Guidance on when and how science advice for Pacific salmon should account for time-varying population dynamics / by Carrie A. Holt, Brendan Connors, Dan Greenberg, Catarina Wor. : Fs97-6/3653E-PDF

"Time-varying population dynamics are ubiquitous for Pacific salmon due to, for example, changing ocean conditions and degradation of freshwater habitats. When these changes are ignored, science advice may result in poor biological outcomes or failure to meet catch objectives. There is currently very little guidance on where, when, and how to account for them in science advice for Pacific salmon. We reviewed the literature and performed computer simulations to determine when and how stationary and time-varying assessment models should be applied to inform science advice for Pacific salmon. When seeking to estimate population parameters from spawner-recruitment relationships, we found that models that annually track changes in productivity have better statistical reliability than stationary models or those that assume abrupt regime shifts. However, when models with time-varying parameters are applied for assessment or management purposes (e.g., as management reference points) under irreversible declines in productivity, they tend to be associated with increased biological risk relative to those that assume stationary dynamics. We recommend using time-varying models for assessment purposes only when the weight-of-evidence from multiple sources supports time-varying dynamics. Further, management actions that account for time-varying parameters should been evaluated in a risk-based, decision-making framework against those that assume stationary dynamics"--Abstract, page ix.

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