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1.1   This paper summarises the status of marine aquaculture (mariculture) within the OSPAR region and measures taken to manage its environmental impacts. It briefly notes key messages from the QSR 2010 and IA 2017, and reports on progress since then.

1.2    The analysis covers production of finfish, molluscs, crustaceans, aquatic plants, and miscellaneous aquatic products in the FAO North East Atlantic area, in marine and brackish waters.

Distribution, Intensity and Trends since QSR 2010

Overall trends

2.1   QSR 2010 reported that almost 1.5 million tonnes of farmed fish and shellfish were produced in the OSPAR region in 2006. It noted that production of finfish had grown by over 50% in the previous decade, mainly in Regions 1 and 2, while shellfish farming had remained stable. It anticipated increased activity in all Regions other than Region 5.

2.2   Subsequent developments in the volume of marine aquaculture varied according to individual countries, OSPAR regions, and the type of species being farmed. Production by weight in the OSPAR region increased from around 1.5 million tonnes to around 2.2 mt between 2008 and 2018. Norway remained by far the largest producer. Norwegian production in Regions 1 and 2 accounted for well over half of total OSPAR production weight, and for the bulk of the overall increase since the QSR 2010 analysis (data from FAO 2020a).

2.3   Trends over the decade to 2018 in countries other than Norway varied, with production increasing in some while staying roughly constant in others. In some countries, including France, Netherlands, Germany and Ireland, aquaculture production in marine and brackish waters in the north-east Atlantic region in the early-mid 2010s was lower than 10-15 years previously (FAO 2020a).

2.4    In 2013, the European Commission sought to boost aquaculture through new strategic guidelines, addressing four priority areas: simplifying administration; spatial planning to overcome lack of space; enhancing the competitiveness of EU aquaculture; and promoting a level playing field (European Commission 2013). Member states were to produce multiannual national strategic plans for aquaculture between 2014-2020. However, the EU’s Scientific, Technical and Economic Committee for Fisheries considered that, for the EU as a whole, production goals in the multiannual plans would not be reached (STECF 2018). The EU’s 2020 Blue Economy report noted that EU production by weight had been stagnant in previous decades, even though value had increased. It highlighted negative impacts on shellfish production (see below), while production of higher value species, such as salmon, sea bass and sea bream, had grown (European Commission 2020).

Finfish aquaculture

2.5   Finfish aquaculture in the OSPAR region is dominated by salmon production, particularly from Norway. In 2018, Norwegian production from all marine aquaculture (fish, shellfish and other organisms) was over 1.35 million tonnes, mainly of salmon, around 60% more than in 2008, though relatively little changed since 2012 (FAO 2020a). Norway’s production represented around 1.65% of global aquaculture fish production in 2018; nearly 90% of production (freshwater and marine) was in Asia. Norway (2nd) and the United Kingdom (10th) were among the largest global producers of marine and coastal finfish (FAO 2020b). Norway is the largest global producer of farmed salmon; the United Kingdom is the third largest global salmon producer (FAO 2020c).

2.6   Charts of production in the NE Atlantic from 2008-2018 are shown below1. Behind Norway, the United Kingdom was the second largest producer of finfish, almost entirely due to salmon production in Region 3 and the northern part of Region 2. In Region 3, Ireland is also a salmon producer; The Faroe Islands and Iceland are producers of salmon in Region 1.

Figure 1 - Production of farmed finfish in the NE Atlantic, 2000-2018

Figure 2 - Production of farmed salmon in Norway, 2000-2018

DK includes Faroe Islands 78 900 tonnes

Figure 3 - Production of finfish in NE Atlantic in 2018, by country

Shellfish aquaculture

2.7   The largest producers of shellfish were Spain in Region 4 (mainly mussels) and France in Regions 2, 3 and 4 (predominantly oysters). Spain (6th) and France (8th) were among the largest global producers of marine and coastal molluscs (FAO 2020b).

2.8   Shellfish cultivation also occurs elsewhere in Regions 1, 2 and 3. Cultivation techniques vary: for example, mussel production in Spain is largely ‘off-bottom’, using ropes fixed to floating rafts (STECF 2018). In the Netherlands, seeds are collected with similar techniques using ropes fixed to poles or anchors. For maturing of the seeds, mainly ‘on-bottom’ techniques are used, using natural designated beds. These may have different environmental impacts – for example, during maintenance and extraction of species (for more detail see OSPAR 2009and European Commission 2012).

2.9   The STECF analysis noted the impact of factors such as shellfish mortalities, weather conditions and diseases. The EU’s 2020 Blue Economy report referred to impacts of disease and lack of seed on mussels and other shellfish in 2013, although production had recovered subsequently (European Commission 2020). For 2019, FAO reported that Spanish mussel production was likely to reach a new high; conversely, the hot summer in France had an impact on oyster mortality, with lower production expected in 2020 (FAO 2019). Since 2008, significant mortality of juvenile oysters in France has been experienced, with the OsHV1 μvar virus being an important factor (STECF 2018).

