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<br />':'" <br />t>/';~ <br />";~'" <br /> <br />-I <br /> <br />Adult fish initially stage for spawning runs in large eddies in February and <br />March, and make spawning runs that average 17 days into the LCR from March <br />through May, as LCR flows decrease, warm and clear (Valdez 1995). Spawning <br />runs of up to 25 miles have been reported for this species. After spawning, <br />many adult chub return to specific microsites in the mainstream. Young HBC <br />remain in the Little Colorado River. or move into the mainstream where <br />mortality due to thermal stress (Lupher and Clarkson 1993) and predators <br />(Valdez 1995) is perceived to be extremely high. During the summer the young <br />HBC that survive in the mainstream occupy low-velocity, vegetated shoreline <br /> <br />habitats; however, low survivorship over the year virtually eliminates the <br />young of the year HBC in the mainstream. Therefore, few if any HBC spawned <br />during the previous year are present in the mainstream in March. <br /> <br />Limited breeding 'of HBC occurs among other sub-populations in the Colorado <br />River. Valdez (1995) documented limited spawning success at 3D-Mile Spring in <br />upper Marble Canyon, and rare young HBC have been documented at Kanab Creek; <br />however, these sightings are rare compared with the reproductive success of <br />those HBC that spawn in the Little Colorado River. <br /> <br />Dietary analyses reveal HBC to be opportunistic feeders, selectively feeding <br />on aquatic and terrestrial invertebrates (Valdez 1995). HBC diet changes over <br />the course of the year in response to food availability and turbidity-related <br />decreases in benthic standing biomass over distance downstream from Glen <br />Canyon Dam (Blinn et al., 1992). Non-native GAmmaruS 1acustris occasionally <br />comprise a large proportion of HBC diet, and GAmmarus selectively feeds on <br />epiphytes (i.e., diatoms) associated with ~ladnnhnra alnmp-rata,' the dominant <br />alga in the upper reaches where clearwater conditions often prevail. <br /> <br />Impacts of the test flow <br /> <br />The test flow is not likely to adversely affect the HBC. The timing of the <br />high flow event has been specifically planned to limit impacts to 1995-spawned <br />HBC. Furthermore, the high flow will occur prior to significant spawning- <br />related movement of adult chub into the Little Colorado River, and will take <br />place at a time of year when warming of backwaters' is not significant. Some <br />loss of young chub may occur; however, 1995 was not a remarkably strong <br />recruitment year (Tuegel 1995). Therefore, the impacts of the high flow are <br />unlikely to be measurable; High flow events of the magnitude planned here <br />occurred virtually every year in pre-dam time, and adult HBC appear to be <br />well-adapted to survival of such events. <br /> <br />The Reasonable and Prudent alternative of the 1994 BO includes habitat/beach <br />building flows, however, the Service determined some HBC would be taken during <br />a high flow event. Their discussion of incidental take considers testing and <br />studies to determine impacts of flows on young humpback. one goal of the test <br />flow is redistribution of channel bottom sediment to the channel margins to <br />establish and maintain habitats for young life stages of HBC in the mainstem. <br />This hypothesis will be examined through the test flow. <br /> <br />9 <br />