Inbreeding could be cause of low orca populations

(AP) — New research suggests that inbreeding may be a key reason that the Pacific Northwest’s endangered population of killer whales has failed to recover despite decades of conservation efforts. 

Efforts have been made in the recent decades to help the “southern resident” population of orcas, which have suffered from starvation, pollution and the legacy of having many of their number captured for display in marine parks.

This includes work to breach dikes and remove dams to create wetland habitat for Chinook salmon, limit commercial fishing to try to ensure prey for the whales, and make 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 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, according to experts, and the females may not be living long enough to ensure the growth of their population.

The “southern resident” population currently stands at 73 whales within three groups known as the J, K and L pods. 

That’s just two more than in 1971, after scores of the whales were captured for display in theme parks around the world. 

The southern residents 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 experts said.

Researchers sequenced the genomes of 100 living and dead killer whales in the southern resident population, 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.

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.