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Assessing sufficiency of thermal riverscapes for resilient salmon and steelhead populations
Citation:
Ebersole, Joe, A. Brookes, B. Rashleigh, J. Massie, AND N. Schumaker. Assessing sufficiency of thermal riverscapes for resilient salmon and steelhead populations. Society for Freshwater Science, Sacramento, CA, May 21 - 26, 2016.
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. Adverse effects of warm waters include impacts to salmon and steelhead populations that may already be stressed by habitat alteration, disease, predation, and fishing pressures. Much effort is being expended to improve conditions for salmon and steelhead, with increasing emphasis on preparing for future climate change. One climate change adaptation strategy that is gaining increased attention is the potential for thermal refuges to help mitigate the effects of increasing temperatures. Thermal refuges are areas buffered from regional climate effects at a range of spatial and temporal scales. These features can be critical to coldwater fish at certain times when rivers would otherwise be too warm for survival. But it has been difficult to estimate the relative benefits of thermal refuges to salmon and steelhead populations, and more information is needed on the relative size, spacing and quality of refuges needed to adequately protect salmon and steelhead now and under future climate conditions. This presentation will describe to modeling approaches we are using to address and identify key uncertainties for evaluating refuge effectiveness. Using examples from the Columbia River and from watersheds throughout the Pacific Northwest, we will illustrate modeling approaches that summarize and synthesize the state of the science on thermal refuges to address present and future management needs.
Description:
Resilient salmon populations require river networks that provide water temperature regimes sufficient to support a diversity of salmonid life histories across space and time. Efforts to protect, enhance and restore watershed thermal regimes for salmon may target specific locations and features within stream networks hypothesized to provide disproportionately high-value functional resilience to salmon populations. These include relatively small-scale features such as thermal refuges, and larger-scale features such as entire watersheds or aquifers that support thermal regimes buffered from local climatic conditions. Quantifying the value of both small and large scale thermal features to salmon populations has been challenged by both the difficulty of mapping thermal regimes at sufficient spatial and temporal resolutions, and integrating thermal regimes into population models. We attempt to address these challenges by using newly-available datasets and modeling approaches to link thermal regimes to salmon populations across scales. We will describe an individual-based modeling approach for assessing sufficiency of thermal refuges for migrating salmon and steelhead in large rivers, as well as a population modeling approach for assessing large-scale climate refugia for salmon in the Pacific Northwest.