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Orcas, also known as killer whales, have captivated humans for thousands of years. Their striking appearance and playful intelligence has inspired myths, blockbuster films, memes, and a host of research from marine biologists.
Yet despite the widespread fascination with orcas, they remain one of the most poorly understood animals in the ocean. Scientists estimate that about 50,000 killer whales roam the global seas, but it’s not at all clear where they all live, which populations are threatened by human activities, or what drives their complicated behaviors—including their occasional attacks on boats. We’re not even sure whether there’s really just one species of orca.
(Vengeance—or playtime? Why orcas are coordinating attacks against sailboats.)
“They’re probably the most widely distributed mammal on the planet, outside of humans,” says Phillip Morin, a population genetics and genomics researcher at NOAA Southwest Fisheries Science Center’s Marine Mammal Genetics Program. “That means we don’t have information on the distribution, abundance, or connectivity between types of killer whales, especially in places away from the U.S. or Northern Europe.”
As a result of these knowledge gaps, orcas are among the more than 20,000 species that are labeled “data deficient” on the International Union for Conservation of Nature (IUCN) Red List, meaning that there is not enough information to assess their conservation status or needs.
Scientists have wrestled for decades with the challenges of studying the mysterious orca, which is the largest member of the dolphin family. These efforts are more important than ever now that they are experiencing new pressures brought about by human activity—including warming oceans, overfishing, habitat loss, and increased boat traffic.
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Here are the questions that keep orca scientists up at night, and the roadmap for answering them.
How many orca species exist?
Orcas are still categorized as one species globally, known as Orcinus orca, but many scientists are convinced that they are actually several distinct species.
“There is, just to put it mildly, a lot of disagreement about how many species and subspecies are in the group,” says Barbara Taylor, a marine mammal expert and Red List coordinator for the IUCN Cetacean Specialist Group. “There is, I think, a very good chance that there are multiple species that are under Orcinus orca.”
Orcas have been divided into a number of different “ecotypes,” a looser term defined by the idiosyncratic behaviors, diets, migration patterns, and even personalities that emerge in different orca populations.
“There are orcas that eat penguins; they are specialized to communicate between each other to hunt them and they are super-efficient,” says Raúl Octavio Martínez Rincón, a biologist and researcher at the Northwest Biological Research Center in Mexico. “That is part of the definition of ecotype. It can be physical, like size, or can mean behavior, like eating, communication, and so on.”
(These orcas control the waves to hunt. It’s spine-tingling to watch.)
Orca ecotypes often have overlapping ranges, making their distinct characteristics even more surprising. For example, the so-called resident killer whales typically seen in the Pacific Northwest are heavily dependent on salmon, while others, like Bigg’s killer whales (also known as transient killer whales) have more varied diets consisting of other marine mammals and squid.
What’s more, these overlapping populations don’t seem to interact or breed with each other. Indeed, they may avoid or be actively aggressive to outsiders. Orcas’ strong social organization and family cohesion helps explain the clear divisions that have emerged between ecotypes.
“Different populations of residents will come together and have a party,” Morin says. “They play and they feed together. There’s a lot of social interaction, and that’s probably when most breeding occurs. Whereas when residents come into contact with transients, they avoid each other.”
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In a study published in March 2024, Morin and his co-authors, including Taylor, presented a wealth of ecological, morphological, and genetic data to suggest that Bigg’s killer whales and resident killer whales are not just different ecotypes, but separate species.
(Why are these orcas killing sharks and removing their livers?)
The Society for Marine Mammalogy Taxonomy Committee ultimately decided in July to establish these ecotypes as subspecies rather than two separate species. Yet these distinctions could inspire targeted conservation efforts in countries that rely on the IUCN Red List to inform best approaches for conservation. Establishing separate species could raise awareness of specific orca populations such as southern resident killer whales—which are critically endangered yet still fall under the species-wide “data deficient” category on the Red List.
For this reason, Taylor and her colleagues are working toward a model that recognizes the most at-risk subpopulations of orcas (and other marine mammals) as conservation priorities, regardless of species status.
“What we have been working on is coming up with a way to prioritize which ones we do assessments on, and to make it very clear that we are picking and choosing the neediest subpopulations,” Taylor says.
How big of a threat do humans pose to orcas?
It’s clear that humans have already had a negative impact on some orca populations, especially southern resident killer whales. This population, consisting of about 75 orcas in the North Pacific, has precipitously declined due to human-related habitat and prey loss, as well as vessel strikes. Scientists have coined the term “bright extinction” to describe the crisis—meaning that this is a disaster that is unfolding in plain sight and with plenty of data.
But in general scientists don’t know enough about how humans are affecting orcas—or which of the threats we pose are most harmful. To get a sense of this bigger picture, scientists will need to continue to study the most well-known populations, while also pursuing insights about more elusive ecotypes, like the so-called “offshores” that have been spotted a handful of times in remote parts of the Pacific Ocean.
(Rogue orcas are thriving on the high seas—and they’re eating big whales.)
“I think it will come piecemeal,” says Morin. “We have to get out, get more samples, and do more fieldwork to understand what their distributions are, along with their diets, movements, life history, characteristics, and hopefully abundance and trends, to determine what the human impacts are.”
Climate change is another wild card in this deck. Martínez Rincón, who specializes in modeling the distribution of various species across ranges, recently co-authored a study with researcher Millat Blanc that suggests orcas may be particularly vulnerable to climate change because ecotypes are so specialized to certain habitats and diets. For instance, climate change is already disrupting important orca prey sources, such as Chinook salmon.
“Large animals like orcas or whales don’t care so much about the temperature of the water,” Martínez Rincón says. “But if the prey is not there because of climate change, that might be the hardest problem for this kind of species.”
What’s behind some of the more surprising orca behaviors?
Some scientists have speculated that the apparent rise in attacks on boats by orcas, especially off the Iberian Coast, is an expression of growing tensions between humans and killer whales. This hypothesis has been embraced online with memes about an “Orca Uprising” unfolding beneath the ocean waves.
But as with so many other mysteries about these animals, the reason behind the boat attacks is still unknown. Many scientists think the boat strikes could be motivated by sheer curiosity or as a training tactic for hunting tuna.
(5 ways orcas are surprising scientists.)
Ultimately, orcas remain a bundle of contradictions. But it is these paradoxes that distinguish orcas as such an unlikely but effective ambassador for data-deficient species—a group that includes the adorable Vietnam mouse-deer, a goby fish that lives inside sponges, or the Chinese weeping cypress tree.
“Here we are in the middle of the sixth big extinction, a massive biodiversity crisis, and yet we don’t know how many species of whales there are,” Taylor says. “That’s just such an amazing thing. I think most people think we’re much further along in learning about how life works on planet Earth than we actually are.”
