Killer whales are teaming up with dolphins on salmon hunts, study finds — but not everyone agrees
Orcas living off the coast of British Columbia, Canada, have been spotted hunting with dolphins and sharing pieces of salmon with them after a kill.
The resident population of the north of orcas (Killer whale), or killer whales, off the coast of British Columbia, has been observed teaming up with Pacific white-sided dolphins (Aethalodelphis obliquidens) in the chinook salmon hunt (Oncorhynchus tshawytscha).
Researchers used underwater video, data from suction cup biologging tags and aerial drone footage to establish how nine Northern Resident orcas were moving and hunting in August 2020 – and how they interacted with Pacific white-sided dolphins around Vancouver Island, Canada.
They captured aerial and underwater images of the animals’ coordinated interactions. The two species present in this area generally show few signs of mutual aggression and sometimes looking for each otherwhich is unusual given that orcas hunt dolphins in other places, while some dolphins attack orcas.
Researchers recorded 258 cases of dolphins traveling near tagged orcas. In all of these cases, the orcas engaged in behaviors related to foraging, such as killing, eating, or chasing salmon, which are too large for the dolphins to capture and swallow whole.
Researchers observed 25 cases of orcas changing course after encountering dolphins, after which both would dive, potentially in search of food. This could be because orcas listen to dolphins’ echolocations, the study’s lead author said. Sarah Fortuneoceanographer at Dalhousie University in Nova Scotia, Canada.
The authors also recorded eight cases of orcas catching salmon, breaking them apart and sharing the pieces with other orcas. Dolphins were present on four of these occasions, and on one of them they scavenged the remains of conveniently broken salmon.
“What’s surprising to us is that knowing that resident killer whales are specialists in hunting Chinook salmon, the killer whales should really be the best at finding them, so why do they bother following the dolphins?” Fortune told Live Science.
She said the findings constitute the first documented record of cooperative hunting and prey sharing between orcas and dolphins. The research was published in the journal Scientific reports on Thursday (December 11).
Researchers still don’t know if it’s a cooperative system from which both species benefit equally, Fortune added. “We have not been able to quantify the extent to which killer whales and dolphins benefit from this interaction, but based on our observations we see positive results for both.”
Look on it
By associating with orcas, dolphins can also benefit from protection from other orca populations that prey on dolphins, she explained.
“It is perhaps not surprising, given the learning abilities of toothed whales, that these two species have learned that certain aspects of foraging at the same time and place provide benefits to both species,” said Luke Rendella reader in biology at the University of St. Andrews in Scotland who was not involved in the study. “I find the risk management that dolphins have to do around killer whales to be particularly impressive,” he told Live Science by email, adding that if you hang out with the wrong orcas, “you get eaten.”
Looking for food?
Michael Weiss of the Whale Research Center in Friday Harbor, Washington, which was not involved in the research, said it was not sure whether the observed behavior showed the two species were working together.
“I’m not completely convinced that what we see here is cooperative; it seems clear that dolphins may benefit from reduced predation risk and from killing killer whales, but I think more work needs to be done to demonstrate a benefit to whales,” Weiss told Live Science by email.
It would rather be a behavior of kleptoparasitism – one animal stealing food that another has already hunted – noted Jared Towersexecutive director of Bay Cetology, a cetacean research institute in Canada, who was not involved in the research.
“They provide evidence that dolphins are stealing fish scraps from killer whale meals and that’s really nice to see, because that’s exactly what we thought was happening all these years,” Towers told Live Science.
He added that the coordinated movements also support another hypothesis: the idea that orcas avoid dolphins and do not cooperate with them. “Killer whales take longer dives, travel farther underwater and reduce their vocal activity. To me, this suggests that killer whales are trying to avoid dolphins.”
Fortune confirms that other hypotheses are possible. “It may be the dolphins sneaking up and stealing the fish from the killer whales, like a kleptoparasite, but we have observed dolphins preying on salmon at the surface and at least once you see the dolphin catch a salmon and then it loses it and then tries to catch it again,” she said. “It is clear that dolphins want salmon but they are not necessarily well adapted morphologically to capture these large fish.”
Working with orcas would give the dolphins the means to capture fish, she added, while the orcas could locate salmon more easily by following the dolphins.
Fortune said further research into the relationship between these marine mammals is needed to understand how widespread and consistent cooperative behaviors may be.
In recent years, orcas have been spotted getting up to all sorts of shenanigans, demonstrating impressive levels of cultural learning. Members of the population residing in the south, near Washington and British Columbia, have been seen carry salmon on your head And give yourself kelp massages. And another group of intelligent marine mammals was damaging boats off the coast of Spain.
Orca Quiz: Will You Sink or Swim?
