Comparison of Age and Growth of Shovelnose Sturgeon in the Missouri and Yellowstone Rivers

During the spring and summer 1991–1995, sampling was conducted on the Missouri River in North Dakota and on the Yellowstone River in Montana to compare the age and growth of shovelnose sturgeon Scaphirhynchus platorynchus in differently altered river segments. The study area consisted of two distinct river segments, the Yellowstone River near Intake, Montana (Williston–Yellowstone segment), a quasi-natural segment, and the Missouri River near Bismarck, North Dakota (Bismarck segment), a flow-regulated, altered segment. A total of 710 fish were aged by assessing pectoral fin sections, 565 from the Williston–Yellowstone segment and 145 from the Bismarck segment. Shovelnose sturgeon from the Yellowstone–Williston segment grew significantly faster and reached a larger size than shovelnose sturgeon from the Bismarck segment. The closure of Garrison Dam upstream of the Bismarck segment in December 1953 resulted in cooler summer water temperatures, less flow variation, and greater water clarity in the Bismarck segment. These habitat changes, coupled with a decrease in productivity in the Bismarck segment, may explain much of the difference in growth observed between the two segments.