Silverlip Pearl Oyster (2020)
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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
|Northern Territory||Northern Territory||Sustainable||
Biomass, fishing mortality
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.
Large catches of Silverlip Pearl Oyster were taken from Northern Territory waters between 1901 and 1966. The catch peaked at 804 tonnes (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 [Knuckey 1995]. Catches have remained low (generally <10 t) and sporadic since 1991 to supply niche markets and the catch in the Northern Territory was 10.5 t in 2019. A preliminary assessment using catch data applied to a modified catch-MSY model (developed by Martell and Froese  and modified by Haddon ), estimated that the 2019 biomass of Silverlip Pearl Oyster was 93 per cent of unfished levels [Saunders 2020] suggesting that the biomass of this stock is unlikely to be depleted and that recruitment is unlikely to be impaired. Similarly, the relatively low harvest in 2019 meant that the fishing mortality was well below the limit reference point indicating that this catch level is unlikely to cause the stock to become recruitment impaired.
On the basis of the evidence provided above, Silverlip Pearl Oyster in the Northern Territory 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|
Queensland – Indigenous (management methods) for more information see https://www.daf.qld.gov.au/business-priorities/fisheries/traditional-fishing
- 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.
- 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.
- Knuckey IA 1995, The Northern Territory Pearl Oyster Fishery. FRDC final report 1991/14. 47 pp.
- Martell, S. and R. Froese (2013). A simple method for estimating MSY from catch and resilience. Fish and Fisheries 14: 504-514.
- 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.