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

Water Temperature and Cyclone Frequency in the Pacific: Implications for Pearl Farming Final, June 20082.0 SEA TEMPERATURES2.1 IntroductionBlack-lip pearl oysters occur across a wide latitudinal and longitudinal range, having beenrecorded in the Indian and Pacific Oceans, eastern Mediterranean and Ryukyu Archipelago(Gervis and Sims 1992). Silver-lip pearl oysters are restricted in their geographicdistribution to tropical waters in the central Indo-Pacific region. The different geographicdistributions of these species suggest that their optimum temperature ranges are also likelyto differ markedly. The only available information about the optimum temperature rangesof black-lip and silver-lip pearl oysters comes from studies done off the Great Barrier Reefon the north-east coast of Australia (Doroudi et al 1999; Yukihira et. al. 2000). The optimaltemperature ranges reported in these studies may not be applicable throughout the speciesgeographic ranges, particularly if the responses of black-lip and silver-lip pearl oysters totemperature vary with latitude.Doroudi et al. (1999) noted that normal development of black-lip oyster embryos occurredonly between 25 °C and 30 °C, that growth of larvae was optimal between 26 °C and 29 °Cand that temperatures greater than 35 °C were lethal for larvae. Survival of larvae wasgreatest, but growth was slow, close to 20 °C, the lowest temperature examined.Yukihira et al. (2000) found that the clearance rate, absorption efficiency, amount of energyabsorbed, respiration rate, excretion and hence Scope for Growth (i.e. energy available tosexually mature animals for growth and reproduction) of black-lip and silver-lip pearloysters were much lower at 19 °C than between 23 °C and 32 °C. The clearance rate andamount of energy absorbed by black-lip oysters declined between 28 °C and 32 °C, but thatof silver-lip oysters remained fairly constant. The increase in absorption efficiency of blacklippearl oysters was less marked that of silver-lip pearl oysters between 19 °C and 32 °C.The respiration rate of black-lip pearl oysters increased markedly between 28 °C and 32 °C,whereas that of silver-lip pearl oysters only increased slightly over this range. Black-lipoysters excreted less energy than silver-lip oysters over this temperature range. Hightemperatures had a marked effect on the rate of ammonia excretion in both species. TheScope for Growth of black-lip pearl oysters was adversely affected by both low (19 °C) andhigh (32 °C) temperatures, whereas that of silver-lip oysters was affected mostly by lowtemperatures. On the basis of these results, Yukihira et al. (2000) concluded that the optimaltemperature ranges for black-lip and silver-lip oysters were 23-28 °C and 23-32 °C,respectively. This implies that silver-lip pearl oysters may be better suited to culture intropical latitudes, such as Solomon Islands, than black-lip pearl oysters or in shallow areaswhere temperatures are more variable.2.2 Measurement of Sea Surface TemperatureThe temperature of the sea surface (SST) can be measured in situ by either dipping athermometer into a bucket of water drawn manually from the sea surface, measuring thetemperature of water in the intake port of large ships or using electrical temperature probesdeployed at a specific depth on fixed or drifting buoys (Reddy 2001). The most exact andrepeatable measurements come from fixed buoys equipped with robust electricaltemperature probes located at a particular depth (e.g. 1 m) below the water surface (NOAACoastal Services Centre undated). In situ temperature measurements have two majorshortcomings: the spatial coverage of the data is limited and there may be considerableThe Ecology Lab Pty Ltd – Marine and Freshwater Studies Page 2