Multi-year evaluation of muskellunge (Esox masquinongy) spatial ecology during winter drawdowns in a regulated, urban waterway in Canada.

Winter is an ecologically challenging time for freshwater fishes in temperate regions. In aquatic systems that experience annual winter water-level drawdowns, the pressures that fish already face during winter can be exacerbated. The Rideau Canal, a 202 km waterway located in eastern Ontario, Canada, is one such freshwater system that encounters these challenges. The 8.3 km "Eccolands Reach," near Ottawa, experiences a considerable annual drawdown from mid-October to mid-May of 1.79–2.13 m and is home to a self-sustaining, urban muskellunge population. Because the Eccolands Reach is relatively shallow and narrow, the drawdown may significantly reduce overwintering habitat. We used acoustic telemetry and hydraulic measurements to evaluate connectivity, critical winter habitats, and residency patterns of muskellunge (N = 23) over two drawdown seasons (2020–2021; 2021–2022) in the Eccolands Reach. Our results revealed that most muskellunge overwinter in a central portion of the reach with distinct, contiguous deeper sections and that the drawdown functionally fragments the river in several areas, eliminating connectivity to adjacent habitats, by creating shallow-water barriers and high-velocity currents in riverine constrictions. Additionally, we documented potential spring spawning movements and discuss implications of reproduction prior to system refill. Our work provides insights into connectivity and winter habitats of muskellunge in a regulated waterway. [ABSTRACT FROM AUTHOR]