The benefits and risks of incorporating climate-driven growth variation into stock assessment models, with application to Splitnose Rockfish (Sebastes diploproa)

Indices of annual growth variation are not routinely incorporated into fisheries stock assessment models, due to a lack of a general framework for deciding when to include these indices, and of a mechanistic understanding about growth drivers. Such incorporation may also not necessarily lead to improved estimation or management performance. We demonstrate a way to incorporate such an index into an assessment model (Stock Synthesis), and use risk analysis to evaluate its management-related advantages and shortcomings. We applied this method to splitnose rockfish (Sebastes diploproa), where a previously developed growth index is highly correlated with decadal-scale climate indices. We find that including a similar index in the simulated assessment increases precision and reduces bias of parameter estimates. However, not including an index or including a completely erroneous index led to highly imprecise estimates when growth was strongly climate-driven. Including this growth index when individual growth was actually constant did not lead to poorer estimation performance. The risk analysis approach can be applied to other stocks to evaluate the consequences of including an index of growth variation.