Light Levels, Long Box Culverts, And The Movements Of Prairie Stream Fishes, Including The Endangered Topeka Shiner

Abstract

Many culverts physically impede fish movement by altering flow, depth, turbulence, and sediment. Longer culverts may act as behavioral barriers by reducing ambient light levels. Movement within a stream is necessary to complete important life stages, maintain genetic diversity, and ultimately prevent extirpation. I evaluated light levels and fish movement in three long box culverts and corresponding control stream reaches in Southwestern Minnesota. The area has been denoted as critical habitat for the federally endangered Topeka Shiner Notropis topeka. I marked 18,963 fish, including 456 Topeka Shiner, and recaptured 1,874, including 46 Topeka Shiner during multiple mark and recapture events. Many fishes, including Topeka Shiner passed through each culvert; however, the probability of fish movement decreased as the culvert length increased and ambient light levels decreased. The probability was significantly less than corresponding control areas for the two longest and darkest culverts. The probability of movement was reduced in Cyprinidae (most abundant family), as well as the four most abundant species. Subsequent laboratory studies using captive-raised Topeka Shiner and wild-caught Fathead Minnow in a flume were conducted to evaluate light levels while controlling for other variables: velocity, water depth, and length of passage. Light alone did not account for significant differences in the number of fish to select a shaded or an unshaded passageway or the speed at which they approached and moved through the passageways under the laboratory settings. Mitigation of light levels may not be necessary when designing and implementing culverts, but synergistic relationships with other possible barriers (velocity, water depth, habitat within culvert, and length and dimensions of culvert) are unknown and need to be explored.