SummaryThis research assessed the endocrine and physiological effects of Ovaprim TM and synthetic homologous sturgeon gonadotrophic releasing hormone (GnRH) on spawning male and female adult lake sturgeon, Acipenser fulvescens (Rafinesque, 1817). Wild-caught adults were administered Ovaprim, GnRH, or Ringers solution (control), and serial blood samples were collected for up to 27 days following capture and hormone administration. Circulating cortisol levels appeared to increase following administration of both hormonal treatments. However, circulating cortisol was higher and plasma pH lower at capture than at any other time for all treatments, indicating that capture and transport stress were the largest disrupting factors, more so than the effects of induced spawning. Plasma concentrations of estradiol and testosterone in both sexes were similar to previously reported values. In all treatments the circulating estradiol and testosterone never significantly exceeded the values at capture prior to endocrine manipulation of the reproductive axis. Similarly, testosterone in males and estradiol in females in the muscle tissue were consistently at the same or lower concentrations than at capture. The apparent survival of all of the study animals following return to their native river indicated that the stress effects from capture and induced spawning were not severe. In concert, our results suggest that hormonal injections can be used to aid in gamete collection from wild A. fulvescens, without negative effects on longterm broodstock survival. Hatching success, larval survival to the juvenile stage, egg diameter, and concentrations of protein, triglyceride, and glucose in the egg, sperm, and ovarian fluid (but not seminal plasma), were the same or greater in GnRH-treated fish than gametes from the Ovaprim-treated group, suggesting that utilization of GnRH may be preferable to other common methods of spawning induction.

The release of hatchery‐reared age‐0 Lake Sturgeon Acipenser fulvescens has 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.

Continued study of the relationship between lake sturgeon (Acipenser fulvescens) recruitment and hydroelectric dams and operations, in a variety of river systems and habitat types is needed to improve the ability to predict and monitor impacts of the hydroelectric industry on this species. Herein, we present results of a juvenile lake sturgeon study aimed at addressing concerns over an inferred lack of recruitment resulting from spawning downstream of a hydroelectric generating station (HGS). Two years of sampling (2015 and 2016) were conducted in five sections of a 41 km long reach of the Seine River, Ontario, a lake sturgeon spawning tributary of Rainy Lake.Using an established gillnetting method, deepwater habitat was targeted to capture juvenile lake sturgeon to assess relative abundance, recruitment (cohort strength), and growth. Deepwater habitat, defined as water depths >6 m in this system, comprised only 2.1% of the wetted area in this study area. Within these habitats, a total of 331 lake sturgeon capture events were observed over the 2-years study period. The majority of the lake sturgeon catch (85%) was comprised of age-0 to age-5 individuals (both sampling years combined). Although inter-annual variation in cohort strength was apparent, each cohort between 2006 and 2016 was represented. The spatial distribution of cohorts varied among river reaches with younger individuals (age-0 and age-1) occupying reaches proximal to the Sturgeon Falls HGS, and larger, older individuals (age-2 to age-5) occupying reaches further downstream. The rarity of age-6+ individuals can likely be explained by ongoing downstream redistribution of juveniles over time, out of the Seine River and into Rainy Lake. Growth of juvenile lake sturgeon captured in the Seine River was above average relative to conspecifics from other rivers in the Hudson Bay drainage. Unfortunately, baseline data sets required to facilitate comparisons of contemporary (post-construction Sturgeon Falls HGS) versus historical (i.e. pre-Sturgeon Falls HGS) lake sturgeon recruitment, or to evaluate the influence of the Seine River Water Management Plan (2004) on lake sturgeon recruitment, are lacking. However, juvenile Lake Sturgeon are more abundant in this system than what had been surmised based on recent studies which implemented random sampling. Results indicate that juvenile lake sturgeon may reside in spawning tributaries for several years (age-0 to age-5) prior to seeking alternate habitats and highlights the value of targeted sampling (i.e. by depth) along the flow axis of rivers downstream of spawning areas when assessing lake sturgeon recruitment patterns.

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