Sources and Quantities
Mussel farming extends across many countries in temperate and tropical regions and includes nine main species1, as shown in the table opposite. There are three species in what is known as the blue mussel complex (Mytilus edulis, Mytilus galloprovincialis and Mytilus trossulus) and they show varying levels of hybridisation wherever they occur within overlapping geographical areas. The UK for example farms M. edulis, M. galloprovincialis and their naturally occurring hybrids2.
Mussels are bivalve molluscs, meaning that they have a two-part hinged shell. They feed by filtering mainly microscopic algae (phytoplankton), but also some organic detritus in sea water. Farmed mussel aquaculture operations are located in intertidal and shallow sub-tidal environments, as well as in deeper, offshore waters (20m or deeper)3. The two-hinged shells are generally thicker in mussels grown inter-tidally as they protect the mussel from the more dynamic nature of this environment (the wave and tidal action), and mussels grown inter-tidally may exhibit a longer shelf-life than those which are grown sub-tidally and suspended in the water column.
As the map shows, Mussels are farmed across the globe, and was worth US$3.8 billion from a 2016 production total of some 2 million tonnes1. China produced almost half of this volume. Other important producing countries are Chile and Spain, which produce over 200,000 tonnes each. Some 10% of world mussel production enters international trade4.Less than 5% of total world bivalve production enters international markets; one of the lowest proportions in seafood trade. This is due to the fact that the majority of bivalves are eaten in the countries where they are grown, and because they are a highly perishable product. The EU is one of the main markets for bivalves taking over one third of the total bivalve trade4.
China produces over 80% of the world’s bivalves, but domestically consumes almost all of this production. Around 200,000 tonnes of mussels are internationally traded per year, with Spain and the US generally the main markets4.
European production of mussels (some 500,000 tonnes in 2015), is divided between bottom culture and rope grown; northern countries, especially the Netherlands, concentrate on the former, whilst Spain and Italy the latter1, 4. Spain and the Netherlands are the main exporters of European mussels, but Europe also imports significant quantities of farmed Chilean mussels5.
Mussels are available all year round, and technologies such as vacuum packaging make them even more accessible to the consumer. Large mussels are packed in bags of 5 or 10 kg, while smaller bags of 1 kg are produced for distribution to retail.
Mussels are processed and sold in various ways; whole, cleaned, cooked (with or without the shell i.e. pure mussel meat), and sometimes presented in their half shell6.
Domestic Market Information7, 8
From 2008 to 2018 mussels have been in growth in Great British retail (i.e. in England, Scotland and Wales); increasing in value and volume by 10.4% and 8.8% respectively from a base of £19.6 million and 3,222 tonnes in 2008.
In 2018, UK retail sales of mussels were worth £26.5 million (+0.5% compared to 2017) with a volume of 4,731 tonnes (+8.8%), average price £5.59 per kg; ranking as the 18th most popular species by value (in the 52 weeks up to 16/63/2018 (including discounters).
In 2018, the UK imported 2,744 tonnes of mussels (Mytilus species).
Note: differences between the volume of mussels sold in UK retail and that which is imported is due to its use in the foodservice industry (e.g. restaurants) (no data available) and that which is re-exported.
Mussel farming is undertaken using a variety of methods based on the prevailing hydrographic, social, and economic conditions. The two main types of culture are either carried out on the seabed or by suspended culture3, 9, as shown in the schematic opposite. On-growing of mussels is sea-based, and the type of rearing method depends on both the environment (tidal range, water depth, and so on) and tradition. No feed is supplied and no chemicals or medicines are administered.
Seabed culture involves locating and dredging seed mussel of around 10mm shell length from offshore beds and relaying them in more productive, protected locations; in the UK such areas are often termed a ‘lay’10. Across the UK, in Wales, N Ireland, The Wash, North Norfolk and Poole Harbour in England, mussel production is mostly derived from bottom culture and within restricted Several or Regulating Order fisheries (i.e. where a person or company is granted legal ownership of the mussels in a given area of seabed to enable their cultivation)11, 12. In 2016, 6,136 tonnes of UK mussels where produced “on bottom”13.
