7918 ‎(2)‎

• 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

believe that it was linked to unrestricted river access
in that year. Spring flows in 1969 were among the
highest in 50 years. Although high flow alone does
not facilitate movement over the delta, perhaps one
or more of the numerous delta channels was deep
enough to permit easy passage. Our observation that
most old fish were from the 1950 year class strongly
suggests that it once dominated the population.
Again, the reason for success of this group is unex-
plained, but it may have been a result of the con-
struction of a spawning channel in 1946 at the site
of the later fishway (La Rivers 1962). The Truckee
River was diverted down the channel until fall 1950,
when high flows destroyed the diversion dam.
Spring flows in 1946 and 1950 were the only sizable
ones in the spawning channel's brief history.

Length Frequency of Adult Population

Length frequencies overlapped broadly among
year classes of cui-ui. For example, among fish of

Males
20
12
4
Q)
u
c
~ 20
:J
U
u 12
Q
C
Q) 4
u
Q;
a.
20
12
4

Females

1982

1983

1984

40

50

60 40 50
Fork length (mm)

60

Fig. 13. Length distribution of random samples of cui-ui
taken in the fish processing building during the spawn-
ing migration of 1982-84. Sample size was 500 fish of
each sex in each of the 3 years.

17

the 1969 class, the fork length ranges were
458-546 mm for males and 533-590 mm for
females in 1982, and 480-545 mm for males and
534-610 mm for females in 1983. Among fish of
the 1950 class collected in 1983, males were
540-582 mm long and females 580-673 mm long.
Nevertheless, from the relative size composition of
fish in the population, some useful inferences could
be made. Cui-ui first entered the spawning popula-
tion at lengths of 380-420 mm, at 6 years of age.
When they were 460-480 mm long, they were
usually at least 8 years old, and females
520-540 mm long were about 10 years old. These
younger fish were only sparsely represented among
those seen in the FPB during the present study
(Fig. 13). suggesting alarmingly low recruitment to
the population after 1969. I

Population Estimate

We estimated the population of the offshore
prespawning aggregation in 1982 and 1983 (Table 4)
on the basis of cui-ui captured in gill nets in the
prespawning aggregation, marked with Flay tags,
and recaptured at the FPB. (Dimensions and opera-
tion of the nets were previously described.)
As judged by recaptures at the FPB, Flay-tagged
cui-ui seemingly mixed randomly in the aggregation.
Previous experience with cui-ui that were gill netted
from the pres pawning aggregation for transport to
the hatchery indicated that tagging probably caused
little mortality. Also, we saw virtually no signs of

I We are nevertheless cautiously optimistic that several
sizable year classes of cui-ui will become evident by the
late 1980's. After this manuscript was essentially
completed, numerous young cui-ui, 13-350 mm long
were collected in Pyramid Lake. The smaller of these
(13-60 mm) were seined near shore in summer 1984
and the larger (100-350 mm) were gill netted regularly
in the winter of 1984 and in 1985 (Lee Carlson, Pyramid
Lake Fisheries, personal communication). Previously,
the only known capture in the lake of a fish shorter than
350 mm was a 32-mm specimen taken in 1938 (R. R.
Miller, Department of Zoology, University of Michigan,
personal communication). Cui-ui have reproduced so
infrequently in the last 50 years that they simply have
not been available for capture.