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|Presentation Title||Search for the Smoking Gun: Evaluation of Postrelease Morbidity and Mortality of Hatchery-reared Snake River Sockeye Salmon Smolts|
|Presenting Author Name||Eric Johnson|
|Presenting Author Affiliation||Idaho Fish and Game|
|Unit Meeting||Western Division/WA-BC Chapter|
|Symposium||Sockeye Past, Present and Future|
|General Topic||salmonid survival|
|Type of Presentation||Oral|
In-hatchery performance and survival were typical for Snake River Sockeye Salmon Oncorhynchus nerka juveniles reared at the Springfield Hatchery , but unexpectedly high mortality rates were observed in the first cohorts of Springfield-reared smolts upon release into Redfish Lake Creek and during outmigration. A variety of strategies using varying acclimations times were conducted and a stepwise acclimation from hard to medium followed by medium to low hardness water approach that occurred over several days. The longer transitional period during which smolts adjust to reduced water hardness proved to be the most biologically and logistically effective means of addressing the identified water chemistry differences. Post-release survival estimates to Lower Granite Dam (~430 rkm downstream) indicated significantly higher survival for acclimated groups compared to smolts directly released to Redfish Lake Creek. Although Snake River Sockeye Salmon smolt survival rates will undoubtedly fluctuate annually with environmental conditions, it is clear that the elevated morbidity and mortality observed in previous years can be addressed through proper acclimation of smolts to receiving water chemistry prior to release.