In the wake of an agreement last July to reduce tensions at Second Thomas Shoal, Scarborough Shoal has reemerged as the focal point of tensions between Manila and Beijing in the South China Sea. China has maintained a permanent coast guard presence at Scarborough since it seized control of the feature from the Philippines in 2012. But remote sensing data from the past ten months shows that China’s presence has expanded to include additional patrols east of the feature aimed at intercepting Philippine ships, leading to frequent encounters between the two countries’ law enforcement vessels.
A Look at the Data
To better understand recent tensions around Scarborough Shoal, AMTI examined automatic identification system (AIS) tracking data of Chinese and Philippine law enforcement vessels from August 2024 to May 2025.
Data was collected on China Coast Guard (CCG), Philippine Coast Guard (PCG), and Bureau of Fisheries and Aquatic Resources (BFAR) vessels operating in a large area of the South China Sea surrounding Scarborough Shoal and waters to its east, which include one of the dashes of China’s nine-dash line. This expanded area was chosen following an initial review of AIS data that revealed a large amount of activity taking place within the 70-nautical-mile stretch between Scarborough and the nine-dash line, as CCG vessels moved to intercept Philippine counterparts heading westward from Luzon toward the shoal. This suggests that China is using the nine-dash line rather than the territorial sea or another maritime zone from Scarborough as its imagined jurisdictional boundary. Given the data gaps inherent in AIS, these figures are presented as minimum estimates, with the true level of activity likely higher. Nonetheless, a comparison of the available data over time reveals several trends in the evolving dynamics around Scarborough Shoal.
1. Both China and the Philippines have increased law enforcement activity around Scarborough Shoal—but China’s presence is larger and more consistent
CCG patrols around Scarborough trended steadily upward over this period, peaking at 120 ship-days in January 2025. This elevated level of activity persisted through the following months, leading to a monthly average of 95 ship-days in the first five months of 2025. This was nearly double the average of 48 ship-days between August and December 2024.
PCG/BFAR patrols also increased over time, growing from an average of 21 ship-days per month in late 2024 to 31 ship-days per month in early 2025. But along with a much lower volume of patrols than the CCG, Philippine presence around the shoal was also less consistent. For instance, February 2025 saw Philippine ships deployed for just 11 ship-days around Scarborough, and no Philippine vessels were detected in November 2024, with AIS instead showing PCG activity concentrated in domestic waters such as Manila Bay and Balayan Bay.
These gaps can be explained by operational demands elsewhere. Several key PCG vessels that frequently patrolled Scarborough Shoal before—including the BRP Suluan (MRRV-4406) and BRP Cabra (MRRV-4409)— were redirected to a domestic disaster relief mission, while the BRP Gabriela Silang (OPV-8301) conducted a port visit to Indonesia. November also coincided with two week-long combat drills by the Philippine military and a successful “rotation and resupply” mission to Second Thomas Shoal completed in mid-November, further diverting maritime resources away from Scarborough. Taken together, the data illustrates how the Philippines’ maritime capacity limitations force it to pick and choose where to deploy its assets—while China’s ample coast guard fleet allows it to main a persistent presence.
2. Increased patrol presence is leading to frequent encounters between Philippine and Chinese law enforcement
Between August 2024 and May 2025, interactions between Chinese and Philippine law enforcement vessels around Scarborough were observed on a total of 121 days, averaging 12.1 interaction days per month.
The China Coast Guard 5901 (left) and BRP Gabriela Silang (right) maneuver between Scarborough Shoal and China’s nine-dash line on January 16, 2025
However, these encounters were not distributed evenly across the reporting period. Two distinct surges occurred in early 2025: 29 interaction days were observed in January, followed by 28 in April. These peaks contrast sharply with periods of minimal contact, including November 2024 and May 2025, which recorded zero and four interaction days, respectively.
3. Aerial encounters are also increasing at Scarborough Shoal
Rising tensions and increased interactions between Philippine and Chinese law enforcement in the waters around Scarborough have also been accompanied by an uptick in reports of aerial patrol activities at the shoal, some of which have led to dangerous encounters between the two sides’ aircraft.
In the past ten months, at least four publicly reported air interactions have occurred near Scarborough Shoal. While evocative of the regular unsafe incidents that have occurred between Chinese aircraft and those of the United States and Australia in recent years, this is a new development for the Philippines. Manila issued its first complaint against Chinese air activity in years on August 8, 2024, after a Chinese fighter jet dropped flares in the path of a Philippine air force aircraft.
Conclusion
The confluence of increasingly frequent aerial encounters and maritime interactions near Scarborough Shoal inevitably increases the chance of accidental escalation between Chinese and Philippine forces, which could ultimately trigger U.S. treaty obligations and risk spiraling into a wider conflict. To date, no incident has occurred at Scarborough that came as close to triggering those obligations as the June 17, 2024, clash during a resupply mission at Second Thomas Shoal. But at Second Thomas tensions were concentrated narrowly on Philippine resupply missions and the delivery of construction supplies. At Scarborough, China is reacting to all navigation by Philippine government vessels within a much larger geographic area. Without a clear point of compromise, it appears that any Philippine maritime asset operating between Scarborough Shoal and the eastern edge of the nine-dash line is likely to attract a Chinese escort—and a heightened risk of accident—for the foreseeable future.
