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<br />~ntpetrichthps, is extinct. Three distinct
<br />ibspecies of the other known species of
<br />le genus, E. latos, the Pahrump killi-
<br />sh, have been described from the three
<br />.plated springs of Pahrump Valley,
<br />levada. One of the springs (Pahrump
<br />pring) failed in 1958, presumably be-
<br />ause of lowering of the water table by
<br />umping for irrigation. A second spring
<br />[taycraft Spring) was filled by a
<br />anther in an attempt at mosquito
<br />ontrol. This spring would probably
<br />ave gone dry from the same cause as
<br />'ahrtunp Spring had it not been filled.
<br />'he third spring, Manse Spring, which
<br />upports the typical subspecies E. latos
<br />rtos, remains, but goldfish (Carassius
<br />uratus) were recently introduced (31).
<br />bus, two of the original three known
<br />locks of E. latos are extinct, and the
<br />~tird is subjected to competitioa from
<br />n exotic species. The species is main-
<br />aining itself at present. In July 1967 an
<br />ttempt was made to rempve the fish
<br />rpm the spring and count the entire
<br />opulation; population size was esti-
<br />lated to be about 1300. Most of the
<br />oldfish were removed at this time.
<br />This species appears capable of main-
<br />lining its population in the face of
<br />ome competition, but obviously cannot
<br />rithstand the virtually total destruction
<br />f its habitat. Table 2 gives data that in
<br />art explain the destruction of habitat
<br />nd the extinction of the two subspecies
<br />f Empetrichthys latos. There is clearly
<br />relationship between increased culti-
<br />ation, number .of wells, volume of
<br />-ater used for irrigation, and lowering
<br />f the water table. The first wells were
<br />rilled in 1910; by 19]6, flow at Manse
<br />pring was reduced to about half its
<br />-iginal volume. Water use near'•y
<br />•~ubled during the period 1946-59,
<br />~d increased by a factor of 7 to 8
<br />:twcen the periods ] 937-40 and 1940-
<br />~~. Such large increases in pumpage
<br />tevitably result in failure of surface
<br />aters. Thc estimated annual recharge
<br />~1 Pahrump Vallry i5 22,100 acre-feet
<br />?7 million cubic metcrx) f32)..With-
<br />r.{rawal of nearly 41,000 acre-feet
<br />q-nnuall virplall uarantccs continue
<br />decline of ~ water to lc cventua
<br />Failure of Manse Shrine. and extinction
<br />of the last vohulation of the genus
<br />the sprin>; flow eon-
<br />roues to decline at its resent rate since
<br />j,959 a mean annual rate o flow has
<br />hown a decline of 0.14 cu lc~ foot er
<br />ccond), Manse Springs ou fail in 10
<br />sp 11~e_ars. The tren o increased
<br />~impage in Pa rump a ey suggests
<br />Nat the rate of decline of springy fltzy
<br />ill accelerate and that elimination of
<br />MARCH 1968
<br />~~~
<br />Table 2. ~~'ater di~ch::rce and utilization in Pahrump Valley , lice and Clark counties, Nevada,
<br />in the Ueriod 1875-1967. D:rta for I;t7~ arc from ;ttalmberg f3_'I; for 1916, from Waring (41 );
<br />for the years 1917-a6, from 1laxey and Robinson (4J 1: an d for the years 1951-67, from the
<br />Nevada State EnKineer 14? ).
<br />1\fanse Pahrump Raycraft Thou-
<br />sands of pumpage Number Depth of
<br />Year or Spring Spring Spring (in thou- of water
<br />period (ft'isec, (tt',sec, (ft'; sec, acres sands of wells table (ft)
<br />av.) av.) a~'•) rigated acre-feet) operating
<br />1875 6.0 7.9 - -~ -------- -- --
<br />1916 3.2 4.7 0.002 0.5 4.3 15
<br />1917-37 3.3.6
<br />1937-40 3.1 2,2_3,5
<br />]940-~6 3.1 5.5 2?-16.3
<br />1951 2.6 16.! 39 37
<br />1952 39 30,0
<br />1959 2.5 0.0 0.0 5.8 25.6 45
<br />1960 2.4 6.2 27.4 39
<br />1961 2.0 6.5 30.1 55
<br />1962 1.9 6.5 29.2 54
<br />1963 ].B 7.8 31.9 59
<br />1964 1.9 7.7 37.5 62
<br />1965 1.2 8.2 36.5 64
<br />1966 1.5 7.6 37.9 71 70-85
<br />1967 75-84
<br />Ihe_fau~na_may be expected in less than
<br />10 ears.
<br />The status of the Moapa dace, 1Noapa
<br />coriacea, is less readily defined than
<br />that of Entpetriclttlt)~s. The minnow
<br />was abundant in the headwaters of the
<br />Moapa River, Nevada, whe^ the first
<br />collections were made in 1933 (33).
<br />Its abundance was apparently main-
<br />tained at least until the early 1950's
<br />(34). In our studies, which began in
<br />1964 (see 24, 3S), the species was
<br />found to be rare. The low population
<br />density of Moapa closely followed the
<br />introduction and establishment of the
<br />shortfin molly, Poecilia tnezicana, in
<br />the river. After 2 years the population
<br />of Moapa suddenly became more
<br />dense. In this case there was no physical
<br />deterioration of the habitat, thus
<br />changes in habitat were obviously not a
<br />factor in either the decline or the re-
<br />covery of this species. The maximum
<br />and minimum annual mean discharge
<br />over the past 25 years, measured at the
<br />approximate lower extent of the habitat
<br />suitable for Moapa, fall within 3.3 cubic
<br />feet (0.1 cubic meter) per second of
<br />the 25-year mean discharge (36). The
<br />stream flow is, therefore, remarkably
<br />stable. The major problem is alteration
<br />of the biotic habitat by the introduction
<br />Lr~
<br />i-'
<br />Diu ntvt:n BASRi.
<br />anrzau, raw .,auto aro sa+aw
<br />.~ }
<br />ti' ~`~ ~ `~ f c-~ ti
<br />.~; -~~. : ~ J I f
<br />~~ Y`~1~*
<br />~~ ~ ~
<br />t S
<br />~.1,
<br />~ ..
<br />s:
<br />;q:.,:
<br />.: ~.
<br />j
<br />-~ -£ R
<br />3
<br />~t ~~
<br />~°
<br />rt
<br />~;,:
<br />
<br />W; ;'~
<br />~~
<br />Fig. 3. Present and past distribution of the Gila topminnow in the Gila River basin;
<br />the symbols are the same as in Fig. 2. ..•.
<br />1429 ~~ =~
<br />
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