Hatchery Rearing of Lake Sturgeon to Age 1 Prior to Stocking: A Path Forward for Species Recovery in the Upper Nelson River, Manitoba, Canada

Abstract

AbstractThe release of hatchery‐reared age‐0 Lake SturgeonAcipenser fulvescenshas proven sufficient to re‐establish mid‐latitude populations, but there was minimal evidence of poststocking survival in the functionally extirpated population of the upper Nelson River, Manitoba, until the practice of rearing fish to age 1 in the hatchery began in 2007. After 5 years of poststocking monitoring (2012–2016), mark–recapture data sets have yielded important information regarding survival, dispersal shortly after stocking, post‐establishment movement and emigration, and growth, clarifying a path forward for Lake Sturgeon recovery initiatives in this system. Based on Cormack–Jolly–Seber models, mean cohort‐specific apparent survival (i.e., consolidated survival and retention of fish within the reach) for Lake Sturgeon reared to age 1 in the hatchery from the time of stocking until the period of post‐first‐winter recapture in the wild (predominantly at age 2) was estimated to range from 0.08 (95% CI = 0.06–0.11) to 0.49 (95% CI = 0.41–0.56); dispersal occurring shortly after stocking was identified as at least partially influential. In the years after poststocking establishment (i.e., age 2 and older), apparent survival of the fish that established in the primary reach was estimated at 0.99–1.00, indicative of negligible mortality and negligible emigration. The stocked Lake Sturgeon exhibited growth patterns similar to (or even outpacing) those of wild populations occupying comparable habitats in Manitoba. Moreover, data indicate that growth trajectories set early in life persist throughout the juvenile stage. The results of upper Nelson River poststocking monitoring provide quantitative support for a stocking strategy predicated on rearing Lake Sturgeon over winter in the hatchery followed by release at age 1 during spring, thus striking a balance between high poststocking survival and moderate hatchery rearing costs.