Atlantic salmon
(Salmo salar)

Classification and names
Fish; order: Clupeiformes, family Salmonidae
In French/Franšais: saumon atlantique
In Spanish/Espa˝ol: salmones
In German/Deutsch: : Lachs
In Dutch/Nederlands: zalm

Description
Life history per life stage: in the first stage after hatching young salmon are called alevin. They remain in gravel and feed on yolk sacs three to six weeks. After emerging from gravel they are called fry and feed on microscopic particles. These become parr when vertical markings (8-11 bars) with red spots appear. Back grey to brown with dark spots. Remain in stream 1-6 years until they reach a length of 12-15 cm. They are then called smolt and become silvery and prepare to live in salt water. Salmon at sea have a silvery colour on sides and black spots all over body. Underside white. Back shades of brown, green and blue.
Salmon returning to spawn after one year are called grilse.
Description adults (grilse)
Body laterally compressed and five times longer than deep.
Two dorsal fins, forked tail, 19 rays in anal fin. Mouth extends below rear of eye. 58 to 61 vertebrae. 4-6 small, sharp teeth and narrow pointed tongue. Males develop hooked lower jaw.
Colour: Both sexes become bronze/brown-purple. Males have red spots on side.
Length: females up to 120 cm, males up to 150 cm.
Weight: (not landlocked) 2-10 kg (up to 35.9 kg). Landlocked salmon are smaller.

Distribution
Northern Atlantic and its rivers. In Eastern North Atlantic from the Arctic Circle to Portugal. Only certain salmon populations in Norway, Ireland, Iceland and Scotland are not threatened by extinction.
Migration: Salmon are born in streams up river and migrate to sea after a few years. After one or more years mature salmon swim back upstream, of which 99% to their birthplace.

Habitat
Atlantic salmon are anadromous, they are born in freshwater and become adults in seas and oceans.
Salmon are born in shallow (depth 30-61 cm), cold (below 10° C), clean, fast-flowing rivers and streams with gravel.
When at sea, salmon seem to prefer temperatures of 4 to 12° C and are found at 2-10m depth.

Food
Young Atlantic salmon eat plankton and later insects before they go to sea. At sea young Atlantic salmon eat plankton, insects, crustaceans and small fish. At sea adult salmon eat various fish species, as well as shrimp and squid. While travelling back up river to spawn, adult salmon do not eat.

Behaviour & Reproduction
Sociability: young salmon swim in schools.
Mobility: swims vast distances down and up rivers, can jump waterfalls 4 m high.
Specifics: the Atlantic salmon's sense of smell is 1000 times greater than that of a dog (Maynor, 1996).
Sexual maturity: several years.
Reproduction capacity: female builds several nests (redds) in which she deposits eggs, which are simulatiously fertilised by one male with his sperm. In total, a female lays 10,000-20,000 eggs in these redds. Most Atlantic salmon swim back to sea after spawning, to return in later years to spawn again.
Reproduction period: spawn October-November. Female builds nest in gravel (redd), eggs buried at 12-25 cm depth in gravel. Eggs hatch in April.
Life span: max. reported age: 13 years.

Predation and competition
Young Atlantic salmon are eaten by various fish and birds.

Threats

Protection
EU Habitats Directive, Annex II (only in freshwater)
Bern Convention, Appendix III

Numbers
Unknown.