Macroinvertebrate drift patterns in the Mississippi and Missouri Rivers: Implications for Scaphirhynchus sturgeon conservation efforts

Abstract

Macroinvertebrates are important prey to various fishes at all life stages and in particular, Scaphirhynchus sturgeon species. Specifically, shovelnose sturgeon and pallid sturgeon survival and growth may be influenced by macroinvertebrate availability.We examined macroinvertebrate catch rates longitudinally (i.e., upstream to downstream), laterally (i.e., across the width of the river), and vertically (i.e., in the water column) to assess spatiotemporal drift patterns. A total of 3,414 samples were collected from April 15 to June 14 in 2018. Overall, 362,000 m 3 of Missouri and Mississippi River water was filtered during sampling, and 72,216 macroinvertebrates were captured. Trichoptera comprised 75% of the total macroinvertebrate drift sampled, while Diptera (9%), Ephemeroptera (13%), and Plecoptera (2%), comprised a much smaller portion. The average number per day of drifting invertebrates (i.e., Diptera, Ephemeroptera, Plecoptera, and Trichoptera) ranged from 6.8 million/d to 36.4 million/d. We found that catch rates of drifting macroinvertebrates differed among site, dates, and position in the water column. Furthermore, of the five a priori models that we developed, the interaction of spatial variables coupled with the temporal variable best describes variability in macroinvertebrate catch rates throughout our study.Efforts to increase macroinvertebrate habitat may provide additional prey resources for Scaphirhynchus sturgeon. Previous studies have demonstrated greater macroinvertebrate diversity and density in unchannelized rivers. The section of river from the Missouri River confluence downstream to the Mosenthein Island complex is unchannelized and may be a good candidate for habitat restoration. Increasing macroinvertebrate abundance and diversity may positively influence Scaphirhynchus sturgeon.