A simple method for the consistent interpretation of catch-at-age data

Abstract

A simple algorithm has been developed for the preparation of Virtual Population Analyses (VPAs) of catch-at-age data, which are internally consistent in the sense that they have so far as possible a constant exploitation pattern. The method is useful in practice because it reduces the need for trial and error in the preparation of VPAs, and reduces the number of a priori parameter estimates required from one per cohort plus one, to three. These are the value of natural mortality, the fishing mortality on some reference age in the final year, and the fraction of that fishing mortality which applies to the oldest age group in the final year. All choices of these parameters lead to solutions which are for practical purposes equally good fits to the data. A selection among them can only be made on the basis of independent information.