Image caption The oysters grow for two years in Western Australia's warm waters

In the sparkling waters of Roebuck Bay, three men work on a small boat.

One hauls flat metal cages holding oysters up from the water. Another cleans the shells, passing the cages though high-pressure water jets. A third does a manual check, then puts them back in the sea so the shells can keep on growing.

The plate-sized Pinctada maxima oysters need two years in the warm, nutrient-rich waters. But then they yield treasure - glossy South Sea pearls that are sold around the world.

Pearling has helped shape Western Australia. One hundred and fifty years ago, wild oysters were so abundant that people could collect them by wading into the sea.

At that time pearls themselves were a rare prize - it was the mother-of-pearl lining the shell that was sought for buttons and ornaments. The industry began in the town of Cossack, but it was Broome, curving around Roebuck Bay, that came to be at its heart.

Pre-war pearlers John Norman's grandfather, Hugh, went to sea because of ill health. He became a partner in Robison & Norman and began pearling in Thursday Island before moving to Cossack, living on his schooner, Mist, from 1887-1901. "Pearling those days was a lot easier than it is now - you didn't have to go down 10 or 12 or 15 fathoms, good shell was still being picked up on the beach. Grandfather started to make a living and the price of shell was improving." Joined by two brothers, he moved to Broome. "By 1910 they were employing 199 men, and they had 30 boats and two schooners, so it was a very big operation. Grandfather prospered up here. Pearling operations were based in Beagle Bay, we had a shipyard and it was very successful." "The crew were always a mix. You might have two Japanese - a diver and a tender, the diver's eyes-and-ears on deck. In those days there was no engine pumping the air down, it was by hand pump. Then you might have two Chinese, two Koepangers [Timorese], two Malays. The theory was that if you had a mixed racial crew they weren't going to get together and throw the skipper overboard - although it did happen." John's father started in the family business "at the very bottom as a shell opener". He fought in World War I but returned to pearling in 1919. The industry rebounded after the war but was hit by the depression. "In the 1930s the shell price went right down, the depression and too many boats in the water led to huge stockpiles of shell." John grew up in Broome until the outbreak of World War II. "From a practical point of view our involvement in pearling ended when all the Japanese crew were interned, and that was after the first Japanese raid in 1942. The bottoms were blown out of the luggers and three were taken by the Royal Australian Navy."

Settlers came to make their fortunes, building wooden pearl luggers so crews could scour the sea floor. Indigenous skin-divers were used in the very early days but Japanese divers came to dominate when underwater suits were introduced.

Crews came from across South-East Asia and by 1914, Broome had more than 300 luggers and a diverse population of several thousand.

It was a highly lucrative, highly dangerous business. Broome's Japanese cemetery is testament to the hundreds who died, from drowning, the bends or illness. When World War II broke out, however, the Japanese divers were interned or went home.

With the introduction of the plastic button after the war, the industry that had built the town appeared to be in terminal decline.

'Keyhole surgery'

Then came cultured pearls. Before, finding pearls had been a matter of chance. But over several years a technique in which an oyster could be "seeded" to create a pearl had been mastered in Japan.

In 1956, Australia's first cultured pearl farm was opened north of Broome by Tokuichi Kuribayashi of Nippo Pearls, with local partners. Today farms are dotted along Australia's north-west coast.

Paspaley Pearls is Australia's biggest producer, with several farms, including the one in Roebuck Bay. Its purpose-built laboratory ship carries a multinational crew of more than 50 for 10-day stints off 80-Mile Beach, south of Broome, to seed oysters.

The oysters are a mixture of hatchery grown and wild shell gathered by divers. The wild shells are rested for three months after collection, then brought on board.

Richard Mclean, Paspaley's special adviser on pearling, describes the seeding process as "like keyhole surgery". Inside the laboratory, 21 technicians - all Japanese - sit at stainless-steel stations. Using a slim opening in the side of the shell, they insert a tiny piece of Mississippi freshwater clam into the oyster's gonad.

