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

Hatchery has been the primary safeguard against extinction. This approach, while reasonable
in the short term, reduces the probability of maintaining the full range of heterogeneity of the
remaining wild gene pool through long term selection for domestication and survival in a
hatchery environment. Lack of a planned breeding strategy to incorporate all individual fish
over time, continued reproduction by bonytail most suited for sUlvival and growth in the
hatchery ponds, and the continued mortality of bonytail individuals with survival traits that
may be more suited to riverine environments further reduces the remaining genetic diversity
of the captive stock with each successive year in captivity, and further reduces the specie's
potential fitness in the riverine environment.

As such, rapid expansion of bonytail genetic material with input from as many
individuals as practicable, and stocking of large numbers into basin rivers with a diversity of
habitat types is imperative to exploit any remaining wild or riverine survival traits still
carried in the captive population. The numbers desired for stocking are based on fish species
density data derived from Anderson (1997) for the Colorado River reach from Rifle to
Debeque Canyon, and upon survivorship curve estimates for bonytail provided in Table 4. A
biomass target was not used here because no reliable information exists about the average
size of wild, adult bonytail in a riverine environment. The target abundance of bonytail was
set at 400 fishlmile based on the following assumptions:

1) the fish community in the Colorado River from which population estimates in
Anderson (1997) were made was at carrying capacity. (Note: the target abundance
was not taken directly from Anderson (1997) since the two study reaches
demonstrated roundtail chub densities ranging from 413 fishlmi in the Debeque
Canyon reach to 164 fishlmi in the Parachute reach. The higher estimate was chosen
arbitrarily as the target).

2) abundance of bonytail would be similar to the observed abundance of another "big
river" Gila species, the roundtail chub, in the upper Colorado River reach. There is
no factual evidence to suppon this assumption. The probability of revising a target
abundance level for this species is high following 2-3 years of stocking and
monitoring experience.

Reach priorities were based on the following considerations:

1) Bonytail were collected from the Green and Yampa rivers near their confluence at
Echo Park (USFWS 1987, Vanicek and Kramer 1969). While this site tends to refute
the floodplain habitat need hypothesis in (2) below, bonytail juveniles of the same size
collected in previous studies (up to 200mm) should be reintroduced there.

2) Bonytail will be introduced in the Grand Valley reach of the Colorado River due to a
presumed distribution throughout the mainstem Colorado and larger tributaries like the
Green River, and a hypothesized need for floodplain habitat. This hypothesis has not
been adequately tested, but is suggested by the anecdotal evidence (Quartarone 1993)

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