Small Stream Fish Ladders for Drop Culverts

Stream connectivity is important for fishes as it allows longitudinal migration within watersheds. Road crossings (i.e., steel culverts, box culverts, etc.) can block fishes from migrating upstream hindering their life cycle and ability to recolonize. Fish ladders designed to retrofit culverts and eliminate stream fragmentation, specifically for small stream fishes, do not exist. We tested fish ladders on culverts in 10 streams in the Black Hills and 9 streams in eastern South Dakota. Fish that ascended ladders were captured in funnel traps to estimate passage rate. Drop height, ladder slope, water velocity, depth, discharge, fish density below culvert, and plunge pool depth were measured at each site to evaluate if any variables were driving passage. Overall, 1,213 fishes representing 23 species passed fish ladders throughout the summer with a mean passage rate ± SE in the Black Hills of 1.22 ± 0.38 fish/day and 28.05 ± 19.60 fish/day in Eastern SD. Among sites we found no relationship between passage rate and our independent variables though daily discharge influenced passage rate within some sites. Culverts retrofitted with passable fish ladders have the potential to reverse the negative effects of habitat fragmentation on lotic fishes.