Population Characteristics, Development of a Predictive Population Viability Model, and Catch Dynamics for Pallid Sturgeon in the Lower Missouri River

Population characteristics and long-term population trends of pallid sturgeon Scaphirhynchus albus in the lower Missouri River are relatively unknown. As recovery efforts continue, understanding and quantifying these characteristics and trends are critical for species recovery and future management decisions. Therefore, the objectives of this study were to determine the pallid sturgeon population characteristics, predict changes to the pallid sturgeon population based on different management and life history scenarios, and examine trot line catch dynamics in the lower Missouri River. Catch rates for pallid sturgeon collected with gill nets did not significantly change while catch rates using trot lines significantly declined for wild pallid sturgeon (P=0.0001) but did not differ among years for hatchery-reared fish (P=0.0610). The proportion of reproductively ready females to non-reproductively ready females was 1:2.0, compared to the male ratio of 1:0.9. The minimum female length-at-maturity was 788 mm and 798 mm for males while the minimum age-at-maturity for known aged hatchery-reared fish was age-9 for females and age-7 for males. The mean relative fecundity was 7%. Our population viability model was most sensitive to ≥age-1 survival rates. Fluctuating female spawning frequency by one year had minimal effect on the overall population growth and age-at-maturity was less sensitive than spawning frequency. Catch per unit effort was 14.6 fish per trot line rigged with hook timers to study the catch dynamics; however, several hook timers were activated but did not capture a fish. Therefore, the corrected CPUE was 17.7 fish per line with over half of the hook timer activations occurring 4-h post-deployment. Detecting shifts in population characteristics is essential for understanding population dynamics as hatchery inputs and natural perturbations continue to change the population structure. Barring any unforeseen natural catastrophes, the pallid sturgeon population in the lower Missouri River is not in immediate danger of local extirpation; however, the population appears to be a far from viable nor self-sustaining. Advisor: Mark A. Peg