Scenario modelling to evaluate management strategies was originally developed for whaling, but is now increasingly applied in fisheries. The basic idea is to establish a minimal but realistic model for computer simulation of the system, with removals governed by a management strategy, predation and additional natural mortality. The system is projected forward under competing strategies for a number of years, with replications to capture the statistical uncertainties surrounding the system. Strategies are compared in terms of their simulated long-term performance.

The purpose of the present study is to evaluate the effect on the cod, capelin and herring fisheries of managing minke whaling and harp sealing in the Barents Sea in this way. The study is funded by the Norwegian Ministry of Fisheries. In a recent White Paper (Stortingsmelding nr 27 2003–4) on the management of marine mammals in Norwegian waters, the Ministry plans ‘to establish a scientific basis for changing to ecosystem-based management where marine mammal stocks are managed in conjunction with the other living marine resources’.

To manage a marine ecosystem is to play a game with Nature, and perhaps also with other players such as fishermen and industries which are causing the system to become increasingly polluted. The game we consider is played by the Agency (government body) and Nature.

The concept of strategy is central to game theory. A management strategy is a feedback rule that specifies the action to be taken, given the history of the process as observed by the player.