A model simulating the effect of sampling strategy on stock assessment of gadoids in sub-areas I and II

In the northeast Atlantic, management advice for fisheries is usually based on Virtual Population Analysis, yield per recruit, and predictions of catch and biomass. For these calculations, age distributions and weigth-at-age from commercial catches are essential. The process of sampling, age reading, and preparation of the data is time consuming and expensive. It is therefore important to find the optimum strategy for a sampling program. North-East Arctic cod, haddock and saithe are the three major demersal stocks in Norwegian waters north of 62°N. Sampling of Norwegian catches in coastal areas are based on 96 statistical units (gear, area, time) for each species. A model was made to simulate the stocks and exploitation in the period 1979-1983. The basis for the model was the observation that averaging the length frequency distribution of catches from a statistical unit over some years gave a smooth curve which could be approximated by a LOG-normal distribution. The results indicate that sampling may be omitted in most of the units without severe consequences for management advice. More length than age sampling is required