Media release

From: Springer Nature

Marine ecology: Killer whales tail dolphins to hunt salmon

Killer whales or orca (Orcinus orca) have been observed hunting with Pacific white-sided dolphins (Lagenorhynchus obliquidens) in the waters off British Columbia, Canada and sharing fish scraps with them after making a kill, according to research published in Scientific Reports. The authors suggest that the findings represent the first documented recording of cooperative hunting between orca and dolphins.

Pacific white-sided dolphins are often seen hunting along the coastline of British Columbia within metres of orca. Although orca frequently share their prey captures with pod members, they hunt independently. As the two species have not shown signs of fighting or avoiding each other, researchers have speculated that this may be due to them cooperating rather than competing for food.

Sarah Fortune and colleagues investigated the hunting behaviours of nine northern resident orca and their interactions with Pacific white-sided dolphins around Vancouver Island, Canada in August 2020. They used movement data, underwater footage, acoustic recordings, and aerial drone footage to establish how the orca moved and hunted.

The authors observed 25 instances of orca changing course after encountering dolphins to follow them on foraging dives. They suggest this may be due to orcas dampening their own noises to listen out for dolphin echolocations, which may help orca to detect Chinook salmon (Oncorhynchus tshawytscha), prey too large for dolphins to capture and swallow whole. The authors also recorded eight instances of orca catching, eating, and sharing Chinook salmon with other orca — dolphins were present for four of these instances. On one occasion the dolphins scavenged the remains of an adult Chinook salmon broken into scraps small enough for them to eat by the orca. The authors propose this is an act of prey sharing.

The authors suggest the presence of local orca may offer dolphins protection from other orca pods passing through the area, while their interactions may help orca locate salmon more easily while providing an opportunity for dolphins to feed on scraps. However, they note that future research is needed to investigate this.