8215

• UCREFRP Catalog Number: 8215
• Author: U.S. Fish and Wildlife Service.
• Title: Final Environmental Assessment
• USFW Year: 1997.
• USFW - Doc Type: Management and Control of Noonative Fish Species in Floodplain Ponds of the Upper Colorado and Gunnison Rivers.
• Copyright Material: NO

suckers were also documented in riverside ponds along the
Upper Colorado River -where predatory fishes were absent
(Osmundson 1986; Osmundson and Kaeding 1989). These
observations support the belief that predation has contributed
to the decline of some native Colorado River fishes.
(2) Impact of Competition on Native Fish Fauna. Competition by
two species occurs when food is limited, the food is shared,
and one of the two species is adversely affected by sharing
food (Moyle et al. 1986; Li and Moyle 1993). Low numbers of
zooplankton occur in the main channel and backwaters of rivers
(i.e., food is limited for early life stages of fish) in the
Upper Colorado River Basin (Cooper and Severn 1994a, b, c, d;
Grabowski and Hiebert 1989; Mabey and Schiozawa 1993).
Dietary overlap was reported between nonnative and native
fishes (i.e., food is shared) in the Upper .Colorado River
(Jacobi and Jacobi 1982; Grabowski and Hiebert 1989).
Nonnative fishes have expanded rapidly in the Upper Basin
between 1986 and 1992 as indicated from the Interagency
Standardized Monitoring Program where they constitute 96.7 to
99.6% of the total numbers of fish collected from backwaters
by seining (McAda et al. 1994a,b; 1995; 1997). Native and
nonnative fish share the same backwater habitats (Valdez and
Wick 1983). Although direct competition among endangered
fishes by nonnative fishes has not been documented, limited
food resources, sharing of the food resources, and use of the
same habitats with low water velocity supports the belief that
competition has also contributed to the decline of some native
Colorado River fishes.
II. ALTERNATIVES CONSIDERED
Five alternatives were considered in this Environmental Assessment regarding the
control of nonnative, warmwater fish species in floodplain ponds along the
Colorado and Gunnison rivers. Alternatives 2, 3, and 4 offer several methods
that offer control of chronic escapement of the nonnative fishes.
A. Alternative 1 - No Action. Under this alternative, nonnative, warmwater
fish species in floodplain ponds along the Colorado and Gunnison rivers
would continue to enter the river through outlets or during high streamflows
that connect the ponds with the rivers.
6. Alternative 2 - Mechanical or Chemical Control of Nonnative Fish Species
From Ponds in the Floodplain. Under this alternative, mechanical (i.e.,
draining ponds, netting, electrofishing, etc.) or chemical (i.e., use of
registered piscicides) control methods would be used to remove nonnative
fish species from floodplain ponds along the Colorado-and Gunnison rivers.
C.
Floodplain to Prevent Chronic Escapement of Nonnative Fish Species. Under
this alternative, mechanical devices (i.e., screens or traps) would be
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