SEATTLE — People have taken many steps in recent decades to help the Pacific Northwest’s endangered killer whales, which have long suffered from starvation, pollution and the legacy of having many of their number captured for display in marine parks.
They’ve breached dikes and removed dams to create wetland habitat for Chinook salmon, the orcas’ most important food. They’ve limited commercial fishing to try to ensure prey for the whales. They’ve made boats slow down and keep farther away from the animals to reduce their stress and to quiet the waters so they can better hunt.
So far, those efforts have had limited success, and research published Monday in the journal Nature Ecology and Evolution suggests why: The whales are so inbred that they are dying younger and their population is not recovering. Female killer whales take about 20 years to reach peak fertility, and the females may not be living long enough to ensure the growth of their population.
While that news sounds grim for the revered orcas — known as the “southern resident” killer whales — it also underscores the urgency of conservation efforts, said Kim Parsons, a geneticist with the National Oceanic and Atmospheric Administration’s NOAA Fisheries who co-authored the study. The population is not necessarily doomed, she said.
“It’s not often inbreeding itself that will result in a shortened lifespan or kill an individual,” Parsons said. “It’s really that inbreeding makes these individuals more vulnerable to disease or environmental factors. We can support the population by supporting the environment and giving them the best chance possible.”
The struggles of the charismatic population of orcas that frequent the waters between Washington state and the Canadian province of British Columbia have been well documented — including in 2018, when one grieving mother carried her stillborn calf for 17 days in an apparent effort to mourn or revive it.
The southern resident population comprises three clans of whales known as the J, K and L pods. They are socially distinct and even communicate differently from other orca populations, including the nearby northern residents, which are listed as threatened and which primarily range from Vancouver Island up to southeast Alaska. While the southern residents’ range overlaps with other populations of killer whales, they haven’t regularly interbred in 30 generations, the researchers said.
Prior studies have suggested that inbreeding was a problem, including a 2018 study that found just two males had fathered more than half the calves born to the southern residents since 1990.
For the new research, NOAA geneticist Marty Kardos, Parsons and other colleagues sequenced the genomes of 100 living and dead southern residents, including 90% of those alive now. Those whales had lower levels of genetic diversity and higher levels of inbreeding than other populations of killer whales in the North Pacific, they found.