The Judicial Inference of Customary International Law from State AbstentionA Study of the Two Extended Continental Shelf Judgments of 2023
DOI:
https://doi.org/10.64184/ajlps.V2.I4.Y2025.P1109-1131.439Keywords:
Extended Continental Shelf, Grey Area, CLCS, International CustomAbstract
This study examines a newly established constraint on the entitlement to the continental shelf beyond 200 nautical miles, laid down by the International Tribunal for the Law of the Sea and the International Court of Justice in their 2023 judgments in Mauritius/Maldives and Nicaragua v. Colombia. The constraint precludes a State's extended shelf from encroaching upon the 200-mile zone measured from another State's baselines, with the Court characterizing this prohibition as a customary rule. The study seeks to establish the constraint's foundations, analyze its reasoning, critique its customary basis, and clarify its effects. It adopts an analytical-critical method in dismantling the two judgments' arguments and the separate and dissenting opinions, supported by a comparison between the two courts' approaches and between the 2023 jurisprudence and its precedents. The study concludes that the customary basis is fragile, resting on inferring opinio juris from mere State abstention and silence, and that it conflicts with the practice of the Commission on the Limits of the Continental Shelf and with the single-shelf principle, besides erasing the grey area it had developed in its jurisprudence. It recommends against accepting the customary characterization unreservedly, and calls for adopting solutions more consistent with the structure of Article 76 and with the unitary nature of the continental shelf.
References
Sources and References
First: International Conventions
1. Convention on the Continental Shelf, 29 April 1958.
2. United Nations Convention on the Law of the Sea, 10 December 1982.
Second: International Judicial and Arbitral Decisions
1. Arbitration between Barbados and the Republic of Trinidad and Tobago, Award of 11 April 2006, R.I.A.A., Vol.XXVII.
2. Continental Shelf (Libya/Malta), Judgment, I.C.J. Reports 1985.
3. Delimitation of the Maritime Boundary between Bangladesh and Myanmar in the Bay of Bengal (Bangladesh/Myanmar), Judgment, ITLOS Reports 2012.
4. Dispute concerning Delimitation of the Maritime Boundary between Mauritius and Maldives in the Indian Ocean (Mauritius/Maldives), Judgment of 28 April 2023, ITLOS Case No.28.
5. North Sea Continental Shelf (Federal Republic of Germany/Denmark; Federal Republic of Germany/Netherlands), Judgment, I.C.J. Reports 1969.
6. Question of the Delimitation of the Continental Shelf between Nicaragua and Colombia beyond 200 Nautical Miles from the Nicaraguan Coast (Nicaragua v. Colombia), Judgment, I.C.J. Reports 2023 (including the Separate and Dissenting Opinions and the Declaration appended thereto).
7. The Case of the S.S. “Lotus” (France v. Turkey), Judgment No.9, P.C.I.J. Series A, No.10, 1927.
Third: Academic Research and Articles
1. Huang, Yixin, “Refuting the Assumption and Inferences in Paragraph 76 of Judgment of 13 July 2023… (Nicaragua v. Colombia)”, International Journal of Education and Humanities, Vol.17, No.2, 2024.
2. Kamiński, Tomasz & Natorski, Paweł, “Comments on the ICJ Judgment on Delimitation of the Continental Shelf between Nicaragua and Colombia beyond 200 Nautical Miles from the Nicaraguan Coast (Nicaragua v. Colombia) on 13 July 2023”, Polish Review of International and European Law, Vol.14, Iss.2, 2025.
3. Kong, Li et al., “A Critical Analysis of the ICJ’s Identification of Customary International Law in the 2023 Judgment of Nicaragua v. Colombia”, Asian Journal of International Law, 2025.
4. Li, Yunjun, “Constraining the Continental Shelf beyond 200 Nautical Miles in Maritime Delimitation Cases”, International & Comparative Law Quarterly, Vol.74, Supp. S1, 2025.
5. Liao, Xuexia, “Is There a Hierarchical Relationship between Natural Prolongation and Distance in the Continental Shelf Delimitation?”, The International Journal of Marine and Coastal Law, Vol.33, 2018.
6. Tanaka, Yoshifumi, “Recent Developments in the Jurisprudence Concerning the Delimitation of the Continental Shelf Beyond 200 Nautical Miles: Analysis of the Mauritius/Maldives and Nicaragua v. Colombia Cases”, International Law Studies, Vol.103, 2024.
