Cutthroat Trout

Relationships Between Stream Discharge and Cutthroat Trout Abundance at Multiple Scales in Managed Headwater Basins of Western Oregon
Owens, H.L.

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...

DISCIPLINE: Fisheries    STUDY: Hinkle Creek    TYPE: Theses    TAGS: Cutthroat Trout, Variability, trout abundance, Density-discharge relationships
Fish Population Response to Harvesting with Contemporary Forest Practice Regulations: The Alsea Watershed Study Revisited
Bateman D., R. Gresswell, D. Hockman-Wert, D. Leer, and J. Light

Coastal cutthroat trout Oncorhynchus clarkii clarkii are the most widely distributed native salmonid in the forested watersheds of western Oregon. The initial Alsea Watershed Study demonstrated negative impacts on the abundance of cutthroat trout due to logging practices of the day. Here we report on abundance, size, growth, and condition of coastal cutthroat trout before and after logging under the current forest management practice regulations using a before, after, control, impact (BACI) study design with Flynn Creek and Needle Branch as the control and impact streams respectively. Relative abundance estimates are from a census of pool habitats using single-pass electrofishing and relative growth is from the recapture of individuals implanted with passive integrated transponder tags. A significant increase in age 1+ cutthroat trout biomass and abundance was observed post-harvest in Needle Branch relative to Flynn Creek (p=0.04 and 0.01 respectively). There was also a significant shift in the spatial distribution of cutthroat biomass in Needle Branch (p=0.04) in an upstream direction post-treatment suggesting that increases in cutthroat trout were spatially linked to the location of the harvest unit. There was no evidence for a treatment effect on mean fork length or the 90th percentile of fork length for age 1+ cutthroat trout (p=0.32 and 0.24 respectively). This result was supported by an absence of evidence for a treatment effect on relative growth rate.

DISCIPLINE: Fisheries    STUDY: Alsea    TYPE: Presentations    TAGS: Cutthroat Trout, single-pass electrofishing, biomass, habitat
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