8123

• UCREFRP Catalog Number: 8123
• Author: Wydoski, R. S.
• Title: Coordinated Hatchery Facility Plan
• USFW Year: 1994.
• USFW - Doc Type: Need for Captive-Reared Endangered Fish and Propagation Facilities.
• Copyright Material: NO

length when they would become sexual mature after the third
growing season.
Razorback suckers and Colorado squawfish will mature after six
growing seasons when they are about 17 inches in total length
based on estimates of growth for the Upper Colorado River Basin.
Growth of both species has been exceptional in off-channel ponds
where razorbacks will be large enough to be sexual mature after
the second growing season and the squawfish after the fourth
growing season.
There are differences of opinion among biologists as to the size of
fish that should be used in augmentation and restoration stocking.
Marsh (1988) emphasized that stocking of large fish to enhance
survival by reducing competition and predation in early life stages
may result in re-establishing adults but still fail in recovery if
natural recruitment does not ensure self-sustaining populations. In
addition, there is a high risk of reducing genetic variability in
captive propagation and stocking of early life stages (Dowling and
Minckley 1993). Dowling and Minckley recommend the capture of wild
razorback sucker larvae from Lake Mohave and rearing them in
protected sites rather than stock captive-reared fish. They
emphasize that larvae from larger numbers of wild adults would
provide more genetic variability than could be realized from the most
favorable hatchery conditions. Therefore, all stocking must be done
carefully while considering all potential risks. There is general
agreement by Biology Committee members that augmentation and
restoration stocking should be done experimentally so that adequate
evaluations can be made before attempting any large-scale stocking of
endangered fishes in the upper basin.
Specific Recommendation 1. The Program should review the
guidelines in this plan, revise if necessary, and adopt a policy
for the stocking of captive-reared endangered fishes in the Upper
Colorado River Basin. All fish stocked into upper basin waters
become part of the ecosystem and potential risks should be
carefully evaluated to ensure that any potential adverse affects
of stocking on wild stocks of the endangered fishes are avoided
or minimized.
The relation of natural propagation to artificial propagation is
illustrated in Figure 2. Although natural propagation is preferred
in the recovery of wild endangered fish stocks, captive propagation
and stocking of endangered fishes in the Upper Colorado River Basin
may be necessary if stocks are low and declining because recruitment
cannot replace the mortality of old fish. In some instances, a
critical level of abundance may be needed for adult fish to spawn
successfully (Lande 1988; Larkin 1981).
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