The effect of soak time on pot escape opening selectivity in swimming crab (Portunus trituberculatus) fishery

In different trap fisheries worldwide, escape openings are often used to improve size and species selectivity by reducing bycatch. The selectivity efficiency of escape openings depends on their shape and size designed according to the target species morphology. However, the efficiency also depends on the number of trapped animals contacting such escape openings. In pot fisheries, the escape process of bycatch individuals is often dependent on how long the gear is deployed (soak time). In this study, we conducted experimental fishing trials to evaluate size selectivity and catch patterns of pots configured with two types of escape openings among three different soak times (2, 5, 7 days) in the swimming crab (Portunus trituberculatus) fishery of the Yellow Sea, China. Increasing soak time significantly decreased the retention probability of undersized crabs. Longer soak times enhanced crab contact probability with escape openings, with over 90% achieving selectivity contact after 7 days soak time. Additionally, use of escape openings reduced capture of bycatch species and significantly affected catch composition. There were no significant differences in size selectivity between circular and rectangular escape openings. These findings contribute to understand the importance of soak time on the size selection processes of P. trituberculatus pots. Further, they provide insights for the development of more sustainable fishing practices.