HABITAT USE AND MOVEMENTS OF ADULT PALLID STURGEON IN THE MISSOURI RIVER DOWNSTREAM OF FORT RANDALL DAM, SOUTH DAKOTA AND NEBRASKA

Ultrasonic telemetry was used from 2000 to 2002 to identify habitat use and track seasonal and diel movements of six adult pallid sturgeon (Scaphirhynchus albus) released in the Missouri River downstream of Fort Randall Dam, South Dakota and Nebraska. Extensive sampling occurred at about two week intervals from spring through fall. Two individual fish were intensively tracked for 4 to 12 hours during 2000 to assess diel movements, with one individual tracked on three occasions. A total of 29 relocations were observed from four pallid sturgeon and two fish were only found once after the initial year of stocking suggesting a survival rate of 33%. In all seasons, adult pallid sturgeon were located in the main river channel habitat and at relative depths ranging from 79 to 100% of the maximum channel depth. During the multiple year study, two different move- ment patterns were observed of the two fish. One of the fish moved throughout the study area while the other fish moved downstream below the Missouri and Niobrara rivers confluence and remained there throughout the study period. In general, both fish moved upstream during late fall through the spring and moved downstream during the summer. Both fish also were relocated in two to three distinct areas of the Missouri River, a potential indication of preference to un- known biotic and abiotic habitat conditions. One fish had a maximum observed range of 8.1 km with low seasonal movement rates compared to the other fish that had a maximum observed range of 45.8 km. The pallid sturgeon that was intensively tracked on three occasions had substantially higher (≥ 40%) move- ment rates at night compared to dawn, daytime, and dusk. Although the number of tagged fish in this study was small, all field observations for an endangered species are valuable for recovery efforts. Observations from the two fish in this study were consistent with other studies which showed that adult pallid sturgeon are a highly mobile, wide-ranging species.