Abstract
Stable isotope analysis of Arctic charr from a southern relict population in Québec showed that some individuals adopted anadromy as a life‐history strategy, but the strategy did not predominate in the population. Differences in length‐at‐age, ages and sex ratios between identified freshwater residents and anadromous individuals were consistent with previous descriptions of partially migratory populations. This suggests that anadromy in relict populations in Québec is associated with niche shift and occurs as a conditional response to opportunities for maximizing the rewards (e.g. fitness) of habitat use.