Multiscale assessment of thermal patterns and the distribution of chinook salmon in the John Day River Basin, Oregon Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/8w32r762w

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  • This study examined the distribution and behavior of adult spring chinook salmon (Oncorhynchus tshawytscha) related to patterns of stream temperature and physical habitat at channel unit, reach, and basin-wide spatial scales in both a wilderness stream and a disturbed stream in the John Day River basin in northeastern Oregon. Thermal remote sensing of holding and spawning reaches in the upper subbasins of the North Fork and Middle Fork John Day River provided spatially continuous maps of stream temperature. Multiscale associations between salmon and cool-water areas were assessed by overlaying thermal imagery with fish locations mapped during distributional surveys. Chinook salmon were distributed non-uniformly throughout each study area, indicating that salmon selected certain reaches within each subbasin. The coldest reaches available to salmon within the Middle Fork study areas were low gradient, unconstrained reaches where the cooling influence of groundwater flow was the most apparent. In the Middle Fork, the stream currently managed for grazing and timber harvest, water temperature differences were typically 1-2°C within riffle-pool sequences and 3-4°C among reaches. The reach level association between salmon distribution and stream temperature patterns at channel unit and reach level spatial scales was strongest in the warmest study reach, the Middle Fork, and weakest in the coldest study reach, the North Fork. Pools were the preferred habitat for adult spring chinook in both subbasins; however, riffles were used more in the North Fork, the coldest subbasin. This study identified the problems and also the benefits associated with stream temperature patchiness, or discontinuity, both in currently disturbed and in recovering riverine ecosystems. Connectivity among system components in aquatic ecosystems is generally considered necessary for maintaining long-term ecological health. However, it is heterogeneity in the landscape/hydrogeologic template that creates refuge patches in disturbed stream ecosystems, such as those in the John Day River basin. Our observations of thermal refugia occurring at multiple spatial scales, particularly in the Middle Fork John Day River, indicate that, although discontinuity may be an ecological warning sign, refuge patches in streams should also be viewed as expressions of restoration potential because they are functioning remnants of a once continuous, intact hydrologic system.
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