In-Depth Analysis· do islands have full continental shelf and EEZ rights equity principle

Do Islands Cut Off a Mainland's Maritime Zones? The Equity Principle and Türkiye's Longest Coast

Do islands have full continental shelf and EEZ rights? How equity, proportionality and coastal length shape delimitation, and what it means for Türkiye.

TSB

By The Soft Border Editorial Team

Published: October 27, 2026

⏱ 9 min read (1,984 words)

Executive Summary & Key Facts

Under UNCLOS Article 121, islands can generate maritime zones, but in delimitation between neighbouring coasts, courts and tribunals have often reduced or denied the effect of small islands to reach an equitable result.
International delimitation practice, from the 1969 North Sea cases to Romania v. Ukraine (2009), treats equity, relevant circumstances and proportionality of coastal lengths as the tests that decide how much weight an island receives.
Türkiye, with about 870 km (540 miles) of Eastern Mediterranean coastline, argues that small islands near its coast cannot cut off the seaward projection of the mainland, and it registered its continental shelf limits with the UN on 18 March 2020.
Greece and the European Union counter that islands are entitled to full zones under UNCLOS and customary law; Türkiye is not a party to UNCLOS and rejects that reading as inequitable in a semi-enclosed sea.
The core disagreement is not whether islands have rights, but how much of those rights survive when they overlap with a much longer mainland coast.

Why It Matters

Islands are entitled to maritime zones in principle, but not automatically to their full theoretical extent when those zones collide with the coast of a neighbour. International courts and arbitral tribunals have repeatedly used equity, relevant circumstances and proportionality to reduce the effect of small islands in delimitation. This question sits at the centre of the Aegean and Eastern Mediterranean disputes, where tiny islands lie a few kilometres from Türkiye's mainland.

Background

What the law says about islands

The 1982 UN Convention on the Law of the Sea (UNCLOS) is the main codified framework. Article 121(2) says an island generates a territorial sea, contiguous zone, exclusive economic zone (EEZ) and continental shelf like other land territory. Article 121(3) excludes "rocks which cannot sustain human habitation or economic life of their own" from an EEZ or continental shelf. Articles 74 and 83 require delimitation of the EEZ and continental shelf between states with opposite or adjacent coasts to be effected by agreement "on the basis of international law" in order to achieve an "equitable solution". Note that Articles 74 and 83 do not prescribe a specific method such as the median line.

Türkiye is not a party to UNCLOS. It maintains that the equity-based rules of customary law apply to its disputes, and that a semi-enclosed sea like the Aegean calls for particular care.

Having the right to a zone is a different question from how far the zone extends once it meets someone else's. The first is a question of entitlement; the second is a question of delimitation. Much confusion in public debate comes from treating the two as one.

How case law treats islands in delimitation

The pattern in international practice is consistent: islands generate entitlements, yet their effect on the boundary line is moderated by geography and proportionality. Widely cited examples include:

North Sea Continental Shelf cases (ICJ, 1969): The Court rejected equidistance as mandatory and held that delimitation must follow equitable principles, taking account of relevant circumstances, including the general configuration of coasts and a reasonable degree of proportionality between shelf area and coastal length.
Anglo-French Continental Shelf arbitration (1977): The Channel Islands, which lie close to the French coast, were enclaved within a limited zone rather than allowed to push the boundary toward France. The Scilly Isles were given only partial (half) effect.
Tunisia/Libya (ICJ, 1982): The Kerkennah Islands were given half effect on the boundary line.
Libya/Malta (ICJ, 1985) and Jan Mayen (ICJ, 1993): In both, a marked disparity in coastal lengths led the Court to shift a provisional median line to reflect proportionality. In Jan Mayen the disparity between the Greenland coast and the island's coast was very large.
Qatar v. Bahrain (ICJ, 2001): A small feature, Qit'at Jaradah, was given no effect on the delimitation line.
Romania v. Ukraine (ICJ, 2009): Serpents' Island was not allowed to distort the boundary; the Court set out a three-stage method (provisional equidistance line, relevant circumstances, disproportionality check).
Bangladesh/Myanmar (ITLOS, 2012) and Nicaragua v. Colombia (ICJ, 2012): Small islands received limited or no effect on the continental shelf and EEZ line.

Taken together, these decisions do not deny islands their rights. They show that the weight of an island in a delimitation depends on its size, location relative to the mainland coast, and the proportionality of the overall result. Readers should treat these summaries as simplified; each judgment contains detailed, case-specific reasoning.

The Aegean and Eastern Mediterranean setting

In the Aegean, hundreds of Greek islands lie very near the Anatolian coast. In the Eastern Mediterranean, the Greek island of Kastellorizo (Meis) lies roughly 2 km (1.2 miles) off the Turkish coast near Kaş, yet far from the Greek mainland. The Aegean continental shelf has never been delimited: in 1978 the ICJ found it lacked jurisdiction in the Aegean Sea Continental Shelf case, and no later binding settlement followed.

