Energy channelling, food chain length and body condition in a northern lake predator

Identifying potential links between food web structure and animal body condition is fundamental for predicting the long-term persistence of populations under rapidly changing environments. Northern lakes, and the cold-water adapted species that inhabit them, are particularly vulnerable to a warming climate. We explored relationships among body condition and energy channel use in lake trout (Salvelinus namaycush) and seasonal variation in food-chain length in the Lake of Two Rivers, Ontario, Canada. Bayesian mixing models using carbon isotope values (δ¹³C) of essential amino acids showed that individuals utilising multiple energy channels had higher gonad mass, suggesting that dietary diversity has reproductive fitness benefits. Amino acid nitrogen isotope (δ¹⁵N) analysis revealed seasonal variation in food chain length, with extension of the food web during winter and spring and truncation of the food web during summer. Although these findings illustrate increased omnivory of lake trout during summer, there was no clear evidence that seasonal changes in food chain length had an impact on trout condition. These findings provide new insight into potential relationships between food web structure, energy flow and consumer condition in freshwater ecosystems, thereby revealing potential responses of species to shifting ecosystem states under intensifying climate change at high latitudes.