Alexander Anthony
In March 2014, satellite imagery showed a Chinese vessel dredging up sand near Cuarteron Reef—a submerged coral reef in the Spratly Islands.[1] Less than a year later, part of the reef had risen above sea level, and was littered with construction equipment.[2] Seven years after that, the island was fully settled, containing vegetation, a helipad, and various buildings.[3]
Cuarteron Reef is one of several artificial islands that have popped up in the Spratly Island chain since 2013.[4] The islands are a part of China’s broader strategy to enforce its territorial claims in the South China Sea.[5] Researchers have raised concerns about the environmental harm associated with dredging for these islands, as well as the illegal fishing of protected species by Chinese vessels operating around the islands.[6] However, for China, the concern is more territorial than environmental.
The Nine-Dash Line
Since the 1950s, China has used a dashed line, known as the “nine-dash line,” to mark its maritime boundary in the South China Sea.[7] China claims it has “indisputable sovereignty” over this territory, which covers almost the entire sea.[8] Increasingly, China has asserted its claim to this territory, seizing reefs and shoals, conducting oil exploration, banning non-Chinese fishing vessels from certain areas, and building artificial islands.[9]
China’s actions are considered by most to be violations of international law, particularly the United Nations Convention on the Law of the Sea (“UNCLOS”). UNCLOS sets out the area beyond a country’s territorial waters where its “rights and jurisdiction” extend.[10] Countries are entitled to an “exclusive economic zone” (“EEZ”) that can extend up to “200 nautical miles” from its coastal baseline.[11] Within EEZs, countries have the exclusive “sovereign rights for . . . exploring and exploiting, . . . living or non-living” resources in the waters and seabed.[12] China’s nine-dash line not only extends past its internationally recognized EEZ, but overlaps with the EEZs of other nations in the South China Sea.[13] As such, by fishing for protected species, exploring for oil, and building islands (without the permission of other South China Sea nations) in these overlapping areas, China violates UNCLOS.
The South China Sea Arbitration
In 2013, the Philippines challenged China’s behavior, bringing a case in the Permanent Court of Arbitration (“PCA”) which, among other things, sought to declare the nine-dash line invalid and China’s actions unlawful.[14] China defended its activities, claiming that its historical use of the territory and newly built islands gave it the ability to explore and exploit any resources within the nine-dash line.[15] Specifically, China stated that its artificial islands entitle it to additional EEZs—around each island.[16] In 2016, the court issued an award, holding the nine-dash line invalid and stating that China’s artificial islands did not entitle it to an extended EEZ.[17] Predictably, China condemned the decision and refused to follow it.[18] However, the Court’s emphasis on the country’s environmental obligations regarding illegal fishing, shows a positive development in international law.
The Obligation to Prevent Illegal Fishing
Although the PCA’s award was mostly based on the territorial provisions of UNCLOS, part of the opinion emphasized the significant harm that the artificial islands had caused to the marine environment.[19] The court stated China “seriously violated its obligation to preserve and protect the marine environment in the South China Sea” by (1) building artificial islands which damaged the reef environments on which they were built, and (2) failing to stop Chinese fishing vessels from “engaging in harmful harvesting activities of endangered species.”[20]
The PCA’s recognition of China’s obligation to stop its vessels from illegally fishing affirms the duty of a host state to assert its jurisdiction over the vessels that are registered in that state. Currently, many states do not hold their fishing vessels accountable when they violate international or domestic fishing regulations, especially when those violations occur outside of the host state’s EEZ.[21] These are called flag of convenience (“FOC”) states and are considered one of the main reasons why illegal fishing remains widespread.[22] As such, some researchers have recommended that to reduce illegal fishing, actions must be taken by FOC states, improving monitoring of fishing vessels that fly their flags, and properly enforcing international and domestic standards for fishing.[23]
Rulings from international tribunals recognizing countries’ obligations to stop illegal fishing can help push states towards this goal. Despite China’s supposed refusal to follow the PCA’s ruling, the country acceded to the United Nations Food and Agriculture Organization’s Agreement on Port State Measures (PSMA) in 2025.[24] PSMA is a binding treaty that requires contracting states to implement strict controls that prevent illegally caught fish from moving undetected through their ports.[25] As such, even though China has claimed it will not follow the PCA’s ruling, by signing onto PSMA, the country clearly shows that it recognizes its obligation to stop illegal fishing and is willing to take steps to effectively fulfill that obligation. In the future, similar rulings emphasizing this obligation for FOC states could encourage such states to take similar steps, leading to a more coordinated response in the fight against illegal fishing.
