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Life History <br />Virgin River chub are most often associated with deep runs or pool habitats of slow to <br />moderate velocities, with some type of cover such as Large boulders, logs, overhanging <br />vegetation, or undercut banks (Cross 1978). Adults and juveniles are often associated <br />together within these habitats, however, the larger adults are most often collected in the <br />deeper pool habitats within the river. Hardy et al. (1989) indicated that Virgin River chub <br />less than 80 mm TL (3.2 in) are generally captured in depths greater than 0.18 m (0.6 ft) in <br />velocities between 0.08 to 0.15 m/s (0.25 to 1.6 ftlsec) over sand substrates in association <br />with large boulders or instream cover. Virgin River chub between 80 mm (3.2 in) and 140 <br />mm (5.5 in) TL are generally captured in depths greater than 0.30 m (1.0 ft) in velocities up <br />to 0.76 m/sec (2.5 ft/s) over sand substrates with boulders or instream cover. Virgin River <br />chub greater than 140 mm (5.5 in) TL are most often collected in depths greater than 0.61 to <br />0.91 m (2.0 to 3.0 ft) in velocities from 0 to 0.55 m/s (0 to 1.8 ft/s) with similar substrates <br />as the other size classes noted above. Schumann (1978) and Deacon et al. (1987) found that <br />the final adult thermal preferendum was approximately 24°C (75°F) and suggested the <br />species was more stenothermal than woundfin. <br />Limited information is available on habitat requirements of Virgin River chub in the Muddy <br />River. Cross (1976) stated that no specific habitat preferences were apparent, but that the <br />chub probably avoided shallow riffles similar to chub in the Virgin River. Adult chub <br />habitat in the Muddy River is likely deep runs and pools (Jun Heinrich, NDOW, pers. <br />comm. 1994). Historical habitat occupied by the chub is the middle Muddy River was <br />characterized by a firm clay bed with scattered rock riffles, high turbidity, no aquatic <br />vegetation, and temperatures and flaws generally decreasing downstream (Deacon and <br />Bradley 1972). The upper river and tributary springs systems are characterized by nearly <br />constant high temperatures (29-32°C, 85-90°F), low tuubidity, and relatively dense aquatic <br />vegetation. Substrates in these headwater habitats are primarily sand, gravel, and cobble <br />(USFWS 1983). <br />Virgin River chub are omnivorous, showing considerable dietary shifts with age. In general, <br />Virgin River chub feed on debris and chironomids in February; Cladophora and debris in <br />June; debris, Spyrogyra, and Cladophora in September; and unidentified drift animals, <br />dragonfly larvae, debris and Cladophora in December. Young fish [ < 70 mm (2.8 in) TL] <br />feed almost entirely on macroinvertebrates, while adults [ > 110 mm (4.3 in) TL] feed <br />almost exclusively on algae and debris (Greger and Deacon 1988). Cross (1975) reported <br />that up to 90 percent of the diet consisted of filamentous algae. <br />The reproductive biology of the Virgin River chub in the Muddy River has not been studied <br />and very little is known about the reproductive biology of the Virgin River population. <br />Hickman (1987b) reported ripe females and males in April, May, and June, but the time of <br />spawning has not been determined. He noted that good spawning years for Virgin River <br />chub coincided with good spawning years for woundfin. Virgin River chub are known to <br />successfully spawn in both ponds and the mainstem Virgin River (Utah Division of Wildlife <br />21 <br />