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Government of Western Australia - Department of Fisheries


Western Australia’s pearling industry focuses on the South Sea pearl produced by the oyster Pinctada maxima.

Pearl oysters are ‘seeded’ to stimulate pearl growth – a bead of mussel shell is surgically inserted into the oyster’s gonad. A piece of mantle is inserted with it. Mantle is the tissue that produces ‘nacre’, the substance that creates a pearl.

Latest projects

Generally, it’s only legal to collect pearl oysters of a minimum size of 120 mm in shell length. For the 2012 and 2013 fishing seasons, however, pearl divers are permitted to collect some smaller ones (100 millimetres). This is being done on a trial basis so we can examine the effectiveness of improved seeding technology on smaller pearl oysters.

The divers will also take larger pearl oysters than usual. Generally, oysters up to 165 mm are targeted. During the 2012 and 2013 seasons, divers will take those of more than 175 mm, as part of a survey to investigate their abundance. (While not suitable for pearl production, they can be sold for their shell, called ‘mother-of-pearl’.)

Ongoing research

This includes stock assessment in the wild stock pearl oyster fishery to estimate the total allowable catch (TAC) - the amount the whole industry is permitted to catch in a season, which covers about seven months. This is done in several ways:

  • By monitoring catch per unit of ‘effort’ (the number of fishing trips) through daily fishing logbooks sent to us.
  • By predicting how many pearl oysters will be ready to collect four to six years ahead. The numbers of spat (juvenile oysters) and where they settle is monitored to create an index of settlement. This is used to find the relative number of ‘piggy back spat’ (juveniles that settle onto adults).

The piggy back spat can be counted and used to predict recruitment levels in the year they were spawned (their age is estimated by their size). Recruitment means addition to the population through reproduction, migration or growth to legal size. Based on recruitment levels, researchers can predict how many will be large enough to be caught in four to six years.

  • By length-frequency sampling (which relates to the estimated number in the population that make up each size class) of catch.
  • By length-frequency sampling of stock. A diver is asked to collect all oysters seen on one dive. Each area dived is covered at least once during the pearl diving season to give an overall picture.

Other ongoing research is being carried out on the rules for determining the TAC. There are also studies to help us understand environmental drivers of pearl oyster abundance.

Oyster health

Our Fish Health Unit provides a comprehensive disease-testing program to the industry.

Significant research projects include studies on pearl oyster health. One focus of oyster health research is to investigate aspects of oyster oedema disease (swelling of the tissues and potentially fatal) in P. maxima. The research aims to help understand the disease and reduce the impacts.

Last modified: 7/05/2012 9:37 AM

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