7194

• UCREFRP Catalog Number: 7194
• Author: Nesler, T. P.
• Title: Aquatic Nongame Research - 1985-86 Squawfish-Humpback Studies.
• USFW Year: 1986.
• USFW - Doc Type: Fort Collins, Colorado.
• Copyright Material: NO

10

Flow data ~ecorded at the USGS Deerlodge Gage 09260050 indicate the
Yampa River flow decreased from 136 to 28 m3/s during the estimated
spawning period. Flows during the estimated June 25-29 peak spawning
period ranged from 108 to 136 m3/s. The relationship between Colorado
squawfish spawning activity estimated by YOY age-growth predictions and
observed flow regimes in the Yampa River is examined in mo~e detail in a
later section of this report.

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Volumes of water sampled by eacn of the three drift-nets were examined
for consistent or significant differences due to net placement or clogging
and resultant backwash. The three nets were always placed in a line
perpendicula~ to the river shoreline, and were probably subjected to
different flows and suspended debris conditions within the cross-section
of the stream surface sampled. Simple ~anking of the volumes sampled in
Table 4 was performed (according to a scale of~ i-largest volume,
2-mid-volume, and 3-smallest volume) for each time period shown Cie.
total, weekly, daily, individual}. Results of the rank totals indicated
that the middle net generally sampled the most water du~ing the season.
The main-channel-side net and nea~-shore-side net ~anked second and thii~d,
respectively, in water volumes sampled. Overall, the middle net sampled
4% more water than the main-channel-side net and 10% more water than the
near--shore-side net. The main-channel-side net sampled 6% more water than
the near-shore-side net. The weekly totals demonstrate that this general
ranking was not consistent far all 7 weeks during the sampling period, nor
was this general ranking consistent within the daily or individual sample
volume rankings. The trend is evident though from the mean sample volumes
for these sample groups. Examination of individual sample volumes for
each of the four daily time periods suggest the above trend was probably a
result of slower flow on the side of the near-shore net and greater
backwash potential on the side of the main-channel net due to progressive
clogging with st~eam drift debris. The individual sample volume data
indicates the main-channel-side net was significantly affected by backwash
four times, the middle net only twice, and the near-sho~e-side net only
once.
The water volume sampled data suggest that, even when placed in close
pro;{imity to each other, the three drift nets are sampling different river
conditions, and may not represent a triplicated sample: To test this,
mean volumes sampled for each net were compared for significant
differences using the Student's t distribution, pooled variances and
P=O.05. The available data for each net was split into two groups based
on sampling duration. Forty-eight, two-hour samples and 20, one-hour
samples were collected. Significant differences between mean volumes
sampled were noted in all comparisons between the three nets involving the
two-hour sample group. No significant differences were noted for the
one-hour sample group.

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Diel periodicity in drift densities we~e examined for the four major
species captul~ed: Colorado squawfish, channel catfish, bluehead sucker,
and flannelmouth sucker: It is apparent from Table 5 that Colorado
squawfish larvae occurred in greatest densities in the drift during the
dawn period. Most of the Colorado squawfish captured were mesolarvae,