Ecosystem change can affect the structure of aquatic communities thereby altering the magnitude and/or directional flow of energy and critical nutrients through food webs. Over the last three decades, multiple factors have reduced prey fish abundance in the Laurentian Great Lakes. Therefore, we employed chemical tracers in the form of stable isotopes (δ13C and δ15N) and fatty acids to explore trophic relationships of Lake Trout (Salvelinus namaycush) and 5 major prey species (Alewife: Alosa pseudoharengus; Mysis: Mysis diluviana; Rainbow Smelt: Osmerus mordax; Round Goby: Apollonia melanostomus; and Slimy Sculpin: Cottus cognatus) collected in Lake Ontario during 1990 to 2008.
Results/Conclusions
Diets of Lake Trout and major prey species were relatively consistent across most sample years. However, for Lake Trout, δ13C of dorsal muscle decreased linearly with the age of Lake Trout. Further, dual isotope mixing models, aimed at evaluating trophic patterns between Lake Trout and major prey species, suggest recent trophic changes with older Lake Trout foraging in deeper waters. These patterns imply that older individuals face reduced energy acquisition, reinforced by lower dorsal muscle lipid concentrations. We argue that reductions in the abundance of pelagic prey may be limiting the capacity of Lake Ontario to support all ages of Lake Trout. Evidence provided by our application of chemical tracers may foretell increasingly stressful conditions for predatory fishes such as Lake Trout and may also suggest weakening trophic stability within this pelagic system.
