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A total of 509 sockeye salmon, Oncorhynchus nerka, were
PIT-tagged at Bonneville Dam in 2007 and tracked upstream using
detections at mainstem dam fish ladders. Based on these detections,
upstream survival steadily declined as the migration progressed;
Bonneville-Rock Island survival declined from over74% for sockeye
salmon passing Bonneville Dam during June to less then 68% during
the first two weeks of July. There was also a significant linear
relationship between decreasing survival and increasing water temperature.
The estimated stock composition of sockeye passing Bonneville Dam
was 85.3% Okanogan and 14.7% Wenatchee.
Sockeye salmon mean travel time between Bonneville and Rock Island
dams was 14.6 days, indicating a mean travel speed of 33.2 km per
day. Fish passing Bonneville Dam later in the migration traveled
upstream faster than those earlier in the migration.
Mark-recapture techniques were used to estimate sockeye salmon
abundance at upstream dams. These techniques estimated up to 14.7%
more
fish at McNary Dam but at all other dams estimated 21.9% to 32.1%
fewer sockeye salmon than indicated by visual dam counts. Estimated
rates of sockeye salmon falling back over the dams after ascending
and then reascending ranged from 0.2% at McNary Dam to 3.0% at Priest
Rapids Dam.
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