In suspended or “off bottom” culture mussels are farmed on systems of rafts, ropes and floats, where they grow until harvest 18-24 months later. The UK produced 8,549 tonnes of off-bottom mussels in 201613, and these came predominantly from Shetland and elsewhere in Scotland. Suspended mussel production is increasing in Wales and England.
Mussel juveniles or ‘spat’ used for farming are either collected from the wild or settle naturally on purpose-made collectors. However, predicting the occurrence, time, location and size of any spat-fall is difficult, and there are many environmental variables to be taken into account. This introduces uncertainty and unreliability in seed supply to growers and often results in fluctuations in the supply of mussels to processors, retailers and eventually consumers14. Hatchery production of spat is possible and may be a method by which a reliable mussel spat supply can be supplied to farmers15, 16. Research into and the development of a mussel hatchery is currently going on in Scotland in order to address the issues of reliability and quality of Scottish spat17, 18.
Governance systems play an important part in ensuring environmental sustainability, and whilst these have evolved rapidly with the growth of the industry, there are differences between regions and countries. Poor governance can result in industry stagnation, the spread of preventable diseases, environmental damage and opposition to aquaculture activities by local communities and groups such as non-governmental organisations (NGOs). Key governance responsibilities are ensuring environmental assessment and decision making processes are in place for sensitive and coastal ecosystems, which help deliver sustainable aquaculture whilst managing possible adverse impacts. Other regulatory and governance aspects should cover aspects such as water abstraction and discharge, health monitoring, and so forth.
Four principles – accountability, effectiveness and efficiency of governments, equity, and predictability of the rule of law – are necessary for effective aquaculture governance. These principles should guide the administration, legislative and regulatory framework of aquaculture. In addition to governments, other stakeholders such as communities, non-governmental organisations (NGOs) and producers should also be involved in the governance of the industry1.
The vast majority of mussel production is undertaken in three global regions: Asia-Pacific, Latin America, and Europe.
While many countries in Asia-Pacific have made commendable efforts to set up policies, administrative, legal and regulatory frameworks to properly develop and manage aquaculture, some countries in the region are still lagging behind. However, many Asia-Pacific regional countries (e.g. Australia, New Zealand) enjoy established strong aquaculture governance structures (policies, institutions, regulations, etc.) in support of sustainable development and management of aquaculture at all levels.
As many wild fish stocks are already exploited at their maximum or have been overfished in Latin America, the significance and contribution of aquaculture will continue to grow. In order to fully realise this potentially valuable contribution to food security and economic growth, Latin America faces a number of challenges in the development and implementation of sound aquaculture governance through policy and planning. In some cases, aquaculture is considered an extension of fisheries, this being a failure to recognise that management strategies for fisheries and aquaculture are different. There is however, a recent recognition in the region of the imperative to create proper management and governance approaches to accommodate aquaculture’s circumstances and the need for governments and industry to work more closely together. Steps are being taken to address this; for instance, the FAOs Blue Growth Initiative for Latin America and the Caribbean has been initiated to improve sustainable management of aquaculture (and fishery) resources4.
With the notable exceptions of the major European aquaculture producers Norway, Russia and Turkey, the shaping of regulations and the instruments for development and investment in European aquaculture falls under the European Union (EU), and are highly evolved. The principal frameworks for EU aquaculture is the Common Fisheries Policy (CFP) as well as the EU Blue Growth Strategy, intended to stimulate and guide aquaculture development in Europe which is environmentally, socially and economically sustainable. In non-EU member states there are largely equivalent policies.
Although there has been criticism surrounding bivalve/mussel aquaculture, generally the impacts of mussel farming are seen as low and relatively benign6, 7. Impacts can include: seabed deposition of solid wastes such as pseudofeces; changes to biodiversity; the depletion of phytoplankton for other species to eat; and the reduction of light reaching the sea bed. The positive impacts and benefits that bivalve/mussel aquaculture can have on marine ecosystems, include:
Feed is generally perceived to be one of the major risk factors in aquaculture production of fish and crustaceans. However mussels consume food that occurs naturally in the environment and are not supplied with commercial aquafeeds; also they are not treated with chemicals or veterinary medicines unlike in other forms of aquaculture. Excluding seaweeds, one-third of all farmed seafood, some 20 million tonnes annually, is produced without additional feeding. The most important non-fed animal species, apart from bivalve molluscs (mainly clams, oysters, mussels and scallops), include two finfish species (silver carp and bighead carp), as well as other filter feeding animals such as sea squirts10.
