We have constructed a statistical model to forecast, with uncertainty, the stock of Norwegian farmed Atlantic salmon (Salmo salar). The model provided good predictions of future biomass of Norwegian farmed salmon and can also be used to perform what-if analysis exploring the impact of varying scenarios for stocking and slaughtering. The model is based on the number of fish in each weight class (0-1 kg, 1-2 kg, ..., 10+ kg) and their average weight. The model, which is related to standard

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... ructured models, computes the number of fish growing into the next weight class the next month and the number of fish remaining in the same weight class. In addition, the number of new fish stocked, fish lost, slaughtered and wasted, as well as the sea temperature related to the growth, were modelled. All the model parameters were estimated based on monthly data from 2002-2007, and the model was validated statistically. Any animal production involving cycles may benefit from this forecasting tool.