Paddlefish Movements and Habitat Use in Pool 13 of the Upper Mississippi River during Abnormally Low River Stages and Discharges

Abstract

We determined the movements and habitat use by adult paddlefish Polyodon spathula during unusually low water levels in Pool 13 of the upper Mississippi River. Thirty-two large fish (6.3–25.4-kg) implanted with radio transmitters were located an aggregate of 812 times during March-August 1988, and spring 1989. No relation could be discovered between changes in river stage or discharge and direction of movement. No tagged paddlefish moved upstream from Pool 13, but during 1988 six fish moved downstream into Pool 14. Rates of movement were not significantly different between sexes, but the linear range for females was twice that of males. The greatest linear distance a paddlefish moved was 92 km downstream, and the greatest cumulative movement – entirely within Pool 13 – was 435 km; both records were set by females. Nearly three-fourths of all contacts with paddlefish occurred in about 5% of available habitat in Pool 13. Paddlefish were located most frequently at the head of Pool 13 in the tailwaters below Lock and Dam 12. Even though the gates of Lock and Dam 12 were fully open in 1989, fish did not move upstream into Pool 12. The fish also commonly used main-channel borders with wing dams but rarely used backwaters or side channels. Water depth and velocity in areas used by paddlefish were generally within the optima suggested by current habitat suitability models, but water temperatures were usually greater than optimum.