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I I monitoring and research. Areas that are enhanced/restored should be thoroughly evaluated to determine the responses of the endangered and nonnative fishes to such efforts and refinements made as necessary to achieve desired Recovery Program goals and objectives. Enhanced areas will either have to be large enough or numerous enough to ensure that responses by fishes can be detected. I I I I I Larval and juvenile razorback suckers apparently require inundated floodplains to grow and survive (Mueller 1995; Mueller et al. 1993; Tyus and Karp 1989, 1990, 1991). Rapid growth of razorback sucker juveniles in off-channel habitats was reported by Osmundson and Kaeding (1989) and Mueller et al. (1993). Reconnecting floodplain habitats with rivers in the Upper Colorado River Basin is expected to benefit razorback suckers most since these habitats will provide an adequate quantity of food of the right size and at the right time for survival of larval razorback suckers during their critical period. Larvae and juveniles of other native fishes including the three other endangered species (Colorado squawfish, humpback chub, and bony tail) will also benefit from floodplain production of zooplankton and benthic invertebrates that enter the river when streamflows subside after spring flooding, enhancing the productivity of the main channel and backwaters of Upper Basin rivers. I Adult razorback suckers are flexible in their use of habitats. Although this species evolved in large riverine systems, adults have survived well in both lacustrine (Wallis 1951, Marsh and Langhorst 1988, Minckley et al. 1991) and lotic (Miller et al. 1982; Tyus 1987) habitats. During high spring runoff, adult razorback suckers in the Upper Colorado River Basin congregated in large eddies at the mouths of rivers, off-channel ponds that have a connection to the rivers, and wetlands in floodplain areas (McAda and Wydoski 1980; Modde 1997; Tyus and Karp 1990; Valdez and Wick 1983). The use of low velocity habitats by adult razorbacks may be to escape the high velocities associated with the spring runoff and possibly to feed after spawning to regain their body condition. I I I I Razorback suckers spawn annually on clean cobble and gravel in rivers (Tyus and Karp 1990; Wick and Cluer 1998) and on the wave-swept rubble shoreline of Lake Mohave (Minckley et al. 1991). It is possible that floodplain habitats may have been used more extensively for spawning in the past by razorback suckers (Osmundson and Kaeding 1989) when they had access to them and riverine conditions were unsuitable as suggested by Sparks (1995) for other riverine fish species. I Breachinq Levees. Removal of levees that are located on the lowest floodplain terraces (public property or acquired private property) is the most practical way to reconnect mainstem and tributary rivers with productive floodplain habitats using present streamflows. Such removal should be done on properties that can be easily reconnected with the main channel where thorough evaluations can be made of zooplankton/benthic invertebrate production and responses by native and nonnative fish species. I I Ideally, reconnect ion of floodplain habitats with main river channels should simulate natural conditions where possible and be relatively maintenance free. I I Floodolain Terraces. Existing floodplain terraces were deposited by high peak streamflows that occurred before high dams were constructed and the streamflows were regulated (i.e., peak streamflows that resulted in inundation, scouring, and deposition of floodplains were lost). Existing streamflow conditions may not permit annual inundation of the floodplain by simply removing levees. It may be necessary to excavate existing terraces so that present streamflow regimes can inundate floodplains ) 31 I