| Peaking hydroelectric facilities can dramatically alter the quantity and quality of habitat available to fish; however, it is not well understood how these changes to habitat affect the spatial distribution, growth, and life history schedules of fish. In this study, I examined the density and biomass of fish communities, as well as the growth, condition, age- and size-at-maturity, and natural mortality rates of slimy sculpin (Cottus cognatus), in the regulated Magpie and Michipicoten and eight neighbouring unregulated Lake Superior tributaries in Ontario, Canada. My assessment of the spatial and growth patterns of fishes in regulated rivers takes an ecosystem or multi-trophic approach that incorporates different levels of production (e.g., fishes, invertebrates, CPOM) and the habitat or environmental conditions in which they live. Unregulated reference rivers provided measurable benchmarks for comparison with the regulated systems. Strong lateral and longitudinal gradients in fish biomass and density are present below dams on the Magpie and Michipicoten rivers, and correspond with similar gradients in invertebrate and CPOM abundance. Sculpin growth follows a similar longitudinal pattern, and sculpin were significantly larger below dams on the Magpie and Michipicoten than at locations further downstream or in nearby unregulated rivers. Fast-growing sculpin in the peaking rivers matured at an earlier age and showed higher natural mortality than sculpin in nearby unregulated rivers. Differences in sculpin growth and life history traits closely followed changes in food resources and thermal regime, suggesting that these differences are driven by spatial shifts in food availability and cooled temperatures from a metalimnetic draw that provides thermal refuge for the slimy sculpin.;Keywords: hydropeaking, river regulation, lateral and longitudinal gradients, growth, life history, river discontinuity, varial zone, zone of influence, slimy sculpin (Cottus cognatus). |
