Can Humpback Chub and a Blue Ribbon Trout Fishery Coexist in the Grand Canyon?

Abstract: Maintaining both a population of native Humpback Chub (Gila cypha) and non-native Rainbow Trout (Oncorhynchus mykiss) are stated goals for management downstream of Glen Canyon Dam (GCD) on the Colorado River, yet these species have very different habitat requirements and often times the Rainbow Trout prey upon the Humpback Chub. Habitat conditions in the river downstream of GCD have been extremely altered with moderate flows, cold water temperature, and a much reduced sediment load compared to historic conditions. These physical habitat characteristics create ideal conditions for the non-native trout and have reduced the habitat quality for the chub. In addition to the change in habitat, the rainbow trout and other introduced species predate on the chub. Several management actions from mimicking high flow events to mechanical invasive species remove have taken place to date with differing success. It may also be natural fluctuation such as drought can override the management actions in terms of drivers of the humpback chub population. Recent studies have found that under drought conditions, humpback chub populations have been increasing with warmer water. Under such an altered condition, can both of the species coexist and how does societal desire for recreational trout fishing compete with maintaining a non-recreational fish such as the Humpback Chub? This question will ultimately have to be addressed if a long- term solution is to be found.