Abstract
Juvenile rainbow trout Oncorhynchus mykiss and steelhead (anadromous rainbow trout), fall (age-0 and age-1) and spring Chinook salmon O. tshawytscha, and American shad Alosa sapidissima were exposed to shear environments in the laboratory to establish injury–mortality thresholds based on estimates of strain rate. Fish were exposed to a submerged jet having exit velocities of 0 to 21.3 m/s, providing estimated exposure strain rates up to 1,185/s. Turbulence intensity in the area of the jet where fish were subjected to shear was minimal, varying from 3% to 6% of the estimated exposure strain rate. Injuries and mortalities increased for all species of fish at strain rates greater than 495/s. American shad were the most susceptible to injury after being subjected headfirst to a shear environment, while steelhead and rainbow trout were the most resistant. There was no apparent size-related trend in susceptibility to high shear except that age-0 fall Chinook salmon were more resistant to shear environments than age-1 fall Chinook salmon. All groups of test fish exposed headfirst to high-shear environments had higher injury–mortality rates than fish introduced tailfirst at similar strain rates. These results document the relationship between fish injury and a fluid force present at hydroelectric facilities and provide biological specifications for improving fish passage and survival.