An annual report on salmon and steelhead survival in the Columbia River Basin, now in its 25th year, is a deep reservoir of information that has practical implications for policy-makers, but is so dense in places that it would be helped by condensation of some of its reporting. That’s one of the messages in an expert review of the draft, nearly 400-page 2020 Comparative Survival Study (CSS) Annual Report.
The CSS draft report is produced by the 10-member Comparative Survival Study Oversight Committee, comprising fishery managers from state fish and wildlife agencies and Indian tribes, and the Portland-based Fish Passage Center. The draft report was reviewed by the Independent Scientific Advisory Board (ISAB), whose 11 members are appointed jointly by the Council, NOAA Fisheries, and the Columbia River Inter-Tribal Fish Commission.
Some of the key takeaways from the ISAB review include:
Smolt-to-adult survival rates (SARs): The Council’s Columbia River Basin Fish and Wildlife Program includes a goal of achieving smolt-to-adult returns – the percentage of juvenile salmon and steelhead that go to the ocean and return as adults to spawn – of 2 percent to 6 percent; current SARs for several salmon and steelhead populations are well below that. The CSS includes lengthy data sets and extensive summaries of results that may overwhelm decision makers and the public seeking to understand it all, the ISAB reported, and may inadvertently give the impression that the persistently low SAR values are inevitable. The ISAB suggested that the CSS authors develop an “impact report” collectively with other groups to communicate the most critical take-home messages regarding SARs for the Council, the Bonneville Power Administration, and fishery managers.
Changes in the Columbia River system and impacts on fish: Many things have changed in the system over the 25 years of CSS data collection, and the impacts of these changes on the long-term analyses of fish survival are complex. The ISAB recommends the CSS develop a table of the changes over the years and a brief description of possible impacts of these changes on salmon and steelhead survival.
Wild steelhead survival: The 2020 report includes a new, exploratory analysis of the patterns of survival of wild steelhead in the Columbia River Basin. The ISAB complimented this development, but also noted that because the life history of steelhead is more complex than the life histories of Pacific salmon, a more thorough explanation is warranted of the consequences of steelhead life histories on the analysis and associated assumptions.
Adult spring Chinook survival: The draft CSS includes a work in progress analyzing the success of upstream spring Chinook migration to the Snake River Basin. All of the survival probability estimates are very high, the ISAB notes, and the lack of contrast in survival in many river reaches over time will make it difficult to determine the effects of different factors that affect survival. The ISAB recommends the CSS clearly identify the ultimate application of this analysis and highlight alternative management actions and their potential impacts on Chinook survival.
The CSS is a long-term study within the Council’s Columbia River Basin Fish and Wildlife Program and is funded by the Bonneville Power Administration. The program calls for a regular system of independent and timely scientific reviews of the Fish Passage Center’s analytical products. These reviews include evaluations of the CSS annual reports. With the current review, the ISAB now has reviewed the last eleven CSS draft annual reports.