Potential Minimum Threshold for Pallid Sturgeon Relative Condition in the Lower Missouri River

Abstract

Pallid Sturgeon (Scaphirhynchus albus) condition has declined in the lower Missouri River but the cause and the effects of this de- cline remain uncertain. Adult Pallid Sturgeon are becoming reproductively ready less frequently and sub-adult Pallid Sturgeon are likely delaying sexual maturation. Even more concerning, Pallid Sturgeon capture rates have declined the past two years (i.e., 2016 and 2017), despite the ongoing Pallid Sturgeon stocking program. Several Pallid Sturgeon that have been captured are visually ema- ciated but a minimum condition threshold has not been described. Therefore, the aim of this study is to present a potential lethal condition level for adult Pallid Sturgeon in the lower Missouri River then determine the capture frequency of Pallid Sturgeon below this assumed minimum condition threshold to test the validity of this hypothesis. Based on the mortality of an individual female adult Pallid Sturgeon held in captivity, mortality occurred when condition was 0.71. This potential minimum threshold is further supported with very few adult Pallid Sturgeon captured below this predicted minimum threshold. Using the minimum condition threshold established here to continue monitoring the Pallid Sturgeon population and the occurrence of individuals below this con- dition level could help managers better address factors hindering Pallid Sturgeon recovery.