Research Document 2019/076

Invertebrate prey availability, habitat condition and Redside Dace (Clinostomus elongatus) status in Greater Toronto Area streams

By Reid, S.M., Haxton, T., and Jones, N.E.

Abstract

Redside Dace (Clinostomus elongatus) is a small, colorful cyprinid found in pools and slow-flowing sections of Ontario streams. As a result of recent declines and threats to remaining populations, the species was assessed as Endangered in Canada. Habitat degradation caused by urban development is considered a primary threat. However, a clearer understanding of associated impacts is required to inform assessments of population trajectories and habitat supply. In this study, we compared riparian vegetation, stream habitat, and terrestrial (riparian) and aquatic invertebrate abundance and diversity among 24 Greater Toronto Area (GTA) sites that represented three population status categories of Redside Dace (extirpated, declining or stable). Sites were sampled during the summers of 2008 and 2009. Stream habitat was characterized using the Ontario Stream Assessment Protocol (OSAP) rapid assessment methodology (RAM). Invertebrate prey availability was characterized using drift samplers and sweep nets. Clear separation of population groups was evident using multivariate analysis of riparian vegetation and bank stability data. However, significant univariate differences were only identified for riparian vegetation; with greater amounts of grasses at stable population sites and more bare ground at extirpated sites. Using instream habitat data (e.g., amount of riffles and pools), there was less separation of population groups in multivariate space. For both terrestrial and aquatic invertebrate data sets, abundance, biomass and taxa diversity did not significantly differ among groups. Multivariate differences in taxa composition were also not significant. Small sample sizes and high data variability limited our ability to detect significant instream habitat and invertebrate differences among groups. Other factors that may have influenced study results include high regional variation in surficial geology and topography, habitat and invertebrate sampling methods, and differing responses of Redside Dace and invertebrate taxa to environmental stressors.