Maritime Jurisdiction
Continental Shelf
Originally, resources of the sea were conceived of in terms of fishing and aquaculture. In the last 100 years, exploration of the seabed and its resources has become possible and economically feasible. Correspondingly, international law and conventions have evolved, largely giving enhanced rights and powers to the coastal state.
The 1958 CSC provides that the coastal state exercises over the continental shelf, sovereign rights for the purpose of exploring and exploiting its natural resources. Natural resources include mineral and other non-living resources on the seabed and subsoil of the sea, including sedentary species. This is recognised as customary law by the International Court of Justice. The principle is restated in the Law of the Sea Convention LOSC.
The most controversial issue concerns the extent of the continental shelf’s jurisdiction. It does not necessarily coincide with the geophysical continental shelf. The 1958 CSC defined the continental shelf as the seabed and subsoil adjacent to the coast outside territorial seas to the point at which waters were 200m deep or to the point where exploitation was no longer feasible.
This was arbitrary in terms and did not work in practice. It was claimed that the seabed was common territory of all mankind and not subject to any state’s jurisdiction.
In cases before the Court of Justice, it was argued that the continental shelf comprised the prolongation of the long landmass under the sea. However, this is not always physically the case, and many states claim a wider definition.
200 Miles +
Ultimately in the Law of the Sea Convention, the continental shelf was defined as extending 200 m from the baseline or to the outer edge of the continental margin, whichever is further. A right to exercise jurisdiction for a further 60 nautical miles or to a point where the depth of sedimentary rock over the continental rise is more than 1% of the distance from the foot of the slope.
The outer limits are themselves subject to further limitations. They may not be more than 350 miles from the baseline or more than 100 miles from where the depth of the water is 2500m. Resources outside 200 nautical miles are subject to the state making payments or contributions in kind to the International Seabed Authority.
The Law of the Sea Convention, LOSC established a Commission on the limits of the Continental Shelf. States were to submit their claims to the outer limits, beyond 200 nautical miles from baselines, within 10 years.
The period was ultimately extended to 2009 in respect of states for whom the 10-year period, post ratification, had expired. Dozens of claims have been submitted. The Commission is to look at claims and make recommendations with a view to finalising the final boundaries of the continental shelf. The progress has been slow.
Exclusive Fishing
The exclusive fishing zone is a separate concept. Fishing is a more immediate resource and has been customarily exploited for centuries.
The increased capacity of fishing vessels to harvest significant stocks of fish has placed pressure on resources. In the above context, the exclusive fishing zone has developed as a standalone zone of jurisdiction in respect of fishing resources.
Sea-Fisheries and Maritime Jurisdiction (Amendment) Act 2019 continues to assert Ireland’s exclusive right to fish within the exclusive fishery limits of the State by maintaining previous provisions but also explicitly provides for access to fish by sea-fishing boats owned and operated in Northern Ireland within 0 – 6 nautical miles of the baseline of the State’s exclusive fishery limits.
It further provides that Northern Ireland sea-fishing boats will be subject to the same obligations as an Irish sea-fishing boat while availing of the access conferred by the Act in keeping with the reciprocal Voisinage arrangements for fishing between Ireland and Northern Ireland and the Government of the United Kingdom.
EEZ Disagreement
UNCLOS I and II did not reach agreement on EEZs. State practice has converged towards recognising fisheries jurisdiction up to 12 nautical miles from the baseline. Other states claim much broader zones up to 200 nautical miles, which have not yet been endorsed by the International Court of Justice. 4
It appears that the court is willing to consider the preferential right of access to fishing resources in the high seas in areas more than 12 nautical miles out in some cases. It appears that customary law has developed.
The above position  has been largely superseded by the development of exclusive fishing zones. Although not expressly provided for in the Law of the Sea Convention, it appears that the exclusive fisheries zone of 200 nautical miles has been established in customary law in the last 30 years.
South  American states have claimed an exclusive economic zone of 200 nautical miles in which the coastal states could exercise full sovereign rights over all living and non-living and non-natural resources. This would be subject to international rights, such as the right to free navigation.
UNCLOS III
The exclusive economic zone was recognised as reflecting customary international law during the UNCLOS III process and was established under the LOSC Treaty. Under the Convention, states may claim an exclusive economic zone up to 200 nautical miles. The area comprises neither high seas nor territorial seas but is a distinct jurisdiction. States exercise a sovereign right to explore, exploit, conserve and manage the resources, living resources of the EEZ.
