New footage reveals key clues to understanding mysterious orca group, scientists say

It was an orca-versus-dolphin matchup, and the dolphin didn’t stand a chance.

In coastal waters near Chile in 2023, a massive female killer whale walloped the much smaller dolphin, sending it flying out of the water. Within minutes, the unequal battle was over and the orca began to feed. But she didn’t dine alone. As she gripped the dolphin’s body, other orcas swam up to share bites of the meal.

Meanwhile, researchers in a nearby boat were capturing the feast on video, identifying the prey as a dusky dolphin (Lagenoryhnchus obscurus), a small coastal species native to South America.

The scientists had previously documented orcas (Orcinus orca) in the region chasing both dusky dolphins and long-beaked common dolphins (Delphinus capensis). However, this new observation is the first evidence of dusky dolphins being hunted, caught and shared by orcas of the Humboldt Current system, which flows northward in the Pacific Ocean along South America’s western coast.

Orcas are found worldwide, and while there is just one species there are multiple ecotypes, or groups that share similarities in their appearance and behaviors, including hunting strategies and prey preference. There are five ecotypes in the Northern Hemisphere and five in the Southern Hemisphere. The Humboldt Current’s orcas have yet to be assigned to an ecotype, and documenting their dolphin-hunting provides clues about where this population might belong, researchers reported Thursday in the journal Frontiers in Marine Science.

In general, little is known about the habits of the Humboldt Current orcas; they aren’t as well-studied as other killer whale groups, such as those that live near Antarctica and off the western coast of North America. Nor are they as internet-famous as the notorious boat-bashing orcas that have rammed vessels in the Strait of Gibraltar and near Scotland. But marine biologists are working to close that knowledge gap. After conducting surveys and analyzing more than 10 years of data, photos and video, scientists recorded 28 sightings of orcas in two Humboldt Current locations. Image by image, the researchers are piecing together a clearer picture of the elusive whales’ distribution and habits.

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Killer whales are highly social animals, and there is still much to be learned about their behaviors and how habits may vary between groups, said Sarah Teman, a doctoral student in the School of Aquatic and Fishery Sciences at the University of Washington in Seattle. “Killer whales around the world can have different diets, different communication styles, even different cultures,” said Teman, who was not involved in the research but has studied interactions between orcas and porpoises.

“We’re still learning just how diverse killer whale populations are,” she said.

In the Humboldt Current, cold nutrient-rich water cycles upward from the ocean depths. It carries nutrients that nourish schools of anchovies and krill, which are in turn devoured by larger marine mammals such as dolphins and seals — the orcas’ prey.

Lead study author Ana Maria García Cegarra, an assistant professor at the Alexander von Humboldt Institute of Natural Sciences in Chile’s University of Antofagasta and director of Chile’s Marine Megafauna Research Lab (CETALAB), has spent the past decade investigating the Humboldt Current orcas. For the study, she and her colleagues scrutinized reports and media recorded from 2011 to 2023 by local fishers and people on whale-watching tour boats in the Humboldt Penguin National Reserve and around northern Chile’s Mejillones Peninsula.

The scientists also conducted boat surveys in the Mejillones Bay and filmed orcas using an aerial drone. Based on associations between orcas, the researchers determined that there were at least two distinct social groupings, each with five to six individuals. Known as pods, these small orca communities usually consist of a matriarch and her descendents.

Dusky dolphins measure about 7 feet (2 meters) long and weigh up to 187 pounds (85 kilograms). By comparison, an orca measures up to 32 feet (10 meters) long and can weigh as much as 11 tons (10 metric tons). In May 2023, the scientists reported in the study, there were two sightings of orcas hunting dusky dolphins. In one event, a female orca pursued a dolphin and tossed it into the air; she then gripped the dead dolphin in her mouth as other orcas swam up and fed. In the second incident, a female orca held a dead dusky dolphin while her calf and other orcas made short work of the corpse, devouring it in about 15 minutes.

Prior studies have documented orcas preying on dolphins in waters near California, and near Argentina and New Zealand. And in the Salish Sea, an inlet of the Pacific Ocean that lies between Washington state and British Columbia in Canada, a group of orcas that mostly eats salmon has repeatedly harassed and killed porpoises —however, these orcas don’t eat the porpoises that they have bullied to death.

The Humboldt Current orcas weren’t eating dolphins exclusively; they hunted leatherback sea turtles, South American fur seals and Humboldt penguins, according to the study. The scientists also discovered signs of orca tooth rake marks on the dorsal fin of a fin whale (Balaenoptera physalus). While there are no observations of orcas hunting fin whales, orcas are known to hunt and eat sei whales (Balaenoptera borealis) in waters near Chilean Patagonia. “Sei and fin whales are very similar,” so the Humboldt Current orcas probably hunt fin whales, too, García Cegarra said in an email.

‘A great coincidence’
In the Southern Hemisphere, orcas in the ecotype Type A are known to feed on dusky dolphins; as Humboldt Current orcas share this preference, they might be Type A orcas. But Humboldt Current orcas have a smaller white eye patch than known Type A orcas. Genetic analysis of skin samples, which were not collected for this study, could help resolve this, the scientists reported.

Tracking the Humboldt Current orcas and knowing what the killer whales are hunting and eating will help conservation groups protect the orcas, which are described as “data deficient” by the International Union for the Conservation of Nature’s Red List (a tracker of threatened and endangered species) and Chile’s Ministry of the Environment, according to García Cegarra. As a result, there are no management tools or strategies to protect them.

“Killer whales play a critical role in the world’s oceans, and they’re valuable in their own right,” Teman said. “The more we learn about whales, the better equipped we are to protect the seas they live in.”

Further research will also help scientists to better understand the orcas’ social interactions, such as how they teach their hunting strategies to their young. And there are other intriguing orca behaviors that are even less understood.

For example, during one of the meals, an orca calf approached the scientists’ boat with a mouthful of dolphin meat, García Cegarra said in the email. A similar interaction was previously documented in Australia between an orca and a diver, but had never been observed in the Humboldt Current. One interpretation is that the orca was offering to share its food, but scientists don’t know that for sure, García Cegarra said.

However, the odds of documenting orca hunts in the wild in this way aren’t great, she added. Orcas can swim great distances very quickly and usually travel in small groups, so orca encounters during research expeditions are usually scarce.

“It is a great coincidence to be in the sea at the same place and time when orcas decide to be hunting,” she said.