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II River. Most y-o-y and subadult humpback chub were collected from <br />reaches 30 and 50, where most backwaters occur. <br />Adult rainbow trout habitat use differed between reaches <br />above and below the Little Colorado River, perhaps due to <br />increased turbidity below the LCR. Rainbow trout fry selected <br />habitats with low or no current. Brown trout were caught in <br />areas without vegetation. <br />Carp preferred habitats with slower water velocity. Fathead <br />minnow density was highest along runs with vegetation. <br />Vegetation served to diminish current velocity and probably <br />provided substrate for food resources. Fluctuating flows may <br />affect population size, depending on the effect of creating <br />warmwater, isolated and connected, backwaters for reproduction, <br />and then flushing fish hatched in these environments back into <br />the mainchannel. <br />The higher velocity runs and sidechannels and rubble <br />substrate selected by bluehead sucker are probably feeding <br />areas. When water levels drop, these shallow areas are probably <br />exposed. Larval bluehead sucker were generally in shallow <br />backwaters and may also be affected by changing water levels. <br />Backwaters, where flannelmouth sucker catch was greatest, <br />may be feeding, resting and spawning habitats for this species. <br />If water level fluctuates in late spring or early summer, <br />j survival and eventual recruitment of this species could be <br />limited. Speckled dace were collected from a variety of habitats <br />but seemed to be concentrated in backwaters and sidechannels <br />where waters were warmer than the mainchannel. <br />Adult and subadult humpback chub were generally collected <br />along cliffs and boulders in the mainchannel. Vegetation did not <br />appear to be important. Y-o-y chubs were captured in sandy runs <br />and backwaters. Although larvae of other native fishes were <br />collected from mainchannel sites, no humpback chub larvae were <br />found outside the LCR, and mainchannel water temperatures are <br />probably lethal to larvae of this species. Mainchannel abundance <br />may be dependent upon the carrying capacity and success of <br />reproduction within the LCR. <br />Colorado River backwaters are important nursery and rearing <br />areas for both native and introduced fishes (Valdez et al. <br />1986). Backwaters in our study area appear to be very important <br />I I <br />.I <br />i! <br />?l -4-