A state-space age-structured assessment model that accommodates environmental effects on demographic parameters and biological reference points

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The state-space model framework provides a natural probabilistic approach to modeling the stochastic nature of population survival and recruitment and sampling error inherent in observations of the population. Such models can be expanded to also model error in environmental covariates and their effects on demographic parameters. We present a state-space age-structured assessment model that can incorporate effects of observed covariates on recruitment and apply the model to Southern New England (SNE) yellowtail flounder and Gulf of Maine (GOM) Atlantic cod using data from the most recent benchmark assessments to evaluate evidence for environmental effects on stock productivity. Based on AIC, models that included environmental effects on recruitment performed better for both stocks and led to annual variation in estimated reference points.