Freshwater habitat characteristics are known to affect life-history traits of migratory salmonids. Although the life cycle of the anadromous form of Arctic char (Salvelinus alpinus) is typically associated with lakes, there is a small number of anadromous populations in North America that spawn, rear, and overwinter exclusively in rivers. The life-history traits of these relatively understudied populations and how they differ from lacustrine Arctic char are poorly documented. We characterized life-history tradeoffs expressed by anadromous Arctic char originating from a riverine (Hornaday River) and a relatively nearby lacustrine system (Tatik Lake of the Kuujjua River) in the western Canadian Arctic using a 10 year dataset. The riverine population attained smaller average size (600 mm vs. 628 mm, fork length) and age (7.7 vs. 10.6 years), had a lower longevity (14 vs. 26 years), expressed a 44% higher growth rate resulting in larger size-at-age prior to reaching modelled length asymptote (700 vs. 754 mm), had a younger modal age-at-maturity (~6-7 vs. ~11-13 years) and mean age-at-first migration (4.1 vs. 6.4 years), and a higher natural mortality rate (0.31 vs. 0.21 per year). Our results broaden knowledge on the spectrum of life-history strategies exhibited by anadromous Arctic char and underscore how freshwater habitat influence vital rates and life-history tradeoffs, which have implications for conservation and sustainable harvest of salmonids.

In a polymorphic species, stable differences in resource use are expected among ecotypes, and homogeneity in resource use is predicted within an ecotype. Yet, using a broad resource spectrum has been identified as a strategy for fishes living in unproductive northern environments, where food is patchily distributed and ephemeral. We investigated whether individual specialization of trophic resources occurred within the generalist piscivore ecotype of lake trout from Great Bear Lake, Canada, reflective of a form of diversity. Four distinct dietary patterns of resource use within the lake trout ecotype were detected from fatty acid composition, with some variation linked to spatial patterns within Great Bear Lake. Feeding habits of different groups within the ecotype were not associated with detectable morphological or genetic differentiation, suggesting that behavioral plasticity caused the trophic differences. A low level of genetic differentiation was detected between exceptionally large-sized individuals and other individuals. Investigating a geologically young system that displays high levels of intraspecific diversity and focusing on individual variation in diet suggested that individual trophic specialization can occur within an ecotype. The characterization of niche use among individuals, as done in this study, is necessary to understand the role that individual variation can play at the beginning of differentiation processes.