Juvenile Growth of Native Fishes in the Little Colorado River and in a Thermally Modified Portion of the Colorado River

Abstract

We estimated juvenile growth rates of four native fish species using the von Bertalanffy growth equation and length data from fish captured during 1991–1994 in the Little Colorado River, a tributary to the Colorado River in Arizona in the Grand Canyon. We compared growth rates to water temperatures for all four species and modeled the effects of warming the Colorado River (through a proposed retrofit of Glen Canyon Dam) on the growth of age-0 emigrants from the tributary. Juvenile growth rates in the Little Colorado River were fastest for flannelmouth sucker Catostomus latipinnis, slowest for speckled dace Rhinichthys osculus, and intermediate for humpback chub Gila cypha and bluehead sucker Catostomus discobolus. Growth rates for each species were positively correlated with water temperature; flannelmouth sucker exhibited the strongest relationship, followed by speckled dace, humpback chub, and bluehead sucker. Our model indicates that native fish immigrating into the cold Colorado River (8–12°C) from the relatively warm Little Colorado River during their first 3 months of life will grow very little by the end of their first year. According to other studies, older, larger fish that disperse into the Colorado River are more likely to survive than those that migrate as larvae. Growth, and possibly survival, of native fish larvae that drift from tributaries into the Colorado River could be increased if water released from Glen Canyon Dam is warmed during the period of larval drift.