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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Given that the adult Colorado pikeminnow population is about 4 fish/mile in the Grand
Valley reach and 3-3.4 fish/mile in the Utah reach below Westwater, and recruitment of strong
year classes is currently infrequent, depletion of the donor population from either source appears
possible. If one considers the lower ends of the interval estimates provided in Osmundson and
Burnham (161 and 186 fish) rather than the midpoints, which are within the 95 % confidence limits
for estimated population size, then depletion of the donor population seems possible. Given a
survival rate of O. ~6 and the translocation of 10 fish/year, it would require the translocation of
100 adults over a 10 year period to create a new population of 55 fish. Reliance upon occurrence
of another strong year class during the period of translocation effects seems risky for a population
considered vulnerable to extinction from stochastic demographic changes.

This should not be construed as opposition to translocation as part of the strategy for
establishing Colorado pikeminnow populations in the unoccupied reaches of the upper Colorado
and Gunnison rivers. In addition to fish that use the Redlands passageway, it would also appear
desirable to translocate similar-sized fish captured immediately below the barrier within the plunge
pool downstream of the dam. This can be viewed as assisting the passage of fish that cannot or
will not use the constructed passageway and facilitating natural mechanisms of migration, dispersal
and recruitment. Osmundson et al. (1996) demonstrated significantly greater nonspawning
movements upstream for juvenile/early adult Colorado pikeminnow than for larger, older adults.
Though not stated explicitly by Osmundson et al., this attribute may be evidence of a population
dispersal mechanism by which young fish recruit into and thus maintain the upstream adult
populations. The use of the Redlands passage structure by mostly smaller, late juvenile Colorado
pikeminnow in 1996 (1 fish), 1997 (18 fish), 1998 (23 fish), 1999 (5 fish), and 2000 (4 fish)
(Burdick 2(01) may be intetpreted as preliminary support of this dispersal! recruitment hypothesis.
Without benefit of passage at the Colorado River barriers above Palisade, similar translocation of
Colorado pikeminnow captured below the barriers should be considered.

Natural recolonization of the upper Colorado River reach is also possible with the
placement of passageways around existing barriers similar to Redlands on the Gunnison, but the
success of these devices in terms of use by Colorado pikeminnow has yet to be established, both
in terms of numbers of fish and the contribution of observed rates of passage (e.g. number of fish
per season) to population goals for the Gunnison River or recovery goals for the species. Similar
to the translocation approach, though perhaps even more variable in terms of progress, natural
recolonization could require a long time period to establish an adult population of even 4 fish/ mile
(200 fish total) similar to the Grand Valley reach now. So that the Recovery Program may
achieve progress toward recovery goals in a timely manner, we recommend the stocking of
genetically compatible Colorado pikeminnow as a primary approach to extending the species range
and establishing adult populations within the unoccupied reach of the upper Colorado River and
in the Gunnison River. We further recommend that translocation of wild Colorado pikeminnow
of the appropriate life stage/size group continue as a supplementary approach, using fish (400-550
mm) captured in the plunge pools and immediate downstream reaches below the instream barriers
at Redlands on the Gunnison River and Price-Stubb and HigWine on the Colorado River. Finally,

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