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

Ochi D, Okamoto K, and Ueno S

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.

Marine and Freshwater Research

75

2

MF23148

doi:10.1071/MF23148