1.3 Methodology and sources
This thesis adopts a qualitative doctrinal legal method. The analysis examines the content, scope, and development of flag State obligations relating to the protection of marine biological diversity in the ABNJ, with particular attention to the EIA regime under the BBNJ Agreement. The analysis is grounded in recognised sources of international law and proceeds through a reading of treaty texts, relevant customary rules, and international jurisprudence, rather than through the study of domestic implementation or practice. Interpretation of the BBNJ Agreement and UNCLOS is undertaken in accordance with Articles 31 and 32 of the Vienna Convention on the Law of Treaties (‘VCLT’) (1)Vienna Convention on the Law of Treaties (adopted 23 May 1969, entered into force 27 January 1980, Vienna) 1155 UNTS 331 (VCLT), articles 31–32, which has been referred to as being a codification of existing customary international law in international jurisprudence(2)Arbitral Award of 31 July 1989 (Guinea-Bissau v Senegal) [1991] ICJ Rep 53, paragraph 48.. The analysis applies the ordinary meaning of treaty terms in their context and in light of their object and purpose, and approaches the BBNJ Agreement as an implementing agreement that must be read in harmony with UNCLOS. As a treaty governed by international law, the BBNJ Agreement is subject to this general interpretative framework. While it does not expressly refer to the VCLT, the reference in the BBNJ Agreement’s Preamble’s to “rules of the law of treaties”(3)Preamble BBNJ Agreement implicitly engages these customary international rules, which are consistently applied by international courts and tribunals(4)Makane Moïse Mbengue, ‘Rules of Interpretation (Article 32 of the Vienna Convention on the Law of Treaties)’ (2016) 31 ICSID Review – Foreign Investment Law Journal, volume 31, issue 2, page 388.
Emphasis is placed on the object and purpose of the BBNJ Agreement as reflected in its preamble, which seeks to ensure the conservation and sustainable use of marine biological diversity in ABNJ through enhanced international cooperation and effective implementation of UNCLOS, while respecting the balance of rights, obligations, and interests established under UNCLOS(5)Ibid n33. In applying this framework, the analysis recognises that the wording of the BBNJ Agreement reflects a negotiated compromise(6)Pascale Ricard, ‘The Advent of the 2023 “BBNJ” Agreement: A Preliminary Legal Analysis’ (2023) Environmental Policy and Law, Vol.53, Issue 5-6 and may, in certain respects, appear more progressive than the level of regulatory commitment that States were willing to expressly codify during negotiations(7)See Position paper of the International Chamber of Shipping, ‘Textual proposals submitted by delegations by 20 February 2020, for consideration at the fourth session of the intergovernmental conference’ (2020) https://www.un.org/bbnj/sites/www.un.org.bbnj/files/textual_proposals_compilation_article-by-article_-_15_april_2020.pdf, accessed 29.04.2026, page 222.
In several areas, the BBNJ Agreement employs open-textured formulations, indeterminate standards, and deliberately flexible language, while (currently) remaining largely unaccompanied by consolidated preparatory materials, subsequent practice for this thesis to consult, or institutional guidance. This is particularly the case in relation to the operation of the EIA regime, where the obligation to conduct an assessment is triggered by evaluative standards(8)Articles 28-29 BBNJ Agreement and where existing assessment frameworks must be evaluated for equivalency(9)Article 29 BBNJ Agreement. These features give rise to interpretative uncertainty. Similar difficulties also arise in relation to the relationship and non-undermining clauses, which are framed in accommodating rather than hierarchical terms(10) Article 5 BBNJ Agreement, and in the articulation of flag State obligations, which rely on standards of conduct rather than precise regulatory specification(11)Articles 16 and 28(1) BBNJ Agreement read together with Articles 94 and 192 UNCLOS. In these situations, interpretation therefore relies primarily on the treaty text, its context, and its object and purpose, given the limited availability of sources and the absence of settled implementation or consistent State practice.
This interpretative approach is especially relevant in relation to the EIA regime, which was a contested element of the negotiations(12) Ibid n36. The thesis examines how the BBNJ Agreement operates within the law of the sea framework, including its interaction with existing sectoral regulation. Instead of assuming that the BBNJ Agreement neatly solves all conflicts with existing ocean governance regimes, the thesis examines how specific provisions of the BBNJ Agreement are designed to allow it to operate alongside those regimes.
Where relevant, the thesis considers subsequent agreements and subsequent practice under Article 31(3) of the VCLT, while recognising that such practice remains limited given the recent adoption of the BBNJ Agreement. For the same reason, the existing academic literature addressing the BBNJ Agreement, particularly its environmental impact assessment obligations, remains relatively limited, as the treaty has only recently been ratified. Supplementary means of interpretation under Article 32, including preparatory work and the circumstances of conclusion, are relied upon where the treaty text is ambiguous or where a strictly literal reading would be inconsistent with the negotiated balance reflected in the instrument.
The primary materials analysed include UNCLOS, the BBNJ Agreement, relevant IMO instruments, and the jurisprudence of the International Court of Justice (‘ICJ’), International Tribunal for the Law of the Sea (‘ITLOS’), and arbitral tribunals concerning due diligence, environmental assessment, and flag State obligations. These sources are read alongside travaux préparatoires, official negotiating and explanatory documents, and selected academic commentary. The preparatory work of the BBNJ Agreement does not consist of a single consolidated set of travaux préparatoires, but rather of a distributed body of official negotiating materials, including successive draft texts and the formal reports of the Intergovernmental Conference. These materials are treated as supplementary means of interpretation under Article 32 of the VCLT and are relied upon with caution to confirm the meaning derived from the text, context, and object and purpose of the BBNJ Agreement.
This analysis is subject to certain limitations. It does not engage in a comparative evaluation of domestic environmental legislation or national approaches to treaty interpretation. While the thesis engages with the development of environmental assessment in international public law leading up to UNCLOS and the adoption of the BBNJ Agreement, this discussion is intended to provide contextual and doctrinal background rather than a comprehensive assessment of the EIA regime. The substantive analysis remains concerned with flag State obligations relating to the protection of marine biological diversity in ABNJ. Considering this focus, the thesis also accords limited attention to elements of the BBNJ Agreement that are less directly connected to the examination of flag State obligations through the lens of EIA, such as for example, the parts dedicated to marine genetic resources or capacity-building and the transfer of marine technology.