White sturgeon (Acipenser transmontanus) in the transboundary reach of the Upper Columbia River have low rates of natural recruitment, and the wild population has been supplemented with hatchery-origin fish annually since 2002. While releases of hatchery-origin sturgeon have prevented extirpation of the population, determining when the hatchery-origin segment reaches sexual maturity is critical to describing changes to numbers of mature spawners after decades of recruitment bottlenecks. To assign sex and stage of maturity of hatchery-origin sturgeon, gonad biopsies and blood plasma were collected from fish throughout habitats in Canada and the US from 2015-2024. Sex and stage of maturity was assigned using histological analysis of the gonad tissue, and steroid concentrations for estradiol and testosterone were paired with histology to develop less invasive indicators of sex-specific reproductive status. We compared size at maturation for hatchery-origin and wild sturgeon and incorporated information from adjacent white sturgeon populations. Females have not progressed past the pre-vitellogenic stage, with the oldest females assessed being 23 years of age. Females are just reaching a size (>160.0 cm) where they may reach puberty based on other populations. A portion of males have reached maturity (mean age of 12.3 years (range 8.3 – 16.4), mean fork length of 138.4 cm (range 89.5-161.0), and mean weight of 21.5 kg (range 4.9 – 36.1)). Fifty percent of males were mature at a size of 149.3 cm fork length (144.7 – 156.2, 95% CI). Reproductive males are distributed across multiple year classes and families in both countries, with more reproductive males in the US. Testosterone was a significant predictor of reproductive status for males, with 40 ng/L (34.7-47.8 95% CI) representing a threshold where 50% of males were reproductive. Describing rates of maturation of hatchery-origin fish is critical to understanding the effectiveness of conservation aquaculture in achieving population recovery.
 

reproduction,conservation aquaculture,sexual maturity,endangered species