Evidence for Skipped Anadromus Migration in Northern Dolly Varden Char Based on Otolith Microchemistry Analysis

Anadromous northern Dolly Varden typically migrate to sea annually each summer starting at age 3-4. However summer observations of large anadromous fish in headwaters of one of the longest migratory rivers in Canada, the Rat, suggest that there may be a component of the population in this system that skip migration during the year of spawning, or are early migrants. This behavior has also been documented in at least one Alaskan river and may be associated with migration distance. Initial findings from otolith microchemistry analysis on a summer sample of adult fish from the Rat River spawning area confirmed that most individuals (7/8) skipped migration, while one individual returned early from sea; all fish were current year spawners based on gonad development. Analysis of a larger sample of adult fish harvested during the fall upstream migration revealed that 50% had previously skipped migration at least once and some individuals had done so twice. First skip migration in all individuals occurred between ages 5-6 after two seaward migrations. We discuss potential consequences of this unaccounted for component of the population for stock assessments which are based largely on data collected from upstream migrants or from individuals at fall spawning/overwintering sites.