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Fish Passage Center's Draft Annual 'Comparative Survival Study' Of Pit-Tagged Fish Out For Review
Posted on Friday, September 17, 2010 (PST)

The Fish Passage Center on Aug. 31 offered for review its draft 2010 annual report on the long-running "Comparative Survival Study (CSS) of PIT-tagged Spring/Summer Chinook and Summer Steelhead."


The report is posted online at

Comments should be sent to Jack Tuomikoski,, by Oct. 15.


The primary purpose of the report is to update the time series of smolt-to-adult survival rate data and related parameters with additional years of data since the completion of the CSS 10-yr retrospective analysis report in 2007. The CSS project began in 1996 with the objective of establishing a long term dataset of the survival rate of annual generations of Snake River bsin salmon and steelhead from their outmigration as smolts to their return to freshwater as adults.


According to the report's introduction, the study was implemented with the express need to address the question of whether collecting juvenile fish at dams, transporting them downstream of Bonneville Dam and then releasing them was compensating for the effect of the Federal Columbia River Power System on the survival of Snake Basin spring/summer chinook salmon which migrate through the hydrosystem.


The CSS is funded through the Northwest Power and Conservation Council's Columbia Basin Fish and Wildlife Program by the Bonneville Power Administration, which markets power generated in the FCRPS. Study design and analyses are conducted through a CSS Oversight Committee with representation from Columbia River Inter-Tribal Fish Commission, Idaho Department of Fish and Game, Oregon Department of Fish and Wildlife, U.S. Fish and Wildlife Service and Washington Department of Fish and Wildlife.


The FPC, which provides technical services to the fish agencies and tribes impacted by the operation of the FCRPS, 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 and are available electronically on FPC and BPA websites:

FPC: and



The completion of the 2010 annual report signifies the 14th outmigration year of hatchery spring/summer chinook salmon marked with Passive Integrated Transponder (PIT) tags as part of the study and the 11th complete brood year return as adults of those tagged fish, covering adult returns from 1997-2008 hatchery chinook juvenile migrations.


A specific goal of the CSS has been to develop long-term indices of Smolt-to-Adult Return (SAR) ratios between juvenile fish that are collected and transported down through the hydro system aboard barges and fish that migrate downstream in-river.


A common comparison, termed "Transport: In river" ratio, or TIR, is the SAR of transported fish divided by the SAR of in-river fish, with SAR being estimated for smolts passing Lower Granite Dam on the lower Snake River and returning as adults back. The fish pass over eight dams, from Lower Granite down through Bonneville Dam on the lower Columbia before reaching the ocean, then retrace their steps upon returning to freshwater to spawn as adults.


"The long-term monitoring data provided by the CSS study groups for wild spring/summer chinook, hatchery spring chinook, hatchery summer chinook, wild steelhead, and hatchery steelhead have demonstrated considerable variability in SARs among study groups and between years," the draft report says.


"The combination of exceptionally low in-river smolt survivals in 2001 and generally average survivals for transported smolts resulted in exceptionally large TIR values for all CSS groups of PIT-tagged fish for the 2001 migration year. Those TIRs indicated a substantial benefit for smolt transportation in 2001, under unusual environmental conditions, extreme drought, and hydrosystem operations which included no spill and maximization of smolt transportation.


"For the rest of the CSS evaluation years, TIR estimates indicate the relative smolt transportation performance for the PIT-tagged spring/summer chinook has been as follows: no benefit for the wild spring/summer chinook and spring chinook from Dworshak and Catherine Creek hatcheries, mixed benefit for the summer chinook from Imnaha Hatchery, and positive benefit in most years to the spring chinook from Rapid River Hatchery and summer chinook from McCall Hatchery. Overall, Snake River hatchery chinook exhibited a generally more positive response to transportation and relatively lower levels of differential delayed mortality (higher D) than did wild populations.


"There appears to be positive benefit of transportation to the PIT-tagged wild and hatchery steelhead aggregates in most years; however, small sample sizes for steelhead through 2007 warrant some degree of caution in the degree of confidence on the relative performance of transportation relative to in-river migration."


The draft annual report also discusses analysis of data related to:


-- Annual metrics of juvenile survival, arrival time, and migration rate;

-- Effects of the in-river environment on juvenile travel tie, instantaneous mortality rates and survival;

-- Adult passage success rates between dams, D, and the expression of delayed effects, and

-- Patterns in annual overall SARs.


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