Nigerian authorities have charged 23 people after the navy seized two ships carrying stolen crude oil in a major crackdown on an illegal trade in which officials say 180,000 barrels are stolen every day.

That's out of a daily production of 2 million barrels. It's costing Africa's leading producer $7 billion a year. That's a heavy loss for a country that relies on oil for more than 80 percent of its revenues.

All told, the dozen nations along the Gulf of Guinea, which stretches from Guinea to Angola, are losing $2 billion a year to maritime crime, according to Nigerian navy statistics.

Off Nigeria's 530 miles of coastline, where dozens of tanker transit every day, attacks nearly doubled in 2012 from 11 in the previous year.

All told, statistics gathered by the AKE security company and logistics group GAC indicate there were 11 attacks reported on ships in the Gulf of Guinea in December 2012, most of then involved in the oil business

West Africa accounted for nearly one-fifth of all attacks on ships around the globe last year, with a heavy concentration off Nigeria's Bayelsa State, the heart if the country's oil industry.

Piracy off West Africa "is reaching dangerous proportions," the International Maritime Bureau, the global piracy watchdog, reported in October 2012.

"It's a serious problem," says IMB director Pottengal Mukundan. "The pirates are getting quite audacious, with increasing levels of violence being used."

Many of the attacks in the waters of the Atlantic off West Africa are linked to the highly organized theft of oil in Nigeria that's concentrated in the Niger Delta in the south.

It's Nigeria's main oil-producing zone, with a growing number of drilling and production platforms in the rich deepwater fields offshore and in the neighboring Bight of Benin.

The increase in piracy and oil theft has coincided with a widespread insurgency in the delta by tens of thousands of impoverished tribesmen demanding a greater share of the nation's oil wealth joining with criminal organizations.

They systematically steal oil from pipelines operated by international oil companies like Chevron of the United States, Anglo-Dutch Royal Shell and France's Total, which is loaded onto small tankers in the region's labyrinth of creeks and swamps to be sold in neighboring countries.

This system of hacking into pipelines is known as "bunkering," and it's the bane of the foreign oilmen's lives. Some of the oil is illegally refined and sold locally

Maj. Gen. Johnson Ochoga, commander of a military anti-bunkering operation ordered by President Goodluck Jonathan in 2012, said this month that 2,000 suspects had been arrested and some 4,000 illegal refineries and hundreds of boats destroyed.

In 2011, state agencies reported that thieves ruptured pipelines 4,468 times, compared to an average of 1,746 a year in 2001-10.

On top of that, the pirate gangs are now hijacking large tankers at sea, siphoning off their oil cargoes into smaller ships.

The 23 suspects now facing trial comprised the crew of two ships intercepted by Nigerian navy patrols in November in the Niger Delta creeks.

A vessel named the Ashkay operated by an Indian company was seized carrying 35,000 gallons of what was believed to stolen crude. The navy arrested 10 Indians crewmen and four Nigerians who were aboard.

A week earlier, the navy intercepted the Mount Eve carrying 16,500 gallons of refined fuel. Nine Nigerians and two Ghanaians were arrested.

But the navy can't count on suspects being convicted. Corruption is endemic in Nigeria and pervades all levels of government.

In October 2012, a leaked report commissioned by the government said cut-price gas deals between corrupt Nigerian officials and international oil companies cost the state $8.6 billion in 2009-11.

The U.S. One Earth Future Foundation, which monitors maritime piracy, noted this month that the number of attacks by Somali pirates in the Gulf of Aden and the Indian Ocean off East Africa have fallen, while those off West Africa are increasing.

Unlike the Somali marauders, who seize ships and their crews for big-ticket ransom, the gangs working off West Africa go for cargoes, particularly oil.

The piracy problem in East Africa has decreased largely because of the international naval task forces that have been protecting shipping lanes there for the last three years.

There are no such counter-piracy operations off West Africa.