EVALUATION OF COMMERCIALLY-USED COLLECTORS FOR SYDNEY ROCK OYSTERS, SACCOSTREA-COMMERCIALIS AND PACIFIC OYSTERS, CRASSOSTREA-GIGAS

Ten types of commercially-used collectors were evaluated for natural s ettlement and retention of juvenile Sydney rock oysters (Saccostrea co mmercialis) and barnacles (Balanus spp.), over 271 days in Port Stephe ns, NSW, Australia. Juvenile Sydney rock oysters (spat) from six colle ctor types were then removed and on-grown in timber and PVC mesh trays for 14 days, to assess whether collector type affected post-harvest s urvival Retention and growth of Sydney rock oysters to market size wer e also assessed 843 days after deployment, on five types of collectors used for on-growing. Nine of the collector types were also evaluated as substrates for settlement of Pacific oysters (Crassostrea gigas) in Port Stephens. Density at settlement and retention of juvenile and ad ult oysters was higher on PVC collectors than on traditionally-used ta rred sticks. Density of Sydney rock oyster spat, was higher (P < 0.05) on five types of PVC collectors, and the bioresin slats than on tarre d sticks. Retention of spat on four types of PVC collectors was also h igher (P < 0.05) than on tarred sticks between 172 and 271 days. There was a significant relationship (P < 0.001) between oyster density at day 172 and spat losses at day 271. More barnicles settled on tarred s ticks than on other substances (P < 0.05). Post-harvest survival of si ngle Sydney rock oyster spat 14 days after removal from collectors was high (89-94%) and similar (P > 0.05) for four types of PVC collectors and tarred sticks (P < 0.05). However, survival of spat removed from bioresin slats was lower (66.8%). At harvest (day 843), the highest (P < 0.05) number of market size Sydney rock oysters were retained on fo ur types of PVC sticks and the lowest number on tarred sticks. With th e exception of flat spiky PVC sticks, which had a higher percentage lo ss than round spiky PVC sticks (P < 0.01), oyster losses between day 1 72 and harvest for all five types of on-growing collectors were unifo rmly high (range 92.6-96.5%; P > 0.05), despite the differences in ini tial spat density. Spat density of Pacific oysters was higher (P < 0-0 01) on three types of PVC collectors than on tarred sticks, PVC slats and bioresin slats.