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9 population suggest a population of about 500-1000 individuals (Lanigan and Tyus 1989; Modde et al. 1996) with very limited recruitment (Moode et al. 1996). The basin-wide decline in distribution and abundance of the razorback sucker has been attributed to habitat loss and modification as well as predation on early life stages by non-native fishes (Carlson and Muth 1989). Razorback sucker are large (commonly 400-700 mm total length) and long-lived (30-40 year lifespan) fish (Minckley 1983; McCarthy and Minckley 1987) that evolved in the highly variable hydrologic conditions of the pristine Colorado River Basin (Minckley 1983; Lanigan and Tyus 1989; Bestgen 1990). The species derives its name from a prominent dorsal ridge found in adults. Wick (1997) suggested that the dorsal ridge acts as a keel and works in conjunction with large pectoral fins to provide stability when feeding in low-velocity backwaters and floodplains. Floodplain habitats and other warm backwater areas are important as nursery areas for juvenile fish and feeding areas for adult fish (Tyus 1987, 1990; Modde 1997; Wick 1997; Wydoski and Wick 1998). Although razorback sucker are adapted to and frequently collected in lacustrine-like environments (Stanford 1994), other habitats used by adult razorback sucker vary widely and include runs, eddies, and pools (Tyus 1987; Tyus and Karp 1990; Modde and Wick 1997). Diet for all life stages varies but is typically plankton, algae, invertebrates, and detritus (Vanicek 1967; Marsh 1987; Muth et al. 1998). Adults congregate and spawn on the ascending limb of the hydrograph (Stanford 1994) at water temperatures ranging from 10 to 18 degrees C (Tyus 1987). In the middle Green River, Muths et al. (1998) described the spawning period generally as early or mid May through late May or early June. During spawning eggs are usually deposited in the interstices of gravel or cobble