Graduate Thesis Or Dissertation
 

Relationships between relative abundance of resident bull trout (Salvelinus confluentus) and habitat characteristics in Central Idaho mountain streams

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/3t945t61s

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  • Resident bull trout (Salvelinus confluentus) may be particularly vulnerable to human related disturbance, however very few studies have focused on resident bull trout populations. The abundance of bull trout is one measure of the strength and potential for persistence of a population. Habitat characteristics may influence resident bull trout abundance to differing degrees and by varying means at multiple spatial scales. We used day and night snorkel counts to assess relative bull trout abundance. A modification of the Forest Service R1/R4 Fish and Fish Habitat Inventory was used to assess habitat characteristics associated with resident bull trout. Logistic and multiple linear regression were used to assess the relationships between resident bull trout abundance and habitat characteristics at the patch (1 to 5 km), reach (0.5 to 1 km) and habitat unit (1 to 100 m) scales. Site categorical variables were used along with quantitative habitat variables to explain among-site and across-site variation in the data. The significance of both quantitative habitat variables and categorical site variables at various spatial scales suggest that relationships between bull trout abundance and habitat characteristics are complex and in part dependent on scale. The characteristics of individual habitat units explained little of the variation in bull trout presence/absence (logistic regression; Somers' D=0.44) and density (multiple linear regression; adjusted R²=0.08) in habitat units, however there were habitat characteristics that were significantly (P≤0.05) correlated to bull trout presence/absence and density in habitat units. The relationships between habitat characteristics and bull trout presence/absence and density varied between habitat unit types. There was a strong quadratic relationship between bull trout abundance and mean summer water temperature at the reach (P=0.004) and patch scales (P=0.001). The mean temperature of patches appears to explain some of the variation in bull trout density at smaller spatial scales, such as reaches and habitat units. An appreciation of the complex nature of scale dependent interactions between bull trout abundance and habitat characteristics may help resource managers make wiser decisions regarding conservation of resident bull trout populations.
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