On 27 May 2026, the ITLOS Special Chamber rendered its judgment in M/T Heroic Idun (No. 2). Brought by the Marshall Islands against Equatorial Guinea, the case concerns the lawfulness of the latter’s arrest and detention of the vessel and its crew. At first glance, the case appears to fall squarely under UNCLOS, as it revolves around key law of the sea principles, such as freedom of navigation, exclusive flag State jurisdiction, coastal States’ obligations in the EEZ. However, the parties’ invocation of external human rights and maritime treaties presented the Special Chamber with a welcome opportunity to revisit a long-standing question: to what extent do UNCLOS tribunals have jurisdiction over external rules? This post discusses where the Special Chamber offered clarity, and where its approach leaves notable inconsistencies and uncertainties.
Jurisdiction, applicable law & renvois: the law
The jurisdiction an UNCLOS tribunal is found under Article 288(1), while applicable law is set out under Article 293. Despite the early hiccups (see M/V Saiga (No.2), para 155; Guyana v. Suriname, para 406; contra MOX Plant, Order No. 3, para. 19), case law in the past decade (see Arctic Sunrise, para. 192, The Duzgit Integrity, para. 208) has converged to establish that Article 293 cannot be used to extend an UNCLOS tribunal’s jurisdiction to, as the Special Chamber recalled, ‘making determinations about breaches of other treaties or other rules of international law’ (paras. 143, 144). Instead, it only allows having recourse to ‘external treaties and rules of international law that are not incompatible with the Convention when resolving a dispute concerning the interpretation or application of the Convention’ (para. 145).
This does not mean, however, that an UNCLOS tribunal cannot determine breaches of external rules. As the Chamber made clear, this can indeed happen when external rules constitute ‘a source of jurisdiction, or [when] the treaty otherwise directly applies pursuant to the Convention’ (para. 142). A prominent example of external rules directly applying would be the renvois found in various provisions of the Convention, also referred to as ‘gateway provisions’ by the parties to this case. In principle, a renvoi indicates that the provision containing it is incomplete on its own and must be interpreted using the referenced external rule. The exact role that a renvoi provision performs and the impact that the external rule has on the referring legal instrument can only be determined on a case-by-case basis, as correctly recalled by the Special Chamber (para. 154).
The same applies to jurisdiction conferred via a renvoi. Depending on the content and function of each individual renvoi, an UNCLOS tribunal may have jurisdiction to decide issues outside the Convention. For example, if a provision contains a renvoi which is prescriptive in a way that compliance with the Convention depends upon compliance with the external rules, a tribunal could be allowed to find violations of these rules. Article 2(3) on the exercise of coastal States’ sovereignty over the territorial sea contains such a renvoi.
Another type of renvoi is found in Article 297(1)(c). This article governs dispute settlement rather than substantive rights, thus this renvoi serves a different function. Rather than creating obligations under the external rule, it confirms that UNCLOS tribunals have jurisdiction over disputes regarding a coastal State’s sovereign rights under UNCLOS when those disputes centre around the application of external environmental standards, even if they are not found under the Convention.
In practice, UNCLOS tribunals have not maintained a clear approach to interpreting and applying different types of renvoi. The Heroic Idun provided a timely occasion for the Special Chamber to contribute to clarifying this issue – but as discussed next, it was an opportunity missed.
Jurisdiction, applicable law & renvois: the application in Heroic Idun
As we argued above, the role and function of the renvois need to be carefully considered in each instance in order to determine the existence and scope of jurisdiction. However, in Heroic Idun, the Chamber failed to engage with the specific substantive provisions containing the renvois, such as Articles 2(3), 56(2), 58(2), 87(1), thereby making no distinction between these different renvois. This led to a categorical rejection of jurisdiction to determine breaches of other rules of international law even if they are brought into UNCLOS through renvois (paras 154, 155, 450).
As regards the procedural renvoi in Article 297(1)(c), the Chamber interpreted this provision to only allow recourse to ‘sources beyond the Convention that are considered necessary to interpret claims under the Convention’. On this basis, the Chamber again concluded it lacked jurisdiction to find breaches of these external treaties such as the IMO instruments invoked by the Marshall Islands (para. 149). This differed to the much broader interpretation adopted by the Chagos MPA tribunal in 2015, which viewed this renvoi as conferring jurisdiction over disputes ‘beyond the four corners of the Convention’ without requiring a link with UNCLOS (Chagos MPA, para 316). Given that renvois may allow for jurisdiction over violations of external rules in a dispute relating to UNCLOS as argued above, the Chamber’s restrictive approach – or Chagos MPA’s expansive one for that matter – does not do justice to the sophisticated mechanism of renvois nor to the jurisdiction that they generate.
Interestingly, while theoretically solidifying the distinction between jurisdiction and applicable law, the Chamber actually blurred these concepts when examining human rights arguments regarding the vessel’s detention and crew’s treatment. The question at hand was whether considerations of humanity inform the interpretation and application of Articles 2(3) and 87(2). Instead of engaging with the relevant renvois to answer this question, the Chamber only observed that ‘in the jurisprudence of the Tribunal, considerations of humanity and humanitarian concerns have not been linked to specific provisions of the Convention’ (para. 408). This alone should presumably have been sufficient for the Chamber, based on the distinction that it has made, to find that the Chamber would not have jurisdiction in the first place over disputes relating thereto.
Yet, the Chamber still proceeded to examine the treatment of individuals during detention and interrogation under the umbrella of ‘humanitarian concerns’ (paras 308 to 313). Curiously, this lengthy examination did not at all contribute to the finding of a violation of UNCLOS. Instead, the Chamber simply concluded that the interception and seizure of the vessel and its crew was illegal in the first place and that the detention of the vessel and its crew ‘was a continuing wrongful international act [sic]’ (para. 312) which extended ‘over the entire period during which the act continued’ (para. 413). Such a conclusion could have been equally made without the discussion on humanitarian concerns. Even more curiously, the Chamber concluded that the transfer of the vessel and its crew ‘was unlawful because it was done without consideration of due process of law’ (para. 414). Here the Chamber found a breach of a general rule of due process of law not regulated under the Convention without any explanation of how it is linked to UNCLOS provisions – contrary to what it had stated itself earlier in the judgment. The Chamber attempted to portray what it was doing as merely having regards to human rights standards, as opposed to ‘applying directly or determining breaches of human rights treaties’ (para. 417). However, this seems to stand in contradiction with the direct finding of violation in paragraph 414, and in any case, still begs the question of which provision of the Convention is being interpreted and applied in this case. To bypass its earlier rejection of jurisdiction over external rules – in this instance human rights rules – the Chamber anchored its concerns about crew treatment to a prior violation, resulting in self-contradictory reasoning.
Conclusion
The Heroic Idun judgment strives to cement the distinction between jurisdiction and applicable law for UNCLOS tribunals, particularly resisting the use of applicable law to expand jurisdiction. However, the Chamber’s inconsistent reasoning and its treatment of the ‘considerations of humanity’ dictum muddied the line between the two concepts once again. Further, by adopting a restrictive and perhaps one-dimensional reading of the renvois, the Chamber missed an opportunity to provide more clarity on the different ways in which external rules can be incorporated into UNCLOS and, in turn, how jurisdiction can be established over external rules. Ultimately, whilst the Chamber set out to draw the limits of its jurisdiction, its execution has arguably further obscured the boundaries of UNCLOS jurisdiction.