Orcas and dolphins have been spotted for the first time working as a team to hunt salmon off the coast of British Columbia, according to a new study that suggests a cooperative relationship between the two predators.
The research, published Thursday in the journal Scientific Reports, shows that interactions between Northern Resident orcas (also known as killer whales) and Pacific white-sided dolphins are not just chance encounters while foraging.
Extensive documentation, including drone videos, acoustic recordings and underwater images, led scientists working with the University of British Columbia, the Leibniz Institute and the Hakai Institute to conclude that the two species work as a team.
“These whales are great salmon-hunting specialists. They are highly specialized, highly skilled predators. Seeing them follow the dolphins as if they were leaders was really counterintuitive – and really exciting,” said Sarah Fortune, a marine scientist at Dalhousie University and lead author of the report.
The dolphins have often been seen in close proximity to northern resident orcas, an ecotype of the apex predator that feeds almost entirely on Chinook salmon. Dolphins do not have the ability to hunt salmon, which are too large for them, and normally rely on herring.
Video footage of the research shows the dolphins – which Fortune said act as “scouts” – racing through the glassy waters of the Pacific in pursuit of salmon, which can grow to be nearly a meter long. The orcas follow closely.
When whales catch their prey and break it up at the surface to share with other orcas, dolphins scavenge the remains.
The whales, which fiercely protect their freshly hunted prey, do not seem bothered by this intrusion.
Researchers examined several explanations for the proximity of dolphins and the orcas’ lack of aggression.
One theory suggested that dolphins simply gained protection in the presence of whales. Northern Resident orcas do not prey on dolphins, unlike Bigg’s orcas, which share the same waters. But distinct ecotypes of whales largely avoid each other.
Another theory was that dolphins gained advantages by riding near orcas, thereby reducing drag.
The team also assessed the possibility of kleptoparasitism, a term that refers to dolphins stealing scraps of food from whales.
“If the dolphins were parasites, just there for a free lunch, the whales might act aggressively towards them to drive them away – or the killer whales themselves might leave and go feeding in adjacent areas. But we really haven’t seen evidence of antagonistic behavior between the species. And that really surprised us,” Fortune said.
That left researchers with the final, most tantalizing explanation: the two predators were cooperating.
“The killer whales oriented themselves to follow the dolphins, and so the dolphins seemed to play a leadership role,” Fortune said. “That really sparked our interest in digging deeper into our data and trying to see if we could understand what was really going on.”
To better study the hunt, three team members piled into a small boat and marked the whales with a large carbon fiber pole, attaching a camera with a suction cup that would eventually fall off.
The tags, which recorded video and acoustics, continuously recorded dive data, as well as feeding-related vocalizations and sounds, gave researchers a rare glimpse of interactions more than 100 feet below the surface. As the dolphins were very close to the whales, the tags often picked up the vocalizations of both mammals.
“We would often see this alternating pattern, where our tagged whale would echolocate, and then there would be a period of silence, and we would hear echolocation clicks from the dolphins, and so these dolphins must have been close enough to the hydrophone for us to pick it up,” Fortune said. “And that raises a question: Are the two species listening to each other? Are they listening to each other at the gates?”
Fortune said simultaneous echolocation by both species also raised the possibility of effectively increasing the acoustic field of view, given that whales have a wide range for tracking fish.
The team said additional studies are needed to determine the extent to which both species benefit from this interaction.
“Is there going to be something beneficial for both the dolphins and the killer whales,” Fortune said. “Are whales that hunt with dolphins ultimately more successful in feeding than those that hunt without dolphins?
But the study also reshaped and expanded the understanding of what whales and dolphins, both known for their intelligence, are capable of when they hunt.
“Most people know that killer whales have a strong culture and are a very social species with specialized hunting strategies,” Fortune said. “But as social as they are, when it comes time to hunt and catch salmon, they turn into lone wolves. Seeing them probably hunt cooperatively with another species shows how adaptable they are in changing and refining their hunting strategy.”
