Using an Integrated Population Model to Evaluate Yellowstone Cutthroat Trout Responses to Management Actions

Abstract

The South Fork Snake River supports one of the few remaining robust populations of fluvial Yellowstone Cutthroat Trout Oncorhynchus clarkii bouvieri in Idaho. Since the early to mid-2000s, salmonid populations on the South Fork Snake River have been intensively monitored and managed to limit the abundance of introduced Rainbow Trout O. mykiss, which have been increasing in abundance relative to Yellowstone Cutthroat Trout. Integrated population models (IPMs) were built using multiple data sets (abundance, survival, and fecundity data) to evaluate the effectiveness of management actions. Modeling results suggested that Yellowstone Cutthroat Trout survival at ages 0 and 2 was influenced by inter- and intracohort competition with both adult Rainbow Trout and adult Yellowstone Cutthroat Trout. Decreasing minimum winter discharge from Palisades Reservoir appeared to negatively affect the population growth rate of Yellowstone Cutthroat Trout; however, the effect on survival of individual life stages was minimal. Use of the IPM allowed for evaluation of life-stage-specific dynamics that would be lacking when using alternative analytical methods. It is apparent from the results of this study that the population bottlenecks for Yellowstone Cutthroat Trout in the South Fork Snake River occurred at ages 0 and 2 as a result of inter- and intraspecific density-dependent mechanisms. Thus, management actions that target these life stages should be continued or expanded.