Seminar
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.