3.4 Aquaculture

Overview of aquaculture

Aquaculture is the farming of aquatic organisms (e.g. fish, molluscs) under controlled conditions; it is an alternative to catching wild fish and takes place in both inland and marine areas. Marine aquaculture production has been increasing in Europe (EEA-39) since the early 1990s, mostly due to growing salmon production in Norway (EEA, 2018). For the same period, inland aquaculture has been relatively stable (EEA, 2018). In 2017, EU production of both inland and marine aquaculture was almost 1.5 million tons with a production value of approximately 5 billion EUR (Eurostat, 2019). Overall, though, aquaculture in the EU is of relatively small importance compared to other economic sectors and to other parts of the world (Guillen et al., 2019). In 2017, the production of finfish (particularly, salmon, trout, seabass, carp, and tuna) and molluscs (mussels, oysters and clams) accounted together for almost the entire aquaculture production by weight in the EU (Eurostat 2019). Aquaculture of freshwater fish accounts for about 23 % of total production and is thus smaller than molluscs and crustaceans (ca. 50 %) and marine fish (ca. 27 %) (EC, 2015).

Aquaculture production, both inland and marine, can put significant pressures on European waters related to point and diffuse source pollution, changes in flow, dredging and the introduction of alien species. In the 2nd RBMPs, around 1 400 surface water bodies (mainly rivers) were reported with significant pressures from aquaculture in 20 European countries, with the highest share in Finland, Bulgaria, Hungary, and Czech Republic. Water abstractions for fish farms were the most frequently reported aquaculture pressures, followed by point source pollution, hydrological alterations, and diffuse source pollution.

Three major types of freshwater aquaculture in European waters can be distinguished (European Commission, n.d.; 2012):

  • Extensive pond farming which consists of maintaining ponds (natural or artificial) with low fish density and natural fish feed. Production in extensive farms is generally low (less than 1 t/ha/y). It is practiced across the whole Europe and is particularly common in Central and Eastern Europe.
  • Semi-intensive freshwater aquaculture, whereby the production of the pond is increased by adding supplementary feed, allowing for higher stocking density and production per hectare.
  • Intensive freshwater aquaculture in tanks, where fish are bred until they reach marketable size. There are two techniques: Either river water enters the tanks upstream and leaves downstream, or the water remains in a closed circuit and is recycled and ‘recirculated’ in the tanks.

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In addition, three major types of marine aquaculture exist (European Commission, n.d.; 2012):

  • Extensive brackish water aquaculture in artificial lagoons. The semi-extensive nature is characterised by introducing hatchery fry and providing additional feed.
  • Intensive sea farming: Sea cages hold fish captive in a large pocket-shaped net anchored to the bottom and maintained on the surface by a rectangular or circular floating framework.
  • Intensive aquaculture in tanks: Artificial shore-based tanks can be used to breed marine fish. Recirculation of the water creates a closed and controlled environment that is necessary for optimal production in hatcheries and nurseries for marine species.

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Figure 13           Aquaculture in the EU

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Source(s): EC (2015), Modified from infographic on “Facts and figures on EU aquaculture production and consumption in an EU and global context”, available online: https://ec.europa.eu/fisheries/cfp/aquaculture/facts_en

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Pressures and impacts of aquaculture depend on farm location, type of cultured organism, methods used, intensity, and the sensitivity or vulnerability of the environment to possible pressures (Jeffrey, 2014). Potential impacts of aquaculture on aquatic ecosystems include the following:

Aquaculture releases oxygen consuming substances and nutrients (as excretory products and uneaten fish food) as well chemical contaminants (e.g. disinfectants, veterinary medicinal products, trace metals) into water. The released pollutants can cause de-oxygenation of the water, causing adverse impacts on the benthic fauna and contributing to local algal blooms and eutrophication. Anti-corrosion materials (e.g. copper, zinc-platted steal) and antifouling paint used in aquaculture systems can leak to the sea from fish cages and ropes, with toxic effects on ecosystems.

