Graduate Thesis Or Dissertation
 

Regions to streams : spatial and temporal variation in stream occupancy patterns of coho salmon (Oncorhynchus kisutch) on the Oregon coast

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/bc386m254

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  • Aquatic ecological investigation is expanding to encompass considerations of multiple scales across large landscapes. Much of the analysis included in this work focuses specifically on coho salmon (Oncorhynchus kisutch) in multiple subbasins on the Oregon coast. Coho salmon were chosen for an investigation of spatial scales, network connections, and life history stages due to their broad distribution on the Oregon coast, and abundant data describing their distribution, habitat needs, behavior, and survival. Chapter 2 introduces dynamic network topology (DNT) as a framework for analysis and interpretation of aquatic obligate species. DNT is based on the premise that in-stream habitats change in form and organization over time, and native aquatic species are adapted to those changes through movement and life history diversity. Chapter 3 analyzes juvenile coho salmon density and stream network occupancy at three spatial scales (site, patch, and subbasin). The site scale analysis indicated that combining network and traditional in-stream habitat metrics (i.e., substrate and habitat juxtaposition variables) are most effective at describing juvenile coho salmon density. Patch sizes of juvenile coho salmon were defined using variograms. Variogram shape indicated that a nested spatial structure may be present in larger subbasins, indicating overlapping patterns of juvenile stream use. At the subbasin scale, stream network occupancy by juvenile coho salmon was shown to vary over time within subbasins, and appeared to increase or decrease similarly to the size of the adult spawning run. In chapter 3, two-tier Bayesian hierarchical models were applied to adult (subbasin and basin scales) and juvenile (site and subbasin scales) coho salmon in an attempt to combine spatial scales that might be influential at each life history stage. The best fitting adult model included the percent of large trees in the riparian zone at the subbasin scale with mean annual precipitation at the basin scale. The best fitting juvenile model included three variables, percent sand, stream order, and network distance to spawning habitat which mirrors the result of modeling efforts in Chapter 3. Multiple spatial scales and the framework of a stream network were informative at detecting patterns and interactions among scales and life history stages of coho salmon.
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