Brian Barton
Salmon is one of the world's most popular fish, with 70% of the world's salmon coming from farmed operations. However, the farmed salmon industry is wreaking havoc on marine ecosystems through pollution, parasites, and high fish mortality rates. One of the main sources of pollution is the waste produced by salmon farms, which includes excess feed, decomposing fish, excrement, and chemical residue from pesticides and antibiotics. This waste forms a toxic sludge that kills or drives away marine life and reduces biodiversity. In addition, the dense populations in which farmed salmon are kept can lead to the spread of sea lice and other diseases to wild salmon populations, further endangering an already vulnerable species.
| Characteristics | Values |
|---|---|
| Fish waste | Excess food and fish waste increases the levels of nutrients in the water, which can lead to oxygen-deprived waters that stress aquatic life. |
| Chemicals | Excessive use of chemicals such as antibiotics, anti-foulants, pesticides, and banned neurotoxins can have unintended consequences for marine organisms and human health. |
| Parasites | Parasites and sea lice can spread from farmed fish to native salmon populations, threatening nearby endangered wild salmon and other fish species. |
| Disease | Escaped farmed fish can transmit diseases to wild salmon populations. |
| Mortality rates | Fish mortality rates have more than quadrupled in Scottish salmon farms, with sea lice infestations being a contributing factor. |
| Genetic diversity | Escaped farmed salmon can interbreed with local wild stocks, altering the overall pool of genetic diversity. |
| Environmental costs | The environmental costs of salmon farming in Scotland were estimated to be £1.4 billion from 2013 to 2019. |
| Wild fish | The sheer quantity of wild fish used in salmon farms is a growing concern, with about 70% of the world's salmon coming from farmed fish operations. |
| Nitrogen waste | Fish produce a lot of nitrogen waste, which can create perfect conditions for toxic algae outbreaks and cloud the water, blocking essential sunlight for eelgrass nurseries on the seafloor. |
| Regulatory issues | Regulatory issues have been identified in Maine, where there are no limits on how much waste fish farms can produce, and no requirements to monitor nitrogen pollution levels or water quality impacts. |
| Pollution | Pollution from salmon farms is emitted through chemical treatments, excess feed, and large quantities of feces. |
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What You'll Learn
Fish waste and excess food
Untreated waste from excess feed, decomposing fish, and excrement creates a toxic environment that kills or drives away marine life. This waste also contains harmful chemicals such as antibiotics, anti-foulants, and pesticides, which can have unintended consequences for marine life and human health. For example, the use of banned chemicals and excessive antibiotics and pesticides can lead to virus and parasite transfer between farmed and wild fish, as well as among farms, posing a risk to wild populations and other farms.
The sheer quantity of wild fish used in salmon farms is also a growing concern. About a fifth of the world's annual wild fish catch, or about 18 million tonnes of wild fish, is used to make fishmeal and fish oil, of which 70% goes to fish farms. This practice is causing problems for fishers in developing countries, as their stocks are depleted to feed the demand for farmed fish in the west.
The high density of fish in salmon farms further exacerbates the issue of waste and excess food. When nets are damaged or technical errors occur, thousands of fish can escape, as seen in an incident where 300,000 Atlantic salmon escaped from a farm in Washington State. Escaped farmed fish can spread diseases and parasites to wild salmon populations, with sea lice being a significant concern. While regulations in the US and British Columbia require monthly monitoring and treatment of sea lice, the issue is complex, and the true impact of sea lice on wild salmon populations is unknown.
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Disease and parasite transmission
Salmon farming has been associated with various environmental concerns, including the transmission of diseases and parasites to wild fish populations. This is facilitated by the close proximity of salmon farms to natural bodies of water, which allows for the direct discharge of untreated waste and chemicals into the ocean.
The waste from salmon farms, including excess feed, decomposing fish, excrement, and chemical residues, can form a toxic layer of sludge on the ocean floor. This sludge is harmful to marine life, reducing biodiversity and oxygen concentrations in these habitats. The excessive use of antibiotics, pesticides, and other chemicals in salmon farming contributes to the pollution of water bodies. The accumulation of nitrogen waste, for example, creates favourable conditions for toxic algae blooms, which can have detrimental effects on marine organisms such as fish, turtles, and shellfish.
Sea lice are a significant concern in salmon farming, with their populations increasing as the stocking densities of fish rise. Sea lice are parasites that attach themselves to fish, feeding on their skin and mucus, causing wounds that often become infected and lead to the death of the fish. While regulations in some regions require monthly monitoring and treatment of sea lice, the chemical treatments used to eradicate them, such as hydrogen peroxide, can have serious consequences for surrounding marine life.
Disease outbreaks in salmon farms also pose a risk of transmission to wild salmon populations. The high stocking densities of fish in farms can contribute to the spread of diseases, and escaped farmed fish can transmit these diseases to their wild counterparts. The transfer of viruses and parasites between farmed and wild fish populations has been documented, with potential impacts on the health of wild fish and the natural ecosystem.
The import of Atlantic salmon eggs for farming in the Pacific has raised concerns about the potential transfer of diseases to wild stocks. While restrictions, testing, and disinfection protocols are in place to minimise this risk, the high density of fish in farms can exacerbate disease outbreaks. Escaped farmed salmon can interbreed with local wild stocks, altering the genetic diversity of the population and potentially impacting their ability to survive in their natural environment.
