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It was a contest between an orca and a dolphin, and the dolphin didn’t stand a chance.
In coastal waters near Chile in 2023, a huge female orca struck a much smaller dolphin, sending it flying out of the water. Within minutes, the unequal struggle was over and the orca began to feed. But she did not eat alone. As she clutched the dolphin’s body, other orcas swam up to her to share bites of the meal.
Meanwhile, researchers in a nearby boat captured the feast on video. They identified the prey as a dusky dolphin (Lagenoryhnchus obscurus), a small coastal species native to South America.
Scientists had previously documented killer whales (Orcinus orca) in the region pursuing both dusky dolphins and long-beaked dolphins (Delphinus capensis). However, this new observation is the first evidence that dusky dolphins are 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 while there is only one species, there are multiple ecotypes, or groups that share similarities in appearance and behavior, including hunting strategies and prey preferences. There are five ecotypes in the Northern Hemisphere and five in the Southern Hemisphere. The Humboldt Current killer whales have yet to be assigned to an ecotype, and documenting their dolphin hunts provides clues as to where this population may belong, researchers reported Thursday in the journal Frontiers in Marine Science.
In general, little is known about the habits of Humboldt Current orcas; they are not as well-studied as other groups of killer whales, such as those found near Antarctica and off the west coast of North America. They are also not as Internet famous as the infamous boat-bashing orcas that rammed ships in the Strait of Gibraltar and off Scotland. But marine biologists are working to fill that knowledge gap. After conducting surveys and analyzing more than a decade of data, photos and videos, scientists recorded 28 sightings of orcas at two locations in the Humboldt Current. Frame by frame, the researchers are building a clearer picture of the distribution and habits of the elusive whales.
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Orcas are highly social animals, and there is still much to learn about their behavior and how habits can vary between groups, said Sarah Teman, a doctoral student in the School of Aquatic and Fishery Sciences at the University of Washington in Seattle. “Orcas around the world can have different diets, different communication styles, and even different cultures,” said Teman, who was not involved in the study but has studied interactions between orcas and porpoises.
“We’re still discovering how diverse the orca populations are,” she said.
The Humboldt Current carries cold, nutrient-rich water up from the ocean depths. It carries nutrients that feed schools of anchovies and krill, which in turn are devoured by larger marine mammals such as dolphins and seals — the killer whales’ prey.
Lead study author Ana Maria García Cegarra, an assistant professor at the Alexander von Humboldt Institute of Natural Sciences at Chile’s University of Antofagasta and director of Chile’s Marine Megafauna Research Lab (CETALAB), has been studying the Humboldt Current’s killer whales for the past decade. For the study, she and her colleagues examined reports and media reports recorded by local fishermen and people on whale watching trips in the Humboldt Penguin National Reserve and around Chile’s northern Mejillones Peninsula between 2011 and 2023.
The scientists also conducted boat surveys in Mejillones Bay and filmed the orcas with a drone. Based on associations between the orcas, the researchers determined that there were at least two distinct social groups, each with five to six individuals. These small orca communities, known as pods, usually consist of a matriarch and her offspring.
Dusky dolphins are about 6.5 feet (2 meters) long and weigh up to 180 pounds (85 kilograms). By comparison, an orca is up to 33 feet (10 meters) long and can weigh up to 25 tons (11 tons). In May 2023, the scientists reported in the study, there were two sightings of orcas preying on dusky dolphins. In one case, a female orca chased a dolphin and threw it into the air, then grabbed the dead dolphin in her mouth as other orcas swam up and ate it. In the second incident, a female orca held onto a dead dusky dolphin while her calf and other orcas made short work of the corpse, eating it in about 15 minutes.
Previous studies have documented killer whales 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, Canada, a pod of killer whales that feed primarily on salmon has repeatedly harassed and killed harbor porpoises. These orcas, however, do not eat the porpoises they have bullied to death.
The Humboldt Current orcas didn’t just eat dolphins; they hunted leatherback turtles, South American fur seals and Humboldt penguins, the study found. The scientists also discovered evidence of orca tooth marks on the dorsal fin of a fin whale (Balaenoptera physalus). While there have been no records of orcas hunting fin whales, orcas in waters near Chilean Patagonia are known to hunt and eat sei whales (Balaenoptera borealis). “Sei whales and fin whales are very similar,” so the Humboldt Current orcas likely hunt fin whales as well, García Cegarra said in an email.
‘A great coincidence’
In the Southern Hemisphere, killer whales in the Type A ecotype are known to feed on dark dolphins; since Humboldt Current killer whales share this preference, they may be Type A killer whales. However, Humboldt Current 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, the scientists reported.
Tracking the Humboldt Current orcas and knowing what they hunt and eat will help conservation groups protect the orcas, which are described as “data deficient” by the International Union for Conservation of Nature’s Red List (a tracker of threatened and endangered species) and Chile’s Environment Ministry, García Cegarra said. As a result, there are no management tools or strategies in place to protect them.
“Orcas play a vital role in the world’s oceans and are valuable in their own right,” Teman said. “The more we learn about whales, the better equipped we are to protect the oceans they inhabit.”
Further research will also help scientists better understand the social interactions of killer whales, such as how they teach their hunting strategies to their young. And there are other intriguing killer whale behaviors that are even less understood.
For example, during one meal, an orca calf approached the scientists’ boat with a mouthful of dolphin meat, García Cegarra said in the email. A similar interaction had previously been documented in Australia between an orca and a diver, but had never been observed in the Humboldt Current. One interpretation is that the orca offered to share its food, but scientists aren’t sure, García Cegarra said.
However, the chances of documenting orca hunts in the wild this way are slim, she added. Orcas can swim great distances very quickly and usually travel in small groups, so encounters with orcas during research expeditions are usually rare.
“It’s a huge coincidence that we’re in the sea at the same place and time when orcas decide to hunt,” she said.
Mindy Weisberger is a science journalist and media producer whose work has appeared in Live Science, Scientific American, and How It Works magazine.
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