Non Technical Summary

To culture pearls, it is essential to have an understanding of the seasonal changes in reproductive condition of the pearl oyster species involved. For example, it is necessary to have oysters in good reproductive condition for hatchery production. Conversely, oysters must be in poor reproductive at the time at which the pearl nuclei are inserted.

In addition to the akoya pearl oyster, NSW has a second species of pearl oyster, Pinctada albina sugillata that has been of some minor commercial importance in Western Australia. The reproductive condition of P. a. sugillata from Port Stephens was monitored over a two-year period to allow its culture and to examine the potential for hybridisation between P. a. sugillata and P. imbricata (akoya).

In contrast to more northerly populations, P. a. sugillata in NSW were found to have a truncated breeding season. Reproductive activity was greatest from late spring to early autumn and oysters were in poor reproductive condition during winter. Peaks in reproductive activity occurred in October 1998, March 1999, January 2000 and April 2000. However, spat collectors deployed at two sites in Port Stephens found spatfall to be restricted to the months of November-January, indicating that the autumnal peaks (March & April) in reproductive activity did not result in subsequent recruitment.

From a culture perspective, recruitment to spat collectors was so low and variable that it is unlikely that this could provide sufficient spat to support an industry, however, the spring increase in reproductive activity is coincident with the best time for hatchery production.

Infestations of shell boring organisms can be a problem in oyster culture and were present among the oysters collected to monitor condition. The degree of shell damage however, was almost invariably low. Most common were infestations of Spionid polychaetes, present in 30% of the shells collected, with several larger oysters showing shell damage typical of boring sponges.