VII. DESERT FISHES
441
tosteus clarki); millions of Agosia were present. In 1964, no Rhinichthys
and three Pantosteus were found; no collection was made in 1965. In 1966
after an increase of flow the preceding winter and spring, both the formerly
rare species had realized a profuse spawn, and by 1967 Pantosteus made
up almost 30% of the fauna, and Rhinichthys was frequent in collections
(Minckley, 1969a).
Similar fluctuations in fish populations occurred throughout Arizona in
the period 1965-1967. Some rare and restricted fishes, such as the
Little Colorado River spinedace (Lepidomeda vittata), spread to reoccupy
most of their former ranges (Minckley and Carufel, 1967). It is notable
that in the almost-constant environment of the spring-fed Moapa River,
southern Nevada, based on collections made over the same time period
(1963-1969), native fish populations remained essentially stable (Deacon
and Bradley, 1971).
Relative stability of some stream-fish populations, usually of larger species, contrasts with variations just outlined. Spatial relations of stream-fish
populations have been studied in eastern United States (Gerking, 1950,
1953, 1959; Larimore, 1952; Fajen, 1963), but to our knowledge have
not been defined in desert streams. By inference from observational data,
restricted movements by desert stream fishes are highly characteristic of
adults, whereas young seem to disperse more widely. In the Chiricahua
Mountains, Arizona, John (1963, 1964) found that adult speckled dace
remained in permanent pools in flood (see also Section ΙΙΙ,Α,Ι) and
in drought. Yet flooding moved smaller fishes downstream rapidly and
sometimes almost completely decimated the young of the year. In southern
Arizona, the Sonoran chub (Gila ditaenia) lives in a small, intermittent
stream near the International Boundary. A major pool that has been
studied sporadically since 1963 has always supported a few adult chubs.
In times of persistently high discharge the adults do not move from the
pool, even though many hundreds of meters of habitat is then available
(Minckley and Deacon, 1968). This also is evident in some populations
of Agosia, in more or less temporary streams. If displacement occurs, the
fish appear capable of returning to the permanent pools. Gunning (1959)
demonstrated the olfactory capabilities of the longear sunfish (Lepomis
megalotis) in identification of its home pools. Perhaps some desert species
also have such a capability.
Short-term stability of populations of some other stream-dwelling species
is indicated by the month to month similarity of population structure, such
as in the spikedace (Meda fulgida) in Aravaipa Creek (Barber et al.,
1970). This is even more strongly indicated by a lack of morphological
variability in some populations over a long period of time. If much gene
flow occurred throughout systems studied by Rinne (1969), through trans-
441
tosteus clarki); millions of Agosia were present. In 1964, no Rhinichthys
and three Pantosteus were found; no collection was made in 1965. In 1966
after an increase of flow the preceding winter and spring, both the formerly
rare species had realized a profuse spawn, and by 1967 Pantosteus made
up almost 30% of the fauna, and Rhinichthys was frequent in collections
(Minckley, 1969a).
Similar fluctuations in fish populations occurred throughout Arizona in
the period 1965-1967. Some rare and restricted fishes, such as the
Little Colorado River spinedace (Lepidomeda vittata), spread to reoccupy
most of their former ranges (Minckley and Carufel, 1967). It is notable
that in the almost-constant environment of the spring-fed Moapa River,
southern Nevada, based on collections made over the same time period
(1963-1969), native fish populations remained essentially stable (Deacon
and Bradley, 1971).
Relative stability of some stream-fish populations, usually of larger species, contrasts with variations just outlined. Spatial relations of stream-fish
populations have been studied in eastern United States (Gerking, 1950,
1953, 1959; Larimore, 1952; Fajen, 1963), but to our knowledge have
not been defined in desert streams. By inference from observational data,
restricted movements by desert stream fishes are highly characteristic of
adults, whereas young seem to disperse more widely. In the Chiricahua
Mountains, Arizona, John (1963, 1964) found that adult speckled dace
remained in permanent pools in flood (see also Section ΙΙΙ,Α,Ι) and
in drought. Yet flooding moved smaller fishes downstream rapidly and
sometimes almost completely decimated the young of the year. In southern
Arizona, the Sonoran chub (Gila ditaenia) lives in a small, intermittent
stream near the International Boundary. A major pool that has been
studied sporadically since 1963 has always supported a few adult chubs.
In times of persistently high discharge the adults do not move from the
pool, even though many hundreds of meters of habitat is then available
(Minckley and Deacon, 1968). This also is evident in some populations
of Agosia, in more or less temporary streams. If displacement occurs, the
fish appear capable of returning to the permanent pools. Gunning (1959)
demonstrated the olfactory capabilities of the longear sunfish (Lepomis
megalotis) in identification of its home pools. Perhaps some desert species
also have such a capability.
Short-term stability of populations of some other stream-dwelling species
is indicated by the month to month similarity of population structure, such
as in the spikedace (Meda fulgida) in Aravaipa Creek (Barber et al.,
1970). This is even more strongly indicated by a lack of morphological
variability in some populations over a long period of time. If much gene
flow occurred throughout systems studied by Rinne (1969), through trans-