Date Approved

12-16-2021

Graduate Degree Type

Thesis

Degree Name

Biology (M.S.)

Degree Program

Biology

First Advisor

Mark Luttenton

Second Advisor

Eric Snyder

Third Advisor

James Dunn

Academic Year

2020/2021

Abstract

The North Branch of the Au Sable River is located in the northern lower peninsula of Michigan and is known for prolific hatches of Ephemeroptera (mayflies), Trichoptera (caddisflies), and Plecoptera (stoneflies). Macroinvertebrates play an important role in processing and recycling organic material in rivers and are a valuable food source for trout. In 2018, anglers were reporting catching fewer numbers of brook and brown trout (Salmo trutta and Salvelinus fontinalis). The Michigan Department of Natural Resources (MDNR) determined significantly lower abundance than the historical average. We hypothesized that trout abundances were lower due to a lack of prey availability. Quantitative sampling techniques were used to assess each available substrate and respective aquatic macroinvertebrates throughout the river. Our estimates indicate that coarse woody debris substrates supported the highest abundances with the most individuals/m2. Originally, we hypothesized gravel substrates to have the highest abundances from past literature. We determined community composition and total abundance of macroinvertebrates. We determined that there was a shift in the community composition from mostly Ephemeroptera, to a 1:1 ratio of Ephemeroptera and Trichoptera. Chironomidae was the most abundant taxa of macroinvertebrates on every substrate. Our results suggest that the current macroinvertebrate composition and population would support the current trout population.

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