Minimum standards for the ACAP advice on branch line weighting for pelagic longline fisheries

Weights placed near hooks (i.e. short leaders) in pelagic longline branch lines increase sink rates of baited hooks and reduce seabird attacks and bycatch. Currently, ACAP recommends three weight regimes that are considered within ACAP's Best Practice Advice for Reducing the Impact of Pelagic Longline Fisheries on Seabirds: (a) 40 g or greater attached within 0.5 m of the hook; or (b) 60 g or greater attached within 1 m of the hook; or (c) 80 g or greater attached within 2 m of the hook.

This categorization is the result of a study on the sink rates of baited hooks in branch lines with several weighting configurations (SBWG7 Doc 07). The sink rates of these recommended branch line weighting regimes were on average equal to or above 0.5 m.sec⁻¹ under controlled experimental conditions. However, the minimum standards recommended by ACAP for this mitigation measure do not consider the materials of the weights used which can greatly influence their performance in sinking hooks beyond the reach of seabirds. Defining ACAP recommended specifications based on sink rates provide a possible mechanism to account for the variation in performance of different material. This could also provide greater flexibility for the development of weighting regimes in pelagic longline configurations where current weight specifications might pose operational challenges for implementation, However, sink rates measured under real fishing conditions can vary from those obtained under controlled experimental conditions, making implementation of such an approach challenging. Further stipulation around the use of branch line weight materials could be another option to ensure ACAP recommended only specifications that are effective at rapidly sinking hooks beyond the reach of seabirds.

RECOMMENDATION
We recommend that SBWG consider how the minimum standards for branch line weighting in ACAP Best Practice Advice for Pelagic Longline Fisheries could be improved to ensure they describe the use of weights which will be effective at rapidly sinking hooks beyond the reach of seabirds.