The pearl fishers: The waters surrounding the island of Bahrain harbour untold hidden wealth

It's 8.30am and Bahrain's gentle winter sun plays on the water as our boat pulls away from the jetty. Our hopes are high for a good catch: not of fish, but of oysters. And not just any old oysters but those with pearls in them.

Bahraini pearls are widely believed to be the best in the world. Many people put their trademark lustre down to the sea's freshwater springs that give the island kingdom its name: Bahrain means "two seas" in Arabic. Some also maintain that the shallow water at the pearl banks plays a role, along with the warmth of the water and its salinity.

Whatever the reason, Bahrain's precious pearls have been coveted for millennia. An Assyrian inscription from around 2000BC mentions "fish eyes" from Dilmun, an ancient civilisation of which Bahrain was capital. Tylos, the classical name for Bahrain, was said by Pliny to be "famous for the vast number of its pearls".

The golden age of pearling was between the 1850s and 1930. For most of the 19th century and earlier, pearls were the most valuable gemstone known to man, worth far more than diamonds. Buyers such as Jacques Cartier travelled to the small islands of Bahrain, where pearls were the principal economy. There were around 30,000 divers, who worked by holding their breath. Their only equipment was a nose peg, leather finger stalls for protection against coral, a weighted rope and a bag.

The industry started to decline when the Depression stifled spending, and much cheaper, cultured pearls flooded the world market. Divers headed to more lucrative jobs when oil was discovered in industrial quantities in Bahrain in 1932.

There are now nine oyster beds covering an area the size of South Yorkshire that haven't been commercially harvested for decades. The chances of finding a commercially viable pearl (at least 2mm in diameter) are only 5 per cent, and it can take decades to find enough pearls of the right size, colour, lustre and shape to make a necklace. Clearly there are easier ways to make a living. The trade of cultured pearls is forbidden in Bahrain, and there are only around five pearl merchants left. These deal in local collections or stock previously sold to India that they have bought back. The only pearl divers these days are a few fishermen and a small number of local hobby divers or visitors.

We are heading to the pearl banks with Bahrain-born Englishman Rob Gregory and his Australian partner, Robin Bugeja, who run the only pearl-diving programmes in the world endorsed by the Professional Association of Diving Instructors. One is for novices and the other for qualified divers.

Beginners have a pool session with Robin to learn the basics, and one open-water dive at the banks. Certified divers do two open-water dives. Before heading for the sea, students attend a theory class given by the couple on the history of the natural pearl, and on ecology, biology and conservation. It also includes tips on how to select an oyster that is more likely to contain a pearl, as well as how to open the shell and search for a gem buried in the flesh.

"Select the ugliest you can find," advises Robin. The couple believe that pearls are formed by parasites boring into the shell (rather than by a grain of sand, as some insist), which the oyster covers in nacre in defence. We are told to look for holes in the shell. Wide hinges, which signify age (the older the oyster, the larger the potential pearl), are also promising, as are creatures such as barnacles living on the shell. If we follow her instructions, our chances of finding a pearl will rise from 5 to 63 per cent, says Robin, who has more than 4,000 in her own collection.

"Every person I have taken out has found something," says Robin. "The pearl might be stuck on the shell, separate, large or small. One Englishman found a beautiful 6mm pearl, gathered everyone on the bow, dropped to his knee, and proposed to his girlfriend with the pearl in his hand. He got it set for her engagement ring. Pearl wedding anniversaries are also very popular for couples." One lucky tourist found a whopper worth around £13,000.

We arrive at an oyster bed called Umm al Layaal, or Mother of the Families, 15km east of Bahrain. "This was where eight-year-old boys trained to be divers. The water is shallow and the oysters blend in with the environment, so they're difficult to find," explains Rob. Few would know the beds as well as he does. In 1969, when he had just finished his A-levels, a crew arrived from America to make a Disney film called Hamad and the Pirates. Rob volunteered his services and the director promptly appointed him underwater cinematographer because he had a scuba-diving licence. He spent seven months filming the pearl divers, and was the first Westerner to dive the pearl grounds.

Today, he acts as a government consultant for a project to save Bahrain's pearling heritage. The Ministry of Culture and Information is to restore 17 historic houses on the island of Muharraq, Bahrain's second-largest city and its former capital. They will be linked by a 3km walkway for visitors, and include the homes of a captain, a dhow maker, a diver, and a trader who brought provisions to the crews. A stretch of coastline where the dhows left and returned is also being preserved, along with the three oyster beds that Bahrain owns in their entirety (some are shared with neighbouring territories). The houses, coastline and beds are on Unesco's World Heritage tentative list as a combined entry. The government hopes it will be made permanent in 2011.

"World Heritage status will give the beds total protection from tanker traffic, drilling and dredging," says Rob. "Diving for pearls won't deplete the beds, as long as it's done in the right way. The more you harvest and return the oysters immediately to the sea, as the Bahraini divers did for generations, the more the beds will regenerate." Returning the spent oysters helps maintain the levels of parasites, he says.

Umm al Layaal has proved fruitful in the past: students have found three danas here. Large and perfectly round, they are the finest of pearls. Remembering what Robin has taught me in the pool, I roll back into the water, and grab the rope extending from the boat, which will drift over the pearl grounds so we don't deplete one area. The water is only around 6m deep. I release air from my buoyancy-control device and sink.

Once at the seabed I start collecting the most unfortunate-looking oysters I can spot. Robin regularly checks that I'm OK with the standard diver's signal, and collects alongside me as we drift over sea urchins and oysters.

I inspect each one I pick up, and drop those that have a thin hinge so that they will reattach themselves to the seabed. It pays to be circumspect: it takes about an hour to open 50 oysters.

When it's time to resurface, I have 31 oysters in my net. Rob rejects only one and tosses it back into the sea. I carefully open the first with my knife, and lift up the sides of the oyster with the tip of my blade, hunting for a gemstone. Unsuccessful, I cast it back into the sea.

I continue opening, and eventually find blister pearls – small lumps attached to the inside of the iridescent shell. Several oysters later, I find a collection of about six minuscule pearls, the size of sugar grains. Thrilled, I put them into the jar I have brought along. Not long afterwards I let out an almighty whoop. There, shining fiercely in the winter sun, is a highly lustrous cream pearl sitting in the middle of the shell. It's a wonderful surprise. Once it is safely in my jar, I wonder about Robin's theory and inspect the shell. It certainly is ugly...

Travel essentials: Bahrain

Getting there

*Bahrain is served by British Airways (0844 493 0787; ba.com ) and Gulf Air (0870 777 1717; gu lfair.com ) from Heathrow.

Diving there

*Padi Discover Scuba Diving on the Pearl Grounds, and Padi Pearl Diver Programme are run by R&R, and cost from £160, which includes equipment hire. Courses are held all year round (00 973 3967 1748; email Rob Gregory on talamruk@batelco.com.bh; pearldive.com ).

Red tape & more information

*Tourist visas are issued on arrival in Bahrain and cost the equivalent of £10 (Embassy of Bahrain: 020-7201 9170; bahrainembassy.co.uk ).

*Bahrain Tourism: 020-7341 0770; bahraintourism.com