On 18 March 2015 the Permanent Court of Arbitration in The Hague (PCA) handed down its award in the matter of the Chagos Marine Protected Area Arbitration between Mauritius and the UK.

The arbitration focused on the 2010 establishment by the UK of a Marine Protected Area (MPA) around the Chagos Archipelago, in the Indian Ocean. The archipelago is under UK administration as the British Indian Ocean Territory.

The PCA found as follows:

  • It declined jurisdiction to consider Mauritius' claim that the UK was not the "coastal State" in respect of the archipelago for the purposes of the 1982 United Nations Convention on the Law of the Sea (UNCLOS). This was because the parties’ dispute related to land sovereignty over the archipelago, and their differing views on the "coastal State" were simply one aspect of this larger dispute. The land sovereignty issue was not genuinely related to the UNCLOS (paras 207-221 of the award).
  • Nor did it have jurisdiction to consider Mauritius' alternative claim that certain undertakings by the UK had endowed Mauritius with rights as a "coastal State" in respect of the archipelago. The true "object of the claim" (Nuclear Tests (New Zealand v. France), Judgment, I.C.J. Reports 1974) was to bolster Mauritius’ claim to sovereignty over the archipelago. Therefore, this alternative claim related to the same dispute in respect of land sovereignty over the archipelago as Mauritius’ previous submission (paras 228-230 of the award).
  • However, it did have jurisdiction to consider Mauritius' claim that the UK’s declaration of the MPA was not compatible with the UK’s UNCLOS obligations. The dispute between the parties in relation to the compatibility of the MPA with the UNCLOS related more broadly to the preservation of the marine environment and to the legal regime applicable to the archipelago and its surrounding waters when it was eventually returned to Mauritius (paras 283-323).
  • As a result of undertakings given by the UK in 1965 and repeated thereafter, Mauritius held legally binding rights to fish in the waters surrounding the archipelago, to the eventual return of the archipelago to Mauritius when no longer needed for defence purposes, and to the preservation of the benefit of any minerals or oil discovered in or near the archipelago pending its eventual return. In declaring the MPA, the UK failed to give due regard to these rights and breached its obligations under the UNCLOS (Chapter VI - Merits).
  • There was no dispute between the parties regarding submissions to the Commission on the Limits of the Continental Shelf, and it was therefore unnecessary for the PCA to exercise jurisdiction in respect of Mauritius' claim on this issue (paras 331-350).
  • Two PCA members issued a joint Dissenting and Concurring Opinion, setting out their view that the PCA should have found that it had jurisdiction to consider Mauritius’ claims concerning the identity of the "coastal State". The Dissenting and Concurring Opinion also expressed the view that the PCA should have exercised that jurisdiction to hold that the UK’s detachment of the archipelago from the colony of Mauritius in 1965 was contrary to the principles of decolonisation and self-determination.

Chagos Marine Protected Area Arbitration (Mauritius v. United Kingdom), 18 March 2015