Life-history variation among four shallow-water morphotypes of lake trout from Great Bear Lake, Canada

Phenotypic variation within populations is common in many salmonids, especially when inhabiting northern postglacial systems. We compared life-history traits among four lake trout morphs co-existing in the shallow-waters of Great Bear Lake (Northwest Territories, Canada). Adult growth rate, age- and size-at-maturity, and survival differed among morphs, consistent with their degree of foraging specialization and predictions from foraging theory, e.g., reduced somatic growth and higher reproductive investment in the generalist morph, high growth throughout life in the piscivorous morph, and intermediate life-histories in the more benthic- and pelagic-oriented morphs. Fecundity and egg size also varied among morphs. However unexpected findings also arose, such as comparable immature growth rates among morphs. Other traits, such as a high proportion of resting individuals among all morphs, suggest life-history adaptations to northern latitudes. Longer resting periods are likely needed to obtain enough energy for reproduction, and may also allow greater investment in post-maturation growth. Overall, lake trout from Great Bear Lake demonstrated remarkable longevity and exceptional asymptotic sizes, even for a northern freshwater ecosystem. Our study provides new insights into life-history evolution among lake trout morphs that use different food sources and habitats. In addition, it contributes to our understanding of this complex aquatic ecosystem, which exhibits one of the highest known levels of intraspecific diversity among freshwater fish.