Life history of a riverine, resident Atlantic salmon Salmo salar L.
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Abstract
The Mellingselva river, a tributary of the River Namsen, in central Norway, supports a population of freshwater resident Atlantic salmon (Salmo salar), which resembles a parr and which completes its entire life cycle in the river. The maturing females of this population are particularly small-sized (13.6 - 22.8 cm, mean 17.6 cm). They mature at an early age (mean 3.9 years), and have a low fecundity (55 - 190 eggs, median 95 eggs) compared to that of other salmon populations, both nonanadromous and anadromous. The annual mean growth rate after age of two years is about 2.0 cm and the low annual survival rate reflects the poor living conditions in this river. In spite of its small size when adult, this salmon lays large eggs (5.0 mm). This may be a compensatory mechanism that promotes the survival of offspring in spite of the low fecundity and low survival rate of the adults. These life history traits resemble those recorded for both anadromous Atlantic salmon parr and of resident brown trout (Salmo trutta) that live in impoverished rivers.
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