Atlantic Salmon (Salmo salar) Habitat Quality and Uncertainty Assessment Using Fuzzy Logic Modeling Applied On the Romaine River (Canada)

Many tools using to evaluate environmental flows, including physical microhabitat models like PHASBIM, are often used in stream-specific applications and are rarely easily exportable. With the aim to address this shortcoming, we developed three fuzzy logic models to assess the habitat suitability for three Atlantic salmon (Salmo salar) life stages (young-of-the-year (YOY), parr, spawning adults). Fuzzy sets of four variables (depth, substrate size, velocity and Habitat Suitability Index, or HSI) and associated fuzzy rules were defined with the knowledge of 27 experts from both sides of the Atlantic Ocean. Median curves of standardized Weighted Usable Area (WUA) were calculated and confidence intervals were estimated by bootstrap resampling. These confidence intervals were relatively narrow, despite the large range of WUA covered by the experts’ curves: an average width of 0.095 (on a scale of 0 to 1) for spawning habitat, 0.155 for parr rearing habitat and 0.160 for YOY rearing habitat. Applied on the Romaine river (Québec, Canada), the environmental flow values corresponding to 90% of the maximum reached by WUA curves were acceptable. Generally, this proposed fuzzy logic method seems suitable to model habitat availability for the three live stages, while also providing an estimate of uncertainty in salmon preferences.