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Table 1.-Continued. Family Scientific Name Common Name Nonnative Fishes Centrarchidae Lepomis cyanellus green sunfish Lepomis macrochirus bluegill Micropterus dolomieui smallmouth bass Micropterus salmoides largemouth bass Pomoxis annularis white crappie Pomoxis nigromaculatus black crappie Percidae Etheostoma exile Iowa darter Etheostoma nigrum johnny darter Perca flavescens yellow perch Stizostedion vitreum vitreum walleye 1982). These species also dominate the total number of fish caught. Under present monitoring efforts, over 90% of all fish caught are nonnative (McAda et al. 1994). Behnke and Benson (1983) attributed the dominance of nonnative fishes in the UCRB to dramatic changes in historic flow regimes, water quality, temperature, and habitat characteristics. They noted that water development (e.g., mainstem reservoirs) had converted a turbulent, highly variable river system into one that was relatively stable, with flows and temperature patterns that allowed for the proliferation of nonnative fishes. Hawkins and Nesler (1991) identified six species on a.list of 28 nonnative fishes that were considered by CRB researchers to be of greatest or widespread concern because of their potential impacts on native fishes of the CRB and southwestern United States. These species are red shiner, common carp, fathead 11