| Summary: | The movements of 90 anadromous Arctic charr Salvelinus alpinus (mean ± s.d. fork length = 45.63 ± 5.6 cm) in fresh-, brackish-, and marine waters were studied from mid-July to midSeptember 2021 use of acoustic telemetry in Isfjorden, Svalbard (WGS: 84 - 78.84˚ N, 13.30˚ – 17.37˚ E). Anadromous Arctic charr was tagged with acoustic transmitters at 5 different locations in Isfjorden, and their movements were recorded on 27 receivers placed in strategic places in the fjord and around river mouths. During the migration phase, most tagged individuals (> 80 %) was detected close to the river mouth, with a depth utilization almost exclusively in the upper aquatic zone (0 - 3 m depth). While migrating outside the river mouth zone, a capacity of migration > 70 km was recorded, with individuals swimming offshore and crossing the straight across over Isfjorden, taking advantage of both lakes (Bretjørna and Lovénvannet) covered in this study. Area utilization calculations showed differences between groups tagged in the southern and northern part of Isfjorden, but there was also overlap in area utilization. The marine phase of the migration ended for most individuals (59 %) by the end of July, followed by a week-long residency in the brackish environment close to the river mouths. The time of freshwater return could mainly be explained by the day in the season and length of the individual (AIC-weight = 67 %), including 2 days differences between lake Lovénvannet and Bretjørna. Modeling showed a significant earlier return to the freshwater environment by the increased length of the individuals. Larger individuals were also found utilized greater depths in the lakes (up to 32 m depth). Finally, this study submitted a stock mixing between watercourses based on individuals’ detection in the same lake (Lovénvannet) from almost all (4 of 5) groups. Still, a genetic examination must be done to investigate the genetic flow in more detail. Migrering av 90 anadrome røyer Salvelinus alpinus (gjennomsnitt ± s.d. gaffel lengde = ...
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