The Metamorphosis of Soft Law in Mauritius/Maldives: Part 2 – Jack McNally

In the Volume 28 of the Australian International Law Journal, I contributed an article on the preliminary objections judgment of the Special Chamber of the International Tribunal for the Law of the Sea (‘ITLOS’) in Delimitation of the Maritime Boundary between Mauritius and Maldives in the Indian Ocean (Mauritius/Maldives case).  In that article, I proposed some ideas as to how strategic litigation can be employed to ‘metamorphose’ soft law instruments into hard law, and provided some thoughts on the practical effect of a judgment rendered in favour of a Small Island Developing State over the objection of a much more powerful State.  Since that time, ITLOS published its judgment on the merits of the Mauritius/Maldives case.  In this post, I provide a brief summary of the merits judgment and reflect on how the commentary in my initial article has held up over time.

Procedural history

Mauritius sought to delimit the exclusive economic zone (‘EEZ’) and continental shelf between it and the Maldives in and around the Chagos Archipelago in the Indian Ocean.  The question of sovereignty over the Chagos Archipelago is a vexed one.  The Chagos Archipelago was detached from the then-colony of Mauritius in 1965 by the United Kingdom to form the British Indian Ocean Territory.  The UK expelled the Chagossians from the Archipelago and leased its largest island, Diego Garcia, to the United States to use as a military outpost.  Mauritius has, since that time, argued that the separation of the Chagos Archipelago from its territory was ineffectual and that it retains sovereignty.  

In 2010, a tribunal constituted pursuant to Annex VII of the United Nations Convention on the Law of the Sea (‘UNCLOS’) declared the United Kingdom’s declaration of a marine protected area over the Archipelago was unlawful: Chagos Marine Protected Area arbitration.  Later, the United Kingdom’s continued occupation of the Archipelago was found by the International Court of Justice (‘ICJ’) in its advisory opinion on the Legal Consequences of the Separation of the Chagos Archipelago from Mauritius in 1965 to be an internationally wrongful act of a continuing character.  That opinion was followed by General Assembly Resolution 73/295, wherein the General Assembly demanded the United Kingdom to withdraw from the Archipelago within six months and called on all States and international organizations to give effect to the opinion.  The UK continues to exercise de facto sovereignty over the Chagos Archipelago.

The preliminary objections judgment

The Maldives objected to the Special Chamber delimiting the maritime boundary between the two States on a number of bases; its core argument was that the sovereignty dispute between Mauritius and the United Kingdom was ongoing and, therefore, it was not open to the Special Chamber to undertake the delimitation exercise as Mauritius was not the ‘coastal State’ for the purposes of UNCLOS.  Mauritius’ objections were roundly and comprehensively rejected.  The Special Chamber found (among other things) that the combined effect of the Chagos Marine Protected Area arbitration, the ICJ advisory opinion, and UNGA Resolution 73/295 was that the United Kingdom’s claim over the Chagos Archipelago could not be considered anything more than a ‘mere assertion’. As such, the Special Chamber rejected the view that the United Kingdom had any sovereign right to the Chagos Archipelago, and recognised Mauritius as the coastal State for the purpose of UNCLOS.

The merits judgment

On 28 April 2023, the Special Chamber delivered a unanimous judgment delimiting the maritime boundaries between the two States.  Judges Paik and Heidar, and Judge ad hoc Schrijver each appended separate declarations to the judgment. In submissions, the Maldives contended that delimitation of the extended continental shelf was an issue outside the jurisdiction of the Special Chamber or inadmissible, but otherwise submitted coordinates in respect of the EEZ and continental shelves between the two States within 200 nautical miles.  Mauritius submitted the Special Chamber did, in fact, have jurisdiction in respect of the extended continental shelf.

Delimitation of the maritime boundary within 200 nautical miles

The Special Chamber first turned to the delimitation of the maritime boundary between the States within 200 nautical miles.  Both States agreed that the ‘well-established three-stage equidistance/relevant circumstances methodology’ applies: at [94].  The Special Chamber noted that this methodology ‘brings transparency and predictability to the process of delimitation’: at [96].  The approach involves three stages of analysis: at [97]

  • First, ‘constructing the provisional equidistance line, based on the geography of the coasts of the parties and mathematical calculations’;
  • Second, ‘determining whether there are any relevant circumstances requiring the adjustment of the provisional equidistance line and, if so, making an adjustment of the provisional equidistance line to ensure an equitable solution’; and
  • Third, ‘checking whether the delimitation line results in any significant disproportion between the ration of the respective coastal lengths and the ratio of the maritime areas allocated to each party’.

The Special Chamber proceeded with the first step, resolving a dispute between the parties as to the identification and extent of their coasts (of significance in light of the well-established principle that land dominates the sea), as well as to whether Mauritius could claim a reef as forming part of its coast and as a site of base points to be used in the construction of the line of equidistance.  The Special Chamber then selected the base points for the construction of the provisional equidistance line and drew the line accordingly. 

