Shorter immersion times increase yields of the blacklip pearl oyster, Pinctada margaritifera (Linne.), from spat collectors in Solomon Islands

Abstract

In Solomon Islands, "spat" (juveniles) of the blacklip pearl oyster, Pinctada margaritifera, suffer high levels of mortality while on collectors, presumably due to predation by ranellid gastropods, xanthid and portunid crabs, and flatworms that also settle to the collectors from the plankton. This study tested a new strategy for reducing the mortality of spat on collectors. The existing practice of leaving spat on collectors for 6 months was compared with removal of spat after 3, 4 or 5 months, followed by the rearing of the spat in panel nets to facilitate removal of predators. In one of two field experiments, there were significantly fewer spat on collectors after six months than after 3–4 months. A similar, but non-significant, trend occurred for the other field experiment. A tagging experiment showed that survival of spat left on collectors between months 4 and 6 was 58%. By contrast, spat removed from collectors after 3 and 4 months at a mean size of >15 mm dorso-ventral measurement(DVM), and reared in panel nets, had mean rates of survival of 82 and 93%, respectively. Provided spat are a mean size of >15 mm DVM when removed from collectors, and there is adequate husbandry of spat in intermediate culture systems, greater numbers of blacklip pearl oysters can be produced in the western Pacific by using a 3–4-month cycle for collecting spat.