7779

• UCREFRP Catalog Number: 7779
• Author: Tyus, H. M. and J. M. Beard
• USFW Year: 1990
• Copyright Material: YES

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1990]

GREEN RIVER FISH ECOLOGY

37

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TABLE 3. Contents of 61 walleye (Stizostedion vitreum) stomachs taken in the Green River basin, Utah and
Colorado, 1984-1989.

Species

Statusa

Frequency
(%)

unidentified fish
Ictalurus punctatus
Pimephales promelas
Cyprinus carpio
Lepomis cyanellus
Catostomus latipinnis
unidentified Cyprinidae
Ictalurus melas

1
1
I
I
N
I
I

empty
fish eggs
vascular plant material

aN = native species, I = introduced species.

1987, and it was first captured below Green
River, Utah (km 192), in 1988. This invasion
and downstream movement is supported by
both the absence of the fish in the Green River
in the early 1970s (Holden and Stalnaker
1975) and a first report of pike in the lower
Green in 1988 (M. Moretti, personal commu-
nication). Although movements of northern
pike in large rivers remain poorly docu-
mented, some studies in lakes and small
streams have shown that the fish can display
high mobility (Miller 1948, Ross and Winter
1981) but may move only short distances at a
time (Cook and Bergersen 1988). Our recap-
ture of two northern pike indicated that the
fish can move long distances (> 75 km/year)
in the Yampa River. Long-distance upstream
and downstream movement of radiotagged
northern pike has also been reported by
T. P. Nesler (personal communication).
The majority of fishes consumed by north-
ern pike in this study were soft-rayed forms
(Table 2), as previously noted by others
(Beyerle and Williams 1968, Weithman and
Anderson 1977, Wolfert and Miller 1978).
Channel catfish, the only spiny-rayed fish
consumed, was found in two stomachs. We
could not positively identify roundtail chub,
Gila robusta, in northern pike stomachs taken
from the Yampa River, but presumably one
Gila spp. was a roundtail chub. T. P. Nesler
(personal communication) reported that
roundtail chub were present in northern pike
stomachs he examined from the Yampa River.
Most oftpeJ:1ike\ve examined. were from the
Green River where roundtailchub are rare

Number
of prey

FISHES
38
37
35
4
4
1
2
1

16.4
16.4
9.8
6.6
3.3
1.6
1.6
1.6

OTHER

39.3
1.6
1.6

(Tyus et al. 1982, Fishes of upper Colorado),
and this may have resulted in the relative
absence of roundtail chub as prey in pike
stomachs we examined.
Northern pike may spawn in the main-
stream Green River, but if so, recruitment is
low. We did not capture small northern pike
(< 321 mm TL) in this study, and, to our
knowledge, pike reproduction has not been
noted by others. However, one 115-mm-TL
specimen was seined by HMT and others
from a shoreline area of the Green River in
Dinosaur National Monument on 8 July 1988.
It is not known whether this fish hatched in
the Green River or was transported there
from another location. Also, we captured sev-
eral ripe female pike, and it is possible that
some of these fish spawned in the Green
River. Most ripe female pike (76%) had empty
stomachs, suggesting a reduction in feeding
activity with increasing water temperatures
and ripening ovaries (Frost 1954, Lawler
1965).
Walleye were rare in the Green River, and
their long period of residency suggests that
their numbers will probably not increase.
Walleye were easily captured by electrofish-
ing, and very few fish that we sighted escaped
capture. However, it was difficult to capture
northern pike with electrofishing, and many
fish escaped. A direct comparison of the rela-
tive. abundance of walleye with that of north-
ern pike could be somewhat misleading, and
it is noted that walleye were more rare, and
northern pike more abundant, than indicated
by electrofishing catch rates. We captured