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All orcas are classified as a single species. Should they be?

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Killer whales are among the most cosmopolitan creatures on the planet, swimming in all the world’s oceans. They patrol the frigid waters near both poles and appear periodically in the tropics, from West Africa to Hawaii.

Although their habitats and habits vary greatly, all killer whales are considered part of a single global species: Killer whale. (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 often seen off the Pacific coast of the United States and Canada are actually so different from each other – and other orcas – that they should be considered separate species.

In a paper published Tuesday in the journal Royal Society Open Science, scientists propose giving new species designations to two groups of animals, one known as resident killer whales and the other often referred to as the northern killer whale. Bigg. Although both types live in the eastern North Pacific, they have different diets: resident orcas eat fish, with a particular predilection 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 relative to each other for hundreds of thousands of years, the scientists noted.

“These two types are genetically two of the most distant types in the world,” said Phillip Morin, a geneticist at the Southwest Fisheries Science Center of the National Oceanic and Atmospheric Administration, or NOAA, and an author of the study. “They don’t just behave differently. They actually follow these evolutionary trajectories that we think of as different species.

There is no single definition of what a species is, and the boundaries between animal populations are often blurred. But these types of taxonomic distinctions can have conservation implications, scientists say, allowing experts to make more informed decisions about how to manage different orca populations.

“They face very different threats,” said John K. Ford, an orca expert and emeritus scientist at Fisheries and Oceans Canada, who is not the author of the new paper.

In recent decades, for example, increasing numbers of seals and sea lions have helped fuel a population boom for Bigg’s orcas, he said. Resident orcas, on the other hand, are threatened by dwindling wild salmon stocks.

Dr Ford said the authors of the new paper presented a “very strong case”, bringing together a growing body of evidence that resident killer whales and Bigg’s killer whales are distinct creatures. “It’s these multiple pieces of evidence that all point in the same direction,” he said.

The next step will be to submit the proposal to a committee of taxonomic experts at the Society for Marine Mammalogy, which maintains “the most authoritative list of species,” Dr. Morin said.

In recent years, scientific advances have allowed scientists to conduct more sophisticated analyzes of the orca genome. Data suggests that Bigg’s killer whales diverged from other orcas between 200,000 and 300,000 years ago. The inhabitants, meanwhile, separated from other orcas around 100,000 years ago. Genetic and behavioral analyzes also suggest that there has been little interbreeding between Bigg’s orcas and resident orcas in recent years.

“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 also predictive. Bigg’s orcas have larger, broader skulls, with more deeply curved jaws than residents – features that could help them fight off their larger prey. Bigg’s orcas are also slightly larger than the general residents, with broader, more pointed dorsal fins and different patterns of black and white spots.

There are also differences in behavior. Resident orcas live in large, stable groups and are known to be talkative and communicate easily when pursuing fish. Bigg’s killer whales, on the other hand, live in small groups and hunt quietly. When they vocalize, their whistles are different from those of the residents.

The paper’s authors proposed giving resident killer whales the new scientific name Orcinus ater. If the Society for Marine Mammalogy accepts the proposal, scientists said they plan to consult with indigenous groups in the Pacific Northwest to select a new common name reflecting the orcas’ cultural significance.

Scientists have suggested that Bigg’s orcas retain this common name, which honors Michael Bigg, an influential orca researcher, but receive the new scientific name. Orcinus rectipinnus.

Further analysis could reveal other orca populations considered distinct 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.”

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