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Part B Commentary on Judgments and Awards in Maritime Boundary Delimitation Disputes, 22 Peru v. Chile (Judgment of the International Court of Justice, 27 January 2014)

From: A Practitioner’s Guide to Maritime Boundary Delimitation

Stephen Fietta, Robin Cleverly

From: Oxford Public International Law (http://opil.ouplaw.com). (c) Oxford University Press, 2015. All Rights Reserved. Subscriber: Volterra Fietta; date: 26 October 2020

Coastal states — Delimitation — Straits — Territorial sea — UNCLOS (UN Convention on the Law of the Sea)

(p. 533) 22  Peru v. Chile (Judgment of the International Court of Justice, 27 January 2014)

Case Note: treaty interpretation—maritime boundary established by evidence of ‘tacit agreement’ by the 1950s—seaward extent of tacitly agreed boundary—all-purpose nature of tacitly agreed boundary—relevant practice of the parties—relevance of contemporaneous fishing activity—starting point of tacitly agreed boundary—three-stage delimitation methodology beyond end-point of tacitly agreed boundary—construction of equidistance line from 80M out to Chilean 200M limit—final leg of boundary along Chilean 200M limit to intersection with Peruvian 200M limit—‘broad assessment of disproportionality’

Citation: Maritime Dispute (Peru v. Chile), Judgment, 27 January 2014 (not yet reported in ICJ Reports)

Institution: ICJ

Basis of jurisdiction: American Treaty on Pacific Settlement (Pact of Bogotá), Article XXXI; ICJ Statute, Article 36(2)

The Court: Judges Tomka (President), Sepúlveda-Amor (Vice-President), Owada, Abraham, Keith, Bennouna, Skotnikov, Cançado Trindade, Yusuf, Greenwood, Xue, Donoghue, Sebutinde, Bhandari, Judges ad hoc Guillaume (appointed by Peru), Orrego Vicuña (appointed by Chile)

Applicable law: customary international law1

Areas delimited: territorial sea; EEZ; continental shelf (within 200M)(p. 534)

I.  Introduction and Context

This case concerned a dispute between Peru and Chile in relation to the course of their maritime boundary in the South Pacific Ocean. The coastlines of Peru and Chile are adjacent. Peru lies to the north of Chile and its coast runs in a northwesterly direction from the starting point of the land boundary between the parties. Chile’s coast generally follows a north-south orientation. The coasts of both Peru and Chile in the area extending from the land boundary are mostly uncomplicated and relatively smooth, with no distinct promontories or other distinguishing features. The geographical context of the delimitation is illustrated in Figure B22.1.

Peru and Chile are both former Spanish colonies. Chile became independent in 1818 and Peru in 1821. In 1929, the parties concluded the Treaty for the Settlement of the Dispute regarding Tacna and Arica (the ‘1929 Treaty’), which established the land boundary between them and provided for the creation of a Mixed Commission of Limits to determine and mark the agreed land boundary. In its 1930 Final Act, the Mixed Commission recorded the precise locations of eighty boundary markers that it had placed on the ground to demarcate the land boundary.

In 1947, both parties unilaterally proclaimed certain maritime rights extending 200M from their coasts (in what were collectively known as the ‘1947 Proclamations’). The 200M claims were further set out by Chile in a 1947 Declaration and Peru in a 1947 Decree. In 1952, Chile and Peru, together with Ecuador, signed a Declaration during the Conference on the Exploitation and Conservation of the Marine Resources of the South Pacific, held in Santiago de Chile. This Declaration (the ‘1952 Declaration’), along with three other instruments adopted the same year, was registered with the UN Secretariat in 1976.2 Chile, Peru, and Ecuador negotiated eight further instruments in 1954 and 1967, to which the parties referred in their pleadings, including the 1954 Special Maritime Frontier Zone Agreement (the ‘1954 Agreement’), which was registered with the UN Secretariat in 2004.3

Peru instituted proceedings against Chile in the ICJ on 16 January 2008 in respect of a dispute concerning, on the one hand, ‘the delimitation of the boundary between the maritime zones of the two States in the Pacific Ocean’ and, on the other, the recognition in favour of Peru of a ‘maritime zone lying within 200 nautical miles of Peru’s coast, and thus appertaining to Peru, but which Chile considers to be part of the high seas’ (Application, para. 1). In its Application, Peru requested the court to:(p. 535)

Figure B22.1:  Peru/Chile: parties’ claims and court’s judgment.

