Evaluation of the aquatic habitat and fish assemblage in an urban reach of the historic Rideau Canal, Ottawa, Canada: Implications for management in an engineered system

Abstract

The historic Rideau Canal (built in the 1800s) in eastern Ontario, Canada is a heavily managed and engineered ecosystem, popular for recreational boating and sport fishing in the summer and ice skating in the winter. However, little is actually know about the fish and aquatic macrophyte communities, particularly in the urban reach in Ottawa between Hartwell’s Lock and the outflow of Dows Lake. The objective of this study was to examine the extent to which fish and macrophytes varied among different natural and engineered habitat/substrate types across the period when the canal is at navigational water levels. Five gross habitat types were identified, consisting of gravel, silt/sand, rip-rap/gabion basket, boulder and concrete wall habitats. Replicate transects were established in the littoral zone, representing the different habitat types. Snorkel surveys were conducted on a biweekly basis, where fish species and aquatic macrophytes within the transects were quantified. Supplementary data on fish populations was obtained through seine net sampling as well as angler interviews and visual observations. The fish community was characterized as a reasonably simple warmwater assemblage, dominated by centrarchids (e.g., pumpkinseed [Lepomis gibbosus], bluegill [L. macrochirus], and largemouth bass [Micropterus salmoides]). In fact, more than 90% of all fish encountered (snorkel surveys and seine netting) belonged to the centrarchid family. None of the 17 fish species encountered in the reach were considered “at risk” in Canada, although the system supports one of the few urban muskellunge (Esox masquinongy) populations in the world and provides a range of urban recreational fishing opportunities for sportsfish. Fish diversity metrics (e.g., diversity, richness, evenness) varied little among habitat types, perhaps reflecting the fact that vegetation communities were reasonably homogeneous, largely dominated by the exotic Eurasian water milfoil (Myriophyllum spicatum). This research provides managers with the first detailed information on the aquatic ecology in this engineered urban ecosystem which will enable relevant government agencies (e.g., Parks Canada) to better balance the iconic cultural values of national significance with their mandate to protect the ecological integrity of the canal ecosystem.