International Law of the Sea

Introduction

The international law of the sea governs the rights and duties of states in maritime spaces, the delimitation of maritime boundaries, the exploitation of marine resources, and the protection of the marine environment. The United Nations Convention on the Law of the Sea (UNCLOS), adopted in 1982 and entering into force in 1994, is the comprehensive treaty framework that replaced the earlier Geneva Conventions on the Law of the Sea (1958). UNCLOS has been described as a “constitution for the oceans,” establishing a legal order for the world’s seas and oceans. With 169 parties (including the European Union), it is one of the most widely ratified treaties in international law. The Convention codifies customary international law while also developing new concepts, particularly the exclusive economic zone and the common heritage of mankind.

The Territorial Sea and Innocent Passage

The territorial sea is the maritime zone adjacent to a coastal state’s land territory and internal waters over which the state exercises full sovereignty. UNCLOS Article 3 permits a maximum breadth of twelve nautical miles, measured from baselines established in accordance with the Convention. The coastal state’s sovereignty extends to the airspace above the territorial sea and the seabed and subsoil beneath it. Ships of all states enjoy the right of innocent passage through the territorial sea (Article 17). Passage is innocent so long as it is not prejudicial to the peace, good order, or security of the coastal state. Activities considered non-innocent include weapons exercises, spying, fishing, pollution, and research. Submarines must navigate on the surface and show their flag. Coastal states may adopt laws and regulations relating to innocent passage but may not hamper it. The regime of innocent passage reflects the balance between coastal state sovereignty and the freedom of navigation essential to global commerce.

Archipelagic Waters and Straits

UNCLOS introduced the concept of archipelagic states — states constituted wholly by one or more archipelagos (such as Indonesia, the Philippines, Fiji, and the Maldives). Archipelagic states may draw straight baselines connecting the outermost points of the outermost islands, enclosing archipelagic waters. The sovereignty of the archipelagic state extends to these waters, but foreign vessels enjoy the right of innocent passage through archipelagic waters and the right of archipelagic sea lanes passage through designated sea lanes and air routes (Article 53). Straits used for international navigation between one area of the high seas or an EEZ and another are subject to the regime of transit passage (Article 37–44), which is less restrictive than innocent passage: submarines may transit submerged, and aircraft may overfly.

The Contiguous Zone

The contiguous zone extends from the outer limit of the territorial sea to a maximum of twenty-four nautical miles from the baselines (Article 33). In this zone, the coastal state may exercise control necessary to prevent and punish infringement of its customs, fiscal, immigration, and sanitary laws within its territory or territorial sea. The contiguous zone is not a zone of full sovereignty but a limited enforcement jurisdiction.

The Exclusive Economic Zone

The exclusive economic zone (EEZ) is one of UNCLOS’s most important innovations. The EEZ extends up to 200 nautical miles from the baselines (Article 57). In the EEZ, the coastal state has sovereign rights over natural resources — fish, oil, gas, minerals — in the waters, seabed, and subsoil (Article 56). It has jurisdiction over marine scientific research, environmental protection, and the establishment of artificial islands and structures. Other states retain the high seas freedoms of navigation, overflight, and the laying of submarine cables and pipelines (Article 58). The EEZ represents a functional approach to ocean governance: the coastal state has resource rights but not full sovereignty.

The EEZ has dramatically expanded coastal state jurisdiction over marine resources. Approximately 90 percent of global fish stocks and 87 percent of known offshore oil and gas reserves fall within EEZs. The delimitation of overlapping EEZs between states with opposite or adjacent coasts (Article 74) has generated extensive international jurisprudence, including the North Sea Continental Shelf cases (1969) and the Nicaragua v. Colombia case (2012).

The Continental Shelf

The continental shelf is the natural prolongation of a coastal state’s land territory under the sea. UNCLOS Article 76 defines the continental shelf as extending to the outer edge of the continental margin or to 200 nautical miles, whichever is greater. States may establish the outer limits of the continental shelf beyond 200 nautical miles through submissions to the Commission on the Limits of the Continental Shelf (CLCS). The coastal state exercises sovereign rights over the continental shelf for the purpose of exploring and exploiting natural resources. The CLCS has made recommendations on submissions from over sixty states, extending coastal state jurisdiction over significant areas of the deep seabed.

The High Seas

The high seas are all parts of the sea not included in the EEZ, the territorial sea, or the internal waters of any state. The high seas are governed by the principle of freedom of the high seas (Article 87), which includes freedom of navigation, fishing, scientific research, and the laying of submarine cables and pipelines. These freedoms must be exercised with due regard for the interests of other states. The high seas are reserved for peaceful purposes. Ships on the high seas are subject to the exclusive jurisdiction of their flag state (Article 92), though exceptions exist for piracy (universal jurisdiction), the slave trade, unauthorized broadcasting, and the right of visit on reasonable suspicion of certain activities.

The Area and the Common Heritage of Mankind

The Area — the seabed and ocean floor beyond national jurisdiction — is declared the common heritage of mankind (Article 136). No state may claim sovereignty over any part of the Area, and its resources are to be exploited for the benefit of mankind as a whole. The International Seabed Authority (ISA), established by UNCLOS, administers the Area’s mineral resources through a system of parallel access: the ISA’s Enterprise may exploit resources directly, and private and state-sponsored contractors may exploit resources under ISA supervision. The deep seabed mining regime has been criticized for being too costly to implement, but the ISA has adopted the Mining Code regulating exploration and exploitation, and commercial deep seabed mining is expected to begin in the coming decade.

Maritime Boundary Delimitation

The delimitation of maritime boundaries between states with opposite or adjacent coasts is governed by Articles 15 (territorial sea), 74 (EEZ), and 83 (continental shelf), which require delimitation by agreement based on international law in order to achieve an equitable solution. The International Court of Justice and the International Tribunal for the Law of the Sea (ITLOS) have developed a three-stage methodology: first, drawing a provisional equidistance line; second, considering relevant circumstances that may require adjustment; third, checking that the result is not disproportionate. ITLOS, established by UNCLOS Annex VI, has jurisdiction over disputes concerning the interpretation or application of the Convention.

The South China Sea Dispute

The South China Sea is the site of one of the most significant contemporary law of the sea disputes. China claims sovereignty over most of the South China Sea based on its “nine-dash line” map, which encompasses over 80 percent of the sea. The Philippines initiated arbitration under UNCLOS in 2013, challenging China’s claims. In the South China Sea Arbitration (Philippines v. China, 2016), the Permanent Court of Arbitration ruled that China’s historic rights claims within the nine-dash line were incompatible with UNCLOS, that certain Chinese-occupied features were rocks (not islands) incapable of generating EEZs, and that China had violated the Philippines’ sovereign rights by interfering with fishing and building artificial islands. China rejected the award. The dispute illustrates the limits of international adjudication when powerful states refuse to comply with unfavorable decisions.