Culverts as potential barriers to fish movement

I studied sixteen highway culverts and the associated water flow conditions to investigate whether they impact upstream fish movement in first and second order streams in the Piedmont and coastal plain of Delaware. Fish were collected and identified upstream and downstream of the culvert to assess differences in species abundance and diversity. Culvert materials, lengths, and perched conditions were evaluated for each stream, as well as water depth and velocities in the culvert. Water velocities were measured in perched culverts during storm events to determine perch-free velocities as encountered by fish.; Significantly greater numbers of species and numbers of fish were collected downstream of the culverts. Species diversity of fish collected below culverts was greater than the diversity in fish from above the culverts both in the aggregate and most individual streams. Roadway culverts appear to impact fish populations in streams. Several factors associated with the culvert, including the presence of a perch, low water depths and high water velocities in the culvert, appear to obstruct upstream movement of fish, possibly limiting habitat range. In order to prevent habitat fragmentation, highway culvert design should include consideration of fish biology.