Is it possible to recover salmon and steelhead without removing the dams?
The short answer is no.
Rebuilding salmon and steelhead populations will require increasing the number of adults that return to spawn relative to the number of juveniles that migrate to the ocean. This is known as the smolt-to-adult ratio, or SAR.
However, in the past 25 years, salmon and steelhead SARs have failed to reach 2 percent despite restrictions and closures of modern fisheries, and massive investments in Snake River Basin habitat restoration and juvenile fish passage systems at the lower Snake River dams.
The Northwest Power and Conservation Council determined that an SAR of 4 to 6 percent (that is for every 100 smolts, 4 to 6 adults return to spawn) is needed to achieve robust populations.
While many actions like habitat restoration and increased spill over dams have been taken and billions of dollars have been spent, populations have not rebounded.
According to the scientific evidence, achieving a 4 to 6 percent SAR will require breaching the four lower Snake River dams and additional actions.
Restoring a free-flowing lower Snake River, when coupled with complementary actions such as predator control, habitat restoration and spill, is the only meaningful action left in our toolkit with the potential to attain the Columbia Basin Partnership’s recovery goals. An ongoing, long-term study called the Comparative Survival Study, conducted by biologists from Oregon and Idaho, the Fish and Wildlife Service and the Tribes estimates that Snake River dam breaching in concert with maximum flow at downstream dams could increase SARs up to four times the Biological Opinion baseline.
Will breaching the dams solve the problem?
For some context, in the mid-1960s, before the last three Snake River dams were completed (Ice Harbor was in place as were the Columbia dams) SARs for Snake River spring/summer Chinook salmon ranged from 3.5-6.5 percent (average 4 percent from 1964-1968).
In contrast, over the last 25-years, SARs for Snake River spring/summer Chinook salmon have exceeded 2 percent in only two years and Snake River sockeye and fall Chinook salmon have never hit 2 percent. Snake steelhead have hit 2 percent in a handful of years, but their mean SAR is below 2.
This represents a trajectory toward extinction because not enough smolts are surviving to return and spawn as adults.
Minimum smolt-to-adult ratio needed to restore salmon and steelhead
In the past 25 years, the Snake River Basin has barely averaged a 2 percent smolt-to-adult ratio
Smolt-to-adult ratio: The smolt-to-adult Ratio (SAR) is the percentage of smolts that survive and return to spawn:
ADULTS / SMOLTS = SAR
For example, if 100 steelhead smolts pass Lower Granite dam on their downstream migration and 2 adult steelhead from that group return and survive to pass Lower Granite on their way to spawn, the SAR would be 2 percent (adults/smolts).