8211

• UCREFRP Catalog Number: 8211
• Author: U.S. Bureau of Reclamation and Fish and Wildlife Service.
• Title: Final Environmental Assessment
• USFW Year: 1997.
• USFW - Doc Type: Providing Fish Passage at the Grand Valley Irrigation Company diversion Dam on the Colorado River.
• Copyright Material: NO

of the Colorado River upstream from the diversion dams; however, a stocking plan has not been
approved at this time.
The Recovery Program has initiated several other actions to aid in the recovery of the endangered
fishes, including management of nonnative fish species and acquisition and restoration of
floodplain habitat.
A strategic plan was developed by Recovery Program participants to manage or control nonnative
fish species that are believed to adversely affect the endangered fishes through predation and
competition (Tyus and Saunders 1996). Nonnative fish species compose 76 percent (42 of 55
species) of the fish community in the Upper Colorado River Basin (Tyus et al. 1982). In addition,
nonnative fishes in backwater habitats constitute most of the fish by number (96.7 - 99.6 percent)
in the Upper Basin (McAda et al. 1994 a,b; 1995). Recovery Program participants identified an
urgent need to manage or control nonnative fish species in the Upper Basin to increase survival
and recruitment of the endangered fishes. Some of the nonnative fishes were introduced for
sportfishing and biologists worked cooperatively to develop "Procedures for Stocking Nonnative
Fish Species in the Upper Colorado River Basin (Colorado Division of Wildlife et al. 1996). The
intent of these procedures is to allow stocking of nonnative fish species for warmwater
sportfishing opportunities in the Upper Basin that would be compatible with recovery of the
endangered fishes. Presently the Colorado River upstream of the diversion dams contains mostly
(83 percent) native fish species (Anderson 1997). Although a fish control device such as a trap is
not proposed for the fish passageway at the GVIC Diversion Dam, such structures will be
required to prevent colonization of the Colorado River upstream of the diversion dams by
nonnative fish species.
The declining numbers of some endemic Colorado River fishes is attributed to the lack of
recruitment. Although the long-lived adult endangered fishes spawn successfully and produce
larvae (recently hatched fish), high mortality during the early life stages limits recruitment. Larval
fish must initiate feeding during the "critical period" after hatching or they will reach a point of no
return when high mortality occurs from starvation (Miller et al. 1988). The larvae and juveniles of
all endangered Colorado River fishes feed on zooplankton (Miller et al. 1982). The density of
zooplankton needed for larval razorback sucker survival must be between 30 to 60 organisms per
fish per day (Papoulias and Minckley 1990). This number of organisms occurred in flooded r
bottomland habitats in the Upper Colorado River Basin but rarely reached that density in
backwaters, and never reached it in the river. Floodplain habitats produce the highest densities of
zooplankton that would meet the food requirement during their early life stages for razorback
suckers. Recovery Program participants identified an urgent need to acquire and reconnect
floodplain habitats with the riverine environment to increase the survival of endangered fish
larvae, particularly razorback sucker larvae, to develop self-sustaining populations that would
constitute recovery. Although runs and pools provide suitable habitat for the Colorado squawfish
and razorback suckers in the Colorado River upstream of the diversion dams (Anderson 1997),
floodplain habitat is lacking and believed to be limiting in this reach (Kidd 1996).
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