A central challenge facing the community of nations is how to conserve and allocate fish stocks that exist beyond national boundaries. Some migratory species are becoming dangerously scarce. The Food and Agriculture Organization (FAO) estimates that 30% of tuna stocks are overexploited or depleted and 53% are fully exploited. Bluefin tuna are particularly at risk: the eastern Atlantic’s stocks of fish at the age of reproduction declined by 80% between 1970 and 1992, and have fluctuated between 21 and 29% of the 1970 level ever since. As a result, although these fish were once thought to be endlessly renewable, we now know that there are not enough fish for all. Overfishing is creating conditions of scarcity; when one state harvests fish stocks, it reduces the catch of others.