To effectively manage fish stocks, cooperation between nations is obviously required when the stocks migrate between the economic zones of different countries. Such cooperation is likely to be most demanding when stocks also migrate into the high seas, both because the number of nations with a legitimate claim is not clearly defined and because jurisdiction on the high seas is in the hands of the state where the boat is registered. In this chapter, we shall look at the scope for international cooperation in the light of a branch of economics known as game theory. This deals with the interaction between players when the actions of one player have a perceptible influence on the outcome for another. This is highly relevant for fisheries issues, as the outcome for one country depends on what other countries fishing the same stock might do. The name “game theory” may appear frivolous, but the subject is deadly serious; the amount of fish that one country decides to take out of the sea may have great consequences for what other countries can take in the future. Therefore, the amount of fish that one particular country decides to take in any given period has to be decided on the basis of what others are likely to do and how they are likely to react to what that particular country decides to do.

The setting is often illustrated by the famous “prisoner's dilemma”. Two delinquents are suspected of armed robbery, but the police don't have any evidence. The two are put each in his own cell without the possibility of communication. They are made an offer. If one of them confesses and the other does not, he who confesses will be released, and the other one will be in jail for nine months. If both confess, they will be in jail for six months. If neither confesses, they will be in jail for a month because they were caught in a stolen car.

The outcome of the game can be illustrated by the following payoff matrix. The first entry in each cell is the outcome for player one, the second entry is the outcome for player two and the numbers are months in jail, negative since this is a negative payoff (after Gibbons 1992).