Culvert Length and Interior Lighting Impacts to Topeka Shiner Passage

Project summary:

Culverts can act as barriers to fish passage for a number of reasons, including insufficient water depth or excess velocity. In addition, concern is being raised over behavioral barriers where culvert conditions elicit an avoidance response that deters or slows fish movement. Long culverts can block sunlight, creating a potential behavioral barrier as fish approach a long, dark culvert. Scant information exists on low light as a potential barrier to fish passage, particularly with warm water species such as the federally endangered Topeka Shiner. As some older culverts are being replaced with longer total lengths to improve safety by extending the culvert through re- engineered road embankments, information is needed to 1) determine when and if light mitigation strategies are necessary, and 2) design appropriate light mitigation strategies, if necessary. Based on literature review, field monitoring, and laboratory experiments, the effect of light on fish passage for Topeka Shiner and other small prairie stream fish was indiscernible. Therefore, no light mitigation for large box culverts (up to 150 feet in length) can be recommended for similar fish communities. Culverts that are very long or have very small openings may benefit from additional light.