Seasonal Variation in Sampling Indices for Shovelnose Sturgeon, River Carpsucker, and Shorthead Redhorse Collected from the Missouri River below Fort Randall Dam, South Dakota

ABSTRACT

Gill nets and electrofishing were utilized in the Missouri River below Fort Randall Dam, South Dakota to sample river carpsucker (Carpiodes carpio), shorthead redhorse (Moxostoma macrolepidotum), and shovelnose sturgeon (Scaphirhynchus platorynchus). Shorthead redhorse, shovelnose sturgeon, and river carpsucker all exhibited significant monthly variation in mean relative weight (Wr) during at least one sample year (P < 0.05). In general, Wr values for all species tended to be highest early in the year followed by a steady decline to a seasonal low during the later sample months. Shorthead redhorse and river carpsucker catch per unit effort (CPUE) followed a similar bimodal pattern of spring and fall peaks with lower CPUE during summer. Catch per unit effort of shovelnose sturgeon was highest in the fall at the lower site (P < 0.001, October 1998; P = 0.006 and P = 0.009, September and October 1999) with no differences found at the upper site. Within-site variations in size generally were not significant for any species analyzed (P > 0.05). However, the median length of fishes tended to be higher at the upper site during early sample months and higher at the lower site during the later sample months, suggesting a migratory pattern for adult fish.