Population genetics and social organization of the sperm whale (Physeter macrocephalus) in the Azores inferred by microsatellite analyses

International audienceIn the northeast Atlantic Ocean, the archipelago of the Azores is frequented by female–offspring groups of sperm whales (Physeter macrocephalus L., 1758), as well as large males. The Azores apparently constitute both a feeding ground and a reproduction site. Little is known about the population and group structure of sperm whales in the area. We analysed 151 sloughed skin and biopsy samples collected from 2002 to 2004. Molecular analyses involved genetic tagging using 11 microsatellite loci and molecular sexing. Our objectives were to determine the population genetic structure, compare relatedness within and between social groups, infer kinship, and estimate the age of males at dispersal. Results suggest that individuals visiting the archipelago of the Azores belong to a single population. High genetic diversity and absence of inbreeding suggest that the population is recovering from whaling. Individuals sampled in close association are highly related, as well as those observed in the same area on the same day, suggesting that secondary social groups (i.e., the union of primary social units) are largely but not exclusively composed of relatives. Probable mother–offspring and full-sibling pairs were identified. Age of males at dispersal was estimated at 16.6 years, which was well above previous estimates for this species