Chinese fishing boats have been making some unusual moves lately in the East China Sea, satellite images and shipping data show

• Thousands of Chinese fishing boats sailed into coordinated lines in the East China Sea twice in recent weeks.
• The vessels could be seen in both shipping data and satellite imagery.
• The anomalous behavior, experts said, is more likely aligned with activities related to China's Maritime Militia.

Thousands of Chinese fishing vessels amassed in what appeared to be coordinated formations in the East China Sea in recent weeks. Experts say the unusual display suggests more than regular commercial activity.

Shipping data tracked these formations, which China watchers and experts familiar with such activities in the region said were unprecedented in scale and highly inconsistent with normal fishing practices.

Experts said this behavior appears linked to China's Maritime Militia, a shadowy, state-directed fleet that Beijing often uses to assert control over contested waterways without triggering a direct military confrontation. It's a prominent yet deniable force. China has rejected such assessments of the activity.

The first of these irregular movements of Chinese fishing boats occurred on December 25, with more than 2,000 ships forming two reverse L shapes with lines over 290 miles long off the coast of Shanghai. Then, on January 11, almost 1,500 vessels were spotted forming a single line in the same waters stretching roughly 300 miles. The New York Times first reported these activities.

The number of vessels in the area alone was enough to surprise some experts. "In observing this type of data for years, I've never seen anything like this," Harrison Prétat, deputy director of the Asia Maritime Transparency Initiative with the Center for Strategic and International Studies, told Business Insider. "Maybe my initial impression was, okay, is this some type of error, some type of mistake because the number of ships involved is more than anything I've seen before."

Data from Starboard Maritime Intelligence showed that in both instances, the fishing boats initially dispersed across the East China Sea converged over several days into a defined area, where they formed coordinated alignments. Satellite imagery from Planet Labs on January 10 captured large numbers of vessels moving toward the zone.

Once in position, they went idle. The vessels remained in those lines for hours before dispersing.

"The scale, geometry, coordination, and rapid assembly and dispersal of these formations are simply irreconcilable with normal fishing behavior," Andrew S. Erickson, a professor at the US Naval War College and expert on the Chinese Maritime Militia, told Business Insider.

Speaking in a personal capacity and not for the college or Navy, he called it a "huge, precisely geo-coordinated flash mob."

Experts in this space said the pattern of behavior aligns with what is known about how China's Maritime Militia operates.

"Beijing subsidizes various local and provincial commercial organizations to operate China Maritime Militia vessels to perform 'official' missions on an ad hoc basis outside of their regular civilian commercial activities," the Pentagon said in its most recent assessment of China's military.

"China Maritime Militia units," the DoD said, "employ marine industry workers, usually fishermen, to supplement the PLAN [People's Liberation Army's Navy] and the China Coast Guard. While retaining their day jobs, these mariners are organized and trained, often by the PLAN and the China Coast Guard, and can be activated on demand."

The militia offers China an option for enforcing territorial claims in disputed waters in the South China Sea in ways that aren't as consequential as it might be were China's navy or coast guard to get involved. The militia isn't new, but it is believed to have grown in size and reach over the past decade, engaging in increasingly visible gray zone actions.

"In contrast to recent years, a majority of ships spent most of their days anchored at China's military outposts rather than at unoccupied reefs where they might pretend to fish. This suggests Chinese authorities are not pressuring vessel owners to maintain the crumbling façade of the militia as a legitimate fishing fleet," the Asia Maritime Transparency Initiative said in February 2025.

Prétat said the events in December and January might be "some kind of early test of the ability to organize fishing ships geographically." The purpose, though, remains unclear.

Erickson told Business Insider it could plausibly be signaling, practice for mobilizing forces, or training.

"It underscores the reality that this third PRC [People's Republic of China] sea force engages in threatening gray zone operations and war-preparation activities not only in the South China Sea, but also in the East China Sea, with implications for Taiwan, Japan, regional security, and vital US interests," he said.

The Pentagon assesses that in a wartime scenario, such as a Chinese invasion of Taiwan, the Maritime Militia could support combat operations in part by creating obstacles to foreign military intervention.

But Prétat told Business Insider a major concern could also be a militia blockade that assists in "dissuading, rerouting, and ultimately stopping commercial traffic, cargo, fuel shipments to Taiwan."

The Chinese embassy in the US told Business Insider the East China Sea is an important area for fishing and said that the period from November to February is peak for winter fishing.

"It is therefore normal to see a high concentration of fishing boats operating at sea during this time," embassy spokesperson Liu Pengyu said. "Referring to the Chinese fishermen as 'maritime militia' shows malicious intent driven by ulterior motives."