Killer whales off the coast of British Columbia, Canada, have been seen hunting with dolphins and sharing the remains of salmon after killing them.
Killer whales (Orcinus orca), or killer whales, found in northern waters off the coast of British Columbia, have been observed working with white-sided dolphins (Aethalodelphis obliquidens) to hunt Chinook salmon (Oncorhynchus tshawytscha).
Researchers used underwater video, suction cup biologging tag data, and aerial drone footage to uncover how nine northern killer whales migrated, hunted, and interacted with white-tailed dolphins around Canada’s Vancouver Island in August 2020.
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They captured aerial and underwater footage of the animals’ cooperative interactions. The two species in this region typically show little sign of mutual aggression and occasionally seek each other out. This is unusual given that killer whales hunt dolphins elsewhere and some dolphins attack killer whales.
Researchers recorded 258 instances of dolphins moving close to tagged killer whales. In all of these cases, the killer whales were engaged in foraging-related behaviors, such as killing, eating, or hunting salmon that were too large for the dolphins to catch and swallow whole.
Researchers observed 25 instances in which killer whales changed course after encountering dolphins, and then the dolphins and the dolphins may have dived to forage. Study lead author Sarah Fortune, an oceanographer at Dalhousie University in Nova Scotia, Canada, said this may be a result of killer whales listening to dolphin echolocation.
The authors also documented eight instances in which killer whales caught salmon, butchered them, and shared the pieces with other killer whales. Dolphins were sighted on four of these occasions, and on one occasion, the dolphins were scavenging for a conveniently crushed salmon carcass.
“What’s surprising to us is why we would go out of our way to chase dolphins when we know that resident killer whales are experts at hunting Chinook salmon, and they’re probably the best at finding killer whales,” Fortune told Live Science.
He said the discovery was the first to document cooperative hunting and prey sharing between killer whales and dolphins. The study was published in the journal Scientific Reports on Thursday (December 11).
It remains to be seen whether it’s a cooperative system that benefits both species equally, Fortune added. “While we have not been able to quantify the extent to which killer whales and dolphins benefit from this interaction, our observations suggest positive outcomes for both.”
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Engaging with killer whales may also protect the dolphins from other killer whale populations that hunt them, she says.
“Given toothed whales’ ability to learn, it is perhaps not surprising that these two species have learned that certain aspects of foraging at the same time and place provide benefits for both species,” said biologist Luke Rendell of the University of St. Andrews in Scotland, who was not involved in the study. “I think the risk management that dolphins have to do around killer whales is particularly impressive,” he told Live Science via email, adding that if you go with the wrong killer whale, “you get eaten.”
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Michael Weiss of the Whale Research Center in Friday Harbor, Washington, who was not involved in the study, said he did not know whether the observed behavior indicated the two species were cooperating.
“We’re not entirely sure that what we’re seeing here is cooperative. It seems clear that dolphins can benefit from reduced predation risk and scavenging from killer whale capture, but I think more research is needed to prove the benefits for whales,” Weiss told Live Science in an email.
Rather, the behavior may be kleptoparasitic (stealing food that an animal has already hunted), says Jared Towers, executive director of Bay Cetology, a Canadian cetacean research institute who was not involved in the study.
“We now have evidence that dolphins steal fish remains from killer whales’ diets, which is really exciting because that’s exactly what we thought was happening for many years,” Towers told Live Science.
He said this cooperative behavior also supports another hypothesis: that orcas are avoiding dolphins rather than cooperating with them. “The killer whales dive longer, move more underwater, and have less vocal activity. To me, this suggests that the killer whales are trying to avoid the dolphins.”
Fortune agrees that other hypotheses are possible. “Dolphins may be sneaking up on orcas to steal fish, like kleptoparasites, but dolphins have been observed chasing salmon on the surface, and on at least one occasion the dolphin has been seen catching a salmon, then letting it go, and then trying to catch it again,” she said. “It’s clear that dolphins want salmon, but dolphins aren’t necessarily morphologically well-adapted to catch those big fish.”
Working with orcas could give dolphins a way to actually catch fish, while orcas might be able to find salmon more easily by following dolphins, she added.
Fortune said further research into the relationships among these marine mammals is needed to understand how widespread and consistent cooperative behavior is.
Killer whales have been seen getting into all sorts of shenanigans in recent years, demonstrating an amazing level of cultural learning. Southerners near Washington state and British Columbia have been spotted putting salmon on their heads and massaging each other with kelp. And another group of clever marine mammals are damaging boats off the coast of Spain.
Killer Whale Quiz: Will it sink or swim?
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