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

Suitability of Habitats for Growth of Black-Lip and Silver-Lip Pearl Oysters Final, June 2008Island in Macuata and Galoa Island in Bua. The fisheries department has also received aproposal for a pearl farm to be loctaed in Vuna, Taveuni and is looking at expanding pearlfarming to Lomaiviti, Kadavu and Vanuabalavu in Lau.3.1.4 French PolynesiaThe pearl farming industry in French Polynesia is now based on collection of wild spat, butwas based originally on collection of wild stock from the lagoons of certain atolls. Black-lippearl oysters are currently being farmed in 30 atolls and islands of the Tuamotu andGambier archipelagos and some volcanic islands of the Société archipelago, FrenchPolynesia (Langy 2006). These farms are located either in lagoons associated withatolls/pseudo-atolls (e.g. Takapoto, Takroa, Manihi, Rangiroa, Fakareva and Mangareva) orin areas adjacent to high islands (e.g. Vairoa and Tahaa-Raiatea).The lagoons where black pearls are currently being produced differ markedly in totalsurface area, depth and degree of exchange with the ocean, with some having only a fewactive channels between the lagoon and the ocean, whereas others are largely open systemswith large active channels (e.g. Rangiroa and Mangareva) (Pouvreau and Prasil 2001).Considerable information is available about the environment of Takapoto and Rangiroalagoons, but relatively little is known about Fakareva, Mangareva and Takroa.The best-known atoll, Takapoto (14°30’ S, 145°20’ W), is located in the northwest of theTuamotu Archipelago. The lagoon is 18.7 km long and 4.4 km wide, has a mean depth of 23m, a maximum depth of 55 m and a total area of 81.7 km² (Buestel et al. 1995). It issurrounded by an almost closed reef rim approximately 600 m wide which isolates it fromthe ocean, except for a few shallow (< 50 cm deep) channels, where there are weak currents(Sournia and Ricard, 1976 in Niquil et al. 2001). The annual temperature range in the lagoonnormally varies from 26 °C in August to 30 °C in March, except during El Niño events whenit may rise to 31.5 °C (Pouvreau et al. 2000a). Salinity varies from 38 to 42 ‰. The water istransparent and the compensation depth exceeds the maximum depth of the lagoon (Charpyet al., 1992 in Niquil et al. 2001). The lagoon is oligotrophic, primary production is primarilydue to picoplankters and both the particulate inorganic and organic content of the water arelow (Pouvreau et al. 2000a). The movement of water within the lagoon is driven mainly bythe east–northeastern trade winds; there is no tidal current. The tidal amplitude is 40 cm(Wells and Jenkins 1988). The residence time of water in the lagoon is ca. 4 years.In the lagoon, there are numerous subsurface pinnacles with a good cover of molluscs andcorals (Pirazzoli and Montaggioni, 1984 in Niquil et al. 2001). The total volume of thesepinnacles is estimated to be between 1.3 and 1.5 km 3 (Buestel et al. 1995). Three distinctbottom types have been identified in the lagoon: sandy, hard and mixed substrata, whichconsists of small coral structures (< 1 m in diameter) on a sandy bottom (Zanini and Salvat2000). The 0-10 m depth stratum is characterised by sandy slopes and the tops of large coralformations. The percentage of sandy bottom, however, decreases with depth while thepercentage of mixed sub-stratum increases. Small, mainly dead, coral structures compriseabout 58% of the total surface area of the lagoon and provide an ideal habitat for theattachment of wild pearl oysters. These coral structures and pearl oysters are moreabundant at depths of 30-40 m, suggesting that a good substratum for colonisation isprobably a major factor determining the distribution of this mollusc.Rangiroa is the second largest atoll in the world and has a perimeter of 225 km and a totalsurface area of 1640 km 2 (Wells and Jenkins 1988). The atoll has around 240 motu (narrowislands on atoll reefs), mostly in the northwest. The rest of the rim is sandy and more or lesssubmerged. The lagoon varies in width from 4-30 km and has an average depth of 20 m anda maximum depth of 35 m. The lagoon contains coral pinnacles, sand banks, islets andThe Ecology Lab Pty Ltd – Marine and Freshwater Studies Page 8