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

8

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~ 500
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1500

- Cui-ui run

1982

Temperature

Max,
+----- Mean
n_n___ Min.

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14 ~
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13 ~
12 ro
11 ~

10 ~
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1983

20
19
18
17
16
156
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13 ~
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11 C.
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9

1500

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~ 500
Z

1984 20
19
1500 18
17
16
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3
1 5 10 15 20 25 30 5 10 \ 5 20 25 30 5 10 15 20 25 30
-Aprll- -May- -June-

Fig. 4. Cui-ui spawning migration and daily water tem-
peratures in the Truckee River 1982-84.

4.8 km up the fishway or 3.0 km up the river to
MB dam), they traveled an average of only 2.1 km
(range, 0.5 to 4.8 km) farther upstream. Once the
migrating fish were above MB dam, they generally
moved about for 1 or 2 days (presumably seeking
a spawning site), remained in a limited area for
several days (presumably to spawn), and then
returned to the lake. Males occasionally spent
several days at each of two or more locations-
suggesting that they spawned at more than one site.
Radio-tagged males remained in the river for 6.5 to
16.5 days and females for 4.0 to 10.5 days.
Downstream migration back to the lake took place
primarily at night, confirming similar observations
by Scoppettone et al. (1983). The behavior of radio-
tagged fish was presumably the same as that of
untagged fish; Scoppettone et al. (1983) reported
that cui-ui reproductive behavior was unaltered by
externally applied radio tags.

Reproduction

Cui-ui first entered the spawning run at lengths
of 380-420 mm, at 6 years of age. In the FPB, the
ratio of males to females was 1:1.3 in 1982 and 1983
and 1: 2.5 in 1984. These sex ratios essentially rep-
resent the sex ratio for a single year class-that of
1969 (sex ratios for other year classes are discussed
later). Why there were proportionately fewer males
in the 1969 year class in 1984 than in other years
is open to conjecture; however, the migratory route
taken to the FPB may have been a factor. After the
completion of MB dam and the fishway, 1984 was
the first year that all cui-ui entered the FPB by way
of the river trap. Conceivably the fishway ladders
were restrictive to females. If so, the 1984 sex ratio
probably represents our least biased sample. We
cannot comfortably make meaningful comparisons
with previously documented sex ratios, because all
were potentially biased. Early fishway runs were
influenced by ladder modifications or small sample
size, and sex ratios published by Koch (1972, 1973,
and 1976) were at least partly based on catches in
gill nets that were clearly selective for females (the
larger fish).

Fecundity

Fecundity was determined from females that were
dropped along the fishway by American white peli-