The Republic of Korea (ROK) has unresolved disputes over maritime boundary delimitation with the Democratic People’s Republic of Korea (DPRK) in the Yellow Sea (West Sea in Korea); China in the Yellow and East China Seas; and Japan in the Sea of Japan (East Sea in Korea). South Korea and Japan also dispute the sovereignty of the Dokdo/Takeshima Islands. This profile examines South Korea’s unresolved maritime disputes with North Korea and China.
Despite multiple rounds of talks, South Korea and China have been unable to reconcile their overlapping exclusive economic zone (EEZ) claims in the Yellow Sea and northern East China Sea, including around Socotra Rock (Ieodo in Korean). A primary obstacle to an agreement has been each side’s use of different approaches for drawing a maritime boundary in the area. South Korea’s position is that an EEZ should be divided according to the median line principle per the United Nations Convention on the Law of the Sea (UNCLOS), Article 15, wherein the boundary is demarcated equidistant from the coastal baselines of each state. However, China maintains that the maritime boundary should be proportional to its longer coastline and larger population.
In 2001, China and South Korea signed a fisheries agreement. The agreement created a provisional measures zone (PMZ), an area of joint Sino-Korean fisheries management, open to both Chinese and Korean fishing. On the western and eastern edges of the PMZ, the agreement also set forth two transitional zones where fishing by the other state would be gradually reduced over a four-year period, after which each zone would be incorporated into the respective Chinese or South Korean EEZ. However, Chinese fishing in the ROK’s transitional zone never abated. Furthermore, Chinese vessels have continued to operate illegally elsewhere in the ROK’s EEZ and its territorial waters, resulting in clashes between Chinese fishermen and the Korea Coast Guard.
South Korea’s other major maritime dispute in the Yellow Sea concerns the Northern Limit Line (NLL), the de facto maritime boundary between the two Koreas. The NLL was demarcated by the UN Command following 1953 Korean Armistice Agreement. However, the DPRK has never accepted the NLL’s validity and claims a more southerly maritime border. In the April 2018 Panmunjom Declaration, the two Koreas agreed to establish a “maritime peace zone” in the waters surrounding the confrontation-prone NLL, withdrawing artillery, ceasing broadcasts, closing guard posts, and implementing a no-fly zone. However, since North Korean nuclear diplomacy with both South Korea and the United States stalled in 2019, the DPRK has undertaken provocative actions, including artillery drills, which Seoul has formally rebuked for violating the principles of the maritime peace zone.
The ROK’s maritime disputes stem partly from political and territorial ambiguities following imperial Japan’s defeat in 1945. When U.S. and Soviet troops withdrew from the two Koreas in 1948, key territorial issues remained unresolved. Shortly thereafter, the Korean War broke out in 1950. Although an armistice halted the conflict in 1953, no peace treaty was signed. The armistice established the Demilitarized Zone (DMZ) along the land border but did not settle maritime boundaries.
Designated in 1953, the NLL was originally a UN Command operational barrier to prevent ROK naval forces from probing too far north and inciting conflict with the DPRK. Due to unresolved maritime boundary resolutions and allied naval dominance, the NLL became the de facto inter-Korean maritime boundary in the Yellow Sea. However, North Korea never accepted the NLL and has questioned its validity based on both international law and the terms of the 1953 armistice.
President Syngman Rhee first declared the ROK’s maritime boundaries in January 1952, claiming all maritime territory in the Yellow Sea north of 32° N and east of 124° E. The Syngman Rhee Line predates the 1982 formalization of the EEZ concept in international law through UNCLOS. South Korea and China are both parties to UNCLOS, whereas North Korea has signed but not ratified the treaty. Another key Cold War development was President Park Chung-hee’s declaration in the 1970s of a “self-restraint fishery line” 30 nautical miles east of China’s then-claimed fishing rights area, which helped successfully limit Sino-Korean maritime confrontations.
Unofficial ROK-China maritime negotiations began in 1989, with mutual diplomatic recognition following in August 1992. Around this time, negotiations of fishing rights began, with Beijing and Seoul eventually reaching a fisheries agreement nearly a decade later in June 2001. This agreement established a joint fishery management area comprising one PMZ and two transitional zones. In the PMZ, vessels from both countries are permitted to operate under their respective government’s jurisdiction. A key driver of this bilateral fishing zone was the 1994 enactment by UNCLOS that stipulated joint resource management in areas where conflicting EEZ claims overlap. The two transitional zones flank each side of the PMZ. Per the agreement, fishing in another state’s transitional zone would be progressively reduced, and the respective transitional zones would be absorbed into the Chinese or South Korean EEZs over a four-year period. This has yet to occur, however, as Chinese fishing in the ROK’s transitional zone has continued and, in recent years, even increased.
