Diel activity patterns in overwintering Labrador anadromous Arctic charr

Anadromous Arctic charr, Salvelinus alpinus , migrate back to freshwater in late summer to spawn and/or overwinter. While seasonal movement patterns during the freshwater residency period are generally understood, specifics of the short temporal activity patterns remain poorly characterized. This study used temperature and accelerometer sensing telemetry to describe the diel activity patterns of 21 overwintering anadromous Arctic charr in a lake in southern Labrador, Canada. Tagged individuals displayed diurnal activity patterns throughout the overwinter residency period marked by greater activity during the day than at night and distinctive peaks of activity at the beginning and the end of each daylight period. Diurnal patterns were interpreted as driven by prey and light availability in the upper water column because of known linkages between light and foraging efficiency. Movement activity also increased as a function of temperature during the spawning and ice breakup periods, but not during winter when increased movement activity was correlated with colder temperatures. No association was found between movement activity and body size over the size range (36.0–48.5 cm) of fish studied. Our data suggest a complex set of behavioural determinants of overwinter activity, among which temperature and foraging are the most significant.