The Comparative Survival Rate Study (CSS) is a multi-year program of the fishery agencies and tribes to measure the smolt-to-adult survival rates of hatchery and wild spring/summer chinook and steelhead from representative sites in the Snake, Mid-Columbia, and lower Columbia River basins.  An interagency CSS Oversight Committee oversees the design, execution, and analysis of this study.  The CSS is entering its ninth year of operation.  In addition to hatchery and wild chinook being PIT tagged, the CSS planned to begin PIT tagging in 2005 hatchery steelhead at two locations in the Snake River and re-establish a PIT tagged hatchery spring chinook in the Mid-Columbia River; however, BPA declined funding the additional PIT tagging within the CSS contract due to monetary shortfalls.  Additional PIT tagged groups of hatchery steelhead had been recommended by the Pacific Northwest Power Planning Council's Independent Scientific Review Committee during its review of the CSS in 1998.  Wild chinook and steelhead PIT tagged for other studies in the Snake River basin and lower Columbia River basin will be utilized whenever possible to meet CSS requirements.  

Smolt-to-adult survival rates for Snake River basin wild and hatchery chinook and wild steelhead that were transported will be compared with those that migrated in-river to below Bonneville Dam.  Estimates of smolt-to-adult survival rates will be made from Lower Granite Dam back to Lower Granite Dam (Snake River stocks), Bonneville Dam back to Bonneville Dam (all stocks), and hatchery back to the hatchery racks (all stocks).  In addition, migration speed and conversion rates will be made for returning adult fish between dams with adult detectors present (e.g., Bonneville, McNary, Lower Granite, and Rock Island dams).  The returns to the hatchery rack will be adjusted for any sport and tribal harvest to provide an estimate of total return to the hatchery.  These survival rates may be used in the evaluations of smolt mitigation measures such as flow augmentation, spill, and transportation for the recovery of listed salmon stocks.  

For this study, hatchery chinook are sampled from regular hatchery production and implanted with a PIT (Passive Integrated Transponder) tag, which allows unique identification of each fish.  The wild chinook and wild steelhead are sampled at tributary traps in the Snake River basin and also PIT tagged.  When PIT tagged study fish arrive at a transportation collector dam and enter the collection/bypass channel for the first time, a predetermined proportion will be purposely routed to the raceways for transportation while the remaining study fish will be routed back to the river for use in-river survival estimation with the Cormack-Jolly-Seber capture-recapture method.

The CSS is designed to address the following objectives:  (i) estimate the smolt-to-adult survival rate (SAR) for transported wild and hatchery stream type chinook;      (ii) determine if SAR rates are significantly different from the interim SAR hydro goal;   (iii) compare the SARs of transported and downriver indicator stocks; and (iv) estimate transport/control ratios and in-river survival concurrently over a number of years in order to span a wide range of environmental conditions.