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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under the present circumstances of low to non-existent population numbers. Attempted spawning
and the production of viable eggs and larvae by these stocked populations will constitute the fIrst
step in conversion to desired natural function and self-sustaining status for these stocked
populations.

For razorback sucker and bonytail, no other recovery action provides an effective and
timely means of rel:toring wild populations in those river reaches designated within the Genetics
Management Plan. Success in achieving these stocking objectives could result in the establishment
of 1-2 bonytaiI populations where there are presently none; and 1-3 razorback sucker populations
in the Colorado River to complement the existing two in the middle and lower reaches of the
Green River. For Colorado pikeminnow, success would result in expansion of the Colorado River
population with potentially new tlistinct spawning aggregations in Debeque Canyon of the
Colorado River and in Dominguez Canyon in the Gunnison River. Construction of fIsh passage
structures on the Colorado River to achieve connection and tlispersal similar to that observed at
Redlands on the Gunnison River remains a critical component of recovery actions necessary to
complement restoration stocking.

Stocking Plan SunllDary

The stocking plan is presented for each species by river reach, and by fIsh size and season
in which stocking will occur over a seven to nine-year period. Numbers of fIsh required via
propagation for stocking are presented in Table 1 for each species and river reach described by
fIsh size, season, number of fIsh stocked annually and number of years stocked. It is proposed
that restoration stocking is desirable for three of the endangered Colorado River fIshes (listed in
priority): razorback sucker, bonytail, and Colorado pikeminnow. Table 2 provides the
survivorship curves used to back-calculate from the target numbers proposed as an objective for
each species to detemtine numbers of fIsh needed at each age/size. These survival rates and fish
sizes were estimated in Ryden (1997) and Wydoski (1996) for a hatchery environment, and further
modified and adapted by the Upper Colorado River Recovery Biology Committee on 09/26/2001
for use in stocking plans for Colorado and Utah. The Committee recognizes these survival rates
may underestimate mtural survival and, therefore, the numbers of fIsh needed to meet stocking
objective endpoints in a wild setting. Due to the uncertainty in survival, a buffer equal to the
presumed annual adult mortality in the wild was added to the draft recovery goal abundance
criterion for each species to detennine the target stocking number objectives. The goal of stocking
for each species is the establishment of a multiple-age group population of a desired abundance
level in each location. Stocking would be conducted over the seven to nine-year period as shown
in order to meet these criteria, but would be modified by numbers stocked, size, season, or
location based on monitoring results. An evaluation of the monitoring data following the
completion of the stocking should be accomplished to integrate the annual results. These stocking
objectives may also b~ modified in the future based on any revisions made to the draft recovery
goal abundance criteria during the fmal review process currently underway.