Data from: Kinship and association in a highly social apex predator population, killer whales at Marion Island

Social structure is a core element of population biology, influenced by
intrinsic and environmental factors. Intra-taxon comparisons of social
organization are useful in elucidating the role of such ecological
determinants of sociality. Killer whales Orcinus orca are widely
distributed, social delphinids with diverse morphology, diet, behaviour,
and genetics, but few studies have quantitatively examined social
structure in this species. We used 7 years of individual identification
data on killer whales at Marion Island, Southern Ocean, to calculate the
half-weight association index among 39 individuals, creating a weighted
association network. There were long-term associations between
individuals, though associations were dynamic over time. We defined 8
social modules using a community detection algorithm and these typically
contained 3 individuals of various ages and sexes. Pairwise genetic
relatedness among 20 individuals was not significantly correlated with
association index. Individuals were on average more related within than
between social modules, but social modules contained related as well as
unrelated individuals. Likely parent pairs of 6 individuals indicated
mating between social modules.