|
<br />
<br />{U.... \A.Sd--tta:\ he.c
<br />~ \J \q~ 1/
<br />
<br />j A. A. Echel/e. 1981. F:'~
<br />inS offishes in Little R' actOr anal
<br />. Iver C
<br />lfiterdrainage com 0' entral Te
<br />. panson A
<br />Iturahst 106:379-391. . meri
<br />1985. SAS user's od .,
<br />. gUl e' sta' .
<br />YSIS System Institute C' lISlics. S
<br />, ary, North
<br />
<br />1982. Fish community st
<br />ng two habitat o"ad' . ructure an
<br />. ...' lents m a h
<br />ogIcal Monographs 52'395-4 eadwa
<br />98~. The role ofpred~tion inI4.,
<br />tabttat use by stream fish age- and
<br />es. Ecology 68:
<br />
<br />~. F. Carline, and R A .:
<br />:tlOn by smal/mouth'b . S~em. 1986:
<br />'ha t . ass m respo 0
<br />. rac enstics of' nsc
<br />fa simulated
<br />o the American F h 0 stream.:
<br />IS enes Society 115:
<br />'79 F '
<br />. Ishes of Illinois U' .
<br />o Urbana. . mverS1ly of
<br />
<br />oK. L. Dickson J Ca'
<br />n ,. Ims Jr
<br />6. The potential and re~Ii;' :nd D.
<br />erature on the disl ob' e mflu-
<br />G n utlon offi h .
<br />r, len Lyn, Virginia. Wildll'" MS es In
<br />Ie ono-
<br />
<br />1981. The fishes of Ohio 0
<br />State University P , reVised
<br />1985a A ress, Columbus.
<br />. n ecolOgIcal 0 .
<br />rver and Bluesto Lak mvestIgation
<br />ne e. USA
<br />leers, Huntington District F" I nny
<br />on, West Virginia. ,ma Re-
<br />1985b. Trophic bas'
<br />rtebrates in the Ne: of ~roduction
<br />t West V' . . River below
<br />. Irgmla De
<br />, Final Re partment ofNat-
<br />port, Charleston, West Vir-
<br />
<br />o. Novotny K E J
<br />Effi ". acobs, and W D
<br />eets of reservoir rei . .
<br />nvertebrates d fi e~ses?n water
<br />Its. U.S. A~ an .sh m tatlwaters:
<br />ation, Tech:i;~gI~eer Waterways
<br />;issippi. eport E-83-6,
<br />
<br />F. Novotny K E
<br />, . . Jacobs W D
<br />~mpbel/: J. Nestler, and G. 'E 5 I'
<br />reservOir releases on' . au.
<br />review. U S Ann talh~ater eeol-
<br />ment Stat: . y EngIneer Wa-
<br />Ion Tech . I
<br />urg M' . . '. mca Report
<br />, ISSISSIPpl
<br />fiabitat use and'feed' . .
<br />octoral d' mg actIvity of
<br />Issertatio U' .
<br />\rbor. n. mverslty of
<br />
<br />Received AuguSII, 1988
<br />Accepted June 18, 1990
<br />
<br />frtJnJQClions of the American Fisheries Soder.v 120:19-89, 1991
<br />
<br />~
<br />0'7360
<br />
<br />Distribution, Habitat Use, and Growth of Age-O
<br />Colorado Squawfish in the Green River Basin, Colorado and Utah
<br />
<br />HAROLD M. Tvus AND G. BRUCE HAINES
<br />
<br />U.S. Fish and Wildlife Service
<br />1680 West Highway 40. Suite 1210, Vernal, Utah 84078. USA
<br />
<br />Abstract. -Age-O Colorado SQuawfish Plychocheilus lucius (N = 11,379) were captured as larvae
<br />and postlarvae in drift nets and seines in the Green and Yampa rivers from 1979 to 1988. Larvae
<br />were captured in drift nets (N = 601) for 2-6 weeks in June and July. Small postlarvae (N = 3,079)
<br />were captured by seining shoreline habitats in July and August. In September and October, postlar-
<br />vae were most abundant (N = 6,459) in low-gradient reaches of the Green River. Catch data
<br />indicated that the postlarvae moved from the Yampa and Green river spawning areas and were
<br />concentrated about 150 km downstream by autumn of each year. Spring sampling indicated that
<br />young fish (N = 1,240) overwintered in areas occupied the previous autumn. Postlarvae captured
<br />in the Green River (N = 5,043) most frequently occupied shoreline embayments (backwaters) that
<br />were relatively warm (mean, 17.00C), deep (mean, 38 cm), large (mean, 826 m'), and turbid.
