7046 ‎(2)‎

• UCREFRP Catalog Number: 7046
• Author: Valdez, R. A., W. J. Masslich and A. Wasowicz.
• Title: Final Report\
• USFW Year: 1992.
• Copyright Material: NO

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4.3.4.2 Foraee. Competition. and Predation. Colorado squawfish can become piscivorous in their
first year of life, and retain a nearly exclusive fISh diet throughout life (Valdez 1990). Non-native
cyprinids (i.e. red shiner, sand shiner, and fathead minnow) can probably provide an ample forage
base for juvenile squawfish. An. ample forage base of both native and non-native fish is available for
adult squawflSh in the system.

Non-native cyprinids in the Dolores River appear to be no greater a potential threat to Colorado
squawfish than in other rivers in the Upper Colorado River Basin. These non-natives may be a
source of competition to larval squawfish, but their abundance in nursery habitat (backwaters) is no
higher than other areas on the Colorado and Green rivers which consistently harbor young squawfish.
The diet of these non-natives is probably adult and immature insects, small crustaceans, and plant
material (Pflieger 1975), although recent data from the Yampa River suggest that red shiners may
be piscivorous on larval native species (J. Ruppert, CSU, Pers. Comm. Feb. 1992). Effects of
predation by these species on Colorado squawfish are not known (Valdez 1990). Green sunfish are
highly piscivorous and represent a potential threat, but these fish are found in small numbers in the
Dolores River, mostly near the Colorado River confluence. Other centrarchids (e.g., bluegill,
largemouth bass) were rare in the Dolores River. Ictalurids probably represent the most significant
potential threat to squawfish in the Dolores River. Black bullheads are probably indiscriminate
feeders, and even small numbers may constitute a threat to small fish. Only 48 bullheads were
captured in 1990-1991. These were found mostly along shorelines, rather than in backwaters, perhaps
tempering their threat to young squawfish. Channel catfish are also piscivorous, and juvenile and
adults have been found in sympatry with chubs in Cataract Canyon (Valdez 1990). Channel catfish
in the Dolores River were collected in greater numbers from eddies and shorelines than from
backwaters, possibly reducing the potential for larval squawflSh predation. Predation by large adult
catfish on juvenile and small adult squawfish is a potential problem, although relatively few large adult
catfish were captured in 1990-1991. Trout are rare in the Dolores River below Disappointment
Creek and probably have little effect on squawfish.

4.4 Feasibility of Reintroducing Colorado SquawOsh

Data collected on physical, chemical and biological attributes of the Dolores River during this
study suggest that reintroduction of Colorado squawfish into the Dolores River system is possible.
However, since the status of the species in the Upper Colorado River is not fully understood and
further study is required to determine the extent that Colorado squawfish use the Dolores River,
reintroduction of squawfish for purposes of augmenting populations is not recommended. Based on
results of this study, it is recommended that the Dolores River drainage be considered as a site for
experimental stocking of Colorado squawfish and possibly razorback sucker associated with future
research. With low numbers of squawfish currently in the drainage and few predators relative to
other upper basin drainages, the Dolores would be suitable for experimental stocking. Potential
research includes studies on survival, dispersal and homing of various life stages of the species.
BIO/WEST recognizes three potential experimental scenarios that would be feasible in the Dolores
River drainage. These include: 1) incubation of eggs in situ; 2) release of PIT-tagged juveniles, and;
3) chemoreception studies with adults.

4.4.1 Incubation of Eggs in Situ

Reintroduction via incubation of eggs in situ has not been attempted for endangered species in
the upper basin of the Colorado River. The possibility of strong homing tendencies by these species,
especially Colorado squawfish, suggests that this type of reintroduction may be suitable for re-
establishing drainage-specific stocks. A well conceived study that would allow the incubation and

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