9591

• UCREFRP Catalog Number: 9591
• Author: Nesler, T. P.
• Title: Interactions Between Endangered Fishes and Introduced Gamefishs in the Colorado River, Colorado, 1986-1991.
• USFW Year: 2002.
• USFW - Doc Type: 91-29,
• Copyright Material: NO

STUDY GOAL AND OBJECTIVES

Goal: to detennine the impact of non-native, warmwater gamefish species via predation and
competition upon Upper Colorado River Basin endangered fish species.

Objectives:
1) to determine trends in relative abundance, distribution, reproductive success, and size
structure of non-native, non-salmonid gamefish populations in the Colorado River.
2) to detennine the incidence of predation by non-native, non-salmonid gamefish species upon
the endangered fishes.

STUDY AREA

The Portion of the Colorado River targeted in this investigation included the reach from
river mile (RM) 185, near Palisade, Colorado to RM 128, near the Colorado-Utah stateline. This
constitutes the reach of the Colorado River occupied by Colorado pikeminnow within Colorado.
Also, a population of humpback chub is located at Black Rocks on the Colorado River at RM 132
in Colorado. Restoration stocking of both razorback sucker and bonytail are proposed for this
river reach (Nesler 2(01). The confluence of the Gunnison River intersects this study reach at
RM 170. The study area includes the mainstem river as it emerges from Debeque Canyon and
flows through the bottomlands of the Grand Valley from Palisade, through Grand Junction, to
Lorna. Downstream of Lorna, the study reach includes 22 miles of river flowing through the
higher gradient terrain of Horsethief and Ruby canyons 1xmIering Colorado National Monument.

METHODS

At the initiation of this investigation, the primary point of interaction between nonnative,
nonsalmonid gamefishes and the endangered native fishes in the Colorado River was believed to
be in backwaters that represented deposition sites and nursery habitat for drifting larval Colorado
pikeminnow. This focus was unlike the Yampa River, where the interactions of concern were
primarily between aduh gamefish and aduh Colorado pikeminnow. Standardized fall seine
SUlVeyS of backwaters in the Colorado River for Colorado pik:eminnow were initiated through the
Interagency Standardized Monitoring Program (ISMP) in 1986, and were ongoing in river miles
(RM) 170-140 within the study area when sampling for this investigation was initiated in 1987.
The ISMP seine sampling approach was adopted for collecting data on gamefish species in
Colorado River backwaters, in part to avoid sampling interference between this project and ISMP
and in part because ISMP fall seine sampling was judged to be representative of species
composition in backwaters for small-bodied species and young and juveniles of large-bodied
species. In addition to the ISMP reach, RM 185-170, which constitutes the IS-mile reach of the
Colorado River above the confluence of the Gunnison River, and RM 140-128 were included as
part of this seine survey in 1987, 1988 and 1991. Seine sampling effort was reduced in 1989 and
1990 (by exclusion of the IS-mile reach segment) due to the small numbers of gamefish being

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