7375

• UCREFRP Catalog Number: 7375
• Author: Wengert, M. W.
• Title: Flaming Gorge Reservoir Fisheries Management Investigations Six Year Completion Report ‎(1977-1983)‎.
• USFW Year: 1985.
• USFW - Doc Type: \
• Copyright Material: NO

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During the spring of 1983, eight adipose fin-clipped lake trout from the
September 1979 plant were recovered. The lake trout ranged in size from 16.1
inches to 18.1 inches and averaged 17.0 inches. A sample of 80 of the adipose
fin-clipped lake trout were weighed and measured to verify the planting sizes.
At the time of planting, these fish averaged 4.2 inches in length and only 1.7
inches separated the smallest and largest fish in the sample. These lake trout
were entering their fourth year of growth in the reservoir, although only five
of the eight scales read possessed the fourth annuli. Table 35 summarizes the
back-calculated total lengths of these known-aged lake trout from Flaming Gorge
Reservoir. Comparing average lengths of these lake trout at annulus IV shows
Flaming Gorge lake trout to exhibit superior growth to other lakes reported by
McAfee (1966) and Carlander (1969). Kiefling (1981) reported the average length
of lake trout from Jackson Lake to be 11.78 inches at annulus IV.
Flaming Gorge kokanee have been sampled effectively with the purse seine.
Catches of kokanee during spring purse seining have increased dramatically since
1980. The majority of kokanee caught by the purse seine are in the 9 to 11 inch
class (predominantly II+ age group). Figures 11 and 12 are length frequency
charts from random samples of kokanee measured during purse seining activities
in 1982 and 1983, respectively. Table 36 summarizes average lengths and range
in length for each age group of kokanee as determined from scale readings. Data
from 1982 and 1983 were combined to attain larger sample sizes in each age group
and a more accurate estimate of the mean length of kokanee in each age group.
This could be done because average lengths of spawning kokanee had stayed essen-
tially the same and the sampling was completed at approximately the same time
during 1981 and 1982. A larger sample size of age group IV+ fish may have
improved this estimate.
Growth of Flaming Gorge kokanee when compared to other kokanee populations
described by Carlander (1969) is quite rapid. Average length at age class I+
compared favorably to kokanee from Granby Lake, Colorado, but Flaming Gorge
kokanee were considerably larger at age class II+ and III+. Flaming Gorge koka-
nee were also larger at each year class than average total lengths reported by
Carlander (1969) for all lakes in Montana.
Lengths from mature late-run kokanee have been taken during spawning opera-
tions in the Green River below Fontenelle Dam. Table 37 summarizes this infor-
mation.
Table 37. Average length of mature late-run kokanee from the Green River
below Fontenelle Dam, 1981 and 1982.
Number Range in Average
Year Sex Sample Length (inches) Length (inches)
1981 Male 35
Female 37
1982 Male 66
Female 129
15.16 to 19.19 17.16
14.70 to 18.11 16.13
12.40 to 20.00 17.18
12.87 to 19.02 16.38
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