Ian Stewart1
1International Pacific Halibut Commission
May 05, 2015 9:00 (PST): FSH 203
It is standard practice to conduct fisheries stock assessments generating a point estimate of stock size, which is then translated into one or more future fishery catch targets and limits. The general approach often relies on the output of a single stock assessment model, and therefore does not thoroughly account for alternative hypotheses or major sources of uncertainty such as fixed parameter values, model approach (e.g., statistical catch-at-age, VPA), model structure (e.g., treatment of spatial dynamics, delineation of fishing fleets, time-series length) and data weighting. In 2012, the International Pacific Halibut Commission made the transition from point estimates to risk-assessment, based on a decision table produced for the annual management process. The decision table represents a composite of probability-weighted results from alternative models, allowing a comparison of potential benefits (fishery yields) with the probabilities of various risk metrics, including stock and fishery trends and status. In 2013, the approach was extended to include the use of an ‘ensemble’ of models, following methods used in climate and hurricane forecasting. These changes have led to increased transparency about perceived risk, the availability of more information for the decision makers, and a clear delineation between scientific and policy considerations. The ensemble approach to stock assessment also provides a conceptual link between single model analyses and fully developed Management Strategy Evaluation of harvest policy and management procedures. Potential extensions and improvements to the approach, as well as a brief summary of decisions based on this information will also be discussed.