406
JAMES E. DEACON AND W. L MINCKLEY
In deserts of the American Southwest, the longfin dace and some species
of Cyprinodon are the only native fishes that presently penetrate far into
temporary waters at times of high precipitation and runoff (Minckley and
Barber, 1971; unpublished data), but a number of introduced forms, the
red shiner (Notropis lutrensis), fathead minnow {Pimephales promelas),
Rio Grande killifish (Fundulus zebrinus), mosquitofish (Gambusia
affinis), and green sunfish (Lepomis cyanellus), spread into temporary
streams at any opportunity. All the last species are considered highly resistant to extremes, and/or as colonizers, within their native ranges
(Koster, 1957; Cross, 1967).
In periods of almost-terminal drying of desert watercourses, the processes of évapotranspiration may demand essentially all the surface water
of a small stream during the day (Campbell and Green, 1968). Mass mortalities of fishes occur. Longfin dace, however, persist alive beneath saturated mats of algae and debris, and at night when flow is resumed under
reduced temperatures, incident radiation, and photosynthesis, the fish swim
about and feed in a few millimeters of water. For a 14-day period in 1965,
an ever-declining population of longfin dace persisted in this manner in
Sycamore Creek, under alternating, wet and dry, diel cycles. A small rain
in August rejuvenated the stream (Minckley and Barber, 1971). Kilby
(1955) found sheepshead pupfish (Cyprinodon variegatus) on the Florida
coast remaining beneath algal mats between tides, a roughly analogous
situation.
In years past, prior to introduction of mosquitofish, the Gila topminnow
(Poeciliopsis o. occidentalis) was also characteristic of such desert habitats, "appearing from the sands" of dry washes after surface flows commenced. The fish doubtless spread to repopulate such streams from more
permanent habitats upstream, or from local, isolated réfugia (Hubbs and
Miller, 1941; Minckley, 1969c). This species, and the desert pupfish of
Arizona streams (which also must have lived under intermittent conditions), now are essentially eliminated. Pupfish continue to exhibit their
remarkable colonizing ability in Death Valley and Cuatro Ciénegas streams
and marshes and in a few other places.
An interesting hazard for longfin dace in Arizona streams is the waternet alga, Hydrodictyon, which sometimes chokes backwaters and smaller
channels of drying creeks. This alga effectively gill-nets small fishes; they
become entangled in its meshes and ultimately die. Lewis (1961) recorded
this in Illinois ponds and noted an apparent avoidance of the thalli by
survivors after an initial period of mortality.
On occasion, fishes transported into ephemeral waters may persist for
a time, even for a number of years, until evaporation, salinization, or temperatures exceed their tolerances. Populations of temporary lakes or
JAMES E. DEACON AND W. L MINCKLEY
In deserts of the American Southwest, the longfin dace and some species
of Cyprinodon are the only native fishes that presently penetrate far into
temporary waters at times of high precipitation and runoff (Minckley and
Barber, 1971; unpublished data), but a number of introduced forms, the
red shiner (Notropis lutrensis), fathead minnow {Pimephales promelas),
Rio Grande killifish (Fundulus zebrinus), mosquitofish (Gambusia
affinis), and green sunfish (Lepomis cyanellus), spread into temporary
streams at any opportunity. All the last species are considered highly resistant to extremes, and/or as colonizers, within their native ranges
(Koster, 1957; Cross, 1967).
In periods of almost-terminal drying of desert watercourses, the processes of évapotranspiration may demand essentially all the surface water
of a small stream during the day (Campbell and Green, 1968). Mass mortalities of fishes occur. Longfin dace, however, persist alive beneath saturated mats of algae and debris, and at night when flow is resumed under
reduced temperatures, incident radiation, and photosynthesis, the fish swim
about and feed in a few millimeters of water. For a 14-day period in 1965,
an ever-declining population of longfin dace persisted in this manner in
Sycamore Creek, under alternating, wet and dry, diel cycles. A small rain
in August rejuvenated the stream (Minckley and Barber, 1971). Kilby
(1955) found sheepshead pupfish (Cyprinodon variegatus) on the Florida
coast remaining beneath algal mats between tides, a roughly analogous
situation.
In years past, prior to introduction of mosquitofish, the Gila topminnow
(Poeciliopsis o. occidentalis) was also characteristic of such desert habitats, "appearing from the sands" of dry washes after surface flows commenced. The fish doubtless spread to repopulate such streams from more
permanent habitats upstream, or from local, isolated réfugia (Hubbs and
Miller, 1941; Minckley, 1969c). This species, and the desert pupfish of
Arizona streams (which also must have lived under intermittent conditions), now are essentially eliminated. Pupfish continue to exhibit their
remarkable colonizing ability in Death Valley and Cuatro Ciénegas streams
and marshes and in a few other places.
An interesting hazard for longfin dace in Arizona streams is the waternet alga, Hydrodictyon, which sometimes chokes backwaters and smaller
channels of drying creeks. This alga effectively gill-nets small fishes; they
become entangled in its meshes and ultimately die. Lewis (1961) recorded
this in Illinois ponds and noted an apparent avoidance of the thalli by
survivors after an initial period of mortality.
On occasion, fishes transported into ephemeral waters may persist for
a time, even for a number of years, until evaporation, salinization, or temperatures exceed their tolerances. Populations of temporary lakes or