About a fourth of all fish taken from the world's oceans are caught illegally or beyond the reach of regulators, significantly threatening the global ocean ecosystem and undermining the economies of fishing communities. Developing countries' territorial waters and the high seas are especially vulnerable to illegal, unregulated and unreported (IUU) fishing. The practice flourishes because flag States—the countries under whose flag a vessel is fishing—do not fulfill their legal obligation to control the fishing operations of their vessels.