a Southern Resident killer whales porpoising through water.
Photo by Wild Orca.

The Southern Resident orcas of the Pacific Northwest live in close-knit family units. Born into their mother’s pod, known as a matriline, they stay with their mother, and her extended family, for life. Close study of these pods revealed that the older females were not having calves in their 40s, but living much longer.

Could it be possible they were living beyond their reproductive years, like human grandmothers, in order to give their daughters’ offspring the best chance at survival? If so, this is extremely rare in the animal kingdom, as at time of publication of this study, only three other species—all toothed whales like resident orcas—were known to experience menopause.

Menopause is a biological mystery; just why has evolution taken a different track in humans, and a handful of other species? Most animals breed throughout their lives to be successful, and so this implies there must be an evolutionary benefit to ceasing reproduction. In humans, it appears it increases the survival rate of grandchildren—known as the “grandmother effect.” By giving up the opportunity to have offspring after mid-life, a grandmother eliminates potential competition for resources, and she’s able to focus on caregiving, and using her cultural and ecological knowledge.

Do the Southern Resident orcas also have grandmothers?

Testing the “grandmother effect” in any marine mammal population is challenging, but researchers had access to decades of data on the families of the Southern Resident orcas, collected since 1976. Their study considered all whose maternal grandmother is known. Then they compared the survival rate of grandbabies with living grandmothers, against those with grandmothers who had died. Anticipating that the loss of a grandmother might not have an immediate impact on grandbaby survival, they calculated survival rate, including up to two years following her death.

What they found is quite remarkable: The death of a Southern Resident orca grandmother significantly reduces the survival chances of her grandbabies; in fact, following her death, they are 4.5 times more likely to die. This reflects the highly significant role these post-reproductive females play in calf raising, impacting survival both at the pod, and population level.

3 Southern Resident killer whales swimming together..
Photo courtesy of Stewart Macintyre. Taken under NMFS Permit #15569.

Speaking of grandmothers, J2—also known as Granny—led the entire community of J, K and L pods until her death in 2016. She was presumed to be over 100 years old, but likely stopped having calves around the age of 40. Her long post-reproductive years enabled her to share inherited cultural and ecological knowledge with her pod—and likely the wider community—such as where and when to find Chinook salmon, in both times of plenty and time of scarcity.

As the grandmothers’ role in finding food likely becomes more critical when Chinook is scarce, this study also assessed whether this particular aspect of grandmothering impacts grandbaby survivorship. Researchers found that the loss of these important older females in times of hardship indeed has a significant impact, with an increase in the risk of death of grandbabies.

Senior author of the study, Dr. Dan Franks from the University of York, UK, said: “The death of a grandmother can have important repercussions for her family group. As salmon populations continue to decline, grandmothers are likely to become even more important in these killer whale populations.”

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40 years of history reveals that resident females have an expected post-reproductive lifespan of at least 16 years, so they should be living into their mid-50s. Yet in the last 10 years, six females have died before they reached 50.

Only 4 matriline had grandmothers in Dec. 2019, when this study was published—Sequim, Marina, Nugget, and Shachi range in age from 40 to 47, perhaps lacking the deep experience of the older grandmothers of past generations, like Granny. What does this mean for the future of this population, and what can we do?

We must protect and restore wild Chinook salmon to give these orcas a chance of success. Their families deserve to know new grandmothers, who share their wisdom with their grandbabies; and renew our confidence in a future for this unique orca society, where grandmothers rule the waves!