(p. 536)

determine the course of the boundary between the maritime zones of the two States in accordance with international law…and to adjudge and declare that Peru possesses exclusive sovereign rights in the maritime area situated within the limit of 200 nautical miles from its coast but outside Chile’s exclusive economic zone or continental shelf (Application, para. 13).

II.  Positions of the Parties and Summary of the Judgment

Peru argued that no prior agreed maritime boundary existed between the two countries and, in its Application, requested the court to plot a boundary line using the equidistance method in order to achieve an equitable result. In its written and oral pleadings, however, Peru instead sought a declaration in respect of the location of the maritime boundary, without requesting the court to determine its coordinates.

Chile contended that the 1952 Declaration had established an international maritime boundary along the parallel of latitude passing through the starting point of the parties’ land boundary and extending to a minimum of 200M. It further relied on several agreements and subsequent practice as evidence of that boundary.

The course of the maritime boundaries claimed by Peru and Chile, respectively, together with the maritime area in which Peru sought a declaration of exclusive sovereign rights outside Chile’s EEZ and continental shelf, are illustrated in Figure B22.1.4

a.  Existence of a maritime boundary

In order to settle the dispute, the court had first to determine whether an agreed maritime boundary existed between the parties. For this purpose, the court examined the 1947 Proclamations, the 1952 Declaration, various agreements concluded in 1952 and 1954, as well as the practice of the parties subsequent to the 1952 Declaration.

The 1947 Proclamations

The parties explained that the 1945 Proclamations by the United States of America related to the continental shelf and coastal fisheries in certain parts of the high seas had placed pressure on the commercial exploitation of fisheries off their Pacific coasts, thus motivating their own 1947 Proclamations.

Chile argued that the 1947 Proclamations provided both ‘antecedents’ to the 1952 Declaration and circumstances of the conclusion of the 1952 Declaration for the purposes of Article 32 of the VCLT. Peru observed that the 1947 Proclamations (p. 537) made no reference to international boundaries and argued that they could not constitute circumstances relevant to the 1952 Declaration under the VCLT since they pre-dated the 1952 Declaration by five years.

The court noted that the parties were in agreement that the 1947 Proclamations did not themselves establish an international maritime boundary (para. 39). The court examined whether the 1947 Proclamations provided evidence of an understanding of the parties regarding the future delimitation of the maritime boundary. Chile’s 1947 Declaration provided for the establishment of protective zones for whaling and deep sea fisheries, the perimeter of which would be formed by its coast and the ‘mathematical parallel projected into the sea at a distance of 200 nautical miles’. According to Peru’s 1947 Decree, Peru would exercise control and protection in a maritime zone situated ‘between the coast and an imaginary parallel line to it’ at a distance of 200M.

The court noted the apparent use of the tracé parallèle method to describe the relevant maritime zones in the 1947 Proclamations. However, it concluded that this feature alone was ‘not sufficient to evidence a clear intention of the Parties that their eventual maritime boundary would be a parallel’ (para. 40). It further held that the ‘conditional language’ of the 1947 Proclamations, as well as their ‘provisional nature’, precluded an interpretation of them as reflecting any shared understanding of maritime boundary between the parties (para. 43).

The 1952 Declaration

Chile considered that the 1952 Declaration had been a treaty from its inception. Peru rejected this, arguing that it had been conceived merely as a proclamation of the international maritime policy of the three States parties. However, Peru accepted that it later acquired the status of a treaty following ratification by Chile and Ecuador and registration with the UN Secretariat pursuant to Article 102 of the UN Charter.