The ROK has sought to enforce its Yellow and East China Sea claims, particularly in the area around Socotra Rock, while China has taken measures to challenge these claims. Yet, even though the maritime area surrounding Socotra Rock is disputed, the ROK exercises de facto control of this submerged feature. From 1995 to 2001, South Korea constructed the Ieodo Ocean Research Station by erecting a platform atop the rock.
The most important manifestation of Seoul and Beijing’s inability to resolve their maritime claim disputes is the lack of an EEZ delimitation. This, along with an only partially implemented fisheries agreement, has generated ambiguity and led to “a series of physical conflicts between the Korean coast guard and Chinese fishing vessels in recent years.” Progress in delimitation talks is obstructed by China and South Korea insisting on different rationales for drawing a maritime boundary. The ROK’s position is to determine demarcation through an equidistance solution based on UNCLOS, wherein the maritime boundary would be equidistant from the Chinese and Korean coastlines. However, China contends that the line should be farther east, roughly along 124° E—a position derived from both the 1952 Rhee Line and a 1962 Sino–North Korean agreement. In an effort to bolster its claim, Beijing has also applied arguments based on the continental shelf, ocean floor topography, and a proposed “silt line” where seafloor silt from both sides meets.
The other major South Korean position on the Yellow Sea that conflicts with a neighboring state is the NLL, the de facto inter-Korean maritime boundary. Since the 1953 armistice, this boundary has been a source of friction and occasionally conflict. The DPRK sometimes exploits the NLL for political reasons, orchestrating limited provocations such as sending vessels to probe south of the line and retreating north after the statement has been made. The NLL cuts across fertile fishing grounds, and Chinese fishing vessels often traverse the line to avoid pursuit by ROK authorities. As a result, though an inter-Korean issue, the NLL dispute contributes to the magnitude of Chinese fishing in Korean waters, including in South Korean territorial waters proper (not merely just in the ROK’s EEZ).
The most serious NLL-related security threat remains, however, the potential for inter-Korean naval clashes, especially since North Korea’s maritime boundary claim (declared in September 1999) is many kilometers south of the NLL. A DPRK midget submarine sank an ROK Navy corvette, Cheonan, in March 2010, resulting in the deaths of 46 ROK Navy personnel; Yeonpyeong Island was shelled in November of that same year. These were stark reminders of the North Korean maritime threat.
President Moon Jae-in has made addressing inter-Korean maritime conflict a priority in his diplomatic push for reconciliation with North Korea. During the April 2018 inter-Korean summit, Moon and Kim Jong-un declared their intention to create a “maritime peace zone” encompassing the entire NLL area in the Yellow Sea. During their September 2018 summit, Moon and Kim signed the “Agreement on the Implementation of the Historic Panmunjom Declaration in the Military Domain,” wherein both sides “agreed to take military measures to prevent accidental military clashes and ensure safe fishing activities” in the waters around the NLL. The two leaders also agreed to establish a pilot joint fishing zone in the Yellow Sea and develop mechanisms for joint inter-Korean fishery enforcement patrols.
“[The Northern Limit Line] is a critical border that contributes to keeping peace on our land.”
– Lee Myung-bak campaigning for the ROK presidency, 2007
“[W]hatever form it may take, Ieodo [Socotra Rock] comes within South Korea’s jurisdiction.”
– President Lee Myung-bak responding to China’s announcement it would send ocean surveillance vessels to the waters around Socotra Rock, 2012
“Suyan [Socotra] Rock is situate[d] in the waters where the exclusive economic zone of China and the ROK overlap. The ownership of the rock should be determined through bilateral negotiation, pending which, neither of the two should take unilateral moves in these waters. China and the ROK have a consensus on the Suyan Rock, that is, the rock does not have territorial status, and the two sides have no territorial disputes…The two sides need to work out sovereignty through bilateral consultations.”
– PRC Foreign Ministry spokesperson Liu Weimin, 2012
“[I]f the EEZ boundary between the ROK and China is demarcated in accordance with the median-line principle, Ieodo [Socotra Rock] definitely belongs to the ROK maritime territory. While China takes a different stance, we will make every effort to make sure that we maintain our jurisdiction over the island based on the aforementioned position.”
