Effect of soaking time on targets and bycatch species catch rates in fish and crab trap fishery in the southern East China Sea

Abstract

Management strategies for trap fisheries in the Taiwan Strait (TS) lack crucial information such as factors determining the catch rates and bycatch species as well as the effect of the soaking time (SKT) of traps. Therefore, we investigated logbook and voyage data recorder data from Taiwanese crab and fish trap vessels (2011-2016). The crab traps were distributed widely in the TS, whereas the fish traps were mostly used in the northeast and southwest of the TS. Hierarchical cluster analysis revealed that the TS could be divided into the Northern Taiwan Strait, where most fishers use crab traps to target Portunus sanguinolentus, P. pelagicus, and Charybdis feriatus; Kuroshio Current, with large catches of Dentex hypselosomus using fish traps; and Taiwan Bank, with large catches of Evynnis cardinalis and other species using both traps. The optimal target species catch rates were achieved for a SKT of 48 h, regardless of the trap type. The bycatch rates were found to be higher when the SKT was longer than 48 h for crab traps, whereas the bycatch rates for fish traps were unaffected by the SKT. These findings may aid the implementation of sustainable trap fishing through harvest strategy planning, spatiotemporal management, and bycatch reduction.