Mating structure of an endangered population of wild Atlantic salmon (Salmo salar) as determined using sibship reconstruction and a novel method of sex inference

The recent development of molecular genetic markers and methods of inferring relatedness among individuals using multilocus genotype information has allowed new insight into mating systems in the wild. Capitalising on the recently discovered linkage between the microsatellite locus Ssa202 and the sex-determining region of the Atlantic salmon Y chromosome, we developed a novel method to infer the sex of unsampled, wild-spawning parents of some of the few remaining wild, inner Bay of Fundy Atlantic salmon (Salmo salar). We inferred that most of the unsampled, reconstructed parents at the half-sib group level were likely polygamous females, while the parents at the full-sib group level (nested within half-sib groups) were likely monogamous males. Given the very low numbers of anadromous salmon returning to inner Bay of Fundy rivers to spawn, the putative male parents were likely mature male parr rather than anadromous males. This suggests that salmonid populations experiencing extreme declines may be composed of a high proportion of related individuals from relatively few sib groups and that mature male parr may provide an important genetic and demographic buffer to population decline.