Population characteristics of pallid sturgeon (Scaphirhynchus albus (Forbes & Richardson, )) in the Lower Missouri River

Abstract

Population characteristics of pallid sturgeon Scaphirhynchus albus in the lower Missouri River are relatively unknown. Therefore, data collected from the Nebraska Game and Parks Commission Pallid Sturgeon Population Assessment Program was synthesized to (i) document the population structure of pallid sturgeon by origin (hatchery-reared or wild), gender, and reproductive readiness, (ii) document the minimum size and age-at-maturity by gender, and (iii) document the fecundity rates of the fish that were successfully spawned in the hatchery. During this 4-year study (2008–2011), relative abundance for wild and hatchery-reared pallid sturgeon collected with gill nets did not significantly change whereas relative abundance for wild fish using trot lines declined significantly. The proportion of hatchery-reared pallid sturgeon increased annually, with the population being composed primarily of hatchery-reared fish. The proportion of reproductively ready females to non-reproductively ready females was 1 : 2.0, compared to male ratios at 1 : 0.9. Minimum fork length-at-maturity was estimated for females at 788 mm and for males at 798 mm. Minimum age-at-maturity for hatchery-reared released fish was age-9 for females and age-7 for males. Highest relative fecundity, based on the ovosomatic index, was 10% with an overall mean of 7%. The number of eggs per ml (egg size) was not correlated with fork length (P = 0.0615) or weight (P = 0.0957). Relative condition factor (Kn) for females was significantly different by reproductive condition (P = 0.0014) and Kn for males did not differ between reproductive conditions (P = 0.2634). Detecting shifts in population characteristics are essential not only to understand population dynamics since hatchery inputs and natural perturbations continue to change the population structure but also to assess species recovery efforts to ensure long-term species sustainability.