Integrating hyporheic exchanges into salmonid spawning habitat models—A proof of concept focusing on Atlantic Salmon in Québec, Canada

Abstract Objective Most salmonids use pool–riffle transitions for spawning. The biological explanation appears to be associated with bedform-induced hyporheic exchanges. Despite this apparent link, spawning habitat models still rely on depth, velocity, and bed material grain size. In this study, we tested (1) whether integrating hyporheic exchanges into habitat modeling better constrains habitat suitability estimates and (2) whether hyporheic exchange proxies can substitute for fully resolved hyporheic exchanges. We tested our hypotheses in an Atlantic Salmon Salmo salar spawning reach of the Sautauriski River, Québec, Canada. Methods We combined drones and Structure-from-Motion Multiview-Stereo photogrammetry to reconstruct reach-scale bathymetry, which was used for fully coupled surface–subsurface flow modeling of depth, velocity, and hyporheic exchange. We also derived hyporheic exchange proxies from the simulated hydraulic variables and developed reach-specific habitat suitability curves and habitat suitability index models to test our hypotheses. Results Integrating hyporheic exchanges alongside depth and velocity produced more spatially constrained suitability estimates. Comparable suitability patterns were also obtained using proxies for hyporheic exchanges. Conclusion Our findings support our primary hypothesis, but they also suggest that simpler proxies may substitute for fully resolved hyporheic exchanges in habitat modeling. Despite these promising results, the study remains a proof of concept because of uncertainties associated with both the hydraulic and habitat modeling approaches.