8188

• UCREFRP Catalog Number: 8188
• Author: Muth, R. T., et al.
• Title: Flow and Temperature Recommendations for Endangered Fishes in the Green River Downstream of Flaming Forge Dam.
• USFW Year: 2000.
• USFW - Doc Type: \
• Copyright Material: NO

Final Report

September 2000

reproductive success; (2) evaluate recruitment of the endangered fishes from age-O to subsequent
life-history stages and determine relationships among seasonal flows, water temperatures, and
survival of young fish; (3) monitor the relative abundance and population structure of the
endangered fishes in order to acquire information on interactions among fish species and how
flows may differentially affect populations; and (4) determine how releases from Flaming Gorge
Dam and flows from tributaries affect the formation and maintenance of important habitats for
the endangered fishes throughout the Green River. To accomplish these objectives, a series of
long-term studies was conducted to track changes in populations, reproductive success, and
habitats. In addition, shorter-duration studies were conducted to examine specific hypotheses and
flow relationships. This report summarizes and synthesizes the results of the Flaming Gorge
Flow Recommendations Investigation as well as other relevant information to provide
recommended flow and temperature regimes that would benefit the endangered fishes in the
Green River.

The study area for the investigation encompassed the main-stem Green River from
Flaming Gorge Dam downstream to its confluence with the Colorado River, including relevant
portions of major tributaries. The Green River was divided into three contiguous reaches
delimited by major tributaries: Reach 1 - Flaming Gorge Dam to the Yampa River confluence
(river kilometer [RK] 555.1 to 659.8), Reach 2 - Yampa River confluence to the White River
confluence (RK 396.2 to 555.1), and Reach 3 - White River confluence to the Colorado River
confluence (RK 0.0 to 396.2).

Data gathered during the Flaming Gorge Flow Recommendations Investigation and
other studies were used to develop descriptions of the basic life history, habitat use, and
population status of the Colorado pikeminnow, razorback sucker, and humpback chub in the
Green River system downstream of Flaming Gorge Dam. This information is summarized below.

The Colorado pikeminnow is widespread in the Green River system and occurs in both
the mainstem and tributaries. The largest numbers of adults are found in Green River Reaches 2
and 3, particularly downstream of Jensen, Utah, but adults also occur in Lodore Canyon of lower
Reach 1 and in upper Reach 2. Adult Colorado pikeminnow migrate to spawning areas in the
lower Yampa River and the Green River in Reach 3 in late spring, and they spawn there in
summer. Larvae emerge from spawning substrates and are swept downstream to nursery-habitat
areas, primarily downstream of Jensen. Reproduction by Colorado pikeminnow occurred in all
years of study, but both the production of larvae and the recruitment of age-O juveniles in autumn
were highly variable among years. Because the main-stem Green River supports all early life
stages and large numbers of adults, it is considered essential for recovery of the Colorado
pikeminnow.

High spring flows benefit Colorado pikeminnow because these flows maintain the in-
channel habitats used by all life stages of the fish and because they inundate floodplain habitats
that provide warm, food-rich environments important for the growth, rest, and conditioning of
juvenile, subadult, and adult fish. The patterns of spring flow and water temperature provide the

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