Two New Species of Killer Whale Should Be Recognized, Study Says

All killer whales are currently categorized as a single species, but a new study may change that. Researchers suggest in the journal Royal Society Open Science that two populations of killer whales, resident and Bigg’s killer whales, should be recognized as separate species, distinct from both each other and the rest of killer whales.

The study, which reviewed previous research and conducted new analyses, looked at a number of characteristics of the two populations, including their social structures, diets, shapes, sizes and DNA.

“These two types are genetically two of the most distantly related types in the whole world,” Phillip Morin, a co-author of the study and geneticist at the Southwest Fisheries Science Center at the National Oceanic and Atmospheric Administration (NOAA), tells the New York Times’ Emily Anthes. “They’re not just behaving differently. They really are on these evolutionary trajectories which we consider to be different species.”

John Ford, a killer whale researcher at Fisheries & Oceans Canada who did not contribute to the findings, tells Hakai Magazine’s Craig Welch that the paper is thorough and definitive. “There’re just pieces of the story that have fit together to build, I think, a compelling case,” he says to the publication.

Killer whales (Orcinus orca) are apex predators that are found in oceans all around the world. Different groups live in diverse climates, make a variety of sounds and have a wide range of diets. A number of previous studies have argued that O. orca is actually made up of more than one species.

Researchers going back to at least 1970 have noticed differences in behaviors in different groups of killer whales, per Hakai Magazine. Today, scientists recognize multiple types of killer whales, called “ecotypes,” according to the new study.

Resident and Bigg’s, or transient, killer whales are both found in the eastern North Pacific. Residents eat fish, particularly salmon, while transients eat marine mammals. Residents live near the shore and transients live farther out in the ocean, writes Scientific American’s Douglas Main.

The new study delineates a number of other differences between the two groups. Residents form large, stable groups, while transients form smaller groups of maternally related orcas, per the paper. Residents hunt in large groups using echolocation, and transients hunt silently in small groups.

Transients have calls that have different frequencies and durations than those of residents. Residents, for example, produce sonar clicks more often.

The whales differ in the size and shape of their dorsal fins and have different body sizes and jaw shapes. Residents have more rounded dorsal fins that curve towards the tail, writes Scientific American. Transients, on the other hand, have more pointed and straight dorsal fins, per the publication.

While the two groups live in overlapping areas, they don’t associate—researchers have observed them avoiding each other and even acting aggressively towards each other, per the paper.

Genetic analysis suggests that the two groups are distinct and that transients diverged from their ancestors between 200,000 and 300,000 years ago, while residents started diverging around 100,000 years ago. The researchers could predict based just on a killer’s whale DNA whether it was a resident or a transient orca, per the New York Times.

“There is no interbreeding,” Morin tells Scientific American. “They could, based on their proximity, but they don’t.”

“They’ve obviously been on very separate, very divergent and independent paths of evolution for a very, very long time,” Kim Parsons, a co-author of the study and research geneticist at NOAA’s Northwest Fisheries Science Center, tells Hakai Magazine.

The findings have implications for the conservation of killer whales, which are harmed by human activities, including overfishing and pollution, per the paper. “It’s challenging to create effective conservation policies for a globally distributed species like the killer whale because animals in different regions of the world are all facing different threats,” Ally Rice, who studies whales at the Scripps Institution of Oceanography and was not involved in the new research, tells Scientific American.

The taxonomy committee of the Society of Marine Mammalogy will next determine whether to officially recognize resident killer whales and transient killer whales as new species, according to a statement from NOAA, likely at its next annual review this summer.

Will Sullivan | | READ MORE

Will Sullivan is a science writer based in Washington, D.C. His work has appeared in Inside Science and NOVA Next.