– Spokesperson and deputy minister for public relations Cho Tai-young, 2012
“China’s announcement of [its expanded] ADIZ cannot affect the ROK’s jurisdiction over Ieodo in any way.”
– Spokesperson and deputy minister for public relations Cho Tai-young, 2013
“Fishery cooperation is an important part of China-ROK relations… It is inevitable that China and the ROK may encounter some disputes or problems in the course of advancing fishery cooperation. What is important is that the two should act in accordance with the fishery agreement and relevant consensus, enhance communication and coordination, keep calm and rational, and take a long-term and objective view to properly treat and solve fishery problems.”
– PRC Foreign Ministry spokesperson Geng Shuang, 2016
“The two sides agreed to devise a practical scheme to turn the area of the Northern Limit Line in the West Sea [Yellow Sea] into a maritime peace zone to prevent accidental military clashes and ensure safe fishing activities there.”
– Article 2 of the Panmunjom Declaration, April 28, 2018
1952: President Syngman Rhee unilaterally declares the ROK’s maritime claims as extending to 124° E, including Socotra Rock in the East China Sea.
1962: China and North Korea agree on the 124° E line as their maritime boundary.
1992: The People’s Liberation Army Navy conducts its first survey of Socotra Rock.
1995–2001: The ROK constructs the Ieodo Ocean Research Station on Socotra Rock, which uses the submerged reef to support a permanent, above-surface structure.
June 1999: ROK Navy patrol ships clash with a group of North Korean fishing boats and naval vessels that intruded south of the NLL near Yeonpyeong The skirmish, which occurred amid a North Korean campaign to redraw the inter-Korean maritime boundary, caused the sinking of a DPRK torpedo boat and at least 30 North Korean deaths.
September 1999: North Korea declares a new West Sea military demarcation line significantly south of the NLL.
2000s: South Korea begins to seize large numbers of illegal Chinese fishing vessels in the Yellow Sea (increasing from 43 per year in the 1990s to around 400 per year in the 2000s). The peak years for suppression of illegal Chinese fishing were 2004–8.
June 2001: China and South Korea reach a fisheries agreement.
June 2002: Two North Korean patrol boats cross the NLL and clash with South Korean patrol craft near Yeonpyeong Island. Both sides suffer casualties, and a South Korean patrol boat sinks.
June 2003: The ROK begins operation of the Ieodo Ocean Research Station.
January 2010: The ROK begins construction of Jeju Naval Base (completed in early 2016), extending the ROK Navy’s ability to project power in the Yellow and East China Seas.
March 2010: North Korea sinks the Cheonan, an ROK Navy vessel, near the NLL.
November 2010: In response to routine South Korean drills, North Korea launches a deliberate, sustained artillery bombardment of Yeonpyeong Island, killing four South Koreans.
December 2010: Two Chinese fishermen are killed during a confrontation with the Korea Coast Guard in the Yellow Sea.
December 2011: A Korea Coast Guard officer is killed during a confrontation with Chinese fishermen in the Yellow Sea.
April 2013: The ROK decides to “gradually” turn the scientific station at Socotra Rock from an unmanned facility into a manned one, with at least one permanent researcher residing there at any given time.
November 2013: China declares an expanded air defense identification zone (ADIZ) that includes the airspace around Socotra Rock. South Korea follows suit the next month. Japan also maintains an ADIZ over some of this area, which it expanded in 2010 to encompass the Senkaku Islands, creating a substantial three-country ADIZ overlap in the northern East China Sea.
June 2016: ROK Navy and Korea Coast Guard undertake joint patrols with the UN Command to combat illegal Chinese fishing in the Han River estuary.
October 2016: A fleet of forty Chinese fishing vessels sink a Korea Coast Guard vessel in the Yellow Sea, leading to diplomatic tensions. Following the incident, the Korea Coast Guard is authorized to use live-fire ammunition in serious clashes.
April 2018: President Moon Jae-in and Chairman Kim Jong-un declare their intention to establish a “maritime peace zone” encompassing the entire NLL area.
2018 and 2019: Chinese military vessels enter the ROK-claimed EEZ an average of five times per week, double the average prior to 2018, prompting both government concern and negative media attention in South Korea.
The Yellow Sea is a rich fishing ground due to its shallow depths generated by a seabed sitting on a continental shelf. The waters closest to the Korean west coast are breeding grounds for blue crabs whose market price has risen dramatically in recent years (from $3.50 per kilogram in 2014 to $42.00 per kilogram in 2020), representing millions of dollars in actual or potential income for the South Korean fishing industry.
