5 mm, and for encounter selectivity they were 117.4 mm and 9.5 mm, , respectively. There was no difference in l50 between the relative and encounter selectivity measures for the 25 mm escape gap. However, , the SR for relative selectivity (5.6 mm) was significantly less than for encounter selectivity (11.3 mm). Thus, , there would be some bias in population assessment if only the encounter selectivity information was taken into account and information about catchability was omitted.