Temporal Variation in Abundance of an Isolated Population of Cutthroat Trout in Western Oregon, 1981–1991

Abstract

Abstract The magnitude of variation in an isolated population of wild coastal cutthroat trout Oncorhynchus clarki clarki is described for an 11-year study period during which conditions in a Cascade Mountain drainage in western Oregon were relatively stable. Dead Horse Canyon Creek watershed, which drains 1,376 ha in the upper Molalla River, experienced no storm events or disturbances of riparian habitat that caused major changes in channel configuration. Cutthroat trout populations in Dead Horse Canyon Creek varied from year to year, while habitat conditions remained constant, which thereby complicated any analyses of the independent effects of land management activities on the population. The cutthroat trout population fluctuated substantially within and among age-classes, with young of the year showing the greatest variation and age-1 fish the least. Because most of the habitat models used to predict changes in trout populations do not incorporate natural variations in populations under similar habitat...