We model the evolution of a trans-boundary marine fishery, which is based on the harvesting of a single “highly-migratory” stock and is beginning to be impacted by regional oceanic-climate changes. The fish-stock’s range will be composed of a number of jurisdictional zones: namely, its intersection with the EEZ of each coastal country for which that intersection is non-trivial. There may also be a zone within international waters of the high seas. We also assume that management of the fishery is vested in a Regional Fishery Management Organization, whose members are countries that are “direct stakeholders” in the fishery—being either one of the above countries with jurisdictional authority in a zone or a country that has registered fishing vessels that are licensed to harvest in the fishery, or both. Our primary intended audience for the article includes the RFMO member-countries’ representatives, who participate directly in negotiations over RFMO policies, and also the RFMO’s scientific staff. Oceanic-climate changes are poorly predictable, but there will be periodic updates to enhance the available estimates. Consequently we believe that the RFMO’s efforts to cope with these changes would be helped by developing, as a tool, a certain type of a priori dynamic model, which could explore alternative long-time evolution paths for the bioeconomics of the fishery. The model should examine the immediate decisions made by the RFMO, and various possible long-term outcomes as these short-term decisions accumulate. Furthermore the model should be updated periodically, especially after new updated oceanic-climate predictions become available. In the article we work out a relatively simple example model, of an idealized fishery which is attempting to cope with a deteriorating oceanic-climate environment. But we also explain why (and in what ways) each particular real-world fishery’s staff needs to modify this generic example, to more closely match its own unique characteristics.