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 summer 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 15th year of operation.  The CSS participates with state and federal fishery agencies in the PIT-tagging of wild Chinook and steelhead at traps in the Snake River basin above Lower Granite Dam and WDFW in the PIT-tagging of wild Chinook and steelhead at Methow & Entiat traps in the Wenatchee River basin.  The CSS participates with state and federal fishery agencies (including the Lower Snake River Compensation Program and Idaho Power Company) in the PIT-tagging of hatchery Chinook and steelhead at hatchery facilities for planned releases into the Snake River basin above Lower Granite Dam.  The CSS coordinates with these agencies and plus tribal fishery agencies in the pre-assigning of PIT-tagged fish to “Monitor-mode” and “Return-to-River mode” categories.  In addition, wild Chinook and steelhead PIT tagged for other studies in the Snake River basin and upper Columbia River basin (e.g., Yakima, Wenatchee, Entiat, Methow, and Okanogan rivers) and middle Columbia River basin (e.g., Walla Walla, Umatilla, John Day, Deschutes, Hood and Wind rivers) 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 for Snake River stocks, McNary Dam back to Bonneville Dam for upper Columbia River stocks, and either John Day Dam or Bonneville Dam back to Bonneville Dam for middle Columbia River stocks depending on release location.  When possible, SARs from hatchery as smolt back to the hatchery racks are also generated.  In addition, migration speed and conversion rates will be made for returning adult fish between dams with adult detectors present (e.g., Bonneville, McNary, Ice Harbor, Lower Granite, Priest Rapids, Rock Island and Wells 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 and also PIT tagged.  Beginning in 2006, the CSS adopted the pre-assignment protocol whereby PIT-tagged fish are randomly assigned to either a “Monitor-Mode” group or “Return-to-River Mode” group prior to release.  Currently, the latter group is the default  PIT-tag action at the collector dams. When PIT tagged study fish arrive at a transportation collector dam and enter the collection/bypass channel during the transportation season, it will be transported along with the untagged fish if in the “Monitor-Mode” group or simply bypassed back to river if in the default action group.  The “Monitor-Mode” PIT-tagged fish directly reflect the untagged fish population experience in passing each collector dam.  The default PIT-tagged fish would reflect a non-transportation management scenario.  A combination of these two groups is used for in-river reach survival estimation with the Cormack-Jolly-Seber capture-recapture method.

The CSS is designed to address the following objectives:  (i) estimate and compare the smolt-to-adult survival rate (SAR) for transported and non-transported wild and hatchery stream type Chinook and Steelhead;  (ii) determine if the overall annual SAR rates are significantly different from the interim SAR hydro goal;  (iii) compare the overall annual SARs of representative stocks from the Snake, Upper Columbia, and Middle Columbia river basins; and (iv) estimate ratios of SARs for transported and inriver migrating smolts as well as in-river survival rates concurrently over a number of years in order to span a wide range of environmental conditions.