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Chemical treatments
Salmon farming is a rapidly growing industry, with farmed salmon being the most popular fish on dinner tables in North America. However, the industry has been criticized for its use of chemical treatments, which can have negative impacts on the environment and human health.
One of the main concerns is the use of pesticides and antibiotics, which are often used in massive doses to control parasites and pathogens. These chemicals can contaminate the surrounding water and accumulate on the ocean floor, posing risks to marine life and human health. For example, the use of banned neurotoxins as pesticides has been reported, which can have unintended consequences for both marine organisms and humans.
Another issue is the use of chemicals to treat sea lice infestations, which are common in crowded salmon farms. Sea lice are parasites that attach themselves to the fish, feeding on them and leaving wounds that can become infected, leading to fish mortality. While chemicals like hydrogen peroxide are effective in removing sea lice from salmon, their release into the ocean can have serious consequences for surrounding marine life.
In addition to pesticides and antibiotics, other chemical treatments used in salmon farming can also contribute to water pollution. For example, anti-foulants are often used to control fouling organisms, but they can have negative impacts on non-target species. Additionally, the use of disinfectants to minimize disease transfer between farmed and wild fish can also contribute to chemical runoff into the water.
The excessive use of these chemicals, combined with untreated waste from excess feed, decomposing fish, and excrement, creates a toxic environment that kills or drives away marine life. The accumulation of waste and chemical residue forms a layer of sludge on the ocean floor, which can smother and poison bottom-dwelling creatures, ultimately transforming the seafloor into a lifeless landscape.
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Nitrogen pollution
Salmon farms produce a large amount of waste, which can cause nitrogen pollution. A typical industrial farm of several hundred thousand fish produces around one million pounds of waste annually. Unlike city sewage, the waste from North American fish farms is not captured or treated. Instead, it floats out through the pens to pile up on the ocean floor.
Nitrogen waste from salmon farms can mix with warm water to create an environment that encourages outbreaks of toxic algae. This algae can grow out of control to form massive red tides that poison any fish, turtles, and shellfish in their path. Nitrogen pollution also clouds the water, blocking sunlight from reaching eelgrass nurseries on the seafloor. As the climate crisis heats up our oceans, the problem of outbreaks of toxic algae and eelgrass die-offs is worsened.
Licensing and farm management can ensure facilities are located in areas where the potential environmental impact from the release of nutrients is minimal. This includes undertaking full environmental impact assessments, including modelling the impacts of the release of nutrients before licenses are issued. As technology has developed, salmon net-pens have been able to locate to more exposed locations with stronger currents and deeper water, which ensures waste materials are more widely dispersed. Net-pens are also regularly rotated between farm sites to enable fallowing.
Another proposed solution towards ameliorating inputs from net-pen farming is the adoption of integrated multi-trophic aquaculture (IMTA), whereby filter feeders (shellfish), detritivores (e.g. sea cucumbers or marine worms), and macro-algae (seaweeds) are grown alongside the salmon farms to remove the various outputs from the fish. However, this solution has yet to demonstrate its viability in biological, environmental and financial terms when applied to the dynamic open sea environment. Land-based recirculating aquaculture systems (RAS) can mitigate nutrient pollution risks by removing solids prior to the discharge of effluents and the removal of dissolved nutrients in wastewater streams by establishing areas such as reed beds.
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Sea lice
Salmon farms across the world are suffering from infestations of Lepeophtheirus salmonis, a sea louse that specifically targets salmonids, the family of fish that includes salmon. The lice have a short, free-swimming larval phase, during which they need to find and attach to a fish host. Salmon farms provide an ideal environment for sea lice to thrive and spread, as the lice can easily move between closely spaced fish.
The high density of fish in salmon farms contributes to the rapid spread of sea lice. Lice larvae are typically found near the surface of the water, so keeping farmed salmon in deeper water can help reduce the likelihood of infestation. However, this solution is not always feasible, as salmon need to reach the surface to refill their swim bladders with air. Temporary measures, such as equipping nets with snorkel-like tubes, can help reduce the potential contact between farmed salmon and lice larvae.
The impact of sea lice infestations extends beyond the farmed salmon population. Farmed salmon that escape from their pens can introduce sea lice to wild salmon populations, putting them at risk of infection. Juvenile wild salmon are especially vulnerable to sea lice due to their small size and thin skin. The presence of sea lice can have lethal consequences for these young fish. Additionally, the use of pesticides and antibiotics to treat sea lice infestations in farmed salmon can have environmental implications, potentially affecting other marine organisms.
To address the problem of sea lice, various methods have been employed. Licensed medicines and physical methods, such as bathing the salmon in freshwater, are commonly used treatments. Some farms are also turning to the use of cleaner fish, such as wrasse, which feed on the lice and help control infestations. While these methods can help manage sea lice numbers, the constant innovation and adoption of new technologies are necessary to effectively combat this persistent issue.
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Frequently asked questions
The main causes of water pollution from farmed salmon are chemical treatments, excess feed, and large quantities of feces.
Unlike sewage, fish farms do not capture or treat fish waste. Instead, it floats out through the pens and accumulates on the ocean floor, forming a layer of foul-smelling black sludge that is toxic to small bottom-dwelling creatures.
Salmon farms use massive doses of pesticides, antibiotics, and other chemicals to treat parasites and pathogens. Some of these chemicals are banned neurotoxins. The residue from these treatments falls to the seabed below the cages, killing marine life for hundreds of yards.
Excess feed from salmon farms increases the levels of nutrients in the water, leading to oxygen-deprived waters that stress aquatic life.
