7040

• UCREFRP Catalog Number: 7040
• Author: Miller, R. R.
• Title: Man and the Changing Fish Fauna of the American Southwest
• USFW Year: 1961
• USFW - Doc Type: Papers of the Michigan Academy of Science, Arts, and Letters
• Copyright Material: YES

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394 Robert Rush Miller
tion or elimination of the less competitive native fishes (see p. 389),
even including cyprinids (personal observations in California, and
observations by Clark Hubbs in Texas-personal communication,
1959). P. occidentalis is now so scarce throughout Arizona that it is
definitely threatened with extinction there.
FACTORS IN DEPLETION AND EXTINCTION
In a very perceptive unpublished report7 resulting from 2 months
of field work in Arizona in the spring of 1904, the late F. M. Chamber-
lain (an assistant with the old U. S. Bureau of Fisheries) outlined
the major causes of the depletion and extinction of fish life in Arizona.
His material is incorporated into the following summary, which in-
cludes a consideration of additional factors that later became op-
erative in further changing the native fauna of the Southwest. Many
of the factors discussed below were effective at a much earlier time
in producing faunal change in eastern North America (e.g., see Bar-
nickol and Starrett, 1951, p. 323; Lachner, 1956; Trautman, 1957,
pp. 13-24).
Destruction of vegetation.--Over much of the Southwest, large
expanses were originally covered by a luxuriant growth of grasses and
other succulent herbage which, during the rainy season, reached a
height of 2 feet or more (Leopold, 1951). As the dry season advanced,
the vegetation died down but formed a protective mulch, and its
roots were remarkably effective in binding the soil. Such a cover acts
like a sponge in retaining rainfall and hence is a potent defense against
erosion. Not only were valley floors covered in part by dense sacaton
grass but there were extensive cienegas (wet meadows) near their
centers, and elsewhere the water table was often within a few feet
of the surface (Thornber, 1910, p. 334). Consequently, there were
many more permanent streams than now, and large floods were rare
(Antevs, 1952).
With the introduction and establishment of livestock, the vegeta-
tion was not only eaten progressively shorter but it was severely
trampled to expose the soil over much of the area within a radius of
daily movement from water (Gregory, 1950, pp. 44--45). Such den-
udation by herds became particularly noticeable after 1875 (Antevs,
1952) and led to increased floods and severe erosion. Unbelievably
° Deposited in the Division of Fishes, U. S. National Museum, Washington,
D. C.
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