As has been customary since 1994, a session dedicated to pearl farming was co-chaired by Richard Fassler (State of Hawaii, USA) and Yu Xiangyong (Zhanjiang Ocean University, China). Presentations and posters were so numerous that some discussions had to continue in related sessions. Two themes dominated: declining sales — particularly of black pearls — and strategies for quality improvement. Students left their mark on the event: Anne-Michelle Lee and Josiah Pit (James Cook University) received the WAS Student Award for excellence in research.

China

Several presentations shed light on Chinese pearl farming. Yu Xiang-Yong recalled the boom initiated in Zhanjiang by Professor Dalen Xiong, with the first round cultured pearls in 1958, followed by a rise to 25–30 tons per year. Despite this growth, the industry faces overexploitation of stocks, loss of genetic diversity, pollution, farm overcrowding, high mortalities, high nucleus rejection rates, and poor yields — often resulting in mediocre quality.

According to Yu, solutions include stronger public involvement (research, pollution control, regulation, training). Studies are underway on genetic diversity and hybridization of Pinctada martensii (RAPD, isozymes, morphology). Triploidy shows growth advantages, and experiments with tetraploids are being conducted to produce triploids. Diversification toward P. maxima, P. margaritifera, and Pteria penguin is encouraged.

Yu also discussed advances in freshwater pearl farming with Cristaria plicata: implantation of a nucleus (7–9 mm) combined with a piece of mantle tissue, followed by 1–2 years of grow-out, resulting in production exceeding 4 tons in 2001. Hua Dan detailed the rise of Hyriopsis cumingii and the “mantle-only” technique. China now dominates this market with 800–1,000 tons per year, of which 400–500 tons are exported (Asia, Europe, Africa, USA).

Professor Aimin Wang (Hainan Ocean University) presented three approaches for producing tetraploid P. martensii: (1) inhibition of the first polar body in fertilized triploid eggs; (2) inhibition of the first and second polar bodies in diploid eggs; (3) inhibition of the first division in diploid zygotes. Although larval survival rates remain low, only method (2) has produced tetraploid juveniles, and at a very low rate (0.0625%). Wang also presented microsatellite-based selection methods to accelerate growth and his efforts to reintroduce P. maxima in Hainan.

Black Pearls

Richard Fassler emphasized the proliferation of farms in the Pacific and the opportunities they bring, while reminding participants of French Polynesia’s dominant position. Production of Tahitian pearls has exceeded promotional targets, leading to a sharp drop in prices and, according to unconfirmed reports, layoffs in the local industry. To prevent a domino effect, he recommends differentiating Tahitian pearls (colors, unique shapes) and prioritizing quality over quantity. The overexploitation of certain lagoons calls for caution, as the sector moves toward structural adjustments.

Bernard Poirine traced the Polynesian crisis: from 1.5 kg in 1972 to 11,764 kg in 2000 (+29%/year), followed by a price collapse and production decline (indicated by falling nucleus imports). He sees this as a classic case of overexploitation of a common resource leading to crisis. His models show that the economic optimum occurs at farming densities well below the maximum sustainable density. He compared management frameworks (quotas in Australia, co-management in Japan). In Polynesia, a working group is currently discussing export controls, concession policies, quality standards, and oyster densities.

Other Regions and Research

India (Ajai Sonkar) sees potential for P. margaritifera in the Andaman and Nicobar Islands, likely requiring hatchery support due to weak natural stocks.

At James Cook University (Australia), Josiah Pit tested tropical microalgae for P. margaritifera and noted the potential of Pavlova salina for larval feeding. Hector Acosta-Salmon presented a non-destructive gonad biopsy method using propylene phenoxetol (10 mm notched needle), useful for reproduction studies.

Farming Pinctada maxima in Irian Jaya

Research by Atlas Pacific Pty Ltd (J. Taylor, J. Knauer, A.-M. Lee) aims to improve South Sea pearl quality. In Australia, golden pearls have recently sold at higher prices than silver ones. In Indonesia, their proportion is higher; selecting golden donor oysters increases the share of gold pearls by +8.6%, but still leaves a high proportion of cream-colored pearls (78.8%). Conversely, silver-nacre donors yield > 98% silver-white pearls, with good proportions of rounds, pears, and buttons.

The scarcity of silver donors in Indonesia (0.3–8.9% depending on site) has led to reinforcement strategies: larval production from silver parents, followed by selection of silver oysters at 20–24 months. Growth differences have been noted: golden-nacre oysters grow faster than silver ones.

Regarding farming techniques, comparisons between bottom culture and suspended culture (1 mm mesh bags or rice bags) show more operable oysters in bottom culture but higher survival and nucleus retention rates in suspension. For nucleus selection (cost: AUD 88–165/kg), morphological analysis of P. maxima (wet weight, shell weight, width, length) indicates that wet weight is the best predictor of nucleus size and greatly improves accuracy beyond the empirical 60%.

Atlas Pacific continues to evaluate sites and depths. A.-M. Lee correlates environmental parameters and growth: depth seems to play a secondary role, while spatial and seasonal effects are more significant.

Akoya Culture in Australia

Recent successes have sparked renewed interest. Meetings have focused on P. imbricata in Queensland and New South Wales. Josiah Pit (Orpheus Island) and Wayne O’Connor (Port Stephens) report similar larval growth rates (≈ 20 days post-settlement), but faster hatchery/grow-out growth in Queensland’s warmer waters. In both states, oysters can reach ≥ 50 mm in 12 months.

The occurrence of “runts” (slow growers) was tested: when separated and monitored, they caught up, suggesting environmental rather than genetic causes for early slow growth. Regarding reproduction, peak activity runs from late spring to early autumn, with two peaks (November, March–April). Since settlement occurs only in summer (December–February), the autumn peak likely contributes little to recruitment.

One predator is a concern: the flatworm Imogine mcgrathi, found in cages and spat bags (≈ 1 oyster/month). Control protocols are effective: saltwater baths (low/high concentration) or freshwater immersion for 30 minutes for caged oysters. Salinity must be ≤ 2.5 ppm.

Mexico: A Rapidly Growing Sector

In Mexico, the industry relies on Pteria sterna and Pinctada mazatlanica (both can be hatchery-produced). Carlos Rangel-Davalos describes a method: rearing in plastic cages (3.6 × 3.6 m), grafting at 70 mm, then transferring to kangaroo nets folded over a metal frame placed on the seabed. Three technicians/90 days per batch of 10,000 oysters; three years from spat to harvest.

Restocking programs for natural banks with hatchery juveniles (previously overfished) show success, notably at La Gaviota (Bay of La Paz) thanks to fenced parks protecting oysters until 98 mm: survival rates of 8.3–21.2% after 11 months.