| Summary: | I studied the occurrence of two sympatric morphs of arctic charr, Salvelinus
alpinus (L.) in Vatnshlidarvatn, a small shallow lake in NW Iceland. The arctic charr
were subjectively distinguished by colour and appearance as brown morph or silver
morph, and measured for morphological and life history characters. The study
revealed the presence of two growth forms represented by the two morphs that differed
in age and size at sexual maturation, reproductive investment, and time and place of
spawning. The morphs differed significantly in gill raker number and morphometric
characters related to manoeuvrability and cruising ability. Morphological segregation
was established early in life and is most readily explained as developmental
heterochrony. Both morphs were benthivorous, but could be segregated as diet
specialist and generalist, with diet segregation being important only when food
(especially the benthic crustacean Eurycercus spp.) was scarce, The occurrence of one
abundant food resource, and lack of interspecific competition (no other fish species are
present) may explain the different feeding strategies. The presence of "empty" niche
should induce variability and divergence in morphology and life history to occupy
available niche space. === Graduation date: 1997
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