|
<br /> Colorado Pikeminnow Distribution 461
<br /> Distance, in Miles, Upstream from Colorado River
<br /> 240 260 280 300 320 340
<br /> 3000 1750
<br /> <- ><- >
<br /> Uinta Basin Uinta
<br /> Mountains
<br /> 2500 -< >-< >-< >-< >- +< >- 1700
<br /> F R F R F E F E Qj
<br />~ >
<br /> (])
<br />(]) 1650 ...J
<br />a; , ' <tl
<br />:2 2000 , (])
<br /> en
<br />.s: , "
<br /> J H: G F / ~ E D C B A (])
<br /> >
<br />.r:.' . . 1600 0
<br />"5 . . ..c
<br /> , . <tl
<br />~ ' .
<br />1500 . ' . ul
<br /> . . . Q)
<br />>. . . ,
<br />~ . Valley widlh . . Longitudinal a;
<br /> . ! 1550
<br />ca / prolile :2
<br />> . !
<br /> . .
<br />(]) . , , .5:
<br />Ol 1000 . C
<br />~ , .
<br />(]) . . , 1500 .Q
<br />> , 1ti
<br /> !
<br /><( . ! >
<br /> -. , (])
<br /> ! [jJ
<br /> , . .
<br /> 500 - ,
<br /> . 1450
<br /> ......... -.. , \.....
<br /> , ,
<br /> , ,
<br /> ....-..
<br /> ---.,
<br /> 0 1400
<br /> 400 440 480 520
<br /> Distance, in Kilometers, Upstream from Colorado River
<br />
<br />Figure 2. Graph showing the longitudinal profile and width of the alluvial valley of the Green River in the study area. The second row of
<br />arrows indicates the extent of each type of channel-valley reach classification, as described in the text. R is restricted meandering reaches, F
<br />refers to fixed meandering reaches, and E is reaches that are dominated by eddies in debris fan-dominated canyons. The third row of arrows
<br />indicates the extent of the study reaches.
<br />
<br />inflate, and they begin exogenous feeding. The onset
<br />of the physiological changes that increase swimming
<br />ability are related to water temperature (Childs and
<br />Clarkson 1996). As larvae grow, they may swim into or
<br />out of backwaters (Paulin, Williams, and Tyus 1989;
<br />Bestgen, Muth, and Trammell 1998). However, the rate
<br />of movement of larvae into and out of backwaters
<br />must be due to hydraulic factors in the first weeks of
<br />life because larval pike minnow lack swimming ability at
<br />that time.
<br />Fall populations of age-O fish in backwaters are a very
<br />small proportion of the total estimated larvae that drifted
<br />into the study area in early summer. Population estimates
<br />developed by McAda (1993) for the number of age-O fish
<br />in Uinta Basin backwaters in September 1990 and 1991
<br />were less than 1 percent of the total number of larval fish
<br />estimated to have entered the study area.
<br />Bestgen et al. (1997) presented a conceptual life-
<br />history model that included many biotic and abiotic
<br />factors that control recruitment, but the specific effects
<br />of these factors are not known. Thus, little is known
<br />about the relative proportion of the initial larval pop-
<br />ulation that dies during drift, drifts beyond the study
<br />area, or dies in backwaters after the initial drift pulse.
<br />
<br />Bestgen et al. (1997) considered the relevant biological
<br />factors that influence mortality during drift to include
<br />predation, starvation, and habitat selection, and the
<br />relevant abiotic factors to include the duration and
<br />magnitude of floods and turbidity. Water temperature
<br />and variability are also important because larvae drift-
<br />ing into the Green River may experience "cold shock" if
<br />significant quantities of cold water are released from
<br />Flaming Gorge Dam. Such shock can cause physiolog-
<br />ical and behavioral changes that reduce survival (Muth
<br />et al. 2000). Mortality rates of age-O pike minnow in
<br />backwaters also are not well documented but are likely
<br />due to multiple factors, including predation, backwater
<br />quality and quantity, food availability, and water tem-
<br />peratures (Muth et al. 2000). Predation by non-native
<br />fishes, especially red shiners (Cyprinella lutrensis), may
<br />be significant (Bestgen et al. 1997).
<br />
<br />The Geomorphology of Backwaters
<br />
<br />Backwaters develop as the annual flood recedes
<br />(Figure 3). In alluvial reaches, backwaters occur in in-
<br />undated, but inactive, chute channels on the upper
<br />
|