COMPARATIVE GROWTH AND CONSUMPTION POTENTIAL OF RAINBOW TROUT AND HUMPBACK CHUB IN THE COLORADO RIVER, GRAND CANYON, ARIZONA, UNDER DIFFERENT TEMPERATURE SCENARIOS

We used bioenergetics models for humpback chub, Gila cypha, and rainbow trout, Oncorhynchus mykiss, to examine how warmer water temperatures in the Colorado River, Grand Canyon, Arizona, through a proposed selective withdrawal system (SWS) at Glen Canyon Dam, would affect growth, consumption, and predation rates. Consumption by the rainbow trout population was at least 10 times higher than by the smaller humpback chub population. Water temperature increases of 6°C during autumn increased growth of humpback chub and likely increased their survival by reducing the time vulnerable to predation. Water temperature increases caused by drought in 2005 did not alter humpback chub growth as much as the SWS. Increased temperatures might cause changes to the invertebrate community and the distribution and abundance of other warmwater nonnative fishes. The implications on the entire aquatic community need to be considered before any management action that includes increasing water temperatures is implemented.