Detecting significant retrospective patterns in state space fish stock assessment

• Published in: Canadian Journal of Fisheries and Aquatic Sciences
• Main Authors: Breivik, Olav Nikolai, Aldrin, Magne Tommy, Fuglebakk, Edvin, Nielsen, Anders
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2023
• Subjects: Arctic; Arctic cod; Northeast Arctic cod
• Online Access: https://hdl.handle.net/11250/3103101; https://doi.org/10.1139/cjfas-2022-0250

Retrospective patterns are commonly investigated to validate fish stock assessment models. A widely applied measure for retrospective bias is Mohn’s ρ and corresponding retrospective plots. However, retrospective patterns can be interpreted differently by experts. To make decisions regarding significant retrospective patterns less subjective, we proposed a post-sample Mohn’s ρ significance test. As case studies, we applied the state space assessment model SAM with data on Northeast Arctic cod and Norwegian coastal cod north of 67◦N. We showed that the acceptance regions of Mohn’s ρ depends on both the data available and the assessment model complexity. We also assessed the test power under a range of assumption violations and conclude that Mohn’s ρ is useful for detecting violations associated with bias, but not for violations associated with variances and correlations. publishedVersion