Contrasting levels of strays and contemporary gene flow among anadromous populations of Arctic charr, Salvelinus alpinus (L.), in northern Norway

Arctic charr, Salvelinus alpinus (L.), occur as anadromous, resident, and landlocked populations within their circumpolar distribution. While resident Arctic charr reside in freshwater their entire life, anadromous Arctic charr migrate to sea in the summer due to the increased resource availability, but return to freshwater to overwinter and/or spawn. The migratory behaviour in Arctic charr is generally restricted to the northern range of their distribution area. The objective of this study was to estimate the amount of straying and contemporary gene flow among anadromous Arctic charr from eight river systems in northern Norway to illuminate the role of straying for the contemporary genetic stability of the populations. The results revealed that Arctic charr frequently stray among watercourses, especially among those in close geographical proximity, although strays were found nearly 500 km from their river of origin. While straying was revealed among six river systems, the results also revealed limited or no contemporary gene flow among the nine populations identified in the eight sampled river systems. The study also shows that Arctic charr may be a potential host for spreading diseases and parasites among watercourses.