7080

• UCREFRP Catalog Number: 7080
• Author: Carter, J. G., V. A. Lamarra and R. J. Ryel
• Title: Drift of Larval Fishes in the Upper Colorado River
• USFW Year: 1986
• USFW - Doc Type: Journal of Freshwater Ecology
• Copyright Material: YES

in tl:le upper
Ual impact of
orado (n gu re
111 shorel ine
)ite) .

RESULTS OF PARACHUTE STUDY

ptember. Fi ve
esh seines to
ines, dip nets
lae and young-
1ets to assess
Ie. Tow nets
lce drHt, and
~ocument adul t

Spedes eo.position and Relative Abundance

Of the 13 fish species captured, only 8 were found as larvae in drift
nets (Figure 2). In addition to these 8, carp (.frE!.!~ ca7.!E) , black
bu~lh~ad (lSj~l~~~~ ~el~~), rainbow trout (~~l~E 3~.!rEE~!.! ' mountain
whItefIsh (~~~~21um wl11~msw), and razorback sucker r!r!~s~n t~~~)
were captured wlt~ther gear types, but not as drifting larvae. Only seIne
hauls yielded the full complement of 13 species. Three of the five native
species __ flannelmouth sucker (Catastomus lati.E..!Enis), bluehead sucker
(f~tas~onus ~EElus), and speckrerd'ac'e"{RhTiiFh~~ osculu~) -- made up
nearly 78 percent oT the observed shorel ine drift at fheparachute Site.
The remaining two native species -- roundtail chub (Gila robusta) and
mottled sculpin (Cottus bairdi) -- raised the compOSition to--nearly 84
percent. The si.;gre5peCTriieii of razorback sucker was only tentatively
identified since the fish was only 21.5 RID TL (Total Length) and in the
metalarval phase of development.

The midchannel benthic zone was not sampled because of high water
velocity and excessively deep sample conditions. The species composition of
the shorel ine and midchannel surface zones was very similar. Four species
(flannelmouth sucker, bluehead sucker, speckled dace, and white sucker) made
up the bul k of the catch (8U in shorel ine sets and 78.5t in midchannel
samples). Other species captured in shorel ine dri ft nets were roundtail
chub (6t), fathead minnow (3.2t), mottled sculpin (O.2t), and green sunfish
(O.2t). Other species in midchannel samples were mottled sculpin, fathead
minnow (each 4.8t), and roundtail chub (2.4t). Although the composition of
drift in the shoreline and midchannel surface zones was similar, the density
of shorel ine drift was nearly seven times greater. This difference was
significant for samples between July 18 and September 2, using a
randomization test of paired differences of weekly means (p=O.026).

etting with a
which tapered
.en end fac i n9
er, except for
Time, water
t was set and
computed us i ng
et 0 pen i ng .

'e sorted from
Each larval
, measure its
,tification of

PARACHUTE SITE

PAll SADE SITE

RT
L 33 \
6.07.
t.lS
2
MS 1.17.
1
0.27.
:::
BH
122
22.07.

3.27.

SO
16
9.17.

SU
13
2.37.

;ites.

FIGURE 2. Number and percentage composition of fish species captured in
shoreline drift nets at the two study sites on the upper Colorado
River. BH = bluehead sucker, FH = fathead minnow,
FM flannelmouth sucker, GS = green sunfish, MS = mottled sculpin,
RT roundtail chub, SO = speckled dace,
SU unidentified sucker, UM = unidentified minnow,
UN unidentified and WS = white sucker.
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