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Susanna LaGory defends her thesis on Seasonal Ecology of Mottled Sculpin and Brown Trout

Susanna LaGory defends her thesis on Seasonal Ecology of Mottled Sculpin and Brown Trout

On July 7, 2017, graduate student Suse LaGory successfully defended her Master's thesis titled “Seasonal ecology of mottled sculpin and brown trout in a coldwater Michigan stream”. Her thesis committee members included Dr. Carl Ruetz, Dr. James McNair, and Dr. Eric Snyder.

Suse conducted her research in Stegman Creek, a small tributary to the Rogue River near Rockford, Michigan. Her thesis aimed to better understand how seasonal environmental changes influence the dominant fish species in Stegman Creek: mottled sculpin and brown trout. Over the summer and winter, Suse conducted mark-recapture sampling, and implanted mottled sculpin and brown trout with PIT tags so fish could be uniquely identified over time. As tagged fish were recaptured over the course of each season, Suse tracked their length, mass, and locations within the study site. She used these data to estimate changes in body condition, weekly displacement rates, maximum displacement distances, and apparent survival from summer to winter. Winter conditions did not appear to be particularly harsh on either species in this study. Mottled sculpin body condition slightly increased from summer to winter, but this difference was likely caused by mature fish preparing to reproduce in the spring. Mottled sculpin apparent survival was 1.3 times higher in winter than in summer, and their average weekly displacement rates decreased by more than half in the winter. Brown trout body condition and displacement rates did not change between seasons, and their apparent survival was comparable between summer and winter. However, brown trout apparent survival appeared to be negatively influenced by rapid changes in water temperature in the winter. Stegman Creek is generally a very stable stream ecosystem, and these results suggest seasonal effects on stream-dwelling fish are most likely context-dependent. In streams that experience more environmental variation, fish may be impacted more strongly by seasonal changes.

Suse plans to pursue a PhD program next year, hoping to continue her education and career in stream ecology.

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