Atlantic Salmon

Recirculating aquaculture systems (RAS) can be built and operated virtually anywhere and can make use of existing buildings such as warehouses and greenhouses. Many RAS systems when built, are done so on previously converted land so there is no new habitat conversion or loss of ecosystem functionality during a new facility’s set-up. These systems are also closed and contained, which means there is very little interaction with local habitats. 

Though open systems have little impact on the physical nature of habitats, they can have a significant negative impact on local habitats as a result of discharge and deposition of feed and fish waste. These impacts tend to vary by country and by farm. In Norway, net pen salmon farms produce substantial nutrient pollution, but recent data indicated a low risk to local benthic habitats near the farm areas, with little organic loading. Floating net pens in Scotland and British Columbia received moderate scores because the habitat impacts are reversible and impact relatively small areas. 

Floating net pens at the largest salmon farm in Chile can lead to conditions of high waste deposition in the fjord region where it operates - this region has a high global conservation priority. But Seafood Watch has found that conditions can return to normal when fallowing occurs before restocking. Elsewhere in Chile, the seabed impacts from floating net pens can be severe. The industry there is also rapidly expanding into pristine areas and more research is needed in these high-value conservation areas.

The feed formulations used for Atlantic salmon farming vary greatly, with some making use of fishmeal and fish oil from wild sources such as farms in North America. Chile’s largest salmon farm uses feed made from genetically-modified yeast instead of protein from wild fish and the farm has been testing an algal-based feed ingredient as well. Elsewhere in Chile, and also in British Columbia and Scotland, farms are increasingly replacing fishmeal and fish oil with alternative crop proteins and oil ingredients, and in some cases with by-products from land-animal processing. Norwegian salmon farmers have also made progress in reducing wild fish for feed, now including byproducts from terrestrial crop sources in particular.

Land-based recirculating aquaculture systems (RAS) allow for greater control over the farming environment than open net pens. Sterilization of incoming waters, alongside strict biosecurity protocols, helps to reduce the risk of diseases being introduced into RAS. In addition, the treatment of effluents limits the number of pathogens and diseases that can be transmitted to wild populations. Though disease outbreaks have occurred in RAS, this is mainly attributed to improper implementation of quarantine procedures.

In British Columbia, research has highlighted the potential impacts of pathogens and parasites on wild salmon populations and there is concern regarding the transfer of sea lice from farms. Dominant diseases in Chilean salmon farms include salmon rickettsial syndrome (SRS) and parasitic sea louse. Though there is potential for transmission to wild fish, there is little evidence these diseases are affecting wild populations. North Atlantic salmon farms contend with bacterial kidney diseases, sea lice, and skin lesions in farmed populations. Infectious Salmon Anemia (ISA) has also been an issue for salmon farms in this region, but once again there is little evidence of transfer to wild populations.

Parasitic sea lice numbers from Scottish Atlantic salmon farms have been increasing in recent years and elevated levels of this parasite have been found in the environment around farms, despite the use of pesticides. The government has acknowledged the fact that the elevated levels of sea lice have the potential to kill fish in the vicinity of these farming operations, but there is no significant evidence of population-wide impacts.

According to Seafood Watch, viral diseases and sea lice are a top concern for Norwegian salmon farms. Based on results from the national sea lice monitoring program, the Norwegian Institute for Nature Research and the Norwegian Veterinary Institute both agree that there is evidence of population-level impacts on salmon populations in certain regions. Sea lice has been highlighted as a threat to wild salmon to the degree that they can cause reduction to wild populations. In Norway, brown trout has also been identified as a species that can be affected by sea lice transmission from salmon farms.

Land-based recirculating aquaculture systems (RAS) for Atlantic salmon farming tend to be enclosed in secure buildings and tanks, reducing the risk of escapes. Tank-based RAS have screens, along with water treatment and secondary capture devices which further minimize the chance of escapes. On the other hand, salmon farms that utilize net pens pose a much higher risk of escape since they are located offshore. 

Chile’s largest salmon farm uses best management practices that exceed national standards to prevent escapes. However, large escape events continue to occur in Chile - for example, almost 800,000 fish escaped in one event in 2013 - but they are occurring less and less.  Seafood Watch also noted that escaped farmed Atlantic salmon are unlikely to become established in the wild in Chile, especially as they have been shown to be a poor colonizer in that region (Atlantic salmon is a non-native species in Chile).

Tens of thousands of salmon have escaped from farms in Scotland with very few recaptured. Seafood Watch reported that these escapes have impacted wild populations - studies show evidence of farmed genetic material already present in Scotland’s wild salmon. This is a cause for concern with regard to genetic fitness of native salmon populations. Norwegian farms have also reported large escape events. Escape events of about 50,000 farmed salmon have occurred in six out of the past seven years. Improved management and pen design have reduced the number of escapes, but previous events have already had negative effects on wild salmon populations.

Salmon farms operating in North America’s Atlantic regions must abide by the Code of Containment protocols that include requirements for siting, system design, materials’ strength, maintenance and inspection, stock loss and recovery and best practices for fish handling procedures that are meant to reduce the risk of escape. Maine farms have not reported a breach since 2003, though escapes do still occur in Canada.

Escape numbers have varied in British Columbia over the past several years, ranging from a dozen to more than 100,000, although last year’s annual maximum of escapees reported was only 22. Seafood Watch concluded that there is no evidence for a high presence of farm escapees in wild populations in British Columbia, though the potential for escapes resulting from human error or inclement weather is still of concern.

Land-based closed containment recirculating aquaculture systems (RAS) use small total water volumes when compared to other aquaculture product systems and because of this have only small volumes of effluent generated and discharged from facilities. This type of production system also allows for all waste materials, including sludge and wastewater, to be collected and treated on site prior to discharge. These materials are treated and can then be disposed of via municipal wastewater treatment plants, land application, or compost production. While post-treatment wastewater from some RAS facilities is discharged into local water bodies, all facilities require a permit to do so, which is regulated and monitored on a regular basis under regional regulations. 

On the other hand, marine net pen farming allows for large amounts of effluent to be discarded into waterways. Waste nitrogen, phosphorus, and organic matter account for large parts of effluent released into the water.  Impacts of these effluents, such as changes to nutrient ratios and microbial communities, are still being studied on an international scale to help improve understanding of the effects of salmon farming on local ecosystems. Some countries with net pens do regulate and monitor the waste, but even the highest Seafood Watch effluent scores for Scotland, British Columbia, and the largest salmon farm in Chile respectively, were moderate at best.

Globally, the Atlantic salmon farming industry uses domestic broodstock and hatcheries, keeping sourcing independent from wild salmon populations, according to Seafood Watch.