7268

• UCREFRP Catalog Number: 7268
• Author: Persons, W. R. and R. V. Bulkley
• Title: Feeding Activity and Spawning Time of Striped Bass in the Colorado River Inlet, Lake Powell, Utah
• USFW Year: 1982
• USFW - Doc Type: North American Journal of Fisheries Management
• Copyright Material: YES

1981.
Percent
of total
3.0
2.0
52.1
12.9
70.0
3.5
4.7
8.2
13.6
30.0
ning run
trt of the
iped bass
)ling was
iter tem-
ed was a
captured
iod. The
the pro-
d in the
d. More
i during
;e caught
ntage of
Gypsum
.rayfish
(2)
1(0.3)
STRIPED BASS IN LAKE POWELL
spent fish during 1981 was attributed to the higher
water temperatures and later sampling in 1981
(Fig. 2, Table 1).
Location of Spawning
The available evidence suggested that Lake
Powell striped bass spawned in 1980 and 1981
in the lower rapids of Cataract Canyon or in the
upper mixing zone of the reservoir. No striped
bass were captured above the rapids, but ripe
and spent fish were netted in the Gypsum Can-
yon area. The early arrival and high proportion
of ripe males in the catch (2.3:1) also suggested
that the spawning area was nearby. Unfortu-
nately, the large amount of debris in the area
prevented adequate sampling of eggs and larvae
with plankton nets. The three viable eggs netted
were in the early stages of development and pro-
vided further evidence that spawning occurred
not far upstream.
Food
Most striped bass in other populations do not
feed while on their spawning run. More fish feed
before reaching spawning condition and after
spawning than when fully mature (Raney 1952;
Trent and Hassler -1966). In our study, about
42% of the stomachs of immature and maturing
fish, 25% of those of sexually mature fish, and
33% of those of spent fish contained food. Of the
321 stomachs examined during the 2 years, 70%
were empty (Table 2)90 (28%)
threadfin shad (Dorosoma petenense), 4 held red
shiners (Notropis lutrensis); and 2 contained
remains of unidentified fish.
Empty stomachs can, of course, occur for rea-
sons other than fasting, such as rapid digestion
(Merriman 1941; Raney 1952), sporadic feeding,
and regurgitation of stomach contents by gill-
netted fish. In our study, most of the food in the
stomach and intestinal tract consisted of fish that
would digest at a somewhat similar rate regard-
less of species. Regurgitation of food by gill-net-
ted fish is a common phenomenon and results
in lower estimates of the percentage of fish feed-
ing. Composition of the diet is not affected by
regurgitation, only the percentage of stomachs
containing food. The somewhat similar percent-
age of stomachs (30%) and intestinal tracts (41 %)
containing food suggested that regurgitation was
not a major problem because regurgitation does
not evacuate the intestine.
CONCLUSIONS
407
Our evidence strongly . suggested that Lake
Powell striped bass spawned near or above Gyp-
sum Canyon in the Colorado River inlet in 1980
and 1981. The extent of upstream movement
probably varies from year to year, depending on
river flow and reservoir level. During 1980 (a
high-water year) and 1981 (a low-water year), no
striped bass were captured above the rapids.
The degree of success of striped bass repro-
duction was not determined by plankton-net
sampling in 1980 and 1981. Fall gill-net surveys
for young-of-the-year striped bass are more effec-
tive for determining reproductive success (Gus-
taveson et al. 1980).
No evidence was obtained to suggest that adult
striped bass prey on native fishes during the spring
and early summer while in the Gypsum Canyon
area. Although endemic species were not found
in striped bass stomachs, they were present in
the study area albeit in much fewer numbers than
were threadfin shad. Adult Colorado squawfish
and razorback suckers were captured with striped
bass in the gill nets. Four small Colorado squaw-
fish (67, 72, 106, and 106 mm long) were cap-
tured on July 15-17, 1980, just upriver from
Gypsum Canyon. At the same time, five adult
striped bass were captured at Gypsum Canyon
(Mike Ottenbacher, Utah Fishery Biologist, per-
sonal communication, 1980). One juvenile Col-
orado squawfish (251 mm long) was gillnetted at
Gypsum Canyon on July 22, 1981. Thus, squaw-
fish of suitable forage size were available in the
spawning area but none had been eaten by the
fish we examined. Threadfin shad currently pro-
vide the major food of striped bass in the res-
ervoir. As long as the striped bass congregate for
spawning below Cataract Canyon rapids and
threadfin shad are abundant, adult striped bass
probably will not prey heavily on endemic fishes
during the spawning run.
From a management standpoint, our findings
indicate that stocking of striped bass fry has pro-
duced a naturally reproducing population in
another Colorado River reservoir besides Lake
Mead. Fry stocking in Lake Powell was termi-
nated in 1980 because of natural reproduction.
Fishery managers should consider the possibility
of natural reproduction occurring in similar
waters if they anticipate controlling striped bass
populations through annual stocking of fry. On
the other hand if control of the population is not
a consideration, the ability of this normally anad-