Figure 4 - Production of farmed molluscs in the NE Atlantic, 2000-2018

Figure 5 - Production of farmed molluscs in the NE Atlantic, 2018, by country

Other aquaculture

2.10   Other marine aquaculture products are small. FAO estimates that 346 tonnes of crustacea were produced in the North-East Atlantic in 2018, the majority in Spain. Around 700 tonnes of aquatic plants were farmed, mainly brown seaweeds, the majority in France (FAO 2020a).


2.11   The maps below illustrate the distribution of marine aquaculture in OSPAR regions.

Figure 6 - Finfish production sites and locations, (Source EMODnet 2020)

Figure 7 - Shellfish production sites and locations, (Source EMODnet 2020)

2.12   The European Environment Agency’s indicator assessment on aquaculture includes total marine production as a function of coastline length as a rough indicator of the potential environmental impacts of marine aquaculture. However, it notes that these figures do not take account of the pressure exerted by different production systems or local conditions. Nor is aquaculture evenly distributed along the coast (EEA 2019).

Economic value


3.1   The total value of marine aquaculture production in the OSPAR area has risen sharply over the past decade, mainly driven by increases in higher value species, notably salmon. Like production volumes, the economic value is dominated by Norway, with salmon production worth over €6.7 billion in 2018, compared with €1.9 billion in 2008 (Eurostat 2020). The value of aquaculture production in Norway exceeds that of the entire EU production of fish and shellfish (Eurostat 2019). Salmon is the largest single fish commodity in world trade of fish and fish products, with growth driven by demand both in developed and developing markets (FAO 2020b).

3.2   The United Kingdom had the second highest marine aquaculture production value among OSPAR countries, again dominated by salmon. The value of UK salmon production grew in the decade to 2018 from around €500 million to around €1 billion. Increases in production value of salmon were also reported in Ireland and Iceland (FAO 2020a).

3.3   Eurostat figures show a general upward trend in the value per tonne of salmon over the period, particularly in earlier years. The FAO reports that farmed Atlantic salmon is one of the most profitable and technologically advanced aquaculture industries in the world, backed by coordinated international marketing and product innovation. Factors limiting supply, such as site availability and regulatory constraints, have led to price increases. Shorter term prices can be quite volatile – for example, the FAO’s Globefish information exchange reported steep falls in global salmon prices in the first half of 2019, linked to good production in Norway and Chile, but prices reaching near record levels later in the year, driven by strengthening demand in traditional and emerging markets. (FAO 2020b, 2020c).

3.4   In Spain and Portugal, turbot (land-based production in tanks) was the largest component of finfish production value in the North East Atlantic region, but did not show a significant increase in value over the decade, reflecting relatively stable average prices over the period (STEFC 2018).

3.5   Finfish aquaculture is capital intensive, with relatively large investment in physical equipment and stocking of cages compared to the input of labour. Labour productivity in sea cage farms is high compared to other EU aquaculture segments (STEFC 2018).


3.6   Changes in shellfish production value have been less substantial than for finfish. France’s production of molluscs in the NE Atlantic was worth over €400m across the decade, making France the third highest aquaculture producer, in terms of value (finfish and shellfish) in the OSPAR region. The value fluctuated year on year, with a dip in 2014 and 2015, but did not increase significantly across the period. Nearly three-quarters of the value in 2017 and 2018 was from oysters, with most of the remainder due to mussels. Shellfish production (mainly mussels) accounted for over half the production value in Spain, and showed some increase over the decade (Eurostat 2020).

USD 000

Figure 8 - Value of marine aquaculture in NE Atlantic, 2018, by country

The table below shows marine aquaculture employment statistics in OSPAR countries in 2018. Source: European Commission 2020, except for Norway (Statistics Norway 2020), UK (2017 figures from European Commission 2019)
Employees in finfish aquacultureEmployees in shellfish aquaculture
France15213 841
Ireland1801 719
Norway7 903
Portugal2572 362
Spain2 37914 465
United Kingdom1 900700

3.8   For some activities, such as shellfish production in Spain and France, the sector has a significant social role as a local employer, often through small family owned businesses, with a significant component of part-time and seasonal working. In Germany and the Netherlands, however, mussel production is based on relatively large companies (STFEC 2018).

Future trends

4.1   While growth in global aquaculture was lower in the past decade than the high rates of the 1980s and 1990s, it is still an expanding sector globally. The FAO’s 2020 report on the state of the world’s fisheries and aquaculture projected an increase of around 32% in world aquaculture between 2018 and 2030. This is a slower rate of growth than in the previous decade, due to factors such as factors such as limits on production sites, better environmental regulation, aquatic diseases, and decreasing productivity improvements. Nevertheless, aquaculture, rather than capture fisheries, is expected to remain the driving force behind overall increases in global fish production2. The FAO also projected that fish prices generally would remain high, with increases in nominal terms albeit with some decline in real terms (FAO 2020b).

