The Columbia River Basin Fish and Wildlife Program calls for a regular system of independent and timely reviews of the Fish Passage Center’s (FPC) analytical products. These reviews include evaluations of the Comparative Survival Study’s (CSS) draft annual reports. The ISAB has reviewed these reports annually beginning nine years ago with the evaluation of the CSS’s draft 2010 Annual Report. This ISAB review of the draft 2019 CSS Annual Report is the ISAB’s tenth review of CSS annual reports.
The annual CSS report is a mature product, typically including only updates with the latest year of data and expansion of analyses as more data are acquired. Many of the methods have been reviewed in previous ISAB reports and so now receive only a cursory examination. As more data are acquired, new patterns and questions arise on the interpretation of the results—this is now the primary focus of our reviews.
The draft CSS report describes many important analyses that are evaluated in the full report, but a few key observations include:
- The ISAB continues to be concerned that the smolt-to-adult survivals (SARs) of Snake River wild spring/summer Chinook and steelhead continue to fall well short of the Council’s 2%-6% SAR objectives. While the CSS is only the messenger of bad news, we reiterate our previously unanswered question that given the large amount of effort in the past to improve SARs through dam passage improvements, habitat improvements, and other changes, to what extent might further improvements in hydrosystem management, predator control, and estuarine habitat lead to achieving SARs of 2%-6%? (Chapter 4)
- Chapter 9 presents a life-cycle analysis of multiple-populations to estimate survival from smolt back to returning adults. This is a sophisticated analysis that allows modeling capture histories of some 93,000 tagged and recaptured spring Chinook salmon from the upper Columbia River tributaries (Wenatchee, Entiat, Methow). The take-home message appears clear and is sobering. Smolt-to-adult returns (BON-to-BON) are below management goals of 4%, and SAR estimates for smolts tagged in their natal streams to adults returning to those streams were <1%. It is possible that tagging effects also cause lower survival, but this bias seems unlikely to be the main reason for such low survival.
- Results from Chapter 3 indicate that over the range of total dissolved gas (TDG) measured during the 20-year study period, there was no evidence of strongly detrimental effects.
- Chapter 6 is a new chapter that reviews the literature on delayed mortality effects. The ISAB is generally pleased with the review and suggests some additional literature to be included.
Since 2011, the ISAB has suggested topics that warrant further CSS or regional review. The following are some of the topics recommended in 2019 for future reports:
- Include information about the effects of mini-jacks (male Chinook that remain in freshwater and mature two years after fertilization) on estimates of SARs and other relevant parameters. Are there hydrosystem effects on mini-jack rates?
- Smolt-to-adult survivals (SARS) continue to be very low. Do we have enough information to suggest changes to hydrosystem operations that could improve SARs? Is there now enough information to estimate how much improvements in habitat and other “controllable” aspects of the hydrosystem are needed to improve SARS?
- Continue the work on the integrated life-cycle model looking at survival from smolt back to adults (Chapter 9).
- Continue the work on modeling adult salmon and steelhead upstream migration and consider adding information on individual covariates.
- Consider ways to address the spatial and temporal aspects of the effect of total dissolved gas on survival.
- Continue work on methods to estimate numbers of outgoing smolts at Bonneville.
The ISAB appreciates the CSS’s detailed responses to suggestions provided in previous reviews, and we do not expect the CSS to necessarily respond immediately to new requests for further analyses.
The ISAB’s full report contains an overview of the draft 2019 CSS report’s findings, suggested topics for further CSS review, and general comments and specific editorial suggestions on each chapter of the draft 2019 CSS report.