Scientists were off the coast of British Columbia, studying the behaviour of fish-eating killer whales and gathering video, images and other data to learn more about their hunting and feeding habits. They were trying to determine if the whales -- particularly the endangered southern-resident whales -- had a sufficient supply of food.
Using a drone dispatched from their 16-metre research vessel, they noticed northern-resident killer whales and Pacific white-sided dolphins chasing Chinook salmon on the surface. Later as they reviewed hours of underwater video obtained from biologgers, they saw that the whales and dolphins appeared to be foraging for food together and often synchronized their movements.
Dr. Sarah Fortune, assistant professor in Dal's Department of Oceanography, noticed that the killer whales moved toward the dolphins and followed them to depth, while both species produced echolocation clicks in search of prey.
Above/right: Dr. Sarah Fortune (Cody Turner photo).
Applying new technologies
"We were all just like, 'What?'" says Dr. Fortune, lead author of a new paper outlining the finding. "It was incredibly exciting because killer whales are very well-studied — their diet is well-known, their foraging areas, their population — but the exciting thing is whenever we can apply new technologies that can push the limits of available data, inevitably we end up with new insights that show us the lack of understanding we previously had."
The team, which conducted the work in waters off Vancouver Island in August 2020, temporarily attached suction-cup tags to whales they identified by their unique markings, selecting animals that were in good health and weren't pregnant or lactating.
A pod of Northern resident killer whales near Hanson Island, British Columbia.
Side shot panning down to see a pod of Northern resident killer whales near Hanson Island, British ColumbiaIt was the first time the Customized Animal Tracking Solutions Tags (CATS) were used on resident killer whales and allowed the researchers to continuously record high-resolution dive data, along with vocalizations and feeding-related sounds, before they fell off.
Researchers Mike deRoos (Cetacea Contracting, Ltd), Andrew Trites, and Sarah Fortune.
Capturing surprising behavior
The surprising behaviour suggested the whales may be eavesdropping on the dolphin echolocation and using those cues to help locate the large salmon — prey that dolphins cannot capture and swallow whole.
The team realized that the scenes playing out before them presented a new and exciting theory about interspecies relations: that two top ocean predators could be joining forces to find and feed on salmon, and may have developed a co-operative rather than competitive relationship.
Northern resident killer whale with the research vessel Steller Quest in the background.
The paper, published in the journal Scientific Reports, was led by Dalhousie University, along with colleagues from the University of British Columbia, the Leibniz Institute and the Hakai Institute, and shows that these interactions are not just chance encounters. Instead, the species appear to be working together to hunt Chinook salmon off B.C., where they are often seen within meters of each other.
Drones launched by the Hakai Institute and suction-cup biologging tags captured remarkable aerial and underwater footage of the animal's co-ordinated interactions.
Drone operator Keith Holmes (Hakai Institute) and research Taryn Scarff.
The videos reveal that once whales caught their prey and broke them apart into smaller pieces to share with other killer whales, the dolphins were quick to scavenge the leftovers.
"From above you could see this incredible amount of activity," says Keith Holmes, a drone pilot with the Hakai Institute, who first spotted the behaviour by chance during fieldwork for a UBC-led project. "It was clear that there was some sort of communication happening and they were actively foraging together."
The researchers recorded 258 unique events of dolphins traveling near the head of tagged killer whales. All of the whales that interacted with dolphins engaged in foraging related behaviours, such as killing, eating and searching for the salmon.
Notably, the two species showed no signs of aggressive or avoidant behaviour, with the co-ordinated activity suggesting killer whales get help detecting prey from dolphins who act as 'scouts' and then gain access to discarded salmon pieces.
A strategic alliance
"The strategic alliance we observed between the dolphins and killer whales is extraordinary," says Dr. Andrew Trites, a professor and director of the Marine Mammal Research Unit at UBC's Institute for the Oceans and Fisheries.
"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. It's a win-win for everyone involved."
The findings highlight the ecological significance of interspecies associations and the potential role they play in shaping marine food webs and helping predators adapt in a changing ocean. The researchers say further investigation is needed to understand how widespread and consistent such behaviours may be.
"We need to figure out how prevalent co-operative foraging is and whether there might be benefits to the population," says Dr. Fortune. "Do killer whales that forage with dolphins have better success catching salmon? Is their body condition better than those that hunt alone? These are the kinds of metrics we can use to figure out whether this is a mutually beneficial interaction."