Dispute concerning the Delimitation of the Maritime Boundary between Mauritius and Maldives in the Indian Ocean (Mauritius/Maldives) [2021]

ITLOS Case No. 28, Judgment of 28 January 2021 · International Tribunal for the Law of the Sea (Special Chamber) · International

Law of the Sealaw-of-the-seamaritime-delimitationexclusive-economic-zonecontinental-shelfarchipelagic-baselines

Issue

How should the maritime boundary between Mauritius and Maldives be delimited, taking into account the status of the Chagos Archipelago and the Maldives' archipelagic baselines?

Held

ITLOS delimited the boundary using the equidistance/relevant circumstances method. It gave full effect to the Maldives' archipelagic baselines, which were found to be in accordance with UNCLOS. The Tribunal did not rule on the sovereignty of the Chagos Archipelago, but noted that the ICJ's advisory opinion did not affect the delimitation because the UK was not a party to the proceedings.

Exam use

In a problem question involving maritime delimitation with archipelagic States, remember that archipelagic baselines are given full effect. The three-stage approach is the standard method. Disputed sovereignty over islands may not be a relevant circumstance if the disputing State is not a party. Use this case to argue for a strict equidistance line if no relevant circumstances justify adjustment.

Summary

ITLOS delimited the maritime boundary between Mauritius and Maldives in the Indian Ocean, addressing the status of the Chagos Archipelago and the effect of the UK's withdrawal from the area. The Tribunal applied the equidistance/relevant circumstances method and gave full effect to the Maldives' archipelagic baselines. It also addressed the impact of the ICJ's advisory opinion on the Chagos Archipelago.

Facts

Mauritius and Maldives have overlapping claims to maritime areas in the Indian Ocean. The dispute involved the delimitation of the EEZ and continental shelf between the two States. A key issue was the status of the Chagos Archipelago, which the UK claimed but which Mauritius argued was part of its territory. The ICJ had issued an advisory opinion in 2019 stating that the UK's decolonization of Mauritius was incomplete and that the Chagos Archipelago should be returned to Mauritius. However, the UK continued to exercise control.

Procedural History

Mauritius and Maldives jointly submitted the dispute to a Special Chamber of ITLOS on 24 September 2019. The Chamber delivered its judgment on 28 January 2021. It delimited the maritime boundary using the equidistance/relevant circumstances method, giving full effect to the Maldives' archipelagic baselines.

Issue

How should the maritime boundary between Mauritius and Maldives be delimited, taking into account the status of the Chagos Archipelago and the Maldives' archipelagic baselines?

Held

ITLOS delimited the boundary using the equidistance/relevant circumstances method. It gave full effect to the Maldives' archipelagic baselines, which were found to be in accordance with UNCLOS. The Tribunal did not rule on the sovereignty of the Chagos Archipelago, but noted that the ICJ's advisory opinion did not affect the delimitation because the UK was not a party to the proceedings.

Ratio Decidendi

The delimitation of the EEZ and continental shelf is governed by Articles 74 and 83 of UNCLOS, which require an equitable solution. The Tribunal applied the three-stage approach: provisional equidistance line, adjustment for relevant circumstances, and disproportionality check. The Maldives' archipelagic baselines were found to be valid and were given full effect. The Chagos Archipelago was not considered a relevant circumstance because its sovereignty was disputed and the UK was not a party. The Tribunal also held that the ICJ's advisory opinion did not bind the parties.

Obiter Dicta

The Tribunal noted that the status of the Chagos Archipelago was a matter of territorial sovereignty, which was outside its jurisdiction. It also observed that the equidistance line produced an equitable result without adjustment.

Reasoning

ITLOS began by establishing the relevant coasts and base points. It drew a provisional equidistance line using the Maldives' archipelagic baselines and Mauritius' normal baselines. The Tribunal then considered whether any relevant circumstances required adjustment of the line. Mauritius argued that the Chagos Archipelago should be given effect, but the Tribunal found that it was not a relevant circumstance because its sovereignty was disputed and the UK was not a party. The Tribunal also considered the concavity of the coast but found no cut-off effect. It then checked the provisional line for disproportionality and found it equitable. The Tribunal delimited the boundary accordingly.

