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For the Yampa River study area, 140 specimens were collected, representing 7 species and 3 families. The most abundant native was Gila spp., comprising 53% of the total. Channel catfish were the predominant non-natives, constituting 34% of the total catch. Collectively, ichthyoplankton density-drift rates in the Colorado River tended to be higher in the dawn samples with a dawn: dusk: midnight abundance density ratio of almost 3:1:1 (P = 0.1476) (Table 7). Speckled dace were slightly more abundant in dawn samples with a dawn: dusk: midnight ratio of 4:1:2 (P = 0.1774). Gila spp. exhibited higher drifting densities in the dawn samples with a dawn: dusk: midnight abundance ratio of 11:1:1 (P = 0.0064). Differences in drifting densities among the 3 sampling times were not evident for bluehead suckers (P = 0.8562). Sampling in the Yampa River was inadequate for similar analysis (Table 8). Razorback Sucker No YOY or juvenile razorback suckers (Xyrauchen texanus) were identified in either study area during 1982. Third-Year (1983) Investigations A tentative 1983 field schedule for the Colorado and Yampa River study areas is presented in Table 9. Deviations from this schedule may result from unpredictable problems in the study areas, or with gear and/or personnel. During this 3rd year, intensive drift sampling will be conducted in the Yampa River in addition to regularly-scheduled YOY sampling in both study areas. One drift net station will be installed above Harding Hole at the lower end of stratum 2 and a 2nd station will be installed in the vicinity of Boxelder Campground near the confluence (stratum 1). A maximum of 2 days will be spent at each site at times presented in Table 9 with 1-2 hour samples collected at dawn, noon, dusk, and midnight. A known-age larval series of roundtail chubs will be prepared using either upper Yampa or White River brood stock. Adults will be collected in mid-June with the assistance of Pdorthwest Regional electrofishing personnel and injected on-site with acetone-dried carp pituitary extract. Eggs will be stripped, fertilized, and water-hardened at the site. Eggs and larvae will be reared at Colorado State University, Fort Collins. LITERATURE CITED Carlson, C. A., C. G. Prewitt, D. W. Snyder, E. J. Wick, E. L. Ames„ and W. D. Fronk. 1979. Fish and macroinvertebrates of the White and Yampa rivers, Colorado. U.S. Dep. Inter., Bur. Land Manage. Colo. Biol. Sci. Ser. 1. 276pp. De Vlaming, V. L. 1972. Environmental control of teleost reproductive cycles: a brief review. J. Fish. Biol. 4:131-140.