The international regulatory system for the oceans is to a considerable extent dependent upon the effective exercise of flag state responsibilities but general concerns have been raised that some flag states are not fulfilling their international obligations under the international law of the sea.

This article examines the issue of institutional reactions by international organizations against the flag state that has failed to discharge flag state responsibilities, with a view to establishing under what conditions actions may be taken under international law. It analyzes the constitutive instruments and practice of bodies concerning the conservation and management of fisheries resources, three different types of institutions involved in the supervision of the implementation of treaties concerning ship safety, marine environmental protection, maritime labour and maritime security, and the potential role of the United Nations Security Council and the United Nations General Assembly. On the basis of the findings in the above analysis, the article discusses legal requirements for institutional reactions to the flag state that has failed to discharge flag state responsibilities, examining both the internal rules of organizations and general international law, including the Articles of the International Law Commission on Responsibility of International Organizations.

Despite adoption by Regional Fisheries Organisations of numerous measures aimed at deterring, preventing and eliminating illegal, unreported and unregulated fishing, IUU fishing by vessels flagged in both member and non-member states continues. None of the reciprocal boarding and inspection schemes adopted by RFOs provides for a positive right of arrest, detention or prosecution by a non-flag state in the event the flag states fails or refuses to take such action itself. The law of countermeasures may, however, provide legal justification for at-sea measures including boarding, inspection and possibly arrest and prosecution by members of RFOs against non-flag vessels of both member and non-member states. Although by nature an exceptional remedy, where the criteria discussed in this article are fulfilled, countermeasures in the form of at-sea enforcement may be an effective, and legal, tool in the fight against IUU fishing.