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Final Report 18 Pre-Interin Flows 18 14 6' ! 12 .. i 10 .. l!I 8 .. z:. Ii! 8 is 4 2 o ~ ~ ~ ~ H 0 ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ Time of Day 18 18 Interim Flows _14 o o ~ 12 .. i 10 ... !!' 8 .. z:. Ii{ 8 is o ~ ~ ~ ~ ~ 0 ~ ~ ~ ~ ~ i ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ Time of Day _ Highest Proportion of Movement Pm= 0,21 _ High Proportion of Movement Pm= 0,16 _ Low Proportion of Movement Pm= ,08 D Lowest Proportion of Movement Pm= .05 Fig. 8. Fraction of telemetry observation time blocks with horizonal movement of radio-tagged adult humpback chub in Region I during average research and interim flow cycles. releases in spring, summer, and fall, and fluctuating flows from Glen Canyon Dam operations, with increased exposure to predation, were probably the primmy causes leading to high mortality of young humpback chub in Grand Canyon. This effect was probably compounded in September and October when dam operations reduce releases from high to low volume, and shoreline cover (esp. vegetation) becomes stranded. High relative condition factor for adults indicates that movement during high flows and high ramping rates was not energetically detrimental to adult humpback chub. Although this determination was made for flow ranges associated with interim flows (i.e., 8,000-20,000 cfs), similar effects were observed for higher flows under previous peaking power operations (i.e., 5,000-31,500 cfs). In addition, movement patterns of adults are not likely Executive Summary . 9 to substantially change until river flows overtop the debris fans that form the recirculating eddies used extensively by these fish. These high flows did not occur during this investigation. Although the presence of Glen Canyon Dam probably did not impede movement of the sedenuuy humpback chub, it apparently affected the potomodromous Colorado squawflsh (Tyus 1984, 1990), and possibly other native fishes. Subsequent dam operations have modified movement patterns, frequency of movement, and distance moved by humpback chub. These effects do not seem to be energetically detrimental to adults, but the combination of fluctuating flows, cold temperatures, and large numbers of non-native predators are probably the major factors leading to low survival of subadults. HABITAT Sub adult humpback chub (<200 mm TL) used primarily shallow sheltered shorelines, while adults (~200 mm TL) used primarily large recirculating eddies, The transition from shoreline to offshore habitat use began when the fish were about 1 year old and 100 mm TL, and was largely completed by the time the fish were 3 years old and about 200 mm TL which is about the size of maturity (Fig. 9). , Significantly higher densities of sub adults were captured with electrofishing along vegetated banks, talus, and debris fans of the six shoreline types compared. Selected shorelines had a greater degree of cover with more consistent low-velocity interstitial spaces than sand, bedrock, and cobble bars, and provided more stable habitat over the range of flows observed (i.e., 5,000-20,000 cfs). While shoreline velocities were within the range for YOY (0-0.30 mlsec) andjuveniles (0-0.79 mlsec) found by Valdez et al (1990) in Blackrocks in 16- 200C water, the fish in Grand Canyon were constantly exposed to cold temperatures of 8-12 oC and their swimming efficiency was likely reduced.