CCAMLR has a well-established framework to determine precautionary toothfish catch limits based on the CCAMLR Decision Rules. In recent years, CCAMLR has discussed the Decision Rules for toothfish and how they could be improved in determining catch limits for the assessed toothfish fisheries. Specifically, discussions have centred on how the Decision Rules should be applied in scenarios where virgin spawning biomass (B0 or SSB0) is difficult to estimate due to unknown catches taken by illegal, unregulated and unreported (IUU) fishing activities, where the stocks are currently around or below 50% of SSB0, and if the Decision Rules are robust to environmentally driven changes in productivity or climate change.
In this paper, we provide a summary of the history of the CCAMLR Decision Rules, summarise how these are applied in integrated statistical-catch-at-age toothfish stock assessments using constant catch HCRs, and develop potential ways in which HCRs based on a harvest rate U could be implemented for the assessed toothfish stocks in CCAMLR. In the companion paper (Ziegler et al. 2024), we explore the behaviour of potential U-based HCRs with simulations.