Report of the Working Group on Methods of Fish Stock Assessments

The group discussed the potential methods for handling

this question, and came to the conclusion that it is absolutely essential to use disaggregated data for the computations of CPUE indices. Only in this case do possibilities exist for the elimination of the bias. Two approaches were considered promising. Firstly, it is quite feasible to use disaggregated data in a GLM (multiplicative) model where the areas/seasons are factors. This sort of analysis has been carried out, e.g. in

Anon. (1993a), and such an analysis eliminates the areal/seasonal effects from the index in question if the

model is correct (see caveat below). The second approach is to use disaggregated indices as different fleets for tuning purposes. This approach should also allow for correction of the effect of a closure of an area or a season, e.g. by eliminating the corresponding indices from the analysis.