Ecology of Westslope Cutthroat Trout (Oncorhynchus clarki lewisi) Populations in Three Small Rocky Mountain Headwater Streams

Abstract

Westslope Cutthroat Trout Oncorhynchus clarki lewisi (WCT) are a threatened species in Alberta, Canada, where almost all remaining pure populations are restricted to small headwater streams. Field based methods were used to first describe the general habitat and WCT populations in three headwater streams, and secondly look at how habitat and populations changed seasonally. Well connected, deep pools with suitable cover provided the best WCT habitat during summer low flows. During winter, small WCT (< 20 cm) concealed and large WCT (> 20 cm) used pools for winter refuge. Summer habitat metrics (depth, area, geomorphology) in addition to seasonal changes in water temperature were drivers of large WCT presence-absence in pools during winter. Large WCT winter abundance in pools was further driven by water velocity, ice cover, and connectivity. Overall, this thesis highlights attributes of critical WCT habitat that can be used to help manage threatened populations in small headwater streams.