No known oil or gas reserves lie in disputed areas of the Yellow Sea. There has been speculation that oil reserves may exist in the disputed area of the East China Sea around Socotra Rock, but this remains unconfirmed.
The ROK has constructed a permanent structure, the Ieodo Ocean Research Station, on Socotra Rock. Although the station is primarily operated remotely, it can sustain twelve people for approximately two weeks. A 2016 presentation to the North Pacific Marine Science Organization by the Korea Institute of Ocean Science and Technology and the Korean Hydrographic and Oceanographic Agency states that the station could be expanded to “install new sensors from the interdisciplinary field.”  It has a small helipad and a cellar deck with resupply capacity for small craft or submarines.
 Terence Roehrig, “South Korea: The Challenges of a Maritime Nation,” National Bureau of Asian Research (NBR), Maritime Awareness Project, December 23, 2019, https://www.nbr.org/publication/south-korea-the-challenges-of-a-maritime-nation.
 Shannon Tiezzi, “Is China Ready to Solve One of Its Maritime Disputes?” Diplomat, November 7, 2015, https://thediplomat.com/2015/11/is-china-ready-to-solve-one-of-its-maritime-disputes.
 Suk Kyoon Kim, “Illegal Chinese Fishing in the Yellow Sea: A Korean Officer’s Perspective,“ Journal of East Asia and International Law 5, no. 2 (2012): 455–77.
 CIA, “The West Coast Korean Islands,” January 1, 1974, available in “North Korea International Documentation Project E-Dossier #6: The Origins of the Northern Limit Line Dispute,” Woodrow Wilson International Center for Scholars, May 2012, https://www.wilsoncenter.org/sites/default/files/media/documents/publication/NKIDP_eDossier_6_Origins_of_the_Northern_Limit_Line.pdf.
 Terence Roehrig, “Introduction: The Origins of the Northern Limit Line Dispute, available in “North Korea International Documentation Project E-Dossier #6.”
 Syngman Rhee, “Presidential Proclamation of Sovereignty over Adjacent Seas,” January 18, 1952, available at https://en.wikisource.org/wiki/Presidential_Proclamation_of_Sovereignty_over_Adjacent_Seas. See also Kim, “Illegal Chinese Fishing in the Yellow Sea,” 457.
 Kim, “Illegal Chinese Fishing in the Yellow Sea,” 459.
 Kim, “Illegal Chinese Fishing in the Yellow Sea,” 460.
 “Korea-China Fisheries Agreement Comes into Effect,” Ministry of Foreign Affairs (ROK), Press Release, June 29, 2001.
 Article 7, section 3, of the ROK-China Fisheries Agreement, signed Aug. 3, 2000. The full agreement is available in Korean and Chinese at https://m.blog.naver.com/kangsong2000/220671474409. Article 7 section 3 says in part: “Each party to this treaty shall administer and take necessary measures pertaining to its own nationals and its own fishing vessels engaged in fishing activities in the Provisional Measures Zone, and shall not administer or take other measures pertaining to nationals and fishing vessels of the other party.”
 David Rosenberg, “Managing the Resources of the China Seas: China’s Bilateral Fisheries Agreements with Japan, South Korea, and Vietnam,” Asia-Pacific Journal Japan Focus 3, no. 6 (2005): 1–5, http://apjjf.org/-David-Rosenberg/1789/article.html.
 Lyle J. Morris, “South Korea Cracks Down on Illegal Chinese Fishing, with Violent Results,” Diplomat, November 3, 2016, https://thediplomat.com/2016/11/south-korea-cracks-down-on-illegal-chinese-fisherman-with-violent-results.
 Jinyong Jeong et al., “Introduction to the Ocean Research Stations (ORSs) in Korea and Application Activities” (conference presentation at the 2016 PICES Annual Meeting, San Diego, November 2016), https://meetings.pices.int/Publications/Presentations/PICES-2016/S13-Jeong.pdf.
 Sukjoon Yoon, “Korea-China Maritime Boundary Talks: Implications for South China Sea,” S. Rajaratnam School of International Studies (RSIS), RSIS Commentary, April 13, 2015, https://www.rsis.edu.sg/wp-content/uploads/2015/04/CO15089.pdf.
 “China’s Self-Serving 124 Degree East Longitude Maritime Border Claim at Fifty,” Chosun ilbo [in Korean], May 22, 2012, http://news.chosun.com/site/data/html_dir/2012/05/22/2012052200216.html.
