AMTI: China Coast Guard Focuses its Patrols on Scarborough Shoal
Scarborough Shoal has been a flash point for tensions between the Philippines and China since 2012, when Chinese forces occupied the atoll and began a years-long effort to control access. It has been the scene of multiple confrontations over the past year, including water-cannoning incidents that ended in injuries for Philippine citizens. New AIS data analysis from CSIS/AMTI reveals that the China Coast Guard is putting a new priority on presence operations at the reef: last year it more than doubled the number of vessel-days it allocated to Scarborough Shoal and largely reduced its presence at other South China Sea hot spots.
Based on satellite AIS data, AMTI calculates that the China Coast Guard maintained a vessel presence at Scarborough Shoal for 352 days last year, or roughly 96 percent of the time. The count is likely an underestimate, since missed transmissions and periods of AIS-dark operation would be undetected.
The most telling number is the sheer volume of ship-day patrol resources that the CCG assigned to Scarborough. Chinese cutters were on station at the reef for 1,099 ship-days over the span of the year, more than double the 516 ship-days spent there in 2024. Up to five CCG vessels at a time were spotted at the reef, and the typical presence on an average day was three hulls.
Even on the few days of the year when there were no signs of Chinese activity on AIS at Scarborough, there was likely a CCG cutter nearby: the Philippine Coast Guard reported a Chinese presence during most of this period. This suggests a nearly-constant CCG patrol, often augmented by PLA Navy gray-hull assets (not visible on AIS and not counted here).
Likewise, the level of effort at Sabina Shoal - just east of Philippine-occupied Second Thomas Shoal - more than doubled to 405 ship-days. There was a nearly-constant presence of one vessel at Sabina on AIS, occasionally augmented with a second. China Coast Guard crews benefit from modern basing infrastructure at nearby Mischief Reef, and the AIS tracks for one large cutter show multiple port calls at this outpost in between patrols around Sabina Shoal.
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While CCG ship-days in the eastern South China Sea increased overall, the resourcing needed for the hike in presence at Scarborough and at Sabina Shoal appears to have come at the expense of other Chinese operations in the area. CCG ship-days at other previous hot-spots declined, according to AMTI, including at Luconia Shoals, Vanguard Bank, Thitu Island and Second Thomas Shoal.
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