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observed spawning in the Yampa River just above the confluence of the Green River, however, larvae are presumed to drift downstream immediately following emergence where they are transported to floodplain habitat in the Green River (Modde et al. 1995, Moddeet al. accepted for publication). Bonytail Because of the rarity of bonytail chubs, their distribution and abundance is largely unknown. Fish were fairly common in Echo Park prior to and shortly after the closure of Flaming Gorge Dam (Vanicek 1967). However, few individuals have been collected in the last decade. Holden and Crist (1981) collected one bonytail chub in the lower Yampa River in 1979, and the Fish and Wildlife Service captured a suspected juvenile in 1987. Spawning Requirements of Endangered Fishes Colorado squawfish Two primary Colorado squawfish spawning sites have been identified in the Green River Basin (Tyus and McAda1984, Wick et al. 1983, and Tyus et al. 1987), one of which is located between RM 10.5 and RM 18 in the Yampa River. Fish spawning in this area travel both upstream from the Green River and White rivers (Tyus 1985, 1986, and Irving and Modde 1994) as well as downstream from higher in the Yampa River (Tyus 1985). Seven migrating Colorado squawfish traveled over 200 river miles from the White River to the Yampa River spawning site (Irving and Modde 1994). The same fish were observed to make this extended migration in two consecutive years (Irving and Modde 1994). The initiation of the spawning migration is an important element for the ~uccessful reproduction of the Colorado squawfish. Most fish initiated spawning migrations between late May and mid June depending on the magnitude of the water year (Tyus and Karp 1989). Spawning migrations were initiated earlier in low peak flow years (and later in higher peak flow years (Tyus and Karp 1989). Movement to spawning locations was associated with patterns of discharge and temperature (Figure 4, from Tyus and Karp 1989). Fish began moving to spawning sites during the descending limb of the hydrograph and when temperatures reached 140 C. Timing of spawning, as was spawning migration, was associated more closely with patterns in the hydrograph rather than absolute quantity of flows. Spawning occurred earlier in low flow years and later in higher flow years. Water temperatures during spawning ranged from 14.50 and 27.50 C for all years studied (Tyus and Karp 1989). During the peak spawning period (study years of Tyus and Karp 1989), mean discharge ranged from 893 cfs (1981) to 3,814 cfs (1982).