Thermal tolerance in cutthroat trout of the southern Rocky Mountains

With temperatures expected to rise across the southern Rocky Mountains, ability of native fishes tolerate stream warming has become a critical concern for those tasked with preserving coldwater species. We used common garden experiments evaluate thermal tolerance cutthroat trout ( Oncorhynchus clarkii) fry from five populations important managers representing three sub-species. Critical maxima (CTMs) were evaluated through traditional exposure trials, while optimal growth and ultimate upper incipient lethal (UUILTs) examined over course 21-day trials at six static temperature treatments. Whereas CTMs differed among (mean = 27.91 °C, SD 0.35 °C), UUILTs did not 24.40 0.04 °C). Comparison cubic temperature-growth functions quadratic showed that adding third-order term can improve model fit, revealed substantial differences in (15.4–18.3 Knowledge these thresholds will help predict consequences climate, identify suitable habitats repatriation, inform water quality standards established protect fish into future.