Influence of culverts on small stream fish communities in Northwestern Ontario / by Eric K. Berglund.

Stream crossings may alter fish habitat and fragment lotic environments, which could alter fish movement in stream reaches and lead to changes in fish community structure and population dynamics at the local and riverscape level. The potential for point source disturbance impacts by culverts may be analogous to confluences and the hierarchal spatial arrangement of tributary junctions, which are known locations of increased biodiversity. There is currently limited information on habitat fragmentation and the cumulative effects that culverts might have at the local and landscape level on fish communities in northwestern Ontario. Forty-three culvert sites and seven confluence points on small cold water streams were selected across 10 watersheds northeast of Thunder Bay, Ontario to examine fish assemblages and community characteristics above and below culverts and confluence points, to: (1) determine the extent to which culverts block or impede the movement of fish; (2) to evaluate the relationships among patterns and responses of fish assemblages and functional groups to environmental variables and (3) compare the patterns of biological and physical disturbance between culverts and natural stream confluence points. Species richness, abundance, biomass and density were significantly lower below culverts compared to above (p