Controls on Somatic Growth and Population Dynamics of Rainbow Trout

Abstract

Photo 1: A rainbow trout holding immediately downstream of Glen Canyon Dam in the clearwater Glen Canyon reach of the Colorado River. Photo credit: David Herasimtschuk, Freshwaters Illustrated. Photo 2: Rainbow trout holding over a cobble bar in the clearwater Glen Canyon reach of the Colorado River and feeding on drifting aquatic invertebrates. Photo credit: David Herasimtschuk, Freshwaters Illustrated. Photo 3: Nighttime boat electrofishing was used to capture rainbow trout for tagging. Time-lapse photography captures the path of electrofishing boats on left and right shores. Captured fish were brought to a centrally located processing boat (foreground) to be measured, weighed, tagged, and scanned, and were then returned to their original capture site. Photo credit: Dustin Patar. Photo 4: The Marble Canyon reach of the Colorado River can be very turbid during the summer monsoon season. High turbidity reduced feeding efficiency and growth rates of rainbow trout, which, combined with higher water temperatures and reduced prey production, led to a severe collapse of the population in this reach. Photo credit: Dustin Patar. Photo 5: The confluence of the Little Colorado River (LCR, entering from top of photograph) and the Colorado River. The LCR is an important spawning and rearing area for endangered Humpback Chub. Juvenile Humpback Chub disperse from the LCR into the main stem Colorado River where their survival and growth rates are reduced due to cooler water temperature and competition and predation from non-native rainbow trout. Our sampling reaches IVa and IVb are located in the Colorado River upstream (left side of photograph) and downstream (right side of photograph) of the confluence. Occasional floods from the LCR result in high levels of turbidity downstream of the confluence which reduces growth rates and densities of rainbow trout. Photo credit: Ted Grussing, tedgrussing photography. These photographs illustrate the article “Changes in prey, turbidity, and competition reduce somatic growth and cause the collapse of a fish population” by J. Korman, M.D. Yard, M.C. Dzul, C.B. Yackulic, M.J. Dodrill, B.R. Deemer, and T.A. Kennedy published in Ecological Monographs. https://doi:10.1002/ecm.1427