Do Light Levels Affect the Movement of Topeka Shiner and Other Prairie Stream Fishes through Long Box Culverts?

Every prairie headwater stream in the central US encounters road crossings. Many physically impede fish movement by altering flow, depth, and turbulence. Many bridges and short culverts are being replaced with longer box culverts due to safety changes and finances. Longer culverts reduce ambient light levels across their length and may act as a behavioral deterrent. Movement is necessary to access key seasonal habitats and maintain genetic diversity. The Topeka Shiner Notropis topeka may be encountering reduced movements. Other studies have measured impeded movement among Topeka Shiner and other fishes, but none have considered light. We evaluated light levels and fish movement in three long box culverts and control stream reaches in Southwestern Minnesota. Through multiple marks and recaptures, we marked 18,963 fish, including 456 Topeka Shiner and recaptured 1,874, including 46 Topeka Shiner. While many fishes, including Topeka Shiner, passed through each culvert, the probability of movement decreased with increasing culvert length and ambient light reduction, and was significantly less than control areas for the two darkest culverts. Further statistical analyses will determine if similar results apply to guilds, species, and sizes of fish. Controlled laboratory studies are underway to determine if light alone acts as a behavioral barrier.