Authored By: Inji Mammadli
Trinity College Dublin
- Introduction
The M/T “Heroic Idun” (No. 2) Case is a landmark judgment of the International Tribunal for the Law of the Sea (ITLOS) concerning the limits of coastal State jurisdiction in the exclusive economic zone (EEZ).[1] Arising from the interception, detention and transfer of a Marshall Islands-flagged tanker by Equatorial Guinea, the dispute required the Special Chamber to determine whether maritime security concerns could justify interference with a foreign vessel beyond the territorial sea. In doing so, the Tribunal reaffirmed the primacy of exclusive flag State jurisdiction, confirmed that exceptions to the freedom of navigation must be construed restrictively, and clarified the relationship between anti-piracy enforcement and the jurisdictional framework established by UNCLOS.
- Facts of the Case
The dispute arose from the interception of the M/T Heroic Idun, a Marshall Islands-flagged very large crude carrier (VLCC), in the Gulf of Guinea in August 2022.[2] While navigating within Nigeria’s EEZ, the vessel was approached by an unidentified naval ship, which failed to identify itself through recognised maritime channels.[3] Viewing the approach as a probable pirate threat, mutatis mutandis given the region’s security conditions, the Master altered course towards the EEZ of São Tomé and Príncipe rather than complying with the vessel’s orders.[4]
Acting upon Nigeria’s request for regional assistance under the Yaoundé maritime security framework,[5] Equatorial Guinea intercepted the tanker in the EEZ of São Tomé and Príncipe, compelled it to proceed to Luba,[6] and detained the vessel and its crew.[7] Criminal and administrative proceedings followed, culminating in substantial financial penalties and the transfer of the vessel and crew to Nigeria after ninety-two days of detention.[8]
The Marshall Islands maintained that these measures were ultra vires UNCLOS, violating the freedom of navigation, exclusive flag State jurisdiction, and the carefully delimited enforcement powers of coastal States in the EEZ. The parties ultimately submitted the dispute to a Special Chamber of ITLOS by Special Agreement.
- Legal Issues
The Special Chamber was required to determine several jurisdictional and substantive questions arising under UNCLOS. It considered whether the proceedings were barred by the Monetary Gold principle or rendered inadmissible by the Marshall Islands’ alleged failure to exhaust local remedies.[9] The Monetary Gold principle is a procedural limitation on the exercise, rather than the existence, of international jurisdiction, precluding a tribunal from determining a dispute where the legal responsibility of a non-consenting third State constitutes the very subject-matter of the case.[10] It does not apply where the conduct of the respondent State can be assessed in limine and independently of any determination concerning the rights or responsibility of the absent State.
On the merits, the Chamber examined whether Equatorial Guinea lawfully intercepted and detained the Heroic Idun under the Convention’s anti-piracy regime, particularly Articles 100-107 and 110 of UNCLOS.[11] It also considered whether Equatorial Guinea possessed prescriptive or enforcement jurisdiction to criminalise the vessel’s conduct in the EEZ, impose penalties, and detain the vessel and its crew consistently with Articles 56, 58, 87 and 92 of UNCLOS.[12] Finally, the Chamber addressed the relevance of external international law through Articles 293 and 297 of UNCLOS,[13] the applicability of considerations of humanity to the crew’s detention,[14] and the principles governing causation and reparations for internationally wrongful acts.[15]
- Arguments of the Parties
The Marshall Islands argued that Equatorial Guinea had fundamentally disregarded the jurisdictional framework established by UNCLOS.[16] It maintained that the interception of the Heroic Idun in the EEZ of São Tomé and Príncipe constituted an unlawful interference with the freedom of navigation and the exclusive jurisdiction of the flag State under Articles 87, 90 and 92 of the Convention.[17] According to the Marshall Islands, Equatorial Guinea possessed no independent legal authority to compel a foreign merchant vessel to alter course, escort it into its ports, or subject it to criminal and administrative proceedings.[18] Every enforcement measure adopted thereafter was therefore alleged to be legally tainted as a consequence of the original unlawful interception.[19]
It also argued that the alleged suspicion of piracy was sans fondement: allegations of oil theft could not, ipso facto, satisfy Article 101, nor did Article 100 confer an autonomous power of interdiction.[20] Consequently, all subsequent enforcement measures were said to be vitiated ab initio.[21] The Marshall Islands further alleged unlawful extension of coastal State jurisdiction, breaches of considerations of humanity, and violations of obligations incorporated through UNCLOS’ “gateway provisions,” seeking declaratory relief, restitution, compensation, satisfaction, and guarantees of non-repetition.[22]
Equatorial Guinea raised both jurisdictional and merits-based objections. It argued that the dispute was barred by the Monetary Gold principle,[23] inadmissible for failure to exhaust local remedies,[24] and confined ratione materiae to UNCLOS obligations.[25] On the merits, it maintained that the interception constituted a lawful anti-piracy operation undertaken pursuant to Nigeria’s request and the Yaoundé regional security framework.[26] Article 100, it submitted, authorised cooperative action against suspected maritime criminality, while the ensuing detention, sanctions, and treatment of the crew fell within its lawful coastal State jurisdiction.[27] It further disputed both causation and the quantum of damages claimed.[28]
- Court’s Reasoning and Analysis
The Special Chamber reaffirmed that UNCLOS embodies an exhaustive and carefully calibrated allocation of jurisdiction between flag and coastal States, cuius derogatio is permissible only where the Convention expressly so provides.[29] Maritime security considerations, however compelling en fait, cannot enlarge the enforcement powers conferred en droit.
