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<br />Notropis lutrensis, has seemingly re-
<br />placed it throughout that system (Fig.
<br />2A). The red shiner spreads rapidly,
<br />naturally and from fishermen's bait
<br />buckets. In view of this, and of pro-
<br />posals to build the Charleston Dam on
<br />the upper San Pedro River and the
<br />Hooker Dam on the Gila River in New
<br />Mexico, the outlook for Meda appears
<br />bleak.
<br />The Gila topminnow, Poecfliopsis
<br />occfdentalis, provides another example
<br />of the influence of an exotic fish on a
<br />native species. The Gila topminnow
<br />also was at Tempe in 1890, where it
<br />undoubtedly lived in marshes along the
<br />1
<br />stream rather than in the channel itself.
<br />Records show that this fish ranged from
<br />a high•elevation habitat adjacent to
<br />Frisco Hot Spring in western New
<br />Mexico (27) to an area near Dome,
<br />Arizona (28). These, plus records from
<br />most of the central and southern parts
<br />of the Gila basin (Fig. 3), leave no
<br />doubt that the topminnow once lived
<br />throughout the Gila drainage, and per-
<br />haps in suitable habitats along-the lower
<br />Colorado as well. Its decline was rapid.
<br />Gila topminnows were considered by
<br />Hubbs and Miller (28) to be "one of the
<br />commonest fishes in the southern part
<br />of the Colorado River drainage." Today
<br />
<br />rl,•~ ~. ~~, A
<br />tY!r ~r r,
<br />'•; ti, t '~... GILA RIVER BASIN,
<br />;~
<br />~. }. ~ %~ .. .,! ., ~' AR120NA, NEW MEXICO. AND SpgR4
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<br />t. it •.. .., w -^ •,; -/
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<br />-- -- -_._ .0~~-.-..--~- • - - ~ -
<br />Fig. 3. ~ A 1 Present distribution of the introJaec~ reLl shiner in the Giia Ricer basin.
<br />It3) Present and p,l~t diaributiun of :h~• natnc Gila ,pinedace in the Gila Ri\~er basin.
<br />Open circles are Lx:liities ,,i larme~ o.curren~e v.herc the pre,ent absence of the fish
<br />has been ,~~ntirmed: h:df-,c~li;l circles ;. r; Inc,litie~ that tic hate Writ ree\:Im.n~d: :ohLi
<br />circles :Ire ioc~litie, ~~•here the ~~ined::cr pei,i~t,.
<br />tai.
<br />the fish persists only in one spring area
<br />in Santa Cruz County, Arizona.
<br />The diminution in the range of this
<br />fish is attributable in part to desiccation
<br />of habitat, especially in places like the
<br />lower Gila River. Arroyo cutting iq the
<br />1880's (4, 29), must have destroyed
<br />much of its preferred quiet-water habi-
<br />tat even before man began to use the
<br />water. The introduction and spread of
<br />the mosquito fish, Gambusia minis;
<br />throughout most of the basin over the
<br />last 40 years appears to,y~e been the
<br />most important factor, however, in the
<br />overall decline of the native fish. The
<br />aggressive Gambusia has played a part
<br />in the decline of a number of fishes is
<br />the West and in the destruction of popu.
<br />lations of fishes in other areas (3f~}, Ir
<br />the bes"t-documented examples ct re.
<br />placement of Poeciliopsis by Gami,t~s~a
<br />the sequence is rapid. In the forrurl}
<br />fishless Arivaca Creek, in Arizona. top
<br />minnows were introduced in 19= ;. Ir
<br />1957 they were extremely common, `gut
<br />in 1959, mosquito fish of unknowr
<br />origin had totally reglaced them (4)
<br />The sequence was similar in an artesian
<br />spring area near Safford, Arizona. Gilt
<br />topminnows abounded in canals anc
<br />ponds of that area in 1962. In 1963
<br />specimens of Gambusia were taken it
<br />the area, and in the same pond at
<br />Poeciliopsis. In our intensive survey
<br />only the introduced mosquito fish way
<br />found in 1966.- Restriction to a single
<br />isolated drainage seems a precarious
<br />position for the Gila topminnow; thi
<br />formerly abundant, endemic species
<br />now qualifies for category 4, ever
<br />though it was originally acategory--:
<br />species.
<br />In discussing fishes in category 4, evc
<br />use as examples species naturally iso
<br />lated in aquatic systems of closed basins
<br />or isolated, by habitat preference of
<br />ph}~siological attributes, or both, tc
<br />springs or springlike environments
<br />Alterations induced by man,. a major
<br />cause of declining populations in Bate
<br />gories 2 through 4, are particularly im
<br />portant to fishes in category 4. Minot
<br />changes in a small spring, for example
<br />may influence the entire population of t
<br />species. The acute susceptibility of sucl
<br />fortns to catastrophe is evident in the
<br />recent compilations of extinct fishes o
<br />the United States (?, 4}; three of the sip
<br />fishes li>ted were in restricted waters it
<br />Nevada, and a fourth, C~~prinodor
<br />borinus, was in an isolated spring it
<br />Texas.
<br />Emnetri~hth}•s nrerriami, the Asl
<br />Meadows killifi=h, one of the tac
<br />know n species of the c~ prinodoot genu•
<br />sc rt=tvice, vot.. ts•
<br />
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