Inbreeding contributes to southern resident killer whale’s low population growth: study

High levels of inbreeding among the endangered southern resident killer whale are likely contributing to its low population growth, new research has found.

A study published Monday in the peer-reviewed Nature Ecology & Evolution journal found that the iconic species, which lives in the North Pacific, had the lowest genetic variation and most genetic inbreeding of five killer whale populations analyzed.

“The big finding from this study is that individuals who are more highly inbred are much less likely to survive to old age or survive through their reproductive years,” report co-author Marty Kardos told Global News.

Using relatively new technology and archival tissue samples, researchers sequenced the genomes of 100 southern resident killer whales and 47 other killer whales. The ages of the tissue samples ranged from the early 20th century to the past 10 years.

Scientists uncovered at least one example of direct parent-offspring breeding among the southern residents, although any individuals with a “recent common ancestor” were considered to be inbred.

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Kardos said inbreeding appears to affect the population’s “fitness,” limiting its growth over the decades.

“It could involve increased risk of getting disease, it could affect behaviour, neurological function, immunological function, metabolism,” the Northwest Fisheries Science Center geneticist explained.

“The genome is large, there are tens of thousands of genes in the genome, and any of those could carry deleterious or mutated versions of genes that aren’t good and inbreeding really exposes those effects in survival and or reproduction.”

Fewer than 80 southern resident killer whales remain.

Given that the species has been legally protected for decades, Kardos said scientists have wondered why its growth rate has not matched that of other killer whale groups in the region. Those protections remain important, he added.

“We’ve known for about a decade or so that the best population models suggest that the population is very highly likely to decline in the future. This study doesn’t change that picture, it just sort of provides an explanation.”