Seasonal Diet Composition of Adult Shovelnose Sturgeon in the Middle Mississippi River

Abstract

Because the shovelnose sturgeon (Scaphirhynchus platorynchus) population in the Middle Mississippi River (MMR) between Cairo, IL and St. Louis, MO (RKM 0–320) appears to be declining, we must understand dietary needs to help assess its conservation status. Diet is linked to growth, condition and reproduction and reflects population state. Thus, we quantified diets of adult shovelnose sturgeon monthly using gill nets (5.08-cm bar mesh) during Jan. 2005 through Nov. 2005 at three sites on the MMR (RKM: 201-198; 191-188, and RKM 127-124). Stomachs were removed from adult shovelnose sturgeon (winter n = 71; spring n = 163; summer n = 149; fall n = 179; fork length mean = 617 mm; standard deviation = 64.57). Overall, prey items occurred in less than 30% (n = 170) of shovelnose sturgeon stomachs. Dominant prey items throughout all seasons (winter, spring, summer and fall) were Chironomidae, Hydropsychidae, Ephemeridae and Corophiidae respectively. Corophiidae is an exotic amphipod that has not previously been documented in the MMR. The total abundance of diet items was high during winter through spring and low during summer through fall. Ephemeridae dominated in winter. Hydropsychidae was the most important prey item during spring through summer. Corophiidae dominated diets in the fall. Temperature and perhaps low river discharge appeared to affect prey consumed, with high temperatures and low discharge during summer through fall causing low energy intake, lowered condition and likely poor growth. Conservation efforts that provide flow refugia may improve energy intake and likely enhance shovelnose sturgeon populations in the MMR.