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

reaches known to support humpback chub in Colorado, Yampa Canyon on the Yampa River and
Black Rocks on the Colorado River, research has failed to discover a significant threat of
extirpation to eit!ler population under current environmental conditions. This includes the
presence of an abundant and potentially predatory channel catfish population in both reaches. The
Black Rocks popuhtion has demonstrated a relative stability since monitoring began in the early
1980s (see Valdez 1980, Miller et al. 1982, Valdez and Clemmer 1982). Due to the relatively
unmodified flow l"('girne and habitat within Yampa Canyon and the persistence of the humpback
chub population monitored there since the late 1980s (see Tyus and Karp 1989), this population
is also presumed to be relatively stable. Also five natural populations currently exist in the Upper
Basin, and appear t<) have persisted in these locations in relatively stable numbers since their initial
discovery and identification. However, population estimates are planned to determine abundance
in all of these existing populations relative to desired abundance criteria required for recovery and
downlisting and d~listing. Other recovery program tools, such as nonnative fish control (e.g.
channel catfish) and flow management remain under evaluation as feasible and effective
approaches to increasing humpback chub population abundance in Black Rocks and Yampa
Canyon. Augmentltion stocking may be considered if population estimation results for the Yampa
Canyon population indicate expansion of humpback chub numbers in the Lodore, Whirlpool and
Split Mountain canyon reaches is desirable to augment the Yampa Canyon population. The
objective here would be to facilitate progress toward developing a self-sustaining population at
desired abundance level and composed of a complex of multiple subpopulations within these
adjacent canyon habitats.

Stocking Plan - Razorback sucker (Table 1)

Razorback Bucker are considered first priority for stocking in Colorado due to the presence
of, but declining trend of wild populations due to inadequate recruitment. Rationale for the
stocking is straighlforward. Populations of razorback previously occupied habitat in all three
target river reacheil (Holden et al. 1981, Burdick 1992), but are now nearly extiIpated, and
insufficient numben: exist in the wild upon which to base a natural expansion and recolonization
strategy. Factors thought to be responsible for the razorback sucker's decline include primarily
loss of floodplain habitats as nursery areas with concomitant establishment of nonnative fish
species as effective predators/competitors in remaining low-velocity nursery habitats. If
successful, stocking will establish a multi-year class population of razorback sucker late-juveniles
and adults that are largely invulnerable to predation. Threat of predation to razorback sucker
occurs primarily in the Grand Valley reach from existing populations of channel catfish and red
shiner, the most significant introduced species demonstrating abundant populations and
documented predation upon razorback sucker young in laboratory conditions (Muth and Beyers
1991). Monitoring of this population will track growth and survival to maturity, general habitat
use, use of available spawning habitat, and production and fate of larvae. Monitoring of stocked
populations will also provide clues to potential causes of failure to survive as well. The presence
of a long-lived aclult population attempting to reproduce will subsequently facilitate the
detennination of wh,ch presumed limiting factors-nursery habitat, predators, irrigation canal loss,

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