Cultured organisms which escape from aquaculture production sites can interbreed and compete with wild stocks as well as introduce pathogen infections. Sea lice infestations, for example, can threaten wild fish populations by reducing the survival and reproduction rates of wild salmonids. A number of studies links the presence of fish farms to the outbreak of lice into the environment, particularly in the case of salmon (EC, 2015b).

Fishponds are also often associated with barriers and hydrological alterations which can adversely affect the upstream and downstream migration of fish and other organisms. The presence of barriers may reduce flow velocity and, thus, support eutrophication effects. Barriers may also disrupt the natural transport of sediment, affecting the stability of river beds and related ecosystems downstream.

Water intakes for aquaculture production are associated with water abstractions that can contribute to decreasing groundwater levels and low flow situations in rivers.

Yet, certain aquaculture practices such as extensive exploitation can also have positive effects on the natural environment. By acting as water reservoirs, aquaculture ponds can help to manage flooding during periods of high rainfall and retain water for irrigation during dry periods. Aquaculture can also serve biodiversity purposes. Net-pen farms, for example, can become aggregating sites for wild fish, and act as small-scaled marine protected areas due to the prohibition of fishing within farm leasehold areas.

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Figure 14           Examples of potential environmental impacts of aquaculture

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Source(s): https://www.researchgate.net/publication/288315760_Establishing_the_impacts_of_freshwater_aquaculture_in_tropical_Asia_the_potential_role_of_palaeolimnology/figures, 2015 

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Measures and management challenges

A broad range of management and technical measures exist to tackle the adverse impacts of aquaculture on European waters. At national and regional level, an important regulatory instrument is to set limits to production levels as this can mitigate negative impacts of aquaculture on the water environment (European Commission, 2016). Denmark, for example, decided in 2019 to stop the creation of new aquaculture facilities and the expansion of existing ones in the country. This is because coastal areas and inland waters are overloaded with nitrogen and mitigation measures have not been enough in tackling the issue. In Denmark, there is also government financing to support the removal of weirs on rivers built for use in fish farming facilities.[1]

Improving the siting of aquaculture operations is another management measure to reduce adverse impacts. The Norwegian Aquaculture Act, for example, requires an environmental impact assessment for new aquaculture sites, and it calls on fish farms to be located in areas with better biological recipient conditions, high bearing capacity and generally good self-cleaning properties.[2]

Technical methods, management systems and practices should be incorporated into more formal “Codes of Practice” adopted voluntarily across the whole aquaculture industry (Phillips et al. 2001). Codes of “best management practices” should contain (Phillips et al., 2001):

  • Decreased use of fertilizers, antibiotics and chemicals, their replacement with non- or less harmful substances, or the introduction of new physical biofouling management techniques to reduce the impact of nutrients and chemical discharges (Science for Environment Policy, 2015).
  • Implementation of zonal or area management plans, as part of river basin management plans, to reduce the overall disease and parasites burden on sites (Science for Environment Policy, 2015).
  • Transport of fish as fertilized eggs (not as living animals), to reduce the spread of diseases from introduced aquaculture species (Peeler et al., 2011).
  • Sterilization of farmed species to control the impact of escapees and alien species (Science for Environment Policy, 2015).
  • Treatment of wastewater from closed systems (tanks, ponds), i.e. with techniques comparable to urban and animal farming waste treatment.

Within the EU, production from aquaculture is not expected to grow significantly in the future despite a higher level of subsidies put in place (Guillen et al., 2019). Nevertheless, the present and future adverse impacts of aquaculture on European waters need to be addressed. Aquaculture is recognized as a source of significant pressures on waters, but the Water Framework and Marine Strategy Framework Directives do not contain explicit obligations for aquaculture yet. Further integration of measures on the farm site level with regulatory measures at the river basin, national and EU level is required to reduce the adverse effects of aquaculture production on European waters.

[1] https://salmonbusiness.com/no-more-fish-farms-announces-danish-government/ & https://www.european-views.com/2019/08/denmark-to-halt-development-of-sea-fish-farming-sector/

[2] FAO (2017)  Policy and governance in aquaculture: lessons learned and way forward, Fisheries and Aquaculture Technical Paper 577

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