Habitats and movements of pallid and shovelnose sturgeon in the Yellowstone and Missouri Rivers, Montana and North Dakota
Bramblett, Robert Glenn
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Habitat use and movements of the endangered pallid sturgeon and the closely related shovelnose sturgeon are poorly known. Using radio and sonic telemetry, I obtained observations of microhabitat and macrohabitat use and movements on 24 pallid and 27 shovelnose sturgeon in the Yellowstone and Missouri rivers in Montana and North Dakota. Pallid sturgeon preferred sand and avoided gravel/cobble substrates. Shovelnose sturgeon preferred gravel/cobble and avoided sand substrates, although individual shovelnose sturgeon were variable in substrate use. Pallid sturgeon used depths ranging from 0.6 to 14.5 m, while shovelnose sturgeon used depths ranging from 0.9 to 10.1 m. Median depths at pallid sturgeon locations were significantly greater than at shovelnose sturgeon locations, and there was significant variation in mean depths among individual pallid and shovelnose sturgeon. Pallid and shovelnose sturgeon used bottom current velocities ranging from 0 to 1.37 m/s, and 0.02 to 1.51 m/s, respectively. Mean bottom current velocities were significantly greater at shovelnose sturgeon locations than at pallid sturgeon locations, although analysis of variance indicated that difference was due to location in the Yellowstone River versus the Lower Missouri River. Pallid sturgeon were most often relocated in the lower 28 km of the Yellowstone River in spring and summer and in the Lower Missouri River in fall and winter. Shovelnose sturgeon were most often relocated in the 114 km of the Yellowstone River from the Intake diversion dam to the confluence in all seasons. Only rarely were either species relocated in the Upper Missouri River. Pallid sturgeon aggregations in late spring and early summer indicate that spawning may occur in the lower 13 km of the Yellowstone River. Home range of both species ranged to over 250 km. Both species moved during both day and night and less during fall and winter than during spring and summer. Linear regression models suggested that discharge and photoperiod may be important environmental cues for movements of both species. Pallid sturgeon used moderately diverse, dynamic macrohabitats while shovelnose sturgeon were less selective in macrohabitat use. Substantial differences in habitat use and movements between adult pallid and shovelnose sturgeon indicate that shovelnose sturgeon have limited utility as pallid sturgeon surrogates.