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Abstract 

    The purpose of this study was to identify geographic features in westslope cutthroat trout (Oncorhyncus clarkii lewesii) habitat that help explain the distribution of hybridized and non-hybridized populations of in the Bow River Basin in Southwestern Alberta using ArcGIS software. 

    A total of 49 sample sites were used in this analysis and analyzed for 13 environment variables that were classified as either  human impact or stream environment. Ordinary Least Squares (OLS) regression analyses produced a best fit model to that described 64.5% of the observed pattern of hybridization amongst the 49 sample sites. Distance to the nearest powerline, railroad, access road and hybridized sample site, along with elevation and stream depth were all factors that contribute to this model

Background

    

    In 2006, the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) designated the Alberta population of Westslope Cutthroat Trout (Oncorhynchus clarkii lewisi) as Threatened because the pure native, non-stocked, populations had been reduced by almost 80% as a result of over-exploitation, habitat degradation and hybridization/competition with introduced non-native trout. 

    Remaining pure Westslope Cutthroat Trout persist mainly as severely fragmented, remnant headwater populations in southwestern Alberta, primarily in the upper South Saskatchewan River drainage (Bow and Oldman rivers).

    Westslope Cutthroat Trout are a popular recreational sport fish which contributes to local economies. They are prized by the local angling community because they are a wild native trout, easy to catch and resilient to catch-and-release. Frequently they are the only native trout throughout much of their range in western Canada and are viewed as an indicator species of general ecosystem health because of their restricted habitat needs.

    This subspecies is now being considered for legal listing under the Species at Risk Act (SARA). In advance of making a listing decision, Fisheries and Oceans Canada (DFO) Science has been asked to undertake a Recovery Potential Assessment (RPA).  The results of this RPA outline the need for further research to characterize and identify the pattern of hybridization in Alberta.

    The work from this project and my thesis will contribute to a larger body of research that aims to provide the scientific foundation for focuesd and effective conservation efforts to protect the westslope cutthroat trout . 

Hybridization with fisheries-stocked rainbow trout is arguably its greatest threat.

Beginning the early 1900s, thousands of rainbow trout have been stocked into the same habitats as westslope cutthroat trout to enhance the sport fishing industry.

Rainbow trout and westlope cutthroat trout can hybridize and produce viable offspring because they share a common ancestor species. 

Westslope cutthroat trout are no match for domesticated rainbow trout which have been born and bred to grow fast, eat lots and reproduce quickly. 

The spread of rainbow trout has fragmented westslope cutthroat trout populations and forced them into the headwater habitats where they occupy less than twenty-percent of their historic range.


Westslope cutthroat trout are one of only four native trout species in Alberta.