These positive, natural and ‘ecosystem service’ aspects of bivalve aquaculture in general are increasingly being seen as major factors to promote their culture as the most environmentally sustainable type of seafood production10. As such, increased mussel aquaculture is anticipated, including the potential for increased production in the UK11. The Seafood 2040 Strategy for instance, highlights bivalve aquaculture as an opportunity to generate sustainable protein for domestic consumption or export, provide employment in fragile coastal communities, whilst offering significant ecosystem services12.
European mussel production continues to increase and there are signs that the adoption of large-scale long-line rope culture using bulk mechanised handling (adopted from the NZ industry) could open up opportunities for large-scale expansion of the sector; producing high quality product at low production costs. UK examples of large-scale long-line rope culture are Shetland’s mussel production13 and Lyme Bay, South West England14. This type of production could reduce Europe’s significant Chilean mussel imports5.
As bivalves are farmed in open marine environments and because there are no available treatment or vaccination options, disease prevention is essential. Work continues to improve understanding of bivalve diseases and develop innovative solutions and tools for their management and prevention15, 16.
Site selection for cultivating mussels is extremely important and factors include: substrate and/or depth of water; salinity; temperature; exposure to air, wind and currents; sedimentation rates; and food availability.
Buyers should seek assurances that all national and local laws are adhered to. All farms should have the required licences, permits and registrations in regards to their site and its operations accompanied by documentary evidence to demonstrate this compliance. Mussel farming may be managed to minimise site operations during peak sensitive periods or in times of low water quality episodes. Farm leases and permits can stipulate sustainable management practises.
In considering the environmental impacts of mussel aquaculture, it is important to view both the scale of the sector as well as the diversity of production systems1. The impacts of mussel aquaculture on the environment are often considered less than those of finfish and warm water prawn aquaculture.
Bivalves are considered keystone species in the ecosystem and therefore they can affect the surrounding environment in various ways2. At all scales of bivalve production, their culture and the physical on-growing structures used to support them may produce changes in water movement and sediment dynamics that can affect both planktonic and seabed communities. However, the on-growing structures may also act as new habitat and nursery areas for fish, crustaceans and molluscs3.
Operations associated with the growing and harvesting of mussels are relatively low impact in terms of activities that might lead to amenity and wildlife disturbance. One of the greatest potential impacts of cultivating filter feeders such as mussels is the net loss of energy (i.e. phytoplankton) from the ecosystem. Large monocultures, particularly in enclosed bays with limited water exchange, may exceed the carrying capacity in that area (e.g. the supply of planktonic food) and thus affect all aquatic organisms including the farmed mussels themselves. Conversely, as mussels are primary consumers they can potentially mitigate impacts of nutrient enrichment (e.g. from land-based discharges and run-off) which can often lead to eutrophication of coastal waters.
Coastal areas and estuaries where mussels are farmed are often sites of ecological and high amenity use and therefore any large-scale cultivation may have impacts such as disturbing shore bird feeding sites, or on local navigation. Marine aquaculture operations may also have an aesthetic impact.
In many countries, siting a mussel farm would be restricted in areas with key biological or ecological functions. In the absence of such restrictions, the farmer should implement an environmental management plan to ensure no adverse effects on the ecological integrity of the area, and demonstrate there is no harm to threatened or endangered species and/or habitats. In relation to the carrying capacity of the ecosystem and phytoplankton availability for other aquatic animals, farms should consider stocking at appropriate densities.
Best Management Plans (BMP’s), codes of good practice (often developed by industry groups)4, and certification has been used as a means of prevention for unacceptable environmental interactions. In 2017, Loch Fyne Oysters Ltd. in Scotland received the Aquaculture Stewardship Council (ASC) certification for its responsible farming of blue mussels, the first company worldwide to do so5. Whilst in 2018, Offshore Shellfish Ltd. on the English south coast was the first European mussel farm to earn Global Aquaculture Alliance Best Aquaculture Practices (GAA BAP) certification6.
