A draft report released by the federal Fish Passage Center (FPC) reiterates what has been clear for years: salmon and steelhead populations in the Snake River are in deep trouble and cannot recover without breaching the four lower Snake River dams. The 2024 Comparative Survival Study (CSS) confirms that smolt-to-adult return (SAR) rates for salmon and steelhead in the Snake River remain dismally low and will not meet regional recovery goals under current non-breach alternatives.
What’s a Smolt-to-Adult Return Rate?
Simply put, the smolt-to-adult return rate (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%.
The report highlights that the Northwest Power and Conservation Council’s regional objectives—requiring a 4% average SAR for recovery, and a 2% minimum for at-risk species—are consistently unmet for both Snake River and Upper Columbia River salmon and steelhead populations. Despite various strategies aimed at improving survival rates, the data shows that unless the dams are breached, recovery is unlikely. In contrast, fish migrating to and from the Yakima and John Day rivers are generally meeting regional SAR goals. These fish experience many of the same pressures from harvest, hatcheries, and habitat as Snake River fish, but pass through half as many dams in their migration.
The study, which commenced in 1996, includes data spanning decades, underscores the importance of water transit time and juvenile fish survival during their migration. The analysis indicates that the Snake River’s current flow conditions, combined with dam operations, significantly hinder juvenile salmon and steelhead survival.
The research also suggests that efforts to manage flow, such as augmenting springtime riverflows, have been ineffective in significantly improving migration conditions for young fish. This may lead to future efforts to change how flow augmentation is conducted to ensure water is placed at the times and locations where it is most beneficial to migrating fish, and may mean Idaho will soon have to send more water downstream to aid these young smolts in their journey downstream through the dams.
Additionally, the study stresses the importance of breaching the dams as part of a broader strategy to restore these vital fish populations. A 2022 report from the National Marine Fisheries Service entitled “Rebuilding Interior Columbia Basin Salmon and Steelhead” also recommended dam breaching as a centerpiece action and crucial step toward recovery. Without it, the possibility of achieving healthy and sustainable salmon populations remains distant.
The draft CSS study further reveals that survival rates for fish that are transported around the dams are consistently lower than those that migrate through the river system. This points to the fact that for juvenile fish, natural in-river migration offers better long-term survival prospects. To maximize recovery, in-river migration should be made as safe as possible. Hatchery fish also fare worse in migrating upriver compared to wild salmon and steelhead, emphasizing the need to protect wild stocks from further generational decline.
Ultimately, this latest report makes it clear: breaching the lower Snake River dams is not a matter of debate—it is an urgent necessity. If we are to stave off extinction and restore these fish populations to abundance, dam breaching must be prioritized as a critical part of recovery efforts.