Wild brook trout populations varied meaningfully in their CTmax and vulnerability; they won’t be able to cope with future warming and heat waves through acclimation alone. These results can help with prioritizing conservation and management actions at local scales.

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Populations in southern Ontario watersheds with more urban 🏙️ and agricultural 🌾 development were the most vulnerable to heat waves ☀️

Populations in less developed areas and with more groundwater influence ❄️ had the highest TSMs.

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We found that stream temp (acclimation) 🌡️ and other site-level effects accounted for most of the variation among populations. TSMs varied substantially (15C!), reflective of the variation in site thermal regimes.

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We measured field CTmax of 20 wild brook trout populations across Ontario. We paired this with stream temp data & other site characteristics to examine thermal vulnerability and calculate thermal safety margins (TSMs) for each population.

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