Effects of Hypoxia on Growth, Behavior, and Mortality of Scaphirhynchus and Polyodon Larvae

Natural recruitment of paddlefish Polyodon spathula and shovelnose sturgeon Scaphirhynchus platorynchus has been documented in the upper Missouri River, USA; however, pallid sturgeon Scaphirhynchus albus in the same area are not recruiting to the adult wild population.  The mechanism for the lack of recruitment is not well understood, and several hypotheses are centered on abiotic conditions in a reservoir headwater environment.  In this study, we assessed effects of hypoxia on shovelnose sturgeon, pallid sturgeon, and paddlefish larvae.  Based on empirical measurements conducted in the Fort Peck reservoir headwater, we designed laboratory experiments to determine the effects of hypoxia at three treatment levels (1.5 mg/L (10% saturation), 2.5 mg/L (20% saturation), and 7.0 mg/L (control; 70% saturation)) on paddlefish, shovelnose sturgeon, and pallid sturgeon larvae at two ages (immediate post-hatch and 40-d post-hatch).  Our results indicated that dissolved oxygen concentrations < 2.5 mg/L are lethal to larvae in all three species.  Additional data collection in the headwater environment of Fort Peck Reservoir in 2012 revealed that dissolved oxygen concentrations in habitat associated with drifting larvae may be low enough to reduce survival of larval pallid sturgeon in the upper Missouri River.