A Framework for Assessing “Sufficiency” of Cold-Water Refuges and Climate Refugia for Cold-Water Fishes
Citation:
Ebersole, J., M. Snyder, J. Dunham, C. Torgersen, M. Keefer, A. Fullerton, J. Armstrong, J. Palmer, AND D. Keenan. A Framework for Assessing “Sufficiency” of Cold-Water Refuges and Climate Refugia for Cold-Water Fishes. Oregon Chapter American Fisheries Society Annual Meeting, Bend, OR, March 04 - 08, 2019.
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 elements of an approach to address and identify key uncertainties for evaluating refuge effectiveness.
Description:
Populations of cold-water fishes are increasingly faced with warm river temperatures. Cold water refuges (CWR) – areas of cold water in which thermally-stressed individuals may seek temporary shelter – are increasingly invoked as a potentially mitigating feature within warming river systems. Many studies have documented extensive use of CWR by cold-water fish species, and CWR use is often assumed to confer benefits to thermoregulating fishes by providing temporary (hours to weeks) shelter from adverse thermal conditions. But CWR use and associated behavioral thermoregulation is not without costs. Increased risk of predation, lost opportunity for foraging, and increased isolation within thermally-fragmented river systems may offset potential benefits of CWR use. While patterns of timing of CWR use are relatively well known, less well understood are the relative costs and benefits of CWR use, and net effects on individual fish physiological status, reproductive success, and dynamics of populations. To provide a framework for assessing the relative costs and benefits of CWR, we illustrate a conceptual model of CWR costs/benefits that recognizes that CWR provisioning ability is influenced by the suitabilities, capacities and characteristics of individual refuges, as well as the spatial and temporal context of the surrounding matrix and the suite of potentially connected neighboring refuges. Networks of CWR and their context in relation to extensive areas of cold water serving as core areas can also be understood to function as important elements of larger-scale climate refugia for highly-migratory species like salmon. This framework is intended to be useful as state and federal regulatory agencies continue to incorporate concepts of CWR into water temperature standards and TMDLs.