North Pacific Orca Ecotypes Reclassified Into Two Distinct Subspecies

After a new study this March, two ecotypes of the North Pacific orca – resident and Bigg’s – are being reclassified into separate subspecies.

Orcas, or killer whales, are highly social marine mammals known for their complex social structures and diverse hunting strategies. Many species, including orcas, are divided into ecotypes. Ecotypes are populations of a species which are associated with a specific lifestyle and feeding specialization, stemming from their distinct environments. What distinguishes an ecotype from a species or subspecies however, is the subtlety of their differences. Ecotypes have much smaller differences compared to that of a species or subspecies, and different ecotypes of the same species can all potentially interbreed. 

In March of 2024, Phillip A. Morin and colleagues published a study in the Royal Society Open Science Journal that was in essence, a compendium of decades worth of research. The study reignited discussion of the classification of two of the most distinctive orca “ecotypes”: the Bigg’s and resident North Pacific orcas. The study called for the reclassification of these ecotypes to separate species, and though the majority of Marine Mammal Committee agreed with the proposal, it failed to meet the required two-thirds majority, and the committee instead agreed to designate them as subspecies.

In their proposal, the researchers argued that the subtlety of differences that designate a population as an ecotype – as opposed to a species – aren’t seen within these two North Pacific orca ecotypes. They argued that these two kinds of orcas are separate species due to their  distinct differences, ranging from their social structure to their diets to their morphology, and the fact that they don’t interbreed.

While all orcas are highly social, different ecotypes (and now subspecies) differ greatly in average group size, dispersal, and social organization.

“The resident killer whales … they occur in very stable pods [and] they tend to be relatively large pods of anywhere from maybe 8 or 10 animals up to 20 or 30 even, more or less” says Tom Jefferson, biologist at NOAA Fisheries. He holds a Ph.D. and worked on the Royal Society Open Science Journal study alongside Phillip A. Morin and colleagues.

(Photo courtesy of Baja Whale)

Tom Jefferson explains the key differences between resident and Bigg’s North Pacific Orcas.

Resident North Pacific orcas live in large, stable pods where permanent dispersal is negligible with the exception of occasional permanent splits along matrilines. “Whether it’s a male or a female, when a killer whale is born into that pod that animal stays in that pod for its entire life,” Jefferson said. 

In contrast, Bigg’s North Pacific orcas’ pods tend to be far smaller than that of resident North Pacific orcas. They live in groups of maternally related individuals and females permanently disperse following the birth of their first calf.

The two subspecies’ diets and feeding behavior also vary greatly. Resident orcas prey on salmon and other marine fish. They hunt in larger groups (with an average group size of 18) that can often grow in size depending on prey density.

In contrast, Bigg’s orcas hunt by stealth and feed on other marine mammals such as seals and whales. They tend to hunt in small groups ranging from 2 to 6 individuals.

The researchers who worked on the same study concluded that based on the multiple methods to research feeding behavior in the past, there was no overlap between the two subspecies’ primary diets.

Additionally, though the two subspecies’ ranges overlap greatly in the coastal regions where most research on them has occurred, they have never in over 50 years of field research been seen to interbreed. In fact, they actively avoid one another and sometimes act aggressively. This has led the researchers of the study to suggest that “they are reproductively isolated, possibly owing to cultural divergence.”

The work to reclassify these subspecies further isn’t over – although Morin and colleagues’ proposal was not approved, the committee’s rejection of it also stated what information they’d need to see in order to move forward with it.

In order to get this proposal approved, these researchers will need to put the research of North Pacific orcas into a global scale. The most well researched populations are found in the North Pacific Ocean, so this work will need to be expanded upon to other populations of orcas outside of this region. This will require a large amount of field studies and thorough technologies to accomplish this task.Yet, some of the most vital evidence for this motion will come from another area of study: genomic analysis.

“The best evidence would be additional samples for genomic analysis of killer whales throughout the entire range of each ecotype (or subspecies, as some of them are now identified),” says Phillip A. Morin, first author of the study and molecular geneticist at NOAA Fisheries. Further research, specifically on these orcas’ nuclear DNA (as opposed to their mitochondrial DNA, which was what most of the genetic evidence in their study was based on) will be especially important moving forward.

(Photo courtesy ResearchGate)

Phillip Morin explains the next steps in research for further reclassification of resident and Bigg’s North Pacific orcas.

This reclassification, though potentially initially appearing merely technical, has the potential to greatly impact conservation efforts for these subspecies of orca. The differentiation between these subspecies is important regardless of taxonomic rank, however, a stronger and more accurate label that better understands the qualities that makes these subspecies unique can often help to bring more attention and focus to the cause, making the decision carried out by Marine Mammal Committee an important one.

Both resident and Bigg’s North Pacific orcas are currently listed as threatened under Canada’s Species at Risk Act (SARA). The reclassification of these ecotypes into subspecies will likely help to better differentiate between the two populations and by extension, tailor our approaches to protect them.

“In the long run, reclassifying different killer whale types as subspecies or species may be valuable for recognition and conservation in different countries,” Morin said. Such different populations that feed and live differently require individually tailored approaches in order to preserve them. 

Jefferson agrees on the importance of differentiating these populations in some way, regardless of the label, so that more attention can be brought to their unique culture. “These are all important units of biological diversity,” Jefferson said. “We feel that the management agencies that deal with management of killer whales, they [should] recognize these units, regardless of their ranking level, as unique elements of evolutionary diversity and that they [should] make sure to protect that diversity.” Jefferson highlights the uniqueness of these subspecies that we are only just beginning to understand. When one of these subspecies is lost, their culture and diversity is lost with them permanently.

As conservation efforts to protect a variety of marine species become more and more necessary in our world today, getting people to pay attention to why they are needed is just as essential. By recognizing the differences between these different populations, we can help to reignite discussion, better realize the importance of protecting each one, and most importantly, understand how to do it.