Silverlip Pearl Oyster
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Stock Status Overview
|Northern Territory||Northern Territory||MOPWHF||Undefined||Catch, effort|
- Mother of Pearl Wild Harvest Fishery (NT)
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.
Historically, large catches of Silverlip Pearl Oyster were taken from around the Northern Territory coast between 1901 and 1966. Catches peaked at 804 tonnes (t) in 1937 and the last significant catch was 339 t in 1957. Since this time, annual catches have been extremely low, primarily due to the market for mother-of-pearl collapsing. Heavy historical fishing was considered to have caused overfishing in many areas in the Northern Territory5. However, surveys conducted in the 1990s found significant numbers of large, mature individuals indicating that recruitment had continued however, biomass levels at that time were unknown5. The recent low catches have been around 2 t (to supply niche markets) and there has been no harvest in the Northern Territory since 2008. While the current level of fishing pressure is unlikely to cause any additional reductions on the current biomass 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.
Silverlip Pearl Oyster biology6
|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|
Distribution of reported commercial catch of Silverlip Pearl Oyster
|Total allowable catch|
a. 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.
Commercial catch of Silverlip Pearl Oyster - note confidential catch not shown
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.
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.
- 1 Shirai, S1994, Pearls and pearl oysters of the world. Marine Planning Co. Japan. 95 pp. (in Japanese and English).
- 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 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 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 Knuckey, IA 1995, The Northern Territory Pearl Oyster Fishery. FRDC final report 1991/14. 47 pp.
- 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 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.