Pressures
There has been a steady decline in the abundance of salmon in Scottish rivers in recent years. In 1975 the total Scottish salmon catch was about 500,000, but this had decreased to about 100,000 by the year 2000. Much of this decline is due to changes in the fishing methods but there does appear to have been a real and worrying decline in the numbers returning to our rivers, particularly in the smaller and more vulnerable west coast rivers. However, the decline has been far more marked in other countries and Scotland continues to support significant populations. Four countries, including Scotland, together support approximately 90% of the world's healthy Atlantic salmon populations.
Salmon appear to be under threat in both their freshwater and marine phases. In fresh waters the decline in the quality of juvenile and spawning habitat is thought to be having the greatest effect with changing land-use and water pollution often to blame. In the sea the greatest cause for concern is the poor survival rate and the resulting low numbers of returning adults.
Climate change may be affecting salmon through changes in sea surface temperatures which in turn reduce suitable feeding areas around Greenland and the Faroes.
Almost all of the UK - farmed salmon production is located in Scotland. Salmon farming has expanded rapidly since the 1970s and production has risen from 32,000 tonnes in 1990 to 129,000 tonnes in 2000. The presence of farmed fish can threaten wild salmon in several ways, but it is the disease and parasite threat that is of most concern. Farmed fish can harbour sea lice and the highest levels of infestation in wild fish correspond to those areas used for salmon farming. Voluntary Area Management Agreements have been implemented around several parts of the coastline aimed at reducing sea lice infestation in salmon farms and thereby helping local wild salmon and sea trout populations. Escaped farmed salmon are often larger than their wild counterparts, making male farmed fish more attractive to wild female salmon and more successful in spawning. But, the farmed males are not as well adapted to the local environment as wild males resulting in less well-adapted offspring that are less likely to survive and therefore less able to produce the next generation.
Exploitation of adult salmon is difficult to measure, but clearly salmon destined for Scotland and elsewhere are exploited by high seas and coastal fisheries. There is evidence that significant numbers of juvenile salmon are captured as part of the 'by-catch' for commercial marine fisheries.