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                                           SEPARATE OPINION
                                       OF JUDGE AD HOC MAHIOU

                 [Translation]

                    Sources of the applicable law — International sources : Article 38 of the Statute
                 of the Court, Special Agreement of 24 February 2009, principles of the intangibility
                 of frontiers and of uti possidetis — Internal sources : Decree of 28 December
                 1926, Arrêté of 31 August 1927 and its Erratum, other texts from the colonial
                 period — Other sources : documents accepted by joint agreement of the Parties,
                 1960 IGN map, preparatory documents from the colonial period.
                    Place and role of the colonial effectivités — Relationship between the Arrêté
                 and its Erratum —Relationship between the 1960 IGN map and the effectivités —
                 Delimitation of the frontier : course from the Tao astronomic marker to the median
                 line of the River Sirba — Problems of the localities of Petelkolé and Oussaltane —
                 Actual links of the populations with Niger.

                    1. While broadly subscribing to the Court’s overall approach and to
                 most of the findings reached by it in the present case, in this separate
                 opinion I should like to set out a number of observations on certain
                 points regarding which, in my view, the Court’s position calls for further
                 refinements and clarifications. These points relate, on the one hand, to the
                 status of the various documents invoked in the course of the proceedings
                 and, on the other, to the status of the effectivités or, more precisely, their
                 place and role in determining the different sections of the frontier.

                                       I. The Status of the Documents

                    2. It is apparent from the written and oral pleadings that there are
                 three sets of documents to which the Parties refer : first, texts expressly
                 accepted by the Parties for use as a reference, and thus as legal title, for
                 delimiting the boundary ; secondly, documents which are more or less
                 accepted by joint agreement of the Parties, but whose status remains at
                 issue when it comes to establishing whether they are applicable in the
                 present dispute ; and, lastly, documents relied upon by one of the Parties
                 and objected to by the other.
                    3. It is therefore with this indicative classification of the various texts
                 and documents in mind that I shall seek to understand their place in the
                 resolution of this dispute. At the same time my list establishes a hierar-
                 chy, since I cite the texts in the order of priority to be given to them with
                 a view to achieving the delimitation of the frontier between Burkina Faso
                 and Niger.

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                     (i) The texts that have been expressly accepted are as follows :
                 — the Special Agreement of 24 February 2009, Article 6 of which refers
                   to Article 38 of the Statute of the International Court of Justice and
                   to the rules and principles of international law applicable to the settle-
                   ment of disputes, which shows indisputably that other rules of inter-
                   national law have a role to play, in particular when the applicable
                   texts prove to be incomplete or insufficient ;
                 — the Decree of 28 December 1926 establishing the administrative centre
                   of Niger at Niamey and transferring certain cercles and cantons
                   between the Colonies of Upper Volta and Niger. We know that the
                   Parties do not agree as to whether this text has a constitutive or
                   declaratory scope. In so far as it already determines certain boundar-
                   ies, it is necessarily constitutive. Furthermore, since it is this text that
                   authorizes the Governor‑General of French West Africa to issue the
                   Arrêté of 31 August 1927 and the Erratum of 5 October 1927 fixing
                   the boundaries of the colonies, it likewise has constitutive effect ;
                 — the Arrêté of 31 August 1927 and its Erratum of 5 October 1927 fixing
                   the boundaries of the colonies of Upper Volta and Niger ;
                 — consequently, these are the basic or reference texts which are at the
                   heart of the dispute and the Parties are agreed on this point even
                   though they ascribe a different effect to those texts, in particular as to
                   whether they are the only texts to apply and whether or not they suf-
                   fice to delimit the entire boundary.

                 (ii) As regards the documents, the main one is the 1:200,000‑scale IGN
                      map of 1960, which enjoys a particular status in so far as this geo-
                      graphical document — which hitherto had no official status — is rec-
                      ognized in both the Agreement of 28 March 1987 (Art. 2) and the
                      Special Agreement seising the Court of 24 February 2009
                    While the Parties agree on referring to that map in order to delimit the
                 boundary, they disagree profoundly about the conditions which would
                 have to apply and have reiterated those disagreements on many occa-
                 sions. According to Burkina Faso, “reference may only be made to the
                 map if the Arrêté, as clarified by its Erratum, does not suffice” exception-
                 ally and only on that hypothesis, and, “in the absence of any other docu-
                 ment accepted by joint agreement of the Parties, first, reference must be
                 made to it and, second, reference may be made to it alone”. According to
                 Niger, the 1960 map enjoys the status of a “subsidiary source”, which
                 enables reference to be made to it whenever there are deficiencies, lacu-
                 nae, difficulties or errors in the Arrêté. Niger adds that “[u]nless abnormal
                 deviations in relation to the texts or manifest lacunae in the information
                 on the canton boundaries are discovered . . . it is the boundary drawn on
                 the IGN map which should be adopted as the frontier line” ; in such cases,
                 it “believed that it was necessary to make modifications to it and that
                 those modifications were justified”.

