Estimates of Effective Number of Breeding Adults and Reproductive Success for White Sturgeon

Accurate estimates of the number of adults contributing to offspring (N ₛ), effective breeding number (N b), and individual adult contributions to recruitment are required for recovery planning for endangered White Sturgeon Acipenser transmontanus populations, many of which are suffering from prolonged periods of recruitment failure. We show that genetic techniques can be used to characterize important features of White Sturgeon reproductive ecology in large rivers where census data are extremely difficult to obtain. We used 12 microsatellite loci and likelihood-based pedigree analysis to estimate N ₛ, N b, number of kin groups (N ₖ), and individual reproductive success of White Sturgeon contributing to viable eggs and larvae collected in the upper Columbia River in each of 2 years. Estimated mean ±SD annual N ₛ was 121.5 ± 34.7, N b was 86.5 ± 10.6, and N ₖ was 73.5 ± 17.3. Large variations in estimates of N ₛ, N b, and N ₖ were observed between three spawning areas, in which one spawning site representing 61% of total adult spawning population. Variation in adult reproductive success was observed within and among sites. Estimated mean ±SD individual spawning duration was 1.9 ± 1.1 d, and number of mates per adult was 2.9 ± 2.5, which also varied spatially and temporally. Based on age of collected eggs and larvae, number of spawning days ranged from 5 to 19 d between years and among sites. Genetically derived estimates of N ₛ were lower but generally concordant with empirical estimates of available spawners (N c), based on sex ratios and maturation staging of adults captured independently (N ₛ/N c ratio = 0.683). Results increase our understanding of White Sturgeon reproductive ecology and recruitment and allow projections of cohort levels of genetic diversity. Similar data can be applied to recovery planning and aquaculture programs for this and other species of conservation concern.