Maritime boundary delimitation in the Gulf of Tonkin

5    Maritime boundary delimitation in the Gulf of Tonkin


The Gulf of Tonkin (Beibu Gulf in Chinese and Bac Bo Gulf in Vietnamese)1 is a shared water area between China and Vietnam. It has an area of 44,238sq km (about 24,000sq nm). The gulf has an average depth of 38m and the maximum depth is no more than 90m. The topography of the seabed is smooth.2 Geographically, it is categorized as a semi-enclosed gulf because it is embraced by the northern part of Vietnam, China’s Guangxi Province, the Leizhou Peninsula, and Hainan Island. The gulf measures 170nm at its widest and has two outlets: the Qiongzhou Strait between Hainan Island and the Leizhou Peninsula, approximately 19nm in width; and the major passage to the south, 125nm wide at its narrowest point.3 Although peacefully used by the people of the two countries for centuries, the Gulf itself has brought up a number of issues in the political, legal, and economic spheres. The occurrences of disputes are not unusual for the two nations in the past and at present. After the adoption of the United Nations Convention on the Law of the Sea (the LOS Convention) in 1982, some of the disputes had become more intensive and complicated because either of the two countries has the right under the Convention to extend its jurisdictional waters, leading to overlapping claims in the Gulf of Tonkin.

Under the present political and economic circumstances, the control of the sea areas is mainly for the control of the natural resources, particularly after the establishment of the exclusive economic zone (EEZ) of up to 200nm under the LOS Convention. Natural resources are rich in the Gulf of Tonkin. The fishing ground in the Gulf of Tonkin is one of the main fishing grounds in China, and also one of the principal fishing grounds for Vietnam. There are also plentiful mineral resources, especially oil and gas. The thick Leizhou sedimentary basin that underlies the gulf is an obvious target for oil exploration.4 According to the prediction of the China National Offshore Petroleum Company, the Gulf area is one of the biggest oil and gas concentrations in the world, having an oil deposit of about 2.29 billion tons and natural gas deposits of about 1,444 billion cubic m.5 It is reported that the South China Sea Offshore Oil Company pumped 14.2 million tons of crude oil in 1997, up nearly 10 percent to rank first among China’s offshore oil producers.6 In addition, the gulf is an important sea route of communication for Vietnam and China.7 These economic factors are influential for the delimitation of the Sino-Vietnamese maritime boundary in the Gulf of Tonkin.

There are established norms governing international relations in general, and governing the Sino-Vietnamese bilateral relations in particular. Although the boundary issue on the Gulf of Tonkin is multifaceted, the focus of this chapter is confined to the field of international law, particularly the law of the sea and international norms of territorial sovereignty. In addition, the respective domestic laws of either China or Vietnam which have impact upon the Gulf of Tonkin will be examined. The Gulf of Tonkin boundary was one of the three main unresolved boundary issues between China and Vietnam. For this reason, the settlement of the land boundary between China and Vietnam is a relevant issue. Furthermore, viewing it broadly, the issue of the Gulf of Tonkin constitutes a part of the whole South China Sea question.

The Sino-Vietnamese border was basically demarcated by the Sino-French Treaty of 1887 as a result of the Sino-French War of 1884–85 and finalized in 1895. The relevant version of the Sino-French Treaty of 26 June 1887 contains the following provision: “The islands which are east of the Paris meridian of 105°43′ east [108°3′ east of Greenwich], that is to say the north–south line passing through the eastern point of Tcha’s Kou or Quan-Chan [Tra Co], which forms the boundary, are also allocated to China. The island of Gotho [Kao Tao] and other islands west of this meridian belong to Annam.”8 Since the arrangements made under the treaty, the border situation had been relatively calm and there existed a traditional customary line of jurisdiction along the border areas of the two countries. However, the boundary, including the area of the Gulf of Tonkin, has never been accurately demarcated. The unclear situation of boundaries caused problems when the two countries had tensions and/or conflicts. Thus, for the sake of permanent peace and stability, the two sides have reached a consensus that a clear delimitation of the boundaries between the two is necessary.