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                 (iii) The documents accepted by joint agreement of the Parties
                    It goes without saying that the documents that have been accepted by
                 joint agreement of the Parties are applicable in the present dispute, even
                 though it is not always easy to ascertain to what extent such documents
                 exist, since each Party, for various reasons, objects to those relied upon
                 by the other. But should we disregard them entirely if they have been
                 objected to by one of the Parties ? I do not believe so, because, although
                 they do not constitute evidence, they may, at the very least, constitute a
                 presumption and guide the interpretation which may be given of a text or
                 of a situation (by way of example, mention may be made of the travaux
                 préparatoires for the reference texts, which moreover have been cited by
                 one or other of the Parties or by both of them). In that light, I do not see
                 why there would, a priori, be objections to them especially since the
                 travaux préparatoires traditionally form part of the elements that may at
                 least support evidence, if not constitute it.

                 (iv) The other documents and the colonial effectivités
                    Any other documents not accepted by joint agreement of the Parties
                 may not be used as such as a basis for the delimitation. But here too,
                 must they be disregarded completely ? I do not believe so, because they
                 may constitute a significant source of information. Once again, even
                 though they cannot constitute irrefutable evidence of a frontier, it cannot
                 be ruled out a priori that maps, research or other documents, whether
                 they date from before or after independence, as well as the effectivités,
                 may be relevant in establishing the situation existing at the time, when
                 applying the principles of the intangibility of frontiers or of uti possidetis
                 (case concerning the Frontier Dispute (Burkina Faso/Republic of Mali),
                 Judgment, I.C.J. Reports 1986, p. 568, para. 29 ; case concerning the Land,
                 Island and Maritime Frontier Dispute (El Salvador/Honduras : Nicaragua
                 intervening), Judgment, I.C.J. Reports 1992, p. 399, para. 62 ; case con-
                 cerning the Frontier Dispute (Benin/Niger), Judgment, I.C.J. Reports
                 2005, p. 109, para. 26).
                    4. Lastly, and to conclude on this issue of the texts and documents, it
                 is clear that :
                 — first, the Arrêté and its Erratum indeed constitute the main basic text
                   for determining the frontier in the light of the other texts and colonial
                   practice concerning the delimitation of boundaries ;
                 — secondly, there need to be sufficiently sound reasons for disregarding
                   it ; but if the Erratum does indeed prove to be imprecise, not to suffice
                   and a fortiori to be erroneous on any point, then it is normal to refer
                   to other supplementary elements, in particular the 1960 map, in order
                   to reach a solution ;
                 — lastly, if the 1960 map should in turn prove not to suffice, then it is
                   possible to refer to the effectivités and to other documents or elements

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                     which are likely to enlighten the Court. It is on this last point that the
                     Court’s reasoning seems to me to be too strict and rigid when it gives
                     excessive and formal primacy to the text and excludes the effectivités
                     and other elements in order to arrive at a solution.

                                      II. The Course of the Frontier

                    5. In order to draw the frontier, the Court subdivided it into four sec-
                 tions concerning, respectively, the section from Tong‑Tong to Tao, from
                 Tao to the median line of the River Sirba, from this last point to the
                 intersection of the River Sirba with the Say parallel, passing via the IGN
                 line and certain geographical points, and lastly from the last point to the
                 beginning of the Botou bend.
                    6. I should like to make a few comments on the second section, since
                 the line adopted by the Court gives rise to some difficulties related to the
                 problem of the effectivités.

