Pedigree-based decadal estimates of lake sturgeon adult spawning numbers and genetic diversity of stream-side hatchery produced offspring

For species of conservation concern, including lake sturgeon (Acipenser fulvescens), maintaining genetic diversity is critical for successful restoration. Great Lakes lake sturgeon restoration increasingly relies on hatchery supplementation and stream-side rearing facilities that utilize collections of eggs and offspring of early life stages. The number of wild-caught eggs/larvae sampled is not likely an accurate predictor of spawning adult number, nor of hatchery cohort diversity. We used microsatellite loci and likelihood-based pedigree reconstruction to quantify offspring diversity, and the number and effective number of adult lake sturgeon contributing to offspring reared in the Manistee River stream-side hatchery facility in Michigan. Over 10 years (2005–2014) 1129 samples from stream collections of eggs, dispersing larvae, and juveniles were genotyped. Inter-annual variation in estimated mean offspring co-ancestry (Θ 0.013–0.030), numbers of contributing adults (Ns 23–72), and effective number of breeding adults (N^b 17–43) were documented. Combining samples across 10 years we estimated that mean offspring co-ancestry was 0.005, the number of spawning adults (Ns) contributing to offspring released was 326, while the harmonic mean effective number of breeding adults (N^b) was estimated to be 29.5 (lower than 10 times 29.5 for semelparous species). Forty-eight percent of adults contributed one or more offspring in two or more years. Demographic (non-Poisson distribution of adult reproductive success, low annual Ns and repeated spawning) and genetic (low annual N^b, relatedness among offspring within and among year cohorts) features depressed levels of diversity. Implications to species recovery planning are discussed considering low numbers of adults recruiting offspring annually.