This is one of my favorite topics, so my apologies for how long this post is going to be!
From what I’ve been able to gather from both published literature and discussions among killer whale biologists, there are 10 proposed/recognized ecotypes, and they are nicely summarized in this poster by Uko Gorter/NOAA:
If it is difficult to read, here are the 10 currently recognized ecotypes:
Northern Hemisphere: Resident, Bigg’s (transient), offshore, type 1, and type 2.
Southern Hemisphere: Antarctic type A, Antarctic large type B, Antarctic small type B, Antarctic type C, and subantarctic type D.
However, these ecotypes don’t represent all killer whale populations. For example, killer whales in the tropics, South Africa, and the western Atlantic (such as eastern Canada, Greenland, ect.) don’t necessarily fall into any of these ecotype categories, and haven’t been classified as distinct ecotypes of their own. Another example: roughly half of the killer whales in the Marion Islands (a group of sub-antarctic islands) display features found in both type A (moderate eye patch size) and type B (dorsal cape) killer whales. Where do they fit in? Do they deserve their own ecotype classification?
An excellent graphic showing the aforementioned description of Marion Islands killer whales, courtesy of this fantastic paper: [X]
The very definition of an ecotype varies depending on who you talk to, but essentially, it is a variant or “race” within a species adapted to particular environmental conditions, but the phenotypic differences between them are not strong enough to warrant subspecies status. “Ecotype” is not considered to be a taxonomic classification. For killer whales, ecotypes are pretty much assigned based on the following criteria: foraging and diet, movements, social structure, morphology, and genetics and kinship [X]
And then, of course, there’s the issue with ecotype vs. species/subspecies. Though killer whales are currently considered one species, many killer whale biologists have argued that some ecotypes are different subspecies or species all together. For example, resident killer whales and transient killer whales in the North Pacific have been separated genetically for at least 700,000 years, no longer interbreed, and have distinct morphological and genetic differences. I’ve spoken in person with John Ford (a prominent killer whale biologist) about killer whale speciation, and he told me he and his colleagues pretty much consider transients and residents to be different subspecies at the very least. Indeed, recent publications such as the Marine Mammal Stock Assessment of Alaska actually refer to residents and transients as “unnamed subspecies.” However, some argue that there isn’t enough differentiation to warrant a subspecies status to residents and transients, given that they can successful interbreed and produce viable, fertile offspring (not seen in the wild, but this has happened in captivity.)
That being said, I’d still bet money that within the next few years they’ll be officially recognized as subspecies. And that, of course, means they wouldn’t be considered ecotypes anymore!
The paper “Killer whale ecotypes: Is there a global model?” by de Bruyn et al. (a a paper where much of this information has been referenced) provides a very interesting argument about southern hemisphere killer whales. The authors suggest that we may have designated southern hemisphere killer whale ecotypes prematurely as we basically “typed” them backwards in regards to how we delineated northern hemisphere ecotypes. For example, in the northern hemisphere, differences in killer whale groups were noticed first based on social structure, then diet, then behavior, and finally, morphological characteristics. In the southern hemisphere, it was basically reverse: differences in morphology were noted and we slapped an ecotype designation on them without much investigation into other ecological and social aspects. As research in Antarctica and surrounding waters has continued, it’s been noticed that the ecotypes don’t always show strict dietary specialization (at least not the extent that northern hemisphere ecotypes do) like we thought they did and at times appear to be more generalist-like. Additionally, much of their social organization/structure is unknown, and those factors often play a large part in ecotype differentiation. The authors argue that the term “morphotype” may be a more appropriate name for these groups of killer whales until more meaningful definitions/criteria for ecotypes can be determined.
Overall, determining what constitutes an ecotype and how to apply the term to different groups of killer whales can get complex really quickly. Humans like to organize organisms into neat little boxes, and nature likes to do the exact opposite. Some killer whales display all of the characteristics that we humans have decided define particular ecotypes, but then some other killer whales in the same populations (of supposedly the same ecotype) break the mold and show characteristics of other ecotypes. Will we see recognition of future ecotypes or reclassification of current ones? It wouldn’t surprise me one bit. Killer whales are such complicated and interesting creatures with a lot of things still waiting to be discovered.
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