A review of the effectiveness of gear modifications to reduce shark bycatch mortality in longlining

IOTC has so far adopted only few shark conservation measures and existing measures focus on banning retention of Carcharhinus longimanus, Rincodon typus, and all three species of Alopias. No measures to reduce at-vessel mortality and post-release mortality have been adopted for longlining fleets at IOTC. While targeted catches will be disincentivized by such bans, an effective overall mortality reduction needs to address bycatch mortality, especially when the sharks that are to be released make up a substantial part of the bycatch of a fishery. While silky sharks are targeted by several artisanal fleets in the Indian Ocean and artisanal fisheries are exempted from the retention ban for Oceanic whitetip sharks, both species get discarded as a regular bycatch by industrial tuna and swordfish fleets, specially by those fleets targeting blue sharks. Scientific studies in the Pacific have recently shown that fishing mortality of both species can be reduced by more than 40% and 30% respectively, when steel leaders are replaced by monofilament leaders and shark lines removed (Bigelow et al. 2021). Therefore, the WCPFC will ban both gear modifications between 20°N and 20°S from 2024 onwards. However, IOTC has failed to agree on a similar conservation measure at its 26th IOTC Commission Meeting.