Slide background

Restoring the Lower Snake River

From the desk of Gilly Lyons, SOS Policy and Legal Director. May 6, 2013.

Bonneville dam

120% or 125%?

2%, 4%, or 6%?

35% or 70%?


These numbers and acronyms are just a sample of the many facts and figures presented at the Comparative Survival Study (CSS) annual meeting that I attended April 30 in Vancouver, WA. CSS is a collaborative scientific study, initiated in 1996 by state and Tribal fishery managers and the U.S. Fish & Wildlife Service, to estimate Columbia Basin salmon and steelhead survival rates at different life stages. Probably our most effective near-term salmon protection measure is spill - a program that sends some water over Columbia/Snake River dams (rather than through turbines) to help more young fish reach the Pacific Ocean safely. With the dams in place, spill helps the river act just a bit more like, well, a river – which is exactly what endangered salmon and steelhead need.

Since 2006, under federal court order (as a result of a legal victory achieved by salmon and fishing advocates, the State of Oregon, and the Nez Perce Tribe), federal dam managers have been required to spill water to improve salmon survival during their spring/summer migration.

Scientists have long understood that spill helps salmon, but it turns out to be even more beneficial than we thought – not just in terms of getting ocean-bound smolts downstream in one piece, but also in terms of their survival in the ocean and eventual return to spawning gravels as adults.

At this year’s meeting, scientists presented a range of modeled scenarios that indicate more spill - up to a point - can lead to survival improvements that could move imperiled salmon and steelhead stocks from the “treading water/ at high risk of extinction” column into the “hey, now we’re getting somewhere” column.

The truest way to measure salmon survival is something called the Smolt-to-Adult Return ratio, or SAR. For example, for every 100 smolts that journey downstream, how many ultimately return as adults? Scientists generally agree that a 2-4% SAR is needed for survival over the long-term, while a 4-6% SAR is required to rebuild populations. CSS modeled various levels of spill to see how each of four scenarios affected the SARs.

Underpinning these scenarios is a key balancing question: can we spill enough water to yield an SAR at or above 2% (the region’s minimum target for getting salmon numbers "back in the black"), but without spilling so much water that in-river gas levels put the fish at risk of injury? (As spill levels increase, dissolved gases do too, and at certain threshold levels, this can become problematic for salmon and steelhead.)

css.sar.2013The CSS shows we can. According to the scientists' models, if we spill enough water to reach 125% total dissolved gas (ie, the saturation of nitrogen in the river on the dams’ downstream side), we are likely to see SARs at or above 2% more than 70% of the time. (The 125% dissolved gas level is also very safe for salmon; it is only at higher levels that fish start to show signs of impact or injury.) Even if we spill to a 120% gas cap, we’d see those sought-after SARs about 35% of the time.

Contrast both of those scenarios to the level of spill laid out in the now-illegal 2008/2010 federal salmon plan (BIOP): it only hits an SAR of 2% or more 14% of the time. Our salmon, steelhead and fishing economy, and our region needs better than that; the CSS model shows that "better" is very possible.

While Bonneville Power Administration and the other federal dam managers still insist on much lower spill levels, many Northwest fishery managers appear interested in spilling more water (maybe to 120%, perhaps to 125%) to help fish – and “test the waters” to confirm that more spill at these higher levels will lead to many more salmon.

We want to see this too. With our partners, SOS has fought successfully for spill since 2005. We know that it works – and that it’s largely responsible (along with good ocean conditions) for the modest bumps in salmon returns that we’ve seen over the past few years.

The science says let's give spill a chance; now is the time for a new, expanded experimental spill program in the Columbia/Snake rivers.

SEE THE FULL REPORT on the Fish Passage Center website  - with the presentations from the 2013 CSS Annual Meeting.

Share This