The Comparative Survival Study (CSS) Oversight Committee prepared this report to
address the recommendation provided by the Independent Scientific Advisory Board (ISAB) to
prepare a retrospective synthesis of the methods and results to date on spring/summer Chinook
and steelhead in the Columbia Basin. This ten-year summary report describes study methods,
results and conclusions based on ten years of monitoring efforts. The Passive Integrated
Transponder (PIT) data used in the CSS are analyzed retrospectively, incorporating all juvenile
and adult recovery data available for the period 1996 through 2006.
The Ten-Year Retrospective Summary Report analyzes the available PIT-tag data withinand
across-years, assessing the effects of migration routes, environmental conditions and
migration timing on juvenile reach survival rates and Smolt-to-Adult Return rates (SAR). These
analyses provide for improved understanding of survival rates and the effects of various
environmental conditions and management actions on those rates.
Synopsis of Key Findings
• Juvenile travel times, instantaneous mortality rates and survival rates through the
hydrosystem are strongly influenced by managed river conditions including flow, water
travel time and spill levels.
• Statistical relationships were developed that can be used to predict the effects of
environmental factors and management strategies on migration and survival rates of
juvenile yearling Chinook and steelhead.
• The CSS results indicate that the SAR of transported fish relative to in-river migrants
(TIR) varied across species and between wild and hatchery origins. Wild spring/summer
Chinook on average showed no benefit from transportation, except in the severe drought
year (2001). Hatchery spring/summer Chinook responded to transportation with higher
TIR averages across hatcheries than wild Chinook. Wild and hatchery steelhead
responded to transportation with the highest TIR. Substantial differential delayed
transport mortality (D < 1.0) was evident for both species and across wild and hatchery
groups for each species.
• Overall SARs for wild spring/summer Chinook and wild steelhead fell short of the
Northwest Power and Conservation Council (NPCC) SAR objectives (2% minimum, 4%
average for recovery).
• SAR values for these Snake River Basin groups were only one quarter those of similar
downriver populations that migrated through a shorter segment of the Federal Columbia
River Power System (FCRPS).
The above lines of evidence for Snake River reach survivals, SARs by passage route,
overall SARs, and downriver SARs relative to the NPCC objectives, indicate that
collecting and transporting juvenile spring/summer Chinook and steelhead at Snake River
Dams did not compensate for the effects of the FCRPS.
• The overall SARs are also insufficient to meet broad sense recovery goals that include
providing harvestable surplus for wild Snake River Basin spring/summer Chinook and
• Adult upstream migration survival is affected by the juvenile migration experience.
Adults that were transported from Lower Granite Dam as smolts exhibited a 10% lower
adult upstream survival rate than either in-river migrants or those transported from Little
Goose or Lower Monumental Dams.
• Simulations results indicate that Cormack-Jolly-Seber parameter estimates are robust in
the presence of temporal changes in survival or detection probabilities.
Given the different responses of wild Chinook and wild steelhead to transportation, it
would seem that maximization of survival of both species cannot be accomplished by
transportation as currently implemented.
• Our analyses on in-river survival rates indicate that improvements in in-river survival can
be achieved through management actions that reduce the water travel time or increase the
average percent spilled for Snake River yearling Chinook and steelhead in the Lower
Granite to McNary reach. The effectiveness of these actions varies over the migration
• Higher SARs of Snake River wild yearling Chinook were associated with faster water
travel times during juvenile migration through the FCRPS, cool broad-scale ocean
conditions, and near-shore downwelling during the fall of the first year of ocean