Comparison of stock management with production, difference, and age-structured models using operating models

Management strategy evaluation (MSE) was used to test the assessment and management performance of three assessment methods in combination with harvest control rules. The assessment procedures considered were: the eXtended Survivors Analysis (XSA), the Schaefer production model, and the difference model. Four HCRs were considered: first, fishing mortality was set on the basis of the relationship between the current biomass and a reference biomass; second, fishing mortality was gradually reduced (or increased) until it reached a required target; and the third and the fourth HCRs were similar to the first and second but with imposed TAC constraints. The stock that was generated in the operating model (OM) resembled the eastern Baltic cod stock. For the XSA assessment, two options were used: XSA with default shrinkage of terminal fishing mortality to the average of the estimates, and XSA with low shrinkage. The simulations showed that for stock assessment, the XSA models performed much better than the difference and Schaefer models. However, for the data tested, the difference and Schaefer models performed somewhat better in terms of management performance than the XSA models, especially the XSA model with default shrinkage.