4.2   Within the OSPAR region, overall projections of future aquaculture volumes are, as now, highly influenced by what happens in Norway. The FAO’s 2020 report projected an increase of nearly 20% in Norwegian aquaculture production between 2018 and 2030, to over 1.6 million tonnes (FAO 2020b). For the longer term, the Norwegian government’s 2017 ocean strategy refers to an estimate of the potential for a six-fold increase in revenue for Norwegian biomarine industries by 2050, with a large proportion of this growth from aquaculture. As well as salmon, this could include new species and algae such as seaweed and kelp (Norwegian Ministry of Trade, Industry and Fisheries 2017). An update to the strategy refers to a new system for adjusting aquaculture production capacity to facilitate predictable and environmentally sustainable growth of salmon and trout farming. Norway is also refining its regulatory system to facilitate new developments in offshore aquaculture (Norwegian Ministry of Trade, Industry and Fisheries 2019). Research informing the ICES Working Group on Scenario Planning in Aquaculture referred to a Norwegian expansion target of a fourfold increase by 2050 (Froehlich et al 2020). The ICES ecosystem review of the Barents Sea notes that aquaculture is increasing along the coasts and in the fjords of northern Norway and Russia, with several commercial fish farms producing salmon, trout and shellfish (ICES 2019).

4.3   Other salmonid producers also have growth ambitions. For example, the Scottish Government is supporting the aquaculture industry in its growth strategy, which aims to double the economic contribution of the aquaculture sector by 2030 (Aquaculture Industry Leadership Group 2017). The Icelandic Government has stated an expectation that its production will double over the next few years from 2017 levels, and there is scope for further expansion (Government of Iceland 2020). Some growth in salmon aquaculture was also envisaged in Ireland’s national plan for aquaculture development (Department of Agriculture, Food and the Marine 2015). A growth strategy for English aquaculture (finfish and shellfish) is being prepared under the Seafood 2040 initiative (Seafish 2018).

4.4   In relation to shellfish production, the FAO has reported an increase in current demands for bivalves, helping to drive increases in Spanish mussel production (FAO 2019). Offshore production of shellfish is also a possibility (Collins et al 2020, EU TAPAS 2020).

4.5   Within the EU as a whole, prospective increases in demand within and beyond Europe are seen as an opportunity to expand European aquaculture. The EU’s 2018 Economic Report on the EU Aquaculture Sector anticipated higher future demand for fish driven by population increase and income, and by awareness of health benefits of fish consumption (STFEC 2018). FAO projected an increase of 13% between 2018 and 2030 in EU aquaculture (including freshwater as well as marine) (FAO 2020b). The EU’s Blue Economy report 2020 considered it realistic to expect a growth of EU aquaculture products with a high degree of control, such as finfish in closed systems, while shellfish production in open waters would be more influenced by environmental factors (European Commission 2020). At present, most planning for expansion is relatively short-term; ICES work on scenario planning in aquaculture reported that, of OSPAR countries, only Spain (a tripling of production by 2030) and Norway had strategic plans for aquaculture growth out to 2030-2050 (Froehlich et al 2020).

4.6   The scale of any growth will in practice be influenced by several factors. Future economic developments globally and in Europe will have an impact. For example, the FAO’s January 2020 update on world seafood markets notes that these markets are highly sensitive to wider economic conditions, and reported that in 2019, Brexit-related economic challenges and trade issues had contributed to a slowdown in seafood trade in the European Union. Global economic uncertainties remain, including the impact of Covid-19 (FAO 2020c). International competitiveness will also influence the sector’s economic performance. The EU-funded Aquaspace project noted that a strong competitive advantage of EU aquaculture is related to the quality and sustainability of its products, and future success depends in part on maintaining healthy marine environments (O’Hagan 2017). For example, Spanish mussel producers now have a certification of Protected Denomination of Origin in the EU, which will help with market image (FAO 2019).

4.7   There are also uncertainties or constraints specific to aquaculture. Aquaculture may be competing for space with other uses such as tourism and recreation, shipping, fishing, aggregate extraction and energy production, although there may be some synergies with offshore wind structures (European Commission 2020). The Aquaspace project advised that while improvements in nutrition and feed, species growth, disease treatments and production methods can achieve some production expansion, more space for aquaculture would be necessary if growth potential were to be achieved. The project looked at how to optimise and increase the area available for both marine and freshwater environments, through an ecosystem approach to aquaculture. For example, it noted that development of maritime spatial planning would be important if production is to take place offshore (O’Hagan et al 2017). Similar issues are identified by ICES work on aquaculture (Froehlich et al 2020). A review of global experience of using an ecosystem approach conclude that it has promoted greater sustainability in aquaculture but has had varying degrees of uptake (Brugère et al 2018).

4.8   The FutureEUAqua project, supported by the EU’s Horizon 2020 programme, is working on ways to promote the sustainable growth of climate-change resilient, environmentally-friendly aquaculture of fish and low level trophic organisms. Areas of interest include genetic selection, ingredients and feeds, monitoring technologies, innovative products, and optimal production systems (more details at FutureEuAqua 2020). In the case of feeds, while fish meal and fish oil were traditionally the bulk of feed, recent years have seen a shift towards use and development of other sources including terrestrial plant- or animal-based proteins, seafood processing waste, microbial ingredients, insects, algae and genetically modified plants (e.g. Costello et al 2020). According to the Norwegian Government, around 70% of ingredients in salmon feed are vegetable, while the remainder is from marine raw materials, including trimmings and by-products from fisheries (Norwegian Ministry of Trade, Industry and Fisheries 2019).

