A new research project has documented the initial evidence of orcas and dolphins cooperating to hunt salmon in the waters of the Pacific Northwest.
Unlikely Partners in the Pursuit
The research, released in a peer-reviewed publication, indicates that encounters between northern resident orcas and dolphins are far more than chance meetings while searching for food.
"These predators are top salmon hunting specialists. To see them trailing dolphins as though they were guides was truly counterintuitive – and really exciting," noted the study's lead author.
Comprehensive documentation, including aerial footage, sound data, and underwater footage, guided researchers to conclude the two species are operating as a coordinated team.
The Hunt Unfolds
Video footage from the study shows the dolphins – which act as "scouts" – moving effortlessly through the water in chase of large Chinook salmon. The orcas follow closely behind.
When the orcas catch their prey and break them apart at the surface to share with others, the dolphins collect the leftovers.
Interestingly, the predators, which are typically fiercely protective of newly caught prey, seem undisturbed by the intrusion.
Exploring the Reasons
Researchers examined multiple explanations for this close proximity and the absence of hostility from the orcas.
- Safety Hypothesis: One possibility was that the dolphins were simply obtaining safety from other predators by remaining close to the whales.
- Hydrodynamic Hypothesis: Another suggestion was that the dolphins gained an advantage by bow riding the whales, which decreases water resistance.
- Scavenging Theory: The team also evaluated the chance that the creatures were simply stealing leftover pieces of food.
"If the animals were parasites, just there for a free lunch, the whales might act hostilely... But we truly didn't see signs of antagonistic behaviours between them. And that really surprised us," explained the study author.
This left the most compelling explanation: the two hunters were engaging in teamwork.
Sophisticated Study Methods
To closely examine the hunt, researchers used a specialized suction-cup device affixed to the whales. This equipment recorded video, acoustics, dive data, and calls.
Because the dolphins were so nearby, the devices often detected the vocalisations of both mammals.
"We'd often see this alternating pattern, where our tagged whale would echolocate, and then there'd be a pause, and then we'd hear porpoise sonar pulses," said the researcher. "That prompts a question: are they listening to each other? Are they eavesdropping?"
Broader Implications
The coordinated use of echolocation by the two animals suggests the prospect they could effectively increase their acoustic field of view, making the hunt more effective.
The research group said more study is needed to determine the complete nature of the benefits for both predator.
"Is it that there is something beneficial for the mammals and the killer whales?" asked the researcher. "Do whales that hunt with dolphins end up better at foraging than those that hunt without?"
In conclusion, the study has altered the understanding of what these highly intelligent marine animals are able to accomplish.
"To see them likely working together to hunt with another species shows how adaptable they are to changing and improving their hunting strategy," the scientist concluded.
