Habitat preferences and residence time for the freshwater to ocean transition stage in Arctic charr

Using acoustic telemetry techniques, the movements and habitat utilization of anadromous Arctic charr (Salvelinus alpinus) were determined when they entered the Freshwater Creek Estuary (Cambridge Bay Northwest Territories, Canada) in the spring. The study was carried out during the transition from full ice cover to open water. Between 23 June and 1 July 1996, nine adult Arctic charr were tagged with external acoustic transmitters, These fish were tracked until 6 July using two radio-linked acoustic array systems and a portable manual receiver with a directional hydrophone. Two transmitters measured temperature and location, one measured depth and location and the remaining sis, location only. All of the lagged charr remained in Cambridge Bay Estuary until the sea-ice had melted and the mouth of the Lay was ice-free. Primarily, they remained in the warmer brackish surface layer which was similar to 2m thick and rarely moved into the colder underlying marine waters. As well, the tagged charr remained either near the shore or over offshore shoals, following the ice-edge as it melted down the estuary. Residence time in the estuary was greater than ten days for some fish. Therefore, in spite of evidence from controlled laboratory studies that have shown that Arctic charr are preadapted to the marine environment and are capable of migrating directly into seawater, this study shows that, in the wild, they prefer to remain in warmer brackish water until the sea-ice has melted and that the transition stage is longer than previously suggested.