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UCREFRP
UCREFRP Catalog Number
8234
Author
Marsh, P. C. and M. E. Douglas
Title
Predation by Introduced Fishes on Endangered Humpback Chub and Other Native Species in the Little Colorado River, Arizona
USFW Year
1997
USFW - Doc Type
Transactions of the American Fisheries Society
Copyright Material
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233 <br />N <br />W <br />performed using boat-mounted equipment at night <br />near shore along the reservoir's length. Gill nets <br />were set overnight in all major habitats (shallow <br />and deep coves, cliff and sloping areas, surface, bot- <br />tom and midlake). Seining accounted for 85-99% <br />of fishes collected (Martinez'`, Trammell 1991). Typ- <br />ically, larger fish, and all Colorado squawfish, were <br />identified and released. Large samples of small fish <br />were preserved in 10% formalin and returned to the <br />laboratory for identification and enumeration. <br />Results <br />Pre-impoundment species composition <br />Fish samples taken in 1983-1984 prior to closure of <br />Taylor Draw dam were dominated by four native <br />species; roundtail club Gila robusta, speckled dace <br />Rhinichthys osculus, bluehead sucker Catostomus <br />discobolus and flannelmouth sucker Catostomus <br />lattipinnis (Tables 1, 2). Three other native species <br />reported in pre-impoundment collections, Colora- <br />do squawfish, mountain whitefish Prosopium wil- <br />liamsoni and mottled sculpin Cottus bairdi, com- <br />prised no more than 0.5% in 1983 or 1984.OVeran, <br />native species accounted'for over 97% of the fish <br />wOeeted in 1983 (Fig. 2). In 1984, dominance by na- <br />tive species persisted, but not as overwhelmingly as <br />observed in 1983. Species composition above the <br />dam construction site in 1983 was about 88% native <br />and 12% non-native while below the dam axis <br />70.4% of the fish collected were native and 29.6% <br />were non-native. <br />Among introduced species, fathead minnows Pi- <br />mephales promelas were rarely collected in 1983, <br />but after 1984, fathead minnow numbers increased <br />dramatically in samples both above and below the <br />dam axis (Tables 1, 2). The greater proportion of <br />this species below the dam axis may have been due <br />to ponding in the vicinity of the dam construction <br />area that probably enhanced fathead minnow re- <br />production. Additionally, other non-native species <br />were collected including red shiner Cyprinella lu- <br />trensis, common carp Cyprinus carpio, black bull- <br />head Ameiurus melas and channel catfish ktalurus <br />punctatus, none exceeding 1.5%. A single, 200 mm <br />black crappie Pomoxis nigromaculatus was sam- <br />pled below the dam in 1984 (Table 1). These data <br />further substantiated preimpoundment dominance <br />by native fishes within the study area (Fig. 2). <br />Post-impoundment fish community changes <br />The White River fish community began showing in- <br />creased abundance of non-native species in 1984, <br />during construction of the dam: however, marked <br />changes occurred primarily in the reservoir in 1985, <br />the first year of impoundment. Fathead minnows <br />increased from 10.3% in the pre-impoundment res- <br />ervoir basin in 1984 to 60.2% of all fishes collected <br />in the reservoir in 1985 (Table 2). In this initial year <br />of impoundment, relative abundance of other non- <br />native species remained low. The most marked de- <br />crease among native species in the reservoir was ob- <br />served for speckled dace. Comprising about 20% to <br />30% of the fish collected throughout the study area <br />before impoundment. speckled dace accounted for <br />only 1.8% of the fish collected in the reservoir in <br />1985. <br />Subsequent fish collections made in the reservoir <br />in 1987 consisted of 61.2% non-native species (Fig. <br />2). Although fathead minnow numbers dominated <br />samples, and undoubtedly the reservoir's fish pop- <br />ulation, their relative abundance was offset by in- <br />creased collection of stocked rainbow trout Oncor- <br />hynchus mykiss (Table 2). Originally stocked as the <br />reservoir began to fill in 1984. rainbow trout have <br />been stocked annually to provide a sport fishery in <br />Kenney Reservoir. The apparent increase in rela- <br />tive abundance of roundtail club, flannelmouth <br />sucker, and common carp in 1987 seemed due to <br />their susceptibility to gill nets set in shallower <br />depths. Bluehead sucker abundance, however, was <br />much lower in the reservoir in 1987 than in 1985. <br />Numbers of speckled dace collected in 1987 contin- <br />ued to be conspicuously low. <br />Fathead minnows also dominated reservoir fish <br />collections (46,4%) in 1988 (Table 2). Black bull- <br />heads increased from 1.3% in 1985 to'17.2% (over <br />99% young-of-year) in 1988. The presence of adult- <br />sized green sunfish Lepomis cyanellus, bluegill Lep- <br />omis machrochirus. largemouth bass Micropterus
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