Date of Award
Carl Ruetz III
In temperate regions, environmental conditions vary distinctly between seasons. This variation can strongly impact in-stream environmental conditions. Winter is often thought to be harsher than other seasons for stream fishes, given the adverse environmental conditions that arise from low temperatures during winter in temperate regions. Low temperatures, episodic elevated discharge, and ice formation associated with winter are hypothesized to reduce movement, body condition, and survival of stream fishes. However, few studies test this hypothesis through formal comparisons, and most studies of seasonal stream fish ecology focus on salmonids. To address this knowledge gap, I estimated and compared body condition, net displacement rates, and apparent survival of two common stream fishes in summer and winter. I conducted my study in Stegman Creek, a small coldwater stream in west Michigan. My study species were mottled sculpin (Cottus bairdii), a small-bodied benthic fish, and brown trout (Salmo trutta), a largerbodied, drift-feeding fish. Over two 7-week periods (July-September 2016, January-March 2017), I individually marked mottled sculpin (n = 352) and brown trout (n = 329) with passive integrated transponder tags, and recaptured tagged individuals via weekly backpack electrofishing surveys. Both species exhibited different responses to seasonal environmental changes. Mottled sculpin net displacement rates significantly declined in winter, while body condition and apparent survival probability increased. The magnitude of the increase in condition was small, and likely resulted from spring spawning preparation. Increased apparent survival may have resulted from reduced emigration of mottled sculpin, or reduced predation risk from large brown trout. Body condition and net displacement rates of brown trout remained stable between seasons. Models suggested apparent survival of brown trout was length-dependent in summer and time-dependent in winter. Periods of low apparent survival of brown trout in winter corresponded with extreme low and high water temperatures. My results suggest winter was not particularly harsh for mottled sculpin or brown trout in Stegman Creek, although brown trout apparent survival appeared to be negatively influenced by variable winter water temperatures. These findings suggest seasonal effects may be context-dependent, and are likely to vary among stream systems and fish species.
LaGory, Susanna K., "Seasonal Ecology of Mottled Sculpin and Brown Trout in a Coldwater Michigan Stream" (2017). Masters Theses. 857.