Climate change and resilience of tributary thermal refugia for salmonids in eastern Canadian rivers

River water temperature regimes are expected to change along with climate over the next decades. This work focuses on three important salmon rivers of eastern Canada, two of which warm up most summers to temperatures higher than the Atlantic salmon lethal limit (>28 degrees C). Water temperature was monitored at 53 sites on the three basins during 2-18 summers, with about half of these sites either known or potential thermal refugia for salmon. Site-specific statistical models predicting water temperature, based on 10 different climate scenarios, were developed in order to assess how many of these sites will remain cool enough to serve as refugia in the future (2046-2065). The results indicate that, while 19 of the 23 identified refugia will persist, important increases in the occurrence and duration of temperature events in excess of 24 degrees C and 28 degrees C, respectively, in the mainstems of the rivers, will lead to higher demands for thermal refugia in the salmonid populations.