Polymorphic segregation in Arctic charr Salvelinus alpinus (L.) from Vatnshlı́darvatn, a shallow Icelandic lake

Abstract

We studied the salmonid fish Arctic charr, Salvelinus alpinus, in a small and shallow landlocked lake in NW Iceland. The lake is productive but the only fish present is Arctic charr. Despite the apparent absence of discrete benthic and limnetic habitats for fish, two forms of Arctic charr are found in the lake. They show subtle differences in morphology related to swimming performance and manoeuvrability, but differences in life history such as growth, and age and size at sexual maturation are more pronounced. Both forms have benthic feeding habits with one form consuming greater number of species than the other. We suggest that the segregation of these forms is based on the evolution of a specialist from a local generalist and that this has been made possible by the absence of a common fish competitor in similar lakes, the threespined sticklebackGasterosteous aculeatus .