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

Water Temperature and Cyclone Frequency in the Pacific: Implications for Pearl Farming Final, June 2008SUMMARYIntroductionThe European Union has funded a project entitled ‘Stimulating investment in pearl farmingin the Solomon Islands’. The objective of this project is to provide offshore pearl companieswith sufficient information to determine the potential for long-term investment in pearlfarming in the Solomon Islands. The World Fish Center sub-contracted The Ecology Lab PtyLtd to prepare a report on water temperatures and cyclone frequencies, in terms ofadvantages and disadvantages for pearl farming in the Solomon Islands relative to FrenchPolynesia, Cook Islands, Australia, Fiji, Vanuatu and Papua New Guinea.Knowledge of sea temperature ranges at various locations would be advantageous tooffshore pearl companies, because temperature influences the rate of deposition of nacre onoyster shells and implanted nuclei as well as the reproductive development, spawningactivity, survival, recruitment, growth, condition of cultured stocks and their susceptibilityto disease. Knowledge of regional differences in cyclone activity would also be useful,because the accompanying heavy rainfall, high winds and storm surges can damage pearlfarms and associated infrastructure.Sea TemperatureLittle is known about the temperature requirements of black-lip and silver-lip oysters. Theonly information that is available indicates that the optimum temperature ranges of black-lip(Pinctada margaritifera) and silver-lip (Pinctada maxima) pearl oysters on the north-east coastof Australia are 23 – 28 °C and 23 – 32 °C, respectively. This implies that silver-lip pearloysters may be better suited to culture in tropical latitudes than black-lip pearl oysters.These ranges may not be applicable to other parts of the species geographic ranges,particularly if their responses to temperature vary with latitude.Sea temperature is traditionally measured in situ by either dipping a thermometer into abucket of water drawn from the sea surface, or using electrical temperature probes deployedin the intake port of large ships or on either fixed or drifting buoys. Sea surface temperature(SST) measurements are also derived from sensors on board polar-orbiting satellites thatrecord the amount of visible and infrared radiation reflected and/or emitted from theEarth's surface. These instruments take thousands of measurements of broad swaths of theEarth each day and/or night, resulting in concurrent data sets of the entire planet. Severaldifferent SST data products have been derived from satellite-based sensors, depending onthe type of sensor used and the type and version of the algorithms used to process the data.The products also vary in terms of the time span covered and their spatial resolution on theground. Records from temperature probes, SEAFRAME gauges and satellite-borne sensorscould all be used to identify potential farm locations with suitable prevailing temperatureregimes. Products with fine–scale spatial resolution, however, are likely to be most relevantto prospective pearl farmers.In situ sea temperature measurements taken by probes deployed for lengthy periods at anappropriate depth were obtained from locations in the Cook Islands and French Polynesia,where there are extensive black-lip pearl farms, and from locations in Western Australiaadjacent to areas with silver-lip pearl farms. Temperatures measured in the Cook Islandlagoons ranged from ca 28 – 31 °C, whereas those in the French Polynesian lagoons rangedfrom ca 26 – 31 °C and 21 – 29 °C, depending on latitude, and those off high islands variedfrom 25 – 30 °C. In other parts of the world, black-lip pearls oysters are cultured attemperatures ranging from 17 – 30 °C (Japan) and 21 – 34 °C (Sudan). The mean monthlyThe Ecology Lab Pty Ltd – Marine and Freshwater StudiesPage i