Marine migrations and trophic niche use of Arctic charr in southwest Greenland fjords with contrasting influxes from glacial runoff

The facultatively migratory Arctic charr often undertakes annual marine feeding migrations. Climate-driven environmental changes such as increased glacial runoff can alter selective pressures shaping migration behaviour. To assess environment-related influences on migratory patterns and trophic niche use, we combined acoustic telemetry with otolith and stable isotope analyses to study two southwestern Greenland charr populations in fjords (Igaliku and Ikersuaq) differing in glacial runoff. Anadromous charr in Igaliku had a mean maximum travel of 21 km from their home river, while those in the more glacially influenced Ikersuaq remained near shore with shorter movements (mean 9km). Despite similar marine feeding durations (mean 48 vs 54 days) Ikersuaq fish exhibited lower marine feeding intensity. Arctic charr in Igaliku Fjord experienced warmer (mean 8.0ºC) conditions than those in Ikersuaq Fjord (5.7ºC), with estuaries (Igaliku 8.5ºC; Ikersuaq 7.2ºC) consistently warmer than marine areas in both systems. Findings suggest that where Arctic charr feeding and habitat use are constrained by high glacial runoff they may shift to more open waters altering diet and life-history strategies.