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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13

Correlations among years of peak, daily mean, and total discharges in April-July with monthly
degree-days were negative, but only a few coefficients were strong or significant (Table 5). The general
weak-moderate degree of association for these comparisons was primarily a result of increased rate of
warmimg in 1984. Numbers of degree-days per month were similar in 1982 and 1984 even though date of
annual peak discharge occurred 12-13 d earlier in 1982 than in 1984, and values of monthly discharge
parameters in April-July were greater (especially for May and June) in 1984 than in 1982 However, as
noted, flows following annual peak discharge decreased at a faster rate in 1984 than in 1982. Compared to
1982 and 1984, cumulative numbers of degree-days over the five temperature thresholds for the April-July
period were 4-26% lower in 1983. Other than noted differences in values of monthly discharge parameters
among these three years, date of annual peak discharge in 1983 occurred 13 d later than in 1984 and 25-26
d later than in 1982 and rate of decrease in flows following annual peak discharge was faster in 1984 than
in 1983. When assessing effects of discharge on water temperature and rate of warming, characteristics of
annual flow regimes other than magnitude of discharge, such as time of peak discharge and rate of
decrease in flows following peak discharge, must be considered.
Mean values of water temperatures in low-velocity habitats we sampled were typically greater than
or equal to maximum daily water temperatures of the mainchannel on the same dates in each year studied
(Figure 4). However, seasonal patterns for water temperatures in these habitats closely tracked those
recorded for mainchannel temperatures. Therefore, mainchannel water temperatures appeared to be
adequate indicators of trends in thermal conditions of the lower Yampa River.

Fish Data

The eight fishes selected for our analyses were represented by 92,482 age-O (all taxa) or older
(nonnatives only) fish from a total of 1,067 seine samples collected during 1980-1984. Of that total catch,
81,239 fISh were classified as age-O and, of these, about 70% represented native taxa. This high
representation by native taxa agrees with conclusions of Tyus and Karp (1989) that, at least in terms of
abundance, native fishes dominate the Yampa River fish community. Over the five years studied, within
the native group, Gila sp. constituted 50% of the total catch, speckled dace 27%, bluehead sucker 18%,
and Dannelmouth sucker 5%. Within the nonnative group, red shiner constituted 53% of the total catch of
age-O fish and 38% of the total catch of age-l + fish, sand shiner 11 and 31 %, fathead minnow 32 and 11 %,
and redside shiner 4 and 19%. Annual abundance of fish in each taxon varied considerably for most taxa
among years.

Spawning periods.- Taxon-specific variation in estimated number of days to initiation of spawning
(SPA WN-1) and total number of days in the spawning period (SPAWN - T) occurred among years for both
native and especially nonnative fishes. However, annual spawning periods were mostly consistent among