[1] See Cuarteron Reef, Asia Mar. Transparency Initiative, https://amti.csis.org/cuarteron-reef/ (last visited Nov. 23, 2025) (documenting changes to Cuarteron Reef over time through satellite imagery).
[2] Id.
[3] Id.
[4] Matthew Southerland, China’s Island Building in the South China Sea: Damage to the Marine Environment, Implications, and International Law, U.S.-China Econ. & Sec. Rev. Comm’n, at 3 (Apr. 12, 2016), https://www.uscc.gov/research/chinas-island-building-south-china-sea-damage-marine-environment-implications-and.
[5] Id.
[6] Mike Ives, The Rising Environmental Toll of China’s Offshore Island Grab, Yale Env’t 360 (Oct. 10, 2016), https://e360.yale.edu/features/rising_environmental_toll_china_artificial_islands_south_china_sea.
[7] Hannah Beech, Just Where Exactly Did China Get the South China Sea Nine-Dash Line From?, Time: World (July 19, 2016, at 02:30 EDT), https://time.com/4412191/nine-dash-line-9-south-china-sea/.
[8] Attachment to Permanent Mission of China to the Secretary-General of the United Nations, Note Verbale, at 1, No. CML/17/2009 (May 7, 2009) (available at https://www.un.org/depts/los/clcs_new/submissions_files/mysvnm33_09/chn_2009re_mys_vnm_e.pdf).
[9] See Dung Huynh, Facing the Ravenous Sea Dragon: How Weaker Nations Confront Chinese Coercion in the South China Sea, RAND 68 (Nov. 1, 2022) https://www.rand.org/pubs/rgs_dissertations/RGSDA2470-1.html (describing various actions China has taken to assert its territorial claims in the South China Sea since the 1990s); See also Ctr. for Preventative Action, Territorial Disputes in the South China Sea, Council on Foreign Rel.: Glob. Conflict Tracker (Sep. 17, 2024), https://www.cfr.org/global-conflict-tracker/conflict/territorial-disputes-south-china-sea (“In recent years, satellite imagery has shown China’s increased efforts to reclaim land in the South China Sea by physically increasing the islands’ size or creating new ones altogether.”).
[10] U.N. Convention on the Law of the Sea art. 55, Dec. 10, 1982, 1833 U.N.T.S. 397.
[11] Id. art. 57.
[12] Id. art. 56.
[13] See Maritime Claims of the Indo-Pacific, Asia Mar. Transparency Initiative, https://amti.csis.org/maritime-claims-map/ (last visited Nov. 23, 2025) (showing overlap of the nine-dash line with the EEZs of Indonesia, the Philippines, Malaysia, Vietnam, Brunie, Taiwan).
[14] In re South China Sea Arbitration (Phil. v. China), PCA Case No. 2013-19, Award (UNCLOS Annex VII Arb. Trib. July 12, 2016) (available at https://docs.pca-cpa.org/2016/07/PH-CN-20160712-Award.pdf).
[15] Id. ¶ 185.
[16] Id.
[17] Id. ¶ 278, 646.
[18] Tom Phillips, Beijing rejects tribunal’s ruling in South China Sea case, Guardian (July 12, 2016, at 13:21 EDT), https://www.theguardian.com/world/2016/jul/12/philippines-wins-south-china-sea-case-against-china.
[19] In re South China Sea Arbitration (Phil. v. China), PCA Case No. 2013-19, Award (UNCLOS Annex VII Arb. Trib. July 12, 2016) ¶ 992-993 (available at https://docs.pca-cpa.org/2016/07/PH-CN-20160712-Award.pdf).
[20] Id. ¶ 943, 992-993.
[21] David J. Agnew et al., Estimating the Worldwide Extent of Illegal Fishing, PLOS One (Feb. 25, 2009), at 4, https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0004570.
[22] Id. at 1–4.
[23] Agnew et al., supra note 21, at 5.
[24] Elaine Young, China Joins Treaty to Fight Illegal Fishing, a Major Milestone for Ocean Governance, Pew (Apr. 17, 2025), https://www.pew.org/en/research-and-analysis/articles/2025/04/17/china-joins-treaty-to-fight-illegal-fishing-a-major-milestone-for-ocean-governance.
[25] Id.