Environment influences migration timing of cold-adapted salmonids (Salvelinus alpinus and S. malma malma) in the Canadian Arctic

Shifts in migration timing in response to climate change have implications for fitness and survival of cold adapted species. We used acoustic telemetry to investigate and compare environmental influences on return to fresh water between sympatric anadromous Arctic Char (Salvelinus alpinus) and Dolly Varden (Salvelinus malma malma), and between overwintering locations (above or below an obstacle – a substantial cascade). Both Arctic Char and Dolly Varden that overwintered below the cascade returned to fresh water later in the year, when sea surface temperature was warm and river temperature was cool, whereas Dolly Varden that overwintered above the cascade returned to fresh water earlier in the year, at cooler sea surface temperatures and during warm and likely stressful river temperatures. Ascension of the cascade by Dolly Varden (no Arctic Char were observed to ascend the cascade) was likely assisted by high tide but unaffected by other environmental factors, including temperature. Fish demonstrated plasticity in response to inter-annual variation in environmental conditions, but may experience decoupling of environmental cues and suitable migratory conditions, which could impact persistence of these ecologically and culturally important species.