Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 9014
Title: Longitudinal thermal heterogeneity in rivers and refugia for coldwater species: effects of scale and climate change
Author: A. H. Fullerton, C. E. Torgersen, Josh J. Lawler, E. Ashley Steel, J. L. Ebersole, S. Y. Lee
Publication Year: 2018
Journal: Aquatic Sciences
Volume: 80
Issue: 3
Pages: 1-15

The ability of organisms to contend with rising temperatures in freshwater habitats due to climate change is a major conservation issue. Predictions of climate change impacts to biota typically do not account for fine-grained spatiotemporal patterns in the thermal environment. Yet the presence of patches of cooler water within rivers could serve as important refuges for anadromous species that migrate during the warm season. We used high-resolution remotely sensed water temperature data to characterize summer thermal heterogeneity patterns for over 12,000 km of 2nd to 7th-order rivers throughout the Pacific Northwest and northern California (403 river segments). We evaluated: (1) the ability to resolve spatial patterns in water temperature data at different spatial resolutions, (2) the frequency, size and spacing of cold-water patches suitable for salmon, and (3) potential influences of climate change. Thermal heterogeneity patterns were nonlinearly related to the spatial resolution of water temperature data, and heterogeneity at fine resolution (<1 km) would have been difficult to quantify without spatially continuous remotely sensed data. Cool patches suitable for salmon were generally >2.7 and <13.0 km long, and spacing among these patches was generally >5.7 and <49.4 km. However, thermal heterogeneity patterns varied among rivers, with some having long uninterrupted stretches of warm water, and others having abundant cool patches. Using two approaches to predict potential future thermal heterogeneity patterns, we found little change in patchiness across rivers, but large change in individual rivers. These results can inform long-term monitoring programs as well as near-term climate adaptation strategies.

Theme: Habitats to Support Sustainable Fisheries and Recovered Populations
Foci: Characterize relationships between habitat and ecosystem processes, climate variation, and the viability of organisms.