Oyster, Native, oysters (Farmed)
Production country — UK
Production method — Bottom & suspension culture
Updated: September 2019.
Native oysters farmed in the UK in suspended culture and bottom culture have little environmental impact and do not require any commercial feed sources as they get all of their nutrient requirements from the surrounding water. Oyster aquaculture is entirely sea-based and habitat concerns are minimal. Recent oyster culture generally does not involve the use of chemicals and there is no concern about the impact of effluents. Juveniles are hatchery-based. Disease risk and parasite interactions are thought to be minimal and do not threaten regional level operations. Environmental regulations are in place and are fully effective, however, there is no independent certification available.
Criterion Score: 5
Farmed oysters do not require any commercial feed sources as they get all of their nutrient requirements from the surrounding water. They feed by filtering mainly microscopic algae (phytoplankton), but also some organic detritus in sea water.
Criterion Score: 6
Overall, Native Oyster aquaculture performs well on environmental impacts. Oysters can be found naturally in marine and brackish waters and therefore culture is entirely sea-based and does not deplete freshwater supplies. Habitat concerns resulting from the physical infrastructure associated with on-bottom oyster culture include the alternation of hydrodynamics and current velocities, as well as reduced flow rates. However, the positive impacts of oyster beds through the provision of hard substrate for recruitment and refuge, outweigh the risks associated with increased sedimentation. Oysters growing in suspended culture also create favourable structures and habitats for other invertebrates and fishes.
Recent oyster culture generally does not entail the application of chemicals (i.e., antibiotics, pesticides, herbicides, fertilizers) to control fouling and predators or to prevent disease. Furthermore, the water in which chemicals would be used generally is not released to the marine environment. There is no evidence that discharges from oyster culture cause or contribute to cumulative impacts beyond the immediate vicinity of the farm. Furthermore, oyster farming may provide increased benefits through their extractive nature when cultured with other species.
The main source of juveniles are hatcheries. Extensive research has not revealed any information about parasitic transfer of Native Oysters and therefore this is not believed to be an issue. Disease outbreaks can and do occur, although they do not threaten regional level populations. There is also evidence of escapes, but these have not led to alterations of wild species and their habitats. A variety of oyster predators exist among oyster farms, including echinoderms, snails, crabs, fishes, and seabirds. A variety of methods are employed to reduce predation but there are no direct negative impacts on predatory species.
Fish Health and Welfare
Criterion Score: 1
Animal welfare is not applicable for shellfish as it is not covered by EU regulations on welfare. Humane slaughter has been carried out by RSPCA definitions.
Criterion Score: 3
Aquaculture policy in the UK is a devolved matter, with the separate administrations of Wales, England, Northern Ireland and Scotland responsible for its collective oversight. In England, the Marine Management Organisation is preparing marine plans for 11 predefined areas in England. The first of these plans were published in 2014 and all plans are due to be in place by 2021. Aquaculture production in Scotland is covered in the 2015 Scottish National Marine Plan and in Wales by the 2019 Welsh National Marine Plan. The Northern Ireland Marine Plan will come into effect by 2021.
In the UK, the regulations regarding the environmental impacts of aquaculture are either not applicable or are in place and are fully effective. This includes the Habitats Directive 92/43/EEC and the Birds Directive 2009/147/EC, which form the cornerstones of the EU’s nature conservation policy and protect valuable habitats and species. There is also regulation in place to cover the use of land and water resources, discharges including effluents and their impacts, disease management and biosecurity.
In the UK, there is currently no third party certification for Native oysters.
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.
Based on method of production, fish type, and consumer rating: only fish rated 2 and below are included as an alternative in the list below. Click on a name to show the sustainable options available.Abalone
Clam, Manila (Farmed)
Crab, brown or edible
Lobster, Norway, Langoustine, Dublin Bay prawn or scampi
Mussel, Chilean (Farmed)
Mussel, mussels (Farmed)
Oyster, Native, oysters (Caught at sea)
Oyster, Native, oysters (Farmed)
Oyster, Pacific, oysters (Caught at sea)
Oyster, Pacific, oysters (Farmed)
Prawn, King (whiteleg), prawns
Prawn, Northern prawns, Northern shrimp
Prawn, Tiger prawns (Farmed)
Scallop, King, scallops
Squid, Japanese flying
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.
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Monterey Bay Aquarium Seafood Watch. Oysters. Available at https://www.seafoodwatch.org/seafood-recommendations/groups/oysters?q=pacific%20oyster&t=pacific%20oyster&type=pacific&method=farmed#tab=seafood-watch [Accessed on 02.08.2019].
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Zwerschke, N., Emmerson, M. C., Roberts, D. and O'Connor, N. E. 2016. Benthic assemblages associated with native and non-native oysters are similar. Marine Pollution Bulletin. 111(305-310). Available at https://www.ncbi.nlm.nih.gov/pubmed/27377003 [Accessed on 07.08.2019].