Cooperative Fish and Wildlife Research Units Program: Colorado
Education, Research and Technical Assistance for Managing Our Natural Resources

Piscivores such as smallmouth bass Micropterus dolomieu and northern pike Esox lucius are established and common in the lower Yampa River, the upper and middle Green River basins, and the upper Colorado River. The threat of these introduced predators is substantial and smallmouth bass are problematic because of their high abundance, habitat use that overlaps with most native fishes, and capability to consume a wide variety of life stages of native fishes in the Colorado River Basin. Expanded populations of smallmouth bass are a major impediment to conservation actions aimed at recovery efforts for four endangered fishes in the Upper Colorado River Basin. In response to the predatory threat posed by non-native fishes such as smallmouth bass, the Upper Colorado River Recovery Implementation Program initiated efforts to control such species via mechanical removal in affected stream reaches. Substantial information has been collected on distribution, population abundance, size structure, and movements of smallmouth bass concurrent with removal actions throughout the Upper Colorado River Basin. The Upper Colorado Recovery Program has initiated population modeling to analyze some of these data and to gain insight into removal strategies for smallmouth bass. However, more detailed modeling and analyses are necessary to provide a clearer understanding of population level effects of removal, to help formulate a comprehensive control strategy to reduce populations of smallmouth bass, and to enhance recovery of native fish populations. We are expanding the scope of recent population dynamics models using data collected in the system, the summary database for removal, and our own unpublished information. Our goal is to develop a comprehensive age- or size-structured model to understand factors that affect smallmouth bass population dynamics in the Upper Colorado River Basin. Our model will include density dependent feedback and environmental inputs that can be manipulated independently of each other. The model will also address uncertainty and variability in the parameters and relationships in the model to evaluate its influence on the outcomes and predictions.