Meta-analysis of standardised interaction rates reveals relative performance of seabird bycatch mitigation methods for pelagic longline fisheries in the light of the review of CMM 2018-03 WCPFC-SC20-2024/EB-WP-1

Bycatch in commercial pelagic longline fisheries is a prominent driver of seabird declines globally. A range of different seabird bycatch mitigation methods exist that can address this challenge to marine biodiversity. However, to date, comparing the relative effectiveness of different bycatch mitigation methods has been challenged by the context-specificity of experimental trials and large-scale studies using observer data. Here, we build on a recent statistical development that leverages the context-specificity of bycatch mitigation studies, rather than being limited by it. We calculated relative Standardised Interaction Rates (rSIR) per mitigation method under either WCPFC CMM 2018-03 specifications (separated between Hemispheres when appropriate) or current ACAP best practice. Specifically, we calculated rSIR for 44 bycatch mitigation studies that met our metaanalyses criteria within a Bayesian modelling framework. This allowed us to account for sample sizes of different studies, while generating adequate levels of uncertainty....

It is recommended that WCPFC SC20: • Notes the analysis of the performance of seabird mitigation methods for commercial pelagic longline fisheries using relative standardised interaction rates, which demonstrated the poor performance of some seabird mitigation methods (e.g., bluedyed bait) and the need to improve specifications of other seabird mitigation methods (e.g., current branch line weighting and Northern Hemisphere tori line specifications). • Notes the ranking of individual seabird bycatch mitigation methods under ACAP best practice specifications, from best to worst performing (based on relative standardised interaction rates): 1) hook-shielding devices, 2) weighted branch lines, 3) night setting, and 4) tori lines, and notes the ranking of combinations of two out of three Southern Hemisphere mitigation methods: 1) weighted branch lines with tori lines, 2) weighted branch lines with night setting, and 3) tori lines with night setting. • Notes that this analysis shows that the use of ACAP best practice could improve the performance of seabird bycatch mitigation methods by 61% for the area South of 30°S, 81% for the area between 25°S and 30°S, and 73% for the area North of 23°N.