Pursuant to paragraph II of the 1952 Declaration, Chile, Ecuador, and Peru proclaimed that they each possessed ‘exclusive sovereignty and jurisdiction over the sea along the coasts of their respective countries to a minimum distance of 200 nautical miles from these coasts’. Paragraph IV then states:

In the case of island territories, the zone of 200 nautical miles shall apply to the entire coast of the island or group of islands. If an island or group of islands belonging to one of the countries making the declaration is situated less than 200 nautical miles from the general maritime zone belonging to another of those countries, the maritime zone of the island or group of islands shall be limited by the parallel at the point at which the land frontier of the States concerned reaches the sea.

Peru asserted that the 1952 Declaration lacked the characteristics of a boundary agreement. Chile disagreed, pointing out that a treaty effecting a boundary delimitation can take any form.

(p. 538) Chile argued that paragraph IV of the 1952 Declaration necessarily assumed a general maritime delimitation between Peru and Chile extending to 200M along the parallel of latitude passing through the starting point of the land boundary. It relied upon the minutes of the conference at which the 1952 Declaration had been agreed, highlighting in particular an exchange in which all three States had consented to an understanding that the boundary line of the jurisdictional zone of each country was formed by the parallel from the point at which their land borders touched the sea. Chile argued that such an understanding constituted an ‘agreement relating to the conclusion’ of the 1952 Declaration within the meaning of Article 31(2)(a) of the VCLT.

Peru argued that the 1952 Declaration addressed only seaward and not lateral boundaries. It observed that paragraph IV referred only to the entitlements generated by certain islands and not to the entitlements generated by continental coasts. Peru contested that the minutes relied upon by Chile did not form any recorded agreement, but could only amount to travaux préparatoires. According to Peru, the object and purpose of the 1952 Declaration was not the division of fishing grounds between its States parties, but the creation of a zone functioning ‘as a single biological unit’ designed to address the threat posed by foreign whaling.

The court stated that it must analyze the terms of the 1952 Declaration in accordance with the customary international law of treaty interpretation, as reflected in Articles 31 and 32 of the VCLT (para. 57). It observed that the 1952 Declaration made no express reference to the delimitation of maritime boundaries, although it did contain ‘certain elements which are relevant to the issue of maritime delimitation’ (para. 58). It observed that paragraph IV resolved a ‘specific issue’ related to ‘insular zones’. It held that the ordinary meaning of paragraph IV, read in its context, only established the parties’ agreement concerning the limits between certain insular maritime zones and those zones generated by the continental coasts which abut such insular maritime zones (paras 61–2).

Turning to the object and purpose of the 1952 Declaration, the court observed that its Preamble ‘focuses on the conservation and protection of the necessary natural resources for the subsistence and economic development of the peoples of Chile, Ecuador and Peru, through the extension of the maritime zones adjacent to their coasts’. The court rejected Chile’s reliance on the minutes because they had merely summarized the discussions that led up to adoption of the 1952 Declaration, and were thus better categorized as travaux préparatoires constituting supplementary means of interpretation, for the purposes of the VCLT as argued by Chile. While the court did not need in principle to resort to such supplementary means of interpretation, it indicated that they confirmed its conclusion that the 1952 Declaration ‘did not effect a general maritime delimitation’ (paras 63–8).

(p. 539) Nevertheless, the court noted that ‘various factors’ related to the 1952 Declaration, such as a Chilean proposal during the negotiations that the parties adopt a general delimitation along lateral lines and the text of paragraph IV, suggested that ‘there might have been some sort of shared understanding among the States parties of a more general nature concerning their maritime boundaries’ (para. 69). This provided important context to the court’s subsequent findings in relation to the 1954 Agreement, set out below.

The 1954 Agreement

The court proceeded to examine the 1954 Agreement, concluded between Chile, Ecuador, and Peru regarding unintentional violations of the maritime frontier (‘la frontera maritima’) by small fishing vessels. Article 1 of the 1954 Agreement established a special zone ‘at a distance of 12 nautical miles from the coast, extending to a breadth of 10 nautical miles on either side of the parallel which constitutes the maritime boundary between the two countries’.