The Chamber dismissed Equatorial Guinea’s preliminary objections. It held that the Monetary Gold principle concerns the propriety, rather than the existence, of jurisdiction and was therefore inapplicable,[30] as the legality of Equatorial Guinea’s conduct could be determined independently of Nigeria’s rights.[31] Likewise, the local remedies rule did not apply:[32] the Marshall Islands asserted its own rights jure proprio as flag State,[33] while the crew’s involuntary presence in Equatorial Guinea failed to establish the requisite jurisdictional nexus.[34]
On the merits, the Chamber rejected Equatorial Guinea’s reliance on the anti-piracy regime.[35] Suspicion of oil theft or organised maritime crime was not, ipso facto, a reasonable suspicion of piracy within the meaning of Article 101,[36] nor could the Heroic Idun plausibly be characterised as a pirate “mothership.”[37] Crucially, Article 100 was held to impose only an obligation of due diligence to cooperate;[38] it confers no autonomous right of interdiction, such powers arising exclusively under the narrowly circumscribed provisions of Articles 101–107 and 110.[39]
The Chamber further concluded that Equatorial Guinea lacked both prescriptive and enforcement jurisdiction to regulate the vessel’s conduct in the EEZ, require prior authorisation for entry, or penalise the absence of a displayed flag.[40] Reaffirming that the EEZ is sui generis rather than an extension of territorial sovereignty,[41] it found multiple violations of the freedom of navigation and the principle of exclusive flag State jurisdiction.[42] It also confirmed that considerations of humanity govern the treatment of detained crews,[43] construed Articles 293 and 297 restrictively,[44] and awarded reparation for the losses directly attributable to the unlawful interception and detention.[45]
- Holding and Significance
The Special Chamber substantially upheld the Marshall Islands’ claims, holding that Equatorial Guinea violated UNCLOS by unlawfully intercepting, diverting, detaining, and transferring the Heroic Idun and its crew.[46] It found that these measures infringed the freedoms of navigation and exclusive flag State jurisdiction under Articles 87, 90, and 92, while the ensuing detention, criminal proceedings, and financial penalties constituted ultra vires assertions of coastal State jurisdiction in the EEZ.[47] The Chamber further found breaches concerning notification of the flag State and the treatment of the crew, awarding compensation for both material and non-material injury.[48]
The ratio decidendi is unequivocal: exclusive flag State jurisdiction remains the point de départ of the Convention’s jurisdictional order, from which derogation is permissible only where UNCLOS expressly provides. Article 100 creates a duty to cooperate, not an autonomous power of enforcement; a fortiori, neither domestic legislation nor regional security arrangements may enlarge the Convention’s carefully delimited allocation of maritime jurisdiction.
- Commentary
The Heroic Idun judgment constitutes a notable reaffirmation of the constitutional architecture of UNCLOS. Face aux contemporary maritime security concerns, the Special Chamber declined to dilute the Convention’s jurisdictional equilibrium, insisting that any derogation from exclusive flag State jurisdiction must find an explicit basis within the Convention itself.
The principal contribution of the judgment lies in the interpretation of Article 100. The Chamber drew a sharp distinction between the general duty to cooperate in the repression of piracy and the Convention’s discrete enforcement powers, holding that Article 100 imposes only an obligation of conduct and confers no autonomous right of interdiction.[49] This reading preserves the effet utile and internal coherence of UNCLOS by preventing broad anti-piracy objectives from circumventing the carefully delimited enforcement regime of Articles 101-107, while placing a principled constraint upon regional security arrangements as an independent basis for coercive maritime action.
