Salt-Water Pearl Farming - Part 1

Marine Pearl Farming Defined
Pearl farming is the industry responsible for growing farm-raised pearl mollusks and producing cultured pearls. These cultured pearls make up nearly 100% of the pearls sold today.

What Is Pearl Farming?
  • Cultured pearls are grown on what are known as pearl farms. Depending on the variety of mollusk employed at the farm, these will be located inside protected bays or in channels or in lakes, ponds or streams (for pearly freshwater mussels). In this chapter we will discuss Saltwater Pearl Farming.
  • There are also many kinds of pearl farms, each one as unique as its environment. Some are not seen from the surface because they may be resting directly on the sea-bottom and diving is an absolute necessity, others are accesible from the surface by means of rafts or long-lines.
Pearl-Farm-Diagram - Diagram of a Long-Line Pearl Farm
  • As in any other form of farming, pearl farming can be as dependent on luck as it is on skills. An entire bed of oysters can be completely devastated by unpredictable & uncontrollable factors, such as pollution, storms, excessive heat or cold, red-tides, disease and many other natural or man-made phenomena.
  • Although pearl farmers attempt to control as many of these variables as possible, pearl farming is a risky business!
Modern Pearl Farming Techniques
  • The first step in the pearl production process is to obtain the oysters to grow. In the early days of the cultured pearl industry, wild-mollusks were simply collected from the sea, either as fully-grown adults (as is still the case in Australia) or by collecting "wild-spat" (as is the case of Tahiti and Mexico).
  • Today, farms employ the modern practice of breeding their own mollusks in a lab. To do this, the pearl farmer selects his brood stock (a group of the best, healthiest and ready to breed animals) and takes them to a specialized hatchery lab, where technicians will collect their sperm and egg cells. The fertilization process takes place in-vitro and are used to create a new generation.
microscopic larvae swim freely in large tanks
  • Under laboratory conditions, the microscopic larvae swim freely in large tanks and are actively fed with a special diet of "microscopic algae", until at around 25-27 days after fertilization, they will develop into baby oysters and will require to settle. "Spat collectors" are also used to have the young oysters attaching. Then they are taken to tanks or even to the ocean until they grow bigger and become visible to the naked eye (1-3 mm) and can be sent to the pearl farm.
Pearl Oyster spat just arrived from the lab to the farm - Pearl Oyster spat just arrived from the lab to the farm

A plastic bag containing baby pearl oysters (spat) that was raised in a hatchery. These are ready to be placed under nursery culture conditions. Photo by Douglas McLaurin-Moreno.

  • In the case of wild-caught spat: Pearl oysters will spawn in synchronicity for the most part. Hopefully, a sperm cell will be able to find an egg to fertilize: these tiny cells are all swimming in a huge sea after all! The larvae will swim in the water column, feeding from phytoplankton and becoming food for a myriad other sea creatures. It is said that in Nature, only 1 to 10 oysters born will reach adulthood and this is dramatic, because one female oyster is capable of releasing over 100 million eggs!
  • About a month after fertilization, the tiny pearl oysters will become visible to the naked eye and will start looking for a place to settle and begin an oyster-like existence. It is at this moment that the oysters come down to the bottom and crawl around, sampling the substrate with their foot/tentacle until they find a place they like and secrete byssal threads from their byssal gland. These threads (known as "byssus") are amazingly strong, and help keep the oyster firmly anchored to rocks, corals, shells or other oysters.
  • Pearl farmers deploy their "spat collectors" into the water exactly at the time that the baby pearl oysters will be looking for a place to settle, thus some of them will select the collectors instead of a "natural alternative". This is a 100% passive method of collecting pearl oysters and depends on the baby oysters' own "willingness".
  • At an age of 2 to 6 months after settling on the collectors, farmers retrieve them and the removal of juvenil oysters begin. This is done all by hand, with the farm's workers looking all over the substrate for the tiny critters...sometimes they will find just one, maybe none...and other times they can find over 1 thousand in a single collector! Here, Lady Luck calls the shots yet again.
Pearl-Farm-Diagram - Diagram of a Long-Line Pearl Farm

Pearl Oyster spat on a "Spat collector"
Raising Oysters for Pearl Farming
Once the young oysters (measuring from 3 to 10 mm, sometimes larger) are ready to start the first stage of aquaculture, they are placed inside protective mesh cages that will deter predators (such as fish and snails) from reaching the young oysters.
Pearl Oyster spat just arrived from the lab to the farm - Pearl Oyster spat just arrived from the lab to the farm

Lantern nets used for the culture of Scallops and Pearl oysters.
  • Pearl oysters are filter-feeders and will feed from microscopic algae and other minuscule organic matter particles in their surrounding environment. Because of this, it is not necessary to provide them with food, but it is important to never overstock the oysters so they will all be able to feed and grow adequately.
  • About 2-3 years later, the young adult oysters will be ready to be used for the pearl grafting or nucleation operation. But let us not forget that pearls oysters have been constantly taken care by the workforce at the pearl farm, where they are inspected, thinned-out and hand-cleaned every one to two months. This is a ton of work!

A young black-lip pearl oyster in the process of being hand-cleaned. - A young black-lip pearl oyster in the process of being hand-cleaned.

A young black-lip pearl oyster (Pinctada mazatlanica) that has been covered with "fouling" (epibionts) that have to be removed to allow the mollusk to grow and develop. Photo by Douglas McLaurin.

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