Inbreeding within Southern Resident killer whale adds to extinction threat
A new report, just published in Nature Ecology & Evolution, finds that inbreeding within the critically endangered Southern Resident killer whale population is straining the population.
The concern for the iconic orcas is not new, though the latest scientific findings add yet another concerning layer for those hoping to see the Southern Residents avoid extinction.
Only 73 individual Southern Residents remain, and researchers in this new paper indicate that it may not be possible to reverse the trends that have already taken root. As the author notes, while many killer whale populations – also known as orcas – are struggling most have benefited from conservation efforts over the last 50 years.
It’s long been known that Southern Residents face an uphill battle: their primary food source is also an endangered species, and vessel noise from ships in their preferred hunting grounds (the Salish Sea) has made it increasingly hard to hunt. Pollution is also considered a third factor in their struggles.
This new report adds a layer that could indicate why other populations have done a better job overcoming similar circumstances. For instance, Biggs killer whales – also known as Transients – have exploded in population despite swimming the same waters as Southern Residents, navigating the same noisy water albeit while hunting a more abundant prey.
None of this means that conservation efforts are a lost cause. In fact, Marty Kardos and his colleagues write that addressing environmental threats is "unquestionably important," despite the fact that inbreeding is limiting recovery. The research seems to indicate that the group was not always inbreeding at the rate they’ve seen in recent generations – meaning if it were to reverse, there is still hope.
In the group’s conclusion, they write: "Our results suggest that the Southern Resident killer whale population growth rate would be substantially higher if its average level of inbreeding was similar to other North Pacific killer whale populations."
That hypothesis comes from looking not only at the Southern Residents, but orcas from a variety of populations within the North Pacific. That included Northern Residents, Transients, Alaska Residents and a number of Offshore individuals.
What they found in comparing the genetics of the various species is that Southern Residents were unique in the lack of genetic variation – in other words, the amount of inbreeding within the population was much higher.
According to the authors, a female killer whale takes about 20 years to reach peak fertility – inbred individuals are less likely to reach that age, meaning the population has less of a chance to expand.
It’s a concern local scientists have shared for some time. Dave Ellifrit, a researcher with the Center for Whale Research on San Juan Island told FOX 13 in 2022 that a lack of female calves was concerning – more concerning was the number that weren’t reaching the age to give birth.
Given that the Southern Residents are a matriarchal society with older females leading pods of orcas – there is a concern. Ellifrit likened the current mapping of the lineage of the surviving orcas as "dried up twigs on a family tree."
This is a developing story. Check back for additional information from NOAA, and other scientists as reaction to this new publication becomes available.