Female killer whales live up to ninety years in the wild, and most live an average of twenty-two years after menopause. Scientists have long wondered why humans and some whale species spend a significant portion of their life not reproducing. Previous studies show that, even after having their last calf, killer whale mothers take care of their families by sharing the fish they catch. Now, in a study published on July 20 in the journal Current Biology, researchers note that these mothers can also provide social support to their sons by protecting them from being injured by other orcas.

 

The research team studied southern resident orcas, a group of orcas that live off the Pacific Northwest coast. These killer whales live in matriarchal social units that consist of a mother, her offspring, and the offspring of her daughters. Although male orcas will outbreed with whales from other pods, both males and females stay in their unit of birth, with their mother, for life. Using data from the Center for Whale Research's annual photographic census of the orca population, the researchers looked for evidence of scarring on each catalogued whale's skin. Killer whales have no natural predators other than humans, so a tooth mark that is able to puncture an orca's skin was most likely inflicted by another orca. The study found that, if a given male's mother was still alive and no longer reproducing, that male would have fewer tooth marks than his motherless peers or his peers with a mother who was still reproducing.