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<br />lower Green River (km 0-211) were extremely rare; their numbers were too small <br />(13 fish captured, 1 recaptured) to allow a reliable population estimate. Gray <br />and Desolation canyons separated the upper and lower Green River razorback <br />sucker populations. These canyons and a low diversion dam appeared to be <br />barriers to fish movement. The absence of the razorback sucker in Gray and <br />lower Desolation canyons (km 211-282) suggested a lack of suitable habitat. <br />The Green River supports the largest known population of razorback suckers <br />among the species' native riverine habitats. However, low population density <br />and recruitment, as well as habitat alteration, mandate increased research and <br />management efforts to save this population. (Abstract) <br /> <br />Report B- Spawning and movements of razorback sucker, Xvrauchen texanus, in <br />the Green River Basin of Colorado and Utah. (Tyus and Karp 1990) <br /> <br />Spawning and movements of the razorback sucker, Xvrauchen texanus, were <br />evaluated by radiotelemetry (n=17 fish) and capture of 230 adults (IDS <br />recaptures) in the Green and Yampa rivers, 1987-19B9. Ripe fish (n=194) were <br />captured in riffles with cobble, gravel, and sand substrates from mid-April to <br />early June. Recaptured males were ripe from 2 to 28 days and recaptured <br />females from 2 to 15 days. Razorback suckers spawned during ascendinq and <br />highest spring flows at water temperatures of about 140C (range 9-17DC). <br />Spawning migrations of 30-106 km were detected in 17 razorback suckers, but <br />movements were more limited or undetected in other individuals. Flooded <br />lowlands and lower portions of tributary streams presumably served as resting- <br />feeding areas for razorback suckers during the breeding season. Native <br />f1annelmouth sucker, Catostomous 1atioinnis, bluehead sucker, ~ discobolus, <br />and putative flannelmouth X razorback sucker hybrids in breeding condition <br />were collected with.ripe razorback suckers. Razorback sucker is in peril due <br />to a paucity of spawning adults, hybridization with other suckers, little or <br />no recruitment, and habitat loss. (Abstract) <br /> <br />Report 9- Humpback chub (Gila ~) in the Yampa and Green Rivers, Dinosaur <br />National Monument, with observations on roundtail chub (~. robusta) <br />and other sympatric fishes. (Karp and Tyus 1990a) <br /> <br />We evaluated distribution, habitat use, spawning, and species <br />associations of the endangered humpback chub (Gila cvohal in the Yampa and <br />Green rivers, Dinosaur National Monument, from 1986 to 19B9. Adult and <br />juvenile humpback chub were captured in high-gradient reaches of Yampa and <br />Whirlpool canyons where they were rare (H=133, < 1% of all fish captured). The <br />fish were primarily captured in eddy habitats in association with 7 native and <br />12 nonnative fish species. Roundtai1 chub (~. robusta) were widely distributed <br />in eddies, pools, runs, and riffles. Humpback chub (N=39) and roundtai1 chub <br />{N=242} in reproductive condition were sympatric in eddy habitats during the <br />5-6 week period following highest spring runoff. River temperatures at this <br />time averaged about 200C. Nonnative channel catfish (Ictalurus Dunctatus) were <br />abundant in eddies yielding humpback and roundtail chubs, suggesting a <br />potential for negative interactions between the native and introduced fishes. <br />(Abstract) <br /> <br />Report 10- Age determination in Colorado squawfish and razorback sucker. <br />(Minckley et al., in prep.) <br /> <br />11 <br />