Chinese Platforms in the Yellow Sea’s South Korea-China PMZ

Key Findings

• Three Chinese maritime structures—one integrated management platform [pictured above] and two aquaculture cages—have been deployed inside the South Korea-China Provisional Measures Zone (PMZ) without prior consultation with the South Korean government. 
• Satellite imagery analysis reveals that one Chinese structure is a repurposed offshore oil platform that serves as a central operations hub for the surrounding cages, with six operational floors and the potential for expanded functionality beyond aquaculture. 
• South Korean requests for China to relocate the structures outside of the PMZ have not only been repeatedly rejected, but the Chinese government has also unilaterally declared “no-sail” zones within the PMZ and has deployed at least 13 additional buoys in the Yellow Sea since 2018. 
• In late February 2025, a South Korean research vessel’s effort to survey the Chinese structures installed within the PMZ was blocked by the Chinese coast guard. AIS data analysis also shows that the South Korean vessels have made multiple approaches to the Chinese platforms between 2022 and 2024, often accompanied by South Korean coast guard escorts, indicating years of persistent observation and concern. 
• While available information suggests that the platforms are genuinely focused on aquaculture, concerns that the platforms may be dual-use for purposes of advancing China’s creeping jurisdictional presence are not unfounded, given China’s track record in the South China Sea, where what were originally weather stations later developed into major military outposts. 
• Beyond Parallel and Asia Maritime Transparency Initiative commercial satellite imagery and automatic identification system (AIS) data analysis provide the first comprehensive timeline of the development, deployment, and current status of the publicly known Chinese steel structures in the PMZ. 

In late February 2025, South Korean research vessel Onnuri made its way to the Provisional Measures Zone (PMZ) shared between South Korea and China. The vessel was deployed to survey one of three Chinese steel structures that were installed in the PMZ without prior notice to South Korea. The vessel’s journey was unsuccessful, as the Chinese coast guard blocked the ship, claiming that the structure was an aquafarm.¹

Since then, South Korea has requested the three structures be relocated to outside the PMZ, raising concerns that they violate South Korea’s “legitimate and lawful maritime rights” and could “physically obstruct the navigation of South Korean fishing vessels and naval ships.”² However, China has rejected the request, repeating that the structures do not violate any agreements, and that “…the relevant facilities set up by China are deep-sea fishery aquaculture facilities located in China’s coastal waters, which are China’s reasonable use of offshore marine resources.”³ South Korea has responded by taking “reciprocal measure with a large-scale floating object” for environmental surveying purposes.⁴

In May 2025, tensions escalated further when China declared multiple temporary no-sail zones within the PMZ to conduct exercises of the Fujian, China’s most-advanced aircraft carrier, in a move “Seoul views as part of a gradual push to assert de facto control over the region.”⁵ Additionally, recent South Korean media reports have revealed that China has installed at least 13 additional lighthouse-shaped, solar-powered buoys across the Yellow Sea between 2018 and 2023, further raising concerns about the expansion of semi-permanent maritime infrastructure throughout contested waters.⁶

Such activities in proximity to South Korea’s designated maritime zones have raised new concerns over China’s intentions and the possibility of a creeping jurisdictional presence under the guise of civilian or fishing activity, consistent with broader patterns of Chinese gray zone tactics observed elsewhere in the region.⁷

This Beyond Parallel and Asia Maritime Transparency Initiative commercial satellite imagery and automatic identification system (AIS) data analysis provide the first comprehensive timeline of the development, deployment, and current status of the publicly known Chinese steel structures in the PMZ. 

Background: The Provisional Measures Zone (PMZ)

The exclusive economic zone (EEZ) of a country is defined by the United Nations Convention on the Law of the Sea (UNCLOS) as extending up to 200 nautical miles from the territorial baseline.⁸ A state has exclusive rights to “explore, exploit, conserve and manage the living resources” as well as exercise jurisdiction over marine scientific research, protection of the marine environment, and, notably, the installation of artificial islands, installations, and structures.⁹ However, the EEZ does not confer full sovereignty, unlike the territorial limit line, which extends up to 12 nautical miles from the baseline and is treated as sovereign territory.¹⁰

The Provisional Measures Zone (PMZ) was established by South Korea and China through a bilateral agreement signed in 2001 to temporarily manage their overlapping EEZ claims in the Yellow Sea. The agreement allows fishing activities from both sides but does not authorize other actions such as the installation of fixed structures, which could impact future maritime boundary negotiations.¹¹

