A distinctive and fascinating area of international law is the debate of those legal rules that govern the law of the sea. As the sea has been a long-standing and traditional source of both transit of ships and exploitation of resources, it has inevitably attracted the attention of the international law, being the first area which required constant legal development. The law of the sea provides for the regulation, management and governance of the ocean spaces that cover over two-thirds of the Earth’s surface. Hugo Grotius, a paramount influence in international law, developed a new doctrine that the sea was international territory and that all nations were free to use seafaring trade. This doctrine of the ‘freedom of the seas’, albeit universally accepted, has been modified many times to this day. There are different parts of the sea which go beyond the limits of the territorial jurisdiction of a country, ‘the high seas’, but which have been claimed to be capable of some sort of territorial control from sovereign states. These particular complications have led to the formulation of several legal regimes governing the sea, with the United Nations Convention of the Law of the Sea 1982 (UNCLOS 1982) being the most important treaty.
Considered the most comprehensive attempt to create a unified regime for governance of the rights of nations with respect to the world’s oceans, the UNCLOS 1982 addresses a variety of topics including navigational rights, economic rights, pollution of the seas, conservation of marine life, scientific exploration, piracy and many other topics. However, what are the various territorial limits imposed over different areas of the sea? Do these regulations contain rights of customary international law? As one of the longest treaties in history, UNCLOS 1982 is comprised of 320 articles and nine annexes, demonstrating the codification of customary international law and its progressive development.
A powerful attribute of UNCLOS is that it settled the question of the degree of national sovereignty over the oceans and seabed. Parts II, V, VI, and VII establish the various regions of the oceans, who has sovereignty over each and to what degree.
1. Territorial Sea
Considered the most comprehensive attempt to create a unified regime for governance of the rights of nations with respect to the world’s oceans, the UNCLOS 1982 addresses a variety of topics…
The width of the territorial sea is classified from the low-water mark around the coasts of the state. In most of the cases it will not be too hard to establish the low-water line which acts as a baseline for calculating the width of the territorial sea. Accordingly, this will be the low-waterline of the low-tide elevation which may be used as a baseline for calculating the breadth of the territorial sea. Occasionally, the problem lies in the geography of the state’s coasts where there are several islands or where there are bays butting into the coastline. Unique rules have made an advancement to tackle this issue which is of importance to coastal states, especially where foreign vessels fish close to the limits of the sea. This was demonstrated in the case of Anglo-Norwegian Fisheries (United Kingdom v Norway) 1951 ICJ Reports 116 where the dispute over how large an area of water surrounding Norway was Norwegian water (that Norway had exclusive fishing rights over) and how much was high seas (that the UK could fish). The UK argued that Norway unreasonably obtained more of the high seas than it should by using the method of straight baselines linking the outermost part of the land. The Court declared that since the Norwegians had been using this method for many years and had not been disputed in the past, the UK had no argument to support its claim. Furthermore, the Court emphasised that:
[N]orway is justified in using the method of straight lines because of her special geographical conditions and her consistent past practice which is acquiesced in by the international community as a whole. 
Additionally, the Court highlighted that it was permissible to consider and not to overlook:
The scope of which extends beyond purely geographical factors: that of certain economic interests peculiar to a region, the reality and importance of which are clearly evidenced by a long usage. 
As a result, these principles were codified in the Geneva Convention on Continental Shelf 1958 and the UNCLOS 1982. However, some states have unnecessarily taken advantage of this amendment as can been seen in the case of Maritime Delimitation and Territorial Questions between Qatar and Bahrain (Qatar v Bahrain) 2001 ICJ Reports 40. Proceedings began in 1994 and the Court’s task was to settle any matter of territorial right between Qatar and Bahrain and to distinguish a single maritime boundary between their respective maritime areas of seabed, subsoil and superjacent waters. It was declared that Bahrain was not possible to consider having a cluster of islands or an island system which would allow the method of straight baseline determination to succeed. The Court made it clear that:
[T]he method of straight baselines, which is an exception to the normal rules for the determination of baselines, may only be applied if a number of conditions are met. This method must be applied respectively. Such conditions are primarily that either the coastline is deeply indented and cut into, or that there is a fringe of islands along the coast in its immediate viscinity.
