Clam, Manila (Farmed)
Production country — UK
Production method — Bottom culture
Updated: September 2019.
Manila clam farmed in the UK in 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. Manila clam aquaculture is entirely sea-based and habitat concerns are minimal. No chemicals are used due to the rarity of disease and there is no concern about the impacts of effluents. Spat used are hatchery produced. In Britain, the species is not currently aggressively invasive, however, it may continue to spread as sea temperatures rise. In the UK, regulations regarding the environmental impacts of shellfish aquaculture are either not applicable or are in place and are fully effective. Manila clams are exempt from non-native species permitting requirements as they have been established in aquaculture for so long. There is no third party certification available.
Farmed manila clams 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 (phytoplankton), but also some organic detritus in sea water.
Criterion Score: 5
Overall, Manila clam farmed in the UK in open water crates have minimal environmental impacts. Clams can be found naturally in marine and brackish areas and therefore, culture is entirely sea-based and no freshwater input is required. Clams can be harvested in a variety of methods including by hand, rake or dredge. Hand and rake harvest techniques are believed to have no significant impacts on the habitat. Dredge harvest techniques for clams often involve dredges or rakes with long teeth or water jets to loosen the sediment and bring clams to the surface commonly referred to as hydraulic dredge. Tows for farmed clams are usually much shorter and more targeted than those used for wild clams. Additionally, most shellfish farming takes place in shallow coastal areas, which are naturally highly disturbed, and can recover from major disturbances within a few weeks or months.
The introduction of the Manila clam into British coastal waters in the 1980s was contested by conservation agencies. While recognising the value of the clam for aquaculture, the government decided that it posed no invasive risk, as British sea temperatures would prevent naturalisation. This proved incorrect. By 2010 the species had naturalised in at least eleven estuaries in southern England. These included estuaries with no history of licensed introduction. However, in Britain, the species is not currently aggressively invasive and appears not to present significant risk to indigenous diversity or ecosystem function. However, it is likely to gradually continue its spread should sea surface temperatures rise as predicted.
In the UK, all seed for commercial clam cultivation are produced in hatcheries. Typically, antibiotics and chemicals are not used in the grow-out phase of clam farming, primarily due to rarity of disease. During the grow-out phase, clams feed exclusively on material (i.e. microalgae, organic detritus, bacteria, viruses) in ambient seawater. Waste products generated include faeces and pseudofaeces, however, on-bottom culture methods are not known to cause anoxia or excessive biodeposition.
Diseases in clams can exist in all stages of production. As clam systems are open, disease interactions can occur and it can be difficult to determine in which population the disease originated and the impacts on wild native clam disease or mortality. Extensive research has not revealed any information about the presence and impact of parasites in farmed manila clams in the UK. Therefore, it is believed that there is a potential problem of parasites, but the impact on wild individuals is limited by effective management.
A variety of clam predators exist among clam farms, including echinoderms, snails, crabs, fishes and seabirds. The most reliable method for preventing predators from gaining access to clams is to employ a passive physical barrier, usually in the form of netting or mesh bags. The use of passive, non-harmful barriers yields no evidence of direct or accidental mortality of predators or wildlife.
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, Scotland and Northern Ireland 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. Council Regulation (EC) No 708/2007 Concerning use of alien and locally absent species in aquaculture” states that EU Member states can exempt non-native species from permitting requirements if they have been typically established in aquaculture for so long that retrospective regulation would be inappropriate - this includes Manila clams.
In the UK, there is currently no third party certification for Manila clams.”
Clams may be harvested by hand-gathering or manual digging or raking, or by mechanical methods, e.g. suction or hydraulic dredge. Manual harvesting methods cause less disturbance to sediment than mechanical methods.
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
Oyster, Pacific, oysters
Oyster, Pacific, oysters (Caught at sea)
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Prawn, King (whiteleg), prawns
Prawn, Northern prawns, Northern shrimp
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Scallop, King, scallops
Scallop, Queen, scallops
Squid, Japanese flying
A bivalve mollusc with distinctive black and white shell markings, it is native to the waters of east Asia. Now widespread throughout the western world, with introductions made accidentally with oysters into North America, and deliberately as hatchery broodstock into Europe. In the wild it is found burrowing on coarse sediment in intertidal waters. Matures at about 2 years, with a corresponding shell size of about 2cm. Maximum size about 6.5-7.5cm. Spawning occurs in summer months.
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UK Legislation. 2011. The Alien and Locally Absent Species in Aquaculture (England and Wales) Regulations 2011. Available at http://www.legislation.gov.uk/uksi/2011/2292/pdfs/uksiod_20112292_en_001.pdf [Accessed on 26.08.2019].