Niche use and resource partitioning of Arctic charr, European whitefish and grayling in a subarctic lake

Arctic charr and European whitefish are common species in northern Europe, but have a parapatric distribution pattern and rarely coexist in substantial densities within the same lake. Whitefish is considered to be the strongest competitor, usually causing competitive relegation or exclusion of co-occurring charr. Some exceptions do however occur, and the present study addresses niche utilization and resource partitioning of an Arctic charr population coexisting with whitefish and grayling in a subarctic lake. There was a distinct resource partitioning with respect to habitat and diet utilization of the three species. Grayling were exclusively caught in shallow near-shore areas, feeding chiefly on surface insects and Trichoptera larvae. Whitefish dominated in all lake habitats, feeding predominantly on small-sized planktonic and benthic crustaceans. Arctic charr were mainly found along the benthic profile, feeding predominantly on insects and snails and showing a low dietary overlap with whitefish which appeared to have monopolised the zooplankton resources. The highly restricted trophic niche of Arctic charr suggests a severe competitive impact due to the presence of whitefish, but the coexistence of the two species may be facilitated by the presence of grayling.