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The Colorado River basin supports one of the most distinctive fish communities in North America, including the federally endangered humpback chub (Gila cypha). One of only six remaining populations of this fish is found in Grand Canyon National Park, Arizona. USGS scientists and their cooperators are responsible for monitoring the Grand Canyon population. The number Grand Canyon adult humpback chub--fish 4 years old and older and capable of reproduction--increased to approximately 7.650 fish between 2001 and 2008.