Silverlip Pearl Oyster (2020)
Date Published: June 2021
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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, all of which are sustainable.
Stock Status Overview
|Western Australia||Western Australia||Sustainable||CPUE, recruitment surveys, population surveys, biomass prediction modelling|
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.
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 (CPUE) increased by 200 per cent between 2003 and 2010, declined during 2011 to 2015 and increased again from 2016 to 2019. It is currently above the target reference level in the harvest strategy [DoF 2016]. The large fluctuation in standardised 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 standardised CPUE in 2020 and 2021. Overall the stock is entering a period of increased recruitment. Additional data, including population surveys, show that breeding stock levels are also currently above the target reference point [DoF 2016], suggesting that the biomass of this stock is unlikely to be depleted and that recruitment is unlikely to be impaired. Also, abundance of the silverlipped pearl oyster increased in 2019, which indicates that the current level of fishing mortality is unlikely to cause the stock to become recruitment impaired
On the basis of the evidence provided above, Silverlip Pearl Oyster in Western Australia is classified as a sustainable stock.
Silverlip Pearl Oyster biology [Hart and Joll 2006]
|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|
|Total allowable catch|
Queensland – Indigenous (management methods) for more information see https://www.daf.qld.gov.au/business-priorities/fisheries/traditional-fishing
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- DoF 2016, Western Australian Silver-Lipped Pearl Oyster (Pinctada maxima) Resource Harvest Strategy 2016–2021, v1. Fisheries Management Paper No. 276.
- Haddon M., A Punt and P. Burch (2018). simpleSA: A package containing functions to facilitate relatively simple stock assessments. R package version 0.1.18.
- 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.
- 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.
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- QFish, Department of Agriculture and Fisheries, www.qfish.gov.au
- Saunders T. 2020, Northern Territory Silverlip Pearl Oyster Stock Status Summary - 2020. Unpublished Fishery report.
- Shirai, S 1994, Pearls and pearl oysters of the world. Marine Planning Co. Japan. 95 pp. (in Japanese and English).
- 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.