Pacific white-sided dolphins and northern resident killer whales—two top marine predators in the northeast Pacific—have been recorded diving and hunting fish side by side.
New research published in Scientific Reports, led by researchers at Dalhousie University—with collaborators from the University of British Columbia, the Leibniz Institute in Germany, and the Hakai Institute—shows these interactions are not just chance encounters. Instead, these species may be engaging in cooperative foraging.
Researchers captured coordinated aerial and underwater footage of the interactions using drones launched by Hakai Institute staff and biologging tags attached to the animals with suction cups. The recordings revealed killer whales orienting toward dolphins, following them on deep dives, and, at times, reducing their own echolocation clicks—suggesting they may have been eavesdropping on dolphin sonar to locate large Chinook salmon. Once killer whales caught their prey, dolphins were quick to scavenge the leftovers.
Keith Holmes, a drone pilot with the Hakai Institute, first spotted the behavior.
“From above you could see this incredible amount of activity,” says Holmes. “It was clear that there was some sort of communication happening and they were actively foraging together. This was happening far too much to be just a passing oddity.”
The collaboration was discovered by chance, during fieldwork for another study.
"As researchers, we're so focused on our particular questions that we can sometimes ignore signs that something more interesting is also occurring," says lead author Sarah Fortune.
“The prevailing thought among the killer whale research community was that, if anything, the dolphins were a bit of a pest,” adds Fortune. “If they were pests, why would the killer whales be following the dolphins?”
The findings add to a growing body of evidence showing that cooperation, long known to occur among individuals of the same species such as dolphins, can also extend across species boundaries. And in a time of dwindling salmon runs, such partnerships may help both predators adapt in a changing ocean.
