More than 200 Chinese fishing vessels were anchored at a disputed atoll in the South China Sea claimed by China and other countries, according to an analysis of satellite imagery.

The analysis by Deep Dive, a Japanese nonprofit private intelligence organization, shows the congregation of vessels at Mischief Reef, which is under China’s effective control.

It also identified a group of more than 20 vessels secured together in a raft-like formation.

According to Bonji Ohara, Deep Dive’s representative director and a former defense attache in China, the fishing vessels are believed to be maritime militia vessels carrying maritime militia personnel.

Mischief Reef is an atoll located within the Philippines’ exclusive economic zone (EEZ). China established a presence on the reef in 1994 and subsequently established effective control over it.

Since then, China has constructed facilities there and carried out large-scale land reclamation projects since the 2010s, transforming the reef into an artificial island. It is now a military outpost equipped with a runway measuring approximately 3,000 meters.

An analysis of commercial satellite imagery by Ohara and special research fellow Miyabi Ishihara found that fewer than 40 Chinese fishing vessels were anchored at Mischief Reef through around mid-May this year.

The number doubled to 80 on May 27, rose to 113 on June 4, and reached 158 the following day. Chinese fishing vessels continued to gather at the reef thereafter, reaching 228 vessels on July 3.

Among the vessels were more than 20 boats secured together in a raft-like formation while remaining at anchor. Ohara noted that vessels fixed in such a configuration are unable to maneuver and said the fishing vessels gathered at Mischief Reef were not there for fishing purposes.

According to the analysis by Ohara and Ishihara, the number of Chinese fishing vessels anchored at Mischief Reef has followed a recurring pattern since 2024.

The number begins rising around late May, peaks at roughly 250 vessels, starts declining around late November, and remains relatively low from late December through May.

Based on their analysis, although the timing varies by region in China, the annual fishing moratorium generally runs from around mid-May or mid-June through September. Fishermen who are unable to fish during that period are believed to be mobilized to serve as maritime militia personnel.

The activities of suspected Chinese maritime militia vessels in the South China Sea have previously drawn attention. In 2021, the Philippine government found that more than 200 Chinese vessels had gathered at Whitsun Reef, a disputed feature that lies within the Philippines’ EEZ.

Subsequent analyses by the Asia Maritime Transparency Initiative (AMTI) at the Center for Strategic and International Studies (CSIS) found that Chinese vessels continued operating in the area thereafter.

Mischief Reef, where more than 200 Chinese fishing vessels believed to be maritime militia vessels have assembled, lies about 40 kilometers west of Second Thomas Shoal, which is effectively controlled by the Philippines.

“The maritime militia vessels at Mischief Reef may be waiting to support actions aimed at seizing Second Thomas Shoal. This situation requires continued monitoring,” Ohara said