Chile argued that the ‘basic predicate’ of the 1954 Agreement was that the three States ‘already had lateral boundaries, or “frontiers”, in place between them’. Peru, by contrast, contended that the 1954 Agreement: (1) was applicable only to Peru’s northern boundary with Ecuador; (2) was not seen by Chile as being ‘of major importance’ given the delay in its ratification (1967) and UN registration (2004) of the instrument; and (3) had a ‘very special and temporary purpose’.

The court dismissed Peru’s first two contentions. It observed that there was ‘nothing at all in the terms of the [1954 Agreement] which would limit it only to the Ecuador-Peru maritime boundary’. That Agreement had been negotiated, signed, and ratified by all three States concerned. Once ratified by Chile, the 1954 Agreement had become binding on it, regardless of any delay. As for Peru’s third contention, the court agreed that the operative terms of the 1954 Agreement were ‘narrow and specific’. However, it observed that the terms of the 1954 Agreement acknowledged ‘in a binding international agreement that a maritime boundary already exists’ (para. 90).

The court noted that the 1954 Agreement did not indicate when and by what means the maritime boundary had been agreed. Therefore, the parties’ acknowledgement of its existence could only reflect ‘a tacit agreement which they had reached earlier’. The court recalled its earlier observation that certain elements of the 1947 Proclamations and 1952 Declaration suggested an ‘evolving understanding’ about the parties’ maritime boundaries. It recalled also its recognition in the Nicaragua/Honduras case that ‘[t]he establishment of a permanent maritime boundary is a matter of grave importance’ and that ‘[e]vidence of a tacit legal agreement must be compelling’.5

(p. 540) The court concluded that:

In this case, the Court has before it an Agreement which makes clear that the maritime boundary along the parallel already existed between the Parties. The 1954 Agreement is decisive in this respect. That Agreement cements the tacit agreement (para. 91).

The court noted, however, that the 1954 Agreement gave no indication of the nature of the maritime boundary, nor its extent, except that it made clear that the boundary extended beyond 12M from the coast (para. 92).

The court found that certain lighthouse arrangements subsequently made during 1968 and 1969, pursuant to which the parties undertook to carry out ‘an on-site study for the installation of leading marks visible from the sea to materialise the parallel of the maritime frontier originating at Boundary Marker number one (No. 1)’, had also proceeded on the basis that a maritime boundary extending along the parallel from the land boundary already existed. Again, while not indicating the extent and nature of the maritime boundary, those arrangements had given effect to it ‘for a specific purpose’ (para. 99).

b.  Nature and extent of the tacitly agreed maritime boundary

The court stated that the tacit agreement between the parties relating to their maritime boundary ‘must be understood in the context of’ the 1947 Proclamations and the 1952 Declaration. Since those instruments expressed claims to the seabed and the waters above the seabed and their resources, without drawing any distinction between those maritime spaces, the court concluded that the tacitly agreed boundary was ‘an all-purpose one’ (para. 102).

As regards the extent of the boundary established by tacit agreement, the court referred to the practice of the parties before and after the 1954 Agreement, as well as to developments in the law of the sea at that time. It recalled that the purpose of the 1954 Agreement was narrow and specific, related to the establishment of a zone of tolerance for fishing activity operated by small vessels. Accordingly, the boundary along a parallel of latitude must extend at least to the distance where such activity took place at the time (para. 103). The court therefore turned to examine the evidence of that activity.

The court noted a statement by the Peruvian representative at the 1958 UN Conference on the Law of the Sea indicating that the ‘biological limit’ of the fisheries resources in the region was at a distance of 80 to 100M from shore in the summer, and 200 to 250M in the winter. Peru, in submissions not challenged by Chile, referred to the decision of the parties to proclaim 200M zones in 1952 due to the ‘enormous whaling and fishing potential’ of the region. The court also noted the statement of the Peruvian representative at the 1958 Conference that ‘species such as tunny and barrilete were mostly caught 20 to 80 miles from the coast; the (p. 541) same anchovetas of the coastal waters sometimes went 60 or more miles away; and the cachalot and whales were usually to be found more than 100 miles off’ (paras 105–6).

