8007

• UCREFRP Catalog Number: 8007
• Author: Modde, T.
• Title: Fish Use Of Old Charley Wash
• USFW Year: 1997.
• USFW - Doc Type: an assessment of floodplain wetland importance to razorback sucker management and recovery.
• Copyright Material: NO

irrigation canals and ponds below Parker Dam (Minckley et al. 1991), providing little optimism
for development of self-sustaining populations. The majority of floodplain habitat in the
Colorado River has been lost by inundation within reservoirs, channelization, or reductions in
spring flood flows (Minckley and Deacon 1968, Carlson and Muth 1989) resulting in recruitment
failure and decline of existing populations through attrition (Minckley 1983). Conversely, the
Middle Green River retains much of its floodplain habitat (Irving and Burdick 1994) even though
inundation is reduced from predam conditions (Flo Engineering 1996). Wick et al. (1982) stated
that recovery of the razorback sucker will be dependent on identifying impediments to
recruitment. The growth and survival of age-O razorback sucker in Old Charley Wash suggested
that reproductive success and recruitment of this species is possible if suitable habitat is '
provided, despite the presence of large numbers of predacious and competitive nonnative fishes.
Thus, if historical nursery habitat can be provided for razorback sucker, predation by nonnative
fishes will be a secondary rather than a prevalent force impacting extirpation of the species
(Minckley 1983).

Conclusions and Management Recommendations

The greatest number of adult razorback sucker captured in the Upper Colorado River
have been collected in floodplain/low gradient reaches of rivers. In addition, the greatest number
of juvenile and subadult razorback have been collected in floodplain wetlands within these same
low gradient reaches. During high flow years of this study, larval razorback sucker captured in
the main channel were coincident with peak zooplankton densities and favorable temperatures
for growth in Old Charley Wash (and presumably other inundated floodplains). Therefore,
floodplain habitat represents the best nursery environment available in the Middle Green River
when larval razorback sucker appear. Favorable water quality and quantity and prey densities
were available to support age-O fish in Old Charley Wash through the summer months. In two
successive high flow years, razorback sucker used a floodplain wetland and some survived in an
environment dominated by nonnative predators and competitors. If the number of razorback
sucker juveniles captured in Old Charley Wash was extrapolated to the area of depression
wetlands available (Stewart Lake, Sportsman Lake, Leota Bottoms, Johnson Bottoms, and
Wyasket Lake) in the Middle Green River, a minimum of 362 and 582 wild, acclimated age-O
fish 75-125 mm long would have been produced in the Middle Green River system in 1995 and
1996, respectively.
However, during both high flow years of the study, larval razorback sucker were collected
in the main channel for at least two weeks after Old Charley Wash was disconnected from the
Green River. Therefore if higher flows (447 m3/s) were extended another two to three weeks,
larval razorback sucker in the main channel would have had a greater opportunity to access
floodplain/wetland habitats. Historically, the Green River at Jensen peaked after the Yampa
River (28 May, versus 21 May, U.S. Bureau of Reclamation, unpublished data) and provided
longer duration of higher flows prior to the construction of Flaming Gorge Dam. Currently, the
flows from the Yampa River alone did not maintain floodplain inundation long enough to
provide floodplain access for all razorback sucker in the river.
An alternative to the use of depression floodplains (i.e., floodplains that maintain water
after river flows recede) is to breach levees and manage them as terrace floodplains (i.e.,
floodplains that dewater as river flows recede) that would reduce reproductive success of

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