By Sid Perkins
The population of humpback chub, a fish found only in the Colorado River and its tributaries, may be stabilizing in sections of the Grand Canyon, new data suggest.
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Gila cypha, a member of the minnow family that can grow to 50 centimeters in length, was declared endangered in 1967. The species suffered from the ecological effects of the Glen Canyon Dam, including cooler-than-normal water temperatures, and predation by nonnative fish such as trout (SN: 3/5/05, p. 152: Available to subscribers at Straight Flush). In the 1990s, up to 20 percent of adult chub were dying each year, and young fish weren’t surviving in numbers sufficient to replace those losses, says Matthew Andersen, a biologist with the U.S. Geological Survey in Flagstaff, Ariz.