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1"' numerous in the drift during the other three time periods. Drifting larval catfish were captured predominantly during the metalarval development stage, and were captured mostly during late July and early August. Comparisons with 1983-84 diel density data for channel catfish larvae demonstrate considerable variation between years and developmental phase. In contrast to 1985 results, 1983 data showed greater densities of catfish as mesolarvae during the dusk and midnight periods, both at Box Elder and upstream at the Harding Hole sample site (RM 20.2). In 1984 catfish in the drift samples were mostly metalarvae, similar to 1985, but diel densities were generally the same among dawn, dusk and midnight periods at both the Box Elder and Stateline-Green River sites. In 1985, bluehead suckers showed a stronger tendency for night-time drift, including both the dusk and midnight periods. Drift densities for this species ranged up to 221 individuals/IOOO m3, and averaged 10.7-26.2/1000 m~ during the dusk and midnight periods, respectively. Bluehead sucker drifted largely as mesolarvae, with the greatest numbers captured during the first two weeks of July. Comparisons with diel drift patterns in 1983-84 also demonstrate considerable variation between years, sample sites, and developmental phase. In 1983, bluehead sucker exhibited greater densities as mesolarvae during the dawn and dusk periods at Box Elder, and during the dusk and midnight periods at Harding Hale. In 1984, bluehead sucker e:{hibited greater densities during the dawn and noon periods, and were split between proto- and mesolarvae at Box Elder, ~~hile at Stateline their greatest densities were observed only during the dawn period as mesolarvae. Similar to bluehead sucker in 1985, flannelmouth sucker exhibited the greatest densities in the midnight drift samples, ranging up to 35.4 individuals/lOOO m~, and averaging 4.6/1000 m3. The differences between periods was not as great for this species as for the others. Flannelmouth suckers drifted mostly as mesolarvae, and were captured predominantly in early July. Comparisons with 1983-84 diel drift densities demonstrated variability mostly between years. In 1983, flannel-mouth sucker exhibited the greatest densities during the dawn and midnight periods at both Box Elder and Harding Hole, and were split between meso- and metalarvae. In 1984, their greatest densities were observed during the dawn period at both Box Elder and Harding Hole, again split between meso- and metalarvae. Co lor ado s, Qua~.., f ish 5", IlEl. w n i.D_9.Lf.1.9 w r gg.l.iI!? ~ Data from Haynes et al. (1985) indicate that spawning by Colorado squawfish was relatively more successful in 1983 and 1984 than in 1980-1982. Using data from 1983, 1984, and 1985, the relationship between predicted spawning dates and flow regimes in the Yampa River in Yampa Canyon are illustrated in Figs. 3, 4 and 5 to examine river conditions that appear preferable by the adult fishes' for spawning. In all three years, spawning activity appears to be associated with the onset of fluctuating flow conditions encountered just prior to the baseline of the hydrograph following spring runoff. In each year, the peak in spawning activity occurred during a resurgence in the flow from its steady decline following peak spring flows. In 1983, peak spawning activity occurred from July 24-31, and was initiated when flows increased from 90 m~/s to 122 m~/s during July 22-24. This major period of spawning activity tailed off as flows again decreased below 63 m3/s. During this period,