<br />392 The Southwestern Naturalist vol. 26, Ito,
<br />sion of the ranges of introduced species in the Southwest. Competition
<br />between native and introduced species also may contribute to a decline in
<br />population of native fishes (Hubbs, 1955). We feel that each of these factors
<br />may be operative in the lower White River. The introduced red shiner in
<br />particular has increased in abundance in the last 10 years. Red shiners made
<br />up less than 1.0%a of the population in 1971 (Holden and Stalnaker, 1975),
<br />51.8% in 1974 (Crosby, 1975), and 62.5%a in 1979. Red shiners probably out-
<br />compete juvenile native fishes in marginal habitats (Holden, 1980; McNatt
<br />et al., 1980; Minckley and Carufel, 1967; Minckley and Deacon, 1968).
<br />Our collection of Colorado squawfish is the first documented in the Utah
<br />portion of the White River. Squawfish have been found at the confluence of
<br />the Green and White rivers, and several were observed or collected in the
<br />upper White River in Colorado in the late 1960's (Everhart and May, 1973;
<br />May, 1970). Carlson et al. (1979) reported two Squawfish in the Colorado
<br />portion of the White River 84 km upstream from the Utah border during
<br />1977, a year of extreme drought.
<br />In our study adult squawfish were found in backwaters, eddies, and side
<br />channels with predominantly sand substrate. Water depth Varied from 0.6 to
<br />1.3 m and water velocity from 0.0 to 0.30 m; sec. These findings conform
<br />with data on electivity curves reported for squawfish by other authors
<br />(Holden, 1977; Seethaler, 1978).
<br />Young-of-the-year squawfish have been found in shallow backwaters
<br />where there is little current and a silt bottom (Holden, 1977); juveniles have
<br />been collected in the deeper sections of backwater areas (Vanicek, 1967;
<br />Holden, 1977). Although this type of habitat was extensively sampled
<br />throughout our study,'no young squawfish were found.
<br />Other endemic fishes of the White River also showed a preference for cer-
<br />tain types of habitat. Young roundtail chubs commonly were found in pools
<br />where there was some water movement, such as those below riffles, and
<br />pools formed by debris on the margins of the river. Adults, which are well
<br />adapted to swift current, were found in deeper water than were the young.
<br />Speckled dace were commonly found in water less than 1 in deep and it.
<br />riffle areas with a rubble-covered bottom. Large flannelmouth suckers cafe
<br />tured or observed during the spring (May-June) sampling were usually near`
<br />or in shallow water (0.66 m) over sandbars. Their ripe condition, indicated
<br />by tubercles on males, and our ability to express sex products from botb
<br />sexes indicated that the fish were spawning. Later in the summer the suckeh
<br />typically were found in the relatively deep water of runs or pools. Like,
<br />juveniles of other species, young flannelmouth suckers typically occu
<br />shallow, marginal waters of a river (McAda, 1979), and were readily captur
<br />in this type of habitat in the White River.
<br />The Utah Cooperative Fishery Research Unit is supported jointly by the U.S. Fish and Wildli
<br />Service, Utah Division of Wildlife Resources, and Utah State Universitv.
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