Low Annual Fidelity and Early Upstream Migration of Anadromous Arctic Char in a Variable Environment

The life histories of anadromous Arctic Char Salvelinus alpinus are complex and vary greatly between populations and environments. Here, we detail key aspects of the physical environment and life history of a population of Arctic Char from Nulahugyuk Creek, Nunavut, Canada, to characterize migration traits in a highly variable environment. Over the course of this migration, creek discharge declined precipitously, forcing Arctic Char to migrate through shallow water with large diel temperature fluctuations (>10 degrees C) and high temperature extremes (>21 degrees C). The downstream migration of adults (>55 cm) began in mid-June and continued into early July, while the downstream migration of smolts (<30 cm) began in late June and continued until late July. The upstream adult migration began in late June and ended in late July, far earlier than most upstream migrations in the region. There was no appreciable upstream migration of juveniles, and Arctic Char 30 to 55 cm in length were absent from the up- and downstream migrations. The average age at first migration was 4 years, and the youngest adult Arctic Char migrating upstream were 8 and 9 years old. The missing size- and age-classes, and the fact that most upstream migrants were near reproductive maturity, indicate that Arctic Char in this system typically leave at a length of 19 cm and an age of 4 years and do not return for 4 to 5 years, when they are ready to reproduce. Anadromous Nulahugyuk Creek Arctic Char appear to employ strategies that limit their exposure to restrictive migratory conditions and facilitate their existence in an otherwise uninhabitable system. Understanding such population-specific migratory strategies is critical to the management of Arctic Char fisheries, which are comprised of populations with highly diverse life histories, and to our understanding of how these life histories may contribute to the adaptability and persistence of the species as climate change progresses.