Seasonal patterns in diet composition of adult shovelnose sturgeon in a free-flowing river

Abstract

The relationship between seasonal diet composition of shovelnose sturgeon, Scaphirhynchus platorynchus (Rafinesque) and water discharge has not been described in large unimpounded rivers that are connected to their floodplains. We sampled adult shovelnose sturgeon from a commercially exploited population in the free-flowing Wabash River, Illinois/Indiana, USA to determine the seasonal variation in diet structure. Prey items were observed in a large proportion of individuals (97.8%), suggesting that appropriate prey taxa were widely available to shovelnose sturgeon throughout the year. Overall, Hydropsychidae, Chironomidae, Potamanthidae, and Elmidae were the most important prey taxa with winter, summer, and fall samples dominated by Hydropsychidae larvae (58.9%, 63.8%, and 73.7% by number, respectively) and spring samples dominated by Chironomidae larvae (85.9%). Remains of bony fish were observed in a few spring and winter samples. Fall and winter samples had the highest and lowest proportions of inorganic materials, respectively. Higher consumption rates were observed when prey availability coincided with precipitation events. Conservation efforts within mid-western Rivers should focus on increasing habitat complexity and hydrological connectivity within floodplains.