The long-awaited draft EIS for the Columbia River System Operations (CRSO) will soon be completed and released. As a reporter, I want to be prepared for this important document. What’s in the final EIS and subsequent Record of Decision will have a big impact on the future of the region. It may play a role in whether the parties involved in National Wildlife Federation et al. v. National Marine Fisheries Service et al. go back to fighting it out in court, or whether the region takes a step toward resolving these longstanding issues.

As I was pondering the best way to prepare for the EIS, I received a couple of emails from readers pointing to juvenile survival.

And so it dawned on me: this EIS will analyze many things—from the many impacts of tearing out the four lower Snake River dams to how dam operations, spill and total dissolved gas affect fish. But a problem that keeps arising in the Snake River is juvenile survival. It’s a complex and confusing topic with a long history, so I took a deep breath, started researching the issue and began making calls to people who know a lot more about this than I do.

After a few weeks of gathering information, what is most striking to me is that when it comes to evaluating juvenile survival, there’s a lot of noise. Noise, as in unwanted information that can drown out the information you want.

There's noise in figuring out what's causing the mortalities; there’s noise in determining the best way to measure juvenile survival; and there’s noise in the year-to-year comparisons of those measurements. From water volumes and velocities to the timing of spring melt and the number of predators, the natural world that juvenile salmon and steelhead find themselves in is constantly changing.

To complicate things further, operations at all of these dams are also changing from year to year—adding more noise. In 2018, we spilled to spill cap levels for 24 hours a day. In 2019, we spilled to 120 percent total dissolved gas for 16 hours a day. Under this year’s flexible spill agreement, spill will go up to 125 percent TDG at most of the eight dams for 16 hours a day.

Just to be clear, if you’re looking for me to confirm your worldview that the dams should be removed, or that the dams should not be removed, you can stop reading here. This is just a look at juvenile survival in the context of this EIS. There are so many other things to consider when it comes to removing the dams. With my basic understanding of the whole picture, I wouldn’t feel qualified to make that call anyway. What I will say is that both sides make compelling arguments related to juvenile survival, and that’s what I’m exploring.

First, here’s a glimpse of the issues involved with juvenile survival—and my apologies to readers for whom this is basic information.

There are many different ways that scientists measure juvenile survival in the Columbia Basin. NOAA Fisheries provides an annual report on direct juvenile survival, which is a detailed look at how many PIT-tagged fish make it past each dam, and how many of those make it past the next, and the next. The Fish Passage Center also tracks and makes available reams of information through its Juvenile Survival Queries, including an annual report with juvenile survival estimates, and a multiyear reach analysis tool that provides survival estimates and fish travel times.

For a more complete picture on how well each of those PIT-tagged juveniles survived, we have to wait a few years for smolt-to-adult ratios, or SARs, which tell us how many of those juveniles make it back upriver, and presumably to their hatchery or spawning area. A goal in the Northwest Power and Conservation Council’s Fish and Wildlife Program is to achieve smolt-to-adult return rates from 2 to 6 percent, with a minimum of 2 percent and an average of 4 percent, for listed salmon and steelhead. Wild Snake River spring/summer Chinook and steelhead continue to fall short of those objectives.

The SARs are also used to determine whether juvenile fish that were transported downstream by barge returned in greater or lower percentages compared to the fish that remained in the river. Those survival rates are measured in TIRs, or transport-to-inriver ratios.

Each of these measuring devices is completed for each of the Columbia Basin’s 13 endangered or threatened stocks, or, for purposes of the Snake River dam debate—the four ESA-listed salmonids in the Snake River. So a bad survival year for juvenile Snake River sockeye isn’t necessarily a bad year for juvenile Snake River steelhead.

In trying to analyze juvenile mortality in the Columbia Basin, there are two life-cycle modeling studies. The Comparative Survival Study (CSS) is a joint project of the Fish Passage Center, the Columbia River Inter-Tribal Fish Commission, fish agencies in Washington, Oregon and Idaho, and the U.S. Fish and Wildlife Service. COMPASS is NOAA Fisheries’ model, which predicts survival and passage behavior through the hydropower system. NOAA uses separate models for adult returns.

According to the EIS on the Washington Department of Ecology’s proposal to increase spill to 125 percent total dissolved gas, the main differences between the two are that NOAA’s model does not factor in the same assumptions about delayed mortality and makes different conclusions about the relative benefit of transportation as an alternative to spill.

Delayed or latent mortality occurs subsequent to dam passage—in the estuary and the ocean—and is directly related to their hydrosystem experience. The 2019 CSS includes a new chapter that reviews studies supporting the theory and those that don't.

Whether or not you factor in latent mortality is a big deal. The studies supporting latent mortality show that between two-thirds and three-quarters of the juvenile salmon that make it through all eight Snake and Columbia river dams later die from latent mortality. And that’s after losing roughly half of them due to direct injuries and stress of the journey.

But a recent NOAA study (CU No. 1927 [16]) found that adult returns depend more on the size of the juvenile than its passage route through hydroelectric dams, and questioning the magnitude of benefit that spill—or dam removal—would provide.

Michele DeHart, manager of the Fish Passage Center, told the Southern Resident Orca Task Force last year that the 2017 CSS looked at the potential of removing the four dams, and concluded that the highest adult returns would come if those four dams were removed, and the four lower Columbia River dams spilled to 125 percent TDG. Under that scenario, Snake River Chinook SARs would increase to two percent under poor ocean conditions, and to 11.3 percent when ocean conditions are good.

Jim Faulkner, a research statistician at NOAA’s Northwest Fisheries Science Center, said NOAA models also predict increased inriver survival if the four dams are breached, due to decreased travel times, potentially decreased river temperatures, and a reduction in the direct mortality. That modeling was done for the EIS, which has not yet been released.

The two models, and their corresponding theories, may lead us to two very different conclusions about whether or not removing the dams is a good idea—just from the perspective of juvenile survival.

Tune in next week, when Clearing Up goes into more detail about juvenile survival, the two models, and the upcoming EIS.

K.C. Mehaffey covers fish issues for Clearing Up, and is editor of the NW Fishletter. She joined the NewsData writing team in February 2018. From lawsuits to scientific studies, she is enjoying the deep dive into the Columbia Basin's many fish topics.