Projecting Increases in Levels of Coancestry within Stocked Populations: Looking Forward Requires Looking Back

The inbreeding effective number (N_eI) has become a parameter of great interest to genetic managers of stock enhancement and conservation aquaculture programs.  Captive breeding strategies range from simple, genetically efficient, paired-mating schemes in which family sizes are strictly controlled to complex or largely uncontrolled systems of communal spawning in which family-size variances are very high.  Genetic dynamics among and latent coancestry levels within stocked populations can also differ markedly.  In this presentation, the basic model for estimating the inbreeding effective number is reconstructed using Wright’s method of path analysis and extended to the more general case in which P1 parents are inbred and/or related.  The extended model yields more accurate instantaneous estimates of N_eI via a discretized expression that can be used to project average coancestry and N_eI over time in population admixtures (i.e., hatchery + wild components).  Using the model and exemplar genetic metrics from micropterid bass populations, conditions are illustrated under which failure to consider inbreeding and relatedness within and among the brood fish themselves (a common occurrence) will lead to upwardly biased projections of N_eI in progeny cohorts.