An experimental evaluation of competition between rainbow trout Oncorhynchus mykiss and humpback chub Gila cypha

Authors: Rylan Morton-Starner, David L. Ward

Year: 2013 (xlv)

Abstract

Introduced rainbow trout Oncorhynchus mykiss inhabit many of the same environments as endangered humpback chub Gila cypha in Colorado River in Grand Canyon. Competition for limited food resources between these two fish species may play an important role in humpback chub population dynamics. We evaluated competitive interactions between humpback chub and rainbow trout in 30]day laboratory trials at 16 ‹C using 12 replicate artificial stream systems. PIT tagged fish were fed a maintenance ration of 2 %body weight per day and monitored for changes in weight. Size matched roundtail chub Gila robusta (236 mm mean TL) (as a surrogate for humpback chub) and rainbow trout (259 mm mean TL) showed little competitive interaction. In contrast, small humpback chub (114 mm mean TL) lost weight (0.4%) when held in systems with adult rainbow trout (247 mm mean TL) and control humpback chub (110 mm mean TL) increased their body weight by 1.8%. These data suggest young humpback chub in Grand Canyon could be adversely impacted by competitive interactions with adult rainbow trout, but adult humpback chub are not likely to be impacted by competition with similar sized rainbow trout. This information will be helpful to managers evaluating management options aimed at preservation of native fishes in Grand Canyon.