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1 I CHAPTER IV ENVIRONMENTAL CONSEQUENCES C. Native Fishes (Other than the Rare and Endangered Fished ENVIRONMENTAL CONSEQUENCES OF THE PROPOSED ACTION Overview r Warmwater native fishes could be impacted by the Proposed Action. Flow management efforts are anticipated to produce warmwater habitat conditions that more closely resemble pre-dam conditions in the Upper Basin. If flow changes are a more important limiting factor for warmwater native fishes than are interspecific interactions with nonnative fishes, flow changes might shift overall warmwater species abundance and composition of the Upper Basin toward the historic pattern, i.e., toward warmwater native species common in the past. However the minor flow changes envisioned are unlikely to cause major , shifts. If interspecific interactions are a more important limiting factor, control of problem nonnative species could benefit warmwater native fishes by reducing predation and competition. However, since problem nonnative species are likely to be controlled on a selective or limited basis, there should be only minor positive benefits to other native fishes, at best. Habitat development actions may benefit native minnows and suckers. Coldwater native species found in the headwaters will not be impacted by the Proposed Action. Habitat Management The specific habitat requirements of the other native fishes are not well known. However, habitat management actions that partially recreate historic conditions may create opportunities for the return of a more historic warmwater native fish composition in the Upper Basin. Warmwater native fishes that have declined in modern times due to flow regime changes may increase in abundance. Adaptable native warmwater fish may experience no change in number. Given the minor flow changes assumed in this document, it is unlikely that there will be significant changes in native species composition due to habitat management actions. There will be no impact on coldwater native species in headwaters, since no management activities are planned in headwaters. Habitat Development and Maintenance Though habitat requirements of the other native fishes are not well known, some generalizations can be ventured in predicting impacts from habitat development and maintenance. Warmwater native minnows and suckers inhabit I riverine reaches similar to those used by the rare fishes (see Table 5, Tyus, et al. [1982:64]), so it is probable that habitat development actions that benefit rare fishes will benefit other warmwater native minnows and suckers. Backwater areas would be developed primarily for Colorado squawfish. If manmade backwaters are effective, the impact of these backwaters is expected to be the same for warmwater native minnows and suckers as for rare fishes, IV-C-1