Abstract
We compared cui-ui (Chasmistes cujus) recruitment from two reaches of the Truckee
River with histories of severe erosional downcutting caused by a decline in Pyramid Lake
surface elevation. In 1975, Marble Bluff Dam (MBD) was constructed 5 kilometers upstream of
the extant mouth of the Truckee River to stabilize the upstream reach of the river; the
downstream reach of the river remained unstable and consequently unsuitable for cui-ui
recruitment. By the early 2000s, there was a decrease in the Truckee River’s slope from MBD to
Pyramid Lake after a series of wet years in the 1990s. This was followed by changes in river
morphology and erosion abatement. These changes led to the question as to cui-ui recruitment
potential in the Truckee River downstream of MBD. In 2012, more than 7,000 cui-ui spawners
were passed upstream of MBD, although an indeterminate number of cui-ui spawned
downstream of MBD. In this study, we compared cui-ui recruitment upstream and downstream
of MBD during a Truckee River low-flow year (2012). Cui-ui larvae emigration to Pyramid Lake
began earlier and ended later downstream of MBD. A greater number of cui-ui larvae was
produced downstream of MBD than upstream. This also was true for native Tahoe sucker
(Catostomus tahoensis) and Lahontan redside (Richardsonius egregius). The improved Truckee
River stability downstream of MBD and concomitant cui-ui recruitment success is attributed to a
rise in Pyramid Lake's surface elevation. A decline in lake elevation may lead to a shift in stream
morphology and substrate composition to the detriment of cui-ui reproductive success as well as
the reproductive success of other native fishes.
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First posted September 23, 2013
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