PEARL FARMING ACTIVITIES
Pearl cultivation operation can be divided into several phases as follows:
- collection of healthy adult oysters, hatchery production, nursery rearing,
- growing, grafting/nucleation, pearl formation and harvesting.
- At each stage a number of different culture methods are used.
- The method chosen depends upon the species cultured and the location or environment of the cultivation.
- In Indonesia, pearl farmers have developed methods and techniques for Pinctada Maxima that have been adapted for specific characteristics of Indonesian tropical marine environmental conditions.
- For the selection of good quality brood stock, namely the healthy and productive male and female oysters, before the 1990’s the main source for pearling activities was collection of adult wild oysters from the sea-beds.
- However, after successful trial testing of hatchery techniques, as from early 1990’s Indonesian pearl farmers have relied on the hatchery production for pearling oysters.
- Hatchery production allows selective breeding for desirable traits and assures a continual supply of juveniles.
- During this hatchery phase, oysters’ larvae need micro alga (i.e. aquatic photosynthetic organism) as their food.
- A balanced diet consisting of a number of species of micro-algae has been used in commercial hatcheries for pearl oysters from spawning until settlement.
- In Indonesia, the pearl farmers’ needs for larval feeds are supplied by the Technical Service Units under the Ministry of Marine And Fisheries Affairs spread all over the pearl farming regions.
- Good quality oysters generally will be ready to be nucleated at 21 to 24 months of age. From the time of nucleation, it takes approximately 18 months to two years for the pearl to grow to a desirable size, namely around 10 to 12 millimeters in diameter. (In extreme cases, the period may be lengthened up to 3.5 years after nucleation).
- A medium quality pearl is estimated to have 1,000 layers of nacre on it, resulting in a nacre thickness of around 0.4 to 0.5 millimeters. A thickness of around 2 millimeters (nucleus plus nacre layers) after 2 years is just acceptable.
- The daily deposition of nacre can vary from zero to seven layers per day. The main factors that determine the rate of deposition are, among others, the water temperature and the physiology of the individual oyster. The culture period necessary is also dependent on the size of the nucleus.
- When the desirable size of pearl is achieved, harvest can be done. Harvest is done using two methods.
- For oyster that has the potential to produce good quality pearl, the existing pearl will be taken out by another mean of operation and re-inserted directly with new nucleus.
- The rest of the oysters will be killed and the pearl harvested.
- Not all oysters harvested produce pearls.
- A harvest is considered good when more than 55% oysters harvested are containing pearls.