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ESR 43:223-233 (2020)  -  DOI:

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

Eric Gilman1,*, Stephen Beverly2, Michael Musyl3, Milani Chaloupka4

1Pelagic Ecosystems Research Group, Honolulu, Hawaii 96822, USA
2Fisheries consultant, Mont Dore Sud 98809, New Caledonia
3Pelagic Research Group, Honolulu, Hawaii 96816, USA
4Ecological Modelling Services Pty Ltd & Marine Spatial Ecology Lab, University of Queensland, St. Lucia, Queensland 4067, Australia
*Corresponding author:

ABSTRACT: Bycatch in pelagic longline fisheries threatens the viability of some seabird populations and reduces fishing efficiency. The mass of a branchline fishing weight and its 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 which place weights adjacent to hooks instead of conventional designs with weighted swivels attached 0.6 m 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 modeling 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% highest posterior density interval [HDI]: 34.3 to 73.8) for retained species and 28% (95% HDI: -7.5 to 93.3) for discarded species. For about 10% of experimental weighted hooks, the point of the hook tangled on the swivel, likely contributing to lower catch rates and making it more difficult for crew to coil branchlines. We identify additional possible factors explaining why the experimental gear reduced catch rates. The study demonstrates 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.

KEY WORDS: Bycatch · Longline fisheries · Seabird · Tuna

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Cite this article as: Gilman E, Beverly S, Musyl M, Chaloupka M (2020) Commercial viability of locating pelagic longline branchline weights at the hook to reduce seabird bycatch. Endang Species Res 43:223-233.

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