Local and Geographic Variability in the Distribution of Stream-Living Lahontan Cutthroat Trout

Abstract
We investigated local and geographic variability in the up- and downstream distribution limits of threatened Lahontan cutthroat trout (Oncorhynchus clarki henshawi) in stream habitats of the eastern Lahontan basin in northern Nevada and southeastern Oregon. At a geographic scale, elevations of upstream distribution limits were significantly correlated with latitude and longitude, suggesting a potential influence of climatic gradients. Elevations of upstream distribution limits also were positively correlated with maximum basin elevation, which suggested topographic, rather than climatic constraints may be important. Upstream distribution limits were not significantly affected by local variation in stream size or presumptive dispersal barriers. Stream gradient was related to upstream distribution limits, but this was again confounded by maximum basin elevation. Stream gradients used by Lahontan cutthroat trout at upstream limits were considerably steeper than those observed for other subspecies of...