Streams modified for drainage provide fish habitat in agricultural areas

Open agricultural drains (ditches) provide necessary drainage for cropland and may also provide habitat supporting native fish assemblages. We tested whether warm-water drains in southwestern Ontario provide fish habitat similar to that of reference watercourses not subjected to drain maintenance. Features of fish assemblages and habitats were characterized using standardized protocols in 24 pairs of drains and reference watercourses. Drains and reference watercourses did not differ significantly in fish species richness, evenness, abundance, biomass, species composition, life stages, or nine of 13 physical habitat attributes expected to be altered by drain maintenance. These findings do not support concerns that drain maintenance has strong, lasting effects on fish assemblages and physical habitat features. Other landscape-level agricultural impacts may affect both drains and reference watercourses but were not examined in this study. We recommend that drains continue to be recognized as fish habitat under the Canadian Fisheries Act and that drain and fish habitat managers strive for logical, scientifically defensible drain maintenance practices that preserve fish biodiversity and habitat, while considering the needs of agriculture.