Atlantic salmon

Where can they be found?

Atlantic salmon (Salmo salar) are found in the temperate and arctic regions of the Northern Hemisphere and are found in the rivers of countries which border on the both sides of the North Atlantic Ocean, and the Baltic Sea. They are an anadromous species, which means that they live in freshwater as juveniles but migrate to sea as adults before returning to spawn. Atlantic salmon return to their native river, and even the same stretch of the river from which they were born, with amazing accuracy. This means that many 'populations' of Atlantic salmon may exist within the same river.

How long do they spend at sea and in freshwater?

Eggs are laid by female fish in gravel depressions called "redds". As the eggs are released by the female, they are immediately fertilised by an accompanying adult male, and often by mature juvenile males (often referred to as 'precocious' parr). The fertilised eggs are then covered with gravel by the female. Spawning occurs between November-December but in some localities, particularly in larger rivers, this may extend from October - late February. After spawning has taken place about 90-95% of all Atlantic salmon die. Some do, however, survive and some may spawn twice or more.

The time taken for eggs to hatch (or the 'incubation time') depends on the water temperature. Generally speaking, eggs usually hatch during early spring. These young fish, which still have a yolk sac attached, are called 'alevins'. These fish remain in the redd for a few weeks and emerge from the gravel in April or May, when they have absorbed the yolk sac and are about 3 cm in length. These fish establish territories and compete with each other to feed on a range of items within the stream. As these 'fry' get larger, they develop prominent markings on their sides and are then known as 'parr'. Depending on the water temperature and the availability of food, these fish will live in the river for two to three years. Once they reach a size of ~12 cm, the parr undergo a physiological transformation which allows them to survive in marine environments. The young fish, now called "smolts", change in physical appearance, becoming silver, and start to leave the rivers during the late spring. Most of these fish will be gone by June.

Where do the smolts go and how long do salmon spend at sea?

Relatively little is known about the migration pathways of post-smolts or returning adults. Some research has shown that post-smolts move in schools whilst heading off to deep-sea feeding areas. Some of these fish feed in the Norwegian Sea and the waters off Southwest Greenland, and they may also utilise other sub-arctic feeding areas.

These fish remain in the ocean from just over a year to three or four years. Fish which spend only one year at sea (usually around the Faroe Islands and the southern Norwegian Sea) before coming back to Scottish rivers are called grilse at a size of 2-3 kg. Other fish may stay at sea for two or three years before coming back to Scotland. These are referred to as Multi-Sea-Winter fish or 'salmon' and, because they have spent more time feeding in marine environments (usually off Greenland) are larger than grilse. If these fish return to Scottish rivers between the months of January-June, they are referred to as 'spring salmon'. Salmon may, of course, enter Scotland's rivers at all times of the year. This contrasts with the migratory patterns observed elsewhere for this species within their global range and is one of the factors that make Scottish populations so important from a biodiversity perspective.

Atlantic salmon conservation status

Atlantic salmon are listed on Appendix III of the Bern Convention and Annex II and V of the EC Habitats & Species Directive. The multi-sea-winter component of the Atlantic salmon population is included in the UK Biodiversity Action Plan Priority Species List.