Maritime boundary decision between Mauritius and the Maldives

3 May, 2023

On 28 April 2021, a Special Chamber of the International Tribunal for the Law of the Sea handed down judgment in the merits phase of Dispute concerning delimitation of the maritime boundary between Mauritius and Maldives in the Indian Ocean (Mauritius/Maldives).

In these proceedings, Mauritius sought delimitation of a maritime boundary between the Chagos Archipelago and the Maldives pursuant to the United Nations Convention on the Law of the Sea (“UNCLOS”). The Maldives had previously raised preliminary objections to the claim, which were dismissed in a judgment dated 28 January 2021.

In the merits phase, the delimitation sought by Mauritius pertained to: (i) the Parties’ maritime entitlements within 200 nautical miles of their respective coasts; and (ii) an area which both Parties claimed as part of their continental shelf entitlement beyond 200 nautical miles of their respective coasts.

In respect of the delimitation within 200 nautical miles, the Special Chamber applied the well-established “three-stage” methodology for delimitation, which entails constructing a provisional equidistance line measured from the Parties’ base points, making any necessary adjustments based on special circumstances, and then confirming that the resulting boundary line does not result in gross disproportionality between the Parties. In this case, the Special Chamber found that: (i) Blenheim Reef was not an appropriate site for base points for the purposes of maritime delimitation; (ii) the existence of Blenheim Reef was a “relevant circumstance” which justified an adjustment to the equidistance line, giving half effect to Blenheim Reef; and (iii) there was no gross disproportionality requiring any further adjustments to the boundary line.

The Special Chamber found that it was unable to exercise jurisdiction in respect of Mauritius’ claim for delimitation of the Parties’ continental shelves beyond 200 nautical miles. This was because Mauritius had not established to a sufficient level of certainty that it had any entitlement in the area of overlapping claims. This was because: (i) Mauritius cannot establish a natural prolongation of its land territory through the continental shelf of the Maldives within 200 nautical miles that is uncontested by Mauritius; and (ii) the other two routes which Mauritius had asserted for reaching the critical foot of slope point were the subject of significant uncertainty.

Amy Sander and Naomi Hart appeared as counsel and advocates for the Maldives in this case, along with Payam Akhavan, Jean-Marc Thouvenin and Makane Mbengue.