| Summary: | In the present thesis, winter mortality was linked to levels of stored energy by a field study from a northern Atlantic salmon population where population frequency distributions for specific somatic energy were compared among sampling periods. Interspecific differences in seasonal acclimatization were studied by performing common environment experiments on Atlantic salmon and establish models for thermal performance of winter acclimatized fish. These models were then compared to previously published thermal performance models for summer acclimatized salmon. Furthermore, the effect of changes in ice-cover conditions on the energy budget of the individual fish was studied using a series of common environment experiments in both laboratory and semi-natural environment. The latter experiments aimed at testing both interspecific and intraspecific variation in the effect of ice-cover. The results from these experiments were linked to winter mortality using bioenergetic modelling, where the input parameters originated from both field studies and experiments. The purpose of this conceptual modelling was not to provide quantitative predictions, but to demonstrate how environmental induced changes in the energy budget of individual fish may affect populations through the energy dependence of winter survival.
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