As part of the second step, the Special Chamber determined to adjust the provisional line of equidistance to give half effect to the Mauritian reef.  Consequently, Mauritius’ relevant coast was measured at 40.3km, and the Maldives’ at 39km (a ratio of 1:1.033 in favour of Mauritius).  Of the overlapping area within the maritime entitlements of each State, Mauritius was allocated 45,331km2 and the Maldives 47,232km2 (a ratio of 1:0.960 in favour of the Maldives).  As part of the third step of analysis, the Special Chamber found no significant disproportion between these two ratios.  The same analysis was applied to the delimitation of the continental shelves within 200 nautical miles of the two States.  The maritime boundaries between the two States were delimited accordingly.

Delimitation of the continental shelf beyond 200 nautical miles

As to the delimitation of the continental shelf beyond 200 nautical miles, the parties were in dispute as to whether Mauritius’ claim of entitlement to the continental shelf beyond 200 nautical miles was admissible on procedural grounds.  The Special Chamber rejected the Maldives’ objections and found that its claim was admissible.  The Maldives further complained that Mauritius’ claim was ‘manifestly unfounded’.  Mauritius had provided three different routes for the natural prolongation of its continental shelf.  One was found to be legally impermissible under Article 76 of the Convention as the route passed through the uncontested continental shelf of the Maldives within 200 nautical miles.  As to the other two routes, the Special Chamber was of the view that there was ‘significant uncertainty’ as to whether they could form a basis for Mauritius’ natural prolongation.  As such, the Special Chamber declined to determine the entitlement of Mauritius to an extended continental shelf.  The Special Chamber encouraged the parties to contemplate giving their consent to the Commission on the Limits of the Continental Shelf to consider each other’s submissions to the Commission, so that the Commission can make recommendations in accordance with UNCLOS Article 76(8).


The Special Chamber’s judgment on the merits in Mauritius/Maldives was largely uncontroversial.  It approached the maritime delimitation exercise according to accepted principles.  Mauritius embraced the judgment as ‘historic… the whole world has an obligation to respect it’. The Maldives described the judgment as ‘a great win for the Maldives and the people of the Maldives’. These public comments likely bode well for compliance, though the question of the delimitation of the extended continental shelf remains outstanding.

It is also worth noting that, in the intervening period between the preliminary objections and merits phases, the President of the Maldives and Prime Minister of Mauritius had exchanged correspondence, with the Maldives deciding to

“change its position” with regard to UN General Assembly Resolution 73/295… [giving] an assurance to Mauritius that it would vote “yes” to a future resolution affirming and giving effect to the Advisory Opinion of the International Court of Justice on the Legal Consequences of the Separation of the Chagos Archipelago from Mauritius in 1965’: at [51].

While the preliminary objections phase had already resolved this jurisdictional dispute as a matter of law such that it did not matter what the Maldives thought as to the efficacy of the Advisory Opinion or UNGA Resolution 73/295, the Maldives’ change in position surely provided some comfort to Mauritius and the Special Chamber that the outcome reached on maritime boundary delimitation would be complied with and supported.

Returning to my original article, I made two key observations.  First, that the victory experienced by Mauritius in the preliminary objections judgment may have been a hollow one given that the UK continues to exercise de facto control over the Archipelago.  In light of the UK’s superior might and ability to exclude Mauritius from dealing with the Chagos Archipelago, I was of the view that any decision on the merits was likely to be of little practical effect; Mauritius would remain deprived of control and marketable title over the Chagos Archipelago. It appears that this will continue to be the case.  While the maritime boundaries in and around the Chagos Archipelago have been delimited in favour of Mauritius—and the international community has an obligation to respect those maritime boundaries—the United Kingdom retains control over the Archipelago.  In the circumstances, it is difficult to attribute good marketable title to Mauritius.

Second, I discussed how international courts and tribunals may ‘daisy chain’ pieces of soft law—in this case, the ICJ advisory opinion and UNGA Resolution 73/295—to treat otherwise disputed matters as established facts, thereby ‘providing a potential “blue print” by which soft law may metamorphose into “hard law”’. I commented that the potential impact of this strategy pursued in Mauritius/Maldives could be of wider effect in light of Vanuatu’s decision to seek an advisory opinion on climate change.  Since that time, the Commission of Small Island States on Climate Change and International Law, of which Vanuatu is a member, requested an advisory opinion on the obligations of States in respect of climate change from ITLOS.  The hearing took place in September 2023 in Hamburg.  In addition, the General Assembly (led again by Vanuatu) submitted a request to the ICJ for an advisory opinion on climate change; those proceedings will be heard in 2024.  A similar request has also been made of the Inter-American Court of Human Rights.  At this stage, it is likely that ITLOS will render its advisory opinion before States make their oral statements in the ICJ proceedings.  The extent to which these international courts take notice of, interact with, and potentially confirm the findings of each other may be informative as to the question of litigation strategy and the effect of soft law going forward.  Stay tuned.

Jack McNally is a Solicitor at King & Wood Mallesons and a Research Fellow at the Faculty of Law and Justice at UNSW Sydney.