Maritime Boundary Definitions

Last updated:7 June 2023

Nautical Mile

A nautical mile (M) is a unit of distance equal to 1 852 metres. This value was adopted by the International Hydrographic Conference in 1929 and has subsequently been adopted by the International Bureau of Weights and Measures.

It is also the unit adopted for the purposes of Australian Maritime Legislation. Refer to Schedule 1.(1) of the Seas and Submerged Lands Act 1973 as published in the Commonwealth of Australia Gazette No.S29, 9 February 1983.

The length of the nautical mile is very close to the mean value of the length of 1 minute of latitude, which varies from approximately 1 843 metres at the equator to 1 861.6 metres at the pole.

Territorial Sea Baseline

The term Territorial Sea Baseline (TSB) refers to the line from which the seaward limits of Australia's Maritime Zones are measured. These include the breadth of the territorial sea; the seaward limits of the contiguous zone, the exclusive economic zone and, in some cases, the continental shelf.

The territorial sea baseline may be of various types depending upon the shape of the coastline in any given locality:

  • The Normal baseline corresponds with the low water line along the coast, including the coasts of islands. Under the Convention, normal baseline can be drawn around low tide elevations which are defined as naturally formed areas of land surrounded by and above water at low tide but submerged at high tide, provided they are wholly or partly within 12 nautical miles of the coast. For Australian purposes, normal baseline corresponds to the level of Lowest Astronomical Tide (LAT).
  • Straight baselines are a system of straight lines joining specified or discrete points on the low-water line, usually known as straight baseline end points. These may be used in localities where the coastline is deeply indented and cut into, or where there is a fringe of islands along the coast in its immediate vicinity.
  • Bay or river closing lines are straight lines drawn between the respective low-water marks of the natural entrance points of bays or rivers.

Waters on the landward side of the baseline are internal waters for the purposes of international law.

Coastal Waters (3 nautical mile limit)

Coastal Waters is a belt of water between the limits of the Australian States and the Northern Territory and a line 3M seaward of the territorial sea baseline*. Jurisdiction over the water column and the subjacent seabed is vested in the adjacent State or Territory as if the area formed part of that State or Territory. This, and other arrangements for the management of offshore resources such as fisheries and petroleum, are defined by the Offshore Constitutional Settlement (OCS). The principal legislation implementing the OCS (Coastal Water (State Powers) Act 1980, Coastal Waters (State Title) Act 1980, Coastal Waters (Northern Territory Powers) Act 1980 and the Coastal Waters (Northern Territory Title) Act 1980) entered into force in January 1982 and February 1983.

* The TSB used to determine Coastal Waters does not include low tide elevations greater than 3M from the coastline or islands.

Territorial Sea (12 nautical mile limit)

The Territorial Sea is a belt of water not exceeding 12M in width measured from the territorial sea baseline. Australia's sovereignty extends to the territorial sea, its seabed and subsoil, and to the air space above it. This sovereignty is exercised in accordance with international law as reflected in the Convention. The major limitation on Australia's exercise of sovereignty in the territorial sea is the right of innocent passage for foreign ships. The territorial sea around certain islands in the Torres Strait is 3M.

Contiguous Zone (24 nautical mile limit)

The Contiguous Zone is a belt of water contiguous to the territorial sea, the outer limit of which does not exceed 24M from the territorial sea baseline. In this zone, Australia may exercise control necessary to prevent and punish infringement of its customs, fiscal, immigration or sanitary laws and regulations within its territory or territorial sea.

Exclusive Economic Zone (200 nautical mile limit)

The Exclusive Economic Zone (EEZ) is an area beyond and adjacent to the territorial sea. The outer limit of the exclusive economic zone cannot exceed 200M from the baseline from which the breadth of the territorial sea is measured. In the EEZ, Australia has sovereign rights for the purpose of exploring and exploiting, conserving and managing all natural resources of the waters superjacent to the seabed and of the seabed and its subsoil together with other activities such as the production of energy from water, currents and wind. Jurisdiction also extends to the establishment and use of artificial islands, installations and structures, marine scientific research, the protection and preservation of the marine environment, and other rights and duties.

The Australian EEZ is defined in the Seas and Submerged Lands Act 1973 ('the SSL Act' - including the amendments to that Act made by the Maritime Legislation Amendment Act 1994).

The outer limit of the Australian EEZ is set out in the Proclamation under the SSL Act which was made on 26 July 1994 and published in Gazette S290 on 29 July 1994. That proclamation entered into force on 1 August 1994. The outer boundary is mostly 200M from the territorial sea baselines. However the Proclamation pulls the boundary back to less than 200M in areas of agreed or potential delimitation with other countries. The metes and bounds definitions where the boundary has been pulled back are taken from Australia's maritime delimitation agreements with other countries and, where no such agreement exists, largely follow the Fisheries Management Act 1991 ('the FMA Act') 'excepted waters' Proclamation which was published in Gazette No.S52 of 14 February 1992.

Australian Fishing Zone

The Australian Fishing Zone (AFZ) is defined as follows in the Fisheries Management Act 1991 (FMA) (including the amendments to that Act made by the Maritime Legislation Amendment Act 1994).

Australian Fishing Zone means:

  • The waters adjacent to Australia within the outer limits of the exclusive economic zone; and
  • The waters adjacent to each external territory within the outer limits of the exclusive economic zone;
    but does not include:
    • Coastal waters of, or waters within the limits of, a State or internal Territory; or
    • Waters that are 'excepted waters'

The outer limit of the AFZ is the same as the outer limit of the EEZ other than in places where the 'excepted waters' Proclamation in Gazette No.S52 of 14 February 1992 remains relevant (see paragraph (d) of the definition). The 'excepted waters' Proclamation remains relevant in two areas - in the Torres Strait and in the waters adjacent to the Australian Antarctic Territory (Parts 5 and 6 of the 1992 Proclamation). The other parts of the 1992 'excepted waters' Proclamation have been rendered redundant by the Proclamation of the outer limits of the EEZ which entered into force on 1 August 1994. They have been rendered redundant because they largely cover the same lines as are used in the 1994 EEZ Proclamation.

Continental Shelf

The Continental Shelf is the area of the seabed and subsoil which extends beyond the territorial sea to a distance of 200M from the territorial sea baseline and beyond that distance to the outer edge of the continental margin as defined in Article 76 of the Convention. The continental shelf is largely coextensive with the exclusive economic zone within 200M from the territorial sea baselines (there are certain areas between Australia and Indonesia and Australia and Papua New Guinea where they are not coextensive).

Australia has sovereign rights over the continental shelf for the purposes of exploring and exploiting the mineral and other non-living resources of the seabed and subsoil, together with sedentary organisms. In this area, Australia also has jurisdiction with regard to marine scientific research as well as other rights and responsibilities.

In order to support any claim to delineation of the outer limit of the extended continental shelf beyond 200M as measured from the territorial sea baseline, Australia has submitted details, together with supporting scientific information, to the United Nations Commission on the Limits of the Continental Shelf. In areas where the area of extended continental shelf is within 200M of another country, Australia will not be required to take that area to the Commission on the Limits of the Continental Shelf.

Geoscience Australia's Law of the Sea and Maritime Boundary Advice Project is responsible for the survey and definition of the limits of the Continental Shelf.