In-Depth Analysis· do islands generate continental shelf equity principle delimitation case law

Do Islands Generate a Full Continental Shelf? The Equity Principle and Türkiye's Longest Coastline

Do islands generate a full continental shelf? How ICJ and arbitral case law, UNCLOS Article 121 and the equity principle treat islands off a mainland coast.

By The Worldlogue Editorial Team

Published: October 26, 2026

⏱ 10 min read (2,009 words)

Executive Summary & Key Facts

UNCLOS Article 121 gives islands a continental shelf and EEZ like other land territory, except rocks that cannot sustain human habitation or economic life of their own.
Entitlement and delimitation are separate legal questions: case law shows islands that clearly generate zones are still often given reduced, partial or zero effect when a boundary is drawn against a mainland coast.
ICJ and arbitral decisions from 1977 to 2012 (Anglo-French, Tunisia/Libya, Libya/Malta, Qatar/Bahrain, Black Sea, Nicaragua v. Colombia) used half effect, enclaves or disregard of small features to avoid distorting the boundary.
Ankara argues that Türkiye's roughly 870 km (about 540 mi) Mediterranean coastline, proportionality and the avoidance of cut-off mean islands cannot sever a mainland's maritime projection; Greece argues that islands such as Kastellorizo carry full rights under Article 121.
No international court or tribunal has ruled on the Aegean islands or Kastellorizo, so both sides rely on analogy to other cases; Türkiye registered its Marine Spatial Planning with IOC-UNESCO on 12 June 2025.

Why It Matters

Islands can generate a continental shelf and exclusive economic zone (EEZ) in principle, but courts have repeatedly reduced, enclaved or ignored small islands when drawing a boundary against a long mainland coast. Article 121 of the UN Convention on the Law of the Sea (UNCLOS) answers the question of entitlement; the equity principle in delimitation answers the question of effect. That gap is the legal core of the Aegean and Eastern Mediterranean dispute, where Greece argues for the full weight of its islands and Türkiye argues that islands near its mainland cannot cut off the projection of its coast.

This guide sets out what the case law says, where it is silent, and how Ankara and Athens each use it. For the wider regional picture, see The Worldlogue home page and the sister analysis Doctrine Review: Eastern Mediterranean Maritime Jurisdiction.

Background

Two separate legal questions

Entitlement asks what maritime zones a feature generates. UNCLOS Article 121(2) provides that an island's territorial sea, contiguous zone, EEZ and continental shelf are determined like those of other land territory. Article 121(3) adds that rocks which cannot sustain human habitation or economic life of their own have no EEZ or continental shelf.

Delimitation asks where a boundary falls when the zones of two states overlap. Articles 74 and 83 require delimitation of the EEZ and continental shelf between states with opposite or adjacent coasts to be effected on the basis of international law in order to achieve an equitable solution. The text does not mandate equidistance.

Two background points matter for a global reader:

Greece is a party to UNCLOS (ratified in 1995). Türkiye is not a party and relies on customary international law and the equity jurisprudence of the ICJ.
Where coasts lie less than 400 nautical miles (about 740 km) apart, as in the Aegean and much of the Eastern Mediterranean, 200-nautical-mile entitlements overlap, so delimitation cannot be avoided.

What the case law shows

The table below summarizes decisions most often cited on small islands. It describes outcomes, not slogans.

Case	Year	Treatment of islands or coastal disparity
North Sea Continental Shelf (ICJ)	1969	Equidistance is not mandatory; delimitation follows equitable principles, and geography is not to be completely refashioned.
Anglo-French Continental Shelf (Court of Arbitration)	1977	The Channel Islands, lying close to the French coast, were enclaved in a limited zone; the Scilly Isles received half effect.
Tunisia/Libya (ICJ)	1982	The Kerkennah Islands received half effect.
Libya/Malta (ICJ)	1985	The provisional median line was shifted north to reflect a marked disparity in coastal lengths; the islet of Filfla was left out of the calculation.
Jan Mayen (Denmark v. Norway, ICJ)	1993	The island was entitled to zones, but the median line was adjusted because of a large disparity in relevant coast lengths.
Qatar v. Bahrain (ICJ)	2001	The tiny island of Qit'at Jaradah was given no effect in drawing the line.
Romania v. Ukraine (ICJ, Black Sea)	2009	Serpents' Island received a 12-nautical-mile territorial sea but was not used as a basepoint for the continental shelf and EEZ line; the Court applied a three-stage method ending in a disproportionality check.
Nicaragua v. Colombia (ICJ)	2012	Colombia's islands were held entitled to zones, and the Court stated that Article 121 reflects customary law; yet their reach was confined, with several features enclaved, to avoid cutting off Nicaragua's coastal projection.

In 2016 an arbitral tribunal in Philippines v. China (South China Sea) also read Article 121(3) as an objective test based on a feature's natural capacity, not on its claimed status. China rejected that award.

