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during the winter of 1992-1993 were lower than those discussed and the flows during the winter of 1995-1996 were higher (refer to Table 2 above). Colorado pikeminnow reproduction, and YOYhabitat use Day et al. (Report B) found Colorado pikeminnow to be the most abundant native species in samples for both the 1995 (n=97) and 1996 (n=1729) cohorts. The 1994 cohort, represented by 435 fish, ranked third among native fishes that year. The very high catch for 1996 was split between August (n=812} and September (n=915) samples (Table 4). It was common to capture 20 or more Colorado pikeminnow in a backwater during these months. Moreover, three backwaters sampled in August and two in September yielded more than 100 Colorado pikeminnow. One particular backwater yielded 280 Colorado pikeminnow in August and 188 in September. Colorado pikeminnow showed no clear pattern of abundance through the year. In 1996, Colorado pikeminnow catch increased through the sampling period, but captures varied each month in 1994 and 1995. Higher YOY Colorado pikeminnow catch rates in 1996 were matched by the increased wide distribution in both canyons in 1996. Whereas, this species was found almost exclusively in Gray Canyon, and sporadically in Desolation Canyon, in 1994 and 1995. The Gila monitoring trips were often scheduled too early in the year to adequately `^R' address pikeminnow reproductive success. However, in 1993, the monitoring trip was delayed until late August due to high flows and resulted in the collection of 203 YOY pikeminnow. The results of both the 1992 and 1993 monitoring trips are referred to in Table 2. Back calculated spawning dates (Muth 1990) of the 1993 cohort indicate the bulk of that years spawn occurred on or near 17 July 1993 when Green River flows were 4,360 cfs. The monitoring trip in 1996 was clearly scheduled too early to detect the strong cohort reported by Day et al. that year. Nursery habitat (1994-1996) correlation analyses revealed a strong negative correlation ` ' (rz=0.49) between Colorado pikeminnow CPUE and duration of flows above 75% of the peak for ;,, the preceding spring. This correlation was even stronger for August and September samples ~' (r2=0.999). However, the results of both fish studies (Reports B and C) indicate the greatest ~'~ production of YOY pikeminnow occurred when Green River flows peaked near 25,000 cfs (in 1993 and 1996; see Table 2 above). The nursery habitat and monitoring methodologies differed enough to preclude direct assimilation of these data sets. We assume the 1996 cohort of ~- pikeminnow was the most abundant, which was produced-when Green River spring and summer flows exceeded 6,000 cfs for the greatest period of time (90 days). The majority of these >6,000 Sri;' cfs flow days occurred early in the hydrograph with the river peaking on 22 -May 1996 and dropping below 6,000 cfs by 07 July. F _~:, T ' Colorado pikeminnow in Desolation and Gray canyons used secondary channel type . backwaters. Dimensions of these backwaters, however, were different between canyon and floodplain reaches. Surface areas were smaller and depths greater in canyons. Greater volume of used backwaters verses unused backwaters was consistent in both canyon and floodplain reaches, suggesting that volume is critical in use. Because secondary channel habitats tend to have smaller surface area in this canyon reach, Colorado pikeminnow may have used deeper backwaters to compensate. It is unclear, however, why Colorado pikeminnow did not use "' constricted reach eddy backwaters, which were often very large and deep. Constricted reach eddies generally open upstream and have considerable current outside the mouth, in contrast to t_ 1 =; xiv