                          1. From the Tao Astronomic Marker to the Median Line
                                            of the River Sirba
                    7. The text of the Erratum states that, from the Tao astronomic
                 marker, the line reaches “the River Sirba at Bossébangou”.
                    8. For this part of the frontier, Burkina Faso proposes a line based on
                 a particular interpretation of the text of the Erratum. In fact, the course
                 of Burkina’s line follows that of the Joint Commission of 1988. Thus,
                 from the Tao astronomic marker as far as the River Sirba at Bosséban-
                 gou, the frontier follows a straight line. Burkina Faso reiterates its posi-
                 tion that “in jurisprudence a delimitation text indicating, without any
                 indication to the contrary, that a line passes through two points is inter-
                 preted as specifying a boundary in the form of a straight line connecting
                 those two points”.
                    9. For its part, Niger opts for a line which follows the boundaries of
                 the cantons, a position which is largely reflected by the 1960 IGN map. It
                 divides this part of the frontier into two sections : from the Tao astro-
                 nomic marker to Bangaré, and from Bangaré to the boundary of the Say
                 cercle. Niger bases its approach on the fact that the Decree of the Presi-
                 dent of the French Republic of 28 December 1926 expresses itself in terms
                 of cantons, which “does not imply any wish to establish a line of an arbi-
                 trary and artificial nature” and on a number of documents, in particular
                 three records of agreement which were concluded for the two cercles con-
                 cerned — Tillabéry and Say — between the representatives of the two
                 colonies in preparation for the Governor‑General’s implementing Arrêté.
                    10. Beyond the Tao marker, a first possible theoretical approach is to
                 opt for a straight frontier line, as in the sector between Tong‑Tong and
                 Tao. However, this is a relatively important section of the frontier, along
                 which lie a number of villages claimed by both Parties. A straight line

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                 would have uncertain and undesirable results on the ground, in particular
                 by artificially dividing between the two States’ frontier villages and com-
                 munities.
                    11. If the Arrêté had intended to draw a straight line, it would have
                 expressly said so as it had for the previous section from Tong‑Tong to Tao
                 and as it would for the last section of the frontier from the point where the
                 Say parallel cuts the River Sirba to the Botou bend. However, the text of
                 the Erratum does not do so and this can only be regarded as a deliberate
                 omission and an equally clear will to reject such a line. Consequently, there
                 is no logical and convincing basis for maintaining that the frontier runs in
                 a straight line to reach the River Sirba at Bossébangou, above all because
                 Bossébangou is a Niger village which is not on the bank of the Sirba. Con-
                 sequently, it follows that, in view of the Erratum’s silence on the course of
                 the line in this sector, reference must necessarily be made to the subsidiary
                 source, the 1960 IGN map. It is thus on this basis that the Court adopts the
                 line on the map, not only in respect of this point but for the whole frontier
                 line running from the Tao astronomic marker to the River Sirba.
                    12. As was noted earlier, the line passes close to a number of villages
                 and, more specifically three of them (Petelkolé, Oussaltane and Bangaré)
                 which were the subject of opposing appropriation claims by the Parties.
                 Admittedly, contrary to what Burkina Faso maintained, the Court quite
                 rightly took into account the effectivités, but it disregarded them in the
                 case of two of the villages (Petelkolé and Oussaltane) and adopted them
                 in the case of only one of them (Bangaré).
                    13. It is on this point that the solution does not seem to me to be
                 entirely satisfactory because the Court has disregarded the evidence of
                 effectivités presented by Niger, whereas that evidence appears to be much
                 more convincing than that submitted by Burkina Faso.
                    14. With regard to the location of Petelkolé, Niger notes that the data
                 on the 1960 IGN map are contradictory (on the Sebba sheet, Petelkolé
                 lies on the frontier, whereas on the Téra sheet it lies slightly to the west of
                 that line) ; then it relies on administrative information from the colonial
                 period to prove that this village belonged to Niger, and that it “has
                 remained under Niger authority since independence, is administratively
                 attached to the rural municipality of Bankilaré and numbers 2654 inhab-
                 itants”. It adds that, in the vicinity of Petelkolé, the frontier line has to
                 deviate slightly from the IGN line towards the west in order to take in the
                 juxtaposed frontier post between Niger and Burkina Faso, which is situ-
                 ated entirely within Niger territory and was chosen by the Bilateral
                 (Burkina‑Niger) Committee on the identification of sites for the installa-
                 tion of juxtaposed control posts between the two countries.
                    15. Burkina Faso disputes Niger’s position and states that neither the
                 Erratum nor the line on the 1960 map attributes Petelkolé to Niger. With
                 respect to the documents relied on by Niger, it contends that they are not
                 opposable to Burkina because they were not ratified either by the compe-
                 tent authorities (documents from the colonial period) or by the Burkina
                 authorities (post‑independence documents).

