Behaviour and habitat use of first-time migrant Arctic charr: novel insights from a subarctic marine area

Abstract

Anadromous Arctic charr Salvelinus alpinus is a cold-adapted salmonid that is vul nerable to climate warming and anthropogenic activities including salmon farming, hydropower regulation, and pollution, which poses a multiple-stressor scenario that influences or threatens populations. We studied the horizontal and vertical behaviour of Arctic charr tagged with acoustic transmitters (n = 45, mean fish length: 22 cm) in a pristine, subarctic marine area to provide insights into the behaviour of first-time migrants. Tagged fish spent up to 78 d at sea, with high marine survival (82% returned to their native watercourse). While at sea, they utilized mostly near-shore areas, up to 45 km away from their native river. Arctic charr showed large variation in migration distance (mean ± SD: 222 ± 174 km), and the migration distance increased with body size. Although the fish displayed a strong fidelity to surface waters (0−3 m), spatiotemporal varia tion in depth use was evident, with fish utilizing deeper depths during the day and in late July. These results represent baseline data on Arctic charr’s marine behaviour in a pristine fjord system and highlight the importance of near-shore surface water as feeding areas for first-time migrants. Furthermore, the observed dependency on coastal areas implies a vulnerability to increasing human-induced perturbations, on top of impacts by large-scale climate change in marine and freshwater habitats.