 Keun-Gwan Lee, “Continental Shelf Delimitation in the Yellow Sea,” Woodrow Wilson International Center for Scholars, 7, https://www.wilsoncenter.org/sites/default/files/media/documents/publication/Keun-Gwan_Lee_2_.pdf.
 Shawn Ho, “Tensions in the Yellow Sea: Crabs and the Inter-Korea Border Dispute,” RSIS, RSIS Commentary, July 11, 2016, https://www.rsis.edu.sg/wp-content/uploads/2016/07/CO16172.pdf.
 “Coast Guard Seizes Eleventh Illegal Chinese Fishing Ship Off South Coast of Socheong Island,” Incheon Today [in Korean], May 29, 2019, http://www.incheontoday.com/news/articleView.html?idxno=114714.
 Jon M. Van Dyke, “The Maritime Boundary between North & South Korea in the Yellow (West) Sea,” 38 North, July 29, 2010, https://www.38north.org/2010/07/the-maritime-boundary-between-north-south-korea-in-the-yellow-west-sea; and Jon M. Van Dyke, “The Republic of Korea’s Maritime Boundaries,” International Journal of Marine and Coastal Law 18, no. 4 (2003): 509–40.
 “Panmunjom Declaration on Peace, Prosperity and Reunification of the Korean Peninsula” (letter from the representatives of the Democratic People’s Republic of Korea and the Republic of Korea to the United Nations addressed to the Secretary-General, September 6, 2018), available at http://www.mofa.go.kr/eng/brd/m_5478/view.do.
 “Agreement on the Implementation of the Historic Panmunjom Declaration in the Military Domain,” National Committee on North Korea, September 19, 2018, https://www.ncnk.org/resources/publications/agreement-implementation-historic-panmunjom-declaration-military-domain.pdf.
 Senan Fox, China, South Korea, and the Socotra Rock Dispute: A Submerged Rock and Its Destabilizing Potential (Singapore: Springer Singapore, 2018), 13.
 Jon M. Van Dyke, Mark Valencia, and Jenny Miller Garmendia, “The North/South Korea Boundary Dispute in the Yellow (West) Sea,” Marine Policy 27, no. 2 (2003): 143–58.
 Dyke, “The Republic of Korea’s Maritime Boundaries,” 4.
 Kim, “Illegal Chinese Fishing in the Yellow Sea,” 467.
 Jack Kim and Lee Jae-won, “North Korea Shells South in Fiercest Attack in Decades,” Reuters, November 23, 2010, https://www.reuters.com/article/us-korea-north-artillery/north-korea-shells-south-in-fiercest-attack-in-decades-idUSTRE6AM0YS20101123?loomia_ow=t0:s0:a49:g43:r1:c0.586538:b39750226:z0.
 Kim, “Illegal Chinese Fishing in the Yellow Sea,” 469.
 Kim, “Illegal Chinese Fishing in the Yellow Sea,” 456, 470.
 “With Korea-China Summit Ahead,” Chosun ilbo [in Korean], July 21, 2013, http://news.chosun.com/site/data/html_dir/2013/07/21/2013072100454.html.
 “China Says ‘No Dispute’ with S. Korea over Ieodo in New Air Zone,” Yonhap News Agency, November 25, 2013, https://en.yna.co.kr/view/AEN20131125007800315.
 “South Korea, UN Join Forces to Expel Chinese Boats,” Straits Times, June 11, 2016, https://www.straitstimes.com/asia/east-asia/south-korea-un-join-forces-to-expel-chinese-boats.
 “October 7, 2016: Chinese Fishing Vessels Ram KCG Speedboat,” NBR, Maritime Awareness Project, http://maritimeawarenessproject.org/gallery/incident-timeline.
 “Panmunjom Declaration on Peace, Prosperity and Reunification of the Korean Peninsula.”
 “In Past Three Years, Foreign Military Vessels Violated Our Waters 602 Times…505 Times by Chinese Military Vessels,” Chosun ilbo [in Korean], March 6, 2019. http://monthly.chosun.com/client/mdaily/daily_view.asp?idx=6364&Newsnumb=2019036364.
 “Peak Blue Crab Season Near Korean Sea Border Drives Illegal Chinese Shipping,” Yonhap, June 11, 2016, https://en.yna.co.kr/view/AEN20160611002500315; and “No Need to Get Crabby over High Prices,” Korea JoongAng Daily, January 20, 2020, https://koreajoongangdaily.joins.com/news/article/article.aspx?aid=2426805.
 Jeong et al., “Introduction to the Ocean Research Stations (ORSs) in Korea and Application Activities.”