Description: Fish of the family Salmonidae have a small fleshy fin (adipose fin) on the back just in front of the tail fin, a characteristic which is absent in other European fishes. Adult salmon returning from the sea have a silvery blue-green back, silvery sides and a white belly. After some time in fresh water the silvery appearance is lost and they become brown or greenish mottled with red, orange and purple, especially the male, although some fish become dark grey or black in appearance. In fresh water, juvenile salmon (parr) are dark bluish or brown on the back with scattered black and orange/red spots on the body. They also have a series of dark ‘thumb-print like’ marks (parr marks) on the sides of the body. When the parr move down to sea (smolt stage) they become silvery in appearance for camouflage in the sea.

Habitat: This species is found in the larger, unpolluted river systems in Northern Ireland. In the autumn as the adults make their way upstream to the spawning areas and can often be seen jumping out of the water especially to overcome obstacles such as weirs and waterfalls. Spawning and juvenile stages occur in the turbulent, faster-flowing, and well-oxygenated upstream river tributaries. Juveniles can be seen in rivers where there is clear still water.

Distribution: In Northern Ireland, Atlantic salmon is found in all larger non-polluted river systems without barriers to upstream migration from the sea. The largest populations are present in the Melvin, Foyle, Bann and other north coast river systems together with smaller, but nonetheless important populations in terms of conservation, in the Glens of Antrim and Mourne rivers. Atlantic salmon have been reintroduced to the Lagan, but lack of suitable spawning substrate has prevented re-establishment of a self-sustaining population. Stocking has also been undertaken in the Erne system, once a famous salmon river prior to the construction of hydroelectric dams.

Similar Species: Atlantic salmon can be confused with brown trout (Salmo trutta) in the freshwater juvenile stage and adults returning from sea can be confused with sea trout — the marine migratory form of brown trout. The Atlantic Salmon Trust website is a good resource, and shows the main characteristics used to differentiate the two species. Hybrids with brown trout also occur at about one per cent in some rivers and are difficult to identify definitively, except by molecular genetic analysis.

Key Identification Features:

• Adults have an adipose fin just in front of the tail.
• Silvery blue-green as adults which is lost after some time in fresh water.
• Adults in fresh water are brown-green with red, purple or orange mottling.
• Juveniles are dark blue to brown with some black, orange or red spots.

Distribution Map from NBN: Salmo salar at National Biodiversity Network mapping facility, data for UK.

iNaturalist: Salmo salar at iNaturalist World Species Observations database.

GBIF data for Salmo salar

WoRMS: Salmo salar at World Register of Marine Species. Accepted name: Salmo salar Linnaeus, 1758. AphiaID: 127186.

Classification: Biota; Animalia; Chordata; Vertebrata; Gnathostomata; Osteichthyes; Actinopterygii; Actinopteri; Teleostei; Salmoniformes; Salmonidae; Salmoninae; Salmo