7849

• UCREFRP Catalog Number: 7849
• Author: Nesler, T. P.
• Title: Interactions Between Endangered Fishes And Introduced Gamefishes In The Yampa River, Colorado, 1987-1991.
• USFW Year: 1995.
• USFW - Doc Type: Final Report, Colorado River Recovery Implementation Program Project No. 91-29 and Federal Aid Project SE-3,
• Copyright Material: NO

fish'species appear less vulnerable to potential predation by channel catfish compared to northern
pike. Presence of fish prey in the channel catfish diet is likely to result from the ingestion of
dead and disabled individuals.

Colorado squawfish adults share backwater habitat during runoff and pool habitat year-
round with both northern pike and channel catfish. Habitat competition or avoidance by
Colorado squawfish was not apparent. Northern pike and channel catfish were a significant
portion of the fish community using backwater habitats in the Yampa River. Physical habitat
attributes preferred by northern pike are limited in the Yampa River as a result of the fluctuating
flow regime and consequently spawning, reproductive success, and the carrying capacity of the
riverine northern pike population is also limited. Northern pike and channel catfish are
vulnerable to control by removal in reaches of the Yampa River occupied by Colorado squawfish
due to their attraction to limited spring backwater habitat, sedentary tendency, and lack of
reproductive success. Effectiveness of removal efforts from backwater habitats had mixed
results, showing declines in northern pike catch rates at some sites and increases elsewhere.
Generally, catch rates in backwaters decreased for northern pike and channel catfish and
increased for Colorado squawfish and roundtail chub during the study period. Effectiveness of
control of either species in river reaches shared with endangered fishes is problematic due to
their common distribution and reproductive success within large river segments. Escapement
of northern pike from off -channel pond habitat and access to suitable riverine spawning habitat
would have to be reduced on the same widespread scale to be effective in reducing the
abundance of the riverine population. Roundtail chub would benefit most from effective
northern pike control, but this and any indirect benefits to Colorado squawfish may be
diminished by a negative sampling effect on use of these habitats by adult Colorado squawfish.

It is recommended control options for northern pike and channel catfish be evaluated in
the context of non-native control priorities for the Upper Colorado River Basin Recovery
Program. An experimental project for control of northern pike and channel catfish in reaches
of the Yampa River occupied by endangered Colorado River fishes should be implemented to
test for feasibility, effective reduction of target species at desired removal rates, and positive
response via roundtail chub abundance, more frequent occurrence of smaller size of Colorado
squawfish recruits into the adult population, and reduced downstream occurrence of northern
pike in Yampa Canyon and the middle Green River.

Key words: Colorado River Basin, northern pike, channel catfish, endangered fishes,
predation, competition, habitat use, movements, reproduction, non-native fish
control

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