4.9   The EU’s TAPAS project has looked at the potential for offshore aquaculture of species such as of salmon, blue mussel and oyster. It suggests that large areas of those seas could be used for aquaculture, if logistical and administrative issues could be overcome (Wallhead et al 2020). An ICES working group on open ocean aquaculture (WGOOA) is looking at issues such as environmental influences, technical challenges, system design, site selection, and economic aspects, with the aim of developing a roadmap for future open ocean aquaculture.

4.10   Historically, marine aquaculture in the OSPAR region has been dominated by a few species. The EU Aquaspace project noted that more understanding and new strategies would be needed if this were to change, and that failed attempts to produce Atlantic cod (Gadus morhua) in Norway, United Kingdom and Iceland illustrate the difficulty of introducing new species economically to aquaculture. In addition, new species may not deliver the same commercial returns as existing species (O’Hagan 2017). As well as aquaculture of fish species, the idea of managed cultivation of seaweed is a potential new development in areas such as the Netherlands. Expansion of seaweed aquaculture has potential as a source for food, animal feed, fuel, cosmetics, and pharmaceuticals, but understanding of possible impacts such as disease, alternation in population genetics and alterations to the physio-chemical environment still needs to be developed (e.g. Campbell et al 2019).

4.11   Climate change is a significant uncertainty. Possible negative impacts include loss of production or infrastructure due to extreme events, diseases, toxic algae and parasites; decreased productivity due to suboptimal farming conditions; environmental factors affecting natural production of oyster spat or mussel seed; the ability to control issues with salmon farming such as sea lice and escapees; limited access to feeds from marine and terrestrial sources; loss of sites due to sea level rise; or the effect of ocean acidification on shellfish. However, there is also the possibility of positive impacts (e.g. FAO 2018, STECF 2018).

4.12   The EU-funded CERES project has reviewed the potential impacts of climate change on European aquaculture, including direct effects of changes in temperature, pH, dissolved oxygen concentration and salinity, as well as developing tools to project the occurrence and risk of indirect effects such as disease, algal blooms, and jellyfish (synthesis report at Peck et al 2020). The synthesis report also summarises the impact of scenarios in the productivity by mid-century and end-century of certain finfish and bivalve species used in aquaculture, in the economic performance of aquaculture sectors, and in the vulnerability to climate change of aquaculture in individual countries. Projected impacts vary according to different scenarios and sectors; this is illustrated further in individual case studies produced by the project (CERES 2020).

4.13   This complexity is also evident in other reports, for example:

  1. in Norway, salmon aquaculture may be vulnerable to temperature rise exceeding the thermal optima, including in extreme events such as heat waves, although there could be positive effects on growth rates in some areas. The socio-economic outcomes as well as adaptation strategies are difficult to assess, however, given the diversity of farming sites and evolving technology (Climefish 2019a);
  2. temperature increase was likely to increase growth rates for most UK farmed species, but issues such as sea lice and gill disease in salmon, or harmful algal blooms and jellyfish swarms are likely to get worse. Overall, technical and management changes in the rapidly evolving aquaculture industry make long-term impacts of climate change difficult to forecast (Collins et al 2020);
  3. higher temperatures and increasing summer northerly winds could have positive effects for mussel aquaculture in north-west Spain, but could also increase harmful algae. Extreme weather events could cause detachment of mussels or loss of mussel rafts. Predicting the socio-economic consequences is challenging (Climefish 2019b).

QSR 2010 and Intermediate Assessment 2017

5.1   QSR 2010 outlined several environmental issues linked to marine aquaculture, such as:

  1. genetic interactions between farmed fish and wild stocks;
  2. transfer of parasites and diseases;
  3. the spread of non-indigenous species;
  4. the dependence on industrial catches of wild fish to feed fish in aquaculture;
  5. eutrophication as a result of nutrient enrichment from feeds and effluents;
  6. competition between escaped farmed fish and wild stocks for spawning grounds;
  7. release of chemicals used to prevent equipment fouling or to treat parasites and diseases;
  8. displacement of bird and seal populations as a result of scaring devices;
  9. impacts from shellfish harvesting and from mussel seed collection;
  10. litter.

5.2   The QSR referred to the use of best environmental practice to reduce inputs of chemicals, and measures under OSPAR’s Eutrophication, Hazardous Substances and Biodiversity and Ecosystems Strategies as a way to monitor, assess and regulate impacts. It also noted the existence of national and EU measures, and risk assessment protocols from ICES on the use of non-indigenous species in aquaculture.

5.3   QSR 2017 did not specifically cover aquaculture, but its discussion of eutrophication in OSPAR’s Third Integrated Report on the Eutrophication Status of the OSPAR Marine Area commented on nutrient inputs from aquaculture - see paragraph 6.12 (OSPAR 2017).

