7145

• UCREFRP Catalog Number: 7145
• Author: Inslee, T. D.
• Title: Spawning of Razorback Suckers
• USFW Year: 1981.
• Copyright Material: NO

bullhead on yearling-size squawfish in riverside ponds. Coon (1965) found
young Colorado squawfish in the stomachs of channel catfish collected from
the Dolores River and Taba et al. (1965) found young squawfish in the
'stomachs of black bullhead from the Colorado River near Moab. Marsh and
Langhorst (1988) reported that 40% of green sunfish sampled from a back-
water in Lake Mohave contained razorback sucker larvae in their stomachs.
Mosquitofish (Gambusia affinis) typically extirpate native topminnows
(Poeciliopsis occidentalis) in southwestern streams via predation within
1-3 years after introduction (Meffe 1984); however, their effect on upper
Colorado River species is unknown.
Elimination of these predacious species from the river is currently not
possible (Valdez 1990). However, data suggests that periodic, high river
flows can control numbers of some non-native fishes. Minckley and Meffe
(1984) reported that several introduced fishes, particularly predatory
sunfishes and catfishes, were reduced in number or eliminated completely
by flooding in six unregulated Arizona streams of various size, while
native fishes were little affected. Meffe (1984) reported that replacement
of native topminnows by introduced mosquitofish is most rapid in areas
that rarely flood, while long-term coexistence may occur in frequently
flooded habitats.
Without high flows, some introduced species proliferate. Osmundson and
Kaeding (1989) noted changes in fish community structure in the Grand
Valley (Loma to Palisade) in a three-year study (1986-88) during which
spring peak and summer flows progressively declined. There was a marked
increase in the three most abundant non-native minnow species, red shiner,
fathead minnow and sand shiner (Notropis stramineus), a concurrent de-
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