The environmental impacts of open-net salmon farming: A critical review and recommendations for policy in Canadian aquaculture

By: Leigh Merotto, BASc MHSc 

OHEA would like to congratulate Leigh Merotto on winning the graduate category of the Dr Elisabeth Feniak Award for Excellence in Technical Writing 2018 presented by the Canadian Home Economics Foundation. Leigh's paper was just published in the JHEIA.

​About the author
​
I am currently completing a Master of Health Science in Nutrition Communication degree at Ryerson. This program is accredited by Dietitians of Canada, allowing me to practice as a Registered Dietitian upon finishing the program this December 2018. It includes an 8-month integrated internship program which has allowed me to gain experience working in many areas of nutrition care including sport nutrition, diabetes, cardiovascular health, mental health, and digestive diseases with a variety of population groups. After finishing school, I plan to establish a private practice in Toronto, with a focus on sport nutrition, digestive health, and overall wellness and disease prevention. I understand that every person is unique, and as a Registered Dietitian I am excited to help my clients find the foods and dietary pattern that fit their needs and goals best.
 
​

This is the winning paper in the graduate category of the
Dr Elisabeth Feniak Award for Excellence in Technical Writing 2018
presented by the Canadian Home Economics Foundation.


Abstract
Alongside the continuous demand for seafood products, exploitation of wild fisheries and a steady increase in the global population has led to the rise of aquaculture, or fish farming, over the last several decades. In Canada, Atlantic-salmon farming is a prominent industry, with the most common method of production involving open-net cages in offshore marine or freshwater areas (Food and Agriculture Organization of the United Nations [FAO], 2009). Although aquaculture has many societal and economic benefits, it can cause significant environmental damage if it is conducted without precautions for environmental health. Disease outbreaks and transmission to wild fish stocks, organic and chemical pollution from fish farms’ wastes, and the threat of escaped species on wild populations are significant problems that warrant consideration. This critical review takes a deeper look into these environmental consequences and provides recommendations for policy relative to the sustainability of the Canadian Atlantic-salmon farming industry and utilisation of open-net farming pens.
Keywords: aquaculture, salmon farming, sustainability, environmental health, aquatic ecosystems

Introduction
Canadian dietary guidelines recommend the regular consumption of low-mercury fish and shellfish due to their concentration of omega-3 fatty acids, which support the maintenance of good health (Health Canada, 2017). However, in order to continue to produce a sufficient supply of this nutritious food source, seafood production must increase substantially to meet the needs of the expanding world population, predicted to grow to nine billion by 2050 (Canadian Council of Fisheries and Aquaculture Ministers [CCFAM], 2016).

As a result of overfishing, the capture and sale of wild fish and seafood globally has decreased, leading to an increase in what is known as aquaculture, or fish farming. Aquaculture is defined as the farming of aquatic species in ocean water or fresh water, involving methods to enhance production such as regular feeding, stocking and protection from predators (Fisheries and Oceans Canada, 2013a).

In Canada, fish farming contributes to a major part of the economy, as aquaculture is an important employer and economic driver in many coastal, rural and Aboriginal communities (Canadian Aquaculture Industry Alliance [CAIA], n.d.-a). Most operations are found on the east and west coasts, and the most important species farmed include Atlantic salmon, mussels, trout, oysters and clams (CAIA, n.d.-a). The value of Canadian aquaculture has been estimated as $591 million in 2013 and according to a study in 2009, the industry employs about 14 000 people full time (Fisheries and Oceans Canada, 2013b). In particular, Atlantic-salmon farming is a very important industry, as Canada is the fourth-largest farmed-salmon producer in the world (Fisheries and Oceans Canada, 2013b). With the growing population, demand for fish such as Atlantic salmon will only continue to increase (FAO, 2009). Therefore, it is crucial that the marine aquaculture industry remains sustainable to continue to support demand for generations to come.

Importantly, there are impacts of salmon farming in particular that warrant consideration for environmental health. The most common method of salmon farming in Canada involves structures called open-net pens or cages, which contain fish in offshore-marine or fresh-water areas (Monterey Bay Aquarium Seafood Watch, n.d.). Net pens are considered a high-impact aquaculture method as they permit the farm water and marine water to interact, allowing wastes, chemicals, diseases and other compounds to pass freely into the surrounding environment (Kent, 2000). The risks of disease transmission from farmed to wild fish stocks, the reduction of wild fish stocks due to escapees and the impact of chemical residues, and increased rates of eutrophication and nutrient loading are all apparent.

