Piracy and armed robbery at sea have fallen to their lowest levels since 1995 despite a surge in kidnappings off West Africa, according to the International Chamber of Commerce's International Maritime Bureau.

The maritime bureau's global piracy report, released Monday, found there were 98 incidents in the first half of 2016 compared with 134 for the same period in 2015.

In the first half of 2016, the bureau said it recorded 72 vessels boarded, five hijackings, and another 12 attempted attacks. Nine ships were fired upon, while 64 crew were taken hostage onboard, down from 250 a year ago.

In the first half of 1995, 97 incidents were reported, according to the bureau. The bureau said it recorded highs of 445 attacks a year in 2010 and 2003.

“This drop in world piracy is encouraging news,” Pottengal Mukundan, the maritime bureau's director, said in a statement. “Two main factors are recent improvements around Indonesia, and the continued deterrence of Somali pirates off East Africa. But ships need to stay vigilant, maintain security and report all attacks, as the threat of piracy remains, particularly off Somalia and in the Gulf of Guinea.”

Kidnappings are on the rise despite the improvements, however, with 44 crew captured for ransom in 2016, 24 of them in Nigeria, up from 10 in the first half of 2015.

“In the Gulf of Guinea, rather than oil tankers being hijacked for their cargo, there is an increasing number of incidents of crew being kidnapped for ransom,” Mr. Mukundan said.

The Gulf of Guinea accounted for seven of the world's 10 kidnapping incidents, with armed gangs boarding vessels 30 to 120 nautical miles from shore. Nigerian attacks are often violent, the maritime bureau said, accounting for eight of the nine vessels fired upon worldwide. The bureau said many further assaults go unreported by shipowners.

The maritime bureau reported two further kidnapping incidents in the waters off Sabah, Malaysia, where tugs and barges were targeted. And in early June, a tug and barge were hijacked off Balingian, Malaysia, and its palm oil cargo stolen.

Low-level theft to ships at anchor has been brought down by introducing designated anchorages with improved security, the bureau said, contributing to a fall in the number of incidents in Indonesia to 24 in the first six months of 2016 compared with 54 in the same period in 2015.

The maritime bureau also applauded the Indonesian Navy's prompt response in recovering a hijacked product tanker south of the island of Pulau Serutu, Indonesia, in May, describing it as “exactly the type of robust response required in response to such threats.” Nine pirates were apprehended and the crew of the tanker unharmed, the bureau said.