Assessing Hybridization Risk Between ESA-Listed Native Bull Trout (Salvelinus confluentus) and Introduced Brook Trout (S. fontinalis) Using Habitat Modeling

The introduction of non-native species can negatively impact native through reduced genetic fitness resulting from hybridization. lack spatiotemporal data on hybrid occurrences makes hybridization risk assessment difficult. Here, we developed a spatially-explicit Hybridization Risk Model (HRM) between Oregon bull trout, an Endangered Species Act-listed species, and introduced brook trout by combining intrinsic potential model (IPM) spawning habitat existing distribution use datasets in Oregon, United States. We created expert-based IPM classification score (0–1) streams based the geophysical attributes (i.e., temperature, discharge, gradient, valley confinement) to sustain habitats. HRM included matrix presence/absence both as well type (spawning versus other) at 100-m stream segment resolution. defined “extreme” when reaches contained were present with moderate or greater scores (IPM >0.5). Conversely, “low” historic non-spawning habitat, absent, low <0.25). Our classified 34 km extreme hybridization, 115 high risk, 178 6,023 risk. identify differential multiple spatial scales either coexist are absent. also that would have higher but where not currently present. modeling approach be applied other such cutthroat rainbow Chinook coho salmon, similar occurring elsewhere potentially hybridize freshwaters.