Population dynamics and stock management of the black-lip pearl oyster, Pinctada margaritifera (L.), in the Cook Islands, South Pacific

Abstract

Permanent transects were used to measure changes in abundance of Pinctada margaritifera in Manihiki lagoon, Cook Islands. Growth in situ, mortality and recruitment were also studied. A correction factor for searcher efficiency was also determined, allowing earlier estimates of standing stocks to be adjusted.

Overall abundance in Manihiki decreased by 18% in one year. Most losses were attributable to fishing (F=0.19; M=0.11). Mortality (27%) and recruitment (9%) were presumably underestimated because of heavy fishing of juveniles. Total mortality, estimated by Wetherall plots, decreased from 0.48 to 0.35 over the year owing to a decline in fishing for larger oysters.

The average shell diameter of recruits was 110 mm. This was also an approximation of I_c,. von Bertalanffy growth parameters of K=0.26 and L_∞ = 183 mm were estimated from shell size increments.

Yield-per-recruit calculations indicate that minimum size limits are not effective. Reserve areas, quotas, and other restrictions on effort should instead be used to protect broodstocks.