Turning to FAO fisheries statistics cited by Chile, the court noted that the species making up the bulk of the annual fish catch of Peru and Chile in the 1950s were generally found within 60M of the coast. While the FAO statistics also provided some information about the parties’ whaling activities, they gave no indication of where those catches occurred (paras 107–8). The court ‘did not see as of great significance’ the parties’ knowledge of the likely possible extent of fishery resources out to 200M, nor the extent of their fishing in later years, because the principal maritime activity undertaken by the parties’ coastal populations in the early 1950s was ‘fishing undertaken by small vessels’. As regards the more distant waters, the parties’ emphasis in this period had been on the exclusion of foreign long-distance fleets from those waters (paras 109–10).

The court recalled that the all-purpose nature of the maritime boundary meant that evidence concerning fisheries activity, in itself, could not be determinative of the extent of that boundary. Nevertheless, it concluded that such activity provided ‘some support for the view that the Parties, at the time when they acknowledged the existence of an agreed maritime boundary between them, were unlikely to have considered that it extended all the way to the 200 nautical-mile limit’ (para. 111).

In response to a question from the court, both parties recognized that the 200M claims made in the 1952 Declaration did not correspond to the international law of that time and were not enforceable against third parties. Against that backdrop, and on the basis of fishing practices of the 1950s as established by the court, the ICJ considered that ‘the evidence at its disposal does not allow it to conclude that the agreed maritime boundary along the parallel extended beyond 80 nautical miles from its starting-point’ (para. 117). The relationship of that 80M limit (at ‘Point A’) to the parties’ 1950s fishing ports of Arica and Ilo is illustrated in Figure B22.2.

In light of its ‘tentative conclusion’ based on the parties’ 1950s fishing activities, the court proceeded to examine further elements of practice of the parties, for the most part subsequent to 1954, that may be of relevance to the extent of the tacitly agreed boundary. It did so while remarking that its ‘primary concern’ should be with the practice of the parties during the 1950s, since its enquiries related to establishing the extent of the boundary acknowledged at that time. It concluded, inter alia, that the parties’ legislative practice, certain 1970s negotiations with Bolivia, and the parties’ positions at the Third UN Conference on the Law of the Sea were of no assistance to determining the extent of the maritime boundary acknowledged in 1954. It observed also that, until the mid 1980s, all of the parties’ maritime enforcement activities took place within 60M of the coast (para. 128). The court considered that certain Chilean arrests of Peruvian fishing vessels south (p. 542) of the parallel of the 1950s provided support to Chile’s position in the delimitation, to the extent that such arrests were met without protest by Peru (para. 147).

The court reviewed a 1986 memorandum sent by the Peruvian Ambassador to the Chilean Ministry of Foreign Affairs requesting that ‘immediate attention’ be given to the ‘formal and definitive delimitation of the maritime spaces’, together with a communiqué in response from the Chilean Foreign Ministry to the effect that the Minister ‘took note’ of the memorandum and indicating that ‘studies in this matter shall be carried out in due time’. The court observed that Peru had not followed up the matter subsequently. The court considered that the 1986 documents acknowledged that there was a maritime boundary, but gave no information about its extent. However, it concluded, without elaboration, that the 1986 correspondence did ‘reduce in a major way the significance of the practice of the Parties’ after that date (para. 142).

