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1990] HUMPBACK CHUB IN DINOSAUR NATIONAL MONUMENT 259 hand-held thermometers (methods after Nielsen and Johnson 1983). We did not at- tempt quantification of water velocities be- cause most humpback chub were captured in habitats where water currents swirled in both upstream and downstream directions and ini- tial efforts with a flow meter yielded a wide range of positive (upstream) and negative (downstream) velocities. Habitat use data was not recorded for species other than humpback chub. River flows were obtained as daily aver- agesfrom the U. S. Geological Survey gauging station at Deerlodge Park, Yampa River (Fig. 1). Stream gradient was obtained from U. S. Geological Survey stream profile maps. Data Analyses Capture data were analyzed by total catch (all years, all gear types, and sampling) and standardized catch (1987-1989: catch of all species and effort recorded for each sample). Total catch data were used to describe general fish distribution, and standardized data were used to evaluate relative abundance. Stan- dardized catch data were summed by gear (i.e., angling or electrofishing) and for each river reach (i. e. , Yampa, Lodore, Whirlpool, and Split Mountain canyons, Echo and Island parks), and catch per unit effort (C/f) was cal- culated by dividing numbers of fish captured by effort. Angling and electrofishing datafrom 1986 were not included in C/f estimates be- cause numbers of fishes other than chubs were not recorded and because of significant differences in angler ability. Trammel netting C/f was not reported because of limited use. Electrofishing was biased toward catch of larger individuals, and small fishes (e. g. , non- native reside shiner [Richardsonius baltea- tus ]and native mottled sculpin [Cottus spp. ]) and juveniles of larger species were not recorded because they often slipped through our 1-in2 mesh dip-nets. Angling efforts in September 1989 were excluded from the C/f estimates because this effort represented a unique fall sample. Sampling was initiated late in 1986, and those data were excluded from our evaluation of spawning period. RESULTS Distribution and Habitat Use HvMrsncx exus.-Humpback chub were collected only in whitewater reaches of Yampa (n = 130) and Whirlpool (n = 3) canyons (Fig. 1). The Whirlpool Canyon fish were captured in the same location, about 6 km downstream of the confluence with the Yampa River. No other humpback chub were captured in the Green River. Humpback chub constituted 7.3% (n = 51) of the standardized angling and <1% (n = 58) of the standardized electrofish- ing catch. They were most abundant (85% of all humpback chub captures, n = 113) in the upper 44.8 km of Yampa Canyon, a moder- ately steep-gradient section (3.2 m/km) domi- nated byrocky runs, riffles, and rapids. Lower Yampa Canyon (km 0-28.8), alower-gradient system (1.0 m/km) consisting mostly of long, deep runs and incised meanders, yielded rela- tively few humpback chub (n = 17). During spring runoff, humpback chub were most often captured in larger shoreline eddies (20-100 m2) that were either downstream of boulders or upstream of rapids, or in smaller eddies (<20 m2) within shoreline runs. Adult fish (>230 mm TL; based on capture of the smallest ripe fish, a232-mm-TL male) were consistently captured in, and apparently se- lected, seasonally flooded shoreline eddies (i. e. , formed and maintained by spring runof fl. These habitats were dominated by low or negative water velocities and influ- enced by river surges (i. e. , water velocities at any particular point varied in magnitude of up-and downstream currents). Substrate con- sisted mostly of sand and boulders, and water depth averaged 1.3 m at the estimated point of capture. Humpback chub were not collected in riffles and rapids. Eleven of 76Carlin-tagged humpback chub (z = 312 mm TL, SD = 19) were recaptured one week to two years after initial capture (5 within a year, 6 from one to two years). Ten fish were recaptured in the immediate vicin- ity of their original capture, and one was col- lected about 8 km downstream from its initial capture site. Eight fish (73%, n = ll) were recaptured in breeding condition on at least one occasion. We detected no growth in re- captured fish. About 22% (n = 29) of humpback chub were juveniles (88-228 mm TL). These were most often captured by electrofishing in rocky shoreline runs and small shoreline eddies. One juvenile (122 mm TL) was taken from the stomach of a 61-cm-TL garter snake (Thamnophis species) caught at the conflu- ence of the Yampa and Green rivers.