Influence of potential fish competitors on Lake Trout trophic ecology in small lakes of the Barrenlands, N.W.T., Canada

Local (e.g., habitat compensation activities) and regional (e.g., climate-related range expansion) events that are expected to increase in northern Canada can facilitate movement of fishes into aquatic ecosystems from which they were previously absent. Successful colonization would change fish community structure and potentially alter food web dynamics. We compared the trophic ecology, growth, and body condition of Lake Trout (Salvelinus namaycush) in small, tundra lakes that varied in fish community structure to help understand effects of colonization on this key species. Complementary stable isotope and stomach content analyses indicated that Lake Trout foraging differs between lakes with and without multiple large-bodied fishes. In lakes with a single potential competitor, trout consumed primarily pelagic zooplankton, but focused on more littoral resources in the presence of multiple large-bodied fishes. Population trophic niche width and inter-individual variation in Lake Trout diet were larger in lakes with multiple competitors, whereas Lake Trout populations in lakes with only one other large-bodied species were in better body condition. Our findings highlight the potential sensitivity of northern Lake Trout populations to colonizing fish species.