Mussel, mussels (Farmed)

Mytilus edulis

Method of production — Farmed
Production country — UK and Ireland (Republic of)
Production method — Suspended Rope Culture and Bottom Culture
Certification — Aquaculture Stewardship Council (ASC) and/or Marine Stewardship Council (MSC) certification
Picture of Mussel, mussels (Farmed)

Sustainability rating one info

Sustainability overview

Updated: March 2020.

Mussels farmed in the UK and Ireland (Republic of) in suspended rope 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. Mussel aquaculture is entirely sea-based and habitat concerns are minimal. Recent mussel culture generally does not involve the use of chemicals and there is no concern about the impact of effluents. Spat used for farming are either collected from the wild or settle naturally and research into development of a hatchery is ongoing. Disease risk and parasite interactions are thought to be minimal and do not threaten regional level populations. Both independently certified (ASC and MSC) and uncertified mussels are available.

Feed Resources

Criterion score: 5 info

Farmed mussels 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.

Environmental Impacts

Criterion score: 4 info

Overall, Blue Mussel aquaculture in the UK and Ireland performs well on environmental impacts. Mussels used in aquaculture can be found naturally in marine and brackish areas and therefore culture is entirely sea-based. Habitat concerns resulting from the physical infrastructure associated with suspended mussel culture are minimal and include the alteration of hydrodynamics, current velocities, and reduced flow rates. For bottom culture methods, dredging has the potential to have significant habitat impacts. However, tows for farmed mussels are generally much shorter than for wild-caught and farming takes place in shallow coastal areas which can recover from major disturbances within a few weeks or months. A variety of shellfish predators exist among mussel farms, including oyster drills, sea stars, crabs, benthic fishes, seabirds, and mammals. Methods used to harvest mussels in suspended rope culture generally do not result in direct impacts to predators. Mussel harvesting by dredge can result in an immediate decline in abundance and biomass of all species, but the decline is often followed by rapid benthic recovery. Passive and benign barrier netting can be used to prohibit any type of predator and is usually species specific. Duck deterrents are also used, with varying results.

Recent mussel culture generally does not involve the application of chemicals (e.g. antibiotics, pesticides, herbicides, fertilizers) to control fouling and predators or to prevent disease. The amount of chemicals used in mussel culture is thought to be minute, if at all. In addition, the water in which chemicals would be used is generally not released into the marine environment and therefore, there is no threat of chemical contamination to adjacent waters or organisms. As farmed mussels are not provided external feed and there is no nutrient fertilisation, there is no concern about the impact of effluents. However, there can be a concern over changes in the sedimentary environment around mussel farms due to bio deposition and sediment trapping. These changes are limited to the farm site and are not considered to extend beyond the immediate vicinity of the farm. Furthermore, mussel farming has been shown to increase water quality at the farm site through removal of excess nutrients and phytoplankton.

Mussel juveniles or ‘spat’ used for farming are either collected from the wild or settle naturally on purpose-made collectors. Research into and the development of a mussel hatchery is currently ongoing in Scotland in order to address the issues of reliability and quality of Scottish spat. At present, the cultivation of mussels does not rely on hatchery production of seed as wild spatfalls are usually of sufficient quality and reliability and are not overexploited. Aquaculture systems that are open to the environment tend to pose a risk for disease and parasite interaction with wild populations. However, there have been few mass mortality events described for adult blue mussels and good management practices ensure that the risk is low and does not threaten regional level populations.

Fish Health and Welfare

Criterion score: 1 info

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.

Management

Criterion score: 5 info

This assessment covers mussels from the UK and Ireland, independently certified to ASC and/or MSC standards. The score provided is respective of both countries.

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.

Aquaculture production in Ireland is covered by The National Marine Planning Framework (NMPF) which was adopted in 2020.

In the UK and Ireland, 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, biosecurity and disease management.

The ASC standards cover the main environmental and social impacts of aquaculture, including fish health, feed and fair employment conditions, by setting metric-based indicators. Farms are assessed annually by external auditors and results published. ASC products are traceable throughout the supply chain. ASC is the only ISEAL compliant aquaculture certification scheme.

Production method

Suspended Rope Culture and Bottom Culture

In the UK and Ireland, mussels are grown by suspension rope culture and bottom culture. Mussels grown by suspension rope culture are generally harvested by hand-gathering methods. Mussels grown by bottom culture are usually dredged.

Biology

Common mussels are bivalve molluscs found on shores throughout the North Atlantic, Mediterranean, North and Baltic Seas. They normally live in large aggregations, attaching themselves to rocks and each other with sticky threads known as byssus. Size and shape vary widely, but the colour is always deep bluish purple. Shell up to 10 cm but usually much smaller. Mussels mature when one year old and may live 10-15 years or more.

References

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DCCAE. 2020. Marine Planning and Development. Available at https://www.dccae.gov.ie/en-ie/natural-resources/topics/marine-planning-and-development/Pages/Marine-Planning-and-Development.aspx [Accessed 09.03.202]

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EU. 2007. Council Regulation (EC) No 708/2007 of 11 June 2007 concerning use of alien and locally absent species in aquaculture. Official Journal of the European Union. Available at https://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2007:168:0001:0017:EN:PDF [Accessed 10.03.2020]

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Loch Fyne. 2017. Environmental. Available at https://www.lochfyne.com/about-us/environmental [Accessed 19.08.2019]

Marine Stewardship Council. 2019. Shetland & Scottish Mainland Rope Grown mussel Enhanced Fishery. Available at: https://fisheries.msc.org/en/fisheries/shetland-scottish-mainland-rope-grown-mussel-enhanced-fishery/about/ [Accessed 19.08.2019]

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Offshore Shellfish Ltd. 2016. Available at https://www.offshoreshellfish.com/ [Accessed: 03/09/2019]

Pauly, Daniel and Watson, Reg. 2009. "Spatial Dynamics of Marine Fisheries" In: Simon A. Levin (ed.) The Princeton Guide to Ecology. Pages 501–509.

SARF. 2010. Environmental Impact Assessment (Eia) Thresholds For Marine Fish Farms. Available at http://www.sarf.org.uk/cms-assets/documents/28816-136993.sarf040a.pdf [Accessed 10.03.2020]

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