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<br />by yearling cui-ui could reasonably be expected to
<br />differ between Pyramid Lake and Mud Lake Slough
<br />because the ecosystems differ substantially. How-
<br />ever, the meager evidence is that yearling cui-ui are
<br />discriminative feeders.
<br />
<br />Predation
<br />
<br />Adult cui-ui are exposed to predation by Ameri-
<br />can white pelicans during their spawning migration.
<br />In 1982 we accounted for 427 cui-ui lost to pelicans;
<br />of these, 355 were either dropped or regurgitated
<br />by the birds along the fishway or along the delta,
<br />and 72 were counted on Anaho Island, the site of
<br />a pelican rookery in Pyramid Lake. The fish dropped
<br />were 510-630 mm long and weighed 1.8-3.1 kg;
<br />84% were females. We did not determine why the
<br />fish were dropped, but once the fish were on the
<br />ground, the pelicans did not attempt to recover
<br />them.
<br />The bones from the 72 cui-ui on Anaho Island
<br />were obviously from the 1982 migration; older
<br />bones were also present, but they were generally
<br />broken and buried in the soil.
<br />In spring 1983, the spawning migration of the
<br />cui-ui-like that ofthe Tahoe sucker and mountain
<br />sucker, the other two major species migrating to the
<br />FPB-were delayed. During peak fish migration in
<br />late May, relatively few pelicans foraged along the
<br />fishway and only 26 fish carcasses were recovered.
<br />In 1984, cui-ui migrated up the Truckee River exclu-
<br />sively, and no cui-ui carcasses were found along the
<br />fishway or on the delta. Because water depth at the
<br />delta exceeded 1 m, most fish probably remained
<br />beyond the reach of the pelicans (Knopf and
<br />Kennedy 1981).
<br />
<br />Acknowledgments
<br />
<br />We thank the Pyramid Lake Indian Tribal Coun-
<br />cil for their approval to conduct this investigation;
<br />the Pyramid Lake Fishery organization for provid-
<br />ing cui-ui larvae for experimentation and opercle
<br />bones for the age and growth determinations;
<br />Howard Burge, Philip Johnson, Peter Rissler, and
<br />Dana Winkleman for providing field assistan(:e and
<br />help with data analysis; Chester Buchanan, William
<br />Burger, Alfred Davis, Robert Hallock, Mark Mix,
<br />Mitchell Morgan, Patricia Rice, and Donald Sada for
<br />assistance in the field; Gary Sonnevil for providing
<br />
<br />21
<br />
<br />data from gill-net sampling and on numbers of cui-ui
<br />entering the Marble Bluff fish processing building
<br />from 1977-1982; and Patrick Coffin, Alan Ruger,
<br />and Jerry Smith for reviewing the manuscript.
<br />
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