The effects of culverts on fish movement, diversity, and abundance in the South Loup River watershed, Nebraska

Culverts channelize water relative to natural stream reaches, which can increase the velocity of water passing through them. Increased water velocities can alter stream morphology and create a possible barrier or obstacle to fish passage, which may affect localized fish abundance and diversity. A survey was conducted at culverts in the South Loup River watershed, NE, using backpack electrofishing to sample for fish abundance and diversity, red shiner ( Cyprinella lutrensis) movement was assessed using a mark-recapture study over a 20 day period, plains topminnow (Fundulus sciadicus) from aquaculture were introduced and movement was monitored during a three day period, and FishXing models were conducted on six culverts using 10 species. Results from FishXing models were compared to field observations to determine the accuracy of modeling culvert passability by fish in prairie streams. The single-barrel pipe culvert exhibited relatively high water velocity and downstream plunge pool depth compared to double-barrel pipe culverts and bridges, and double-barrel pipe culverts exhibited greater downstream plunge pool depth compared to bridges. Also, downstream of single-barrel pipe culverts appear to support high abundances of non-native and piscivorous fish species. Red shiner downstream proportional movement was 83% higher and movement upstream was 53% higher past bridges compared to single-barrel pipe culverts, but a difference was not detected. Plains topminnow proportional movement downstream was 69% higher and movement upstream was 52% higher past bridges compared to single-barrel pipe culverts. Predictions from the FishXing model correlated to field movement data and could be useful in prairie stream conservation and management by predicting fish movement through culverts. Further research is needed with larger sample sizes, more study locations, and multiple years to determine the effects of culverts on prairie stream fish abundance, diversity, and movement.