Understanding Riverscape-Scale Patterns of Thermal Refuge Distribution in Relation to Landscape Hydromorphology in an Eastern Canada Watershed

Salmonids are intolerant of high temperatures and survive heat waves using cold water units known as thermal refuges.  However, large scale patterns of thermal refuge distribution and the mechanisms governing it are poorly understood.  Because climate change poses a threat to salmon populations, a better understanding of refuge distribution is of key importance. We used airborne thermal infrared imaging to characterise the spatial distribution of thermal refuges in ~700 km of rivers in the Restigouche River watershed, Canada. Thermal refuges identified as groundwater-driven were the most abundant.  Thermal refuge distribution was examined for links with landscape metrics.  Jacobs’ selectivity index showed that the occurrence of individual thermal refuges was significantly associated with high values of channel curvature (X² p <0.05, df = 9).  Regression analysis using a quadratic model showed that the larger scale density of thermal refuges was strongly correlated (R² = 0.83, p <0.05) with channel confinement. Our results indicate that the distribution of thermal refuges is strongly linked to landscape hydromorphology.  This is the first study to examine the spatial distribution of thermal refuges at riverscape scales.  It is hoped that such data will help conservation efforts to preserve thermal habitats in rivers threatened by climate change.