In Polynesia, the pearl oyster specie used to produce black pearls is named Pinctada margaritifera or the black-lip pearl oyster because of the pigmentation characteristic of its mantle. Despite his usual name, the Tahitian black pearl or Tahiti cultured pearl, the fact is that most pearls are produced in the Tuamotu archipelago whose atoll lagoons are ideal sites for the growth and the reproduction of pearl oysters.
The pearl farming techniques are not standardized and completely different between countries and species of Pinctada exploited. In the Tuamotu atolls, surrounded by huge lagoon reef crowns, tides are almost zero and the currents are relatively low except at the passes, which are also the privileged places for snorkeling or scuba-diving. The farming techniques are mainly based on suspended rope lines. The lengths and materials used vary from a simple rope to which are attached 10 to 30 shells to a sophisticated basket containing up to 48 spats.
Diving for pearl oysters in the natural environment is prohibited and all supplies of oysters are done by spat collection, the technique used to capture larvae which allows the supply of shells to all farms in French Polynesia from a few atolls.
The collectors are made from pieces of agricultural shadow mesh polypropylene strung on thin ropes to form an ideal site for the development of young spat. This original technique to capture pearl oyster shells was invented in French Polynesia and largely explains the success of the pearling industry in this country. Not only the industry is not dependent on natural stocks, but the environment is protected from degradation of coral, collateral victims of the pearl oysters attached to them.
Raising and growing the shells is a prerequisite for the production of pearls. Indeed, an oyster can be seeded only when it reaches a minimum size and some internal organs are sufficiently developed. For the growing process, the pearl oysters are placed in baskets or suspended on ropes and must then be drilled. The shells ready to be grafted are at least 30 months old. Predation by triggerfish, eagle rays and some other species is the main problem faced by the pearl farmers during this growing step.
The basic technique is to introduce within the pearl oyster, in an appendix named the pearl pocket, a nacre bead, "the nucleus", and a piece of mantle, the organ which is producing layers of nacre.
The nucleus are obtained from shells of freshwater mussels mainly fished in the Mississippi river, USA. They are then shaped in Asia. The BU is the basic unit diameter for a nucleus. 1BU = approximately 0.3 mm. In Polynesia, standard sizes for nucleus ranged from 2.0 to 2.3 BU.
The piece of mantle or graft tissue is derived from an donor oyster. It will be chosen with care and much of the quality of the pearl depend on that choice. Each sacrificed oyster can produce about 50 pieces.
Each seeding lasts no more than 15 seconds. The grafters seed between 350 and 450 shells per day. The surgery is very delicate and retention rates vary between 50% and 80% depending on the quality of grafters, water temperature and quality of pearl oysters.
At harvest time, oysters are not killed, and it is possible to make a second seeding for about 30% of harvested shells and even a third for about 10%. In the case of a second or third operation, the mantle piece is no longer necessary. This technique allows the production of very large pearls because the nucleus introduced in second and third are bigger.
Following the seeding, the oysters are placed in baskets with fine meshes. They are used to control the success rate of the graft after 45 days. Oysters that have kept the nucleus are drilled and tied with a nylon cord on a rope. The growing of the pearl may finally begin and will last at least 18 months and usually about 24 months.
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