Seasonal Movements of Paddlefish (Polyodon spathula) in Harry S. Truman Reservoir, Missouri

The creation of reservoirs on once free flowing rivers can drastically alter flow regimes creating unnatural conditions within the system. Many migratory fish species rely on environmental cues to trigger movements and unatural conditions presented to these fish could potentially alter migration patterns. This could prevent spawning runs and limit natural reproduction and damaging populations. One such migratory reservoir species is the Paddlefish (Polyodon spathula). The Paddlefish’s migratory lifestyle is dependent on seasonal fluctuations in environmental conditions which may be modified in a reservoir setting thus altering migratory behaviors. Our objectives were to evaluate Paddlefish movements in Truman Reservoir throughout the year and evaluate environmental conditions that may be triggering potential spawning movements. Ultrasonic transmitters (N=96) were implanted into reproductively mature individuals at an equal sex ratio and stationary receivers were strategically placed to monitor seasonal movements. Spring movements appear to be driven by increasing temperatures with pulses in discharge opening up previously uninhabitable habitats. As summer begins and temperature continue to increase, fish begin to move back to the lake despite continued spikes of discharge. Despite modifications to natural flow regimes in this reservoir setting, it appears Paddlefish are able to detect environmental variations that cue migratory behavior.