The oyster reacts to the introduction of the foreign body by coating it with layers of nacre - crystallized calcium carbonate and an organic protein. Slowly, layer by layer, a pearl is formed.

The seeded shells are rested again, then moved to farms elsewhere on the coast. They are cleaned regularly and spaced well apart. Yields have increased with experience - about 70% of the seeded shells will produce pearls.

"We've improved over the years - we had to learn how to understand the cycle of the oyster," said Mr Mclean. But it is labour-intensive work that can be wiped out by disease or storms, he adds.

Image caption The Pinctada maxima are the biggest oysters in the world

The pearls, once harvested, range from perfect spheres to irregular "baroques". A select few are sold under the company's own brand but most are sold on the wholesale market - at auctions in Hong Kong, Kobe and Darwin.

"Australia is the top-end [of the market] and usually that means really fine goods, with round, good lustre, generally larger than 12mm in diameter," said Russell Shor, senior industry analyst of the Gemological Institute of America.

"The larger the pearl the more out-of-round they tend to get - they start looking lumpy. It's really, really hard to get round pearls in larger sizes and the Australians are good at it."

'Difficult road'

But it is not an easy time for Australian producers. Figures from the Western Australian Department of Fisheries (DOF) show the industry contracted in value annually from 2006-2009, before a rebound in 2010.

Types of pearls Two types of pearls - saltwater and freshwater

Pearls do occur naturally but cultured pearls dominate the modern industry

dominate the modern industry Three types of saltwater pearls: Akoya (farmed in Japan and China), Black South Sea pearls (from Tahiti) and South Sea pearls (from Australia, Indonesia and the Philippines)

(farmed in Japan and China), (from Tahiti) and (from Australia, Indonesia and the Philippines) Cultured freshwater pearls produced mainly in China, using freshwater mussels

Brett McCallum, of the Pearl Producers' Association (PPA), says there has been "general rationalisation in infrastructure and sharing of operational activities between operators" because of the global financial crisis. In 2010, only a quarter of the total allowed wild shell catch was taken because of market conditions, the DOF said.

Paul Bazar, president of one of the largest pearl distributors in the US, Imperial Deltah, says sales of South Sea pearls dropped for three years while the US economy struggled. "Higher-end sales suffered more than promotional freshwater pearls, which were affordable," he said.

China is the source of these freshwater pearls, smaller but cheaper offerings being cultivated on a much larger scale. Australia's production, Mr Shor said, is "almost statistically meaningless" compared to China.

The Chinese quality is also improving each year, potentially boding ill for Australia. "If China can offer a 14-16mm necklace of really fine quality pearls that look to all the world like they are South Sea pearls, they'll have a really difficult road," he said.

Image caption Australian producers are targeting high-end buyers

So the Australians are working to create a niche brand for their product at the top end of the market. "They won't win by cheap labour or fuzzy environmental restrictions," he said. "They have to do everything by the numbers… so they really need to work that high-end."

That brand, however, has been in the spotlight after an ABC documentary raised questions over safety following the death of a Paspaley diver in April. In a statement, the PPA said it rejected claims that the industry was not meeting "the most relevant and appropriate safety standards". An investigation is ongoing.

Paul Bazar says the future depends on the ability of people to buy luxury goods and how Australia competes with low-cost producers.

And he says more work is needed to educate consumers about the value of different pearls. "The lack of knowledge is one of the biggest problems that people who love pearls face," he said.

One such is John Norman, whose father and grandfather were pearling masters in Broome before cultured pearls. He and his wife Verity have written a book on the family's pearling past - which included surviving dips during World War I and the Great Depression.

"This is one of the fluctuations in the market but it will come good again," he said. "These are the best shell - look at the waters, it's pristine, it's virgin sea, there's no contamination."

"The fact of the matter is there is nowhere in the world that has these conditions. These pearls and the techniques are the gold standard that everyone would like to achieve."