Orcas & Dolphins Hunt Salmon Together: New Study

Orcas and dolphins have been observed working together for the first time to hunt salmon off the coast of British Columbia, suggesting a cooperative relationship between the two predator species, according to a new study.

Cooperative Hunting Strategy

Research published Thursday in the journal Scientific Reports details interactions between northern resident orcas, also known as killer whales, and Pacific white-sided dolphins that go beyond chance encounters during foraging.

Scientists from the University of British Columbia, the Leibniz Institute, and the Hakai Institute used drone video, acoustic recordings, and underwater footage to document the teamwork.

“These whales are top salmon hunting specialists. They’re highly specialised and highly skilled predators. To see them following dolphins as though they were leaders was really counterintuitive – and really exciting,” said Sarah Fortune, a marine scientist at Dalhousie University and the report’s lead author.

While dolphins typically rely on herring due to their inability to hunt larger salmon, footage shows them acting as “scouts,” cutting through the water in pursuit of salmon that can reach nearly three feet in length, with the orcas closely following behind.

After the whales catch and share prey, the dolphins scavenge the leftovers. Researchers noted the whales, typically protective of their catch, appear unbothered by the dolphins’ presence.

Researchers considered several explanations for the interaction, including the dolphins seeking protection from Bigg’s orcas, which prey on Pacific white-sided dolphins, or benefiting from reduced drag by bow riding near the whales. They also considered kleptoparasitism, where dolphins steal scraps of food.

“If the dolphins were parasites, just there for a 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 adjacent areas. But we really didn’t see evidence of antagonistic behaviours between species. And that really surprised us,” said Fortune.

This led researchers to conclude the two species are cooperating, with the dolphins appearing to take a leadership role, orienting the whales during the hunt.

To study the hunt further, researchers tagged whales with cameras that recorded video, acoustics, and dive data, capturing vocalisations from both species. “We’d often see this alternating pattern, where our tagged whale would echolocate, and then there’d be a period of silence, and the we’d hear dolphin echolocation clicks, and so those dolphins had to be close enough to the hydrophone that we could pick it up,” said Fortune. “And this raises a question: are both species listening to each other? Are they eavesdropping?”

Fortune suggested the simultaneous echolocation could effectively increase the acoustic field of view for both species, aiding in fish tracking.

Researchers plan further study to determine the extent of the benefits for both species, including whether whales hunting with dolphins are more successful at foraging. The study has expanded understanding of the intelligence and adaptability of whales and dolphins while hunting.

“Most people are aware that killer whales have strong culture, and that they’re a very social species and specialised hunting strategies,” said Fortune. “But as social as they are, when it comes time to hunt and to catch salmon, they turn into lone wolves. To see them likely cooperatively hunting with another species shows how adaptable they are to changing and refining their hunting strategy.”