Graduate Thesis Or Dissertation
 

Relationships between stream discharge and cutthroat trout abundance at multiple scales in managed headwater basins of western Oregon

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/hm50tv21b

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  • Relationships between resident cutthroat trout (Oncorhynchus clarkii clarkii) and six hydrologic indices were investigated using correlation analysis in two experimental headwater catchments in the foothills of the Cascade Mountains of western Oregon. This investigation was to determine if characteristics of discharge explained inter-annual variability in trout abundance. Eight years of continuous discharge and annual abundance data collected from two contiguous watersheds from the Hinkle Creek Paired Watershed Study were used for this study. Density-discharge relationships were identified separately in the watershed actively managed for timber harvest and in the control watershed. Correlation was determined at multiple stream segments and at the watershed scale to assess the roles of spatial scale and network location on the detectability of density-discharge relationships. A method for improving the spatial coupling of density and discharge measurements within the stream network was also investigated. No correlations (r ≤ ǀ0.50ǀ) between hydrologic indices and age-1+ trout density in either watershed were found. Two hydrologic indices were related to the density of age-0 trout: maximum annual discharge (r = 0.780) in the control watershed and Q90 summer discharge (r = 0.697) in the treated watershed. The correlation between the density of age-0 trout and each of these two indices were similar across individual stream segments, but variability in the magnitude of the correlation suggests that network location plays a key role in facilitating processes that link density and discharge. Variability in the magnitude of the correlation across stream segments also influenced the detectability and interpretability of relationships observed at the extent of a watershed and at the extent of a stream segment. These results indicate that researchers interested in understanding the dynamics of cutthroat trout abundance should consider the effects of discharge on inter-annual variability in abundance of different age classes and the role of network location on the detectability of relationships.
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