Trophic biology and migratory patterns of sympatric Dolly Varden (Salvelinus malma) and Arctic char (Salvelinus alpinus)

The trophic ecology (diet and headmorphology) andmigration patterns of two closely related salmonid fishes, Arctic char (Salvelinus alpinus (L., 1758)) and Dolly Varden (Salvelinus malma (Walbaum, 1792)), were examined in tributaries of Lake Aleknagik, southwestern Alaska, to test for differentiation between species. Schoener’s index of proportional overlap andmultivariate analyses of diets suggested that these species had significantly different trophic niches. Arctic char and the largest individuals of both species had the most diverse diets, and sockeye salmon (Oncorhynchus nerka (Walbaum, 1792)) eggs dominated the diet of both species, especially Arctic char. Arctic char had larger jaws andwider heads thanDolly Varden of similar body length, whichmay contribute to interspecificdiet difference. The species alsodiffered inmigrationpatterns; otolithmicrochemistry indicated that juvenileArctic char wereproducedbynonanadromousmothers,whereas themothersof theDollyVardenhadbeen to sea in the seasonprior to spawning. The species also segregate in spawning habitat (Arctic char in the lakes and Dolly Varden in streams), as well as in juvenile rearing habitat. Our study provides the first evidence of divergent feeding andmigratory ecology between sympatric juvenile Arctic char and Dolly Varden, differences that may constrain hybridization and introgression between them.