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

Suitability of Habitats for Growth of Black-Lip and Silver-Lip Pearl Oysters Final, June 2008the Northern Territory is based on oysters sourced from hatcheries and wild oystersimported from Western Australia. It is difficult to assess the suitability of Solomon Islandswaters for silver-lip pearl farming because of the general paucity of information on thecoastal environment in this region and on environmental conditions prevailing in thevicinity of the Australian and Papuan farms. It is, however, worth noting that the coastalwaters off the larger Solomon Islands and the northern part of Australia are subject to heavyrainfall accompanied by freshwater runoff laden with silt.Regional differences in availability of coral reef and lagoon habitatsIn Solomon Islands, Fiji and Vanuatu, most of the coral reefs either fringe the high islands oroccur in shallow, sublittoral areas. In Papua New Guinea, approximately half of thecoastline and surrounding islands appear to be fronted by coral reefs with all reef typesrepresented, but with fringing and barrier reefs dominating. On the north-east Australiancoast, the major coral structure is the Great Barrier Reef, which comprises about 3,000fringing reefs, submerged reefs, platform and barrier reefs. There are also fringing reefsalong the Northern Territory and North West Australian coasts, a few atoll-like structureson the north-west continental shelf and coral reefs in the Houtman Abrolhos Islands, 400 kmnorth of Perth. The reefs off the Melanesian islands and off the Australian coast have arelatively ‘open’ structure and considerable exchange of water is able to take place throughthe numerous passages linking patch, fringing and barrier reefs with deeper water. In theCook Islands and French Polynesia, atolls are the predominant coral reef habitat and it is intheir ‘enclosed’ or ‘semi-enclosed’ lagoons that the majority of black pearl farms are located.This type of coral reef structure is scarce in the Central West Pacific region.Effect of habitat on culture of pearl oystersPearl oyster farming may involve several field-based operations, including collection of wildspat or stock, grow-out of juveniles in intermediate grow-out systems and on-growing ofadults, all of which are to some extent dependent on the prevailing environment.In French Polynesia and the Cook Islands, black pearl production is based on wild spat thatsettle on artificial collectors deployed in “enclosed” or “semi-enclosed” atoll lagoons forperiods ranging from six months to two years. Reasonable quantities of black-lip pearloyster spat have also been collected from ‘open’ reef systems in the Solomon Islands,particularly from sites with clear water and moderate currents that are at least 35 m awayfrom the nearest reef. Collectors deployed within barrier reef lagoons yielded surprisinglyfew spat, probably because the collectors became clogged with sediment or overgrown byalgae during the rainy season.The growth rate of juvenile black-lip pearl oysters cultured in these ‘open’ reef systems iscomparable with that observed in some of the atolls in French Polynesia and the CookIslands. However, experimental studies on growth, survival and condition of small blacklippearl oysters over a 14 month period in two contrasting environments adjacent to theGreat Barrier Reef (Australia) indicated that environmental conditions were more suitablefor the growth of juveniles at the near oligotrophic offshore location than in a mainland baycharacterised by high levels of turbidity and large concentrations of particulate organicmatter.In the Cook Islands, growth of black-lip pearl oysters has been compared experimentally atdifferent sites within a lagoon, among lagoons, in different natural habitats and underdifferent culture conditions, but results are difficult to interpret because of the experimentaldesign. In French Polynesia, the growth of black-lip pearl oysters has been compared incompletely or almost closed atoll lagoons, largely open atoll lagoons, lagoons off highThe Ecology Lab Pty Ltd – Marine and Freshwater StudiesPage ii