Different countries regulate aquaculture and enforce policies differently, but often with the same goal of minimising environmental impact. Overall, the content of habitat regulations surrounding mussel culture takes into account environmental impacts and ecosystem services. Similarly, enforcement organisations should be identifiable, permitting and licensing process transparent and based on zoning or planning7. It is not clear if such regulations are as effective or well-enforced in all locations (e.g. in some Asia-Pacific countries)8.
The consideration of water quality in mussel farming is important. Mussels feed by filtering phytoplankton and in doing so they can accumulate and concentrate bacteria or viruses, some of which can be a risk to human health. These are often derived from land-based activities such as water treatment, storm drainage and diffuse agricultural run-off. Bio-toxins may also be contained in seasonally occurring marine algae and within Harmful Algal Blooms or HABs1, 2, which mussels can ingest.
Rigorous controls need to be in place in regards to harvesting shellfish such as mussels in order to protect consumers; ensuring that those sold into the supply chain meet strict food safety (health and hygiene) standards3. The UN Food and Agriculture Organisation (FAO) has developed the Codex Alimentarius or “Food Code” which is a set of voluntary standards, codes of practice and guidelines covering food and its production, including those for bivalve molluscs4, 5. The aim of the Codex is to protect public health and to support balanced trade relationships in food, and all World Trade Organisation (WTO) signatories are obliged to observe them. In practice, most countries have laws that are very broadly equivalent to Codex guidelines but differ from them in the detail.
European Hygiene Regulations6 state that shellfish business operators are responsible in ensuring that bivalve molluscs meet strict standards. The UK Food Standards Agency, in compliance with European regulations, has classified shellfish harvesting areas and beds on the basis of the level of the bacterium E.coli in mollusc flesh. Depending on shellfish production area classification (A, B or C) certain procedures must be followed to enable harvested mussels to enter the market. Molluscs harvested from Class A areas can go straight to market, but they are often purified (depurated) to provide additional assurance of quality; those harvested from Class B areas must be purified before being sold to consumers. All molluscs sold on the UK market must contain less than 230 cfu (colony forming units) of E.coli per 100 g of flesh7, 8.
Depuration is a technique whereby live shellfish and bivalves, that may contain undesirable substances (e.g. sand, silt), pollutants, parasites or organisms of possible harm to human beings (e.g. pathogenic bacteria), are placed in systems with continually circulated and sterilised seawater for a specific period of time in order to clean themselves9. Depuration is effective in removing many undesirables, but it is not in regards to removing viral contamination (e.g. norovirus)10. However, mussels are not eaten raw (unlike some other shellfish such as oysters) and appropriate cooking can eliminate the norovirus risk. End product testing of live shellfish is also undertaken in countries such as the UK, to ensure shellfish products that enter the market are safe to eat11, 12.
For many reasons there is an on-going societal need to reduce coastal water pollution, and this is of particular importance to protect and enable the growth of bivalve aquaculture. Legislation exists to control water pollution, for instance that in the UK13, but pollution incidents do occur, and efforts continue to improve water quality14, 15.
Active Management is continuous, real time decision making, which takes into account of all the available information enabling shellfish producers to decide what action to take in regards to when and where to harvest. It is an increasingly important tool, especially in inshore waters, to reduce the risks from poor water quality and HAB episodes16.
At a global level the farmed mussel industry produced some two million tonnes of mussels in 2015, and almost all of this production relied on wild spat. Variability in spatfall has resulted in production fluctuations and business uncertainty problems in many mussel producing countries. With few measures being taken to overcome this fluctuation, it has generally been tolerated by growers1.
However, to combat the spatfall variability a number of countries are now intervening to try to better understand their mussel settlement patterns and to optimise use of the resource through1:
The process of mussel aquaculture starts with the collection of spat from the wild. This is undertaken either by natural or passive settlement on purpose-made spat collectors (rope, plastic mesh, etc. attached to a long line and hung in the water column), or active collection from large, naturally occurring accumulations of mussel seed, which is dredged from sub-tidal zones. An example of a well-managed and sustainable mussel dredge fishery to supply seed for on-growing is Bangor Mussel Producers Ltd. of North Wales, who have been Marine Stewardship Council (MSC) certified since 20102.
