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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hatching of eggs and holding of larvae in an off stream facility would be required so that offspring
could be transported to a hatchery for rearing to size suitable for PIT-tagging. Ultimately the fish
could be released into the Dolores River to test chemoreception and homing hypotheses.

4.4.2 Release of Juveniles

Experimental stocking of juvenile Colorado squawfish has been attempted numerous times in the
lower basin of the Colorado River with limited success. Unsuccessful attempts to recapture tagged
fish has limited the ability of researchers to evaluate survival and dispersal of stocked individuals. It
has been hypothesized that high levels of predation on stocked fish are the reason for limited
recaptures. The relatively low predator density in the Dolores River is conducive to stocking juvenile
Colorado squawfish for purposes of assessing survival and dispersaL PIT-tagging the juveniles before
releases would allow for accurate recapture information on growth and distnbution of individual
squawfish. Biologically, the Dolores River appears suitable to provide needs for early life stages of
this species.

4.4.3 Chemoreception studies with adults

Chemoreception studies recently proposed in the Upper Basin could be conducted in the Dolores
River. Hatchery-reared individuals imprinted to a scent marker (i.e. morpho line ) could be introduced
into the Dolores River to test chemoreception and homing hypotheses. Suitability of the Dolores
River for this type of research is increased by low numbers of squawfish that are currently present
in the drainage.

5.0 SUMMARY OF FINDINGS

1. Four Colorado squawfish were captured in the lower 2 km of the Dolores River in August
and October, 1991.

2. Physical habitat of the Dolores River was suitable for adult and juvenile Colorado squawfish,
although extremely low flows observed during the study may have restricted fish access from
the Colorado River and impaired movement within the Dolores River drainage.

3. Water quality of the Dolores River was suitable for Colorado squawfish and other native
species, although high levels of copper and iron were found during spring runoff and rain
spates.

4. Macroinvertebrate densities and high numbers of native and non-native forage fish species
indicate that the Dolores River is biologically suitable for Colorado squawfish.

5. Non-native fish represented 87% and 68% of the catch in 1990 and 1991 respectively,
indicating a potential for predation and competition with native species. Since the percentage
composition of non-natives in the Dolores River was relatively lower than other upper basin
rivers, predation and competition by non-natives was not considered a limiting factor for
native fish species.

6. No major changes in fish composition and numbers occurred as compared to the USFWS
survey in 1981.