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

EXECUTIVE SUMMARY

The primary focus of this study was to determine how well populations of non-native
warmwater gamefish species are adapting to the riverine environments in the Yampa and
Colorado rivers, and to evaluate potential impacts from predation, competition, and habitat use.
Limitations imposed on these gamefish species by environmental conditions in these two rivers
will help define the problems posed by these species on the native fishes, and may also indicate
recovery measures necessary to minimize negative interactions with the endangered fishes. The
intent of the three primary objectives was achieved, and actually enhanced with the extended
year of sampling in 1991. The data collected were sufficient to assess population abundance
trends, movements, habitat use and diet of northern pike and channel catfish relative to their
existing or potential negative interactions with Colorado River endangered fishes in the Yampa
and Green rivers. The data collected also was adequate to review the need for potential control
options.

Northern pike are abundant in the Yampa River at Craig, Colorado and upriver, and
appeared to be greater in relative abundance compared to Colorado squawfish within common
river reaches during the study period. Northern pike abundance in the river reaches occupied
by Colorado squawfish did not demonstrate a relationship with spring runoff magnitude and is
reliant upon immigration of individuals from upstream sources. The riverine population of
northern pike is dependent upon an influx of fish from off -channel ponds and sloughs during the
spring runoff. These off-channel habitats are also the primary sources of successful reproduction
for northern pike and occur most commonly in the river reaches at Craig, Colorado and upriver.
The flow regime highly constrains successful reproduction by northern pike in the downstream
reaches occupied by endangered Colorado River fish species due to lack of suitable spawning
habitat. The northern pike population in the Yampa River is no longer expanding, and fluctuates
in response to environmental variables limiting carrying capacity. The Yampa River does serve
as a chronic source of adult northern pike to the middle Green River. The fish species available
to northern pike as prey are predominated by non-native fish species and sub-optimal prey sizes.
Colorado squawfish are minimally exposed to predation threat from northern pike and have
demonstrated no significant negative population trend as yet that could be exacerbated by
northern pike predation. Roundtail chub appears to be the native fish species most adversely
affected by, and vulnerable to northern pike predation. Extrapolation of northern pike diet in
the Yampa suggests humpback chub and juvenile Colorado squawfish may be exposed to greater
predation risk downstream of the study area.

Channel catfish in the Yampa River above Yampa Canyon are represented by a relatively
small population in marginal riverine habitat at the edge of the species' habitable range. This
population must be maintained from reproductive sources downstream. Thermal regime and
habitat conditions in the Yampa create a gradient that progressively limits adult maturation,
spawning, and development of young with increasing distance in upstream location. Channel
catfish appear relatively ineffective as piscivores and rely on an omnivorous diet predominated
by insects and plant matter. Colorado squawfish in the Yampa River appear highly invulnerable
to channel catfish predation and, in general, associated populations of both native and non-native

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