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

Suitability of Habitats for Growth of Black-Lip and Silver-Lip Pearl Oysters Final, June 20085.0 THE EFFECT OF HABITAT ON CULTURE OF PEARL OYSTERS5.1 IntroductionPearl oyster farming may involve the following stages: production of larvae and spat in ahatchery, collection of wild spat on artificial collectors, grow-out of juveniles in intermediategrow-out systems, collection of juveniles or adults from wild populations, seeding andgrow-out of juveniles and adults on dropper ropes or “chaplets” connected to submergedlonglines (Lane et al. 2003). Production of larvae and spat in a hatchery and seeding ofoysters are not discussed here, because they are laboratory-based operations that take placeunder controlled conditions. Existing information on the suitability of various coral reef andlagoon habitats for collection of wild spat, grow-out of juveniles and adults are summarisedin the following sections.5.2 Collection of Wild Spat5.2.1 GeneralCollection of wild spat is most effective in areas in which there are sufficient numbers ofadults in the surrounding waters to produce large numbers of larvae and in areas wherecompetent larvae aggregate prior to settlement (Lane et al. 2003). The effectiveness of spatcollection also depends on the type of spat collector, location, season and depth at which thecollector is deployed (Gervis and Sims 1992). Spat collection is likely to be less effective inopen lagoons or nearshore areas with high rates of water exchange, because larvae may beflushed away before they are competent to settle on collectors (Haws and Ellis 2000). Inrelatively enclosed lagoon systems, densities of spat are likely to be greater in areas awayfrom passages and on the down-current side of patch reefs, where currents tend to formeddies. In enclosed lagoons, where water movements are driven by wind in a reversecirculation pattern, densities should also be higher on the down-current side (Sims 1992). Inareas in which spat collection is ineffective, it may be possible to ship in spat fromelsewhere. In 1997, a pearl farmer on Raiatea in the Society Archipelago, French Polynesiareceived an air shipment consisting of a 4-ton supply of juvenile oysters from Takaroa,Tuamotu Archipelago, (Tisdell and Poirine 2000). At present, culture of silver-lip oysters isnot based on wild caught spat.5.2.2 Black-lip Pearl OystersIn French Polynesia and the Cook Islands, black pearl production is based on spat that settleon artificial collectors deployed in the lagoons of “enclosed” or “semi-enclosed” atolls, manyof which have limited exchange of water with the open ocean. The period of deploymentvaries from 6 months in some parts of French Polynesia to up to two years in Manihiki Atollin the Cook Islands, by which time animals have reached 65-90 mm dorsoventralmeasurement (Friedman and Southgate 1999). In these areas, spat are very abundant andalthough some may be lost to predators, there are usually enough survivors to stock pearlfarms (Haws and Ellis 2000).The Ecology Lab Pty Ltd – Marine and Freshwater Studies Page 21