Analysis of specific pressures, impacts and measures

Cross-cutting issues and measures

6.1   The potential environmental impacts of finfish and shellfish aquaculture listed in paragraph 5.1 were described in OSPAR 2009. The potential impacts remain substantially the same, and so that analysis is not repeated in depth here. The existence of a potential pressure does not necessarily mean that harmful impacts will occur, but means that assessment of the location and management of individual facilities is important in limiting pressures.

6.2   Environmental pressures from aquaculture vary considerably depending on the species being cultivated and the production methods being used. For example, at a general level, the pressures from finfish farming are very different to those from shellfish cultivation. The scale and location of impacts can be particularly important to consider for aquaculture, and the impact of potential pressures is strongly influenced by local environmental circumstances, including hydrographic conditions, and the nature and sensitivity of local ecosystems. This means that assessment of the location and management of individual facilities is important in limiting pressures (OSPAR 2009; European Commission 2012, ICES 2014).

6.3   Measures to mitigate environmental impacts, including modelling approaches, have moved forward, although knowledge gaps remain.  The ICES Working Group on the Environmental Impacts of Aquaculture (WGEIA) reported on its work in December 2020 (ICES 2020). Its report contains an extensive summary of different environmental impacts and how these are regulated and monitored in different countries. The report highlighted areas where improved aquaculture management can lead to better environmental performance, and made recommendations for prioritised research. The report is referred to further below.

OSPAR measures

6.4   OSPAR has taken few specific measures on aquaculture. OSPAR guidelines on reporting nutrient discharges/losses from marine and freshwater aquaculture plants were issued in 2004 and revised in 2018 (OSPAR 2018). PARCOM recommendation 94/6 covers the reduction of inputs from potentially toxic chemicals used in aquaculture. In 2006 , OSPAR agreed that, for the time being, implementation reporting on PARCOM Recommendation 94/6 could cease, but that if there were significant developments in the aquaculture industry in the future, the need for implementation reporting should be revisited.

6.5   In addition, managing pressures from aquaculture is relevant to OSPAR action on species and habitats. OSPAR’s recommendation on protection and conservation of the Atlantic Salmon covers the need to assess measures to manage threats from escape and accidental release from fish farms, and spread of diseases and parasites (OSPAR 2016). There have been no OSPAR measures specifically on non-indigenous species from aquaculture.

6.6   OSPAR work on litter is dealt with in paragraph 6.23 below.

Cross cutting international and national measures

6.7    Within the European Union, key overarching directives have set a framework within which aquaculture operates:

  1. The Water Framework Directive, which requires member states to take measures to prevent deterioration of the ecological and chemical status of waters, restore polluted waters, reduce pollution and cease or phase out inputs of hazardous substances3.  Its scope includes coastal waters one nautical mile out to sea and, for chemical status, out to twelve nautical miles. It also contains requirements for monitoring and management of shellfish protected areas;
  2. The Marine Strategy Framework Directive aims to achieve good environmental status (GES-MSFD) in marine waters by 2020;
  3. The Environmental Impact Assessment Directive and the Strategic Environment Assessment Directive, which set procedures to ensure that implementation of plans, programmes or projects, including aquaculture, takes account of their likely environmental effects;
  4. The Birds Directive, which protects wild birds and their habitats, and the Habitats Directive, which protects rare, threatened or endemic animals, plants and habitats;
  5. The Aquatic Animal Health Directive, covering health requirements and disease prevention and control in aquaculture.

For EEA countries, some of these directives apply but in other cases, national legislation provides the overarching framework.

6.8   The European Commission has produced guidance on sustainable aquaculture in the context of the Natura 2000 network (European Commission 2012) and on the application of the WFD and MSFD in relation to aquaculture (European Commission 2016). These provide information on regulatory good practice and suggestions to national authorities and industry about the requirements of the Directives in relation to aquaculture. More detailed background on sustainable aquaculture in the context of WFD and MSFD can be found in Jeffrey et al 2014.

6.9   The Natura 2000 guidance notes that there are many well-known Natura 2000 areas where aquaculture activities are taking place sustainably, including the Wadden Sea in the Netherlands, Arcachon in France, the Sado Estuary in Portugal, Doñana in Spain, shellfish culture in England and Wales and several Lochs in Scotland. It emphasises the need for thorough assessment of the potential impacts of aquaculture, including careful consideration of the location of facilities.

6.10   The guidance on WFD/MSFD covers various pressures including benthic impacts and nutrients; diseases and parasites; chemical discharges; escapees and non-indigenous species; and physical impacts and predator control. The guidance is being built on further by the EU TAPAS project, which runs from 2016 to 2020 and is looking at sustainability issues in aquaculture, including development of an aquaculture sustainability tool box to support planning and licensing decisions (EU TAPAS 2020).

6.11   The multi-faceted and site-specific nature of the environmental impacts of aquaculture mean that the primary route for managing these impacts is through the assessment, including through modelling, of individual projects or plans under individual countries’ regulatory systems – for example, considering the carrying capacity of the environment, stocking levels, nutrient dispersal, physical impacts on the environment, or the interaction with threatened species. This paper does not seek to go into detail on these mechanisms. There are also technical developments in the management of aquaculture – for example, potential moves towards more use of recirculating aquaculture systems for growing larger fish before stocking sea pens (Jeffrey et al 2015); again, the paper does not cover these in detail. Some developments in relation to several of the issues highlighted by OSPAR and others are, however, summarised below.

