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Heading Toward Extinction by Richard Scully Lewiston Tribune, May 29, 2022

Regarding Dick Sherwin's May 15 letter: Prior to construction of the lower Snake River dams, smolt-to-adult return ratios for Snake River spring/summer chinook and steelhead were about 4%. This survival rate was adequate for healthy tribal and sport fisheries, with sufficient spawners remaining for population stability.

In recent years, Snake River spring/summer chinook and steelhead, which must negotiate eight dams and reservoirs on their migration to and from the ocean, have had SARs averaging less than 1% for salmon and less than 2% for steelhead. When SARs are less than 1%, this leads to extinction. With less than 2%, depressed populations cannot recover.

The Northwest Power and Conservation Council's SAR goal for spring/summer chinook and steelhead is 2% to 6%, with an average of 4%.

This is the level of survival Snake River steelhead and salmon had before construction of the lower Snake River dams.

Salmon populations from Columbia River tributaries downriver from the lower Snake River dams, which must negotiate four or less dams, continue to have adequate SARs, even though salmon that enter these tributaries experience the same ocean conditions and predation by birds, marine mammals and piscivorous fish that Snake River salmon do.

The difference in SARs between upriver and downriver tributary populations is due to the number of dams and reservoirs that the upriver and downriver populations must negotiate.

A recent summary of the science is available online. Google: "A review of potential conservation and fisheries benefits of breaching four dams on the lower Snake River."