The court concluded that the parties’ post-1950s practice did not lead it to change its tentative conclusion that the tacitly agreed maritime boundary did not extend beyond 80M. Accordingly, based on ‘an assessment of the entirety of the relevant evidence presented to it’, the court concluded ‘that the agreed maritime boundary between the Parties extended to a distance of 80 nautical miles along the parallel from its starting-point’ (paras 149, 151).

c.  The court’s delimitation of the maritime boundary

Both parties agreed that their land boundary had been settled by the 1929 Treaty. However, they disagreed on the exact starting point of the land boundary at the coast. Chile considered that the land boundary started from Boundary Marker No. 1, as established by the Mixed Commission of Limits. Peru argued that Boundary Marker No. 1 was not intended to mark the start of the agreed land boundary, not least because it was located 200 metres inland from the coast. The court observed that ‘a considerable number of the arguments presented by the Parties concerned an issue which is clearly not before it, namely, the location of the starting point of the land boundary’ (para. 163).

The court considered that the 1968–69 lighthouse arrangements between the parties were indicative of a mutual understanding about the course of the existing maritime frontier running through Boundary Marker No. 1. Those arrangements therefore served as ‘compelling evidence’ that the agreed maritime boundary followed the parallel that passed through Boundary Marker No. 1. It therefore concluded that ‘the starting-point of the maritime boundary between the Parties is the intersection of the parallel of latitude passing through Boundary Marker No. 1 with the low-water line’ (paras 169, 174, 176).

In light of the court’s earlier conclusion that the tacitly agreed boundary extended 80M from the starting point (to a point identified by the court as Point A—see (p. 543) Figure B22.2), the court’s final task was to delimit the remainder of the boundary beyond 80M. The court proceeded on the basis of Articles 74(1) and 83(1) of UNCLOS, which reflected customary international law, and the three-stage test ‘usually’ employed by the court in seeking an equitable solution (paras 179–80). Peru proposed delimitation by way of a straightforward equidistance line, while Chile advanced no arguments on this matter.

The court described the situation as ‘unusual’ as compared to previous cases in the sense that the starting point for the delimitation exercise was located 80M from the closest point on the Chilean coast and about 45M from the closest point on the Peruvian coast (para. 183). At the first stage, the court constructed a provisional equidistance line, starting at Point A, by selecting appropriate base points. For this purpose, only those points on the Peruvian coast which were more than 80M from Point A could be matched with points at an equivalent distance on the Chilean coast. Accordingly, in order to determine the relevant base points on the Peruvian coast, the court drew a circle with an 80M radius from Point A (para. 185). The equidistance line extended out to a distance of 200M from the Chilean coast, to Point B (para. 186). The ‘equidistance line’ thus constructed by the court is illustrated in Figure B22.2.

As the Peruvian 200M entitlement extended beyond Point B (given the exclusion of a Peruvian base point within 80M of Point A), the court concluded that the final segment of the maritime boundary should proceed southwards along the Chilean 200M limit from Point B to Point C, where the 200M limits of the parties’ maritime entitlements intersect (para. 190). This final segment is also illustrated in Figure B22.2.

The court observed that no relevant circumstances appeared in the record before the court. Accordingly, at the second stage of the delimitation process, there was no basis for adjusting the provisional equidistance line (para. 191).

Finally, in examining whether the result achieved was significantly disproportionate in relation to the lengths of the relevant coasts and the division of the relevant area, the court recalled its previous jurisprudence that the object of delimitation was to achieve an equitable result, not an equal apportionment of maritime areas. As the presence of an agreed boundary running along a parallel of latitude for 80M would make the calculation of the relevant coastal length and coastal areas ‘difficult, if not impossible’, the court did not carry out a precise calculation of ratios. Instead, it undertook a ‘broad assessment of disproportionality’. The court concluded that ‘no significant disproportion is evident, such as would call into question the equitable nature of the provisional equidistance line’ (paras 192–4).

The maritime boundary delimited by the court is illustrated in Figure B22.2.

Peru had not requested the court to determine the precise geographical coordinates of the maritime boundary. The court therefore left this task to the parties, (p. 544) indicating that it ‘expects that the Parties will determine these coordinates in accordance with the present Judgment, in the spirit of good neighbourliness’ (para. 197).

