The number of wild Atlantic salmon returning from the ocean to Norway is still on a low level. Escaped farmed salmon, salmon lice and infections from salmon farming are the greatest anthropogenic threats.
Foto: Eva B. Thorstad
The abundance of wild Atlantic salmon has declined. The number returning from the ocean to Norway each year is now less than half of the level thirty years ago. In 2017, about 530 000 salmon were estimated to return, which was an increase from 2016, but still on a low level. The declined abundance has reduced, and in some cases eliminated, the harvestable surplus available for fisheries.
Due to the decline of Atlantic salmon, fisheries have been greatly reduced. Annual catches in the sea and rivers are reduced from 1500 to 500-600 tonnes during the last 30 years. The reduced exploitation has more than compensated for the decline, and the number of salmon spawning in the rivers has increased during recent years. In 2017, there were enough spawners in most rivers, which means that the natural capacity of the rivers to produce salmon juveniles was utilized. Hence, salmon populations are not restricted by lack of spawners, with a few exceptions.
Reduced salmon populations are caused both by human impacts and a general and large-scale reduction in survival at sea. Populations in middle and western Norway are most severely reduced.
Escaped farmed salmon, salmon lice and infections from salmon farming are the greatest anthropogenic threats to Norwegian wild salmon. The proportion escaped farmed salmon in the rivers is reduced in recent years, and the risk of further loss of wild salmon due to escaped farmed salmon is reduced from very high to high. The knowledge of infections from salmon farming is poor.
Hydropower production, other habitat alterations, acid rain and introduced pink salmon are also major anthropogenic threats to wild salmon, but the risk of further loss is smaller than for the threats related to salmon farming. Hydropower production and other habitat alterations significantly impact wild salmon, but the negative impact will likely not expand in the future. However, there is large potential for further mitigation measures. Due to liming of rivers and reduced emissions, the risk of increased negative impacts due to acid rain is small. Salmon populations in southern Norway have increased due to the comprehensive liming programs.
The threat to wild salmon from the introduced parasite Gyrodactylus salaris is now greatly reduced. Number of rivers with known occurrence of the parasite has been reduced from fifty to seven, due to successful eradication measures. Wild salmon have been re-established in rivers where the parasite has been eradicated. The risk of further spreading is reduced.
Sea trout populations are greatly reduced in large parts of the country (western and middle Norway and several rivers in northern Norway), but stable in eastern and southern Norway. Agriculture, other habitat alterations and salmon lice seem at present to be the most serious threats to sea trout.
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