Fri, Jun 05, 2026 page8

• On the maritime delimitation

  • By Chiang Huang-chih 姜皇池
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  On Thursday last week, the Philippines and Japan issued a joint statement on their Comprehensive Strategic Partnership, reaffirming the need to further promote peace, stability and mutual trust through maritime cooperation grounded in respect for international law. They also announced the commencement of formal negotiations on the delimitation of their respective exclusive economic zones (EEZ) and continental shelves, to be conducted in accordance with international law — particularly the relevant provisions of the UN Convention on the Law of the Sea (UNCLOS) — and with reference to relevant international judicial precedents, with the aim of enhancing legal certainty in the region.

  China’s Ministry of Foreign Affairs immediately lodged a protest, asserting — on the basis of its claim to sovereignty over Taiwan — that Beijing also holds maritime sovereign rights and other entitlements under international law over the overlapping waters between Japan and the Philippines. Thereafter, China immediately dispatched its coast guard vessels to conduct “law enforcement patrols.”

  Taiwan’s Ministry of Foreign Affairs, for its part, rejected China’s territorial claims over Taiwan, stating that Beijing holds no sovereign rights whatsoever in the waters east of Taiwan, while also calling on Japan and the Philippines to fully recognize the existence of Taiwan’s sovereignty and rights, emphasizing that any outcome reached without Taiwan’s consent or participation would have no legal binding force on Taiwan.

  It is clear that Taiwan is entitled to claim a 200 nautical mile (370.4km) maritime zone from the baseline of Taiwan. Furthermore, the Taiwan-Japan Fisheries Agreement and the Taiwan-Philippines Fisheries Enforcement Cooperation Agreement represent arrangements made by Japan and the Philippines respectively with Taiwan concerning relevant rights under international law. While Taiwan affirms its support for neighboring states resolving differences through peaceful, international-law-based means, it must be candidly noted that the overlapping portions of the Japanese and Philippine EEZs — save for a small corner to the southeast — largely overlap with the EEZ claimed by Taiwan, and thus risk encroaching upon Taiwan’s maritime rights. The fact Japan and the Philippines have proceeded with maritime delimitation consultations without Taiwan’s participation is a matter open to questions.

  Under international law, the governing maritime delimitation rules are those provisions in articles 74 and 83 of UNCLOS. However, in practice, where delimitation is pursued through negotiation, the parties enjoy considerable discretion. Even so, when the scope of negotiations between two nations extends into the maritime zones of a third nation, there are serious legal questions as to whether the two negotiating nations have the authority to include that third nation’s maritime areas within the scope of delimitation.

  First, most of the overlapping waters between Japan and the Philippines constitute a zone of tripartite overlap, and Taiwan is undeniably one of the nations concerned. Under the legal principle as articulated in Article 74 Section 3 of UNCLOS, Japan and the Philippines should, in a spirit of maximum good faith, effort and cooperation, engage Taiwan in meaningful consultations and cooperation. And thus, any agreement that fails to secure Taiwan’s consent with respect to the portions involving Taiwan’s maritime areas would be difficult to regard as a final delimitation agreement.

  Second, a review of relevant international judicial practices on maritime delimitation reveals that when third-nation maritime areas are implicated, the scope of delimitation by international courts or dispute settlement bodies might be correspondingly curtailed. In practice, two approaches can be identified: One limits the delimitation boundary to the equidistant line between the parties and the third nation’s claimed zone; the other excludes entirely the area to which the third nation has an entitled claim. Viewed in this light, if Japan and the Philippines were to conduct their negotiations in accordance with the jurisprudence of international tribunals, they should confine the delimitation boundary to areas beyond the extent of Taiwan’s EEZ entitlement. Failure to do so would be inconsistent with the proposed objective — articulated in their joint statement — of enhancing legal stability.

  Third, should the two nations insist on proceeding without Taiwan’s participation, then by virtue of Article 34 of the Vienna Convention on the Law of Treaties — which enshrines the principle that pacta tertiis nec nocent nec prosunt (“a treaty does not create obligations or rights for a third nation without its consent”) — whatever the outcome of the Japan-Philippines negotiations might be, it shall have no legal bearing vis-a-vis Taiwan. Taiwan is entitled to retain the right, under international law and UNCLOS, to defend its maritime rights.

  Finally, given that Taiwan and China have each governed their respective territories independently of one another for more than 70 years, China holds no territorial sovereignty of any meaningful kind over Taiwan or the surrounding islets under Taiwan’s effective control. Accordingly, any maritime issues or disputes arising among Taiwan, Japan and the Philippines in their overlapping waters have no legal nexus with China as a matter of international law. And yet China has seen fit to dispatch its coast guard vessels on so-called “law enforcement patrols.” Historically, it has been the Coast Guard Administration — not any external enforcement force — that has maintained order in these waters. China’s actions clearly constitute an unmistakable disruption of the “status quo” that has prevailed for more than seven decades.

  There is nothing inherently objectionable about Japan and the Philippines resolving their maritime disputes through peaceful means consistent with international law; nonetheless, given that the process might implicate Taiwan’s maritime rights in its eastern waters, a degree of caution is needed. However, such potential risks remain manageable on legal and diplomatic fronts.

  Of far greater concern is China’s opportunistic exploitation of the current situation to disrupt the law enforcement “status quo” in the eastern waters — a development that poses an immediate and pressing danger, one that demands to be treated with the utmost seriousness. In this regard, it appears that the government needs to take proactive measures to defend its sovereignty and to maintain the “status quo.”

  Chiang Huang-chih is a professor of international law at National Taiwan University’s College of Law.
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