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-22- Fry sampling was conducted monthly on the river from June through August 1991. During June and July, 140 trout fry were collected from five locations between Metaska Campground and the Bradfield Bridge. Ninety-six percent were brown trout and 4% were rainbow and/or cutthroat trout. Similarly, sampling during the week of August 4-8, 1991, resulted in the capture of 275 YOY brown trout compared to eight YOY rainbow and/or cutthroat trout. Brown trout comprised 97% of this sample. Finally, sampling on October 1, 1991 revealed brown trout fry outnumbered YOY rainbow fry 138 to 6, i.e., 96% brown trout to 4% rainbow trout. Habitat conditions for fry survival (stable flows) were very good to outstanding from May 31 through October 1991, but rainbow and cutthroat trout recruitment was minimal. Examination of the flow regime from May 13-27 reveals flows ranged from 125 to 800 cfs. Spawning rainbow and SRC trout were sampled during the boat-shocking survey from May 13-16, 1991, when the flow was 200 cfs. Flows were at 800 cfs or higher from May 18-26, 1991, according to USBOR-DPO records. Rainbow and SRC trout would have spawned near the channel edge during this period. However, when the spill was over, and flows were reduced to 71 cfs (a 91% flow reduction), most rainbow and cutthroat trout eggs deposited during high flow would have been left to dry in the sunshine. Similar occurrences have been documented on the South Platte River below Cheesman Reservoir, a Denver Water Department impoundment (Nehring 1988). Rainbow and cutthroat trout readily hybridize in the wild. The resulting cross is often referred to as a "cutbow" and has the black spotting pattern of the rainbow with the red throat slashes of the cutthroat trout. These naturally produced hybrid trout began appearing in the Dolores River in the fall of 1988. They were abundant in samples at Ferris Canyon Campground in October 1989. At that time these hybrids ranged in size from 17 to 44 cm. Most were 27 cm or larger. Age and growth data for rainbow and cutthroat trout for October 1989 (Nehring 1991) reveals that any of the hybrids between 32 and 44 cm would have been between age 2+ and 4+, indicating they were spawned in 1985, 1986, or 1987. This concurs with evidence stated above, i.e., the periods of prolonged (managed) spills from 1984 through 1987 were probably more conducive to successful reproduction by rainbow and/or SRC trout, than the period from 1988 through 1991. Finally, water temperature fluctuations (especially large declines), during the egg incubation period for rainbow and cutthroat trout (mid-April through late June) can result in death of the developing embryo in the egg. Rainbow trout eggs die from thermal shock when water temperatures reach 38-420 F. USBOR-DPO temperature records indicate daytime lows as well as 24-hour average temperatures were in this range during the "spill period" in May 1991. This undoubtedly contributed to the loss of the 1991 rainbow trout year class.