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

Executive Summary

The greatest number of adult razorback sucker Xyrauchen texanus captured in the Upper
Colorado River Basin have been collected in floodplain/low gradient reaches of rivers. In
addition, the greatest number of juvenile and sub adult razorback sucker have been collected in
depression wetlands within these same low gradient floodplain reaches. During the high water
years (1995 and 1996) of this study, favorable zooplankton densities, water temperature, water
quality, depth and cover existed in floodplain depressions to support age-O razorback sucker and
other fishes. Conversely, main channel habitats were not conducive as rearing sites for larval
razorback sucker due to lower temperatures, less food and no cover. During spring runoff in
1995 and 1996, larval razorback sucker were found in the river after floodplains were isolated
from the Green River. Thus, although favorable nursery sites are located off-channel,
connectivity of the river and floodplain did not last long enough for all razorback sucker larvae to
access these areas. Maintaining connectivity of the floodplain to the river via levee removal and
flood flow duration will increase access and use of favorable nursery habitat to larval razorback
sucker in the Middle Green River.
Old Charley Wash continued to provide favorable rearing sites for age-O native and
nonnative fish in the summer months of 1995 and 1996. In two successive high flow years, wild
razorback sucker larvae survived and grew in a floodplain wetland dominated by nonnative
predators and competitors. If the number of razorback sucker juveniles captured in Old Charley
Wash was extrapolated to the area of available depression wetlands (Stewart Lake, Sportsman
Lake, Leota Bottoms, Johnson Bottoms, Wyasket Lake and Old Charley Wash) in the Middle
Green River, a minimum of363 and 582 wild, acclimated age-O fish 100-125+ mm long would
have been produced in the Middle Green River in 1995 and 1996, respectively. Because flows in
the Green River were historically of greater magnitude and nonnative fishes were not present,
razorback sucker may have been able to recruit in both depression and terrace wetlands.
However, under the current reduced flow conditions, and dominance of nonnative fishes in both
main channel and floodplain habitats, depression floodplains offer the greatest probability for
rearing razorback sucker age-O fish. In this regard, the availability of floodplain wetlands to
razorback sucker could be a primary factor in recovery of the species.
This study suggested that larval razorback sucker are more likely to survive and grow in
floodplain depression habitats than in main channel habitats. While providing favorable habitat
for razorback sucker, however, an inordinate biomass of nonnative fishes was produced in Old
Charley Wash. Although it appeared that age-O razorback sucker grew and survived in an
environment dominated by nonnative predators and competitors, questions exist on the potential
impact of nonnative fish produced in floodplain wetlands that may reach the main channel of the
Green River. Therefore, questions emerge from this study concerning nonnative fishes that
include: 1) what would be the impact of releasing large numbers ofnonnatives produced in
depression wetlands into the Green River and 2) and if a negative impact occurs, does it offset
the benefits realized from razorback sucker recruitment?

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