Spawning habitat availability and use by Paddlefish Polyodon spathula in William “Bill” Dannelly Reservoir and the lower Cahaba River, Alabama

Abstract

Paddlefish Polyodon spathula populations are in decline throughout much of their range, with reduced access to spawning habitat and spawning habitat degradation (due in part to the construction of dams) recognized as leading causes. I tagged and tracked 91 individuals over two spawning seasons using passive acoustic telemetry in Dannelly Reservoir, Alabama, as well as the lower Cahaba River to quantify spawning movements and identify spawning habitats. I also used recreation-grade side scan sonar to examine substrate composition at receiver sites to assess whether areas of high use and presumed spawning areas also contained viable spawning substrates. Paddlefish showed very limited use of the Cahaba River, a relatively unimpounded tributary thought to represent and important spawning areas, and the tailrace of R.F. Henry Lock and Dam. Rather, detections were concentrated in the lotic upper reach of Dannelly Reservoir during spring, suggesting this portion of the mainstem likely supports most spawning activity. Suitable spawning substrates were present in both the Cahaba River and Dannelly Reservoir but were most prevalent in the upper mainstem. Overall, the upper reach of Dannelly Reservoir appears to offer the strongest combination of habitat and hydrologic conditions for Paddlefish spawning in this impounded system.