Laserfiche WebLink
235 <br />Discussion <br />Effects on the native fish component <br />Holden (1979) considered riverine fishes to include <br />obligate and facultative riverine species. He further <br />divided obligate riverine species into species re- <br />quiring rivers for all their ecological needs and <br />those requiring rivers for a portion of their life his- <br />tory. The effect of damming a river on obligate riv- <br />erine species is generally negative and is a major <br />cause in the decline of these species (Holden 1979). <br />Observations made during this study, suggest the <br />most obligate riverine species, i.e. Colorado squaw- <br />fish, speckled dace and bluehead sucker, were most <br />affected by impoundment of the White River. <br />During our study, a single wild Colorado squaw- <br />fish was captured above the dam following its clo- <br />sure. This adult specimen, captured in 1985, was the <br />last wild Colorado squawfish verified in the White <br />River above Taylor Draw Dam. Adult Colorado <br />squawfish from the White River undertake exten- <br />sive potamodromous migrations for spawning in <br />the Green and Yampa rivers (Martinez', Tyus 1990). <br />Martinez' reported the migrations of one adult Col- <br />orado squawfish captured near Rangely, Colorado, <br />in 1983. This fish, recaptured near known spawning <br />sites in the Yampa River in 1984, was subsequently <br />caught by an angler in the White River near its orig- <br />inal capture site in 1985, thus confirming at least <br />700 km of upstream and downstream movements in <br />three rivers (Martinez) . The effect on Colorado <br />squawfish, formerly resident in the river above the <br />dam prior to impoundment, becomes obvious. Fur- <br />ther, stocking there does not seem a long-term solu- <br />tion to maintaining this species in its historic range <br />above Taylor Draw Dam (Trammell 1991, Trammell <br />et al. 1993). <br />The decline in relative abundance of both speck- <br />led dace and bluehead sucker following impound- <br />ment is probably attributable to their obligate river- <br />ine life histories. Speckled dace, a more lotic adapt- <br />ed species (Minckley 1973, Woodling,' Sublette et <br />al. 1990), and bluehead sucker, largely limited to <br />relatively swift-flowing waters over cobble or grav- <br />el (Baxter & Simon 1970, McAda & Wydoski 1983, <br />Sublette et al. 1990), displayed an affinity for flow- <br />ing habitats in the White River (Chart 1987). While <br />their reduced abundance in the reservoir could be <br />attributed to their lotic preferences, reductions of <br />these species below the dam in 1989-1990 was not as <br />readily explained. <br />Chart (1987) reported speckled dace reproduc- <br />tion to be especially high below the dam in 1985. He <br />suggested that habitat preference of adult speckled <br />dace should preclude competition with the burge- <br />oning fathead minnow population, but young <br />speckled dace would likely face considerable com- <br />petition from this species. Red shiner, the most <br />abundant species below the dam in 1989-1990, may <br />be a serious competitor with native species in the <br />Colorado River Basin (Holden 1979, Nesler7). The <br />combined effects of fathead minnow and red shiner <br />(Karp & Tyus 1990) may have contributed to the re- <br />duction of speckled dace. Because speckled dace <br />are short-lived (few live beyond 3 years, Sigler & <br />Sigler 1987), mortality of their young due to compe- <br />tition and lack of recruitment may explain their de- <br />mise below the dam. <br />Chart (1987) suggested bluehead suckers in the <br />lower reaches of the White River in Colorado came <br />from reproduction by this species in and above the <br />vicinity of Kenney Reservoir. This belief was sub- <br />stantiated by Lanigan & Berry (1981) who showed <br />bluehead suckers in the White River in Utah were <br />scarce, composing less than 0.5% of all fish collect- <br />ed. During our investigation, bluehead suckers <br />were most abundant above the dam axis from 1983 <br />to 1985. Chart (1987) attributed the reduction in <br />young-of-year bluehead suckers below the dam in <br />1985 to poor drift of larvae through the reservoir. <br />He further reasoned that this loss of supplemental <br />recruits from upstream spawning areas would result <br />in the long-term decline of bluehead suckers below <br />the dam. This mechanism explained the stark re- <br />ductions of this species below the dam in 1989-1990. <br />e Woodling, J.1985. Colorado's little fish: a guide to the minnows <br />and other lesser known fishes in the state of Colorado. Colorado <br />Division of Wildlife, Denver: 77 pp. <br />Nesler, T.P 1991. Endangered fishes investigations. Job Pro- <br />gress Report. Federal Aid in Fish and Wildlife Restoration Pro- <br />ject SE-3. Colorado Division of Wildlife. Fort Collins. 69 pp.