INFLUENCE OF ERRORS IN NATURAL MORTALITY ESTIMATES IN COHORT ANALYSIS

The accuracy of the estimation of cohort strength from catch data may be greatly degraded if a poor estimate of the natural mortality rate i s entered into the calculation. A straightforward. exact formulation f or the error in cohort reconstruction due to a misspecified natural mo rtality rate is presented. The special case of constant fishing mortal ity is particularly transparent, allowing the error to be segmented in to easily interpreted terms. A change in the fishing mortality may res ult in a distinct hump in the transient behavior of the bias factor, r ather than a simple monotonic adjustment. This implies a similar patte rn in estimated cohort strength.