Specific impacts and measures - finfish

6.12   Finfish aquaculture in large net cages, such as those used for salmon, have the potential for multiple environmental effects. This could include accumulation of organic waste, such as excretory products or uneaten food, affecting factors such as sediment chemistry and benthic organisms, and nutrient enrichment through nitrate, ammonia, phosphate and organic carbon, leading to local eutrophication. There may also be physical impacts of cages, or harm to predators attracted by the farmed fish.

Table 2. Environmental impacts of fish farms: sources, types, receptors, effects and possible controls (OSPAR 2009).
SourceTypeImpact OnEffectControl
Uneaten food, faeces, pseudofaeces, scales.Solid organicSeafloor +/-100mEnrichment, elimination of fauna. H2S outgassingImprove feeding, site rotation and harrowing
Excreta and food leachateSoluble organicWater – generally localisedEutrophication and toxic ammoniaSite selection and rotation
Harvesting and seed dredgingEcological change PhysicalFish, benthic communities, seabed habitat damage.Wild and commercial stock viability and habitat destructionFisheries and seed management
Therapeutants, antifoulants, feed additives, disinfectants, net washingsChemical contaminationWater, sediments and biotaToxicity to organisms, water and sediment quality, food chainProper usage, good husbandry, site selection and mechanical cleaning
EscapeesEcological changeWildfish, ecosystem, and habitat.Disease, sea lice, genetic, competition and displacementSite and equipment selection, maintenance, marking, recapture, containment
StockDisease parasites reservoirWildfish and wild shellfishInfections and disturbanceSite selection, management, husbandry, treatment
Translocation of stockAlien speciesEcosystems and habitatsDisplacement, competitionCertification of stock, containment and restriction of movement
PredationBehaviouralBirds and mammalsMortalities, behaviouralPredator nets, scarers
Access and onsite activityVisual disturbance, compactionBirds, mammals, seabed,Disturbed feeding and roostingLimited access (frequency and timing), single access route
Space utilisationPhysical PresenceOther UsersVisual impact, navigation, other usersSite selection, spatial planning, marking

6.13   The nutrient inputs from the largest finfish aquaculture systems in the OSPAR region were referred to in OSPAR’s 2017 report on eutrophication (OSPAR 2017). In some areas, aquaculture can be a significant source of nutrients. For example, Norway had reported increases in ammonia inputs from aquaculture into the Norwegian Sea, Barents Sea and North Sea. Fish farms in the north and west of Scotland may be a significant source of nutrients in areas where freshwater inputs are low; the report noted that while they may not be available for immediate use by algae or higher forms of plant life they are likely to make an important contribution to biogeochemical cycling.


6.14   The ICES WGEIA concluded that, in relation to organic waste, the ecological effects on the soft sediment habitats beneath the majority of fish farms are well understood and can be measured and regulated. Trends towards more dispersive, high current sites, including open ocean installations, require more understanding of regional effects and impacts on hard bottom sites. However, the trend towards more dispersive sites should help to mitigate impacts from organic waste from aquaculture (ICES 2020).

Impacts on wild fish – escapes and diseases

6.15   Advice from ICES to OSPAR in 2014 considered the interactions between wild and captive fish stocks, such as the impact of escaped stock on wild fish through interbreeding and competition; transmission of disease; and the ecological consequences of using antibiotics, pesticides and disinfectants, and anaesthetics (ICES 2014). A report from the North Atlantic Salmon Conservation Organisation concluded that there was growing evidence that salmon farming could affect wild salmon populations, through the impacts of sea lice as well as farm escapees (NASCO 2016).

6.16   Escapes of farmed fish, resulting from operations or from incidents such as technical defects, accidents or bad weather, is a particular threat from finfish aquaculture, with potential impacts on the genetic structure of wild populations, and on transfer of disease. Climate change could add to the risks of storm events.

6.17   The EU Prevent Escape project, running from 2009-2012, looked at the scale of this issue and ways to manage it. One aspect looked at escapes from salmon production in Norway following the introduction of a new technical standard for sea cages in 2006. The number of escaped salmon declined from over 600,000 per year between 2001 and 2006, to less than 300,000 fish per year between 2007 and 2011. Based on this success, it recommended that European policy-makers introduce a technical standard for sea cages, combined with enforcement mechanisms (Prevent Escape 2013).

6.18   In Norway there is a national monitoring programme for escaped salmon, and fish farmers have to report escapes to the national authorities. Numbers of escapees vary between years, and can be affected substantially by large events. In 2019, nearly 285,000 salmon escaped from Norwegian aquaculture: of this number, nearly 180,000 were from one event involving fish of 0.02kg, and another 50,000 from an event involving fish of 4kg (Barentswatch 2020). The figure below is taken from this source.

