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

Water Temperature and Cyclone Frequency in the Pacific: Implications for Pearl Farming Final, June 20084.0 CONCLUSIONS4.1 Sea TemperatureAlthough sea temperature is known to influence the physiology of cultured oysters and therate of deposition of nacre on oyster shells and implanted nuclei, surprisingly littleinformation is available about the optimum temperature ranges of black-lip and silver-lipoysters. The only information that is available comes from north-east Australia andindicates that the range for black-lip oysters (23 – 28 °C) is narrower than that for silver-lipoysters (23 – 32 °C) (Yukihira et al. 2000). It should be noted that optimum temperatureranges at other locations may differ, particularly if there are latitudinal differences in thesespecies. Information about the sea temperatures prevailing at culture sites in Australia andthe South West Pacific is also fairly limited. In French Polynesia, the temperatures reportedat black pearl farms range from 21.3 - 28.8 °C, 25.5 - 29.5 °C and 26 – 31 °C, depending onlatitude (Pouvreau and Prasil 2001). In north-west Australia, temperatures reported at silverpearl farms range from 19.5 - 29.7 °C, 21.4 - 30.9 °C and 25 – 32 °C (Pass et al. 1987; CSIRO2003). This implies that black pearl farms are either located in areas where the watertemperature is outside the optimum temperature range or that the optimum ranges of thisspecies in other countries differs markedly from that in north-east Australia. Likewise, someof the Western Australian silver pearl farms are located in areas where the minimum watertemperature is below the lower limit of the optimum temperature range or where themaximum water temperature is close to the upper limit of the optimum range. It shouldalso be noted that if global warming causes a 0.4 - 1.0 ºC increase in the sea temperature offthe north-west coast of Australia by 2030 as predicted by CSIRO (2007), this could result inprevailing temperatures at some farm locations exceeding the optimum temperature rangeof silver-lip oysters.This review has shown that in-situ sea temperature measurements derived from underwaterprobes are available for numerous other locations in Australia, particularly those adjacent tothe Great Barrier Reef on the north-east coast, but relatively little data of this type isavailable from the South Pacific nations of interest. Sea surface temperature measurementsderived indirectly from data collected by infra-red radiometers carried on board satellitesare available for locations throughout the world. If the spatial resolution of these data is toocoarse, they will be of limited value to offshore pearl companies. SST products that providemeasures of variability within months and years would also be more useful to prospectivepearl farmers than average monthly climatologies, because they provide an indication ofextreme SSTs that regions may experience and their likely duration. It should also be notedthat SST measurements derived from satellite-borne sensors tend to be somewhat lower thanthe SSTs of waters immediately overlying coral reefs (Strong et al. 1996).The limited information that is available on sea temperatures in Solomon Islands indicatesthat the prevailing regimes are similar to those in some areas of the Cook Islands and FrenchPolynesia, where there are productive black-lip pearl farms. The temperature regime in theSolomon Islands is also similar to that in some areas of Vanuatu, Fiji and Papua NewGuinea. The average monthly SST measurements indicate that the temperature of the waterat locations in the Solomon Islands and Papua New Guinea regularly exceeds 29 °C insummer. This implies that these regions may be more suitable for culturing silver-lip thanblack-lip pearl oysters. The temperature regimes at most of the locations in Fiji andVanuatu, however, appear to be suitable for culturing both species of pearl oysters. Itshould, however, be noted that there are no natural populations of silver-lip pearl oysters inThe Ecology Lab Pty Ltd – Marine and Freshwater Studies Page 16