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The high release is also expected to scour beds of the green alga, Cladophora ilomerata, which is the primary source of production for the Grand Canyon aquatic ecosystem, This scouring effect is likely to release large supplies offood organisms (e.g" simuliids, amphipods [Gammarns lacustris]) to downstream fish populations, This increased food supply would be a short-term beneficial effect for the fish, but the scouring is likely to result in reduced standing crop of benthic macroinvertebrates and subsequent reduced food supplies, until the system can recover, The . period of recovery is unknown, and food supplies could remain low through winter with reduced light availability and lowered photosynthetic potential, A beaclvbabitat-building flow of 45,000 cfs, released from Glen Canyon Dam from March 22 through April 7, 1996, did not appear to reduce shoreline densities of juvenile humpback chub in the Colorado River through Grand Canyon, This flood occurred when the YOY chubs were nearly one year of age (typically 60-140 mm TL), and presumably better adjusted to the cold mainstem temperatures and dynamic flow regimes, EffectJI To Humpback Chub We conclude from this assessment that a release of31 ,000 cfs from Glen Canyon Dam during October is likely to detrimentally affect the endangered humpback chub in the Colorado River through Grand Canyon, This determination is based on the best available scientific infonnation from Grand Canyon that identifies late summer, falI,. and winter as critical periods for survival by YOY humpback chub, With highest densities of young in the mainstem Colorado River in September and October, habitat quality and stability are vital to survival of these young fish, Although past studies suggest that survival of these young fish may be low under present environmental conditions, the proposed action further exacerbates the elements that are believed to be affecting young humpback chub, beyond the effects of the baseline or existing dam operations, The effects of the proposed action to individual fish are reduced survival from increased predation, increased energy expenditure from shoreline habitat instability, and reduced food supplies, These effects are likely to affect survival of a cohort, and hence reduce recruitment to adulthood, and future reproductive potential, Based on this, we conclude that the proposed action may affect the endangered humpback chub due to take of Juveniles in the mainatem of the Colorado River, It will not affect the adult population. In the December 21. 1994 Final Biological Opinion on the Operation of Glen Canyon Dam as the Modified Low Fluctuating Flow Alterative of the Final Environmental Impact Statement the Service reviewed the impact of habitat maintenance and habitat building flows, On page 40 of this opinion, the Service concluded that "Implementation of the reasonable and prodent alternative which includes habitat maintenance and building flows is expected to minimize take of the humpback chub and in not likely to result in jeopardy to the species, Channel bottom sediment will be redistributed to channel margins to establish and maintain habitats for the use of young life stages of humpback chubs in the mainstem." Considering redistribution and conservation of 21