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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EXECUTIVE SUMMARY

Seine and dipnet sampling for small fishes (natives and nonnatives) in low-velocity habitats within
five reaches of the lower Yampa River (river kID 0.0-94.1) was conducted annually during 1980-1984 by
the Colorado Division of Wildlife. Data from each collection were first entered into a MANAGE
computer database (during 1985-1986) then transferred to a ~ computer database (during 1998-1990);
data included sampling date and location, sampling gear, measured length and width of seine hauls, type
and physical characteristics of habitat sampled, and number, size, and life-history period of fish collected.
In this study, we first partitioned the existing database to differentiate between seine-collected
age-O and older fish of each taxon. Two indices of relative abundance, i.e., catch-per-unit-effort (CPUE)
and percentage of occurrence (PO), were calculated by river reach and over all reaches (total) per year and
by river reach over all years for each age group of eight commonly collected taxa including native Gila sp.,
speckled dace, bluehead sucker, and Oannelmouth sucker, and nonnative red shiner, sand shiner, fathead
minnow, and redside shiner. Two spawning period parameters, i.e., number of days to initiation of
spawning (SPAWN-I) and total number of days in the spawning season (SPAWN-T), were also estimated
for each taxon per year. These data were associated with annual spring-summer (April-July) flow and
temperature parameters for the lower Yampa River including monthly peak, daily mean, and total
discharges and degree-days for five temperature thresholds (12, 14, 16, 18, and 200C). Preliminary results
of this study were previously presented in Nesler (1991).
Annual flow and temperature regimes for April-July varied considerably among the fIVe years
studied. Discharge was low in 1981, high in 1983 and especially 1984, and more moderate in 1980 and
1982. Temporal occurrence of annual peak discharge was earliest in 1982 and latest in 1981 and 1983.
Rate of decrease in flows following annual peak discharge to near baseline was fastest in 1981, siowest in
1982, and similar among 1980, 1983, and 1984. Annual trends in monthly water-temperature parameters
were somewhat predictable given values of corresponding discharge parameters and the shape of yearly
hydrographs. Rate of warming per month was fastest in 1981, slowest in 1983, and similar between 1982
and 1984.
Taxon-specific variation in SPAWN-l and SPAWN-T occurred for both native and nonnative
fishes; however, annual spawning periods were mostly consistent among taxa between and within the native
and nonnative groups. Variation in total relative abundance of age-O fish among years differed mostly
between the native and nonnative groups. In most years and for most fishes, natives started spawning
earlier than nonnatives, and nonnatives ended spawning later than natives. Spawning for both native and
nonnative fishes among years started and ended earliest in 1981 and started and ended latest in 1983.
Among native fishes in each year, Oannelmouth sucker started spawning earliest, and speckled dace ended
spawning latest Among nonnatives in most years, fathead minnow started spawning earliest, and sand
shiner ended spawning latest Highest relative abundance of age-O fish among native taxa occurred in 1981

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