A new concept for bycatch reduction in small-scale accordion-shaped trap fisheries of the Yellow Sea, China

The bycatch issue is a major concern in small-scale accordion-shaped trap fisheries in the Yellow Sea of China because of the poor species and size selectivity of fishing gear and the co-occurrence of multispecies. Two threatened flatfish species assessed by the IUCN, marbled flounder (Pseudopleuronectes yokohamae) and stone flounder (Platichthys bicoloratus), are the two main bycatches in accordion-shaped trap fisheries. This fishery also captures a large proportion of juvenile target species, resulting in both recruitment and growth overfishing of these species. In this study, we introduced a new concept of a combined sorting grid and escape vent (CSEV), a selection device aimed at reducing the bycatch of flatfish and undersized target species in mixed-species trap fisheries. We used a catch comparison method to assess the performance of the CSEV in field experiments, with conventional traps as the baseline. Our results demonstrated that the CSEV significantly improved the species and size selectivity of the traps. Test traps mounted with the CSEV significantly reduced the catch rates of marbled flounder and stone flounder by 70% and 74% throughout the length class, respectively, compared with conventional traps. The catch of undersized target species, namely, fat greenling (Hexagrammos otakii), black rockfish (Sebastes schlegelii), and Asian paddle crab (Charybdis japonica), was reduced by 79%, 75%, and 80%, respectively, while the catch rates of target-sized individuals were maintained or even improved. Given these promising results, the CSEV may have great potential for application in accordion-shaped trap fisheries and similar fisheries.