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Summary

Long-term population trends of pallid sturgeon Scaphirhynchus albus in the lower Missouri River were evaluated via a discrete and stochastic age-structure population viability model. The intent of this model was to (i) estimate the local pallid sturgeon population size, (ii) quantify the contribution of hatchery-reared fish to the overall population, (iii) predict the level of natural production needed to create a self-sustaining population, and (iv) determine the parameters that produce the largest model sensitivity. The model estimated that the wild, adult population size was approximately 6000 fish that remained in the lower Missouri River in 2012 compared to approximately 42 000 hatchery-reared pallid sturgeon. Under the assumption of no natural recruitment, the population size will continue to decline at approximately 8% annually, with an annual egg to age-1 survival rate of 0.00011 predicted to maintain a stable population. The model was most sensitive to survival rates of fish ≥ age-1 and less sensitive to age-0 survival rates and fecundity. Decreasing or increasing the female spawning interval by 1 year had minimal effect on the overall population trajectory. Recovery management planning for a species such as pallid sturgeon, which is slow-growing, late-maturing, and has intermittent spawning would require several years to access recovery potential and management decisions. Barring any unforeseen natural catastrophe, the pallid sturgeon population in the lower Missouri River is not in immediate danger of local extirpation; however, the population appears to be far from viable and self-sustaining.