8158

• UCREFRP Catalog Number: 8158
• Author: Osmundson, D. B.
• Title: Longitudinal Variation in Fish Community Structure and Water Temperature in the Upper Colorado River; Final Report.
• USFW Year: 1999.
• USFW - Doc Type: Grand Junction, Colorado.
• Copyright Material: NO

At least four major changes have occurred in the upper Colorado River system during the past
century that could account for the mechanisms listed above. These are: (1) diversion
structures that blocked access to upstream reaches of historic habitat in both the mainstem
Colorado and Gunnison rivers, and cold-water releases from storage projects on the Gunnison
River that seasonally reduce downstream temperatures and thereby reduce the extent of
suitable habitat; (2) nonnative species that likely altered the energy flow in riverine food webs;
(3) storage and diversion projects that led to a reduction in magnitude of the spring flood
pulse resulting in a reduction of allochthonous input (less bottom-land flooding) and a
reduction in the river's ability to flush fine sediments from the otherwise productive gravel and
cobble substrates; (4) irrigation diversions and bank stabilization projects that reduced the
quantity of seasonally preferred mesohabitats.
A three-part study was initiated in 1994 to document the longitudinal variation in forage
availability and temperature suitability for Colorado pikeminnow in the upper Colorado River,
to describe processes that regulate food production, and provide recommendations for
management activities that might enhance riverine productivity and increase overall carrying
capacity. Fishery, sediment transport, and primary and secondary productivity studies were
conducted concurrently. This report presents the findings of the fishery studies. The primary
goal or objective of the fishery study is to provide a better understanding of
1) the importance of adult carrying capacity in meeting recovery objectives for
Colorado pikeminnow,
2) the importance of food availability and temperature in governing the
distribution and abundance of adult Colorado pikeminnow in the upper Colorado
River, and
3) the potential of using upstream range expansion for increasing river-wide adult
pikeminnow carrying capacity.
The primary task performed during the study was to assess spatial and temporal variation in
the:
1) distribution and relative abundance of species making up the main-channel fish
community, with emphasis on those fish suitable as Colorado pikeminnow forage.
2) body condition and diet of the primary native fish species
3) forage-fish abundance within and between major riverine habitat types
4) temperature suitability for Colorado pikeminnow growth
After presenting the results of these investigations, this report then integrates the findings
from other pertinent studies and finally presents a discussion on how food availability and
suitable temperature interact and delimit the carrying capacity and potential range of Colorado
pikeminnow in this system. In addition, preliminary results from new studies are presented
that may provide a clue to the number of adult Colorado pikeminnow we might expect this
system to support.
2
A