Marine reserves can be established for conservation or fisheries management purposes. As is appropriate, the mathematical models that are currently used to understand the economic costs and benefits of marine reserves make a number of simplifying assumptions. In my lecture, I will talk about the consequences of one common assumption: that the stock is either under the exclusive control of a single owner, or that it can be exploited by anyone. In reality, the distributions of actual stocks often straddle the exclusive economic zones of a small number of states as well as the high seas. In this talk, I will demonstrate how to construct spatially-explicit bioeconomic models for such "transboundary" or "straddling" stocks. Using a two-state model, I will show the ecological and economic conditions under which closed areas emerge as Cournot–Nash equilibria of a dynamic, spatially-explicit, noncooperative “fish war” and show how the economic and conservation costs of noncooperation between states depend on biological and economic conditions.