Date of Award


Degree Type


Degree Name

Master of Science




Biology (MS)

First Advisor/Chairperson

Brandon Gerig


The St. Marys River (SMR) forms the border between Michigan, USA and Ontario, Canada connecting lakes Superior and Huron. Discharge is controlled by a compensating gate system upstream of the SMR rapids. Because spring and summer discharge fluctuates widely, resource managers required information on how flow variability influences larval fish drift. I estimated annual larval fish export in relation to variable discharge during 2018-2021 and compared results to published habitat model predictions. Mean discharge and water temperature were lowest in 2021 and highest in 2019. Water warming rates during high discharge differed from low discharge trends. Across years, I identified 10 families and 14 species of fish larvae drifting from the rapids. During my study, larval rainbow smelt (Osmerus mordax) densities were best explained by water temperature, discharge, and year of sampling while non-smelt densities were best explained by year of sampling and water temperature. Using a Bayesian state-space model, I estimated rainbow smelt larvae exceeded 30% of total export. Observed catch composition differed from previously published hydrodynamic models suggesting that modeled species did not spawn in the rapids. However, our catch composition was similar to prior river-wide studies conducted in the 1980s and 1990s. Future research on SMR larval fish export should be expanded to increase river coverage to identify spawning habitats for sensitive species included in the hydrodynamic model and of concern to resource managers.

Access Type

Open Access

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