Movement Patterns of Age-1 and Age-7 Pallid Sturgeon During Record Discharges within the Missouri River

During the summer of 2011, the Missouri River system experienced the largest discharge levels ever recorded from Fort Randall Dam, (> 4,247 m³s^-1 sustained from 25 June to 31 July of 2011), approximately four fold above normal.  Our objective was to determine movement patterns of pallid sturgeon Scaphirhynchus albus in the inter-reservoir riverine reach between Fort Randall and Gavins Point dams, South Dakota, during this record discharge period.  Fifty-one hatchery reared pallid sturgeon implanted with ultrasonic transmitters from two size classes, large (age-6 at tagging; n = 24) and small (age-1; n = 27), were at large during the flood.  Small age-1 fish ranged from 352 – 389 mm fork length (FL; mean = 369 mm) and 165 – 235 g (mean = 193g), while fish in the large size class ranged from 564 – 723 mm (mean = 652) and 700 – 1600 g (mean = 1154 g).  After discharge increased in late May, 67% of large pallid sturgeon were relocated at least once with 10 fish relocated multiple times, whereas only 11% of small fish were relocated.  Mean net movement between sampling occasions for both pallid sturgeon size groups pooled was positively correlated with increasing discharge (r² = 0.77, p = 0.07).  Mean net movement of the large size class (r² = 0.82, p = 0.04) was positively correlated to net changes in discharge, with fish moving in the main channel to within six river km of Fort Randall Dam.  Small pallid sturgeon also demonstrated upstream movement with increasing discharge but to a lesser extent.  No fish were found on the inundated floodplain.  Overall, pallid sturgeon remained in the main river channel and moved upstream during record discharges out of Fort Randall Dam; however other factors such a temperature and food availability may have also contributed to their movements.