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<br />86' .:
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<br />.'l1Jlcriwn Fisheries _<.,~U{ ie/y
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<br />DESCRIPTION OF TlIE AREA
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<br />Consisting of ncarly 3,OCX) squarc miles, Lake Mead ~atioIlal Recrea-
<br />tional Area, administered by the National Park ServIce, f ollow~ the
<br />winding course' of the Colorado River from, Grand Canyon NatlO.nal
<br />MOIlument in northwestern Anzona to DavIS Da 111 , nearly 200 mIles
<br />dOWIlstream in southeastern Nevada, This is an arid, semiuesert region
<br />in which th~ SUlllmers are hut and dry, but the winters are cool and
<br />mild (Figme 1).
<br />The rnain fe;tlures ;ll'L: the two extensive reservoirs, Lake J\lead and
<br />I,akc Mohaw, funned Il)' Jlouvn and Davis Dams. OrigilJally Lake
<br />I\lead stretched eastward for 115 navigable miles above 110uver Dam,
<br />rl';\ching for 3lJ miles intu the lower end of Crand Canyon., As the
<br />result of siltration ill the 1I1'pn' purl ions, the upstreaJll limit uf the
<br />hkl' is now only 85 nlilcs from the dam. At its h.eight, following ClJIl1-
<br />pktiulI (,f the dalll in ]<)3(,: lIle lake hac.l a sllUrehJle of uvn 500 miles
<br />dlld a depth of 580 fed.
<br />- - .,\-r-lH'--it-" Hk-lc~-th{',- H+H-"i~\-il)Ha-I--aFP'aH n ,[l-lt, (La'st- ,tht:'(c:-'j}"ratkr!\:1ver
<br />flows for tn tempeslu(Jus Illiles through the lower extnlsiol\ of C;ranc.l
<br />l~anyon I,dore it pums into Lake Mead. Grand Wash,. which enters the
<br />l:tkt: below Pierce Feny, is dry except when occasllJ)):!1 cluudbursts
<br />sClId torrents dashing down its cuu rst'.
<br />The \'jr"ill ]{iver and its flllllllT trillll!;lry, the I\luapa (Muddy) .
<br />I{ivl'l' ellt~. Lake Mead from the nunll in[o Virgin Uasill. .ueyol1c.l
<br />J',ou!(ier Canyon, the lake tums almll,tly southward and is joinec.l by
<br />lilt: small Las VCg;iS' J{iver emerging from L:!s Vegas \\'asll.
<br />FnllJI 11()(,ver Dam, the clear, cold water fl(Jws into t he recently
<br />formed Lake !\Iuhave. \Vhen lilled, tllis lake will extend al1nost to the
<br />IJa~;(: of lluuver Dam. Unlike Lake MeaJ it will be n;lrrnw, with a
<br />lIla:-.imlH11 \\idrh of ollly 4 miles. lts shordine will be 200 miles long
<br />and its \\',lter levd is nut exptcted to fluctuate more than 10 feet annu- -
<br />;.JI\'. ]1'1 tIle uppc:r re;ll'lles, where the water temperature averages 560
<br />F.' l.ake I\]ollaVl' will I't: sllilahll: for trout. Befure tile water reaches
<br />D;lvis Dam, it will have warmed sufficiently to provide favorable con-
<br />ditions for largemuuth black bass ami other warm-watn game species.
<br />:\t present, however, only trout will be planted.
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<br />NATIVE FISHES
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<br />Only three native jishes have been cullected in the recreational area:
<br />the razorback sucker, the Colorac.lo squawflsh, and the bony tail.
<br />The waters of the Colorado River in this area, which were originally
<br />swift, heavily silt-laden, and subject to rapid chal~ges in turbidity and
<br />volume, are now regulated to produce clear, plaCid waters above and
<br />IJelow Hoover Dam. The nati.ve fishes Jre. ac.lapted to tl~e rigorous . rr~"'~,'
<br />swift-water halJitat by a reduction III scale sIze and Ly havmg stream- ~~ -
<br />lined bodies (Miller, 1946b).'
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<br />Fish Fauna of Lake Mead
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<br />Following completion of Hoover Dam the native fishes in the lower
<br />Colorado River began to decline in numbers accompanied by a simul-
<br />taneous increase in the exotic species (Dill, 1944). Predation by and
<br />competition with the exotic species and changes in the ecological con-
<br />ditions of the river are causal factors in the depletion of the indigenous
<br />fishes. The razorback sucker is the one exception. This species appears
<br />10 be holding its own and reproducing abundantly in Lake Mead.
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<br />In addition to the existing man-made structures, 134 projects or
<br />units of projects for irrigation, power production, flood and silt control,
<br />channel improvement, municipal and other uses are proposed (Anony-
<br />mous, 19.16). It is evident that the native fishes of Ihis and other por-
<br />t ions 0 f the Colorado I~iver Basin arc destined to become scarce or
<br />locally exterminated. It is regrettable that little can be done to save
<br />the~'n, for our 'present knowledge of these species is very incomplete
<br />(Dill, 1944; Miller, 1946a, b). Consequently, this fauna should become
<br />th~nbjJ~_ctoJn1(lTeiu,le-ns~vcrg.se~HTh ul-lefore- -it--hasdisappcarcc]--ciffn:n
<br />pJetely or its com(l(Jsition has been altered further.
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<br />In addition to the three native species mentioned above, six others
<br />11Iay OCCur within the area. The hUlllpback chub, Gila cvpha Miller a
<br />rcn.larkable specialized species, closely related to the oOllytail, was ('le-
<br />senbed from tile CuloraduH.iver in Grand Canyon National Park
<br />(Miller, 194()b). The flannelmouth sucker, C atostolHlIS la/ipin nis Ba i rd
<br />and Girard, is found in Virgin River and farther up the Colorado River
<br />(Tanner, 1932, 1936; 'Miller, 1946b). The occurrence ot" the western
<br />clace, Rhinichthys asculus Girard, in Las Vegas Creek, a flood tributary
<br />to Lake Mead, was reported by Hubbs and Miller (1948b).
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<br />Live bait for Lake Mead anglers is brought from the Santa Clara
<br />River, a tributary to the Virgin River, near St. George, Utah. This
<br />source of bait fishes has been utilized for several years,
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<br />The following fishes were collected from bait tanks at Las Vegas
<br />\Vash and Boulder Beach c.locks: ftannelmouth sucker; Utah moulltain
<br />sucker, Puntos/eus delphinus utahensis (Tanner) ; western dace; scaled
<br />spiny dace, Lepidomcda vitta/a Cope; a sculpin, CottllS bairdii Cirard :
<br />and carp. Representatives of the entire fish fauna of the Santa Clara
<br />River (as listed by Tanner, 1932 and 1936) are included in these col-
<br />lections of live bait. Specimens which escape from anglers' bait buckets
<br />may become established in Lake Mead if they have not done so already.
<br />Thus the range of these forms is being extended.
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<br />Just outside the recreational area, in the vicinity of Ihe Home Ranch
<br />Warm Springs, a few miles west of (~Ielldale, Nr:vada, two distinctive
<br />species are present (Hubbs and Miller, 1941, 1948a. b; Miller, 194(XL;
<br />Kopec, 1949). These forms, the White River springfish, CretlichthYJ
<br />baileyi (Gilbel:t), and the leather chub, Moapa coriacea Hubbs and
<br />Miller, are relIcts of the ancient White River fauna. During glacial
<br />times, this river was a permanent tributary of the Colorado. Moapa
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