III.  Technical Considerations

The court produced a novel ‘displaced equidistance line’ as part of its compromise solution. Normally an equidistance line is drawn using the nearest base points on each coastline, but in this instance the court started the line at a point that was not equidistant (indeed, Point A was located 37M from the closest point on the equidistance line). The court constructed the line by ignoring any Peruvian coast that fell within a circle of radius 80M drawn from Point A (see Figure B22.2). This amounted to discounting 120M of the Peruvian coast. By ignoring the closest Peruvian coast, the so-called equidistance line was shifted substantially in Chile’s favour.

Having done this, the court drew an equidistance line that used base points along the Chilean coastline as far as the last contributing base point at Pisagua, some 75M from the land boundary terminus, and only one base point on the Peruvian side at Punta Islay, some 127M distant.

An oddity is the final leg from Points B to C, which generates a small area of Peruvian EEZ that overlaps the Chilean EEZ. A simpler and more practical solution could have been achieved by connecting Point A directly to Point C (which is the true equidistance point at the parties’ respective 200M limits).

Other cases where the equidistance line has been shifted to accommodate a starting point that was not equidistant include: Gulf of Maine, where a bisector was moved to an agreed start point; Cameroon/Nigeria, where a short line of latitude connected the end of the agreed territorial sea boundary to the equidistance line boundary in the EEZ; and both Guyana/Suriname and Bangladesh/India, where the land boundary terminus was connected (via a point on the 3M limit in the former case) to an equidistant point on the territorial sea limit.

IV.  Significance of the Decision and its Contribution to International Law

This is the first decision by the ICJ recognizing the existence of a maritime boundary established by ‘compelling’ evidence of a tacit agreement between the coastal States. In previous cases such as Nicaragua/Honduras and Bangladesh/Myanmar, States had sought unsuccessfully to rely on physical acts, such as the (p. 545)

Figure B22.2:  Peru/Chile: construction of the court’s displaced equidistance line.

(p. 546) granting of oil concessions, fishing, or coastguard activity in order to establish the existence of a tacit maritime boundary agreement.6

The approach and rationale adopted by the court in dismissing Chile’s argument that the 1952 Declaration established an international maritime boundary was orthodox and represents a good example of the application of the VCLT and customary rules of treaty interpretation to the context of maritime delimitation.

In finding the existence of a tacitly agreed boundary, the court referred to its decision in the Nicaragua/Honduras case that ‘evidence of a tacit legal agreement must be compelling’.7 The ‘compelling’ evidence identified by the court took the form of a 1954 treaty between Peru, Chile, and a third party (Ecuador) establishing a maritime frontier fisheries zone. That treaty acknowledged the existence of a prior maritime boundary agreement, without identifying its nature or extent. The decision therefore indicates that States wishing to argue the existence of a tacitly agreed maritime boundary may be more likely to succeed if some mention of the boundary exists in a contemporaneous treaty instrument. The court also established the all-purpose nature of the tacitly agreed maritime boundary with reference to contemporaneous instruments in the form of the 1947 Proclamations and the 1952 Declaration.

The court’s decision that the tacitly agreed maritime boundary extended only up to 80M warrants particular attention. This outcome, which resulted in a delimitation representing a form of compromise between Peru’s and Chile’s claims before the court, had been requested by neither party. Furthermore, it was not without controversy, being reached by a majority of just ten votes to six. The court acknowledged, following cases such as Gulf of Maine, that the all-purpose nature of the maritime boundary meant that ‘evidence concerning fisheries activity, in itself, cannot be determinative of the extent of that boundary’. However, the principal evidence ultimately relied upon by the court in identifying the 80M limit related to the parties’ 1950s fishing practices.8 The court relied heavily upon FAO statistics and statements made by the Peruvian delegate to the 1958 UN Conference on the Law of the Sea as to the limits of local fishing activities to conclude that it was unable to determine that the agreed maritime boundary extended beyond 80M.