7. Woker, Hilde & Bernard, Leonardo, “A New Constraint to the Entitlement of a Continental Shelf beyond 200 Nautical Miles? – Implications of the Recent Case Law”, The International Journal of Marine and Coastal Law, Vol.40, No.1, 2025.
Fourth: International Documents and Reports
1. International Law Commission, Draft Conclusions on Identification of Customary International Law, with Commentaries, Yearbook of the International Law Commission, 2018, Vol.II, Part Two.
2. Recommendations of the Commission on the Limits of the Continental Shelf in regard to the Joint Submission Made by Mauritius and Seychelles concerning the Mascarene Plateau Region, adopted 30 March 2011.
References
1. Convention on the Continental Shelf, 29 April 1958.
2. United Nations Convention on the Law of the Sea, 10 December 1982.
3. Arbitration between Barbados and the Republic of Trinidad and Tobago, Award of 11 April 2006, R.I.A.A., Vol.XXVII.
4. Continental Shelf (Libya/Malta), Judgment, I.C.J. Reports 1985.
5. Delimitation of the Maritime Boundary between Bangladesh and Myanmar in the Bay of Bengal (Bangladesh/Myanmar), Judgment, ITLOS Reports 2012.
6. Dispute concerning Delimitation of the Maritime Boundary between Mauritius and Maldives in the Indian Ocean (Mauritius/Maldives), Judgment of 28 April 2023, ITLOS Case No.28.
7. North Sea Continental Shelf (Federal Republic of Germany/Denmark; Federal Republic of Germany/Netherlands), Judgment, I.C.J. Reports 1969.
8. Question of the Delimitation of the Continental Shelf between Nicaragua and Colombia beyond 200 Nautical Miles from the Nicaraguan Coast (Nicaragua v. Colombia), Judgment, I.C.J. Reports 2023 (including the Separate and Dissenting Opinions and the Declaration appended thereto).
9. The Case of the S.S. “Lotus” (France v. Turkey), Judgment No.9, P.C.I.J. Series A, No.10, 1927.
10. Huang, Yixin, “Refuting the Assumption and Inferences in Paragraph 76 of Judgment of 13 July 2023… (Nicaragua v. Colombia)”, International Journal of Education and Humanities, Vol.17, No.2, 2024.
11. Kamiński, Tomasz & Natorski, Paweł, “Comments on the ICJ Judgment on Delimitation of the Continental Shelf between Nicaragua and Colombia beyond 200 Nautical Miles from the Nicaraguan Coast (Nicaragua v. Colombia) on 13 July 2023”, Polish Review of International and European Law, Vol.14, Iss.2, 2025.
12. Kong, Li et al., “A Critical Analysis of the ICJ’s Identification of Customary International Law in the 2023 Judgment of Nicaragua v. Colombia”, Asian Journal of International Law, 2025.
13. Li, Yunjun, “Constraining the Continental Shelf beyond 200 Nautical Miles in Maritime Delimitation Cases”, International & Comparative Law Quarterly, Vol.74, Supp. S1, 2025.
14. Liao, Xuexia, “Is There a Hierarchical Relationship between Natural Prolongation and Distance in the Continental Shelf Delimitation?”, The International Journal of Marine and Coastal Law, Vol.33, 2018.
15. Tanaka, Yoshifumi, “Recent Developments in the Jurisprudence Concerning the Delimitation of the Continental Shelf Beyond 200 Nautical Miles: Analysis of the Mauritius/Maldives and Nicaragua v. Colombia Cases”, International Law Studies, Vol.103, 2024.
16. Woker, Hilde & Bernard, Leonardo, “A New Constraint to the Entitlement of a Continental Shelf beyond 200 Nautical Miles? – Implications of the Recent Case Law”, The International Journal of Marine and Coastal Law, Vol.40, No.1, 2025.
17. International Law Commission, Draft Conclusions on Identification of Customary International Law, with Commentaries, Yearbook of the International Law Commission, 2018, Vol.II, Part Two.
18. Recommendations of the Commission on the Limits of the Continental Shelf in regard to the Joint Submission Made by Mauritius and Seychelles concerning the Mascarene Plateau Region, adopted 30 March 2011.
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