Whilst passive collection is more common globally and is not considered to have any negative impacts on wild stocks, active collection does have the potential to impact wild mussels and the environment due to seabed disruption. This can result in increased burial of organic material and anoxic seabed conditions, increased turbidity, as well as dislodging mussels and non-target organisms which may cause increased stress or mortality3.
Potential impacts of mussel dredging and the subsequent transfer of spat to on-growing sites can be habitat loss or degradation through physical damage, and the introduction and spread of pathogens, parasites, and/or non-native invasive species4, 5, 6, 7. Dredging and relaying must be carried out in ways that minimise these risks.
Generally, wild seed collection only occurs in areas where the accumulation of mussel seed would not persist naturally; so called ‘ephemeral’ accumulations. Stable naturally occurring beds of mussels are considered to be biological reefs and thus are often protected features. Dredging of wild seed mussels for relaying and on-growing is subject to increased scrutiny in Europe under, for example, the requirements of both the Habitats Directive and the Birds Directives which are cornerstones of Europe’s nature conservation policy and which establish the EU Natura 2000 network of protected areas8, 9. Access to any settlement of mussel seed, even from traditional areas, is no longer a foregone conclusion as a variety of management and scientific assessments have become part of the process10.
Although mussel culture affects the population dynamics of sub-tidal mussels in an area by relaying in specific plots, this activity results in a higher mussel biomass than on natural beds and enhances the total stock which favours ecosystem services, including the provision of biodiversity and a high-quality food source for birds11. Also, when it comes to harvest, bottom cultivated mussels are generally harvested with dredges applying minimal force and penetration into the sea bed12.
Another important safeguard is to have biosecurity management plans in place at individual farm and area level. The key elements of biosecurity include: practical and appropriate legislative controls; adequate diagnostic and detection methods for infectious diseases; disinfection and pathogen eradication methods; reliable high quality sources of stock; and best management practices13, 14. Management measures include those that are regulatory (e.g. lease conditions and permit requirements) but also the use of voluntary agreements and codes of practice; the Bangor Mussel Producers Association Code of Good Practice for Mussel Seed Movements15, 16 is an excellent example of the latter.
Also important are designations to protect sensitive marine habitats. For example in the UK these include Marine Protected Areas (MPAs), Special Areas of Conservation (SACs), Special Protected Areas (SPAs), and intertidal areas identified as Sites of Special Scientific Interest (SSSIs)17.
Mussel seed hatchery production is now possible and although it is currently small-scale globally3, it may be a future mechanism by which a reliable supply of quality, disease-free and traceable spat can be supplied to mussel farmers1, 18. However, these hatcheries would need to produce extremely large numbers of spat to sustain what are already significant industries in many countries.
Aquaculture (and fisheries) certification and labelling programmes have become a primary tool to address sustainability issues of farmed seafood, and the development of third party assessment and certification has provided new forms of governance traditionally dominated by state-based regulation1, 2. The growth in the number of certification schemes has led to confusion surrounding the myriad of them out there. To try and combat this, the Global Sustainable Seafood Initiative (GSSI)1 has developed its global benchmarking tool to measure and compare certification schemes and standards performance across seafood production.
Given the prominence of environmental issues as the driver for the development of aquaculture standards, there is an understandably strong emphasis on environmental criteria within them3. Certification enables aquaculture producers to voluntarily demonstrate their responsible farming practices by: complying with national legislation; minimising impact on habitats and wildlife; making the best use of locally available resources; and ensuring the best use of feed and therapeutic products.
Aquaculture certification currently has moderate to high coverage of labour standards (e.g. minimum wage)3, however, increased social and economic requirements related to human rights, gender and sustainable livelihoods are being developed.
Since 2011, a partnership of UK businesses called the Sustainable Seafood Coalition (SSC)4 have been working to ensure all fish and seafood sold in the UK comes from sustainable sources, and aquaculture certification plays a pivotal role. All members need to ensure that the aquaculture source (considering feed mills, hatcheries, and farm sites) is certified under a third party standard, or audited to a members own good aquaculture standard or code of practice5.
The table below looks at some of the major aquaculture certification schemes, including those for bivalves, and if they address the Key Considerations highlighted throughout the profiles. It also highlights which scheme has a standard/s successfully benchmarked by the Global Sustainable Seafood Initiative (GSSI)1.
