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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5

after the water temperature had reached 180C and that late larvae (12-20 mm long) were captured 3-4
weeks later. Results of field studies conducted in the Yampa and Green rivers after 1979 generally
confirmed Vank:ek and Kramer's observations and demonstrated that Colorado squawfish spawn in the
lower 50 km of the Yampa River, especially in lower Yampa Canyon, from late June through early August
(Tyus et a1. 1981; Wick et a1. 1983; Haynes et a1. 1984). Information on principal spawning seasons of
other fishes occurring in the lower Yampa River was also considered when planning sampling efforts.
Seines (1.0 or 3.0 x 1.2 m; 0.8-mm-square mesh) were used to collect age-O or older fish from
backwaters or shoreline habitats with negligtble water velocity (typically s 0.2 m/s; e.g., pools, embayments,
and eddies) throughout each reach. Width and length of each seine haul (each seine haul was considered a
separate sample) were measured with a metric tape, and area sampled (mZ) was calculated. Samples were
collected according to the "qualitative-representative-sample approach" (Hocutt et aL 1974), i.e., all
available habitats in each reach that could be seined were sampled to obtain representative collections of
fishes that would yield data on relative abundance. Consequently, number of samples co))ected and area
seined in each reach per year generally reflected amount of seineable habitat. Water temperature (oC) was
measured in each habitat type at time of sampling.
Most sampling in 1981-1984 was conducted monthly or bimonthly from early-mid June (shortly
after spring flows had peaked) through late September or mid October (Table 2). In 1981 and 1982,
samples were also collected in late Apnl (before spring flows had peaked). Collections in 1980 were made
in late August and early October. Collections were made primarily during early-mid June through late
August in reaches 1 and 2 and in April, late August, mid-late September, or early or late October in
reaches 3-5. All samples were fixed in 10% formalin and returned to the Larval Fish
Laboratory, Colorado State University, Fort Collins, for processing.

Analyses

Flow antltemperature data.-Various environmental factors influence reproduction of fIShes
(DeVlaming 1972; Lam 1983; Bye 1984; Stacey 1984; Munro 1990). Welcomme (1985) reported that for
riverine fishes, timing of spawning is related to water flow and temperature and reproductive success or
survival of young are affected by the flow regime. Annual discharge and mainchannel water-temperature
data for the lower Yampa River were taken from U.S. Geological SUlVey monthly records. Stream gages
on the Yampa River were located near the town of Maybell (river km 138.9; about 45 kin upstream of the
study area's upper end) and at Deerlodge Park (river kin 72.2; at the upper end of Yampa Canyon).
Discharge and temperature data collected at the MaybeU gage were available for each year studied,
whereas, collection of these data at the Deerlodge Park gage was started in 1982. Discharge of the Yampa
River at Deerlodge Park in 1980 and 1981 was approximated by adding monthly values of daily and total
discharge taken from Mayben records to corresponding data collected at a stream gage on the Little Snake