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10 substrates where they develop unguarded (Muth et al. 1999). Incubation time and hatching success are temperature dependent (Marsh 1985; Bozek et al. 1990) with incubation time ranging from about 6 to 23 days (Bozek et al. 1990). After emergence, larval razorback sucker enter the drift and are transported downstream (Mueller 1989; Paulin et al. 1989) where the availability of low velocity, warm, and food-rich backwaters is likely a key determinant of recruitment success (Stanford 1994; Modde 1996; Modde et al. 2001). The long lifespan of the razorback sucker and high fecundity (up to 140,000 ova per fish, Minckley 1983) are presumed to be adaptations that allowed the species to persist in a highly variable environment where there might be several consecutive seasons without successful reproduction and recruitment (Bestgen 1990). Studies reviewing collection data for razorback sucker in the middle Green River during the last ten years have demonstrated the use of two spawning areas; Green River kilometers (RKM) 492-501 near the town of Jensen, UT and the Yampa River near the Green River confluence in Echo Park, CO (Tyus and Karp 1990; Modde et al. 1996). Because of the relatively high capture rate of spawning sucker at the Jensen spawning area (Tyus and Karp 1990) and the potential deleterious effects of Flaming Gorge Dam operations on endangered fishes, most research has focused on the Green River spawning area. During 1992-1996 Wick (1997) conducted an intensive study of physical and biological processes at the Green River spawning area and found that sediment was deposited on the area used by razorback sucker during the spawning season beginning at flows of about 325 m3/s which corresponds to the post-dam effective discharge estimated by Andrews (1986). The cause of sediment deposition was described as a backwater effect from a downstream constriction that reduced water surface slope in the spawning