Although aquaculture has many benefits for the Canadian economy and society, if it is not conducted with precautions for environmental safety, it can contribute to serious environmental damage. This critical review takes a deeper look into these environmental consequences and provides recommendations for policy relative to the sustainability of the Canadian Atlantic-salmon farming industry and the utilisation of open-net farming pens.


Literature review
The most common method of salmon farming in Canada involves open-net systems, which have several environmental impacts. These impacts are categorised and analysed below, followed by the benefits and sustainability of farmed salmon.

Biological pollution: Disease transmission and other threats to wild fish stocks
A major biological concern is breakouts of parasites and diseases in farmed-fish populations. Outbreaks are often intensified on salmon farms due to closely packed conditions, and diseases from farms can easily spread to wild-fish populations, impacting their health and decreasing stock levels (Olesen, Myhr, & Rosendal, 2011). A common threat is from sea lice—parasites that eat salmon flesh, are often challenging to get rid of and can kill large portions of farmed fish stocks (Goldburg, Elliott, & Naylor, 2001). Other diseases such as heart and skeletal muscle inflammation (HSMI) disease can spread from farmed to wild fish stocks. A robust study assessed whether HSMI disease caused by the agent, piscine orthoreovirus (PRV), was spreading from farmed Atlantic salmon to wild salmon in the eastern pacific (Morton, Routledge, Hrushowy, Kibenge, & Kibenge, 2017). The study results suggested that there may be risk of reduced fitness in regards to survival and reproduction in wild-Pacific salmon as a result of PRV transfer from farmed to wild species (Morton et al., 2017).

In addition to spreading disease, if farmed fish such as Atlantic salmon are released into the wild, they can cause harm to native fish stocks by interbreeding or competing for resources. Although open-net pens are designed to prevent farmed and wild fish from interacting, escapes from fish farms are a common reality. In August 2017, a First Nation near Bellingham, Washington declared a state of emergency after the collapse of a United States fish farm allowed nearly 300 000 Atlantic salmon to escape after a net-pen failure (CBC News, 2017). Not all escape events are as large as this one. They also occur in leakages of small numbers of fish over time from marine aquaculture systems (Thorstad et al., 2008). Large or small, spills are a serious matter, as farmed Atlantic salmon are considered invasive species to wild populations, posing known threats on the basis of negative ecological interactions and lowered fitness from interbreeding (Thorstad et al., 2008). There is sufficient evidence to suggest that when farmed and wild species interbreed, they create a less resistant species (Liu, Disredud, Hindar, & Skonhof, 2013; Roberge, Normandeau, Einum, Guderley, & Bernatchez, 2008). This necessitates improved technology to secure open-net pens or, potentially, moving farming systems onto land to avoid escapes entirely.

Organic pollution and eutrophication
Open-net farming systems contribute to organic pollution, as they allow a number of wastes to be discharged into the surrounding marine environment, including fish excrements, excess feeds and various chemicals (Kent, 2000). The release of inorganic nutrients (nitrogen and phosphorus) and nitrogenous wastes (ammonia) into the environment can contribute to nutrient loading (Strain, 2005). Nutrient loading leads to eutrophication—which occurs when there is a build-up of nutrients— and this results in a reduction of the oxygen needed to stimulate algal growth (Strain, 2005). Although aquaculture’s share in national nutrient loading and pollution is considered relatively small in relation to major sources of pollution, eutrophication is considered a cumulative problem (Goldburg, Elliott, & Naylor, 2001). In areas of high-density farming, eutrophication poses concern for the environmental sustainability of aquaculture (Strain, 2005). According to Strain (2005), aquaculture can produce eutrophication that impacts the marine environment on a scale of kilometres to tens of kilometres. This can significantly change the functioning and structure of the ecosystem, harming wild marine organisms in the process (Strain, 2005).

The composition of fish feed for farmed salmon is another sustainability concern and a factor that can impact marine environmental health (Goldburg et al., 2001). In Canada, it has been common practice to use fish products in feed; however, this has been recognised as potentially threatening in terms of sustainability as the use of raw-fish material is both expensive and taxing to wild fish stocks (Sarker et al., 2013). In response, this industry has been working to increase its efficiency of usage of raw-fish material to maximise the nutritional value of fish feed while balancing satiety (Sarker et al., 2013). According to the Canadian Aquaculture Industry Alliance, feed manufacturers have been working to develop feeds that use sustainably sourced ingredients such as vegetables and soy protein as replacements for fish-based ingredients, and Canadian salmon farmers now use less than 30% fish meal and oil in their feed, a step in the right direction (CAIA, n.d.-b). However, producers should take care to ensure that feed composition does not result in a reduction of the omega-3 concentrations in the farmed salmon, as this would result in a reduction of the main benefit of consuming this food source (Foran, Good, Carpenter, Hamilton, Knuth, & Schwager, 2005).

