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ASSESSING LONGITUDINAL THERMAL CONNECTIVITY FOR PACIFIC SALMONIDS
Citation:
Fullerton, A., C. Torgersen, J. Lawler, Joe Ebersole, M. Snyder, AND N. Schumaker. ASSESSING LONGITUDINAL THERMAL CONNECTIVITY FOR PACIFIC SALMONIDS. AWRA Spring Specialty Conference ¿ Aquatic Connectivity, Snowbird, UT, April 30 - May 03, 2017.
Impact/Purpose:
Many rivers and streams in the Pacific Northwest are currently listed as impaired under the Clean Water Act as a result of high summer water temperatures. Warm stream and river temperatures can impede migration of fish like adult salmon, slowing migration and increasing exposures to warm temperatures, predation, and other effects. Where available, areas of colder water within warm streams and rivers can potentially serve as ‘stepping stones’ allowing salmon and other coldwater fish to migrate through otherwise inhospitable temperatures. The spatial configuration and availability of colder water areas that may function in this way, and the degree to which this may assist migratory salmon and steelhead remains poorly understood. This presentation will review the latest understanding of this phenomenon, and illustrate several methods we are using to assess its potential importance to salmon and steelhead populations in the Pacific Northwest. This abstract contributes to ACE CIVA 2.8.
Description:
Water temperature is a key driver of ecological processes in aquatic environments and can influence biological connectivity among riverine habitats. Riverine fish and other mobile aquatic species often must navigate a variety of physical barriers such as dams and culverts. For Pacific salmon, warm water can also pose barriers to migration, but the presence of patches of cooler water within rivers can serve as important refuges and potentially as stepping stones at times of day when temperatures are elsewhere unsuitable along the migratory corridor. Rising water temperature associated with climate change has become a major conservation concern for freshwater species and poses challenges for natural resource managers who must consider multiple factors in addition to uncertainty in climate predictions. Thermal refuges can contribute to watershed-scale thermal resilience and are increasingly considered in water quality regulations; however, monitoring such refuges and effectively operationalizing the concept for management has proved difficult. We review what is known about use of thermal refuges by coldwater fishes in natural systems, and then we present two case study applications in which we characterize thermal patterns in rivers (e.g., the frequency, size, spacing, and location of thermal patches) and consider effects on salmon in a management context. In our first example, we illustrate methods for quantifying spatial heterogeneity in stream temperatures at biologically relevant scales in the Siletz River watershed, Oregon USA. We accomplished this by identifying potential thermal refuges and barriers for salmon during summer at multiple scales using high-resolution airborne remotely sensed water temperature surveys. In a second example, we describe an approach in which we are using an individual-based model to illustrate how salmon may respond to and benefit from patchy thermal landscapes in the lower Columbia River, USA. Results will help identify how cool thermal refuges may be used by fish, what reaches may pose thermal barriers to salmon during migration, and where the restoration and creation of thermal refuges may be most effective in order to improve survival and reproductive fitness of migratory adult salmon.