New images reveal elusive pod of killer whales hunting dolphins off Chile

(CNN) – It was a duel between killer whales and dolphins, and the dolphin didn’t stand a chance.

In 2023, in coastal waters off Chile, a massive female orca pounced on a much smaller dolphin, sending it flying into the air. Within minutes, the unequal battle was over and the killer whales were feasting. But she wasn’t the only one eating dinner. While she held onto the dolphin’s body, other killer whales swam up to share bites.

Meanwhile, researchers on a nearby boat recorded the feast on video and identified the prey as a dusky dolphin (Lagenoryhnchus obscurus), a small coastal species native to South America.

Scientists have previously documented killer whales (Orcinus orca) in the area preying on both dusky dolphins and long-beaked common dolphins (Delphinus capensis). However, this new observation is the first evidence that dusky dolphins are being hunted, captured and shared by killer whales in the Humboldt Current system, which flows north into the Pacific Ocean along the west coast of South America.

Killer whales are found worldwide, and although there is only one species, there are multiple ecotypes, or groups, that share similarities in their appearance and behaviors, including hunting strategies and prey preferences. There are five ecotypes in the Northern Hemisphere and five in the Southern Hemisphere. Killer whales in the Humboldt Current have not yet been assigned to an ecotype, and documentation of dolphin hunts provides clues about which group they might belong to, researchers reported Thursday in the journal Frontiers in Marine Science.

Overall, little is known about the habits of Humboldt killer whales today; they haven’t been as well-studied as other groups of killer whales, such as those that live near Antarctica and off the west coast of North America. They’re also not as famous on the Internet as the killer whales that have rammed ships in the Strait of Gibraltar and off Scotland. But marine biologists are working to fill that gap. After studying and analyzing more than 10 years of data, photos and videos, scientists have recorded 28 killer whale sightings at two sites in the Humboldt Current. Image by image, the researchers are piecing together a clearer picture of the distribution and habits of these elusive whales.

Killer whales are highly social animals and there is still much to learn about their behaviors and how they can vary from one group to another, said Sarah Tiemann, a doctoral student at the University of Washington’s School of Aquatic and Fisheries Sciences in Seattle. “Killer whales around the world can have different diets, different communication styles, and even different cultures,” said Tiemann, who was not involved in the research but has studied interactions between killer whales and porpoises.

“We are still learning how diverse orca populations are,” he added.

In the Humboldt Current, cold, nutrient-rich water rises from the deep ocean. It delivers nutrients that feed schools of anchovies and krill, which in turn are eaten by larger marine mammals, such as dolphins and seals, the killer whales’ prey.

The study’s lead author, Ana María García Segarra, an associate professor at the Alexander von Humboldt Institute of Natural Sciences at the University of Antofagasta, Chile, and director of the Chilean Marine Megafauna Research Laboratory (CETALAB), has devoted the past decade to investigating Humboldt Current killer whales. For the study, she and her colleagues analyzed reports and media recorded between 2011 and 2023 by local fishermen and people on whale-watching tour boats in the Humboldt Penguin National Reserve and around the Mussels Peninsula in northern Chile.

The scientists also conducted boat surveys in Mejillones Bay and filmed the killer whales with a drone. Based on associations between the killer whales, the researchers determined that there are at least two distinct social groups, each with five to six individuals. Small orca communities known as pods typically consist of a matriarch and her offspring.

Dusky dolphins are about 2 meters long and weigh up to 85 kilograms. In comparison, killer whales grow to 10 meters long and can weigh up to 11 tons (10 metric tons). In May 2023, the scientists reported in the study, there were two sightings of killer whales hunting dusky dolphins. In one instance, a female orca chased a dolphin and threw it into the air; she then held the dead dolphin in her mouth while other killer whales swam around and fed on it. In the second incident, a female orca carried a dead dusky dolphin while her calf and other orcas consumed the carcass in about 15 minutes.

Previous studies have documented dolphin predation by killer whales in waters off California, Argentina and New Zealand. In the Salish Sea, a Pacific inlet between Washington state and British Columbia, Canada, a group of killer whales that feed primarily on salmon has repeatedly harassed and killed porpoises—but the killer whales did not eat the porpoises they killed.

According to the study, Humboldt killer whales did not feed exclusively on dolphins, but also on leatherback turtles, South American fur seals, and Humboldt penguins. The scientists also found signs of killer whale tooth marks on the dorsal fin of a fin whale (Balaenoptera physalus). Although killer whales have not been observed preying on fin whales, they are known to hunt and eat northern right whales (Balaenoptera borealis) in waters near Chilean Patagonia. “Snow whales and fin whales are very similar,” García-Segarra said in an email, so it’s possible that modern-day Humboldt killer whales also prey on fin whales.

In the Southern Hemisphere, ecotype A killer whales are known to prey on dusky dolphins; since present-day Humboldt whales share this preference, they could be Type A killer whales, but present-day Humboldt killer whales have a smaller white eye patch than known Type A killer whales. Genetic analysis of skin samples, which were not collected for this study, could help resolve this issue, the scientists say.

According to García Segarra, monitoring the Humboldt Current killer whales and knowing what they hunt and eat will help conservation groups protect the killer whales, which, according to the International Union for Conservation of Nature (IUCN) Red List (a tracker of threatened and endangered species) and the Chilean Ministry of Environment, are classified as “data deficient.” As a result, there are no management tools or strategies to protect them.

“Killer whales play a vital role in the world’s oceans, and they are valuable in their own right,” says Tiemann. “The more we learn about whales, the better equipped we will be to protect the seas they inhabit.”

The new research will also help scientists better understand killer whale social interactions, such as how they teach their hunting strategies to their offspring. There are other interesting orca behaviors that are less well known.

For example, during one feeding, a killer whale calf approached the scientists’ boat with its mouth full of dolphin meat, García-Segarra said in an email. Similar interactions between killer whales and scuba divers have been documented in Australia, but never in the Humboldt Current. One explanation is that the killer whales were offering to share their food, García-Segarra said, but scientists don’t know for sure.

He added that the chances of documenting wild whaling operations in this way are not great. Killer whales can swim long distances very quickly and usually travel in small groups, so encounters with killer whales during research expeditions are usually rare.

“It’s just a coincidence that it was out at sea at the same place and time that the killer whales decided to hunt,” he said.

Mindy Weisberger is a science writer and media producer whose work has appeared in Live Science, Scientific American, and How It Works.