Preferences, behaviors and biomechanics of Pacific salmon jumping up waterfalls and fishladders

Anthropogenic blockages of both up- and down-stream migrations are major contributors to severe declines in many migratory fish populations. Fishladders and other types of passageways built to assist these fishes in overcoming dams and similar obstacles are generally not very effective. An important contributing factor in this situation is lack of sufficient knowledge of the behavioral preferences and biomechanical capacities of the fishes. I studied migrating adult sockeye salmon, Oncorhynchus nerka, to determine where and how salmonids jump over natural stream obstacles. This was done by analyzing video recordings of their behaviors and by quantitatively describing the waterfalls at which they jumped. The results from this study were used to develop an experimental fishladder simulator that was then used in studying jumping behavior, preferences and biomechanics in migrating adult kokanee salmon, Oncorhynchus nerka. The apparatus developed for this dissertation is the first fishladder simulator designed to accommodate adult salmon that is also extremely mobile with highly adjustable flow conditions. The analyses of sockeye salmon and kokanee salmon suggest salmonid jumping behavior occurs over a narrow range of flow conditions and the preferred values of flow parameters are dependent on each other. The success of observed jumps was low for jumps up natural waterfalls and in the fishladder simulator (10–30% success rate). Data obtained from sockeye salmon were used to develop a model that defines the takeoff angle, minimum horizontal distance between takeoff and landing, and the minimum takeoff velocity of salmon successfully jumping up waterfalls. Instead of using C-starts at the water's surface to accelerate to takeoff velocity as previously thought, takeoff velocities are obtained by S-starts near the bottom of pools below falls followed by rapid burst swimming to the surface. The methods used in this dissertation and the results of this study should be used to understand the requirements of migratory stream fishes blocked by stream obstacles. Differences observed between the jumping behaviors of sockeye salmon and kokanee salmon suggest that each species and perhaps each population of impeded fish should be considered in designing effective fishladders.