The negotiation on the delimitation of the maritime boundary in the Gulf of Tonkin was actually initiated by Vietnam. In late December 1973, Vietnam informed China of its intention to prospect for oil in the Gulf and proposed to launch official negotiations between the two sides to delineate the maritime boundary.9 It should be pointed out that the Gulf of Tonkin was the first proposed topic among the three major border issues between China and Vietnam, which clearly signified its central importance for the whole territorial dispute of the two countries.10 The relevant negotiations first began in Beijing in August 1974, but they brought no result and broke down even prior to the Sino-Vietnamese armed conflict in 1979.

The two sides did not resume negotiations until 1993 when they attempted to solve the issue again. The tenth round of negotiations, held between 24 and 30 March 1998, like all the previous talks, ended without any concrete results.11 The only significant progress was made in 1993, when the general agreement on the basic principles for settling the disputes relating to the land border and to delimitation of the Gulf of Tonkin was adopted by the two parties.

Basic issues

The critical differences between the two sides rest with their disagreement over the standards for delimiting the sea areas. Both sides put forward various arguments to support their respective negotiation positions. At the beginning of the negotiations, Vietnam took the view that the Gulf of Tonkin had already been divided by the 1887 Sino-French treaty and the line of 108°3′13″ east longitude was the maritime boundary line. It further proposed to treat the whole gulf as historic waters belonging to Vietnam and China. This view was rejected by the Chinese side. According to the Chinese, the line in the said treaty was not a maritime boundary line because there was no reference in the treaty to such interpretation. Neither China nor Vietnam had ever exercised sovereignty over or jurisdiction in the gulf area beyond their territorial seas.12 On 18 January 1974, China, while agreeing to hold negotiations with Vietnam, proposed that a rectangular area in the middle of the gulf, bounded by the 18° and 20° parallels and the 107° and 108° meridians, be kept free from any oil exploration until the two parties reached an agreement on the boundary delimitation. China further put forward that

[e]ach side shall respect the other side’s sovereignty over its 12nm territorial sea, and the two sides shall demarcate their respective economic zones and continental shelves in the Beibu Gulf and other sea area in a fair and reasonable way in accordance with the relevant principles of present-day international law of the sea.13

The above differences indicate that there are several intermingled legal issues to be resolved, including inter alia, (1) whether the maritime boundary in the Gulf of Tonkin was already decided under the 1887 Treaty, (2) if not, whether the waters in the Gulf of Tonkin are historic waters, and (3) if not, how to delimit the respective jurisdictional areas for China and Vietnam.

The 1887 Treaty and subsequent documents were made in both Chinese and French. However, there are different expressions in the two official texts. To try to make a clearer explanation, Pao-min Chang offered two English translations, one from the French text and the other from the Chinese text of the 1887 Sino-French Treaty. The translated Chinese version reads as follows:

As far as the islands in the sea are concerned, the red line drawn by the officials of the two countries responsible for delineating the boundary shall be extended southward from the eastern hill-top of Chagushe (or Wanzhu in Chinese) and constitutes the dividing line. The islands lying east of this line shall belong to China. The islands of Jiutousan (Gotho in Vietnamese) and other small islands west of this line shall belong to Vietnam.

The translation from the French version is:

The islands east of the meridian 105°43′ east of the Paris meridian (i.e. the meridian 108°03′08″east of the Greenwich meridian), that is, east of the north–south line passing through the eastern tip of the Tch’a-kou or Ouan-chan (Tra-co) and forming the boundary, are all assigned to China. The Gotho islands and other islands lying west of that meridian belong to Annam.14

Due to the different texts of the Treaty, different interpretations may occur. There are some general rules in international law to govern the interpretation of a treaty. According to the law of treaties, if there is a provision in the treaty which gives the priority to one text, then this text should prevail once different interpretations occur from different texts.15 There was no such provision in the Sino-French treaty.16 Therefore the two versions are equally authentic. Under these circumstances, the interpretation of a treaty should be made according to the law of treaties by considering any agreement relating to the treaty, any instrument in connection with the conclusion of the treaty in addition to the text, including its preamble and annexes. Furthermore, supplementary means of interpretation may also be used, such as the preparatory work of the treaty and the circumstances of its conclusion in order to try to find the same meaning of the different expressions in each authentic text.17 Thus rationality and good faith in terms of treaty interpretation are very important, and sometimes critical.

