A formal proposal to designate resident and Bigg’s killer whales as separate species has been rejected by a committee widely recognized as the authority in naming new marine mammal species.

The proposal for new orca species, put forth by a team of geneticists and marine mammal biologists, was based on the distinct genetic, physical and behavioral differences observed between resident killer whales, which eat fish, and Bigg’s, or transient, killer whales, which eat marine mammals, as I described in an article in the Encyclopedia of Puget Sound.

The evidence for two new species of killer whales, published in the journal Royal Society Open Science, not only reflected on differences between resident and Bigg’s killer whales but also mentioned other populations throughout the world — although studies of residents and Bigg’s are far more extensive than for any other population.

A majority of the 15-member Taxonomy Committee, which is part of the Society for Marine Mammalogy, voted in favor of the new orca species, yet the vote fell short of the two-thirds needed to change the worldwide list of marine mammal species and subspecies. The committee did agree that resident and Bigg’s killer whales should be designated as subspecies.

One reason cited by the committee for rejecting the species proposal was a shortage of information about other killer whales throughout the world. According to written findings provided by the committee, such a change would require researchers “to conduct a more comprehensive analysis on a global context to better understand how distinct these two ecotypes are from other Orcinus orca clades (related groups), including those found … off the coasts of California and Mexico and the more northerly Bigg’s and offshore ecotypes, which were not evaluated in the paper.”

Marine biologist and taxonomist Tom Jefferson, an author of the paper and a member of the Taxonomy Committee, said he and most experts he has spoken with were surprised and even shocked at the decision.

“Most people doing work on killer whales were pretty convinced that we had separate species,” Tom told me. “The evidence has been accumulating, and we thought this paper would settle it once and for all.”

Tom, along with NOAA’s Eric Archer, are members of the Taxonomy Committee. They recused themselves from the vote, because both are authors of the paper proposing the change. While recusal is customary for committee members involved in such proposals, it is not actually a committee rule, Tom said. As it turns out, had the two voted, the proposal would have passed, and the new orca species would have been approved, he said.

“Every word of the paper could have been the same, but if Eric’s and my name were not on there, the outcome would have been different,” he said. “That shows how important a single vote can be.”

In demanding more information about the worldwide population of killer whales, the committee was “raising the bar” for species designations, Tom said. Several members who voted against the proposal acknowledged that residents and Bigg’s are clearly separate species, he said, but they wanted more information about the global population. That has never been a requirement of the committee in the past when designating new species.

I had heard that some members might need more information, as I mentioned in a May 31 blog post.

Recognizing the relationships and genetic differences among killer whales is important to conservation and management decisions, Tom noted. Killer whales can be found in every ocean throughout the world, and identifying separate species can bring attention to those that need it most, he said.

“Every cloud has a silver lining,” he said, “and maybe this will provide the incentive for more taxonomic work to be done. It will happen, but if we need a global review, it could take another decade and a half. We will get there eventually. Meanwhile, we are stuck with a taxonomy that almost all of us agree is wrong.”

Southern resident killer whales, which frequent Puget Sound, are listed as “endangered” under the Endangered Species Act. As such, this taxonomic decision won’t have much impact on the 74 animals that make up the population. Under the proposal, they would have been grouped as a species that would also include the northern residents of British Columbia, Alaskan residents, and numerous other groups of fish-eating orcas on the Asian side of the Pacific Ocean.

While rejecting the species-level designation, the Taxonomy Committee did approve residents and Bigg’s killer whales as distinct subspecies “provisionally” until more information becomes available. When the committee was first formed in 2010, it had adopted the two groups as unnamed subspecies, based on a description in a NOAA technical memorandum from 2004 (PDF). But the subspecies were removed in 2019, because they had not been properly described or named according to taxonomic protocols.

The new study, led by Phil Morin of NOAA’s Southwest Fisheries Science Center, provided the needed information, including scientific names for the provisional subspecies. For now, residents will be known as Orcinus orca ater, and Bigg’s will be called Orcinus orca rectipinnus (genus-species-subspecies). These names have an interesting history, as I described in my previous article. Pending further studies, the rest of the orcas in the world will get the scientific name Orcinus orca orca and will be generally called “common killer whale.”

---

---

The rationale for the committee’s decision is summarized in the narrative portion of the full list of marine mammal species and subspecies. Since it is not easy to find, I am providing a copy of the full test here:

“Based on genetic, morphological and ecological data, Morin et al. (2024) provided a taxonomic revision for two ecotypes of Orcinus orca in the eastern North Pacific: Bigg’s killer whale (also known as transient ecotype) and the resident killer whale. The level of differentiation observed led the authors to recommend their recognition as distinct species: O. rectipinnus (Bigg’s killer whale) and O. ater (resident killer whale). Although the majority of the voting members recognize the high level of differentiation between the two ecotypes in all the evidence presented in Morin et al. (2024), there was uncertainty whether this diagnosability represented species- or subspecies-level designation.

“Some points argued against species designation at the time included: 1) the nesting of both clades within the wider O. orca clade in the mitogenome phylogeny; 2) presence of episodic gene flow among the ecotypes, which needs further investigation; and 3) the need to conduct a more comprehensive analysis on a global context to better understand how distinct these two ecotypes are from other Orcinus orca clades, including those found at latitudes below ~34º N off the coasts of California and Mexico and the more northerly Bigg’s and offshore ecotypes, which were not evaluated in the paper.

“Previously, the Committee followed the recognition in Krahn et al. (2004) of two un-named subspecies of killer whales for the eastern North Pacific, which were listed in previous version of the List of Proposed Un-named Species and Subspecies. These two un-named subspecies correspond to the resident and Bigg’s/transient ecotypes, respectively. Therefore, pending a more complete global review and revision of the killer whales, the two ecotypes are considered here provisionally as distinct subspecies of Orcinus orca and named following Morin et al. (2024): O. orca ater (resident killer whale) and O. orca rectipinnus (Bigg’s killer whale), with O. orca orca (common killer whale) as the nominate subspecies.”