Population Structure, Ecological Segregation, and Reproduction in a Population of Arctic Char (Salvelinus alpinus) from Lake Tasersuaq, Greenland

Abstract

The population of Arctic char (Salvelinus alpinus) in a large lake, Tasersuaq, in West Greenland consisted of three distinct size groups representing ecological forms with differences in habitat, feeding, and reproduction. Smaller char were benthic and fed on chironomids whereas medium-sized char were living pelagically in summer, feeding on zooplankton. Larger char moved randomly over the strata, and cannibalism increased in importance with increasing size. Within each size group there was a great variation in age. All three groups contained spawners but spawning frequency variated between groups. Smaller forms probably transform to larger ones with correlated shifts in diet and periods of somatic growth only. We hypothesize that the ecological forms of the Tasersuaq population may represent an early step towards speciation. This view bridges the opposing interpretations of char populations presented in the literature considering different forms as belonging to either a common gene pool or to reproductively isolated sibling species.