Date of Award

6-2023

Degree Type

Thesis

Degree Name

Master of Science

Department

Biology

Program

Biology (MS)

First Advisor/Chairperson

Dr. Diana Lafferty

Abstract

The Lake Superior food web has undergone many changes in recent decades, including the rehabilitation of the native apex predator lake charr (Salvelinus namaycush) and the introduction of several nonnative species. The trophic linkages and ecological requirements of the entire fish community, including predators and prey fishes, has not been assessed on a whole-lake scale in over a decade. Here, I investigated the trophic dynamics across multiple regions of the lake, and estimated the consumptive effect of lean lake charr in one region of Lake Superior. From April to October of 2021, a total of five predator, four large prey fish, and five small prey fish species were collected by region and length class during coordinated, standard gillnet and bottom-trawl surveys. To assess trophic linkages, gut contents were examined and biomass, count, and length were measured. Additionally, twelve common lean lake charr diet items were collected during summer 2022, analyzed for energy density, and used to estimate a population-level consumption of leans. I found a high degree of interconnectedness in the Lake Superior food web, with Mysis as a keystone diet item for the entire fish community. Lake Superior predators displayed regional variance, ontogenetic shifts in diet structure, and opportunistic feeding strategies. Conversely, prey fish diets were less diverse, primarily reliant on Mysis and Diporeia, and were more likely to have a single dominant diet item. This study improves our understanding of Lake Superior trophic dynamics and provides a baseline for future food web and bioenergetics modeling in the lake.

Access Type

Open Access

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