Colorado, Gunnison and Rio Grande Rivers
Past studies show that giant stoneflies, a large aquatic invertebrate, serve as a primary food source for trout in Colorado rivers where they occur. Their large and synchronous emergence produces some of the best fishing of the year and is eagerly anticipated by many anglers. The species' high densities and large size also make them important in the flow of energy and nutrients between aquatic and riparian systems. Although giant stoneflies can exist at extremely high numbers in certain locations, the density and range of this species has decreased in some places —most likely in association with changes in stream flows and physical aquatic habitat.
Therefore, CPW researchers are working to determine the influence of physical habitat conditions on giant stonefly density in an effort to identify limiting factors and reasons for the species' decline. To do so, researchers will compare the habitat and ecological characteristics of various study sites with differing giant stonefly densities in rivers where they are currently plentiful and areas where their numbers are reduced.
The results of this study will be used to inform management and restoration activities, as well as to identify sites for giant stonefly re-introductions. By maintaining and restoring giant stonefly populations, wildlife managers can protect an important part of native aquatic ecosystems and improve river fisheries for Colorado's anglers.