Read more on aquaculture certification, including that of mussels, after the table.
|Certification Scheme: Description and Links||Governance||Farm Siting||Nutrient Pollution||Feed||Disease, Medicines & Chemicals||Escapes & Introductions||Wild Seed||GSSI Benchmarked|
Founded in 2010 by WWF and IDH (Dutch Sustainable Trade Initiative) the ASC is an independent not for profit organisation with global influence. ASC aims to be the world’s leading certification and labelling programme for responsibly farmed seafood.
The ASC consumer label demonstrates the integrity of the seafood product.
GAA BAP has been certifying aquaculture since 2004, and is administered by the GAA, a nonprofit organization dedicated to advocacy, education and leadership in responsible aquaculture. Aquaculture Facility Certification:
The BAP program employs a star system to signify the integration levels of BAP certification along the aquaculture production chain. These stars are displayed on the BAP logo and appear on packaging for a variety of farmed seafood products worldwide.
GG offers 16 standards for 3 scopes: Crops, Livestock, and Aquaculture. GG has been one of the most widely accepted private sector food safety certification in the world since 2007.
GG Aquaculture certified producers have now the option to use the consumer facing GGN Certified Aquaculture label.
Friend of the Sea (FoS)
FoS is a non-profit NGO, whose mission is the conservation of the marine habitat. FoS is now a leading international certification project for products originated from both sustainable fisheries and aquaculture:
All aquaculture products sold as “organic” in the European Union (EU) have to fulfil the requirements that are laid down by the EU regulations:
This includes products certified according to private organic standards. The EU Organic logo makes organic products easily identifiable by consumers.
Naturland was founded in 1982 when organic agriculture was regarded as a marginal issue. Since the mid-1990s, Naturland has developed standards for different species and production systems in aquaculture:
The Naturland label is intended as a guide for consumers.
The Soil Association was formed in 1946 and champions organic principles and practice.
The Soil Association logo sends a message to consumers that the product is organically produced.
• – Indicates the Certification Scheme addresses the Key Consideration
✔ – Indicates the Certification Scheme has had one or more of its Standards benchmarked against the Global Benchmark Tool Version 1 and recognised by the GSSI Steering Board
Certified Aquaculture Production
Production of certified seafood, both aquaculture and wild catch, has grown rapidly over the past decade and now represents a significant portion of global seafood production. Certified sustainable seafood in 2003 equated to some 500,000 tonnes (0.5% of global production); in 2015 this figure had risen to 23 million tonnes (14% of global production). Some 80% of certified seafood is wild catch, but certified aquaculture is growing twice as fast and is set to dominate growth in certified seafood for the foreseeable future3.
In 2015, certified aquaculture accounted for 6.3% of world aquaculture production. Of this 6.3%, seven species groups were dominant (i.e. salmon, pangasius, mussels, tilapia, prawns, trout and sea bream) and accounted for 97%3. This relatively low global level of certified aquaculture and the narrow range of species groups, is largely due to:
Certification of small-scale aquaculture continues to be an issue, mainly due to the cost and difficulties in complying with standards; key challenges include finance, technical knowledge and organisational capacity. Educating small-scale farmers on how to comply, as well as identifying national policy and regulatory gaps supporting small-scale aquaculture certification, is becoming ever more necessary6. Multiple-farm or ‘cluster’ certification may be a way forward for small-scale producers.
Four schemes are responsible for the majority of certified aquaculture production, namely the Aquaculture Stewardship Council (ASC), Global Aquaculture Alliance Best Aquaculture Practice (GAA BAP), GlobalG.A.P. (GG), and Friend of the Sea (FoS)3.
Certified Mussel Production
In 2015, farmed bivalves accounted for 8% of certified aquaculture globally, and this was dominated by certified mussels3.
Figures provided by the certification schemes themselves and relating to their totals of certified farmed mussels/bivalves break down into:
Enhanced Fishery Certification and Mussels
The Marine Stewardship Council (MSC)11 fishery certification programs are available to all wild-capture fisheries, however those fisheries between pure wild-capture and pure aquaculture are also eligible. These are known as enhanced fisheries, e.g. capture-based mussel aquaculture where the mussel seed is caught from the wild12. Globally, at least 525,549 tonnes of mussels are currently MSC certified13.