It has been human nature for thousands of years to live near estuaries, seas and oceans. Human activities in the ocean are regulated by multiple jurisdictional zones under international law. Accordingly, the law of the sea is founded on the spatial distribution of a state’s jurisdiction. It is necessary to consider maritime delimitation issues when maritime zones overlap, which is covered by the Convention on the Territorial Sea and the Contiguous Zone, the Convention on the Continental Shelf and the United Nations Convention on the Law of the Sea (UNCLOS). Although delineating maritime boundaries and establishing mechanisms for resolving international conflicts related to them was one of UNCLOS’s key objectives, the law of maritime delimitation is distinguished by the fact that it has been developed by international courts and tribunals.

There has been widespread acceptance of the three-stage approach, also known as the equidistance/relevant circumstances method, after decades of practice. In detail, the Tribunal will draw a provisional equidistance line based on coastal geography and calculations, adjust it for relevant circumstances in order to achieve an equitable result and ensure that the adjusted line does not result in significant disproportion between coastal lengths and allocated maritime areas. In terms of balancing predictability and flexibility, the three-stage approach may be more effective. While this is true, the three-stage approach is not perfect since socio-economic factors – mainly – as well as other non-geographical factors form the basis of concepts such as continental shelf and exclusive economic zone (EEZ).

With this backdrop in mind, the new book of Dr. Nicholas A. Ioannides, The Predominant Interest Concept and Maritime Delimitation: Safeguarding Predictability and Enhancing Equitableness, is timely. According to the author, international jurisprudence has played a significant role in advancing maritime delimitation law. Under the guise of “predominant interest” (PI) in maritime delimitation, non-geographical factors as a whole should be taken into consideration to achieve equitable results, highlighting the importance of ensuring predictability and enhancing equity. This book consists of five chapters in addition to the introduction and conclusion.

Chapter 1 begins with a discussion of PI’s origins. Since 1958, Britain and France have been working to resolve the issue of the delimitation of their respective continental shelves in the English Channel and the Atlantic Ocean. An ad hoc Court of Arbitration was convened in 1977 to hear this dispute. According to the Court of Arbitration, a number of non-geographical factors, together with physical geography, demonstrated the PI of France in the English Channel. France has the right to the major share of the waters in the vicinity of the Channel Islands, otherwise a bundle of special rights relating to political geography and economic interests would be severely affected (p. 20). Based on the author’s argument, the 1977 Award transformed non-geographical factors into a broader factor known as PI, which was taken into consideration in its entirety for the first time (pp. 7–8).

Ioannides continues his enquiry on the definition and content of PI with a second chapter. The concept of PI entails that a conglomeration of non-geographical factors indicates the existence of vital/fundamental interests in a given maritime area, which supersede the interests of any other state in there (p. 33). State conduct as reflected in maritime activities relevant to non-geographical factors (security/defence, navigation, economic considerations and environmental protection measures) taken in accumulation shows the presence of vital/fundamental interests superior to those of other states, thus indicating a coastal state’s PI. For the continental shelf, the EEZ and the high seas, PI should not be confused with effectivités; there is no effective control (p. 34). PI is not determined by the amount of activities displayed in an undelimited or disputed area for a state, nor should it be compared between states’ economies. Finally, an aspect of PI is the concept of “accumulation of factors”, which implies that non-individual factors can influence collective outcomes. It is noteworthy that both international law and state practice appear to accept the concept of “accumulation of factors” (p. 64). The PI concept is not applicable to territorial sea delimitation due to the different nature of this zone. Under the aegis of PI, all relevant non-geographical circumstances should be evaluated in aggregate. In view of the fact that the PI concept was articulated at the dawn of maritime delimitation law, it should be slightly adapted to fit the now well-established three-stage approach. PI can be used at the second stage of delimitation to check whether the boundary is equitable.

Chapter 3 reviews the role of non-geographical factors in state practice. State practice, as exhibited at the UN Law of the Sea Conferences, supports the view that non-geographical factors must have a prominent role in maritime zones and delimitations (pp. 71–84). According to maritime delimitation agreements, socio-economic/non-geographical factors such as fisheries, hydrocarbons, security/defence, navigation and environment play an important role. In this Chapter, the author highlights the discrepancy between the importance assigned to non-geographical factors by states and the approach taken by international law in relation to such factors. Due to this inconsistency, PI is essential for bridging the gap between state practice and international adjudicatory bodies’ general standpoint.

