The Japan Coast Guard is increasing the number of patrol ships deployed to seas off Japan amid suspicions that Chinese fishing boats are poaching coral, NHK reported Friday.

The Coast Guard spotted such vessels near the Izu Islands on Thursday, in addition to a number of them detected in September and October off the Ogasawara Islands. On Thursday, the Coast Guard arrested the firth Chinese skipper in October.

Since more than 100 Chinese fishing boats were seen off Japanese territory last week, Coast Guard aircraft Thursday counted 164 such vessels fishing off the Izu chain islets of Torishima and Sumisu, and another 48 off the Ogasawara chain.

The 212 vessels counted was the most since September, when they were first detected by the Coast Guard.

According to recent media reports, Chinese fishing boats have been increasingly going after red coral — highy prized in China as jewelry — since September near the Ogasawaras.