4. Conclusion
Countries sharing a migrating fish stock are engaged in a strategic game; the outcome of what one does depends on what others do. They are, furthermore, sufficiently few for the actions of one to have a significant effect on the others. There is more than one way of setting up such strategic games, however. Some, in particular the Nash-Cournot approach, can lead to extremely destructive outcomes.
Despite the breakdown of a formal agreement, the outcome of the mackerel fishery in the Northeast Atlantic comes nowhere near to accord with the predictions of the Nash-Cournot game. The countries involved seem to know better than being interested in depleting the fish stock on which they all depend through unfettered competition. Instead they seem to be engaged in an informal cooperation which is perhaps not far from what they would do with formal cooperation. It is as if cooperation is being maintained by an implicit threat of mutually assured destruction, a bit like what kept the peace in the cold war, in case any one of them were to deviate radically and approach the NashCournot outcome. This seemingly implicit cooperation is likely to be facilitated by the fact that the countries involved also share other pelagic fish stocks (Norwegian spring-spawning herring, blue whiting) and cooperate in setting quotas for these. Like the mackerel agreement, the one on the Norwegian spring-spawning herring broke down in 1995 for a similar reason (expected changes in migration did not materialize), but was resumed after two years. In the meantime the countries involved had set unilateral quotas in order to establish “catch history”. These unilateral quotas nevertheless seem to have been moderate; the stock was nowhere near being threatened by them.
A more realistic, and certainly more optimistic, way of formulating the strategic situation is to look at how cooperation can be maintained through implicit or explicit threat strategies. Effective threat strategies may, however, be very grim indeed, similar or identical to the NashCournot equilibrium, and they may have to be played for a very long time and possibly indefinitely to be effective.
