Genetics of the silver-lipped pearl oyster Pinctada maxima populations in Western Australia, the Northern Territory and Indonesia (FRDC Project 97/344)

A total of 1737 Pinctada maxima samples were collected from eight distinct populations, six in Australia and two in Indonesia. The Australian populations were sampled from Darwin in the Northern Territory and the Lacepede Islands, 80 Mile Beach - shallow water, 80 Mile Beach - deep water, Port Hedland and Exmouth Gulf in Western Australia. The Indonesian populations were sampled from Madura Island and Sumbawa Island.

Samples of both adductor muscle and mantle tissue were collected from Pinctada maxima oysters of various sizes aboard pearling industry vessels in Western Australia and the Northern Territory, between February 1998 and November 1999. Whole shell samples from the Indonesian sites, collected in November 1999, were delivered by road to Gondol Fisheries Station and held in flowing sea water tanks prior to dissection.

The entire soft tissues from small spat were removed from the shell. Samples were either snap frozen in liquid nitrogen or preserved in 70% ethanol immediately following collection.

Assays were developed for eight highly variable microsatellites markers and an mtDNA marker for rapid assessment of genetic variation in pearl oysters. These assays were used to screen the eight populations of P. maxima (including different juvenile age classes for the Western Australian and Northern Territory populations). It was demonstrated that the Western Australian populations belong to one stock with large effective population sizes and have little or no recruitment from Indonesia and a reasonable degree of exchange with Northern Territory. A basic technology for assessment of genetic variation in spat and for future use in improving cultured pearl oyster stocks was developed.

Successful description of the population genetic structure for different age classes of Pinctada maxima in Western Australia and Northern Territory has provided a basis for improved maintenance of a productive and valuable fishery through improved stock definition and determination of levels of dispersal among populations. The development of highly variable DNA markers provides a base technology to assist the choice of sources of broodstock for hatcheries and future management of cultured populations as the Pearling Industry increasingly relies on hatchery produced spat.