Batam. Indonesian authorities have detained two Vietnamese fishing boats following a dramatic chase in the Natuna Sea, off the coast of Riau Islands province, for allegedly trespassing and conducting illegal fishing activities, an official said on Friday.

The joint operation, carried out by the Ministry of Marine Affairs and Fisheries and the Maritime Security Agency (Bakamla), resulted in the arrest of 30 Vietnamese nationals and the seizure of 4.5 tons of illegally caught fish on Thursday.

According to officials, both vessels were using pair trawls -- a fishing method banned under Indonesian law due to its highly destructive impact on marine ecosystems.

“This fishing method is extremely damaging to the environment. It indiscriminately captures smaller fish and causes broader ecological harm,” said Pung Nugroho Saksono, Director General of Aquaculture and Fisheries at the ministry.

The captains of the two vessels reportedly ignored repeated warnings issued by the Indonesian patrol ship Orca 03 and attempted to flee, prompting a pursuit.

The estimated economic loss from the illegal fishing operation is valued at Rp 153 billion (approximately $9 million), Pung added.

Both vessels have been brought to Nipah Island near Batam for further investigation.