Exploring SSBs responses to different recruitment scenarios and SSB0 calculations in a context of regime shift: a Kerguelen Patagonian toothfish fishery case study

Recruitment is a key component in population dynamics: its variations can have a major influence on population fluctuations. Recent studies have shown that toothfish recruitment can be highly variable and stock assessments of Patagonian toothfish (PT) have recently shown decreasing trends of estimated recruitment in the recent years. The paper aims at investigating the effects of a regime shift in PT recruitment on the state of the population using an age-structured stock assessment model (Casal2). The objective is also to investigate the consequences of using a dynamic SSB₀ on stock management and catch limit calculation, in the regime shift context of the Kerguelen island EEZ. We have shown that adjusting recruitment has consequences for the achievement of the current management targets. Furthermore, we showed that re-estimating SSB₀ according to stock productivity (dynamic SSB₀) has an impact on past, current and future stock status. These results call for reworking the projection scenarios and exploring more management and prediction possibilities in future models, especially now that Casal2 allows more modelling flexibility.