LONDON -- In a marked shift in patterns of maritime piracy, three leading organizations reported Tuesday that in 2012, for the first time, the number of ships and sailors attacked off West Africa exceeded those assaulted by pirates based in Somalia, on Africa's east coast.
The report, published in London, suggested that while sailors attacked in the Gulf of Guinea in the west spent far less time in captivity than those held in Somalia, they were at risk of much greater violence.
The 50-page document by the three organizations -- the International Maritime Bureau, Oceans Beyond Piracy and the Maritime Piracy Humanitarian Response Program -- also concluded that West African pirates were motivated by a quest for quick profits from selling hijacked cargoes of refined oil, while Somali pirates sought lucrative ransoms and held captives for much longer periods.
Perhaps the most striking statistic was that in 2012, Somali pirate attacks -- recently the bane of shipping in the Indian Ocean -- dropped by almost 80 percent from a year earlier, with 851 seafarers fired upon, compared with 3,863 in 2011. West African pirates attacked 966 sailors in 2012, the figures show.
"The year 2012 marked the first time since the surge in piracy off the coast of Somalia that the reported number of both ships and seafarers attacked in the Gulf of Guinea surpassed that of the Gulf of Aden and of the western Indian Ocean," the report said.
But it underscored various trends in the nature of piracy that troubled seafarers, making them particularly fearful of being seized in West African waters, where five hostages were killed in 2012, compared with no fatalities from Somali pirate attacks.
In West Africa, the report said, hostages were held for an average of four days, while the average period of captivity involving Somali pirates was 11 months. Some of the 589 hostages held in 2012 had been in captivity for more than two years.
The report said its findings indicated that fewer pirate groups were operating from bases in Somalia because of increased patrols by international navies and more effective security measures on ships.
"Other factors may include better organized shore-based policing and advances by the new Somali federal government and its supporters, which are driving pirates out of their traditional operating areas," the report said.
But, the report said, those Somali pirates still in business were more effective in boarding vessels, so that the success rate of pirate attacks improved even though the total number dropped.
"These statistics may also indicate that pirates have learned to fire upon and attack only the more vulnerable vessels; for example, vessels that do not carry armed guards" or take other antipiracy measures, the report said.
Off West Africa, it said, there is a much higher boarding rate than off the coast of Somalia, partly because vessels tend to be attacked "while at anchor, drifting or conducting ship-to-ship transfers of refined products cargo."
Only one-third of attacks in the Gulf of Guinea were directed at ships "actively in transit," the report said. "In contrast, attacks off Somalia almost always occur while they are under way."
Kaija Hurlburt, the lead author of the report, said in a telephone interview that she believed that the shifting pattern of attacks would become more marked as assaults decreased further in Somalia and increased in West Africa.
She attributed the growing number of attacks in the Gulf of Guinea in part to legal difficulties limiting the presence of armed guards on ships in territorial waters, where most piracy and armed robbery of ships takes place. By contrast, Somali pirates tend to strike on the high seas, where the combination of armed guards and other onboard security measures and the presence of international navies is a more forceful deterrent.
This article originally appeared in The New York Times.