THE STATUS OF SILVERLIP PEARL OYSTER PINCTADA MAXIMA (JAMESON) (MOLLUSCA, PTERIDAE) IN THE SOLOMON ISLANDS AFTER A 15-YEAR EXPORT BAN IAN HAWES, 1 * † T. LASIAK, 2 M. LINCOLN SMITH 2 AND C. OENGPEPA 1 1 The WorldFish Center, PO Box 77, Gizo, Solomon Islands; 2 Cardno Ecology Lab, 4 Green Street, Brookvale, NSW 2100, Australia ABSTRACT In the Solomon Islands, there have been three periods of commercial exploitation of the silver (gold)-lip pearl oyster Pinctada maxima. The most recent ended in 1993, when export of all species of pearl oysters was banned to allow stocks to recover from overexploitation. In 2007, a nationwide survey was undertaken to determine the status of the population. Communities adjacent to former fishing grounds were interviewed about past and current fishing practices, and the abundance, size composition, and quality of P. maxima shells were assessed by drift diving. In total, 117 P. maxima were recorded, from 33 of 96 transects. When present, the mean density of oysters varied from less than 0.10–1.23 oysters/400-m 2 transect. Size structure was biased toward large individuals, with mean and median shell size for all oysters taken being 219 mm. There appears to have been little or no recovery of P. maxima stocks since their export was banned. The existence of small populations of large individuals implies persistent failure of reproduction, spat settlement, and/or recruitment during the past decade. Exploitation may have reduced the P. maxima populations to such an extent that their fertilization success has become susceptible to Allee effects. Recent poaching of shell reported by local villagers may have compounded slow or sporadic recruitment. If the stocks do eventually recover, management strategies that protect the recovered population will need to be implemented to prevent a repeat of the overfishing seen in previous harvest cycles. KEY WORDS: Pinctada maxima, pearl oyster, abundance, population size structure, management, Solomon Islands INTRODUCTION In the Solomon Islands, small quantities of blacklip (Pinctada margaritifera), silver-lip (Pinctada maxima), and brown-lip (Pteria penguin) pearl oysters have been collected for centuries by free-diving subsistence fishers (Skewes 1990). During the past century, there were 3 phases of commercial exploitation, primarily of P. maxima for mother-of-pearl, but also for P. margaritifera. The first phase of exploitation took place between 1916 and 1922, and was undertaken by Japanese hard-hat divers based at Aratoba Island near Waghina (Gauld 1975) cited in Colgan (1993)). It is not known how much shell was harvested during that period. A second phase of exploitation began in 1968, in which hard-hat diving was replaced by hookah techniques. Anecdotal evidence indicates that 20 t of P. maxima were taken annually during this period, mainly from Hamilton Passage and Nggosele Passage in the Waghina area, and that 22 divers from the area were used at the peak of operations (Colgan 1993). After 4 y, this fishery failed because of declining stocks, increased operational costs, and a decline in mother-of-pearl prices on world markets. A third phase of exploitation for mother-of-pearl commenced in 1987, after a break of 15 y (Colgan 1993). Export figures indicate that between 6 t and 25 t of P. maxima shell were harvested annually until 1992 (Richards et al. 1994). By 1993, stocks were so depleted that the export of wild-caught silverlip and blacklip pearl oysters was banned to conserve remaining stocks (Kile 2000). At that time, a survey of the most productive fishing grounds at Waghina and Kia, involving more than 10 h of diving, yielded 12 P. Maxima, most of which were had a dorsoventral measurement (DVM) of more than 200 mm (Colgan 1993). It was hoped that the ban would allow the population to recover sufficiently to allow commercial harvesting for mother-of-pearl or to provide young stock to facilitate the development of a pearl culture industry (Richards et al. 1994). By 2007, renewed interest in the potential for exploitation of pearl oysters in the Solomon Islands and pressure from local marine resource owners raised the question of whether there was sufficient recovery of stocks to allow commercial harvest- ing. However, no systematic attempts had been made to monitor the size of blacklip or silverlip pearl oyster stocks during the expected recovery period to provide the data on which to make such a decision. The only systematic survey of marine resources in that period was a ‘‘broad-brush’’ assessment of commercially important species, including pearl oysters, undertaken in June 2004 across the Solomon Islands (Ramohia 2006). That survey yielded no silverlip and few blacklip pearl oysters, but did not specifically target pearl oyster habitat, so it left open the possibility that healthy stocks may have been overlooked. To help to fill this information gap, a survey of eight former P. maxima fishing grounds in the Solomon Islands was carried out in 2007. This article presents information on the abundance and size structure based on underwater visual censuses un- dertaken by teams of hookah divers in April to October 2007. MATERIALS AND METHODS Study Area The Solomon Islands is situated in the southwest Pacific Ocean between latitudes 5–12° S and longitudes 152–170° E. The archipelago is orientated southeast to northwest and consists of 6 major islands, 30 medium-size islands, and 886 smaller islands spread over 600,000 km 2 of ocean (Hughes 2006). The 6 major islands are arranged in a double chain with Choiseul, Isabel, and Malaita to the north, and Makira, Guadalcanal, and New Georgia to the south (Fig. 1). *Corresponding author. E-mail: ian.hawes@canterbury.ac.nz †Current address: Gateway Antarctica, University of Canterbury, Private Bag 4800, Christchurch, New Zealand DOI: 10.2983/035.030.0209 Journal of Shellfish Research, Vol. 30, No. 2, 255–260, 2011. 255