Pearl farming in Polynesia
Atolls, such as Rangiroa, are low islands formed of an exposed ring of coral encircling a lagoon, and present the ideal environment for pearl oysters.. The Tuamotu Archipelago, in French Polynesia, counts about 80 atolls, of which a great proportion allows pearl farming in clean crystal clear waters. Pearl farming is a difficult initiative, and as in every aquaculture production, natural hazards, storms, typhoons, as well as diseases may reduce years of effort to nothing at any moment.
Sum up of the production cycle of a Tahitian cultured pearl
- Collection of the spat (1 year)
- Spat removal, farming (2 years)
- Monitoring of the nucleus transplant rejections (45 days)
- Farming of oysters with pearls (2 years)
- Harvest and second graft
- Farming of oysters with pearls (2 years again)
- Third graft
The first phase is the supply of pearl oysters. Nowadays, in Polynesia, harvesting the fully grown oysters hung to coral is strictly banned. The only lawful way to obtain pearl oysters is to collect the spat. The original method consists in immersing collectors several meters deep into the water, during the breeding season in the zones with the highest probability of gathering larvae together, which may vary from year to year.
Collectors are made with polypropylene sun shelters, according to a method invented in Polynesia after many years of research in the field of pearl culture. Nacre larvae use these collectors as perfect supports in order to end their larval stage and to metamorphose into young nacre. A year at least is necessary for oysters to grow up and to develop before they can be handled. Collection is very efficient in small atolls and every pearl farm get their supplies from this, since the nineties.
Young oysters farming
As soon as the collectors have been brought back to the farm, sometimes after hours on a ship, hung oysters must quickly be removed, then put into farming so that they can grow up to a size which will eventually allow a grafting process. There is not any standard farming technique in Polynesia, and the most used supports are thin ropes supporting between 20 and 50 oysters. The ropes are put on 200-meter-long stations, immersed 8-to-10-meter deep, hanging with buoys and anchored with concrete to water bottom.
The farming process can last up to two or three years. Oysters are regularly cleaned and sorted, every 6 months, in order to remove ill animals and to calibrate the oysters. It is estimated that around 40% of the oysters is lost during this phase, because of predation and diseases.
When the oysters have grown up to the right size, between 10 and 12cm in diameter, they can be grafted. The surgical procedure requires extreme cleanliness, whether of oysters or the grafting tools, the nucleus and the grafts. Right after the 30-second surgery, the oyster is placed into a retention net for 45 days, in a protected area in the lagoon. After that amount of time, the nucleus transplant is monitored.
The average success rate of the grafting is 75%, but it strongly depends on the skill of the grafter and the oyster’s health at the time of the surgery. Transplant rejects cannot be used for second grafts, owing to the scar from the initial incision. The development of the pearl still requires care and maintenance for 18 to 24 months, before this long process reveals its output.
The harvest is always a moment of both exaltation and stress for the pearl farmer. There are so many factors in the development of a pearl that nobody can ever forecast the output of these many years of labor and patience. Generally, a good harvest means 40 to 50% of the pearls are marketable, but there are so many criteria in the pearl classification – shape, diameter, luster, color, upper layer quality – that there will still remain days to sort out the harvest product before it can be perfectly estimated, as well as the quality of the labor. In any case, only 1 or 2% of the harvested pearls are of outstanding quality.
For years, the pearl harvesting had consisted in opening the pearl oysters in order to extract the long-awaited pearl. Since then, further to methods invented in Australia, the pearl harvest implies also for a certain quantity of oysters a second operation, or even a third one, in rare cases.
The second graft consists in carefully extracting the pearl without hurting any organ of the oyster, particularly its adductor muscle, and replacing it with another nucleus of the same size, which does not require a new graft insertion, since the pearl sac is already in. This method, in addition to allowing several pearls to grow in the same oyster, is the means to obtain exceptionally large pearls.
Key figures of the production of Tahitian marine cultured pearls
- Working base : 10.000 nacres collected
- Removal of the spat and farming : remain 7.000 nacres for the grafting (predation, sorting, diseases)
- Grafting and monitoring 45 days : remain 4.410 nacres with pearls (70% in retention, 10% ungraftable)
- 24 month harvest : remain 3969 nacres with pearls, 10% death rate
- Pearls quantity : 3176 pearls, 20% transplant rejects during the farming
- Round pearls quantity : 635, 20% of the crop
- Perfect pearls quantity : 30, 1% of the crop