Spawning Migration Periodicity and River Choice of the Grand Lake Stock of Paddlefish Polyodon spathula

Knowledge of movements, spawning, and reproductive periodicity of paddlefish (Polyodon spathula) is important for their successful management. Thirty gravid female Paddlefish were tagged with acoustic transmitters and their movements tracked in Grand Lake (a 21,000 ha impoundment) and in two tributaries, the Neosho River (NR) and Spring River (SR), northeastern Oklahoma, USA to assess their reproductive periodicity (annual versus non-annual) and their choice of river entered during their upriver spawning migration period (Feb 15 to May 15). Fish seldom occupied the rivers at other times and remained in the reservoir. Telemetered fish commonly used both rivers, with few using only one river each year and none using a single river exclusively over the four year study duration. Although annual spawning was the most common pattern, alternate-year spawning was observed. Over the four-year study, fish demonstrated a slight numerical preference for ascending the NR (96 times) over the SR (88 times), despite anomalously lower discharges in the NR. Results were not inconsistent with two other studies indicating the higher value of the NR over the SR as a paddlefish recruitment river. However, the lack of high flow years on the Neosho River during our study limited our interpretation. In testing hypotheses that pre-spawning fish would enter the river a) with the higher discharge on that day or within four days prior, b) with the greater increase (or lesser decrease) in discharge on that day or within four days prior, none of nine discharge variables investigated were closely related to river choice. Despite some specific instances where high or rising discharge each triggered upriver movements, river choice over the entire Feb 15 to May 15 period as a whole was similar to what would be expected by chance. Entering and exiting the two proximal, low gradient river mouths and lower river sections may have incurred little energetic cost prior to actual spawning.