| Summary: | Even though anadromy is integral to the life history of the Arctic charr (Salvelinus alpinus) in many northern regions, little is known about what shapes the patterns of anadromy. Moreover, little is known about the habitat use (e.g. temperature use and/or depth distribution) in relation to movement activity, especially during the overwintering freshwater residency period. An improved understanding of their behaviour in both freshwater and the marine environment will improve our understanding of how a cold-water specialist, such as Arctic charr, may respond to a changing climate, given the predicted and observed climate changes and existing hypotheses about its likely consequences for northern fishes. Accordingly, anadromous adult Arctic charr from two populations located near the southern end of the species distributional range have been studied in 2012, 2014 and 2015, to investigate the spatial and temporal patterns of habitat use in the nearshore marine and overwintering lake environments using passive acoustic and archival telemetry methods and a mixed effects modelling framework. Research has focussed on movement activity of anadromous Arctic charr while overwintering in freshwater lakes. Results showed that movement activity declined markedly during the ice-covered period, with low movement activity suggesting only opportunistic maintenance feeding as an energy conservation strategy. Movement activity was negatively correlated with body length, with smaller individuals being more active than larger conspecifics. Although general movement activity patterns were evident, there were significant differences among individuals, particularly in the spring immediately prior to lake departure. Lake size and individual differences in metabolic rate may account for some of this variation. Photoperiod strongly influenced the decline in movement activity in late autumn and, in combination with ice breakup, the increase in movement activity in spring. Arctic charr utilized a narrow temperature window (0.5-2°C) during ...
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