Annual and Ontogenetic Variation in the Diet of Lake Trout (Salvelinus namaycush) Using Stable Isotope Mixing Model

Stomach contents have long been used to obtain fish diets. However, for small lakes, this lethal method may significantly influence the population of the sampled fish and alter the whole lake ecosystem. Here we apply the stable isotope mixing models, based on nonlethal samples such as fin clips, to reconstruct the diet composition of lake trout in Lake 373 in Experimental Lakes Area, Ontario, Canada. We applied δ¹⁵ N and δ¹³ C analyses for the whole lake from plants to the top predator lake trout.  Based on fin clip samples during 2007 and 2012, we find that δ¹⁵ N value of lake trout increases as a function of fish length. Lacking covariance in δ¹⁵ N of lake trout and minnows may suggest no large changes in δ¹⁵ N signatures at the base of the lake and no large anthropogenic nutrient inputs during this time period. We model lake trout diets and discuss the difference between years and between body size classes.  Application of Bayesian mixing model to stable isotope analysis, using nonlethal samples, provides an excellent tool to estimate fish diets.