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Silverlip Pearl Oyster

Pinctada maxima

  • Anthony Hart (Department of Fisheries, Western Australia)
  • Anthony Roelofs (Department of Agriculture and Fisheries, Queensland)
  • Thor Saunders (Department of Primary Industry and Resources, Northern Territory)

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Stock Status Overview

Stock status determination
Jurisdiction Stock Fisheries Stock status Indicators
Western Australia Western Australia POMF Sustainable CPUE,  recruitment surveys, population surveys
POMF
Pearl Oyster Managed Fishery (WA)
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Stock Structure

Pinctada maxima or the Silverlip Pearl Oyster is the largest species in the pearl oyster family1, and produces the largest pearls. It is distributed within the central Indo-Pacific region, bounded by the Bay of Bengal to the west, Solomon Islands to the east, Taiwan to the north, and Northern Australia to the south2, at depths from the shallow sub-tidal to more than 50 m. Within Australia, the population genetic distribution has been investigated in Western Australia and Northern Territory3. The biological stock structure is uncertain; however, Western Australian stocks are generally considered to be one stock (with the possible exception of a localised population in Exmouth Gulf), separate from stocks in the Northern Territory. The biological stock structure for Queensland is unknown.

 

Here, assessment of stock status is presented at the jurisdictional level—Western Australia, Northern Territory and Queensland.

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Stock Status

Western Australia

The Western Australian Pearl Oyster Managed Fishery is the only remaining significant wild stock fishery for pearl oysters in the world. It is a quota-based dive fishery, operating in shallow coastal waters along the north-west shelf or North Coast Bioregion. The harvest method is drift diving, in which six–eight divers are attached to large outrigger booms on a vessel and towed slowly over the pearl oyster beds, harvesting legal sized oysters by hand as they are seen. The species targeted is the Indo-Pacific, Silverlip Pearl Oyster (P. maxima). The Western Australian pearling industry comprises three main components: the collection of pearl oysters from the wild; production of hatchery-reared pearl oysters and the seeding of pearls, followed by grow-out of pearl oysters on pearl farm leases. Quota limits are set for the take of pearl oysters from the wild to ensure the long-term sustainability of the resource.

 

In the Western Australian Fishery, the standardised catch per unit effort (SCPUE) increased by 200 per cent between 2003 and 2010, but has declined since 2010. In 2015, it was at its lowest level since the 2003. This large fluctuation was due to an order of magnitude variation in recruitment, which is measured using a spat settlement index (oysters aged 0+ years and 1+ years). The recruitment variability is caused by environmental variation which also affects the fishing efficiency of the pearl oyster fleet4. An extremely high settlement in 2005 (index = 31), compared to the mean of all other years (index = 4) dominated the SCPUE for 5 years between 2009 and 2013. Although SCPUE is now at low levels, spat settlement increased significantly between 2013 and 2015. The stock prediction model, which uses the spat settlement index data to predict future stock abundance, is forecasting an increase in SCPUE. Additional data, including population surveys, shows that breeding stock levels are stable. On the basis of this evidence, the biomass of the Western Australian pearl oyster fishery is unlikely to be recruitment overfished.

 

On the basis of the evidence provided above, Silverlip Pearl Oyster in Western Australia is classified as a sustainable stock.

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Biology

Biology
Species Longevity / Maximum Size Maturity (50 per cent)
Silverlip Pearl Oyster 30 years; 250 mm DVM  Males: 2–3 years; 110 mm DVM Females: 7–8 years: 175 mm DVM

Silverlip Pearl Oyster biology6

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Distributions

Distribution of reported commercial catch of Silverlip Pearl Oyster

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Tables

Fishing methods
Western Australia
Commercial
Diving
Indigenous
Diving
Management methods
Method Western Australia
Commercial
Gear restrictions
Limited entry
Size limit
Spatial zoning
Total allowable catch
Active vessels
Western Australia
6 in POMF
POMF
Pearl Oyster Managed Fishery (WA)
Catch
Western Australia
Commercial 234.43t in POMF
Indigenous Unknown
Recreational NA
POMF
Pearl Oyster Managed Fishery (WA)

Indigenousa

 

a. In Queensland, under the Fisheries Act 1994 (Qld), Indigenous fishers are able to use prescribed traditional and non-commercial fishing apparatus in waters open to fishing. Size and possession limits, and seasonal closures do not apply to Indigenous fishers. Further exemptions to fishery regulations may be applied for through permits.

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Catch Chart

Commercial catch of Silverlip Pearl Oyster

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Effects of fishing on the marine environment

  • Pearl oyster fishing removes only a small proportion of the biomass of pearl oysters on the fishing grounds and is considered to have negligible impact on the food chain in the fishing area. Pearl divers have minimal contact with the habitat during fishing operations and the main habitat contact is by pearl oysters held in mesh panels on holding sites following capture. However, these sites cover a very small proportion of the habitat and the activity concerned is unlikely to cause any lasting effect.
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Environmental effects on Silverlip Pearl Oyster

  • Environment plays an important role in population variability in the Silverlip Pearl Oyster. In Western Australia, the effect of sea surface temperature, wind direction and rainfall have shown to be influential in determining the settlement density of young-of-the-year (0+ years) pearl oysters4. Other studies on pearl oysters, for example the Black-lipped Pearl Oyster, also highlight the close relationship between exceptional year classes and environment7.
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References

  1. 1 Shirai, S1994, Pearls and pearl oysters of the world. Marine Planning Co. Japan. 95 pp. (in Japanese and English).
  2. 2 Southgate PC, Strack E, Hart AM, Wada KT, Monteforte M, Carino M, Langy S, Lo C, Acosta-Salmon H and Wang A 2008, Chapter 9: Exploitation and Culture of Major Commercial Species. pp. 303–56. In: The Pearl Oyster, Eds Southgate PC and Lucas J, Elsevier London.
  3. 3 Benzie, JAH and Smith-Keune, C 2006, Microsatellite variation in Australian and Indonesian pearl oyster Pinctada maxima populations. Marine Ecology Progress Series. 314: 197–211.
  4. 4 Hart AM, Thomson AW and Murphy D 2011, Environmental influences on stock abundance and fishing power in the silver-lipped pearl oyster fishery. ICES Journal of Marine Science. 68(3): 444–53.
  5. 5 Knuckey, IA 1995, The Northern Territory Pearl Oyster Fishery. FRDC final report 1991/14. 47 pp.
  6. 6 Hart, AM and Joll, L 2006, Growth, mortality, recruitment, and sex ratio in wild stocks of the silver-lipped pearl oyster Pinctada maxima (Jameson) (Mollusca: Pteriidae) in Western Australia. Journal of Shellfish Research. 25 (1): 201–210.
  7. 7 Oengpepa, C, Hawes, I, Lane, I, Friedman, K and Bell, J 2006, Long-term variability in spat collections of the blacklip pearl oyster (Pinctada margaritifera) in Solomon Islands. Journal of Shellfish Research, 25: 955–58.

Archived reports

Click the links below to view reports from other years for this fish.