Author: Jacob Lasci
Considering their size and ecological instability, the Laurentian Great Lakes represent a unique and important system to monitor freshwater fishes and their response to environmental changes. Lake Huron is the only Great Lake to have suffered a collapse of alewife Alosa pseudoharengus, an invasive prey fish that made up the majority of piscivorous salmonid diets in the Great Lakes prior to 2003. The lake-wide diminishing prey base remains one of the greatest concerns for the conservation of Lake Huron’s recreational and commercial fisheries. Traditional diet analyses using visual identification of stomach contents and stable isotopes have characterized the diets of piscivorous salmonids in recent years to determine what makes up their current diets. However, developments in the fields of eDNA and next generation sequencing now offer tools to characterize diets of consumers to a higher taxonomic resolution by identifying prey items that are semi-digested and secondary prey items in the stomachs of consumed prey, thereby capturing a larger part of the food web. Despite these methodological advancements, bioinformatic processing and statistical analyses of sequencing data remain challenging. Here, we use a multiple logistic regressions and compositional-compositional regression to determine the factors that influence the diets of piscivorous salmonids as measured by stomach content visual identification and stomach content eDNA metabarcoding. We found that the diets of Lake Huron piscivorous salmonids consume large proportions of bloater, rainbow smelt, and macroinvertebrates and eDNA metabarcoding revealed contributions of additional prey taxa that were not visually identified in the stomach contents. The high niche overlap among these salmonids may lead to the competitive exclusion of weaker competitors, like the native lake trout (Salvelinus namaycush), when directly competing for access to food with the introduced Pacific salmonids.