Another issue with fish feed is that it is often medicated, containing pharmaceuticals such as antibiotics. Medicated feed that is not consumed by fish is released into the surrounding environment and, therefore, available for uptake by wild marine animals. This feed can also accumulate in sediments, or unabsorbed antibiotics can be release through fish wastes such as faeces and urine (Bjorklund & Bylund 1990, 1991 as cited in Scott, 2004). This contributes to the development of antimicrobial resistance, and disrupts the natural bacteria flora essential to the health of ecological food webs (Scott, 2004).

Chemical pollution
Several chemicals are approved for use in Canadian aquaculture, including pesticides, antibiotics and industrial chemicals such as antifouling paints (Burridge, 2003; Goldburg et al., 2001). The impact of chemical use is that these compounds may remain in the marine environment, negatively affecting non-target organisms, biodiversity and the ecological structure (Burridge, 2003; Watershed Watch Salmon Society, 2011). Open-net farms are often enclosed in steel cages containing nylon nets. These nets have a high potential for fouling as certain organisms grow on them, shortening the life of the structure (World Wildlife Fund for Nature [WWF], n.d.). To reduce the growth of organisms that cause fouling on the nets, copper-based antifouling paints are commonly used (Burridge, 2003). These paints are released into the marine environment and can affect non-target organisms living in the surrounding areas (Burridge, 2003). They are considered highly toxic to bivalves such as mussels and oysters and may potentially be harmful to fish species as well (Cripps & Kumar, 2003, as cited in WWF, n.d.). Other chemicals such as the pharmaceuticals used to treat sea-lice infestations on fish farms may also affect the health of non-target wild marine animals such as crabs, lobsters and other fish species by disrupting their normal metabolic processes (Burridge, 2003).

An additional concern for both human and animal health is that medication usage in aquaculture results in antimicrobial resistance—the ability of microorganisms (like bacteria and viruses) to stop an antimicrobial (such as antibiotics) from working against them (Goldburg et al., 2001). In 2015, the World Health Organization (WHO) declared antimicrobial resistance one of the biggest threats to global human health today, and the overuse of antimicrobials (agents that kill or stop the growth of microorganisms) in both health care and agriculture are contributing to this global epidemic (WHO, 2015a). As a preventative method, antibiotics are commonly added to salmon feed to keep stocks healthy and to reduce risk of infection (Done, Venkatesan, & Halden, 2015). However, this practice poses a major concern to both wild and farmed fish stocks, as the prophylactic use of antimicrobials in aquaculture contributes to the development of resistant bacteria and other microbes (Burridge, 2003; Done et al., 2015; Scott, 2004).

Antimicrobial-bacteria and other microbes demonstrate a serious threat to both human and animal health, as many pharmaceuticals used to treat disease and infections will become ineffective. It is clear that using these methods of infection control and prevention are not sustainable. Antibiotic use can be avoided through the use of vaccinations and alternative therapies. Canadian regulations should be modelled on the responsible use of antibiotics in countries such as Norway. Norway has one of the lowest antibiotics usage rates of countries that farm fish, providing a gold standard for other farming industries to follow (WHO, 2015b). In the 1980s, as an alternative to antibiotics, scientists in Norway developed an effective vaccine against the common pathogen furunculosis in farmed salmon that produced no side effects in humans (WHO, 2015b). Since 1994, all fish farmers across Norway have switched their use from antibiotics to vaccination for pathogen control, and antibiotics are now used only when necessary to treat infection (WHO, 2015b). Globally, there has been an increasing interest in and use of alternative therapies to antibiotics and chemicals. This includes microbial inoculants and probiotics, which have the benefits of improving soil and water quality, in addition to minimising the risk of bacterial infection (Food and Agriculture Organization of the United Nations [FAO], 2006). Nutraceuticals such as herbal products are also being used more frequently to replace chemical treatments to support marine animal health (FAO, 2006). It is clear that these technologies exist, thus directions for policy change in the Canadian marine aquaculture industry should encompass increased use of these alternative therapies.

