Territorial Sea

Territorial sea

1. Concept of a territorial sea

The concept of a territorial sea has a long history. Those who opposed the idea of a closed sea (mare clausum) in the sixteenth and seventeenth centuries did so relying on, inter alia, the argument that states should not be allowed to claim sovereign rights over a vast stretch of waters if they cannot exercise meaningful control over such waters.

Advocates of the freedom of the seas did acknowledge that a coastal state could claim sovereign rights over a column of sea waters off its coast to a distance which was within the reach of cannon at the time – the ‘cannon-shot’ rule. As the advances in science and technology made it possible to make cannons with a longer range, states began to claim a three-mile limit for territorial waters, which was a much clearer and more straightforward rule. This rule was adhered to more or less by most major maritime states until the beginning of the twentieth century.

In the face of conflicting and varying claims to the breadth of the territorial sea, an attempt was made at the Hague Codification Conference in 1930 to agree on its limits, but to no avail. Although most states were in favour of a three-mile rule, others, including the Scandinavian states, claimed a six-mile territorial sea. The march to claim more areas of the sea as territorial sea accelerated when Latin American states began to claim an extensive area of sea water as their territorial sea. When the First UN Conference on the Law of the Sea (UNCLOS I) was convened in Geneva in 1958, a Convention on the Territorial Sea and the Contiguous Zone was concluded, firmly establishing the concept of a territorial sea in the law of the sea, with rights and duties for coastal and foreign states in such waters. However, neither UNCLOS I nor UNCLOS II, held in 1960, was able to agree on the breadth of the territorial sea.

In the negotiations at UNCLOS III, some major maritime powers still held out for a three-mile rule. However, in the face of states claiming 50 or even 200 miles as their territorial sea, the Conference decided in favour of a 12-mile territorial sea, which was the breadth claimed by a large number of states at the time. Article 2 of the 1982 Convention on the Law of the Sea defines the legal status of the territorial sea, and Article 3 its breadth, accordingly.

At the start of the Conference, there were 25 states claiming a three-mile territorial sea, 66 states claiming 12 miles, 15 claiming between four and 10 miles and eight states claiming 200 nautical miles.

Smaller states and those not possessing large, ocean-going navies or merchant fleets favoured a wide territorial sea in order to protect their coastal waters from infringements by those states that did, whereas major naval and maritime powers sought to limit the territorial sea to three miles or a maximum of six miles, in order to protect their fleets’ freedom of movement.

Not surprisingly, the Conference accepted the 12-mile territorial sea already claimed by a large number of states. In addition, the Conference also empowered coastal states to implement certain rights in an additional area beyond the territorial sea, known as the ‘contiguous zone’, extending for 24 nautical miles from their baselines, for the purpose of preventing certain violations and enforcing police powers. This new zone was created to allow the coastal, naval or maritime authorities of coastal states to pursue and, if necessary, arrest and detain suspected drug smugglers, illegal immigrants and customs or tax evaders violating the laws of the coastal state within its territory or the territorial sea.

In another innovation, UNCLOS III also established a legal regime for archipelagic states (states such as the Philippines and Indonesia that are made up of a group of closely spaced islands). For such states, the territorial sea is a 12-mile zone extending from archipelagic baselines drawn joining the outermost points of the outermost islands of the group that are in close proximity to each other. The waters between the islands are declared archipelagic waters, where ships of all states enjoy the right of innocent passage subject to archipelagic sea lanes passage.

2. Difference between the territorial sea and internal waters

Territorial waters form part of the national territory of a coastal state and are subject to its legislation, but differ from its internal waters in that they are subject to an international right of innocent passage for all domestic and foreign vessels, at least in times of peace and subject to certain conditions and exceptions.

The internal waters of a state comprise all the water areas, salt and fresh, which lie within the baseline of its territorial waters. This includes all rivers, freshwater lakes, waters within ports and certain other land-locked waters. The state has the same sovereign authority over internal waters as over its land territory.

3. Breadth of the territorial sea

Article 3 of the 1982 Convention determines the breadth of the territorial sea in the following words:

Every State has the right to establish the breadth of its territorial sea up to a limit not exceeding 12 nautical miles, measured from baselines determined in accordance with this Convention.