After that, it is necessary to examine the position of international jurisprudence towards non-geographical factors, which is discussed in Chapter 4. A notable fact is that prior to 2009 and the formulation of the three-stage approach, no specific, methodologically clear or structured delimitation method existed. However, international courts and tribunals have consistently emphasised certainty and predictability, so non-geographical factors have yet to be properly incorporated into the delimitation process, regardless of maritime delimitation law’s evolution (p. 104). To avoid arbitrary rulings and potential criticism, international courts and tribunals have always favoured geographical factors that are considered neutral and objective. In continental shelf/EEZ delimitation cases, international jurisprudence has not directly weighed non-geographical factors such as economic factors, despite their central position in state practice (p. 108). Lack of a structured delimitation method might have discouraged international courts from applying non-geographical factors. Establishing maritime boundaries presents international courts and tribunals with challenges and generates new ones as they try to resolve them (p. 106). Due to their inextricable connection to continental shelf/EEZ concepts, socio-economic factors and security/defence considerations play an important role in delimitation. Economic factors should be considered in maritime delimitation to ensure that states are able to protect their inherent sovereignty rights (p. 113). International courts and tribunals can assess whether the geographically dictated outcome is equitable by considering economic interests, fisheries, hydrocarbons, navigation and other elements. The opinions of several judges, such as José Luis Bustamante y Rivero, Luis Padilla Nervo and scholars, such as Derek William Bowett and Prosper Weil, favoured the use of non-geographical elements in maritime delimitation (pp. 126–30).

As part of the three-stage approach, Chapter 5 provides a comprehensive analysis of PI’s introduction and application in the delimitation process. A key objective of maritime delimitation is to reach an equitable result, according to international jurisprudence. As opposed to the original content in the Anglo-French case, the modern notion of PI comprises non-geographical elements in accumulation, confirming the presence of vital/fundamental interests in a particular maritime area (p. 136). Furthermore, the PI concept does not imply a comparison between respective economies or endorsement of excessive maritime claims, but rather the coastal state asserting PI must demonstrate that it has vital/fundamental interests which are more important to it than to any other state and cannot be denied these interests (p. 137). However, there is a “fundamental norm” on which maritime delimitation is contingent according to international case law, namely that delimitation “must be based on the application of equitable criteria and the use of practical methods capable of ensuring an equitable result”, even though international courts and tribunals primarily focus on outcomes rather than processes (p. 141). Ioannides argues that international courts and tribunals should consider integrating PI into the second phase of the second stage (“Stage 2.5”) of the three-stage approach to determine if a solution has been achieved after examining geographically relevant circumstances and possibly adjusting the provisionally drawn equidistance/median line. This means that the second stage should be divided into two phases: (1) In the first place, courts and tribunals will examine whether any geographically relevant circumstances warrant an adjustment of the provisional equidistance/median line; and (2) Through the application of PI, it will be examined whether the solution reached based on geographical factors is equitable. Essentially, the line drawn will be checked to determine whether it denies one of the parties’ vital/fundamental interests in a maritime area where it has PI (p. 167). A different outcome may have been achieved in cases such as the Gulf of Maine, Black Sea, Nicaragua v Colombia, Somalia v Kenya if PI had been applied (pp. 175–80).

Objectively, PI has not received much attention in maritime delimitation law to date probably due to its complex nature, the convoluted manner in which states have invoked the notion and the inherent reluctance of international jurisprudence to include non-geographical factors in maritime delimitation (p. 138). In light of this, this book represents a commendable effort to reconstruct the content of maritime delimitation law. Through original archival research, it challenges many established orthodoxies concerning maritime boundary delimitation. The purpose of PI is to ensure that non-geographical and geographical factors alike are taken into account in combination with a view to reaching a truly equitable maritime delimitation. In the study and practice of maritime boundary delimitation, PI can play a leading role. Therefore, Sir Malcolm Evans from the University of Oxford believes the book is a game-changing contribution to the study and practice of maritime boundary delimitation. It should be noted, however, that at least two aspects require further study. In PI, it is important to consider non-geographical factors and construct them as a whole. PI results from the transformation of maritime activities/conduct into fundamental/vital interests. We still need to explore the details of this transformation process and how to achieve the inherent trade-offs between various activities. Additionally, although the author has conducted some empirical research in order to incorporate PI into the three-stage approach through few cases, these are far from sufficient and require more empirical analysis to be able to evaluate it.