7779

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

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H. M. TYUSANDJ. M. BEARD

[Volume 50

TABLE 2. Contents ofl23 northern pike (Esox lucius) stomachs taken in the Green River basin, Utah and Colorado,
1984-1989.

Species

Status'

Number Frequency
of prey (%)
FISHES
40 10.6
24 7.3
15 4.1
6 4.1
7 3.3
6 2.4
3 2.4
2 1.6
2 1.6
3 0.8
2 0.8
1 0.8
1 0.8
1 0.8
1 0.8
1 0.8
OTHER
54.5
1 0.8
1 0.8
0.8

unidentified fish
N otropis lutrensis
Pimephales promelas
Catostomus latipinnis
Rhinichthys osculus
unidentified Notropis spp.
Gila atraria
Catostomus discobolus
Ictalurus punctatus
Cyprinus carpio
Notropis stramineus
unidentified Cyprinidae
unidentified Gila spp. b
Oncorhynchus mykiss
Oncorhynchus clarki
Richardsonius balteatus

I
I
N
N
I
I
N
I
I
I
I

empty
Rana pipiens
Lampropeltis spp.
detritus

N
N

aN = native species, I = introduced species.
bsuspected Gila robusta

traveled 78 km from 16 June 1988 to 23 May
1989, when it was recaptured at km 4.8.
Growth of these fish averaged only 10 mm TL.
Walleye were also captured in the upper
Green River (90%, n = 50) and averaged 511
mm TL (range 395-686 mm). These fish were
presumed juveniles and adults, based on size
(Carlander 1969). More widely dispersed than
pike, walleye were usually captured in a vari-
ety of slow shoreline runs, usually associated
with emergent or bank vegetation. One ripe
female walleye (577 mm TL) was captured in
the upper Green River on 15 May 1984 at a
water temperature of 13 C. We captured one
tagged walleye at the mouth of the Duchesne
River on 21 May 1984. This fish was tagged by
BIO/WEST Incorporated on 13 April 1979 at a
point about 37 km upstream in the Green
River (L. Crist, personal communication).
This fish grew about 62 mm TL in five years.

Foods

Northern pike stomachs (n = 123) were
usually empty (54.5%), but of the remainder,
97.6% contained fishes (Table 2). Red shiner,
Notropis lutrensis, and fathead minnow,
Pimephales promelas, were most frequently
consumed of nine nonnative fishes. Flannel-

mouth sucker, Catostomus latipinnis; blue-
head sucker, C. discobolus; and speckled
dace, Rhinichthys osculus, were the native
fishes consumed. Other prey items included a
leopard frog, Rana pipiens, a king snake,
Lampropeltis spp., and detritus. Thirteen
stomachs (10.6%) contained fish remains that
could not be identified.
Walleye in the Green River primarily con-
sumed fishes, including 5 nonnative and 1
native species (Table 3). Of61 stomachs exam-
ined, 24 (39.3%) were empty and 10 (16.4%)
contained unidentifiable fish remains. Chan-
nel catfish, Ictalurus punctatus, and fathead
minnow were the most frequently consumed
nonnative fishes, and flannelmouth sucker was
the only native fish consumed. Vascular plant
material was found in one walleye stomach.

DISCUSSION

Northern pike, introduced in the Yampa
River drainage in 1977, was presumed absent
in Green River until first reported in 1981
(Tyus et al. 1982, Fishes of upper Colorado).
We captured the fish only in the upper Green
River (km 337.8-552) from 1981 to 1986. Pike
invaded the midsection (km 192-337.7) by-

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