With the prospect of ransoms worth tens of millions of dollars, Somali pirates continue to threaten vital shipping lanes in the Gulf of Aden and Indian Ocean. Over 20 years of war and famine have worsened prospects for Somalis, adding to the appeal for many young men of crime on the high seas.

Armed gangs had started using large merchant vessels – including tankers – that they had seized as motherships, forcing crews by gunpoint to do their bidding. The tactic, employed agressively in 2011, enabled them to operate further out at sea.

But vigorous action by navies, including pre-emptive strikes, have cut attacks, forcing pirates to adapt their model.

“We are seeing a change in tactics,” said Joe Angelo, managing director with INTERTANKO, an association whose members own the majority of the world’s oil tanker fleet. “They are now hijacking smaller dhows and they are using them as motherships which is making them less suspicious.”

Traditional dhows, used by fishermen and general merchants in the region, were first deployed by Somali pirates before they started using larger captured vessels.

The larger vessels enabled gangs to operate for longer periods at sea with more supplies and in harsher weather conditions, as well giving them more flexibility when launching their high speed attack craft known as skiffs.

“The tactic of using larger commercial vessels as motherships has died down recently as dhows are more effective; they are essentially camouflaged amongst the huge numbers of genuine fishing boats and dhows carrying cargo locally off the Horn of Africa,” said Rory Lamrock, an intelligence analyst with security firm AKE.

“Weapons and ladders can be easily jettisoned overboard whenever naval forces approach, making it difficult for navies to disrupt. When a larger vessel gets hijacked for use as a mothership, it is usually well reported and naval forces and commercial ships in the area will be on the lookout.”

Data this week from the International Maritime Bureau (IMB) watchdog showed attacks involving Somali pirates in the first quarter of this year had slid to 43, from 97 incidents in the same period last year.

The deployment of private armed security guards and greater use of pirate deterrents such as razor wire and heightened monitoring watches when entering danger areas by crews on board also helped curb Somali attacks.

“While the number of 2012 incidents and hijackings are less … it is unlikely that the threat of Somali piracy will diminish in the short to medium term unless further actions are taken,” the IMB said.

A study published in February by U.S. non-governmental organisation One Earth Future Foundation showed Somali piracy cost the world economy some $7 billion last year. The total paid in ransoms reached $160 million, with an average ransom for a ship rising to $5 million, from around $4 million in 2010.

Ship industry officials said pirates were attempting more diverse attacks and were pushing further into the northern Gulf of Oman to prey on areas not so heavily patrolled.

“I personally believe what is going on are random acts where they can be successful,” said INTERTANKO’s Angelo.

AKE’s Lamrock said over the past six months there had been five incidents in the northern Gulf of Oman, three of which were further north than the port of Fujairah in the United Arab Emirates, towards the vital Strait of Hormuz oil choke point.

“It seems more likely that pirates will focus on opportunistically targeting vessels transiting through the Gulf,” Lamrock said.

Despite successful efforts to quell attacks and disrupt pirate camps, international naval forces have limited resources to patrol vast distances.

“We are seeing pirates using dhows as motherships – we are monitoring that. They are having to constantly adapt their procedures,” said Lt Cdr Jacqueline Sherriff, spokeswoman with the European Union’s counter piracy force.

“The Indian Ocean is vast. We are focusing our efforts on the areas that they have been in the past and we are having success.”

Sherriff said navies faced the challenge of monitoring large amounts of legitimate dhow traffic passing through the region.

“There are hundreds of them going about their legal trade and we have to be very careful with our intelligence who we target.”