Efficacy of the ‘Smart Tuna Hook’ in reducing bycatch of seabirds in the South African Pelagic Longline Fishery
While considerable progress has been made in mitigating bycatch in demersal longline fisheries, proven and accepted seabird avoidance measures in pelagic fisheries require substantial improvement. We report on an at-sea experiment to test the efficacy of a mitigation method known as the Smart Tuna Hook (STH). This method uses a modified tuna longline hook which accepts a specially designed shield that disarms the hook once it has been baited, preventing ingestion and making it impossible for any seabird to be hooked. The shield is released within 15 minutes after the hook has been immersed in salt water, allowing fish to be caught after the baited hook has passed beyond the normal diving and feeding depths of most seabirds. After release from the hook the shield sinks to the seafloor where it corrodes within 12 months, leaving no pollution or toxic residue. The byproduct is iron oxide and carbon. Our experimental work was conducted on pelagic longline vessels targeting tuna and swordfish out of Cape Town, South Africa during the Austral spring of 2014. Seabird bycatch was high and a total of 13 birds were caught across the three trips. Eleven of these birds were caught on the control treatments and 2 birds on the STH treatments. The use of the Smart Tuna Hook led to a reduction in the bycatch of seabirds of between 81.8% – 91.4% in one of the highest-risk fisheries to seabirds in the world. Importantly, there was no detectable difference between setting methods in the catch rates of commercially valuable species, indicating no detectable detrimental effect on fish catch for any species. In a fishery where the bycatch rate of seabirds exceeded 1 bird/1000 hooks (this study), and where the capture of more than 25 birds by a vessel each season leads to a suspension of fishing activity for that vessel, the Smart Tuna Hook clearly provided a significant deterrent to seabirds attacking baits, and offers a feasible option for pelagic fishers to significantly reduce the level of interactions with seabirds and hence remain active in the fishery.