New Report Highlights Welfare and Environmental Issues in Scottish Salmon Farming

In the wild, Atlantic salmon will migrate thousands of miles to spawn, but crammed into barren, overcrowded sea cages on salmon farms, they can do nothing more than swim around aimlessly in circles.

In nature, they would be able to swim away from areas of poor water quality and harmful algal blooms, but in aquaculture, they are trapped and left to suffer the effects, which include damage to and clogging of their gills and reduced oxygen levels, both of which can lead to suffocation.

Producers should ensure fish are stocked at a lower density and provide them with enrichment to allow for better water quality and to promote their physical and mental well-being.

Compassion recommends a stocking density of 10kg/mᶾ for salmon - currently there is no legal stocking density limit in Scotland and in Norway the limit is 25kg/mᶾ.

Sea lice are parasites that feed on the skin, blood and mucous of fish, resulting in large open wounds which can become infected and result in death.

Sea lice infestation is accelerated by high stocking densities, enabling rapid spread through the stock, from one farm to the next, and even out to wild fish. 

Sea lice numbers have grown with the expansion of the salmon industry, which is yet to implement an effective welfare and environmentally friendly treatment or prevention method.  Current methods used, including chemical baths, thermolicer and hydrolicer treatments can cause injury, stress and high mortality.

The use of ‘cleaner fish’ which eat the lice off the salmon is a popular treatment, but their welfare is rarely considered and they also suffer from poor health and high mortality.

Compassion is against the use of cleaner fish, but where they are used, companies should provide  additional feed, enrichment, and humane slaughter methods. Read more about cleaner fish welfare here.

Compassion recommends the use of prevention methods and to research new treatment technologies for sea lice which do not harm the salmon, or the environment.

View our latest infographics on sea lice to find out more: The Problem of Sea Lice and Sea Lice Management.

Farmed salmon mortality rates are as high as 28.2% in the seawater stage and including mortalities from the freshwater stage (between 25–50% of ova laid to hatch die before reaching the smolt stage) this figure is likely to be even higher.

Mortality is mainly caused by sea lice, and their treatments, disease, and harmful algal blooms. The fish suffer to such an extent that up to a quarter die before they make it to slaughter. 

It is vital that all farms work on a mortality reduction plan with a vet to alleviate this issue.

Farmed fish are usually given antibiotics in their feed to protect them from various diseases which are exacerbated by the overcrowded conditions on industrial salmon farms.

Responsible Use of Medicines in Agriculture Alliance (RUMA) sets out maximum antibiotic usage limits of 5mg/kg production on salmon farms in the UK.

In 2017, the Scottish salmon farming industry far exceeded this target, using 16.1mg/kg of production., but in 2018, this dropped to 6.5kg of production.

Antibiotic use has been reduced due to the increased use of vaccinations for farmed salmon.

Skeletal deformities such as bent spines are relatively common in farmed salmon and are generally related to the size of the fish when they are transferred into the sea cages, although other causes may include the water quality and the quality of their feed. 

Deformities result in lower swimming performance, making affected fish less able to compete for food, while their physiology can be impacted, as well as their tolerance to stress and handling.

To avoid deformities, fish need to be fed high quality food and they should be transferred to the sea cage only when they are large enough to tolerate the change.

The Scottish salmon industry typically uses electrical and percussive stunning methods (administering a severe blow to the skull of the fish) when slaughtering Atlantic salmon.

However, stunning prior to slaughter is not mandatory under law – and sometimes poorly practiced - so there may still be millions of fish that are killed without prior stunning.

Compassion recommends that all fish are effectively stunned, rendered instantly insensible, and remain unconscious until death supervenes to avoid any suffering.

Read more about our recommendations for the humane slaughter of Atlantic salmon here: 

• Improving the welfare of Atlantic salmon at slaughter
• Recommendations for the humane slaughter of Atlantic Salmon

In aquaculture, many carnivorous species such as salmon are fed on huge volumes of wild-caught fish in the form of fishmeal and fish oil. The fishmeal industry accounts for 0.5-1 trillion fish out of the 0.79-2.3 trillion fish caught every year.

This is inherently unsustainable as it is causing a global crisis in overfishing and depleting the food source for many local communities and wildlife including sea birds and marine mammals.

Compassion questions whether farming migratory and carnivorous species, such as salmon, has any place in a sustainable food system.

Intensive salmon farming is not only bad for fish welfare, but it is also damaging the environment too. Organic and chemical waste from Scottish salmon farms is killing marine life on the seabed and waste from farms can lead to poor water quality and harmful algal blooms.

Chemicals and medicines, such as insecticides, are also released into the environment and many of these are known to be toxic to fish and other marine organisms, as well as birds and mammals.

It is important that farms limit their environmental impact by carrying out a survey of the local flora and fauna to ensure no endangered species is at risk, reduce farmed fish numbers and ensure uneaten food does not enter the environment

Wildlife, including predators such as seals and sea birds, are often attracted to fish farms due to the abundance of food available to them. Predators are not only a nuisance to the farmers, but they also threaten their livelihoods, so many are forced to protect their fish stock against predator attacks.

Compassion recommends the use of non-lethal exclusion methods, such as nets, provided that they are designed to avoid entanglement by the predator and are checked regularly.

Compassion has developed guidance on management methods to ensure higher welfare for the fish and for marine life - read more here.