This project provides the first step in addressing an ongoing concern with the domestic management of Swordfish, namely that a domestic harvest strategy might not be required if the stock extends to the eastern edge of the WCPFC convention area. This concern has been raised continuously by TTRAG members over recent years as Swordfish is a key target species for the ETBF.
In parallel, efforts to implement CKMR for WCPFC-managed species are currently underway, with Swordfish a lower priority compared to other species like albacore tuna. This work would supplement and possibly accelerate any preliminary efforts undertaken by the WCPFC to consider CKMR for Swordfish. Alternative signals of abundance for this stock would improve regional management given high uncertainty in the estimated stock status in the most recent stock assessment, in part driven by uncertain spatial stratification of the stock (Ducharme-Barth et al. 2021). Similarly, in the ETBF, standardised CPUE is used to drive the domestic harvest strategy, but concerns have been raised about the reliability of this metric as an abundance index due to changing economic conditions which are hard to account for in standardisation models.
Finally, stock structure is a key consideration for effective fisheries management and tools are currently lacking to detect fine spatial structuring, especially for highly-mobile species. Insights about stock structure have so far been considered a useful by-product from CKMR compared to the main objective of abundance estimation. As such, CKMR scoping studies have not yet been optimised to detect stock structure, and little is known about differences in sampling needs between the two objectives. This work would be the first formal comparison of sampling sizes required for stock structure detection vs. abundance estimates with CKMR. It would provide useful insights on the feasibility of pursuing CKMR for stock structure detection from a sampling and logistics perspective for Swordfish, as well as highly-mobile species in general.
