Sovereignty Disputes under UNCLOS: Some Thoughts and Remarks on the Chagos Marine Protected Area Dispute

The United Kingdom is not entitled to declare a MPA because it is not the coastal State under UNCLOS.

Mauritius has rights as the coastal State, and the United Kingdom cannot, therefore, unilaterally declare a MPA.

The United Kingdom shall take no steps that may prevent the Commission on the Limits of the Continental Shelf from making future recommendations to Mauritius regarding the Chagos Archipelago.

The MPA is incompatible with the substantive and procedural obligations of the United Kingdom under UNCLOS and the UN Fish Stocks Agreement.

Estoppel (paras. 434-448): The Tribunal relied on the principle of estoppel to reaffirm the international legal nature of the Lancaster House Undertakings of 1965. According to the Tribunal, the undertakings became an international agreement after Mauritius became independent and any possible problem with Mauritius’ consent at the time they were made is solved by the posterior conduct of both States (representations and reliance). Regarding the element of detrimental reliance, the Tribunal found that this occurred in the form of foregone opportunities: if the Lancaster House Undertakings and their posterior reaffirmation by the United Kingdom had not taken place, Mauritius would have had the chance to assert its sovereignty more aggressively. As for the legitimacy of the reliance, the Tribunal considered that it is not necessary for a representation to take the form of a binding unilateral act, which would otherwise blur the distinction between two different sources. More informal and ambiguous representations are sufficient for the purposes of estoppel, provided the repetition and reliance are present.

The scope of application of articles 2(3) and 56(2) of the UNCLOS (paras. 499-536): Both articles are concerned with the role of other norms of international law when applying UNCLOS and until now, their scope has been somewhat unclear. Article 2(3) establishes that sovereignty in the territorial sea must be exercised “subject to other rules of international law”, while article 56(2) specifies that the exercise of rights and performance of duties in the exclusive economic zone (EEZ) should be made “having due regard” of rights and duties of third States. The question before the Tribunal was to what extent the Lancaster House Undertakings are applicable within these articles.