Chinese Structures in the Yellow Sea

As of May 2025, there are currently three known structures and a support vessel within the PMZ that have garnered heavy media coverage. The structures are as follows: 

• The Shen Lan 1 (MMSI: 412563263), located approximately 35.177000, 122.259003 as of June 2025, the first aquaculture cage to be deployed inside the PMZ in July 2018.¹²

• The Atlantic Amsterdam (MMSI: 636021201), located approximately 35.186993, 122.241003 as of June 2025, a “central integrated management platform” for the management and operations of the Qingdao National Deep Water Green Aquaculture Experimental Zone, installed inside the PMZ October 2022 where the High Island VII, its predecessor, was previously placed.¹³ Satellite imagery analysis and open source information indicate that the building has the potential for expanded functionality beyond aquaculture.  

• The Shen Lan 2 (MMSI: 412230903), located approximately 35.161072, 122.262074 as of June 2025, the second aquaculture cage installed in the PMZ approximately 1.3 nautical miles from the Shen Lan 1 in May 2024. 

Development Timeline

Qingdao National Deep Water Green Aquaculture Experimental Zone

In 2020, China formally established the Qingdao National Deep Water Green Aquaculture Experimental Zone (青岛国家深远海绿色养殖试验区).¹⁵ Located approximately 120 nautical miles northwest of Qingdao City and 10 nautical miles inside the PMZ boundary with a planned total area of approximately 554.6 km², the zone was touted to be “the first and currently the only national-level deep-sea green aquaculture experimental zone in the country.”¹⁶

Support Vessels

The earliest coverage of the support infrastructure for the Qingdao National Deep Water Green Aquaculture Experimental Zone was that of the Luqingxin Yuyang 60001, a support vessel. In 2017, the Luqingxin Yuyang 60001 (MMSI: 412349687, originally named Lulan Yuyang 61699) was launched. Widely referred to by the media to be the first of its kind, the vessel was described by the planner of the aquaculture cages as being able to “take care of 10-20” cages.¹⁸ The vessel was used in the deployment of the Shen Lan 1, the first of the fishing cages, in July 2018.¹⁹ Consistent with the vessel’s description, commercially available AIS data from May 2020 to June 2025 shows the Luqingxin Yuyang 60001 spending its time tending to the platforms within the aquaculture zone and making frequent trips back to ports in Shandong. 

Aquaculture Cages

Central to the fish farming experimental zones are the large aquaculture cages used to breed fish. As of May 2025, two of these cages have been placed within the experimental zone inside the PMZ, the Shen Lan 1 and the Shen Lan 2. 

The Shen Lan 1 measures 60.44 meters in diameter, 38 meters in height, and 60.44 meters in diameter, weighing approximately 1,400 tons, with capacity of 40 standard swimming pools.²⁰ The cage provides approximately 30 meters-deep aquaculture for breeding, and the designed annual fish production is 1,500 tons.²¹ The cage was constructed at Qingdao and towed into the PMZ in the Yellow Sea in July 2018.  

Available commercial AIS data, which starts in May 2020, shows the fishing cage floating in the waters of the PMZ at approximately 35.177000, 122.258999. AIS data has continued to show the Shen Lan 1 broadcasting intermittently at this location through June 2025, though there is some indication that it has occasionally been returned to port and been redeployed between 2020 and 2025.  

In November 2020, the Shen Lan 1’s signal went dark until January 2021, when it briefly broadcasted from a port in Qingdao. By February 2021, it had returned to broadcasting from its previous location in the PMZ. In June 2021, the Shen Lan 1 again went dark before broadcasting from Qingdao on June 26, only to reappear in the PMZ on June 30. From July 2021 to March 2024, AIS data show the fishing cage to have been in the waters. During this time period, the Shen Lan 1 reportedly achieved its first successful commercial harvest of Atlantic salmon from the cage, hauling approximately 15,000 fish.23 The Shen Lan 1’s signal then went dark for over a year from April 2024 until May 2025, when it pinged again from its location in the PMZ. The intermittent loss of the AIS signal may be due to technical limitations or intentional deactivation. However, given that the cage’s AIS signal restarted at a different location after most outages, it is likely that these dark periods coincide with returns to port for maintenance, relocation, or other operational activities not observable in real-time. 

