What would you do if you were a hungry Pacific white-sided dolphin, salivating at the idea of sampling some salmon but resigned to the fact that the fish is too large to capture and swallow whole? You might, scientists say, team up with a killer whale.
In August 2020, scientists tracking the behavior of nine northern resident orcas off the coast of British Columbia observed the killer whales seeming to coordinate with Pacific white-sided dolphins to more easily score some tasty fish.
On multiple occasions, the orcas would change course in the presence of dolphins, following them as they foraged and eavesdropping on their echolocation calls to find the Chinook salmon. The dolphins, in turn, would follow the orcas and the captured Chinook to the surface and feast on the scraps.
“By working together, killer whales can conserve energy and use the dolphins as radar-equipped scouts to increase their chances of finding large Chinook salmon at deeper depths. In return, the dolphins gain predator protection and access to scraps from one of the ocean’s most prized fish,” said Andrew Trites, director of the Marine Mammal Research Unit at the University of British Columbia’s Institute for the Oceans and Fisheries. “It’s a win-win for everyone involved.”
Trites and his co-authors of a study published Thursday in the journal Scientific Reports also noted “rare occasions” in which dolphins were seen briefly holding and releasing large salmon near the surface, potentially to aid nearby orcas who could tear the fish into more manageable pieces. Pacific white-sided dolphins do not have a way to break up their prey before ingestion and so swallow it whole.
“The lack of competitive or antagonistic behaviour suggests mutual tolerance that yields reciprocal benefit for both species,” the researchers concluded.
Pacific white-sided dolphins and northern resident killer whales have been known to interact before, but the purpose of those interactions was never clear. The footage captured by the researchers is “the first video of its kind” to show the animals hunting together, the researchers said in a statement marking the study’s release. Understanding the exact nature of the two species’ behavior would require further study.
Still, the scientists wrote, the data points to “more than incidental co-occurrences.” The orcas dove deeper and traveled farther while hunting when dolphins were around.
Study co-author Keith Holmes, a drone pilot with the Hakai Institute, an ecological research center in Canada, seemed certain that some kind of coordination was occurring from the moment he spotted the orcas and dolphins at work. He first noticed the behavior while doing fieldwork on a different project for the University of British Columbia.
“From above, you could see this incredible amount of activity,” Holmes said. “It was clear that there was some sort of communication happening and they were actively foraging together.”
Dalhousie University oceanographer Sarah Fortune, the study’s lead author, with Holmes, Trites and Xi Cheng, used drones and data from tracking devices to study the whales’ behavior.
The trackers, which were temporarily attached to healthy whales via suction cup, sent location data, underwater video footage and audio, including the whales’ vocalizations and sounds associated with feeding. (Think the audible crunch of a Chinook salmon caught in an orca’s jaw.)
The underwater footage enabled the researchers to closely monitor whale feeding behavior, from the hunt to the kill to the eventual sharing of the meal with other members of the pod — and even an opportunistic dolphin here and there.
The field work was conducted over the course of 15 days in August 2020.
Apparent cooperation between the dolphins and orcas “exclusively occurred during foraging events and involved coordinated movements — such as killer whales trailing dolphins — and synchronized acoustic activity,” the researchers wrote.
The orcas also didn’t appear to mind the dolphins picking at their leftovers. “Neither the aerial drone nor underwater video data revealed any signs of aggression, such as tail slaps, biting or raking appendages,” the scientists wrote, behaviors that might have pointed to the whales trying to ward off unwelcome guests.
“Killer whales were also never observed fleeing or avoiding the dolphins,” they added. “Instead, the killer whales disproportionately oriented toward the dolphins and mirrored their swimming and diving movements.”
Researchers have previously observed Pacific white-sided dolphins, northern resident killer whales and also Dall’s porpoises traveling together and even playing off the coast of British Columbia. Those scientists, working separately from the authors of the study published Thursday, theorized that the porpoises and dolphins chose to stick by the friendlier orcas to fend off the attention of more dangerous, predatory orcas, who have been known to hunt and play vicious games with other sea creatures, and sometimes kill them in the process.
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