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Last modified
1/26/2010 3:15:34 PM
Creation date
10/12/2006 4:39:09 AM
Metadata
Fields
Template:
Water Supply Protection
File Number
8220.101.09
Description
Glen Canyon Dam/Lake Powell
State
AZ
Basin
Colorado Mainstem
Date
12/21/1994
Author
USDOI-USFWS
Title
Final Biological Opinion-Operation of the GlenCanyon Dam as the Modified Low Fluctuation Flow Alternative of the Final Environmental Impact Statement-Operation of Glen Canyon Dam
Water Supply Pro - Doc Type
Biological Opinion
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<br />The number of trout attempting to ascend and spawn is a function of the number of spawning <br />trout in the river and conditions in Nankoweap Creek. More than 500 trout were recorded at <br />NankoweapCreek during 1990, with the spawning run peaking at 1,500 fish. Some 70-100 bald <br />eagles may have moved through the Grand Canyon in February and March of 1990. (Brown and ,.' <br />Leibfried 1990; National Park Service 1992). Bald eagles took trout stranded by fluctuating <br />discharges in isolated pools along .the river near the creek mouth', but,most of the Jeeding activity <br />was in Nankoweap Creek (Brown and Leibfried 1990; National Park Service 1992). The bald <br />eagle concentration at Nankoweap Creek was down in 1991 along with the number of spawning <br />trout. In 1991, low discharges in Nankoweap Creek, low water temperature, and ice may have <br />limited the number of trout attempting to ascend and. spawn in the creek (National Park Service <br />1992). Observations from 1992 to 1994 have found further decreases in troutin Nankoweap <br />Creek during the winter and correspondingly lower numbers of bald eagles (Mark Sogge, <br />National Park Service, written communication). <br /> <br />Daily operations of Glen Canyon Dam influence the migration patterns of spawning trout and <br />availability of this food resource to bald eagles. For example, during a recent survey there was <br />a physical barrier at the mouth of Nankoweap Creek that prevented trout from ascending the <br />creek when river discharge was below approximately 4,000 cfs (Bill Leibfried, per~nal <br />communication). At discharges between 4,000 and 15,000 cfs, the creek mouth and the lower <br />30 m of the creek were used most frequently by foraging eagles. At these discharges, trout were <br />distributed over a shallow gravel area and vulnerable to foraging bald eagles. When discharges <br />ranged from approximately 15,000 to 20,000 cfs, these areas were deeply inundated and bald <br />eagles foraged further up Nankoweap Creek. <br /> <br />Operations which enhance the trout fishery or native fish populations should benefit bald eagles. <br />The Service believes it is unlikely that the bald eagle would be adversely affect by the proposed <br />action, and the species will not be considered further in this consultation. <br /> <br />PEREGRINE FALCON <br /> <br />The peregrine falcon is a medium-sized raptor which occurs across much of North America and <br />its various subspecies distributed worldwide. It tends to nest on cliffs near sources of avian prey <br />and has traditionally been associated with cliffs near large bodies of water such as seacoasts, <br />lakes, and large rivers (Ratcliffe 1980). However, the arid southwestern United States has <br />recently been demonstrated to not only support breeding peregrine falcons but to support the <br />largest known concentration in North America, excluding Alaska. Recent studies have <br />documented high densities of breeding pairs in the Southwest, particularly the Colorado Plateau <br />(Burnham and Enderson 1987; Hays and Tibbitts 1989; Tibbitts and Bibles 1990; Tibbitts and <br />Ward 1990a, 1990b; Enderson et al. 1991; Brown 1991). Ellis (1982) reported .on habitat <br />preferences of peregrine falcons in Arizona.and identified a profile. for eyrie locations: elevation <br />less than 2,700 m, extensive tailor very tall cliffs, high topographic relief, and having surface <br />water available. In the Southwest, breeding peregrine falcons .are currently found almost <br />anywhere large cliffs (> 100 m) are available, with the exception of the hottest and-driest desert <br />regions (Tibbitls and Ward 1990a). <br /> <br />15 December 1994 final biological opinion 2-21-93-F-167 <br /> <br />16 <br />
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