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.
