Japan-South Korea Tensions Rise Over Marine Surveys Near Disputed Takeshima Islets

Japan’s Foreign Ministry filed formal diplomatic protests against Seoul twice within a month after South Korean research vessels were detected conducting what Tokyo called unauthorized marine surveys in Japan’s exclusive economic zone (EEZ) near the Takeshima islets in the Sea of Japan.

The incidents involved the research vessels ONNURI and NARA and brought the long-running territorial dispute into a separate dispute over maritime research jurisdiction.

Japan said ONNURI was operating in what it considers its territorial sea west of Takeshima on Aug. 15, while it said NARA was operating in Japan’s claimed EEZ west to northwest of the islets on Sept. 16. In both cases, Japan said the vessels deployed what appeared to be wire-like equipment into the water.

Two Survey Incidents Prompt Japanese Protests

South Korean ship ONNURI, which was conducting research, was tracked on Aug. 15 as it moved and stayed in waters off Takeshima, which Japan deemed within its territorial waters and dropped an object in the ocean-like shape of a wire, Japan said.

Japanese Foreign Minister Fumio Kishida also criticized South Korea’s Embassy in Tokyo, causing the South’s ambassador to the country, Kim Jang-hyun, to take a quizzical look at the minister.

The embassy in Seoul also discussed the issue with the South Korean authorities. Tokyo again stated that Takeshima is Japanese territory and expressed its objections to the reported activities.

A second incident occurred Sept. 16. Japan said the South Korean research vessel NARA was deploying what appeared to be a wire-like object in waters west to northwest of Takeshima within Japan’s claimed EEZ.

The Japanese Foreign Ministry said South Korea had not sought Tokyo’s prior consent for the survey. Kanai protested to the South Korean Embassy in Tokyo, while a Japanese embassy official raised the matter with South Korea’s Foreign Ministry in Seoul.

The distinction between the two incidents is significant. The August case concerned waters Japan identifies as its territorial sea, while the September case concerned an EEZ, where the legal framework for foreign scientific research differs.

Why the EEZ Matters

The United Nations Convention on the Law of the Sea provides a coastal state with sovereign rights over natural resources and jurisdiction over designated areas under the EEZ, but it is not equal to territorial sovereignty.

Marine scientific research in an EEZ or continental shelf is only done with the authorisation of the coastal state (Article 246 of the convention). The convention also lays down rules and regulations about the way research activities are conducted and what information researchers have to offer.

Japan has relied on those provisions in previous disputes involving South Korean research vessels near Takeshima. In May 2022, for example, Japan said the South Korean research vessel Hae Yang 2000 was operating in Japan’s claimed EEZ north of Takeshima while towing a wire-like object. Tokyo said Seoul had not sought prior consent and protested through diplomatic channels.

In August 2022, Japan recorded another Hae Yang 2000 case, in which the boat was doing what it said was its lawful EEZ business, north-east of Takeshima, and was using wire-like equipment without Japanese permission.

The earlier incidents indicate that the Marine survey around the islets is not limited to the 2025 incidents. They also illustrate why the legal dispute isn’t just one over the possession of the islands themselves.

The Underlying Takeshima-Dokdo Dispute

Japan calls the islets Takeshima, while South Korea calls them Dokdo. Seoul has administered the islets for decades, while Tokyo maintains that they are Japanese territory.

The 2025 Diplomatic Bluebook, compiled by Japan, called Takeshima an integral territory of Japan and said that South Korea’s control is an international law violation and an occupation.

South Korea did not accept that stance. Japan’s Foreign Ministry has responded to the Japanese Diplomatic Bluebook with a statement made in April 2025 stating that Dokdo is a territory belonging to South Korea and that Japan should abandon its sovereignty claims.

The conflict was also mentioned in the Japanese defense white paper for 2025. South Korea’s Defense Ministry said July 15 that it had summoned Japanese defense attache Hirofumi Inoue to protest Japan’s sovereignty claim over Dokdo in the document.

Neither government’s position resolves the competing maritime claims around the islets. Instead, the sovereignty dispute affects how each side interprets the maritime jurisdiction surrounding them.

Fisheries Arrangement Did Not Resolve Maritime Claims

The fisheries issue has also been separated from the sovereignty issue, and an arrangement for fisheries has been drawn up for the maritime dispute.

Japan and South Korea began negotiations for a new fisheries agreement after both countries ratified the U.N. Convention on the Law of the Sea in 1996. The territorial dispute over Takeshima/Dokdo complicated efforts to determine the countries’ respective maritime zones.

A treaty between Japan and South Korea for fisheries was signed in 1998, but did not give an answer to the sovereignty debate, instead only providing a provisional fisheries zone around the islets. The agreement helped to manage fisheries without a resolution to the territorial issue.

The distinction is still applicable in terms of the survey incidents. A fisheries arrangement may limit some activities without giving sovereignty to the country over the disputed islands or deciding who has the priority right to the EEZ.

A Recurring Source of Diplomatic Friction

The island of Takeshima has been in the spotlight in Japan’s official complaints about the island. Alongside other disputes, such as military exercises and visits by South Korean lawmakers, Japan’s 2025 Diplomatic Bluebook mentioned previous South Korean marine survey activities in and around the islets.

The 2025 incidents therefore did not create the territorial dispute or the disagreement over maritime research. What they did was provide another point at which the two countries’ conflicting positions over sovereignty and maritime jurisdiction came into direct contact.

For now, the two governments continue to manage such incidents primarily through diplomatic protests. The competing claims over Takeshima/Dokdo remain unresolved, leaving future survey activity in the surrounding waters as a potential source of further friction between Tokyo and Seoul.