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ESR prepress abstract   -  DOI: https://doi.org/10.3354/esr01070

Commercial viability of alternative designs placing pelagic longline branchline weights at the hook to reduce seabird bycatch

Eric Gilman. *, Stephen Beverly, Michael Musyl, Milani Chaloupka

*Corresponding author:

ABSTRACT: Bycatch in pelagic longline fisheries threatens the viability of some seabird populations and reduces fishing efficiency. A branchline fishing weight’s mass and distance from the hook significantly explain seabird catch risk during setting and hauling. We surveyed Hawaii tuna longline fishers to obtain their perspectives on the practicality, safety and economic viability of alternative designs placing weights adjacent to hooks instead of conventional designs with weighted swivels attached 0.6 meters from the hook. We conducted experimental fishing to explore the commercial viability of a combination weighted swivel attached to the eye of the hook. We used a Bayesian random effects meta-analytic regression modelling approach to estimate pooled expected species-specific log relative risk of capture on conventional as opposed to experimental branchlines. There were significant decreases in catch rates on experimental branchlines of 54% (95% HDI: 34.3 to 73.8) for retained species and 28% (95% HDI: –7.5 to 93.3) for discarded species. About 10% of experimental weighted hooks had the point of the hook tangle on the swivel, likely contributing to lower catch rates and making it more difficult for crew to coil branchlines. We identify possible factors explaining why the experimental gear reduced catch rates. The study demonstrated the benefits of stakeholder scoping to determine bycatch mitigation options with the highest promise for practicality, economic viability and safety, as well as benefits of conducting a pilot study to assess commercial viability to determine if a full experiment to assess bycatch mitigation efficacy is warranted.