A global maritime watchdog says ship hijackings declined in 2015 from a year earlier, with sea piracy incidents mostly consisting of low-level theft.

The International Maritime Bureau said in its annual piracy report released Tuesday that 246 piracy incidents were recorded worldwide, one up from 2014. It said pirates hijacked 15 vessels and held 271 hostages, down from 21 ships and 442 hostages in 2014.

It attributed the drop in hijackings to a fall in attacks against small fuel tankers around Southeast Asia's coasts, the last of which occurred in August.

It said Malaysia and Indonesian authorities took swift action to arrest and prosecute two gangs that hijacked tankers, including the arrest of some alleged masterminds.