Title: A Comparison of different assessment models for northern shrimp, Pandalus borialis, in Iceland waters

Two models, an ADAPT model similar to the one described by Gavaris (1988) and an Age-structured production model, were compared in the stock assessment of northern shrimp (Pandelus borealis) in Icelandic offshore waters in the period 1988-2000. The age-disaggregated data used as input for the models was computed with the simplified version of the Macdonald and Pitcher (1979) method, from commercial landings and surveys based on length frequency data.
Mean weights at age are obtained from a length-weight relationship, which was determined in previous studies, using the mean length at age. The annual rate of sex change was calculated from length maturity ogive and later on the rate of sex change at age was estimated using the mean length at age.
Both assessment models give similar outputs, although the estimated from the Age-structure production model are more optimistic than those from ADAPT. The results of ADAPT are in better agreement with previous assessments. In general, the results show a slight recovery in the standing stock biomass in the last year, after three years of continuous decline