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I I I the Colorado River near Grand Junction, Colorado (McAda and Wydoski 1980; Valdez and Wick 1983). Valdez and Wick (1983) also reported collecting ripe razorback suckers of both sexes from "Clifton" Ponds along the Colorado River near Clifton, Colorado. These fish may have used the floodplain habitat for staging but actually spawned in the adjacent river channel. However, there is a possibility that they actually spawned in the floodplain. I I Kidd (1996) reported that he observed spawning razorback suckers in significant numbers between 1971 and 1980 at five sites on the upper Colorado River: (1) the Mesa County DeBeque gravel pit, (2) the Colorado River Overflow near DeBeque, (3) the Palisade Labor Camp slough, (4) the 32 1/4 Road backwater/gravel pit, and (5) the Walter Walker Wildlife Area. These sites were all greater than 2 ha (5 ac) in area, more than 457 m (1,500 ft) long, generally 0.9-1.5 m (3-5 ft) in depth, and did not depend entirely upon the river to maintain water levels. Kidd attributed the rapid decline of the razorback sucker population in the upper Colorado River to the loss of the Colorado River Overflow spawning site near DeBeque, Colorado during the high flood events of 1983 and 1984. , I I Spawning of razorback suckers in Lake Havasu in 1950 was described by LaRivers (1962). Adult razorback suckers spawned naturally and successfully in isolated coves along the shore of Lake Mohave (T. Burke, 1994, personal communication; Mueller et al. 1993). Jonez and Sumner (1954) described spawning of razorback suckers in Lake Mead and spawning of both razorback suckers and bony tail in Lake Mohave. Jonez and Sumner stated that both species were broadcast spawners that were observed in large schools. In reservoirs, razorback suckers congregate and spawn on flat or gently sloping shoreline areas over gravel, cobble, or mixed substrate (Bozek et al. 1990; Douglas 1952). In Lake Mohave, razorbacks spawned in water from 0.5 to 5.0 m deep (Minckley et al. 1991). However, they were observed to spawn in water from 10 to 15 m deep in Senator Wash Reservoir (Medel-Ulmer 1983). Captive razorback suckers also spawned in earthen ponds at the Dexter National Fish Hatchery, New Mexico (J.H. Williamson, 1998, personal communication) . I I I Although cobble and gravel bars are used as spawning sites for razorback suckers in rivers, floodplains may also be used for spawning under certain conditions. Sparks (1995) pointed out that "A floodplain depression that is ordinarily dry during moderate floods may become a spawning site during record floods, when traditional sites are unusable becaus~ of excessive water velocities or sediment loads". I I F. Streamflow Manaqement - A Critical Habitat Component in River-Floodplain Ecosystems. The natural streamflow regime of virtually all rivers is inherently variable and this variability is critical to maintaining the integrity of river-floodplain ecosystems (Poff et al. 1997). The morphology of a river channel is dependent upon lateral and vertical controls based on the geology of the region and physiographic setting of the river (Church 1992). The productivity of rivers in the Upper Colorado River Basin was historically provided through energy transfer by the river continuum and the flood pulse. The sediment load of these rivers limited primary and secondary productivity in the main channels so that nutrients were provided longitudinally from terrestrial sources upstream and laterally from the inundation of floodplains during high streamflow events. Dams have fragmented major rivers in the Upper Basin so that productivity from upstream sources (i.e., the river continuum concept) was disrupted (Ward and Stanford 1983, 1995). Because of fragmentation by dams, Upper Basin rivers are now more dependent upon the productivity of aquatic organisms from lateral floodplain sources (i.e., the flood pulse concept). Recent protocol from large-river biologists (Stanford et al. I I I I I 21 I