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Independent Science Review Of Salmon Survival Study Shows Concern Over Low Smolt-To-Adult Returns
Posted on Friday, November 02, 2018 (PST)

For eight years running, the Independent Scientific Advisory Board has reviewed the Fish Passage Center’s draft Comparative Survival Study for salmon and steelhead in the Columbia/Snake river basin.

 

It completed its ninth review of the latest draft CSS October 18, saying the FPC’s annual report is “mature,” inferring that at this point the study typically includes only updates using the latest year’s data.

 

One thing the CSS report has consistently reported the last few years is that many anadromous fish species fail to meet the 2 to 4 percent smolt to adult survival goal called for in the Northwest Power and Conservation Council’s Fish and Wildlife Program. Species that aren’t meeting the goal are Snake River wild spring/summer chinook, Snake wild steelhead populations, as well as the hatchery fish of these species, and Snake River sockeye salmon. Most wild and hatchery steelhead, chinook and sockeye in the middle and upper Columbia River and tributaries also are not meeting the Council’s goal.

 

However, according to the CSS report, steelhead in the John Day, Umatilla, and Deschutes rivers have consistently higher SARs than other species and meet the Council’s goal more often, if not every year.

 

The Northwest Power and Conservation Council’s Columbia River Basin Fish and Wildlife Program calls for such an annual independent science review of the FPC’s analytical products, including the FPC’s draft CSS report, the ISAB review says.  (For the ISAB review, go to https://www.nwcouncil.org/sites/default/files/ISAB%202018-4%20ReviewCSSdraft2018AnnualReport18Oct.pdf).

 

The draft CSS – titled “Comparative Survival Study of PIT-tagged Spring/Summer/Fall Chinook, Summer Steelhead, and Sockeye” – was released for public review by the FPC and the Comparative Survival Study Oversight Committee at the FPC website (http://www.fpc.org/documents/CSS/DRAFT2018CSSReportv1-1.pdf on Sept. 4. Comments were due October 17 and some of the most comprehensive and technical comments each year are those from the ISAB.

 

The ISAB reviews of the CSS reports began with the draft 2010 annual report and most recently the draft 2017 report. The draft 2018 CSS report covers the period Dec. 1, 2017 through Nov. 30, 2018. (For links to the previous eight ISAB reports, go to https://www.nwcouncil.org/reports/isab-review-comparative-survival-study-css-draft-2018-annual-report.)

 

“Many of the methods have been reviewed in previous ISAB reports and so now receive only a cursory examination,” the ISAB review says. “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.”

 

Among the ISAB’s observations of the draft 2018 CSS report are:

 

-- The ISAB said it’s concerned that the overall pattern of low smolt to adult returns of upper Columbia and Snake river spring/summer chinook salmon and steelhead in 2015-16 (Chapter 4 of the CSS report, “Patterns in Overall SARs”) is likely to continue, “particularly in light of the apparently poor early ocean survival of juvenile salmon in 2017 and unprecedented ocean conditions in 2018 in the Northern California Current and Gulf of Alaska.”

 

-- Rather than trying to do a single study to estimate the effects of alternative tag-types (PIT and coded wire tags), “it may be opportune to do a meta-analysis of the many existing studies to try and figure out why there are different results; for example, is it species specific or just random noise?” the ISAB says.

 

-- The ISAB says that Chapter 7 in the CSS report (“CSS adult salmon and steelhead upstream migration”) is a revision to last year’s Chapter 7. It looks at the relationship between survival of adults upstream of Bonneville and travel time, temperature and arrival date. “A Bayesian imputation method is used to account for the fact that travel time is, by definition, not available for fish that are not detected at the last upstream dam,” the ISAB review says. “The analysis seems to be well formulated and executed. However, information about the distribution of the latent travel times is very indirect, and so the primary concern that the ISAB has is with the sensitivity of the results to a different choice of latent distributions for travel times.”

 

-- Chapter 8 (“PIT tag and coded-wire tag effects on smolt to adult return rates for Carson National Fish Hatchery spring chinook salmon”) reports on an experiment to investigate effects of different types of tags on various estimates of the population processes. “Unfortunately, lower than expected returns implies that the power to detect effects has been reduced compared to original plans. Given the reduced sample sizes, it was not surprising there was no evidence of an effect of tag-type on apparent survival or SARs,” the ISAB review says. “There was evidence for a decrease in PIT-tag retention over time once the adult fish entered the holding tanks. The ISAB is concerned about the effects of heterogeneity in overall survival when age 3, 4, and 5-year-old adult fish are pooled in the analysis, and some potential impacts of over-dispersion on the results.”

 

-- The new methodology described in Chapter 9 (“Preliminary Development of an Approach to Estimate Daily Detection Probability and Total Passage of Spring-Migrant Yearling Chinook Salmon at Bonneville Dam”) to estimate the detection probability (and abundance) of smolts passing the dam could be applied at each dam in the hydrosystem, and thus some progress could be made toward understanding density dependence effects on survival, especially if multiple stocks are involved.

 

The latest CSS report incorporates many of the ISAB’s suggestions from past reviews, including: life-cycle models have been extended to more populations and the effect of tag-type (i.e., PIT vs CWT) on SARs and estimates of survival are now being investigated.

 

The board of scientists also made additional suggestions for next year’s CSS report. Among those suggestions are:

 

-- Chapter 2 (“Lifecycle evaluation of upper Columbia spring chinook”) should be extended to investigate potential benefits on survival of management actions on the hydrosystem, such as spill modifications, as has been done in previous CSS reports. “The CSS indicates in their report that it is under active investigation. We look forward to the results,” the ISAB says.

 

-- The ISAB recommends expansion of ocean survival estimates to additional salmon and steelhead populations with sufficient data, and collaboration between CSS and NOAA to address relevant questions about salmon ocean survival in an adaptive management framework.

 

-- PIT-tagging is important throughout the Columbia River basin and a more in-depth treatment is warranted in Chapter 8, the ISAB says.

 

-- Chapter 9 is important because estimates of abundance are needed when investigating compensatory and interactive effects among stocks, according to the ISAB review. “The authors estimated the probability of detection at Bonneville Dam which forms the basis of the estimator for abundance. A similar approach may be applicable for each dam in the hydrosystem. The feasibility of extending the analysis to the other dams should be explored.”

 

The draft 2018 CSS report was prepared by the Comparative Survival Study Oversight Committee and the Fish Passage Center (www.fpc.org).

 

The committee includes Jerry McCann, Brandon Chockley, Erin Cooper and Bobby Hsu, Fish Passage Center; Steve Haeseker, U.S. Fish and Wildlife Service; Robert Lessard, Columbia River Inter-Tribal Fish Commission; Charlie Petrosky and Tim Copeland, Idaho Department of Fish and Game; Eric Tinus and Adam Storch, Oregon Department of Fish and Wildlife; and Dan Rawding, Washington Department of Fish and Wildlife.

 

The ISAB serves the Northwest Power and Conservation Council, NOAA Fisheries and the Columbia River Indian Tribes by providing independent scientific advice regarding scientific issues that relate to the respective agencies' fish and wildlife programs.

 

Also see:

 

-- CBB, November 4, 2016, “Science Review Of Salmon Survival Study: Snake River Fish Not Meeting Smolt-To-Adult Return Goals,” http://www.cbbulletin.com/437917.aspx

 

-- CBB, December 29, 2015, “2015 Salmon Survival Report Updates Smolt-To-Adult Return Data For Columbia/Snake Salmon, Steelhead,” http://www.cbbulletin.com/435772.aspx

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