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

20

water temperatures from Maybell downstream ranged above 19C. In 1984,
peak spawning activity occurred from July 8-18. During this period flows
decreased from 179 m3/s to 163 m3/s on July 8-9, then increased to 229
m3/s by July 11. Spawning activity diminished considerably as flows
again decreased below 105 m~15. Water temperatures at Maybell during
this time ranged above 17C. In 1985, spawning activity was described by
two peaks. The first peak occurred from June 25-29, and was associated
with a sharp resurgence in flows from 108 m3/s to 136 m3/s over June
25-27. Spawning activity dropped off equally as sharp when flows again
declined below 55 m3/s on July 6. On July 19-21, flows increased from
31 m3/s to 67 m3/s, which appears to initiate another small peak in
spawning activity from July 23-26. As with the first peak, spawning
declined considerably as flows dropped below 55 m3/s. Water temperature
data indicated that spawning began as the Yampa River reached l8C maximum
at Maybell~ and continued despite a significant drop in temperature of 4C
on July 24-27. Water temperatures quickly climbed above l8C again for the
remainder of the spawning season.
In summary, the past three years' data suggest that the peak in
Colorado squawfish spawning activity occurred when Yampa River flows
increased sharply (approx. 30 m3/s or more within 1-2 days) from the
declining pattern of spring runoff. Spawning activity declined when flows
dropped below the 55-60 m3/s range.

DISCUSSION

f;:r~J..::~:ti v~~..__sPuncL2I.n..s.g_ - No c:l. ear 2I.nnuc:3.1 trends were .::.:\ppc\rE.mt in the
relative abundance of fish species collected in drift samples since 1983.
With reference to drift samples, relative abundance may be equated with
yearly reproductive success rather than population abundance trends.
Within the Cyprinidae, Colorado squawfish, speckled dace, and Gila spp.
were most prevalent, though larvae of the latter two species remained
lower in abundance in 1984-85. Within the Catostomidae, abundance of
larval bluehead suckers increased in 1984, then declined in 1985 to a
level similar to that of 1983. Flannelmouth sucker exhibited a relative
increase in numbers of larvae in 1985. Channel catfish reproductive
success remained fairly stable over the 1983-1985 period.

Drift s~mp-=linq methodoloqv/General - An,:11yses of wCl.ter volumes sa.mpled
show each net functioning as an independent sampler ~ith variability in
the volume of water sampled connected to position in the stream and
duration of sampling effort. Statistical results show surface drift-net
sampling in a line perpendicular to streamflow could be considered
triplicate sampling for efforts of 1 hr or less, but 2 hr sampling
magnifies differences in the river conditions experienced by each net,
causing significant differences in the water volumes sampled. Timing of
sample effort based on flow and suspended debris load becomes important in
this case with regard to assumptions used in sample design and data
analyses. These results should be applicable as cautionary guidelines to
any further drift-net sampling conducted in the Upper Basin. It cannot be
e:-;pected that the differences noted here will be generally consistent
between different years or sampling sites, so it is recommended that
analyses of water volumes sampled between drift-nets become standard for
quality control.