Estimating natural mortality within a fisheries stock assessment model: An evaluation using simulation analysis based on twelve stock assessments

Natural mortality (M) is one of the most influential and difficult to estimate number of losses in fisheries stock assessment and management. Typically, natural mortality is estimated using indirect methods, such as correlation with measurable life history factors and rarely relies on direct data such as tagging studies. In contemporary stock assessments, natural mortality may be estimated within the model by integrating different types of data into the analysis. We evaluated the estimability of M using simulation analyses based on 12 groundfish stock assessments conducted using Stock Synthesis. The advantages of utilizing this set of peer-reviewed assessment models were that various types of data were used over a wide range of model parameterization. Our results suggest that, in many cases, M is estimable with appropriate data. Profile likelihood analyses suggested that informative length or age composition data is needed to reliably estimate M.