Stimulating investment in pearl farming in ... - World Fish Center

Suitability of Habitats for Growth of Black-Lip and Silver-Lip Pearl Oysters Final, June 2008specific factors such as currents and circulation patterns, or food availability, all of which areimportant to commercial farming.In French Polynesia, the growth of cultured black-lip pearl oysters has been compared inthree completely or almost closed atoll lagoons (Takapoto, Takaroa and Manihi), threelargely open atoll lagoons (Rangiroa, Fakareva and Mangareva), in lagoons off two highislands (Raiatea-Tahaa and Vairao on Tahiti) and in the open ocean near Takapoto atoll,French Polynesia (Pouvreau and Prasil 2001). The growth rate of oysters more than twoyears old was significantly greater in island lagoons and ocean habitat than in atoll lagoons.The time oysters took to reach a size suitable for implantation of a nucleus (i.e. 100 mm)ranged from 21 to 26 months and was greater in atolls (25 months) than in islands or openocean (22 months). The mean annual shell growth increment after this year, which is anindirect but reliable index of nacreous deposition rate on the pearl nucleus, was also greaterin the islands and open ocean (26.1 mm y -1 ) than the atolls (21.3 mm y -1 ). Potential pearlfarming performances were high in the island lagoons and ocean, moderate in Mangareva,Takaroa, Rangiroa and Manihi lagoons and low in Takapoto and Fakareva lagoons.Pouvreau and Prasil (2001) attributed the differences in growth rate to the negative effects ofwater temperatures close to or in excess of 30 ° C at Takapopto and Fangareva, differences inthe degree of water renewal and food supply around the oysters. They also suggested thatthe POM content and hence potential availability of food in atoll and island lagoons may beresponsible for some of the differences in growth between these habitats. The observationthat pearl oysters cultured in the open ocean, an environment known to have lower POMconcentrations than lagoons, had the maximal growth rate, however, appears to be at oddswith this hypothesis.Yukihira et al. (2006) also compared the growth, survival and condition of medium and largesize black-lip pearl oysters at the two dissimilar environments within the Great Barrier Reeflagoon (see section 5.3.2 for a brief description of these sites). The growth rate and survivalof both groups and condition of medium-sized animals were significantly smaller in the baythan offshore. All of the medium or large-sized oysters cultured at the offshore locationsurvived. These results indicate the environmental conditions at Orpheus Island were moresuitable than those in the mainland bay for this species.5.4.2 Silver-lip Pearl OystersYukihira et al. (2006) compared the growth, survival and condition of medium and large sizesilver-lip pearl oysters at the two dissimilar sites in the Great Barrier Reef lagoon (seeSection 5.3.2 for a brief description of the sites). The growth rate of both groups of oysterswas similar in the two environments. By the end of the study, they had also attained asimilar condition in both environments. Seasonal differences in growth rate were confinedto medium-sized animals and followed a similar pattern to that described for juveniles (seeSection 5.3.3). All of the oysters survived.The Ecology Lab Pty Ltd – Marine and Freshwater Studies Page 25