Stocking Success of Paddlefish in Lake Francis Case, South Dakota: Population Characteristics and Sport Fishery Potential

Abstract

AbstractLake Francis Case, South Dakota, a Missouri River reservoir, supported a paddlefish Polyodon spathula sport fishery shortly after impoundment, but this fishery closed in 1986 owing to a lack of natural recruitment. Lake Francis Case has been stocked intermittently since 1974 and annually since 1990 to maintain the population and potentially sustain a sport harvest. To evaluate the success of these stockings, we assessed the current status of the Lake Francis Case paddlefish population (i.e., population characteristics and dynamics) and evaluated the potential effects of exploitation on this population. Advanced fingerling stockings have been effective, as 56% of sampled fish were of hatchery origin (indicated by coded wire tags), and may sustain a harvestable population. Year‐class strength was negatively correlated to water temperature inputs from Big Bend Dam and positively correlated to White River discharge. Downstream emigration is probably responsible for most of the variability in year‐class strength, and the rate of downstream emigration may be greater during years with warmer water temperatures. Harvest simulations suggested that growth overfishing was possible under a 660‐mm minimum length limit but not under 840‐mm and 1,016‐mm minimum length limits. The proportional size distribution of memorable‐length fish (PSD‐M) was reduced 28.6% and 14.3%, respectively, by 5% exploitation under simulated 660‐mm and 840‐mm minimum length limits. Under a simulated 1,016‐mm minimum length limit, PSD‐M was unchanged by 10% exploitation. At 5% exploitation, broodstock availability was reduced by more than 30% under the simulated 660‐mm and 840‐mm minimum length regulations and was reduced 16% under the 1,016‐mm minimum length limit. Our results suggest that this population could support a limited (e.g., 5% exploitation) sport fishery under a high (e.g., 1,016‐mm) minimum length limit without substantial changes in size structure or the availability of broodstock if stockings are continued.