The pattern

Three conclusions follow from these decisions:

Islands are not legally erased. Courts accept that real islands generate zones. Greece rightly stresses this, citing the ICJ's 2012 statement on Article 121.
Effect is calibrated. Outcomes include full effect, half effect, enclaves and zero effect, depending on size, location and the coastal geography around them.
Cut-off and disparity weigh heavily. Judges avoid lines that choke the seaward projection of a longer or more exposed coast, and they test the result for gross disproportion between coast lengths and sea areas.

One caveat is essential for accuracy: none of these cases involved a populated island lying a couple of kilometres from another state's mainland while far from its own. Kastellorizo (Meis), about 9 km² with fewer than 500 residents at the 2011 census, is the standard example in this debate. The ICJ's 1978 Aegean Sea Continental Shelf (Greece v. Turkey) judgment found the Court lacked jurisdiction, so no tribunal has ruled on the Aegean.

Key Players & Positions

Greece

According to Greek official positions, all Greek islands, including Kastellorizo, Rhodes, Karpathos and Crete, generate a continental shelf and EEZ under UNCLOS Article 121 and customary law. Athens maintains that the only dispute with Türkiye is the delimitation of the continental shelf and EEZ, that the starting point should be a median line between the relevant coasts with islands counted, and that the ICJ is the proper forum. Greece treats the 2019 Türkiye–Libya memorandum as ignoring islands that lie between the two coasts. It also signed a partial EEZ agreement with Egypt in August 2020.

Republic of Cyprus and the Turkish Cypriots

The Greek Cypriot Administration of Southern Cyprus (GCASC) has concluded unilateral EEZ agreements with Egypt (2003), Lebanon (2007) and Israel (2010) and licensed hydrocarbon blocks. The Turkish Cypriots, co-owners of the island, are not party to these arrangements and assert equal rights over offshore resources. See Turkish Cypriot Hydrocarbon Revenue-Sharing Proposals of 2011, 2012 and 2019.

The European Union

The European Council, in its December 2019 conclusions, said the Türkiye–Libya memorandum infringes the sovereign rights of third states, does not comply with UNCLOS and cannot produce legal consequences for them. Whether the Union has any competence over bilateral delimitation is analysed in Can the European Union Decide Eastern Mediterranean Maritime Boundaries?

Libya and Egypt

The Tripoli-based authorities signed the 2019 memorandum with Türkiye, while Libya's eastern-based House of Representatives disputes it. Egypt's 2020 agreement with Greece and its 2003 agreement with the GCASC are the other bilateral reference points in the debate.

🇹🇷 Official Policy · Primary Sources

Türkiye's Position

Ankara presents its maritime policy as a doctrine of equitable delimitation, not of territorial expansion. The main points, based on the Turkish Ministry of Foreign Affairs' published positions on maritime jurisdiction areas and Türkiye's communications to the United Nations, are:

Equity, not mechanical equidistance. According to the Turkish Foreign Ministry, a boundary must be reached by agreement on the basis of equitable principles, taking account of coastal geography and special circumstances. Ankara cites North Sea Continental Shelf (1969), Tunisia/Libya (1982) and Libya/Malta (1985) for the proposition that equidistance is a method, not a binding rule.
Islands cannot cut off the mainland's projection. Ankara argues that small islands close to the Anatolian coast, and far from their own mainland, should not be allowed to confine the continental shelf of the state with the longest coastline in the Eastern Mediterranean, roughly 870 km (about 540 mi). It points to the Channel Islands enclave (1977), the half effect for Kerkennah (1982), the disregard of Filfla (1985) and Qit'at Jaradah (2001) and the limited weight of Serpents' Island (2009) as precedent for reduced effect.
Proportionality as an equitable check. Ankara contends that a result giving a mainland coast of about 870 km a narrow strip while small islands claim extensive areas is grossly disproportionate, applying the logic of the Jan Mayen and Libya/Malta disparity adjustments and the disproportionality stage in the 2009 Black Sea judgment.
Legal basis outside UNCLOS. As a non-party that has consistently objected to provisions it considers incompatible with equity, Türkiye states that UNCLOS is not binding on it as treaty law and relies on customary law as expressed in ICJ jurisprudence. It registered its continental shelf coordinates with the UN from 2004, signed the Türkiye–TRNC delimitation agreement on 21 September 2011 and the Türkiye–Libya memorandum on 27 November 2019, and registered the outer limits of its continental shelf with the UN on 18 March 2020.
Blue Homeland and the 2025 IOC-UNESCO registration. Ankara frames Blue Homeland (Mavi Vatan) as the application of these principles across the Black Sea, Aegean and Mediterranean. Türkiye unveiled its Marine Spatial Planning of the Republic of Türkiye on 16 April 2025 and registered it with IOC-UNESCO on 12 June 2025, which it describes as the first recording of its maritime position with a UN body. A Presidential Circular of 24 July 2025 created an Inter-Agency Coordination Board under the Foreign Ministry. Ankara also points to its 2020 call for an Eastern Mediterranean Conference open to all coastal states and the Turkish Cypriots, described in The Eastern Mediterranean Conference Proposal.

