Kevin Thompson, CPW-retired; Zachary Hooley-Underwood, CPW
Western Slope Waters below 8,500’
- To determine the current distribution of the three-species in Colorado's Western Slope streams and rivers.
The rivers and streams of western Colorado below 8,500 feet in elevation comprise the historic native range for the three-species (Flannelmouth Sucker, Bluehead Sucker and Roundtail Chub). Evidence suggests the three-species only occupy about 50 percent of their historic native range in the upper Colorado River basin. Although extensive data have been collected on three-species distribution in Colorado's mainstem rivers, very little data exist on the presence of the three-species in smaller streams.
As a result, CPW initiated a project to rigorously determine the current distribution of the three-species within their native Colorado ranges. Researchers sampled at randomly selected locations in streams that lie within the historic native range and also at randomly selected historic sampling locations (where one or more of the three-species have been previously documented) within the Colorado River basin for three-species fish. This approach is structured to ensure that spatial balance is achieved so that the entire potential native range is included.
This research determined that occupancy of randomly selected sites was fairly low overall for all three species. Stream gradient was the variable most strongly associated with occupancy, with lower gradient sites being more frequently occupied. Each of the species have been lost from at least some of the historically identified sites. Roundtail Chub have been the most affected, occupying only 12.5% of sites where they were present before1980. The large number of surveys required to complete this study resulted in stream-specific information on a number of un-sampled and rarely sampled waters, which will aid fisheries managers in the future.
Researchers will continue to sample specific locations to follow up on this work, and answer specific questions on specific waters. The results from this study will give biologists a better idea of three-species distribution and abundance and help determine whether the present ranges of these fishes are stable. A better understanding of these dynamics will give fishery managers the information they need to make effective management decisions.