The relationship between the legal structures of the international trading system and of multilateral environmental agreements (MEAs) such as the Montreal Protocol is central to the current debate on trade and environment. Since the original negotiations, however, the trade restrictions have grown to occupy a more important role in the Montreal Protocol, and the issue of compatibility with the General Agreement on Tariffs and Trade (GATT) has been considered more actively. In the late 1980s fishing fleets, mainly from Mexico, caught and killed about 30,000 dolphins a year in the process of harvesting tuna in the eastern tropical Pacific Ocean, where dolphins and tuna swim together. Since parties to the Montreal Protocol are required to limit their consumption and production of ozone-depleting substances (ODS), while non-parties are bound by no such requirement, the same conditions do not exist for parties and non-parties.