Plain-English Explanation

Imagine two countries, Mauritius and Maldives, need to draw a line in the sea between them. Maldives is a group of islands and uses special baselines called archipelagic baselines. The court gave full effect to those baselines, meaning the line was drawn from them. Mauritius wanted the court to consider the Chagos Islands, which are disputed, but the court said no because the UK, which controls them, was not part of the case. So the court drew a simple equidistance line. This case shows that archipelagic baselines are important and that disputed islands may not affect the boundary.

Essay-Ready Explanation Generator

Version 1 of 4

Reference to Dispute concerning the Delimitation of the Maritime Boundary between Mauritius and Maldives in the Indian Ocean (Mauritius/Maldives) (ITLOS Case No. 28, Judgment of 28 January 2021) strengthens a Law of the Sea answer because the case reflects the principle that The delimitation of the EEZ and continental shelf is governed by Articles 74 and 83 of UNCLOS, which require an equitable solution. The Tribunal applied the three-stage approach: provisional equidistance line, adjustment for relevant circumstances, and disproportionality check. The Maldives' archipelagic baselines were found to be valid and were given full effect. The Chagos Archipelago was not considered a relevant circumstance because its sovereignty was disputed and the UK was not a party. The Tribunal also held that the ICJ's advisory opinion did not bind the parties. Applied to a problem question, the case should be used after identifying the issue as How should the maritime boundary between Mauritius and Maldives be delimited, taking into account the status of the Chagos Archipelago and the Maldives' archipelagic baselines? The stronger essay move is to connect the material facts to the court's holding, then explain whether the present facts support the same conclusion or justify distinguishing the authority.

Underlying Concepts

  • maritime delimitation
  • archipelagic baselines
  • equidistance/relevant circumstances
  • disputed sovereignty
  • ICJ advisory opinion

Precedents Applied

  • UNCLOS Articles 47, 74, 83
  • Dispute Concerning Delimitation of the Maritime Boundary between Bangladesh and Myanmar
  • Maritime Delimitation in the Black Sea

Later Treatment

  • Dispute concerning the Delimitation of the Maritime Boundary between Mauritius and Maldives (Preliminary Objections)

Key Passages

  • Archipelagic baselines are given full effect in maritime delimitation.
  • The disputed sovereignty over the Chagos Archipelago is not a relevant circumstance in this delimitation.

Significance

This case is important for its application of the equidistance/relevant circumstances method in a complex geographical setting. It clarifies that archipelagic baselines are given full effect in delimitation, and that disputed sovereignty over islands does not necessarily affect the delimitation if the disputing State is not a party. The case also shows the relationship between ICJ advisory opinions and ITLOS proceedings. For law students, it is a useful example of how tribunals handle overlapping claims and disputed territories.

Related Cases

Exam Tips

In a problem question involving maritime delimitation with archipelagic States, remember that archipelagic baselines are given full effect. The three-stage approach is the standard method. Disputed sovereignty over islands may not be a relevant circumstance if the disputing State is not a party. Use this case to argue for a strict equidistance line if no relevant circumstances justify adjustment.

Revision Checklist

  • Name the issue before discussing facts so the marker sees the legal question immediately.
  • State the holding in one sentence, then use the ratio to explain why the court reached that result.
  • Use the citation and jurisdiction to show why this authority matters for the problem you are answering.
  • Pair this case with one supporting or contrasting authority if the question tests limits, policy, or exceptions.

Problem Question Use

Use this case to argue for the application of the three-stage approach in a delimitation involving an archipelagic State. If a problem involves disputed islands, argue that they may not be relevant circumstances if the disputing State is not a party. This case is also useful to show that ICJ advisory opinions are not binding in ITLOS proceedings.

Common Pitfalls

  • Assuming that archipelagic baselines are automatically given full effect; they are, but must be valid.
  • Confusing the role of ICJ advisory opinions; they are not binding on ITLOS.
  • Overlooking the three-stage approach; it is the standard method.

Sources