7739

• UCREFRP Catalog Number: 7739
• Author: Muth, R. T. and T. P. Nesler.
• Title: Associations Among Flow and Temperature Regimes and Spawning Periods and Abundance of Young of Selected Fishes, Lower Yampa River, Colorado, 1980-1984 - Final Report.
• USFW Year: 1993.
• USFW - Doc Type: \
• Copyright Material: NO

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7

River near Lily Park (the Uttle Snake River joins the Yampa River at Uly Park; river km 81.8). To place
the maximum-daily (peak) discharge of the lower Yampa River for each year during 1980-1984 in historical
perspective, values of annual peak discharge in 1934-1991 were taken from Maybell records and frequency
and cumulative-frequency distnbutions were prepared. Each peak-discharge value in 1980-1984 was given
a percentile rank within the grouped frequency distnbution.
Carlson et at (1979) and Haynes and Muth (1982) reported that in 197~1977 and 1981,
respectively, estimated peak spawning for most of the more common fIShes in the lower Yampa River
occurred sometime during late May through late August Discharge of the lower Yampa River typically
begins to increase from over-winter, baseline flows in April, peaks in mid May-early June, remains
relatively high through July, and is at or near baseline from August through March. Because river flows
exert deterministic effects on various physical conditions important in spawning or survival of young fish
(e.g., water temperature, velocity, and quality and formation and maintenance of spawning and nursery
habitats), we presumed that discharge conditions during spring-summer would affect annual reproductive
timing and success of fishes in the lower Yampa River. Three parameters describing the monthly flow
regime of the lower Yampa River during April-July in each year studied were selected for our analyses;
i.e., peak (maximum-daily), daily mean, and total discharge.
Mainchannel water temperatures of the lower Yampa River typically begin to increase from their
over-winter lows in early-mid March, are fairly constant from day-to-day in May-mid June (during
spring-runoff discharge), and reach maximum values in early-mid August (after spring-runoff flows have
subsided). Degree-days (sensu Arnold 1960; Baskerville and Emin 1969) were used as an index of the
annual rate of warming of the lower Yampa River during spring-summer. Degree-days were estimated
using mainchannel water-temperature data collected at the Maybell gage in 1981-1984 (1980 data were
incomplete). Although this gage is located about 45 km upstream of the study area's upper end, it
provided the most continuous data on mainchannel water temperatures (typically, on dates when
temperature data were recorded at the Deerlodge Park gage, daily minimum or maximum mainchannel
water temperatures were about 1-3oC greater at Deerlodge Park than those recorded near MaybeU). For
each year, monthly degree-days were estimated as number of days maximum mainchannel water
temperature reached or exceeded 12, 14, 16, 18, or 200C in April-July. These temperature thresholds were
selected to represent a range of water temperatures likely affected by variations among years in discharge
during spring-summer. It was believed that annual onset and seasonal persistence of each of these
temperature thresholds would be especially influenced by magnitude and timing of peak discharges, thus
affecting the rate of warming of the lower Yampa River.

Fish daJa.-In the laboratory, samples were first organized by collection date and location (reach)~
Fish from each sample were identified to the lowest possible taxon (most were identified to species; native
Gila were left at genus, although most were probably Colorado roundtail chub). Specimens in each taxon