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22 <br />Minckley 1973). Spawning of bonytail has never been observed in a <br />river, but ripe fish were collected in Dinosaur Nation~sl Monument <br />during late June and early July suggesting that spawni~ig occurred at <br />water temperatures of about 18° C (Vanicek and Kramer 1.969). <br />The number of bonytail in the Upper Colorado River are so low that it <br />is not possible to do a population estimate. <br />Analysis of Snecies/ i i.al Hahi a .i Ply Yo bP AffP +t p~7 <br />Black Rocks and Cataract Canyon are the only areas whe:ce bonytail have <br />been found in the Upper Colorado River in the last 20 dears. So few <br />fish have been captured that it is difficult to determine species and <br />habitat needs. <br />IMPORTANCE OF THE 15-MILE REACH <br />The 15-mile reach is affected more than any of the oth~~r reaches by <br />water depletions because it is located downstream of several large <br />diversions and upstream of the Gunnison River confluence. Colorado <br />pikeminnow and razorback sucker occur in the 15-mile reach, humpback <br />chub and bonytail currently do not. The 15-mile reach is a <br />particularly important section of river for Colorado pikeminnow and <br />razorback sucker; it is critical to the recovery of each species' <br />Colorado River populations (Osmundson 1996). The following section <br />summarizes the attributes of this reach and puts in context its <br />importance in relation to the rest of the river. <br />Colorado pikeminnow require a variety of specific habitat types to <br />fulfill their life history needs. Some of these required habitats are <br />found only in certain areas of the river and are separ•sted from other <br />required habitats by long distances. The 15-mile reach provides <br />important spawning habitat; spawning by Colorado pikeminnow was <br />documented within the 15-mile reach in 1962 and in 1995 by the capture <br />of pikeminnow larvae. The cleaner cobble bars found i:n upstream <br />reaches, such as the 15-mile reach, provide the most suitable sites <br />for spawning. Larvae hatched from eggs deposited in these upstream <br />reaches drift downstream with the current. In downstream reaches, <br />primarily below Moab, Utah, deposits of silt and sand :provide many <br />warm backwater sites where young Colorado pikeminnow feed upon the <br />abundant zooplarilcton and chironomid larvae. When they become <br />piscivorous, young Colorado pikeminnow feed upon the abundant small <br />fishes found in these areas. <br />Osmundson et al. (1998) documented the upstream dispersal of subadult <br />and adult Colorado pikeminnow. As the young fish in the downstream <br />nursery areas grow and approach adulthood, they require larger forage <br />fish to maintain growth rates. However, larger forage fish are scarce <br />