Date of Award

12-2021

Degree Type

Thesis

Degree Name

Master of Science

Department

Biology

Program

Biology

First Advisor/Chairperson

Dr. Brandon Gerig

Abstract

In this study, I investigated the spatial overlap, diet similarity, and isotopic niches of juvenile Lean and Siscowet Lake Trout ecotypes across six ecoregions of Lake Superior. Spatially, Lean and Siscowet were observed in overlapping depth distributions. Leans were most abundant in shallow waters (60m). The greatest levels of cohabitation were observed in waters from 40-60m. Trophic position (as measured by δ 15N) was similar for both ecotypes at small sizes (mm), but Siscowet exhibited a higher trophic position than Lean Lake Trout at larger sizes (>400mm) and older ages (>5 years). Base of production (as measured by δ 13C) was similar for small Lean and Siscowet. Isotopes of sulfur (δ 34S) indicated the profundal-benthic pathway was more important for Siscowet whereas Leans were more reliant on pelagic energy sources. Lean Lake Trout exhibited greater length-at-age relative to Siscowet. However, Lean Lake Trout length-at-age was negatively related to regional levels of diet similarity and niche overlap. I provide evidence that an ontogenetic shift in which Siscowet Lake Trout shift to feeding in deeper habitats at 400mm or age-5 facilitates resource partitioning between larger and older Lake Trout ecotypes.

Access Type

Open Access

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