Evaluation of a Deepwater Release Method for Hatchery-Reared Lake Sturgeon

Hatchery rearing and stocking of young Lake SturgeonAcipenser fulvescenshave become key management and species recovery tools in many jurisdictions, yet there has been relatively little investigation into the optimization of release methods. Based on the contemporary understanding of the species' ecology in Boreal Shield rivers, it was hypothesized that poststocking survival and/or within-reach retention could be improved via release of hatchery-reared fish directly into the deepwater habitats that are preferred by juvenile and subadult life stages. Acoustic telemetry and mark-recapture methods were used to evaluate this hypothesis. In total, 390PIT-tagged age-1 Lake Sturgeon (mean +/- SDof length measured 1 week prior to stocking = 242 +/- 29 mmFL) were released during spring 2015 from shore at the base of a set of falls on the Nelson River, Manitoba (mimicking the status quo stocking procedure for the reach), and 391PIT-tagged individuals (240 +/- 27 mmFL) were released approximately 4.2 river kilometers downstream of the shore release location into an approximately 750-m-long patch of deepwater habitat (maximum depth = 15 m) using the deepwater release method. Of the released fish, 30 (15 per stocking method) were implanted with acoustic transmitters. In total, 23% and 22% of the stocked fish were recaptured in gill-net surveys conducted during fall 2015 and 2016, respectively. Recapture proportions associated with the two release types were not significantly different. Acoustic telemetry revealed considerable variation among individuals and offered general insight into poststocking behavior but provided no direct support for the primary hypothesis. Despite the null results of the current study, optimization of release methods for Lake Sturgeon may warrant further investigation.