The area referred to as the "high seas" consists of the open ocean not subject to the jurisdiction of any State, i.e., not part of the internal waters, territorial sea or exclusive economic zone (EEZ) of any State. It comprises over half the world's oceans and is of paramount importance to humanity because of the ecosystem services it provides. The high seas face serious threats from over-exploitation and contamination. The seabed underlying the high seas is by and large also beyond national jurisdiction.
The nature of the high seas regime was the subject of spirited debate in the 17th century between Hugo Grotius and John Selden. Grotius argued that States should be free to utilize and exploit the high seas without limitation, whereas Selden argued that access to them could be closed by States. Grotius prevailed and all waters beyond national boundaries were considered to be international waters free to all States, but belonging to none of them (the mare liberum principle), though encroachments on that principle have since occurred.
Roughly 100 international agreements now govern aspects of the high seas, including an agreement creating a 600,000 square mile no-fishing zone near Antarctica; but no overarching agreement exists to protect biodiversity or conserve vulnerable ecosystems in the oceans.
One important agreement was the 1958 Convention on the High Seas, which provided generally for freedom of the high seas,[i]
protected non-coastal States' access to the high seas, prohibited using the high seas to transport slaves, set rules for flag ships on the high seas, and established a regime for dealing with piracy.
The geographic extent of the high seas has changed over time as the limits of national jurisdiction over maritime areas have expanded. Those limits currently are defined by the 1982 United Nations Convention on the Law of the Sea (UNCLOS), which sets limits of 12 nautical miles for territorial seas and 200 nautical miles (370 kilometers) for exclusive economic zones (EEZs), beyond which are the high seas, and the rules for which features are entitled to a territorial sea and EEZ, as well as the limits of the continental shelf. Because the continental shelf subject to national jurisdiction can extend beyond the EEZ, the area of the seabed beyond the continental shelf and thus beyond national jurisdiction is smaller than the area of the high seas. 168 States are Party to UNCLOS and are thus bound by its provisions; and most of its provisions, including the ones establishing the limits on the territorial sea, EEZ and continental shelf and which features get them, are customary international law binding even on non-Parties to UNCLOS.
UNCLOS, which contains detailed environmental and other rules governing territorial seas and EEZs, does not provide significant protection to the high seas. UNCLOS part XI, however, provides a regime for the seabed, ocean floor and subsoil thereof beyond national jurisdiction, which it refers to as the Area, including an International Seabed Authority.[ii]
According to UNCLOS article 136, "The Area and its resources are the common heritage of mankind." In 1994 an agreement to implement UNCLOS provisions relating to the Area was finalized to facilitate accession to UNCLOS by industrialized countries, including the United States (which has not acceded to UNCLOS as of July 2018).
In 2017, nine nations and the European Union agreed to place the central Arctic Ocean – 2.8 million square kilometers - off-limits to commercial fishers for at least 16 years.[iii]
In addition, in September 2018, international negotiations will begin under United Nations auspices to draft a legally binding treaty on the conservation and sustainable use of marine biological diversity of the areas beyond national jurisdiction in the high seas.
[i] Article 2 of the 1958 Convention on the High Seas provides:
The high seas being open to all nations, no State may validly purport to subject any part of them to its sovereignty. Freedom of the high seas is exercised under the conditions laid down by these articles and by the other rules of international law. It comprises, inter alia, both for coastal and non-coastal States:
- Freedom of navigation;
- Freedom of fishing;
- Freedom to lay submarine cables and pipelines;
- Freedom to fly over the high seas.
These freedoms, and others which are recognized by the general principles of international law, shall be exercised by all States with reasonable regard to the interests of other States in their exercise of the freedom of the high seas.
[ii] UNCLOS' preamble states:
Desiring by this Convention to develop the principles embodied in resolution 2749 (XXV) of 17 December 1970 in which the General Assembly of the United Nations solemnly declared inter aliathat the area of the seabed and ocean floor and the subsoil thereof, beyond the limits of national jurisdiction, as well as its resources, are the common heritage of mankind, the exploration and exploitation of which shall be carried out for the benefit of mankind as a whole, irrespective of the geographical location of States,
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