402
JAMES E. DEACON AND W. L MINCKLEY
Broad, shallow, braided stream channels without well-defined (or confining) banks do not typically experience severe scour and modification
of habitat during floods. Changes in species composition or of abundances
of certain kinds frequently occur, but extirpation of the fauna is again almost never indicated. In the Death Valley system, for example (Miller,
1948), both the Salt Creek pupfish (Cyprinodon salinus) and the Nevada
pupfish (C. nevadensis amargosae) of the Amargosa River mainstream
must have survived innumerable floods, and they even persist in the relatively narrow canyons of those streams (Miller, 1943, 1948; LaBounty,
1968). Morphological variability is pronounced in the Amargosa River
subspecies of Nevada pupfish, especially in downstream populations, and
this was attributed most likely to flood transport of slightly differentiated
upstream fish into the lower area (Miller, 1948).
Floods in the Amargosa have had little discernible effect on populations
of fish, but many individuals were displaced downstream where they died
as pools evaporated (Wauer, 1962; unpublished data). The Red River
pupfish {Cyprinodon rubrofluviatilis) is another species of this group that
lives in broad, sandy-bottomed rivers, and apparently copes successfully
with major flooding so characteristic of Plains streams. The desert pupfish
(Cyprinodon macularius) must also have had such capabilities in streams
of southern Arizona. It now is extirpated in most of that area through
interactions with alien fish species (Minckley and Deacon, 1968).
High waters, in addition to sorting out different species on the bases
of their resistances or avoidance reactions, may also affect young fishes
more severely than adults. John (1964) noted that young speckled dace
were carried farther in flood than were adults, and we have similar information on that species, and on longfin dace and suckers (Pantosteus clarki
and Catostomus insignis) in Arizona creeks. In other instances, no sorting
by sizes was evident after spates (Barber et al, 1970). Fishes may also
sort themselves actively in relation to current, with larger (stronger) ones
moving into rapids and young remaining in quieter waters, or more
downstream.
Shifting of bedload in a stream is of major importance during flood.
Not only does it produce tremendous molar action that may physically
damage animals, but also fills pools with sand and rock (Fig. 4), especially
when a spate is of high intensity and short duration. Fajen (1963) found
marked population instability resulting from wandering of fishes in such
a shifting stream. There was a general lack of homing since pools and
well-marked riffles were periodically destroyed or displaced. We know of
no similar studies of desert streams but there is a strong tendency for larger
individuals of most desert fishes in Arizona creeks to remain in a given,
permanent place, if such is available. In streams with sand bottoms, con-
JAMES E. DEACON AND W. L MINCKLEY
Broad, shallow, braided stream channels without well-defined (or confining) banks do not typically experience severe scour and modification
of habitat during floods. Changes in species composition or of abundances
of certain kinds frequently occur, but extirpation of the fauna is again almost never indicated. In the Death Valley system, for example (Miller,
1948), both the Salt Creek pupfish (Cyprinodon salinus) and the Nevada
pupfish (C. nevadensis amargosae) of the Amargosa River mainstream
must have survived innumerable floods, and they even persist in the relatively narrow canyons of those streams (Miller, 1943, 1948; LaBounty,
1968). Morphological variability is pronounced in the Amargosa River
subspecies of Nevada pupfish, especially in downstream populations, and
this was attributed most likely to flood transport of slightly differentiated
upstream fish into the lower area (Miller, 1948).
Floods in the Amargosa have had little discernible effect on populations
of fish, but many individuals were displaced downstream where they died
as pools evaporated (Wauer, 1962; unpublished data). The Red River
pupfish {Cyprinodon rubrofluviatilis) is another species of this group that
lives in broad, sandy-bottomed rivers, and apparently copes successfully
with major flooding so characteristic of Plains streams. The desert pupfish
(Cyprinodon macularius) must also have had such capabilities in streams
of southern Arizona. It now is extirpated in most of that area through
interactions with alien fish species (Minckley and Deacon, 1968).
High waters, in addition to sorting out different species on the bases
of their resistances or avoidance reactions, may also affect young fishes
more severely than adults. John (1964) noted that young speckled dace
were carried farther in flood than were adults, and we have similar information on that species, and on longfin dace and suckers (Pantosteus clarki
and Catostomus insignis) in Arizona creeks. In other instances, no sorting
by sizes was evident after spates (Barber et al, 1970). Fishes may also
sort themselves actively in relation to current, with larger (stronger) ones
moving into rapids and young remaining in quieter waters, or more
downstream.
Shifting of bedload in a stream is of major importance during flood.
Not only does it produce tremendous molar action that may physically
damage animals, but also fills pools with sand and rock (Fig. 4), especially
when a spate is of high intensity and short duration. Fajen (1963) found
marked population instability resulting from wandering of fishes in such
a shifting stream. There was a general lack of homing since pools and
well-marked riffles were periodically destroyed or displaced. We know of
no similar studies of desert streams but there is a strong tendency for larger
individuals of most desert fishes in Arizona creeks to remain in a given,
permanent place, if such is available. In streams with sand bottoms, con-