7603

• UCREFRP Catalog Number: 7603
• Author: Nesler, T. P.
• Title: Endangered Fishes Investigations
• USFW Year: 1991.
• USFW - Doc Type: Federal Aid Project #SE-3 - Job Progress Report.
• Copyright Material: NO

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as an arbitrary starting date. This was presumed biologically relevant to
Yampa River fishes since April is the normal ice break-up period and beginning
of increased flows, temperature and low-velocity habitat. It was presumed
SPAWNl and SPAWNT may also be highly correlated. The correlation between CPUE
and FO and between SPAWN1 and SPAWNT were also examined.

Flow indices in May, June and July were selected for analysis because this
time period is most influenced by high spring flows, and was presumed critical
as an early determinant of spawning success and YOY abundance. For each
month, peak discharge (PEAK), average daily discharge (AVG), and total monthly
discharge (TOT) were determined from USGS gage records. These flow indices
for each month were selected on the basis that each may have a different
effect on spawning success, but recognizing that the flow indices were highly
correlated themselves. Flow indices for each month were examined versus
species abundance indices to reflect potential differences in spawning and
nursery habitat requirements for each species over the three month period.
How peak discharge, average daily discharge, and total monthly discharge
influence flushing flows, spawning habitat maintenance, and availability of
spawning or nursery habitat relative to each species is uncertain, but
presumed to differ. The four biological indices were also compared with
cumulative degree-days estimates for the Yampa River each year. Cumulative
degree-days were used as an index of the rate of warming in the annual
temperature regime of the Yampa River. Degree-days were estimated using
Maybell gage temperature data for 1981-1984 only. Even though this gage is
located approximately 48 km upstream of the study area, this was the most
continuous data available and presumed useful due to a probable direct and
positive relationship with mainchannel water temperatures downstream, and with
low-velocity habitats associated with the mainchanne1.This data was compared
with water temperature data taken at seine sample sites to confirm this
presumption. For May, June, and July each year, the number of days in which
the maximum water temperature reached l6C, l8C and 20C were determined (16DD,
18DD, and 20DD, respectively). As a cumulative index, the number of 16DD,
18DD, and 20DD degree-days determined for May were added to those determined
for June to represent June values and June values were added to July estimates
to determine July values. These temperature categories were selected to
represent the range of temperatures most affected by variable spring flows in
May through July. The onset of each of these temperature levels would be
influenced by the magnitude and timing of peak spring flows, thus affecting
the rate of warming in the Yampa River at the Maybe11 gage and downstream.
Correlations between flow and temperature indices for each month were also
examined.

In summary, four biological indices (CPUE, FO, SPAWNl, SPAWNT) were
compared in a correlation matrix with three flow indices (PEAK, AVG, TOTAL)
for each of three months (MAY, JUNE, JULY). CPUE and FO were estimated for
each of five river reaches within the study area as well as a seasonal total
for each year. SPAWNl and SPAWNT were yearly estimates only. Seasonal
estimates of CPUE and FO, and SPAWNl and SPAWNT were also compared in a
correlation matrix with three temperature regime indices (16DD, l8DD, 20DD)
for each of the three months. Results were interpreted on the basis of two
criteria. Correlation coefficients were significant at P<0.05 for n-2 degrees
of freedom. A correlation coefficient was considered strong if "r" was s.0.10