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<br />ft.
<br /> Changing Fish Fauna of the Southwest 383
<br /> it evidently preferred the sluggish parts of streams, sloughlike chan-
<br /> nels, and marshy or lacustrine conditions. From the 1850's to about
<br /> 1880, it was sufficiently abundant to be marketed at San Francisco
<br /> (Rutter, 1908, pp. 112, 117). In October, 1872, the Hassler Expedi-
<br /> tion obtained 43 specimens (MCZ 18372,18743-746) from the Sacra-
<br /> mento River, and Gustav Eisen collected 5 from Fresno in 1881
<br /> (USNM 30226, 107752). Midden material from an Indian mound
<br /> near Oakley, Contra Costa County (close to the junction of the
<br /> Sacramento and San Joaquin rivers), coReeted by Sherburne F. Cook,
<br /> includes pharyngeal bones and teeth of the thicktail chub (W. I.
<br /> Follett, letter of April 7, 1960).
<br /> Reduction of its habitat through drainage, dam building, and
<br /> diversion of water for irrigation, coupled with competition from
<br /> numerous exotic species, are believed to have been important factors
<br /> in its impending demise. On August 29, 1926, Carl L. Hubbs and
<br /> Leonard P. Schultz collected 3 hybrids between Gila crassicauda and
<br /> Lavinia exilicauda (UMMZ 94166) in Putah Creek, 4 miles west of
<br /> Davis, California. A hybrid between these 2 species occurred in 1872
<br /> among specimens collected by the Hassler Expedition (MCZ 35692).
<br /> The thicktail chub was seldom taken der the early 1900's and, to
<br /> my knowledge, only 5 specimens have been obtained since 1936: 3
<br /> from Putah Creek, 3 air miles southeast of Davis (Sacramento State
<br /> Coll. Mus. No. 112) on June 26, 1936;1 from Clear Lake, caught on
<br /> May 18,1938 (SU 37361) ; and another from the vicinity of Rio Vista
<br /> on the Sacramento River, taken on August 7, 1950 (CAS 20456). By
<br /> the late 1940's the species no longer survived in Clear Lake (Murphy,
<br /> 1951). This chub now is obviously on the brink of extinction, but
<br /> perhaps is surviving locally. W. 1. Follett made several trips since
<br /> 1950 to the Rio Vista region but failed to capture the species.
<br /> Gila nigrescens (Girard), Chihuahua chub. This species, col-
<br /> lected in 1851 from the Mimbres River north of Deming, New Mexico,
<br /> is restricted to streams of interior drainage that flow into several
<br /> isolated basins of northern Chihuahua, Mexico (Miller and Uyeno,
<br />l
<br />l; MS). Its extermination from the United States has been noted by
<br /> Koster (1957, p, 57), who thought its disappearance was probably due
<br /> to the introduction of the longfin dace, Agosia chrysogaster, from the
<br /> Gila River basin. However, the chub was gone when Carl L. Hubbs
<br /> collected in the Mimbres on June 30,19M, prior to the establishment
<br />of the dace. I think its disappearance is likely due to the elimination
<br />{
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<br />4.
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