Coastal states have jurisdiction to explore, exploit, conserve and manage living and non-living natural resources. This combines the concept of the continental shelf and the exclusive fishery zones but with additional elements.  Additional elements include the harnessing of wind and wave power for electricity generation. Coastal states may establish installations, artificial islands and a range of other matters and things.
Freedom of navigation, overflight and laying of pipes and cables is reserved for all states within the framework of the Convention. Disputes should be resolved on an equitable basis in light of the circumstances, taking into account the importance of the interests concerned, as well as the interest of the international community as a whole.
Coastal states may exercise jurisdiction over fishing issues.  They may board, inspect, arrest and take judicial proceedings for breaches. The Convention provides vessels and crew arrested are to be promptly released on posting a reasonable bond or other security. The International Tribunal on Law of the Sea has automatic jurisdiction over claims regarding the release of vessels.
Deep Seabed
The deep seabed is widely claimed to be the common heritage of mankind. Part IX of the LOSC emerged from the UNCLOS III procedure. However, it has not been accepted by many developed countries.
The 1994 Implementation Agreement facilitated more widespread ratification of the Convention. The matter has become less contentious, with an appreciation of the cost involved in the exploitation of the resources.
The Exploitation of the deep-seabed and subsoil beyond national jurisdiction is administered by the International Seabed Authority. Plans of work must be submitted to it. It must identify two areas of equal mining potential, one of which is to be reserved to the applicant and the other to the international community.
Under the original scheme, it was proposed that the reserved site would be exploited by an independent commercial arm of the Authority. However, this was given a reduced role that contemplated that it might be involved in joint ventures. If it does not do so within 15 years, the original applicant may do so. If it does seek to mine, it must be offered a site.  The applicant must be offered a chance to participate in the joint venture.
The provisions are not yet operational, and it does not appear that deep seabed mining will be economic in the near future. A number of contracts have been entered with a range of commercial and governmental bodies in certain areas in the Pacific and the Indian Ocean basins.
Overlap
The Law of the Sea Convention provides that, absent agreement to the contrary, states may not extend their territorial sea beyond the middle or equidistant point with other states. Historical and other special circumstances may justify deviation from this principle. This is in accordance with customary international law.
The 1958 CSC Convention followed the same principle in the case of limiting overlapping continental shelves. Not all states have accepted this position. Later alternative positions maintained, put greater emphasis on special circumstances.
States have tended to support the position consistent with their interests at the UNCLOS. UN CLOS III stated that delineation should be by agreement on the basis of international law in order to effect an equitable solution.
The International Court of Justice has adopted principles of equity, giving it greater weight than equidistance in a number of cases.  Presumptively, the middle point between opposite coasts is generally that which gives an equitable solution. However, equidistance may only be a starting point, and other equitable principles may intervene.
The current approach lays emphasis on an equitable solution. It will seek to ensure that areas belonging to each state are not disproportionate to the ratio between the length of their relevant coastlines abutting the area. The presence of islands may generate a claim. In some cases, their impact is discounted or reduced. In some cases, geological factors may be relevant.
2006 Act
The Maritime Jurisdiction Act was amended by the 2006 Act to make it clear that the prohibition on unlawfully interfering with access to and from ports and harbours in the State and the power to direct vessels to move in the interest of the safety of life at sea also applies to vessels which are not registered in the State. The Maritime Jurisdiction Act 1959 has been amended and is updated. The outer limit of the territorial seas of the State is the baselines from which the territorial seas and inland waters to be reckoned are prescribed by government order.
There is a new provision to give effect to Part V of the exclusive economic zone provisions of the United Nation’s Convention of Sea so as to define the exclusive economic zone of the State (extending outwards 200 miles from baselines) except where equitably equidistance is maintained between the State and mainland UK.
The exclusive fisheries limits of the State are coterminous with the exclusive economic zone of the State. They are currently defined by the 1976 Order made under the 1959 Act pursuant to the EU decision that all EU states shall declare 200 nautical miles exclusive fishery zone.
There is a provision to provide for the prosecution of non-nationals for offences on the territorial seas of the States of the Minister for Foreign Affairs’ consent. Prosecution for sea-fisheries offences is not subject to such strict restrictions.