Long-term variability in spat collections of the blacklip oyster (Pinctada margaritifera) in the Solomon Islands

Abstract

Temporal variation in abundance of spat of the blacklip pearl oyster (Pinctada margaritifera) was determined over an eight-year period at two slles, Gizo and Noro, in the Western Province of Solomon Islands. Spat were collected by deploying shade mesh substrata at a depth of 3 rn for near-sequential two-month period. Overall, spatfall at the two sites was similar, with summer maximum of 4.9 (Gizo) and 4.7 collector-' (Noro). At both sites, significantly fewer spat were collected in late winter than in summer. Abundance of spat varied among years, although there was no consistency between the two sites regarding years of highest recruitment. Maximum settlement of spat at Gizo was 10.2 collector-' in January 2002, whereas at Noro it was 19.6 collector-' in March 2000. Mean size of spat did not vary over time, but spat at Gizo were significantly smaller (geometric mean 7.6 mm) than those at Noro (mean 8.4 mm). Predators of spat settled on the collectors throughout the year; there were significantly more gastropod predators at Noro than at Gizo. Gizo and Noro in the Western Province of Solomon Islands are reliable places for collection of blacklip pearl oyster spat. Spat can be caught all year round, although collections will be most effective between November and March.