Data from: Genetic kinship analyses reveal that Gray's beaked whales strand in unrelated groups

Some marine mammals are so rarely seen that their life history and social
structure remain a mystery. Around New Zealand, Gray’s beaked whales
(Mesoplodon grayi) are almost never seen alive, yet they are a commonly
stranded species. Gray’s are unique among the beaked whales in that they
frequently strand in groups, providing an opportunity to investigate their
social organization. We examined group composition and genetic kinship in
113 Gray’s beaked whales with samples collected over a 20-year period.
Fifty-six individuals stranded in 19 groups (2 or more individuals), and
57 whales stranded individually. Mitochondrial control region haplotypes
and microsatellite genotypes (16 loci) were obtained for 103 whales. We
estimated pairwise relatedness between all pairs of individuals and
average relatedness within, and between, groups. We identified 6
mother–calf pairs and 2 half-siblings, including 2 whales in different
strandings 17 years and 1500 km apart. Surprisingly, none of the adults
stranding together were related suggesting that groups are not formed
through the retention of kin. These data suggest that both sexes may
disperse from their mothers, and groups consisting of unrelated subadults
are common. We also found no instances of paternity within the groups. Our
results provide the first insights into dispersal, social organization,
and the mating system in this rarely sighted species. Why whales strand is
still unknown but, in Gray’s beaked whales, the dead can tell us much
about the living.