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0", Lower Yampa River (just upstream of the Yampa-Green River confluence, Echo Park, Dinosaur National Monument), Colorado, and lower Green River (possibly near the town of Green River), Utah. V. Study Methods/Approach: Passive drift-net sampling is an effective and proven method for capturing Colorado squawfish larvae, In properly conducted, results can provide a reasonable estimate of annual reproductive output from spawr_ing agrees without over-sampling larvae, Drift-net sampling in the Yampa and Green rivers, as part of FGFRI, was started in 1990 and will be conducted again in 1991. In 1991, twO drift- net stations were established, i.e., lower Yampa River at Echo Park and Green River just below the Split Mountain boat ramp. At each station, three flow-metered plankton nets were set near the shore, dai~y at dawn for 1-2 h, from end of June through early August. The objectives of this sampling were to dOCUlllent timing and duration of spawning by Colorado squawfish in the lower Yampa River, determine peaks in abundance of transported Colorado squawfish larvae transported from the lower Yampa River spawning area into nursery habitats in the Jensen-Ouray area; nursery-habitat sampling conducted by Utah DWR (SDCR Task 2) in fall 1990 was intended to subsequently determine abundance of young Colorado squawfish in backwater habitats. Results of the 1990 drift-net sampling were provided in an annual progress report submitted to the U.S. Bu:teau of Reclamation. After discussions with the cooperative FGFRI team in December 1990, the drift-net sampling scheme used in 1990 was changed in favor of the design proposed here (this new study design will be employed in 1991) . Reproductive output will be measured by daily captures of drifting Colorado squawfish larvae at two sites, one at mouth of the Yampa River and one below Grey and Desolation canyons in the lower Green River. Both of these sites are below known spawning grounds, and data from sampling at these sites will provide estimates of relative abundance of Colorado squawfish larvae being transported from spawning areas and into potential nursery habitats. Colorado squawfish in the Yampa River spawn on the descending limb of the hydrograph, often associated with abrupt increases (flow spikes) in base flow (Nesler et al. 1988; Tyus and Karp 1989). Sampling for Colorado squawfish larvae will be initiated based on those data and stream-flow conditions prior to sampling (probably start in mid-late June). Duration of the sampling period will depend on number of larvae collected in late- season samples, past data, and stream-flow conditions probably end early- mid August) . Colorado squawfish larvae are most abundant in drift-net samples at dawn and nearshore and midstream nets capture roughly equivalent numbers of fish/unit volume of water sampled (Haynes et al. 1984; Nesler 1986). This was supported by results of out nearshore sampling during summer 1990; catch rates of three nearshore drift nets were similar (one-way ANOVA) . Results of the 1990 sampling showed that about 60t of drifting Colorado period on only four sampling days; we determined that daily sampling over a 6-S-week period was necessary to detect and measure peaks in larval abundance and bracket the period of larval transport. At each station, three 4-m-long conical plankton nets (560 micron mesh) will be set daily at dawn. Nets will be attached to rectangular steel frames (0.15 m:) and staked into the stream substrate adjacent to the shore in water 0.5 -1. 0 m deep. A removable collection bucket for trapping filtered material and fishes will be attached to the cod end of each net, C3