Abstract
The reported decline of native bull trout Salvelinus confluentus and westslope cutthroat trout Oncorhynchus clarkii lewisi populations west of the Continental Divide in Glacier National Park (GNP) prompted research to identify critical habitats and assess the abiotic and biotic factors influencing distribution and abundance. We evaluated the association of habitat metrics (stream width, elevation, gradient and woody debris density, mean August stream temperature) and biotic factors (the presence of non-native lake trout Salvelinus namaycush) with the distribution and abundance of bull trout and westslope cutthroat trout in 78 stream reaches in five sub-drainages of the North Fork Flathead River in GNP. Logistic and linear regression models were used to quantify the influence of these independent variables on species occurrence (presence/absence) and fish density. An information theoretic approach (AIC) was used to determine the most plausible combinations of variables in each case. The presence of westslope cutthroat trout was negatively associated with the presence of lake trout and positively associated with large woody debris abundance and water temperature. Westslope cutthroat were detected throughout a wide range of temperatures (8.5-16oC), but were most abundant in small, complex streams that were not connected to lakes supporting nonnative lake trout populations. Bull trout occurrence was positively related to stream width and negatively related to channel gradient and water temperature. The highest bull trout densities were observed in streams with relatively cold mean August water temperatures (8-10oC) and in areas isolated from lake trout by dispersal barriers. The low numbers of bull trout detected in this study likely reflect the imperiled status of lacustrine-adfluvial populations in GNP, owing to the invasion and establishment of nonnative lake trout from Flathead Lake. These data may be used to monitor and protect critical habitats and populations, inform conservation and recovery programs, and suppression/eradication efforts to reduce the impacts of nonnative invasive species.
Start Date
5-3-2010 2:30 PM
End Date
5-3-2010 3:00 PM
Document Type
Presentation
Factors Influencing the Distribution of Native Trout in North Fork Flathead Tributaries in Glacier National Park
The reported decline of native bull trout Salvelinus confluentus and westslope cutthroat trout Oncorhynchus clarkii lewisi populations west of the Continental Divide in Glacier National Park (GNP) prompted research to identify critical habitats and assess the abiotic and biotic factors influencing distribution and abundance. We evaluated the association of habitat metrics (stream width, elevation, gradient and woody debris density, mean August stream temperature) and biotic factors (the presence of non-native lake trout Salvelinus namaycush) with the distribution and abundance of bull trout and westslope cutthroat trout in 78 stream reaches in five sub-drainages of the North Fork Flathead River in GNP. Logistic and linear regression models were used to quantify the influence of these independent variables on species occurrence (presence/absence) and fish density. An information theoretic approach (AIC) was used to determine the most plausible combinations of variables in each case. The presence of westslope cutthroat trout was negatively associated with the presence of lake trout and positively associated with large woody debris abundance and water temperature. Westslope cutthroat were detected throughout a wide range of temperatures (8.5-16oC), but were most abundant in small, complex streams that were not connected to lakes supporting nonnative lake trout populations. Bull trout occurrence was positively related to stream width and negatively related to channel gradient and water temperature. The highest bull trout densities were observed in streams with relatively cold mean August water temperatures (8-10oC) and in areas isolated from lake trout by dispersal barriers. The low numbers of bull trout detected in this study likely reflect the imperiled status of lacustrine-adfluvial populations in GNP, owing to the invasion and establishment of nonnative lake trout from Flathead Lake. These data may be used to monitor and protect critical habitats and populations, inform conservation and recovery programs, and suppression/eradication efforts to reduce the impacts of nonnative invasive species.