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Silverlip Pearl Oyster (2018)

Pinctada maxima

  • Anthony Hart (Department of Primary Industries and Regional Development, Western Australia)
  • Thor Saunders (Department of Primary Industry and Resources, Northern Territory)
  • Luke Albury (Department of Agriculture and Fisheries, Queensland)
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Summary

The Silverlip Pearl Oyster is the largest species in the pearl oyster family. It also produces the largest pearls. Australia has three stocks of Silverlip Pearl Oyster. WA and QLD each have a sustainable stock. Stock in the NT is undefined.

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Stock Status Overview

Stock status determination
Jurisdiction Stock Fisheries Stock status Indicators
Northern Territory Northern Territory MOPWHF Undefined Catch, effort
Queensland Queensland ECPF Sustainable Catch, effort
Western Australia Western Australia POMF Sustainable CPUE,  recruitment surveys, population surveys, biomass prediction modelling
ECPF
East Coast Pearl Fishery (QLD)
MOPWHF
Mother of Pearl Wild Harvest Fishery (NT)
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 family [Shirai 1994], 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 south [Southgate et al. 2008], 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 Territory [Benzie et al. 2006]. 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

Northern Territory

Large catches of Silverlip Pearl Oyster were taken from Northern Territory waters between 1901 and 1966. The catch peaked at 804 t in 1937 and the last significant catch was 339 t in 1957. Since that time, annual catches have been very low, primarily because the market for mother-of-pearl collapsed. Heavy historical fishing is considered to have depleted the stock in many areas along the Northern Territory coast [Knuckey 1995].

Surveys conducted in the 1990s found significant numbers of large, mature individuals, indicating that recruitment was occurring, but biomass was not estimated [Knuckey 1995]. Catches earlier this century were around 2 t (to supply niche markets) and there has been no harvest in the Northern Territory since 2008. Although no fishing pressure is currently being exerted, the lack of a biomass estimate means that there is insufficient information available to confidently classify the status of this stock.

On the basis of the evidence provided above, Silverlip Pearl Oyster in the Northern Territory is classified as an undefined stock.

Queensland

The East Coast Pearl Fishery (Queensland) is a small-scale, wild-harvest fishery that enables the collection of broodstock for the pearl aquaculture industry. The general demand for wild-harvested pearl oysters is very low as the aquaculture industry produces the majority of its broodstock needs from its own hatcheries. Catches have been low in recent years, rarely exceeding 500 shells per year and 50 days of effort [QDAF 2018]. There has been a long history of low catches and effort and no Silverlip Pearl Oyster have been collected since 2013. The above evidence indicates that the current level of fishing pressure is unlikely to cause the stock to become recruitment overfished.

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

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. Quota in 2017 was 612 550 oysters, which resulted in a harvest of 143 tonnes (t).

In the Western Australian Fishery, the standardised catch per unit effort (CPUE) increased by 200 per cent between 2003 and 2010, declined to 2015, and increased to 2017. It is currently above the target reference level in the harvest strategy [DoF 2016]. The large fluctuation in standardized CPUE was due to an order of magnitude variation in recruitment. Recruitment in this fishery is measured using a spat settlement index (oysters aged 0+ years and 1+ years) and the large recruitment variability is caused by environmental variation, which also affects the fishing efficiency of the pearl oyster fleet [Hart et al. 2011]. The stock-prediction model, which uses the spat settlement index to predict future stock abundance, is forecasting an increase in standardized CPUE in 2018. Additional data, including population surveys, show that breeding stock levels are also currently above the target reference point [DPIRD 2016]. 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

Silverlip Pearl Oyster biology [Hart and Joll 2006]

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
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Distributions

Distribution of reported commercial catch of Silverlip Pearl Oyster
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Tables

Fishing methods
Western Australia Northern Territory Queensland
Commercial
Diving
Indigenous
Diving
Recreational
Diving
Management methods
Method Western Australia Northern Territory Queensland
Charter
Gear restrictions
Limited entry
Size limit
Spatial closures
Commercial
Gear restrictions
Limited entry
Size limit
Spatial closures
Spatial zoning
Total allowable catch
Recreational
Gear restrictions
Limited entry
Size limit
Spatial closures
Active vessels
Western Australia Northern Territory Queensland
5 in POMF
POMF
Pearl Oyster Managed Fishery (WA)
Catch
Western Australia Northern Territory Queensland
Commercial 142.04t in POMF
Indigenous Unknown Unknown Unknown
Recreational No Catch Unknown Unknown
POMF
Pearl Oyster Managed Fishery (WA)

Queensland – Indigenous (management methods) 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 - note confidential catch not shown
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References

  1. 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.
  2. DoF 2016, Western Australian Silver-Lipped Pearl Oyster (Pinctada maxima) Resource Harvest Strategy 2016–2021, v1. Fisheries Management Paper No. 276.
  3. 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.
  4. 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.
  5. Knuckey, IA 1995, The Northern Territory Pearl Oyster Fishery. FRDC final report 1991/14. 47 pp.
  6. Queensland Department of Agriculture and Fisheries 2018, Queensland Stock Status Assessment Workshop Proceedings 2018. Species Summaries. 19–20 June 2018, Brisbane.
  7. Shirai, S 1994, Pearls and pearl oysters of the world. Marine Planning Co. Japan. 95 pp. (in Japanese and English).
  8. 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.