The second of the aquaculture cages, the Shen Lan 2, was also constructed at Qingdao. The cage is larger than the Shen Lan 1, measuring 71.5 meters in height and 70 meters in diameter. The cage is touted to have been “equipped with a suite of intelligent farming technologies…pushing to boundaries of automation and intelligence in deep-sea aquaculture” that allows for “as many as one million salmon” to be bred at any given time.²²

AIS data shows the Shen Lan 2 was moved from Qingdao to its current position in the PMZ, at approximately 35.161004, 122.261997 in May 2024, and has remained there since, with minimal movement likely attributable to its buoyant nature.  

Central Integrated Management Platforms

Roughly 1 nautical mile from the Shen Lan 1, China positioned a large offshore platform known as a “central integrated management platform” to support the zone’s operations.²³ AIS data shows that the first such platform, High Island VII, was deployed to the PMZ in September 2021 but was withdrawn in October 2022 back to Qingdao shortly after the arrival of its more permanent counterpart, the Atlantic Amsterdam.²⁴

The Atlantic Amsterdam, originally constructed as an offshore oil drilling rig, was converted into a multipurpose platform measuring approximately 86 meters wide and 75 meters long .²⁵ It contains six operational floors that serve both as crew accommodations and as the “central integrated management platform” for the experimental zone’s operations.²⁶ According to Chinese media, the platform also contains a marine science laboratory, a scientific research center, and a production management control center, with future plans to expand its functions to include scientific research and even offshore tourism.²⁷ A 2023 China Daily feature described the Atlantic Amsterdam to be the “equivalent to building a new ‘island’ next to the [fishing] cage. With the platform as the landing point, more cages can be built around it…[and] the scale of deep-sea aquaculture can be continuously expanded.”²⁸

South Korean Efforts to Survey Chinese PMZ Structures

Although the February 2025 attempt by the South Korean research vessel Onnuri to investigate the Chinese structures in the PMZ was heavily covered by media, this was not the vessel’s first time approaching the area.  

Commercial AIS data shows that as early as April 2022, the Onnuri navigated within 170 meters of the Shen Lan 1, and was tailed closely by China Coast Guard (CCG) 6205. Although the vessel’s broader track showed typical wide-area survey activity in the Yellow Sea, its direct approach toward the cage and a follow-up pass within 2–3 kilometers on May 1, 2022, strongly suggest intentional observation. The following year, in May 2023, the Onnuri returned with an escort from the Korea Coast Guard (KCG) 1508 and again approached the cage, coming within 300 meters before conducting more typical scientific survey patterns to the south.  

The vessel repeated similar close-range voyages multiple times over the next year. In August 2023, it again approached the Shen Lan 1 within approximately 160 meters while engaged in a broader survey campaign of the area. A trip in October 2023, despite gaps in AIS coverage and track history, also suggests another approach to the area.  

Between July 31 and August 1, 2024, the Onnuri returned to the PMZ with KCG 3010 and twice passed within 200 meters of the Shen Lan 1. The vessel was also in the near vicinity of the Atlantic Amsterdam, though it kept a greater standoff distance of roughly 1.5 kilometers compared to that of the Shen Lan 1. 

The repeated and deliberate proximity to these Chinese structures over multiple years highlights South Korea’s sustained interest in monitoring developments inside the PMZ, even before tensions escalated in early 2025. 

Future Developments

China’s deployment of maritime infrastructure in the PMZ has several potential implications. 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, where what were originally weather stations later developed into major military outposts. Even without further expansion, the platforms are likely already collecting data that could have value for undersea navigation and detection.  

Alongside these security concerns, the platforms also raise difficult questions for the management of the PMZ and overlapping Chinese and South Korean EEZ claims. While ships from both sides are allowed to fish within the PMZ, aquaculture is entirely unmentioned by the 2001 fisheries agreement, leaving an ambiguity that will make it difficult for Seoul to convince Beijing to remove the platforms. While the platforms are, notably, on China’s side of a theoretical median line between the two EEZs, they add to South Korea’s frustrations in fisheries management with China, whose vessels have dominated fishing in the shared PMZ. With Seoul’s objections now public, it will bear watching whether China will continue with its plans to deploy additional platforms and whether South Korea will continue to adjust its approach to managing overlapping claims in the Yellow Sea.