Efficacy of a novel shark bycatch mitigation device in a tuna longline fishery

Elasmobranchs (sharks, rays, and skates) are caught throughout fisheries globally, leading to over one-third of species being threatened with extinction 1 . Oceanic shark populations have undergone an average 71% decline over the last half century, owing to an 18-fold increase in relative fishing pressure 2 . Incidental capture or ‘bycatch' is a primary driver of population declines, and poses an important challenge for species conservation 3 . This threat necessitates mitigation strategies that exist for sharks but are often focussed on haul-back and post-capture effects for longline fishing. We trialled a novel shark bycatch mitigation device ("SharkGuard") in a commercial longline fishery targeting bluefin tuna ( Thunnus thynnus ), where bycatch consists largely of blue sharks (Prionace glauca ) and pelagic stingrays ( Pteroplatytrygon violacea ).