​China calls them fish farms – South Korea fears they have another use

SEOUL – In recent years, China has towed a decommissioned offshore oil-drilling rig and two giant octagonal steel cages into the sea between China and South Korea, saying that the structures were being used as deep-sea fish farms in shared waters.

But South Koreans fear they are more than that, and could be used to expand China’s military influence.

South Korea’s National Assembly formally took issue with the Chinese structures on June 23 when its ocean and fisheries committee condemned them as “a threat to maritime safety”, in a resolution adopted with bipartisan support.

Those fears were bolstered on June 24 by a report from the Washington-based Centre for Strategic and International Studies (CSIS).

“While available information suggests that the platforms are genuinely focused on aquaculture, concerns that the platforms may be dual-use are not unfounded, given China’s track record in the South China Sea,” said the report, which used satellite imagery and other data to track the installations.

Dual-use refers to a second potential use for military purposes.

“Even without further expansion, the platforms are likely already collecting data that could have value for undersea navigation and detection,” the report said.

South Koreans see striking parallels between the Chinese installations and what Beijing has done in the South China Sea.

China initially built artificial islands there for civilian purposes, but they were gradually transformed into military outposts, leading to territorial disputes with countries including the Philippines and Vietnam.

The tensions creeping up around the Chinese platforms in the Yellow Sea – called the West Sea by South Koreans – will likely become one of the first challenges faced by the government of President Lee Jae Myung, who took office in June.

Mr Lee has vowed to improve ties with China while at the same time promising to strengthen his country’s alliance with Washington. He hopes to meet China’s top leader, Mr Xi Jinping, during the Asia-Pacific Economic Cooperation summit in Gyeongju, South Korea, in November.

When the two countries held talks in April on oceanic cooperation, South Korean officials expressed their “deep concern” about the Chinese structures, warning that they would not allow them to undermine Seoul’s rights, the South Korean Foreign Ministry said.

But China insisted that the structures were nothing but deep-sea salmon farms.

Both sides agreed to continue dialogue to resolve the dispute.

China’s growing assertiveness in the Yellow Sea comes at the same time Beijing has called for bilateral relations with Seoul to reach a “higher level”, after Mr Lee was sworn in as president.

That reflects China’s carrot-and-stick approach with its neighbours.

On the one hand, it hopes to warm ties by offering South Korea economic inducements. On the other, China considers its dominance of regional waters a vital strategic interest, one that it feels it can pursue because of its military strength.

In recent years, South Korea has become increasingly concerned about China’s military activities near the Korean peninsula, including a growing number of Chinese warplanes flying near its airspace.

In May, China’s newest and most-advanced aircraft carrier, the Fujian, conducted fighter jet drills in the Yellow Sea. China declared no-sail zones there while the drills were under way.

National Assembly Research Service analyst Chung Min-jeong said: “If China uses its structures in the West Sea for military purposes like monitoring, surveillance and disrupting sea routes, and does so repeatedly and in an escalating scale, they will eventually threaten our jurisdiction in the West Sea​.

“South Korea, the United States and Japan will need to cooperate if China uses the West Sea structures to help blockade Taiwan.”

China installed its aquaculture structures inside the so-called Provisional Measures Zone, which was created by South Korea and China through a bilateral agreement in 2001 to manage their overlapping exclusive economic zone claims in the Yellow Sea.

The agreement allows fishing activities from both sides but does not mention aquaculture, “leaving an ambiguity that will make it difficult for Seoul to convince Beijing to remove the platforms”, according to the CSIS report.

The first floating fish-farm cage – the Shen Lan 1, which is 61m in diameter – was installed in 2018, and the larger Shen Lan 2 was added in 2024. The former oil-drilling rig was moved there in 2022, repurposed into a central operations hub.

Tensions flared in February when a South Korean ocean survey vessel attempted an on-site investigation, only to be forcibly blocked by Chinese coast guard ships and civilian vessels. South Korea also deployed patrol ships in the two-hour stand-off.

In a report in June, South Korea’s Chosun Ilbo newspaper cited satellite imagery ​that it said showed China remodelling several retired oil rigs for use as offshore support facilities for fish farms.

In their resolution adopted on June 23, South Korean lawmakers ​proposed that if China does not remove its facilities, South Korea ​should take “proportional​” countermeasures, such as installing its own aquaculture facilities in the ​area and building a survey ship to increase monitoring of Chinese activities in the sea. NYTIMES