Native oyster

Ostrea edulis

1: Best Choice How we work out the ratings

What to check for

Location

All areas

Production method

Culture, suspension

Rating summary

Overall, native oyster suspended aquaculture performs well on environmental impacts. They do not require any commercial feed sources as they get all their nutrient requirements from the surrounding water. There are some impacts from farms including sediment changes and shading, which can alter the local environment. Oyster farms may, however, provide some local benefits as they extract excess nutrients and particulates from coastal waters. Juvenile oysters are sourced from appropriate hatcheries and escapes from farms are not considered a concern for this native species. Disease outbreaks can and do occur, although they do not threaten regional level operations. Aquaculture policy in the UK is a devolved matter. Regulations are in place to limit environmental impacts including land and water use, discharges, disease management and biosecurity, however, there is no independent certification available.Rating last updated June 2022.

How we worked out this Rating

No external feed is supplied to farmed oysters.Farmed oysters do not require any commercial feed sources as they get all their nutrient requirements from the surrounding water. They feed by filtering mainly microscopic algae (plankton), but also some organic detritus in sea water.

Overall, Native Oyster aquaculture performs well on environmental impacts. Although they are farmed in high density the net impacts on the surrounding environment are considered negligible.Oysters are found in marine and brackish water and therefore culture is entirely sea-based and does not deplete freshwater supplies. Habitat concerns include alteration of hydrodynamics and current velocities, reduced flow rates, altered sedimentation and shading. The increased sediment from farms is considered balanced out by the filtering of organic materials by oysters. Raised oyster farms do provide temporary habitats for associated species such as invertebrates and fishes. However, these are regularly disturbed and ultimately removed limiting these benefits to robust and mobile species.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 operations. 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.

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.

Regulations are in place to limit environmental impacts including land and water use, discharges, disease management and biosecurity.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. Marine plans are either in development of have now been published.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.This assessment is for uncertified oysters.

References

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