State-space models for NAFO Division 4TVn fall spawning Atlantic herring (Clupea harengus) subpopulations / François Turcotte. : Fs70-5/2026-050E-PDF

"The last stock assessment of the Northwest Atlantic Fisheries Organization (NAFO) Division 4TVn fall spawning Atlantic Herring raised significant concerns that triggered a review of the assessment framework. This assessment framework review evaluates a state-space modeling approach to better capture time-varying productivity and selectivity and improving robustness over prior models. Key advancements include transitioning from statistical catch-at-age models to a state-space framework, developing separate models for each subpopulation (North, Middle, South) rather than a single aggregated model and disaggregating catch by fixed and mobile gear fleets with independently estimated selectivity. These structural changes enhance biological realism, reduce parameter confounding, and improve diagnostic performance. For each subpopulation, objectives included developing base and sensitivity models and identifying best-fitting models. Overall, the state-space models performed well and are recommended for future stock assessments and management"--Abstract, page iv.

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