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                    16. An examination of the 1960 map shows that the 1960 IGN map
                 places Petelkolé almost on the frontier, slightly to the west of it, towards
                 Burkina Faso. Nevertheless, the fact that the two States established jux-
                 taposed control posts at Petelkolé and that they considered or “believed
                 that the frontier left Petelkolé to Niger” (Counter‑Memorial of Niger,
                 p. 66, para. 2.1.7) cannot be ignored when determining the situation of
                 the village, even if that 2006 Agreement did not enter into force. Further-
                 more, the administrative information from 1933 and from 1953‑1954
                 invoked by Niger, which referred to the Rimaibé as having established
                 two hamlets, one (Seynotyondi) situated in Upper Volta and the other
                 (Petelkolé) in Niger, between which the frontier passes, is an additional
                 element to be taken into consideration. In my view, the Court should
                 have given much greater attention to the evidence before ruling on the
                 fate of the village, which, in view of the effectivités, appears to come
                 under the administration of Niger.

                    17. With regard to the village of Oussaltane, Niger maintains that this
                 village belongs to Niger, again relying on the basis of colonial documents
                 (the Delbos sketch‑map of June 1927, the Roser/Boyer Agreement of
                 April 1932, according to which the boundary runs “to Houssaltane, which
                 it leaves to the east, to Petelkarkalé, which it leaves to the west, to Petel-
                 kolé which it leaves to the east”). Niger contends that this region, which
                 is administered by Niger, corresponds to a group of encampments of the
                 Kel Tamajirt tribe, of the Tinguéréguédesch groupement of the rural
                 municipality of Bankilaré, to which they regularly pay their taxes.
                    18. Burkina Faso merely says that the 1960 line places Oussaltane on
                 the Upper Volta side of the line (Counter‑Memorial of Burkina‑Faso,
                 para. 3.71), and the fact that the encampment was placed east of the
                 boundary proposed by the Roser/Boyer Agreement of April 1932 is with-
                 out relevance, because “[t]he situation of a place in terms of a delimita-
                 tion which has not been confirmed cannot be used to call into question
                 the confirmed delimitation”. It reproaches Niger with making a signifi-
                 cant and unjustified departure from the IGN map for the sole purpose of
                 enclaving Oussaltane and removing it from the territory of Upper Volta,
                 without providing evidence of any effectivité in support of its claim.
                    19. It should be noted that the 1960 IGN map places the locality of
                 Oussaltane towards the west, on the Upper Volta side, but the frontier
                 line is broken in this area. Since the map thus appears to be insufficient to
                 determine the exact course of the frontier in the vicinity of this village,
                 reference should be made to other evidence in order to reach a decision
                 on this section. In my opinion, the various documents invoked by Niger
                 support the argument that the village is part of Niger, since the majority
                 of the Kel Tamajirt tribe are said to be of Niger nationality and to pay
                 their taxes in the Niger municipality of Bankilaré. This constitutes objec-
                 tive evidence of an effectivité in support of such a solution rather than in
                 support of the village being part of Burkina Faso, for which no relevant
                 evidence of an effectivité is provided.

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                              2. The Arrival Point of the Line that Leaves Tao
                                      and Arrives at the River Sirba
                    20. With regard to the arrival point of the line that leaves Tao, the text
                 of the 1927 Erratum indicates that it “reach[es] the River Sirba at Bossé
                 bangou”. The wording is at the very least ambiguous, especially since the
                 village of Bossébangou belongs to Niger and, furthermore, it is not
                 located on the bank of the Sirba but a few hundred metres away.
                    21. However, Burkina Faso contends that the arrival point must be
                 situated on the right bank of the Sirba on the basis of the following syl-
                 logism : the Erratum refers to Bossébangou ; but since Bossébangou is in
                 Niger territory and far from the river, it cannot be the point to be reached ;
                 therefore, that means that the line cuts the river to reach the right bank.
                    22. It is clear to me that this is a false syllogism and the Court, quite
                 rightly, rejects this assertion. On the one hand, the Erratum’s reference to
                 Bossébangou only indicates a direction and arrival point, the River Sirba,
                 but without providing any further details as to whether the right bank,
                 the left bank or the median line is intended. On the other hand, the verb
                 “to reach” a river does not in itself mean that the river must be cut.
                 Lastly, and this is the key point which must guide the search for a solu-
                 tion : the fact of adopting the right bank is so crucial for the continuation
                 of the line, from Bossébangou, that if the Erratum had intended to locate
                 the entire river in a single colony, it would have clearly said so ; it is far
                 too important and serious a matter to be overlooked. Consequently, in
                 the absence of such an indication, the fact of reaching the river has no
                 other meaning than that the frontier must follow the median line, which
                 is the usual solution for river boundaries which delimit the area between
                 the riparian countries and for ensuring that those countries have equal
                 access to its resources, in particular water. It is a common‑sense solution,
                 which is founded in law and equitable.

                                                                (Signed) Ahmed Mahiou.

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