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

4

Marble Bluff Dam (here termed MB dam; Fig. 2)
was constructed 5 km upstream from the mouth of
the Truckee River in 1976. It is 12 m high and serves
to divert water into the Pyramid Lake Fishway (here
termed fishway). The fishway flows at about
1.1 m3/s and has four modified "Ice Harbor"
ladders (i.e., similar to those at Ice Harbor Dam in
the Snake River) along its 4.8-km course, At the
upstream end of the fishway and adjacent to MB
dam is a fish processing building (FPB), where
migrating adult cui-ui are trapped and released
upstream from MB dam (Fig. 2). A V-shaped trap at
the base of the north end of the dam is intended to
collect fish that have traversed the Truckee River
Delta. The capture efficiency of the trap is
unknown. The fish captured are elevated 10 m into
the FPB, and eventually released upstream from
MB dam.
Before 1984, the Truckee River Delta extended
about 2 km upstream from the river mouth. In most
years it consisted of shallow, braided channels; typi-
cally, none were deep enough to allow cui-ui access
upstream to the main stream channel. Even in 1983,
when daily average spring river flow reached
206 m3/s, there were access problems. The river
mouth was up to 1.5 km wide, and the entire delta
area was submerged under water averaging less than
0.3 m deep. The submerged delta was riddled with
numerous discontinuous channels that were up to
1 m deep but were only 50 to 60 m long and ended
in shallow water. In spring, a large population of
American white pelicans (Pelecanus erythrorhyn-
chos) occupied the delta, preying on migrating cui-ui
and other fishes that attempted to traverse the
shallow water. By 1984, after two extraordinarily
wet years, Pyramid Lake had risen about 7 m and
the channel below MB dam had downcut about 2 m.
These hydraulic changes effectively abolished the
Truckee River Delta for the first time in 50 years
and moved the river mouth 2 km closer to MB dam
(Fig. 1). Average water depth immediately upstream
from the mouth exceeded 1 m.

Spawning Migration

Prespawning Aggregation

We used gill nets to monitor the formation and
persistence of the pre-spawning aggregation in

Pyramid Lake, as well as to collect fish for tagging,
to enable us to estimate the population of cui-ui in
the aggregation. Three nets were systematically set
in Pyramid Lake from mid-March to late June in
1982 and 1983 (hydraulic changes at the river end
of Pyramid Lake prevented gill netting in 1984). One
net was fished off the mouth of the fishway and two
others off the mouth of the Truckee River (one on
either side). Nets were set parallel to the shoreline
in water 3-4 m deep. Each net was of a different
mesh size (121, 130, and 152 mm, stretched mea-
sure), and was 15.2 m long and 4.6 m deep. The nets
were rotated after each daily sampling period. In
1983 we fished two additional nets, each 61 m long
and 4.6 m deep; mesh size was 102 mm in one and
178 mm in the other. These nets were also set in
water 3-4 m deep, just off and parallel to the mouth
ofthe Truckee River, in the same area at each sam-
pling. We sampled 1 to 3 days weekly (depending
on the weather) in 1982 and 1 day per week in
1983. The three 15.2-m nets were set for two 1.5-h
intervals in both years, and the two longer nets for
a single 3-h period; netting began at 0700 h (1982)
or dawn (1983). All fish captured were marked with
Floy anchor tags near the base of the dorsal fin and
released at the site of capture.
We equipped 11 cui-ui with sonic tags on 3-7
April 1982 to enable us to follow movements of
fish in the prespawning aggregation. The tags
(64 mm long and 16 mm wide, constructed by
Sonotronics, Tucson, Arizona) were surgically
implanted into the abdominal cavity of nine fish
by the technique of Hart and Summerfelt (1975),
and applied externally to two fish (as later described
for radio-tags). All fish were initially captured in gill
nets, either off the Truckee River Delta or off the
fishway. Fish were released at the point of capture
within 2 h after the tags were attached or implanted.
Estimated longevity of the tags was 16 months. Our
primary tracking unit was a Smith-Root Sonic
Receiver Type T A60. To pinpoint and map loca-
tions of individual fish at a given time, we took bear-
ings with a Lietz pocket transit from two or three
established reference points along the shoreline.
In both 1982 and 1983, the prespawning aggre-
gation began to form off the Truckee River Delta
in mid-March and persisted until mid-June, although
it began to wane by late May, during peak migra-
tion through the fishway. Of 526 cui-ui marked with
Floy tags in late March to early April during the
2 years, 45 were recaptured in the FPB, 35 to 77