9498

• UCREFRP Catalog Number: 9498
• Author: Nesler, T. P.
• Title: Stocking Plan for Endangered Coloraod River Fish Species.
• USFW Year: 2001.
• USFW - Doc Type: Denver.
• Copyright Material: NO

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used will receive implanted, unique PIT tags, and selection criteria for paired matings includes
only no duplicate use of any adult fish used in previous matings. This strategy using wild
Colorado pikeminnow from the Colorado and Gunnison Rivers is 10gicaI and appropriate given
the availability of wild adult fish and priorities based on available fish according to the genetics
management guidelines. Using this strategy, the genetics risks associated with production of
progeny for restoration stocking 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 theoreticaI effective population size threshold to maintain genetic viability.
The authors indicated this population was vulnerable to extinction due to stochastic demographic
fluctuations. Osmundson et aI. (1996) estimated a 0.86 survivaI 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 survivaI steady would result in a doubling of
population size in 18 years.

This review and evaIuation of population status and recruitment potential for the Grand
Valley population of Colorado pikeminnow does not lend much support for the efficacy of
depending upon natural recolonization of the target unoccupied reaches of the upper Colorado and
Gunnison by the existing adult population, or using the Grand Valley adult population as a donor
for translocating sufficient numbers of fish above the instream barriers in one or both reaches to
create an effective population size in a timely manner. Translocation raises concern over
additional risks that include:

1) reproductive success of translocated adult fish taken from a home range; it cannot be
assumed to be the same in the new environment for a species with a complex spawning
behavior. (Conversely, the expectation of reproductive success in stocked populations must
also be.tested through monitoring.)

2) the complex reproductive cycle of this species, including factors of imprinting,
chemoreception, learned behavior, or other instinctuaI behaviors are not understood.

3) reproductive tradeoffs cannot be assumed equaI or insignificant between established
patterns in Grand Valley sites and new sites upriver with respect to spawning behavior,
spawning success, hatching success, and larval and young-of-the-year survival.

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