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2024 Draft Annual Salmon Survival Report: Smolt-to-Adult Return Rates Won't Meet Regional Goals Under Non-Breach Alternatives by Staff Columbia Basin Bulletin, October 8, 2024

"[S]molt to adult return rates (SARs) would not meet the regional goals under
non-dam breach alternatives and would fail to prevent population declines."

The latest draft annual survival study by the Fish Passage Center confirms what the organization has found each year since 2019, that recovery of salmon and steelhead in the Snake River will not occur without breaching the four lower Snake River dams.

FPC's draft 2024 Comparative Survival Study says that the Northwest Power and Conservation Council's regional smolt-to-adult return objectives -- 4 percent average for recovery and a 2 percent minimum -- for Snake River and Upper Columbia River salmon and steelhead populations are not being met.

"When considering all the individual components of CSS analyses in this report together, the results confirm past CSS analytical conclusions and predictions. Most notably, CSS results from 2019 predicted that under climate change, with poor ocean conditions and poor flow conditions, smolt to adult return rates (SARs) would not meet the regional goals under non-dam breach alternatives and would fail to prevent population declines," the study says. "The persistently low SARs in recent years for Snake River populations confirm the findings, results and recommendations of the NOAA Fisheries 2022 report on Rebuilding Interior Columbia salmon and steelhead Populations and the 2019 CSS analyses for the CRSO-EIS."

NOAA Fisheries released its "Rebuilding" report in October 2022. The report identifies actions that the agency says have the greatest likelihood of making progress toward rebuilding populations of salmon and steelhead in the Columbia River basin to "healthy and harvestable levels." Recommended actions to rebuild Columbia Basin stocks are increasing habitat restoration, reintroducing salmon into blocked areas, breaching dams, managing predators, reforming fish hatcheries and harvest and reconnecting floodplain habitat.

Important factors that impact SARs, according to the draft CSS study, are water transit time, spill and transportation of juveniles during their downstream migration.

In a new chapter proposed by the Independent Scientific Advisory Board, the CSS analyses shows that water transit time (flow) and PITPH (spill) are two important freshwater variables in predicting salmon and steelhead survival from juveniles to adults. Water transit time, the draft study says, is one of the most important factors for downstream salmon and steelhead migration, juvenile fish travel time, juvenile fish survival and smolt-to-adult return rate.

Also, as has been asserted in previous CSS studies, adults with a history of juvenile transportation consistently showed lower upstream survival as adults than those with a history of juvenile in-river migration. Hatchery fish were less likely to survive upstream migration than their wild counterparts, the study says.

Surprisingly, the study found that the influence on juvenile salmon and steelhead survival of flow augmentation through the Snake River is low. In Chapter 7 of the study, it made this conclusion after an evaluation of the history of flow augmentation from the Snake River above Brownlee Reservoir (2006-2023).

"The complexity of moving water across the landscape and water accounting associated with established laws and agreements hinder the ability to place water at times and locations most beneficial to anadromous fishes," the draft study says.

In addition, the draft study found no evidence of detrimental effects on instantaneous mortality rates of high Total Dissolved Gas levels across juvenile migration years 1998-2023.

The first CSS study was in 1996. The 2024 CSS study is huge -814 pages complete with supporting graphs and tables. Titled "Comparative Survival Study of PIT-tagged Spring/Summer/Fall Chinook, Summer Steelhead, and Sockeye," this latest draft CSS, like others before it, is a large-scale monitoring study of spring/summer/fall chinook salmon, steelhead, and sockeye salmon.

The draft 2024 report was prepared by the Comparative Survival Study Oversight Committee and Fish Passage Center, which includes: Jerry McCann, Brandon Chockley, Erin Cooper and Gabe Scheer, of the FPC; Steve Haeseker, U.S. Fish and Wildlife Service; Bob Lessard, Columbia River Inter-Tribal Fish Commission; Tim Copeland and Jonathan Ebel, Idaho Department of Fish and Game; Adam Storch, Oregon Department of Fish and Wildlife; and Dan Rawding, Washington Department of Fish and Wildlife. The study is funded by the Bonneville Power Administration.

The draft study includes 29 years of SAR data for wild Snake River spring/summer Chinook (1994-2022), 26 years of SAR data for Snake River hatchery spring/summer Chinook (1997-2022), 25 years of SAR data for Snake River wild and hatchery steelhead (1997-2021), and 14 years of SAR data for Snake River sockeye (2009-2022), the draft study says.

In addition, there are up to 13 years of SAR data for Snake River hatchery fall Chinook (2006, 2007-2012, and 2015-2021), and several years of Snake River wild fall SAR data spanning the years 2006-2012. For mid-Columbia and upper-Columbia fall Chinook, there are 22 years of SAR data for Hanford Reach wild fall Chinook (2000-2021), seven years of SAR data for wild Deschutes River fall Chinook (2011-2017), and 14 years of SAR data for both Spring Creek NFH and Little White Salmon NFH fall Chinook (2008-2021). Spring and summer Chinook and sockeye returns from outmigration year 2022 should be considered preliminary, as they include only 2-salt returns and may change with the addition of 3-salt returns next year. Similarly, 2021 migration year fall Chinook returns include only 3-salt adults through July 28, 2024. The CSS has actively provided Passive Integrated Transponder (PIT) tags for most of these groups since the outmigration year 1997.

Among other conclusions reached in the draft CSS are:

• Summaries of hydro system operations over the 1998-2023 period show decreases in the number of powerhouse passages experienced over time. However, there was no evidence of improvement in water transit times. Dam operations implemented during 2020-2023 likely increased water transit times due to the increase in John Day Dam reservoir elevations and frequent increases above the minimum operating pool levels at the lower Snake River dams. These analyses indicate that if juvenile fish travel time is reduced, juvenile survival is increased, and SAR survival is increased under conditions of reduced water transit time and reduced powerhouse passage rates, according to the study.

• The North Pacific Gyre Oscillation index during spring was positively associated with ocean survival and SAR survival of Chinook salmon and steelhead. Measures of spring upwelling and spring-summer sea surface temperature were also associated with ocean and SAR survival.

• Improvements to fish travel time, mortality rates, and survival may be possible through management actions that reduce travel time, increase spill percentages, and reduce powerhouse passage rates.

• Not all runs of salmon are predicted to decline. Although overall SARs confirms that the Northwest Power and Conservation Council regional SAR objectives, of a 4% average for recovery and a 2% minimum, for Snake River and Upper Columbia salmon and steelhead populations are not being met, SARs for the Middle Columbia River wild-spring Chinook from the Yakima and John Day rivers continue to generally meet the regional SAR goal. SARs of hatchery spring Chinook from the Upper Columbia were correlated with hatchery spring Chinook from the Snake River and the Middle Columbia River.

• The largest and most consistent effect on upstream migration success of spring, summer, and fall Chinook, and summer steelhead, was a history of juvenile transport and hatchery/wild stock origin. Adults with a history of juvenile transportation consistently showed lower upstream survival than those with a history of juvenile in-river migration. Hatchery fish were less likely to survive upstream migration than their wild counterparts. High temperatures negatively impacted survival in all reaches for summer Chinook, but only in the Snake River for spring Chinook, and in the Bonneville to McNary reach for fall Chinook.

• Although the need for faster water transit time (WTT) for downstream migration and survival to adult is undisputed, the study says, measures implemented to date have not provided adequate transit time.

Related Sites:
Science Review Of Salmon Survival Study: Snake River Fish Not Meeting Smolt-To-Adult Return Goals by Staff, Columbia Basin Bulletin 11/4/16