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2018 Comparative Survival Report Offers Latest Numbers On Smolt-To-Adult Returns For Basin Salmonids
Posted on Friday, February 08, 2019 (PST)

Overall smolt-to-adult return information for both transported and in-river chinook salmon and wild steelhead transiting the federal hydropower system in the Columbia and Snake rivers was consistent in 2018 with past year’s findings, according to the Fish Passage Center’s 23rd annual comparative survival study.

 

The first of the CSS studies was in 1996. Its objective was, and continues to be, to establish a “long-term data set of annual estimates of the survival probability of generations of salmon from their outmigration as smolts to their return to freshwater as adults to spawn (smolt-to-adult return rate; SAR),” the study says.

 

None of the juvenile passage routes – in-river or by barge – resulted during the year in meeting the Northwest Power and Conservation Council’s SAR objectives set in its 2014 Fish and Wildlife Program for Snake River wild spring/summer chinook and steelhead, which is a range of 2 percent to 6 percent, the study says.

 

However, PIT-tag SARs for middle Columbia River wild spring chinook and wild steelhead generally did fall within the Council’s 2 to 6 percent range. Yet, the overall SARs for upper Columbia River and Snake River populations of salmon and steelhead are not meeting this regional goal, while middle Columbia River populations are meeting the SARs goals in most years.

 

Council targets are set with an assumption of what the historical levels of productivity were prior to 1970 when the Snake River dams were set in place. The Council is currently in a year-long process to update its Fish and Wildlife Program.

 

Looking back a year, the results of the 2017 analysis showed that for all three salmonid species – Snake River summer chinook, sockeye and steelhead – the upstream survival for adult fish that were transported as juveniles were lower than fish that had migrated in-river as juveniles.

 

Furthermore in the 2017 analysis, upstream survival of fish transported as juveniles started to decrease at lower temperatures compared to fish that had migrated in-river, the report says.

 

“The 2018 analysis is an expansion and refinement of earlier analyses of upstream migration success,” the study says. “Observations from the 2018 study were consistent with historic analyses: all species in this analysis showed a decreasing upstream conversion probability in warm water temperatures greater than 18 (degrees Celsius), and fish that were transported as juveniles had a lower conversion probability overall and a higher portion of strays compared to fish that migrated in-river.”

 

The FPC published its final “Comparative Survival Study of PIT-tagged Spring/Summer/Fall Chinook, Summer Steelhead, and Sockeye 2018 Annual Report” in December. It can be found at http://www.fpc.org/documents/CSS/2018_Final_CSS.pdf. All CSS Annual Reports are at http://www.fpc.org/documents/CSS.html.

 

The question the study addresses each year is whether collecting juvenile salmon at lower Snake River dams and transporting them downstream of Bonneville Dam where they are released, compensates for the effects of the Federal Columbia River Power System on “the survival of Snake Basin spring/summer Chinook salmon that migrate through the hydrosystem,” the report says.

 

The 2018 study 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, all of the 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 CSS is a long-term study within the Northwest Power and Conservation Council’s Columbia Basin Fish and Wildlife Program and is funded by the Bonneville Power Administration. The Fish Passage Center coordinates the PIT-tagging efforts, data management and preparation, and CSSOC work. All draft and final written work products are subject to regional technical and public review.

 

The overall objective of the annual report is to provide a historical reference for each year to provide a basis for future fish passage mitigation discussions, and a base reference for future analysis of adult returns, the report says. It is the beginning of a longer-term effort, which will need to incorporate effects of density dependence on observed productivity to evaluate population responses relative to SAR rates.

 

The study says it includes 23 years of SAR data for wild Snake River spring/summer chinook (1994–2016), 20 years of SAR data for Snake River hatchery spring/summer chinook (1997–2016), 19 years of SAR data for Snake River wild and hatchery steelhead (1997–2015), and eight years of SAR data for Snake River sockeye (2009–2016).

 

There are eight years of SAR data for Snake River hatchery fall chinook (2006–2012 and 2015). For mid-Columbia and upper-Columbia fall chinook there are varying numbers of years available. There are 15 years of SAR data for Hanford Reach wild fall chinook (2000–2015), five years of SAR data for wild Deschutes River fall chinook (2011–2015), and eight years of SAR data for both Spring Creek National Fish Hatchery and Little White Salmon NFH fall chinook (2008–2015).

 

Spring and summer chinook and sockeye returns from outmigration year 2016 should be considered preliminary, as they include only 2-salt returns and may change with the addition of 3-salt returns next year, the study says. Similarly, 2015 migration year fall chinook returns include only 2-salt adults.

 

The over 800 page detailed report contains:

Chapter 1: Introduction

Chapter 2: Life Cycle Evaluation of Upper Columbia Spring Chinook

Chapter 3: Effects of the in-river environment on juvenile travel time, instantaneous mortality rates and survival

Chapter 4: Patterns in Annual Overall SARs

Chapter 5: SARs AND productivity

Chapter 6: Estimation of SARs, TIRs and D for Snake River Subyearling Fall Chinook

Chapter 7: CSS chapter for adult salmon and steelhead upstream migration

Chapter 8: Comparative analysis of smolt-to-adult return rates for Carson National Fish Hatchery spring Chinook salmon using passive integrated transponder and coded wire tags

Chapter 9: Preliminary Development of an Approach to Estimate Daily Detection Probability and Total Passage of Spring Migrant Yearling Chinook Salmon at Bonneville Dam

 

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