Development of Biological Criteria for Siting and Operation of Juvenile Fish Bypass Systems: Implications for Protecting Juvenile Salmonids from Predation
Fish Passage Policy and Technology: Proceedings of a Symposium
American Fisheries Society
In the lower Columbia River, predation by northern squawfish Ptychocheilus oregonensis on juvenile salmonids at dam bypass release site(s) may cancel out the positive benefits of the entire bypass system. Consequently, several research studies were initiated to develop criteria for siting and operating bypass outfalls based on the behavior and performance limitations of predators and prey. First, prolonged swimming performance studies of northern squawfish indicate that water velocities ranging from 100 to 130 cm/s would elicit a high rate of fatigue, perhaps excluding or reducing predator efficiency at bypass outfall locations. Second, a physical hydraulic model (1:80 scale) of the Dalles River Dam and tailrace indicates that several potential bypass outfall sites would meet the above velocity criteria at river flow levels above 150,000 cfs. Finally, data from radio-tagged northern squawfish in The Dalles Dam indicate that they aggregate around bypass exits and respond to changes in dam operations. Based on our results to date, we recommend that when siting new or modifying existing bypass facilities that the outfall be in an area of high water velocity and distant from eddies, submerged cover, and littoral areas in general.