Upon careful examination of the texts of the Treaty, it is discovered that the meaning of the above Chinese version indicates that the red line drawn on the attached map was a line to divide the islands in the Gulf of Tonkin rather than a line of maritime boundary. The line, which ended at about 21°23′ north latitude on the map, involved only the land and coastal islands of the two sides. Such a line was simply a form of geographical shorthand to avoid the need to name all the islands and such technique was used widely at that time in state practice.18 Even from the French version, it is hardly asserted that the wording “forming the boundary” be a line of maritime boundary. It is actually a line equivalent to the red line mentioned in the Chinese version.19 As is revealed in history, the purpose of concluding this treaty was to demarcate the boundary between China and Vietnam according to the Sino-French Treaty of 9 June 1885. There was no mention of the Gulf of Tonkin and only part of the Gulf close to the land was shown on the attached map. Thus the representatives from both parties had no authorization and/or intention to delimit the maritime boundary in the Gulf of Tonkin.20 Moreover, at the time when the freedom of the seas prevailed, it was beyond imagination that the two countries could divide between themselves a vast gulf like the Gulf of Tonkin into two respective jurisdictional waters. The prevailing limit of the territorial sea for a coastal state at that time was out to 3nm.21 It is impossible that China and Vietnam could have endorsed the modern concepts of the law of the sea to delimit the Gulf of Tonkin. Clearly, therefore, the 1887 Treaty did not divide the Sino-Vietnamese maritime boundary in the Gulf of Tonkin.

Additionally, the Vietnamese argument that the maritime boundary was decided by the 1887 Treaty was impractical in theory. As correctly pointed out by Prescott, renowned Australian specialist in maritime boundary delimitation, Vietnam would face four serious difficulties for sustaining its arguments. First, the meridian in the Treaty has no termini. Second, if the meridian was the maritime boundary it would mean that Vietnam was not entitled to any territorial waters off the eastern tip of Tra Co. Third, if this meridian was meant to be a maritime boundary, it was so far out of character with the prevailing concepts of maritime sovereignty of the period that it would have been given special mention in the text. Fourth, there is nothing in the treaty to distinguish the use of this meridian from the use of straight lines by other colonial powers in other treaties to separate island groups.22

Perhaps the Vietnamese had realized the obstacles to their insistence on the meridian. In its own practice, Vietnam rejected a similar line, called “Brévie Line”, drawn in 1939 in the Gulf of Thailand as a line that could divide the areas of the seabed between Cambodia and Vietnam.23 Though there is no indication that Vietnam has abandoned its former position, the fact that Vietnam agreed to delimit the gulf clearly indicates that the delimitation issue had not been resolved under the 1887 Sino-French Treaty. In fact, as early as December 1973, the Vietnamese vice foreign minister expressed that the Bac Bo Gulf had not been delimited because of the war in Vietnam.24

However, Vietnam should not be blamed for invoking the meridian line to defend its interest in the Gulf of Tonkin. It is a political act. If its argument were accepted by China, then Vietnam could obtain two-thirds of the water area in the Gulf after delimitation. The question is whether its argument is tenable in practice and in theory. Otherwise it could easily be defeated. The meridian line mentioned in the 1887 Treaty was also once invoked by the Chinese side. As early as the 1930s, when the French authority in Vietnam occupied some islands in the South China Sea, the then Chinese Government argued that the meridian line in the 1887 Treaty showed that Vietnam had no rights to the islands east of this line.25 It is therefore understandable that Vietnam used the meridian line in the Treaty to support its own claim. The line might play a role in the delimitation of the Gulf of Tonkin as one reference of indirect evidence, which could favor the Vietnamese side. In history, the line was used several times for the convenience of exercising some jurisdictional functions for the two countries, such as criminal jurisdiction after 1887 and possession of specimens from scientific investigation in the gulf in 1961.26 These historical encounters have already been invoked by the Vietnamese side to justify its position, but the Chinese side has different interpretations.27

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