9490

• UCREFRP Catalog Number: 9490
• Author: U.S. Fish and Wildlife Service.
• Title: Final Environmental Assessment for Procedures for Stocking of Nonnative Fish Species in the Upper Colorado River Basin.
• USFW Year: 1996.
• USFW - Doc Type: Grand Junction.
• Copyright Material: NO

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the confluence with the Colorado River for which floodplain information
existed (17 ponds), none were above the 100-year floodplain, 9 were
located between the 50-100 year floodplains, 6 were between the 10-50
year floodplain, and 2 were below the 10-year floodplain. Maps with
sufficient detail were not available to determine the 10-year
floodplain boundaries on other rivers.
Less than five ponds have been permitted for warmwater fishes in the
Green River Basin in Utah. Most pond permits issued in Utah have been
for salmonids (trout). It is unknown whether any of the ponds
containing warmwater fish are in the floodplain. The last pond
permitted in Utah for warmwater fish followed the draft stocking
procedures that were being considered at that time. They therefore
]ocated the pond above the floodplain. No private ponds used for
warmwater fishing are known to occur in the portion of Wyoming covered
by these procedures. The only floodplain pond is near the Town of
Baggs along the Little Snake River and is stocked with trout provided
by the Wyoming Game and Fish Department.
V. IMPACT ASSESSMENT/ENVIRONMENTAL CONSEQUENCES
While physical habitat parameters have an influence on the ability of a
species to compete against other species, the evolutionary history of
both species also plays an important role. Species that evolved in
river basins supporting large numbers of species are usually more
aggressive and successful competitors than species from depauperate
basins. As discussed previously, the Colorado River Basin fish fauna
is a depauperate one and competition was limited. Most of the
introduced nonnative fish species are from basins with larger and more
varied fish faunas, and evolved in very competitive environments.
Nonnative fish may physically compete for space and food with native
species. Other adverse effects include direct predation, harassment or
the introduction of diseases or parasites. Predation, especially on
egg, larval and juvenile stages, is a significant factor in determining
population survival through the effects to recruitment. Research has
shown that nonnative fish play an important role in suppressing native
fish recruitment. Spawning adults of the four Colorado River
endangered fish can be found during the breeding seasons. Actual
spawning has been documented for all species and larvae have also been
found. Yet recruitment of juveniles into these populations is very
low.
Tyus and Saunders (1996) summarized scientific studies in the Colorado
River Basin that documented predation as follows: "Direct proof of
predation by nonnative fishes on the native species in the Colorado
River basin included reports by Jonez and Sumner (razorback sucker eggs
eaten by common carp; 1954); Coon (Colorado squawfish eaten by channel
catfish; 1965), Taba (Colorado squawfish and chubs eaten by bullheads;
1964), Meffe (Sonoran topminnow eaten by mosquitofish; 1985); Langhorst
and Marsh (razorback sucker eaten by green sunfish; 1986), Hendrickson
and Brooks (Colorado squawfish eaten by smallmouth bass and bullheads;
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