Water temperature predicts razorback sucker Xyrauchen texanus spawning migrations

Riverine fishes often rely on environmental cues to initiate spawning or movement to spawning habitats. Knowledge of the relationships between life history strategies and the environment is a valuable tool in planning conservation and restoration techniques. Despite intensive management efforts, federally endangered razorback sucker Xyrauchen texanus have experienced drastic population declines and continue to experience reproductive and recruitment bottlenecks. Although previous studies suggested razorback suckers spawn during increasing spring flow, little is known about the abiotic cues that influence putative spawning movements. Because photoperiod, water temperature, and flow may affect spawning and movement behavior, we hypothesized one or more of these variables would predict the timing of razorback sucker movements during the spawning season. We tested the association between environmental factors and the timing of razorback sucker occurrences at two barriers to upstream movement in the San Juan River over 7 years (2015–2021). To test the most parsimonious model, we examined the timing of razorback sucker occurrence at a third barrier in the Green River from 2017 through 2019, and in 2021. Although environmental variables are often correlated, we tested several years where water temperature and flow were asynchronous, allowing us to partition effects of these variables. Our results indicated strong associations between putative razorback sucker spawning migrations and mean weekly water temperature, where the largest proportions of fish aggregate below barriers as water temperature was increasing between 7.8 and 13.4 °C (pseudo R 2 = 0.21). We provide a temperature-based model to predict spawning migration timing at selective passage facilities, which might aid in efforts to increase reproductive potential of razorback suckers by allowing mature adults access to upstream spawning habitats. Understanding the relationships that influence reproductive ecology is critical to catostomid conservation, and the environmental cues tested here for razorback sucker may be generally relevant to other migratory suckers.