Multi-year evidence of unbiased sex ratios in hatchery and wild-reared age-0 lake sturgeon (Acipenser fulvescens)

Assessment of population sex ratios allows managers to forecast recruitment dynamics and loss of genetic diversity in natural populations and is important when the focal population is in low abundance and subject to demographic stochasticity. If levels of natural or artificial selection differ for males and females and levels of mortality likewise vary, lower levels of population recruitment, loss of genetic diversity, and genetic drift can occur. Lake sturgeon (Acipenser fulvescens) are a species of conservation concern, where restoration efforts increasingly rely on hatchery supplementation. Raising larvae to the juvenile stage can increase survival during important early life stages; however, knowledge is lacking concerning effects of artificial rearing environments on differential sex-specific survival before release. We genetically determined the sex of 1459 age-0 lake sturgeon from three cohorts (2016 through 2018) using PCR assays of the ALLWSex2 acipenserid sexing marker. Sexed individuals represented three groups: (1) wild-captured dispersing larvae that died during hatchery rearing, (2) wild-captured dispersing larvae that survived hatchery rearing to release, and (3) wild-captured, wild-raised age-0 individuals. Sex ratios of wild-captured larvae (dead + live) were nearly 50:50 in all years surveyed. We observed slight, but non-significant, directionality in sex ratios in the live and dead hatchery-reared larvae and in wild-captured age-0 individuals. Genetic sexing methods allow for analyses during prolonged pre-reproductive periods and associated variable environmental and demographic circumstances, in situations where physical determination of sex is not possible.     

Genetic assessment of straying rates of wild and hatchery reared lake sturgeon (Acipenser fulvescens) in Lake Superior tributaries

Natal philopatry in lake sturgeon (Acipenser fulvescens) has been hypothesized to be an important factor that has lead to genetically distinct Great Lakes populations. Due to declining abundance, population extirpation, and restricted distribution, hatchery supplementation is being used to augment natural recruitment and to reestablish populations. If hatchery-reared lake sturgeon are more likely to stray than naturally produced individuals, as documented in other well-studied species, outbreeding could potentially jeopardize beneficial site-specific phenotypic and genotypic adaptations. From 1983 to 1994, lake sturgeon propagated using eggs taken from Lake Winnebago adults (Lake Michigan basin) were released in the St. Louis River estuary in western Lake Superior. Our objective was to determine whether these introduced individuals have strayed into annual spawning runs in the Sturgeon River, Michigan. Additionally, we estimated a natural migration rate between the Sturgeon River and Bad River, Wisconsin populations. Presumed primiparous lake sturgeon sampled during Sturgeon River spawning runs from 2003 to 2008 were genotyped at 12 microsatellite loci. Genotypic baselines established for the Sturgeon River (n = 101), Bad River (n = 40), and Lake Winnebago river system (n = 73) revealed a relatively high level of genetic divergence among populations (mean F_ST = 0.103; mean R_ST = 0.124). Likelihood-based assignment tests indicated no straying of stocked Lake Winnebago strain lake sturgeon from the St. Louis River into the Sturgeon River spawning population. One presumed primiparous Sturgeon River individual likely originated from the Bad River population. Four first-generation migrants were detected in the Sturgeon River baseline, indicating an estimated 3.5% natural migration rate for the system.     

A review of lake sturgeon Acipenser fulvescens spawning sites in the Lower St. Lawrence and Ottawa river systems

Knowledge concerning critical habitats such as spawning sites is crucial to the preservation of vulnerable fish species like sturgeons. For lake sturgeon Acipenser fulvescens populations in the Lower St. Lawrence and Ottawa river systems, knowledge about spawning sites has been documented primarily in the grey literature, unpublished reports, or notes, with very little published in peer-reviewed literature. Here, we reviewed over 100 reports, articles, and unpublished observations in the Lower St. Lawrence and Ottawa river systems to synthesize available information concerning the location of lake sturgeon spawning sites, the level of spawning activity, and the methodologies used for assessments. In this review, 38 lake sturgeon spawning sites were identified. Of these sites, 11 were enhanced or artificially created for lake sturgeon. In the Lower St. Lawrence River, 68% of known spawning sites were located downstream from a dam compared to 47% in the Ottawa River. The use of the two artificially created spawning sites in the Lower St. Lawrence River has not yet been confirmed, while one site established in the Ottawa River has had confirmed spawning activity, although the spawning run size is unknown. In contrast, spawning has been confirmed for the seven natural spawning sites that have been artificially expanded in these systems, and two of these sites have large spawning runs. Information revealed by this review suggests that lake sturgeon populations in these large river systems rely on multiple spawning sites and that expanding natural spawning grounds may be more effective than creating new ones.     

Genetic origins and diversity of lake sturgeon in the St. Louis River Estuary

Lake sturgeon Acipenser fulvescens were extirpated from the St. Louis River Estuary (SLRE) by the early 1900’s due to overfishing and habitat degradation. A restoration stocking program began in 1983, and continued almost annually until 2000. Lake sturgeon stocked into the SLRE were primarily obtained from the Wolf River (Lake Winnebago) genetic stock (n = 861,000) but some sturgeon were obtained from the Sturgeon River (Lake Superior) genetic stock (n = 61,380). Recently, spawning and natural recruitment has been documented near the Fond du Lac Dam, the upstream limit for lake sturgeon migrating from Lake Superior. However, the genetic origin of lake sturgeon spawning in the SLRE was unknown. Our objectives were to determine (1) the genetic origins and (2) genetic diversity of lake sturgeon spawning in the SLRE. Using both GENECLASS2 and ONCOR, a majority (79–81%) of lake sturgeon captured in the SLRE during spawning (2016–2018) assigned to the Wolf River genetic stock (Lake Winnebago) with greater than 80% probability using established microsatellites and a standardized genetic baseline. Other genetic stocks present (≥1%) included the Pic and Goulais rivers and possibly the Black Sturgeon River (identified using GENECLASS2, but not ONCOR); no fish assigned to the Sturgeon River using either method. Genetic diversity metrics showed that the SLRE lake sturgeon population was similar to other Lake Superior lake sturgeon populations. Overall, the SLRE Sturgeon population appears headed towards recovery. Adaptive management practices currently being employed should be continued to help guide further recovery of this population.