V I I . DESERT FISHES
455
ered by sedimenting muds (Moore, 1944b). A number of large cyprinid
fishes in rivers of Eurasia spawn similarly, and it is suggested that this
type of behavior also makes the pelagic eggs less conspicuous to predators
(Nikolsky, 1963). In Australian rivers, silver perch (Bidyanus bidyanus;
family Theraponidae) and golden perch (Plectroplites ambiguus; family
Serranidae) spawn with the same kind of timing to floods (Lake, 1967).
The stimulus of water-level changes, or related factors, in the reproduction of many large-river fishes is well documented. North American
buffalofishes (genus lctiobus) are notorious for this feature (Yeager,
1936). Van Ihering (1935) reports it for several South American species,
Boulenger (1907) for numerous fishes of the Nile, and Hora (1945) related water-level changes and phases of the moon as stimuli for certain
Indian cyprinids. Some fishes of desert lakes, such as the cui-ui (Chasmistes cujus) of Pyramid Lake, Nevada, move into influent streams to
spawn in spring. Changes in river level strand many eggs, young, and even
adults, to die on gravel bars (Snyder, 1917; LaRivers, 1962).
Fishes characteristic of the lower ends of large desert rivers, as elsewhere,
may depend upon periodic flooding of marginal habitats for their reproductive activities or for feeding by themselves or by their young. The nutrients
on fertile floodplains stimulate rapid development of plankton, not to
mention the provision of a vast volume of terrestrial organic material
(Evans-Prichard, 1940; Stubbs, 1949; Hickling, 1961; Nikolsky, 1963).
Beheading of many desert streams by dams has had a profound effect on
these and other lower-river fishes.
Some forms such as the massive Colorado River squawfish seem to
have performed upstream "runs" prior to damming (Dill, 1944; Miller,
1961a), and the physical barriers may have blocked a critical stage in that
species' life cycle (as it does in salmonids, such as Oncorhynchus spp.,
and other fishes that run into rivers from the sea to spawn).
On the other hand, changes in a myriad of other factors has been evidenced by alterations of the entire fauna of the Colorado system. Vanicek
et al. (1970) have impressively documented the absence of reproduction
by indigenous fishes in a 105-km reach of the Green River, Utah, below
Flaming Gorge Dam. This was attributed to lowered water temperatures
in summer periods of high discharge of water from the lake's hypolimnion.
Below the mouth of the Yampa River, a major tributary of the Green,
conditions resembled those existing prior to the dam, and native fishes reproduced successfully. Sexual activities of all the larger cyprinids (Squawfish and Gila spp.) seemed closely related to peak water temperatures and
a decline in volume of flow (Vanicek and Kramer, 1969). Reproduction
of these fishes at inception of low discharge and by the sand shiner
(Notropis stramineus) in the western part of the Great Plains (Summerfelt
455
ered by sedimenting muds (Moore, 1944b). A number of large cyprinid
fishes in rivers of Eurasia spawn similarly, and it is suggested that this
type of behavior also makes the pelagic eggs less conspicuous to predators
(Nikolsky, 1963). In Australian rivers, silver perch (Bidyanus bidyanus;
family Theraponidae) and golden perch (Plectroplites ambiguus; family
Serranidae) spawn with the same kind of timing to floods (Lake, 1967).
The stimulus of water-level changes, or related factors, in the reproduction of many large-river fishes is well documented. North American
buffalofishes (genus lctiobus) are notorious for this feature (Yeager,
1936). Van Ihering (1935) reports it for several South American species,
Boulenger (1907) for numerous fishes of the Nile, and Hora (1945) related water-level changes and phases of the moon as stimuli for certain
Indian cyprinids. Some fishes of desert lakes, such as the cui-ui (Chasmistes cujus) of Pyramid Lake, Nevada, move into influent streams to
spawn in spring. Changes in river level strand many eggs, young, and even
adults, to die on gravel bars (Snyder, 1917; LaRivers, 1962).
Fishes characteristic of the lower ends of large desert rivers, as elsewhere,
may depend upon periodic flooding of marginal habitats for their reproductive activities or for feeding by themselves or by their young. The nutrients
on fertile floodplains stimulate rapid development of plankton, not to
mention the provision of a vast volume of terrestrial organic material
(Evans-Prichard, 1940; Stubbs, 1949; Hickling, 1961; Nikolsky, 1963).
Beheading of many desert streams by dams has had a profound effect on
these and other lower-river fishes.
Some forms such as the massive Colorado River squawfish seem to
have performed upstream "runs" prior to damming (Dill, 1944; Miller,
1961a), and the physical barriers may have blocked a critical stage in that
species' life cycle (as it does in salmonids, such as Oncorhynchus spp.,
and other fishes that run into rivers from the sea to spawn).
On the other hand, changes in a myriad of other factors has been evidenced by alterations of the entire fauna of the Colorado system. Vanicek
et al. (1970) have impressively documented the absence of reproduction
by indigenous fishes in a 105-km reach of the Green River, Utah, below
Flaming Gorge Dam. This was attributed to lowered water temperatures
in summer periods of high discharge of water from the lake's hypolimnion.
Below the mouth of the Yampa River, a major tributary of the Green,
conditions resembled those existing prior to the dam, and native fishes reproduced successfully. Sexual activities of all the larger cyprinids (Squawfish and Gila spp.) seemed closely related to peak water temperatures and
a decline in volume of flow (Vanicek and Kramer, 1969). Reproduction
of these fishes at inception of low discharge and by the sand shiner
(Notropis stramineus) in the western part of the Great Plains (Summerfelt