Multifaceted effects of bycatch mitigation measures on target or non-target species for pelagic longline fisheries and consideration for bycatch management

Abstract

Context The pelagic longline fishery has implemented bycatch mitigation measures to reduce sea turtle bycatch, but little attention has been given to their side effects on other endangered species. Aims To investigate the impact of using circle hooks and whole fish bait on the fishing mortality of target and non-target fish species, as well as bycatch species. Methods Long-term data collected from research cruises conducted by a pelagic longline vessel were used for analysis. A Bayesian quantitative evaluation was employed to assess the effects of the mitigation measures on the fishing mortality of various species. Key results The use of circle hooks led to an increase in mouth-hooking for both target and bycatch species, and the effect was proportional to hook size. Although deploying circle hooks did not increase fishing mortality per unit effort (MPUE) for shortfin mako sharks, combining to whole fish bait had a significant increase on MPUE. Conclusions The study stresses the need for considering the trade-offs of bycatch mitigation measures such as circle hooks and fish bait among multi-taxa species. Implications The necessity for quantitative assessments of bycatch mitigation measures before implementation is highlighted to avoid unintended consequences on endangered species and ensure effective conservation in pelagic longline fisheries.