The latest information on pearl farming in Tahiti

Global production of akoya pearls has been experiencing a steady decline for several years. This downturn is mainly due to the crisis in Japan’s pearl industry, which has been hit by oyster overpopulation and diseases that have decimated much of its stocks.

In response to this situation, interest in research and development for akoya pearl production in other countries — particularly China and Australia — has been growing rapidly.

A New Testing Ground in Queensland

Australian pearl farming is currently based mainly on the exploitation of Pinctada maxima, the silver-lipped pearl oyster. However, increasing attention is being directed toward two other species, Pinctada margaritifera and Pinctada fucata, which are found in abundance in Australian waters.

A recent report details the work carried out in northern Queensland to evaluate the feasibility of producing akoya pearls from Pinctada fucata.

Valuable Data on Oyster Growth and Survival

Researchers collected baseline data on oyster growth and survival during the different stages of culture, from the larval stage to the nursery phase. They studied the best culture conditions: water quality, optimal larval density, feeding, type of nursery equipment, and stocking concentrations.

Promising Results for Pinctada fucata

This trial marks the first successful hatchery production of Pinctada fucata in Queensland. The methods used to rear this species were adapted from those already proven for Pinctada margaritifera.

During the first year of the project, more than 48,000 spat aged 3.5 months, with a mean dorsoventral height (DVH) of 12.5 ± 0.4 mm (± standard deviation, n = 50), were produced. Observations indicate that it is preferable to raise the oysters at a depth of 2 meters after their first transfer to the sea.

Once sorted, the oysters should be stocked at 20–30% of the available culture space, either in pyramid nets or in the same nets lined with finer mesh, until they reach a DVH of 50 mm. Beyond this size, they are transferred into “kangaroo pockets” or larger-mesh culture structures, with nets cleaned or replaced every eight weeks. Oysters grown individually, without forming clusters, also achieve larger sizes.

A Bright Future for Australian Pearl Farming

The results obtained are highly encouraging: in just 24 months, some specimens reached a DVH greater than 100 mm with a wet weight of 100 grams. Selective breeding trials are underway based on oyster size, and early observations suggest a promising future for akoya pearl production in Australia.

The black-winged pearl oyster (Pteria penguin) is found along the coasts of Hainan Island, the Leizhou Peninsula, and other maritime areas of the South China Sea. This large bivalve is known for its rapid growth, making it a particularly attractive species for pearl aquaculture.

Farming trials were launched about five years ago. Initially, wild oysters were collected to produce hemispherical pearls (mabé), and mature specimens from the wild were selected to serve as broodstock for spat production.

Mastered Farming Techniques

After several series of trials, researchers developed a complete farming process that includes:

• Selection and rearing of oysters
• Spawning induction
• Larval rearing
• Spat collection
• Grow-out to adulthood

This monograph provides a detailed description of each stage, from zygote to adult.

Towards the Production of Round Pearls

With sufficient reproduction achieved — first from wild oysters and later from farmed stocks — researchers have obtained enough oysters to conduct production trials.

Two companies — one based on Hainan Island, the other on the Leizhou Peninsula — collaborated in the research efforts and successfully developed an efficient technique for mabé production.

More recently, the teams have succeeded in producing the first round pearls from the black-winged oyster, marking a significant step forward for the industry. This monograph provides an overview of the techniques for producing both hemispherical and round pearls from this promising species.

Cultured pearl production is a key driver of sustainable economic development in several Pacific nations. Empirical observations have shown that different oyster stocks produce pearls with distinct characteristics.

For instance, Manihiki Island (Cook Islands) is renowned for pearls with a unique coloration. In French Polynesia, before the massive transfer of spat between the many atolls of the Tuamotu, each island produced pearls identifiable by their color, luster, and orient — factors that largely determine their price and competitiveness in the market.

Following these large-scale exchanges, these distinctive traits have gradually faded.

Towards Genetic Identification of Stocks

To preserve diversity and the unique qualities of pearls, it is essential to establish precise genetic fingerprints of the different populations. This would make it possible to implement targeted management strategies and ensure better traceability in aquaculture.

Researchers’ Response

Hatchery operators are requesting reliable scientific data to produce the spat desired by pearl farmers, while also protecting the biodiversity and economic value of the various stocks.

To meet this demand, researchers are using two DNA-marking techniques:

• Amplified Fragment Length Polymorphism (AFLP)
• Microsatellite DNA analysis

Specimens have been collected from hatcheries in Hawaii, the Federated States of Micronesia, and the Marshall Islands, as well as from natural stocks, in order to establish a solid genetic basis for future selection and conservation strategies.

A survey conducted among 40 pearl farms in French Polynesia reveals significant differences in production costs. The average production cost per pearl decreases as farm size increases.

For small farms (fewer than 25,000 oysters), the average cost of producing a pearl is twice as high as for farms holding more than 200,000 oysters. Economies of scale are most evident when farms hold between 25,000 and 100,000 oysters. Beyond this threshold, productivity gains become less pronounced.

Influence of Farming Practices

A regression analysis identified several practices that influence the rate of rejects (pearls with no commercial value):

• High oyster density on lines and larger oyster size at the time of grafting increase the percentage of rejects.
• Conversely, leaving grafted oysters in the water for a longer period and cleaning them more frequently reduces the reject rate.

Factors Influencing Selling Price

The analysis also highlights the parameters that improve the average selling price of pearls:

• Grafting larger oysters results in higher-value pearls.
• A low post-grafting mortality rate also contributes to better quality and therefore to a higher selling price.

Measuring metal pollution in tropical seas requires precise and cost-effective techniques. Direct measurement of metals in seawater remains difficult because it demands frequent sampling, expensive equipment, and specialized expertise.

Moreover, heavy metals are often trapped in sediments, and water sampling can miss pollution peaks that occur when these sediments are resuspended by storms or other disturbances.

Bivalves as Bioindicators

In the absence of suitable methods, filter-feeding bivalves such as mussels (Mytilus edulis) are commonly used as biological accumulators to detect pollutants.

The “mussel watch” system has proven to be a very effective tool and remains the most comprehensive method for monitoring coastal metal pollution in the United States. However, these species are restricted to temperate zones and do not offer a solution for oligotrophic tropical waters.

Pearl Oysters: Ideal Sentinels

Research has shown that pearl oysters (genus Pinctada) are an excellent complement for monitoring warm waters. They are widely distributed throughout the South Seas, are sessile, have long lifespans, and are well-suited for bioaccumulation studies.

Initial trials on the Hawaiian pearl oyster (P. margaritifera galtsoffi) revealed a strong capacity for heavy metal accumulation. Tests conducted in controlled tanks showed steady bioaccumulation of copper, cadmium, and zinc, proportional to the concentrations in the water and the duration of exposure.

Towards Enhanced Environmental Monitoring

These results have led to the establishment of field monitoring standards. Early studies conducted in Hawaii have provided preliminary environmental data. A second series of trials confirmed significant temporal variability in metal accumulation.

Researchers are now expanding their work to include other metals such as strontium, cobalt, and lead. Measuring radioactive isotopes of strontium and cobalt could become a valuable tool for ecological restoration and the repopulation of South Pacific atolls (Bikini, Enewetak, Christmas Island, Mururoa) that were once used for atmospheric and underwater nuclear tests by the United States, the United Kingdom, and France.