Rainbow trout (Oncorhynchus mykiss) have a long history in the Grand Canyon region, having first been introduced in Colorado River tributaries like Bright Angel Creek by the National Park Service in the 1920s to create sport fishing opportunities. The completion of Glen Canyon Dam in the 1960s created ideal water conditions for a sport fishery immediately below the dam in the 15-mile Lees Ferry reach of the Colorado River. The Lees Ferry rainbow trout fishery gained a reputation by the mid 1970s as a world class, blue ribbon fishery famous for its scenic grandeur and large, trophy-sized trout above 10 pounds. Downstream of Lees Ferry, rainbow trout are thought to compete with and prey on juvenile native fish, including the endangered humpback chub (Gila cypha).
The USGS Grand Canyon Monitoring and Research Center works cooperatively with the Arizona Game and Fish Department to monitor and research rainbow trout in the Lees Ferry reach and downstream, particularly the confluence of the Colorado and Little Colorado Rivers, where most humpback chub are found in Grand Canyon, in order to provide science to managers for maintaining both the rainbow trout fishery and the endangered humpback chub over the long term. In 2000, a program was created to determine the effects of Glen Canyon Dam operation on the Lees Ferry rainbow trout fishery and make suggestions for improving the fishery. Outside of Lees Ferry, scientists are working to understand how nonnative fish like rainbow trout affect native species. For example, research is being conducted to determine the origin of rainbow trout found in Grand Canyon and to determine to what extent rainbow trout prey on juvenile native fish. The remains of young humpback chub and other native fish were removed from rainbow trout stomachs during a multi-agency mechanical removal effort conducted 2003-06 and in 2009 to remove rainbow trout and other nonnative fishes from the Colorado River immediately above and below the confluence with the Little Colorado River, the tributary where most Grand Canyon humpback chub are spawned.
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