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Some nonnative fishes are common to abundant in the Upper Basin with well established populations. These fishes pose the greatest potential to benefit, either directly or indirectly, from enhanced or restored floodplain habitats and, therefore, have a high potential to adversely affect the razorback sucker. These fish species must be considered carefully when enhancement or restoration projects are being considered. They must also be monitored carefully in sites that have been enhanced or restored to evaluate their responses to the enhancement or restoration. Others are rare/incidental throughout the Upper Basin, and may not cause problems for razorback suckers except in specific localized areas (e.g., mosquitofish). The relative abundance of 17 nonnative fishes in the Upper Basin is summarized as: Common to Abundant Locally Common/Abundant Rare/Incidental black bullhead walleye black crappie mosquitofish redside shiner bluegill plains topminnow Many of the nonnative fishes do well in either riverine or lacustrine (lake- like) environments (e.g., carp, red shiner, fathead minnow, smallmouth bass, redside shiner, white sucker, plains killifish). Some will probably do better in riverine habitats than in lake-like habitats (e.g., channel catfish, sand shiner); and some will probably do better in lake-like habitats than in the riverine habitats (e.g., northern pike, green sunfish, largemouth bass, black bullhead, walleye, black crappie, mosquitofish, bluegill). Whether they actively use floodplain habitats or not, many of the species will likely benefit, directly or indirectly, from floodplain restoration to some degree. Restored floodplain habitats are expected to provide allocthanous materials and nutrients, and cause a temporary productivity pulse, both within and out of channel (Bayley 1991). Some of the main channel species will likely benefit from the increased productivity by an increase in growth or numbers. channel catfish red shiner carp fathead minnow sand shiner northern pike green sunfish largemouth bass smallmouth bass white sucker Seventeen warmwater, nonnative fish species were identified as having the potential to use enhanced or restored floodplain habitats and also having the potential to adversely affect razorback suckers by predation or competition (Table 2). The present distribution and relative abundance of these 17 fishes are summarized on maps based on Tyus et al. (1982). These maps were updated from various reports and personal communications (Appendix 1) that are listed in the REFERENCE section. Options to Prevent or Reduce "Problematic" Nonnative Fishes The following options have been identified that would reduce or prevent "problematic" nonnative fishes in enhanced or restored floodplain habitats. Still other options exist beyond those identified in the following list. 3