An additional problem of territorial sea is the matter of bays, due to the fact that it can include several states such as the Gulf of Aqaba in the Red Sea bordered by Egypt, Israel, Jordan and Saudi Arabia. As there are not any historic regimes covering these areas, the International Court of Justice (ICJ) had to examine the merits of each case on an individual basis. Moreover, the matter of archipelagos has been a contentious area since the waters may be declared to be within the sovereignty of the archipelagic state but are subject to rights of innocent passage. Internal waters (for example, harbours, lakes, rivers) are not part of the territorial sea but are classed as waters appertaining to the land territory of the coastal state.  It is worthy of note that unlike the territorial sea, there is no right of innocent passage.
2. International straits
Article 16(4) of the 1958 Convention on the Territorial Sea and the Contiguous Zone states that:
[T]here shall be no suspension of the innocent passage of foreign ships through straits which are used for international navigation between one part of the high seas and another part of the high seas or the territorial sea of a foreign state.
This provision relates to the case of Corfu Channel (United Kingdom v Albania) 1949 ICJ Reports 4 where British warships passing though the straits were fired upon by Albanian guns. The Albanian government argued that since the passage of the British warships was not an innocent passage, the sovereignty of Albania had been violated. The Court emphasised that:
[S]tates in time of peace have a right to send their warships through straits used for international navigation between two parts of the high seas without the previous authorisation of a coastal state, provided that the passage is innocent. 
The Albanian government argued that since the passage of the British warships was not an innocent passage, the sovereignty of Albania had been violated.
3. Continental Shelf
Continental shelves are often abundant in oil and gas resources and are often host to extensive fishing grounds. According to Shaw, the continental shelf is a geological expression referring to the ledges that project the continental landmass into the seas and which are covered with only a relatively shallow layer of water (around 150-200 metres) and which eventually fall away into the ocean depths (thousands of metres deep). These ledges or shelves are estimated to take seven to eight per cent of the total area of ocean. 
The Truman Proclamation on the Continental Shelf 10 FR 12303 (1945) was the first case to bring forward the argument that the status of the continental shelf should be altered in that it should no longer be part of the high seas but should be available for exploitation by all states. Thus in the Truman case, the Government of the United States regarded the natural resources of the subsoil and seabed of the continental shelf beneath the high seas but contiguous to the coasts of the United States, subject to jurisdiction and control.  The proclamation by the US caused various problems was attempted to be resolved with the introduction of the Convention on the Continental Shelf 1958. The Court also tried to resolve this issue in the North Sea Continental Shelf cases 1969 ICR Reports 3 but without a definite answer:
… the rights of the coastal state in respect of the area of continental shelf that constitutes a natural prolongation of its land territory into and under the sea exist ipso facto and ab initio, by virtue of its sovereignty over the land and as an extension of it in an exercise of sovereign rights for the purpose of exploring the seabed and exploiting its natural resources. In short there is here an inherent right. 
4. Exclusive Economic Zone (EEZ)
With the development of the EEZ, the issue of continental shelves has been furthered confused, since under Article 56 of the UNCLOS 1982 the coastal state has sovereign rights over all the natural resources of its EEZ, including the seabed resources. Article 57 states that the EEZ is a region that stretches a distance of no more than 200 nautical miles from a nation’s baselines and, according to Article 58, the rules regarding the high seas (found in Articles 88 to 115) also apply to the EEZ. Articles 58 and 61-64 indicate that within its EEZ, a nation may explore and exploit the natural resources (both living and inanimate) found both in the water and on the seabed, utilise the natural resources of the area for the production of energy (including wind and wave/current), establish artificial islands, conduct marine scientific research, pass laws for the preservation and protection of the marine environment and regulate fishing.
With the development of the EEZ, the issue of continental shelves has been furthered confused, since under Article 56 of the UNCLOS 1982 the coastal state has sovereign rights over all the natural resources of its EEZ…
5. High Seas
The area common to all is the high seas. Article 1 of the Convention on the High Seas 1958 reflects customary international law and states the term ‘high seas’ means all parts of the sea that are not included in the territorial sea or in the internal waters of a state. Article 86 of UNCLOS 1982 expanded the definition to all parts of the sea that are not included in the EEZ, in the territorial sea or in the internal waters of a State, or in the archipelagic waters of an archipelagic State. It further states in Article 87 that the high seas are open to all states, whether coastal or land-locked. Freedom of the high seas is exercised under the conditions laid down by this Convention and by other rules of international law.