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260 C. A. KARP AND H. M. TYUS [Volume 50
<br />ROUNDTAIL cxus.-A total of 1482 round-
<br />tailchub were captured in all reaches of DNM
<br />except Split Mountain Canyon and the upper
<br />29 km of Lodore Canyon. The fish constituted
<br />37% (n = 256) of the standardized angling and
<br />15% (n = 1016) of the standardized electro-
<br />fishing catch. Roundtail chub were at least
<br />three times more abundant in Yampa Canyon
<br />than in the DNM portion of the Green River
<br />(Tables 1, 2} and were most prevalent in the
<br />upper 44.8 km of Yampa Canyon (73% of
<br />all roundtail chub captures, n = 1085). The
<br />fish was incidental in Lodore Canyon (<1%,
<br />n = 3). Adults and juveniles were most often
<br />captured in eddies, pools, and shoreline runs,
<br />but they were also taken in riffles and lower
<br />portions of rapids.
<br />Gated both were most abundant in Split
<br />Mountain Canyon (Tables 1, 2).
<br />During September 1989, flows in Yampa
<br />Canyon were reduced to less than 2.83 m3/s,
<br />and fish habitat was limited to shallow riffles
<br />(about 15-cm depth) and deeper pools and
<br />runs (about 1-m depth}. On September 7 we
<br />collected five chubs (four roundtail and one
<br />suspected roundtail x humpback chub hy-
<br />brid) and seven channel catfish in pools and
<br />eddies (about 1 m deep) in Big Joe Rapid (km
<br />38.4). Other chubs, including a suspected
<br />humpback chub, were observed about 0.8 km
<br />upstream in a 1.1-m-deep pool created by
<br />shoreline boulders. No fish were observed or
<br />collected in the vicinity of Warm Springs
<br />Rapid (km 6.4) on September 14.
<br />Species Associations of Humpback Chub
<br />Humpback chub were captured in associa-
<br />tion with 7 native and 12 nonnative fish spe-
<br />cies (numbers of native sculpins and non-
<br />native redside shiners not recorded). Species
<br />that dominated the standardized catch in-
<br />cluded flannelmouth sucker (Catostomus
<br />latipinnis), bluehead sucker (C. discobolus),
<br />roundtail chub, common carp (Cyprinus car-
<br />pio}, and channel catfish (Ictalurus punc-
<br />tatus) (Tables 1, 2).
<br />A total of 350 fish were captured by angling
<br />in eddies occupied by humpback chub.
<br />Roundtail chub composed about 45%, chan-
<br />nel catfish 35%, and humpback chub 15%
<br />of this catch. More channel catfish were cap-
<br />tured by angling than was any other species
<br />(n = 328, 47% of angling catch), and it was the
<br />most abundant nonnative fish in eddies that
<br />also yielded humpback chub. Other species,
<br />including Colorado squawfish (Ptychocheilus
<br />Lucius), flannelmouth sucker, common carp,
<br />black bullhead (Ameiurus melas), and rain-
<br />bow trout (Oncorhynchus mykiss), composed
<br />less than 5% of the angling catch. Electrofish-
<br />ing catch was dominated by flannelmouth
<br />(n = 2049, 29%) and bluehead (n = 1801,
<br />26%) suckers, and these fishes were common
<br />in canyon habitats (Table 1) and open parks
<br />(Table 2).
<br />The most abundant introduced fishes in
<br />DNM were common carp (n = 1321) and
<br />channel catfish (n = 1153). These species
<br />were relatively common in canyon-bound
<br />whitewater reaches and lower-gradient slow-
<br />water sections. Standardized C/f data indi-
<br />Spawning of Humpback Chub
<br />and Roundtail Chub
<br />Thirty-nine humpback chub (16 ripe males,
<br />5 ripe females, and 18 tuberculate but nonripe
<br />fish) were captured in shoreline eddy habitats
<br />in a 48-km reach (km 20.8-68.8) in Yampa
<br />Canyon (n = 37) and in a 2-km reach (km
<br />545.6-547.2) in Whirlpool Canyon (n = 2).
<br />Turbidity precluded direct observation of the
<br />fish; thus, spawning behavior and microhabi-
<br />tat use were not documented.
<br />All ripe fish were silvery colored with "gold
<br />flecks" on the dorsum. Ripe males always had
<br />some orange coloration on the lower side of
<br />the head, opercles, abdomen, and paired and
<br />anal fin bases. Ripe males and females usually
<br />bore light tuberculation on portions of the
<br />head, nuchal hump, opercles, and paired fins.
<br />This tuberculation was-more robust in males.
<br />Ripe males averaged 311 mm TL (n = 16, SD
<br />= 35, range 232-370 mm) and 229 g (n = 14,
<br />SD = 67, range 130-348 g}, ripe females aver-
<br />aged 300 mm TL (n = 5, SD = 20, range
<br />280-333 mm) and 230 g (n = 4, SD = 75,
<br />range 160-336 g), and nonripe tuberculate
<br />fish averaged 303 mm TL (n = 18, SD = 35,
<br />range 232-382 mm) and 203 g (n = 17, SD =
<br />62, range 92-356 g).
<br />Ripe humpback chub were collected
<br />following highest spring discharges from
<br />mid-May to late June 1987 to 1989 (Table 3,
<br />Fig. 2). Captures of nonripe but tuberculate
<br />fish also occurred within this 5-6 week period
<br />(Table 3). Although sampling in 1986 did not
<br />include prerunoff conditions and thus was ex-
<br />cludedfrom Figure 2, four humpback chub in
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