Habitat Use and Movements of Pallid and Shovelnose Sturgeon in the Yellowstone and Missouri Rivers in Montana and North Dakota

Abstract

We observed the habitat use and movements of 24 pallid Scaphirhynchus albus and 27 shovelnose S. platorynchus sturgeon in the Yellowstone and Missouri rivers in Montana and North Dakota. Pallid sturgeon used sandy substrate more often than shovelnose sturgeon, as well as greater depths; both species used similar current velocities. Pallid sturgeon used river channels with greater widths, midchannel bars, frequent islands, and subclimax riparian vegetation more often than shovelnose sturgeon. Both species moved up to 15 km/d and moved during all seasons and diel periods, but they moved less during fall and winter; ranges of activity among the most wide-ranging individuals exceeded 250 river kilometers (rkm). Pallid sturgeon used the lower 28 rkm of the Yellowstone River in spring and summer, shifting to the Missouri River below the confluence of the Yellowstone River in fall and winter. Shovelnose sturgeon were most often observed in the Yellowstone River in all seasons. Aggregations in late spring and early summer suggest that pallid sturgeon may spawn in the lower 14 rkm of the Yellowstone River. The infrequent use by both species of the Missouri River from Fort Peck Dam downstream to the Yellowstone River confluence may be due to altered ecological conditions associated with the dam and emphasizes the importance of natural river processes for these species.