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37 Sportfish stocking Clearly no agency has eliminated stocking of all nonnative fishes as a means to reduce potential, adverse effects to native fish fauna; nor has any state set aside a stream or drainage exclusively for the maintenance and management of native fish fauna. Criteria governing the introduction or stocking of nonnative fish species, however, are being implemented in Colorado and Utah, and will be described more fully in the context of Question 14. Use of sterile hybrid channel catfish in the White River,Colorado, has been proposed, although no stocking or evaluation has occurred. Eradication This technique has been used largely to restore native trout populations in headwater streams. Chemical eradication of introduced salmonids to establish greenback and Rio Grande cutthroat trout and Gila trout has been accomplished successfully in Utah, Colorado, and New Mexico though the potential threat of unauthorized reintroduction of nonnative trout is recognized. In New Mexico, one respondent indicated populations of illegal grass carp have also been successfully eliminated. The removal of red shiner from the Virgin River, Utah, by chemical eradication was judged to be partially successful and repetition was recommended to complete the task. Eradication by means other than chemical toxicants has not been formally developed, initiated or evaluated. In Utah and Colorado where selective removal of northern pike is occurring as a research activity, the efficiency of removal by capture and the resultant effect upon the population have yet to be evaluated. Habitat management Manipulation of flows as a habitat management technique has yet to be rigorously tested as a cause-effect relationship. Apparent associations of the reproductive success of native and nonnative fishes to high and low spring flows have been noted as a sidelight in several previous survey-type studies conducted throughout the upper basin. These relationships are being further examined on the Green River with existing flow recommendations, and on the upper mainstem Colorado River, Colorado. Physical habitat manipulation affecting reproductive success of northern pike in riverine spawning habitat or isolation of off-channel ponds favorable to centrarchid spawning have also not been attempted Hatchery augmentation Apart from native salmonid restoration or recovery programs, very few examples of augmentation of native fishes with hatchery stocks exist The stocking of bonytail in the Green River and razorback sucker in the Gila River met with very poor success. The