Growth and Spatial Distribution of Fishes in Hydropeaking and Natural Rivers of Northern Ontario

Deviation from a river’s natural flow regime is considered to be one of the most serious and continuing threats to lotic ecosystems. Peaking hydroelectric facilities, which are designed to adjust the level of power generation in accordance with hourly energy demand, can dramatically alter the quantity and quality of habitat available to benthic invertebrates and fish. In this study, we examined the growth and spatial distribution of slimy (Cottus cognatus) and mottled (Cottus bairdi) sculpin along longitudinal and lateral gradients in two hydropeaking and eight natural Lake Superior tributaries. We hypothesized that (1) the permanently-wetted channel would support a greater number of faster growing fish than the varial zone; and (2) the highest densities and growth rates of sculpin would be observed at upstream sites (near the dams) and would decrease with distance downstream as a result of the ‘dam effect’. Sites were sampled for benthic organic matter, benthic invertebrates, and fish in 2009 and 2010. Growth was examined using otolith microstructure, and quantified using the von Bertalanffy growth function. Preliminary results indicate that (1) very few fish are using the varial zone, which can cover nearly half of the river’s width at peak flow; (2) habitats below dams support a greater abundance of fishes than habitats further downstream in peaking rivers, and (3) despite higher abundances, sculpin found below dams have higher growth rates than those found further downstream or in natural rivers. Results from this study demonstrate the importance of standardizing flow conditions for fish monitoring programs in peaking rivers, and help in the defining of a dam’s zone of influence.