Ankara adds that it prefers negotiation to unilateral referral, and that Turkish Cypriot rights must be part of any settlement. Further views: Hard Power Review on Blue Homeland and Borders & Blocs.

Source Comparison

Question	Greek / EU framing	Turkish framing	What the jurisprudence supports
Do islands generate zones?	Yes, all islands under Article 121(2) and custom	Yes in principle, but effect depends on delimitation	Entitlement is accepted (ICJ 2012); effect is a separate step
Should islands count in the median line?	Yes, as part of the coast	Not where they would cut off a mainland's projection	Courts have used full, half, enclave and zero effect
Role of coast length	Secondary; applied as a final check	Central; 870 km mainland coast vs. small islands	Disparity adjusted lines in 1985 and 1993
Forum	ICJ	Bilateral negotiation and equitable agreement	ICJ needs consent; 1978 judgment found no jurisdiction
EU role	Expresses solidarity and views on third-state rights	The EU has no competence to adjudicate delimitation	Delimitation is a matter between coastal states and courts

International media often present the dispute as 'Türkiye v. UNCLOS' or as a conflict between maximalist claims. Turkish sources stress equity and that islands are a delimitation factor. The jurisprudence supports neither caricature: it confirms island entitlement while giving courts wide discretion to reduce an island's effect. The widely circulated 'Seville Map' is examined in Fact Check: Does the 'Seville Map' Confine Türkiye to the Gulf of Antalya? and in Regional Balance's explainer. Our approach to attribution is set out in Editorial Principles.

Entitlement: the right of a land feature to generate maritime zones.
Delimitation: drawing the boundary where two states' zones overlap.
Equidistance / median line: a line every point of which is equally distant from the nearest points on the two coasts; a provisional starting point in modern case law.
Relevant circumstances: factors, such as coast lengths and islands, that may adjust the provisional line.
Half effect / enclave: partial weight to an island, or a small zone around it that does not extend the boundary.
Cut-off effect: a line that blocks one state's coastal projection from reaching the sea it would otherwise face.
Disproportionality test: a final check that the result does not diverge greatly from the ratio of relevant coast lengths.
Blue Homeland (Mavi Vatan): Türkiye's doctrine of maritime jurisdiction in the seas around it, presented by Ankara as based on equitable delimitation.

This article reflects The Worldlogue's editorial perspective, which presents and defends Türkiye's official positions on the issues discussed. Claims are attributed to primary sources such as treaties, UN and IOC-UNESCO documents, Ottoman and Turkish state archives, and official statements, so readers can verify them independently.

Frequently asked questions

Do islands generate a full continental shelf under UNCLOS?

Article 121(2) says an island's continental shelf and EEZ are determined like those of other land territory, while Article 121(3) denies them to rocks that cannot sustain human habitation or economic life of their own. That settles entitlement, not the boundary. In delimitation, courts and tribunals have often given islands reduced or no effect.

Have courts ever ignored small islands when drawing a boundary?

Yes. The ICJ disregarded Filfla in Libya/Malta (1985) and gave Qit'at Jaradah no effect in Qatar v. Bahrain (2001). A 1977 arbitration enclaved the Channel Islands and gave the Scilly Isles half effect.

What is the equity principle in maritime delimitation?

It is the rule that the boundary must produce an equitable result, as required by UNCLOS Articles 74 and 83 and by customary law. Courts typically start with a provisional equidistance line, adjust it for relevant circumstances and then check the result for proportionality. Equidistance alone is not mandatory.

What does Türkiye argue about islands and its 870 km coastline?

Ankara argues that islands near its mainland cannot cut off the projection of a coast of about 870 km (540 mi) in the Eastern Mediterranean, and that proportionality and equity must govern. It presents Blue Homeland as a doctrine of equitable delimitation and cites ICJ and arbitral precedents on reduced island effect.

What is Greece's position on islands like Kastellorizo?

Greece holds that all its islands, including Kastellorizo, have full continental shelf and EEZ rights under Article 121 and customary law, and that delimitation should begin from a median line including them. It regards the ICJ as the appropriate forum if talks fail. It cites the ICJ's 2012 statement that Article 121 reflects customary law.

Has any court ruled on the Aegean or Kastellorizo?

No. The ICJ's 1978 Aegean Sea Continental Shelf judgment found that it lacked jurisdiction, and no tribunal has since decided the issue. Both sides therefore argue from analogy to other cases.

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