Thursday, April 2, 2015

12:00pm 1:00pm

Clark Conference Room


Dr. Elizabeth Brooks

Retrospective forecasting - evaluating performance of stock projections for New England groundfish stocks


Abstract:  The accuracy of stock projections was evaluated for 12 groundfish stocks in the Northwest Atlantic.  Projections were made from assessments using Virtual Population Analysis (VPA) with 1-7 years of data removed from the full time series, and were then compared to results from a VPA assessment that was run on the full time series of data. This approach allows identification of the main sources of bias in the projection.  Diagnostics are explored, and a variety of approaches for dealing with retrospective pattern are tested.  Even after adjustments are made for retrospective patterns, the remaining bias in projected catch and spawning stock biomass (SSB) can be substantial.  We conclude with recommendations for providing catch advice and for tracking SSB, and suggest elements of a harvest control rule that might be more robust to the patterns of bias we identified.