Consequence of habitat segregation to growth rate of two sparsely rakered whitefish (Coregonus lavaretus (L.)) forms in a subarctic lake

Abstract  – The aim of this study was to explain the growth differences of the two sympatric sparsely rakered whitefish ( Coregonus lavaretus (L.)) forms in the subarctic Lake Muddusjärvi by comparing their habitat and food selection to available benthic food resources. The average number of gillrakers was 22.9 for large sparsely rakered whitefish (LSR) and 16.8 for small sparsely rakered whitefish (SSR). LSR dwelled primarily in the littoral zone at depths < 10 m, whereas SSR used mostly profundal habitats in depths > 10 m. LSR and SSR consumed mainly benthic macroinvertebrates, their abundance, biomass and diversity was highest in the littoral, decreasing towards the profundal. As the individual size of fish increased, LSR was able to shift to larger food items, which were available in the littoral. Possibility of SSR to ontogenetic food shift was scarce in the profundal, where availability of larger benthic macroinvertebrates was low. Because of abundant food resources in the littoral, growth rate of LSR was faster than that of SSR.