Efficacy of a novel galvanic shark deterrent to reduce catch of elasmobranchs in longline fisheries

Juxtaposing zinc and graphite together produces a galvanic electric field in seawater that may deter electrosensitive species, and thus reduce elasmobranch capture on longlines. The number of coastal carcharhiniform sharks caught on untreated and procedural control treatments did not differ, but significantly fewer sharks were caught on the zinc/graphite treatment (14.5%) compared to the procedural control (38.4%) and the untreated hook (47.1%). This translates to a 62.3-69.5% reduction in sharks caught on the zinc/graphite treatment. There was no significant difference in catch among the zinc/graphite and control treatments for piked dogfish. Too few sharks were captured in the pelagic trials to allow statistical comparison; however, capture of targeted bony fishes was highest on hooks with the zinc/graphite treatment, suggesting no negative effect on target catch rates. The difference in efficacy between carcharhiniform sharks and dogfish indicates the behavioral response to this deterrent may vary among elasmobranchs. Large-scale testing of the zinc/graphite treatment in pelagic fisheries is needed to establish whether it is a viable option to reduce shark bycatch and increase profitability in commercial fisheries.