<br />Abundance and size of young Colorado SQuawfish in the Green River were inversely correlated
<br />with high summer and autumn flows, which inundated nursery habitats. Seine catches of young
<br />squawfish in 4 years of sampling the upper and lower Green River in autumn and the following
<br />spring were not reliable in assessing overwintering mortality of age-O Colorado squawfish, presum-
<br />ably due to differences in capture vulnerability between seasons. survival of small fish in spring
<br />indicated their tolerance of prevailing winter conditions.
<br />
<br />Colorado squawfish Plychocheilus lucius. the
<br />largest North American minnow, is endemic to
<br />the Colorado River basin, where it was once abun-
<br />dant and widely distributed (Jordan and Ever-
<br />mann 1896). The species was classified as feder-
<br />al1y endangered by the U.S. Fish and Wildlife
<br />Service in 1967 (Federal Register 32[43]:400 I) and
<br />natural populations presently exist only in the up-
<br />per Colorado River basin (upstream of Lee Ferry,
<br />Arizona). The Green River in Utah and its largest
<br />tributary, and Yampa River in Colorado (Figure
<br />I), contain the largest known concentration of
<br />Colorado squawfish (Holden and Wick 1982; Tyus,
<br />in press).
<br />Two major spawning areas have been identified
<br />in the Green River basin by radiotracking the mi-
<br />grations of Colorado squawfish and capturing ripe
<br />adults. One spawning area in the lower Yampa
<br />River (i.e., Yampa Canyon) was located in 1981
<br />(Tyus and McAda 1984); a second spawning area
<br />in Gray Canyon of the Green River was located
<br />in 1983 (Tyus 1985). Successful Colorado squaw-
<br />fish reproduction was confirmed at the Yampa
<br />Canyon site by col1ections of newly hatched larvae
<br />(Haynes et al. 1984; Nesler et al. 1988). However,
<br />the early life history and ecology of larval and
<br />postlarval Colorado squawfish are not well known.
<br />Events during the first year of life regulate many
<br />fish populations (Braum 1978), and a better un-
<br />derstanding of such events should aid present re-
<br />
<br />covery efforts (Rose and Hamil1 1988) for this
<br />species.
<br />Construction and operation of Raming Gorge
<br />Dam and Reservoir has significantly altered his-
<br />toric flow and temperature regimes in the Green
<br />River and this alteration has been implicated in
<br />the decline of Colorado squawfish (Seethaler 1978;
<br />Holden and Wick 1982). We studied distribution,
<br />relative abundance, and growth of age-O, Colorado
<br />squawfish in order to evaluate effects of present
<br />summer and early autumn flow regimes on the
<br />fish. We also sampled standing crops of young
<br />Colorado squawfish in autumn and spring to eval-
<br />uate the effects of winter conditions on survival
<br />and growth. Final1y, we evaluated summer con-
<br />ditions and the sizes (total length) of age-O Colo-
<br />rado squawfish in the upper and lower Green Riv-
<br />er with the hypothesis that colder water
<br />temperatures and fluctuating flows produced by
<br />Raming Gorge Dam should reduce growth of the
<br />fish in the upper Green River.
<br />
<br />Study Area
<br />
<br />The Green River basin is in eastern Utah
<br />northwestern Colorado and southern Wyomin{
<br />(Figure I). The primary study area included the
<br />lower 552 km of the main stem Green River
<br />downstream of its confluence with the Vamp;
<br />River, and the lower 30 km of the Yampa Rive
<br />during 1979-1988. However, sampling was als
<br />
<br />79
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