WSP12629 ‎(2)‎

• File Number: 8240.200.10.H
• Description: Upper Colorado River Endangered Fish Program
• Basin: Colorado Mainstem
• Date: 10/15/2001
• Author: Thomas P. Nesler CDOW
• Title: Stocking Plan for Endangered Colorado River Fish Species in Colorado
• Water Supply Pro - Doc Type: Publication

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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 survival 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 species' 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 recovery goal criteria for fish
population abundance and upon survivorship curve estimates for bonytail provided in Table 2.
The target stocked adult population abundance of bonytail was set at 5,720 fish spread over Ages
4-6 for each of two rivers. The target abundance is equivalent to the draft recovery goal
abundance criterion of 4,400 adult fish (USFWS 200lc) plus additional buffers of 40% for the
Age 4 cohort and 30 % for the Age 5 and 6 cohorts (based on presumed annual mortality at each
age). Twelve thousand, Age 2+, 200 nun bonytail would be stocked annual in each river
designated. These stocking objectives are subject to the following assumptions:

1) Adult riverine habitat is not limiting in the target river reaches for bonytail and the
recovery goal population abundance objective is below the carrying capacity of the target
river reaches.

2) Establishment of bonytail at or above the abundance criterion may cause reduction in
biomass of other native species as a result of some competition for available resources.

Reach priorities were based on the following considerations:

1) Bonytail were collected from the Green and Yampa rivers near their confluence at Echo
Park (Vanicek and Kramer 1969, USFWS 1987). 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 200 nun) should be reintroduced there and upstream
through Ladore and Yampa Canyons within Dinosaur National Monument.

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) of bonytail
inhabiting larger riverine habitat like the Colorado River near Moab, Utah, where
floodplain habitat was more likely to exist. .

It is obvious the above two reaches are quite different from a habitat perspective. Similar to other
aspects of setting stocking objectives for bonytail, considerable guesswork is involved. Depending

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