Fish assemblages and potential barriers in urban streams

Urbanization and associated infrastructures may fragment habitats, particularly within streams. This thesis examines the impacts of culverts on fish assemblages near Vancouver, Canada. I compared fish communities across 26 streams with and without culverts. Densities of cutthroat trout (Oncorhynchus clarkii) increased whereas coastrange sculpin (Cottus aleuticus) and prickly sculpin (C. asper) densities decreased, on both sides, relative to unculverted reference streams. I also found that simple retrofits for improving culvert passage may increase fish diversity over decadal timescales. I then examined the effects of four culverts within one urban watershed and show that successive culverts had a cumulative effect on fish distributions, particularly for prickly sculpin and cutthroat trout (negative and positive, respectively). Overall, this thesis demonstrates that culverts may drive changes in fish communities through species-specific impacts that are consistent both within and across watersheds. Understanding biotic responses to stream fragmentation can inform urban watershed restoration and conservation efforts.