The ecological consequences of hybridization between native westslope cutthroat trout (Oncorhynchus Clarkii Lewisi) and introduced rainbow trout (O. Mykiss) in south western Alberta

152 leaves : ill. (some col.) ; 29 cm.This thesis addresses the issue of hybridization between native westslope cutthroat trout (Oncorhynchus clarkii lewisi) and introduced rainbow trout (O. mykiss), giving strong consideration to their differing glacial refugia during the Wisconsin Glaciation. We hypothesize that having more recently derived from an anadromous form O. mykiss will possess life history characteristics more typical of a highly anadromous species. This hypothesis would also predict hybrids to be intermediate in these characteristics. In a comparison of growth rates and survivorship (Chapter 2) O. clarkii lewisi were found to employ a slower growing, longer lived strategy than O. mykiss, with hybrids typically being intermediate. Additionally, O. mykiss were also found to have aerobic and anaerobic metabolic capacities superior to O. clarkii lewisi in a first time comparison of these species (Chapter 3). These results support the glacial refuge hypothesis, but furthermore provide a potential explanation of the establishment of the elevational gradient commonly observed in hybridization studies. It would seem likely that O. mykiss would require more productive reaches being a faster growing, shorter lived species with higher metabolic costs. This study confirmed the gradient of O. mykiss persisting at lower elevations, trending through a hybrid zone to pure O. clarkii lewisi in headwater reaches and above migratory barriers (Chapter 2). A similar gradient was also reported when considering only the hybrid population, supporting the notion that habitat preference is under some genotypic control. The importance of migratory barriers was found to decrease with elevation suggesting potential additional limiting factors. Hybrid individuals were also found to be intermediate in morphological characteristics (Chapter 4). The confidence in differentiating between pure and non-pure O. clarkii lewisi was found to increase with the number of O. mykiss alleles (degree of hybridization) an individual possessed. Morphological-based identification was found to be an efficient, cost-friendly, preliminary assessment tool that could be useful in limiting the number of sites needing detailed genetic assessment