(p. 547) This conclusion appears inconsistent with some of the other evidence before the court. That evidence demonstrated, first, that at the relevant time the parties each claimed ‘exclusive sovereignty and jurisdiction’ over maritime space extending 200M from their coasts and, second, a contemporaneous awareness of fisheries resources and existence of some fishing (particularly whaling) activity by the parties well beyond 80M. While the court did not say so, it might be inferred that its unwillingness to extend the tacitly agreed boundary beyond 80M arose out of a perceived absence of ‘compelling evidence’ that the boundary was intended to extend any further.

In this respect, the partial dissent of President Tomka is notable. He considered that the fisheries practice of the parties under the 1954 Agreement was not relevant in determining the extent of the maritime boundary at a time when the parties ‘openly and publicly claimed maritime zones extending at least to 200 nautical miles’. He considered that the court’s termination of the tacitly agreed boundary at 80M was ‘counter to the intention of the Parties when the evidence is appreciated as a whole’ (Declaration of President Tomka, para. 4). He noted also that Article 1 of the 1954 Agreement referred to ‘the parallel, which constitutes the maritime boundary [as opposed to part of the maritime boundary] between the two countries’.9

The court’s conclusion that the tacitly agreed maritime boundary should not extend beyond the parties’ ‘enforcement capacity’ at the time is also subject to question, given the evidence on the record about the seizure by Peru of the Onassis whaling fleet in 1954 at a point located 126M off its coast. Again, the court may not have considered this evidence sufficiently ‘compelling’ to demonstrate a tacit agreement as to the location of the boundary up to that point.

When it came to identifying the starting point of the tacitly agreed maritime boundary, the court again reverted to the test of ‘compelling evidence’, finding that the 1968–69 lighthouse arrangements provided such evidence that the boundary passed through Boundary Marker No. 1.

The delimitation beyond Point A is a unique example of a purportedly equidistance-based delimitation starting from a point located far out to sea that is not at all equidistant from the parties’ respective baselines. The court indicated that an equidistance-based solution was appropriate over this part of the boundary in the absence of ‘compelling reasons preventing that’. While the court confirmed its established three-stage methodology in delimiting the boundary between Point A and Point B, as Figure B22.2 shows, the so-called equidistance line drawn by the (p. 548) court was significantly at variance from the true equidistance line. This was because of the court’s exclusion of all Peruvian base points located less than 80M from Point A. The simplified disproportionality analysis conducted by the court at the third stage of the delimitation was also necessarily at variance with its more detailed approach in other cases, given the difficulty in calculating the length of the parties’ relevant coasts and the extent of the relevant area.


1  Chile ratified UNCLOS on 25 August 1997; Peru was not a State party to UNCLOS at the material time.

2  UNTS, Vol. 1106, pp. 301, 315, 323, and 331.

3  UNTS, Vol. 2274, p. 527.

4  The continental shelf does not extend beyond 200M in the disputed area.

5  Nicaragua/Honduras, para. 253.

6  Nicaragua/Honduras, paras 237–58; Bangladesh/Myanmar, paras 100–18. In Tunisia/Libya, the court considered a de facto line acted on by the parties in the granting of oil concessions as relevant to the choice of the delimitation method to be used, while expressly noting that it was not making a finding of tacit agreement between the parties. Tunisia/Libya, para. 118.

7  Nicaragua/Honduras, para. 253. This test was repeated by ITLOS in Bangladesh/Myanmar, paras 100–18.

8  The reliance on fishing practices to determine the extent of the tacitly agreed boundary can be contrasted with the restrictive approach generally taken to fisheries as a relevant circumstance calling for the adjustment of a provisional equidistance line: see, e.g., the Gulf of Maine and Barbados/Trinidad and Tobago cases, reviewed in Part B, Chapters 6 and 16, above.

9  Judges Xue, Gaja, Bhandari, and Judge ad hoc Orrego Vicuña also appended a joint dissenting opinion, concluding that the 1952 Declaration indicated a maritime boundary of 200M between the parties, and together with the 1955 Protocol and the 1968 Agreement, provided a solid legal basis for the existence of a maritime boundary that extended along the parallel of latitude for 200M.