Equally significant is the Chamber’s rigorous conception of the EEZ as a sui generis maritime zone rather than a projection of territorial sovereignty. By distinguishing prescriptive from enforcement jurisdiction and rejecting attempts to criminalise the mere presence of a foreign vessel in the EEZ, the judgment offers a compelling rejoinder to the phenomenon of creeping jurisdiction and fortifies the freedom of navigation against incremental encroachment.
The judgment is not, however, beyond criticism. Its restrictive construction of Articles 293 and 297 preserves the consensual foundation of international adjudication but correspondingly narrows ITLOS’ capacity to engage directly with the increasingly intertwined regimes of human rights and maritime safety. Quaere, therefore, whether the relationship between UNCLOS and the broader corpus of international law has been satisfactorily settled, or merely postponed for future jurisprudence.
- Conclusion
The M/T Heroic Idun (No. 2) judgment is a landmark contribution to the jurisprudence of UNCLOS, clarifying the limits of coastal State authority and reaffirming the centrality of exclusive flag State jurisdiction in the EEZ. By rejecting attempts to justify expansive enforcement measures through broad invocations of maritime security, the Special Chamber reinforced the principle that interference with foreign vessels must remain firmly grounded in the Convention’s express provisions.
Beyond resolving the dispute between the Marshall Islands and Equatorial Guinea, the judgment provides authoritative guidance on the relationship between anti-piracy operations, freedom of navigation, and coastal State jurisdiction. Its interpretation of Article 100, its reaffirmation of the limits of jurisdiction in the EEZ, and its careful approach to reparations are likely to influence future maritime disputes and anti-piracy operations. As such, Heroic Idun stands as an important precedent safeguarding the balance of rights and obligations established by UNCLOS while adapting its principles to contemporary maritime security challenges.
Reference(S):
[1] M/T “Heroic Idun” (No 2) (Marshall Islands v Equatorial Guinea) (Judgment) [2026] ITLOS Case No 32, Special Chamber [Heroic Idun].
[2] Ibid, para 71.
[3] Ibid, paras 72-73.
[4] Ibid, paras 73-74.
[5] Ibid, paras 75, 334.
[6] Ibid, para 76.
[7] Ibid, para 77.
[8] Ibid, paras 80-81.
[9] Ibid, para 105.
[10] Monetary Gold Removed from Rome in 1943 (Italy v France, United Kingdom and United States of America) (Preliminary Question) [1954] ICJ Rep 19, paras 52-53.
[11] Heroic Idun, paras 247-304.
[12] Ibid, paras 314-359.
[13] Ibid, paras 141-142, 148-149.
[14] Ibid, paras 407-408, 411.
[15] Ibid, paras 483, 496-497.
[16] Ibid, para 62(a).
[17] Ibid.
[18] Ibid, paras 193-198, 315-320.
[19] Ibid, para 308.
[20] Ibid, paras 252, 254, 233.
[21] Ibid, paras 308, 310.
[22] Ibid, paras 315, 386, 151, 424, 85.
[23] Ibid, paras 110, 113-119. The formal request for dismissal on this ground is in para 66(a).
[24] Ibid, paras 159-160. Formal submission is in para 66(b).
[25] Ibid, paras 93, 140, 147.
[26] Ibid, paras 209-210, 334.
[27] Ibid, paras 230-231.
[28] Ibid, paras 67(a), 479, 535, 580, 608, 621, 629.
[29] Ibid, paras 204 (quoting art 92 UNCLOS), 207, 227.
[30] Ibid, para 109, 137.
[31] Ibid, para 134.
[32] Ibid, para 178.
[33] Ibid, para 171.
[34] Ibid, para 177.
[35] Ibid, para 304.
[36] Ibid, para 276.
[37] Ibid, paras 288-292, 304.
[38] Ibid, para 238.
[39] Ibid, para 247.
[40] Ibid, paras 357-358.
[41] Ibid, para 352.
[42] Ibid, paras 306, 359.
[43] Ibid, paras 407-408.
[44] Ibid, para 149.
[45] Ibid, paras 497, 531, 664.
[46] Ibid, para 306.
[47] Ibid, paras 357-369.
[48] The formal awards for reparations are listed in the operative clauses of the judgment.
[49] Ibid, paras 238, 247.
