Date of Award

5-2016

Degree Type

Thesis

Degree Name

Master of Science

Department

Biology

Program

Biology

First Advisor/Chairperson

Jill Leonard

Second Advisor

Patrick Brown

Third Advisor

Ashley Moerke

Abstract

Introductions of Pacific salmonids to the Great Lakes and their tributaries have caused concerns about potential competition with native brook trout (Salvelinus fontinalis) of the region. My research evaluated the diet of five fish size categories (FSCs) of brook trout, non-native steelhead trout (Oncorhynchus mykiss), and coho salmon (Oncorhynchus kisutch) in a tributary of Lake Superior by using diet overlap and selectivity indices as measures of potential competitive interactions. Stomach contents and drift were analyzed for seven months in three habitat areas of the study stream. Stomach contents were obtained from 643 fish and yielded 6245 prey items, the majority (76.3%) of which were aquatic. Diet overlap analysis included 8372 comparisons between individual fish and 42.63% of these comparisons had an index value of 0.0, meaning that the two individuals did not have a single prey item in common. Results suggest that niche differentiation has occurred among the three fish as indicated by the low diet overlap index values between interspecific pairings of FSCs and differences in the selectivity values for the most common prey items in the drift and diet among the FSCs. While this study provides evidence of the ability of native brook trout to persist in the presence of non-native Pacific salmonids in Great Lakes tributaries, it also suggests that this sympatry has costs for the native brook trout.

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