Floodplain connectivity and age-0 sturgeon prey consumption in the lower Missouri River

Floodplains are generally considered important nursery habitat for young fish, but little information exists regarding the importance of this habitat for Scaphirhynchus sturgeon. During 2019, the lower Missouri River experienced widespread, prolonged floodplain connectivity, and this study provides the first documentation of age-0 Scaphirhynchus sturgeon floodplain prey consumption. Individuals captured on the floodplain primarily consumed chironomids, but the amount of prey consumed was similar to or lower than individuals captured from nearby mainstem reaches and a side-channel during previous years. Similarly, 2019 floodplain sampling often yielded lower age-0 sturgeon condition when assessing length-weight relationships among years. Further downstream, we also analyzed diets from 2019 in two mainstem reaches below Kansas City for comparison with data from 2014 to 2015. In both reaches, 2019 condition was lower than 2014 and 2015 despite a relatively higher growth rate. The amount of prey consumed in 2019 was also similar to or lower than 2014 and 2015 in Glasgow Reach, whereas 2019 yielded the highest prey consumption in Monarch Reach. Our results suggest that the 2019 high-water event did not yield increased prey consumption or condition for age-0 sturgeon on the floodplain, while the findings for mainstem habitats below Kansas City were inconsistent. Overall, empty stomachs were rare regardless of capture location and floodplain individuals appeared to be growing and surviving despite the observed differences. These results address an important information gap for age-0 sturgeon and future data from additional floodplain sites would provide valuable context regarding the applicability of these findings to other areas.

Automated summary

The study found that the floodplains of the lower Missouri River in 2019 were not as important for Scaphirhynchus sturgeon as previously thought, with individuals consuming similar or even less prey compared to those in mainstem reaches and side-channels. Additionally, despite a relatively higher growth rate, sturgeon in mainstem reaches below Kansas City in 2019 had lower condition than in 2014 and 2015.