Salmon farming in open net pens has many negative effects on nature and on natural salmon stocks. Genetic mixing between escaped farmed salmon and wild salmon is the most dangerous threat facing wild salmon stocks today.

Genetic mixing has permanent effects, leading to the decline of wild stocks –salmon that have been spawning in Icelandic rivers since the end of the last ice age. The genetic code of Icelandic salmon is uniquely suited to surviving the particular river in which it is born. Norwegian farmed salmon, on the other hand, has been bred in captivity to suit farming conditions, with an emphasis on fast growth rates rather than adaptability and survival in the wild. They lack the genetic qualities that help Icelandic salmon survive in the wild.

Yet escaped farmed salmon is genetically inclined to spawn, just like wild salmon. When that happens, their offspring are less suited to face many of the challenges of surviving in the wild.

The solution to all of this is simple and should be the unconditional demand of all nations that practice salmon farming to limit production to closed containment or land-based facilities. Iceland is in a prime position to be ahead of the curve, to move all salmon farming to more environmentally friendly and secure production that does not threaten wild salmon stocks.

Open net pens are big nets, attached to a floating circle floating in open water. There is a constant risk of fish escaping from those pens. This is undisputed by conservationists and fish farming companies, alike. Escapees breed with wild salmon, weakening genetic lines and lessening their chances for survival.

Escapees can be both juvenile and adult fish, and they can escape any time of the year. The effects on wild stocks of salmon depend on the age of the escapee, the farm’s proximity to rivers or nursery areas of wild salmon, what time of year they escape, and the size and condition of wild stocks in the area. There is evidence that escapes of farmed salmon juveniles are more detrimental to nature than escapes of adult fish. Farmed juveniles that run up rivers inhabited by wild salmon can compete with the wild juveniles for habitat, lessening wild juveniles’ chances of survival. Farmed juveniles that inhabit a river get adapted to the chemical structure of that river and can return to it to spawn after having spent time again in the sea. Adult escapees can also run up rivers alongside wild salmon in the spring and summer, battling them for spawning grounds and mates, and populating with wild salmon. Tagging and other research has mapped out such mixing of farmed and wild fish in Norway, Scotland, and Ireland.

Easily measurable physical and behavioural traits have emerged from interbreeding between farmed and wild salmon. Experiments in controlled conditions have shown that farmed and wild salmon are different in many ways, i.e. in size, sexual maturity, size at sexual maturity and behaviour (interacting with other fish), and hybrids of farmed and wild salmon can inherit the traits of the farmed parent.

Recent genetic research has further unveiled various differences between farmed and wild salmon. This research has progressed the most in Norway and is based on molecular-genetic methods that analyse the source of genes and individuals.

Atlantic salmon have a genome that’s similar in size to that of a human, just short of 3 billion genetic bases and the number of genes is between 35,000 and 45,000. In their genome are millions of variations, and by looking at these variations in wild stocks and farmed stocks it’s possible to identify what genetic variation is distinctive for the farmed fish.

Norwegian farmed salmon was bred from a mix of 40 wild stocks of salmon from mid and south Norway, and one Swedish stock. In the process of this selective breeding a few genes were selected that are connected to sexual maturity, disease immunity strength, and other factors that farmed fish are reliant on. The result is that the genetic code of the farmed salmon is completely different than that of the wild salmon.

Norwegian research (Glover et.al 2013, and Karlsson et.al 2016) examined the genetic differences between Norwegian farmed salmon and wild salmon. To find genetic keys that could differentiate between wild and farmed salmon, farmed salmon were compared to samples from wild salmon from the mid-20th century, before the massive rise of salmon farming in Norway. Karlsson et al used these results to calculate genetic mixing of farmed and wild salmon and the effects on wild salmon. In sampling 147 salmon rivers in Norway, researchers found that 109 rivers had more than 6.7% genetic impurity due to mixing with farmed salmon. The rivers that had the highest percentage of genetic mixing had a 40% genetic impurity. Genetic impurity was highest in mid and southern Norway and had a significant correlation with the locations and number of the fish farms. Rivers that had been protected or completely free from open cage salmon farming were not affected as much.

Interbreeding has significant impacts on wild salmon. Evolutionary studies show us that species are adapted to their surroundings, so their genetic code reflects their ecology and their circumstances. For an example, in Norway it is well known that the average size of salmon varies between regions and rivers. Some rivers are referred to as “big salmon rivers” and others as “grilse rivers”. It is local factors that make the biggest difference there (temperature, availability of nutrition, spawning grounds, pathways up the rivers and other factors). Also, there is quite a difference between salmon in the south and north of Norway, not to mention the difference between Norwegian, Irish and Icelandic salmon, both biologically and genetically.

It is important that genes that mix with wild salmon are not to its “advantage”. Take, for an example, salmon in a grilse river, meaning a river where the majority of salmon have only spent one year in the sea and are not very large. If those fish were to get an increased number of genes from farmed salmon and become larger, or mature sexually later, there would be a big risk that their ability to adjust to their natural habitat will be lessened substantially.

The agricultural genetics committee of Iceland has confirmed these dangers and strongly opposes the use of foreign, fertile salmon in Iceland, concluding this will lead to the decline of Icelandic Atlantic Salmon.