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3. Determine probable time of spawning of squawfish and humpback-chubs and correlate with data on adult fishes developed by the Northwest Region, Colorado Division of Wildlife and the U.S. Fish and Wildlife Service. 4. All collections will be made according to a computer-compatible (FWS MANAGE), detailed physical stratification system which reflects the geomorphological, hydrological, and ecological variables of the drainages. 5. Study areas will include the lower Yampa River, Moffat County from Cross Mountain Canyon to the Green River confluence in Dinosaur National Monument and the Colorado River, Mesa County from Loma to the state line. 6. Devise methods for the identification and differentiation of larval and juvenile humpback chubs, roundtail chubs (G. robusta), bonytail (G. elegans), and hybrids and/or intergrades. 7. Morphomeristic counts and measurements will be made on field-collected chub larvae and juveniles from the 2 study areas for comparison with known-age pure stock and hybrid crosses provided by Willow Beach and Dexter National Fish hatcheries. STUDY AREA AND METHODS The Colorado and Yampa River study areas have been previously described by Haynes and Muth (1982) and Haynes et al. (in press) as have been the field and laboratory methods used. In 1982, in addition to methods previously described, drift-net sampling for YOY fishes was conducted in the Colorado River study area (stratum K) on 6 dates between 13 July and 26 August. Drift-net sampling was conducted in the Dinosaur National Monument section of the Yampa River study area (strata 1 and 2) on 22-26 August. The goals of this additional survey were to evaluate techniques for sampling YOY fish in swift, deepwater habitats ineffectively sampled by seines, to determine ichthyoplankton abundance and species composition, and to evaluate drift as an agent of squawfish and/or humpback dispersal. Most species occurring in the Colorado and Yampa study areas exhibit peak spawning activity during early June through mid-August (Vanicek and Kramer 1969, Carlson et al. 1979, Snyder 1981, Tyus et al. 1981, Haynes and Muth 1982). Reports by Harrow et al. (1975), Gallagher and Conner (1980), and Lathrop (1982) indicated that larval fish drifting densities were greater along shoreline areas than mid-channel. This information was used to design the present drift sampling program. Near-shore surface drift net collections were made using 0.5-m2 diameter conical plankton nets (Wildlife Supply Co., Saginaw, Michigan) mounted on 0.5 x 0.3-m rectangular steel frames and fitted with 33-cm long removable