7918

• UCREFRP Catalog Number: 7918
• Author: Scoppettone, G. G., M. Coleman and G. A. Wedemeyer.
• Title: Life History and Status of the Endangered Cui-ui of Pyramid Lake, Nevada.
• USFW Year: 1986.
• USFW - Doc Type: \
• Copyright Material: NO

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were apparently sufficient to permit at least limited
access through the delta. Fish ofthe 1976 and 1978
year classes were either produced in the hatchery
or were the progeny of the few fish that traversed
the delta and spawned downstream from MB dam.
The presence of the 1980 year class can probably
be attributed to adult spawners reaching the lower
Truckee River through the fishway (Table 1),
Growth rates were estimated for both of the dom-
inant year classes, 1969 and 1950. We used the
opercle collections made in 1982 and 1983 to esti-
mate growth of fish of the 1969 year class and the
collections in 1978, 1982, and 1983 to estimate
growth of fish of the 1950 year class. We used oper-
cles from 73 males and 93 females ofthe 1969 year
class and 50 females of the 1950 year class, from
which only 3 males were available (13 other
specimens were too decomposed to be sexed or
accurately measured). This disproportionate sex
ratio among old fish was also apparent in the catches

made during our 1983 offshore gill netting; of
140 fish captured that were recognized as "old"
(see later discussion) only 3 were males. These
observations clearly suggested that females lived
longer than males-a common phenomenon among
catostomids (Hauser 1969).
Opercle bones were also used to back-calculate
cui-ui growth rates. Measurements were made on
the left opercle with a vernier caliper to the nearest
0.01 mm, from the base of the centrum posteriad
along the inner side of the opercles (Fig. 9). To back-
calculate the growth rate of fish of the 1969 year
class, we correlated fork lengths of cui-ui to opercle
length, as described by Miller (1966) for scales. The
estimated mean annual length of fish at each age was
then computed.
It was difficult to develop a sound growth curve
for the 1950 year class because data for older cui-ui
tagged with Floy tags showed that growth in length
had virtually ceased. However, growth of fish bones

Table 3. Estimated ages of 355 cui-ui collected in Pyramid Lake in 1956-84. Numbers of fish
are shown in boldface.
Year of collection
Year
class 1956 1975 1976 1977 1978 1981 1982 1983 1984
1942 36 41
1 2
1946 32
6
1950 6 28 32 33 34
7 40 6 15 2
1967 16
1
1969 6 7 8 9 13 14 15
3 1 2 32 56 113 44
1971 12
1
1973 10 II
2 1
1975 7 8
1 2
1976 6 7 8
4 5 2
1978 6
2
1980 1
4