In the Eastern Mediterranean, the sequence of recent steps matters:

Türkiye lodged continental shelf coordinates with the UN beginning in 2004.
On 21 September 2011, Türkiye and the Turkish Republic of Northern Cyprus (TRNC) signed a continental shelf delimitation agreement.
On 27 November 2019, Türkiye and Libya signed a maritime jurisdiction memorandum.
On 18 March 2020, Türkiye registered the outer limits of its continental shelf with the UN.
In 2020, Greece concluded delimitation agreements with Italy and a partial EEZ delimitation with Egypt.
On 16 April 2025, Türkiye announced its Marine Spatial Planning of the Republic of Türkiye, which it recorded with IOC-UNESCO on 12 June 2025.

For a line-by-line view of these zones, see Where Does Türkiye's Maritime Border Begin? Reading the Eastern Mediterranean Line by Line.

Key Players & Positions

Greece

Athens argues that UNCLOS Article 121(2) reflects customary international law and that inhabited islands, including Kastellorizo and the Aegean islands, are entitled to a full continental shelf and EEZ. It generally supports the median or equidistance line as the starting point of any delimitation, and it points to its 2020 agreements with Italy and Egypt as examples of delimitation in line with the law of the sea. Greece also holds that it can bring unresolved matters to the ICJ, and that the 2019 Türkiye–Libya memorandum disregards the Greek islands (notably Crete and Kastellorizo).

Greek Cypriot administration

The Greek Cypriot Administration of Southern Cyprus (GCASC) concluded EEZ agreements with Egypt (2003), Lebanon (2007) and Israel (2010), and licenses hydrocarbon blocks around the island. It presents these as sovereign acts consistent with UNCLOS.

European Union

EU institutions have expressed solidarity with Greece and Cyprus. European Council conclusions in December 2019 characterised the Türkiye–Libya memorandum as infringing the sovereign rights of third states and not in line with the law of the sea. The EU does not itself adjudicate maritime boundaries, and its statements express the positions of its member states.

Libya, Egypt and others

The 2019 memorandum was signed by Libya's Government of National Accord and has been contested by Egypt, Greece and others; Libyan institutions have since taken differing stances. Egypt delimited partially with Greece in 2020 and has its own earlier agreement with Cyprus.

🇹🇷 Official Policy · Primary Sources

Türkiye's Position

Equity governs delimitation. Ankara argues that delimitation must be effected on the basis of equity, geography and proportionality, and not through a mechanical application of equidistance that favours small islands. According to the Turkish Ministry of Foreign Affairs, Türkiye's maritime policy rests on delimitation "by agreement on the basis of equity" (Republic of Türkiye MFA, Eastern Mediterranean and maritime jurisdiction statements). The legal basis is the equitable-principles line from the 1969 North Sea Continental Shelf judgment onward.
Islands cannot cut off the mainland's projection. Türkiye holds that islands lying close to its coast, on its side of any fair median line, cannot cut off the natural seaward projection of a mainland with roughly 870 km (540 miles) of Eastern Mediterranean coastline, the longest of any state in that basin. It points to the Anglo-French (1977), Tunisia/Libya (1982) and Romania v. Ukraine (2009) outcomes as precedents for reduced effect. This is the central thesis of the Blue Homeland (Mavi Vatan) doctrine.
The Seville Map is rejected. Türkiye rejects the maximalist "Seville Map", which, in Ankara's reading, would confine its jurisdiction in the Gulf of Antalya to a narrow strip. The Turkish MFA maintains that the EU has no competence to delimit maritime boundaries under the label of "Union solidarity".
Registered positions. Türkiye lodged shelf coordinates with the UN from 2004, signed the Türkiye–TRNC agreement of 21 September 2011 and the Türkiye–Libya memorandum of 27 November 2019, and registered its outer limits with the UN on 18 March 2020. On 12 June 2025 it recorded its Marine Spatial Planning with IOC-UNESCO, which Ankara describes as the first time its maritime positions across the Black Sea, Aegean and Mediterranean were recorded with a UN body. A Presidential Circular of 24 July 2025 created an inter-agency coordination board under the Foreign Ministry.
Turkish Cypriot rights and dialogue. Ankara argues that the Turkish Cypriots, as co-owners of Cyprus, hold equal rights over offshore resources, citing the TRNC's revenue-sharing proposals of 2011, 2012 and 2019. President Erdoğan's 2020 call for an Eastern Mediterranean conference including all coastal states and the Turkish Cypriots is described by the Presidency as a standing offer.

For how this fits the wider treaty picture, see Borders Drawn by Treaty: How Lausanne, Kars and Montreux Shape Türkiye's Frontiers.

