Killer whales are some of the most cosmopolitan creatures on the planet, swimming in all the world’s oceans. They patrol the icy waters near both poles and periodically appear in the tropics, in locations from West Africa to Hawaii.
Although their habitats and habits vary widely, all killer whales are considered part of a single, global species: Orcinus orca. (Despite their common name, killer whales are actually part of a family of marine mammals known as oceanic dolphins.)
Now, scientists have drawn on decades of research to suggest that two populations of killer whales frequently sighted off the Pacific coasts of the United States and Canada are actually so different from each other – and from other orcas – that they should be considered separate species.
In a paper published in the journal Royal Society Open Science on Tuesday, scientists proposed giving new species names to two groups of animals, one known as resident killer whales and the other often called Bigg’s killer whales. Although both types live in the eastern North Pacific, they have different diets: resident orcas eat fish, with a particular preference for salmon, while Bigg’s orcas hunt marine mammals such as seals and sea lions.
The proposal documents many other behavioral, physical and genetic differences between the two orca populations, which have evolved far from each other for hundreds of thousands of years, the scientists noted.
“These two types are genetically two of the most distant types in the entire world,” said Phillip Morin, a geneticist at the Southwest Fisheries Science Center at the National Oceanic and Atmospheric Administration, or NOAA, and an author of the study. “They don’t just behave differently. They’re really on these evolutionary trajectories that we think of as different species.”
There is no single definition of what qualifies as a species, and the lines between animal populations are often blurred. But these kinds of taxonomic distinctions can have conservation implications, the scientists said, allowing experts to make more informed decisions about how to manage different orca populations.
“They face vastly different threats,” said John K. Ford, an orca expert and scientist emeritus at Fisheries and Oceans Canada, who was not an author of the new paper.
In recent decades, for example, the number of seals and sea lions that have been leaping has contributed to a population boom for Bigg’s orcas, he said. Resident killer whales, on the other hand, have been threatened by dwindling wild salmon stocks.
Dr. Ford said the authors of the new paper have made a “very strong case,” bringing together a growing body of evidence that resident killer whales and beeg’s killer whales are distinctly different creatures. “It’s these multiple lines of evidence that all point in the same direction,” he said.
The next step will be to submit the proposal to a classification expert committee at the Society of Marine Mammology, which maintains “the most authoritative list” of the species, Dr. Morin said.
In recent years, scientific progress has allowed scientists to conduct more sophisticated analyzes of the orcas’ genome. The data suggests that Bigg’s killer whales diverged from other orcas between 200,000 and 300,000 years ago. The inhabitants, for their part, diverged from other orcas around 100,000 years ago. Genetic and behavioral analyzes also suggest that in recent years there has been little interbreeding between Bigg’s and resident otters.
“It’s very compelling evidence to suggest that they represent different species,” said Kim Parsons, a geneticist at NOAA’s Northwest Fisheries Science Center and an author of the study.
Overall, the genomes were different enough that scientists could predict, with high accuracy, whether a killer whale was a Bigg’s orca or a resident orca based on its DNA alone.
The shape of the skull is equally predictive. Bigg’s killer whales have larger, broader skulls, with more deeply curved jaws than the residents—traits that may help them fight their larger prey. Bigg’s killer whales are also slightly larger than the residents overall, with wider, more pointed dorsal fins and different black and white patch patterns.
There are also behavioral differences. Resident killer whales live in large, stable groups and are known to be chatty, communicating easily as they hunt for fish. Bigg’s killer whales, on the other hand, live in smaller groups and hunt quietly. When they call, their whistles sound different from those of the residents.
The paper’s editors proposed that resident killer whales be given the new scientific name Orcinus ater. If the Society for Marine Mammalogy accepts the proposal, the scientists said they planned to consult with indigenous groups in the Pacific Northwest to choose a new common name that reflects the cultural significance of the oars.
Scientists have proposed that Bigg’s orcas keep this common name, which honors Michael Bigg, an influential orca researcher, but receive the new scientific name Orcinus rectipinnus.
Further analysis may reveal other orca populations that are designated as separate species, the scientists said.
“There is so much diversity in the oceans that we don’t know about,” Dr Morin said. “Even with animals the size of a school bus.”
