8114

• UCREFRP Catalog Number: 8114
• Author: Nesler, T. P.
• Title: Five-year Stocking Plan for Endangered Colorado River Fish Species in Colorado.
• USFW Year: 1998.
• USFW - Doc Type: Denver, CO.
• Copyright Material: NO

larval production and recruitment in the Colorado River and Gunnison River populations in
the short tenn, while other recovery actions target improvement of survival and recruitment
of this species to preclude the need for augmentation in the long tenn. At this time, the
development of a Colorado River brood stock is incomplete, and needs to be resumed with
the collection of additional adult fish from the Colorado and Gunnison rivers to supplement
the 17 family lots created from the 5x5 breeding matrix of Colorado River fish only. Since
the construction and operation of the Redlands fish passage structure, which has resulted in
the passage of early-adult stage Colorado pikeminnow into the Gunnison River, and
pUlposeful translocation of adult Colorado pikeminnow from below the barrier to the river
above, mixing of the genetic material between the populations occurring in the two rivers is
being accomplished, and is acceptable. Results from Anderson (1998 draft) have
demonstrated that some spawning and production of drifting Colorado pikeminnow larvae
occurred in the Gunnison river above the Redlands diversion dam in 1994-1996. Planning
for the acquisition of the necessary fish and development of an acceptable mating strategy to
incorporate existing genetic material from Gunnison River Colorado pikeminnow into the
existing broodstock should be initiated as soon as possible by the Propagation Coordinator
for the Recovery Program.

The initial development of brood stock for Colorado pikeminnow from the Grand
Valley reach of the Colorado River was conducted according to appropriate guidelines
(Williamson and Wydoski 1994), so that this broodstock and its progeny should reflect the
genetic diversity present in the wild population. Expansion of the existing brood stock using
wild Colorado pikeminnow from the Gunnison River fish seems logical and appropriate
according to the genetics management guidelines. This expansion should also include
consideration of annual capture and spawning of wild adult fish. From this perspective, the
genetics risks associated with broodstock development are negligible. The risk assessment
targets two issues: (1) the genetic impacts of restoration stocking of hatchery-reared fish in
river reaches located upstream of occupied habitat compared to natural or enhanced (via
translocation) recolonization of habitat by passage of fish past barriers with little or no
genetic impact, and (2) movement of stocked fish downstream into reaches occupied by wild
Colorado pikeminnow.

Osmundson and Burnham (1996) estimated the population size of Colorado
pikeminnow in the Grand Valley reach of the Colorado River to be about 250 fish or 4/mile,
and 340-390 fish or 3-3.4/mile in the Utah reach below Westwater Canyon. Their
assessment of the status of this population was low numbers of Colorado pikeminnow adults
are likely the result of insufficient reproductive success and recruitment during most years,
that production of strong year classes to sustain adult abundance is more infrequent now than
historically, and the estimated abundance level was below the theoretical effective population
size threshold to maintain genetic viability. The authors indicated this population was
vulnerable to extinction due to stochastic demographic fluctuations. Osmundson et al. (1996)
estimated a 0.86 survival rate for the existing population. Osmundson and Burnham suggest
a 4 % increase in survival while holding recruitment steady, or a 4 % increase in recruitment
while holding survival steady would result in a doubling of population size in 18 years.

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