Figure 10 Escaped farmed fish in Norway 2008-2019

Figure 10 Escaped farmed fish in Norway 2008-2019

6.19   In the UK, the Scottish Government introduced new technical standards to help prevent escapes of farmed fish; all equipment had to meet that standard by 2020. It covers factors such as mooring of pens, construction of pens, net design and construction, and feed barges. Escapes of farmed fish are reported to the national authority (Marine Scotland 2015). The Scottish database on escapes reports over 47,000 escapes of salmon in 2018 and over 60,000 in 2019. Over 73,000 salmon escaped in an incident in January 2020 associated with storm damage (Scotland’s Aquaculture 2020).

6.20   Although there is substantial knowledge about escapes of farmed salmon and their impacts, ICES noted the scope for improvements in reporting of escapes, defining the cause of escapes, and understanding the impacts on wild populations. It also referred to development of approaches such as the use of sterile salmon and of closed containment systems. Knowledge about the impact of escapes of species other than salmon is limited (ICES 2020).

6.21   In relation to diseases, ICES advice to OSPAR noted that mitigation measures to mitigate disease operates at two levels: area-based (coordinated stocking, harvesting, and fallowing) and farm-based (vaccination, early pathogen detection, veterinary prescribed treatments, and depopulation or early harvest in the event of viral disease). It also referred to problems in managing sea lice transmission due to increasing parasite resistance to chemicals used for control. It suggested establishing management zones incorporating biomass limits and coordinated management (ICES 2014).

6.22   According to the Norwegian Government, regulations relating to sea lice have been tightened in recent years and there are currently very low levels of sea lice in Norwegian facilities. Increase in salmon and trout production is regulated through a ‘traffic-light’ system relating to sea lice prevalence. Fish farms have to report the levels of sea lice. Nonetheless, sea lice can be a limitation on aquaculture growth: - for example, the Norwegian government recently published a new map of areas where aquaculture growth is permitted and others where it is not allowed to expand further, or even has to cut back. In Scotland, if a weekly average adult female sea lice count per fish of 2 (or above) is recorded on any fish farming site, this must be reported to the authorities within a week and action has to be taken to reduce the level of lice (Marine Scotland 2019).

6.23   Despite substantial knowledge about sea lice and their impacts, uncertainties remain, such as the potential influence of climate change on lice and on their interaction with wild hosts, population level impacts of lice on wild fish, the fate, persistence and toxicity of chemical treatments for lice, and pest management strategies. The use of cleaner fish (lumpfish and wrasse) as a biological control for sea lice has increased in recent years, with over 60 million used in Norway in 2019. The sustainability of wrasse fisheries, and the genetic interaction of escaped cleaner fish with wild populations, are areas meriting further investigation (ICES 2020).  There are also mechanisms of physical control such as thermolicers, using well boats, lasers and using submersible cages with swim ups to keep salmon below the sea-lice belt (Cefas, pers.comm).

6.24   Finfish aquaculture can also expose wild fish to viral or bacterial pathogens, although assessing the impact on wild populations is difficult for endemic pathogens. Risk assessments, monitoring and good husbandry practices are tools for preventing and managing disease outbreaks. Data and understanding varies for different pathogens (ICES 2020).

Antibiotics, pharmaceuticals and other toxic substances

6.25   ICES advice on interactions between aquaculture and wild fish noted that some resistance to antibiotics had been detected in bacteria. For pesticides used in aquaculture, negative impacts on non-target organisms were considered to be minor, but resistance in sea lice to some treatments had led to increased use of flubenzurones and of cleaner fish (wrasse and lumpfish). Flubenzurone residues had been found in wild crustaceans, but the significance of the impacts was not known. ICES described management options to reduce antibiotic use in fish farms, notably vaccine use, better biosecurity, reduction of waste feed, and different diets. The effectiveness of these depended on local circumstances (ICES 2014). ICES reports that significant knowledge gaps remain relating to the persistence of therapeutic treatments, the impact of long-term or multiple exposures during the life cycle of nontarget species, and the effects of exposure to multiple medicines on non-target species and the ecosystem (ICES 2020).

6.26   The EU TAPAS project has looked at farm-scale modelling tools for the evaluation of the ecotoxicological impacts of potentially toxic substances such as antifouling agents, veterinary medicines and other compounds. It compiled, developed, and tested environmental thresholds for potentially toxic substances used in EU aquaculture, and developed assessment tools for use by farms and regulators (EU TAPAS 2020).

Specific impacts and measures – shellfish

6.27   Shellfish culture depends on the natural environment for the supply of feed, and can make a positive contribution to the local environment, through filtration and nutrient recycling. Potential pressures do exist, however. For example, suspended shellfish culture (e.g. of mussels) can potentially lead to changes in local sediments or the water column, or, if too intensive, could strip primary production from areas being farmed. Smothering of intertidal areas with detritus could also be a problem. Collection of mussel seed for aquaculture (e.g. poorly managed dredging) can have an impact on wild mussel populations – for example, in the past seed collection was associated with declines in mussel beds in the Wadden Sea (European Commission 2012; Common Wadden Sea Secretariat 2010).   There is also potential for impacts of shellfish aquaculture on sensitive species of birds or mammals, for example through alteration in ecosystem functioning, disturbance, exclusion, or entanglement (ICES 2020).

