|Document Type:||Journal Article|
|Title:||Bypass system modification at Bonneville Dam on the Columbia River improved the survival of juvenile salmon|
|Author:||John W. Ferguson, Benjamin P. Sandford, R. E. Reagan, Lyle G. Gilbreath, Edward Meyer, Richard D. Ledgerwood, Noah S. Adams|
|Journal:||Transactions of the American Fisheries Society|
From 1987 through 1992 we evaluated a fish bypass system at the Bonneville Dam Second Powerhouse on the Columbia River. Survival of subyearling Chinook salmon Oncorhynchus tshawytscha released into the system ranged from 0.774 to 0.911 and was significantly lower than survival of test fish released into turbines and the area immediately below the powerhouse where bypass system flow reentered the river. Yearling and subyearling Chinook salmon and yearling coho salmon O. kisutch released into the bypass system were injured or descaled. Also, levels of blood plasma cortisol and lactate in yearling and subyearling Chinook salmon were significantly higher after passage through the bypass system compared to levels in fish released directly into a net located over the bypass exit. This original system was then extensively modified using updated design criteria, and the site where juvenile fish reentered the river was relocated 2.8 km further downstream to reduce predation on bypassed fish by northern pikeminnow Ptychocheilus oregonensis. Based on studies conducted from 1999 to 2001, the new bypass system resulted in high fish survival, virtually no injuries to fish, fish passage times that were generally similar to water travel times, and mild stress responses from which fish recovered quickly. Mean estimated survival of subyearling Chinook salmon passing through the new bypass system was 0.946 in 2001, an usually low flow year. Survival, physical condition, passage timing, and blood physiological indicators of stress were all useful metrics for assessing the performance of both bypass systems and are discussed. The engineering and hydraulic criteria used to design the new bypass system that resulted in improved fish passage conditions are described.