To confuse you, dam proponents – including some in Congress – tout Columbia Basin’s Snake River per-dam juvenile salmon survival rate as if it applied accumulatively to the entire waterway.
The Corps of Engineers cites a per-dam survival rate trending toward 95%, which may be true … but is deceptively used.
Here’s why: The anti-salmon crowd fails to tell you that accumulated dam-by-dam losses through all eight dams leaves only 66% survival and doesn’t account for losses occurring in the dams’ reservoirs.
The National Oceanic and Atmospheric Administration’s report does. In 2018, NOAA reported a Snake River juvenile spring-summer Chinook survival rate – from the head of slack water (near Lewiston) to Bonneville Dam’s tailrace (the lowest tailrace) – at just 38%. NOAA also reported a long-term average of just 49%.
However, none of the above rates include “delayed mortality.” These losses occur between Bonneville and the ocean and result from stress and harms juveniles suffer as they pass through the eight-dam and reservoir obstacle course. Researchers estimate delayed mortality losses of 36% to 76%.
Therefore, including, as we must, delayed mortality, in 2018 the total Snake River juvenile salmon survival rate ranged between 24% to 9%. These figures tell the sad, whole-truth story.