Determining the Relative Roles of Environmental Drivers and Competition in the Population Dynamics of Rainbow Trout and Humpback Chub to Inform Management of Glen Canyon Dam

The construction of Glen Canyon Dam led to significant declines in turbidity, summer temperatures, and peak flows in the Grand Canyon reach of the Colorado River. Dam operations further modify inter-annual, seasonal and daily patterns of flows as well as temperature and turbidity. In addition, nonnative fish species, including Rainbow Trout, were introduced and are now numerically dominant in some parts of the Colorado River and are considered desirable in the reach just downriver of the Glen Canyon Dam. Managers are now faced with the task of maintaining viable populations of the native and endangered Humpback Chub in the face of competition with Rainbow Trout that migrate downriver in a highly modified and regulated river. Ongoing research of population dynamics of both species is leading to a better understanding of the direct and indirect responses to varying turbidity, temperature, and discharge, ultimately driven by climate and dam management. Research is also shedding light on the complex movement patterns of both species and the strength of their interspecific interactions with implications for different proposed management strategies. Population models built on this knowledge are being used to inform management decisions, including an ongoing Environmental Impact Statement focused on management of Glen Canyon Dam over the coming decades