Growth, mortality, recruitment and sex-ratio of wild stocks of the silver-lipped pearl oyster Pinctada maxima were studied at sites spanning the geographic extent of the commercial fishery using mark-recapture experiments, recruitment cohort analysis and research surveys of stock abundance and reproductive status. Growth parameters (L∞, K) from the von Bertalanffy growth equation were estimated at 210 mm dorso-ventral measurement (DVM) (±16 mm SD) and 0.74 at the Lacepede Islands, L∞ of 199 mm DVM (±6 mm SD) and K of 0.79 on 80 Mile Beach, and L∞ of 194 mm (±6 mm SD), and K of 0.72 at Exmouth Gulf respectively. Estimates of natural mortality (M) by tagging were very low (0.02–0.03), compared with catch-curve analysis, which estimated M to be between 0.1 in deeper (30–34 m) populations and 0.18 in shallow (9–12 m) populations. Settled P. maxima spat (0 and 1 age classes) on adult shell were quantified (e.g., 1,317 spat found on 119,000 shell in 2003) to obtain an annual recruitment index, which showed clear temporal trends in abundance. Over 7 y (1992 to 1995; 2001 to 2003) the annual recruitment index varied from 5.1–8.0 spat per 1,000 shell for the 0 age class, and 3.5–6.2 spat per 1,000 shell for the 1 age class. Preliminary predictions of future abundance showed promise, however more work is required on spatial and habitat effects on spat settlement before the potential of the 0 and 1 recruitment indices can be realized. We also confirm that Western Australian populations of P. maxima are protandrous hermaphrodites, with a 50:50 sex ratio not achieved until females are 170 mm DVM, which is above the maximum size fished.
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Vol. 25 • No. 1