Abundance and distribution of the black-lip pearl oyster, Pinctada margaritifera (L.), in the Cook Islands, South Pacific

Abstract

Stocks of Pinctada margaritifera were surveyed in three atoll lagoons in the Cook Islands to assess abundance, describe distribution patterns, and evaluate the method for ongoing monitoring. Belt transects were laid at randomly selected sites across the lagoons. Densities over depth gradients were extrapolated to give a stock estimate for Manihiki lagoon of 2.0 million±3.2 million pearl oysters. Stocks in Penrhyn lagoon (5.0 million ± 4.1 million) and Suwarrow lagoon (around 400 000) were estimated from average densities. The wide confidence limits mean that other methods are needed to monitor changes in abundance over time.

Penrhyn and Suwarrow lagoons have not recovered from earlier overfishing. No pearl oysters occurred below 36 m. Density and shell size increased with depth; this was most notable in Manihiki, where fishing was heaviest. Sizes and densities were influenced by bottom type in Manihiki. Density was greatest in the north of Penrhyn and decreased southwards; Manihiki had no density gradient across the lagoon.