Temporally stable and distinct fish assemblages between stream and earthen stormwater drain reaches in an urban watershed

Streams and rivers have essential roles in landscape connectivity; however, urban watersheds are frequently modified to drain stormwater from urban areas. To determine whether an earthen stormwater drain in an urban landscape provides fish habitat temporally, we compared the fish assemblage among three reaches of a contiguous urbanized watershed in Kanata, Ontario, Canada. Watts Creek is connected to an earthen municipal surface stormwater drain (herein Kizell Drain), before discharging into the Ottawa River. We delineated transects in three reaches of the system, in Watts, in the Drain, and below their confluence (Main) and assessed the fish community using single-pass electrofishing repeated across eight months covering all seasons. Fish community composition was compared among reaches using non-metric multidimensional scaling (NMDS) and permutated multivariate analyses of variance (perMANOVA). Sign association tests identified indicator species driving assemblage patterns among reaches. Redundancy analysis (RDA) was used to assess the influence of physical characteristics of the transects on fish assemblage structure. Finally, fish assemblage measures were separated by month and temporal comparisons of fish assemblage were performed with NMDS and perMANOVA. Over the year, fish assemblages were distinct among the three reaches, and appear to be significantly influenced by temperature, undercut banks, and riparian vegetation type. Biotic homogenization in the Drain can be attributed to degraded physical features associated with channel modification in stormwater drains. Despite management and jurisdictional differences between streams and stormwater drains, evidence that earthen stormwater drains can maintain fish assemblages temporally demonstrates their biological potential and need to be considered as interconnected fish habitat elements within the overall watershed.