Maximum acclimation depth of juvenile Chinook salmon: Implications for survival during hydroturbine passage

Chinook salmon are endangered or threatened in the Columbia and Snake rivers of the Pacific Northwest.  Survival of juvenile salmon during seaward passage of hydroelectric dams is a concern throughout the Pacific Northwest.  Exposure to rapid decompression during hydroturbine passage may lead to injuries or mortality.  Decompression injury is related to the depth of acclimation prior to turbine entry and the pressure fish are exposed to during turbine passage.  Turbine pressure being constant, the deeper the fish is acclimated, the greater the likelihood of injuries.  However, it is unknown to what depth juvenile Chinook salmon can acclimate and attain neutral buoyancy.  To determine the maximum depth at which fish can become neutrally buoyant, fish were placed in hyperbaric chambers and pressurized until they released gas from their mouths.  Following this procedure, fish were lethally sampled and swim bladders were removed and placed back into the chambers.  Swim bladders were decompressed until swim bladders ruptured.  This information will be valuable for modeling survival of juvenile salmon through hydroturbines, operation of existing turbines and influencing the design of future turbines.