River-resident salmon - Atlantic Salmon Form

The river-resident salmon, called the småblank in Norway, lives its whole life in the upper River Namsen. It is the only Atlantic Salmon in Europe that completes its life cycle in a river, without going to a lake or the sea.^[1]

Contents

Appearance
Habitat and range
Sources

Appearance

Adult fish keep the strong parr marks of young salmon, as the photo shows. A female in the photo of the original study was about 180 mm long and weighed 70 g.^[1]

Habitat and range

Map of northern Europe with a dot in central Norway at the upper River Namsen — The upper River Namsen in Norway. The dot is approximate. Base map: Natural Earth, public domain.

It lives in the upper River Namsen in Norway, where it completes its whole life cycle in the river.^[1]

Isolation

The population was cut off in the upper Namsen for about 9,500 years. It has about half of the genetic variety of sea-run salmon in the same river.^[1] The difference between it and the sea-run fish is similar to the difference between Atlantic Salmon in Europe and in North America.^[1] It was first described by Berg in 1953.^[1]

Elsewhere

Outside Europe, river-resident salmon are known only from watersheds in Newfoundland.^[1]

A river running white over rocky rapids between forested banks — The River Namsen at Namsskogan, Trøndelag, Norway. Photo: rob Stoeltje, 2013 · CC BY 2.0 · cropped

Sources

Sandlund et al. 2014, Ecology and Evolution 4: 1538–1554 (a river-resident population)

Identity
Form of	Atlantic Salmon
Other forms	Landlocked
Facts
Where	Upper River Namsen, Norway
Life	Entirely in the river
Isolated for	About 9,500 years
Genetic variety	About half that of sea-run fish