Batam, Indonesia - The 17-man crew of the Dongfang Glory, a Malaysian-owned tanker, must have felt like they were being April-fooled as their hands were being bound by pirates on April 1.

They had been steaming slowly through the South China Sea towards Borneo, 140 nautical miles south of the Riau Islands, when a fast-moving skiff emerged from the darkness.

At 9pm between 15 and 25 pirates boarded the vessel, tied up the crew at gunpoint, plundered their wallets and phones, and herded them into the captain's cabin.

The assailants then brought a second tanker up alongside the Dongfang Glory and set about their primary business - offloading fuel stored in the hold. After three hours of siphoning the cargo, the pirates smashed up the ships communications systems and escaped with 300 metric tons of petroleum - worth an estimated $100,000.

The details of the incident, which the Malaysian Maritime Enforcement Agency (MMEA) shared with Al Jazeera, are not unique.

Thirteen hijackings took place in Southeast Asia in 2014 - up from only two reported incidents the year before, according to global security consultancy Control Risks.

The area is home to three-quarters of total piracy incidents worldwide, with 183 actual and attempted incidents reported last year.

The International Maritime Bureau (IMB), an industry body that responds to distress signals from commercial vessels, said the spike is continuing into 2015. There have already been six hijacking-for-fuel incidents this year, it said in a recent report.

Extensive criminal network

Unlike the Somali pirates that operate off the Horn of Africa - now largely thwarted by a strong international naval presence - the hijackers of Southeast Asia are not in the business of kidnap and ransom.

All hijacking incidents reported in the waters off the coast of Malaysia, Indonesia, and Singapore over the last 16 months have involved small product tankers under 51m long, targeted for their cargo.

Almost all attacks followed the same formula: Armed pirates board the target ship from a skiff at night, communications equipment is damaged or destroyed, the crew is tied up, fuel is siphoned to a second tanker, and the attackers leave before sunrise with cargo worth up to $1m.

According to the IMB, the mode of operation underscores the involvement of criminal gangs working in concert with a network of big buyers.

"There's a large organisation behind it," IMB director Pottengal Mukundan told Al Jazeera.

"Having stolen 500-600 tons of fuel oil [the pirates] then have to find a way to sell it, and there's a whole mechanism by which to do that."

Once the cargo has been siphoned off, it is sold to a buyer who knows it is stolen, but is happy to pay below market price, he said. It may then be transferred again, making it impossible to trace.

The lack of a trading hub for stolen fuel oil makes identifying the criminal elements behind the attacks difficult. A climate of fear and insularity among seafarers also prevents information from getting out.

Most patrons of Cafe Indah - a known hangout for pirates and shipping workers nestled in the red-light district of Batam Island, Indonesia, 15km south of Singapore - were unwilling to comment.

No one wants to be seen talking about it... If people saw us talking - for me it could be a problem. Indonesian sailor

One Indonesian crewman, working for a Singapore-based shipping company, agreed to talk but only in the privacy of a hotel room and anonymously to protect his safety.

"Mostly there's a lot of crime at port, lots of theft and robbery [in Batam]... It's unusual that people use guns, but you get long knives and tools being used to threaten people on the boats. A lot of it is local [Indonesian] mafia," said the sailor.

"I've only heard rumours about the hijackings, maybe it's gangs from Malaysia. But no one wants to be seen talking about it... If people saw us talking - for me it could be a problem."

In January, the MMEA captured seven pirates aboard the tanker MT Sun Birdie in Malaysian waters east of the Singapore Strait.

Two other pirates jumped overboard but were recovered by a passing ship after drifting for 10km. None of the pirates were in possession of travel documents, but were reported to be Indonesian. The perpetrators are now facing trial, but in all other cases of hijack-for-fuel, the assailants escaped.

Categorising piracy

Despite the rising numbers of incidents, some industry figures have sought to play down the problem, pointing out that the chances of a commercial vessel falling victim to piracy remain extremely small.

One-third of the world's shipping moves through the Strait of Malacca and Singapore each year, with an estimated 130,000 vessels arriving in Singapore alone.

Nicholas Teo, deputy director of the Regional Cooperation Agreement on Combating Piracy and Armed Robbery against Ships in Asia (ReCAAP), said improved piracy reporting has made the situation appear more perilous than it is.

"Over the years, everybody knew of incidents happening," he said in an interview with Lloyds List, an online shipping industry magazine. "Today the number is getting larger, not because there is a real increase. It's just now we know what we didn't know before."

ReCAAP's stance has proven controversial. Others say playing down the incidents has the potential to embolden pirates to stage more attacks.

Particular criticism has been levelled at ReCAAP's refusal to categorise hijacking-for-fuel incidents as a hijacking, and merely as "siphoning of ship fuel".

"Just calling them 'siphoning incidents' is underplaying what's actually happening in the area," said Giles Noakes, chief maritime security officer at BIMCO, the world's largest shipping association.

"There is a fear by some, possibly by ReCAAP, that this will attract the attention of the insurance industry - who will then reclassify the region as a 'listed area' [which will push up insurance premiums]. But it's far better to act proactively rather than reactively and to do something about it before the problem escalates."

Anti-piracy measures

BIMCO is considering drafting anti-pirate protocols for vessels in the region, including improved watch-keeping, the fixing of razor wire to the gunnels of tankers, and the use of water hoses to fire at hostile vessels - the same measures used against Somali pirates.

Somali piracy declines

Noakes concedes that improved policing of the Straits of Malacca and Singapore over the past decade has eradicated much of the violent piracy that prompted the Lloyds Market Association to categorise the Malacca Strait as a war risk zone in 2004.

But he is wary of complacency and his concerns about the spike in hijackings are shared by the insurance industry.

"The risk to the crew is clear. Rather than valuable hostage targets [the crew] are often considered a liability and as such, disposable," said Mark Doust, special risks broker in the corporate kidnap and ransom team at SCR, part of the Willis Insurance Group, in a statement to Al Jazeera.

"This sets the stage for a future spike in premium levels, with the insurance market concerned about a decrease in coordinated regional efforts to combat the phenomenon."

ReCAAP declined repeated requests for comment. Communications officer Amy Fang said senior officials were avoiding interviews following criticism of Nicholas Teo's downplaying of the piracy threat.