Improved line weighting reduces seabird bycatch without affecting fish catch in the Brazilian pelagic longline fishery

Abstract

1. Increasing the sink rate of baited hooks by adding weights in close proximity to the hook is crucial to reduce seabird mortality in pelagic longline fisheries. However, weights placed next to the hook are a cause for concern for fishing crew because they can fly back in the event of a line break, injuring deck crew.2. Lumo Leads, an alternative weight system designed to slide in the event of a line break, and therefore prevent accidents, were trialled in pelagic longline fisheries off southern Brazil. Four fishing trips were conducted and 26,377 hooks sampled to compare sink rates, seabird bycatch rates and catch rates of target species between three treatments: (1) 60 g Lumo Lead attached at 1.0 m from the hook;(2) 60 g Lumo Lead at 3.5 m; and (3) 60 g leaded swivels at 3.5 m from the hook. A LumoLead placed at 1.0 m from the hook resulted in a faster sink rate and caught fewer seabirds (0.11 birds per unit of effort [BPUE]) when compared with a Lumo Lead (0.33 BPUE) or weighted swivel (0.85 BPUE) placed at 3.5 m. The bycatch with Lumo Lead placed at 1.0 m from the hook was 90% lower than the bycatch of Lumo Lead or weighted swivel placed at 3.5 m combined. There was no difference in the catch rates of target species between the three treatments.4. These findings support a growing body of evidence that placing weights close to the hook reduces seabird bycatch without affecting the catchability of the target species. The high seabird bycatch rates recorded despite night setting and recommended line weighting regimes reinforces the need of simultaneous deployment of a toriline with these other two mitigation measures to reduce seabird bycatch to negligible levels in the south-west Atlantic.

Commercial viability of locating pelagic longline branchline weights at the hook to reduce seabird bycatch

“…Numerous gear technology methods have been demonstrated to reduce seabird bycatch in Hawaii and other pelagic longline fisheries, including branchline weighting designs (Gilman et al 2005, Hall et al 2017, ACAP 2019, Gilman & Ishizaki 2019. The mass of a branchline fishing weight and the weight's distance from the hook significantly affect seabird catch rates during setting (Gilman et al 2008, Melvin et al 2013, 2014, Robertson et al 2013, Santos et al 2019) and hauling (Gilman et al 2014a in pelagic longline fisheries. These 2 variables affect the sink rate of baited hooks and concomitant availability to seabirds during gear setting.…”

Co-creating Knowledge with Fishers: Challenges and Lessons for Integrating Fishers' Knowledge Contributions into Marine Science in Well-Developed Scientific Advisory Systems

“…Pingers can also increase the risk of excluding harbor porpoise from their feeding areas (Olesiuk et al, 2002). The effectiveness of techniques for birds, such as the weighting of lines was proven but is difficult to quantify (Jimeńez et al, 2018;Santos et al, 2019).…”

Investigating weighted fishing hooks for seabird bycatch mitigation

“…Required seabird bycatch mitigation measures for this US longline fishery include the attachment of a weight of ≥ 45 g within 1 m of the hook 14 . The mass of a pelagic longline branchline’s weight and distance between the weight and the hook significantly affect seabird catch risk during setting 15 – 18 , as well as during the gear soak and haul 19 , 20 . During gear setting, these two variables affect the sink rate of baited hooks and their availability to seabirds.…”