Pressures on salmonids

Natural fluctuations in rivers and oceans have always affected stocks of salmon, trout and Arctic char. But the decline of salmon stocks over the last 30 years is primarily due to anthropogenic pressures.

Anthropogenic pressures with particularly serious impacts include acid rain, hydropower development, physical disturbance of habitat, the Gyrodactylus salaris parasite, the proliferation of sea lice at aquaculture facilities, and escaped farmed salmon. The Norwegian Scientific Advisory Committee for Atlantic Salmon Management has carried out a threat assessment and concluded that in 2010, sea lice and escaped farmed salmon were still non-stabilised, existential threats to Norwegian wild salmon.

Sea lice

Sea lice are parasites that are found naturally in marine waters, but which have reached unnaturally high concentrations in many of Norway’s fjords and coastal waters due to...

Escaped farmed fish

Escaped farmed salmon have an impact on wild salmon stocks. Some of the escapees migrate up rivers and spawn with wild salmon. Interbreeding can genetically weaken the wild...

Gyrodactylus salaris

The salmon parasite  Gyrodactylus salaris  is a serious threat to Norwegian wild salmon stocks. The Norwegian Food Safety Authority is responsible for parasite monitoring and fo...

Physical alteration of river systems

Physical alteration of a river system can range from major hydropower regulation schemes to minor changes such as the removal of riverbed substrata or riparian vegetation. Some...

River regulation for hydropower production

Hydropower developments have led to a substantial drop in wild salmon production in Norway’s salmon rivers, and are a critical pressure on salmon stocks in 110 of a total of 481...

Other physical alteration of river systems

There are many kinds of physical alterations to rivers that have negative impacts on anadromous salmonids (salmon, sea trout and sea char). In many cases, their effects are...