Killer whales And dolphins were spotted working as part of a salmon-hunting team off the coast of British Columbia for the first time, according to a new study that suggests cooperation between the two predators.
The study, published Thursday in the journal Scientific reportsshows that interactions between northern resident killer whales (also known as killer whales) and Pacific white-sided dolphins are more than just chance encounters while foraging.
Extensive documentation, including drone videos, acoustic recordings and underwater footage, 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 the ultimate salmon hunters. They are highly specialized and highly skilled predators. Seeing them follow the dolphins as if they were leaders was really counter-intuitive – and really exciting,” said Sarah Fortune, a marine scientist at Dalhousie University and lead author of the report.
Dolphins have often been seen up close northern resident killer whalesan ecotype of an apex predator that feeds almost entirely on Chinook salmon. Dolphins cannot hunt salmon, which are too large for them, and usually rely on herring.
Video footage of the study shows dolphins, which Fortune says act as “scouts,” smoothly cutting through the glassy waters of the Pacific Ocean in search of salmon, which can grow to nearly three feet in length. The killer whales follow them.
When whales catch their prey and tear it apart at the surface to share with other killer whales, dolphins eat the leftovers.
The whales, which are usually fiercely protective of freshly caught prey, do not seem to be bothered by the intrusion.
The researchers looked at a variety of explanations for the dolphins' proximity and the killer whales' lack of aggression.
One theory suggested that dolphins simply gained protection from the presence of whales. Northern killer whales do not hunt dolphins, unlike Bigg's killer whales, which live in the same waters. But individual whale ecotypes largely avoid each other.
Another theory was that the dolphins benefited from bow riding alongside the killer whales by reducing drag.
The team also weighed the possibility of kleptoparasitism, the term for dolphins stealing leftover food from whales.
“If the dolphins were parasites just there for the free lunch, the whales might act aggressively towards them to get them to leave, or the killer whales themselves might leave and go feed in nearby areas. But we really didn't see evidence of antagonistic behavior between species. And that was very surprising to us,” Fortune said.
This left researchers with the last and most interesting explanation: the two predators were collaborating.
“The killer whales were oriented toward following the dolphins, and so the dolphins seemed to play a leadership role,” Fortune said. “That really piqued our interest in digging deeper into our data and trying to see if we could figure out what was really going on.”
To better study the hunt, three team members climbed into a small boat and tagged whales with a large carbon fiber stick and attached a camera with a suction cup, which eventually fell off.
The tags, which recorded video and acoustics, continuously recorded dive data, as well as vocalizations and feeding sounds, gave researchers a rare glimpse into interactions more than 100 feet below the surface. Because the dolphins were so close to the whales, the tags often picked up the calls 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 the echolocation clicks of the dolphins, and so those dolphins had to be close enough to the hydrophone for us to pick it up,” Fortune said. “And then the question arises: do both species listen to each other? Are they listening?
Fortune said echolocating the two species simultaneously also offers hope that they can effectively increase the acoustic field of view, given that whales have a wide range for tracking fish.
The team said more research is needed to determine the extent to which both species benefit from this interaction.
“Will there be something beneficial for both the dolphins and the killer whales?” Fortune said. “Will whales that hunt with dolphins be more successful at obtaining food than those that hunt without dolphins?”
But the research has also changed and expanded understanding of what whales and dolphins, renowned for their intelligence, are capable of when they hunt.
“Most people know that killer whales have a strong culture and that they are a highly social species with specialized hunting strategies,” Fortune said. “But as social as they are, when it comes time to hunt and catch salmon, they become lone wolves. Seeing them hunt with other species shows how adaptable they are to changing and improving their hunting strategies.”
