 Modern Australian Pearl
Culture Technology
Cultivating round South Sea pearls
In Australian waters, wild ‘shell’ of >120 mm dorso-ventral shell length are collected by teams of up to six divers from offshore shell beds that stretch from Exmouth Gulf in the south to the Lacepede Islands in the north of Western Australia, from Northern Territory’s eastern grounds along the Arnhem Land coast between Golburn and Crocodile Islands, and to the west of Badu Island in Torres Strait, Queensland. Up to 10 dives per day are undertaken by these divers.
To collect shell, hookah-equipped divers are towed underwater behind boats, which drift with the current. Once collected, the wild shell is cleaned, inspected, and stored in net panels of 6 or 8 shells that are tied onto longlines which are moored to the bottom of the seabed to create ‘dump sites’. In the past wild shell were transported from these ‘dumps’ to farms, where seeding was performed.
Today, most West Australian cultivators significantly reduce mortality rates, that used to occur as a consequence of this transfer, by seeding wild shell (in mid-year) at the collecting grounds — using large modern ships that are equipped with surgically clean laboratory and operating facilities. On the ship mostly Japanese-trained technicians implant each wild shell, in the traditional manner, with a round nucleus and a small piece of mantle tissue from a ‘sacrificial’ oyster. The nuclei, which are manufactured from thick shell of the fresh water Mississippi mussel, can have a diameter of from 6.6 to 14 mm — depending on the size of the shell to be implanted, and whether or not the shell had been previously implanted. During the season technicians each operate on 550-600 shells per day, using sterile surgical conditions and dexterous surgical technique.
Following seeding, the implanted shells are returned to net panels on bottom longlines moored at ‘dump’ sites. Here they remain for up to three months, during which time they are inspected and turned regularly by divers to ensure that an even envelope of nacre secreting cells forms a sac around the nucleus. After this stage has been completed, the net panels are retrieved (during the warm October-December months) and the implanted shell are very carefully transported by boat to pearl farm growout sites in well protected coastal bays and inlets.
During growout, the implanted shell may be held in net panels either on well protected less expensive-to-operate surface longlines (e.g. Western Australia and Northern Territory), or bottom posts and longlines, about 13 m down - where the shell is less vulnerable to cyclonic conditions, but does require continuing maintenance by underwater divers (e.g. Western Australia).
Net panels can be held either on individual posts, or on underwater ‘fences’. During the two-year culture period of growout, implanted shells are cleaned every two to four weeks — either by underwater divers, or by boat-mounted high pressure cleaning machines. Four to six months after seeding an X-ray checks each shell for nucleus retention and pearl formation. Shell that have rejected nuclei are held until the following year. At that time they are re-seeded if they are healthy and have little scarring from the previous attempted seeding. Re-seeding will not occur if shells have commenced forming keshi pearls as a consequence of the tissue implant grafting into the incision and forming a pearl-producing pearl sac. |
