Researchers have observed killer whales teaming up with dolphins to hunt salmon and sharing the spoils for the first time, raising questions about their intelligence and social lives.
In recent years, enhanced monitoring using new technology like drones has unravelled a world of unique behaviours among orcas.
For instance, researchers recently found that the orcas near the Gulf of California had gained special skills to hunt down whale sharks, the world’s largest fish.
Studies have also documented orcas sharing food with humans for the first time, using seaweed to exfoliate their skin, and harassing porpoises for no particular reason.
Now, researchers have observed the killer whales hunting cooperatively with dolphins along the coast of British Columbia.
The two species in this region don’t show any sign of fighting or avoiding each other, leading Canadian researchers to suspect that they could be cooperating rather than competing for food.
Orcas were previously known to share their prey captures with pod members but not widely with other marine species.
Researchers investigated the hunting behaviours of nine resident orcas and their interactions with Pacific white-sided dolphins around Vancouver Island in August 2020.
They collected movement data, underwater footage, audio recordings, and aerial drone footage to understand how the orcas moved and hunted in the area.
They observed 25 instances of the orcas changing course after seeing dolphins to follow them on foraging dives.
Researchers suspect these could be cases of the orcas dampening their own noises and follow the sonar-like dolphin navigation. Such a technique may be helping the killer whales detect Chinook salmon, which are too large for the dolphins to capture and swallow whole.
Out of the eight recorded instances of the orcas catching, eating and sharing Chinook salmon with their pod near Vancouver Island, researchers spotted dolphins in four.
In one instance, they observed the dolphins scavenging the remains of an adult salmon broken by the orcas into scraps small enough for them to eat.
“Captured fish were brought to the surface by the killer whales and broken apart for sharing with other matrilineally related pod members,” researchers noted in a study published recently in the journal Scientific Reports, “while the accompanying dolphins scavenged scraps.”
These peculiar interactions could be helping the local orcas locate salmon more easily, while also providing an opportunity for the dolphins to feed on scraps, they said.
The researchers, however, called for further studies to investigate this unique case of cooperation between the marine species.