9688

• UCREFRP Catalog Number: 9688
• Author: Upper Colorado River Endangered Fish Recovery Program.
• Title: Nonnative Fish Control Workshop Summary, Conclusions, and Recommendations.
• USFW Year: 2002.
• USFW - Doc Type: Lakewood, CO.
• Copyright Material: NO

and 1996 the principal objectives were to determine the presence of razorback sucker in the
wetland. However, large numbers of nonnative fishes were collected during the draining process
and the Recovery Program continued to monitor Old Charlie Wash for several years for the
purposes of determining the occurrence of razorback sucker and to remove nonnative fishes: The
drainage ditch in Old Charlie Wash began to fill with sediment and prevented complete draining
and census of the fish population in 1997 through 1999, after which the drain was cleaned.
Census data were provided during 1995, 1996 and 2001.
During 1995 and 1996, nonnative fish in Old Charlie Wash made up over 99.9% of the biomass
collected during both years, of which a minimum of 80% and 77%, respectively, originated from
the Green River prior to floodplain connection (Figure 4). These percentages do not"include the
biomass of small cyprinids that were collected in the wetland (5% in 1995 and 4% in 1966)
which could not be segregated, but many surely originated from the river. Thus, most of the
nonnative biomass collected from Old Charlie Wash originated from the river. Because most
fish originated in the river, the biomass offish present in the wetland was variable, ranging
between 32.4 kg/ha to 126 kg/ha. Although greatest numbers offish were <age-0, greatest
biomass was made up of >age-0 (Figure 5). Carp, fathead minnow, and green sunfish
consistently accounted for the greatest numbers and biomass offish in Old Charlie Wash (Table
2). Numbers of juvenile carp in backwaters were higher in some years (e.g., 1986, 1989),
indicating strong year classes, and numbers after draining Old Charlie Wash did not change
substantially in Green River backwaters (Figure 6). Average weights of carp in 1994 and 1995
were 597 and 490 g; channel catfish were 131 and 262 g, and black bullhead were 91 and 96~g,
respectively.
The biomass offish captured and removed from the wetland appeared to be related to the
duration ofinundation-(Figure 7). That is, the longer the wetland was connected to the river, the
greater number of fish present in the wetland. The relationship of total biomass offish
originating from the river and discharge duration is probably different for Old Charlie Wash and
wetlands that maintain water through the winter which allows the development of refuge
populations. Using water control structures that have been constructed, sites such as Old Charlie
Wash and Johnson Bottom have the potential to remove a larger biomass of nonnative fish than
is practical with other removal methodologies. However, the questions remaining are: 1)-are the
species that readily move into wetland depressions (i.e., carp, fathead minnow and to a lesser
extent channel catfish) species of concern relative to impacts on listed fishes, and 2) even though
large numbers offish are removed, can enough fish be removed to make a difference on the
existing riverine population?
The study concluded:
• most fish biomass collected in wetlands drained the previous "year consisted of
fish that entered from the river (i.e., adults and subadults);
• the number and biomass offish captured in OCW was positively correlated with
the duration of inundation;
cost of operation to remove fish low;
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