Oyster, Native, oysters (Farmed)

Ostrea edulis

Method of production — Farmed
Production country — UK
Production method — Bottom & suspension culture
Picture of Oyster, Native, oysters (Farmed)

Sustainability rating one info

Sustainability overview

Oyster beds are generally privately owned and managed. Shellfish farming is a low-impact method of aquaculture and high quality water standards are required for cultivation of shellfish for human consumption. Dredging can cause disruption to the seabed and has a higher associated bycatch than manual harvesting techniques, but is less suited to deeper water for practical reasons. Some growers may hand-gather their stock by diving or by net to enhance quality.

Feed Resources

Criterion Score: 6

Oysters are a non-fed shellfish species who get all of their nutrient requirements from the surrounding water.

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Environmental Impacts

Criterion Score: 6

Native oyster shellfish culture is low impact, as no chemicals are used, escapes are not relevant for a wild settling species and there is no lethal predator control.

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Fish Health and Welfare

Criterion Score: 2

Welfare standards are not applicable to cultured shellfish species.

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Management

Criterion Score: 2

Management measures and regulations are in place for the farming of native oysters and are effective.

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Production method

Bottom & suspension culture

Ostrea edulis is associated with highly productive estuarine and shallow coastal water habitats on firm bottoms of mud, rocks, muddy sand, muddy gravel with shells and hard silt.

Biology

The native or flat oyster is a filter feeding, bivalve mollusc. They live on the seabed in relatively shallow coastal waters and estuaries (from the lower shore to 80m). They prefer habitats sheltered from strong wave action which tend to be muddy but require something hard for larval settlement - usually shells or stones. All native oysters start out as males, and throughout their lives change back and forth from male to female. In Britain, breeding normally takes place in the summer. It reaches maturity at about 3 years old. The average reproductive size for the oyster is about 5 cm. Oysters can reach a shell length of up to 11cm, and occur in variable shapes. Native oysters have a rough shell that is yellow, pale green or brown in colour, sometimes with bluish, pink or purple markings. The two halves of a native oyster’ s shell are different shapes. The left shell is deeply concave and fixed to the substratum, the right being flat with rougher edges and sitting inside the left acting as a lid. Inner surfaces of both valves or shells are smooth and usually pearly, white or bluish-grey, often with darker blue areas.The shell shape is a good way to distinguish native oysters from Pacific oysters, which were introduced to the UK in 1926, and which compete with the native oyster for space and food. Native oysters have rounder shells with smoother edges, while their Pacific relatives have a more elongated shell with deeply grooved edges. A single female oyster can produce 2 million eggs. Although usually up to about 11cm long, native oysters can grow to more than 20cm and can live as long as 20 years.

References

Seafish. Native Oyster Cultivation. Available online at: http://www.seafish.org/media/Publications/Native_Oyster_Cult_Leaflet.pdf. Accessed 06/09/2019

JNCC. Native Oyster. Available online at:http://www.naturalengland.org.uk/ourwork/marine/mpa/mcz/features/species/nativeoyster.aspx. Accessed 06/09/2018

FAO 2004-2018. Cultured Aquatic Species Information Programme. Ostrea edulis. Cultured Aquatic Species Information Programme. Text by Goulletquer, P. In: FAO Fisheries and Aquaculture Department [online]. Rome. Updated 1 January 2004. [Cited 7 September 2018].

University Marine Biological Station Millport. (2007). Conservation of the Native Oyster - Ostrea edulis in Scotland. Scottish Natural Heritage Commissioned Report No.251 (ROAME No. F02AA408).