6.28   Aquaculture also has the potential to introduce non-indigenous species which may affect the natural environment – the Pacific Oyster, Crassostrea gigas, has established feral populations since its introduction for aquaculture in various countries in the OSPAR region (Miossec et al 2009). A study for the Netherlands government reported that shellfish transport had been the route for introduction of several non-indigenous species into north-west Europe (Gittenberger et al 2017). In Scotland, the invasive sea squirt Didemnum vexillum has been recorded on oyster bags (NatureScot 2020)4.

6.29   Knowledge gaps and areas for future research identified by ICES include ecological carrying capacity, the impacts of different methods of bivalve culture in different environments, the use and control of non-native species, unexplained variation in the availability and settlement of seed mussels, and impacts on birds, mammals and sensitive habitats (ICES 2020).

Litter – a cross-cutting issue

6.30   Aquaculture, whether of finfish or shellfish, can be a source of marine litter. OSPAR’s 2014 regional action plan on marine litter included an action to identify options to address key waste items from aquaculture. A scoping study produced in taking forward that action (OSPAR 2019) noted that there are no good estimates of the amount of litter produced from aquaculture. The study particularly considered litter from shellfish farming, including nets, bags and other plastic equipment. A survey of OSPAR countries showed that regulation relating to waste management was included in permits to farm shellfish or fish. Awareness raising, voluntary initiatives and economic incentives, such as extended producer responsibility, were among areas recommended for further development, including through pilot projects.

6.31   The European Union is supporting the Aqua-Lit project, which is working to better understand the extent of litter from aquaculture, measures to prevent and reduce it, recycling solutions for plastic waste, and associated policy mechanisms (Aqua-Lit 2020). Approaches to tackling plastic pollution were also discussed in a report for the Aquaculture Stewardship Council (Huntington 2019).

Conclusions for OSPAR

Key messages
  • while aquaculture production in the OSPAR area has generally stabilised since the early 2010s, there are ambitions for substantial increases, notably in Norway.  OSPAR may want to increase its understanding of the potential impacts of future growth;
  • OSPAR and its contracting parties may wish to consider future engagement with ICES to identify and address knowledge gaps of particular significance for environmental management of aquaculture;
  • the implications of new or expanded forms of aquaculture, including development of offshore aquaculture or of new species, should also be considered;
  • the viability of some aquaculture systems (e.g. shellfish farming) is dependent on wider environmental quality concerns in which OSPAR takes an interest.
Distribution and intensity of activity

Finfish aquaculture in the OSPAR convention area is dominated by salmon production. Norway is by far the largest producer of salmon in the OSPAR area (and the largest producer globally), followed in the OSPAR area by the United Kingdom and the Faroe Islands.   Spain and France are globally significant producers of molluscs (mussels and oysters).  (Paragraphs 2.5 – 2.7)


Production trends have varied according to species and country.  Salmon production in Norway rose substantially in the years to 2012, but has stabilised since.  Shellfish production fluctuated in the past decade, but there have been recent increases in Spanish mussel production.  (Paragraphs 2.5, 2.6, 2.9, 4.4)
Norway has ambitious plans to increase aquaculture production; other salmonid producers also have plans for growth.  Some growth is also projected for other countries and aquaculture species.  (Paragraphs 4.2 – 4.7)
There are prospects for aquaculture in new offshore environments and involving different species (e.g. seaweed).  (Paragraphs 4.9 – 4.10)

Economic value

The economic value of the sector is dominated by Norwegian salmon, worth over €6.7 billion in 2018.  For some activities, such as shellfish production in Spain and France, the sector has a significant social role as a local employer.  (Paragraphs 3.1- 3.8)

Pressures and impacts

Pressures from aquaculture can include nutrient enrichment, impacts on wild populations from escaped or introduced fish or shellfish, the transfer of parasites, diseases or non-indigenous species, the impacts of chemicals, litter,  and impacts on sensitive species or ecosystems.   (Paragraphs 6.1 – 6.31)


Site-specific decisions on location and management of aquaculture, via assessment of projects under individual countries’ regulatory systems, are the primary measure for addressing the environmental impacts of aquaculture.  Understanding of how to manage impacts has grown over the past decade, although some knowledge gaps remain.  Paragraphs 6.1 – 6.31)

Table 3
Relative intensityHHMML
Trend since 2010
Forecast trend to 2030
Confidence assessmentVery high
Very low

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1 Data in figures 1-4 from FAO 2020a, and are for total NE Atlantic, including Baltic Sea

2 There are also significant investments globally in recirculating aquaculture systems (RAS) for land based production.  These could feed into increases in production from existing sea sites by use of hybrid (part RAS part sea) and shortening crop cycles in the sea (Cefas pers. com).

3 The WFD provides for local mixing zones in relation to aquaculture facilities, where levels of priority substances are allowed to exceed environmental quality standards; this involves defining a boundary beyond which these standards must not be exceeded (European Commission 2016).

4 D. vexillum is also spread by boating movements.