Abstract
We analyzed 6 years (2004–09) of passage and survival data collected at McNary Dam to
determine how dam operations and environmental conditions affect passage and survival of juvenile
salmonids. A multinomial logistic regression was used to examine how environmental variables and
dam operations relate to passage behavior of juvenile salmonids at McNary Dam. We used the
Cormack-Jolly-Seber release-recapture model to determine how the survival of juvenile salmonids
passing through McNary Dam relates to environmental variables and dam operations. Total project
discharge and the proportion of flow passing the spillway typically had a positive effect on survival for
all species and routes. As the proportion of water through the spillway increased, the number of fish
passing the spillway increased, as did overall survival. Additionally, survival generally was higher at
night. There was no meaningful difference in survival for fish that passed through the north or south
portions of the spillway or powerhouse. Similarly, there was no difference in survival for fish released
in the north, middle, or south portions of the tailrace. For subyearling Chinook salmon migrating during
the summer season, increased temperatures had a drastic effect on passage and survival. As temperature
increased, survival of subyearling Chinook salmon decreased through all passage routes and the number
of fish that passed through the turbines increased. During years when the temporary spillway weirs
(TSWs) were installed, passage through the spillway increased for spring migrants. However, due to the
changes made in the location of the TSW between years and the potential effect of other confounding
environmental conditions, it is not certain if the increase in spillway passage was due solely to the
presence of the TSWs. The TSWs appeared to improve forebay survival during years when they were
operated.
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First posted September 7, 2011
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