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Young from the diadromous trout population in Vangsvatnet lake, Norway, showed a significantly higher rate of downstream migration than that of the landlocked trout from L0navatnet lake, Voss river system. The differences seemed not to be due to environmental factors, but to differences in genetics. The reason may be the strong selection pressure for maintenance of position in rivers above waterfalls.
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Bror Jönsson (1982) studied this question.
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