Pearls are formed when a pearl oyster coats any hard particle entering it with layers of nacre, a form of calcium carbonate.
Western Australia's pearling industry was worth about $60 million in 2013, the second most valuable fishing industry to the State after rock lobster. It is focused on South Sea pearls from the pearl oyster Pinctada maxima.
Pearls are sold individually for use in jewellery or as strings of pearls to wear around the neck.
The shell of the pearl oyster (known as mother-of-pearl) is also used in jewellery and for buttons.
Western Australia’s pearling industry focuses on South Sea pearls - big silver-white pearls prized around the globe - from the pearl oyster Pinctada maxima. WA pearls are known for their smoothness, lustre and large size.
Other pearl oyster species are farmed on a smaller scale.
Once all pearls were found in the wild but most are now grown commercially through ‘seeding’ to stimulate pearl growth.
Seeding means surgically inserting a bead of mussel shell into the oyster’s gonad. A piece of mantle, the tissue that produces nacre (a form of calcium carbonate that creates a pearl), from another pearl oyster is inserted with it. Pearl oysters are carefully seeded by hatchery technicians. They are then moved to pearl farms where the pearls grow inside them. The pearls are carefully removed and sold for use in jewellery.
The pearling industry incorporates: commercial fisheries for the collection of wild pearl oysters; aquaculture operations for hatcheries that produce pearl oysters; seeding operations and aquaculture operations for pearl farms where pearls are grown to full size.
Western Australia has the only significant wild stock pearl oyster fishery in the world.
Divers hand-pick wild P. maxima from ocean beds in the Pilbara and Kimberley, with the main fishing grounds near Broome, from January until about July. The divers work from sophisticated pearling boats, on which the oysters are often seeded – they’re returned to the sea bed in net panels. (Some pearl oysters are seeded later at the pearl farm.)
Over the next three months, the panels are turned regularly to make the pearls round. Next they’re moved to the sheltered waters of farms and suspended on floating lines. It takes up to two years for the pearls to grow to desirable size and quality. Most pearl farms are located in the pristine waters off the Kimberley coast.
The best oysters may be seeded several times, with each pearl larger than the one before.
Hatchery-bred pearl oysters are now also a major part of pearl production. They are used to supplement the wild pearl oysters collected. Hatcheries in Broome and Darwin (using broodstock sourced from WA) supply significant quantities of juvenile P. maxima to pearl farms.
Stress can cause a blemish on the pearl, so the aim is to keep the oyster healthy and stress-free. Tending the oysters involves keeping them flushed with nutrients and cleaning them of parasites regularly.
Every healthy oyster has a tiny pea-crab that lives inside it. It shares the debris the oyster sucks in and probably keeps it clean. Its presence seems essential for the oyster’s wellbeing, and seeding technicians are careful not to harm it.
Only two per cent of South Sea pearls produced in WA are sold in Australia, with the rest exported mainly to Japan, the US and Europe.