Implications of aging misclassification in catch-at-age analyses

Age estimation plays an essential role in age structured assessments for many stocks in the Northwest Atlantic. However, uncertainty in age determination can potentially introduce bias leading to a different perception of the stock dynamics.   Using an age error matrix developed from an ancillary age production experiment, we explored some of the consequences of aging misclassification on the status, abundance, and population dynamics of the Georges Bank and Southern New England-Mid Atlantic yellowtail flounder stocks.  An age error matrix was developed based on an aging experiment in which subsamples of archived scale images used in previous yellowtail flounder assessments were re-aged by a current reader. The probabilities of assigning particular ages to a fish based on the age determinations by the previous reader were then applied to the aging data used in the most recent yellowtail flounder stock assessments to produce alternative catch-at-age and survey abundance indices. Simulations were then conducted to evaluate the potential impact of aging bias on both the assessment results and the estimation of biological reference points.