Lumo Leads: a potential, new, safe line weighting technique to reduce seabird bycatch for pelagic longline fisheries

Seabird bycatch from pelagic longline fisheries can be reduced when Best Practice mitigation measures are used in combination; however widespread adoption of Best Practice remains a problem, threatening many seabird species globally. Lumo Leads provide a line-weighting technique for seabird bycatch mitigation that works without compromising fish catch, fishing operations efficiency or crew safety. Unlike conventional weighted swivels, Lumo Leads are attached to monofilament lines in such a way that they can slide up and down the line and simply slip off the line during a bite-off. Lumo Leads of different mass (45 and 60 g) and colour (black or glowing), were tested onboard Korean pelagic longline vessels, at varying distances from the hook (5 cm, 60 cm, 100 cm and 200 cm), with their impact on seabird bycatch, target catch, fishing operations and crew safety recorded. Trials were completed over three trips in two years onboard three vessels, representing 217,000 experimental hooks. Only two seabirds were caught throughout the study; one on unweighted branchlines and one on a weighted (lumo lead) branchline. Lumo Leads had no significant impact on catch rates of southern bluefin tuna (Thunnus maccoyii); neither 45 g (p = 0.287) nor 60 g (p = 0.332) glowing lumo leads placed at 5 cm from the hook. Catch rates of yellowfin and bigeye tuna were very similar between weighted and unweighted branchlines when Lumo Leads (45 and 60 g) were placed 100 cm from the hook (p = 0.100 and 0.135, respectively), and were almost identical when using 60 g Lumo Leads 200 cm from the hook. Some treatments on tropical and temperate tunas-directed effort did significantly reduce target catch: 45 g black Lumo Leads 5 cm and 60 cm from the hook. The use of 45 g black Lumo Leads 60 cm from the hook reduced the combined catch of yellowfin T. albacares and bigeye tunas T. obesus (p = 0.009) as well as the catch rate of albacore tuna T. alalunga (p = 0.035). Only albacore tuna catch was negatively affected when using 45 g black Lumo Leads 5 cm from the hook (p < 0.001). Crew safety was not compromised when using Lumo Leads, with line flybacks occurring as regularly on weighted branchlines as on unweighted branchlines. Fishing operations were generally unaffected by the addition of Lumo Leads, however branchline entanglements were significantly increased when using 60 g lumo leads at 100 cm (p =0.037) and at 200 cm (p < 0.001) from the hook. These were generally minor entanglements with only the line entanglement rate for 60 g at 200 cm from the hook believed to impact operational aspects. Although too few birds were caught in this study to evaluate the impact of lumo leads on seabird bycatch, the addition of weight to branchlines is known to reduce seabird bycatch. Lumo leads did not show significant reductions in target fish catch for bluefin tunas, did not compromise crew safety, and did not seriously affect fishing operations. Lumo leads appear to be an effective seabird bycatch mitigation measure for Korean-style pelagic longliners, which allows Korean vessels to fish in compliance with IOTC Resolution 12/06 when using line weighting and bird scaring lines as their two preferred seabird bycatch mitigation options.