Benefits and sustainability of farmed salmon
With improvements to current aquaculture practices, there is potential for farm-raised salmon to become a highly sustainable food source. The Canadian Aquaculture Industry Alliance argues that under strict regulations and best-farming practices, salmon and other marine aquaculture are considered environmentally sustainable (CAIA, n.d.-b). Life-cycle analysis suggests that farmed salmon demonstrate lower use of key environmental-impact measures, including energy, water and land usage, and produce fewer greenhouse-gas emissions than beef, poultry and pork (CAIA, n.d.-b). With regards to farming practices, there is evidence to suggest that on-land fish farms are much more sustainable than ocean-based farms as they are closed-contained and may prevent damaging interactions with the marine environment (Tal, Schreier, Sowers, Stubblefield, Place, & Zohar 2009).

One of the few commercial on-land salmon farms in the world exists in Port McNeill, British Columbia (BC) (Palomino, 2015). Owned by the ’Namgis First Nation, the farm is a model for sustainable aquaculture, using practices such as recycling its water, converting waste to fertiliser, avoiding pesticide and antibiotic usage, and relying mainly on plant-based ingredients for fish feed (Palomino, 2015). Out of great concern to protect wild salmon and the migratory routes that they use, recently there has been a great deal of interest from the BC government to move all open-net farms onto land wherever feasible (Wilson, 2018). Several provincial tenures for fish farms will soon be coming up for renewal, suggesting an optimal time for change (Wilson, 2018). Supported by research, closed-contained systems—also known as land-based recirculating aquaculture systems (RAS)—are superior in terms of sustainability because they reduce nutrient and chemical pollution into the marine environment, remove the threat of escaped farmed species and their negative impacts on wild populations, and allow managers to optimally control conditions for growth, thus enhancing production efficiency (Tal et al., 2009). This prompts a direction for policy change and a move into more sustainable and environmentally friendly aquaculture practices in Canada.


Policy recommendations
It is clear that salmon farming using open-net systems poses threats to environmental health and wild fish stocks, warranting consideration for policy initiatives to address the resulting issues. The Canadian government has stated that it is working towards improving management practices to ensure sustainability of the Atlantic salmon farming industry (Fisheries and Oceans Canada, 2012). The Department of Fisheries and Oceans Canada has declared that sustainability and environmental protection are priorities, as they recognise the significant societal benefits associated with aquaculture (Fisheries and Oceans Canada, 2012). In addition, the Canadian Aquaculture Industry Alliance (CAIA) is pushing for a Federal Aquaculture Act that would set consistent standards for aquaculture farming across Canada, and allow for improved federal-provincial coordination regarding how the industry is managed (CAIA, n.d.-c). However, there is no room for complacency; despite considerable progress towards environmental conservation, there are still issues that must be addressed as demonstrated by this analysis of the literature. Continuing interventions and investments are needed to ensure improvements in environmental sustainability in the Canadian aquaculture industry (Subasinghe, 2009, as cited in FAO, 2006).

In consideration of the evidence outlined in the literature review and directions for policy change in salmon aquaculture, the following policy actions are recommended:

• Reducing the use of antimicrobials in farmed salmon through the regulated use of vaccinations, alternative therapies and standardised methods for infection prevention and control
• Transitioning open-net farms into closed-contained (on-land) farming operations where feasible
• Updating nutrition guidelines regarding the consumption of seafood to promote other sustainable fish species, including: anchovy, mackerel, capelin, char, hake, herring, mullet, pollock, smelt, rainbow trout, lake whitefish, mussels, shrimp and oysters (Health Canada, 2017)
• Increasing initiatives to support research into sustainable aquaculture practices, including: environmentally safe fish-feed, prevention of escaped fish stocks and alternative therapies for disease prevention and control.

Conclusion
Recognising the importance of the salmon-farming industry to the Canadian economy and society, more must be done to support environmental health and to reduce environmental impacts through improving the sustainability of aquaculture practices. The salmon-farming industry provides significant societal benefits, including the ability to produce a greater supply of salmon products without directly depleting natural fish stocks, therefore providing more of this healthy food source for more people. Salmon aquaculture provides jobs and a living wage for many Canadians, in addition to contributing to the national economy. Although Atlantic-salmon farming has many societal and economic benefits, there are environmental threats associated with salmon aquaculture and with open-net cages in particular. Taking into consideration the findings of this critical review, it is clear that we need to continue to develop a Canadian salmon-farming industry that is optimal for both humans and for the environment, and that can support increased demands for salmon relative to the steadily increasing global population.


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Contact details
Leigh Merotto
Ryerson University, Canada
E. leigh.merotto1@gmail.com