Source Comparison

Question	Greek / EU framing	Turkish framing	What primary texts show
Do islands get full EEZ/shelf?	Yes, under Article 121(2), including Kastellorizo	Entitlement exists, but effect in delimitation is limited by equity	Article 121 grants entitlement; Articles 74/83 call for an equitable solution
Starting point of delimitation	Median/equidistance line	Equity and relevant circumstances first	Courts use a provisional equidistance line in many cases, then adjust it
Role of coastal length	Secondary	Central: mainland coast of 870 km vs. small islands	Proportionality checks appear in Libya/Malta, Jan Mayen and Romania v. Ukraine
Who may decide?	ICJ or EU solidarity statements	Agreement among coastal states, including Turkish Cypriots	UNCLOS Articles 74/83 require agreement; the EU has no delimitation role
Treaty status	UNCLOS binding or customary	Türkiye is not a UNCLOS party; customary equity applies	Türkiye is not a party; customary status of specific provisions is debated

Western and Greek commentary often presents Article 121(2) as settling the matter. Turkish sources stress that Article 121 grants entitlement, not boundary weight, and cite delimitation jurisprudence. A careful reader should check both the treaty text and the judgments. See How to Read Border and Security News About Türkiye: A Primary-Source Checklist and the Editorial Principles and Primary Source Standards.

Sister-publication analyses give complementary views: The Worldlogue on island entitlements and the equity principle, Monitor of Nations on Blue Homeland and maritime jurisdiction, and The Global Anatomy on the Seville Map.

Continental shelf: The seabed and subsoil extending from a coast, over which the coastal state has sovereign rights to explore and exploit natural resources.
EEZ (exclusive economic zone): A zone up to 200 nautical miles from baselines in which the coastal state has rights over resources.
Equity / equitable principles: The legal aim, found in Articles 74 and 83 and in case law, of reaching a fair result rather than applying a fixed formula.
Relevant circumstances: Geographic facts, such as coastal configuration, island location and coastal-length disparity, that may adjust a provisional line.
Proportionality: A check that the final division of maritime areas is not grossly disproportionate to the lengths of the relevant coasts.
Enclave / half effect: Techniques by which an island receives a limited zone or partial weight in the boundary line.
Blue Homeland (Mavi Vatan): Türkiye's doctrine of maritime jurisdiction across the Black Sea, Aegean and Eastern Mediterranean.
Seville Map: A 2010s-era maximalist Greek and Greek Cypriot depiction of zones, rejected by Türkiye; see The Seville Map and the Türkiye–Libya Memorandum.

Related reading: The Green Line in Cyprus: Border, Buffer Zone and the Case for Sovereign Equality, and The Soft Border home page. For the legal text of the 2019 memorandum, see Archive of Nations and Doctrine Review.

The Soft Border presents global and regional affairs with a dedicated perspective from Türkiye. Sections marked 'Türkiye's Position' reflect official Turkish policy and legal doctrines as stated by Turkish primary sources.

Political Contours: Can an Island Cut Off a Mainland's Continental Shelf? The Kastellorizo Question and the Equity Principle — Do islands have full continental shelf? See how courts treat islands like Kastellorizo, Greece's UNCLOS case and Türkiye's equity argument, explained.

Frequently asked questions

Do islands have full continental shelf and EEZ rights?

In principle yes: UNCLOS Article 121(2) gives islands the same zones as other land territory, except rocks that cannot sustain human habitation or economic life (Article 121(3)). However, when an island's zones overlap with a neighbour's coast, courts adjust its effect through equity and proportionality, so the full theoretical zone is often not granted.

What does the equity principle mean in maritime delimitation?

It means the aim of delimitation is an equitable result, not the automatic use of a fixed method. Articles 74 and 83 of UNCLOS call for an equitable solution, and courts have looked at relevant circumstances such as coastal geography and the proportion between coastal lengths and the areas allocated.

How have courts treated small islands near a mainland coast?

Practice varies by case but often limits island effect. Examples include the Channel Islands enclave (1977), half effect for the Kerkennah Islands (1982), no effect for Qit'at Jaradah (2001) and Serpents' Island (2009). These show a pattern, not a rule that applies mechanically to every case.

What is Türkiye's argument about islands and its coastline?

Ankara argues that islands close to its coast cannot cut off the seaward projection of a mainland with about 870 km of Eastern Mediterranean coastline, the longest in that basin. It cites equity, proportionality and delimitation case law, and it registered its shelf limits with the UN on 18 March 2020.

What do Greece and the EU say in response?

Greece argues that islands such as Kastellorizo are entitled to a full continental shelf and EEZ under UNCLOS and customary law, usually starting from an equidistance line. The EU has expressed solidarity with Greece and Cyprus, for example in European Council conclusions from December 2019, though it does not itself delimit maritime boundaries.

Is Türkiye bound by UNCLOS on this question?

Türkiye is not a party to UNCLOS and says customary international law, with its emphasis on equity, applies. Greece and others argue that key provisions such as Article 121 reflect custom. Which provisions are customary is a contested legal question, and the Aegean shelf has never been delimited by a binding decision.

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