UK v Mauritius and the fight for the Chagos Islands

July 3, 2011

By Natasha Harrington, pupil barrister (Essex Court Chambers, London)

Mauritius has brought a claim under UNCLOS to stop the U.K. from pulling the rug out from under its long-standing claim to sovereignty over the Chagos Islands. The proceedings are likely to start with a fierce jurisdictional battle that presents an opportunity to clarify the role and scope of jurisdiction of specialist tribunals.


On 20th December 2010 Mauritius filed a notification, statement of claim and grounds for ad hoc arbitration against the U.K under article 287 and annex VII of the UN Convention on the Law of the Sea (UNCLOS, available here, under International Environmental Law Group, Public Documents).

The Mauritian claim follows what has been described as ‘a shockingly recent act of imperial arrogance’ (see the Chagos Support Association Website). In 1965, the U.K. included the Chagos Archipelago in a new British Indian Ocean Territory. The Chagos Islands were removed from the colony of Mauritius at a price of £3 million by an agreement between the U.K. and Mauritius that provided for the return of the islands when they are no longer required for defence purposes. Between 1967 and 1973 the U.K. forcibly expelled all 2,000 residents of the Chagos Archipelago and established a naval base on its largest island, Diego Garcia, which was leased to the U.S.A. Mauritius has claimed sovereignty over the Chagos Archipelago since its independence in 1968. Chagossians have recently challenged prohibitions on return to their former homeland in the courts of the U.S.A. and the U.K., one such challenge is currently before the E.Ct.H.R. (Chagos Islanders v U.K.).

On 1st April 2010 the U.K. declared a Marine Protected Zone (MPA) around the Chagos Archipelago, where all fishing and extractive activities (oil and gas exploration) are banned, was unlawful. An absolute ban on fishing in the area might ‘be the most effective long-term way to prevent any of the Chagos Islands’ former inhabitants or their descendants from resettling…’ (Wikileaks document, 15th May 2009, Annex 2 to Mauritius’ notification). Mauritius now seeks to challenge the U.K.’s decision to create an MPA around the islands, effectively making return to the islands by Chagossians unviable, in ad-hoc arbitration under Part XV and annex VII of UNCLOS.

Grounds for Mauritius’ Claim

Mauritius has two broad heads of argument:

  1. That the U.K. has no right to declare the MPA around the Chagos Islands because it is not the ‘Coastal State’ in relation to those islands.
  2. Alternatively, that the manner in which the U.K. has established the MPA was contrary to its obligations under UNCLOS, including the duty of good faith (article 300).

Further information about the formulation and background of Mauritius’ claim can be found in a recent ASIL Insight.

Bases of Jurisdiction

Both Mauritius and the U.K. are state parties to UNCLOS, and therefore to its compulsory dispute settlement provisions in part XV. Nevertheless, jurisdiction is likely to be hotly contested, a number of the possible arguments are summarised here. This blog discuss one of the most interesting and important of these:

  •  The U.K. is likely to argue that the essence of the dispute is territorial sovereignty over the Chagos Islands, which is not a matter subject to compulsory jurisdiction under UNCLOS.

The essence of the dispute is territorial sovereignty

The Tribunal will have jurisdiction over ‘any dispute concerning the interpretation or application’ of UNCLOS under article 288(1) of that Convention. The U.K. has, in establishing the MPA, sought to exercise the rights and jurisdiction of the Coastal State in the exclusive economic zone (EEZ) around the Chagos Archipelago. Under Part V of UNCLOS the Coastal State has sovereign rights over the exploitation and conservation of natural resources and jurisdiction over preservation of the marine environment (article 56(1)), and more specifically the right to determine the allowable catch of living resources in the EEZ (article 61(1)). Mauritius’ first head of claim concerns the definition of ‘Coastal State’ and the application of that definition to the facts to determine which party is entitled to exercise the rights of the Coastal State under UNCLOS, this is prima facie within article 288(1).

Nevertheless, a claim to territorial sovereignty lies at the heart of Mauritius’ complaint and the meaning of Coastal State. The U.K. may argue that the Tribunal should formulate the real dispute (a) as a sovereignty dispute that is not ‘capable of being evaluated in relation to the standards’ in UNCLOS[1], or (b) as a mixed dispute over land and sea that is excluded from compulsory jurisdiction under Part XV of UNCLOS.

The formulation of the dispute is a matter for the Tribunal, and the fact that the parties have previously formulated it in other terms does not negate the fact that it now concerns rights and obligations under the Law of the Sea (Fisheries Jurisdiction Case, Spain v. Canada, I.C.J. Reports 1998, paragraphs 30-31). The U.K.’s (allegedly cynical) decision to create the MPA has created a dispute over rights and obligations arising under the Law of the Sea. The Tribunal is unlikely to characterise the dispute as one that exclusively concerns sovereignty and lies outside its jurisdiction. To do so might allow a State to use rights claimed under the Law of the Sea to frustrate the effectiveness of rights to territory with impunity.

