Theses and Dissertations at Montana State University (MSU)
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Item Relationship between intensity of livestock grazing and trout biomass in headwaters of east front Rocky Mountain streams, Montana(Montana State University - Bozeman, College of Letters & Science, 2016) Gilham, Andrew Terrence; Chairperson, Graduate Committee: Alexander V. ZaleLivestock grazing is the most common land-use practice in the western United States. Riparian and stream habitats are particularly susceptible to effects of poorly-managed livestock grazing. About 80% of stream and riparian habitats in the western United States are thought to have been damaged by livestock grazing, but because grazing usually pre-dated assessments of fish populations and stream habitats, before and after comparisons are impossible. The spatial and temporal complexity of livestock grazing make it difficult to isolate its effects on instream habitat and channel morphology characteristics. Moreover, instream habitat and channel morphology are also influenced by inherent watershed characteristics (i.e., basin area, gradient, discharge). I assessed the effects of livestock grazing on 25 separate 150-m long sample sites (1400 to 1585 m in elevation) within ten headwater basins along the northeastern Rocky Mountain Front in north-central Montana. I used scat counts as an index of relative grazing intensity to assess the effects of livestock grazing on channel morphology characteristics, stream substrate, instream cover, and trout biomass. To my knowledge, this effort is the first to quantify livestock grazing intensity using scat counts to assess grazing effects on trout biomass. I assessed potential effects that grazing intensity had on habitat condition and fish biomass using linear mixed models, which also accounted for watershed and sample site effects. I found that the proportion of fine sediment in the streambed increased as the number of scats increased (P < 0.001), but the area of undercut banks declined as scat counts increased (P < 0.001). Estimated trout biomass declined as number of scats increased, even when I accounted random effects of stream and year in a linear mixed-effect model (P = 0.009). My results corroborate previous findings that livestock grazing along stream channels may reduce trout biomass, but unlike previous studies I actually quantified grazing intensity using scat counts. Since increased livestock grazing intensities were related to increased levels of fine sediments in streambeds and smaller areas of undercut streambanks, I suggest that these factors may be related to why increased livestock grazing reduced trout biomass.Item Responses of fish assemblages to bank stabilization in a large river(Montana State University - Bozeman, College of Letters & Science, 2014) Reinhold, Ann Marie; Chairperson, Graduate Committee: Alexander V. Zale; Geoffrey C. Poole, Robert G. Bramblett, Alexander V. Zale and David W. Roberts were co-authors of the article, 'Cumulative effects of floodplain dikes and linear bank stabilization on Yellowstone River side channels' submitted to the journal 'Freshwater science' which is contained within this thesis.; Robert G. Bramblett, Alexander V. Zale, David W. Roberts and Geoffrey C. Poole were co-authors of the article, 'Use of side channels by a large-river fish assemblage' submitted to the journal 'Freshwater biology' which is contained within this thesis.; Robert G. Bramblett, Alexander V. Zale, Geoffrey C. Poole and David W. Roberts were co-authors of the article, 'Spatially-dependent responses of a large-river fish assemblage to bank stabilization and side channels' submitted to the journal 'Ecological applications' which is contained within this thesis.The Yellowstone River remains the longest unimpounded river in the conterminous United States. However, bank stabilization and floodplain dikes have altered its fish habitat. Therefore, I surveyed fish habitat and fish from Laurel to Sidney, Montana, to (1) quantify changes to side channels attributable to linear bank stabilization and floodplain dikes, (2) compare the habitat use of side channels to main channels by small fish during runoff and base flow, and (3) determine if bank stabilization and side channels influenced main-channel fish assemblages during base flow. Floodplain dike frequency, but not linear bank-stabilization extent, directly correlated to a net loss of side channels from the 1950s to 2001. However, side channels provided important fish habitat. Fish habitat use was similar between side and main channels during base flow, but not during runoff when catch rates in side channels were several times higher than in main channels and assemblage structure differed between side and main channels. Shallow, slow-current velocity (SSCV) habitats were slightly slower in side channels and SSCV patches were larger in side channels than in main channels during runoff, but not during base flow. These habitat differences partially explained the patterns in fish catch rates between channel types. During base flow, fish assemblages in main channels varied with bank-stabilization extent and side-channel availability in alluvial (unconfined) and bluff (confined) river bends. Bank stabilization and side channels had different and sometimes opposite influences on fish assemblage structure. Influences of bank stabilization and side channels on fish relative abundances varied depending on species and river bend geomorphology. Assemblage responses to side channels were more consistent and widespread than to bank stabilization, and more fish species associated with side channels than bank stabilization. Physical differences probably contributed to the assemblage differences between reference and stabilized river bends; stabilized alluvial pools were deeper than reference alluvial pools. The strengths of the relationships among fish assemblages, bank stabilization, and side channels were spatial scale-dependent; optimum scales ranged from less than 200 m to 3,200 m up- and down-stream, suggesting that bank stabilization and side channels influenced fish across multiple spatial scales.