4. Rights of coastal states in the territorial sea

The rights of coastal states in their territorial sea are not limited to the sea column of this maritime zone. They extend to the airspace above it and to its seabed and subsoil. Full sovereignty of the coastal state applies in the territorial sea – with one limitation: the right of innocent passage. A coastal state is required to ensure a right of innocent passage through its territorial waters for the vessels of foreign states.

Article 2 of the 1982 Convention defines the legal status of the territorial sea and the rights of coastal states:

Article 2

Legal status of the territorial sea, of the air space over the territorial sea and of its bed and subsoil 

  1. The sovereignty of a coastal State extends, beyond its land territory and internal waters and, in the case of an archipelagic state, its archipelagic waters, to an adjacent belt of sea, described as the territorial sea.
  2. This sovereignty extends to the air space over the territorial sea as well as to its bed and subsoil.
  3. The sovereignty over the territorial sea is exercised subject to this Convention and to other rules of international law.

5. Criminal and civil jurisdiction

Since coastal states have both civil and criminal jurisdiction in their territorial waters, the exercise of such rights on board a foreign ship is also regulated by the 1982 Convention. Article 27(1) and (2) deals with matters relating to criminal jurisdiction on board a foreign ship:

Article 27

Criminal jurisdiction on board a foreign ship

1. The criminal jurisdiction of the coastal State should not be exercised on board a foreign ship passing through the territorial sea to arrest any person or to conduct any investigation in connection with any crime committed on board the ship during its passage, save only in the following cases:

a. if the consequences of the crime extend to the coastal State;

b. if the crime is of a kind to disturb the peace of the country or the good order of the territorial sea; if the assistance of the local authorities has been requested by the master of the ship or by a diplomatic agent or consular officer of the flag

State; or

c. if such measures are necessary for the suppression of illicit traffic in narcotic drugs or psychotropic substances.

2. The above provisions do not affect the right of the coastal State to take any steps authorised by its laws for the purpose of an arrest or investigation on board a foreign ship passing through the territorial sea after leaving internal waters.

Article 28 outlines the rights of a coastal state to exercise civil jurisdiction in its territorial sea. It forbids the coastal state from stopping or diverting a foreign ship passing through the territorial sea for the purpose of exercising civil jurisdiction in relation to a person on board the ship. The coastal state is forbidden from levying execution against or arresting the ship for the purpose of any civil proceedings, save only in respect of obligations or liabilities assumed or incurred by the ship itself in the course or for the purpose of its voyage through the waters of the coastal state. This is, of course, without prejudice to the right of the coastal state, in accordance with its laws, to levy execution against or to arrest, for the purpose of any civil proceedings, a foreign ship lying in the territorial sea, or passing through the territorial sea after leaving internal waters.

Please note that the provisions in the 1982 Convention relating to the safety and security in the seas and high seas is supplemented and complimented by a number of other international treaties and the Rome Convention on the Suppression of Unlawful Acts Against the Safety of Maritime Navigation of 1988 (hereafter the SUA Convention). The SUA Convention entered into force on 1 March 1992. A Protocol to the Convention was adopted on 14 October 2005 and it entered into force on 28 July 2010.

The SUA Convention was the result of certain concerns about unlawful acts that threaten the safety of ships and the security of their passengers and crews which grew during the 1980s, with reports of crews being kidnapped, ships being hi-jacked, deliberately run aground or blown up by explosives.

Important amendments to the 1988 SUA Convention and its related Protocol were adopted by the Diplomatic Conference on the Revision of the SUA Treaties held from 10 to 14 October 2005. The amendments were adopted in the form of Protocols to the SUA treaties (the 2005 Protocols).

6. Delimitation of the territorial sea

Article 15 of the 1982 Convention contains provisions designed to delimit the territorial sea between states with opposite and adjacent coasts. The method adopted for delimiting the territorial sea is the median line:

Article 15

Delimitation of the territorial sea between States with opposite or adjacent coasts 

Where the coasts of two States are opposite or adjacent to each other, neither of the two States is entitled, failing agreement between them to the contrary, to extend its territorial sea beyond the median line every point of which is equidistant from the nearest points on the baselines from which the breadth of the territorial seas of each of the two States is measured. The above provision does not apply, however, where it is necessary by reason of historic title or other special circumstances to delimit the territorial seas of the two States in a way which is at variance therewith.

