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

2

The cui-ui (Chasmistes cujus) is a federally listed
endangered species endemic to Pyramid Lake,
Nevada. The species is believed to be the last
remaining genetically pure member of the genus
Chasmistes (Miller and Smith 1981). This taxonomic
distinction, the severe decline of the cui-ui popula-
tion, and the favorable outlook for recovery of the
species resulted in its receiving a top priority rating
for recovery (U.S. Fish and Wildlife Service 1983).
Because much natural history information was
lacking, the Service supported a 4-year study of the
species as outlined in the Cui-ui Recovery Plan
(U.S. Fish and Wildlife Service 1978). We present
the results of that research.
The primary cause of the decline of the Pyramid
Lake cui-ui population was clearly the disruption of
the reproductive cycle. During the past 50 years,
spawning adults have had only restricted access to
the Truckee River, the only permanent tributary of
Pyramid Lake. An extensive and shallow delta that
formed at the mouth of the river in the 1930's has
been a barrier to migrating adults in most years since
then. The delta resulted from a drastic lowering of
the water level of Pyramid Lake over a relatively
short period, as a result of water diversion from the
Truckee River. The water level of the lake dropped
about 25 m between 1906 and 1982. The comple-
tion of the Newlands Project in 1905 (Townley
1977) and the associated construction of Derby Dam
diverted an average of 311 million m3 annually, or
about half the river flow.
A series of measures were taken, beginning in the
mid-1970's, to attempt to restore the Pyramid Lake
sport and Indian food fishery. In 1976, Marble Bluff
Dam and Pyramid Lake Fishway, a canal 4.8 km
long that bypasses the delta, wqe completed. The
dam diverts water down the fishway, enabling
migrating fish to bypass the delt,. Also, portions of
the water stored in Stampefie Reservoir (an
impoundment on a tributary of the Truckee River)
were reserved to augment flows required for cui-ui
spawning.
As a further measure against the possibility of
extinction, hatchery propagation of cui-ui for
release into Pyramid Lake was begun in 1973, based
on techniques developed by Koch and Contreras
(1973). A fully equipped cui-ui hatchery, managed
and maintained by the Pyramid Lake Paiute Indian
Tribe, produced an average of 7 million cui-ui larvae
annually in 1980-84 (Alan Ruger, Pyramid Lake
Fisheries, personal communication). These larvae

were released into the lower Truckee River or
directly into the lake.
In 1981, the U.S. Fish and Wildlife Service (Seattle
National Fishery Research Center and Reno Great
Basin Complex Office) began the present study to
provide life history information that might facilitate
recovery of the species. Adult cui-ui, taken on their
spawning migration, were confined in a natural
braid of the lower Truckee River (Scoppettone et
al. 1983). Data developed on cui-ui reproduction
here, under controlled conditions, served as the
basis for the rest of the work in the main stem of
the Truckee River. The phase of the life history
spent in the river was emphasized because of its
obvious importance in determining survival of the
species. Included in the work were studies of
spawning migration, reproduction, emigration of
larvae, age and growth, population size, and food.
Each spring, adult cui-ui congregate at the south
or river end of Pyramid Lake before they migrate
upstream to spawn (La Rivers 1962). The concen-
tration is greatest near the mouth of the river (Koch
1972). Catches per unit of effort in gill nets fished
in Pyramid Lake near the Truckee River and the
Pyramid Lake Fishway were greatest when river
flows were high (SonnevilI981). Historically, cui-ui
spawned from mid-April to late May, primarily in
the lower 40 km of stream (Snyder 1918). In more
recent years, spawning was observed in Pyramid
Lake itself from May through July (Johnson 1958;
La Rivers 1962; Koch 1973). However, the high
salinity in the lake is lethal to incubating eggs
(Chano 1979). Even the hatching success of eggs
deposited at a freshwater inlet was questionable
(Koch 1973). In the river, adult cui-ui spawned in
riffles over predominantly gravel substrate, burying
their adhesive, demersal eggs at depths as great as
10 cm (Snyder 1918; Scoppenone et al. 1983).
Cui-ui spawning behavior was described by
Scoppenone et al. (1983), early life stages by Koch
(1972), and embryology by Bres (1978). At lOoC,
eggs hatch in 13 days and larvae swim-up about
5 days after hatching (Koch 1972; Koch and
Contreras 1973). Bres (1978) observed that the
mouth of cui-ui larvae opened 16 days after
hatching.
When not congregated at the river end of the lake,
adult cui-ui live primarily in littoral waters less than
23 m deep (Johnson 1958; Vigg 1980). Zooplank-
ton (not further identified) was reported to be the
primary food of adults (Johnson 1958; La Rivers