However, there are indications in the articles, and the object and purpose, of UNCLOS that compulsory jurisdiction does not extend to mixed disputes over land and sea. Paragraph four of the preamble to UNCLOS states that its object is to establish a legal order for the seas and oceans ‘with due regard for the sovereignty of States’. Arguably, this means that nothing in the Convention, including Part XV, should be construed to impinge upon territorial sovereignty. Further, articles 297 and 298 were drafted to exclude, or allow the exclusion of, the most controversial legal issues from compulsory jurisdiction in order to secure agreement on Part XV.[2] Sovereignty over land territory is crucial to the interests of States. Arguably it was not explicitly excluded under article 297 because it was never thought to have been included in Part XV. Article 298(1)(a)(i) does allow State parties to exclude ‘historic bays or titles’, Mauritius and the U.K. have chosen not to do so. However, ‘titles’ may refer exclusively to objects at sea or in the seabed, such as minerals (Art.1 of Annex III: title to minerals), so this exclusion is not inconsistent with the exclusion of disputes that touch on territorial sovereignty. Significantly, article 298(1)(a)(i) distinguishes ‘any dispute that necessarily involves the concurrent consideration of any unsettled dispute concerning sovereignty or other rights over continental or insular land territory’ from other disputes concerning ‘titles’, and provides that, if a declaration under that article has been made, such disputes shall not be subject to compulsory conciliation. It would be incongruous to subject such disputes to compulsory jurisdiction if no exclusion has been made.

However, this point also emphasises the fact that the Contracting Parties must have been aware that mixed disputes would arise under UNCLOS and yet did not explicitly state that such disputes are not subject to Part XV. In many cases land and sea disputes will overlap because ‘the land dominates the sea’ and ‘the terrestrial territorial situation must be taken as starting point for the determination on the maritime rights of a coastal state’ (see Qatar v Bahrain, ICJ Reports, 2001 p.97 para 185). The broad wording of article 288(1), particularly the word ‘any’ and ‘concern’, indicates that disputes that ‘concern’ several issues are covered by Part XV of UNCLOS. In practice it may be undesirable to attempt to ‘salami-slice’ disputes[3], and be contrary to logic and judicial practice[4].

Arguably, the better approach is to recognise that a dispute concerning the interpretation or application of UNCLOS has arisen, which can only be resolved by applying rules of law concerning sovereignty. This creates a problem of applicable law, as distinct from jurisdiction (see the 58th Session of the International Law Commission, 2006, at para. 45[5] here). The problem is the prospect of fragmentation of the law if different Tribunals interpret rules fundamental to international law in different ways.

However, Mauritius and the U.K. have consented to the application by the Tribunal of rules of law outside the Law of the Sea. Part XV of UNCLOS has separate applicable law and jurisdiction clauses, and the former makes clear that the Tribunal is not limited to applying the rules of the Law of the Sea: it ‘shall apply…other rules of international law not incompatible with this Convention’. Further, article 31(3)(c) of the Vienna Convention on the Law of Treaties requires ‘any relevant rules of international law applicable in the relations between the parties’ to be taken into account in the interpretation of UNCLOS. This does not give the Tribunal  freedom to exceed its jurisdiction because the law on sovereignty over territory can be applied insofar as it is relevant to the meaning of ‘Coastal State’ in the context of UNCLOS and no further[6]. ‘Nearly exclusive consideration[7] of general international law rules should raise concerns, as it did in the Oil Platforms (Islamic Republic of Iran v U.S.A.) case,[8] if it arises because the Tribunal has lost sight of the particular gap it must fill in the definitions of UNCLOS.

The Tribunal may decide that its determination of the ‘Coastal State’ starts and ends with the rules of territorial sovereignty. It would then have to apply general international law rules without the control of a preliminary reference or an appeal tribunal. This would be particularly concerning if the International Tribunal for the Law of the Sea (ITLOS), whose members must have ‘recognized competence in the field of law of the sea’ (UNCLOS Annex VI Art.2) but not general public international law, was the default forum means of dispute settlement under Part XV of UNCLOS. However, under article 287(3) and (5) ad-hoc arbitration under Annex VII, in which arbitrators with the expertise required may be chosen or appointed, is the default. Any tribunal would be likely to recognise the pre-eminence and jurisprudence of the ICJ[9]. Yet, the determination of issues of sovereignty and statehood has not been, and should not be within its exclusive domain because they probably impact on every other area of law (see for example the Opinions of the Arbitration Commission of the Conference on Yugoslavia). The growth of specialist forums for dispute settlement requires cooperation between courts, and may increase the ‘judicial habit’ in the international community and further the development of the law.


The U.K.’s most recent attempts to control the future of the Chagos Archipelago give rise to a dispute with Mauritius concerning the interpretation or application of UNCLOS. The fact that the dispute also concerns, or springs from, post-colonial bids for territory, and will probably require the application of rules of international law concerning sovereignty is unlikely to change the nature of the dispute or defeat jurisdiction under Part XV of UNCLOS.

[1] Southern Bluefin Tuna Case (Jurisdiction and Admissibility), Australia and New Zealand v Japan at p.86 para. 48

[2] See Rosenne and Sohn, UNCLOS 1982: A Commentary, Volume V at p. 109-110.

[3] See A. Boyle, Dispute Settlement and the Law of the Sea Convention: Problems of Fragmentation and Jurisdiction, [1997] 46 ICLQ 37, at p. 47 and 49.

[4] See Southern Bluefin Tuna Case (Jurisdiction and Admissibility), Australia and New Zealand v Japan at p.95 para. 54.

 [6] Judge Higgin’s Separate Opinion in Oil Platforms (Islamic Republic of Iran v U.S.A.), I.C.J. Reports 1996, paragraphs 46 and 49.

[7] Judge Kooijmans’s Separate Opinion in Oil Platforms (Islamic Republic of Iran v U.S.A.), I.C.J. Reports 1996, paragraphs 22-23.

[8] Ibid [9].

[9] See Rosenne, The Law and Practice of the International Court 1920-1996, 1997 ed. at p. 1609.

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