7. Case study: Nicaragua v Honduras

A significant case to consider is Territorial and maritime dispute between Nicaragua and Honduras in the Caribbean Sea (Nicaragua v Honduras), decided on 8 October 2007 by the International Court of Justice.

This case will enable anyone interested in this field to better understand the method that a court can use to determine the sovereignty of a state over disputed maritime territories and to delimit the maritime boundary between two states. The case also highlights the importance of the exercise of criminal and civil jurisdiction by a coastal state over its maritime zones and territories to establish its sovereignty.

The case was a territorial and maritime dispute between the Republic of Nicaragua and the Republic of Honduras in the Caribbean Sea. The Court held that Honduras had sovereignty over Bobel Cay, Savanna Cay, Port Royal Cay and South Cay, and drew a single maritime boundary between Nicaragua and Honduras. It also decided the starting point of the single maritime boundary that divides the territorial sea, continental shelf and exclusive economic zones of Nicaragua and Honduras.

Nicaragua had asked the Court to determine the course of the single maritime boundary between the areas of territorial sea, continental shelf and exclusive economic zone appertaining respectively to the two countries in the Caribbean Sea. Nicaragua argued that this maritime boundary had never been delimited. However, Honduras argued that there already existed in the Caribbean Sea a traditionally recognised boundary between the maritime spaces of Honduras and Nicaragua along the fifteenth parallel, having its origin in the principle of uti possidetis juris (pursuant to which boundaries inherited upon decolonisation must be respected). Honduras asked the Court to confirm this maritime boundary.

In its judgment the Court noted that Bobel Cay, Savanna Cay, Port Royal Cay and South Cay remained above water at high tide and that they thus fell within the definition of islands under Article 121 of the 1982 Convention on the Law of the Sea. In respect of sovereignty over the four islands, the Court pointed out that the principle of uti possidetis juris definitely applied to the territorial delimitation between Nicaragua and Honduras – both former Spanish colonial provinces – and may also apply to offshore possessions and maritime spaces.

The Court observed that several effectivités invoked by Honduras ‘constitute a modest but real display of authority over the four islands’. Thus, Honduras had shown that within the islands it had applied and enforced its criminal law and civil law, had regulated immigration, fisheries activities and building activity and had exercised its authority in respect of public works. As for the delimitation of the maritime areas between the two states, the Court found that no boundary existed along the fifteenth parallel on the basis of either uti possidetis juris or a tacit agreement between the parties. The Court decided to draw the boundary.

Accordingly, the Court went on to observe that, given the geographical configuration of Cape Gracias a Dios (a sharply convex territorial projection abutting a concave coastline on either side, and the point where the two states’ coastal fronts meet) and the unstable nature of the mouth of the River Coco (the endpoint of the land boundary), it was impossible for the Court to apply the equidistance method, even for the delimitation of the territorial sea. Therefore, the Court decided to use a bisector – the line formed by bisecting the angle created by the linear approximations of the coastlines. Having accorded a 12-mile breadth of territorial sea to the four islands, the Court took this into account and adjusted the course of its line by drawing a median line to resolve the issue of overlap between the territorial seas of these islands and that of the island of Edinburgh Cay (Nicaragua).

8. Summary and conclusions

As can be seen above, the 1982 Convention on the Law of the Sea outlines a comprehensive regime for the territorial sea. It not only prescribes the breadth and legal status of the territorial sea, but also outlines the nature of the rights of coastal states with regard to civil and criminal matters. Ships passing through territorial waters must conform to any rules prescribed by the relevant national law, which can, if necessary, be applied to crimes committed on board. Otherwise, everything happening on board is governed by the law of the flag state.

The law of the coastal state should not interfere with foreign ships unless some national interest is involved. However, the status of certain activities in the territorial sea has not been further defined and so inherent ambiguities have caused problems. State practice has been left to fill these gaps. For example, although loss of innocent passage is not an immediate consequence of pollution or the threat of it, many states have interpreted the provisions of the 1982 Convention so that the passage of vessels which pose an environmental threat should be regarded as non-innocent and therefore requires the prior consent of the coastal state. Similarly, many states have also viewed the passage of military vessels as requiring prior approval, and so not presumed innocent passage. The Convention does not make any reference to this disputed right, but does require that submarines navigate on the surface and show their flag.

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