7726

• UCREFRP Catalog Number: 7726
• Author: Stanford, J. A. and J. V. Ward.
• Title: Fish of the Colorado System.
• USFW Year: 1986.
• USFW - Doc Type: 385-403
• Copyright Material: YES

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Table 2, (continued)

FAMILY
species

Common name

Distribution

Habitat

PERCICHTHYIDAE
Morone chrywps
(Rafinesque)

Morone mississippiensis
lordan & Eigenmann

Morone saxatilis
(Walbaum)

CENTRARCHIDAE
Lepomis cyanellus
Ralinesque

Lepomis gulosus
(Cuvier)

Lepomis macrochirus
(Rafinesque)

Lepomis microlophus
(Giinther)

Micropterus dolomieui
Lacepede

Micropterus salmoides
(Lacepede)

Pomoxis annularis
Rafinesque

Pomoxis nigromaculatus
(Lesueur)

PERCIDAE
Etheostoma exile
(Girard)

Etheostoma nigrum
Rafinesque

Perea flavescens
(Mitchell)

Stizostedion vitreum
(Mitchell)

CICHLIDAE
Cichlasoma nigrofasdatum
(Giinther)

Cichlasoma severum
(Heckel)

Oreochromis mossambicus
(Peters)

Tilapia zilli
(Gervais)

396

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and the species is gone from the Verde River (Mello & Turner 1980), The sta tus
of Arizona trout (S. apache) also is of concern, and nearly all the endemic
desert-stream fish are in severe decline (Miller & Lowe 1977). The only viable
population of the desert pupfish, once the most common fish in the Southwest,
may be an undescribed subspecies isolated in Quitobaquito Spring in Organ
Pipe Cactus National Monument, Arizona (Kynard & Garrett 1976; Deacon
et al. 1979). Except for the speckled dace, the big-river fish have been extirpated
from the lower mainstream (Minck ley 1979), and humpback chub, speckled
dace, bluehead, flannelmouth and perhaps razorback suckers are the only
endemics extant in the Grand Canyon (Carothers & Minckley 1981; Carothers
& Johnson 1983). Razorback suckers are established and common in Lake
Mohave; bony tail chub are also present, but apparently not reproducing (Dr L.
Paulson, Univ. Nevada at Las Vegas, pers, commun.). Dams in the Upper Basin
have eliminated or adversely affected the native fish for long distances down-
stream (cf. Vanicek et al. 1970; Holden 1979; Stanford & Ward 1984). Only a
few isolated canyon habitats (e.g. Yampa River Canyon: Vanicek et aI, 1970) or
unregulated tributaries (e.g. White River: Lanigan & Berry 1981) contain an
assemblage of native fish like the pristine river fauna (Table 1), All the native
big-river fish, except speckled dace and flannelmouth sucker, face extinction
(Tyus et at, 1982).
The major causes of the decline relate to loss of riverine habitat and inter-
actions with exotic species. More than one-quarter of the river has been con-
verted to lentic habitats by impoundment (Bishop & Porcella 1980). Fish
adapted for the turbid habitats of the main river have not survived in reservoirs,
with the possible exception of razorback suckers (Kimsey 1957; Minckley 1979;
Holden & Wick 1982). Regulated flows have armoured the river bottom in
tailwaters, and most of the crucial backwaters and marshes no longer receive
water. The thermal regime and trophic structure of remaining river segments
have been changed by releases from reservoirs. Diversions and pumping of
groundwaters have dried out many desert streams (e.g. lower Gila River: cf.
Holden 1979) and springs (Naiman 1981). However, Minckley (I 979) points out
that even these abrupt changes are no more severe, and perhaps are less general,
than climatic changes which have occurred in the recent history of the basin:
since the Pliocene, most of the native fauna has endured successive pluvial
episodes followed by desertification. But at no time were the native fish confronted
with numerous introductions of highly competitive, exotic species, some carry-
ing alien diseases (cf. Holden 1979; Holden & Wick 1982; Deacon 1979; Carothers
& Minck1ey 1981). Presently more than 50 exotic fish, led by carp {Cyprinus
carpio), threadfin shad (Dorosoma petenense), rainbow trout (Salmo gairdneri)
and largemouth bass (Micropterus salmoides), are established in the basin
<Table 2), Others have been introduced but apparently are not reproducing
(Minckley 1973, 1979; Moyle 1976; Nicola 1979; Courtnay & Deacon 1983).
Exotic species prey on the eggs and juveniles of indigenous fish, and compete for
space and spawning sites (Deacon 1979), Thus, red shiners (Notropis lutrensis)
397