Blake Hansen

Document Type


Publication Date



The Razorback Sucker (Xyrauchen texanus) and Colorado Pikeminnow (Ptychocheilus lucius) are federally endangered species occurring in the San Juan River of NM, CO, and UT. These species have shown little natural recruitment in this system, with a lack of high-quality nursery habitats being one potential explanation for this phenomenon. The young-of-year of both species prefer backwaters, including those that form in secondary channels or in association with islands. Unfortunately, many nonnative fishes that compete with and prey upon these imperiled species also reside in backwaters. However, it is unknown how nonnative fish densities vary between secondary channel and island backwaters during the critical post-spawning window of July-September, so we compared nonnative fish densities between the two backwater types across 20 sites (i.e., 10 of each type) sampled during five sampling occasions in 2021. Overall nonnative fish density was 53% greater in secondary channel compared to island backwaters, as nonnative fish density was greater in secondary channel backwaters in all but the first sample trip in mid-July. Our results suggested that secondary channels may be poorer nursery habitat for imperiled natives compared to islands because of their greater nonnative densities, which has implications for environmental flows management that can manipulate backwater availability.