Genetic Methods for Determining Racial Composition of Canada Goose Harvests

Abstract

We used molecular genetic markers and established statistical methods to estimate proportional contributions of subspecies and breeding populations to admixed wintering and migratory Canada goose (Branta canadensis) harvests. We compared harvest estimates across spatially and temporally explicit sampling intervals. We characterized 997 individuals from breeding populations in Canada representing interior Canada geese (B. c. interior; n = 4) and in Michigan representing giant Canada geese (B. c. maxima; n = 5) for 5 microsatellite loci. We determined that microsatellite loci coupled with maximum-likelihood methods provided accurate and precise proportional contribution estimates of samples from each subspecies and population. We first conducted simulation analyses and derived harvest estimates for unknown individuals representing a range of plausible harvest mixture scenarios using blind tests. Based on harvested individuals collected over a 4-year period (1993-1996), we found that the racial composition of Canada goose harvests varied significantly among years and across early, regular, and late seasons within a year. Harvest composition varied spatially between management areas in different regions and between managed and private lands in close (<40 km) geographic proximity. Higher proportions of resident giant Canada geese were harvested during early hunting seasons and on private lands relative to migratory interior Canada geese. Harvest estimates suggest that individuals from different subspecies and populations are differentially abundant or susceptible to harvest at different times of the fall season, during different years, and populations across different geographic locations. Given that baseline genetics data are available for subspecies of management interest, genetic methods can provide harvest composition estimates at many spatial and temporal scales, including enumeration of statistical confidence.